Molecular cloning of a somatostatin-28 receptor and comparison of its expression pattern with that of a somatostatin-14 receptor in rat brain.
The tetradecapeptide somatotropin-release inhibiting factor somatostatin-14 regulates the release of peptide hormones and also functions as neurotransmitter. The octacosapeptide somatostatin-28, the N-terminally extended form of somatostatin-14, shows similar biological activities yet with different potencies. Both peptides most likely function through distinct receptors. Here we report on the molecular and functional characterization of a somatostatin-28 receptor (SSR-28) cloned from a rat brain cDNA library. The nucleotide sequence contains an open reading frame for a protein of 428 amino acid residues with a predicted molecular mass of 47 kDa. Binding assays using radiolabeled somatostatin-14 and membranes from COS cells transfected with the cloned cDNA show that this receptor, SSR-28, has a higher binding affinity for somatostatin-28 (IC50 = 0.24 nM) than for somatostatin-14 (IC50 = 0.89 nM). RNA blot analysis reveals a 4.4-kilobase mRNA in rat cerebellum and at significantly lower abundance in other brain regions. In situ hybridization indicates that SSR-28 mRNA is present in the granular and Purkinje cell layers of the cerebellum and in the large cells of the hypoglossal nucleus of the brain stem. Signals for SSR-28 mRNA do not overlap with those of a previously cloned rat receptor that preferentially binds somatostatin-14 (SSR-14). SSR-14 mRNA is found in the medial cerebellar nucleus, horizontal limb of the diagonal band, various hypothalamic nuclei, and in layers IV and V of the cortex. In the rat cerebellum, SSR-14 and SSR-28 mRNAs are developmentally regulated; the levels of the former are highest around birth and levels of the latter are highest at the adult stage.
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000502:physiology*; D003001:Cloning, Molecular / Q000379:methods; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D015870:Gene Expression; D017403:In Situ Hybridization; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D011061:Poly A / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012313:RNA / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016372:RNA, Antisense; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017481:Receptors, Somatostatin / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013004:Somatostatin / Q000378:metabolism*; D053561:Somatostatin-28; D014162:Transfection
D016372:RNA, Antisense; D012333:RNA, Messenger; D017481:Receptors, Somatostatin; D011061:Poly A; D013004:Somatostatin; D012313:RNA; D053561:Somatostatin-28; D004247:DNA