Newly-identified receptors for peptide histidine-isoleucine and GHRH-like peptide in zebrafish help to elucidate the mammalian secretin superfamily

• Published in: Journal of molecular endocrinology Vol. 41; no. 5; pp. 343 - 366
• Main Authors: Wu, Sheng, Roch, Graeme J, Cervini, Laura A, Rivier, Jean E, Sherwood, Nancy M
• Format: Journal Article
• Language: English
• Published: England Society for Endocrinology 01.11.2008; BioScientifica
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Growth Hormone-Releasing Hormone - genetics; Growth Hormone-Releasing Hormone - metabolism; Humans; Molecular Sequence Data; Peptide PHI - genetics; Peptide PHI - metabolism; Peptides - genetics; Peptides - metabolism; Phylogeny; Receptors, Cell Surface - classification; Receptors, Cell Surface - genetics; Receptors, Cell Surface - metabolism; Regular papers; Secretin - classification; Secretin - genetics; Secretin - metabolism; Sequence Alignment; Tissue Distribution; Zebrafish - genetics; Zebrafish - metabolism; Zebrafish Proteins - classification; Zebrafish Proteins - genetics; Zebrafish Proteins - metabolism
• ISSN: 0952-5041; 1479-6813
• DOI: 10.1677/JME-08-0083

A group of ten hormones in humans are structurally related and known as the secretin superfamily. These hormones bind to G-protein-coupled receptors that activate the cAMP pathway and are clustered as the secretin or B family. We used an evolutionary approach with zebrafish as a model to understand why some of these hormones, such as peptide histidine-methionine (PHM) and pituitary adenylate cyclase-activating polypeptide (PACAP)-related peptide (PRP) in humans lack a receptor. We used molecular techniques to clone two full-length receptor cDNAs in zebrafish, which were analyzed for amino acid sequence and ligand-binding motifs, phylogenetic position, synteny, tissue expression, functional response, and signaling pathway. Evidence is provided that the two cDNAs encoded the peptide histidine-isoleucine (PHI) receptor and PRP receptor, which is known as GHRH-like peptide (GHRH-LP) receptor in non-mammals. Further, we cloned a zebrafish cDNA encoding the peptides PHI and vasoactive intestinal peptide (VIP). The PHIR had been previously labeled as one type of a VIP–PACAP (VPAC2R) shared receptor based only on sequence data. The PHIR cDNA, transfected into COS7 cells, responded to zebrafish PHI in a sensitive and dose-dependent manner (EC50=1.8×10−9 M) but not to PACAP and VIP. The GHRH-LP receptor responded to both zebrafish GHRH-LP1 and GHRH with a 3.5-fold greater response to the former. For comparison, two zebrafish receptors (PAC1R and VPAC1R) and two human receptors (VPAC2R and GHRHR) were tested with human and/or zebrafish peptides. Unexpectedly, zebrafish VIP activated its PAC1R suggesting that in evolution, PAC1R is not always a specific receptor for PACAP. We conclude that zebrafish, like goldfish, have a specific receptor for PHI and GHRH-LP. Our evidence that zebrafish PHI is more potent than human PHM in activating the human VPAC2R (EC50=7.4×10−9 M) supports our suggestion that the VPAC2R and PHIR shared a common ancestral receptor.