title: Characterization of an orphan G protein-coupled receptor, GPR20, that constitutively activates Gi proteins.
abstract: GPR20 was isolated as an orphan G protein-coupled receptor from genomic DNA by PCR amplification. Although GPR20 was closely related to nucleotide or lipid receptors, the functional role of this receptor, as well as its endogenous ligand, remains unclear. Here we demonstrate that GPR20 is constitutively active in the absence of ligand, leading to continuous activation of its coupled G proteins. When GPR20 was exogenously expressed in HEK293 cells, both the basal level and the prostaglandin E(2)-induced production of cAMP were significantly decreased. A remarkable increase in [(35)S]guanosine 5'-(gamma-thio)triphosphate (GTPgammaS) binding to membrane preparations was also observed in GPR20-expressing cells. These effects of GPR20 overexpression were diminished in cells treated with pertussis toxin, suggesting that the expression of GPR20 results in the activation of G(i/o) proteins. Involvement of GPR20 in the activation of G(i/o) proteins was also supported by evidence that the disruption of a conserved DRY motif in GPR20 attenuated both [(35)S]GTPgammaS incorporation and inhibition of the prostaglandin E(2)-induced cAMP production. Knockdown of GPR20 in PC12h cells resulted in an elevation of the basal cAMP level, suggesting that the endogenous GPR20 achieves a constitutively or spontaneously active conformation. Furthermore, enhancement of [(3)H]thymidine incorporation was also observed in the GPR20-silencing cells, implying that the GPR20 expression seems to attenuate PC12h cell growth. Taken together, these data indicate that GPR20 constitutively activates G(i) proteins without ligand stimulation. The receptor may be involved in cellular processes, including control of intracellular cAMP levels and mitogenic signaling.
authors.affiliation: Department of Biochemistry and Molecular Biology, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Momoko
authors.initials: M
authors.lastname: Hase
authors.forename: Takehiko
authors.initials: T
authors.lastname: Yokomizo
authors.forename: Takao
authors.initials: T
authors.lastname: Shimizu
authors.forename: Motonao
authors.initials: M
authors.lastname: Nakamura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D000242:Cyclic AMP / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010802:Phylogeny; D011485:Protein Binding; D034622:RNA Interference; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: C529474:GPR20 protein, human; D043562:Receptors, G-Protein-Coupled; D000242:Cyclic AMP; D019206:GTP-Binding Protein alpha Subunits, Gi-Go