MAMMALIAN PEROXISOME PROLIFERATOR-ACTIVATED RECEPTORS AND USES THEREOF

Abstract: Peroxisome proliferator-activated receptor subunits designated PPAR gamma and PPAR delta are described. Nucleic acid sequences encoding the receptor subunits, expression vectors containing such sequences and host cells transformed with such vectors are also disclosed, as are heterodimeric PPAR receptors comprising at least one of the invention subunits, and methods for the expression of such novel receptors, and various uses therefor.

Description: M A MMALIANPEROXISOME PROLIFERATOR-ACTrVATCD RECEPTORS AND USES THEREOF RELATED APPLICATIONS This application is a continuation-in-part of United States Application Serial Number 08/270,643, now pending, which is a continuation-in-part of United States Application Serial Number 07/907,908, filed July 2, 1992, now abandoned, which is a continuation-in-part of United States Application Serial Number 07/497,935, filed March 22, 1990, now abandoned. FIELD OF INVENTION The present invention relates to novel members of the steroid/thyroid superfamily of receptors, as well as uses therefor. BACKGROUND OF THE INVENTION Peroxisome proliferators are a structurally diverse group of compounds which, when administered to rodents, elicit dramatic increases in the size and number of hepatic and renal peroxisomes, as well as concomitant increases in the capacity of peroxisomes to metabolize fatty acids via increased expression of the enzymes required for the β-oxidation cycle (Lazarow and Fujiki, Ann . Rev . Cell Biol . 1:489-530 (1985); Va ecq and Draye, Essays Biochem . 24:1115-225 (1989); and Nelali et al., Cancer Res . 48:5316-5324 (1988)) . Chemicals included in this group are the fibrate class of hypolipidermic drugs, herbicides, and phthalate plaεticizers (Reddy and Lalwani, Crit . Rev . Toxicol . 12:1-58 (1983)) . Peroxisome proliferation can also be elicited by dietary or physiological factors such as a high-fat diet and cold acclimatization. Insight into the mechanism whereby peroxisome proliferators exert their pleiotropic effects was provided by the identification of a member of the nuclear hormone receptor superfamily activated by these chemicals (Isseman and Green, Nature 347-645-650 (1990)) . This receptor, termed peroxisome proliferator activated receptor alpha (PPARα) , was subsequently shown to be activated by a variety of medium and long-chain fatty acids and to stimulate expression of the genes encoding rat acyl-CoA oxidase and hydratase-dehydrogenase (enzymes required for peroxiεomal β-oxidation) , as well as rabbit cytochrome P450 4A6, a fatty acid w-hydroxylase (Gottlicher et al., Proc . Natl . Acad . Sci . USA 89:4653-4657 (1992) ; Tugwood et al., EMBO J . 11:433-439 (1992); Bardot et al., Bioche . Biophys . Res . Comm . 192:37-45 (1993) ; Muerhoff et al., J . Biol . Chem . 267:19051-19053 (1992) ; and Marcus et al., Proc . Natl . Acad . Sci . USA 90 (12) :5723-5727 (1993) . The foregoing references support a physiological role for PPARα in the regulation of lipid metabolism. PPARα activates transcription by binding to DNA sequence elements, termed peroxisome proliferator response elements (PPRE) , as a heterodimer with the retinoid X receptor. The retinoid X receptor is activated by 9-cis retinoic acid (see Kliewer et al., Nature 358:771-774 (1992), Gearing et al., Proc . Natl . Acad . Sci . USA 90:1440-1444 (1993), Keller et al., Proc . Natl . Acad . Sci . USA 9,0:2160-2164 (1993) , Hey an et al., Cell (58.:397-406 (1992), and Levin et al., Nature 355:359-361 (1992)) . Since the PPARα-RXR complex can be activated by peroxisome proliferators and/or 9-cis retinoic acid, the retinoid and fatty acid signaling pathways are seen to converge in modulating lipid metabolism. BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, there are provided isolated mammalian peroxisome proliferator- activated receptor subunit proteins of the y and δ subtypes, and functional fragments thereof. In addition, there are provided isolated nucleic acids encoding mammalian peroxisome proliferator-activated receptor subunit proteins, as well as fragments thereof. There are also provided vectors containing the above-described nucleic acids, as well as cells containing such nucleic acids and/or vectors. The present invention also provides methods for the recombinant production of mammalian peroxisome proliferator-activated receptor proteins comprising at least one PPAR subunit protein of the y and δ subtype, and functional fragments thereof, as well as methods to identify clones encoding the above-described receptor subunit proteins, and functional fragments thereof. Also provided by the present invention are methods for screening compounds to determine those which bind to mammalian peroxisome proliferator-activated receptor proteins comprising at least one PPAR subunit protein of the y or δ subtype, or functional fragments thereof, as well as bioassays for evaluating whether test compounds are agonists or antagonists for receptor proteins of the invention, or functional modified forms of said receptor protein(s) . BRIEF DESCRIPTION OF THE FIGURES Figure 1 presents a schematic comparison of the members of the PPAR gene family using mPPARS as a reference. Comparisons among the different domains of the proteins are expressed as percent amino acid identity. Figure 2 demonstrates that PPAR}' and PPAR fail to respond to the peroxisome proliferator y 14,643. CV-1 cells were cotransfected with reporter plasmid PPRE 3 -TK-LUC and either no receptor expression plasmid (-) , CMX-PPARα, CMX-PPAR , or CMX-PPAR6 and then incubated in either the absence (-) or presence (+) of 5μM Wy 14,643. Luciferase activities are expressed as percentages of the maximal response where 100% is the activity obtained with PPARα in the presence of 5μM Wy 14,643. Figure 3 illustrates the ability of PPAR and PPAR5 to repress PPARα- ediated responsiveness to Wy 14,643. CV-1 cells were cotransfected with reporter plasmid PPRE 3 -TK-LUC and either no receptor expression plasmid (NONE) or CMX-PPARα (long) in either the absence or presence of CMX-PPAR (lOOng) or CMX-PPAR5 (lOOng) . Cells were then incubated in either the absence (-) or presence (+) of 5μM Wy 14,643. Luciferase activities are presented as fold-activation relative to cells which were not transfected with receptor expression plasmid and were not treated with Wy 14,643. Figure 4 demonstrates that PPAR isoforms are pharmacologically distinct. CV-1 cells were cotransfected with reporter plasmid PPRE 3 -TK-LUC and either no receptor expression plasmid (-) , CMX-PPARα, CMX-PPAR , or CMX-PPAR5 in either the absence or presence of 5μM Wy 14,643 (WY) , 30μM linoleic acid (C18:2), or 30μM LY-171883 (LY) . Luciferase activities are presented as the fold activation achieved in compound-treated versus mock-treated cells. Similar results were obtained in triplicate in three independent experiments. DETAILED DESCRIPTION OF THE INVENTION Two novel PPAR receptor subunits have been cloned and characterized. These novel y and δ isoforms (subunits) together with the α subunit display marked differences in their responsiveness to peroxisome proliferators and fatty acids, as well as differences in their temporal and spatial patterns of expression. These observations suggest a broad role for the PPAR family during development and in adult physiology. The existence of multiple PPAR isoforms with distinct expression patterns has been found to correlate with the fact that the three isoforms have different ligand specificities. Indeed, the PPAR isoforms are shown herein to be pharmacologically distinct. Thus, PPARα, PPAR and PPAR5 are most efficiently activated by Wy 14,643, LY-171883, and linoleic acid, respectively. Remarkably, Wy 14,643, which results in approximately 100-fold induction in reporter expression in the presence of PPARα, fails to activate either PPARK or PPAR6. With regard to this differential responsiveness to activators of peroxisome proliferation, the relationship among the PPAR isoforms may be analogous to that between the glucocorticoid and mineralocorticoid receptors (GR and MR, respectively) . While both receptors can bind to the same response element, and both respond to mineralocorticoids and corticosteroids, MR and GR display differential sensitivities to aldosterone and specific glucocorticoids such as dexamethasone, respectively (Arriza et al.. Neuron 1:887-900 (1988)) . Thus, the ratio of these receptors to their ligands provides a means of determining tissue-specific expression of target genes. Similarly, the existence of multiple PPAR isoforms with overlapping ligand specificities may provide the means for tissue-specific regulation of gene expression by peroxisome proliferators and fatty acids. In addition to their differential responsiveness to peroxisome proliferators, the three PPAR isoforms also display distinct yet overlapping expression patterns. As previously shown, PPARα mRNA is abundant in liver and kidney (Isseman and Green, supra; Beck et al., Proc . R . Soc . Lond . 247:83-87 (1992)), tissues in which peroxisome proliferators result in dramatic increases in the numbers of peroxisomes and concomitant increases in peroxisomal β-oxidation (Nemali et al., supra) . In contrast, the levels of PPARK RNA and PPAR5 mRNA, which can act as dominant repressors of PPARα-mediated responsiveness to Wy 14,643, are low in these tissues. Thus, a pattern emerges in which tissues that are most responsive to peroxisome proliferators such as Wy 14,643 are observed to express high amounts of PPARα mRNA and relatively low amounts of PPARK mRNA and PPAR5 mRNA. These data suggest that the ratio of the PPAR isoforms is likely to play a critical role in establishing the degree of responsiveness of tissues to specific peroxisome proliferators. Widespread expression of PPAR5 is observed in both the embryo and in adult tissues. This observation suggests that this isofor may play a general "housekeeping" role. In contrast, PPARK is observed to be expressed almost exclusively in the adrenal and spleen. The expression of all three PPAR isoforms in the adrenal is particularly intriguing, since diseases which result in peroxisome dysfunction (e.g. adrenoleukodystrophy and Zellweger syndrome) cause gross morphological changes in adrenal cells and, eventually, adrenal deficiency. These observations suggest a critical role for peroxisomes in this tissue (Vamecq and Draye, supra) . Interestingly, peroxisomes can be induced to proliferate in hamster adrenals in response to treatment with adrenocorticotropic hormone and corticosteroids (Black and Russo, Amer . J . Anatomy 159:85-120 (1980)), indicating the presence of adrenal-specific signaling pathway(ε) for peroxisome proliferation. The differential expression of PPARK in the adrenal suggests that this isoform may reεpond to an adrenal-enriched ligand. Accordingly, in accordance with the present invention, there are provided isolated mammalian peroxisome proliferator-activated receptor subunit proteins of the y or δ subtype and functional fragments thereof. Aε employed herein, the phraεe "mammalian peroxiεome proliferator-activated receptor εubunit proteinε of the or δ subtype" refers to isolated and subεtantially purified aε well as recombinantly produced proteins which are members of the steroid/thyroid superfamily of receptors, and which mediate the pleiotropic effects of peroxiεome proliferatorε (such as medium and long-chain fatty acidε) . Such receptors participate in the formation of heterodimeric species with retinoid X receptors (RXRs) and comprise an amino-ter inal domain, a DNA binding domain, and a ligand binding domain. Also contemplated within this definition are variants thereof encoded by mRNA generated by alternative splicing of a primary transcript. Use of the terms "recombinantly produced", "isolated" or "subεtantially pure" in the present specification and claims as a modifier of DNA, RNA, polypeptides or proteins means that the modified subεtances have been produced by the hand of man, and thus are εeparated from their native in vivo cellular environment. Aε a result of this human intervention, the recombinant/ isolated/substantially pure DNAs, RNAs, polypeptides and proteins of the invention are useful in ways that the naturally occurring DNAs, RNAs, polypeptides or proteinε are not, for example, in assays to identify selective drugs or compounds. The novel receptors of the preεent invention also can be included as part of a panel of receptors which are screened to determine the selectivity of interaction of proposed agonists or antagonists of other steroid hormone receptors. Thus, a compound which iε believed to interact selectively, for example, with the glucocorticoid receptor, should not have any substantial effect on any other receptors, including invention receptors. However, if such a proposed compound does interact with the invention receptors, then the probability of side effects caused by the activation of other receptors in addition to the target receptor, is clearly indicated. For example, the use of many drugε in the treatment of hormone-related disorders iε currently restricted by side effects caused by the activation of "non-target" receptors. Employment of the invention receptors in a panel of receptors in a screen to determine the selectivity of interaction of potential ligandε provides a meanε to identify receptor-εpecific ligandε that are therapeutically εuperior than currently used ligands that cauεe unwanted side effects. Aε uεed herein, the term εplice variant referε to variant PPAR encoding nucleic acid(s) produced by differential procesεing of primary transcript(ε) of genomic DNA, resulting in the production of more than one mRNA. cDNA derived from differentially processed primary transcript will encode PPAR receptor proteinε that have regions of complete amino acid identity and regions having different amino acid sequences. Thus, the same genomic sequence can lead to the production of multiple, related mRNAε and corresponding proteins. Both the resulting mRNAs and proteins are referred to herein aε "εplice variants". Accordingly, also contemplated within the scope of the present invention are nucleic acids that encode mammalian PPAR receptor subunit proteins aε defined above, but that by virtue a degenerate genetic code do not necessarily hybridize to the nucleic acidε set forth in SEQ ID NOs: 1 or 3 under specific hybridization conditions. Nucleic acid fragments encoding invention receptor subunit proteins are capable of forming a functional heterodimer with one or more RXR receptor protein isoform(ε) . Typically, unlesε a PPAR receptor protein is encoded by mRNA that arises from alternative splicing (i.e., a εplice variant) , PPAR receptor encoding DNA and encoded protein share substantial sequence homology with at least one of the PPAR receptor-encoding DNAs and encoded proteins described herein. It is understood that DNA or RNA encoding a εplice variant may share less than 90% overall sequence homology with the DNA or RNA provided herein, but include regions of nearly 100% homology to a DNA fragment described herein, and encode an open reading frame that includes start and stop codonε and encodes a functional PPAR receptor protein. Exemplary nucleic acid sequences encoding mammalian peroxisome proliferator-activated receptor subunit proteinε of the y εubtype are represented by nucleotide sequences which encode substantially the same amino acid sequence aε set forth in SEQ ID NO:2. Presently preferred sequences encode the same amino acid sequence as set forth in SEQ ID NO:2. Exemplary nucleic acid sequences can alternatively be characterized as those nucleotide sequences which encode mammalian peroxisome proliferator- activated receptor subunit proteins of the y subtype and hybridize under high stringency conditions to SEQ ID NO:l. Exemplary nucleic acid sequences encoding mammalian peroxisome proliferator-activated receptor subunit proteins of the δ subtype are represented by nucleotides which encode subεtantially the εame amino acid sequence as set forth in SEQ ID NO:4. Presently preferred sequences encode the same amino acid sequence as εet forth in SEQ ID NO:4. Especially preferred sequences are those which have subεtantially the εame nucleotide εequence aε that εet forth in SEQ ID NO:l. Exemplary nucleic acid εequenceε can alternatively be characterized aε those nucleotide sequences which encode mammalian peroxisome proliferator- activated receptor subunit proteins of the δ εubtype and hybridize under high stringency conditions to SEQ ID NO: 3. Eεpecially preferred nucleic acid εequenceε are those which have substantially the same nucleotide sequence as the coding sequences in SEQ ID NO:3. The phrase "stringency of hybridization" iε uεed herein to refer to conditionε under which polynucleic acid hybridε are stable. As known to those of skill in the art, the stability is reflected in the melting temperature (T m ) of the hybrids. T m can be approximated by the formula: 81.5°C - l6.6(log 10 [Na + ]) + 0.41(%G+C) - 600/1, where 1 iε the length of the hybrid in number of nucleotideε. T m decreases approximately 1-1.5°C with every 1% decrease in sequence homology. In general, the stability of a hybrid is a function of εodium ion concentration and temperature. Typically, the hybridization reaction iε initially performed under conditionε of low εtringency, followed by waεheε of varying, but higher, stringency. Reference to hybridization stringency relates to such washing conditions. Thus, as used herein: (1) HIGH STRINGENCY refers to conditions that permit hybridization of only those nucleic acid sequenceε that form stable hybridε in 0.018M NaCl at 65°C (i.e., if a hybrid iε not stable in 0.018M NaCl at 65°C, it will not be stable under high stringency conditions, as contemplated herein) . High εtringency conditionε can be provided, for example, by hybridization in 50% formamide, 5X Denhart'ε εolution, 5X SSPE, 0.2% SDS at 42°C, followed by washing in 0.1X SSPE, and 0.1% SDS at 65°C; (2) MODERATE STRINGENCY refers to conditions that permit hybridization in 50% formamide, 5X Denhart's solution, 5X SSPE, 0.2% SDS at 42°C, followed by washing in 0.2X SSPE, 0.2% SDS, at 65°C; and (3) LOW STRINGENCY referε to conditionε that permit hybridization in 10% formamide, 5X Denhart'ε solution, 6X SSPE, 0.2% SDS at 42°C, followed by washing in IX SSPE, 0.2% SDS, at 50°C. It is understood that these conditionε may be varied using a variety of buffers and temperatureε well known to skilled artisans. As used herein, the phrase "εubεtantial sequence homology" refers to nucleotide sequenceε which share at least about 90% identity, and amino acid sequenceε which typically share more than 95% amino acid identity. It is recognized, however, that proteins (and DNA or mRNA encoding such proteins) containing less than the above- described level of homology arising as splice variants or that are modified by conservative amino acid substitutions (or substitution of degenerate codons) are contemplated to be within the scope of the present invention. As used herein, the phrase "subεtantially the same" referε to nucleotide sequences, ribonucleotide sequences, or amino acid sequenceε, that have slight and non-consequential εequence variationε from the actual εequenceε discloεed herein. Specieε that are "substantially the same" are considered to be equivalent to the discloεed sequences, and as such are within the scope of the appended claims. In this regard, "slight and non- consequential sequence variations" mean that sequenceε that are εubεtantially the εame aε invention εequenceε diεclosed and claimed herein, are functionally equivalent to the sequences disclosed and claimed herein. Functionally equivalent sequenceε will function in εubεtantially the εame manner to produce εubεtantially the εame reεultε aε the nucleic acid and amino acid εequenceε disclosed and claimed herein. Specifically, functionally equivalent nucleic acids encode proteins that have conεervative amino acid variationε, εuch aε substitution of a non-polar residue for another non-polar residue or a charged residue for a similarly charged residue. These changes are recognized by those of skill in the art aε modifications that do not subεtantially alter the tertiary structure of the protein. Fragments of invention nucleic acid sequences are useful as hybridization probes, wherein such fragments comprise at least 14 contiguous nucleotides of the above- deεcribed nucleic acidε, and wherein the fragment iε labeled with a detectable substituent. Suitable detectable substituentε can be readily determined by thoεe of εkill in the art, and include εuch species as radiolabeled molecules, fluorescent molecules, enzymes, ligands, and the like. As used herein, a probe iε εingle- or double- εtranded DNA or RNA that haε a εequence of nucleotides that includes at least 14 contiguous baseε that are the same as (or the complement of) any 14 or more contiguous baεeε set forth in SEQ ID NOε:l or 3. Preferred regionε for the construction of probes include thoεe regionε predicted to encode a DNA binding domain. Such regionε are preferred becauεe they are moεt highly conεerved among memberε of the steroid/thyroid superfamily of receptorε. Aε a particular application of the invention sequences, genetic screening can be carried out using the nucleic acid sequences of the invention as probes. Thus, nucleic acid samples from patientε having conditions εuεpected of involving alteration/modification of any one or more of the PPAR receptor subtypes can be screened with appropriate probes to determine if abnormalities exist with reεpect to the endogenous PPAR receptor proteins. In accordance with yet another embodiment of the present invention, there are provided vectors comprising nucleic acid sequences, as well aε cells and vectors containing such εequenceε. Such host cells, including bacterial, yeast and mammalian cells can be used for expreεsing invention nucleic acids to produce PPAR receptor protein(ε) . Incorporation of cloned DNA into a εuitable expression vector, transfection of eukaryotic cells with a plasmid vector or a combination of plasmid vectors, each encoding one or more distinct genes, and εelection of tranεfected cells are well known in the art (see, e.g., Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor Laboratory Press) . Heterologous DNA may be introduced into host cells by any method known to those of skill in the art, such as transfection by CaP0 4 precipitation with a vector encoding the heterologous DNA (see, e.g., Wigler et al. (1979) Proc . Natl . Acad . Sci . 2^:1373-1376), DEAE-dextran, electroporation, microinjection, or lipofectamine (GIBCO BRL #18324-012) . Transfected host cellε can then be cultured under conditionε whereby the receptor εubunit protein(s) encoded by the DNA is (are) recombinantly expresεed. The preεent invention further provideε a mammalian peroxiεome proliferator-activated receptor, expressed recombinantly in a host cell. The receptor compriseε at leaεt one PPAR subunit, wherein the PPAR subunit is PPARK or PPAR5, and at least one retinoid X receptor isoform. The invention receptor has the ability to repress PPARα-mediated responεeε activated by Wy 14,643, Also provided by the present invention are mammalian peroxiεome proliferator-activated εubunit proteinε, expreεεed recombinantly in a hoεt cell wherein the receptor εubunits have substantially the same amino acid sequence as εet forth in SEQ ID NOε: 2 or 4. In accordance with εtill another embodiment of the preεent invention, there iε provided a method for the recombinant production of mammalian peroxisome proliferator-activated receptor proteinε comprising at least one PPAR subunit of the y or δ subtype, or functional fragments thereof. Such method comprises expreεsing the above-described nucleic acid(ε) in a suitable host cell. In accordance with still another embodiment of the present invention, there is provided a method to identify clones encoding mammalian peroxisome proliferator- activated receptor εubunit proteinε of the y or δ subtype, or functional fragments thereof. Such method comprises screening a genomic or cDNA library with an invention nucleic acid probe under low stringency hybridization conditions, and identifying those clones which display a substantial degree of hybridization to said fragment. Nucleic acids encoding mammalian peroxisome proliferator-activated receptor subunit protein of the y or δ subtype, or functional fragments thereof may be iεolated by screening suitable human cDNA or human genomic libraries under suitable hybridization conditions with nucleic acids disclosed herein (including nucleotide sequences derived from SEQ ID NOs:l or 3) . Suitable librarieε can be prepared from appropriate tissue samples, e.g., brain tissue, heart tisεue, inteεtinal tiεεue, kidney tiεεue, liver tiεsue, spleen tissue, and the like. The library can be screened with nucleic acid including substantially the entire receptor-encoding sequence thereof, or the library may be εcreened with a suitable probe, as deεcribed above. After screening the library, positive cloneε are identified by means of a hybridization signal; the identified clones are characterized by reεtriction enzyme mapping and/or DNA sequence analysis, and then examined, by comparison with the sequences set forth herein to ascertain whether they encode a complete PPAR receptor subunit protein (i.e., if they include translation initiation and termination codons) . If the selected clones are incomplete, they may be used to rescreen the εame or a different library to obtain overlapping cloneε. If the library is genomic, then the overlapping clones may include exons and introns. If the library is a cDNA library, then the overlapping clones will include an open reading frame. In both instances, complete clones may be identified by comparison with the DNA and encoded proteins provided herein. The ligand-binding domain (LBD) of nuclear hormone receptors is a complex multifunctional unit containing subdomains for dimerization, tranεcriptional suppression and hormone-induced transactivation (Forman and Samuels, Mol . Endocrinol . 4 . : 1293-1301 (1990)). The dimerization domain includes a series of heptad repeats flanked by sequences required for ligand binding. Thus, the dimerization domain is embedded within the larger LBD. This structural arrangement raises the posεibility that dimerization may serve as an allosteric modulator of ligand binding and transactivation. It has previouεly been shown that the Drosophila ecdysone receptor (EcR) acquires ligand binding activity after heterodimerization with USP (Drosophila homolog of RXR; see Yao et al., in Nature 366:476-479 (1993)) . Thuε, differential interactionε among receptor LBDs can either restrict, redirect or lead to an acquisition of new ligand binding phenotypes. It haε recently been shown that PPARα binds to its cognate responεe elements as a heterodimer with the RXR (see Kliewer et al., εupra, Gearing et al., εupra, or Keller et al., supra) . The resulting PPARα-RXR complex can respond to both peroxisome proliferatorε and 9-cis retinoic acid (εee Kliewer et al., (1992), εupra) . It has now been found that PPARK and PPAR5 also cooperate with RXR in the formation of heterodimerε, and in binding to DNA aε heterodimerε. Ultimately, the regulation of peroxisome physiology is likely a consequence of a complex interplay among the multiple PPAR and RXR isoforms and the ligands for these receptors. In accordance with the preεent invention, there are provided combinationε of receptorε comprising at least two different members of the steroid/thyroid superfamily of receptorε, wherein one receptor is either PPARK or PPARS, and wherein said receptors are associated in the form of a ultimer, preferably a heterodimer. A particularly preferred combination of receptorε iε a heterodimer compriεing either PPARK or PPAR5 and a εubtype of RXR. Combinationε contemplated by the preεent invention can broadly be referred to as "multimeric species," which is intended to embrace all of the various oligomeric formε in which memberε of the εteroid/thyroid superfamily of receptors (including fragments thereof comprising the dimerization domains thereof) are capable of associating in combination with either PPARK or PPARS. Thus, reference to "combinations" of steroid receptors or "multimeric" forms of steroid receptorε includeε homodimeric combinationε of a εingle PPARK or PPAR5 receptor (including fragmentε thereof compriεing the dimerization domains thereof) , heterodimeric combinations of either a PPARK or PPAR6 receptor and another different receptor (including fragments thereof compriεing the dimerization domains thereof) , homotrimeric combinations of a single PPARK or PPAR5 receptor (including fragments thereof comprising the dimerization domains thereof) , heterotrimeric combinations of two or three different receptorε including PPARK or PPAR5 (including fragmentε thereof compriεing the dimerization domainε thereof) , homotetrameric combinationε of a single PPARK or PPAR6 receptor (including fragments thereof comprising the dimerization domains thereof) , heterotetrameric combinationε of two or more different receptorε including PPARK or PPAR6 (including fragments thereof comprising the dimerization domainε thereof) , and the like. Aε employed herein, the phrase "members of the steroid/thyroid superfamily of receptorε" (also known as "nuclear receptorε" or "intracellular receptorε") refers to hormone binding proteins that operate as ligand-dependent transcription factors, including identified memberε of the steroid/thyroid superfamily of receptors for which specific ligands have not yet been identified (referred to hereinafter as "orphan receptors") . These hormone binding proteins have the intrinsic ability to bind to εpecific DNA sequences. Following binding, the transcriptional activity of target gene (i.e., a gene aεsociated with the specific DNA sequence) is modulated aε a function of the ligand bound to the receptor. The DNA-binding domains of all of these nuclear receptors are related, consisting of 66-68 amino acid residues, and possesεing about 20 invariant amino acid residues, including nine cyεteineε. A member of the εuperfamily can be identified aε a protein which contains the above-mentioned invariant amino acid reεidueε, which are part of the DNA-binding domain of εuch known εteroid receptors aε the human glucocorticoid receptor (amino acidε 421-486) , the eεtrogen receptor (amino acidε 185-250) , the mineralocorticoid receptor (amino acidε 603-668) , the human retinoic acid receptor (amino acids 88-153) . The highly conserved amino acidε of the DNA-binding domain of memberε of the εuperfamily are well-known aε set forth, for example in PCT WO 94/01558. Thus, the DNA-binding domain is a minimum of 66 amino acids in length, but can contain several additional reεidueε. Exemplary memberε of the εteroid/thyroid εuperfamily of receptorε contemplated for use in the practice of the present invention (including the variouε iεoformε thereof) include steroid receptors such aε mineralocorticoid receptor, progeεterone receptor, androgen receptor, vitamin D 3 receptor, and the like; pluε retinoid receptors, such as the various isoformε of RAR (e.g., RARα, RAR?, or RARK) , the various isoformε of RXR (e.g., RXRα, RXR/?, or RXRK) , and the like; thyroid receptors, such aε TRα, TR?, and the like; aε well aε other gene productε which, by their εtructure and propertieε, are conεidered to be members of the superfamily, aε defined hereinabove, including the variouε isoforms thereof. Examples of orphan receptorε include HNF4 [see, for example, Sladek et al., in Genes & Development 4: 2353-2365 (1990)], the COUP family of receptorε [εee, for example, Miyajima et al., in Nucleic Acidε Reεearch 16: 11057-11074 (1988) , and Wang et al., in Nature 340: 163-166 (1989)], COUP-like receptors and COUP homologε, such aε thoεe deεcribed by Mlodzik et al., in Cell 60: 211-224 (1990) and Ladiaε et al., in Science 251: 561-565 (1991) , the ultraεpiracle receptor [see, for example, Oro et al., in Nature 347: 298-301 (1990)], and the like. Presently preferred members of the superfamily for use in the practice c . the present invention are the variouε iεoformε of RXR (e.g., RXRα, RXR?, or RXRK) . The formation of multimeric (e.g., heterodimeric) species can modulate the ability of the first receptor to trans-activate tranεcription of geneε maintained under expreεεion control in the preεence of ligand for said first receptor. The actual effect on activation of transcription (i.e., enhancement or represεion of tranεcription activity) will vary depending on the receptor εpecieε which iε combined with either a PPARK or PPAR5 receptor to form the multimeric species, as well as on the response element with which the multimeric specieε interactε. In accordance with the present invention, there are provided multimeric receptor specieε which belong to the steroid/thyroid superfamily of receptorε, compriεing at least the dimerization domain of at two different members of the steroid/thyroid superfamily of receptors, wherein one of the memberε iε selected from the invention PPARK or PP ' AR<5. As employed herein, the term "dimerization domain" of a member of the steroid/thyroid superfamily of receptors refers to that portion of the receptor which is believed to be involved in the formation of multimeric receptor species. This domain typically comprises the carboxy-terminal portion of the receptor, i.e., that portion of a receptor which is 3 ' with respect to the DNA-binding domain of the receptor. See, e.g., Evans, in Science 240:889-895 (1988), and Forman and Samuels, Mol . Endocrinol . 4 . :1293-1301 (1990) . Presently preferred members of the superfamily for use in deriving the dimerization domain are the various isoformε of RXR (e.g., RXRα, RXRβ, or RXRK) • In accordance with the preεent invention, there are alεo provided heterodimer complexes comprising either PPARK or PPARtS and a εilent partner therefor. Aε employed herein, the term "silent partner" refers to members of the steroid/thyroid εuperfamily of receptorε which are capable of forming heterodimeric εpecies with either PPARK or PPARtS, wherein the silent partner of the heterodimer doeε not have any ligand bound to the ligand-binding domain (LBD) when the εilent partner iε complexed with a PPAR εubtype (i.e., only the PPAR co¬ partner of the heterodimer binds ligand) . Preεently preferred silent partners for uεe in the practice of the present invention are the various isoformε of RXR (e.g., RXRα, RXR , or RXRK) . In accordance with a further embodiment of the present invention, there is provided a method for screening compounds to determine those which bind to mammalian peroxisome proliferator-activated receptor proteins comprising at least one PPAR subunit of the y or δ subtype, or functional fragments thereof. Such method compriεeε employing receptor protein(ε) of the invention in a binding aεεay, which compriεeε, contacting receptor protein(ε) of the invention with test compound, and identifying thoεe compoundε which bind to invention receptor protein(s) . In accordance with a still further embodiment of the present invention, there iε provided a bioaεεay for evaluating whether teεt compoundε are agonists for receptor proteinε of the invention, or functional modified forms of said receptor protein(ε). Such bioaεsay compriseε: (1) contacting εuitable host cells expreεsing said receptor protein with test compound under physiological conditions, wherein said host cells contain DNA encoding a reporter protein, wherein said DNA iε operatively linked to a PPAR-reεponεe element; (2) monitoring said host cells for expression of reporter gene, wherein expresεion of reporter protein reflectε tranεcriptional activity of the receptor protein and, therefore, the preεence of an activated receptor-ligand complex. In accordance with yet another embodiment of the preεent invention, there iε provided a bioaεεay for evaluating whether test compoundε are antagonists for receptor proteins of the invention, or functional modified forms of said receptor protein(ε) . Such bioassay compriseε: contacting εuitable host cellε with (i) increaεing concentrationε of at least one compound whose ability to inhibit the transcription activation activity of agonists of mammalian peroxisome proliferator-activated receptor proteins of the K or δ subtype iε sought to be determined, and (ii) a fixed concentration of at least one agonist for said receptor protein(s) or functional modified formε thereof, wherein suitable test cellε express mammalian peroxisome proliferator-activated receptor proteins comprising at least one PPAR subunit of the y or δ subtype and DNA encoding a reporter protein, wherein εaid DNA iε operatively linked to a PPAR-reεponεe element; and thereafter assaying for evidence of transcription of said reporter gene in said cells as a function of the concentration of said compound in said culture medium, thereby indicating the ability of said compound to inhibit activation of transcription by agoniεtε of mammalian peroxisome proliferator-activated receptor proteinε compriεing at least one PPAR εubunit of the y or δ εubtype. In accordance with a εtill further embodiment of the present invention, there is provided a method for identifying ligandε εelective for heterodimerε compriεing either PPARK or PPAR<5 and a silent partner therefor. Such method comprises comparing the level of expression of reporter when cells containing a reporter construct, either PPARK or PPAR5 and silent partner therefor are expoεed to teεt compound, relative to the level of expreεεion of reporter when cellε containing a reporter construct, either PPARK or PPAR5 and a member of the steroid/thyroid superfamily which iε not a silent partner therefor are exposed to test compound, and selecting thoεe compoundε which activate only the combination of either PPARK or PPAR5 and silent partner therefor. In accordance with yet another embodiment of the present invention, there are provided antibodies generated against the invention proteins. Such antibodies can be employed for studying receptor tisεue localization, subunit composition, structure of functional domains, as well as in diagnostic applications, therapeutic applications, and the like. Preferably, for therapeutic applications, the antibodies employed will be monoclonal antibodies. The above-described antibodieε can be prepared employing standard techniques, as are well known to thoεe of εkill in the art, uεing the invention receptor proteinε or portions thereof aε antigenε for antibody production. Both anti-peptide and anti-fuεion protein antibodieε can be used [see, for example, Bahouth et al. (1991) Trends Pharmacol Sci. vol. JL2.: 338-343 ; Current Protocols in Molecular Biology (Ausubel et al., eds.) John Wiley and Sons, New York (1989)]. Factorε to conεider in εelecting portionε of the invention receptor protein subunit sequences for use as immunogen (as, for example, a synthetic peptide or a recombinantly produced bacterial fusion protein) include antigenicity, acceεεibility (i.e., internal or external domainε) , uniqueneεε to the particular protein εubunit, and the like. The availability of sequence-specific antibodies enables use of immunohistoche ical techniques to monitor the distribution and expreεεion denεity of various protein subunits (e.g., in normal versus diseased brain tissue). Such antibodieε can also be employed for diagnostic and therapeutic applications. In accordance with yet another embodiment of the present invention, there are provided methods for modulating processes mediated by mammalian peroxisome proliferator-activated receptor proteinε comprising at least one PPAR subunit of the y or δ subtype. Such methods comprise contacting mammalian peroxiεome proliferator- activated receptor proteins of the y or δ subtype with an effective, modulating amount of agonist, antagonist or antibody according to the present invention. The antibodies, agonists and/or antagonistε of the invention can be adminiεtered to a εubject employing standard methodε, such as, for example, by intraperitoneal, intramuεcular, intravenous, or subcutaneous injection, implant or transdermal modes of administration, and the like. One of skill in the art can readily determine dose forms, treatment regiments, etc, depending on the mode of administration employed. Proceεεeε which are mediated by mammalian peroxiεome proliferator-activated receptor proteinε of the K or δ εubtype include, for example, macrophage production in the spleen which is believed to be important in atherosclerosis. The invention will now be described in greater detail with reference to the following non-limiting examples. EXAMPLE 1 Screening of cDNA libraries PPARK was iεolated by screening an adult mouse liver ΛZAP cDNA library (Stratagene) with a synthetic oligonucleotide (GGNTTYCAYTAYGGNGTNCAYCG; SEQ ID NO:5) under conditions previously described by Blumberg et al., in Proc . Natl . Acad . Sci . USA B9_ : 2321-2325 (1992) . This oligonucleotide is a mixture of all poεεible DNA sequences encoding the amino acid sequence GFHYGVHA (SEQ ID NO: 6), a sequence present in the loop of the first zinc finger in the Xenopus PPARα, PPARβ and PPARK isoforms. PPAR5 waε iεolated by εcreening an E6.5 mouεe ΛZAPII cDNA library (a gift of D.E. Weng and J.D. Gerhart, Johnε Hopkinε Univerεity) under low stringency conditionε with a cDNA fragment encoding the human retinoic acid receptor αDNA binding domain (Mangelsdorf et al., Nature 345:224-229 (1990)). In both εcreenε, poεitive clones were converted to plasmidε by the automatic exciεion proceεε. EXAMPLE 2 Cotranεfection Aεεay The mammalian expreεεion vectorε pCMX-PPARα, pCMX-PPARκ and pCMX-PPAR5 were conεtructed by inserting the cDNA inεertε of PPARα, PPARK, and PPAR5 into pCMX as previously described by Umesono et al., in Cell 65:1255- 1266 (1991)) . Construction of the reporter PPRE 3 -TK-LUC has also been previously described by Kliewer et al., (1992) supra. Cotransfection aεεayε in CV-1 cells were done in 48 well plates using N-[l-(2, 3-dioleoyloxy) -propyl[N,N,N- trimethyl ammonium methyl sulfate (DOTAP) according to the manufacturer'ε inεtructionε (Boehringer Mannheim) . Transfections contained lOng of receptor expreεsion plasmid vector, 20ng of the reporter PPRE 3 -TK-LUC, 60ng of pCMX-βGAL (β-galactosidase) aε an internal control, and 210ng of carrier plasmid pGEM. Cells were incubated in the presence of DOTAP for 8 hours, waεhed, and incubated in the preεence of peroxisome proliferators or fatty acidε for 36 hours. Cell extracts were prepared and assayed for luciferase and β-galactosidaεe activity aε previously described (Umesono, supra) . All experimental pointε were done in triplicate. EXAMPLE 3 Northern Analyεiε Preparation of poly(A) + RNA from rat tiεsues and Northern analysiε were performed as previouεly deεcribed (Mangelsdorf et al., supra) . Thus, Northern blot analysis of PPAR mRNA was carried out employing adult and embryonic tissue. Adult male rat tissues and mouse embryos from gestation day 10.5 to 18.5 were employed. The exposure time for each of the blots was 48 hourε. The sizes of the transcripts, based on RNA size markers, were 8.5kb (PPARα), 1.9kb (PPARK), and 3.5kb (PPARS) . EXAMPLE 4 DNA Binding Assays Gel mobility shift asεayε were performed aε previously described by Kliewer et al. (1992) supra. PPARα, PPARK, PPARS, RXRα, RXRβ and RXRK were synthesized in vitro using the TNT coupled transcription/tranεlation εyεte (Promega) according to the manufacturer'ε inεtructionε. EXAMPLE 5 Iεolation of three murine PPAR iεoformε The function of peroxiεome proliferatorε haε been moεt extenεively εtudied in rodentε, where treatment with theεe compoundε reεultε in marked increaεeε in peroxiεome εize and number and concomitant increaεeε in the expreεεion of the geneε encoding the enzymes of the peroxisomal β-oxidation pathway. To gain inεight into the function of PPAR iεoformε, mouεe embryonic and adult liver librarieε were screened for PPARα-related gene products. In addition to PPARα, two typeε of PPARα-related cloneε were iεolated. The firεt clone encodeε a 475-amino acid protein that iε 56% identical to mouse (m)PPARα and 76% identical to Xenopus (x)PPARκ- Since this clone is 97% and 84% identical to the DNA binding and ligand binding domainε of XPPARK, reεpectively, it iε deεignated mPPARK (see SEQ ID NOs: 1 and 2) . The second clone encodes a 440-amino acid protein that is closely related to NUC-1 (see SEQ ID NOs: 3 and 4, and Figure 1) , a PPARα-related receptor recently isolated from a human osteoεarcoma library (see Schmidt et al., in Mol . Endo . .6:1634-1641 (1992)) . Since this second clone is not highly homologous to any of the previously identified PPAR iεoformε (i.e., mPPARα, xPPARα, xPPARβ or XPPARK; see Figure 1) , it appears to represent a novel receptor, and is, therefore, designated mPPARδ. Of the approximately 50 poεitiveε characterized during the course of screening, no mouse homolog of xPPARβ was identified. EX/AMPLE 6 PPARα, PPAR , and PPAR5 are differentially expreεεed in the adult and embryo The expression patterns of the murine PPAR isoforms were examined in the embryo and adult. Northern analysiε of poly(A) RNA iεolated from adult male rat tisεueε revealed differential yet overlapping patternε of expreεεion of the three isoformε. Both PPARα and PPAR5 are widely expressed, with PPARα mesεage levelε higheεt in the liver, kidney, heart, and adrenal, and PPAR5 message highest in the heart, adrenal, and intestine. In contrast, PPARK displays a more reεtricted diεtribution pattern, with abundant expreεεion in only the adrenal and εpleen, although mersage iε alεo detectable in the heart, kidney, and intestine. The developmental expresεion of the PPAR iεoformε was also examined through Northern analysiε of whole mouse embryo RNA. PPARα and PPARK diεplayed similar expression patterns during mouse embryogeneεiε, with mesεage firεt appearing at day 13.5 postconception and increasing until birth. In contrast, PPAR5 mesεage waε abundant at all the embryonic time pointε tested, suggesting a broad role for this isoform during development. Thus, the PPAR isoforms are seen to be differentially expresεed in both the embryo and the adult. EXAMPLE 7 Evidence for pharmacological differences between PPARα, PPARf and PPAR The relatively high degree of conservation within the ligand binding domains of PPARα, PPARK and PPAR5 suggested that these PPAR isoforms might respond to the same activators. Accordingly, each of the PPAR isoforms waε firεt teεted for reεponεiveneεε to Wy 14,643, a peroxisome proliferator and potent activator of PPARα (Reddy and Lalwani, Crit . Rev . Toxicol . 12:1-58 (1983)) . Cotransfection of PPARα expreεεion plaεmid reεulted in a dramatic (>100-fold) increase in activation of a reporter construct containing three copies of the acyl-CoA oxidase PPRE (AOX-PPRE) upstream of the thymidine kinaεe promoter driving luciferaεe expreεεion (PPRE 3 -TK-LUC) in reεponεe to Wy 14,643 (Figure 2) . In contrast, no activation of reporter expresεion waε εeen in the presence of Wy 14,643 upon cotransfection of PPARK or PPAR5 expresεion plaεmidε (Figure 2) . Thiε lack of activation iε unlikely to reflect differenceε in binding site specificity, aε each of the PPAR iεoforms bound efficiently to the AOX-PPRE as a heterodimer with RXR (as determined by gel mobility shift aεεayε done uεing in vitro synthesized PPARα, PPARK, and PPAR5, and/or RXRK, and 2 P-labeled AOX-PPRE oligonucleotide) . Additional experiments revealed that overexpresεion of PPARK and PPAR5 interfered with the ability of PPARα to activate through the AOX-PPRE (Figure 3). Thuε, both PPARK and PPAR5 are expreεεed and can function aε dominant repreεεors of PPARα- mediated responεiveneεs to Wy 14,643. Since no activation of PPARK and PPAR5 was detected with Wy 14,643, other potential activators were tested, including a broad spectrum of peroxisome proliferators and fatty acids. As shown in Figure 4, significant activation of PPARK was obtained upon treatment with LY-171883, a leukotriene antagoniεt and peroxiεome proliferator which lackε the carboxyl group typically found in thiε claεε of compounds (Foxworthy and Eacho, Biochem . Pharmacology 42:1487-1491 (1991)). Conversely, no activation of PPARK was εeen in the preεence of linoleic acid (Figure 4) . In contrast to the reεultε obtained with PPARK, PPAR5 was activated in the presence of lin' leic acid, but was not activated upon treatment with LY-171883. Both LY-171883 and linoleic acid are strong activators of PPARα (Figure 4) . Interestingly, each of the three PPAR isoforms was activated with a distinct rank order of efficacy by these compounds: PPAR : Wy 14,643 > LY-171883 > linoleic acid; PPARK: LY 171883 > linoleic acid > Wy 14,643; PPAR δ : linoleic acid > LY-171883 and Wy 14,643. See Figure 4. These data provide evidence that PPARK and PPAR5 can function aε regulated activatorε of gene expreεsion and that the three PPAR isoformε are pharmacologically distinct. While the invention has been described in detail with reference to certain preferred embodimentε thereof, it will be underεtood that modifications and variations are within the spirit and scope of that which is described and claimed. SEQUENCE LISTING SEQ ID NO:l Mouse PPARK 1 ATCGAATCCCGCGCCCCAGGCGCTGCCGCTCTGAGTGCGACGGGCCCCGCCTGGCCGGCC 61 GGAGGACGCGGAAGAAGAGACCTGGGGCGCTGCCTGGGGTATTGGGTCGCGCGCAGTGAG 121 GGGACCGAGTGTGACGACAAGGTGACCGGGCTGAGGGGACGGGCTGAGGAGAAGTCACAC 181 TCTGACAGGAGCCTGTGAGACCAACAGCCTGACGGGGTCTCGGTTGAGGGGACGCGGGCT 241 GAGAAGTCACGTTCTGACAGGACTGTGTGACAGACAAGATTTGAAAGAAGCGGTGAACCA 301 CTGATATTCAGGACATTTTTAAAAACAAGACTACCCTTTACTGAAATTACCATGGTTGAC M V D 3 361 ACAGAGATGCCATTCTGGCCCACCAACTTCGGAATCAGCTCTGTGGACCTCTCCGTGATG T E M P F W P T N F G I S S V D L S V 23 421 GAAGACCACTCGCATTCCTTTGACATCAAGCCCTTTACCACAGTTGATTTCTCCAGCATT E D H S H S F D I K P F T T V D F S S I 43 481 TCTGCTCCACACTATGAAGACATTCCATTCACAAGAGCTGACCCAATGGTTGCTGATTAC S A P H Y E D I P F T R A D P V A D Y 63 541 AAATATGACCTGAAGCTCCAAGAATACCAAAGTGCGATCAAAGTAGAACCTGCATCTCCA K Y D L K Q E Y Q S A I K V E P A S P 83 601 CCTTATTATTCTGAAAAGACCCAGCTCTACAACAGGCCTCATGAAGAACCTTCTAACTCC P Y Y S E K T Q L Y N R P H E E P S N S 103 661 CTCATGGCCATTGAGTGCCGAGTCTGTGGGGATAAAGCATCAGGCTTCCACTATGGAGTT M A I E C R V C G D K A S G F H Y G V 123 721 CATGCTTGTGAAGGATGCAAGGGTTTTTTCCGAAGAACCATCCGATTGAAGCTTATTTAT H A C E G C K G F F R R T I R L K L I Y 143 781 GATAGGTGTGATCTTAACTGCCGGATCCACAAAAAAAGTAGAAATAAATGTCAGTACTGT D R C D L N C R I H K K S R N K C Q Y C 163 841 CGGTTTCAGAAGTGCCTTGCTGTGGGGATGTCTCACAATGCCATCAGGTTTGGGCGGATG R F Q K C L A V G M S H N A I R F G R M 183 901 CCACAGGCCGAGAAGGAGAAGCTGTTGGCGGAGATCTCCAGTGATATCGACCAGCTGAAC P Q A E K E K L L A E I S S D I D Q L N 203 961 CCAGAGTCTGCTGATCTGCGAGCCCTGGCAAAGCATTTGTATGACTCATACATAAAGTCC P E S A D R A L A K H L Y D S Y I K S 223 1021 TTCCCGCTGACCAAAGCCAAGGCGAGGGCGATCTTGACAGGAAAGACAACGGACAAATCA F P L T K A K A R A I L T G K T T D K S 243 1081 CCATTTGTCATCTACGACATGAATTCCTTAATGATGGGAGAAGATAAAATCAAGTTCAAA P F V I Y D M N S L M M G E D K I K F K 263 1141 CATATCACCCCCCTGCAGGAGCAGAGCAAAGAGGTGGCCATCCGAATTTTTCAAGGGTGC H I T P L Q E Q S K E V A I R I F Q G C 283 1201 CAGTTTCGATCCGTAGAAGCCGTGCAAGAGATCACAGAGTATGCCAAAAATATCCCTGGT Q F R S V E A V Q E I T E Y A K N I P G 303 1261 TTCATTAACCTTGATTTGAATGACCAAGTGACTCTGCTCAAGTATGGTGTCCATGAGATC F I N L D L N D Q V T L L K Y G V H E I 323 1321 ATCTACACGATGCTGGCCTCCCTGATGAATAAAGATGGAGTCCTCATCTCAGAGGGCCAA I Y T M L A S L M N K D G V L I S E G Q 343 1381 GGATTCATGACCAGGGAGTTCCTCAAAAGCCTGCGGAAGCCCTTTGGTGACTTTATGGAG G F M T R E F L K S L R K P F G D F M E 363 1441 CCTAAGTTTGAGTTTGCTGTGAAGTTCAATGCACTGGAATTAGATGACAGTGACTTGGCT P K F E F A V K F N A L E L D D S D L A 383 1501 ATATTTATAGCTGTCATTATTCTCAGTGGAGACCGCCCAGGCTTGCTGAACGTGAAGCCC I F I A V I I L S G D R P G L L N V K P 403 1561 ATCGAGGACATCCAAGACAACCTGCTGCAGGCCCTGGAACTGCAGCTCAAGCTGAATCAC I E D I Q D N L Q A L E Q L K L N H 423 1621 CCAGAGTCCTCTCAGCTGTTCGCCAAGGTGCTCCAGAAGATGACAGACCTCAGGCAGATC P E S S Q L F A K V Q K M T D L R Q I 443 1681 GTCACAGAGCACGTGCAGCTACTGCATGTGATCAAGAAGACAGAGACAGACATGAGCCTT V T E H V Q L H V I K K T E T D M S L 463 1741 CACCCCCTGCTCCAGGAGATCTACAAGGACTTGTATTAGCAGGAAAGTCCCACCCGCTGA H P L L Q E I Y K D L Y * 475 1801 CAACGTGTTCCTTCTATTGATTGCACTATTATTTTGAGGGAAAAAAATCTGACACCTAAG 1861 AAATTTACTGTGAAAAAGCATTTAAAAACAAAAAGTTTTAGAACATGATCTATTTTATGC 1921 ATATTGTTTATAAAGATACATTTACAATTTACTTTTAATATTAAAAATTACCACATTATA 1981 AAAAAAAAAAAAAAAAAGGAATTCC 2005 SEQ ID NO: 2 10 25 M V D T E M P F W P T N F G I S S V D L S V M E D H S H S F D I K P F T T 50 65 V D F S S I S A P H Y E D I P F T R A D P M V A D Y K Y D L K L Q E Y Q S 80 90 105 A I K V E P A S P P Y Y S E K T Q L Y N R P H E E P S N S L M A I E C R V 110 130 145 C G D K A S G F H Y G V H A C E G C K G F F R R T I R L K L I Y D R C D L 160 170 185 N C R I H K K S R N K C Q Y C R F Q K C L A V G M S H N A I R F G R M P Q 190 200 215 A E K E K L L A E I S S D I D Q N P E S A D L R A L A K H L Y D S Y I K 225 240 255 S F P L T K A K A R A I L T G K T T D K S P F V I Y D M N S L M M G E D K 270 285 I K F K H I T P L Q E Q S K E V A I R I F Q G C Q F R S V E A V Q E I T E 300 315 325 Y A K N I P G F I N L D L N D Q V T L L K Y G V H E I I Y T M L A S L M N 335 345 360 K D G V L I S E G Q G F M T R E F L K S L R K P F G D F M E P K F E F A V 375 390 405 K F N A L E L D D S D L A I F I A V I I L S G D R P G L N V K P I E D I 410 425 440 Q D N L L Q A L E L Q L K L N H P E S S Q L F A K V L Q K M T D L R Q I V 455 470 T E H V Q L L H V I K K T E T D M S L H P L L Q E I Y K D L Y SEQ ID NO: 3 Mouse PPARδ 1 GAATTCCCTGGGGATTAATGGGAAAAGTTTTGGCaGGAGCTGGGGGATTCTGCGG: CCT 61 GCGGGACggCggCAgcGGCGCGAGAGGCGGCCGGgACAGTGCTGTGCAGCGGTGTC-.iGTA 121 TGCGCATGGGACTCACTCAGAGGCTCCTGCTCACTGACAGATGAAGACAAACCCACGGTA 181 AAGGCAGTCCATCTGCGCTCAGACCCAGATGGTGGCAGAGCTATGACCAGGCCTGCAGCG 241 CCACGCCAAGTGGGGGTCAGTCATGGAACAGCCACAGGAGGAGACCCCTGAGGCCCGGGA M E Q P Q E E T P E A R E 13 301 AGAGGAGAAAGAGGAAGTGGCCATGGGTGACGGAGCCCCGGAGCTCAATGGGGGACCAGA E E K E E V A M G D G A P E L N G G P E 33 361 ACACACGCTTCCTTCCAGCAGCTGTGCAGACCTCTCCCAGAaTTCCTCCCCTTCCTCCCT H T L P S S S C A D L S Q N S S P S S L 53 421 GCTGGACCAGCTGCAGATGGGCTGTGATGGGGCCTCAGGCGGCAGCCTCAACATGGAATG L D Q L Q M G C D G A S G G S L N M E C 73 481 TCGGGTGTGCGGGGACAAGGCCTCGGGCTTCCACTACGGGGTCCACGCGTGCGAGGGGTG R V C G D K A S G F H Y G V H A C E G C 93 541 CAAGGGCTTCTTCCGCCGGACAATCCGCATGAAGCTCGAGTATGAGAAGTGCGATCGGAT K G F F R R T I R M K L E Y E K C D R I 113 601 CTGCAAGATCCAGAAGAAGAACCGCAACAAGTGTCAGTACTGCCGCTTCCAGAAGTGCCT C K I Q K K R N K C Q Y C R F Q K C L 133 661 GGCACTCGGCATGTCGCACAACGCTATCCGCTTTGGACGGATGCCGGACGGCGAGAAGAG A L G M S H N A I R F G R M P D G E K R 153 721 GAAGCTGGTGGCGGGGCTGACTGCCAGCGAGGGGTGCCAGCACAACCCCCAGCTGGCCGA K L V A G T A S E G C Q H N P Q L A D 173 781 CCTGAAGGCCTTCTCTAAGCACATCTACAACGCCTACCTGAAAAACTTCAACATGACCAA K A F S K H I Y N A Y L K N F N M T K 193 841 AAAGAAGGCCCGGAGCATCCTCACCGGCAAGTCCAGCCACAACGCACCCTTTGTCATCCA K K A R S I L T G K S S H N A P F V I H 213 901 CGACATCGAGACACTGTGGCAGGCAGAGAAGGGCCTGGTGTGGAAACAGCTGGTGAACGG D I E T L W Q A E K G V W K Q L V N G 233 961 GCTGCCGCCCTACAACGAGATCAGTGTGCACGTGTTCTACCGCTGCCAGTCCACCACAGT L P P Y N E I S V H V F Y R C Q S T T V 253 1021 GGAGACAGTCCGAGAGCTCACCGAGTTCGCCAAGAACATCCCCAACTTCAGCAGCCTCTT E T V R E L T E F A K N I P N F S S L F 273 1081 CCTCAATGACCAGGTGACCCTCCTCAAGTATGGCGTGCACGAGGCCATCTTTGCCATGCT N D Q V T L K Y G V H E A I F A M L 293 1141 GGCCTCCATCGTCAACAAAGACGGGCTGCTGGTGGCCAACGGCAGTGGCTTCGTCACCCA A S I V N K D G L L V A N G S G F V T H 313 1201 CGAGTTCTTGCGAAGTCTCCGCAAGCCCTTCAGTGACATCATTGAGCCCAAGTTCGAGTT E F L R S L R K P F S D I I E P K F E F 333 1261 TGCTGTCAAGTTCAATGCGCTGGAGCTCGATGACAGTGACCTGGCGCTCTTCATCGCGGC A V K F N A L E L D D S D L A L F I A A 353 1321 CATCATTCTGTGTGGAGACCGGCCAGGCCTCATGAATGTGCCCCAGGTAGAAGCCATCCA I I L C G D R P G L M N V P Q V E A I Q 373 1381 GGACACCATTCTGCGGGCTCTAGAATTCCATCTGCAGGTCAACCACCCTGACAGCCAGTA D T I L R A L E F H L Q V N H P D S Q Y 393 1441 CCTCTTCCCCAAGCTGCTGCAGAAGATGGCAGACCTGCGGCAGCTGGTCACTGAGCATGC L F P K L Q K M A D L R Q L V T E H A 413 1501 CCAGATGATGCAGTGGCTAAAGAAGACGGAGAGTGAGACCTTGCTGCACCCCCTGCTCCA Q M M Q W L K K T E S E T L L H P L L Q 433 1561 GGAAATCTACAAGGACATGTACTAAGGCCgCagCCCaggCCtCCCCtCaggCtCtgCtgg E I Y K D M Y 440 1621 gCCCagCCaCggaCtGT CAGAGGACCAGCCACAGGCACTGGCAGTCAAGCAGCTAGAGC 1681 CTACTCACAACACTCCAGACACGTGGCCCAGACTCTTCCCCCAACACCCCCACCCCCACC 1741 AACCCCCCCATTCCCCCAACCCCCCTCCCCCACCCCGCTCTCCCCATGGCCCGTTTCCTG 1801 TTTCTCCTCAGCACCTCCTGTTCTTGCTGTCTCCCTAGCGCCCTTGCTCCCCCCCCTTTG 1861 CCTTCCTTCTCTAGCATCCCCCTCCTCCCAGTCCTCACATTTGTCTGATTCACAGCAGAC 1921 AGCCCGTTGGTACGCTCACCAGCAGCCTAAAAGCAGTGGGCCTGTGCTGGCCCAGTCCTG 1981 CCTCTCCTCTCTATCCCCTTCAAAGGGAATTC 2012 SEQ ID NO:4 10 25 M E Q P Q E E T P E A R E E E K E E V A M G D G A P E N G G P E H T L P 50 65 S S S C A D L S Q N S S P S S L L D Q L Q M G C D G A S G G S L N M E C R 80 90 105 V C G D K A S G F H Y G V H A C E G C K G F F R R T I R M K E Y E K C D 120 130 145 R I C K I Q K K N R N K C Q Y C R F Q K C L A L G M S H N A I R F G R M P 160 170 185 D G E K R K L V A G L T A S E G C Q H N P Q L A D L K A F S K H I Y N A Y 190 200 215 L K N F N M T K K K A R S I T G K S S H N A P F V I H D I E T L W Q A E 225 240 255 K G L V W K Q V N G L P P Y N E I S V H V F Y R C Q S T T V E T V R E L 270 285 T E F A K N I P N F S S L F L N D Q V T L L K Y G V H E A I F A M L A S I 300 315 325 V N K D G L L V A N G S G F V T H E F L R S L R K P F S D I I E P K F E F 335 345 360 A V K F N A L E L D D S D L A L F I A A I I L C G D R P G L M N V P Q V E 375 390 405 A I Q D T I R A L E F H L Q V N H P D S Q Y L F P K L L Q K M A D L R Q 410 425 440 L V T E H A Q M M Q W L K K T E S E T L L H P L Q E I Y K D M Y SEQ ID NO:5 GGNTTYCAYT AYGGNGTNCA YCG 23 SEQ ID NO:6 GFHYGVHA 8

Claims: That which is claimed is: 1. An iεolated mammalian peroxiεome proliferator-activated receptor subunit protein of the y or δ subtype, or functional fragments thereof. 2. A protein according to claim 1 wherein said protein is of the y subtype, or functional fragments thereof. 3. A protein according to claim 2 having an amino acid sequence εubεtantially the εame aε set forth in SEQ ID No:2. 4. A protein according to claim 1 wherein εaid protein is of the δ subtype, or functional fragments thereof. 5. A protein according to claim 4 having an amino acid sequence substantially the same as set forth in SEQ ID NO:4. 6. A receptor recombinantly expreεεed in a cell containing a vector compriεing isolated nucleic acid encoding a protein according to claim 1. 7. A receptor according to claim 6 comprising at least one PPARK subunit or at least one PPAR5 subunit and at least one retinoid X receptor isoform. 8. A receptor according to claim 6, wherein said receptor is a heteromultimer. 9. A receptor according to claim 7, wherein the PPAR subunit is PPARK- 10. A receptor according to claim 7, wherein the PPAR subunit is PPAR δ . 11. A mammalian peroxiεome proliferator- activated receptor, expressed recombinantly in a hoεt cell, said receptor having the ability to repress PPARα-mediated reεponεeε activated by Wy 14,643, compriεing at leaεt one PPAR subunit, wherein the PPAR subunit is PPARK or PPARS, and at least one retinoid X receptor iεoform. 12. A mammalian peroxiεome proliferator- activated subunit protein, expressed recombinantly in a host cell comprised of an amino acid sequence shown in SEQ ID NOs: 2 or 4. 13. A method for εcreening compoundε to determine thoεe which bind to mammalian peroxiεome proliferator-activated receptor proteinε compriεing at leaεt one PPAR subunit of the y or δ subtype, or functional fragmentε thereof, said method comprising: contacting receptor protein according to claim 11 with a test compound, and identifying those compounds which bind to invention receptor proteins. 14. A bioaεsay for evaluating whether test compounds are agonists for receptorε according to claim 11, or functional modified formε of said receptor(s), εaid bioassay compriεing: (1) contacting εuitable host cells expresεing said receptor with test compound under physiological conditions, wherein said host cells contain DNA encoding a reporter protein, wherein said DNA is operatively linked to a PPAR-response element; (2) monitoring said host cells for expression of reporter protein, wherein expression of reporter protein reflectε tranεcriptional activity of εaid receptor protein and the preεence of an activated receptor-ligand complex. 15. A bioaεεay for evaluating whether test compounds are antagonists for receptors according to claim 11, or functional modified forms of said receptor(ε) , said bioassay comprising: contacting suitable host cells with (i) increasing concentrations of at leaεt one compound whose ability to inhibit the tranεcription activation activity of agonists of mammalian peroxisome proliferator-activated receptors of the y or δ subtype iε sought to be determined, and (ii) a fixed concentration of at leaεt one agonist for said receptor protein(s) or functional modified formε thereof, wherein suitable hoεt cellε expreεε mammalian peroxisome proliferator-activated receptors comprising at least one PPAR subunit of the c or i subtype, and wherein said host cells contain DNA encoding a reporter protein, wherein said DNA iε operatively linked to a PPAR-response element; and thereafter assaying for evidence of transcription of said reporter gene in said cells as a function of the concentration of said compound in said culture medium, thereby indicating the ability of said compound to inhibit activation of transcription by agonistε of mammalian peroxiεome proliferator-activated receptorε of the y or δ subtype. 16. An antibody generated againεt the receptor of claim 11. 17. An antibody according to claim 16, wherein said antibody iε a monoclonal antibody. 18. A heterodimer complex compriεing PPARK or PPAR5 and an iεoform of RXR. 19. A heterodimer complex according to claim 18 wherein εaid iεoform of RXR iε εelected from RXRα, RXR / ? or RXRK- 20. A combination of receptorε compriεing at leaεt two different memberε of the εteroid/thyroid εuperfamily of receptorε, wherein εaid reσeptorε are aεεociated in the form of a multimer, and wherein one of said members is selected from PPARK or PPAR5. 21. A combination of receptors according to claim 20 wherein said combination is in the form of a heterodimer. 22. A multimer comprising at leaεt the dimerization domain of at leaεt two different memberε of the εteroid/thyroid εuperfamily of receptorε, wherein one of εaid memberε iε selected from PPARK or PPAR5. 23. An isolated nucleic acid encoding a mammalian peroxisome proliferator-activated receptor subunit protein of the y or δ subtype, or functional fragments thereof. 24. An iεolated nucleic acid according to claim 23, wherein said protein is of the y subtype, or functional fragments thereof. 25. An iεolated nucleic acid according to claim 23, wherein εaid protein iε of the <S subtype, or functional fragments thereof. 26. An isolated nucleic acid according to claim 23 having a contiguous nucleotide sequence εubεtantially the same as set forth in SEQ ID NO:l [PPAR-K] , or SEQ ID NO:3 [PPAR-5], or variations thereof which encode the same amino acid sequence, but employ different codons for some of the amino acids, or splice variant nucleotide sequenceε thereof. 27. An iεolated nucleic acid according to claim 23 having a contiguouε nucleotide εequence substantially the εame aε εet forth in SEQ ID NOε:l or 3. 28. Iεolated and purified nucleic acid, or functional fragmentε thereof encoding the protein of claim 1, selected from: (a) nucleic acid encoding the amino acid sequence set forth in SEQ ID NO:2 or SEQ ID NO:4, or (b) nucleic acid that hybridizes to the nucleic acid of (a) under moderately stringent conditionε, wherein said nucleic acid encodes biologically active PPAR-K or PPAR-5, or (c) nucleic acid degenerate with respect to either (a) or (b) above, wherein said nucleic acid encodes biologically active PPAR-K or PPAR- δ . 29. A vector comprising a nucleic acid according to claim 23. 30. A cell containing a nucleic acid according to claim 23. 31. A cell according to claim 30, wherein εaid cell further comprises nucleic acid encoding at leaεt one retinoid X receptor isoform. 32. A cell containing a vector according to claim 29. 33. A cell according to claim 32, wherein said cell further comprises nucleic acid encoding at least one retinoid X receptor isoform. 34. A method for the recombinant production of a mammalian peroxisome proliferator-activated receptor compriεing at least one PPAR subunit of the y or δ subtype, or functional fragmentε thereof, said method compriεing expressing the nucleic acid of claim 23 in a suitable host cell. 35. A method according to claim 34, wherein the suitable host cell contains nucleic acid encoding at least one retinoid X receptor. 36. A host cell according to claim 35, wherein said host cell iε a CV-1 cell. 37. An iεolated nucleic acid fragment uεeful aε a hybridization probe, wherein said fragment compriseε at leaεt 14 contiguouε nucleotideε of the nucleic acid according to claim 23, and wherein εaid fragment is labeled with a detectable subεtituent. 38. A method to identify cloneε encoding mammalian peroxiεome proliferator-activated receptor subunit proteins of the y or δ subtype, or functional fragmentε thereof, said method comprising: εcreening a genomic or cDNA library with a nucleic acid probe according to claim 37 under low εtringency hybridization conditionε, and identifying thoεe cloneε which diεplay a 5 εubεtantial degree of hybridization to εaid fragment.

Inventors: EVANS RONALD M, FOREMAN BARRY M, KLIEWER STEVEN A, ONG ESTELITA S, EVANS, RONALD, M., FOREMAN, BARRY, M., KLIEWER, STEVEN, A., ONG, ESTELITA, S.
Applicants: SALK INST FOR BIOLOGICAL STUDI, THE SALK INSTITUTE FOR BIOLOGICAL STUDIES
Application year: 1995
Main classification: C12N15
IPC codes: C07K14, C07K16, C12N5, C12N15, C12P21, C12Q1, G01N33