Cloning and Expressional Characterization of a Novel Galanin Receptor

Abstract

Galanin, a 29 -30 amino acid neuropeptide, is found in the central and peripheral nervous systems and displays several important physiological activities. The actions are believed to be mediated through distinct G proteincoupled receptors. To date, two galanin receptor subtypes have been cloned. In this report, we describe the cloning and expression of a cDNA encoding a novel galanin receptor (GalR3). The receptor has 370 amino acids and shares 36 and 54% homology with the rat GalR1 and GalR2 receptors.125 I-Porcine galanin binds the rat GalR3 receptor expressed in COS-7 cells with high affinity (K d ‫؍‬ 0.6 nM) and could be displaced by galanin and galanin fragments and galanin-chimeric peptides. The pharmacological profile of this novel receptor is distinct from those of GalR1 and GalR2, revealing different pharmacophores within galanin for the three galanin receptor subtypes. Northern blot analysis showed expression in heart, spleen, and testis. Unlike GalR1 and GalR2, no expression of GalR3 was detectable in the brain, suggesting that GalR3 may mediate some of the peripheral functions of galanin.Galanin is a 29 -30 amino acid neuropeptide with no significant homology to any known family of biologically active peptides (1). Galanin is widely distributed in the central and peripheral nervous systems and is highly expressed in various regions of the brain. Many physiological processes are modulated by galanin, including neurotransmitter and hormone release (2), spinal reflexes, nociception (3), firing of noradrenergic neurons, and contraction of gastrointestinal smooth muscle (4, 5). Like neuropeptide Y, centrally administered galanin potently stimulates food intake in animals (6), suggesting a role for galanin in control of body weight.A large body of evidence suggests that galanin mediates the various physiological functions through interaction with distinct receptor subtypes. Pharmacological studies with several peptidic agonists and antagonists of galanin receptor suggest the existence of multiple receptor subtypes (7-9). The first of these receptors (GalR1) has been cloned from several species (10 -13). More recently, a second galanin receptor subtype (GalR2) was cloned. GalR2 is markedly dissimilar to the GalR1 receptor, sharing only 40% sequence homology (14,15). Hydropathy analysis suggests that both GalR1 and GalR2 receptors have seven hydrophobic transmembrane domains, typical of members of the G protein-coupled receptor superfamily (16). The GalR2 receptor is distinguished pharmacologically from the GalR1 receptor by its high affinity for ligand galanin-(2-29). In addition to the pharmacological differences, the GalR2 transcript is widely distributed in both central and peripheral tissues (14, 15), whereas the expression of GalR1 is more restricted to brain and spinal cord (12,13).Given that a large number of physiological actions are modulated by galanin, it is unlikely that the two cloned galanin receptors mediate all the functions of galanin. A complete understanding of the roles of galanin requir...

The galanin receptor type 2 initiates multiple signaling pathways in small cell lung cancer cells by coupling to Gq, Gi and G12 proteins

“…of three independent experiments performed in quadruplicate. (c) Expression of RhoA in lysates of H510 (lanes 1 ± 3) or H69 cells (lanes 4 ± 6) was con®rmed by SDS ± PAGE and immunoblotting using a monoclonal anti-RhoA antibody the brain (Smith et al, 1998;Wang et al, 1997b). Functional data on GALR3 are scant; yet coexpression of the receptor with GIRK1 and GIRK4 potassium channels resulted in inward K + currents providing ®rst evidence for GALR3 being a G i -coupled receptor (Smith et al, 1998).…”

Upregulation of Galanin Binding Sites and GalR1 mRNA Levels in the Mouse Locus Coeruleus Following Chronic Morphine Treatments and Precipitated Morphine Withdrawal

“…Adenylate cyclase activity, as well as G-protein and cAMP levels, are known to be increased in the LC during opiate dependence and withdrawal, and adaptive changes in receptors negatively linked to these effectors might be part of a regulatory mechanism to reduce the activity of these neurons. Three galanin receptor subtypes have been cloned to date: GalR1, GalR2, and GalR3 (Habert-Ortoli et al 1994;Wang et al 1997a;Wang et al 1997b). GalR1 is found in many brain areas, including the ventral hippocampus, olfactory tract, hypothalamus, nucleus accumbens (nAc), and LC.…”

“…GalR2 is found in the dentate gyrus, cingulate nucleus, posterior hypothalamic, supraoptic and arcuate nuclei as well as in the periphery (Kolakowski et al 1998). GalR3 is very abundant in the periphery but is also present in the olfactory cortex, the hippocampal CA regions, and the dentate gyrus (Kolakowski et al 1998;Wang et al 1997b). Based on the distribution of galanin receptors, GalR1 is likely to comprise most galanin binding sites in the LC.…”

Suppressed kindling epileptogenesis in mice with ectopic overexpression of galanin

“…Galanin-binding sites have been mapped (7,8), and three receptor subtypes, GalR1 (9-11), GalR2 (12)(13)(14)49), and GalR3 (15), have been cloned. There is evidence for involvement of galanin in multiple neuronal functions (16,17), as also revealed in recent studies on transgenic mice (18)(19)(20).…”