Growth hormone secretagogue receptor family members and ligands

We have previously reported the cloning and characterization of a new orpha n G-protein-coupled receptor (GPC-R), the growth hormone secretagogue recep tor (GHS-R), and shown that this receptor mediates the activity of the grow th hormone-releasing peptides (CHRPs) and nonpeptide ligands such as L-692, 429 and MK-0677. Because the GHS-R obviously does not belong to any of the known GPC-R subfamilies, we searched for GHS-R family members by screening a human genomic library using low-stringency hybridization and screening a Pufferfish genomic library. The Pufferfish was selected because of its comp act genome. From the human genomic library, a homolog, GPR38, with 52% iden tity to the GHS-R was isolated. From the Pufferfish library, three family m embers were isolated. The Pufferfish gene having 58% identity to the GHS-R, on expression in HEK293 cells, was activated with GHRP-6 and MK-0677. Thes e results indicate that the CHS-R has been conserved for at least 400 milli on years and that the Pufferfish genome is appropriate for isolation of GHS -R family members. In our search for endogenous ligands for the orphan rece ptors CHS-R and GPR38, we showed that adenosine is a partial agonist of the GHS-R and that motilin is the endogenous ligand for GPR38. We also confirm ed that the endogenous ligand ghrelin is a full agonist of the GHS-R.