Molecular Characterization and Expression of Cloned Human Galanin Receptors GALR2 and GALR3

Abstract

Abstract:Galanin is a 29-or 30-amino acid peptide with wide-ranging effects on hormone release, feeding behavior, smooth muscle contractility, and somatosensory neuronal function. Three distinct galanin receptor (GALR) subtypes, designated GALR1, 2, and 3, have been cloned from the rat. We report here the cloning of the human GALR2 and GALR3 genes, an initial characterization of their pharmacology with respect to radioligand binding and signal transduction pathways, and a profile of their expression in brain and peripheral tissues. Human GALR2 and GALR3 show, respectively, 92 and 89% amino acid sequence identity with their rat homologues. Radioligand binding studies with 125l-galanin show that recombinant human GALR2 binds with high affinity to human galanin (K 0 = 0.3 nM). Human GALR3 binds galanin with less affinity (IC50 of 12 nM for porcine galanin and 75 nM for human galanin). Human GALR2 was shown to couple to phospholipase C and elevation of intracellular calcium levels as assessed by aequorin luminescence in HEK-293 cells and by Xenopus melanophore pigment aggregation and dispersion assays, in contrast to human GALR1 and human GALR3, which signal predominantly through inhibition of adenylate cyclase. GALR2 mRNA shows a wide distribution in the brain (mammillary nuclei, dentate gyrus, cingulate gyrus, and posterior hypothalamic, supraoptic, and arcuate nuclei), and restricted peripheral tissue distritution with highest mRNA levels detected in human small intestine. In comparison, whereas GALR3 mRNA was expressed in many areas of the rat brain, there was abundant expression in the primary 01-factory cortex, olfactory tubercie, the islands of Calleja, the hippocampal CA regions of Ammon's horn, and the dentate gyrus. GALR3 mRNA was highly expressed in human testis and was detectable in adrenal gland and pancreas. The genes for human GALR2 and 3 were localized to chromosomes 17q25 and 22q12.2-13.1, respectively. Key Words: Galanin receptor-G protein-coupled receptor-Cloning.

Galanin Protects Against Behavioral and Neurochemical Correlates of Opiate Reward

“…Galanin decreases presynaptic DA release in striatal slices (Tsuda et al, 1998) and one possible explanation for the heightened sensitivity of GKO mice to morphine-induced locomotion and CPP is that knockout of the peptide may result in hyperactivation of DA signaling following opiate administration. Whereas mRNA levels for galanin receptors are low in the NAc, galanin receptor binding is quite prominent (Burgevin et al, 1995;Gustafson et al, 1996;Hawes and Picciotto, 2004;Kolakowski et al, 1998;Waters and Krause, 2000), indicating that localization of galanin receptors on DA terminals might regulate DA release. Galanin is also known to be a potent inhibitory modulator of basal acetylcholine (ACh) release in the striatum (Antoniou et al, 1997) and it has been demonstrated that M1-muscarinic receptors and high-affinity nicotinic receptors regulate the secondary rewarding effects of cues paired with a primary reinforcer such as morphine (Brunzell et al, 2006;Carrigan and Dykstra, 2007).…”

“…All three galanin receptor subtypes, as well as significant galanin binding, are found in the ventral tegmental area (VTA), amygdala, nucleus accumbens (NAc), cingulate cortex, and locus coeruleus (LC) (Burgevin et al, 1995;Gustafson et al, 1996;Hawes and Picciotto, 2004;Kolakowski et al, 1998;Waters and Krause, 2000), areas of the brain known to contribute to drug addiction and reward. Galanin also regulates the levels and release of a number of neurotransmitters, including dopamine, acetylcholine, and norepinephrine (Pieribone et al, 1995;Tsuda et al, 1998;Wang et al, 1999).…”

Galanin and galanin receptor expression in neuroblastic tumours: correlation with their differentiation status

“…The biological activities of Gal-R1 and -R3 receptors are mediated by Gi/G0 G-proteins, leading to the inhibition of adenylate cyclase (Kolakowski et al, 1998). In our study, their associated signalling pathways may have played a role in the poorly differentiated NT (or NB).…”

“…Sequences were complementary to the nucleotides 60 -107, 139 -186 encoding for human preprogalanin (McKnight et al, 1992), to nucleotides 6 -53, 984 -1031 of the mRNA encoding the human Gal-R1 (HabertOrtoli et al, 1994), to nucleotides 91 -138, 1001 -1048 of the mRNA encoding the human Gal-R2 (Kolakowski et al, 1998) and to nucleotides 41 -88, 921 -968 of the mRNA encoding the human Gal-R3 (Kolakowski et al, 1998).…”

“…Accounting for the different biological effects, three distinct G-protein-coupled galanin receptor subtypes termed Gal-R1, Gal-R2 and Gal-R3 have been cloned in human (Habert-Ortoli et al, 1994;Kolakowski et al, 1998). Experiments in animal models suggest a role for this peptide within the sympathetic nervous system during its development (Garcia-Arraras and Torres-Avillan, 1999).…”