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The aim of the present report was to investigate the ligand selectivity of the human orphan G-protein- coupled receptor GPR 100 (hGPR 100), recently identified as a novel bradykinin (BK) receptor, as compared with that of the human B2 receptor (hB2R) stably transfected in Chinese hamster ovary cells. BK was able to inhibit the cAMP production induced by forskolin with a potency 100-fold lower at the hGPR100 (pEC50 = 6.6) than that measured at the hB2R (pEC50 = 8.6). Both effects were inhibited by the B2 receptor antagonist Icatibant (1 pM). The nonpeptide B2 receptor agonist FR 190997 (8 -[2, 6-dichloro-3 -[N-methylcarbamoyl)cinnamidoacetyl]-N-methylamino]benzyloxy]-2- methyl-4-( 2 -pyridylmethoxy)quinoline) did inhibit the forskolin-induced cAMP production (pEC50 = 7.7) at the hB2R, whereas it was not able to exert any effect at the hGPR100. The human insulin-like peptide relaxin 3 did inhibit the cAMP production at the hGPR 100 (pEC50 = 7.3) at a greater extent than BK, and was devoid of any effect at the hB2R. FR 190997 and relaxin 3 responses at the hB2R and hGPR100, respectively, were not inhibited by Icatibant (1 μM). These data indicate FR190997 and relaxin 3 as selective agonists for hB2R and hGPR100, respectively, and support the concept that different agonists may specifically bias the conformational states of a receptor to result in a final common 0 protein coupling, which is differentially recognized by antagonists. [ABSTRACT FROM AUTHOR]

1 G-protein-coupled receptor 100 (GPR100) was discovered by searching the human genome database for novel G-protein-coupled peptide receptors. 2 Full-length GPR100 was amplified from a cDNA library of the neuroendocrine cell line BON, which is derived from a human pancreas careinoid. The open-reading frame, present on a single exon, coded for a protein of 374 amino acids with highest sequence identity (43%) to the human orphan somotostatin- and angiotensin-like peptide receptor. The analysis of chromosomal localisation mapped the GPR100 gene to chromosome Iq21.2—q21.3. 3 The stable expression of GPR100 in Chinese hamster ovary cells together with aequorin as calcium sensor and the promiscuous G-protein subunit α16 as signal transducer revealed bradykinin and kallidin as effectors to elicit a calcium response. Dose—response curves yielded EC[sub50] values for both ligands in the low nanomolar range, while the respective analogues without arginine at the carboxy-terminus were inactive. Calcium mobilisation was inhibited by the phospholipase C blocker U73I22, but not by pertussis toxin, suggesting the involvement of the G-protein subunit αq and not αi or αo in signal transduction. 4 In line with the main function of kinins as peripheral hormones, we found that GPR100 was expressed predominantly in tissues like pancreas, heart, skeletal muscle, salivary gland, bladder. kidney, liver, placenta, stomach, jejunum, thyroid gland, ovary, and bone marrow, but smaller amounts were also detected in the brain and in cell lines derived from tumours of various origins. [ABSTRACT FROM AUTHOR]