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

Abstract

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 histidinemethionine (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 (EC 50 Z1 . 8! 10K9 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 (EC 50 Z7 . 4!10 K9 M) supports our suggestion that the VPAC2R and PHIR shared a common ancestral receptor.

Differential regulation of kit ligand A (kitlga) expression in the zebrafish ovarian follicle cells – Evidence for the existence of a cyclic adenosine 3′, 5′ monophosphate-mediated binary regulatory system during folliculogenesis

“…In agreement with this, hCG and PACAP, which both use cAMP as the major signaling second messenger (Heindel et al, 1996;Wu et al, 2008;Zhong and Kasson, 1994), also suppressed IGF-I-induced kitlga expression and Akt phosphorylation in zebrafish follicle cells, confirming their signaling through the cAMP pathway. Because both hCG and PACAP enhance final oocyte maturation (GVBD) in the zebrafish (Pang and Ge, 1999;Wang et al, 2003;Zhou et al, 2011), the down-regulation of kitlga in the follicle cells may be part of the mechanisms by which hCG and PACAP promote the maturation.…”

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…PAC1-R cDNAs have been cloned in the goldfish C. auratus , the fugu Fugu rubripes (isoforms A and B; Cardoso et al, 2004), the sea bream Sparus auratus (isoforms A and B, and a hop-1 variant from isoform A; Cardoso et al, 2007b), the zebrafish D. rerio (Wu et al, 2008), the frog R. ridibunda (Alexandre et al, 1999), and the chicken Gallus domesticus (Peeters et al, 1999). Consistent with the idea that PAC1-R is a PACAP-specific receptor, both goldfish and sea bream PAC1-Rs are stimulated by PACAP27 and PACAP38, whereas VIP is a much weaker agonist.…”

“…VPAC1-R cDNAs have been cloned in the goldfish (Chow et al, 1997), the fugu (2 isoforms A and B: Cardoso et al, 2004), the dogfish Squalus acanthias (Bewley et al, 2006), the zebrafish (Wu et al, 2008) and the frog R. ridibunda (Alexandre et al, 1999). In contrast to mammals, in which VPAC1-R interacts with VIP and PACAP with similar affinities, VPAC1-R from goldfish and dogfish show higher affinities toward VIP than PACAP.…”

“…VPAC2-R cDNAs have been cloned in the goldfish (Tse et al, 2002) and the zebrafish (Wu et al, 2008). Although these receptors are structurally similar to mammalian VPAC2-R, they exhibit highest affinity to PHI and peptide histidine valine (Tse et al, 2002).…”

Distribution of growth hormone‐releasing hormone‐like peptide: Immunoreactivity in the central nervous system of the adult zebrafish (Danio rerio)

“…GHRH-LP was first isolated and characterized as a peptide in carp (Vaughan et al, 1992) and as a cDNA in salmon (Parker et al, 1993) and later in a number of other fishes (see Adams et al, 2002). A GHRH-LP receptor has been cloned from zebrafish (Wu et al, 2008), goldfish (Chan et al, 1998), and chicken (Wang et al, 2007).…”