CDB15:0000728 GRP — GRPR
Experimentally validated in Human; Orthology-inferred in Mouse, Rat, Frog, Zebrafish, Chicken, Macaque, Pig, Dog, Cow, Chimp, Horse, Marmoset, Sheep
Title
Journal:; Year Published:
Abstract
Characterization of putative GRP- and NMB-receptor antagonist's interaction with human receptors.
Peptides, 2009; PubMed, Homo sapiens GRP — Homo sapiens GRPR
ABSTRACT: The mammalian bombesin (Bn) peptides neuromedin B (NMB) and gastrin-releasing peptide (GRP) actions are mediated by two receptors (NMB-receptor, GRP-receptor) which are widely distributed in the GI tract and CNS. From primarily animal studies NMB/GRP-receptor activation has physiological/pathophysiological effects in the CNS and GI tract including stimulating of growth of cancers and normal tissues. Whereas these Bn-receptors' effects have been extensively studied in nonhuman cells and animals, little is known of the physiological/pathological role(s) in humans, largely due to lack of potent antagonists. To address this issue we compared NMB/GRP-receptor affinity/potency of 10 chemical classes of putative antagonists (35 compounds) for human Bn-receptors by performing binding studies or assessing abilities to activate hGRP/hNMB-receptor [assessing phospholipase C activation] in four different cells containing native Bn-receptors or transfected receptors. From binding studies 23 were GRP-receptor-preferring, 4 were NMB-receptor, and 8 nonselective. For the hGRP-receptor-preferring analogues none showed hGRP-receptor agonist activity, but 13 were full or partial hNMB-receptor agonists at hNMB-receptors. For hNMB-receptor-preferring analogues none were agonists. Analogue #24 ([(3-Ph-Pr(6)), His(7), d-Ala(11), d-Pro(13), Psi(13-14), Phe(14)]Bn(6-14)NH2) and analogue #7 [d-Phe(6), Leu(13), Psi(CH(2)NH), Cpa(14)]Bn(6-14) were the most potent (0.2-1.4nM) and selective (>10,000-fold) for the hGRP-receptor with analogue #7.5 [d-Tpi(6), Leu(13), Psi(CH2NH), Leu(14)]Bn(6-14)[RC-3095] (0.2-1.4nM) slightly less selective. Analogue #34 (PD168368) had the highest affinity for hNMB-receptor (1.32-1.58nM) and the greatest selectivity (2298-6952-fold) for the hNMB-receptor. These results demonstrate numerous putative hGRP/hNMB-receptor antagonists identified in nonhuman cells and/or animals have agonist activity at the hNMB-receptor, limiting their potential usefulness. However, a number were identified which were potent/selective for human Bn-receptors and should be useful for investigating their roles in human physiological/pathophysiological conditions.
Expression and characterization of cloned human bombesin receptors.
Molecular pharmacology, 1995; PubMed, Homo sapiens GRP — Homo sapiens GRPR
ABSTRACT: Little is known about the pharmacology or cell biology of human bombesin (Bn) receptors, because they are usually present at low levels and both subtypes are frequently present in the same tissues. Human gastrin-releasing peptide (GRP) receptors (huGRP-R) and human neuromedin B (NMB) receptors (huNMB-R) were stably transfected into BALB/3T3 fibroblasts. Both receptor types were glycosylated, with 35% of the huGRP-R and 38% of the huNMB-R representing carbohydrate residues. The extent of glycosylation of the transfected huGRP-R was the same as that seen in the human glioblastoma cell line U-118. Radiolabeled agonist ligands were rapidly internalized, whereas noninternalized ligand readily dissociated in a temperature-dependent fashion. The affinities of various agonists for binding to the huGRP-R were Bn (Ki = 1.4 +/- 0.2 nM) = 4 x GRP = 300 x NMB. In contrast, affinities for the huNMB-R were NMB (Ki = 8.1 +/- 5.2 nM) = 4 x Bn = 600 x GRP. [F5-D-Phe6,D-Ala11]Bn(6-13)methyl ester was the most potent huGRP-R antagonist, whereas D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2 was the most potent huNMB-R antagonist. Agonist binding to either receptor type caused activation of phospholipase C and increased cellular [3H]inositol phosphate levels. GRP was potent at increasing [3H]inositol phosphate generation in cells expressing the huGRP-R (EC50 = 13.6 +/- 1.3 nM), whereas NMB was similarly potent when acting upon cells expressing the huNMB-R (EC50 = 9.3 +/- 1.4 nM). However, neither receptor type, when stimulated with agonist, caused an increase in cAMP levels. These data show that stably transfected huGRP-R exhibit similar pharmacology for agonists and antagonists, are appropriately glycosylated, and function similarly with respect to their ability to alter biological activity, compared with natively expressed receptors. Minimal native huNMB-R data are available for comparison, but in general the huNMB-R is similar to the rat NMB receptor in its pharmacology and cell biology.