Patent Publication Number: US-RE42190-E

Title: Method of identifying a compound for inhibiting or stimulating human G protein-coupled receptors

Description:
This application is a continuation of Application Ser. No. 10/272,983, filed Oct. 17, 2002, which is a continuation of Application Ser. No. 09/417,044, filed Oct. 12, 1999, now abandoned, and claims priority benefit of Provisional Application Ser.  No. 60/121,852 filed Feb.  26, 1999, Ser.  Provisional Application  No. 60/109,213, filed Nov.  20, 1998, Ser.  Provisional Application  No. 60/120,416, filed Feb.  16, 1999, Ser.  Provisonal Application  No. 60/123,946, filed Mar.  12, 1999, Ser.  Provisional Application  No. 60/123,949, filed Mar.  12, 1999, Ser.  Provisonal Application  No. 60/136,436, filed May  28, 1999, Ser.  Provisional Application  No.  60/136,439, field  filed  May  28, 1999, Ser.  Provisional Application  No.  60/136,567, file  filed  May  28, 1999, Ser.  Provisional Application  No. 60/137,127, filed May  28, 1999, Ser.  Provisional Application  No. 60/137,131, filed May  28, 1999, Ser.  Provisional Application  No. 60/141,448, filed Jun.  29, 1999, Ser.  Provisional Application  No. 60/136,437, filed May  28, 1999, Ser.  Provisional Application  No. 60/156,653, filed Sep.  29, 1999, Ser.  Provisional Application  No. 60/156,333  60/156,633, filed Sep. 28  29,  1999, Ser.  Provisional Application  No. 60/156,555, filed Sep.  29, 1999, Ser.  Provisional Application  No. 60/156,634, filed Sep.  29, 1999, Ser.  Provisional Application  No. 60/157,280, filed Oct.  1, 1999, Ser.  Provisional Application  No. 60/157,294, filed Oct.  1, 1999, Ser.  Provisional Application  No. 60/157,281, filed Oct.  1, 1999, Ser.  Provisional Application No.  60/157,293, filed Oct. 1, 1999, and Ser.  Provisional Application No. 60/157,282, filed Oct. 1, 1999, the entirety of each of which is incorporated herein by reference. This patent application is related to U.S. Ser.  Application No. 09/170,496, filed Oct. 13, 1999, and U.S. Ser.  Application No. 09/416,760, filed Oct. 12, 1999, both being incorporated herein by reference in their entirety. This patent application is also related to U.S. Ser.  Application No. 09/364,425, filed Jul. 30, 1999, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention disclosed in this patent document relates to transmembrane receptors, and more particularly to endogenous, orphan, human G protein-coupled receptors (“GPCRs”). 
     BACKGROUND OF THE INVENTION 
     Although a number of receptor classes exist in humans, by far the most abundant and therapeutically relevant is represented by the G protein-coupled receptor (GPCR or GPCRs) class. It is estimated that there are some 100,000 genes within the human genome, and of these, approximately 2% or 2,000 genes, are estimated to code for GPCRs. Receptors, including GPCRs, for which the endogenous ligand has been identified are referred to as “known” receptors, while receptors for which the endogenous ligand has not been identified are referred to as “orphan” receptors. GPCRs represent an important area for the development of pharmaceutical products: from approximately 20 of the 100 known GPCRs, 60% of all prescription pharmaceuticals have been developed. This distinction is not merely semantic, particularly in the case of GPCRs. Thus, the orphan GPCRs are to the pharmaceutical industry what gold was to California in the late 19 th  century—an opportunity to drive growth, expansion, enhancement and development. 
     GPCRs share a common structural motif. All these receptors have seven sequences of between 22 to 24 hydrophobic amino acids that form seven alpha helices, each of which spans the membrane (each span is identified by number, i.e., transmembrane-1 (TM-1), transmembrane-2 (TM-2), etc.). The transmembrane helices are joined by strands of amino acids between transmembrane-2 and transmembrane-3, transmembrane-4 and transmembrane-5, and transmembrane-6 and transmembrane-7 on the exterior, or “extracellular” side, of the cell membrane (these are referred to as “extracellular” regions 1, 2 and 3 (EC-1, EC-2 and EC-3), respectively). The transmembrane helices are also joined by strands of amino acids between transmembrane-1 and transmembrane-2, transmembrane-3 and transmembrane-4, and transmembrane-5 and transmembrane-6 on the interior, or “intracellular” side, of the cell membrane (these are referred to as “intracellular” regions 1, 2 and 3 (IC-1, IC-2 and IC-3), respectively). The “carboxy” (“C”) terminus of the receptor lies in the intracellular space within the cell, and the “amino” (“N”) terminus of the receptor lies in the extracellular space outside of the cell. 
     Generally, when an endogenous ligand binds with the receptor (often referred to as “activation” of the receptor), there is a change in the conformation of the intracellular region that allows for coupling between the intracellular region and an intracellular “G-protein.” It has been reported that GPCRs are “promiscuous” with respect to G proteins, i.e., that a GPCR can interact with more than one G protein. See, Kenakin, T, 43 Life Sciences 1095 (1988). Although other G proteins exist, currently, Gq, Gs, Gi, and Go are G proteins that have been identified. Endogenous ligand-activated GPCR coupling with the G-protein begins a signaling cascade process (referred to as “signal transduction”). Under normal conditions, signal transduction ultimately results in cellular activation or cellular inhibition. It is thought that the IC-3 loop as well as the carboxy terminus of the receptor interact with the G protein. 
     Under physiological conditions, GPCRs exist in the cell membrane in equilibrium between two different conformations: an “inactive” state and an “active” state. A receptor in an inactive state is unable to link to the intracellular signaling transduction pathway to produce a biological response. Changing the receptor conformation to the active state allows linkage to the transduction pathway (via the G-protein) and produces a biological response. A receptor may be stabilized in an active state by an endogenous ligand or a compound such as a drug. 
     SUMMARY OF THE INVENTION 
     Disclosed herein are human endogenous orphan G protein-coupled receptors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  provide reference “grids” for certain dot-blots provided herein (see also,  FIGS. 2A and 2B , respectively). 
         FIGS. 2A and 2B  provide reproductions of the results of certain dot-blot analyses resulting from hCHN3 and hCHN8, respectively (see also,  FIGS. 1A and 1B , respectively). 
         FIG. 3  provides a reproduction of the results of RT-PCR analysis of hRUP3. 
         FIG. 4  provides a reproduction of the results of RT-PCR analysis of hRUP4. 
         FIG. 5  provides a reproduction of the results of RT-PCR analysis of hRUP6. 
         FIG. 6  is a reproduction of a photograph of the results of the tissue distribution of RUP3 using multiple tissue (human) cDNA. Based upon these tissues, the data support the position that RUP3 is expressed only in the pancreas. 
     
    
    
     DETAILED DESCRIPTION 
     The scientific literature that has evolved around receptors has adopted a number of terms to refer to ligands having various effects on receptors. For clarity and consistency, the following definitions will be used throughout this patent document. To the extent that these definitions conflict with other definitions for these terms, the following definitions shall control: 
     AMINO ACID ABBREVIATIONS used herein are set out in Table 1: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 ALANINE 
                 ALA 
                 A 
               
               
                   
                 ARGININE 
                 ARG 
                 R 
               
               
                   
                 ASPARAGINE 
                 ASN 
                 N 
               
               
                   
                 ASPARTIC ACID 
                 ASP 
                 D 
               
               
                   
                 CYSTEINE 
                 CYS 
                 C 
               
               
                   
                 GLUTAMIC ACID 
                 GLU 
                 E 
               
               
                   
                 GLUTAMINE 
                 GLN 
                 Q 
               
               
                   
                 GLYCINE 
                 GLY 
                 G 
               
               
                   
                 HISTIDINE 
                 HIS 
                 H 
               
               
                   
                 ISOLEUCINE 
                 ILE 
                 I 
               
               
                   
                 LEUCINE 
                 LEU 
                 L 
               
               
                   
                 LYSINE 
                 LYS 
                 K 
               
               
                   
                 METHIONINE 
                 MET 
                 M 
               
               
                   
                 PHENYLALANINE 
                 PHE 
                 F 
               
               
                   
                 PROLINE 
                 PRO 
                 P 
               
               
                   
                 SERINE 
                 SER 
                 S 
               
               
                   
                 THREONINE 
                 THR 
                 T 
               
               
                   
                 TRYPTOPHAN 
                 TRY 
                 W 
               
               
                   
                 TYROSINE 
                 TYR 
                 Y 
               
               
                   
                 VALINE 
                 VAL 
                 V 
               
               
                   
                   
               
            
           
         
       
     
     COMPOSITION means a material comprising at least one component. 
     ENDOGENOUS shall mean a material that a mammal naturally produces. ENDOGENOUS in reference to, for example and not limitation, the term “receptor,” shall mean that which is naturally produced by a mammal (for example, and not limitation, a human) or a virus. By contrast, the term NON-ENDOGENOUS in this context shall mean that which is not naturally produced by a mammal (for example, and not limitation, a human) or a virus. 
     HOST CELL shall mean a cell capable of having a Plasmid and/or Vector incorporated therein. In the case of a prokaryotic Host Cell, a Plasmid is typically replicated as a autonomous molecule as the Host Cell replicates (generally, the Plasmid is thereafter isolated for introduction into a eukaryotic Host Cell); in the case of a eukaryotic Host Cell, a Plasmid is integrated into the cellular DNA of the Host Cell such that when the eukaryotic Host Cell replicates, the Plasmid replicates. Preferably, for the purposes of the invention disclosed herein, the Host Cell is eukaryotic, more preferably, mammalian, and most preferably selected from the group consisting of 293, 293T and COS-7 cells. 
     LIGAND shall mean an endogenous, naturally occurring molecule specific for an endogenous, naturally occurring receptor. 
     MUTANT or MUTATION in reference to an endogenous receptor&#39;s nucleic acid and/or amino acid sequence shall mean a specified change or changes to such endogenous sequences such that a mutated form of an endogenous, non- constitutively activated receptor evidences constitutive activation of the receptor. In terms of equivalents to specific sequences, a subsequent mutated form of a human receptor is considered to be equivalent to a first mutation of the human receptor if  ( a )  the level of constitutive activation of the subsequent mutated form of the receptor is substantially the same as that evidenced by the first mutation of the receptor; and  ( b )  the percent sequence  ( amino acid and/or nucleic acid )  homology between the subsequent mutated form of the receptor and the first mutation of the receptor is at least about  80   % , more preferably at least about  90   %  and most preferably at least  95   % . Ideally, and owing to the fact that the most preferred mutation disclosed herein for achieving constitutive activation includes a single amino acid and/or codon change between the endogenous and the non - endogenous forms of the GPCR, the percent sequence homology should be at least  98   %. 
     NON-ORPHAN RECEPTOR shall mean an endogenous naturally occurring molecule specific for an endogenous naturally occurring ligand wherein the binding of a ligand to a receptor activates an intracellular signaling pathway. 
     ORPHAN RECEPTOR shall mean an endogenous receptor for which the endogenous ligand specific for that receptor has not been identified or is not known. 
     PLASMID shall mean the combination of a Vector and cDNA. Generally, a Plasmid is introduced into a Host Cell for the purposes of replication and/or expression of the cDNA as a protein. 
     VECTOR sin reference to cDNA shall mean a circular DNA capable of incorporating at least one cDNA and capable of incorporation into a Host Cell. 
     The order of the following sections is set forth for presentational efficiency and is not intended, nor should be construed, as a limitation on the disclosure or the claims to follow. 
     Identification of Human GPCRs 
     The efforts of the Human Genome project have led to the identification of a plethora of information regarding nucleic acid sequences located within the human genome; it has been the case in this endeavor that genetic sequence information has been made available without an understanding or recognition as to whether or not any particular genomic sequence does or may contain open-reading frame information that translate human proteins. Several methods of identifying nucleic acid sequences within the human genome are within the purview of those having ordinary skill in the art. For example, and not limitation, a variety of GPCRs, disclosed herein, were discovered by reviewing the GenBank™ database, while other GPCRs were discovered by utilizing a nucleic acid sequence of a GPCR, previously sequenced, to conduct a BLAST™ search of the EST database. Table A, below, lists the disclosed endogenous orphan GPCRs along with a GPCR&#39;s respective homologous GPCR: 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE A 
               
               
                   
               
               
                   
                   
                 Open 
                   
                 Reference To 
               
               
                 Disclosed 
                   
                 Reading 
                 Percent 
                 Homologous 
               
               
                 Human 
                 Accession 
                 Frame 
                 Homology To 
                 GPCR 
               
               
                 Orphan 
                 Number 
                 (Base 
                 Designated 
                 (Accession 
               
               
                 GPCRs 
                 Identified 
                 Pairs) 
                 GPCR 
                 No.) 
               
               
                   
               
             
            
               
                 hARE-3 
                 AL033379 
                 1,260 bp 
                 52.3% LPA-R 
                 U92642 
               
               
                 hARE-4 
                 AC006087 
                 1,119 bp 
                 36% P2Y5 
                 AF000546 
               
               
                 hARE-5 
                 AC006255 
                 1,104 bp 
                 32%  Oryzias 
                 D43633 
               
               
                   
                   
                   
                 latipes 
               
               
                 hGPR27 
                 AA775870 
                 1,128 bp 
               
               
                 hARE-1 
                 AI090920 
                   999 bp 
                 43% 
                 D13626 
               
               
                   
                   
                   
                 KIAA0001 
               
               
                 hARE-2 
                 AA359504 
                 1,122 bp 
                 53% GPR27 
               
               
                 hPPR1 
                 H67224 
                 1,053 bp 
                 39% EBI1 
                 L31581 
               
               
                 hG2A 
                 AA754702 
                 1,113 bp 
                 31% GPR4 
                 L36148 
               
               
                 hRUP3 
                 AI035423 
                 1,005 bp 
                 30% 
                 2133653 
               
               
                   
                   
                   
                 Drosophila 
               
               
                   
                   
                   
                 melanogaster 
               
               
                 hRUP4 
                 AI307658 
                 1,296 bp 
                 32% pNPGPR 
                 NP_004876 
               
               
                   
                   
                   
                 28% and 29% 
                 AAC41276 
               
               
                   
                   
                   
                 Zebra fish 
                 and 
               
               
                   
                   
                   
                 Ya and Yb, 
                 AAB94616 
               
               
                   
                   
                   
                 respectively 
               
               
                 hRUP5 
                 AC005849 
                 1,413 bp 
                 25% DEZ 
                 Q99788 
               
               
                   
                   
                   
                 23% FMLPR 
                 P21462 
               
               
                 hRUP6 
                 AC005871 
                 1,245 bp 
                 48% GPR66 
                 NP_006047 
               
               
                 hRUP7 
                 AC007922 
                 1,173 bp 
                 43% H3R 
                 AF140538 
               
               
                 hCHN3 
                 EST 36581 
                 1,113 bp 
                 53% GPR27 
               
               
                 hCHN4 
                 AA804531 
                 1,077 bp 
                 32% thrombin 
                 4503637 
               
               
                 hCHN6 
                 EST 2134670 
                 1,503 bp 
                 36% edg-1 
                 NP_001391 
               
               
                 hCHN8 
                 EST 764455 
                 1,029 bp 
                 47% 
                 D13626 
               
               
                   
                   
                   
                 KIAA0001 
               
               
                 hCHN9 
                 EST 1541536 
                 1,077 bp 
                 41% LTB4R 
                 NM_000752 
               
               
                 hCHN10 
                 EST 1365839 
                 1,055 bp 
                 35% P2Y 
                 NM_002563 
               
               
                   
               
            
           
         
       
     
     Receptor homology is useful in terms of gaining an appreciation of a role of the disclosed receptors within the human body. Additionally, such homology can provide insight as to possible endogenous ligand(s) that may be natural activators for the disclosed orphan GPCRs. 
     B. Receptor Screening 
     Techniques have become more readily available over the past few years for endogenous-ligand identification (this, primarily, for the purpose of providing a means of conducting receptor-binding assays that require a receptor&#39;s endogenous ligand) because the traditional study of receptors has always proceeded from the a priori assumption (historically based) that the endogenous ligand must first be identified before discovery could proceed to find antagonists and other molecules that could affect the receptor. Even in cases where an antagonist might have been known first, the search immediately extended to looking for the endogenous ligand. This mode of thinking has persisted in receptor research even after the discovery of constitutively activated receptors. What has not been heretofore recognized is that it is the active state of the receptor that is most useful for discovering agonists, partial agonists, and inverse agonists of the receptor. For those diseases which result from an overly active receptor or an under-active receptor, what is desired in a therapeutic drug is a compound which acts to diminish the active state of a receptor or enhance the activity of the receptor, respectively, not necessarily a drug which is an antagonist to the endogenous ligand. This is because a compound that reduces or enhances the activity of the active receptor state need not bind at the same site as the endogenous ligand. Thus, as taught by a method of this invention, any search for therapeutic compounds should start by screening compounds against the ligand-independent active state. 
     As is known in the art, GPCRs can be “active” in their endogenous state even without the binding of the receptor&#39;s endogenous ligand thereto. Such naturally-active receptors can be screened for the direct identification (i.e., without the need for the receptor&#39;s endogenous ligand) of, in particular, inverse agonists. Alternatively, the receptor can be “activated” via, e.g., mutation of the receptor to establish a non-endogenous version of the receptor that is active in the absence of the receptor&#39;s endogenous ligand. 
     Screening candidate compounds against an endogenous or non-endogenous, constitutively activated version of the human orphan GPCRs disclosed herein can provide for the direct identification of candidate compounds which act at this cell surface receptor, without requiring use of the receptor&#39;s endogenous ligand. By determining areas within the body where the endogenous version of human GPCRs disclosed herein is expressed and/or over-expressed, it is possible to determine related disease/disorder states which are associated with the expression and/or over-expression of the receptor; such an approach is disclosed in this patent document. 
     With respect to creation of a mutation that may evidence constitutive activation of human orphan GPCRs disclosed herein is based upon the distance from the proline residue at which is presumed to be located within TM6 of the GPCR typically nears the TM6/IC3 interface (such proline residue appears to be quite conserved). By mutating the amino acid residue located 16 amino acid residues from this residue (presumably located in the IC3 region of the receptor) to, most preferably, a lysine residue, such activation may be obtained. Other amino acid residues may be useful in the mutation at this position to achieve this objective. 
     C. Disease/Disorder Identification and/or Selection 
     Preferably, the DNA sequence of the human orphan GPCR can be used to make a probe for (a) dot-blot analysis against tissue-mRNA, and/or (b) RT-PCR identification of the expression of the receptor in tissue samples. The presence of a receptor in a tissue source, or a diseased tissue, or the presence of the receptor at elevated concentrations in diseased tissue compared to a normal tissue, can be preferably utilized to identify a correlation with a treatment regimen, including but not limited to, a disease associated with that disease. Receptors can equally well be localized to regions of organs by this technique. Based on the known functions of the specific tissues to which the receptor is localized, the putative functional role of the receptor can be deduced. 
     As the data below indicate, RUP3 is expressed within the human pancreas, suggesting that RUP3 may play a role in insulin regulation and/or glucagon regulation. Accordingly, candidate compounds identified using a constitutively activated form of RUP3 may be useful for understanding the role of RUP3 in diabetes and/or as therapeutics for diabetes. 
     D. Screening of Candidate Compounds 
     1. Generic GPCR Screening Assay Techniques 
     When a G protein receptor becomes constitutively active (i.e., active in the absence of endogenous ligand binding thereto), it binds to a G protein (e.g., Gq, Gs, Gi, Go) and stimulates the binding of GTP to the G protein. The G protein then acts as a GTPase and slowly hydrolyzes the GTP to GDP, whereby the receptor, under normal conditions, becomes deactivated. However, constitutively activated receptors continue to exchange GDP to GTP. A non-hydrolyzable analog of GTP, [ 35 S]GTPγS, can be used to monitor enhanced binding to membranes which express constitutively activated receptors. It is reported that [ 35 S] GTPγS can be used to monitor G protein coupling to membranes in the absence and presence of ligand. An example of this monitoring, among other examples well-known and available to those in the art, was reported by Traynor and Nahorski in 1995. The preferred use of this assay system is for initial screening of candidate compounds because the system is generically applicable to all G protein-coupled receptors regardless of the particular G protein that interacts with the intracellular domain of the receptor. 
     2. Specific GPCR Screening Assay Techniques 
     Once candidate compounds are identified using the “generic” G protein-coupled receptor assay (i.e., an assay to select compounds that are agonists, partial agonists, or inverse agonists), further screening to confirm that the compounds have interacted at the receptor site is preferred. For example, a compound identified by the “generic” assay may not bind to the receptor, but may instead merely “uncouple” the G protein from the intracellular domain. 
     a. Gs and Gi. 
     Gs stimulates the enzyme adenylyl cyclase. Gi (and Go), on the other hand, inhibit this enzyme. Adenylyl cyclase catalyzes the conversion of ATP to cAMP; thus, constitutively activated GPCRs that couple the Gs protein are associated with increased cellular levels of cAMP. On the other hand, constitutively activated GPCRs that couple the Gi (or Go) protein are associated with decreased cellular levels of cAMP. See, generally, “Indirect Mechanisms of Synaptic Transmission,” Chpt. 8, From Neuron To Brain (3 rd Ed.) Nichols, J. G. et al eds. Sinauer Associates, Inc. (1992). Thus, assays that detect cAMP can be utilized to determine if a candidate compound is, e.g., an inverse agonist to the receptor (i.e., such a compound would decrease the levels of cAMP). A variety of approaches known in the art for measuring cAMP can be utilized; a most preferred approach relies upon the use of anti-cAMP antibodies in an ELISA-based format. Another type of assay that can be utilized is a whole cell second messenger reporter system assay. Promoters on genes drive the expression of the proteins that a particular gene encodes. Cyclic AMP drives gene expression by promoting the binding of a cAMP-responsive DNA binding protein or transcription factor (CREB) which then binds to the promoter at specific sites called cAMP response elements and drives the expression of the gene. Reporter systems can be constructed which have a promoter containing multiple cAMP response elements before the reporter gene, e.g., β-galactosidase or luciferase. Thus, a constitutively activated Gs-linked receptor causes the accumulation of cAMP that then activates the gene and expression of the reporter protein. The reporter protein such as β-galactosidase or luciferase can then be detected using standard biochemical assays (Chen et al. 1995). 
     Go and Gq. 
     Gq and Go are associated with activation of the enzyme phospholipase C, which in turn hydrolyzes the phospholipid PIP 2 , releasing two intracellular messengers: diacycloglycerol (DAG) and inistol 1,4,5-triphoisphate (IP 3 ). Increased accumulation of IP 3  is associated with activation of Gq- and Go-associated receptors. See, generally, “Indirect Mechanisms of Synaptic Transmission,” Chpt. 8, From Neuron To Brain (3 rd  Ed.) Nichols, J. G. et al eds. Sinauer Associates, Inc. (1992). Assays that detect IP 3  accumulation can be utilized to determine if a candidate compound is, e.g., an inverse agonist to a Gq- or Go-associated receptor (i.e., such a compound would decrease the levels of IP3). Gq-dependent receptors can also been examined using an API reporter assay in that Gq-dependent phospholipase C causes activation of genes containing API elements; thus, activated Gq-associated receptors will evidence an increase in the expression of such genes, whereby inverse agonists thereto will evidence a decrease in such expression, and agonists will evidence an increase in such expression. Commercially available assays for such detection are available. 
     3. GPCR Fusion Protein 
     The use of an endogenous, constitutively activated orphan GPCR, or a non-endogenous, constitutively activated orphan GPCR, for screening of candidate compounds for the direct identification of inverse agonists, agonists and partial agonists provides a unique challenge in that, by definition, the receptor is active even in the absence of an endogenous ligand bound thereto. Thus, it is often useful that an approach be utilized that can enhance the signal obtained by the activated receptor. A preferred approach is the use of a GPCR Fusion Protein. 
     Generally, once it is determined that a GPCR is or has been constitutively activated, using the assay techniques set forth above (as well as others), it is possible to determine the predominant G protein that couples with the endogenous GPCR. Coupling of the G protein to the GPCR provides a signaling pathway that can be assessed. Because it is most preferred that screening take place by use of a mammalian expression system, such a system will be expected to have endogenous G protein therein. Thus, by definition, in such a system, the constitutively activated orphan GPCR will continuously signal. In this regard, it is preferred that this signal be enhanced such that in the presence of, e.g., an inverse agonist to the receptor, it is more likely that it will be able to more readily differentiate, particularly in the context of screening, between the receptor when it is contacted with the inverse agonist. 
     The GPCR Fusion Protein is intended to enhance the efficacy of G protein coupling with the GPCR. The GPCR Fusion Protein is preferred for screening with a non-endogenous, constitutively activated GPCR because such an approach increases the signal that is most preferably utilized in such screening techniques, although the GPCR Fusion Protein can also be (and preferably is) used with an endogenous, constitutively activated GPCR. This is important in facilitating a significant “signal to noise” ratio; such a significant ratio is import preferred for the screening of candidate compounds as disclosed herein. 
     The construction of a construct useful for expression of a GPCR Fusion Protein is within the purview of those having ordinary skill in the art. Commercially available expression vectors and systems offer a variety of approaches that can fit the particular needs of an investigator. The criteria of importance for such a GPCR Fusion Protein construct is that the GPCR sequence and the G protein sequence both be in-frame (preferably, the sequence for the GPCR is upstream of the G protein sequence) and that the “stop” codon of the GPCR must be deleted or replaced such that upon expression of the GPCR, the G protein can also be expressed. The GPCR can be linked directly to the G protein, or there can be spacer residues between the two (preferably, no more than about 12, although this number can be readily ascertained by one of ordinary skill in the art). We have a preference (based upon convenience) of use of a spacer in that some restriction sites that are not used will, effectively, upon expression, become a spacer. Most preferably, the G protein that couples to the GPCR will have been identified prior to the creation of the GPCR Fusion Protein construct. Because there are only a few G proteins that have been identified, it is preferred that a construct comprising the sequence of the G protein (i.e., a universal G protein construct) be available for insertion of an endogenous GPCR sequence therein; this provides for efficiency in the context of large-scale screening of a variety of different endogenous GPCRs having different sequences. 
     E. Other Utility 
     Although a preferred use of the human orphan GPCRs disclosed herein may be for the direct identification of candidate compounds as inverse agonists, agonists or partial agonists (preferably for use as pharmaceutical agents), these versions of human GPCRs can also be utilized in research settings. For example, in vitro and in vivo systems incorporating GPCRs can be utilized to further elucidate and understand the roles these receptors play in the human condition, both normal and diseased, as well as understanding the role of constitutive activation as it applies to understanding the signaling cascade. The value in human orphan GPCRs is that its utility as a research tool is enhanced in that by determining the location(s) of such receptors within the body, the GPCRs can be used to understand the role of these receptors in the human body before the endogenous ligand therefor is identified. Other uses of the disclosed receptors will become apparent to those in the art based upon, inter alia, a review of this patent document. 
     Although a preferred use of the non-endogenous versions of the human RUP3 disclosed herein may be for the direct identification of candidate compounds as inverse agonists, agonists or partial agonists (preferably for use as pharmaceutical agents), this version of human RUP3 can also be utilized in research settings. For example, in vitro and in vivo systems incorporating RUP3 can be utilized to further elucidate the roles RUP3 plays in the human condition, particularly with respect to the human pancreas, both nonnal and diseased (and in particular, diseases involving regulation of insulin or glucagon, e.g., diabetes), as well as understanding the role of constitutive activation as it applies to understanding the signaling cascade. A value in non-endogenous human RUP3 is that its utility as a research tool is enhanced in that, because of its unique features, non-endogenous RUP3 can be used to understand the role of RUP3 in the human body before the endogenous ligand therefor is identified. Other uses of the disclosed receptors will become apparent to those in the art based upon, inter alia, a review of the patent document. 
     EXAMPLES 
     The following examples are presented for purposes of elucidation, and not limitation, of the present invention. While specific nucleic acid and amino acid sequences are disclosed herein, those of ordinary skill in the art are credited with the ability to make minor modifications to these sequences while achieving the same or substantially similar results reported below. Unless otherwise indicated below, all nucleic acid sequences for the disclosed endogenous orphan human GPCRs have been sequenced and verified. For purposes of equivalent receptors, those of ordinary skill in the art will readily appreciate that conservative substitutions can be made to the disclosed sequences to obtain a functionally equivalent receptor. 
     Example 1 
     Endogenous Human GPCRs 
     1. Identification of Human GPCRs 
     Several of the disclosed endogenous human GPCRs were identified based upon a review of the GenBank database information. While searching the database, the following cDNA clones were identified as evidenced below. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Open 
                   
                   
               
               
                 Disclosed 
                   
                 Complete 
                 Reading 
                 Nucleic 
                 Amino 
               
               
                 Human 
                   
                 DNA 
                 Frame 
                 Acid 
                 Acid 
               
               
                 Orphan 
                 Accession 
                 Sequence 
                 (Base 
                 SEQ ID. 
                 SEQ ID. 
               
               
                 GPCRs 
                 Number 
                 (Base Pairs) 
                 Pairs) 
                 NO. 
                 NO. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 hARE-3 
                 AL033379 
                 111,389 bp 
                 1,260 bp 
                 1 
                 16 
               
               
                 hARE-4 
                 AC006087 
                 226,925 bp 
                 1,119 bp 
                 3 
                 4 
               
               
                 hARE-5 
                 AC006255 
                 127,605 bp 
                 1,104 bp 
                 5 
                 6 
               
               
                 hRUP3 
                 AL035423 
                 140,094 bp 
                 1,005 bp 
                 7 
                 8 
               
               
                 hRUP5 
                 AC005849 
                 169,144 bp 
                 1,413 bp 
                 9 
                 10 
               
               
                 hRUP6 
                 AC005871 
                 218,807 bp 
                 1,245 bp 
                 11 
                 12 
               
               
                 hRUP7 
                 AC007922 
                 158,858 bp 
                 1,173 bp 
                 13 
                 14 
               
               
                   
               
            
           
         
       
     
     Other disclosed endogenous human GPCRs were identified by conducting a BLAST search of EST database (dbest) using the following EST clones as query sequences. The following EST clones identified were then used as a probe to screen a human genomic library. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Open 
                 Nucleic 
                 Amino 
               
               
                 Disclosed 
                   
                   
                 Reading 
                 Acid 
                 Acid 
               
               
                 Human 
                   
                 EST Clone/ 
                 Frame 
                 SEQ 
                 SEQ 
               
               
                 Orphan 
                 Query 
                 Accession No. 
                 (Base 
                 ID. 
                 ID. 
               
               
                 GPCRs 
                 (Sequence) 
                 Identified 
                 Pairs) 
                 NO. 
                 NO. 
               
               
                   
               
             
            
               
                 hGPCR27 
                 Mouse 
                 AA775870 
                 1,125 bp 
                 15 
                 16 
               
               
                   
                 GPCR27 
               
               
                 hARE-1 
                 TDAG 
                 1689643 
                   999 bp 
                 17 
                 18 
               
               
                   
                   
                 AI090920 
               
               
                 hARE-2 
                 GPCR27 
                 68530 
                 1,122 bp 
                 19 
                 20 
               
               
                   
                   
                 AA359504 
               
               
                 hPPR1 
                 Bovine 
                 238667 
                 1,053 bp 
                 21 
                 22 
               
               
                   
                 PPR1 
                 H67224 
               
               
                 hG2A 
                 Mouse 
                 See Example 
                 1,113 bp 
                 23 
                 24 
               
               
                   
                 1179426 
                 2(a) below 
               
               
                 hCHN3 
                 N.A. 
                 EST 36581 
                 1,113 bp 
                 25 
                 26 
               
               
                   
                   
                 (full length) 
               
               
                 hCHN4 
                 TDAG 
                 1184934 
                 1,077 bp 
                 27 
                 28 
               
               
                   
                   
                 AA804531 
               
               
                 hCHN6 
                 N.A. 
                 EST 2134670 
                 1,503 bp 
                 29 
                 30 
               
               
                   
                   
                 (full length) 
               
               
                 hCHN8 
                 KIAA0001 
                 EST 76445 
                 1,029 bp 
                 31 
                 32 
               
               
                 hCHN9 
                 1365839 
                 EST 1541536 
                 1,077 bp 
                 33 
                 34 
               
               
                 hCHN10 
                 Mouse EST 
                 Human 
                 1,005 bp 
                 35 
                 36 
               
               
                   
                 1365839 
                 1365839 
               
               
                 hRUP4 
                 N.A. 
                 AI307658 
                 1,296 bp 
                 37 
                 39 
               
               
                   
               
               
                 N.A. = “not applicable”   
               
            
           
         
       
     
     2. Full Length Cloning 
     a. hG2A (Seq. Id. Nos. 23 &amp; 24) 
     Mouse EST clone 1179426 was used to obtain a human genomic clone containing all but three amino acid hG2A coding sequences. The 5′end of this coding sequence was obtained by using 5′RACE™, and the template for PCR was Clontech&#39;s Human Spleen Marathon-ready™ cDNA. The disclosed human G2A was amplified by PCR using the G2A cDNA specific primers for the first and second round PCR as shown in SEQ. ID. NO.: 39 and SEQ. ID. NO.: 40 as follows:
         5′-CTGTGTACAGCAGTTCGCAGAGTG-3′(SEQ. ID. NO.: 39; 1 st  round PCR)   5′-GAGTGCCAGGCAGAGCAGGTAGAC-3′(SEQ. ID. NO.: 40; second round PCR).       

     PCR was performed using Advantage™ GC Polymerase Kit (Clontech; manufacturing instructions will be followed), at 94° C. for 30 sec followed by 5 cycles of 94° C. for 5 sec and 72° C. for 4 min; and 30 cycles of 94° for 5 sec and 70° for 4 min. An approximate 1.3 Kb PCR fragment was purified from agarose gel, digested with Hind III and Xba I and cloned into the expression vector pRC/CMV2 (Invitrogen). The cloned-insert was sequenced using the T7 Sequenase™ kit (USB Amersham; manufacturer instructions will be followed) and the sequence was compared with the presented sequence. Expression of the human G2A will be detected by probing an RNA dot blot (Clontech; manufacturer instructions will be followed) with the P 32 -labeled fragment. 
     b. hCHN9 (Seq. Id. Nos. 33 &amp; 34) 
     Sequencing of the EST clone 1541536 indicated that hCHN9 is a partial cDNA clone having only an initiation codon; ie., the termination codon was missing. When hCHN9 was used to “blast” against the data base (nr), the 3′ sequence of hCHN9 was 100% homologous to the 5′ untranslated region of the leukotriene B4 receptor cDNA, which contained a termination codon in the frame with hCHN9 coding sequence. To determine whether the 5′ untranslated region of LTB4R cDNA was the 3′ sequence of hCHN9, PCR was performed using primers based upon the 5′ sequence flanking the initiation codon found in hCHN9 and the 3′ sequence around the termination codon found in the LTB4R 5′ untranslated region. The 5′ primer sequence utilized was as follows:
         5′-CCCGAATTCCTGCTFGCTCCCAGCTTGGCCC-3′ SEQ. ID. NO.: 41; sense) and   5′-TGTGGATCCTGCTGTCAAAGGTCCCATTCCGG-3′ (SEQ. ID. NO.: 42; antisense).
 
PCR was performed using thymus cDNA as a template and rTth polymerase (Perkin Elmer) with the buffer system provided by the manufacturer, 0.25 uM of each primer, and 0.2 mM of each 4 nucleotides. The cycle condition was 30 cycles of 94° C. for 1 min, 65° C. for 1 min and 72° C. for 1 min and 10 sec. A 1.1 kb fragment consistent with the predicted size was obtained from PCR. This PCR fragment was subcloned into pCMV (see below) and sequenced (see, SEQ. ID. NO.: 33).
       

     c. hRUP4 (Seq. Id. Nos. 37 &amp; 38) 
     The full length hRUP4 was cloned by RT-PCR with human brain cDNA (Clontech) as templates:
         5′-TCACAATGCTAGGTGTGGTC-3′ (SEQ. ID. NO.: 43; sense) and   5′-TGCATAGACAATGGGATTACAG-3′ (SEQ. ID. NO.: 44; antisense).
 
PCR was performed using TaqPlus™ Precision™ polymerase (Stratagene; manufacturing instructions will be followed) by the following cycles: 94° C. for 2 min; 94° C. 30 sec; 55° C. for 30 sec, 72° C. for 45 sec, and 72° C. for 10 min. Cycles 2 through 4 were repeated 30 times.
       

     The PCR products were separated on a 1% agarose gel and a 500 bp PCR fragment was isolated and cloned into the pCRII-TOPO vector (Invitrogen) and sequenced using the T7 DNA Sequenase™ kit (Amsham) and the SP6/T7 primers (Stratagene). Sequence analysis revealed that the PCR fragment was indeed an alternatively spliced form of AI307658 having a continuous open reading frame with similarity to other GPCRs. The completed sequence of this PCR fragment was as follows: 
     
       
         
           
               
               
            
               
                 5′-TCACAATGCTAGGTGTGGTCTGGCTGGTG 
                 (SEQ. ID. NO.: 45) 
               
               
                 GCAGTCATAGTAGGATCACCATGTGGCACGTG 
               
               
                 CAACAACTTGAGATCAAATCTGACTTCCTATA 
               
               
                 TGAAAAGGAACACATCTGCTGCTTAGAAGAGT 
               
               
                 GGACCAGCCCTGTGCACCAGAAGATCTACACC 
               
               
                 ACCTTCATCCTTGTCATCCTCTTCCTCCTGCC 
               
               
                 TCTTATGGTGATGCTTATTCTGTACGTAAAAT 
               
               
                 TGGTTATGAACTTTGGATAAAGAAAAGAGTTG 
               
               
                 GGGATGGTTCAGTGCTTCGAACTATTCATGGA 
               
               
                 AAAGAAATGTCCAAAATAGCCAGGAAGAAGAA 
               
               
                 ACGAGCTGTCATTATGATGGTGACAGTGGTGG 
               
               
                 CTCTCTTTGCTGTGTGCTGGGCACCATTCCAT 
               
               
                 GTTGTCCATATGATGATTGAATACAGTAATTT 
               
               
                 TGAAAAGGAATATGATGATGTCACAATCAAGA 
               
               
                 TGATTTTTGATATCGTGCAAATTATTGGATTT 
               
               
                 TCCAACTCCATCTGTAATCCCATTGTCTATGC 
               
               
                 A-3′ 
               
            
           
         
       
     
     Based on the above sequence, two sense oligonucleotide primer sets: 
                    (SEQ. ID. NO.: 46; oligo 1)                 5′-CTGCTTAGAAGAGTGGACCAG-3′                 (SEQ. ID. NO.: 47; oligo 7)                 5′-CTGTGCACGAGAAGATCTACAC-3′       and two antisense oligonucleotide primer sets:                 (SEQ. ID. NO.: 48; oligo 3)                 5′-CAAGGATGAAGGTGGTGTAGA-3′                 (SEQ. ID. NO.: 49; oligo 4)                 5′-GTGTAGATCTTCTGGTGCACAGG-3′            
were used for 3′-and 5′-race PCR with a human brain Marathon-Ready™ cDNA (Clontech, Cat# 7400-1) as template, according to manufacture&#39;s instructions. DNA fragments generated by the RACE PCR were cloned into the pCRII-TOPO™ vector (Invitrogen) and sequenced using the SP6/T7 primers (Stratagene) and some internal primers. The 3′ RACE product contained a poly(A) tail and a completed open reading frame ending at a TAA stop codon. The 5′ RACE product contained an incomplete 5′ end; i.e., the ATG initiation codon was not present.
 
     Based on the new 5′ sequence, oligo 3 and the following primer:
         5′-GCAATGCAGGTCATAGTGAGC-3′ (SEQ. ID. NO.: 50; oligo 5)
 
were used for the second round of 5′ RACE PCR and the PCR products were analyzed as above. A third round of 5′ RACE PCR was carried out utilizing antisense primers:
   5′-TGGAGCATGGTGACGGGAATGCAGAAG-3′ (SEQ. ID. NO.: 51; oligo 6) and   5′-GTGATGAGCAGGTCACTGAGCGCCAAG-3′ (SEQ. ID. NO.: 52; oligo7).
 
The sequence of the 5′ RACE PCR products revealed the presence of the initiation codon ATG, and further round of 5′ RACE PCR did not generate any more 5′ sequence. The completed 5′ sequence was confirmed by RT-PCR using sense primer 5′-GCAATGCAGGCGCTTAACATFAC-3′ (SEQ. ID. NO.: 53; oligo 8)
 
and oligo 4 as primers and sequence analysis of the 650 bp PCR product generated from human brain and heart cDNA templates (Clontech, Cat# 7404-1). The completed 3′ sequence was confirmed by RT-PCR using oligo 2 and the following antisense primer:
   5′-TTGGGTTACAATCTGAAGGGCA-3′ (SEQ. ID. NO.: 54; oligo 9)
 
and sequence analysis of the 670 bp PCR product generated from human brain and heart cDNA templates. (Clontech, Cat# 7404-1).
       

     d. hRUP5 (Seq. Id. Nos. 9 &amp; 10) 
     The full length hRUP5 was cloned by RT-PCR using a sense primer upstream from ATG, the initiation codon (SEQ. ID. NO.: 55), and an antisense primer containing TCA as the stop codon (SEQ. ID. NO.: 56), which had the following sequences: 
                        5′-ACTCCGTGTCCAGCAGGACTCTG-3′   (SEQ. ID. NO.: 55)       5′-TGCGTGTTCCTGGACCCTCACGTG-3′   (SEQ. ID. NO.: 56)            
and human peripheral leukocyte cDNA (Clontech) as a template. Advantage cDNA polymerase (Clontech) was used for the amplification in a 50 ul reaction by the following cycle with step 2 through step 4 repeated 30 times: 94° C. for 30 sec: 94° for 15 sec; 69° for 40 sec; 72° C. for 3 min; and 72° C. from 6 min. A 1.4 kb PCR fragment was isolated and cloned with the pCRII-TOPO™ vector (Invitrogen) and completely sequenced using the T7 DNA Sequenase™ kit (Amsham). See, SEQ. ID. NO.: 9.
 
     e. hRUP6 (Seq. Id. Nos. 11 &amp; 12) 
     The full length hRUP6 was cloned by RT-PCR using primers: 
                    (SEQ. ID. NO.: 57)                         5′-CAGGCCTTGGATTTTAATGTCAGGGATGG-3′ and                 (SEQ. ID. NO.: 58)                         5′-GGAGAGTCAGCTCTGAAAGAATTCAGG-3′;            
and human thymus Marathon-Ready™ cDNA (Clontech) as a template. Advantage cDNA polymerase (Clontech, according to manufacturer&#39;s instructions) was used for the amplification in a 50 ul reaction by the following cycle: 94° C. for 30sec; 94° C. for 5 sec; 66° C. for 40sec; 72° C. for 2.5 sec and 72° C. for 7 min. Cycles 2 through 4 were repeated 30 times. A 1.3 Kb PCR fragment was isolated and cloned into the pCRII-TOPO™ vector (Invitrogen) and completely sequenced (see, SEQ. ID. NO.: 11) using the ABI Big Dye Terminator™ kit (P.E. Biosystem).
 
     f. hRUP7 (Seq. Id. Nos. 13 &amp; 14) 
     The full length RUP7 was cloned by RT-PCR using primers: 
                    (SEQ. ID. NO.: 59; sense)                         5′-TGATGTGATGCCAGATACTAATAGCAC-3′           and                 (SEQ. ID. NO.: 60; antisense)                         5′-CCTGATTCATTTAGGTGAGATTGAGAC-3′            
and human peripheral leukocyte cDNA (Clontech) as a template. Advantage™ cDNA polymerase (Clontech) was used for the amplification in a 50 ul reaction by the following cycle with step 2 to step 4 repeated 30 times: 94° C. for 2 minutes; 94° C. for 15 seconds; 60° C. for 20 seconds; 72° C. for 2 minutes; 72° C. for 10 minutes. A 1.25 Kb PCR fragment was isolated and cloned into the pCRII-TOPO™ vector (Invitrogen) and completely sequenced using the ABI Big Dye Terminator™ kit (P.E. Biosystem). See, SEQ. ID. NO.: 13.
 
     g. hARE-5 (Seq. Id. Nos. 5 &amp; 6) 
     The full length hARE-5 was cloned by PCR using the hARE5 specific primers 5′-CAGCGCAGGGTGAAGCCTGAGAGC-3′ SEQ. ID. NO.: 69 (sense, 5′ of initiation codon ATG) and 5′-GGCACCTGCTGTGACCTGTGCAGG-3′ SEQ. ID. NO.: 70 (antisense, 3′ of stop codon TGA) and human genomic DNA as template. TaqPlus Precision™ DNA polymerase (Stratagene) was used for the amplification by the following cycle with step 2 to step 4 repeated 35 times: 96° C., 2 minutes; 96° C., 20 seconds; 58° C., 30 seconds; 72° C, 2 minutes; and 72° C., 10 minutes 
     A 1.1 Kb PCR fragment of predicated size was isolated and cloned into the pCRII-TOPO™ vector (Invitrogen) and completely sequenced (SEQ. ID. NO.: 5) using the T7 DNA Sequenase™ kit (Amsham). 
     h. hARE-4 (Seq. Id. Nos.: 3 &amp; 4) 
     The full length hARE-4 was cloned by PCR using the hARE-4 specific primers 5′-CTGGTGTGCTCCATGGCATCCC-3′ SEQ.ID.NO.:67 (sense, 5′ of initiation condon ATG) and 5′-GTAAGCCTCCCAGAACAGAGG-3′ SEQ. ID. NO.: 68 (antisense, 3′ of stop codon TGA) and human genomic DNA as template. Taq DNA polymerase (Stratagene) and 5% DMSO was used for the amplification by the following cycle with step 2 to step 3 repeated 35 times: 94° C., 3 minutes; 94° C., 30 seconds; 59° C., 2 minutes; 72° C., 10 minute 
     A 1.12 Kb PCR fragment of predicated size was isolated and cloned into the pCRII-TOPO™ vector (Invitrogen) and completely sequenced (SEQ. ID. NO.: 3) using the T7 DNA Sequenase™ kit (Amsham). 
     i. hARE-3 (Seq. Id. Nos.: 1 &amp; 2) 
     The full length hARE-3 was cloned by PCR using the hARE-3 specific primers 5′-gatcaagcttCCATCCTACTGAAACCATGGTC-3′ SEQ.ID.NO65 (sense, lower case nucleotides represent Hind III overhang, ATG as initiation codon) and 5′-gatcagatctCAGTT CCAATATTCACACCACCGTC-3′ SEQ. ID. NO.: 66 (antisense, lower case nucleotides represent Xba I overhang, TCA as stop codon) and human genomic DNA as template. TaqPlus Precision™ DNA polymerase (Stratagene) was used for the amplification by the following cycle with step 2 to step 4 repeated 35 times: 94° C., 3 minutes; 94° C., 1 minute; 55° C., 1 minute; 72° C., 2 minutes; 72° C., 10 minutes. 
     A 1.3 Kb PCR fragment of predicated size was isolated and digested with Hind III and Xba I, cloned into the pRC/CMV2 vector (Invitrogen) at the Hind III and Xba I sites and completely sequenced (SEQ. ID. NO.: 1) using the T7 DNA Sequenase™ kit (Amsham). 
     j. hRUP3 (Seq. Id. Nos.: 7 &amp; 8) 
     The full length hRUP3 was cloned by PCR using the hRUP3 specific primers 5′-GTCCTGCCACTTCGAGACATGG-3′ SEQ. ID.NO.:71 (sense, ATG as intiation codon) and 5′-GAAACTTCTCTCTGCCCTTACCGTC-3′ 
     SEQ.ID.NO.:72 (antisense, 3′ of stop codon TAA) and human genomic DNA as template. TaqPlus Precision™ DNA polymerase (Stratagene) was used for the amplification by the following cycle with step 2 to step 4 repeated 35 times: 94° C., 3 minutes; 94° C., 1 minute; 58° C., 1 minute; 72° C., 2 minutes: 72° C., 10 minutes 
     A 1.0 Kb PCR fragment of predicated size was isolated and cloned into the pCRII-TOPO™ vector (Invitrogen) and completely sequenced (SEQ. ID. NO.: 7)using the T7 DNA sequenase kit (Amsham). 
     Example 2 
     Receptor Expression 
     Although a variety of cells are available to the art for the expression of proteins, it is most preferred that mammalian cells be utilized. The primary reason for this is predicated upon practicalities, i.e., utilization of, e.g., yeast cells for the expression of a GPCR, while possible, introduces into the protocol a non-mammalian cell which may not (indeed, in the case of yeast, does not) include the receptor-coupling, genetic-mechanism and secretary pathways that have evolved for mammalian systems—thus, results obtained in non-mammalian cells, while of potential use, are not as preferred as that obtained from mammalian cells. Of the mammalian cells, COS-7, 293 and 293T cells are particularly preferred, although the specific mammalian cell utilized can be predicated upon the particular needs of the artisan. The general procedure for expression of the disclosed GPCRs is as follows. 
     On day one, 1×10 7 293T cells per 150 mm plate were plated out. On day two, two reaction tubes will be prepared (the proportions to follow for each tube are per plate): tube A will be prepared by mixing 20 μg DNA (e.g., pCMV vector, pCMV vector with receptor cDNA, etc.) in 1.2 ml serum free DMEM (Irvine Scientific, Irvine, Calif.); tube B will be prepared by mixing 120 μl lipofectamine (Gibco BRL) in 1.2 ml serum free DMEM. Tubes A and B are admixed by inversions (several times), followed by incubation at room temperature for 30-45 min. The admixture can be referred to as the “transfection mixture”. Plated 293T cells are washed with 1×PBS, followed by addition of 10 ml serum free DMEM. 2.4 ml of the transfection mixture will then be added to the cells, followed by incubation for 4 hrs at 37° C./5% CO 2 . The transfection mixture was then be removed by aspiration, followed by the addition of 25 ml of DMEM/10% Fetal Bovine Serum. Cells will then be incubated at 37° C./5% CO 2 . After 72hr incubation, cells can then be harvested and utilized for analysis. 
     Example 3 
     Tissue Distribution of the Disclosed Human GPCRs 
     Several approaches can be used for determination of the tissue distribution of the GPCRs disclosed herein. 
     1. Dot-Blot Analysis 
     Using a commercially available human-tissue dot-blot format, endogenous orphan GPCRs were probed for a determination of the areas where such receptors are localized. cDNA fragments from the GPCRs of Example 1 (radiolabelled) were (or can be) used as the probe: radiolabeled probe was (or can be) generated using the complete receptor cDNA (excised from the vector) using a Prime-It II™ Random Primer Labeling Kit (Stratagene, #300385), according to manufacturer&#39;s instructions. A human RNA Master Blot™ (Clontech, #7770-1) was hybridized with the endogenous human GPCR radiolabeled probe and washed under stringent conditions according manufacturer&#39;s instructions. The blot was exposed to Kodak BioMax™ Autoradiography film overnight at −80° C. Results are summarized for several receptors in Table B and C (see  FIGS. 1A and 1B  for a grid identifying the various tissues and their locations, respectively). Exemplary dot-blots are provided in  FIGS. 2A and 2B  for results derived using hCHN3 and hCHN8, respectively. 
     
       
         
           
               
               
             
               
                 TABLE B 
               
               
                   
               
               
                   
                 Tissue Distribution 
               
               
                 ORPHAN GPCR 
                 (highest levels, relative to other tissues in the dot-blot 
               
               
                   
               
             
            
               
                 hGPCR27 
                 Fetal brain, Putamen, Pituitary gland, Caudate nucleus 
               
               
                 hARE-1 
                 Spleen, Peripheral leukocytes, Fetal spleen 
               
               
                 hPPR1 
                 Pituitary gland, Heart, salivary gland, Small intestine, 
               
               
                   
                 Testis 
               
               
                 hRUP3 
                 Pancreas 
               
               
                 hCHN3 
                 Fetal brain, Putamen, Occipital cortex 
               
               
                 hCHN9 
                 Pancreas, Small intestine, Liver 
               
               
                 hCHN10 
                 Kidney, Thyroid 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE C 
               
               
                   
               
               
                   
                 Tissue Distribution 
               
               
                 ORPHAN GPCR 
                 (highest levels, relative to other tissues in the dot-blot 
               
               
                   
               
             
            
               
                 hARE-3 
                 Cerebellum left, Cerebellum right, Testis, Accumbens 
               
               
                 hGPCR3 
                 Corpus collusum, Caudate nucleus, Liver, Heart, Inter- 
               
               
                   
                 Ventricular Septum 
               
               
                 hARE-2 
                 Cerebellum left, Cerebellum right, Substantia 
               
               
                 hCHN8 
                 Cerebellum left, Cerebellum right, Kidney, Lung 
               
               
                   
               
            
           
         
       
     
     To ascertain the tissue distribution of hRUP3 mRNA, RT-PCR was performed using hRUP3-specific primers and human multiple tissue cDNA panels (MTC, Clontech) as templates. Taq DNA polymerase (Stratagene) was utilized for the PCR reaction, using the following reaction cycles in a 40 ul reaction: 94° C. for 2 min; 94° C. for 15 sec; 55° C. for 30 sec; 72° C. for 1 min: 72° C., for 10 min. Primers were as follows: 
                    (SEQ. ID. NO.: 61; sense)                         5′-GACAGGTACCTTGCCATCAAG-3′                 (SEQ. ID. NO.: 62; antisense)                         5′-CTGCACAATGCCAGTGATAAGG-3′.            
20 ul of the reaction was loaded onto a 1% agarose gel: results are set forth in FIG.  3 .
 
     As is supported by the data of  FIG. 3 , of the 16 human tissues in the cDNA panel utilized (brain, colon, heart, kidney, lung, ovary, pancreas, placenta, prostate, skeleton, small intestine, spleen, testis, thymus leukocyte, and liver) a single hRUP3 band is evident only from the pancreas. Additional comparative analysis of the protein sequence of hRUP3 with other GPCRs suggest that hRUP3 is related to GPCRs having small molecule endogenous ligand such that it is predicted that the endogenous ligand for hRUP3 is a small molecule. 
     b. hRUP4 
     RT-PCR was performed using hRUP4 oligo&#39;s 8 and 4 as primers and the human multiple tissue cDNA panels (MTC, Clontech) as templates. Taq DNA polymerase (Stratagene) was used for the amplification in a 40 ul reaction by the following cycles: 94° C. for 30 seconds, 94° C. for 10 seconds, 55° C. for 30 seconds, 72° C. for 2 minutes, and 72° C. for 5 minutes with cycles 2 through 4 repeated 30 times. 
     20 ul of the reaction were loaded on a 1% agarose gel to analyze the RT-PCR products, and hRUP4 mRNA was found expressed in many human tissues, with the strongest expression in heart and kidney. (see, FIG.  4 ). To confirm the authenticity of the PCR fragments, a 300 bp fragment derived from the 5′ end of hRUP4 was used as a probe for the Southern Blot analysis. The probe was labeled with  32 P-dCTP using the Prime-It II™ Random Primer Labeling Kit (Stratagene) and purified using the ProbeQuant™ G-50 micro columns (Amersham). Hybridization was done overnight at 42° C. following a 12 hr pre-hybridization. The blot was finally washed at 65° C. with 0.1×SSC. The Southern blot did confirm the PCR fragments as hRUP4. 
     c. hRUP5 
     RT-PCR was performed using the following hRUP5 specific primers: 
                    (SEQ. ID. NO.: 63; sense)                         5′-CTGACTTCTTGTTCCTGGCAGCAGCGG-3′                 (SEQ. ID. NO.: 64; antisense)                         5′-AGACCAGCCAGGGCACGCTGAAGAGTG-3′            
and the human multiple tissue cDNA panels (MTC, Clontech) as templates. Taq DNA polymerase (Stratagene) was used for the amplification in a 40 ul reaction by the following cycles: 94° C. for 30 sec, 94° C. for 10 sec, 62° C. for 1.5 min, 72° C. for 5 min, and with cycles 2 through 3 repeated 30 times. 20 ul of the reaction were loaded on a 1.5% agarose gel to analyze the RT-PCR products, and hRUP5 mRNA was found expressed only in the peripheral blood leukocytes (data not shown).
 
     d. hRUP6 
     RT-PCR was applied to confirm the expression and to determine the tissue distribution of hRUP6. Oligonucleotides used, based on an alignment of AC005871 and GPR66 segments, had the following sequences: 
                    (SEQ. ID. NO.: 73; sense)                         5′-CCAACACCAGCATCCATGGCATCAAG-3′,                 (SEQ. ID. NO.: 74; antisense)                         5′-GGAGAGTCAGCTCTGAAAGAATTCAGG-3′            
and the human multiple tissue cDNA panels (MTC, Clontech) were used as templates. PCR was performed using TaqPlus Precision™ polymerase (Stratagene; manufacturing instructions will be followed) in a 40 ul reaction by the following cycles: 94° C. for 30 sec; 94° C. 5 sec; 66° C. for 40 sec, 72° C. for 2.5 min, and 72° C. for 7 min. Cycles 2 through 4 were repeated 30 times.
 
     20 ul of the reaction were loaded on a 1.2% agarose gel to analyze the RT-PCR products, and a specific 760 bp DNA fragment representing hRUP6 was expressed predominantly in the thymus and with less expression in the heart, kidney, lung, prostate small intestine and testis. (see, FIG.  5 ). 
     It is intended that each of the patents, applications, and printed publications mentioned in this patent document be hereby incorporated by reference in their entirety. 
     As those skilled in the art will appreciate, numerous changes and modifications may be made to the preferred embodiments of the invention without departing from the spirit of the invention. It is intended that all such variations fall within the scope of the invention and the claims that follow. 
     Although a variety of Vectors are available to those in the art, for purposes of utilization for both endogenous and non-endogenous human GPCRs, it is most preferred that the Vector utilized be pCMV. This vector was deposited with the American Type Culture Collection (ATCC) on Oct. 13, 1998 (10801 University Blvd., Manassas, Va. 20110-2209 USA) under the provisions of the Budapest Treaty for the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure. The DNA was tested by the ATCC and determined to be. The ATCC has assigned the following deposit number to pCMV: ATCC #203351.