A SINGLE GENE ENCODING AORTIC-SPECIFIC AND STRIATED-SPECIFIC MUSCLE CELL ISOFORMS, ITS REGULATORY SEQUENCES AND USES THEREOF

Abstract: Aortic-preferentially-expressed gene-1 (APEG-1) and striated muscle preferentially expressed (SPEG) polypeptide, DNA sequences encoding and controlling the transcription of the APEG-1/SPEG encoding gene, methods of diagnosing vascular injury, methods of conferring smooth muscle-cell specific expression, and methods of inhibiting vascular smooth muscle cell proliferation by increasing the level of APEG-1 at the site of vascular injury.

Description: A SINGLE GENE ENCODING AORTIC-SPECIFIC AND STRIATED-SPECIFIC MUSCLE CELL ISOFORMS, ITS REGULATORY SEQUENCES AND USES THEREOF 5 This application is a continuation-in-part of U.S. Serial Number 09/134,250, filed on August 14, 1998. Background of the Invention The invention relates to diagnosis and treatment of vascular injury. 0 Atherosclerosis and its subsequent complications, such as myocardial infarction, stroke, and peripheral vascular diseases, are the major causes of death in developed countries. Vascular endothelial and smooth muscle cells have important roles in the regulation of 5 normal vascular tone. Damage or dysfunction of these cells can lead to vascular diseases, such as atherosclerosis and restenosis. Atherosclerosis is believed to be a consequence of a response of the vascular wall to injury (Ross, R. , 0 1993, Nature 362:801-9). Upon vascular injury and various other stimuli, cytokines and growth factors from activated vascular cells promote growth and migration of vascular smooth muscle cells in a dedifferentiated status, resulting in the formation of atherosclerotic 5 plaques. The pathogenesis of atherosclerosis is not fully understood, and an effective therapeutic regime has not been developed to prevent or cure atherosclerosis (Ross, R., The Pathogenesis of Atherosclerosis, in Heart 0 Disease, a textbook of cardiovascular medicine, E. Braunwald, Editor, 1992, W. B. Saunders Company: Philadelphia, pp. 1106-24; and Ross, R. : The Pathogenesis of Atherosclerosis: a Perspective for the 1990s, 1993, Nature 362:801-9). Despite extensive research, the molecular mechanisms responsible for the regulation of gene expression in vascular endothelial and smooth muscle cells are largely unknown. In particular, trans-acting factors and cis-acting elements mediating vascular cell-specific gene expression have not been identified, mainly due to the fact that only a few vascular specific genes have been identified. Furthermore, of the genes that have been characterized as endothelial cell-specific (e.g. von illebrand factors, VEGF receptor flk-1, VCAM-1, and E-selection (Hunter, J.J., et al . , 1993, Hypertension 22:608-17) or smooth muscle cell-specific (e.g., CHIP28, SM22, and gax (Gorski, D.H., et al . , 1993, Mol . Cell. Biol . 13 (6) : 3722-33) , many have been found in other cell types at various levels. Summary of the Invention The invention is based on the discovery of a novel gene the expression of which gives rise to variant isoforms, one which is specific to aortic cells, and others which are found in striated muscle cells. Accordingly, the invention features an aortic cell- specific gene, and therefore provides a substantially pure DNA (e.g., genomic DNA, cDNA or synthetic DNA) encoding an aortic-preferentially-expressed gene-1 (APEG- 1) polypeptide. By "substantially pure DNA" is meant DNA that is free of the genes which, in the naturally- occurring genome of the organism from which the DNA of the invention is derived, flank the APEG-1 gene. The term therefore includes, for example, a recombinant DNA which is incorporated into a vector, into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote at a site other than its natural site; or which exists as a separate molecule (e.g., a cDNA or a genomic or cDNA fragment produced by PCR or restriction endonuclease digestion) independent of other sequences. It also includes a recombinant DNA which is part of a hybrid gene encoding additional polypeptide sequence. Hybridization is carried out using standard techniques such as those described in Ausubel et al . , Current Protocols in Molecular Biology, John Wiley & Sons, (1989) . "High stringency" refers to DNA hybridization and wash conditions characterized by high temperature and low salt concentration, e.g., wash conditions of 65° C at a salt concentration of approximately 0.1 X SSC. "Low" to "moderate" stringency refers to DNA hybridization and wash conditions characterized by low temperature and high salt concentration, e.g. wash conditions of less than 60° C at a salt concentration of at least 1.0 X SSC. For example, high stringency conditions may include hybridization at about 42°C, and about 50% formamide; a first wash at about 65°C, about 2X SSC, and 1% SDS; followed by a second wash at about 65°C and about 0.1% x SSC. Lower stringency conditions suitable for detecting DNA sequences having about 50% sequence identity to an APEG-1 gene are detected by, for example, hybridization at about 42 °C in the absence of formamide; a first wash at about 42 °C, about 6X SSC, and about 1% SDS; and a second wash at about 50 °C, about 6X SSC, and about 1% SDS. A substantially pure DNA having at least 50% sequence identity (preferably at least 70%, more preferably at least 80%, and most preferably at least 90%) to SEQ ID NO : 1 , 2, or 11, and encoding a polypeptide having a biological activity of an APEG-1 polypeptide is also within the invention. The percent sequence identity of one DNA to another is determined by standard means, e.g., by the Sequence Analysis Software Package developed by the Genetics Computer Group (University of Wisconsin Biotechnology Center, Madison, WI) (or an equivalent program), employing the default parameters thereof. "Biological activity of an APEG-1 polypeptide" is defined as the ability to inhibit the proliferation or migration of smooth muscle cells at the site of vascular injury. The invention also includes a substantially pure DNA containing a constitutive or inducible, vascular cell-specific promoter, e.g., an APEG-1 promoter which is preferably in a vector into which an heterologous gene may be or has been cloned, and under the control of which the gene may be expressed. The promoter is preferably specific for arterial cells (e.g., cells of the aorta), and most preferably specific for vascular smooth muscle cells. DNA encoding APEG-1 may be operably linked to such regulatory sequences for expression of the APEG-1 polypeptide in vascular cells. By "promoter" is meant a minimal DNA sequence sufficient to direct transcription. Promoters may be constitutive or inducible, and may be coupled to other regulatory sequences or "elements" which render promoter- dependent gene expression cell -type specific, tissue- specific or inducible by external signals or agents; such elements may be located in the 5' or 3 ' region of the native gene, or within an intron. By "heterologous promoter" is meant a promoter other than a naturally occurring APEG-1 promoter. By "operably linked" is meant that a coding sequence and a regulatory sequence (s) are connected in such a way as to permit gene expression when the appropriate molecules (e.g., transcriptional activator proteins) are bound to the regulatory sequence (s). The invention also provides a method of directing vascular cell-specific expression of a protein by introducing into a vascular cell an isolated DNA containing a sequence encoding the protein operably linked to the vascular cell-specific promoter. A cell containing the DNA or vector of the invention is also within the invention. The invention also features a substantially pure APEG-1 polypeptide (e.g., rat APEG-1 (SEQ ID NO:3) or human APEG-1 (e.g., human APEG-1 (SEQ ID NO:12)) and an antibody which specifically binds to an APEG-1 polypeptide. By a "substantially pure polypeptide" is meant a polypeptide which is separated from those components (proteins and other naturally-occurring organic molecules) which naturally accompany it. Typically, the polypeptide is substantially pure when it constitutes at least 60%, by weight, of the protein in the preparation. Preferably, the protein in the preparation is at least 75%, more preferably at least 90%, and most preferably at least 99%, by weight, APEG-1 polypeptide. A substantially pure APEG-1 polypeptide may be obtained, for example, by extraction from a natural source (e.g., an aortic cell); by expression of a recombinant nucleic acid encoding an APEG-1 polypeptide; or by chemically synthesizing the protein. Purity can be measured by any appropriate method, e.g., column chromatography, polyacrylamide gel electrophoresis, or HPLC analysis. A protein is substantially free of naturally associated components when it is separated from those contaminants which accompany it in its natural state. Thus, a protein which is chemically synthesized or produced in a cellular system different from the cell from which it naturally originates will be substantially free from its naturally associated components. Accordingly, substantially pure polypeptides include recombinant polypeptides derived from a eukaryote but produced in E. coli or another prokaryote, or in a eukaryote other than that from which the polypeptide was originally derived. In another aspect, the invention provides a method of detecting injury in a sample of vascular tissue by determining the level of APEG-1 gene expression in the tissue; a decrease in the level of expression detected in the tissue sample compared to that detected in uninjured control vascular tissue indicates the presence of a vascular injury. The invention also includes a method of inhibiting smooth muscle cell proliferation in an animal by contacting an artery of the animal with an APEG-1 polypeptide or a biologically active fragment thereof or with a compound that stimulates the APEG-1 promoter, e.g., stimulates APEG-1 expression. In yet another aspect, the invention includes a method of making an APEG-1 polypeptide, e.g., a rat or human APEG-1 polypeptide, involving providing a cell containing DNA encoding an APEG-1 polypeptide and culturing the cell under conditions permitting expression of the APEG-1-encoding DNA, i.e., production of the recombinant APEG-1 by the cell. The invention further features a substantially pure DNA having an APEG-1 derived enhancer sequence which regulates vascular smooth muscle cell-specific transcription of a polypeptide-encoding sequence to which it is operably linked. By "enhancer sequence" is meant a DNA sequence which contains one or more cis-acting elements which regulate transcription, e.g., cell specific transcription. The elements may be contiguous or separated by DNA not involved in the regulation of transcription, e.g., an enhancer element may be in a position immediately adjacent to the promoter element or up to several kilobases upstream or downstream of the transcriptional start site. The enhancer DNA is preferably derived from the 5' region of a mammalian APEG-1 gene, such as that of the mouse (SEQ ID NO:17), and regulates preferential expression in vascular smooth muscle cells, e.g., aortic smooth muscle cells, of a polypeptide-encoding DNA to which it is operably linked. Preferably, the enhancer includes a sequence which hybridizes under high stringency conditions to SEQ ID NO: 20 or SEQ ID NO: 23, or a complement thereof. More preferably, the enhancer includes the 73 nucleotides of SEQ ID NO: 20, which is located within the sequence of SEQ ID NO: 17. Most preferably, the enhancer includes the 38 nucleotides of SEQ ID NO: 23, which is located within the sequence of SEQ ID NO: 20. In some embodiments, the enhancer includes less than the complete nucleotide sequence of SEQ ID NO: 17, e.g., it can contain less than 2.6 kb, 2.1 kb, 1.7 kb, 1.2 kb, 700 nucleotides, 500 nucleotides, or even 100 nucleotides of SEQ ID NO: 17. In some embodiments, the enhancer contains SEQ ID NO: 20 and is less than 2.7 kb in length, 1.0 kb, 500 bp, 250 bp or 100 bp in length. The enhancer may also include a plurality of copies of SEQ ID NO: 23 or SEQ ID NO : 20. The enhancer including SEQ ID NO: 20 or SEQ ID NO: 23 may be immediately contiguous to a polypeptide- encoding DNA. Alternatively, the enhancer may be separated by 5, 10, 20, 30, 40, 50, 75, or 100 nucleotides from the polypeptide-encoding DNA. In addition to or alternatively, the enhancer may be contiguous to, or be separated by 5, 10, 20, 30, 40, 50, 75, or 100 nucleotides from an APEG-1 promoter or a heterologous promoter. Preferably, expression of a polypeptide under the control of the APEG enhancer (e.g., SEQ ID No: 17, SEQ ID NO:20, or SEQ ID NO:23) is at least 50% greater (e.g., as measured in the amount of polypeptide-encoding mRNA transcript) , preferably at least 100% greater, more preferably at least 200% greater, and still more preferably at least 400% greater in vascular smooth muscle cells than in non-vascular smooth muscle cells. Most preferably, the APEG-1 enhancer directs vascular smooth muscle cell -specific polypeptide expression and directs negligible polypeptide expression in non-smooth muscle cell types. The enhancer sequence may in addition regulate developmental stage-specific expression, e.g., preferential expression in embryonic cells, of a polypeptide-encoding sequence. The DNA of the invention (enhancer sequence) may be operably linked to a DNA sequence encoding a polypeptide that is not APEG-1 (i.e., a heterologous polypeptide) , and function to regulate vascular smooth muscle cell-specific transcription of the polypeptide- encoding sequence. Examples of such polypeptides include tissue plasminogen activator (tPA) , p21 cell cycle inhibitor, nitric oxide synthase, interferon-γ, and atrial natriuretic polypeptide. The invention also includes a vector containing the enhancer DNA of the invention (operably linked to a polypeptide-encoding DNA sequence) and a vascular smooth muscle cell containing the vector. Also within the invention is a method of directing vascular smooth cell- specific expression of the polypeptide by introducing the vector into a vascular smooth muscle cell and maintaining the cell under conditions which permit expression of the polypeptide, e.g., introducing the vector into a human patient for gene therapy. The vector of the invention can be used for gene therapy. For example, the vector can be introduced into a vascular smooth muscle cell to direct vascular smooth muscle cell-specific expression of a polypeptide. The vector of the invention can also be used for directing developmental stage-specific expression, e.g., preferential expression by embryonic cells, of a polypeptide, involving introducing into a vascular smooth muscle cell the vector of the invention. The invention also features a method of inhibiting proliferation of vascular smooth muscle cells by administering to the cells an APEG-1 polypeptide. The invention also features a striated muscle cell-specific variant gene product arising from the same genomic DNA encoding APEG-1, and therefore provides a substantially pure DNA (e.g., genomic DNA, cDNA or synthetic DNA) encoding a striated muscle preferentially- expressed gene (SPEG) polypeptide. The DNA may encode a naturally occurring mammalian SPEG polypeptide such as a human SPEG polypeptide (SEQ ID NO: 14) or mouse SPEG polypeptide (SEQ ID NO: 16) . For example, the invention includes degenerate variants of the human cDNA (SEQ ID NO: 13) or the mouse cDNA (SEQ ID N0:15). The invention also includes a substantially pure DNA comprising a strand which hybridizes at high stringency to a DNA having the sequence of SEQ ID NO: 13 or 15, or the complements thereof. A substantially pure DNA having at least 50% sequence identity (preferably at least 70%, more preferably at least 80%, and most preferably at least 90%) to SEQ ID NO: 13, or 15, and encoding a polypeptide having a biological activity of a SPEG polypeptide is also within the invention. The invention also includes a substantially pure DNA containing a constitutive or inducible striated muscle cell-specific promoter, e.g., a SPEG promoter which is preferably in a vector into which an heterologous gene may be or has been cloned, and under the control of which promoter the gene may be expressed. The promoter is preferably specific for striated muscle cells (e.g., cells of skeletal or cardiac muscle) . DNA encoding SPEG may be operably linked to such regulatory sequences for expression of the SPEG polypeptide in striated muscle cells. The invention also provides a method of directing striated muscle cell-specific expression of a protein by introducing into a cell an isolated DNA containing a sequence encoding the protein operably linked to the striated cell-specific promoter. A cell containing the DNA or vector of the invention is also within the invention. The invention also features a substantially pure SPEG polypeptide (e.g., human (SEQ ID NO: 14) or mouse SPEG (SEQ ID NO: 16) and an antibody which specifically binds to a SPEG polypeptide. The invention further features a substantially pure DNA having an APEG-1 derived cis-acting transcriptional repressor sequence. A "cis-acting transcriptional repressor" as used herein is a nucleic acid which functions to decrease transcription of an operably linked nucleic acid sequence. For example, transcription of an operably linked sequence is decreased when a trans-acting repressor, e.g., an endogenous intracellular protein, binds to the cis-acting repressor sequence, binds to the cis-acting repressor. Inhibiting binding of the trans-acting repressor, e.g., by administering an exogenous compound that binds to the cis-acting transcriptional repressor, leads to derepression and a concomitant increase in expression of the operably-linked nucleic acid. The cis-acting transcriptional repressor sequence may linked to other cis-acting elements, e.g., additional copies of the cis-acting transcriptional repressor sequence. The elements may be contiguous or separated by DNA not involved in the regulation of transcription, e.g., a transcriptional repressor element may be in a position immediately adjacent to the promoter element or up to several kilobases upstream or downstream of the transcriptional start site. In some embodiments, the cis-acting transcriptional repressor sequence hybridizes to a sequence including nucleotides -3337 to -2663 of the 5' region of the mouse APEG-1 gene (SEQ ID NO: 24) . In other embodiments, the cis-acting transcriptional repressor sequence comprises SEQ ID NO: 24. The cis-acting transcriptional repressor sequence can be, e.g., less than 4.0 kb, 3.0 kb, 1.5 kb, 1.0 kb, or even 670 nucleotides in length. In some embodiments, the nucleic acid continuing the cis-acting transcriptional repressor sequence does not include the sequence of SEQ ID NO: 23. The invention also includes a vector comprising the cis-acting transcriptional repressor sequence. In a further aspect, the invention includes a method of evaluating a compound for the ability to bind to a vascular smooth muscle cell cis-acting transcriptional repressor sequence. The method includes contacting the compound with a vascular smooth muscle cell cis-acting transcriptional repressor sequence and determining the amount of binding of the compound to the vascular smooth cell cis-acting transcriptional repressor sequence. The cis-acting transcriptional repressor sequence can be, for example, a sequence which hybridizes under high stringency conditions to SEQ ID NO: 24 and can be SEQ ID NO: 24. In a further aspect, the invention includes a method of evaluating a compound for the ability to bind to a cis-acting transcriptional repressor sequence. In this method, the compound is contacted with a vascular smooth muscle cell containing a nucleic acid comprising a vascular smooth muscle cell cis-acting transcriptional repressor sequence operably linked to a sequence encoding a reporter molecule is contacted. The amount of the reporter molecule expressed by the cell is measured, and an alteration in the level of reporter molecule expressed in the presence of the compound compared to the level in the absence of the compound indicates that the compound binds to a vascular smooth muscle cell cis-acting transcriptional repressor sequence. In another aspect, the invention includes a method of evaluating a compound for the ability to bind to increase APEG-1 expression. In this method, a vascular smooth muscle cell is contacted with a test compound, and the amount of APEG-1 transcript or polypeptide in the vascular smooth muscle cell is measured. An increase in the amount of APEG-1 transcript or gene product indicates the compound increases APEG-1 expression. In a further aspect, the invention includes a method of inhibiting vascular smooth muscle cell proliferation by contacting a compound which binds to a vascular smooth muscle cell cis-acting transcriptional repressor sequence. The compound is provided in an amount effective to inhibit proliferation of the vascular smooth muscle cell. In some embodiments, the cis-acting transcriptional repressor sequence includes a sequence which hybridizes at high stringency to SEQ ID NO: 24. For example, the cis-acting transcriptional repressor sequence comprises SEQ ID NO: 24. Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims. Detailed Description The drawings will first be described. Fig 1. is a flow chart of the differential mRNA display procedure for identifying APEG sequences. Fig. 2A is a photograph of a differential mRNA display showing APEG-1 preferentially expressed in the rat aorta. The differential expression was tested among 6 rat tissues. Unique bands in the aorta that were eluted and reamplified for subsequent analysis are indicated (•) . Fig. 2B is a photograph of a differential mRNA display showing APEG-2 preferentially expressed in the rat aorta. The differential expression was tested among 6 rat tissues. Unique bands in the aorta that were eluted and reamplified for subsequent analysis are indicated (•) . Fig. 2C is a photograph of a differential rriRNA display showing APEG-3 preferentially expressed in the rat aorta. The differential expression was tested among 6 rat tissues. Unique bands in the aorta that were eluted and reamplified for subsequent analysis are indicated (•) . Fig. 2D is photograph of a differential mRNA display showing APEG-4 preferentially expressed in the rat aorta. The differential expression was tested among 6 rat tissues. Unique bands in the aorta that were eluted and reamplified for subsequent analysis are indicated (•) . Fig. 2E is a photograph of a Northern blot analysis showing tissue expression of APEG-1. Ten micrograms of total RNA from each tissue were used in Northern analysis. The loading of each tissue RNA was normalized by comparing 18s rRNA hybridization signals (shown in Fig. 2F) . Fig. 2F is a photograph of a Northern blot analysis showing 18s rRNA. Fig. 2G is a photograph of a Northern blot analysis showing tissue expression of APEG-2. Ten micrograms of total RNAs from each tissue were used in Northern analysis, and the loading of each tissue RNA was normalized by comparing 18s rRNA hybridization signals. Fig. 2H is a photograph of a Northern blot analysis showing tissue expression of APEG-3. Ten micrograms of total RNAs from each tissue were used in Northern analysis, and the loading of each tissue RNA was normalized by comparing 18s rRNA hybridization signals. Fig. 21 is a photograph of a Northern blot analysis showing tissue expression of APEG-4. Ten micrograms of total RNAs from each tissue were used in Northern analysis, and the loading of each tissue RNA was normalized by comparing 18s rRNA hybridization signals. Fig. 3A is a photograph of a Northern blot analysis using full length cDNA of APEG-1 (APEG-1 full cDNA) as a probe . Samples of RNA from twelve rat organs were analyzed. The respective lanes are labelled in Fig. 3D. Fig. 3B is a photograph of a Northern blot analysis using a 3' cDNA fragment originally cloned by differential mRNA display (APEG-1 3' D.D. frag.) as a probe . Samples of RNA from twelve rat organs were analyzed. Fig. 3C is a photograph of a Northern blot showing 18s rRNA bands (18s rRNA) to which RNA loading was normalized. Fig. 3D is a bar graph showing tissue distribution of APEG-1 gene expression. Fig. 4 is a flow chart showing the cloning strategy for APEG-1. A rat aortic cDNA library established in the yeast expression vector pcJATA was screened to isolate full length APEG-1 cDNA. Southern analysis was carried out to confirm the presence of APEG-1 in this cDNA library. Restriction enzyme-digested (EcoRI and Xhol) cDNA fragments were separated on an agarose gel and the portions that contained APEG-1 cDNA, as determined by size markers and Southern analysis, were excised to elute the cDNA contents. Eluted cDNAs were ligated with linearized pSP72 vectors, and the ligated DNAs were used to transform competent E. coli DHc.5 cells to establish a size-selected aortic cDNA sublibrary. This cDNA sublibrary was screened by the APEG-1 cDNA 3' fragment to obtain its full length cDNA. Fig. 5 is a diagram of the nucleotide sequence of rat APEG-1 cDNA (SEQ ID NO:l). The longest open reading frame is located from nucleotide 169 to 511 (BOLD UPPERCASE) and the ATG flanking nucleotides that match the Kozak consensus sequence are indicated (UPPERCASE) . A very short upstream open reading frame is present from nucleotide 102 to 116 (italic) . There is a polyadenylation signal (underline) 21 nucleotides upstream of the poly-A tail . The primer annealing site of the 5' arbitrary primer used in the initial differential display PCR is also indicated (ITALIC UPPERCASE) . Fig. 6 is a diagram of the amino acid sequence (SEQ ID NO: 3) deduced from the longest APEG-1 cDNA open reading frame (SEQ ID NO: 2) . Possible phosphorylation sites of protein kinase C and casein kinase-2 are indicated (bold) . An integrin binding site, RGD, is also shown (bold italic). » *** » represents a stop codon. Fig. 7A is a photograph of in vi tro transcription products of the APEG-1 gene. The 1.3 kb APEG-1 cDNA and a positive control DNA template were transcribed by T7 RNA polymerase . 1 μl of the 20 μl RNA products were resolved on a 1.2% denaturing agarose gel. Fig. 7B is a photograph of in vi tro translation products of the APEG-1 gene. In vi tro transcribed APEG-1 mRNA was translated by wheat germ extract in the presence of [ 35 S] -methionine, and separated on a 10% tricine- SDS-polyacrylamide gel. In the mock reaction, mRNA template was absent . Fig. 8 is an alignment of amino acid sequences of APEG-1 (SEQ ID NO:8), the myosin light chain kinase of chicken (ChkMLCK; SEQ ID NO: 5) and of rabbit (RabMLCK; SEQ ID NO:7), and telokin of chicken (ChkTelo; SEQ ID NO: 4) and of rabbit (RabTelo; SEQ ID NO: 6) . A consensus sequence (SEQ ID NO: 9) is also shown to indicate the amino acid residues that are identical among these proteins. The conserved serine residue that is phosphorylated by cAMP-dependent protein kinase is marked by an asterisk (*) . Fig 9A is a diagram of APEG-1 cDNA. APEG-1 cDNA was divided into four fragments by EcoR I, BamHI , Hind III, and Xhol restriction enzyme digestion. The three large fragments (405, 299, and 432 bp) were used to probe six rat tissue RNAs to show their different hybridization patterns. Fig. 9B is a photograph of a Northern analysis using the 405 bp fragment of APEG-1 cDNA as a probe. Fig. 9C is a photograph of a Northern analysis using the 299 bp fragment of APEG-1 cDNA as a probe. Fig. 9D is a photograph of a Northern analysis using the 432 bp fragment of APEG-1 cDNA as a probe. Fig 10 is a photograph of a genomic Southern analysis of the APEG-1 gene. Genomic DNA from cultured rat aortic smooth muscle cells was harvested and digested with EcoRI, Hindlll, or BamHI. APEG-1 full length cDNA was used as probe in the Southern analysis. The size of each band (indicated on the right) was determined according to the size markers (indicated on the left) . Fig. 11A is a photograph of ethidium bromide staining of the 3 clones of human homologues of rat APEG- 1. Clone 1 (1.1, 1.2), clone 2 (2.1, 2.2), and clone 3 (3.1) were 1.45, 2.0, and 2.7 kb in size, respectively. Fig. 11B is a photograph of a Southern analysis showing hybridization of these human homologues with a rat APEG-1 cDNA probe. Fig. 12 is a photograph of a Northern analysis of APEG-1 expression in vi tro . RNAs from rat aortic smooth muscle cells (RASMC) and from microvascular endothelial cells (RMEC) were purified and separated on a 1.2 % denaturing agarose gel . RNA from normal rat aorta was used as a positive control. APEG-1 cDNA was used as probe in Northern analysis to examine its expression in these two cell types. Fig. 13A is a photograph of a Northern analysis showing expression of APEG-1 in rat carotid artery during balloon injury. RNAs were purified from rat carotid arteries 2, 5, 8 days after balloon injury. Three injured rats were used in each time point and two uninjured rats were used as control. The APEG-1 cDNA was used in Northern analysis and the band intensities were normalized by 18s rRNA signal. Fig. 13B is a bar graph showing expression of APEG-1 in rat carotid artery during balloon injury. Each column represents the mean expression of APEG-1 in the Northern analysis bands shown in Fig. 13A, expressed as a percent of control ± one standard error. Fig. 14A is a photograph of a Coomassie blue stained 10% tricine-SDS-PAGE gel showing the purified FLAG-APEG-1 fusion protein. M, protein size marker. Ext, induced bacterial cell extracts. FT, cell extract that flowed through the FLAG peptide affinity column. Fig. 14B is a photograph of a Western analysis of the purified fusion protein. A monoclonal anti-FLAG peptide antibody, M2 (IBI) , was used to identify the purity of the fusion protein. Un, uninduced bacterial cell extracts. In, induced bacterial cell extracts. FT, cell extract that flowed through the FLAG peptide affinity column. Fig. 15 is a bar graph comparing APEG-1 expression in diabetic rats and control rats. APEG-1 expression was decreased in diabetic rats (unpaired T test: T 10 =3.284, p value=0.0033) . Fig. 16 is a diagram showing the cDNA sequence of human APEG-1 (SEQ ID NO: 11) Fig. 17 is a diagram showing the amino acid sequence of human APEG-1 (SEQ ID NO: 12) . "*" represents a stop codon. Fig. 18A is a photograph showing the results of an in si tu hybridization experiment. The lumen of a rat aorta was sectioned and hybridization carried out using a rat APEG-1 sense strand DNA probe as a control. Fig. 18B is a photograph showing APEG-1 mRNA expression in the lumen of a rat aorta. In situ hybridization was carried out using a rat antisense strand DNA probe to measure rat APEG-1 expression in aortic tissue. Figs. 19A-C are diagrams showing the pattern of exon usage in the APEG-1 and SPEG transcripts. Fig. 19A is a diagram showing the intron/exon arrangement of the APEG/SPEG locus. Fig. 19B is a diagram showing APEG-1 exon usage. Fig. 19C is a diagram showing SPEG exon usage . Fig. 20 is a diagram showing the cDNA sequence of human SPEG (SEQ ID NO: 13) . Fig. 21 is a diagram showing the amino acid sequence of human SPEG (SEQ ID NO: 14) . Fig. 22 is a diagram showing the cDNA sequence of mouse SPEG (SEQ ID NO:15). Fig. 23 is a diagram showing the amino acid sequence of mouse SPEG (SEQ ID NO: 16) . Fig. 24A is a diagram showing the PGL-3 construct. Fig. 24B is a bar graph showing the results of reporter transfection assays using 3.3 kb of APEG-1 5' sequence. Cell lines used: RASMC, rat aortic smooth muscle cells; BAEC, bovine aortic endothelial cells; HeLa, human epidermoid carcinoma cell line; U-2 OS, human osteosarcoma cells; HepG2 , human hepatoma cells; NIH 3T3 mouse fibroblasts. Fig. 25 is a diagram showing the sequence of a 2.7 kb fragment containing the APEG-1 5' vascular smooth muscle cell-specific promoter activity (SEQ ID NO: 17) . Fig. 26 is a diagram showing a comparison of the full-length APEG-1 amino acid sequences of the human, mouse and rat . Fig. 27 is a diagram showing a comparison of partial SPEG amino acid sequences in human and mouse. "*" represents a stop codon. Fig. 28 is a diagram showing the sequence of a 73 nucleotide DNA (SEQ ID NO: 20) containing APEG-1 vascular smooth muscle cell-specific promoter activity. Fig. 29 is a bar graph showing the results of reporter transfection assays using a 73 bp fragment of the APEG-1 5' sequence. Cell lines used: RASMC, rat aortic smooth muscle cells; U-2 OS, human osteosarcoma cells; HeLa, a human epidermoid carcinoma cell line; and BAEC, bovine aortic endothelial cells. Fig. 30 is a bar graph showing the results of reporter transfection assays using reporter plasmids constructed from the APEG-1 promoter region. Fig. 31 is a diagram showing the nucleotide sequence from -3337 to +76 of the 5' region of the mouse APEG-1 gene. Open triangles at -3337 and -2663 denote a cis-acting transcriptional repressor sequence, and open triangles at +38 and +76 indicate a cis-acting transcriptional enhancer sequence. Fig. 32 is a bar graph showing luciferase activity relative in RASMC for constructs p ( -33376/+76) , p(-33376/+76)Rev, and p (-2663/+76) . Activity is shown as a percentage of luciferase activity produced by p(- 2663/+76) . Purification of total RNAs Total RNA was harvested from male Sprague-Dawley rat organs. The dissected organs were washed in phosphate buffered saline and snap- frozen in liquid nitrogen. The adventitia of the aorta was stripped, and the contents of the small intestine were removed before freezing. The frozen organs were homogenized and RNAs were harvested by acid guanidinium thiocyanate-phenol -chloroform extraction (Chomczynski, P. et al., 1987, Anal. Biochem. 162 (1) : 156-9) . Mouse embryo RNA was harvested from whole embryos. The cell culture RNAs were purified by guanidinium/CsCl ultracentrifugation . Differential mRNA Display Fifty micrograms of total RNA were treated with DNase I (Boehringer Mannheim) to remove contaminating genomic DNA in the presence of RNase inhibitor RNasin (Promega) . After phenol/chloroform extraction and ethanol precipitation, the RNA concentration was adjusted to 0.1 μg/ml in DEPC-treated dH20. First strand cDNA was synthesized using MMLV reverse transcriptase (GIBCO, BRL) with the 3' poly-A-anchoring primer T 12 VG (5' -TTTTTTTTTTTTVG-3' ) (SEQ ID NO:10). Subsequently the reaction was heated at 95°C to inactivate reverse transcriptase, and the cDNA products were stored at -20°C. Two microliters of the cDNA were used in 20 μl PCR reactions (2 μl cDNA, 0.2 μM 5' arbitrary primer, 1 μM 3' T 12 VG primer, 1.5 m Mg 2+ , 2.5 μM dNTP, 12.5 μCi 35 S-dATP, 1 unit Taq DNA polymerase; 94 °C for 15 sec, the thermal cycling was 40°C for 30 sec and 72°C for 30 sec; the thermal cycling was repeated for 40 cycles) following the reverse transcription. Sample loading buffer (98% formamide, 0.05% bromophenol blue, and 0.05% xylene cyanol) was added, and the samples were heated at 95 °C before loading onto a 6% sequencing gel. Overnight exposure of the dried sequencing gels to X-OMAT films (Kodak) was usually sufficient to display the differential mRNA patterns. Reamplification of eluted cDNAs Bands of interest on the dried gel were excised, soaked in 200 μl dH 2 0 for 10 minutes at room temperature, and eluted by heating at 95°C for 15 minutes. After a brief centrifugation, the supernatants were transferred into fresh tubes, and the eluted DNAs were ethanol-precipitated at -20°C in the presence of 20 μg glycogen and 300 mM sodium acetate. The precipitated DNAs were collected by centrifugation and washed with 70% ethanol. Dried DNA pellets were resuspended in 10 μl dH 2 0 and nonradioactively reamplified by PCR with the same initial PCR primers and condition, except that the reaction volume was scaled up to 100 μl with 25 μM dNTP. Reamplified cDNAs were resolved on 1% agarose gel to determine their sizes and amounts. RNA gel electrophoresis and Northern blotting Ten micrograms of total RNA were heat-denatured and loaded on a denaturing agarose gel (1.2 % agarose, 1.1% formaldehyde, 0.5 μg/ml ethidium bromide in MOPS buffer) . Electrophoresis was carried out at 10 V/cm for three to four hours . A photograph of the ethidium bromide staining pattern of the RNAs was taken under UV light illumination. The RNAs were then transferred onto a Nitropure membrane (Micron Separation Inc.) by standard blotting procedure (Ausubel, F.M., et al . , ed. Current Protocols in Molecular Biology, ed. K. Janssen., 1994, Vol. 1., Current Protocols :4.9.1-14) . DNA gel electrophoresis and Southern blotting DNAs were loaded and separated on a 1% agarose gel, followed by standard Southern blotting (Ausubel, F.M., et al . , ed. Current Protocols in Molecular Biology, ed. K. Janssen., 1994, Vol. 1, Current Protocols: 2.9.1-15) . The DNAs in the gel were denatured in denaturation buffer (1.5 M NaCl, 0.5 N NaOH) , then neutralized in neutralization buffer (1.5 M NaCl , 1 M TrisCl, pH 7.4) prior to being transferred onto a Nitropure membrane in 20 x SSC solution overnight. Random priming and hybridization Radioactive DNA probes were generated by random priming (Boehringer Mannheim) with 25 to 50 ng of the DNA fragment. Hybridization to the DNA or RNA blots was carried out in QuikHyb solution (Stratagene) with 1 x 10 6 cpm/ml of radioactive probes and 0.2 mg/ml herring sperm DNA (Boehringer Mannheim) at 68°C for one to two hours. The blots were washed and exposed to X-ray films for permanent records . Quantitation of hybridization signals To quantitate the hybridization signals, DNA and RNA blots were exposed to phosphor screens (Molecular Dynamics) overnight. The phosphor screens were then scanned by a Phospholmager scanner (Molecular Dynamics) operated by the ImageQuant program (Molecular Dynamics) running on a PC-DOS/MS Windows computer system (Compaq) . Intensities of the signals were quantified by the same ImageQuant program following the manufacturer' s instructions . DNA sequencing and sequence analysis Dideoxynucleotide chain termination DNA sequencing method was used to sequence DNAs. One microliter of DMSO was always included to reduce the DNA template secondary structures that may interfere with the Sequenase (USB) enzymatic activity. The sequences were resolved on 8% sequencing gel (National Diagnostics) . The DNA sequences were stored into a local computer mainframe (mbcrr.harvard.edu), and analyzed by a sequence analysis software package (Genetics Computer Group) . Fusion protein expression and purification Rat APEG-1 cDNA was cloned into pFLAG-2 vector, then transformed into E. coli BL21 cells. Transformed BL21 cells were grown in large scale to an optical density (OD 595 ) of 1.75. The cell pellet was resuspended in extraction buffer (20 mM TrisCl, pH 7.4, 0.2 mM EDTA, 1 M NaCl, 1 mM PMSF, 1 mM DTT) and sonicated on ice, after which the extract was frozen and thawed three times in liquid nitrogen and a 42 °C water bath. The soluble cell extract was collected by centrifugation (12,000 x g, 4°C, 20 minutes) and used in purification of the fusion protein by affinity chromatography with a M2 anti-FLAG peptide mAb affinity column. The column, loaded twice with the soluble cell extract, was washed sequentially with 50 ml of each of the following solutions, TE/NaCl/NP-40 buffer (20 mM TrisCl pH 7.4 , 0.2 mM EDTA, 150 mM NaCl, 0.5% NP-40), TE/NaCl buffer (20 mM TrisCl pH 7.4, 0.2 mM EDTA, 150 mM NaCl), and TE buffer (20 mM TrisCl pH 7.4, 0.2 mM EDTA). The FLAG-APEG-1 fusion protein was eluted with 10 ml glycine buffer (0.1 M glycine, pH 3.0) and the eluates were slowly collected in 0.8 ml fractions into microfuge tubes containing 50 μl 1 M TrisCl, pH 8.0, and 150 μl 5 M NaCl solutions. The purity of the purified fusion proteins was assayed by protein electrophoresis and Coomassie blue staining as well as western blotting with anti-FLAG mAb. Protein gel electrophoresis and western blotting: A 10% tricine-SDS-polyacrylamide gel system was used to separate bacterial-expressed pFLAG-APEG-1 fusion protein (Schagger, H. et al . , 1987, Anal. Biochem. 166:368-79) . This system was used because a 10% tricine-SDS- polyacrylamide gel has superior resolution for proteins less than approximately 14 kDa compared to a standard glycine-SDS-polyacrylamide gel. After electrophoresis, the protein gel was assembled in a semi-dry transfer apparatus (Hoefer) and the protein samples were transferred onto a PVDF membrane (Millipore) in transferring buffer (25 mM Tris base, 200 mM glycine, 20% methanol) at 125 mA for one hour. In vi tro transcription and translation Rat APEG-1 cDNA was cloned into the pSP72 vector and linearized so that RNA could be transcribed from its upstream T7 promoter with the T7 RNA polymerase . Transcription was carried out in a large-scale T7 transcription system (Novagen) in the presence of 7- me GpppGTP to produce capped mRNA. The in vi tro transcribed mRNA was translated in an in vi tro translation system of wheat germ extract (Promega) with the [ 35 S] -methionine to produce radiolabeled proteins. Cellular localization The expression plasmid c-myc-rAPEG-l/pCR3 was constructed by adding in frame a DNA sequence encoding a c-Myc peptide tag (EQKLISEED) to the rat APEG-1 open reading frame at the 5 'end by PCR techniques known in the art (any other detectable peptide can be used as a tag to localize APEG-1) . This hybrid DNA fragment was then cloned in to the eukaryotic expression vector pCR3 (Invitrogen, San Diego, CA) . COS-7 cells were transiently transfected with the c-myc-rAPEG-1 expressing plasmid by a standard DEAE- dextran method (e.g., the method described in Tan et al . , 1994, Kidney Intern. 46:690). The U-2 OS cells were transiently transfected by the calcium phosphate method known in the art. Twenty-four hours after transfection, cells were transferred to two-well chamber slides. The cells were fixed with 4% paraformaldehyde in PBS after growing for an additional twenty-four hours. Immunostaining was performed with an anti-c-Myc monoclonal antibody (9E10, Oncogene, Cambridge, MA) followed by a rhodamine-conjugated goat anti-mouse IgG secondary antibody (Sigma, St. Louis, MO). Nuclear DNA counterstaining was performed with Hoechst 33258 at a concentration of 1 μ/ml . Cell culture Primary rat aortic smooth muscle cells were maintained in DMEM medium supplied with 10% fetal calf serum, 4 mM L-glutamine, 10 mM HEPES, 100 U/ml penicillin and 100 ng/ml streptomycin. Primary rat microvascular endothelial cells were maintained in DMEM medium supplied with 20% fetal calf serum, 4 mM L-glutamine, 100 U/ml penicillin and 100 ng/ml streptomycin. BAEC were isolated and cultured in Dulbecco's modified Eagle's medium (JRH Biosciences, Lenexa, KS) supplemented with 10% fetal calf serum (HyClone, Logan, UT) , 600 μg of glutamine/ml, 100 units of penicillin/ml, and 100 μg of streptomycin/ml. HepG2 human hepatoma cells (ATCC HB-8065) , U-2 OS human osteosarcoma cells (ATCC HTB-96) , HeLa human epidermoid carcinoma cells (ATCC CRL-7923) , HepG2 human hepatoma cells (ATCC HB-8065) , and NIH 3T3 mouse fibroblasts (ATCC CRL-1658) are available from the American Type Culture Collection. Plasmid DNA purification The mini- (<20 μg) and midiscale (<200 μg) preparations of plasmid DNA were purified by DNA-affinity chromatography (Qiagen) . Large scale purification of plasmid DNA was carried out according to the alkaline lysis/CsCl ultracentrifugation methods (Ausubel, F.M., et al . , ed. Current Protocols in Molecular Biology, ed. K. Janssen., 1994, Vol. 1, Current Protocols: 1.7.1-11). Purification of recombinant λgtll DNA Single positive plaques were picked and soaked in the suspension medium (0.1 M NaCl, 10 mM MgS0 4 , 50 mM TrisCl, pH 7.5, and 0.01% gelatin) with one drop of CHC1 3 . Freshly prepared E. coli strain Y1090 competent cells were mixed and incubated briefly with the resuspended phage . The infected cells were grown overnight in LB medium with 10 mM MgS0 4 and 0.2% maltose. The next morning one drop of chloroform was added into the medium to lyse the bacterial cells for 15 minutes. Bacterial debris was collected by centrifugation, and to the clear supernatant 100 U DNase I and 100 ng RNase A were added to digest E. coli genomic DNA and RNA. The solutions of EDTA, TrisCl (pH 8.0), NaCl, and proteinase K were added subsequently to final concentrations of 50 mM, 100 mM, 200 mM, and 100 ng/ml, respectively. The mixture was incubated at 42 °C for 30 minutes. Phage DNA was then phenol/chloroform extracted once and precipitated by adding 0.6 x volume of isopropanol in the presence of 300 mM NaOAc . Precipitated phage DNA was recovered by centrifugation and washed with 70% ethanol, air dried, then dissolved in 250 μl TE buffer (10 mM TrisCl, pH 8.0, 1 mM EDTA) . Cloning APEG-1 genes To clone genes that are preferentially expressed in the aorta, total organ RNA was prepared from rat aorta with the adventitia removed, and from brain, skeletal muscle, esophagus, heart, and intestine. Using the differential mRNA display technique, a technique that systematically amplifies mRNAs by means of RT-PCR with different sets of 5' arbitrary primers and 3' oligo-dT anchoring primers, the mRNA patterns of different organs were compared. The PCR products were resolved on a denaturing polyacrylamide sequencing gel to display mRNA patterns that distinguish one organ from another. The bands that were separated by gel electrophoresis represent the 3 '-termini of the cDNAs . Therefore, a band that is present in one organ but not in the others suggests that the gene is only expressed in that particular organ (Fig. 1) . Specific mRNAs that were present solely in the aorta were identified and cloned. The organ RNAs were screened with thirty-three 5' arbitrary primers in combination with a T 12 VG 3' oligo-dT anchoring primer. This initial screening covered 21 percent of the 160 primer combinations needed to screen all possible mRNAs to be displayed by this technique. This estimate is based on the assumption that one primer combination displays about 100 different mRNAs from approximately 15,000 different mRNA species present in each cell. From the initial screening, seventeen bands that were present solely in the aorta were identified. These bands were cut from the gel and the cDNA fragments eluted and reamplified by PCR with the same primers that were used in their original RT-PCRs. These reamplified cDNAs were 32 P-labeled, then used in Northern blot analyses to confirm their aortic specificity. Four cDNA fragments were found to be aorta-specific (Figs. 2A - 21) . After cloning these four cDNA fragments by TA-cloning methods, the clones were designated APEG-1, APEG-2, APEG-3, and APEG-4. Their DNA sequences were determined by the dideoxynucleotide chain termination method and compared to known DNA sequences listed in the GENBANK ® database. APEG-2 showed identical sequences to the rat SM22 gene (Shanahan, CM., et al . , 1993, Circ . Res. 73 (1) : 193-204) , a smooth muscle cell specific gene. APEG-4 was found to have a near- identical sequence to chicken and mouse TIMP-3 genes (tissue inhibitor of metalloproteinase-3) (Sun, Y., et al . , 1994, Cancer Res. 54:1139-44; Leco, K.J., et al., 1994, J. Biol . Chem. 269 (12) : 9352-60) . APEG-1 and APEG-3 did not match any known genes. Further examination of the tissue distribution of expression showed that APEG-3 was also expressed in the lung, a result not seen in the initial Northern blot analysis. In contrast, APEG-1 showed the highest expression in the aorta among twelve rat organs (Figs. 3A - 3D), thus confirming the specificity of tissue expression. Cloning and sequence analysis of rat APEG-1 cDNA The APEG-1 3' cDNA fragment, derived from differential mRNA display, was used to screen a rat aortic cDNA library (Fig. 4) . The cloned APEG-1 cDNA was determined to be 1,308 base pairs, consistent with the size of the message seen in Northern blot analysis. Sequences of both cDNA strands were determined by dideoxynucleotide chain termination sequencing with fragment-subcloning and oligonucleotide-walking strategies. The complete cDNA sequence had no homologous counterpart in the GENBANK ® database. The rat APEG-1 cDNA can then be used to screen a genomic library to obtain the vascular cell -specific promoter sequences which regulate expression cell- specific expression of APEG-1. To analyze the protein encoded in APEG-1 cDNA, the sequence was searched for possible ATG initiation codons for translation from the 5' end of the sequence. The longest open reading frame in the rat APEG-1 cDNA (SEQ ID NO:l) spans from 169 to 511 nucleotides (SEQ ID NO:2) downstream of the 5' end of the cDNA. Another ATG sequence was found at nucleotide 102 to 104 (Fig. 5) , but the possible translation from this preceding ATG codon is terminated after four amino acid residues, thus making it unlikely to be the initiation codon used in vivo . The longest open reading frame has a Kozak consensus sequence (Kozak, M., 1987, J. Mol . Biol. 196:947-50) and encodes a protein of 113 amino acids (SEQ ID NO: 3) with a predicted molecular weight of 12,667 daltons and an estimated pi of 9.125 (Fig. 6). This predicted translation product was confirmed by in vi tro transcription and in vi tro translation of the APEG-1 cDNA, which yielded a major translation product of 12.7 kDa as predicted by the deduced amino acid sequence from the longest open reading frame (Figs. 7A - 7B) . Comparison of the APEG-1 deduced amino acid sequence to the SwissProt protein database again showed no identical protein sequence. However, a region was identified that is homologous to proteins of the myosin light chain kinase family, which includes myosin light chain kinases and telokin (Fig. 8) . The myosin light chain kinases (MLCKs) , present in all eukaryotic cells, are members of the Ca 2+ -calmodulin-dependent protein kinases. They phosphorylate the 20 kDa light chain subunit of myosin, a protein that is important in regulating contraction of smooth muscle cells, secretory vesicle movement, cellular locomotion, and changes in cellular morphology (Gallagher, P.J., et al . , 1991, J. Biol. Chem. 266 (35) :23945-52) . The structure of MLCKs is highly conserved and composed of several modular domains . The MLCK carboxyl terminus is the calmodulin-binding domain and has a regulatory function mediated by two specific serines residues which become phosphorylated by cAMP-dependent protein kinase. Phosphorylation at these two sites downregulates MLCK kinase activity by decreasing the affinity of MLCK for Ca 2+ -calmodulin. One of the two phosphorylated serine residues in the MLCK C-terminus is conserved in APEG-1 (Serl2) , suggesting a regulatory site of APEG-1. Telokin, originally purified as an acidic protein from turkey gizzard, is a protein that has the same peptide sequence as the carboxyl terminal domain of MLCKs. Its mRNA transcription initiates from a promoter that is located in one of the MLCK introns . Telokin transcription regulation is independent from that of MLCK despite having a sequence identical to the MLCK carboxyl terminal domain. Telokin has been proposed to be a calmodulin-binding protein (Holden, H.M. , et al . , 1992, J. Mol . Biol. 227:840-51), and it is expressed in almost every smooth muscle cell, except in the aortic smooth muscle cell. It is not expressed in any non-muscle cells (Gallagher, P.J., et al . , supra) . When the APEG-1 polypeptide sequence was compared with those of MLCKs, there was a 33% identity at the amino acid level. However, several lines of evidence indicate that APEG-1 is not a rat homologue of a MLCK. First, peptide sequence comparison of APEG-1 to rat smooth muscle MLCK has only 24% identity, significantly less than the identity between APEG-1 and rabbit or chicken MLCKs. Second, the APEG-1 protein is predicted to be a basic protein, whereas the telokin protein is acidic. Third, rabbit telokin is not expressed in the aorta, in contrast to the specific expression pattern of APEG-1. When the APEG-1 protein was analyzed to identify sequence motifs, several residues were identified as capable of being phosphorylated by protein kinase C and casein kinase-2. An arg-gly-asp (RGD) peptide sequence was found at position 90-92. This motif is present in many proteins involved in cell adhesion as well as signaling, and it interacts with its cell surface receptor, an integrin (Hynes, R.O., 1992, Cell 69:11-25, Ruoslahti, E., et al . , 1987, Science 238:491-6). This observation suggests that APEG-1 protein plays role in cell signaling. The motif of two cysteine residues, four residues upstream and six residues downstream of the integrin-binding RGD sequence, are also conserved in the disintegrins, a family of platelet aggregation inhibitors found in snake venom (Blobel, C.P., et al . , 1992, Curr. Opin. Cell. Biol. 4:760-5). The cysteine residue 6 residues downstream of the RGD sequence was also found to be present in the APEG-1 protein. Cloning of mouse APEG-1 The mouse cDNA encoding an APEG-1 open reading frame was first amplified from mouse aortic RNA by reverse transcription polymerase chain reaction (RT-PCR) with primers conserved between the rat and human sequences. Using nested primers designed according to the open reading frame of mAPEG-1, the 3' end of the mouse cDNA was obtained by 3' RACE. Both strands of the entire mouse APEG-1 cDNA were sequenced at least once by the dideoxy chain termination sequencing method. Northern and Genomic Southern Analyses of APEG-1 The APEG-1 full length cDNA was used as the probe to hybridize a 12 -organ RNA Northern blot. In addition to the 1.3 kb message that appeared in the aorta, two other much larger messages (10-20 kb) were observed in skeletal muscle, esophagus, and heart. These two large messages were not initially identified by the APEG-1 3 '-probe; therefore, it is likely the 5' sequence of APEG-1 cDNA hybridized to these new signals. To test this possibility further, three different probes from the 5', the middle, and the 3' portions of the APEG-1 cDNA sequence were used in Northern analysis (Fig. 9A) . The result indicated that these 10-20 kb messages were recognized by the 5' but not by the 3' portion of the APEG-1 cDNA (Figs. 9B-9D) . To determine the relationship of the 1.3 kb aortic transcript and the larger transcripts, a series of probes spanning the APEG-1 gene was used in Northern blot hybridization analyses of RNA isolated from rat aorta, heart, and skeletal muscle. This analysis revealed that the APEG-1 gene defines a muscle cell-specific protein family that encodes both smooth muscle cell-specific proteins and striated muscle cell-specific proteins. The APEG-1 transcripts were detected only in aortic RNA. The large transcripts correspond to variant isoforms, which have been named SPEGs . SPEGs are detected in striated muscle RNA (skeletal and cardiac tissue) but were not seen in aortic RNA. The patterns of exon usage in APEG-1 and SPEGs are shown in Figs. 19A-C. The APEG-1 gene spans 4.5 kb and is composed of five exons and four introns. SPEG- specific probes detect transcripts 10 and 12 kb in size that are composed of at least seven exons. Three of these exons are shared with the APEG-1 gene, while at least four are unique. The first exon of APEG-1 is separated from the closest upstream SPEG exon by 7 kb. The differential tissue expression patterns of APEG-1 and SPEG arise from utilization of different promoters, alternative splicing, or a combination of the two mechanisms . The partial nucleotide and amino acid sequences of human SPEG are shown in Fig. 20 and Fig. 21, respectively. The partial nucleotide and amino acid sequences of mouse SPEG are shown in Fig. 22 and 23, respectively. A comparison of the human and mouse partial SPEG amino acid sequences is shown in Fig. 27. Chromosomal location of the APEG-1 gene The APEG-1 gene was mapped to human chromosome 2q33-34, which is a region containing several genes involved in cardiovascular disease. Identification of APEG-1 associated sequences conferring vascular smooth muscle cell gene expression To determine whether a smooth muscle cell specific promoter exists 5' to the first APEG-1 exon, a 3.3 kb APEG-1 5' flanking sequence was used in a reporter gene transfection analysis using the luciferase reporter plasmid pGL3-C. As shown in Figs. 24A-B, a high level of promoter activity directed by the APEG-1 5' flanking sequence was detected in both rat aortic smooth muscle cells human aortic smooth muscle cells. In contrast, as shown in Fig. 24A-B, minimal activity was detected in five non-smooth muscle cell types, including human cell lines HeLa, HepG2 , and U-2 OS. The sequences responsible for directing a high level of promoter activity have been further localized within the 3.3 kb fragment to the 2.7 kb sequence shown in Fig. 25. APEG-1 sequences able to confer vascular smooth muscle cell specific gene expression have been still further localized within the 2.7 kb sequence to a 73 nucleotide sequence (SEQ ID NO:20) shown in Fig. 28. The sequence corresponds to nucleotides 2666 to 2738 of the sequence shown in Fig. 25 (SEQ ID NO:17), and to nucleotides +4 to +76 of the APEG-1 transcript, wherein +1 is the first transcribed nucleotide as determined by RNAse protection assays and 5 ' RACE PCR amplification. The 73 nucleotide sequence includes two AP-2 binding motifs and one E-box binding motif. To demonstrate its ability to confer VSMC specific transcription, the 73 bp sequence was cloned in both orientations into the Smal site of the pGL3 -Promoter to generate pGL3-Elbox and pGL3-ElEbox.Rev, respectively. The pGL3-Elbox and pGL3-ElEbox.Rev constructs are shown schematically in the left-hand portion of Fig. 29. The APEG-1 derived sequence is shown as a filled oval, to denote the E-box containing region, and with an arrowhead to indicate the relative orientation of the 73 bp sequence in the two plasmids. Both plasmids in addition contain a promoter (P) derived from SV40. Also shown in the schematic diagram are control constructs pGL3-Promoter, which contains the SV 40- derived promoter (P) but lacks an enhancer element, and pGL3 -Control, which contains the SV40 promoter (P) and an SV40 enhancer region (En) . The SV40 enhancer region is able to direct transcription in a variety of cell types. The constructs were each transfected into rat aortic smooth cells (RASMC) , U-2 OS, HeLa, and BAEC cells. Their ability to activate transcription of the SV40 promoter was determined by measuring luciferase activity. The luciferase activity for each construct in the respective cell types is shown in the right-hand portion of Fig. 29. For the data shown, luciferase activity was measured in each cell type as a percent of the luciferase activity of the pGL3 -Control . Each bar represents the mean ± SEM. In all of the cell types examined, the PGL3- Promoter construct demonstrated negligible luciferase activity. In contrast, the pGL3 -Control plasmid, which contains the SV40 enhancer, was active in all cell lines. Both pGL3-El Ebox and pGL3-El Ebox.Rev expressed levels of luciferase activity comparable to control pGL3 -Control only in RASMC. The promoters directed little or no luciferase in the U2-0S, HeLa, or BAEC cell lines. These results demonstrate that the 73 bp sequence from APEG-1 activates RASMC-specific transcription in an manner that does not depend on the orientation of the 73 bp sequence with respect to the SV40 promoter. The 73 bp sequence was further characterized in gel mobility shift assays for binding activity upon incubation with nuclear extracts. Studies were done using two 18 bp double-stranded oligonucleotides derived from the mouse APEG-1 exon 1 sequence. One 18-mer oligonucleotide, named the E oligonucleotide, had the sequence 5'- GGGCCTCAGCTGGGTCAG-3 ' (SEQ ID NO:21). This sequence corresponds to the E box motif in the 73 bp fragment, as well as 6 nucleotides upstream and downstream of the E box. The second oligonucleotide, named the Emut oligonucleotide, had the sequence 5'- GGGCCTCAGCACGGTCAG-3' (SEQ ID NO: 22). The Emut oligonucleotide was identical in sequence to the E oligonucleotide except that the nucleotide TG in the E box sequence changed to AC in the corresponding positions in the Emut sequence . Each oligonucleotide was end-labeled with [γ- 32P]ATP and incubated with or without RASMC nuclear extract. Omission of RASMC nuclear extract resulted in each labeled oligonucleotide migrating at the positions expected for the free oligonucleotide. Incubation of the E oligonucleotide with the RASMC extract retarded the mobility of the oligonucleotide relative to its migration as a free nucleotide. No altered mobility was observed if the labeled E oligonucleotide was incubated with RASMC nuclear extract in the presence of a 100-fold molar excess of unlabeled E oligonucleotide. In contrast, an altered mobility was still observed following incubation of the labeled E oligonucleotide with RASMC nuclear extract in the presence of a 100-fold molar excess of unlabeled Emut oligonucleotide, or with an unlabeled oligonucleotide having a sequence unrelated to the E oligonucleotide. No altered mobility was observed upon incubation of labeled Emut oligonucleotide and the RASMC nuclear extract. These results show that the Ebox-containing motif binds to one or more components of RASMC nuclear extracts in a sequence-specific manner. Binding to the 73 nucleotide region by a component of RASMC nuclear extracts was also determined in a DNase I footprint assay. An APEG-1 genomic DNA sequence corresponding to the nucleotides from -132 to +76 bp was radiolabeled at either the 5' or 3 ' end with Klenow fragment and [o;- 32 P] dNTP . The end-labeled probes were incubated with either bovine serum albumin (BSA) or RASMC nuclear extract and subjected to varying amounts of DNasel digestion. Incubation with RASMC nuclear extract resulted in protected regions corresponding to the AP2 and Spl binding motifs in the APEG-1 genomic sequence. No protection of these regions were observed upon incubation with BSA. The AP2 and SP1 regions were similarly protected when the DNAsel studies were performed on a fragment having nucleotides -490 to +76 of the genomic APEG-1 sequence. Together, the DNAse I footprint studies reveal that VSMC nuclear extracts have one or more components that bind to the APEG-1 promoter region. A series of 3' deletion constructs based on constructs containing nucleotides -479 to +76 of the 5' APEG-1 region, or nucleotides -122 to +76 of the 5' region (p(-479/+76) and p(-122/+76), respectively) were constructed to further localize the positive cis-acting element and to confirm the presence of the 76-bp exon 1 sequence was important for promoter activity. The constructs were transfected into RASMC and the amount of luciferase activity relative to luciferase generated by a p(-2663/+76) construct determined. The results are shown in Fig 30. Four 5' deletion constructs (p-1073/+76) , p(- 479/+76) , p(-355/+76) and p(-122/+76) were made from p (-2663/+76) . The results demonstrate that most of the APEG-1 promoter activity is contained within p(-122/+76). Two 3' deletion constructs p(-479/+38) and p(-122/+38), which were made from p(-479/+76) and p(-122/+76), showed minimal promoter activity. The p (-479/+76) Emut and p (-122/+76) Emut constructs contain a 2-bp mutation that changes the E box motif in exon 1 from CAGCTG to CAGCAC . The diagram on the left of Fig. 30 shows the relative lengths of the constructs and the positions of the CArG boxes (white boxes) and the E box (black ovals) . The E box mutation is indicated by the hatched ovals. Transfection experiments were repeated at least three times for each construct, and promoter activity is expressed as a percentage of p(-2663/+76) activity. In comparison with p(-479/+76), sequence including -479 to +38 of the APEG-1 5' region or -122 to _38 of the 5' region both had much lower promoter activity (16% and 4%, respectively) These results demonstrate that the sequence between bp +38 and +76 (SEQ ID NO: 23) in exon 1 is essential for APEG-1 promoter activity. The sequence of SEQ ID NO is shown in Fig. 31 as the sequence defined open triangles at nucleotides +38 and +76. The sequence between bp +38 and +76 includes an E box motif (CAGCTG) at bp +39 to +44 (Fig. 31) . To determine if this sequence is required for activity, a construct was prepared in which CAGCTG sequence was altered to CAGCAC in the constructs p(-479/+76) and p(-122/+76) . As demonstrated by transfection experiments with ( -479/+76) Emut and (-122/+76) Emut , mutation of the exon 1 E box motif caused a dramatic reduction in APEG-1 promoter activity (Fig. 30) . These data show that this E box motif located at the 5 ' -untranslated region (5'-UTR) is essential for high-level APEG-1 promoter activity in RASMC. Although not commonly found, transcription regulatory elements have been documented to locate to the 5'-UTR of a few other genes. For instance, the 5'-UTR of the herpes simplex virus type 1 ICP22 gene and the human integrin β3 gene have been reported to contain cis-acting elements that mediate high-level expression of these genes (Greco et al . , J. Gen. Virol. 75:1693-1702, 1994; Wilhide et al . , Blood 90:3951-61, 1997). Furthermore, the human A γ-globin gene also has regulatory elements in the 5'-UTR. One of these elements binds to the erythroid transcription factor GATA-1 and may regulate transcription of the human A γ-globin gene during development (Amrolia et al . , J. Biol. Chem. 270:12892- 12898, 1995) . It is noteworthy that one CArG box and one Carg-like box are located at bp -1531 to -1522 and bp -443 to -434 of the APEG-1 5' -flanking region, respectively. The Carg box is crucial to the expression of several other SMC-specific genes (Kim et al . , Mol . Cell. Biol. 15:2266-2278, 1997; Herring et al . , Am. J. Physiol. 272 :C1394-1404 , 1997; Shimizu et al . , J. biol. Chem. 270:7631-43; Madsen et al . , J. Biol. Chem. 272:6332-6340, 1997), although there is no known SMC-specific, Carg box-binding protein. In the case of the APEG-1 promoter, however, deletion of the Carg and Carg-like boxes did not alter its activity (Fig. 30), indicating that the two boxes are dispensable. This dispensability distinguishes APEG-1 from other SMC-specific genes and suggests the existence of Carg- independent mechanisms of SMC-specific gene expression. Indeed, the Carg-less promoter of mouse CRP2/SmLIM has been shown to direct a high level of VSMC-specific reporter gene expression in transgenic mice (Yet et al . , J. Biol. Chem. 273:10530-37, 1998). Sequences capable of directing striated muscle specific expression of the SPEGs exons are determined by performing the above-described cell transfection assays using sequences 5' to the first SPEG exon. Identification of a transcriptional repressor sequence in the 5' region of the APEG-1 gene The expression of APEG-1 is down-regulated in dedifferentiated VSMC both in vivo and in vi tro . Thus, it was unexpected that the 2.7 kb (SEQ ID NO: 17) of the APEG-1 5' -flanking region directed high levels of promoter activity in cultured, and therefore dedifferentiated, RASMC. One explanation for this anomaly is the presence of negative DNA regulatory elements outside the 2.7-kb APEG-1 5 '-flanking sequence. To test this possibility, plasmids p(-3336/+76) and p (-3336/+76) Rev were constructed by cloning an additional 685 bp of APEG-1 5 '-flanking sequence into p(- 2663/+76) , in both orientations. The nucleotide sequence -3336 to +76 (SEQ ID NO:24) is shown in Fig. 31 at the open triangles at these nucleotide positions. As is shown in Fig. 32, the promoter activity of p(-336/+76) and p (-3336/+76) Rev was only 20% of the activity of the 2.7-kb APEG-1 promoter construct p (-2663/+76) . An additional (upstream) 4-kb DNA sequence did not further decrease promoter activity. These results reveal that an orientation- independent transcription repressor is located between bp -3336 and - 2663 (SEQ ID N0:24) . Expression of APEG-1 and SPEG in mouse development The full-length APEG-1 cDNA was used to probe RNA isolated from mouse embryos at different times in embryonic development . RNA was isolated from the entire embryo for these experiments. The APEG-1 probe hybridized to a 1.3 kb RNA from embryos beginning 9.5 days post-coitus (p.c.) and continuing to 20 days p.c. Strong hybridization was observed to RNA from embryos 11.5 to 20 days p.c. APEG-1 transcript levels were also examined post- natally in RNA isolated from rat heart tissue. Hybridization to the APEG-1 probe was detectable in RNA from two-day old rats, but only faint hybridization was detected in RNA from rats aged 14 and 28 days. In si tu hybridization experiments of post-natal heart tissue using the APEG-1 probe also revealed a decreased level of APEG-1 RNA. Interestingly, as APEG-1 RNA levels decreased, the levels of SPEG RNAs in striated muscle increased. When considered with the tissue specific expression data, these results suggest that APEG-1 transcript levels are high during embryonic development, particularly at day 11.5 p.c. and thereafter. Post- natally, APEG-1 transcript levels, e.g., in cardiac muscle, was generally found to decrease. As global APEG- 1 levels decreased, SPEG transcript levels in striated muscle cells increased. Southern blot analysis suggested that APEG-1 has a single copy in the rat genome, because there was only one 17.1 kb band in the EcoR I -digested rat genomic DNA (Fig. 10) . This result further indicated that the large messages are unlikely to be products of other genes, unless these other genes are closely linked with APEG-1 without any intervening EcoR I sites. From the APEG-1 cDNA sequence two BamH I and one Hind III site were located (Fig. 9A) . This correlated with the Southern analysis data in that three bands (18.7, 2.4, and 1.4 kb) in BamH I- and two bands (12.0 and 6.4 kb) in HindiII - digested genomic DNA were identified. Cloning of the human APEG-1 cDNA The APEG-1 cDNA probe was used to screen a human λgtll aortic 5' -stretch cDNA library (Clontech) . Four positive clones were purified, and the insert cDNA was sized by EcoRI digestion of the phage DNA and sequenced. The sequence of the human APEG-1 cDNA and the predicted amino acid sequence of the open reading frame encoding human APEG-1 are shown in Fig. 16 and Fig. 17, respectively. The human APEG-1 cDNA can then be used to screen a genomic library to obtain the vascular cell-specific promoter sequences which regulate expression cell- specific expression of APEG-1. Comparison of the human, mouse, and rat APEG-1 peptide sequences Fig. 26 shows the aligned human, mouse, and rat APEG-1 peptide sequences, along with a derived consensus sequence (SEQ ID NO: 12, 18, 13, and 19) . A comparison of the human and rat open reading frames revealed 90% identity at the cDNA level and 97% identity at the amino acid level . Comparison of the open reading frames of mouse and rat APEG-1 revealed 95% identity at the cDNA level and 98% identity at the amino acid level. Thus, APEG-1 is highly conserved across species. Deposit A plasmid containing DNA encoding rat APEG-1 (rat APEG-1 cDNA in pSP72 vector) has been deposited with the American Type Culture Collection (ATCC) under the terms of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure on March 3, 1995, and bears the accession number ATCC 97071. A plasmid containing DNA encoding human APEG-1 (human APEG-1 cDNA in pUC18 vector) was deposited with the American Type Culture Collection under the terms of the Budapest Treaty on June 1, 1995, and bears the accession number ATCC 97180. A deposit of a plasmid clone containing 2.7 kb of 5' flanking sequence of the mouse APEG-1 gene was deposited with the ATCC. on Feb. 5, 1997. Applicants' assignee, President and Fellows of Harvard College, acknowledges its duty to replace the deposit should the depository be unable to furnish a sample when requested due to the condition of the deposit before the end of the term of a patent issued hereon, and its responsibility to notify the ATCC of the issuance of such a patent, at which time the deposit will be made available to the public. Prior to that time, the deposit will be made available to the Commissioner of Patents under the terms of CFR §1.14 and 35 U.S.C. §112. The absence of APEG-1 expression in primary culture cells As discussed above, APEG-1 was initially identified in adventitia-removed aortic tissue, a tissue composed of smooth muscle cells and endothelial cells. To identify which of these two cell types express APEG-1 gene, total RNAs were harvested from primary cultured rat aortic smooth muscle cells and microvascular endothelial cells, both at the second passage, and these RNAs were used in Northern analysis. APEG-1 message was not detected in these cell types (Fig. 12) . It is likely that the in vivo expression of APEG-1 was lost during in vi tro cell culture. These data suggest that APEG-1 expression is strictly growth-regulated, such that its expression is downregulated when cells are growing in vi tro, as has been observed with respect to grasl gene expression (Sal, G.D., et al . , 1992, Cell 70:595-607). Alternatively, since cultured smooth muscle cells are believed to exhibit a dedifferentiated phenotype (Pauly, R.R., et al . , 1992, Circulation 86 (suppl III) :III-68-73) , APEG-1 may be expressed solely in fully differentiated endothelial or smooth muscle cells. Consistent with a role in maintaining a differentiated phenotype, which is characterized by the absence of cell division, microinjected APEG-1 inhibited BrdU uptake in rat arterial smooth muscle cells. APEG-1 expression in vivo was found to be vascular smooth muscle cell- specific, as shown in Fig. 18A and 18B. APEG-1 expression in the balloon injury animal model Since APEG-1 gene expression in vi tro is different from that in vivo, APEG-1 expression in vivo was studied. A balloon injury model of the rat carotid artery, which has been used extensively to study vascular smooth muscle cells in atherogenesis and vascular remodeling (Clowes, A.W., et al . , 1983, Lab. Invest. 49 (2) : 208-15 , Clowes, A.W. et al . , 1985, Circ . Res. 56:139-45), was used to study the expression modulation of APEG-1. In this animal model, the rat left carotid artery was injured by a 2F balloon catheter, intimal arterial endothelial cells completely removed, and the medial smooth muscle cell layer distended. After the carotid injury, formation of the neointima was initiated. This involves smooth muscle cells proliferating and migrating from the media. With this model, medial and neointimal smooth muscle cells reach their respective highest rates of proliferation two days and four days after the balloon injury, declining rapidly thereafter. The total number of smooth muscle cells approaches a maximum and remains constant after two weeks (Clowes, A.W. et al . , 1985, supra) . Total RNAs from rat carotid arteries 2, 5, and 8 days after balloon injury were collected and used in Northern analysis with an APEG-1 cDNA probe. The results showed that APEG-1 is downregulated to 15%-20% of non- injured carotid arteries after 2 and 5 days; the expression recovered to 40% of control after 8 days (Figs. 13A and 13B) . These data suggest that APEG-1 expression is involved in the regulation of smooth muscle cell proliferation and/or migration, and expression has to be suppressed for either or both events to occur. Production and purification of recombinant APEG-1 Recombinant APEG-1 was expressed as a fusion protein and purified by the pFLAG expression system (IBI) and subsequently injected into rabbit to produce antiserum. The rat APEG-1 cDNA was cloned into pFLAG-2 expression vector and used to transform the E. coli BL21 cells. The transformed cells were grown and induced by IPTG (isopropyl-jβ-D-thio- galactopyroside) to express the vector-encoded fusion protein. The FLAG-APEG-1 fusion protein was then purified by anti -FLAG monoclonal antibody affinity chromatography from soluble cell extract, and the purity was monitored by both Coomassie blue staining (Fig. 14A) and Western analysis (Fig. 14B) . APEG-1 cellular localization To determine the cellular localization of APEG-1, a plasmid was generated, c -myc-rAPEG-1/pCR3 , that would express a fusion protein of APEG-1 with an N-terminal c- Myc tag. COS-7 cells were then transiently transfected with the c-.myc-rAPEG-l/pCR3 plasmid and immunostained with a monoclonal anti-c-Myc antibody, 9E10. The c-Myc- tagged protein was expressed predominantly in the nuclei of transfected COS-7 cells. The same result was obtained when U-2 OS cells were used as the host cells. Methods of Diagnosis The invention includes a method of detecting injury in a sample of vascular tissue. A depressed level of APEG-1 would predict a high degree of smooth muscle cell proliferation indicative of vascular tissue injury, e.g., restenosis. The diagnostic method of the invention is carried out by determining the level of APEG-1 gene expression in a tissue, e.g, a vascular biopsy obtained at atherectomy. The level of gene expression may be measured using methods known in the art, e.g., in si tu hybridization, Northern blot analysis, or Western blot analysis using APEG-1-specific monoclonal or polyclonal antibodies. A decrease in the level of APEG-1 expression per cell in the test sample of tissue compared to the level per cell in uninjured control vascular tissue indicates the presence of a vascular injury in the test sample. For example, tissue obtained at atherectomy could be tested for APEG-1 expression, e.g., the level of APEG-1 transcript or protein. A depressed level of APEG- 1 (compared to normal tissue) correlates with a high degree of smooth muscle cell proliferation indicating a high probability of restenosis. Such diagnostic procedures are useful to identify patients in need of therapeutic intervention to reduce or prevent restenosis. Methods of Detecting Specific Types of Muscle Cells Because APEG-1 and SPEG mRNAs are enriched in vascular smooth muscle cells and in striated muscle cells, respectively, the APEG-1 and SPEG nucleic acid sequences can be used as probes to identify these cell types. For example, an APEG-1 specific nucleic acid sequence, e.g., a probe corresponding to an APEG-1 specific exon, is hybridized, using methods well known in the art, to RNA sequences in Northern blot hybridization studies or using in si tu hybridization assays. Reactivity to an APEG-1 specific probe is indicative of a vascular smooth muscle cell tissue. Similarly, a SPEG- specific nucleic acid sequence, e.g., a probe corresponding to a SPEG-specific exon, is used to identify striated muscle cells. APEG-1 and SPEG DNA sequences can also be used to make recombinant APEG-1 and SPEG polypeptides, or fragments thereof. Monoclonal or polyclonal antibodies are then raised to the recombinant polypeptides using methods well-known in the art. The anti-SPEG antibodies are then used, e.g., in western or immunofluorescence experiments, to identify vascular smooth muscle cells, in the case of APEG-1, or striated muscle cells in the case of SPEG. Methods of Therapy Upon vascular injury and other stimuli, cytokines and growth factors from activated vascular cells promote growth and migration of dedifferentiated vascular smooth muscle cells, resulting in atherosclerotic plaques and restenosis. Administration of APEG-1 polypeptide to vascular smooth muscle cells in vitro (by microinjection) resulted in a decrease in DNA synthesis, indicative of a decrease in cellular proliferation. Vascular injury such as that caused during surgery or balloon angioplasty can be treated by administering APEG-1 polypeptides or DNA encoding APEG-1 polypeptides operably linked to appropriate expression control sequences. Other vascular conditions, e.g., atherosclerosis, transplant arteriosclerosis, and diabetes, which are characterized by a decrease in APEG-1 expression (Fig. 15) may be treated in a similar manner. APEG-1 polypeptide, DNA encoding an APEG-1 polypeptide, or compositions which stimulate the APEG-1 promoter may administered to increase the level of APEG-1 polypeptide in the injured vascular tissue and thus inhibit the growth of smooth muscle cells. APEG-1 polypeptides may be administered to the patient intravenously in a pharmaceutically acceptable carrier such as physiological saline. Standard methods for intracellular delivery of peptides can be used, e.g. packaged in liposomes. Such methods are well known to those of ordinary skill in the art. It is expected that an intravenous dosage of approximately 1 to 100 μmoles of the polypeptide of the invention would be administered per kg of body weight per day. The compositions of the invention are useful for parenteral administration, such as intravenous, subcutaneous, intramuscular, and intraperitoneal . Compounds which increase APEG-1 expression, e.g., by inhibiting binding of a trans-acting repressor to a cis-acting repressor sequence (e.g. SEQ ID NO: 24) are administered as described above. DNA (e.g., APEG-1-encoding DNA, DNA including vascular cell-specific promoters (e.g., sequences which hybridize at high stringency to SEQ ID NO: 17, SEQ ID NO:20, or SEQ ID NO:23), SPEG-encoding DNA, and striated muscle cell-specific promoters) and vectors of the invention may be introduced into target cells of the patient by standard vectors and/or gene delivery systems. Suitable gene delivery systems may include liposomes, receptor-mediated delivery systems, naked DNA, and viral vectors such as herpes viruses, retroviruses, and adenoviruses, among others. For example, the DNA under encoding an APEG-1 or SPEG polypeptide under the control of a strong constitutive promoter may be administered locally to a blood vessel during balloon angioplasty using an adenovirus delivery system. A vascular cell -specific promoter or enhancer sequence derived from the APEG-1 gene (e.g., SEQ ID NO: 17, SEQ ID NO: 20 or SEQ ID NO: 23) may be used to direct the expression of APEG-1 or genes other than APEG- 1. Thus, vascular diseases may be treated by administering a vascular cell -specific enhancer sequence of the invention operably linked to a sequence encoding a heterologous polypeptide, e.g., an APEG-1 promoter linked to DNA encoding a growth inhibitor gene such as Rb, p21 or pl8. The DNA may encode a naturally occurring mammalian APEG-1 polypeptide such as a rat APEG-1 polypeptide (SEQ ID NO: 3) or human APEG-1 polypeptide (SEQ ID NO: 12) . For example, the invention includes degenerate variants of SEQ ID NO: 2 or SEQ ID NO: 11. The invention also includes a substantially pure DNA comprising a strand which hybridizes at high stringency to a DNA having the sequence of SEQ ID NO:l, 2, or 11, or the complements thereof . Similarly, a striated muscle cell specific- promoter may be used to direct expression of SPEG or genes other than SPEG. Thus, striated muscle diseases may be treated by administering a striated muscle cell- specific promoter of the invention operably linked to a sequence encoding a heterologous polypeptide, e.g., a SPEG promoter linked to DNA encoding a therapeutic gene, e.g., dystrophin to treat Duchenne's or Becker's muscular dystrophy, or a growth inhibitor gene such as Rb, p21, or pl8, to reduce undesirable proliferation of striated muscle cells. The DNA of the invention may be administered in a pharmaceutically acceptable carrier. The therapeutic composition may also include a gene delivery system as described above. Pharmaceutically acceptable carriers are biologically compatible vehicles which are suitable for administration to an animal e.g., physiological saline. A therapeutically effective amount is an amount of the nucleic acid of the invention which is capable of producing a medically desirable result in a treated animal . As is well known in the medical arts, dosage for any given patient depends upon many factors, including the patient's size, body surface area, age, the particular compound to be administered, sex, time and route of administration, general health, and other drugs being administered concurrently. Dosages for the compounds of the invention will vary, but a preferred dosage for intravenous administration is from approximately 10 6 to 10 22 copies of the nucleic acid molecule. Determination of optimal dosage is well within the abilities of a pharmacologist of ordinary skill. Drugs which stimulate the APEG-1 promoter may also be administered as described above to increase the level of expression APEG-1 in vascular tissue. Such drugs can be identified by contacting the APEG-1 promoter linked to a reporter gene with a candidate compound and measuring the level of expression of the reporter gene in the presence and absence of the compound. An increased level of expression in the presence of the compound compared to that in its absence indicates that the compound stimulates the APEG-1 promoter. The invention also includes cells transfected with the DNA of the invention. Standard methods for transfecting cells with isolated nucleic acid are well known to those skilled in the art of molecular biology. Preferably, the cells are vascular smooth muscle cells, and they express an APEG-1 polypeptide of the invention encoded by the nucleic acid of the invention. Cells of the invention may be administered to an animal locally or systemically using intravenous, subcutaneous, intramuscular, and intraperitoneal delivery methods. Alternatively, prokaryotic or eukaryotic cells in culture can be transfected with the DNA of the invention operably linked to expression control sequences appropriate for high-level expression in the cell. Such cells are useful for producing large amounts of the APEG-1 polypeptide, which can be purified and used, e.g., as a therapeutic or for raising anti -APEG-1 antibodies. Methods of evaluating compounds for binding to the VSMC transcriptional repressor sequence The invention includes methods of evaluating a compound for the ability to bind to a vascular smooth muscle cell cis-acting transcriptional repressor sequence. The cis-acting sequence can include a sequence which hybridizes under high stringency conditions to SEQ ID NO: 24, e.g., a sequence containing SEQ ID NO: 24 itself . The compound can be contacted with a vascular smooth muscle cell cis-acting transcriptional repressor sequence using methods known in the art and the amount of

Claims: binding determined using methods known in the art . For example, altered gel mobility assays can be used to ascertain binding of a test compound to the cis-acting transcriptional repressor sequence. Alternatively, assays that detect altered sensitivity to agents such as DNase or dimethyl sulfate (DMS) in the presence of the test compound can be used. Alternatively, a compound can be evaluated for its ability to bind to a cis-acting transcriptional repressor sequence by providing a vascular smooth muscle cell containing a nucleic acid comprising a vascular smooth muscle cell cis-acting transcriptional repressor sequence which is operably linked to a sequence encoding a reporter molecule. The reporter molecule can be, e.g., luciferase or β-galactosidase . The test compound is then added to the cell, and the amount of the reporter molecule expressed by the cell is measured. An alteration in the level of reporter molecule expressed in the presence of the compound compared to the level in the absence of the compound indicates that the compound binds to a vascular smooth muscle cell cis-acting transcriptional repressor sequence . For example, an increase in the level of transcription of DNA encoding the reporter molecule, or an increase in the amount of molecule expressed, indicates that the test compound inhibits binding of a trans-acting repressor factor in a VSMC to the cis-acting sequence and therefore functions therapeutically to increase expression of APEG-1 and decrease VSMC proliferation. Other embodiments are within the following claims. What is claimed is: 1. A substantially pure DNA comprising a vascular smooth muscle cell (VSMC) specific enhancer sequence operably linked to a polypeptide coding sequence, wherein said enhancer sequence includes a sequence which hybridizes under high stringency conditions to SEQ ID NO: 20, or the complement thereof, and wherein said DNA does not contain the complete nucleotide sequence of SEQ ID NO: 17. 2. The DNA of claim 1, wherein the DNA sequence contains less than 2.6 kb of SEQ ID NO: 17. 3. The DNA of claim 1, wherein the DNA sequence contains less than 2.1 kb of SEQ ID NO: 17. 4. The DNA of claim 1, wherein the DNA sequence contains less than 1.7 kb of SEQ ID NO: 17. 5. The DNA of claim 1, wherein the enhancer sequence is less than 100 nucleotides in length. 6. The DNA of claim 1, wherein the enhancer sequence is less than 50 nucleotides in length. 7. The DNA of claim 1, wherein the enhancer sequence comprises SEQ ID NO: 20. 8. The DNA of claim 1 , wherein the enhancer sequence comprises a plurality of copies of SEQ ID NO: 20. 9. The DNA of claim 1, wherein the enhancer sequence hybridizes under high stringency conditions to SEQ ID NO: 23, or the complement thereof. 10. The DNA of claim 1, wherein the enhancer sequence comprises SEQ ID NO: 23. 11. The DNA of claim 1, wherein the enhancer sequence comprises a plurality of copies of SEQ ID NO:23. 12. The DNA of claim 1, wherein said polypeptide coding sequence does not encode APEG-1. 13. The DNA of claim 1, wherein the enhancer is operably linked to a heterologous promoter. 14. The DNA of claim 1, wherein the polypeptide is chosen from a group consisting of tissue plasminogen activator, p21 cell cycle inhibitor, nitric oxide synthase, interferon-γ, and atrial natriuretic polypeptide . 15. A vector comprising the DNA of claim 1. 16. A method of directing vascular smooth muscle cell-specific expression of a polypeptide, comprising introducing into a vascular smooth muscle cell the vector of claim 15. 17. A substantially pure DNA comprising a cis- acting transcriptional repressor sequence which reduces vascular smooth muscle cell-specific transcription of an operably linked sequence. 18. The DNA of claim 17, wherein the cis-acting transcriptional repressor sequence hybridizes under high stringency conditions to SEQ ID NO: 24. 19. The DNA of claim 17, wherein the cis-acting transcriptional repressor sequence comprises SEQ ID NO: 24. 20. The DNA of claim 17, wherein the DNA is less than 4 kb in length. 21. The DNA of claim 17, wherein the DNA does not include SEQ ID NO: 23. 22. A vector comprising the DNA of claim 18. 23. A substantially pure DNA comprising a sequence encoding a striated muscle-preferentially expressed gene-1 (SPEG-1) polypeptide. 24. The DNA of claim 23, wherein said polypeptide is human SPEG-1. 25. The DNA of claim 24, wherein said polypeptide comprises the amino acid sequence of SEQ ID NO: 14. 26. A substantially pure DNA comprising a nucleotide sequence having at least 50% sequence identity to SEQ ID NO: 13. 27. The DNA of claim 26, wherein said polypeptide is mouse SPEG. 28. The DNA of claim 27, wherein said polypeptide comprises the amino acid sequence of SEQ ID NO: 16. 29. A substantially pure DNA comprising a strand which hybridizes at high stringency to a strand of DNA having the sequence of SEQ ID NO: 13, or the complement thereof . 30. A substantially pure DNA having at least 50% sequence identity to SEQ ID NO: 15, and encoding a polypeptide having the biological activity of a SPEG-1 polypeptide . 31. A substantially pure human SPEG-1 polypeptide. 32. The polypeptide of claim 31, wherein said polypeptide comprises the amino acid sequence of SEQ ID NO: 14. 33. A method of evaluating a compound for the ability to bind to a vascular smooth muscle cell cis- acting transcriptional repressor sequence comprising: contacting the compound with a vascular smooth muscle cell cis-acting transcriptional repressor sequence ; and determining the amount of binding of the compound to the vascular smooth cell cis-acting transcriptional repressor sequence. 34. The method of claim 33, wherein the vascular smooth muscle cell cis-acting transcriptional repressor sequence comprises a sequence which hybridizes under high stringency conditions to SEQ ID NO: 24. 35. The method of claim 33, wherein the vascular smooth muscle cell cis-acting transcriptional repressor sequence comprises SEQ ID NO: 24. 36. A method of evaluating a compound for the ability to bind to a cis-acting transcriptional repressor sequence comprising: providing a vascular smooth muscle cell containing a nucleic acid comprising a vascular smooth muscle cell cis-acting transcriptional repressor sequence operably linked to a sequence encoding a reporter molecule; contacting the cell with the compound; and measuring the amount of the reporter molecule expressed by the cell, wherein an alteration in the level of reporter molecule expressed in the presence of the compound compared to the level in the absence of the compound indicates that the compound binds to a vascular smooth muscle cell cis-acting transcriptional repressor sequence. 37. The method of claim 36, wherein the vascular smooth muscle cell cis-acting transcriptional repressor sequence comprises a sequence which hybridizes at high stringency to SEQ ID NO: 24. 38. The method of claim 36, wherein the vascular smooth muscle cell cis-acting transcriptional repressor sequence comprises SEQ ID NO: 24. 39. A method of evaluating a compound for the ability to bind to increase APEG-1 expression, comprising: providing a vascular smooth muscle cell; contacting the vascular smooth muscle cell with the compound; and measuring the amount of APEG-1 transcript or polypeptide in the vascular smooth muscle cell, wherein an increase in the amount of APEG-1 transcript or gene product indicates the compound increases APEG-1 expression. 40. A method of inhibiting vascular smooth muscle cell proliferation, comprising contacting a vascular smooth muscle cell with a compound which binds to a vascular smooth muscle cell cis-acting transcriptional repressor sequence in an amount effective to inhibit proliferation of the vascular smooth muscle cell. 41. The method of claim 40, wherein the vascular smooth muscle cell cis-acting transcriptional repressor sequence comprises a sequence which hybridizes at high stringency to SEQ ID NO: 24. 42. The method of claim 30, wherein the vascular smooth muscle cell cis-acting transcriptional repressor sequence comprises SEQ ID NO: 24.

Inventors: HSIEH CHUNG-MING, LEE MU-EN, HSIEH, CHUNG-MING, LEE, MU-EN
Applicants: HARVARD COLLEGE, HSIEH CHUNG MING, LEE MU EN, HSIEH, CHUNG-MING, LEE, MU-EN, PRESIDENT AND FELLOWS OF HARVARD COLLEGE
Application year: 1999
Main classification: C12N15
IPC codes: C07H21, C07K14, C12N5, C12N15, C12P21, C12Q1, G01N33