Molecular cloning and functional characterization of a rat somatostatin sst_2(b) receptor splice variant

Abstract

1 The mouse somatostatin (SRIF) sst 2 receptor exists in two splice variants, sst 2(a) and sst 2(b) , which di er in their intracellular carboxy-termini only. The murine sst 2(b) receptor was reported to be less prone to agonist-induced desensitization as compared with the sst 2(a) receptor. To determine whether a sst 2(b) splice variant with similar functional characteristics exists in the rat, we have isolated a cDNA fragment from rat gastric mucosa encoding a sst 2(b) receptor and expressed the full-length protein in CHO-K1 cells for functional characterization. 2 This study provides the ®rst evidence for the occurrence in the rat of the sst 2(b) receptor, which has a 15 amino acid carboxy-terminus di ering in composition to the 38 amino acid C-terminus of the rat sst 2(a) receptor. 3 In CHO-K1 cells expressing rat recombinant sst 2(a) or sst 2(b) receptors, SRIF caused concentrationdependent increases in extracellular acidi®cation rates (EAR) with pEC 50 values of 9.0 and 9.9, respectively. Pre-treatment with pertussis toxin (Ptx) caused a rightward displacement of the SRIF concentration-e ect curves with pEC 50 values of 8.3 (sst 2(a) ) and 8.4 (sst 2(b) ). 4 SRIF (3 pM ± 3 nM) also caused concentration-dependent inhibition of forskolin-stimulated cyclic AMP formation in CHO-sst 2(a) cells (pIC 50 10.5) and CHO-sst 2(b) cells (pIC 50 10.4). The degree of inhibition was less with higher concentrations of SRIF resulting in bell-shaped concentration-e ect curves. Following pre-treatment with Ptx, the inhibitory e ect of SRIF was abolished and SRIF caused only increases in cyclic AMP formation. 5 Both the SRIF-induced increases in EAR and inhibition of cyclic AMP formation were susceptible to agonist-induced desensitization, but this was less apparent following pre-treatment with Ptx. 6 This demonstrates that the operational characteristics of the recombinant rat sst 2(a) and sst 2(b) receptors are broadly similar. Both isoforms couple to Ptx-sensitive as well as -insensitive G proteins and are equally prone to agonist-induced desensitization.

Mouse β3a‐ and β3b‐adrenoceptors expressed in Chinese hamster ovary cells display identical pharmacology but utilize distinct signalling pathways

“…Many GPCRs have isoforms with di ering C-terminal tails. These include the prostaglandin EP3 receptor Hasegawa et al, 1996;Jin et al, 1997;Irie et al, 1993), a 1A -AR (Chang et al, 1998;Hirasawa et al, 1995), serotonin 5HT 4 (Gerald et al, 1995) and 5HT 7 receptors (Heidmann et al, 1997), and the somatostatin SSTR 2 receptor (Vanetti et al, 1993;Schindler et al, 1998). Most splice variants share similar pharmacology, but some show marked di erences in signalling properties.…”

Central Injection of the Stable Somatostatin Analog ODT8-SST Induces a Somatostatin2 Receptor-Mediated Orexigenic Effect: Role of Neuropeptide Y and Opioid Signaling Pathways in Rats

“…These data were indicative of an interaction between brain somatostatin signaling and other hypothalamic neuropeptide systems regulating food intake. SST-14 and SST-28 interact with sst [1][2][3][4][5] receptors and display nanomolar affinity to sst 2 (16) including the variants sst 2A and sst 2B generated by alternative splicing (19). Similar to SST, des-AA 1,2,4,5,12,13 -[DTrp 8 ]-somatostatin (ODT8-SST), a long-acting agonist (20) binds to all sst receptors with nanomolar affinity (21) and therefore allows to study the effects that closely resemble those exerted by the endogenous ligand.…”

Antidepressants Influence Somatostatin Levels and Receptor Pharmacology in Brain

“…The hippocampal formation contains sst 1/4 subtypes, with the CA1 expressing predominantly the sst 4 subtype (Thoss et al, 1995;Videau et al, 2003). sst 2A receptor immunoreactivity was most prominent in the Tu, layers II-III of the cerebral cortex, NAc, pyramidal cells of CA1-2 subfields of the hippocampus, central and cortical amygdaloid nuclei (Dournaud et al, 1998;Schindler et al, 1998;Schulz et al, 2000).…”