COMPOSITIONS AND METHODS FOR INCREASING CHOLESTEROL EFFLUX AND RAISING HDL USING ATP BINDING CASSETTE TRANSPORTER PROTEIN ABC1

Abstract: The present invention relates to novel ABC1 polypeptides and nucleic acid molecules encoding the same. The invention also relates to recombinant vectors, host cells, and compositions comprising ABC1 polynucleotides, as well as to methods for producing ABC1 polypeptides. The invention also relates to antibodies that bind specifically to ABC1 polypeptides. In addition, the invention relates to methods for increasing cholesterol efflux as well as to methods for increasing ABC1 expression and activity. The present invention further relates to methods for identifying compounds that modulate the expression of ABC1 and methods for detecting the comparative level of ABC1 polypeptides and polynucleotides in a mammalian subject. The present invention also provides kits and compositions suitable for screening compounds to determine the ABC1 expression modulating activity of the compound, as well as kits and compositions suitable to determine whether a compound modulates ABC1-dependent cholesterol efflux.

Description: COMPOSITIONS AND METHODS FOR INCREASING CHOLESTEROL EFFLUX AND RAISING HDL USING ATP BINDING CASSETTE TRANSPORTER PROTEIN ABCl This application claims priority to U.S. provisional application no. 60/140,264, filed on June 18, 1999; U.S. provisional application no. 60/153,872, filed on September 14, 1999; and U.S. provisional application no. 60/166,573, filed on November 19, 1999. TECHNICAL FIELD OF INVENTION The present invention relates to novel ABCl polypeptides and nucleic acid molecules encoding the same. The invention also relates to recombinant vectors, host cells, and compositions comprising ABCl polynucleotides, as well as to methods for producing ABCl polypeptides. The invention also relates to antibodies that bind specifically to ABCl polypeptides. In addition, the invention relates to methods for increasing cholesterol efflux as well as to methods for increasing ABCl expression and activity. The present invention further relates to methods for identifying compounds that modulate the expression of ABCl and methods for detecting the comparative level of ABCl polypeptides and polynucleotides in a mammalian subject. The present invention also provides kits and compositions suitable for screening compounds to determine the ABCl expression modulating activity of the compound, as well as kits and compositions suitable to determine whether a compound modulates ABC1- dependent cholesterol efflux. BACKGROUND OF THE INVENTION Circulating lipids in human plasma or lymphatic fluid consist of cholesterol, cholesteryl esters, triglycerides and phospholipids. These lipids are transported in large molecular complexes called lipoproteins, which consist of a core of cholesteryl esters and or triglycerides, an envelope of phospholipids and free cholesterol, and apolipoproteins (Scriver et al., Eds., The Metabolic and Molecidar Basis of Inherited Disease, 7 th Ed., p.1841-1851 (McGraw-Hill, New York 1995)). Apolipoproteins are involved in the assembly and secretion of the lipoprotein, as well as the activation of lipoprotein modifying enzymes, such as lecithin cholesterol acyl transferase (LCAT). In addition, apolipoproteins provide structural integrity and are ligands for a large spectrum of receptors and membrane docking proteins. The plasma lipoproteins are categorized into five types according to size: chylomicrons (largest in size and lowest in density), very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), low density lipoproteins (LDL) and high density lipoprotein (HDL). Chylomicrons, VLDLs, IDLs, and LDLs transport exogenous and endogenous cholesterol and tπacylglycerols to peπpheral sites, where the lipids play a role in various metabolic pathways and serve as a major constituent of cell membranes Chylomicrons are assembled in ^ the intestinal mucosa as a means to transport dietary cholesterol and tπacylglycerols to vanous tissues VLDLs are formed in the liver to transport endogenous cholesterol and tnacylglycerols synthesized by the liver to extra-hepatic tissues, such as muscle and adipose tissue In fasting serum, VLDLs contain 10-15% of the total serum cholesterol and most of the tnglycende In circulation, VLDLs are converted to LDLs through the action of lipoprotein pase LDLs are the lϋ primary plasma earners of cholesterol for delivery to all tissues, typically containing 60-70% of the total fasting serum cholesterol In contrast, HDLs are involved in "reverse cholesterol transport", the pathway by which excess cholesterol is transported from penpheral sites back to the liver, where it is excreted in the form of bile salts (Glomset, J.A., J LψidRes., 9, 155-167 (1968)). Nascent HDLs are 15 synthesized de novo m the liver and small intestine, as protein-nch disc-shaped particles devoid of cholesterol and cholesterol esters. In fact, a major function of HDLs is to act as circulating stores of apolipoproteins, pnmanly apo C-I, apo C-II, and apoE. The nascent or protem-nch HDLs are converted into sphencal lipoprotein particles through the accumulation of cholesteryl esters obtained from cellular sources The HDL normally contain 20-30% of the total fasting 20 serum cholesterol According to current theones, the reverse efflux of cellular cholesterol to HDL is mediated through two mechanisms: an aqueous diffusion pathway and an apohpoprotem- mediated pathway The relative importance of these distinguishable mechanisms depends on the cell type and metabolic state (Oram et al, J. Lφid Res., 37.2743-2491 (1996), Rothblat et al., J 25 Lψid Res , 40 781-796 (1999); Stem et al., Atherosclerosis, 144.285-301 (1999)) For many cells, the aqueous diffusion pathway is the pnnciple pathway through which cholesterol efflux occurs (Johnson et al., Biochim Biophys Acta, 1085:273-298 (1991)) This pathway involves the bidirectional exchange of cholesterol between cell membranes and a lipoprotein acceptor, such as HDL, in the extracellular space through a process of passive transport (Remaley et al, M) Arterioscler Thromb Vase Biol, 17 1813-1821 (1997), Rothblat et al., J Lip Res., 40 781-796 ( 1999)) The exchange may occur pnmanly at surface microdomains known as caveolae (Fielding et al , Biochemistry, 34.14288-14292 91995)) Net efflux can be dnven by conversion of cholesterol in the exteracellular compartment to cholesteryl ester by the action of LCAT Alternatively, in macrophage and fibroblast cells, cholesterol and phospho pid efflux is pnmanly mediated through apolipoproteins, such as apo A-I, apo A-II, and Apo E (Remaley, supra (1997), Francis, et al., J Clin Invest., 96:78-87 (1995), Vega et al, J Intern Med., 226:5- 15 (1989), Sakar et al., Biochim. Biophvs. Acta, 1438: 85-98 (1999); Hara et al., J Biol Chem., 266:3080-3086 (1991); Fielding et al., J Lψid Res., 38, 1503-1521 (1997); Oram et al., J Lipid Res., 37, 2743-2491 (1996)). The process of apohpoprotem-mediated lipid efflux particularly dominates in macrophages and other scavenger cells when they are cholesterol-loaded and/or growth-arrested. Apohpoprotem-mediated efflux is an active transport process that requires the direct interaction of the apohpoprotem with the cell surface, the lipidation of the apo poprotein, and the subsequent dissociation of the lipid-apolipoprotem particle from the cell (Oram, supra (1996), Mendez, A.J., J Lψid Res., 38, 1807-1821 (1997); Remaley, supra (1997), Mendez, A.J , JLψid Res , 37, 2510-2524 (1996)) Once removed from the cell, the cholesterol-nch HDL particles are transported to the liver and removed from the body as descnbed. Abnormal lipoprotein function and or metabolism resulting from genetic defect or as a secondary effect of another disorder can have senous biological consequences. In addition to dietary influences, disorders such as diabetes, hypothyroidism, and liver disease can result in elevated plasma levels of LDL-cholesterol and tnglycendes. Elevated levels of LDL-cholesterol and tnglycendes have been identified as major risk factors associated with the incidence of coronary heart disease, which is the pnmary cause of death in the United States and other industrialized nations (Hokanson et al., J Cardiovasc. Risk., 3:213-219 (1996); The Expert Panel, JAMA, 269:3015-3023 (1993)). The accumulation of excess LDL-cholesterol on artenal walls can lead to the formation of atherosclerotic plaques, which play a major role in the development of heart disease. A plaque is believed to form when free radicals released from artenal walls oxidize LDL. According to theory, the oxidized form of LDL tnggers an inflammatory response, attracting circulating cells to the site which contnbute to the formation of a lipid plaque Among these are macrophages and other cells that contain scavenger receptors that accumulate cholesterol in an unregulated manner (Brown et al., Ann. Rev. Biochem., 52:223- 261 (1986)) Vast stores of internal cholesterol result m conversion to a foam cell phenotype, which is believed to be a major contnbutor to the development of vascular lesions. As the plaque builds up, the artenal walls constnct, reducing blood flow to the heart. Interestingly, however, an estimated 60% of heart attacks occur in persons who do not have elevated blood levels of LDL-cholesterol. Of these, an estimated 45% are associated with below average blood levels of HDL-cholesterol, indicating that low HDL-cholesterol level is a significant nsk factor for coronary heart disease In fact, recent studies have indicated that a decreased HDL-cholesterol level is the most common lipoprotein abnormality seen in patients with premature coronary artery disease (Genest J , Circulation, 85 2025-2033 (1992), Genest et al , Arterioscler Thromb , 13 1728-1737 (1993)) Although the basis for the inverse association i between HDL-cholesterol and coronary heart disease is not well understood, it has been suggested that the cardioprotective role of HDL may stem from its activity relating to the promotion of cholesterol efflux from macrophage foam cells in atherosclerotic lesions One example of cardiovascular disease associated with low HDL is Tangier disease (TD), a rare genetic disorder charactenzed by a near or complete absence of circulating HDL In 0 addition to near zero plasma levels of HDL, patients with TD have a massive deposition and accumulation of cholesteryl esters in several tissues, including tonsils, lymph nodes, liver, spleen, thymus. intestine, and Schwann cells (Frednckson, D S , J Clin Invest , 43, 228-236 (1964), Assmann et al , The Metabolic Basis of Inherited Disease, (McGraw-Hill, New York, 1995)) Although the cellular mechanisms have not been previously identified, recent studies 5 have shown that cells from subjects with TD are defective in the process of apohpoprotem- mediated removal of cholesterol and phospholipids (Remaley et al., Arterioscler Thromb Vase Biol , 17, 1813-1821 (1997), Francis et al., J Clin Invest., 96, 78-87 (1995), Rogler et al., Arterioscler Thromb Vase Biol , 15, 683-690 (1995)) These results have led to the proposal that the severe HDL deficiency in TD patients stems from the inability of nascent apo A-I to 0 acquire lipids Because they do not mature into lipid-nch particles, the nascent HDL in TD patients is rapidly catabohzed and removed from the plasma, resulting in the near zero levels of circulating HDL (Remaley, supra (1997), Francis, supra (1995), Horowitz et al , J Clin Invest 91, 1743-1752 (1993), Schaefer et al , J Lip Res , 22 217-228 (1981)) Other disorders associated with severe premature atherosclerosis and high nsk for 21 coronary heart disease resulting from diminished HDL-cholesterol levels are hypoalphahpoprotememia and familial HDL deficiency syndrome (FHA) Persons with these disorders often have normal LDL-cholesterol and tnglycende levels In addition, disorders such as diabetes, alcoholism, hypothyroidism, liver disease, and elevated blood pressure can result in diminished plasma levels of HDL-cholesterol, although many of these disorders are also "0 accompanied by elevated LDL-cholesterol and tnglcende levels Current treatments for coronary heart disease have focused pnmanly on diet manipulations and or drug therapies aimed at lowenng the plasma level of LDL-cholesterol by inhibiting LDL secretion or promoting LDL turnover Denvatives of fibnc acid, such as clofibrate, gemfibrozil, and fenofibrate, promote rapid VLDL turnover by activating lipoprotein hpase Nicotinic acid reduces plasma levels of VLDL and LDL by inhibiting hepatic VLDL secretion In addition, HMG-CoaA reductase inhibitors, such as mevinohn, mevastatm, pravastatm, simvastatin, fluvastatin, and lovastatm reduce plasma LDL levels by inhibiting the > intracellular synthesis of cholesterol, which causes an increase in the cellular uptake of LDL In addition, bile acid-bmdmg resms, such as cholestynne, colestipol and probucol decrease the level of LDL-cholesterol by increasing the catabohsm of LDL-cholesterol in the liver However, many of these therapies are associated with low efficacy and/or side effects that may prevent long-term use For example, use of HMG-CoaA reductase inhibitors carry a 0 significant risk of toxicity because they inhibit the synthesis of mevalonate, which is required for the synthesis of other important isoprenoid compounds m addition to cholesterol Also, gemfibrozil and nicotinic acid are associated with senous adverse effects, including renal injury, myopathy, myoglobmuna and intolerable skm flushing and itching In addition, the role of probucol in treating patients with coronary heart disease is uncertain because its administration 5 results in lower HDL-cholesterol levels as a side effect of reducing LDL-cholesterol Furthermore, treating patients who have isolated low HDL-cholesterol levels provides a particularly difficult therapeutic challenge. For instance, patients with Tangier disease exhibit a 4- to 6-fold increase in cardiovascular disease even though their LDL levels are already reduced by about 50% While there is some evidence that gemfibrozil and nicotinic acid may 0 simultaneously elevate HDL levels, in general, therapies aimed at lowenng plasma LDL- cholesterol levels are not effective for Tangier patients who suffer from coronary heart disease as a result of diminished HDL levels Likewise, patients with hypoalphahpoprotememia, familial HDL deficiency syndrome, or other cardiovascular disease resulting from low levels of HDL will not benefit from therapies aimed at lowenng the level of plasma LDL 25 The problems associated with current therapies for cardiovascular disease stem partially from the fact that the biology involved in the movement of cholesterol in and out of cells is not fully understood Furthermore, the proteins that play a role in cholesterol movement are not fully known Therefore, there remains a need for a better understanding of cholesterol cell biology, as well as new methods for treating humans suffenng from cardiovascular disease and other ) disorders associated with hypercholesterolemia Additionally, there remains a need for new methods of diagnosing cardiovascular disease and new methods of screening patients to identify those at high nsk for developing cardiovascular disease The identification of genes and proteins involved in cholesterol transport would be useful in the development of pharmaceutical agents for the treatment of heart disease and other disorders associated with hypercholesterolemia and atherosclerosis In addition, the identification of such genes would be useful in the development of screening assays to screen for compounds that regulate the expression of genes associated with cholesterol transport The - ^ identification of such regulatory compounds would be useful m the development of further therapeutic agents Furthermore, the identification of genes and proteins involved in cholesterol transport would be useful as diagnostic indicators of cardiovascular disease and other disorders associated with hypercholesterolemia i o SUMMARY OF THE INVENTION The present invention provides novel polypeptides and polynucleotides involved in cholesterol efflux Specifically, the present invention provides novel ATP-Binding Cassette (ABCl) polypeptides and novel polynucleotides that encode ABCl polypeptides The terms "ABCl" and "ABCAl" are alternative names for the same ATP-Bindmg Cassette protein and 15 gene The invention provides ABCl polypeptides, polypeptide fragments, and polypeptide variants In one preferred embodiment, the present invention provides an isolated polypeptide compnsing SEQ ID NO 2. In another preferred embodiment, the present invention provides an isolated polypeptide compnsing an ammo acid sequence that has at least 98% identity to SEQ ID NO 2 The present invention also provides ABC 1 polypeptides from Tangier disease patients 20 In one preferred embodiment, the present invention provides an isolated polypeptide compnsing SEQ ID NO 8 In another preferred embodiment, the present invention provides an isolated polypeptide compnsing SEQ ID NO 10 In addition, the present invention provides ABCl polynucleotides, polynucleotide fragments, and polynucleotide vanants In one preferred embodiment, the present invention 21 provides an isolated polynucleotide that encodes the polypeptide compnsing SEQ ID NO 2 In another preferred embodiment, the invention provides an isolated polynucleotide that encodes a polypeptide compnsing an ammo acid sequence that has at least 98% identity to SEQ ID NO 2 Also, in other preferred embodiments, the invention provides an isolated polynucleotide comprising a nucleotide sequence that is complementary to the polynucleotide encoding the θ polypeptide compnsing SEQ ID NO 2 or an isolated polynucleotide compnsing a nucleotide sequence that is complementary to the polynucleotide encoding the polypeptide compnsing an amino acid sequence that has at least 98% identity to SEQ ID NO 2 In another prefened embodiment, the present invention provides an isolated ABCl polynucleotide compnsing SEQ ID NO- 1. In a further preferred embodiment, the present invention provides an isolated polynucleotide compnsing nucleotides 291-7074 of SEQ ID NO. 1 In yet another prefened embodiment, the invention provides a polynucleotide compnsing a nucleotide sequence that has at least 90% identity with SEQ ID NO: 1 More preferably, the polynucleotide compnses a nucleotide sequence that has at least 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 1 Also, in other preferred embodiments, the present invention provides an isolated polynucleotide compnsing a nucleotide sequence that is complementary to the polynucleotide compnsing SEQ ID NO: 1, an isolated polynucleotide compnsing a nucleotide sequence that is complementary to the polynucleotide compnsing nucleotides 291-7074 of SEQ ID NO 1 , and an isolated polynucleotide that is complementary to a polynucleotide compnsing a nucleotide sequence that has at least 90% identity with SEQ ID NO: 1 The present invention also provides ABCl polynucleotides conespondmg to the 5' flanking region of the ABCl gene. In one prefened embodiment, the invention provides an isolated polynucleotide compnsing SEQ ID NO: 3. In other prefened embodiments, the invention provides an isolated polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1181- 1643, 1292-1643, or 1394-1532 of SEQ ID NO: 3. Preferably, the isolated polynucleotide compnses nucleotides 1394-1532 of SEQ ID NO: 3. In another prefened embodiment, the invention provides an isolated polynucleotide that hybridizes under stnngent conditions to a polynucleotide compnsing SEQ ID NO: 3. Also, in other prefened embodiments, the present invention provides an isolated polynucleotide that hybridizes under stnngent conditions to a polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1532 of SEQ ID NO. 3. In yet another prefened embodiment of the present invention, an isolated polynucleotide that has at least 80% identity to a polynucleotide compnsing SEQ ID NO: 3 is provided More preferably, the polynucleotide has at least 90% identity to a polynucleotide compnsing SEQ ID NO. 3 Even more preferably, the polynucleotide has at least 95% identity to a polynucleotide compnsing SEQ ID NO: 3. Also provided in prefened embodiments is an isolated polynucleotide that has at least 80% identity to a polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1532 of SEQ ID NO. 3 More preferably, the polynucleotide has at least 90% identity, and even more preferably at least 95% identity, to a polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1532 of SEQ ID NO. 3. In addition, the present invention provides an isolated polynucleotide compnsing a nucleotide sequence that is complementary to the above descnbed 5' flanking ABCl polynucleotides. In one prefened embodiment, the invention provides an isolated polynucleotide compnsing a nucleotide sequence that is complementary to a polynucleotide compnsing SEQ ID NO 3 In another prefened embodiment, the present invention provides an isolated polynucleotide compnsing a nucleotide sequence that is complementary to a polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1532 of SEQ ID NO 3 The present invention also provides ABCl polynucleotides conespondmg to the 3' flanking region of the ABCl gene In prefened embodiments, the invention provides an isolated polynucleotide compnsing SEQ ID NO 4, SEQ ID NO 5, or SEQ ID NO 6, and the complementary sequences thereof In other prefened embodiments, the invention provides an 10 isolated polynucleotide that hybndizes under stnngent conditions to a polynucleotide compnsing SEQ ID NO 4, SEQ ID NO 5, or SEQ ID NO 6, and the complementary sequences thereof In still other prefened embodiments, the invention provides an isolated polynucleotide that has at least 80% identity to a polynucleotide compnsing SEQ ID NO 4, SEQ ID NO 5, or SEQ ID NO 6, and the complementary sequence thereof More preferably, the polynucleotide has at l • least 90% identity to a polynucleotide compnsing SEQ ID NO 4, SEQ ID NO 5, or SEQ ID NO 6 Even more preferably, the polynucleotide has at least 95% identity to a polynucleotide compnsing SEQ ID NO 4, SEQ ID NO 5, or SEQ ID NO 6 In addition, the present invention also provides ABCl polynucleotides from Tangier disease patients In one prefened embodiment, the present invention provides an isolated 20 polynucleotide encoding the polypeptide compnsing SEQ ID NO 8 In another prefened embodiment, the present invention provides an isolated polynucleotide compnsing SEQ ID NO 7 In yet another embodiment, the present invention provides an isolated polynucleotide encoding the polypeptide compnsing SEQ ID NO 10 In still another prefened embodiment, the present invention provides an isolated polynucleotide compnsing SEQ ID NO 9 The present 25 invention further provides an isolated polynucleotide compnsing a nucleotide sequence that is complementary to the descnbed polynucleotides In another aspect, the present invention provides a composition comprising any of the above described polynucleotides and a suitable earner In one prefened embodiment, the present invention provides a composition compnsing an isolated polynucleotide encoding a "0 polypeptide compnsing SEQ ID NO 2, a polynucleotide compnsing SEQ ID NO 1, a polynucleotide compnsing nucleotides 291-7074 of SEQ ID NO 1, or a polynucleotide encoding the polypeptide compnsing an ammo acid sequence that has at least 98% identity to SEQ ID NO 2, and a suitable earner In another prefened embodiment, the composition comprises an isolated polynucleotide comprising a nucleotide sequence that has at least 90% identity with the polynucleotide comprising SEQ ID NO: 1 and a suitable carrier. In other prefened embodiments, the composition comprises an isolated polynucleotide comprising SEQ ID NO: 3 or an isolated polynucleotide comprising nucleotides 1-1532, 1080-1643, 1 181-1643, 1292-1643, or 1394-1532 of SEQ ID NO: 3 and a suitable carrier. In still other prefened embodiments, the invention provides a composition comprising a polynucleotide that hybridizes under stringent conditions to the polynucleotide of SEQ ID NO: 3, or a polynucleotide comprising nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1532 of SEQ ID NO: 3, as well as a composition comprising a polynucleotide that has at least 80% identity to the polynucleotide comprising SEQ ID NO: 3, or a polynucleotide comprising nucleotides 1- 1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1532 of SEQ ID NO: 3 and a suitable carrier. Also provided by the present invention is a composition comprising an isolated polynucleotide comprising a nucleotide sequence that is complementary to any of the described polynucleotides and a suitable carrier. In addition, the present invention provides recombinant vectors and host cells comprising any of the described ABCl polynucleotide sequences. In one prefened embodiment, the present invention provides a recombinant vector comprising an isolated polynucleotide encoding a polypeptide comprising SEQ ID NO: 2, an isolated polynucleotide comprising SEQ ID NO: 1, an isolated polynucleotide comprising nucleotides 291-7074 of SEQ ID NO: 1, or an isolated polynucleotide encoding the polypeptide comprising an amino acid sequence that has at least 98% identity to SEQ ID NO: 2. In another prefened embodiment, the recombinant vector comprises an isolated polynucleotide comprising a nucleotide sequence that has at least 90% identity, and more preferably at least 95% identity, with a polynucleotide comprising SEQ ID NO: 1. In still another prefened embodiment, the recombinant vector comprises an isolated polynucleotide comprising SEQ ID NO: 7 or SEQ ID NO: 9. The present invention further provides a recombinant vector comprising an isolated polynucleotide comprising a nucleotide sequence that is complementary to any of the described polynucleotides. In yet another prefened embodiment, the recombinant vector comprises any of the described polynucleotides and further comprises a heterologous promoter polynucleotide. One suitable heterologous promoter is a cytomegalovirus promoter. In a particularly prefened embodiment, the recombinant vector is pCEPhABCl . The present invention also provides a recombinant vector comprising an isolated polynucleotide comprising an ABCl 5' flanking sequence. In one prefened embodiment, the invention provides a recombinant vector compnsing an isolated polynucleotide compnsing SEQ ID NO 3 or an isolated polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1 181-1643, 1292-1643, or 1394-1532 of SEQ ID NO 3 In still other prefened embodiments, the invention provides a recombinant vector compnsing a polynucleotide that hybndizes under stnngent i conditions to the polynucleotide of SEQ ID NO 3, or a polynucleotide compnsing nucleotides 1- 1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1532 of SEQ ID NO 3, as well as a recombinant vector compnsing a polynucleotide that has at least 80% identity to these polynucleotides The present invention further provides a recombinant vector compnsing an isolated polynucleotide compnsing a nucleotide sequence that is complementary to any of the descnbed polynucleotides In yet another prefened embodiment, the recombinant vector comprises any of the descnbed polynucleotides and further compnses at least one polynucleotide encoding a heterologous polypeptide Suitable heterologous polypeptides include luciferase, β- galactosidase, chloramphemcol acetyl transferaseacetyl transferasetransferase, and green fluorescent proteins Preferably, the heterologous polypeptide is a luciferase protein In a 5 particularly prefened embodiment, the recombinant vector is pAPRl In addition, the present invention provides host cells compnsing any of the descnbed recombinant vectors The present invention further provides compositions compnsing any of the descnbed recombinant vectors and a suitable earner The present invention also provides methods for producing the ABCl protein in a 0 mammalian host cell as well as methods for expressing the ABCl protein in a mammalian subject The method for producing an ABCl protein in a mammalian host cell compnses the steps of (a) transfecting the mammalian host cell with a recombinant expression vector compnsing a polynucleotide encoding ABCl in an amount sufficient to produce a detectable level of ABCl protein, and (b) punfying the produced ABCl protein The method for ^ expressing ABCl protein in a mammalian subject compnses the step of administenng to a mammalian subject a recombinant expression vector compnsing a polynucleotide encoding ABCl in an amount sufficient to express ABCl protein in the mammalian subject In addition, the present invention provides compositions and methods suitable for increasing cholesterol efflux from cells of a mammalian subject In one prefened embodiment, ιθ the method compnses administenng to the mammalian subject a recombinant expression vector compnsing a polynucleotide encoding ABCl in an amount sufficient to increase cholesterol efflux from the cells Suitable recombinant expression vectors include vectors compnsing an isolated polynucleotide encoding a polypeptide compnsing SEQ ID NO 2, an isolated polynucleotide compnsing SEQ ID NO 1, an isolated polynucleotide comprising nucleotides 291-7074 of SEQ ID NO 1, and an isolated polynucleotide encoding the polypeptide compnsing an ammo acid sequence that has at least 98% identity to SEQ ID NO 2 Prefened expression vectors include viral vectors, especially adenoviral vectors and lentiviral vectors In other s embodiments, the invention provides non-viral delivery systems, including DNA- gand complexes, adenovirus-hgand-DNA complexes, direct injection of DNA, CaPO 4 precipitation, gene gun techniques, electroporation, posomes and hpofection In another prefened embodiment, the method for increasing cholesterol efflux from cells of a mammalian subject compnses administenng to the mammalian subject a therapeutic amount 0 of a compound that increases the expression of ABCl in the cells One suitable method compnses administenng to the mammalian subject a cAMP analogue Suitable cAMP analogues include 8-bromo cAMP, N6-benzoyl cAMP, and 8-thιomethyl cAMP Another suitable method compnses administenng to the mammalian subject a compound that increases the synthesis of cAMP, e g forskohn Yet another suitable method compnses administenng to the mammalian l ^ subject a compound that inhibits the degradation of cAMP, such as a phosphodiesterase inhibitor Suitable phosphodiesterase inhibitors include rohpram, theophylhne, 3-ιsobutyl-l- methylxanthme, R020-1724, vinpocetme, zapnnast, dipyndamole, milnnone, amnnone, pimobendan, cilostamide, enoximone, peroximone, and vesnannone In addition, another suitable method for increasing cholesterol efflux from cells of a 20 mammalian subject compnses administenng to the mammalian subject a least one ligand for a nuclear receptor in an amount sufficient to increase cholesterol efflux Suitable ligands include LXR, RXR, FXR, SXR and PPAR ligands In one prefened embodiment, the method compnses administering to a mammalian subject a ligand for an LXR nuclear receptor Suitable LXR ligands include 20(S) hydroxycholesterol, 22(R) hydroxycholesterol, 24(S) hydroxycholesterol, 25 25-hydroxycholesterol, and 24(S), 25 epoxycholesterol Preferably, the LXR ligand is 20(S) hydroxvcholesterol In another prefened embodiment, the method compnses administenng to a mammalian subject a ligand for an RXR nuclear receptor Suitable RXR ligands include 9-cιs retinoic acid, retinol, retinal, all-trans retmoic acid, \3-cιs retmoic acid, acitretm, fenretmide, etretmate. CD 495, CD564, TTNN, TTNNPB, TTAB, and LGD 1069 Preferably, the RXR 30 ligand is 9-cιs retmoic acid In another prefened embodiment, the method compnses administering to a mammalian subject a ligand for a PPAR nuclear receptor One suitable ligand is a ligand selected from the class of thiazohdinediones In yet another prefened embodiment, the method compnses administenng at least two ligands for a nuclear receptor In a particularly prefened embodiment, the ligands are 20(S) hydroxycholesterol and 9-cιs retmoic acid In addition, another suitable method for increasing cholesterol efflux from cells of a mammalian subject compnses administenng to the mammalian subject an eicosanoid in an ι amount sufficient to increase cholesterol efflux Suitable eicosanoids include prostaglandin E2, prostaglandm J2, and prostacychn (prostaglandin 12) In another embodiment, the present invention provides a method for increasing cholesterol efflux from cells of a mammalian subject compnsing administering to the mammalian subject a compound that increases ABCl activity in an amount sufficient to increase 0 cholesterol efflux from the cells The present invention also provides methods suitable for increasing the gene expression of ABCl in a mammalian subject In one prefened embodiment, the method compnses administering to the mammalian subject at least one ligand for a nuclear receptor in anamount sufficient to increase the gene expression of ABCl Suitable ligands include ligands for LXR, ■ RXR, FXR, SXR, and PPAR nuclear receptors In another prefened embodiment, the method compnses administenng to the mammalian subject a cAMP analogue in an amount sufficient to increase the gene expression of ABCl In yet another prefened embodiment, the method compnses administenng to the mammalian subject a compound that increases the synthesis of c MP in an amount sufficient to increase the gene expression of ABCl 0 In addition, the present invention provides a method for screening a test compound for ABCl expression modulating activity compnsing the steps of (a) operatively linking a reporter cDNA with an expression modulating portion of the mammalian ABCl gene to produce a recombinant reporter construct, (b) transfecting the recombinant reporter construct into a population of host cells, (c) assaying the level of reporter gene expression in a sample of the host 2 cells, (d) contacting the host cells with the test compound being screened, (e) assaying the level of reporter gene expression in a sample of the host cells after contact with the test compound, and (f) comparing the relative change in the level of reporter gene expression caused by exposure to the test compound, thereby determining the ABCl expression modulating activity The recombinant reporter construct compnses a reporter gene operatively linked to an expression 10 modulating portion of the mammalian ABCl gene, such as any of the ABCl 5' flanking region sequences provided by the present invention In one prefened embodiment, the expression modulating portion of the ABCl gene compnses SEQ ID NO 3 In another prefened embodiment, the expression modulating portion of the ABCl gene compnses nucleotides 1- 1532, 1080-1643, 1181-1643, 1292-1643, 1394-1643, or 1394-1532 of SEQ ID NO: 3. Suitable reporter cDNAs include luciferase, β-galactosidase, chloramphenicol, and green fluorescent protein cDNA. Preferably, the host cell is a mammalian cell. In a particularly prefened embodiment of the method, the recombinant reporter construct is pAPRl Also provided by the present invention is a method for screening a test compound to determine whether the test compound promotes ABCl -mediated cholesterol efflux from cells in culture compnsing the steps of: (a) assaying the level of cholesterol efflux in a sample of mammalian cells maintained in culture to determine a control level of cholesterol efflux; (b) contacting the cells with the test compound being screened; (c) assaying the level of cholesterol efflux in a sample of cells after contact with the test compound; (d) assaying the level of ABCl - mediated cholesterol efflux in a sample of cells after contact with the test compound, thereby determining whether the test compound promotes ABCl -mediated cholesterol efflux from cells in culture The cells can be denved from pnmary cultures or a cell line. Suitable cells for screening the test compound include fibroblast, macrophage, hepatic, and intestinal cell lines. Preferably, the cell line is RAW 264.7. In one prefened embodiment, the ABCl -mediated cholesterol efflux is measured using an anti-ABC 1 antibody that inhibits the activity of ABCl upon binding. In another prefened embodiment, the ABCl -mediated cholesterol efflux is measured using an antisense ABCl polynucleotide. In a particularly prefened embodiment, the antisense polynucleotide compnses SEQ ID NO: 57. In addition, the present invention provides methods for detecting the comparative level of ABCl expression in cells of a mammalian subject. Such methods can be used to determine the susceptibility of a subject to coronary heart disease A method for detecting the comparative level of ABCl expression in cells of a mammalian subject is provided which compnses (a) obtaining a cell sample from the mammalian subject, (b) assaying the level of ABCl mRNA expression in the cell sample; and (c) companng the level of ABCl mRNA expression in the cell sample with a pre-determmed standard level of ABCl mRNA expression, thereby detecting the comparative level of ABCl gene expression in the cells of a mammalian subject. Suitable methods for measunng the level of ABCl mRNA expression include, for example, RT-PCR, northern blot, and RNAse protection assay. The present invention also provides methods for detecting the comparative level of ABC 1 protein in cells of a mammalian subject. Such methods can be used to determine the susceptibility of a subject to coronary heart disease. A method for detecting the comparative amount of ABCl protein in the cells of a mammalian subject is provided which compnses (a) obtaining a cell sample from the mammalian subject, (b) assaying the amount of ABCl protein in the cell sample, and (c) comparing the amount of ABCl protein in the cell sample with a predetermined standard amount of ABCl protein, thereby detecting the comparative level of ABCl protein in the cells of the mammalian subject. The amount of ABCl protein can be determined using various immunoassays available in the art. For example, the amount of ABCl protein can be determined by (a) contacting the cell sample with a population of anti-ABC 1 antibodies and (b) detecting the specific-binding ABCl antibodies associated with the sample. Suitable methods for detecting ABCl antibodies include western blotting, immunoprecipitation, and FACS. In another aspect, the present invention provides antibodies that bind specifically to the described ABCl polypeptides. In one prefened embodiment, the present invention provides an isolated antibody that binds specifically to an isolated polypeptide comprising SEQ ID NO: 2. In another prefened embodiment, the invention provides an isolated antibody that bind specifically to an isolated polypeptide comprising an amino acid sequence that has at least 98% identity with SEQ ID NO: 2. The antibody can be a monoclonal antibody or the antibody can be a polyclonal antibody. In yet another embodiment, the antibody, upon binding to an ABCl polypeptide, inhibits the cholesterol transport activity of the ABCl polypeptide. In addition, the present invention provides kits suitable for screening a compound to determine the ABCl expression modulating activity of the compound comprising a reporter cDNA operatively linked to an expression modulating portion of the mammalian ABCl gene in an amount sufficient for at least one assay and instructions for use. In one prefened embodiment, the kit further comprises means for detecting the reporter gene. In another prefened embodiment, the expression modulating portion of the mammalian ABCl gene comprises SEQ ID NO: 3. In yet another prefened embodiment, the expression modulating portion of the mammalian ABCl gene comprises nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, 1394-1643, or 1394-1532 of SEQ ID NO: 3. Suitable reporter cDNAs include luciferase, β-galactosidase, chloramphenicol, and green fluorescent protein cDNA. Preferably, the reporter cDNA is luciferase. In a particularly prefened embodiment of the method, the recombinant reporter construct is pAPRl . The present invention also provides kits suitable for screening a compound to determine whether the compound modulates ABCl -dependent cholesterol efflux. In one prefened embodiment, the kit comprises an inactivating anti-ABC 1 antibody in an amount sufficient for at least one assay and instructions for use. In another prefened embodiment, the kit comprises an antisense ABC 1 oligonucleotide in an amount sufficient for at least one assay and instructions for use. In a particularly prefened embodiment, the antisense ABCl oligonucleotide comprises SEQ ID NO: 53. BRIEF DESCRIPTION OF THE FIGURES Figure 1A-D is a graphical representation showing the results of control cholesterol efflux and cholesterol efflux in the presence of HDL and apo A-I from normal fibroblast cells ( 1 A, C) and fibroblast cells from Tangier disease patients (IB, D). The open circles represent the cholesterol efflux from cells that were not exposed to HDL or apo A-I, the closed circles represent the cholesterol efflux from cells exposed to HDL, and the closed diamonds represent the cholesterol efflux from cells exposed to apo A-I; Figure 2 is a graphical representation of a gene expression microanay analysis showing a comparison of the gene expression found in cells from a Tangier patient (TDl) and that found in normal cells, whereby a total of 58,800 human cDNAs were hybridized with cDNA prepared from mRNA of cAMP-treated TDl cells cDNA (labeled with Cy3 dye) and with cDNA prepared from mRNA of cAMP-treated normal cells (labeled with Cy5 dye); Figure 3 is a schematic diagram showing a restriction map of the recombinant expression vector pCEPhABCl, which contains the open reading frame of the human ABCl gene; Figure 4 is a schematic diagram of the gene structure of human ABCl, showing a comparison between the published human ABCl amino acid sequence (GenBank, Accession # AJ012376) and the presently disclosed and claimed human ABCl amino acid sequence ("CVT") which has sixty additional amino acids at the N-terminal end; Figure 5 is a graphical representation showing the inhibitory effect that ABCl transport inhibitors 4,4-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and sulphobromophtaleine (BSP) have on apo A-I-mediated cholesterol efflux, wherein the open circles indicate the apo A- I-mediated cholesterol in the presence of BSP and the closed circles indicate the apo A-I- mediated cholesterol in the presence of DIDS; Figure 6 is a graphical representation showing the inhibitory effect of an antisense ABCl oligonucleotide on apo A-I-mediated cholesterol efflux, showing the apo A-I-mediated cholesterol efflux in cells incubated without antisense oligonucleotide, the apo A-I-mediated cholesterol efflux in cells exposed to 30 μM β-globin antisense oligonucleotide, and the apo A-I- mediated cholesterol efflux in cells exposed to 30 μM ABCl antisense oligonucleotide; Figure 7 is a graphical representation demonstrating the stimulation of apo A-I-mediated cholesterol efflux caused by overexpression of the ABCl gene using RAW 264.7 mouse macrophage cells stably transfected with an expression plasmid for human ABCl (pCEPhABCl ), showing the apo A-I-mediated cholesterol efflux in control parental cells (no pCEPhABCl) and the apo A-I-mediated cholesterol efflux in clonal cells transfected with s pCEPhABCl (L3, L5, L6); Figure 8 is a graphical representation of reverse transcnption polymerase chain reaction (RT-PCR) analyses showing the level of ABCl gene expression in normal cells and cells from Tangier's disease patients (TDl and TD2) that have been either exposed to albumin (closed bars), exposed to 8-Br-cAMP (open bars), cholesterol-loaded (shaded bars), or cholesterol-loaded and 0 subsequently exposed to apo A-I (hatched bars); Figure 9 is a graphical representation of the results of RT-PCR analyses showing the level of ABCl gene expression in RAW 264.7 cells exposed to either ethanol (0.1% v/v), 9-cιs retmoic acid {9-cιs RA; lOμM), 20(S) hydroxycholesterol (20(S)-OH, lOμM), or 9-cιs RA and 20(S)-OH (10μM each); 5 Figure 10 shows the results of immunoprecipitation analyses indicating the level of cell- surface ABCl protein found in normal fibroblasts (NL1, 10A) and fibroblasts from a Tangier's disease patient (TDl, 10B) in the presence of either no additives (control), 8-Br-cAMP (lmM), cholesterol (30 μg/ml), or cholesterol and 8-Br-cAMP (30μg/ml and lmM, respectively); Figure 11 is a schematic diagram showing a restnction map of the recombinant 0 expression vector pAPRl, which contains the 5' flanking region of the ABCl gene positioned upstream of the open reading frame of the luciferase reporter gene, Figure 12 is a graphical representation showing the level of luciferase reporter gene expression induced in RAW 264.7 cells transfected with pAPRl in the presence of either EtOH (control), 20(S)-OH (lOμM), 9-cιs RA (lOμM), or both 20(S)-OH and 9-cιs RA (lOμM each); 25 Figure 13 is a schematic diagram of the 5' flanking region of the ABCl gene. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, novel polypeptides that increase the cholesterol efflux from cells are provided. In particular, the present invention provides novel ATP-Bmding " 50 Cassette 1 (ABCl) polypeptides that have been shown to increase cholesterol efflux ABCl is a member of the family of ATP -binding cassette proteins that reside in cell membranes and utilize ATP hydrolysis to transport a wide vanety of substrates across the plasma membrane It should be noted that the terms "ABCl " and "ABCAl " both refer to the same ATP- binding cassette protein. The term "ABCAl" was introduced in 1999 by a nomenclature committee and has received limited acceptance in the field. To date, more than 30 members of this family have been identified in the human genome. These homologous proteins contain channel-like structures through which molecules are transported through the cell membrane and ^ one or two domains which bind to ATP to couple energy generating ATP -hydrolysis to transport Family members include the multidrug resistance factors (MDR/P-glycoprotems; Chen et al.. Cell, 47 381-389 (1986); Stnde et al., Mol. Pharmacol, 49:962-971 (1996)), transporters associated with antigen presentation (Neefjes et al., Science, 261:769-771 (1993), Shepherd et al., Cell, 74 577-584 (1993)), and the cystic fibrosis transmembrane conductance regulator 0 (Chang et al., J Biol Chem., 269:18572-18575 (1994); Rommens et al., Science, 245: 1059- 1065 (1989)) Members of the ABC transporter family are generally composed of 4 domains found withm two symmetnc halves that are linked by a long charged region and a highly hydrophobic segment. Each half contains a hydrophobic domain, containing 6 transmembrane segments and a hydrophilic nucleotide binding domain containing highly conserved Walker A i s and B sequence motifs typical of many ATPases (Hyde et al., Nature, 346 362-365 (1990); Luciani et al., Genomics, 21. 150-159 (1994)). The transporter activity is dependent on the interaction with ATP at the nucleotide binding domains and by regulation via phosphorylation of residues in the region linking the two symmetric halves (Becq et al., J. Biol Chem., 272: 2695- 2699 (1997)) 20 Several lines of evidence described herein identified ABCl as a pivotal protein in the apohpoprotem-mediated mobilization of mtracellular cholesterol stores First, the studies presented herein showed that ABCl is defective in Tangier disease, a genetic disorder characterized by abnormal HDL-cholesterol metabolism. As shown previously, and herein at Example 1, the genetic defect in Tangier disease causes a defect in the pathway of apohpoprotem 25 mediated efflux of cholesterol from withm cells, resulting in significantly decreased cholesterol efflux activity and low HDL-cholesterol levels (Oram et al, J Lipid Res , 37-2743-2491 (1996), Francis et al., J Clin. Invest., 96 78-87 (1995)). Genetic linkage analysis of families with Tangier disease assigned the defective gene to an interval on chromosome 9q31 (Rust et al, Nature Genetics, 20' 96-98 (1998)) A search of public databases revealed that the ABCl gene 30 was localized to chromosome 9q22-9q31 , which is broader than, but includes the interval revealed in Rust et al. (Luciani et al , supra (1994)) Based on that data, radiation hybnd mapping of the human ABCl gene was performed, which placed the gene between two markers squarely within the 7-cM region of human chromosome 9q31 reported by Rust et al. In addition, as shown in Example 2, microanay analysis revealed that the ABCl gene is 2.5-fold underexpressed in Tangier patient cells as compared with normal cells. These studies identified the defective gene in Tangier disease as ABCl . In addition, further studies presented herein linked ABCl activity to cholesterol efflux activity. First, studies showed that inhibitors of ABCl transport activity, such as 4,4-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and sulphobromophtaleine (BSP), also inhibited apoAI-mediated cholesterol efflux from fibroblast cells (see Example 6). Also, inhibition of ABCl gene expression, using an antisense ABCl oligonucleotide, was shown to inhibit apoAI-mediated cholesterol efflux from fibroblast cells (Example 7). In contrast, transfection studies, in which the ABCl gene was transfected into mouse monocyte cells, showed that overexpression of ABCl results in an increase in apoAI- mediated efflux (Example 8). Finally, RT-PCR performed using wildtype and Tangier patient mRNA revealed that ABCl mRNA expression is regulated by cellular conditions related to cholesterol efflux in normal skin fibroblast cells, but not in Tangier patient fibroblasts (Example 9). Based on these findings, it was determined that ABCl plays a major role in cholesterol efflux. It is postulated that ABCl plays a role in the translocation of intracellular cholesterol to the outer leaflet of the plasma membrane. Deficient transport of intracellular cholesterol due to a lack of ABCl or defective ABCl results in a lack of cholesterol in specific membrane domains with which apoAI and other apolipoproteins specifically interact (Stangl et al., J. Biol. Chem., 273: 31002-31008 (1998); Babitt et al., J. Biol. Chem., 272: 13242-13249 (1997))). The failed delivery of cholesterol to apoAI leads to the formation of cholesterol-deficient HDL particles that are rapidly removed from the plasma. (Bojanovski et al., J. Clin. Invest., 80: 1742-1747 (1987)). Definitions The following definitions are provided to facilitate understanding of certain terms used throughout this specification. In the present invention, "isolated" refers to material removed from its original environment (e.g., the natural environment if it is naturally occurring), and thus is altered "by the hand of man" from its natural state. For example, an isolated polynucleotide could be part of a vector or a composition of matter, or could be contained within a cell, and still be "isolated" because that vector, composition of matter, or particular cell is not the original environment of the polynucleotide. As used herein, the term "polynucleotide(s)" is defined to encompass DNA and RNA of both synthetic and natural ongm The polynucleotide may exist as single- or double-stranded DNA or RNA, or an RNA/DNA heteroduplex Thus, the polynucleotide of the present invention can be composed of any polynbonucleotide or polydeoxnbonucleotide, which may be unmodified RNA or DNA or modified RNA or DNA For example, polynucleotides can be composed of single- and double-stranded DNA, DNA that is a mixture of single- and double- stranded regions, or single, double-, and tnple-stranded regions, single- and double-stranded RNA, and RNA that is mixture of single- and double-stranded regions, hybnd molecules compnsing DNA and RNA that may be single-stranded or, more typically, double-stranded or tnple-stranded, or a mixture of single- and double-stranded regions In addition, the l o polynucleotide can be composed of tnple-stranded regions compnsing RNA or DNA or both RNA and DNA A polynucleotide may also contain one or more modified bases or DNA or RNA backbones modified for stability or for other reasons "Modified" bases include, for example, tπtylated bases and unusual bases such as inosine A vanety of modifications can be made to DNA and RNA, thus, "polynucleotide" embraces chemically, enzymatically, or l-i metabohcally modified forms of polynucleotides The term "polynucleotιde(s)" also embraces short polynucleotides often refened to as ohgonucleotιde(s) The term "polypeptιde(s)" refers to any peptide or protein compnsing two or more ammo acids joined to each other by peptide bonds or modified peptide bonds "Polypeptide" refers to both short amino acid sequences, commonly refened to as peptides, as well as longer ammo acid 20 sequences, generally refened to as proteins The polypeptide may contain ammo acids other than the 20 gene encoded ammo acids Moreover, the polypeptide may be modified either by natural processes, such as processing and other post-translational modifications, or by chemical modification techniques, which are well-known in the art A given polypeptide may contain many types of modifications Also, the same type of modification may be present in the same or 2^ varying degree at one or more sites in the polypeptide Modifications may occur anywhere in the polypeptide, including the peptide backbone, the ammo acid side-chains, and the ammo or carboxyl termini Modifications include, but are not limited to, acetylation, acylation, ADP- πbosylation, amidation, formylation, garnma-carboxylation, glycosylation, hydroxylation, lodination. methylation, mynstoylation, oxidation, phosphorylation, prenylation, sulfation, and 30 selenoylation, as well as the covalent attachment of a nucleotide or nucleotide denvative, a lipid or lipid derivative, or a phosphotidyhnositol Other modifications include cross-linking, cychzation, formation of pyroglutamate, GPI anchor formation, proteo lytic processing, racemization. and t-RNA-mediated addition of ammo acids, such as argmylation and ubiquitmation See, for example, Proteins- Structure and Molecular Properties, 2 nd Ed , T E Creighton, W H Freedman and Co., New York (1993); Wold, F , Posttranslational Protein Modification Perspectives and Prospects, in Posttranslational Covalent Modification of Proteins, B. C. Johnson, Ed., Academic Press, New York (1983); Seifter et al., Meth. Enzymol., 182: 626- 646 ( 1990), and Rattan et al., Protein Synthesis: Posttranslational Modifications and Aging, Ann N Y Acad Sci , 663. 48-62 (1992)). The polypeptides of the invention can be prepared in any suitable manner. Such polypeptides include isolated naturally occumng polypeptides, recombmantly produced polypeptides, synthetically produced polypeptides, or polypeptides produced by a combination of these methods. Means for prepanng such polypeptides are well understood in the art. A "polynucleotide" of the present invention also includes those polynucleotides capable of hybndizmg, under stnngent hybridization conditions, to SEQ ID NO:3 or nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, 1394-1643, or 1394-1532 of SEQ ID NO: 3, or the complements thereof A polynucleotide of the present invention also includes those polynucleotides capable of hybndizmg, under stnngent hybndization conditions, to SEQ ID NO.4, SEQ ID NO: 5, or SEQ ID NO- 6 or the complements thereof. "Stringent hybndization conditions" refers to an overnight incubation at 42° C in a solution compnsing 50% formamide, 5x SSC (750 mM NaCI, 75 mM sodium citrate), 50 mM sodium phosphate (pH 7.6), 5x Denhardt's solution, 10% dextran sulfate, and 20 μg/ml denatured, sheared salmon sperm DNA, followed by washing the filters in O.lx SSC at about 65°C As used herein, the term "complementary" refers to the hybndization or base pamng between nucleotides, such as, for example, between the two strands of a double-stranded polynucleotide or between an oligonucleotide pnmer and a pnmer binding site on a smgle- stranded polynucleotide to be amplified or sequenced. Two single-stranded nucleotide molecules are said to be complementary when the nucleotides of one strand, optimally aligned with appropπate nucleotide insertions, deletions or substitutions, pair with at least about 80% of the nucleotides of the other strand. "Identity", as known in the art, is a relationship between two or more polypeptide sequences or two or more polynucleotide sequences, as determined by companng the sequences "Identity" or "similanty" also has an art-recognized meaning that refers to the degree of sequence relatedness between polypeptide or polynucleotide sequences, as determined by the match between strings of such sequences. "Identity" and "similanty" can be calculated using a number of well known methods, including those published in Computational Molecular Biology, Lesk, A M , ed., Oxford University Press, New York, (1988); Biocomputing Informatics and Genome Projects, Smith, D.W., ed., Academic Press, New York, (1993); Computer Analysis of Sequence Data, Part I, Griffin, A.M., and Griffin, H.G., eds., Humana Press, New Jersey, (1994); Sequence Analysis in Molecular Biology, von Heinje, G., Academic Press, (1987); and Sequence Analysis Primer, Gribskov, M. and Devereux, J., eds., M Stockton Press, New York, (1991); and Carillo, H., and Lipton, D., SIAM J Applied Math 48:1073 (1988)). Methods commonly employed to determine identity or similarity between two sequences include, but are not limited to, those disclosed in "Guide to Huge Computers," Martin J. Bishop, ed., Academic Press, San Diego, ( 1994), and Carillo, H., and Lipton, D., SIAM J Applied Math 48: 1073 (1988). Prefened methods to determine identity are designed to give the largest match between the sequences tested. Methods for aligning polynucleotides or polypeptides are codified in computer programs, including the GCG program package (Devereux, J., et al, Nucleic Acids Research (1984) 12(1):387 (1984)), BLASTP, BLASTN, FASTA (Atschul, S.F. et al., J. Molec. Biol. 215:403 ( 1990), Bestfit program (Wisconsin Sequence Analysis Package, Version 8 for Unix, Genetics Computer Group, University Research Park, 575 Science Drive, Madison, Wl 53711 (using the local homology algorithm of Smith and Waterman, Advances in Applied Mathematics 2:482-489 (1981)). When using any of the sequence alignment programs to determine whether a particular sequence is, for instance, 90% identical to a reference sequence, the parameters are set so that the percentage of identity is calculated over the full length of the reference polypeptide or polynucleotide and that gaps in identity of up to 10% of the total number of nucleotides in the reference polynucleotide are allowed. A prefened method for determining the best overall match between a query sequence (a sequence of the present invention) and a subject sequence, also refened to as a global sequence alignment, can be determined using the FASTDB computer program based on the algorithm of Brutlag et al. (Comp. App. Biosci. 6:237-245 (1990)). The term "sequence" includes nucleotide and amino acid sequences. In a sequence alignment the query and subject sequences are either both nucleotide sequences or both amino acid sequences. The result of said global sequence alignment is in percent identity. Prefened parameters used in a FASTDB search of a DNA sequence to calculate percent identity are: Matrix=Unitary, k-tuple=4, Mismatch Penalty=l, Joining Penalty=30, Randomization Group Length=0, and Cutoff Score=l, Gap Penalty=5, Gap Size Penalty 0.05, and Window Size=500 or query sequence length in nucleotide bases, whichever is shorter. Prefened parameters employed to calculate percent identity and similarity of an amino acid alignment are: Matrix=PAM 150, k-tuple=2, Mismatch Penalty= 1, Joining Penalty=20. Randomization Group Length=0, Cutoff Score=l, Gap Penalty=5, Gap Size Penalty=0 05. and Window Sιze=500 or query sequence length in amino acid residues, whichever is shorter As an illustration, a polynucleotide having a nucleotide sequence of at least 90% "identity" to a sequence contained in SEQ ID NO 1 means that the nucleotide sequence of the polynucleotide is identical to a sequence contained in SEQ ID NO 1 except that the polynucleotide sequence may include up to ten point mutations per each 100 nucleotides of the total length of SEQ ID NO 1 In other words, to obtain a polynucleotide compnsing a nucleotide sequence that has at least 90% identity to SEQ ID NO 1, up to 10% of the nucleotides in the sequence contained in SEQ ID NO 1 can be deleted, inserted, or substituted with other nucleotides These changes may occur anywhere throughout the polynucleotide, and may be interspersed either individually among nucleotides or in one or more contiguous groups withm SEQ ID NO 1 Similarly, a polypeptide having an amino acid sequence of at least 98% "identity" to a sequence contained in SEQ ID NO 2 means that the ammo acid sequence of the polypeptide is identical to a sequence contained in SEQ ID NO 2 except that the polypeptide sequence may include up to 2 ammo acid alterations per each 100 amino acids of the total length of SEQ ID NO 2 In other words, to obtain a polypeptide having an ammo acid sequence at least 98% identical to SEQ ID NO 2, up to 2% of the ammo acid residues in the sequence contained in SEQ ID NO 2 can be deleted, inserted, or substituted with other amino acid residues These changes may occur anywhere throughout the polypeptide, and may be interspersed either individually among residues or in one or more contiguous groups withm SEQ ID NO 2 "A polypeptide having biological activity" refers to a polypeptide exhibiting activity similar, but not necessanly identical, to an activity of a polypeptide of the present invention (e g cholesterol transport activity), as measured in a particular biological assay, with or without dose dependency In the case where dose dependency does exist, it need not be identical to that of the polypeptide, but rather substantially similar to the dose-dependence in a given activity as compared to the polypeptide of the present invention (I e , the candidate polypeptide will exhibit greater activity or not more than about 25-fold less and, preferably, not more than about tenfold less activity, and most preferably, not more than about three-fold less activity relative to the polypeptide of the present invention ) "Polypeptide vanant" refers to a polypeptide diffenng from the ABCl polypeptide of the present invention, but retaining essential properties thereof Generally, vaπants are overall closely similar, and, in many regions, identical to the polypeptide compnsing SEQ ID NO 2 Preferably, the polypeptide variant retains its biological activity, i.e., cholesterol transport activity. Variants include, but are not limited to, splice variants and allelic variants, as well as addition, deletion, and substitution variants. Likewise, "polynucleotide variant" refers to a polynucleotide differing from the polynucleotide of the present invention, but retaining essential properties thereof. The variants may contain alterations in the coding regions, non-coding regions, or both. Thus, for example, an ABCl polynucleotide variant has a nucleotide sequence that differs from that of SEQ ID NO: 1 , but encodes a polypeptide that has cholesterol transport activity. Also, for example, a polynucleotide variant has a nucleotide sequence that differs from that of SEQ ID NO: 3, but retains promoter activity. Especially prefened are polynucleotide variants containing alterations that produce silent substitutions, additions, or deletions, but do not alter the properties or activities of the encoded polypeptide. Nucleotide variants produced by silent substitutions due to the degeneracy of the genetic code are prefened. Moreover, variants in which 10-20, 5-10, 1-5, or 1 -2 amino acids are substituted, deleted, or added in any combination are also prefened. Polynucleotide variants can be produced for a variety of reasons, e.g., to optimize codon expression for a particular host (e.g. changing codons in the human mRNA to those prefened by a bacterial host such as E. coli). "Allelic variants" are naturally-occurring variants that refer to one of several alternate forms of a gene occupying a given locus on a chromosome of an organism. (Genes II, Lewin, B., ed., John Wiley & Sons, New York (1985).) These allelic variants can vary at either the polynucleotide and/or polypeptide level. Alternatively, non-naturally occurring variants may be produced by mutagenesis techniques or by direct synthesis. The term "conservative amino acid substitution" refers to a substitution of a native amino acid residue with a normative residue such that there is little or no effect on the polarity or charge of the amino acid residue at that position. For example, a conservative substitution results from the replacement of a non-polar residue in a polypeptide with any other non-polar residue. Another example of a conservative substitution is the replacement of an acidic residue with another acidic residue. Conservative substitutions are expected to produce ABCl polypeptides having functional and chemical characteristics similar to those of the naturally-occurring ABCl polypeptide. The term "ortholog" refers to a polypeptide that conesponds to a polypeptide identified from a different species. For example, mouse and human ABCl polypeptides are considered ortholoes. The term "vector" is used to refer to any molecule (e.g nucleic acid, plasmid, or virus) used to transfer coding informationto a host cell. The term "expression vector" refers to a vector that is suitable for transformation of a host cell and contains nucleic acid sequences that direct and/or control the expression of inserted ^ heterologous nucleic acid sequences Expression includes, but is not limited to, processes such as transcription, translation, and RNA splicing, if mtrons are present As used herein, the term "transcnptional regulatory region" or "expression modulating portion" refers to any region of the gene, including, but not limited to, promoters, enhancers, and repressors 0 As used herein, the term "promoter" refers to an untranscnbed sequence located upstream {ι e , 5') to the start codon of a structural gene (generally withm about 100 to 1000 bp) that controls the transcnption of the structural gene As used herein the term "enhancers" refers to czs-actmg elements of DNA, usually about 10-300 bp in length, that act on the promoter to increase transcnption Enhancers are relatively 5 orientation and position independent They have been found 5' and 3' to the transcnption unit "Host cell" is a cell that has been transformed or transfected, or is capable of transformation or transfection by an exogenous polynucleotide sequence The term includes the progeny of the parent cell, whether or not the progeny is identical in morphology or in genetic make-up to the ongmal parent, so long as the selected gene is present 0 The term "operatively linked" is used herein to refer to an anangement of flanking sequences wherein the flanking sequences so descnbed are configured or assembled so as to perform their usual function Thus, a flanking sequence operably linked to a coding sequence may be capable of effecting the replication, transcnption and/or translation of the coding sequence For example, a coding sequence is operably linked to a promoter when the promoter is 2^ capable of directing transcnption of that coding sequence A flanking sequence need not be contiguous with the coding sequence, so long as it functions conectly Thus, for example, intervening untranslated yet transcnbed sequences can be present between a promoter sequence and the coding sequence and the promoter sequence can still be considered "operably linked" to the coding sequence 30 The term "transfection" is used to refer to the uptake of foreign or exogenous DNA by a cell, and a cell has been "transfected" when the exogenous DNA has been introduced inside the cell membrane A number of transfection techniques are well known in the art and are disclosed herein See, e g , Graham et al , 1973, Virology 52 456, Sambrook et al , Molecular Cloning A Laboratory Manual (Cold Spnng Harbor Laboratones, 1989); Davis et al , Basic Methods in Molecular Biology (Elsevier, 1986); and Chu et al, 1981, Gene 13.197 Such techniques can be used to introduce one or more exogenous DNA moieties into suitable host cells. ABCl Polypeptides The present invention relates to novel human ABCl polypeptides In one embodiment, the ABCl polypeptide compnses the ammo acid sequence shown in SEQ ID NO. 2 In contrast to the human ABCl protein reported by others, the ABCl polypeptide shown in SEQ ID NO: 2 has an additional 60 ammo acids at the ammo terminus, revealing an ABCl protein of 2261 ammo acids rather than 2201 amino acids (see Langmann et al. in Biochem Biophvs Res Comm . 257, 29-33 (1999)). In addition, the ABCl polypeptide shown in SEQ ID NO. 2 differs from other reported sequences at several ammo acid residues. Specifically, the present ABCl polypeptide shown m SEQ ID NO: 2 has a K for R at residue 159, 1 for V at 765, M for I at 823, I for T at 1495, L for P at 1588, K for R at 1914, and L for P at 2108. To remain consistent with published notation, the above ammo acid numbers are those of Lawn et al, J Clin. Invest., 104: R25-31 (1999), rather than those of SEQ ID NO: 2. As discussed m further detail below, the sequence difference likely anses from the fact that the first ABCl cDNA was cloned from mouse using a PCR-based strategy and the subsequently reported human ABCl cDNA sequences were predicted from the sequence of the mouse protein. The ABCl protein has an approximate molecular weight of 240 kD as determined by SDS-PAGE. The present invention also relates to ABCl polypeptides compnsing amino acid sequences which preferably have at least 98% identity over their entire length to the ammo acid sequence of SEQ ID NO. 2 More preferably, the polypeptide has at least 99% identity over its entire length to the ammo acid sequence of SEQ ID NO: 2 Most preferably, the polypeptide has 100% identity over its entire length to the amino acid sequence of SEQ ID NO. 2. As defined previously, the term "identity" refers to the degree of sequence relatedness between polypeptide sequences, which is further defined below. Such related ABCl polypeptides include substitution, deletion, and insertion vanants, as well as allelic vanants, splice vanants, fragments, denvatives, and orthologs. Prefened polypeptides and polypeptides fragments include those polypeptides and fragments that possess the biological activity of ABC 1. In particular, those polypeptides and fragments that mediate reverse cholesterol transport are prefened. Also prefened are polypeptides and fragments that have improved reverse cholesterol transport activity Substitution, deletion, and insertion variants refer to ABCl polypeptides comprising amino acid sequences that contain one or more amino acid sequence substitutions, deletions, and/or additions as compared to the ABCl amino acid sequence set forth in SEQ ID NO: 2. In prefened embodiments, the variants have from about 1 to 5, or from about 1 to 10, or from about 1 to 20, or from about 1 to 40, or from about 1 to 65 amino acid substitutions, additions, and or deletions. For example, the variants can have an addition of one or more amino acid residues anywhere in the polypeptide as well as at the carboxyl terminus and/or at the amino terminus, as long as the variant retains biological function. Also, for example, one or more amino acids can be deleted from any region of the polypeptide, including the carboxyl terminus and/or amino terminus, without substantial loss of biological function (Ron et al., J. Biol. Chem., 268: 2984- 2988 (1993); Dobeli et al, J. Biotechnology, 7: 199-216 (1988)). The amino acid substitution(s) can be conservative, non-conservative, or any combination thereof, as long as the ABCl variant retains its biological activity. In addition, the substitution(s) can be with non-conserved amino acid residues, where the substituted residues may or may not be encoded by the genetic code, and with amino acid residues having a substituent group. Suitable variants of ABCl polypeptides can be determined using well-known techniques. For example, suitable ABCl variants can be determined by identifying regions of the ABCl molecule that may be changed without destroying biological activity. Also, as realized in the art, even regions that may be important for biological activity or for structure may be subject to conservative amino acid substitutions without destroying the biological activity or without adversely affecting the polypeptide structure. Amino acid residues that can be changed without destroying biological activity can be determined by identifying regions of the ABCl polypeptide that are not important for activity (Bowie et al., Science, 247: 1306-1310 (1990)). For example, ABCl polypeptides from various species can be compared to determine the amino acid residues and regions of ABCl molecules that are conserved across species. The conserved amino acid residues are likely important for biological function and or structure. In contrast, changes in regions of the ABCl molecule that are not conserved across species and are thus tolerated by natural selection would be less likely to adversely affect biological activity and/or structure. Accordingly, ABCl polypeptides with additions, deletions, or substitutions in the non-conserved regions are likely suitable variants. Even in relatively conserved regions, chemically similar amino acids may be substituted for the naturally occurring residues while retaining activity. In addition, suitable ABCl variants can be identified using structure-function studies to determine residues in other members of the ATP -binding cassette protein family, such as ABCR and ABC-C, that are important for activity or structure. Such studies allow the prediction of important amino acid residues in an ABCl vanant that conespond to amino acid residues that are important for activity or structure in other ATP-binding cassette proteins For example, based on structure-function studies of other ATP -binding cassette proteins, important ammo acid residues in ABCl are likely found in regions associated with nucleotide binding and sterol transport Suitable vanants include, for example, polypeptides having chemically similar amino acid substitutions for such predicted important ammo acid residues of the ABCl polypeptide Suitable ABCl vanants can also be determined using genetic engineenng techniques to introduce ammo acid changes at specific positions in order to identify regions cntical for polypeptide function Ammo acid changes can be made using, for example, site-directed mutagenesis or alanme-scanning mutagenesis (Cunningham et al , Science, 244 1081-1085 ( 1 89)) The resultant ABCl vanants can then be tested for biological activity using, for example, any one of the cholesterol efflux assays descnbed herein Vanants having a particular ammo acid residue substituion that results in destroyed cholesterol efflux activity would not be considered a suitable ABCl vanant Additional methods for identifying suitable vanants are known in the art Furthermore, one skilled in the art would realize amino acid changes that are likely to be permissive at certain ammo acid positions in the protein (Bowie et al , supra (1990)) For example, it is generally known that the most buned or mtenor (within the tertiary structure of the protein) ammo acid residues require nonpolar side chains, whereas fewer features of surface or extenor side chains are generally conserved Moreover, it is known that tolerated conservative ammo acid substitutions involve replacement of the aliphatic or hydrophobic ammo acids Ala, Val, Leu and He, replacement of the hydroxyl residues Ser and Thr, replacement of the acidic residues Asp and Glu, replacement of the amide residues Asn and Gin, replacement of the basic residues Lys, Arg, and His, replacement of the aromatic residues Phe, Tyr, and Trp, and replacement of the small- sized amino acids Ala, Ser, Thr, Met, and Gly The ABCl vanants can be naturally-occurnng or artificially constructed Examples of naturally-occurnng vanants are allelic vanants and splice vanants Allelic vanants refer to one of several alternate forms of a gene occupying a given locus on a chromosome of an organism or population of organisms (Lewin, B , ed , Genes II, John Wiley & Sons, New York (1985)) Allelic variants can vary at either the polynucleotide and/or polypeptide level Splice vanants refer to a nucleic acid molecule, usually RNA, which is generated by alternative processing of intron sequences in an RNA transcnpt, and the conespondmg polypeptide Alternatively, the ABCl variants can be artificially constructed For example, ABCl vanants can be constructed using the technique of site-directed mutagenesis Also, for example, ABCl vanants can be prepared from the conespondmg nucleic acid molecules encoding said variants, which have a DNA sequence that vanes as descnbed from the wild-type DNA sequence as set forth in SEQ ID NO 1 Polypeptide fragments refer to polypeptides which compnse less than the full length ammo acid sequence of ABCl set forth in SEQ ID NO 2 Prefened polypeptides fragments include those fragments that possess the biological activity of ABCl In particular, those fragments that mediate reverse cholesterol transport or have improved reverse cholesterol transport activity are prefened ABCl fragments can have one or more amino acids deleted from any region of the polypeptide, including the carboxyl terminus and/or ammo terminus, as long as biological function is maintained The ABCl polypeptide fragments can occur naturally, such through alternative splicing or in vivo protease activity, or can be artificially constructed using well-known methods The invention also relates to ABCl polypeptide denvatives, which refer to ABCl polypeptides, vanants, or fragments, as defined herein, that have been chemically modified The denvatives are modified in a manner that is different from naturally-occurnng ABCl polypeptides, either in type or location of the molecules attached to the polypeptide Denvatives may further include polypeptides formed by the deletion of one or more chemical groups which are naturally attached to the ABCl polypeptides In addition, the ABCl polypeptide compnsing the ammo acid sequence of SEQ ID NO 2, as well as the above-descnbed ABCl vanants and fragments, may be fused to a homologous polypeptide to form a homodimer or to a heterologous polypeptide to form a heterodimer. Another aspect of the present invention relates to mutant ABC 1 polypeptides and fragments thereof, conespondmg to polypeptides isolated from Tangier patients In one prefened embodiment, the ABCl polypeptide compnses SEQ ID NO 8 The protein was isolated from a Tangier patient (TDl) and sequenced as decnbed in Examples 1 and 5 The amino acid sequence set forth in SEQ ID NO 8 is similar to the wild-type sequence with the exception of a glutamine to argmine residue substitution at position 537 (the residue number is that of Lawn et al , J Clin Invest , 104 r25-31 (1999), conespondmg to position 597 of SEQ ID NO 8) The location of this residue is within the ammo-terminal hydrophilic domain, near the first predicted transmembrane domain The substitution alters the charge of the amino acid in this region of the protein, resulting in an ABCl protein that has significantly decreased cholesterol efflux activity, as shown in Figure 1 In another prefened embodiment, the mutant ABCl polypeptide comprises SEQ ID NO: 10. The protein conesponds to a polypeptide isolated from a Tangier patient (TD2) and sequenced as decribed in Examples 1 and 5. The amino acid sequence set forth in SEQ ID NO: 10 is similar to the wild-type sequence with the exception of an arginine to tryptophan substitution at residue 527 (the residue number is that of Lawn et al., supra (1999), conesponding to position 587 of SEQ ID NO: 10). Like the TDl polypeptide, this substitution alters the charge of the amino acid residue in the amino-terminal hydrophilic domain of the ABCl protein. The resultant mutant ABCl protein also has significantly decreased cholesterol efflux activity, as shown in Figure 1. ABCl Polynucleotides Another aspect of the present invention relates to isolated polynucleotides that encode the novel ABCl polypeptides and variants thereof. The present invention provides, for example, isolated polynucleotides encoding the full-length ABCl polypeptide, polynucleotides containing the full-lenth cDNA of wild-type ABCl, polynucleotides containing the entire length of the coding sequence of wild-type ABCl, and polynucleotides containing non-coding 5' and 3' sequences of ABCl, as well as polynucleotides of related ABCl variants. The present invention also provides isolated polynucleotides that encode mutant ABCl polypeptides, such as those of Tangier patients. In one prefened embodiment, the isolated polynucleotide comprises a nucleotide sequence encoding the polypeptide comprising SEQ ID NO: 2. Importantly, in contrast to the published sequence of Langmann et al. which codes for a protein of 2201 amino acids based on a predicted start methionine found in exon 3 (Langmann et al., Biochem. Biophys. Res. Comm., 257: 29-33 (1999) (GenBank Accession No. AJO12376), the presently claimed nucleotide sequence contains 50 exons and codes for a protein of 2261 amino acids (see Figure 4). The conesponding nucleotide sequence of the present invention contains a coding sequence that includes an additional 180 nucleotides at the 5' end conesponding to the following 60 amino- terminal amino acids: MACWPQLRLLLWKNLTFRRRQTCQLLLEVAWPLFIFLILISVRLSYPPYEQHECHFPNKA . Given that there is an in-frame stop codon 6 to 9 nucleotides upstream from this location, the newly predicted start site is the first methionine codon that could produce a continuous open reading frame. Alignment of this new ABCl cDNA sequence with related ABC transporter sequences ABCR and ABC-C (also known as ABC3) which also contain open reading frames for the 60 additional amino acids, indicates a high degree of similarity, implying that the homologous ABC transporter proteins begin with sequences related to the amino terminal extension sequence proposed for human ABCl. It is likely that the earlier published start site of the human ABCl was predicted from the published mouse ABCl cDNA sequence (Luciani et al., Genomics, 21150-159 (1994); GenBank Accession no.: X75926) which contains an extra nucleotide "n" in the extension region such that the newly disclosed methionine is not in-frame. However, if the "n" nucleotide in the mouse sequence is ignored, the mouse and human sequences of the extension region are identical. In light of these results, it is likely that the full length human ABCl protein contains 2261 amino acids rather than 2201 amino acids, as previously suggested by Langmann et al. and others. Accordingly, Langmann et al. do not present the full open reading frame of human ABCl . In another prefened embodiment, the isolated polynucleotide comprises the full-lenth ABCl cDNA, including at least a portion of either non-coding 5' and 3' sequences. Preferably, the polynucleotide comprises the nucleotide sequence shown in SEQ ID NO: 1. The 10.4 kb human ABCl cDNA sequence shown in SEQ ID NO: 1 contains an open reading frame of 6783 nucleotides plus 5' and 3' untranslated regions. There is a start codon at position 291 and a stop codon at position 7074. The present ABCl cDNA shown in SEQ ID NO: 1 differs from the published ABCl cDNA (GenBank Accession No. AJO12376) in several respects. First, the present ABCl cDNA includes an additional 350 nucleotides at the 5' end and an additional 3136 nucleotides at the 3' end (not including the poly(A) tail). The present ABCl sequence also differs from the published ABCl cDNA by the substitution of 10 nucleotides in the coding region. Of the ten differences, seven nucleotide differences predict amino acid changes. To remain consistent with published notation, the following nucleotide and amino acid numbers are those of Lawn et al, J. Clin. Invest., 104: R25-31 (1999) and GenBank Accession No. AJO12376, rather than those of SEQ ID NO: 1. The nucleotide and amino acid changes are as follows: ( 1 ) A for G at nucleotide 414; (2) A for G at nucleotide 596 (K for R at amino acid 159); (3) T for C at nucleotide 705; (4) A for C at nucleotide 1980; (5) A for G at 2413 (I for V at amino acid 765); (6) G for A at 2589 (M for I at amino acid 823); (7) T for C at 4604 (I for T at amino acid 1495); (8) T for C at 4883 (L for P at amino acid 1588); (9) A for G at 5861 (K for R at amino acid 1914); and (10) T for C at 6443 (L for P at amino acid 2108). Five of the amino acid changes are conservative amino acid changes and may represent polymorphisms or sequence enors. In two instances, the present sequence predicts important amino acid differences from the GenBank sequence. The differences result in a leucine rather than a proline at residue 1588 and at residue 2108 Interestingly, at both positions, the predicted leucine was also found in each of the three TD samples analyzed as well as the highly conserved mouse ABCl protein sequence The present invention also relates to ABCl polynucleotides comprising nucleotide -> sequences that preferably have at least 80% identity over their entire length to the polynucleotide compnsing SEQ ID NO 1 More preferably, the polynucleotide has at least 90% identity over its entire length to the polynucleotide compnsing SEQ ID NO 1 Even more preferably, the polynucleotide has at least 95% identity over its entire length to the polynucleotide compnsing SEQ ID NO 1 Most preferably the polynucleotide has 100% 0 identity over its entire length to the polynucleotide compnsing SEQ ID NO 1 Such related ABCl polynucleotides include substitution, deletion, and insertion vanants, as well as allelic vanants, splice vanants, fragments, denvatives, and orthologs, wherein one or more nucleotides have been substituted, deleted, inserted, or denvatized Prefened polynucleotides include those polynucleotides that encode ABCl polypeptides possessing biological activity, such as 5 cholesterol efflux activity In another prefened embodiment, the isolated polynucleotide compnses the entire coding sequence of ABC 1 In a particularly prefened embodiment, the polynucleotide compnses the sequence shown as nucleotides 291-7074 of SEQ ID NO 1 This isolated polynucleotide contains an ABCl open reading frame of 6783 nucleotides and encodes a polypeptide of 2261 0 ammo acids, as descnbed above In vet another prefened embodiment, the isolated polynucleotide compnses a nucleotide sequence that encodes an ABCl vanant polypeptide In particular, the isolated polynucleotide compnses a nucleotide sequence that encodes a polypeptide compnsing an ammo acid sequence which is at least 98% identical to the ammo acid sequence of SEQ ID NO 2 Also prefened is 25 an isolated polynucleotide compnsing a nucleotide sequence that encodes a polypeptide compnsing an ammo acid sequence which is at least 99% identical to the ammo acid sequence of SEQ ID NO 2 Accordingly, the invention includes those polynucleotides that encode the above-descnbed ABCl polypeptides, including the descnbed substitution, deletion, and insertion vanants, as well as ABCl allelic vanants, splice vanants, fragments, derivatives, fusion () polypeptides, and orthologs Prefened polynucleotides are those polynucleotides that encode polypeptides that possess the biological activity of ABCl In particular, those polynucleotides that encode polypeptides that mediate reverse cholesterol transport are prefened Also prefened are polynucleotides that enocode polypeptides that have improved reverse cholesterol transport activity. Yet another aspect of the invention relates to isolated polynucleotides that encode mutant ABCl polypeptides from Tangier patients. In one prefened embodiment, the polynucleotide encodes the polypeptide of SEQ ID NO: 8, which polypeptide is isolated from patient TDl and is descnbed above. In another prefened embodiment, the polynucleotide compnses the nucleotide sequence set forth in SEQ ID NO. 7. The nucleotide sequence set forth in SEQ ID NO 7 contains the full open reading frame, as well as 5' and 3' flanking sequences. The open reading frame encodes a polypeptide of 2261 amino acids, containing, among other substitutions, a nucleotide substitution that results ln an A to G substitution at position 537 (using the numbeπng of Lawn et al., supra (1999)). In another prefened embodiment relating to polynucleotides that encode mutant ABCl polypeptides. the polynucleotide encodes the polypeptide of SEQ ID NO 10, which polypeptide is isolated from Tangier patient TD2 and is also descnbed above. In yet another prefened embodiment, the polynucleotide compnses the nucleotide sequence set forth in SEQ ID NO: 9 The nucleotide sequence set forth in SEQ ID NO: 9 contains the full open reading frame, as well as 5' and 3' flanking sequences. The open reading frame encodes a polypeptide of 2261 ammo acids, containing, among other substitutions, a polynucleotide substitution that results in an Arg to Tryp substitution at residue 527 (using the numbenng of Lawn et al., supra (1999)) Another aspect of the present invention relates to isolated polynucleotides that compnse the non-codmg 5' flanking and 3' flankmg regions of ABCl . In one embodiment, the isolated polynucleotide compnses the non-codmg 5' flankmg region of ABCl. Preferably, the 5' flanking region contains, but is not limited to, the ABCl promoter region Thus, in a prefened embodiment, the polynucleotide compnses the sequence shown in SEQ ID NO 3. As demonstrated by heterologous reporter assays, discussed in Example 15, the polynucleotide set forth in SEQ ID NO: 3 contains the transcnptional regulatory region of the ABCl gene. As shown in Figure 13, the polynucleotide set forth in SEQ ID NO: 3 is a 1643 b p. non-codmg sequence that contains several transcnption regulatory elements, including a TATA box at positions 1522, 1435, and 1383, as well as transcnption factor binding sites, including several putative SPI sites, and several nuclear receptor half sites. In addition, an identified sterol response element is found at position 1483-1500 Further heterologous reporter assays described in Example 17 revealed that several discrete portions of SEQ ID NO- 3 retained promoter activity Accordingly, in another prefened embodiment, the polynucleotide compnses nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1643 of SEQ ID NO: 3. In an especially prefened embodiment, the polynucleotide compnses nucleotides 1394-1532 of SEQ ID NO: 3, which sequence has been shown to have ABCl promoter activity (see Example 17). In yet another prefened embodiment, the polynucleotide comprises nucleotides 1480-1510 of SEQ ID NO: 3, which is shown to regulate the ABCl transcriptional response to LXR ligands. The 5' flanking polynucleotide also comprises a nucleotide sequence that hybridizes, under stringent conditions, to the nucleotide sequence set forth in SEQ ID NO: 3, wherein the nucleotide sequence has ABCl promoter activity. In yet another embodiment, the polynucleotide comprises a nucleotide sequence that hybridizes, under stringent conditions, to the nucleotide sequence comprising nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1643 of SEQ ID NO: 3, wherein the nucleotide sequence has ABCl promoter activity. In another embodiment, the isolated polynucleotide comprises the 3' flanking region of ABCl . Several 3' untranslated regions have been identified which may represent alternate sites of polyadenylation of the ABCl transcript. Preferably, the 3' flanking region contains regulatory sequences. For example, the full length 3' UTR (SEQ ID NO: 6) contains 46 sequences (AA)nCU UC(AA)n which have been shown to be necessary for binding of Vigilin. Vigilin, a ubiquitous protein with 14K homology domains, is the estrogen- inducible vitellogenin mRNA 3 '-untranslated region binding protein (J. Biol Chem., 272: 12249-12252 ( 1997)). In addition to binding HDL, Vigilin has been shown to bind to the 3' flanking region of mRNAs and to increase the half-life of the mRNA transcript (Mol. Cell Biol, 18:3991-4003 (1998)). Thus, the 3' flanking region could be altered, for example, to increase the binding of Vigilin, thereby increasing the half-life of the ABCl mRNA. Preferably, the isolated polynucleotide comprises the sequence shown in SEQ ID NO: 4. Also preferably, the isolated polynucleotide comprises the sequence shown in SEQ ID NO: 5. In another prefened embodiment, the isolated polynucleotide comprises the sequence shown in SEQ ID NO: 6. In other prefened embodiments, the polynucleotide comprises a sequence that hybridizes, under stringent conditions, to the nucleotide sequence set forth in SEQ ID NO: 4, SEQ ID NO: 5, or SEQ ID NO: 6. The present invention also includes related ABCl 5' and 3' flanking polynucleotides. Accordingly, the invention relates to polynucleotides comprising nucleotide sequences that have at least 80% identity over their entire length to the polynucleotide comprising SEQ ID NO: 3, the polynucleotide comprising SEQ ID NO: 4, the polynucleotide comprising SEQ ID NO: 5, the polynucleotide comprising SEQ ID NO: 6, or the polynucleotide comprising nucleotides 1- 1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1643 of SEQ ID NO: 3. Preferably, the polynucleotide has at least 80%, more preferably at least 90%, even more preferably at least 95%, and most preferably 100% identity over its entire length to any one of the aforementioned flanking polynucleotides. Prefened polynucleotides include those polynucleotides that possess biological activity, such as transcriptional regulatory activity. It is understood that the present invention further relates to isolated polynucleotides that are complementary to any one of the above-described polynucleotide sequences. As used herein, the term "complementary" refers to the hybridization or base pairing between nucleotides, such as, for example, between the two strands of a double-stranded polynucleotide. Two single-stranded nucleotide molecules are said to be complementary when the nucleotides of one strand, optimally aligned with appropriate nucleotide insertions, deletions or substitutions, pair with at least about 80% of the nucleotides of the other strand. Another aspect of the present invention relates to compositions comprising the novel ABCl polynucleotides described above and a suitable carrier. In one embodiment, the composition comprises a polynucleotide encoding the polypeptide compnsing SEQ ID NO: 2, a polynucleotide comprising SEQ ID NO: 1, a polynucleotide comprising nucleotides 291-7074 of SEQ ID NO: 1 , or a polynucleotide encoding a polypeptide comprising an amino acid sequence which is at least 98% identical to the amino acid sequence of SEQ ID NO: 2 and a suitable canier. In another embodiment, the composition comprises a polynucleotide having at least 80%, preferably 90%, or more preferably 95% identity over its entire length to the polynucleotide comprising SEQ ID NO: 1 and a suitable carrier. In another embodiment, the composition comprises a polynucleotide comprising an ABCl 5' flanking sequence and a suitable carrier. Preferably, the composition comprises a polynucleotide comprising SEQ ID NO: 3 or a polynucleotide comprising nucleotide fragments 1 -1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1643 of SEQ ID NO: 3 and a suitable carrier. Also preferably, the composition comprises a polynucleotide having at least 80%, 90%, or 95% identity over its entire length to the polynucleotide comprising any one of the described 5' flanking sequences and a suitable carrier. In yet another embodiment, the composition compnses a polynucleotide comprising an ABCl 3' flanking sequence and a suitable carrier. Prefened compositions comprise a polynucleotide comprising SEQ ID NO: 4, a polynucleotide comprising SEQ ID NO: 5, or a polynucleotide comprising SEQ ID NO: 6, as well as a polynucleotide having at least 80%, preferably 90%, or more preferably 95% identity over its entire length to any of these polynucleotides, and a suitable carrier. Still other compositions of the invention compnse mutant ABCl polynucleotides Preferably, the composition compnses a polynucleotide compnsing SEQ ID NO 7 or a polynucleotide compnsing SEQ ID NO 9 and a suitable earner In addition, a composition of the present invention may compnse, in any combination, > two or more of the above-descnbed ABCl polynucleotides and a suitable earner Any suitable aqueous earner can be used in the composition Preferably, the earner renders the composition stable at a desired temperature, such as room temperature or storage temperature (I e 4°C to - 20°C), and is of approximately neutral pH Examples of suitable earners are known to those of skill in the art and include Tns-EDTA buffer and DEPC-H.O 0 ABCl Vectors and Host Cells The present invention also relates to recombinant vectors that compnse one or more of the above-descnbed ABCl polynucleotides, host cells that are genetically engineered with the vectors compnsing ABCl polynucleotides, and the production of ABCl polypeptides by 5 recombinant techniques As mentioned, the invention provides recombinant vectors that compnse one or more of the above-descnbed wild-type ABCl polynucleotides In prefened embodiments, the recombinant vector compnses the polynucleotide encoding the polypeptide compnsing SEQ ID NO 2, the polynucleotide compnsing SEQ ID NO 1, and the polynucleotide compnsing nucleotides 291-7074 of SEQ ID NO 1 In another prefened 0 embodiment, the recombinant vector compnses the vanant polynucleotide encoding a polypeptide compnsing an amino acid sequence which is at least 98% identical to the ammo acid sequence of SEQ ID NO 2 Also, in another prefened embodiment, the recombinant vector compnses a vanant polynucleotide that is at least 80% identical to a polynucleotide compnsing SEQ ID NO 1 In still another prefened embodiment, the recombinant vector 5 compnses a polynucleotide that is complementary to any of these polynucleotides In another embodiment, the recombinant vector compnses a polynucleotide compnsing a mutant ABCl polynucleotide isolated from a Tangier disease patient In a prefened embodiment, the recombinant vector compnses the polynucleotide compnsing SEQ ID NO 8 In another prefened embodiment, the recombinant vector compnses the polynucleotide i() compnsing SEQ ID NO 10 The recombinant vectors may also compnse a polynucleotide sequence that is complementary to these sequences It is also understood that the recombinant vector may also compnse, in any combination, two or more of the above-descnbed wild-type, vanant, or mutant ABCl polynulceotides An isolated ABCl polynucleotide, such as any of the above-described wild-type, variant, or mutant polynucleotides, is inserted into a vector using well-known ligation and cloning techniques. Cloning techniques have been described in several standard laboratory manuals, including Davis et al., Basic Methods in Molecular Biology (1986); Sambrook et al., Molecular Cloning: A Laboratory Manual, 2 nd Ed., (Cold Spring Harbor Press, Cold Spring Harbor, N.Y. (1989)); Ausubel et al. eds., Current Protocols in Molecular Biology, (Wiley and Sons (1994)); Goeddel, ed.. Gene Expression Technology (Methods in Enzymology (1991)); Munay, ed., Gene Transfer and Expression Protocols (Human Press, Clifton, NJ). Any vector suitable for ABCl polynucleotide insertion can be used. The vector is typically selected to be functional in the particular host cell employed (i.e., the vector is compatible with the host cell machinery such that amplification and/or expression of the gene can occur). Preferably, the vector is compatible with bacterial, insect, or mammalian host cells. Also preferably, the vector is an expression vector (for a review of expression vectors, see Goeddel, D.V. ed., Methods Enzymol, Academic Press Inc., San Diego, CA (1990)). The vector may be, for example, a phage, plasmid, viral, or retroviral vector. Retroviral vectors may be replication competent or replication defective. In the latter case, viral propagation generally will occur only in complementing host cells. Typically, expression vectors used in any of the host cells will contain sequences for plasmid maintenance and for cloning and expression of exogenous nucleotide sequences. Such sequences, collectively refened to as "flanking sequences" should preferably include one or more of the following nucleotide sequences: a promoter, one or more enhancer sequences, an origin of replication, a transcriptional termination sequence, a complete intron sequence containing a donor and acceptor splice site, a sequence encoding a leader sequence for polypeptide secretion, a ribosome binding site, a polyadenylation sequence, a polylinker region for inserting the nucleic acid encoding the polypeptide to be expressed, and a selectable marker element. The flanking sequences may be homologous {i.e., from the same species and/or strain as the host cell), heterologous (i.e., from a species other than the host cell species or strain), hybrid (i.e., a combination of flanking sequences from more than one source), or synthetic. Also, the flanking sequences may be native sequences which normally function to regulate ABCl polypeptide expression. The source of a flanking sequence may be any prokaryotic or eukaryotic organism, any vertebrate or invertebrate organism, or any plant, provided that the flanking sequence is functional in, and can be activated by, the host cell machinery. The vector should also preferably include at least one selectable marker for propagation in a host A selectable marker is a gene element that encodes a protein necessary for the survival and growth of a host cell grown m a selective culture medium Suitable selection marker genes encode proteins that (a) confer resistance to antibiotics or other toxins, e g , ampicilhn, tetracyc ne, or kanamycm for prokaryotic host cells; (b) complement auxotrophic deficiencies of the cell, or (c) supply cntical nutnents not available from complex media. Prefened selectable markers include zeocin, G418, hygromycm, or neomycin resistence for eukaryotic cell culture and tetracychne, kanamycm, or ampicilhn resistance for cultunng in E colt and other bacteπa. Other suitable selection genes include those that are used to amplify the expressed gene Amplification is the process wherein genes that are m greater demand for the production of a protein critical for growth are reiterated in tandem withm the chromosomes of successive generations of recombinant cells. Examples of suitable selectable markers for mammalian cells include dihydrofolate reductase (DHFR) and thymidine kinase. The mammalian cell transformants are placed under selection pressure wherein only the transformants are uniquely adapted to survive by virtue of the selection gene present in the vector. Selection pressure is imposed by cultunng the transformed cells under conditions in which the concentration of selection agent in the medium is successively changed, thereby leading to the amplification of both the selection gene and the ABCl gene. As a result, increased quantities of ABCl polypeptide are synthesized from the amplified DNA. The vector should also preferably contain a transcnption termination sequence, which is typically located 3' of the end of a polypeptide coding region and serves to terminate transcnption Usually, the transcnption termination sequence m prokaryote cells is a G-C rich fragment followed by a poly T sequence. The sequence can be purchased as part of a commercial vector or synthesized using well-known methods for nucleic acid synthesis. The vector should also preferably contain a ribosome binding site, which is usually necessary for translation initiation of mRNA and is charactenzed by a Shine-Dalgarno sequence (prokaryotes) or a Kozak sequence (eukaryotes) The element is typically located 3' to the promoter and 5' to the coding sequence of the ABCl polypeptide to be expressed. The Shme- Dalgarno sequence is vaned but is typically a polypunne (i e , having a high A-G content) Many Shine-Dalgarno sequences have been identified, each of which can be readily synthesized using well-known methods The vector should also preferably contain a promoter that is recognized by the host organism and operably linked to the encoded polynucleotide The promoter can be an inducible promoter or a constitutive promoter Inducible promoters initiate increased levels of transcnption from DNA under their control in response to some change in culture conditions, such as the presence or absence of a nutnent or a change in temperature In contrast, constitutive promoters initiate continual gene product production, consequently there is little or no control ■ > over gene expression A suitable promoter is operably linked to a polynucleotide, by removing the promoter from the source DNA by restnction enzyme digestion and inserting the desired promoter sequence into the vector As mentioned, a native promoter can be used to direct amplification and/or expression of the polynucleotide Thus, the recombinant vector can compnse any one of the above-descnbed wild-type, vanant, or mutant ABCl polynulceotides 0 and an ABCl promoter, such as that found in SEQ ID NO 3 The recombinant vector can also compnse, in any combination, two or more of the above-descnbed wild-type, vanant, or mutant ABCl polynulceotides and an ABCl promoter Preferably, a heterologous promoter is used if it permits greater transcnption and higher yields of ABCl protein as compared to the native ABCl promoter, and if it is compatible with 3 the host cell system that has been selected for use The heterologous promoter can be used alone or in conjunction with the native ABCl promoter Thus, in one prefened embodiment, the recombinant vector compnses any one of the above-descnbed wild-type ABCl polynucleotides and a heterologous promoter In another prefened embodiment, the recombinant vector compnses any one of the above-descnbed vanant ABCl polynucleotides and a heterologous 0 promoter In yet another prefened embodiment, the recombinant vector compnses any one of the above-descnbed mutant ABCl polynucleotides and a heterologous promoter Prefened embodiments also include recombinant vectors that contain any combination of two or more of the above-descnbed wild-type, vanant, and mutant ABCl polynucleotides and a heterologous promoter 25 Heterologous promoters suitable for use with prokaryotic hosts include, but are not limited to, the beta-lactamase and lactose promoter systems (Villa-Kamaroff et al , 1978, Proc Natl Acad Sci USA , 75 3727-31), alkaline phosphatase, a tryptophan (tip) promoter system, and hybrid promoters such as the tac promoter (Villa-Kamaroff et al , 1978, Proc Natl Acad Sci U S A , 75 3727-31 ) Their sequences have been published, thereby enabling one skilled m "0 the art to ligate them to the desired DNA sequence, using linkers or adapters as needed to supply any useful restriction sites Other suitable heterologous promoters will be known to those skilled in the art Suitable heterologous promoters for use with mammalian host cells are also well known and include, but are not limited to, those obtained from the genomes of viruses such as polyoma virus, fowlpox virus, adenovirus (such as Adenovirus 2), bovine papilloma virus, avian sarcoma virus, cytomegalovirus, retroviruses, hepatitis-B virus and Simian Virus 40 (SV40). Other suitable mammalian promoters include heterologous mammalian promoters, for example, heat- shock promoters and the actin promoter. Additional suitable promoters include, but are not limited to: the SV40 early promoter and late promoter region (Bernoist and Chambon, 1981, Nature 290:304-10); the promoter contained in the 3' long terminal repeat of Rous sarcoma virus (Yamamoto, et al, 1980, Cell 22:787-97); the herpes thymidine kinase promoter (Wagner et al, 1981, Proc. Natl. Acad. Sci. U.S.A. 78:1444-45); and the regulatory sequences of the metallothionine gene (Brinster et al, 1982, Nature 296:39-42). Preferably, the promoter is a cytomegalovirus or SV40 promoter. Thus, in especially prefened embodiments, the recombinant vector comprises one of the above-described wild-type ABC 1 polynucleotides, one of the above- described variant ABCl polynucleotides, or one of the above-described mutant ABCl polynucleotides and a cytomegalovirus promoter. In another especially prefened embodiment, the recombinant vector comprises, in any combination, two or more of the above-described wild- type, variant, or mutant ABC 1 polynulceotides and a cytomegalovirus promoter. The vector also preferably contains an enhancer sequence to increase the transcription of a polynucleotide, such as ABCl. Suitable enhancers for the activation of eukaryotic promoters include viral enhancers, such as the SV40, cytomegalovirus early promoter, polyoma, and adenovirus enhancers. Expression vectors of the invention may be constructed from a starting vector, such as a commercially available vector, which may or may not contain all of the desired flanking sequences. Where one or more of the flanking sequences described herein are not already present in the vector, they may be individually obtained and ligated into the vector. Methods used for obtaining each of the flanking sequences are well known to one skilled in the art. Prefened vectors are those which are compatible with bacterial, insect, and mammalian host cells. Vectors prefened for use in bacteria include, for example, pQE70, pQE60, and pQE-9 (Quiagen, Inc.), pBluescript vectors, Phagescript vectors, pNH16A, pNH18A, pNH46A (Stratagene Cloning Systems, Inc.), ptrc99a, pKK223-3, pDR540, pRIT5 (Pharmacia Biotech, Inc.), and pCEP4 (Invitrogen Corp., Carlsbad, CA). Prefened eukaryotic vectors include, but are not limited to, pWLNEO, pSV2CAT, pOG44, pXTI and pSG (Stratagene), pSVK3, pBPV, pMSG, and pSVL (Pharmacia), and pGL3 (Promega, Madison, Wl). Other suitable vectors will be readily apparent to the skilled artisan. In an especially prefened embodiment, the recombinant vector compnses pCEPhABCl, which is described in Example 4 and shown in Figure 3. The recombinant vector pCEPhABCl compnses the plasmid pCEP4 (Invitrogen), an expression vector containing the cytomegalovirus promoter and enhancer. The vector pCEPhABCl further compnses an ABCl polynucleotide operatively linked to the heterologous cytomegalovirus promoter. The ABCl polynucleotide compnses SEQ ID NO: 1, which contains the full-lenth ABCl cDNA, including non-coding 5' flanking (i.e., native ABCl promoter) and 3' flanking sequences. In addition, the present invention provides recombinant vectors compnsing ABCl 0 flanking sequence polynucleotides. In one embodiment, the recombinant vector compnses a polynucleotide compnsing a ABCl 5' flanking sequence that preferably contains promoter activity Thus, in a prefened embodiment, the recombinant vector compnses the polynucleotide compnsing SEQ ID NO: 3 In another prefened embodiment, the recombinant vector compnses the polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1 181-1643, 1292- 5 1643, or 1394-1643 of SEQ ID NO: 3. In an especially prefened embodiment, the polynucleotide comprises nucleotides 1394-1532 of SEQ ID NO: 3. Also, in another embodiment, the recombinant vector compnses a polynucleotide that hybndizes, under stπngent conditions, to the polynucleotide set forth in SEQ ID NO: 3 or the polynucleotide compnsing nucleotides 1 -1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1643 of SEQ ID NO. 3. In yet 0 another embodiment, the polynucleotide compnses a nucleotide sequence that has at least 80%, more preferably at least 90%, and even more preferably at least 95% identity over its entire length to the polynucleotide compnsing SEQ ID NO: 3 or the polynucleotide compnsing nucleotides 1 -1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1643 of SEQ ID NO: 3 The recombinant vector also compnses a polynucleotide that is complementary to any of the above- -> descnbed 5' flanking sequences. In another embodiment, the recombinant vector compnses a polynucleotide compnsing a 3' flanking sequence of ABCl . In a prefened embodiment, the recombinant vector compnses the polynucleotide compnsing SEQ ID NO: 4 In another prefened embodiment, the recombinant vector compnses the polynucleotide compnsing SEQ ID NO 5 In an equally 10 prefened embodiment, the recombinant vector compnses the polynucleotide compnsing SEQ ID NO 6 Also, in another embodiment, the recombinant vector compnses a polynucleotide that hybridizes, under stnngent conditions, to the polynucleotide set forth in SEQ ID NO' 4, SEQ ID NO 5, or SEQ ID NO: 6 In yet another embodiment, the polynucleotide compnses a nucleotide sequence that has at least 80%, more preferably at least 90%, and even more preferably at least 95% identity over its entire length to the polynucleotide comprising SEQ ID NO: 4, SEQ ID NO: 5, or SEQ ID NO: 6. The recombinant vector also comprises a polynucleotide that is complementary to any of the above-described 3' flanking sequences. An isolated ABCl flanking sequence polynucleotide, such as any of the above-described 5' or 3' flanking sequence polynucleotides, is inserted into a vector using well-known ligation and cloning techniques. Any of the previously described vectors can be used. Preferably, the vector is compatible with bacterial, insect, or mammalian host cells. Also preferably, the vector is an expression vector. The vector may be, for example, a phage, plasmid, viral, or retroviral vector. In addition to the ABCl flanking sequence, the vector may contain one or more of the following flanking nucleotide sequences: a promoter, one or more enhancer sequences, an origin of replication, a transcriptional termination sequence, a complete intron sequence containing a donor and acceptor splice site, a sequence encoding a leader sequence for polypeptide secretion, a ribosome binding site, a polyadenylation sequence, a polylinker region for inserting the nucleic acid encoding the polypeptide to be expressed, and a selectable marker element. Any of the previously described flanking nucleotide sequences are suitable. The flanking sequences may be homologous, heterologous, hybrid, or synthetic. Also, the flanking sequences may be native sequences which normally function to regulate ABCl polypeptide expression. The source of a flanking sequence may be any prokaryotic or eukaryotic organism, any vertebrate or invertebrate organism, or any plant, provided that the flanking sequence is functional in, and can be activated by, the host cell machinery. Prefened vectors are those which are compatible with bacterial, insect, and mammalian host cells. Suitable vectors have been previously described and include pQE70, pQE60, pQE9, pBluescript vectors, Phagescript vectors, pNH16A, pNH18A, pNH46A, ptrc99a, pKK223-3, pDR540, pRIT5, and pCEP4 for use in bacteria and pWLNEO, pSV2CAT, pOG44, pXTI, pSG, pSVK3, pBPV, pMSG, pSVL, and pGL3 for use in eukaryotic cells. In one particularly prefened embodiment, the recombinant vector comprises a polynucleotide comprising the 5' flanking region of the ABCl gene and further comprises at least one polynucleotide encoding a heterologous polypeptide. The heterologous polynucleotide is operatively linked to the ABCl 5' flanking sequence. The ABCl 5' flanking sequence preferably contains the ABCl promoter. Thus, preferably, the 5' flanking sequence comprises the sequence set forth in SEQ ID NO: 3. Equally preferably, the 5' flanking sequence comprises nucleotides 1 -1532, 1080-1643, 1 181-1643, 1292-1643, or 1394-1643 of SEQ ID NO 3 The heterologous polynucleotide preferably encodes a polypeptide that is a complete protein or a biologically active fragment of a protein The vector may also contain more than one heterologous polynucleotide More preferably, the heterologous polynucleotide encodes a reporter protein In such case, the recombinant vector preferably does not contain any additional promoter sequences Examples of suitable reporter proteins include luciferase, β-galactosidase, chloramphemcol acetyl transferaseacetyl transferasetransferase, and green fluorescent protein Preferably, the reporter polypeptide is luciferase Thus, in one especially prefened embodiment, the recombinant vector compnses the 5' flankmg sequence set forth in SEQ ID NO 3 and a luciferase reporter polynucleotide In other equally prefened embodiments, the recombinant vector compnses a polynucleotide compnsing nucleotides 1-1532, 1080-1643, 1181-1643, 1292- 1643, or 1394-1643 of SEQ ID NO 3 and a luciferase reporter polynucleotide Expression vectors compnsing the ABCl 5' flanking sequence can be constructed from a starting vector, such as a commercially available vector, which contains a reporter polynucleotide Examples of suitable expression vectors include pGL3-Basιc, which contains a luciferase reporter gene (Promega, Madison, Wl) and pβGal-Basic (Clontech, Palo Alto, CA) A prefened vector is the pGL3-Basιc luciferase reporter vector, which is promoterless A 5' flankmg sequence containing the ABCl promoter, for example SEQ ID NO 3, can be hgated into one of the above expression vectors using well-known methods, including the methods described herein (see Example 15) Thus, in an especially prefened embodiment, the recombinant vector is pAPRl, a reporter gene construct compnsing SEQ ID NO 3 and a luciferase reporter gene in a pGL3 vector (see Figure 11) The present invention also relates to host cells compnsing any one of the above-descnbed recombinant vectors After the vector has been constructed, the completed vector can be inserted into a suitable host cell for amplification and or polypeptide expression Host cells may be prokaryotic host cells (such as E coli) or eukaryotic host cells (such as a yeast cell, an insect cell, or a vertebrate cell) The host cell, when cultured under appropnate conditions, synthesizes an ABCl polypeptide or, alternatively, a reporter polypeptide, which can be subsequently measured The host cell can be a mammalian host cell, such as a pnmate cell line or a rodent cell line, including transformed cell lines Normal diploid cells, cell strains derived from in vitro culture of pπmary tissue, as well as pnmary explants, are also suitable Candidate host cells may be genotypically deficient in the selection gene, or may contain a dominantly acting selection gene A number of suitable host cells are known in the art and many are available from the American Type Culture Collection (ATCC), Manassas, VA. Suitable mammalian host cells include, but are not limited to, Chinese hamster ovary cells (CHO), CO DHFR- cells (Urlaub et al, 1980, Proc. Natl. Acad. Sci., 97:4216-20), human embryonic kidney (HEK) 293 or 293T cells, or 3T3 cells, monkey COS-1 and COS-7 cell lines, and the CV-1 cell line. Other suitable mammalian cell lines include but are not limited to, mouse neuroblastoma N2A cells, HeLa cells, mouse 1-929 cells, 3T3 lines derived from Swiss, Balb-c or NIH mice, BHK or HAK hamster cell lines, Thp-1, HepG2, and mouse RAW cell lines. Each of these cell lines is known by and available to those skilled in the art of protein expression. A prefened host cell is the mouse monocytic cell line RAW 264.7, which use is described in Example 8. Suitable bacterial host cells include various strains of E. coli (e.g., HB101, DH50, DH10, and MCI 061 ), which are well-known as host cells in the field of biotechnology. Various strains of B. subtilis, Pseudomonas spp., other Bacillus spp., Streptomyces spp., and the like may also be employed in this method. Also, many strains of yeast cells are also available as host cells for the expression of ABCl polypeptides. Prefened yeast cells include, for example, Saccharomyces cerivisae and Pichia pastoris . Additionally, insect cell systems may be suitable host cells. Insect cell systems are described, for example, in Kitts et al, 1993, Biotechniques, 14:810-17; Lucklow, 1993, Curr. Opin. Biotechnol. 4:564-72; and Lucklow et al, 1993, J. Virol, 67:4566- 79. Prefened insect cells are Sf-9 and Hi5 (Invitrogen). The present invention also provides a method for expressing an ABCl protein in a mammalian host cell comprising the steps of: (a) transfecting the mammalian host cell with a recombinant expression vector comprising a polynucleotide encoding ABCl in an amount sufficient to produce a detectable level of ABCl protein; and (b) purifying the produced ABCl protein. In one prefened embodiment, the recombinant expression vector comprises a polynucleotide encoding the polypeptide comprising SEQ ID NO: 2. In another prefened embodiment, the polynucleotide comprising SEQ ID NO: 1. In yet another prefened embodiment, the polynucleotide comprising nucleotides 291-7074 of SEQ ID NO: 1. In still another prefened embodiment, the polynucleotide encoding a polypeptide that is at least 98% identical to the polypeptide comprising SEQ ID NO: 2. Introduction of the recombinant ABCl vector into a mammalian host cell can be effected by methods well-known in the art and described in standard laboratory manuals, such as Sambrook, supra. Preferably, the recombinant vector is introduced into a host cell in a precipitate or in a complex with a charged lipid. Suitable methods for introduction of the ABCl vector include calcium phosphate transfection, DEAE-dextran mediated transfection, cationic lipid-mediated transfection, electroporation, transduction, infection, or other methods known in the art. These methods are described, for example, in Davis et al., Basic Methods in Molecular Biology ( 1986). If the recombinant ABCl vector is a viral vector, it may be packaged in vitro using an appropriate packaging cell line and then transduced into host cells. The ABCl polypeptide can be recovered and purified from recombinant cell cultures using well-known methods, including ammonium sulfate or ethanol precipitation, acid, extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, affinity chromatography, hydroxylapatite chromatoraphy, and lectin chromatography (see, e.g., Smith and Johnson, Gene 67:31-40 ( 1988)). Preferably, affinity chromotography using anti- ABCl antibodies is employed for purification. In addition, the present invention provides a method for expressing ABCl protein in a mammalian subject comprising the step of administering to a mammalian subject a recombinant expression vector comprising a polynucleotide encoding ABCl in an amount sufficient to express ABCl protein in said mammalian subject. Preferably, the recombinant expression vector comprises a polynucleotide encoding the polypeptide comprising SEQ ID NO: 2, the polynucleotide comprising SEQ ID NO: 1, the polynucleotide comprising nucleotides 291-7074 of SEQ ID NO: 1, or the polynucleotide encoding a polypeptide that is at least 98% identical to the polypeptide comprising SEQ ID NO: 2. Introduction of the recombinant ABCl vector into a mammalian subject can be effected by methods well-known in the art and are described in detail herein below. Expression of ABCl can be measured by obtaining a blood sample from the subject to whom the recombinant ABCl vector was administered, separating the monocyte population, and measuring the ABCl gene expression in macrophage cells. The ABCl gene expression can be measured using methods well-known in the art, such as RT-PCR, and methods described herein (see Examples 9 and 10). The level of ABCl protein can be measured by obtaining a blood sample from the subject, separating the monocyte population and measuring the ABCl protein in macrophage cells using well-known methods, such as immunoprecipitation, described herein at Example 11. Methods and Compounds for Increasing Cholesterol Efflux In another aspect of the present invention, a method suitable for increasing cholesterol efflux from cells in a mammalian subject is provided. Such method comprises administering to the mammalian subject a recombinant expression vector compnsing an ABC l polynucleotide in an amount sufficient to increase cholesterol efflux from said cells. The recombinant vector can be any of the above-descnbed vectors containing any of the previously descnbed wild-type or variant ABC l polynucleotides, as long as the encoded ABCl polypeptide has biological activity -> (i.e , cholesterol transport activity) Preferably, the recombinant vector compnses the polynucleotide encoding the polypeptide compnsing SEQ ID NO: 2, the polynucleotide compnsing SEQ ID NO: 1 , the polynucleotide comprising nucleotides 291 -7074 of SEQ ID NO: 1 , or the polynucleotide encoding a polypeptide compnsing an ammo acid sequence which is at least 98% identical to the amino acid sequence of SEQ ID NO: 2. Also, preferably, the 0 recombinant vector compnses a vanant polynucleotide that is at least 80%, 90%, or 95% identical to the polynucleotide compnsing SEQ ID NO: 1 , as long as the encoded ABCl polypeptide has cholesterol transport activity. The administration of a recombinant ABCl expression vector to a mammalian subject can be used to express the ABCl gene in said subject for the treatment of cardiovascular disease. 5 Specifically, this method would achieve its therapeutic effect by the introduction of the ABCl gene into macrophage cells and other cholesterol-accumulating cells found in the artenal lesions of mammals with cardiovascular disease. Expression of the ABCl polynucleotide in target cells would effect greater production of the ABCl protein. The subsequently produced ABCl protein would ameliorate the disease by increasing the efflux of cholesterol from macrophage and other 0 cholesterol-laden cells found in artenal lesions onto nascent HDL particles The cellular efflux would lead to the overall removal of cholesterol from penpheral sites, such as the cholesterol- πch core of arterial plaques. A concunent reduction in the size of these pathological lesions reduces the risk of artenal blockage that leads to heart attacks and angina This method could also be used prophylactically to prevent the accumulation of cholesterol in arterial walls. 5 A sufficient amount of a ABCl expression vector is the amount of ABCl vector that increases cholesterol efflux from the cells of a mammalian subject. Such amount can be determined by measunng the cholesterol efflux in the cells of a subject before (control level) and after administration of the recombinant ABCl expression vector at vanous dosages and determining the dose that effects an increase in cholesterol efflux compared to control level. The i() cholesterol efflux can be measured by obtaining a blood sample from the subject, separating the monocyte population, and measunng the amount of cholesterol efflux in a subject's macrophage cells. Any of the assays descnbed herein can be used to measure cholesterol efflux. In addition, cholesterol efflux can be measured by determining the level of plasma HDL- cholesterol in a subject before (control) and after administration of a recombinant ABCl expression vector. An observed increase in HDL-cholesterol in the serum of a subject following administration of a recombinant ABCl expression vector indicates an increase in cholesterol efflux. HDL-cholesterol levels in serum can be determined using methods well-known in the art. In addition, cholesterol efflux can be measured by measuring the size of atherosclerotic lesions found in the arterial wall of a subject before (control level) and after administration of the recombinant ABCl expression vector. A reduction in the size of the arterial lesion indicates an increase in cholesterol efflux. Assays for measuring arterial lesions are well known in the art. For example, increased cholesterol efflux from arterial lesions can be measured using the mouse model of atherosclerosis described in Lawn et al., Nature, 360: 670-672 (1992)), as well as any of the other known models. Using the LDL receptor knockout mouse described in Lawn et al., cholesterol efflux can be measured before and after administration of the ABCl vector. Fatty streak lesion size in groups of animals fed an atherogenic diet can be measured by oil-red O staining of aortic sections as described in Lawn et al. A reduction in size of fatty streak lesions in the group receiving the ABCl expression vector compared to a group receiving a control vector indicates an increase in cholesterol efflux from the lesions. In humans, the size of atherosclerotic lesions found in arterial walls can be measured using, for example, angiography and non-invasive ultrasound methods. Alternatively, cholesterol efflux can be measured by obtaining a blood sample and measuring the level of ABCl mRNA or ABCl protein in the macrophage cells of a subject before and after administration of a recombinant ABCl expression vector. Routine assays can be performed to determine the conelation between increasing ABCl mRNA concentrations and cholesterol efflux. Likewise, assays can be performed to conelate the amount of ABCl protein with the amount of cholesterol efflux. Using such conelation data, an observed increase in ABCl mRNA or ABCl protein in the cells of a subject following administration of a recombinant ABCl expression vector can be used to indicate an increase in cholesterol efflux. ABCl mRNA and ABCl protein levels can be measured using the assays described herein and other well-known techniques for mRNA and protein quantitation. Therapeutic dosages and formulations are discussed in further detail below. There are available to one skilled in the art multiple viral and non- viral methods suitable for introduction of a nucleic acid molecule into a target cell. For example, viral delivery vectors suitable for gene therapy include, but are not limited to, adenovirus, herpes simplex virus, pox virus (i.e., vaccinia), hepatitis virus, parvovirus, papovavirus, alphavirus, coronavirus, rhabdovirus, papilloma virus, adeno-associated virus (AAV), polio virus, and RNA viruses, such as a retroviruses and Sindbis virus. The ABCl polynucleotide can also be delivered using a non- viral delivery system, such as naked DNA delivery (direct injection), receptor-mediated transfer (DNA-ligand complexes), electroporation, adenovirus-ligand-DNA complexes, calcium phosphate (CaPO 4 ) precipitation, microparticle bombardment (gene gun techniques), liposome- mediated transfer, and lipofection. Genetic modification of a cell may be accomplished using one or more techniques well known in the gene therapy field (Mulligan, R., 1993, Science, 260 (5110): 926-32). Gene therapy materials and methods can include inducible promoters, tissue-specific enhancer- promoters. DNA sequences designed for site-specific integration, DNA sequences capable of providing a selective advantage over the parent cell, labels to identify transformed cells, negative selection systems and expression control systems (safety measures), cell-specific binding agents (for cell targeting), cell-specific internalization factors, and transcription factors to enhance expression by a vector as well as methods of vector manufacmre. Examples of methods and materials for the practice of gene therapy techniques are described in U.S. Patent Nos. 4,970,154 (involving electroporation techniques), 5,679,559 (describing a lipoprotein-containing system for gene delivery), 5,676,954 (involving liposome carriers), 5,593,875 (describing methods for calcium phosphate transfection), and 4,945,050 (describing a process wherein biologically active particles are propelled at cells at a speed whereby the particles penetrate the surface of the cells and become incoφorated into the interior of the cells), and PCT Pub. No. WO 96/40958 (involving nuclear ligands). Adenoviral vectors have proven especially useful for gene transfer into eukaryotic cells (Rosenfeld, M., et al, Science, 252: 431-4 (1991); U.S. Patent No. 5,631,236). The first trial of Ad-mediated gene therapy in human was the transfer of the cystic fibrosis transmembrane conductance regulator (CFTR) gene to lung (Crystal, R., et al, 1994, Nat. Genet., 8 (1): 42-51). Experimental routes for administrating recombinant Ad to different tissues in vivo have included intratracheal instillation (Rosenfeld, M., et al, 1992, Cell, 68 (1): 143-55) injection into muscle (Quantin. B., et al, 1992, Proc. Natl. Acad. Sci. U.S.A., 89 (7): 2581-4), peripheral intravenous injection (Herz, J., and Gerard, R., 1993, Proc. Natl. Acad. Sci. U.S.A., 90 (7): 2812-6) and stereotactic inoculation to brain (Le Gal La Salle, G., et al, 1993, Science, 259 (5097): 988-90). The adenoviral vector, then, is widely available to one skilled in the art and is suitable for use in the present invention. Adeno-associated virus (AAV) has recently been introduced as a gene transfer system with potential applications in gene therapy Wild-type AAV demonstrates high-level infectivity, broad host range and specificity m integrating into the host cell genome (Hermonat, P., and Muzyczka, N , 1984, Proc Natl. Acad. Sci U S A , S I (20): 6466-70) Herpes simplex virus type-1 (HSV-1 ) is a prefened vector system (Geller, A., et al , 1991, Trends Neurosci , 14 (10): 428-32; Gloπoso, J., et al, 1995, Mol Biotechnol, 4 (1): 87-99, Glonoso, J., et al, 1995, Annu Rev Microbiol , 49: 675-710) Vaccinia virus, of the poxvirus family, has also been developed as an expression vector (Smith, G., and Moss, B., 1983, Gene, 25 (1). 21 -8; Moss, B., 1992, Biotechnology , 20- 345-62; Moss, B., 1992, Curr Top. Microbiol Immunol, 158: 25-38) Each of the above-descnbed vectors is widely available to one skilled in the art and would be suitable for use in the present invention. Preferably, the viral delivery system utilizes a retroviral vector. Retroviral vectors are capable of infecting a large percentage of the target cells and integrating into the cell genome (Miller, A , and Rosman, G., Biotechniques, 7(9): 980-2, 984-6, 989-90 ( 1989); U.S. Patent No. 5,672,510) Retroviruses were developed as gene transfer vectors relatively earlier than other viruses, and were first used successfully for gene marking and transducing the cDNA of adenosine deaminase (ADA) into human lymphocytes. Preferably, the retroviral vector is a denvative of a munne or avian retrovirus, or is a lentiviral vector. An especially prefened retroviral vector is a lentiviral vector. Examples of retroviral vectors in which a single foreign gene can be inserted include, but are not limited to: Moloney munne leukemia virus (MoMuLV), Harvey munne sarcoma virus (HaMuSV), munne mammary tumor virus (MuMTV), SIV, BIV, HIV and Rous Sarcoma Virus (RSV). A number of additional retroviral vectors can incorporate multiple genes All of these vectors can transfer or incorporate a gene for a selectable marker so that transduced cells can be identified and generated. Since recombinant retroviruses are defective, they require assistance in order to produce infectious vector particles This assistance can be provided, for example, by using helper cell lines that contain plasmids encoding all of the structural genes of the retrovirus under the control of regulatory sequences withm the LTR The helper plasmids are missing a nucleotide sequence that enables the packaging mechanism to recognize an RNA transcnpt for encapsitation. Thus, helper cell lines produce empty vmons, since no genome is packaged. Suitable helper cell lines include, but are not limited to Ψ2, PA317 and PA12. If a retroviral vector is introduced into such cells in which the packaging signal is mtact, but the structural genes are replaced by other genes of interest, the vector can be packaged and vector viπon produced The vector vmons produced by this method can then be used to mfect a tissue cell line, such as NIH 3T3 cells, to produce large quantities of chimenc retroviral vinons The vectors of the present invention may be constructed using standard recombinant techniques widely available to one skilled in the art Such techniques may be found in common molecular biology references such as Molecular Cloning A Laboratory Manual (Sambrook, et al , 1989, Cold Spnng Harbor Laboratory Press), Gene Expression Technology (Methods in Enzymology, Vol 185, edited by D Goeddel, 1991, Academic Press, San Diego, CA), and PCR Protocols A Guide to Methods and Applications (Innis, et al 1990, Academic Press, San Diego, CA) In order to obtain transcnption of the ABCl polynucleotide withm a target cell, a transcnptional regulatory region capable of dnving gene expression m the target cell must be utilized The transcnptional regulatory region preferably compnses a promoter and/or enhancer, which is operatively linked to the ABCl polynulceotide The promoter can be homologous or heterologous to the ABCl gene, provided that it is active in the cell or tissue-type into which the construct will be inserted The transcnptional regulatory region chosen should dnve high level gene expression in the target cell Preferably, a macrophage-specific promoter, such as a scavenger receptor type A, matnx metalloproteinase promoter (MMP-12), or macrophage-tropic lentivirus promoter (Fabunmi et al , Atherosclerosis, 148 375-386 (1999)), is used A particularly prefened promoter is the 5' region of the scavenger receptor type A gene, which contains a strong macrophage promoter that can be used to dnve the transcnption of the ABCl gene In addition, a means to increase endogenous ABCl polypeptide expression in a cell is to insert one or more enhancer elements into the promoter region, where the enhancer elements can serve to increase transcnptional activity of the ABCl gene Similarly, the enhancer element(s) used is selected based on the tissue in which one desires to activate the gene Thus, for example, enhancer elements known to confer promoter activation in cells found in artenal tissue, especially macrophage cells, will be selected Other transcnptional regulatory regions suitable for use in the present invention include but are not limited to the human cvtomegalovirus (CMV) immediate-early enhancer/promoter, the SV40 early enhancer/promoter, the JC polyomavirus promoter, the albumin promoter, PGK and the α-actin promoter coupled to the CMV enhancer (Doll, R . et al , 1996, Gene Ther 3 (5) 437-47) Other components of the vector construct may optionally include DNA molecules designed for site-specific integration (e g , endogenous sequences useful for homologous recombination), tissue-specific promoters, DNA molecules capable of providing a selective advantage over the parent cell, DNA molecules useful as labels to identify transformed cells, negative selection systems, cell specific binding agents (e.g., for cell targeting), cell-specific internalization factors, transcription factors enhancing expression from a vector, and factors enabling vector production. In one embodiment, the vector can include targeting DNA for site-specific integration. The targeting DNA is a nucleotide sequence that is complementary (homologous) to a region of the gene of interest, for example, the ABCl gene. Through homologous recombination, the DNA sequence to be inserted into the genome can be directed to the ABC 1 gene by attaching it to the targeting DNA. DNA sequences for insertion include, for example, regions of DNA that may interact with or control the expression of an ABCl polypeptide, e.g., flanking sequences. Thus, the expression of the desired ABCl polypeptide is achieved not by transfection of DNA that encodes the ABCl gene itself, but rather by the use of targeting DNA coupled with DNA regulatory segments that provide the endogenous gene sequence with recognizable signals for transcription of an ABCl polypeptide (Sauer, Curr. Opin. Biotechnol, 5:521-27 (1994); Sauer, Methods Enzymol, 225:890-900 (1993)). In yet other embodiments, regulatory elements can be included for the controlled expression of the ABCl gene in the target cell. Such elements are turned on in response to an appropriate effector. In this way, a therapeutic ABCl polypeptide can be expressed when desired. One conventional control means involves the use of small molecule dimerizers or rapalogs to dimerize chimeric proteins which contain a small molecule-binding domain and a domain capable of initiating a biological process, such as a DNA-binding protein or transcnptional activation protein (see PCT Pub. Nos. WO 96/41865, WO 97/31898, and WO 97/31899). The dimerization of the proteins can be used to initiate transcription of the transgene. Another suitable control means or gene switches includes the use of mifepristone (RU486), which is a progesterone antagonist. The binding of a modified progesterone receptor ligand- binding domain to the progesterone antagonist activates transcription by forming a dimer of two transcription factors that then pass into the nucleus to bind DNA. The ligand-binding domain is modified to eliminate the ability of the receptor to bind to the natural ligand. The modified steroid hormone receptor system is further described in U.S. Patent No. 5,364,791 and PCT Pub. Nos. WO 96/4091 1 and WO 97/10337. Yet another control means uses a positive tetracycline- controllable transactivator. This system involves a mutated tet repressor protein DNA-binding domain (mutated tet R-4 amino acid changes which resulted in a reverse tetracyc line-regulated transactivator protein, i.e., it binds to a tet operator in the presence of tetracychne) linked to a polypeptide which activates transcnption. Such systems are descnbed in U.S. Patent Nos. 5,464,758, 5,650,298, and 5,654,168. Additional expression control systems and nucleic acid constructs are descnbed in U.S. Patent Nos. 5,741,679 and 5,834,186 Viral delivery vectors containing an ABCl polynucleotide can be made target specific by altenng the viral coat such that it contains a ligand that is specific for another molecule found on the target cell. This will allow the vector to bind specifically to the desired cell-type. The ligand can be any compound of interest that will bind specifically to a molecule found on the target cell, such as a cell-surface receptor. Preferably, the receptor is found exclusively on target cells and not on other cells For example, ligands for scavenger receptor A can be used to direct viral delivery vectors to macrophage cells. Alternatively, the viral coat can be altered such that it contains an antibody or antibody fragment, such as Fab, or F(ab') 2 , that recognizes and binds to an antigenic epitope on the target cells. The viral coat can be altered by inserting an additional polynucleotide that encodes the ligand into the viral genome. Those of skill in the art will know of other specific polynucleotide sequences which can be inserted into the viral genome to allow target specific delivery of the vector containing the ABCl polynucleotide. In addition, a naked ABCl polynucleotide can be administered. ABCl polynucleotides and recombinant ABCl expression vectors, such as those described above, can be admimstered as a pharmaceutical composition. Such a composition compnses an effective amount of an ABCl polynucleotide or recombinant ABCl expression vector, as previously defined herein, and a pharmaceutically acceptable formulation agent selected for suitability with the mode of administration. Suitable formulation matenals preferably are non-toxic to recipients at the concentrations employed and are descnbed herein below The pharmaceutical composition comprising an ABCl polynucleotide or an ABCl recombinant expression vector may contain formulation matenals for modifying, maintaining, or preserving, for example, the pH, osmolaπty, viscosity, clanty, color, lsotonicity, odor, stenhty, stability, rate of dissolution or release, adsorption, or penetration of the composition. Suitable formulation matenals include, but are not limited to, amino acids (such as glycme, glutamine, asparagine, argmine, or lysine), antimicrobials, antioxidants (such as ascorbic acid, sodium sulfite, or sodium hydrogen-sulflte), buffers (such as borate, bicarbonate, Tris-HCl, citrates, phosphates, or other organic acids), bulking agents (such as manmtol or giycine), chelating agents (such as ethylenediamine tetraacetic acid (EDTA)), complexing agents (such as caffeine, polyvinylpynolidone, beta-cyclodextnn, or hydroxypropyl-beta-cyclodextπn), fillers, monosacchandes, disacchandes, and other carbohydrates (such as glucose, mannose, or dextnns), proteins (such as serum albumin, gelatin, or immunoglobulins), colonng, flavonng and diluting agents, emulsifying agents, hydrophilic polymers (such as polyvinylpynohdone), low molecular weight polypeptides, salt-forming countenons (such as sodium), preservatives (such as benzalkomum chlonde, benzoic acid, salicylic acid, thimerosal, phenethyl alcohol, methylparaben, propylparaben, chlorhexidine, sorbic acid, or hydrogen peroxide), solvents (such as glycenn, propylene glycol, or polyethylene glycol), sugar alcohols (such as mannitol or sorbitol), suspending agents, surfactants or wetting agents (such as pluromcs, PEG, sorbitan esters, polysorbates such as polysorbate 20 or polysorbate 80; tnton; tromethamine, lecithin; cholesterol or tyloxapal), stability enhancing agents (such as sucrose or sorbitol), tomcity enhancing agents (such as alkali metal halides - preferably sodium or potassium chlonde - or mannitol sorbitol), delivery vehicles, diluents, excipients and/or pharmaceutical adjuvants. See Remington s Pharmaceutical Sciences (18 th Ed., A.R Gennaro, ed., Mack Publishing Company 1990) The pharmaceutically active compounds (i.e. ABCl polynucleotide or ABCl vector) can be processed in accordance with conventional methods of pharmacy to produce medicinal agents for administration to patients, including humans and other mammals. Thus, the pharmaceutical composition compnsing an ABCl polynucleotide or an ABCl recombinant expression vector may be made up in a solid form (including granules, powders or suppositones) or in a liquid form (e g , solutions, suspensions, or emulsions). Solid dosage forms for oral administration may include capsules, tablets, pills, powders, and granules In such solid dosage forms, the active compound may be admixed with at least one inert diluent such as sucrose, lactose, or starch Such dosage forms may also compnse, as in normal practice, additional substances other than inert diluents, e g , lubncatmg agents such as magnesium stearate In the case of capsules, tablets, and pills, the dosage forms may also compnse buffenng agents. Tablets and pills can additionally be prepared with entenc coatings. Liquid dosage forms for oral or parenteral administration may include pharmaceutically acceptable emulsions, solutions, suspensions, syrups, and elixirs containing inert diluents commonly used in the art, such as water Such compositions may also compnse adjuvants, such as wetting sweetening, flavonng, and perfuming agents. For example, a suitable earner for injection may be water, physiological saline solution, or artificial cerebrospinal fluid, possibly supplemented with other matenals common in compositions for parenteral administration Neutral buffered saline or saline mixed with serum albumin are further exemplary earners Other exemplary pharmaceutical compositions compnse Tns buffer of about pH 7 0-8 5, or acetate buffer of about pH 4 0-5 5, which may further include sorbitol or a suitable substitute The dosage regimen for treating a cardiovascular disease with a composition compnsing an ABCl polynucleotide or ABCl expression vector is based on a vanety of factors, including ~> the type of cardiovascular disease, the age, weight, sex, medical condition of the patient, the seventy of the condition, the route of administration, and the particular compound employed Thus, the dosage regimen may vary widely, but can be determined routinely using standard methods For example, the amount of ABCl polynucleotide or ABCl expression vector to be administered is an amount sufficient to increase cholesterol efflux from the cells of a mammalian 0 subject Such amount can be determined, for example, by measunng the plasma HDL- cholesterol level of a subject before and after administration of the ABCl polynucleotide or ABCl expression vector A sufficient amount of ABCl polynucleotide or ABCl expression vector is an amount that increases the plasma HDL-cholesterol level of a subject Accordingly, the clinician can titer the dosage and modify the route of administration to obtain the optimal 1 therapeutic effect A typical dosage may range from about 0 1 9 g/kg to about 100 mg/kg or more, depending on the factors mentioned above The frequency of dosing will depend upon the pharmacokinetic parameters of the ABCl polynucleotide or vector in the formulation being used Typically, a clinician will administer the composition until a dosage is reached that achieves the desired effect The composition may 0 therefore be administered as a single dose, as two or more doses (which may or may not contain the same amount of the desired molecule) over time, or as a continuous infusion via implantation device or catheter Further refinement of the appropnate dosage is routinely made by those of ordinary skill in the art and is within the ambit of tasks routinely performed by them Appropnate dosages may be ascertained through use of appropnate dose-response data 25 The cells of a mammalian subject may be transfected in vivo, ex vivo, or in vitro Administration of an ABCl polynucleotide or a recombinant vector containing an ABCl polvnucleotide to a target cell in vivo may be accomplished using any of a vanety of techniques well known to those skilled in the art For example, U S Patent No 5,672,344 descnbes an in vivo viral-mediated gene transfer system involving a recombinant neurotrophic HSV-1 vector i0 The above-descnbed compositions of ABCl polynucleotides and recombinant ABCl vectors can be transfected in vivo by oral, buccal, parenteral, rectal, or topical administration as well as by inhalation spray The term "parenteral" as used herein includes, subcutaneous, intravenous, intramuscular, intrasternal, infusion techniques or mtrapentoneally For oral administration, the pharmaceutical composition containing the ABCl polynucleotide or recombinant ABCl vector may be in the form of, for example, a capsule, a tablet, a suspension, or liquid. The pharmaceutical composition is preferably made in the form of a dosage unit containing a given amount of DNA or viral vector particles. For example, these may contain an amount from about 10 3 -10 15 viral particles, preferably from about 10"-10 12 viral particles. A suitable daily dose for a human or other mammal may vary widely depending on the condition of the patient and other factors, but, once again, can be determined using routine methods. The pharmaceutical composition containing the ABCl DNA or recombinant ABCl vector can also be administered rectally. Suitable suppositories for rectal administration of the vector can be prepared by mixing the vector with a suitable non-irritating excipient such as cocoa butter and polyethylene glycols that are solid at ordinary temperatures but liquid at the rectal temperature and will therefore melt in the rectum and release the vector. A pharmaceutical composition also can be formulated for inhalation. For example, an ABCl polynucleotide or vector may be formulated as a dry powder for inhalation. Also, ABCl polynucleotide or vector inhalation solutions can be formulated with a propellant for aerosol delivery. In yet another embodiment, solutions may be nebulized. The pharmaceutical composition containing the ABCl DNA or recombinant ABCl vector can also be injected. Injectable preparations, such as sterile injectable aqueous or oleaginous suspensions, may be formulated according to the known methods using suitable dispersing or wetting agents and suspending agents. The sterile injectable preparation may also be a sterile injectable solution or suspension in a non-toxic parenterally acceptable diluent or solvent, for example as a solution in 1,3-butanediol. A particularly suitable carrier for parenteral injection is sterile distilled water in which an ABCl polynucleotide or vector is formulated as a sterile, isotonic solution, properly preserved. Among the other acceptable carriers and solvents that may be employed are Ringer's solution, and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium. For this purpose any bland fixed oil may be employed, including synthetic mono- or diglycerides. In addition, fatty acids such as oleic acid find use in the preparation of injectables. Yet another preparation can involve the formulation of the desired ABCl molecule with an agent, such as injectable microsperes, bio-erodible particles, polymeric compounds, beads or liposomes, that provides for the controlled or sustained release of the ABCl product (see, e.g. PCT US93/00829; Eppstein et al., Proc. Natl. Acad. Sci., 82: 3688-3692 (1985)). Also, the pharmaceutical composition containing the ABCl DNA or recombinant ABC l vector can administered topically. For topical administration, the vector may compnse from 0.001 % to 10% w/w, e.g. , from 1% to 2% by weight of the formulation, although it may compnse as much as 10% w/w, but preferably not more than 5% w/w, and more preferably from ^ 0 1% to 1 % of the formulation. Formulations suitable for topical administration include liquid or semi-liquid preparations suitable for penetration through the skin (e g , liniments, lotions, ointments, creams, or pastes) and drops suitable for administration to the eye, ear, or nose. A suitable topical dose of active ingredient of a vector of the present invention is administered one to four, preferably two or three times daily. 0 While the nucleic acids and /or vectors of the invention can be administered as the sole active pharmaceutical agent, they can also be used in combination with one or more vectors of the invention or other agents. When administered as a combination, the therapeutic agents can be formulated as separate compositions that are given at the same time or different times, or the therapeutic agents can be given as a single composition. 5 In another embodiment of the present invention, a target cell is transfected in vivo by implantation of a "producer cell line" in proximity to the target cell population (Culver, K., et al, 1994, Hum Gene Ther., 5 (3): 343-79; Culver, K., et al, Cold Spring Harb Symp. Quant. Biol, 59: 685-90; Oldfield, E., 1993, Hum. Gene Ther., 4 (1): 39-69). The producer cell line is engineered to produce a viral vector containing the ABCl polynucleotide and to release its viral 0 particles in the vicinity of the target cells, i.e. preferably macrophage cells found in atherosclerotic lesions. A portion of the released viral particles contact the target macrophage cells and mfect those cells, thus dehveπng an ABCl polynucleotide to the target macrophage cell Following infection of the target cell, expression of the ABCl polynucleotide occurs, providing the macrophage cell with functional ABCl protein. 5 In another embodiment, the invention provides a method of treating a cardiovascular disease by the ex vivo introduction of an ABCl polynucleotide or recombinant ABCl expression vector In such instances, cells, tissues, or organs that have been removed from the patient are exposed to ABCl compositions after which the cells, tissues, or organs are subsequently implanted back into the patient. For example, one method includes the removal of a blood 30 sample from a subject with cardiovascular disease, ennching the sample for monocytes, and contacting the isolated monocytes with a recombinant expression vector containing the ABCl polynucleotide and, optionally, a target specific gene. Optionally, the monocyte cells can be treated with a growth factor, such as GM-CSF, to stimulate cell growth, before remtroducing the cells into the subject. When reintroduced, the cells will specifically target the cell population from which they were originally isolated. In this way, the transport activity of the ABCl polypeptide may be used to promote cholesterol efflux in a subject. Another method of ex vivo administration involves introducing the ABCl polynucleotide or recombinant ABCl vector into the mammalian subject by means of skin transplants of cells containing the virus. Preferably, a retrovius used for this method of administration. Long term expression of foreign genes in implants, using cells of fibroblast origin, may be achieved if a strong housekeeping gene promoter is used to drive transcription. For example, the dihydrofolate reductase (DHFR) gene promoter may be used. Cells such as fibroblasts, can be infected with virions containing a retroviral construct containing the ABCl polynucleotide together with a gene which allows for specific targeting, such as scavenger receptor A, and a strong promoter. The infected cells can be embedded in a collagen matrix that can be grafted into the connective tissue of the dermis in the recipient subject. As the retrovirus proliferates and escapes the matrix it will specifically infect the target cell population. In this way the transplantation results in increased amounts of cholesterol efflux activity in cells manifesting the transport disorder. In another embodiment, the recombinant expression vector comprising the ABCl polynucleotide can be administered using in vitro techniques, such as described in U.S. Patent No. 5,399,346. For example, an ABCl polypeptide can be delivered by implanting certain cells that have been genetically engineered, using methods such as those described herein, to express the ABC 1 polypeptide. In order to minimize a potential immunological reaction in patients being administered an ABCl polypeptide, as may occur with the administration of a polypeptide of a foreign species, it is prefened that the natural cells producing ABCl polypeptide be of human origin and produce human ABCl polypeptide. Thus, it is prefened that the recombinant cells producing ABCl polypeptide be transformed with an expression vector containing a gene encoding a human ABCl polypeptide. The cells can be autologous or heterologous. Optionally, the cells can be immortalized. In order to decrease the chance of an immunological response, the cells may be encapsulated to avoid infiltration of sunounding tissues. The encapsulation materials are typically biocompatible, semi-permeable polymeric enclosures or membranes that allow the release of the protein product(s) but prevent the destruction of the cells by the patient's immune system or by other detrimental factors from the sunounding tissues. The transfected cells can be administered to a patient using the above-described methods. Techniques for the encapsulation of living cells are known in the art, and the preparation of the encapsulated cells and their implantation in patients may be routinely accomplished. For example, Baetge et al (PCT Pub. No. WO 95/05452 and PCT/US94/09299) describe membrane capsules containing genetically engineered cells for the effective delivery of biologically active molecules. The capsules are biocompatible and are easily retrievable. The capsules encapsulate cells transfected with recombinant DNA molecules comprising DNA sequences coding for biologically active molecules operatively linked to promoters that are not subject to down regulation in vivo upon implantation into a mammalian host. The devices provide for the delivery of the molecules from living cells to specific sites within a recipient. In addition, see U.S. Patent Nos. 4,892,538; 5,011,472; and 5,106,627. A system for encapsulating living cells is described in PCT Pub. No. WO 91/10425 (Aebischer et al). See also, PCT Pub. No. WO 91/10470 (Aebischer et al.); Winn et al, 1991, Exper. Neurol. 113:322-29; Aebischer et al, 1991, Exper. Neurol. 111 :269-75; and Tresco et al, 1992, ASAIO 38: 17-23. Another delivery system for polynucleotides encoding ABCl is a "non-viral" delivery system. Techniques that have been used or proposed for gene therapy include DNA-ligand complexes, adenovirus-ligand-DNA complexes, direct injection of DNA, CaPO 4 precipitation, gene gun techniques, electroporation, lipofection, and colloidal dispersion (Mulligan, R., 1993, Science, 260 (5110): 926-32). Any of these methods are widely available to one skilled in the art and would be suitable for use in the present invention. Other suitable methods are available to one skilled in the art, and it is to be understood that the present invention may be accomplished using any of the available methods of transfection. Several such methodologies have been utilized by those skilled in the art with varying success (Mulligan, R., 1993, Science, 260 (5110): 926-32). Preferably, the non-viral delivery system is a colloidal dispersion system. Colloidal dispersion systems include macromolecule complexes, nanocapsules, microspheres, beads, and lipid-based systems including oil-in-water emulsions, micelles, mixed micelles, and liposomes. The prefened colloidal system of this invention is a liposome, which is an artificial membrane vesicle useful as delivery vehicles in vitro and in vivo. Liposomes are self-assembling, colloidal particles in which a lipid bilayer, composed of amphiphilic molecules such as phosphatidyl serine or phosphatidyl choline, encapsulates a portion of the sunounding media such that the lipid bilayer sunounds a hydrophilic interior. Unilammellar or multilammellar liposomes can be constructed such that the interior contains a desired chemical, drug, or, as in the instant invention, an isolated DNA molecule. For example, it has been shown that large unilamellar vesicles (LUV), which range in size from 0.2-4.0 μm can encapsulate a substantial percentage of an aqueous buffer containing large macromolecules, such as RNA, DNA and intact virions. Once encapsulated within the aqueous interior, these macromolecules can be delivered to mammalian cells in a biologically active form (Fraley, R. and Papahadjopoulos, D. 1981, Trends Biochem. Sci., 6: 77- 80). In order for a liposome to be an efficient gene transfer vehicle, the following characteristics should be present: (1) encapsulation of the genes of interest at high efficiency while not compromising their biological activity; (2) preferential and substantial binding to a target cell in comparison to non-target cells; (3) delivery of the aqueous contents of the vesicle to the target cell cytoplasm at high efficiency; and (4) accurate and effective expression of genetic information (Mannino, R., et al, 1988, Biotechniques, 6 (7): 682-90). The composition of the liposome is usually a combination of phospholipids, particularly high-phase-transition-temperature phospholipids, usually in combination with steroids, especially cholesterol. Other phospholipids or other lipids may also be used. The physical characteristics of liposomes depend on pH, ionic strength, and the presence of divalent cations. Examples of lipids useful in liposome production include phosphatidyl compounds, such as phosphatidylglycerol, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingolipids, cerebrosides, and gangliosides. Particularly useful are diacylphosphatidylglycerols, where the lipid moiety contains from 14-18 carbon atoms, particularly from 16-18 carbon atoms, and is saturated. Illustrative phospholipids include egg phosphatidylcholine, dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine. The targeting of liposomes has been classified based on anatomical and mechanistic factors. Anatomical classification is based on the level of selectivity, for example, organ- specific, cell-specific, and organelle-specific. Mechanistic targeting can be distinguished based upon whether it is passive or active. Passive targeting utilizes the natural tendency of liposomes to distribute to cells of the reticulo-endothelial system (RES) in organs which contain sinusoidal capillaries. Active targeting, on the other hand, involves alteration of the liposome by coupling the liposome to a specific ligand, such as a polyclonal or monoclonal antibody, sugar, glycolipid, or protein, or by changing the composition or size of the liposome in order to achieve targeting to organs and cell types other than the naturally occurring sites of localization. Preferably, the ligand is a polyclonal or monoclonal antibody which can be used to target liposomes to specific cell-surface ligands. The ligand can also be an antibody fragment, such as Fab, or F(ab') 2 , as long as it binds efficiently to an the antigenic epitope on the target cells. Preferably, the antibody or antibody fragment recognizes an antigen that is found exclusively on the target cell. For example, certain antigens expressed specifically on macrophage cells, such as scavenger receptor A. may be exploited for the pmpose of targeting antibody- ABC 1 liposomes directly to a macrophage cell A number of procedures can be used to covalently attach either polyclonal or monoclonal 5 antibodies to a liposome bilayer Also, lipid groups can be incoφorated into the lipid bilayer of the liposome in order to maintain the targeting ligand in stable association with the hposomal bilayer In addition, vanous linking groups can be used for joining the lipid chains to the targeting ligand Studies presented herein showed that ligands for nuclear receptors were able to effect an l o increase in cholesterol efflux Accordingly, in another embodiment, the present invention provides a method suitable for increasing cholesterol efflux from cells in a mammalian subject compnsing the step of administenng to the mammalian subject at least one ligand for a nuclear receptor in an amount sufficient to increase cholesterol efflux from said cells A pharmaceutical composition compnsing a ligand for a nuclear receptor can prepared and administered using the l -5 above-descnbed methods for formulating and administenng pharmaceutical compositions A sufficient amount of a nuclear receptor ligand is the amount of ligand that increases cholesterol efflux. Such amount can be determined by measunng the cholesterol efflux before and after administration of the ligand at vanous dosages and determining the dose that effects an increase in cholesterol efflux The cholesterol efflux can be measured using assays previously descnbed 20 Nuclear receptors are hgand-activated transcnption factors that play a cπtical role in vertebrate development and adult physiology by transducing the effects of small, hpophihc hormones into transcnptional responses Several families of nuclear receptors exist, including peroxisome prohferator-activated receptors (PPARs), liver X receptors (LXR), retinoid X receptor (RXR), the famesoid X receptor (FXR), and the steroid and xenobiotic receptor (SXR) 25 The PPAR family compnses the three closely related gene products PPARα, PPARγ, and PPARβ/δ PPARα has been implicated as a key regulator of intra- and extracellular lipid metabolism When bound to fatty acids, PPARα stimulates the proliferation of peroxisomes and induces the synthesis of several enzymes involved in the β-oxidation of fatty acids The PPARα receptor is also the molecular target for the fibrates, drugs that are prescnbed for the reduction of 30 high tnglyceπde levels (Isseman et al., Nature, 347, 645 (1990)) Fibrates act as PPAR ligands to regulate the transcnption of a large number of genes that affect lipoprotein and fatty acid metabolism In addition, PPARγ ligands, such as compounds belonging to the class of thiazohdinediones compounds, have been shown to increase HDL and reduce tπglycende levels in humans LXR is an oxysterol receptor that regulates the catabohsm of excess cholesterol. LXRα has been shown to bind as a heterodimer with RXR to a DNA response element in the CYP7a gene, which encodes the enzyme responsible for the rate-limiting step in the conversion of cholesterol to bile acids. Studies have shown that mice lacking LXRα accumulate enormous amounts of cholesterol esters in their livers when fed a cholesterol-nch diet, due to their inability to increase CYP7a gene transcnption in response to dietary cholesterol (Peet et al, Cell, 93. 693 ( 1998)) Further studies with LXRα null mice show that LXRα is also involved in the regulation of several other genes that particpate in cholesterol and fatty acid homeostasis. The biological role of a closely related nuclear receptor, LXRβ, which is expressed in several tissues and is activated by the same oxysterols as LXRα, remains unclear (Song et al, Proc Natl Acad Sci., 91 10809 ( 1994), Seol, Mol Endocrmol, 9: 72 (1995)). FXR, which is evolutionary related to LXRα, is also involved in cholesterol homeostasis Like LXRα, FXR functions as a heterodimer with the RXR receptor (Schwartz et al., Curr Opin Lipidol, 9 113 (1998); Vlahcevic et al., Gastroenterology, 113: 1949 (1997)). FXR is activated by the synthetic retmoid TTNPB and supeφhysiological concentrations of all- trans retmoic acid (Zavacki et al., Proc. Natl Acad. Sci., 94: 7909 (1997)) Recent studies indicate that FXR is a nuclear bile acid receptor. First, FXR is abundantly expressed in tissues through which bile acids circulate, including the liver, intestine, and kidney (Seol et al., Mol Endocrmol, 9 72 (1995); Forman et al., Cell, 81 : 687 (1995)) Also, FXR has recently been shown to serve as a receptor for physiological concentrations of several bile salts, among which chenodeoxycho c acid (CDCA) is the most potent (Kliewer et al., Science, 284- 757-284 (1999); Makishima et al., Science, 284: 1362-1363 (1999)). CDCA is known to regulate the expression of several genes that participate in bile salt homeostasis, including those encoding CYP7a and the intestinal bile acid-bindmg protein. As descnbed in detail in Example 13, ligands for LXR, RXR, and PPAR nuclear receptors were shown to increase apoAI-induced cholesterol efflux in cholesterol-loaded mouse macrophage cells. For example, administration of 9 -retinoic acid (30 ng/ml) produced approximately a 3-fold increase in apoAI-mduced cholesterol efflux m these cells. Similarly, administration of 22(R)hydroxycholesterol (5 μg/ml) produced approximately a 3-fold increase in apoAI-induced cholesterol efflux. Cells that received fenfibrate (3 μg/ml) produced an approximate 2-fold increase in cholesterol efflux. These results indicate that nuclear receptors may be modulated to increase the rate of apohpoprotem-mediated cholesterol efflux from macrophages Furthermore, as descnbed in Example 13, 9-cιs-RA mediated cholesterol efflux from macrophage cells in a dose-dependent manner. Other nuclear receptor activators, such as bezafibrate, were shown to increase cholesterol efflux (data not shown). Accordingly, in the method for increasing cholesterol efflux by administenng a nuclear receptor ligand, the ligand is preferably selected from the group consisting of LXR, RXR, PPAR. FXR. and SXR nuclear receptor ligands. In the prefened embodiment wherein a LXR ligand is used to increase cholesterol efflux, the ligand is more preferably selected from the group consisting of 20(S) hydroxycholesterol, 22(R) hydroxycholesterol, 24-hydroxycholesterol, 25- hydroxycholesterol, and 24(S), 25 epoxycholesterol LXR ligands Most preferably, the LXR ligand is 20(S) hydroxycholesterol. In the prefened embodiment wherein a RXR ligand is used to increase cholesterol efflux, the ligand is more preferably selected from the group consisting of 9-cιs retmoic acid, retmol, retinal, all-trans retmoic acid, 13-cis retmoic acid, acitretm, fenretimde, etretinate, CD 495, CD564, TTNN, TTNNPB, TTAB, LGD 1069 Most preferably, the RXR ligand is 9-cιs retmoic acid In another prefened embodiment wherein a PPAR ligand is used to increase cholesterol efflux, the ligand is preferably selected from the class of thiazohdinedione compounds. In another prefened embodiment, more than one nuclear receptor ligand is administered to the mammalian subject to increase cholesterol efflux. Preferably, when two or more nuclear receptor ligands are administered to a subject, the ligands are an LXR and an RXR ligand More preferably, the nuclear receptor ligands are 20(S) hydroxycholesterol and 9-cιs retmoic acid In still another embodiment, the present invention provides a method suitable for increasing cholesterol efflux from cells in a mammalian subject compnsing the step of administenng to the mammalian subject an eicosanoid m an amount sufficient to increase cholesterol efflux A pharmaceutical composition compnsing an eicosanoid can be prepared and administered using the above-descnbed methods for formulating and administenng pharmaceutical compositions. A sufficient amount of eicosanoid is the amount that increases cholesterol efflux. Such amount can be determined by measunng the cholesterol efflux before and after administration of the eicosanoid at vanous dosages and determining the dose that effects an increase in cholesterol efflux. The cholesterol efflux can be measured using assays and methods previously descnbed. As descnbed in Example 14, eicosanoids were shown to increase apoAI-induced cholesterol efflux in cholesterol-loaded mouse macrophage cells For example, administration of PGI2 (25 nm) produced approximately a 2-fold increase in apoAI-induced cholesterol efflux in these cells. Likewise, administration of PGEI (25 nM) produced approximately a 3-fold increase in apoAI-induced cholesterol efflux. These results demonstrate that eicoasnoids can increase the rate of apolipoprotein-mediated cholesterol efflux from macrophages. Accordingly, in a prefened embodiment, the eicosanoid is selected from the group consisting of prostaglandin E2, prostacyclin (prostaglandin 12), and prostaglandin J2 eicosanoids. Methods and Compounds for Increasing ABCl Expression/Activity Given that ABCl functions to promote cholesterol efflux, one way to increase cholesterol efflux is to increase the cellular expression of ABCl. Accordingly, the present invention also provides methods suitable for increasing cholesterol efflux from cells in a mammalian subject by administering to the mammalian subject a therapeutic amount of a compound that increases the expression of ABCl in said cells. A therapeutic amount of compound is the amount of compound that increases ABCl expression. Such amount can be determined by measuring the gene expression of ABCl before and after administration of the compound at various dosages and determining the dose that effects an increase in ABCl gene expression. The ABCl gene expression can be measured by obtaining a blood sample from the subject, separating the monocyte population, and determining the concentration of ABCl mRNA using methods known in the art and described herein, such as RT-PCR. In one prefened embodiment, the method comprises administering a cAMP analogue to increase the gene expression of ABCl . As shown in Figure 8, cAMP increases the expression of ABCl mRNA in normal fibroblast cells approximately 10-fold. Preferably, the cAMP analogue is selected from the group consisting of 8-bromo cAMP, N6-benzoyl cAMP, and 8-thiomethyl cAMP. In another prefened embodiment, the method comprises administering a compound that increases the synthesis of cAMP to increase the gene expression of ABCl . Preferably, the compound is forskolin. In yet another prefened embodiment, the method comprises administering a compound that inhibits the breakdown of cAMP to increase the gene expression of ABC 1. An example of such a compound is a phosphodiesterase inhibitor. Preferably, the phosphodiesterase inhibitor is selected from the group consisting of rolipram, theophylline, 3- isobutyl- 1 -methylxanthine, R020- 1724, vinpocetine, zaprinast, dipyridamole, milrinone, amrinone, pimobendan, cilostamide, enoximone, peroximone, and vesnarinone phosphodiesterase inhibitors. In another prefened embodiment, the method compnses administenng to the mammalian subject a ligand for a nuclear receptor in an amount sufficient to increase the gene expression of ABCl As descnbed in Example 17 and shown in Figure 12, ligands for nuclear receptors can up-regulate the gene expression of ABCl Transfection studies using pAPRl, which contains a luciferase reporter gene under the control of the ABCl promoter, showed that the ABCl promoter was activated m the presence of ligands for LXR and RXR nuclear receptors Specifically, macrophage cells transfected with pAPRl produced a 19-fold increase in luciferase reporter activity in the presence of 20 OH-chol, a 16-fold increase in luciferase activity in the presence of 9-cιs RA, and a 280-fold increase in luciferase activity in the presence of both ligands compared with EtOH control The results indicate that both sterols and retmoids elicit a strong transcription response from the ABCl promoter Further, there is an apparent synergistic effect between the two classes of compounds, as can be seen by the dramatic increase m luciferase activity found in cells treated with both ligands In accordance with the inventive method, preferably, the ligand is selected from the group consisting of LXR, RXR, PPAR, FXR, and SXR ligands In addition to increasing cellular levels of ABCl protein, reverse cholesterol transport can be promoted by enhancing the activity of ABCl protein Thus, in another embodiment, the present invention provides a method suitable for increasing cholesterol efflux from cells in a mammalian subject compnsing the step of administenng to the mammalian subject a therapeutic amount of a compound that increases ABCl activity in an amount sufficient to increase cholesterol efflux A pharmaceutical composition compnsing such a compound can prepared and administered using the above-descnbed methods for formulating and administenng pharmaceutical compositions A therapeutic amount of compound is the amount of compound that increases cholesterol efflux Such amount can be determined by measunng the cholesterol efflux before and after administration of the compound at vanous dosages and determining the dose that effects an increase m cholesterol efflux using methods previously descnbed To determine whether an increase in cholesterol efflux is due to an increase in ABCl activity, the amount of ABCl protein present in a cell sample before and after administration of the compound is determined, using methods descnbed herein (see Example 1 1) For both measurements (l e pre- and post-administration of the compound), the amount of cholesterol efflux activity is divided by the concentration of ABCl protein to determine the amount of cholesterol activity found in a standard concentration of ABCl protein An observed increase in cholesterol activity standardized to protein concentration indicates that the increase is due to an increase in ABCl activity. Methods for Identifying Therapeutic Compounds Another aspect of the present invention relates to methods for screening a compound to determine whether the compound modulates (i.e., up-regulates or down-regulates) the gene expression of ABCl . Such compounds may be useful in the development of therapeutic compounds that increase ABCl expression and thereby promote cholesterol efflux and raise blood levels of HDL-cholesterol. Accordingly, methods for identifying compounds that may be useful in the treatment of cardiovascular disease are provided. In one embodiment, the present invention provides a method for screening a test compound for ABCl expression modulating activity comprising the steps of: (a) operatively linking a reporter cDNA with an expression modulating portion of the mammalian ABCl gene to produce a recombinant reporter construct; (b) transfecting the recombinant reporter construct into a population of host cells; (c) assaying the level of reporter gene expression in a sample of the transfected host cells; (d) contacting the transfected host cells with the test compound being screened; (e) assaying the level of reporter gene expression in a sample of the transfected host cells after contact with the test compound; and (f) comparing the relative change in the level of reporter gene expression caused by exposure to the test compound, thereby determining the ABCl expression modulating activity. First, a recombinant reporter construct comprising a heterologous reporter gene operatively linked to an expression modulating portion of the ABCl gene is constructed. The ABCl expression modulating polynucleotide and reporter gene can be inserted into a vector using well-known ligation and cloning techniques, such as those described herein and in standard laboratory manuals, including Davis et al., Basic Methods in Molecular Biology (1986); Sambrook et al., Molecidar Cloning: A Laboratory Manual, 2 nd Ed., (Cold Spring Harbor Press, Cold Spring Harbor, N.Y. (1989)); and Ausubel et al. eds., Current Protocols in Molecular Biology, (Wiley and Sons (1994)). Alternatively, the ABCl expression modulating polynucleotide can be inserted into a commercially available reporter construct, such as those previously described. Any vector suitable for ABCl polynucleotide and reporter gene insertion can be used. The chosen vector should be functional in the particular host cell employed. Preferably, the vector is compatible with mammalian host cells. Preferably, the expression modulating portion of the ABCl gene is the 5' flanking region of ABCl , containing ABCl promoter activity. In one prefened embodiment, the expression modulating portion of the ABCl gene comprises SEQ ID NO: 3. In another prefened embodiment, the expression modulating portion of the ABCl gene comprises nucleotides 1- 1532, 1080-1643, 1 181-1643, 1292-1643, 1394-1643, or 1394-1532 of SEQ ID NO: 3. Also, preferably the heterologous reporter is selected from the group consisting of polynucleotides that encode the luciferase, β-galactosidase, chloramphenicol, and green fluorescent proteins. More preferably, the heterologous reporter is a polynucleotide that encodes the luciferase protein. In a particularly prefened embodiment, the recombinant reporter construct is pAPRl, shown in Figure 11. Next, the recombinant reporter construct is transfected into a population of host cells. The recombinant reporter construct can be introduced into the host cells using any of the previously described transfection methods, as well as the methods described in Examples 8 and 15. For example, the reporter construct can be transfected using calcium phosphate transfection, DEAE-dextran mediated transfection, cationic lipid-mediated transfection, electroporation, transduction, infection, or any of the other known and described methods (see, e.g., Davis et al., Basic Methods in Molecular Biology (1986)). The host cell can be any cell that, when cultured under appropriate conditions, synthesizes a reporter polypeptide, which can be subsequently measured. Preferably, the host cell is a mammalian host cell. More preferably, the mammalian host cell is a macrophage, fibroblast, hepatic, or intestinal cell. Most preferably, the host cell is selected from the group consisting of RAW 264.7 cells, Thp-1 cells, and HepG2 cells. The concentration of reporter construct and duration of the transfection can vary, depending on the transfection method and the type and concentration of host cell used. Determination of the appropriate concentration of reporter construct and transfection time is well within the skill of the ordinary artisan. Following transfection, a sample of transfected host cells that was not exposed to the test compound is assayed to determine the level of reporter gene expression. The level of reporter gene expression found in the sample of unexposed transfected host cells provides a control measurement. The transfected host cells are lysed and the level of reporter gene expression is assayed using any of the methods well-known in the art. The assays used to measure the level of reporter gene expression differ, depending on the reporter construct used in the transfections. For example, if a luciferase reporter construct is used, the luciferase activity of the cell lysate is measured as light units using a luminometer, as described in Example 15. A different sample of the transfected host cells is contacted with the test compound being screened and the level of reporter gene expression found in these cells is subsequently measured. Preferably, the transfected host cells are contacted with the test compound for about 4-48 hours. More preferably, the transfected host cells are contacted with the test compound for about 8-36 hours. Even more preferably, the transfected host cells are contacted with the test compound for about 24 hours. The same assay used to measure the level of reporter gene expression in unexposed (control) cells should be used to measure the level of reporter gene expression in the cells exposed to the test compound. Finally, the level of reporter gene expression found in unexposed control cells is compared with the level of reporter gene expression found in cells exposed to the test compound to determine whether the test compound has ABCl expression modulating activity. If the level of gene expression in both cell samples are the same or about the same, the test compound does not modulate ABCl gene expression. A higher level of reporter gene expression in cells exposed to the test compound relative to the level of reporter gene expression found in control cells, indicates that the test compound up-regulates the gene expression of ABCl . A lower level of reporter gene expression in cells exposed to the test compound relative to the level of reporter gene expression found in control cells, indicates that the test compound down-regulates the gene expression of ABCl. Another aspect of the present invention relates to methods for screening a test compound to determine whether the compound promotes ABCl -mediated cholesterol efflux. Such method comprises: (a) assaying the level of cholesterol efflux in a sample of mammalian cells maintained in culture to determine a control level of cholesterol efflux, (b) contacting the mammalian cells with the test compound being screened; (c) assaying the level of cholesterol efflux in a sample of cells after contact with the test compound; and (d) assaying the level of ABCl -dependent cholesterol efflux in a sample of cells after contact with the test compound, thereby determining whether the test compound promotes ABCl -mediated cholesterol efflux from cells in culture. The level of cholesterol efflux in a sample of cultured cells can be determined using methods known in the art and described herein (see Example 1). Any mammalian cells that can be maintained in culture can be used to measure cholesterol efflux. The cells can be derived from primary cultures or from immortalized cell lines. For convenience, cells can be immortalized by transfecting them with amphotropic retroviruses containing vectors with inserts of human papillomavirus 16, oncogenes E6 and E7, and a selectable marker gene, as described in Example 1. Preferably, the cultured cells are fibroblast, macrophage, hepatic, or intestinal cells. More preferably, the cultured cells are RAW 264.7 cells. The level of cholesterol efflux in a sample of cells that has not been contacted with the test compound is measured to obtain a control level of cholesterol efflux. In addition, the level of cholesterol efflux in a sample of mammalian cells that has been contacted with the test compound is measured to determine the amount of cholesterol efflux affected by the test compound. Also, the level of ABCl -mediated cholesterol efflux in a sample of mammalian cells that has been contacted with the test compound is measured to determine the amount of ABCl - mediated cholesterol efflux affected by the test compound. Preferably, the cells are contacted with the test compound for about 8-24 hours before cholesterol efflux or ABCl -mediated cholesterol efflux is assayed. The level of ABCl -mediated cholesterol efflux can be assayed using an anti- ABCl antibody that, upon binding, inhibits the activity of ABCl . Alternatively, the level of ABCl -mediated cholesterol efflux can be assayed using an anti-sense ABCl polynucleotide that inhibits the expression of ABCl. For example, the level of ABCl -mediated cholesterol efflux can be assayed using the anti-sense ABCl polynucleotide comprising SEQ ID NO: 57 (see Example 7). The cells should be contacted with the anti- ABCl antibody or anti- sense ABCl polynucleotide at the same time and for the same duration that it is contacted with the test compound. If the level of control cholesterol efflux is the same or about the same as the level of cholesterol efflux found in cells contacted with the test compound, the compound does not promote cholesterol efflux. An increase in the level of cholesterol efflux found in cells contacted with test compound over the control level of cholesterol efflux indicates the amount of cholesterol efflux promoted by the test compound. The difference between the cholesterol efflux found in cells contacted with test compound alone and the cholesterol efflux found in cells contacted with test compound and anti-ABC 1 antibody or anti-sense ABCl polynucleotide indicates the amount of cholesterol efflux mediated through ABCl. For example, if control level of cholesterol efflux is 1.0 and the level of cholesterol efflux found in cells contacted with test compound is 1.1, the test compound promotes cholesterol efflux by 10%. If the cholesterol efflux found in cells contacted with test compound and anti-ABC 1 antibody or anti-sense ABCl polynucleotide is 1.0, the increase in cholesterol efflux caused by the test compound is entirely ABCl -mediated. Methods for Detecting Susceptibility to Coronary Heart Disease The present invention also relates to methods for detecting the comparative level of ABCl gene or protein expression in a mammalian subject, including a human subject. Given the role of ABCl in cholesterol efflux, the determination of a decreased level of ABCl gene or protein expression in a mammalian subject relative to a pre-determmed standard level of ABCl gene or protein expression can be used to indicate a susceptibility to coronary heart disease m the subject Accordingly, the present invention provides a method for detecting the comparative level of ABCl gene expression in a mammalian subject compnsing the steps of (a) obtaining a test cell sample from the mammalian subject, (b) assaying the level of ABCl mRNA expression in the test cell sample, and (c) companng the level of ABCl mRNA expression in the test cell sample with a pre-determined standard level of ABCl mRNA expression, thereby detecting the comparative level of ABCl gene expression in the mammalian subject A test cell sample is first obtained from a mammalian subject, including a human subject The test cell sample can be a blood sample, wherein the monocyte population has been ennched Monocvtes can be ennched using well-known cell separation procedures based on, for example, cell size, cell density or cell affinity Next, the level of ABCl mRNA expression in the test cell sample is assayed The level of ABCl mRNA expression can be assayed using any of the well- known methods for mRNA preparation and detection, including the methods descnbed herein at Examples 2 and 9 For example, the concentration of ABCl mRNA can be determined by reverse transcnption polymerase chain reaction, northern blot analysis, or RNAse protection assay The ABCl mRNA concentration should be standardized to the concentration of total mRNA found in the test cell sample Finally, the ABCl expression in the test cell sample is compared with a pre-determined standard level of ABCl mRNA expression A pre-determined standard level of ABCl mRNA expression can be obtained by determining the average concentrations and distnbution of ABCl mRNA found in cell samples taken from a representative population of mammalian subjects, wherein the mammalian subjects are the same species as the subject from which the test cell sample was obtained, and wherein the mammalian subjects do not have coronary heart disease, Tangier disease, or other disease associated with low HDL-cholesterol and are considered to have cholesterol efflux activity withm a normal range (I e , as indicated by an HDL-cholesterol level within a normal range) The determination of a decreased level of ABCl mRNA expression in the test cell sample of a mammalian subject relative to the pre-determmed standard level of ABCl mRNA expression can be used to indicate a susceptibility to coronary heart disease in the mammalian subject Likewise, the detection of a decreased level of ABCl protein can be used to indicate decreased capacity for cholesterol efflux and a susceptibility to coronary heart disease Accordingly, another embodiment of the present invention provides a method for detecting the comparative level of ABCl protein m a mammalian subject Such method compnses the steps of (a) obtaining a test cell sample from the mammalian subject; (b) assaying the amount of ABCl protein in the test cell sample, and (c) companng the amount of ABCl protein in the test cell sample with a pre-determmed standard amount of ABCl protein, thereby detecting the comparative level of ABCl protein m the mammalian subject. The amount of ABCl protein can be assayed using any of the well-known methods of measuring protein Preferably, the amount of ABCl protein is measured using an immunoassay In one embodiment, the amount of ABCl protein is determined by (a) contacting the cell sample with a population of anti-ABCl antibodies and (b) detecting the anti-ABCl antibodies associated with the cell sample. For example, the ABCl protein can be contacted with an antiserum raised against a synthetic peptide conespondmg to KNQTVVDAVLTSFLQDEKVKES located at the C-terminus, as descnbed in Example 11 The anti-ABCl antibodies can be detected using several methods known in the art, including, for example, western blotting, immunoprecipitation, and FACS, wherein the detection can be accomplished using radioactive, colorometnc, or fluorescent labeling. One prefened method for measunng the amount of ABC 1 protein m a cell sample is immunoprecipitation, wherein biotinylated ABCl proteins are contacted with anti- ABCl antibody and the bound anti-ABCl antibody is detected using streptavidm horse radish peroxidase The amount ABCl protein in the test cell sample is compared with a pre-determmed standard amount of ABCl protein A pre-determmed standard amount of ABCl protein can be obtained by determining the average concentration of ABCl protein found in cell samples taken from a population of mammalian subjects, wherein the mammalian subjects are the same species as the subject from which the test cell sample was obtained, and wherein the mammalian subjects do not have coronary heart disease, Tangier disease, or other disease associated with low HDL- cholesterol and are considered to have cholesterol efflux activity withm a normal range (I e., as indicated by an HDL-cholesterol level withm a normal range) ABCl Antibodies As used herein, the term "antibody" (Ab) or "monoclonal antibody" (Mab) is meant to include intact molecules as well as antibody fragments (such as, for example, Fab and F(ab')2 fragments) which are capable of specifically binding to protein Fab and F(ab')2 fragments lack the Fc fragment of intact antibody, clear more rapidly from the circulation, and may have less non-specific tissue binding than an intact antibody (Wahl et al., J Nucl Med , 24 316-325 ( 1983)) Thus, these fragments are prefened, as well as the products of a FAB or other immunoglobuhn expression library Moreover, antibodies of the present invention include chimenc, single chain, and humanized antibodies. Additional embodiments include chimenc antibodies, e g , humanized versions of munne monoclonal antibodies. Such humanized antibodies may be prepared by known techniques, and offer the advantage of reduced immunogenicity when the antibodies are administered to humans In one embodiment, a humanized monoclonal antibody compnses the vanable region of a munne antibody (or just the antigen binding site thereof) and a constant region denved from a human antibody Alternatively, a humanized antibody fragment may compnse the antigen binding site of a munne monoclonal antibody and a vanable region fragment (lacking the antigen-binding site) denved from a human antibody Procedures for the production of chimenc and further engineered monoclonal antibodies include those descnbed in Riechmann et al (Nature 332 323, 1988), Liu et al (PNAS 84 3439, 1987), Larnck et al (Bio/Technology 7 934, 1989), and Winter and Hams (TIPS 14 139, May, 1993). One method for producing an antibody compnses immunizing a non-human animal, such as a transgemc mouse, with a polypeptide translated from a polynucleotide compnsing SEQ ID NO 1, a polynucleotide compnsing nucleotides 291-7074 of SEQ ID NO 1, or a polynucleotide compnsing a nucleotide sequence that has at least 90% identity with a polynucleotide compnsing SEQ ID NO 1, whereby antibodies directed against the polypeptide translated from the descnbed polynucleotides are generated in said animal Procedures have been developed for generating human antibodies in non-human animals. The antibodies may be partially human, or preferably completely human Non-human animals (such as transgemc mice) into which genetic matenal encoding one or more human immunoglobuhn chains has been introduced may be employed Such transgemc mice may be genetically altered in a vanety of ways The genetic manipulation may result in human immunoglobuhn polypeptide chains replacing endogenous immunoglobuhn chains in at least some (preferably virtually all) antibodies produced by the animal upon immunization Antibodies produced by immunizing transgemc animals with a polypeptide translated from any of the descnbed polynucleotides are provided herein Mice in which one or more endogenous immunoglobuhn genes are inactivated by various means have been prepared Human immunoglobuhn genes have been introduced into the mice to replace the inactivated mouse genes Antibodies produced m the animals incorporate human immunoglobuhn polypeptide chains encoded by the human genetic material introduced into the animal Examples of techniques for production and use of such transgemc animals are described in U.S. Patents 5,814,318, 5,569,825, and 5,545,806, which are incoφorated by reference herein. Monoclonal antibodies may be produced by conventional procedures, e.g., by immortalizing spleen cells harvested from the transgenic animal after completion of the immunization schedule. The spleen cells may be fused with myeloma cells to produce hybridomas, by conventional procedures. A method for producing a hybridoma cell line comprises immunizing such a transgenic animal with a immunogen comprising at least seven contiguous amino acid residues of a polypeptide translated from one of the described polynucleotides; harvesting spleen cells from the immunized animal; fusing the harvested spleen cells to a myeloma cell line, thereby generating hybridoma cells; and identifying a hybridoma cell line that produces a monoclonal antibody that binds a polypeptide translated from one of the described polynucleotides. Such hybridoma cell lines, and monoclonal antibodies produced therefrom, are encompassed by the present invention. Monoclonal antibodies secreted by the hybridoma cell line are purified by conventional techniques. The antibodies, upon specific binding to an ABCl polypeptide, may inhibit the activity of the ABCl polypeptide. Preferably, the antibody, upon binding, inhibits the cholesterol transport activity of the ABCl polypeptide. Such antibodies can be made by immunizing a non-human animal with a polypeptide conesponding to the region essential for cholesterol transport. The antibody can be tested to determine whether it inhibits cholesterol efflux using any of the described cholesterol efflux assays. Such inactivating antibodies can be employed in an in vitro assay, such as any of the cholesterol efflux assays described herein, to determine whether a test compound promotes ABCl -mediated cholesterol efflux. The inactivating antibodies can also be used in in vitro assays to detect the comparative level of ABCl protein in the cells of a mammalian subject. The inactivating antibodies are also useful in kits suitable for screening a compound to determine whether the compound modulates ABCl -dependent cholesterol efflux. Kits for Identifying Therapeutic Compounds The present invention also includes a kit suitable for screening a compound to determine the ABCl expression modulating activity of a compound. The kit includes, in an amount sufficient to perform at least one assay, a recombinant reporter construct comprising a reporter cDNA operatively linked to an expression modulating portion of the mammalian ABCl gene, as a separately packaged reagent. Instructions for use of the packaged reagent(s) are also typically included. The expression modulating portion of the mammalian ABCl gene comprises the 5' flanking sequence. In one prefened embodiment, the expression modulating portion of the mammalian ABCl gene comprises SEQ ID NO: 3. In other prefened embodiments, the expression modulating portion of the mammalian ABCl gene comprises nucleotides 1-1532, 1080-1643, 1 181-1643, 1292-1643, 1394-1643, or 1394-1532 of SEQ ID NO: 3. The reporter cDNA can be any suitable reporter gene, including In a particularly prefened embodiment, the recombinant reporter construct is pAPRl . In another embodiment, the kit further comprises means for detecting the reporter protein. Thus, the kit comprises reagents, such as buffers and substrates, used for reporter protein detection. As used herein, the term "package" refers to a solid matrix or material such as glass, plastic (e.g., polyethylene, polypropylene or polycarbonate), paper, foil and the like capable of holding within fixed limits a recombinant vector of the present invention. Thus, for example, a package can be a glass vial used to contain milligram quantities of a contemplated vector. "Instructions for use" typically include a tangible expression describing the reagent concentration or at least one assay method parameter such as the relative amounts of reagent and sample to be admixed, maintenance time periods for reagent/ sample admixtures, temperature, buffer conditions and the like. In addition, the present invention also includes a kit suitable for screening a compound to determine whether the compound modulates ABCl -dependent cholesterol efflux. In one embodiment, the kit includes, in an amount sufficient to perform at least one assay, an inactivating anti-ABCl antibody, as a separately packaged reagent. Instructions for use of the packaged reagent(s) are also typically included. In another embodiment, the kit includes an antisense ABCl oligonucleotide in an amount sufficient for at least one assay and instructions for use. Preferably, the antisense ABCl oligonucleotide comprises SEQ ID NO: 53. The following examples further illustrate the present invention but should not be construed to limit the present invention in any way. EXAMPLE 1 This example demonstrates that patients with Tangier Disease (TD) have an absence of apo A-I-mediated lipid efflux. Cell Cultures: Human fibroblasts were obtained from skin explants from two normal subjects (NL1) and three unrelated patients with Tangier disease (TD). TDl cells were obtained from a 53 year-old female with extremely low plasma HDL cholesterol and apo A-I levels and clinical symptoms typical of Tangier disease. TD2 cells were obtained from a 56 year-old male with clinical, moφho logical, and biochemical features of Tangier disease, including very low levels of plasma HDL cholesterol and apoA-I (Franc/5, et al., J. Clin Invest , 96, 78-87 (1995)). TD3 cells were obtained from an 18 year-old male with Tangier disease who presented with orange tonsil remnants, asymmetncal motor neuropathy, plasma HDL cholesterol of 5 mg/dL, and LDL cholesterol of 16mg/dL (Lawn et al., J. Clin Invest., 104, R25-R31 ( 1999)). The normal cells and TD subject cells were immortalized as descnbed m Oram et al., J. Lipid Res., 40- 1769- 1781 (1999) Bnefly, the cells were transfected with amphotropic retroviruses containing vectors with inserts of human papillomavirus 16 oncogenes E6 and E7 and a neomycm resistance selectable marker. Control cells were infected with vector alone (mock- infected) Pooled cell populations were selected in the presence of G418 for two passages, after which G418 was excluded from the medium. Fibroblasts were used between the fifth and sixteenth passage (pnmary) or sixth and fourteenth passage (immortalized). The immortalized normal and TD cells were seeded into 16-mm wells or 35-mm dishes and grown to confluence in Dulbecco's modified Eagle's medium (DMEM) plus 10% fetal bovine serum (FBS) before expenmental use. RAW 264.7 mouse monocytic cells (Amencan Type Culture Collection, Rockville. MD) were also maintained in DMEM containing 10% FBS. Assay to Measure Lipid Effux: Apo Al-mediated efflux of cholesterol and phosphohpid was assayed according to the method descnbed in Franczs, et al, J. Clin Invest., 96- 78-87 ( 1995). The cultured skm fibroblasts from normal and TD subjects were labeled by growth to confluence in the presence of 0.2-0.5 μCi/ml [ 3 H]cholesterol (40-60 Ci/mmol, Amersham Coφ., Arlington Heights, IL). The radioactive cholesterol was added to serum-containing growth medium when the cells were 60-80% confluent. After 3 days, the cells were washed twice with PBS/BSA and simultaneously growth-anested and cholesterol-loaded to maximize apohpoprotem-mediated lipid efflux. This was achieved by incubating the cells for 48 hours in serum-free DMEM plus 2 mg/ml fatty acid-free bovine serum albumin (DMEM/BSA) (Sigma Chemical Co., St. Louis, MO) and 30 μg/ml non-radioactive cholesterol. RAW 264.7 cells were cholesterol-loaded through the scavenger receptor by 24-hour incubation with acetylated LDL as descnbed m Smith et al, J Biol Chem., 271.30647-30655 (1996). Bnefly, RAW 264.7 cells m 24-well dishes were cholesterol-loaded and labeled overnight in 0.5 ml of DMEM supplemented with 50 μl/ml 1M glucose, 10 μl ml 200 mM glutamine and 2% BSA and with 50 μg/ml acetylated low density lipoprotein (AcLDL) and [ 3 H]-cholesterol which had been pre-incubated for 30 minutes at 37°C with AcLDL to yield a final concentration of 0.33 μCi/ml [ 3 H]- cholesterol. Cells were subsequently washed five times with PBS containing 1% BSA and incubated overnight (16-18 hours) in DMEM/BSA to allow for equilibrium of cholesterol pools. After equilibrium of cholesterol pools, cells were rinsed four times with PBS/BSA and incubated for one hour at 37°C with DMEM/BSA before the efflux incubations. Efflux medium (DMEM/BSA) containing either albumin alone (control), albumin plus HDL (40μg protein/ml), or albumin plus apo A-I (10 μg/ml, Biodesign International, Kennebunk, ME) was added and the cells were incubated for 4, 24, or 48 hours. Phospholipids were labeled by including 10 μCi/ml [ 3 H]choline (75-85 Ci/mmol, Amersham Coφ.) in the DMEM/BSA overnight equilibrium medium. The radioactivity found in the culture medium was measured by scintillation counting after a 15-minute centrifugation at 12,000g. The radioactivity in the cells was measured by scintillation counting after solubilization in 0.5 ml of 0.2M NaOH (Smith et al, J. Biol. Chem., 271 :30647-30655 (1996)) or extraction in hexane:isopropanol (3:2 v/v) as described in Francw, et al., J. Clin. Invest., 96, 78-87 (1995). Cells containing labeled phospholipids were extracted with 1 ml of isopropanol for 1 hour and then with hexane:isopropanol as described above. The efflux of cholesterol or phospholipid was expressed as the percentage of tritiated lipid counts in the medium over the total tritiated lipid counts recovered from the cells and medium (cpm medium / cpm (medium + lysate) x 100). As shown in Figure 1A and C, the addition of HDL or apo A-I results in the removal of cholesterol from cholesterol-laden fibroblasts obtained from normal subjects. However, in TD cells, the ability of HDL to remove cholesterol is slightly diminished and the ability of apo A-I to remove cholesterol is completely absent. Figure 1 shows that normal and TD fibroblast cells release about 3-4% of the cellular [ 3 H] -cholesterol into the medium during 48-hour incubation with albumin. Addition of HDL to the albumin medium increased the efflux of [ 3 H]-cholesterol from both normal and TD fibroblasts, although to a lesser extent with TD cells (Figure IB, D). Addition of apo A-I promoted the efflux of [ 3 H]-cholesterol from normal fibroblasts (Figure 1A, C), but had little or no effect on [ 3 H]-cholesterol efflux from TD fibroblasts (Figure IB, D). EXAMPLE 2 This example demonstrates that 175 genes show at least 2.5-fold decreased expression and 375 genes show at least 2.5-fold increased expression in TD cells compared with normal cells. The differential gene expression was determined using gene-expression microaπay (GEM) analysis of cDNAs from normal individuals (non-TD) and from patients with TD. Cell Cultures- The immortalized cell cultures obtained from normal individuals and TD patients descnbed in Example 1 were used. Confluent cultures were maintained in DMEM/BSA and supplemented for 24 hours with lmM 8-Bromo cyclic adenosme monophosphate (8-Br- ι cAMP, Sigma Chemical Co., St. Louis, MO). mRNA Extraction and cDNA Synthesis: mRNA from both normal and TD fibroblast cells was prepared from total RNA extracted from cells with Tnzol (Life Technologies Inc., Bethesda, MD, Cat. # 15596-026). The mRNA was isolated using the Ohgotex mRNA kit (Qiagen Inc., Valencia, CA, Cat. # 70022) according to vendor's protocols The mRNA was l o reverse transcnbed using Cy3 or Cy5 fluorescent dye to create fluorescently labeled cDNA according to the method descnbed in DeRisi et al., Science, 24:680-686 ( 1997) The resultant cDNA from TD cells was labeled with Cy3 fluorescent dye and cDNA from normal cells was labeled with Cy5 fluorescent dye (Incyte Genomics, Palo Alto, CA) Microanay Analysis: To analyze differential gene expression in cells from individuals 15 with TD and normal individuals, Cy3 and Cy5 fluorescent labeled cDNA samples prepared as descnbed above were hybndized to a set of Gene Album microanays (GEMs) on microscope slides (Incyte Genomics, Palo Alto, CA). Each of six slides contained about 9,800 human cDNA samples plus 200 control samples, resulting in a microanay of 58,800 partial cDNAs. Therefore, allowing for estimates of redundancy, approximately 30-50% of expressed human genes were 20 represented. The hybridization of Cy3-labeled cDNA prepared from TDl cells and Cy5-labled cDNA from normal cells allowed compaπson of the relative RNA content of TD cells versus normal cells for the expressed genes. In addition, Cy3-labeled cDNA prepared from TD2 cells and Cy5-labled cDNA from normal cells were hybndized to the same set of microanays to examine the vanation of gene expression between different TD patients. 25 Results: Data were analyzed using GemTools software (Incyte Genomics, Palo Alto, CA) and expressed as ratios of TD cell to normal cell mRNA. The results indicated that the majority of genes are comparably expressed in TDl and normal cells. As shown in Figure 2 (m the section above and to the left of the diagonal) only 175 genes were more than 2.5-fold underexpressed in TDl cells compared with normal cells, whereas 375 genes were more than 30 2.5-fold overexpressed in TD l cells compared with normal cells (below and to the πght of the diagonal) Genes more highly expressed in the TD cells could include those that are differentially regulated as a consequence of the Tangier mutation, either as a compensatory response or as a contnbutor to the disease pathology. Among the genes that could contnbute to the observed phenotype of TD and are more highly expressed in TD cells include interferon-β (IFN-β), macrophage inflammatory protein-2α, granulocyte chemotactic protein-2, IL-11, prostaglandin endoperoxide synthase-2 (COX-2), thrombospondin, and monocyte chemotactic proteins 1 , 3, and 4 (Lawn et al., J. Clin. Invest., 104:R25-R31 (1999). No single RNA that was expressed in the normal fibroblasts was found completely absent in either the TDl or TD2 cells. Also, comparison of the differentially expressed genes in TDl and TD2 revealed very little variation between the individual TD patients. For instance, of the most highly down-regulated genes in TD2 cells, 92% were also under-expressed in TDl cells compared with normal cells. One of the genes more than 2.5-fold under-expressed in TDl or TD2 versus normal cells was the gene for ABCl protein. The ABCl gene was pursued due to the ascribed functions of some of its homologues and also because the gene was localized to the approximate chromosome region reported as the TD gene region. EXAMPLE 3 This example demonstrates that the ABCl gene is localized to the human chromosome 9q31. Previous genetic linkage analysis mapped the TD gene to the 7-cM region of human chromosome 9q31 (Rust et al., Nat. Genet., 20, 96-98 (1998)). In addition, in situ hybridization analyses revealed that the ABCl gene was localized to the broader chromosomal interval 9q22 - 9q31 (Luciani et al., Genomics, 21, 150-159 (1994)). Using PCR methods with the GeneBridge 4 panel of human hampster radiation hybrids (Research Genetics, Inc., Huntsville, AL), human ABCl was determined to be located between the markers Wl- 14706 and WI-4062, conesponding to the 7-cM region of human chromosome 9q31. DNA from 93 human/hampster hybrid cell lines was amplified by PCR using human ABCl -specific primers LF: CCTCTC ATT AC ACAAAAACCAGAC (SEQ ID NO: 11 ) and LR: GCTTTCTTTCACTTCTCATCCTG (SEQ ID NO: 12). Each line was scored as positive or negative for the human ABCl amplification product and the mapping of ABCl derived from analysis of this data was accomplished using the Whitehead Institute/MIT Center for Genome Research software, accessed via the internet (http://carbon.wi. mit.edu: 8000/cgi- bin/conti g/rhmapper.pπ. These results were further confirmed by southern blot hybridization to human genomic/yeast artificial chromosome clones (Research Genetics, Inc.) from the equivalent interval. In addition, public database searching (GeneMap '98; National Center for Biotechnology Information) and radiation hybrid mapping eliminated the other significantly underexpressed genes in the microanay data from the location in the reported genetic interval These complementary data demonstrate that the ABCl gene is located on human chromosome 9q31 and further indicate that the ABCl gene is associated with Tangier disease. < EXAMPLE 4 This example shows the determination of the nucleotide sequence of the wildtype ABCl gene, including the flanking regions and the entire coding region. DNA sequencing was performed using an ABI Pnsm 310 Genetic Analyzer or by Davis Sequencing (Davis, CA) Both strands were sequenced throughout. The sequence of the open 0 reading frame of the ABCl gene from a normal subject was determined from a full-length cDNA clone obtained from an expression plasmid library constructed from normal fibroblast RNA To construct the plasmid library, cDNA was synthesized according to the Stratagene kit protocol (Stratagene, La Jolla, CA). Bnefly, first strand cDNA was synthesized from mRNA using an ohgo-dT pnmer with an Xhol site and MMLV reverse transcnptase in the presence of 5-methyl 5 dCTP The second strand was synthesized using RNase H and DNA polymerase I in the presence of unmodified dNTPs. After the cDNA was blunt-ended with pfu DNA polymerase, an EcoRI linker was ligated to the cDNA. The cDNA was then digested with Xhol, creating Xhol ends at the 3' end of the cDNA. The internal Xhol sites were protected from this digestion due to the semi-methylation dunng the first strand synthesis. The synthesized cDNA was cloned into 0 the Hindlll and Xhol sites of the plasmid pCEP4 (Invitrogen Corp., Carlsbad, C A #VO44-50), an expression vector containing the cytomegalovirus promoter/enhancer A 585 bp ABCl probe was generated by reverse transcnptase polymerase chain reaction (RT-PCR) using pnmers based on known ABCl sequence, which were 5'-TCCTTGGGTTCAGGGGATTATC (SEQ ID NO- 13) and 5'-CAATGTTTTTGTGGCTTCGGC (SEQ ID NO: 14). Using this ABCl probe, a 25 clone containing a 10.5 kb insert of human ABCl cDNA was recovered from the library using the CloneCapture selection kit according to the manufacturer's protocol (CLONTECH Laboratones, Inc., Palo Alto, CA). This clone is shown in Figure 3 as pCEPhABCl . The 10.5 kb ABCl cDNA insert sequence is shown in SEQ ID NO: 1. Sequence determination confirmed that pCEPhABCl contains the human ABCl open reading frame of 6783 nucleotides plus 5' and 30 3' untranslated regions, having a larger open reading frame than the cDNA sequence reported by Langmann et al. in Biochem Biophys Res Comm , 257, 29-33 (1999) (GenBank Accession No AJO12376) EXAMPLE 5 This example demonstrates the sequence differences between the wildtype ABCl gene and the TDl. TD2, and TD3 gene sequences. cDNA Synthesis of TDl . TD2. and TD3: cDNA was prepared from TDl, TD2, and TD3 cells by reverse transciption polymerase chain reaction (RT-PCR) using the Superscript Choice cDNA system and the Advantage cDNA polymerase mix following the manufacturer's protocol (CLONTECH, Palo Alto, CA; Cat. #8417-1) using two sets of primer pairs designed from the normal human ABCl gene sequence, designated: (1) saclhabcf, 5'- AGTCGAGCTCCAAACATGTCAGCTGTTACTGGAAGTGGCC (SEQ ID NO: 15); habcr3851 , 5'- TCTCTGGATTCTGGGTCTATGTCAG (SEQ ID NO: 16) and (2) habcf3585, 5'-GGGAGCCTTTGTGGAACTCTTTC (SEQ ID NO: 17); habcrsall, 5'- ACTGGTCGACCATTGAATTGCATTGCATTGAATAGTATCAG (SEQ ID NO: 18). Amplification of 0.2-0.5 μg polyA+ RNA with these primers at a final concentration of 0.4μM generated two overlapping templates of approximately 3.5 kb. The templates were gel-purified using the QIAEX II system (QIAGEN, Inc., Valencia, CA; Cat. #20021) and adjusted to a concentration of lOOng/μl. Sequencing of TDl. TD2. and TD3 cDNA: Eight μl of each template generated as described above was sequenced in a reaction with individual sequencing primers designed on the basis of wildtype ABCl sequence at a final concentration of 0.5 μM. The primers were as follows: IF: 5'- TTTCCTGGTGGACAATGAA (SEQ ID NO: 19), 2F: 5'- AGTGACATGCGACAGGAG (SEQ ID NO: 20); 3F: 5'- GATCTGGAAGGCATGTGG (SEQ ID NO: 21); 4F: 5'- CCAGGCAGCATTGAGCTG (SEQ ID NO: 22); 5F: 5'- GGCCTGGACAACAGCATA (SEQ ID NO: 23); 6F: 5'- GGACAACCTGTTTGAGAGT (SEQ ID NO: 24); 7F: 5'- AAGACGACCACCATGTCA (SEQ ID NO: 25); 8F: 5'- ATATGGGAGCTGCTGCTG (SEQ ID NO: 26); 9F: 5'- GGGCATGAGCTGACCTATGTGCTG (SEQ ID NO: 27); 10F: 5'- AAGAGACTGCTAATTGCC (SEQ ID NO: 28); 1 IF: 5'- AGCGACAAAATCAAGAAG (SEQ ID NO: 29); 12F: 5'- TGGCATGCAATCAGCTCT (SEQ ID NO: 30); 13F: 5'- TCCTCCACCAATCTGCCT(SEQ ID NO: 31); 14F: 5'- TTCTTCCTCATTACTGTT (SEQ ID NO: 32); 15F: 5'- GATGCCATCACAGAGCTG (SEQ ID NO: 33); 16F: 5'- AGTGTCCAGCATCTAAA (SEQ ID NO: 34); IR: 5'- CAAAGTTCACAAATACTT (SEQ ID NO: 35); 2R: 5'- CTTAGGGCACAATTCCACA (SEQ ID NO: 36); 3R: 5'- TGAAAGTTGATGATTTTC (SEQ ID NO: 37); 4R: 5'- TTTTTCACCATGTCGATGA SEQ ID NO- 38); 5R 5'- CTCCACTGATGAACTGC (SEQ ID NO: 39); 6R- 5'- GTTTCTTCATTTGTTTGA (SEQ ID NO: 40); 7R: 5'- AGGGCGTGTCTGGGATTG (SEQ ID NO- 41 ), 8R 5'- CAGAATCATTTGGATCAG (SEQ ID NO: 42); 9R- 5'- CATCAGAACTGCTCTGAG (SEQ ID NO: 43); 10R: 5'- AGCTGGCTTGTTTTGCTTT SEQ s ID NO- 44), 1 IR. 5'- TGGACACGCCCAGCTTCA (SEQ ID NO: 45), 12R: 5'- CCTGCCATGCCACACACA (SEQ ID NO: 46), 13R: 5'- CTCATCACCCGCAGAAAG (SEQ ID NO- 47), 14R: 5'- CACACTCCATGAAGCGAG (SEQ ID NO: 48), 15R: 5'- TCCAGATAATGCGGGAAA (SEQ ID NO: 49), 16R: 5'- TCAGGATTGGCTTCAGGA (SEQ ID NO- 50), UTR1R- 5'- AAGTTTGAGCTGGATTTCTTG (SEQ ID NO- 51) 0 Results The nucleotide numbenng follows the numbenng found in Lawn et al. (1999). Patient TDl retained the full open reading frame, with 2 substantial differences from the wild- type sequence (SEQ ID NO: 8) One of these is an A to G substitution, resulting in a change from a glutamine to argmine residue at position 537 of the 2201 amino acid sequence, as published by Lawn et al. (1999). The location of this residue is within the NH2-termmal 5 hydrophilic domain, near the first predicted transmembrane domain. Patient TD2 also retained the open reading frame with an argmine to tryptophan substitution at residue 527 (SEQ ID NO 10). Thus, both TDl and TD2 contain a substitution altenng the charge of an ammo acid in the same region of the protein. TD3 DNA contains a 14 nucleotide insertion in its ABCl cDNA following nucleotide 5697 in one allele and a 138 bp insertion after nucleotide 5062 in the other 0 allele. Genomic sequencing of the TDl, TD2, and TD3 DNAs confirmed the changes found in the respective cDNAs. The genomic sequence was generated by PCR amplification of a 156 bp region of genomic DNA isolated from fibroblasts that contained the mutations found in the cDNA from TDl and TD2. The genomic sequencing also indicated that patient TDl was homozygous for the glutamine to argmine substitution. Genomic DNA analysis showed that TD2 was a compound heterozygote with one allele containing the detected substitution and the second allele (which failed to produce detectable mRNA) containing an undetermined defect. Neither of the substitution mutations was found in more than 80 alleles of geneomic DNA of non-TD individuals. TD3 insertions were identified by sequence analysis and confirmed by RT- PCR using primers sunounding the insertion points. The 14-bp insertion following nucleotide 5697 causes a frameshift, resulting in the replacement of the wild-type ammo acid sequence from a location before the second ATP binding domain, up to the point of a premature protein termination. The 138 bp insertion following nucleotide 5062 in the other allele contains an inframe stop codon. EXAMPLE 6 This example demonstrates that inhibitors of ABCl transport activity also inhibit apo A- I-mediated cholesterol efflux from fibroblast cells. To test whether inhibition of ABCl could affect the process of apolipoprotein-mediated cholesterol efflux, two compounds reported to be ABCl inhibitors were tested in assays which monitor apolipoprotein mediated cholesterol efflux. The compounds 4,4-diisothiocyanostilbene- 2,2'-disulfonic acid (DIDS) and sulphobromophthaleine (BSP) were reported to inhibit anion transport activities of ABCl in a dose-dependent fashion (Becq et al., J. Biol. Chem., 272:2695- 2699 ( 1997); Hamon et al., Blood, 90:2911-2915 (1997)). The apolipoprotein-mediated cholesterol efflux assays were performed as described in Example 1 with the noted changes. Cholesterol-loaded and [ 3 H]cholesterol-labeled normal fibroblasts (n=3) were incubated for 6 hours with or without 5μg/ml apo A-I and either 0, 0.2mM, or 0.4mM DIDS. In addition, cholesterol-loaded and [ 3 H]cholesterol-labeled normal fibroblasts (n=3) were incubated for 6 hours with or without 5μg/ml apo A-I and either 0, 0.2mM, or 0.4mM BSP. [ 3 H]cholesterol efflux was measured by scintillation counting as described in Example 1 and calculated as the percentage of total radiolabeled cholesterol appearing in the medium. The results are shown in Figure 5 as the mean ± SD (n=3) of efflux in the presence of apo A-I after subtraction of values for apo A-I-free medium. Figure 5 shows that both DIDS and BSP inhibit the 6-hour efflux of tritiated cholesterol mediated by apolipoprotein A-I. In addition, similar inhibition was observed with the efflux of tritiated phosphatidyl choline using DIDS and BSP (data not shown). The results of these tests mimic the efflux defect in fibroblasts derived from patients with TD, described in Example 1. EXAMPLE 7 This example demonstrates that antisense inhibition of ABCl mRNA expression inhibits apo A-I-mediated cholesterol efflux from fibroblast cells. Normal skin fibroblasts were labeled with [ 3 H]cholesterol as described in Example 1. The cells were then loaded with oligonucleotide by scraping in the presence of either 30μM control Moφholino oligonucleotide (5'-CCTCTTACCTCAGTTACAATTTATA-3' conesponding to the antisense complement of a β-globin thalassemic mRNA; SEQ ID NO: 52) or 30μM ABCl antisense Moφholino oligonucleotide (5'- CATGTTGTTCATAGGGTGGGTAGCTC-3'; SEQ ID NO: 53) and reseeding on new dishes. Control cells were mock-loaded after [ 3 H]cholesterol-labeling by scraping and reseeding in the absence of oligonucleotide. Apo A-I-mediated efflux was measured after 12 hours by scintillation counting as the percentage of total radiolabeled cholesterol appeaπng in the medium The results are shown in Figure 6 as the mean ± SEM of three separate expenments, normalized to the value for apo A-I-specific efflux m the absence of oligonucleotide in each expenment. As shown in Figure 6, antisense oligonucleotides directed against ABCl mRNA caused a 50% > reduction in cholesterol efflux from normal fibroblasts compared with control antisense oligonucleotide (β-globm antisense oligonucleotide). EXAMPLE 8 This example demonstrates that over expression of the human ABCl gene results in an increase in apo A-I-mediated cholesterol efflux from monocyte cells Stable Transfection of RAW 264 7 Cells Mouse monocytic RAW 264 7 cells were stably transfected with the pCEPhABCl expression plasmid for human ABCl Construction of the pCEPhABCl plasmid containing the open reading frame of human ABCl is descnbed m Example 4 Approximately 1 x 10 6 RAW 264.7 cells were transfected for 5 hours with 2 μg of pCEPhABCl DNA and 12μl Geneporter transfection reagent (Gene Therapy Systems, Inc., San Diego, CA, Cat. #T201007) in 0.8ml serum-free DMEM. Two days later, cells were split at ratios ranging from 1.2 - 1.50 and selection applied by adding 150 μg/ml hygromycm to the culture medium. After two weeks, hygromycin-resistant colonies were picked and expanded. Apo A-I-mediated Cholesterol Efflux Assay Parental RAW 264 7 cells and three clonal lines (L3. L5, and L6) stably expressing human ABCl were grown to confluence The cells were cholesterol-loaded and labeled by incubation for 24 hours with 0 5 μCi/ml [Η]cholesterol and 50μg/ml acetylated LDL as descnbed in Example 1 After equihbnum of cholesterol pools by an overnight incubation in DMEM/BSA, cells were washed and the efflux medium was added as descnbed in Example 1 Apo A-I-mediated cholesterol efflux was measured as previously described by scintillation counting of the tntiated cholesterol in the cell medium, expressed as a percentage of the total counts recovered from the cells and medium. The results are presented as the mean ± SEM of three separate expenments normalized to the value for apo A-I-specific efflux from parental RAW 264 7 cells within each expenment. Figure 7 shows the apo A-I- mediated cholesterol efflux from parental RAW 264 7 cells and L3, L5, and L6 transfected cell lines As can be seen, transfection with the ABCl expression vector results in a 4-fold (L6) to 8- fold (L3 and L5) increase in apo A-I-mediated cholesterol efflux. These results indicate that overexpression of the ABCl gene can substantially increase the amount of cholesterol efflux from macrophage cells. EXAMPLE 9 This example demonstrates that ABCl mRNA expression is regulated by cellular conditions related to cholesterol efflux in normal skin fibroblasts, but not in TD fibroblasts. To determine whether ABCl plays a rate-limiting role in cellular sterol efflux, the synthesis of ABCl was measured under various cellular conditions related to cholesterol efflux processes. Specifically, normal fibroblasts and TD fibroblasts were individually exposed to conditions of excess cAMP, cholesterol, or Apo A-I. Cell cultures of normal skin fibroblasts and TDl and TD2 fibroblasts were prepared as described in Example 1. The level of ABCl mRNA was measured by RT-PCR. Cell cultures: Immortalized cell cultures of normal skin fibroblasts and TDl and TD2 fibroblasts were prepared as described in Example 1. Cells were grown to subconfluence in DMEM/10% FBS before replacement with DMEM BSA and the indicated additive for 24 or 48 hours. RNA was prepared as described in Example 2. RT-PCR: Quantitative PCR was carried out using the GeneAmp 5700 Sequence Detection System (Perkin-Elmer Applied Biosystems, Foster City, CA). Briefly, 500ng of DNase-treated mRNA was reverse transcribed using random hexamer primers at 2.5μM. Approximately 5% of this reaction was amplified by PCR using the SYBR green core kit (PE Applied Biosystems, Foster City, CA; Cat. #4304886) and human ABCl primers LF: 5'- CCTCTCATTACACAAAAACCAGAC (SEQ ID NO: 11) and LR: 5'- GCTTTCTTTCACTTCTCATCCTG (SEQ ID NO: 12) to yield an 82 bp fragment conesponding to nucleotides 7018-7099 of human ABCl . PCR cycle conditions were as follows: 10 minutes 95°C; followed by 40 cycles of 95°C, 15 seconds; and 60°C, 60 seconds. The mRNA in each sample was quantitated by detecting the increase in fluorescence caused by SYBR green binding to the double-stranded amplification product generated during each PCR cycle. All samples were run in triplicate and normalized against β-actin mRNA, amplified in parallel reactions with primers actinF: 5'-TCACCCACACTGTGCCATCTACGA (SEQ ID NO: 54) and actinB: 5'- CAGCGGAACCGCTCATTGCCAATGG (SEQ ID NO: 55). Standard curves were run for both ABCl and β-actin on the same PCR plate. 8-Br-cAMP Assay: Normal, TDl, and TD2 fibroblast cells were grown to subconfluence in DMEM/10% FBS and then treated with 1 mM 8-Br-cAMP in DMEM/BSA for 24 hours. Cholesterol Assay: Normal, TDl, and TD2 fibroblast cells were grown to subconfluence in DMEM/10% FBS and then treated with 30μg ml free cholesterol in DMEM/BSA for 48 hours followed by 18-24 hours of equilibrium in DMEM/BSA. Apo A-I Assay: Normal, TDl, and TD2 fibroblast cells were grown to subconfluence in DMEM/10% FBS and then treated with 30μg/ml free cholesterol in DMEM/BSA for 48 hours followed by 18-24 hours of equilibrium in DMEM/BSA plus lOμg/ml apo A-I. Results: Figure 8 shows that in normal fibroblasts ABCl mRNA is increased approximately 10-fold by exposure to 8-Br-cAMP and increased approximately 17-fold by exposure to cholesterol in serum-free medium. Subsequent exposure of cholesterol-loaded cells to Apo A-I results in a marked decrease in ABCl mRNA expression. Although the mechanism has not been demonstrated, previous studies have shown that cholesterol efflux is promoted in the presence of such compounds as cAMP and cholesterol (Hokland et al., J. Biol. Chem., 268:25343-25349 (1993)). The present results indicate that in normal fibroblasts, ABCl mRNA is induced by these known effectors of the cholesterol efflux pathway and repressed by exposure to an apolipoprotein cholesterol acceptor, demonstrating that the expression of ABCl is regulated by cellular conditions related to apolipoprotein-mediated cholesterol efflux. In contrast, fibroblast cells from TD patients are not regulated by effectors of cholesterol efflux. First, the cAMP-inducible level of ABCl mRNA in both TDl and TD2 cells is only approximately 40% of that in normal cells. Further, exposure of cholesterol-loaded cells to Apo A-I either did not alter ABCl expression (TDl cells) or slightly increased ABCl expression (TD2 cells). These results reflect the defect in Apo-A-I-mediated cholesterol efflux described for TD cells. Interestingly, growth of cells in serum-containing medium suppressed ABCl message to near the limit of detection (data not shown). This may reflect the fact that functioning of the lipid efflux pathway requires cell quiescence or other cellular states of reduced cholesterol need. In conclusion, conditions that are associated with increased efflux of cellular cholesterol (i.e., cholesterol loading, cAMP treatment, serum deprivation) also result in increased expression of ABCl mRNA in normal fibroblast cells. Conversely, exposure of cholesterol-loaded normal fibroblast cells to apo A-I reduces ABCl expression. EXAMPLE 10 This example demonstrates that ligands for the LXR nuclear receptor, such as 20- hydroxycholesterol, and ligands for the RXR receptor, such as 9-cis retinoic acid, can increase ABCl gene expression in mouse RAW 264.7 cells. LXR nuclear receptors are transcnption factors that form obligate heterodimers with the nuclear receptor RXR, and are activated to enhance transcnption of their target genes by binding a class of oxysterols including 22-hydroxycholesterol and 20-hydroxycholesterol (Janowski et al , Nature, 383 728-731 (1996)) As such, they are candidates for the mediation of cholesterol- induced gene transcnption Further, in light of studies which showed that ABCl mRNA and protein increase in fibroblasts and macrophages m response to cholesterol loading, and other studies which showed that LXR and RXR expression increase m cholesterol-loaded macrophage cells by exposure to oxidized LDL, the LXR and RXR nuclear receptors are highly plausible candidates for transcnptional activators of the ABCl gene To determine whether LXR and RXR receptors play a role in ABCl gene expression, the level of ABCl mRNA was measured in response to 20-hydroxycholesterol and 9-cιs retmoic acid Mouse RAW 264 7 cells were grown to subconfluence in DMEM/10% FBS and then treated for 24 hours in serum- free DMEM/BSA with either 9-cιs retmoic acid (lOμM), 20- hydroxycholesterol (lOμM), or both ligands together (20μM total) Control cells received ethanol vehicle only (0 1% v/v) RNA was extracted, treated with DNase, and ABCl mRNA measured by RT-PCR using PE Biosystems SYBR Green Technology as descnbed in Example 9 Figure 9 shows that treatment with either 20-hydroxycholesterol or 9-cιs retmoic acid results m an increase in ABCl mRNA expression In addition, Figure 9 shows that treatment with both ligands together results in a markedly synergistic effect, with an approximate 6-fold increase over the ABCl expression observed with either hgand alone These results demonstrate that ligands for the nuclear receptors LXR and RXR can increase the expression of the ABCl gene EXAMPLE 11 This example demonstrates that enhanced expression of ABCl protein in the plasma membrane is associated with lipid efflux Cell-surface labeling and immunoprecipitation was used to determine whether increased expression of ABCl protein in the plasma membrane is conelated with an increase in cholesterol efflux (Figure 10) The relative amount of ABCl on the cell surface was determined by cross- linking surface proteins on intact cells with the membrane-impermeable agent sulfo-NHS-biotin, followed by the steps of membrane solubihzation, immunoprecipitation with ABCl antibody, SDS-PAGE, and detection with streptavidin Cell Culture Normal and TDl fibroblast cells were immortalized as descnbed in Example 1 Both normal and TDl cells were cultured under control conditions and conditions known to increase apolipoprotein-mediated cholesterol efflux (Oram, et al., J. Lip. Res., 40: 1769-1781 ( 1999)). Control cells were grown to confluence in DMEM/10% FBS and then incubated in DMEM/BSA for 18 hours with no additives (control). cAMP-treated cells were grown to confluence in DMEM/10% FBS and then incubated in DMEM/BSA for 18 hours with lmM 8-Br-cAMP(cAMP). Cholesterol-loaded cells were grown to confluence in DMEM/10% FBS and then incubated in DMEM/BSA for 48 hours with 30μg/ml cholesterol plus 18 hours with no additives (cholesterol). Cholesterol-loaded cells treated with cAMP were grown to confluence in DMEM/10% FBS and then incubated in DMEM/BSA for 48 hours with 30μg/ml cholesterol plus 18 hours with lmM 8-Br-cAMP (cholesterol + cAMP). Cell-Surface Labelin g : For selective labeling of plasma membrane ABCl, the cells were incubated for 30 minutes at 0°C with PBS containing 1 mg/ml sulfo-NHS-biotin (Pierce, Rockford. IL; Cat. #21217) to biotinylate cell-surface proteins (see Walker et al, Biochemistry, 50: 14009-14014 ( 1993)). Immunoprecipitation : Rabbit antiserum for ABCl was raised against a synthetic peptide conesponding to the deduced peptide KNQTVVDAVLTSFLQDEKVKES located at the C- terminus of human ABCl . Immunoprecipitation was performed by solubilizing the cells in PBS containing 1% Triton X-100 (Sigma, St. Louis, MO) and protease inhibitors leupeptin (lmM), pepstatin ( lmM), and aprotinin (lmM). The cell extract was incubated overnight at 4°C with anti-ABCl antiserum at 1 :200 dilution followed by an additional 1 hour incubation with 5μl proteinA-coated magnetic beads (Dynal, Lake Success, NY; Cat. #1001.01). The antibody- antigen complex was sedimented with a magnet, the beads were washed twice with 1% Triton- X/PBS, and the proteins were eluted with 1% acetic acid. Detection of ABCl Protein: The eluted biotinylated proteins were subjected to SDS- PAGE (6% gel; 150V, 5 hours) and transfened to nitrocellulose membrane (200mA, 18 hours). The nitrocellulose was probed with streptavidin-horse radish peroxidase (Amersham Pharmacia, Piscataway, NJ; Cat. #RPN 1231) diluted 300-fold and detected by enhanced chemiluminescence labeling (ECL) according to vendor's protocol (Amersham Pharmacia, Piscataway, NJ). To test for possible biotinylation of intracellular proteins, the post-immunoprecipitation supernatant was treated with a mouse monoclonal antibody to the intracellular protein β-COP and immunoprecipitated biotinylated β-COP was assayed by streptavidin blotting. None was detected. Results: As shown in Figure 10, the 240 kDa ABCl protein appears as a doublet. The ABCl protein is partially localized to the plasma membrane in both normal ( 10A) and TDl (10B) fibroblast cells. Similar results were seen with a second normal fibroblast cell line and with TD2 fibroblasts (data not shown) Cell-surface expression of ABCl was increased slightly when cells grown m serum (normal and TDl cells) were treated with 8-Br-cAMP Serum depnvation and cholesterol-loading of both normal and TDl cells markedly increased cell- surface expression of ABC 1 , which was further enhanced by cAMP treatment These results indicate that expression of ABCl at the cell surface is regulated by conditions that enhance apohpoprotem-mediated lipid efflux, consistent with the idea that its localization to the plasma membrane plays a key role in its lipid transport function. The mutations in TDl and TD2 cells do not appear to severely impair expression or processing of ABCl, implying that secondary effects on lipid transport or interactions with accessory proteins depend on its NH2-teπmnal domain, where the mutations occur EXAMPLE 12 This example shows that agents that inhibit the degradation of 3'5' cyclic AMP, such as phosphodiesterase inhibitors, increase apolipoprotein A-I-mediated efflux from macrophage cells As shown in Figure 10, cAMP increases the activity of ABCl The present studies were performed to determine the cholesterol efflux from macrophage cells in the presence of elevated cAMP Elevated levels of cAMP can be attained in the presence of agents that either stimulate cAMP synthesis or inhibit the degradation of cAMP. For example, rohpram is a compound that regulates c AMP levels by inhibiting phosphodiesterases, a group of enzymes that degrade cAMP The effect of elevated cAMP on cholesterol efflux was determined using the apolipoprotein-mediated cholesterol efflux assays descnbed in Example 1 Bnefly, RAW 264 7 cells suspended at a density of 1.25 x 10 3 cells/ml were grown in DMEM/10% FBS supplemented with pyruvate After 24 hours, the medium was removed and replaced with DMEM/BSA plus radiolabeled cholesterol (1 μCi/ml 3 [H]-cholesterol) and 50 μg/ml of acetylated LDL for 24 hours The cells were then maintained for 24 hours in equihbnum medium consisting of DMEM BSA plus either apo A-I alone (20 μg/ml), apo A-I and 8-bromo 3', 5' cAMP ( lmM) or apo A-I and rohpram (50 μM) After 12-24 hours, [ 3 H]cholesterol efflux was measured by scintillation counting as descnbed in Example 1 and calculated as the percentage of total radiolabeled cholesterol appeanng in the medium The results indicated that cholesterol-loaded control cells that received no apo A-I showed a 3% cholesterol efflux, while cells that received apo A-I only showed a 5% efflux. Cholesterol-loaded cells that received apo A-I and cAMP showed a 32% cholesterol efflux, demonstrating that elevated cAMP promotes cholesterol efflux. Similarly, cells that received apo A-I and a phosphodiesterase inhibitor (rohpram) showed a 17% cholesterol efflux. EXAMPLE 13 This example shows that agents that are ligands for nuclear receptors, such as LXR, RXR, and PRAR nuclear receptors, increase apolipoprotein A-I-mediated efflux from macrophage cells. To determine whether ligands for nuclear receptors affect the process of apohpoprotein- mediated cholesterol efflux, vanous ligands were tested using the apo A-I-mediated cholesterol efflux assay descnbed in Example 12 The nuclear receptor superfamily includes several members, such as the liver receptor LXR, the retinoid receptor RXR, and the peroxisome prohferator-activated receptor PPAR, which have been implicated in lipid metabolism (Russell. D W , Cell, 97 539-542 (1999); Spiegelman, B.W., Cell, 93-153-155 (1998), Janowski et al., Nature, 383 728-731 (1996)) Further, ligands for some of these receptors have been observed to increase plasma HDL and gene expression profiling (microanay) data have shown that hormone receptors respond to cholesterol loading via oxidized LDL. Using the above-descnbed assay, 9 czs-retinoic acid (RXR ligand), oxysterol (LXR ligand), and fenfϊbrate (PPAR ligand) was tested to determine the effect on cholesterol efflux. Cholesterol-loaded control cells that received no apo A-I showed a 3% cholesterol efflux, while cells that receive apo A-I only showed a 5% efflux In contrast, cholesterol-loaded cells that receive apo A-I and 9 cw-retinoic acid (30 ng/ml) showed a 16% cholesterol efflux Cells that receive apo A-I and oxysterol (5 μg/ml) showed a 14% cholesterol efflux. Cells that receive apo A-I and fenfibrate (3 μg/ml) showed a 10% cholesterol efflux. These results indicate that hormone receptors may be modulated to increase the rate of apolipoprotein-mediated cholesterol efflux from macrophages. Further, when the efflux assay was performed using vanous concentrations of 9-cιs-RA (0.3ng/ml. 3 Ong/ml, or 30ng/ml), the results showed that 9-czs-RA mediated cholesterol efflux from macrophage cells in a dose-dependent manner Specifically, control cells (apo A-I only) showed 1890 c p.m., 0.3 ng/ml 9-cιs-RA showed 1522 c.p.m., 3 0 ng/ml 9-cz5-RA showed 3568 c p m , and 30 ng/ml 9-cιs-RA showed 8597 c.p.m. In addition, using a similar assay where RAW 264 7 cells were cholesterol-loaded for 48 hours, other nuclear receptor activators, such as 22-hydroxycholesterol (LXR ligand) and benzfibrate, were shown to increase cholesterol efflux (data not shown) EXAMPLE 14 This example shows that eicosanoids, such as prostaglandin El and prostacychn PG12, increase apolipoprotein A-I-mediated efflux from macrophage cells Eicosanoids, such as prostaglandms and prostacyclms, have been shown to be effective in the treatment of hypercholesterolemia To determine whether eicosanoids affect the process of apolipoprotein-mediated cholesterol efflux, PGEI and PG12 were tested using the apo A-I- mediated cholesterol efflux assay descnbed in Example 12 This assay showed that cholesterol- loaded control cells that receive no apo A-I have a 3% cholesterol efflux, while cells that receive apo A-I only have a 5% efflux Cholesterol-loaded cells that receive apo A-I and PG12 (25 nm) showed a 10% cholesterol efflux Cells that receive apo A-I and PGEI (25 nM) showed a 15% cholesterol efflux These results demonstrate that eicoasnoids can increase the rate of apolipoprotein-mediated cholesterol efflux from macrophages EXAMPLE 15 This example demonstrates that a reporter gene under the control of an ABCl promoter can be used to test compounds for the ability to regulate ABCl gene expression The pGL3 luciferase reporter vector system (Promega, Madison, Wl) was used to create a recombinant plasmid to measure reporter gene expression under control of the ABCl promoter Construction of Reporter Plasmids Plasmid pGL3-Basιc (Promega, Madison, Wl, Cat #E1751 ) was used as a control plasmid containing the promoterless luciferase gene The reporter construct containing the ABCl promoter and luciferase gene was made by cloning a genomic fragment from the 5' flankmg region of the ABCl gene (hAPRl 5' promoter, conespondmg to nucleotides 1 80-1643 of SEQ ID NO 3) into the Sacl site of the GL3-Basιc plasmid to generate plasmid GL-6a Next, plasmid GL-6a was digested with Spel and Acc65I A BsiWI-Spel fragment excised from a lambda subclone, representing the ABCl genomic sequence conespondmg to nucleotides 1-1534 of SEQ ID NO 3 was hgated into the remaining vector/ ABCl promoter fragment produced by this digestion The resultant plasmid, pAPRl, encodes the luciferase reporter gene under transcnptional control of 1 75 kb of the human ABCl promoter sequence Transfection of Reporter Constructs The above-descnbed control or pAPRl plasmid was transfected into confluent cultures of RAW 264 7 cells maintained in DMEM containing 10% fetal bovine serum Each well of a 12 well dish was transfected for 5 hours with either pGL3-Basιc, pGL3-Promoter or pAPRl DNA (lμg), luciferase plasmid DNA (1 μg), and 12 μl of Geneporter reagent (Gene Therapy Systems, San Diego, CA; Cat. #T201007). In addition, 0.1 μg of pCMVβ plasmid DNA (Clontech, Palo Alto, CA, Cat. #6177-1) was added as a control for transfection efficiency. After 5 hours, the culture medium was replaced with serum-free DMEM/BSA in the presence of or absence of acetylated LDL (100 μg/ml) and incubated for 24 hours. For added convenience in high throughput screening, cultured cells can be stably transfected with reporter plasmids using the following procedure. First, 5xl0 6 RAW 264.7 cells are transfected for 5 hours in a 60mm dish with 9μg of the pAPRl plasmid and pCMVscript (Stratagene, LaJolla, CA) in 10 ml of serum-free DMEM with 50 μl Geneporter transfection reagent (Gene Therapy Systems, San Diego, CA). Subsequently, the transfection medium is replaced with complete medium and the cells incubated overnight at 37°C. Subsequently, the cells are transfened to separate dishes at dilutions ranging from 1 :5 to 1 : 1000 and incubated in selection medium containing 800 μg/ml G418 (Life Technologies, Bethesda, MD) for 20 days. Visible colonies are picked, expanded, and assayed for luciferase activity as described below. Using this method, five clonal cell lines positive for luciferase activity were identified for use in high throughput assays. Luciferase Assay: Following transfection, the cells in each well were lysed in 70 μl of IX cell lysis reagent (Promega, Madison, Wl, Cat. #E3971), subjected to one freeze-thaw cycle, and the lysate cleared by centrifugation for 5 minutes at at 12,000g. After centrifugation, 100 μl of luciferase assay reagent (Promega, Madison, Wl; Cat. #E1501) was added to 10 μl of lysate. The luciferase activity of each lysate was measured as light units using a luminometer. Additionally, the β-galactosidase activity of each lysate was measured using the chemiluminescent assay reagents supplied in the Galacto-light kit according to the manufacturer's instructions (Tropix Inc., Bedford, MA: Cat. #BL100G). The normalized luciferase activity for each lysate was determined by dividing the luciferase activity value by the determined β-galactosidase value and reported as relative light units. Results: The luciferase activity detected in cells transfected with pAPRl was 3.3-fold higher than the activity detected in control cells transfected with pGL3-Basic plasmid containing luciferase cDNA only. These results indicated that the transcriptional regulatory regions of ABCl were in place. When the pAPRl transfected cells were incubated with 100 μg/ml acetyl LDL for 24 hours, the luciferase activity was 3.25-fold higher than in cells that had not been treated with acetyl LDL. These results suggest that the genomic ABCl sequence contains a "cholesterol responsive" element found in the 5'flanking region which mediates the cholesterol loading response of the native ABCl gene. This reporter system can also be used to test other compounds to determine whether the compound modulates ABCl expression. EXAMPLE 16 This example demonstrates an additional assay that can be used to test compounds for the ability to regulate ABCl gene expression using a reporter gene under the control of an endogenous ABCl promoter. This assay involves constructing a recombination vector that contains a promoterless reporter gene and a selection marker gene. The vector is linearized and transfected into cells such that the reporter gene is integrated into the cellular genome downstream of the endogenous ABCl promoter. Using this assay, expression of the reporter gene is driven by the endogenous ABCl promoter in response to a test compound. Construction of Reporter Plasmids: The recombination vector containing a promoterless reporter gene can be made starting with a 7 kb EcoRI genomic fragment of ABCl that contains exon 0 (which includes the ABCl start sites) and part of intronl . Using site-directed mutagenesis, a Sail restriction site can be generated in the exon 0 sequence downstream of the two known start sites. The recombination vector is generated by inserting a DNA fragment containing a promoterless reporter gene, such as luciferase, and a promoterless selective marker, such as puromycin resistance, into the Sail site. An internal ribosome entry signal should be inserted between the reporter gene and marker gene so that the genes will be transcribed in the conect orientation. The recombination vector contains two Eco47III sites, one of which must be eliminated, using, for example, site-directed mutagenesis. The remaining Eco47III site, located upsteam of of exon 0, is used to linearize the vector. Transfection of Reporter Constructs: The linearized recombination vector containing the reporter gene and marker gene is introduced into cultured cells, including human cells, by any of the various transfection methods known in the art. For example, the linearized vector can be transfected using the methods described in Example 15. The linearized recombination vector contains ABCl sequences which allow the vector to integrate into the cellular genome at the site of the endogenous ABCl gene. The addition of an appropriate antibiotic to the culture medium allows the selection of only those cells in which the reporter gene and marker gene have integrated downstream of the endogenous ABCl promoter in the proper orientation. For instance, if the vector contains a puromycin resistance gene inserted downstream of the reporter gene, the transfected cells should be grown in the presence of puromycin Only those cells that have a properly integrated puromycin resistance gene, and can thereby encode a functional protein, will survive in the presence of puromycin Thus, the transfected cells should be grown under conditions that induce ABCl promoter activity in the presence of the appropnate ^ antibiotic Surviving cells can be clonally cultured and the DNA sequenced using PCR or southern blot analysis to test for proper integration of genomic sequences The resultant cells containing a reporter gene under the control of the endogenous ABCl promoter can be used to determine whether a test compound modulates the expression of ABCl The ABCl modulating activity of a compound is determined by assaying the level of reporter 0 gene expression found in the cells exposed to the test compound For example, cells having an integrated luciferase gene can be used to determine the ABCl modulating activity of a test compound by measunng the amount of luciferase activity found in cells exposed to the compound 5 EXAMPLE 17 This example demonstrates that ligands for nuclear receptors up-regulate the expression of a reporter gene under the control of the ABCl promoter To determine whether ligands for the LXRα, LXRβ and RXRα nuclear receptors could regulate ABCl gene expression, the pAPRl plasmid containing the luciferase reporter gene 0 under control of the ABCl promoter was transfected into RAW 264 7 cells treated with at least one ligand for the nuclear receptors (Figure 12) Construction and Transfection of Reporter Constructs Reporter construct pAPRl and control reporter construct pGL3-Basιc were obtained as descnbed m Example 15 RAW 264 7 cells were maintained in culture and transfected with either pGL3-Basιc ( 1 μg) or pAPRl ( 1 μg) 5 as described in Example 15 The transfected RAW 264 7 cells were treated with either ethanol (EtOH) (0 1% v/v), 20(S)-hydroxycholesterol (20(S) OH-chol) (lOμM), 9-cιs retmoic acid (9-cιs RA) (lOμM) or both 20(S) OH-chol and 9-cιs RA (20μM total) for24 hours The luciferase activity was measured and reported as relative light units as descnbed in Example 15 Results The results of this study are shown in Figure 12 Control cells transfected with o pGL3-Basιc showed no luciferase activity (data not shown) Cells transfected with pAPRl produced a 19-fold increase in luciferase reporter activity in the presence of 20 OH-chol, a 16- fold increase in luciferase activity in the presence of 9-cιs RA, and a 280-fold increase in luciferase activity in the presence of both ligands compared with EtOH control These results indicate that both the sterol and retinoid elicit a strong transcnption response from the ABCl 5' flanking sequence in pAPRl Further, there is an apparent synergistic effect of the two classes of compounds, as can be seen by the dramatic increase in luciferase activity found in cells treated with both ligands It is known that LXRα and RXRα receptors form active heterodimers Thus, ^ the hgand-induced activation of both nuclear receptors simultaneously could produce the observed synergistic increase in transcnption These data demonstrate that hydroxy sterols, such as 20(S) hydroxycholesterol, and retmoids. such as 9-cιs retmoic acid, activate the ABCl promoter, indicating that these and related compounds can be useful in the development of therapeutic compounds to increase ABCl 0 expression in macrophage cells to nd penpheral sites of excess cholesterol Additionally, the present ABCl promoter/reporter gene screening assay can be used to screen other compounds that increase ABCl expression to identify further therapeutic compounds EXAMPLE 18 5 This example demonstrates the further charactenzation of the ABCl promoter region, including the identification of an LXR response element To determine which portion of the 5' flanking region of ABCl retains transcnptional activity in response to nuclear ligands, vanous plasmids containing a different portion of the 5' flankmg region and a luciferase reporter gene were transfected into RAW 264 7 cells treated with 0 at least one ligand for the nuclear receptors Using this system, an sterol response element conespondmg to nucleotides 1480-1510 of SEQ ID NO 3 was identified The sterol response element contains a direct repeat-4 element TGACCGatagTAACCT Confirmation of the sterol response element was obtained using site-directed mutagenesis and band-shift assay techniques Construction of Reporter Constructs Reporter construct pAPRl and control reporter -^ construct pGL3 -Basic were obtained as descnbed in Example 15 Reporter constructs containing either nucleotides 1-1532, 1080-1643, 1181-1643, 1292-1643, or 1394-1643 of SEQ ID NO 3 were also constructed A reporter construct containing nucleotides 1080-1643 of SEQ ID NO 3 (GL-6a) was constructed as descnbed in Example 15 A reporter construct containing nucleotides 1-1532 of SEQ ID NO 3 was constructed by digestion of pAPRl with Spe I and Nhe ιo 1, and re-ligation of the gel-punfied vector fragment A reporter construct containing nucleotides 1181 to 1643 was constructed by firstly digesting GL-6a with Sty I. blunting the cohesive ends with Klenow enzyme, digesting the resultant vector with Sac I. and isolating the 462 base pair blunt-S_ac_I cohesive end fragment This was cloned into a vector obtained by digestion of GL-6a with Acc65 I. blunting of the cohesive ends with Klenow enzyme, digestion with Sac I and gel isolation of the vector fragment. A reporter construct containing nucleotides 1292-1643 was constructed by consecutive digestion of GL-6a with Acc65 I. blunting the ends with Klenow enzyme, digestion with Sac II. blunting the ends with T4 polymerase, and re-ligation of the gel- isolated vector fragment. A reporter construct containing nucleotides 1394-1643 was constructed by digestion of GL-6a with Acc65 I. blunting the ends with Klenow enzyme, subsequent digestion with Apa I, end-blunting with T4 polymerase and re-ligation of the gel-isolated vector fragment. Transfection of Reporter Constructs: The RAW 264.7 cells were maintained in culture and transfected with either pGL3-Basic ( 1 μg), pAPRl (1 μg), or one of the other reporter constructs according to the method described in Example 15. The transfected RAW 264.7 cells were treated with either ethanol (EtOH) (0.1% v/v), 20(S)-hydroxycholesterol (20(S) OH-chol) ( lOμM), 22(R)-hydroxycholesterol (22(R) OH-chol) (lOμM), 9-cis retmoic acid (9-cis RA) ( lOμM), or both 20(S) OH-chol and 9-cis RA (20μM total) for 24 hours. The luciferase activity was measured and reported as relative light units as described in Example 15. Site-Directed Mutagenesis: The sterol response element conesponding to nucleotides 1480-1510 of SEQ ID NO: 3 was mutated in the 1080-1643 sequence described above using site- directed mutagenesis. Specifically, the response element containing a direct repeat-4 element TGACCGatagTAACCT was mutated to CTGCACatagTAACCT using the GeneEditor system (Promega, Madison, Wl) according to the manufacturer's protocol. Gel-Shift Assays: Nuclear extract was prepared from RAW 264.7 cells by the method of Ohlsson et al. Cell, 45:35-44 (1986). 32 P-labeled oligonucleotides (5 ng) conesponding to the LXR response element (TCGAGTGACCGATAGTAACCTCTCGA; SEQ ID NO: 56) and its mutated counteφart (TCGAGCTGCACATAGTAACCTCTCGA; SEQ ID NO: 57) were individually incubated with 5 μg of nuclear protein for 30 minutes at room temperature in 20mM HEPES, pH 7.9, 60mM KCL, lmM MgCl,, lmM DTT, 66.6μg/ml poly(dldC), and 10% glycerol in the presence or absence of lμg antiserum to LXRα and LXRβ (Santa Cruz Biotechnology, Cat. No. SC-1591, Santa Cruz, CA) or antiserum to RXR (Santa Cruz Biotechnology, Cat. No. SC-774, Santa Cruz, CA). The protein-DNA complexes were applied to a 4% non-denaturing polyacrylamide gel for 1.5 hours at 150V in 0.5X TBE buffer. The protein- DNA complexes were detected by autoradiography of the dried gel. Results: Transfection with the individual reporter constructs containing the 5' flanking region conesponding to nucleotides 1-1643 (i.e., pAPRl), 1-1532, 1080-1643, 1181-1643, 1292- 1643, or 1394-1643 of SEQ ID NO 3 each produced the same results All of the individual constructs produced a 3 to 4-fold increase in luciferase reporter activity in the presence of 20 (S) OH-chol or 22 (R) OH-chol compared with EtOH control Also, all of the individual constructs produced an 8 to 10-fold increase luciferase reporter activity in the presence of 9-cιs RA In addition, transfection with any of the constructs produced a 25 to 50-fold increase in luciferase activity in the presence of oxysterol ligand (either (20 (S) OH-chol or 22(R) OH-chol)) and retmoid ligand (9-cιs RA) together compared with EtOH control, indicating a synergistic interaction Each of the descnbed constructs demonstrated comparable levels of luciferase activity in response to the ligands tested, indicating that even the shorter 5' flanking sequences contained transcnptional regulatory sequences for sterols and retmoids Specifically, these results demonstrated that the transcnptional regulatory sequences for sterols and retmoids are located in the 5' flanking region conespondmg to nucleotides 1394-1532 of SEQ ID NO 3 These results were confirmed by luciferase assays using a reporter construct containing the wild-type sequence conesponding to nucleotides 1080-1643 of SEQ ID NO 3 and a reporter construct containing a mutated sequence conesponding to nucleotides 1080- 1643 of SEQ ID NO 3, wherein the sterol response element found at nucleotides 1480-1500 was mutated as descnbed above Transfection with the wild-type sequence produced a transcπtional response, as measured by an increase m luciferase activity, in the presence of either 20 (S) OH-chol or 9-cιs RA alone and produced a synergistic response in the presence of both ligands together In contrast, transfection with the mutated sequence did not produce a transcnptional response in the presence of 20 (S) OH-chol or 22 (R) OH-chol Transfection of the mutated sequence preserved a reduced response to 9-cιs RA, producing a 4 to 5-fold increase m transcnptional activity, rather than the 8 to 10-fold increase observed with the wild-type sequence Transfection of the mutated sequence also abolished the synergistic transcnptional response seen in the presence of 20 (S) OH-chol and 9-cιs RA together These results were further confirmed by gel-shift assays using the sterol consensus sequence (nucleotides 1480-1510) and its mutated counteφart The gel-shift assays showed that while nuclear binding proteins isolated from RAW 264 7 cells bound to the sterol consensus sequence, nuclear proteins did not bind to the mutated sequence Furthermore, incubation of nuclear proteins with the wild-type sterol consensus sequence in the presence of LXR antiserum resulted in the formation of supershifted complexes (I e antibody-protem-DNA complexes), identifying the sequence as a sterol response element that binds nuclear receptor LXR In contrast, incubation of nuclear proteins with the wild-type sterol response element in the presence of RXR antiserum did not result m the formation of supershifted complexes, indicating that RXR does not bind to this sequence. These results show that the mutation which destroys nuclear protein binding to the consensus sequence also abolishes the transcnptional response to LXR ligands and diminishes the response to RXR ligands. Furthermore, the nuclear binding studies performed in the presence of LXR or RXR antiserum confirmed that the consensus sequence found at nucleotides 1480-1510 is an LXR response element. This element also mediates a partial response to 9-cιs RA. All of the references cited herein, including patents and publications, are hereby incoφorated in their entireties by reference. While the invention has been descnbed with an emphasis upon prefened aspects of the invention, it will be readily apparent to those of ordinary skill in the art that variations of the prefened embodiments can be used and that it is intended that the invention can be practiced otherwise than is specifically descnbed herein. Accordingly, the present invention includes all modifications encompassed withm the spmt and scope of the invention as defined by the following claims.

Claims: What we claim is: 1 . An isolated polypeptide comprising SEQ ID NO: 2. 2. An isolated polypeptide comprising an amino acid sequence that has at least 98% identity with the amino acid sequence of SEQ ID NO: 2. 5 3. An isolated polynucleotide selected from the group consisting of a polynucleotide encoding the polypeptide of claim 1, a polynucleotide comprising SEQ ID NO: 1, a polynucleotide comprising nucleotides 291-7074 of SEQ ID NO: 1, and a polynucleotide encoding the polypeptide of claim 2. 4. An isolated polynucleotide comprising a nucleotide sequence that is l o complementary to the polynucleotide of claim 3. 5. An isolated polynucleotide comprising a nucleotide sequence that has at least 90% identity with the polynucleotide comprising SEQ ID NO: 1. 6. An isolated polynucleotide comprising a nucleotide sequence that has at least 95% identity with the polynucleotide comprising SEQ ID NO: 1. 15 7. An isolated polynucleotide comprising a nucleotide sequence that is complementary to the polynucleotide of claim 5. 8. A composition comprising the polynucleotide of claim 3 and a suitable carrier. 9. A composition comprising the polynucleotide of claim 4 and a suitable carrier. 10. A composition comprising the polynucleotide of claim 5 and a suitable carrier. 20 11. A recombinant vector comprising the polynucleotide of claim 3. 12. A recombinant vector comprising the polynucleotide of claim 4. 13. A recombinant vector comprising the polynucleotide of claim 5. 14. The recombinant vector of claim 1 1, further comprising a heterologous promoter polynucleotide. 25 15. The recombinant vector of claim 12, further comprising a heterologous promoter polynucleotide. 16. The recombinant vector of claim 13, further comprising a heterologous promoter polynucleotide. 30 17. The recombinant vector of claim 14, wherein said heterologous promoter is a cytomegalovirus promoter. 18. The recombinant vector of claim 17, wherein said vector is pCEPhABCl . 19. A composition comprising the recombinant vector of claim 1 1. 20. A composition comprising the recombinant vector of claim 13. 21. A composition comprising the recombinant vector of claim 14. 22. A host cell comprising the recombinant vector of claim 11. 23. A host cell comprising the recombinant vector of claim 13. 24. A host cell comprising the recombinant vector of claim 14. 25. An isolated polypeptide comprising SEQ ID NO: 8. 26. An isolated polynucleotide encoding the polypeptide of claim 25. 27. An isolated polynucleotide comprising SEQ ID NO: 7. 28. An isolated polypeptide comprising SEQ ID NO: 10. 29. An isolated polynucleotide encoding the polypeptide of claim 28. 30. An isolated polynucleotide comprising SEQ ID NO: 9. 31 . A recombinant vector comprising the polynucleotide of claim 27. 32. A recombinant vector comprising the polynucleotide of claim 30. 33. A method for producing an ABCl protein in a mammalian host cell comprising the steps of: (a) transfecting the mammalian host cell with a recombinant expression vector comprising a polynucleotide encoding ABCl in an amount sufficient to produce a detectable level of ABCl protein; and (b) purifying the produced ABCl protein. 34. The method of claim 33, wherein the recombinant expression vector comprises the polynucleotide of claim 3. 35. A method for expressing ABCl in the cells of a mammalian subject comprising the step of administering to a mammalian subject a recombinant expression vector comprising a polynucleotide encoding ABCl in an amount sufficient to express ABCl in the cells of a mammalian subject. 36. The method of claim 35, wherein the recombinant expression vector comprises the polynucleotide of claim 3. 37. A method suitable for increasing cholesterol efflux from cells of a mammalian subject comprising administering to the mammalian subject a recombinant expression vector comprising a polynucleotide encoding ABCl in an amount sufficient to increase cholesterol efflux from said cells. 38. The method of claim 37, wherein the recombinant expression vector comprises the polynucleotide of claim 3. 39. The method of claim 37, wherein the recombinant expression vector is a viral delivery vector. 40. The method of claim 39, wherein the viral delivery vector is an adenoviral vector. 41. The method of claim 39, wherein the viral vector is a lentiviral vector. 42. The method of claim 37, wherein the recombinant expression vector is a non-viral delivery vector. 43. A method suitable for increasing cholesterol efflux from cells of a mammalian subject comprising administering to the mammalian subject via a non-viral delivery system a polynucleotide encoding ABCl in an amount sufficient to increase cholesterol efflux from said cells. 44. The method of claim 43, wherein the polynucleotide encoding ABCl comprises the polynucleotide of claim 3. 45. The method of claim 43, wherein the non- viral delivery system is selected from the group consisting of DNA-ligand complexes, adenovirus-ligand-DNA complexes, adeno- associated virus-ligand-DNA complexes, direct injection of DNA, CaPO 4 precipitation, gene gun techniques, electroporation, liposomes, and lipofection. 46. A method suitable for increasing cholesterol efflux from cells of a mammalian subject comprising the step of administering to the mammalian subject a therapeutic amount of a compound that increases the expression of ABCl in said cells. 47. The method of claim 46, wherein said compound is a cAMP analogue. 48. The method of claim 47, wherein said compound is selected from the group consisting of 8-bromo cAMP, N6-benzoyl cAMP, and 8-thiomethyl cAMP. 49. The method of claim 46, wherein said compound increases the synthesis of cAMP. 50. The method of claim 49, wherein said compound is forskolin. 51. The method of claim 46, wherein said compound is a phosphodiesterase inhibitor. 52. The method of claim 51 , wherein said compound is selected from the group consisting of rohpram, theophylline, 3-isobutyl-l-methylxanthine, R020-1724, vinpocetine, zaprinast. dipyridamole, milrinone, amrinone, pimobendan, cilostamide, enoximone, peroximone, and vesnarinone. 53. A method suitable for increasing the gene expression of ABCl in the cells of a mammalian subject comprising the step of administering to the mammalian subject a cAMP analogue in an amount sufficient to increase the expression of ABCl in said cells. 54. A method suitable for increasing cholesterol efflux of the cells of a mammalian subject by administering to the mammalian subject a compound that increases ABCl activity in an amount sufficient to increase cholesterol efflux. 55. A method for screening a test compound to determine whether the test compound promotes ABCl -mediated cholesterol efflux from cells in culture comprising the steps of: assaying the level of cholesterol efflux in a sample of mammalian cells maintained in culture to determine a control level of cholesterol efflux; contacting the cells with the test compound being screened; assaying the level of cholesterol efflux in a sample of cells after contact with the test compound; and assaying the level of ABCl -mediated cholesterol efflux in a sample of cells after contact with the test compound, thereby determining whether the test compound promotes ABC1- mediated cholesterol efflux from cells in culture. 56. The method of claim 55, wherein the cultured cells are derived from a cell line. 57. The method of claim 56, wherein the cell line is selected from the group consisting of fibroblast, macrophage, hepatic, and intestinal cell lines. 58. The method of claim 57, wherein the cell line is RAW 264.7. 59. The method of claim 55, wherein the level of ABC 1 -dependent cholesterol efflux is assayed using an anti-ABCl antibody that inhibits the activity of ABCl upon binding. 60. The method of claim 55, wherein the level of ABCl -dependent cholesterol efflux is assayed using an anti-sense ABCl polynucleotide. 61. The method of claim 60, wherein the polynucleotide comprises SEQ ID NO: 57. 62. A method for detecting the comparative level of ABCl expression in the cells of a mammalian subject compnsing the steps of : obtaining a cell sample from the mammalian subject; assaying the level of ABCl mRNA expression in the cell sample; and comparing the level of ABCl mRNA expression in the cell sample with a pre-determined standard level of ABCl mRNA expression, thereby detecting the comparative level of ABCl gene expression in the cells of a mammalian subject. 63. The method of claim 62, wherein detection of the comparative level of ABC l expression in cells of a mammalian subject is used to determine a susceptibility to coronary heart disease of the mammalian subject. 64 The method of claim 62, wherein the level of ABCl mRNA expression is assayed by reverse transcnption polymerase chain reaction, northern blot, or RNAse protection assay 65 A method for detecting the comparative level of ABCl protein in the cells of a mammalian subject compnsing the steps of obtaining a cell sample from the mammalian subject, assaying the amount of ABCl protein m the cell sample, and companng the amount of ABCl protein in the cell sample with a pre-determmed standard amount of ABCl protein, thereby detecting the comparative level of ABCl protein in the cells of the mammalian subject 66 The method of claim 65, wherein detection of the comparative level of ABCl protein in cells of a mammalian subject is used to determine a susceptibility to coronary heart disease of the mammalian subject 67 The method of claim 65, wherein the assay to determine the amount of ABCl protein comprises an immunoassay 68 The method of claim 67, wherein the amount of ABCl protein is determined by (a) contacting the cell sample with a population of anti-ABCl antibodies and (b) detecting the specific binding ABCl antibodies associated with the cell sample 69 The method of claim 68, wherein the ABCl antibodies are detected by western blotting, immunoprecipitation, or FACS 70 An isolated antibody that binds specifically to the isolated polypeptide of claim 1 or claim 2 71 The antibody of claim 70 wherein the antibody is a monoclonal antibody 72 The antibody of claim 70 wherein the antibody is a polyclonal antibody 73 The antibody of claim 70 wherein the antibody, upon binding to an ABCl polypeptide, inhibits the cholesterol transport activity of the ABCl polypeptide 74 A kit suitable for screening a compound to determine whether the compound modulates ABCl -dependent cholesterol efflux compnsing an inactivating anti-ABCl antibody in an amount sufficient for at least one assay and instructions for use 75 A kit suitable for screening a compound to determine whether the compound modulates ABCl -dependent cholesterol efflux compnsing an antisense ABCl oligonucleotide in an amount sufficient for at least one assay and instructions for use 76 The kit of claim 75, wherein the antisense ABCl oligonucleotide compnses SEQ ID NO 53

Inventors: GARVIN MICHAEL, LAWN RICHARD M, ORAM JOHN F, WADE DAVID, GARVIN, MICHAEL, LAWN, RICHARD, M., ORAM, JOHN, F., WADE, DAVID
Applicants: CV THERAPEUTICS INC, GARVIN MICHAEL, LAWN RICHARD M, ORAM JOHN F, UNIV WASHINGTON, WADE DAVID, CV THERAPEUTICS, INC., GARVIN, MICHAEL, LAWN, RICHARD, M., ORAM, JOHN, F., UNIVERSITY OF WASHINGTON, WADE, DAVID
Application year: 2000
Main classification: C12N15
IPC codes: A61K31, A61K35, A61K38, A61K39, A61K45, A61K48, A61P1, A61P3, A61P5, A61P9, A61P25, A61P43, C07K14, C07K16, C12N1, C12N5, C12N15, C12P21, C12Q1, C12R1, G01N33