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

Frédéric Lopez,Jean-Pierre Estève,Louis Buscail,Nathalie Delesque,Nathalie Saint-Laurent,Magali Théveniau,Clara Nahmias,Nicole Vaysse,Christiane Susini

doi:10.1074/jbc.272.39.24448

Abstract

Activation of the somatostatin receptor sst2, a member of the Gi protein-coupled receptor family, results in the stimulation of a protein-tyrosine phosphatase activity involved in the sst2-mediated growth inhibitory signal. Here, we report that SHP-1, a cytoplasmic protein-tyrosine phosphatase containing two Src homology 2 domains constitutively associated with sst2 as evidence by coprecipitation of SHP-1 protein with sst2, in Chinese hamster ovary cells coexpressing sst2 and SHP-1. Activation of sst2 by somatostatin resulted in a rapid dissociation of SHP-1 from sst2 accompanied by an increase of SHP-1 activity. SHP-1 was phosphorylated on tyrosine in control cells and somatostatin induced a rapid and transient dephosphorylation on tyrosine residues of the enzyme. Stimulation of SHP-1 activity by somatostatin was abolished by pertussis toxin pretreatment of cells. Gialpha3 was specifically immunoprecipitated by anti-sst2 and anti-SHP-1 antibodies, and somatostatin induced a rapid dissociation of Gialpha3 from sst2, suggesting that Gialpha3 may be involved in the sst2.SHP-1 complexes. Finally, somatostatin inhibited the proliferation of cells coexpressing sst2 and SHP-1, and this effect was suppressed in cells coexpressing sst2 and the catalytic inactive SHP-1 (C453S mutant). Our data identify SHP-1 as the tyrosine phosphatase associated with sst2 and demonstrate that this enzyme may be an initial key transducer of the antimitogenic signaling mediated by sst2.

Highlights

Somatostatin is a widely distributed inhibitory hormone that exhibits various biological effects, including neurotransmission, inhibition of exocrine and endocrine secretions, and cell proliferation
Chinese hamster ovary (CHO)/sst2-SHP-1 clones expressed sst2 as a protein of 95 kDa detected by immunoblotting as previously reported [34] and SHP-1 as a protein of 68 kDa, whereas these proteins were barely detectable in wild CHO cells (Fig. 1). sst2 immunoprecipitates prepared from CHO/sst2-SHP-1 cells were examined by immunoblotting for the presence of SHP-1
We and others have demonstrated that somatostatin and analogues induce the stimulation of a membrane proteintyrosine phosphatase (PTPase), which may be involved in the inhibitory effect of these peptides on cell proliferation [9, 11, 12, 38]

Summary

Introduction

Somatostatin is a widely distributed inhibitory hormone that exhibits various biological effects, including neurotransmission, inhibition of exocrine and endocrine secretions, and cell proliferation. Somatostatin Promotes Dissociation of sst21⁄7SHP-1 Complexes and Induces Activation and Tyrosine Dephosphorylation of SHP-1—To determine whether the interaction of SHP-1 with sst2 was affected by somatostatin treatment, CHO/sst2-SHP-1 cells were incubated in the presence of the somatostatin analogue, SMS, for various times prior to solubilization and immunoprecipitation with anti-sst2 antibodies.

Results

Conclusion