THE MOUSE GALR2 GALANIN RECEPTOR - GENOMIC ORGANIZATION, CDNA CLONING, AND FUNCTIONAL-CHARACTERIZATION

The diverse physiological actions of galanin are thought to be mediate d through activation of galanin receptors (GalRs). We report the genom ic and cDNA cloning of a mouse GalR that possesses a genomic structure distinct from that of GalR1 and encodes a functional galanin receptor . The mouse GalR gene consists of two exons separated by a single intr on within the protein-coding region. The splicing site for the intron is located at the junction between the third transmembrane domain and the second intracellular loop. The cDNA encodes a 370-amino acid putat ive G protein-coupled receptor that is markedly different from human G alR1 and rat GalR3 (38 and 57%) but shares high homology with rat GalR 2 (94%). In binding studies utilizing membranes from COS-7 cells trans fected with mouse GalR2 cDNA, the receptor displayed high affinity (K- D = 0.47 nM) and saturable binding with I-125-galanin (B-max = 670 fmo l/mg). The radioligand binding can be displaced by galanin and its ana logues in a rank order: galanin similar or equal to M40 similar or equ al to M15 similar or equal to M35 similar or equal to C7 similar or eq ual to galanin(2-29) similar or equal to galanin(1-16) much greater th an galanin(10-29) similar or equal to galanin(3-29), which resembles t he pharmacological profile of the rat GalR2. Receptor activation by ga lanin in COS-7 cells stimulated phosphoinositide metabolism, which was not reversed by pertussis toxin. Thus, the galanin receptor encoded i n the cloned mouse GalR gene is the type 2 galanin receptor and is act ive in both ligand binding and signaling assays.