Molecular cloning and functional expression of a brain-specific somatostatin receptor.

Abstract

The PCR and conventional library screening were used to clone the brain-specific somatostatin receptor rSSTR-4 from a rat genomic library. The deduced amino add sequence encodes a protein of 384 amino acids and displays structural and sequence homologies with members of the G protein-receptor superfamily. The , a cyclic tetradecapeptide, was originally isolated from ovine hypothalamus and found to have potent inhibitory effects on growth hormone and thyroidstimulating hormone secretion from the anterior pituitary (1, 2). SS-14 was subsequently found to have a widespread distribution, occurring primarily in the central nervous system and gut, where it exerts inhibitory effects on secretion, both exocrine and endocrine, as well as on neural function (3). As with many small peptides, SS-14 is synthesized as part of a larger precursor molecule, from which the mature hormone is proteolytically processed. In mammals, a single gene encodes the 92-amino acid common precursor to both SS-14 and somatostatin 28 (SS-28), a second biologically active NH2-terminally extended form of the tetradecapeptide (4).The inhibitory actions of SS-14 and SS-28 are initiated after binding to high-affinity receptors that have been identified on target tissues (5-9). SS-14 and SS-28 appear to exert their inhibitory effects by a dual mechanism involving receptor activation of Gi, the inhibitory guanine nucleotide-binding protein (10). In part, their effects are mediated through inhibition of stimulated adenylyl cyclase activity and reduction of cAMP production (11, 12). In addition, both peptides cause membrane hyperpolarization through effects on a voltage-dependent plasma-membrane potassium channel, leading to a decrease in Ca2+ influx and a reduction of cytosolic Ca2+ concentration (13

Octreotide

“…1A). [8][9][10][11] The genes for these subtypes are located on different chromosomes, suggesting different functions in different organs (Table 1). Indeed, distinct but often overlapping patterns in the expression of these subtypes have been demonstrated.…”

“…There have been no reports of the loss of the suppressive effect of octreotide on growth hormone secretion in patients with acromegaly, even after more than 10 years of uninterrupted therapy. 38,43 The high cost of treatment with octreotide *Data on the five subtypes were obtained from the following reports: subtypes 1 and 2, Yamada et al 8 ; subtype 3, Yamada et al 9 ; subtype 4, Bruno et al 10 ; and subtype 5, O'Carroll et al 11 †IC 50 denotes the concentration required for 50 percent inhibition of the binding of 125 I-labeled somatostatin to the cloned subtype, as expressed in Chinese hamster-ovary or transformed African green-monkey COS kidney cells. Data were obtained from Patel and Srikant.…”

The Tyrosine Phosphatase SHP-1 Associates with the sst2 Somatostatin Receptor and Is an Essential Component of sst2-mediated Inhibitory Growth Signaling

“…Recently five somatostatin receptors have been cloned. They belong to the family of G protein-coupled receptors and can couple to diverse signal transduction pathways (3)(4)(5)(6)(7).…”

Conserved Motifs in Somatostatin, D2-dopamine, and α2B-Adrenergic Receptors for Inhibiting the Na-H Exchanger, NHE1

“…activity was determined by measuring the rate of pH i recovery (dpH i /dt) from an NH 4 Cl-induced acid load in a nominally HCO 3 --free Hepes buffer (28). Cells plated on glass coverslips were maintained in the absence of serum for 16 -20 h before pH i determinations, transferred to a Hepes buffer, and loaded with the acetoxymethyl ester of the pH-sensitive fluorescent dye, 2,7-biscarboxyethyl-5-(6)-carboxyfluorescein (BECEF-AM, 1 M; Molecular Probes, Inc.) for 10 min at 37°C.…”

“…Receptor expression was determined by radioligand binding using [ We found that SSTR3 and -4, but not SSTR5, mediate SST inhibition of NHE1 activity. NHE1 activity was determined in a nominally HCO 3 Ϫ -free Hepes buffer and expressed as the rate of recovery of intracellular pH (pH i ) from an NH 4 Cl-induced acid load. SST (100 nM) had no effect on quiescent NHE1 activity in any of the SSTR-expressing cell lines (n ϭ 3; data not shown), in accordance with its inability to inhibit quiescent cAMP accumulation.…”