Molecular cloning and pharmacological characterization of a new galanin receptor subtype.
Galanin, a 29-30-amino acid neuropeptide, is widely distributed in central and peripheral systems and mediates a variety of physiological functions. Pharmacological studies have suggested the existence of multiple receptor subtypes but only the type I (GalR1) galanin receptor has been cloned. Now we report the cloning by a combination of sib selection and rapid amplification of cDNA ends of a cDNA encoding a new galanin receptor (GalR2) from rat hypothalamus. The receptor is 372 amino acids in length and shares only 40% homology with the rat GalR1 receptor. It contains seven putative transmembrane domains with the amino and carboxyl termini being least identical to GalR1. Northern blot analyses revealed a 2-kilobase pair mRNA species distributed in several tissues, suggesting a broader functional spectrum than GalR1. 125I-Labeled human galanin binding to rat GalR2 receptor expressed in COS-1 cells was saturable (Kd = 0.59 nM) and could be displaced by galanin, several galanin fragments, and chimeric peptides. The pharmacological profiles of GalR1 and GalR2 receptors were distinguishable by galanin fragment(2-29), which bound the cloned GalR2 receptor with markedly higher affinity than the GalR1 receptor. Activation of the cloned receptor by galanin led to inhibition of forskolin-stimulated intracellular cAMP production. The cloning of this new receptor subtype should provide further insights into the mechanisms by which galanin mediates its diverse physiological functions. The identification of galanin(2-29) as a receptor-specific ligand should enhance the understanding of specificity of galanin-receptor interactions.
Wang
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S
The Schering-Plough Research Institute, Kenilworth, New Jersey 07033, USA. suke.wang@spcorp.com
Hashemi
T
T
He
C
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Strader
C
C
Bayne
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M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells / Q000378:metabolism; D003001:Cloning, Molecular; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D018076:DNA, Complementary / Q000235:genetics; D019004:Galanin / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007031:Hypothalamus / Q000737:chemistry / Q000378:metabolism; D007457:Iodine Radioisotopes; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D044088:Receptors, Galanin; D011964:Receptors, Gastrointestinal Hormone / Q000145:classification* / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D014162:Transfection
D018076:DNA, Complementary; D007457:Iodine Radioisotopes; D044088:Receptors, Galanin; D011964:Receptors, Gastrointestinal Hormone; D005576:Colforsin; D019004:Galanin; D000242:Cyclic AMP