Identification and characterization of the chicken galanin receptor GalR2 and a novel GalR2-like receptor (GalR2-L).

In mammals, the neuropeptide galanin exerts a variety of physiological roles in the neuroendocrine system through its interactions with three galanin receptor subtypes (GalR1, GalR2 and GalR3). However, little is known about the characteristics of galanin receptors in birds, and it is only recently that avian GalR1 and a novel GalR1-like receptor were first identified in chickens. In this study, we report the cDNA cloning and characterization of the other two chicken galanin receptors, the galanin type II receptor (cGalR2) and a novel GalR2-like receptor (GalR2-L), which share high degrees of similarity in sequence identity, gene structure and signaling properties. cGalR2 and cGalR2-L cDNAs encode two putative receptors of 371 and 370 amino acids, in which they show considerable amino acid sequence identities (65-67%, and 53-55%, respectively) with the mammalian GalR2. RT-PCR assays revealed that cGalR2 and cGalR2-L mRNA were widely expressed in the adult chicken tissues including the whole brain, intestine, lung, ovary, pituitary and different regions of the oviduct. As assayed with different luciferase reporter systems, chicken galanin (cGal 1-29) and human galanin-like peptide (hGALP 1-60) were demonstrated to stimulate the luciferase activities in Chinese hamster ovary cells expressing cGalR2 and cGalR2-L through the activations of cAMP/PKA, Ca(2+)/calcineurin and MAPK/ERK signaling pathways, hence suggesting that both receptors are functionally coupled to the G(s) and G(q) proteins. Furthermore, the previously identified cGalR1 and cGalR1-L were found to be solely coupled to the G(i/o) proteins, and the hGALP (1-60) exhibited only a low potency to cGalR1, cGalR1-L, cGalR2 and cGalR2-L activations.