title: sst2 somatostatin receptor mediates cell cycle arrest and induction of p27(Kip1). Evidence for the role of SHP-1.
abstract: Activation of the somatostatin receptor sst2 inhibits cell proliferation by a mechanism involving the stimulation of the protein-tyrosine phosphatase SHP-1. The cell cycle regulatory events leading to sst2-mediated growth arrest are not known. Here, we report that treatment of Chinese hamster ovary cells expressing sst2 with the somatostatin analogue, RC-160, led to G1 cell cycle arrest and inhibition of insulin-induced S-phase entry through induction of the cyclin-dependent kinase inhibitor p27(Kip1). Consequently, a decrease of p27(Kip1)-cdk2 association, an inhibition of insulin-induced cyclin E-cdk2 kinase activity, and an accumulation of hypophosphorylated retinoblastoma gene product (Rb) were observed. However, RC-160 had no effect on the p21(Waf1/Cip1). When sst2 was coexpressed with a catalytically inactive mutant SHP-1 in Chinese hamster ovary cells, mutant SHP-1 induced entry into cell cycle and down-regulation of p27(Kip1) and prevented modulation by insulin and RC-160 of p27(Kip1) expression, p27(Kip1)-cdk2 association, cyclin E-cdk2 kinase activity, and the phosphorylation state of Rb. In mouse pancreatic acini, RC-160 reverted down-regulation of p27(Kip1) induced by a mitogen, and this effect did not occur in acini from viable motheaten (mev/mev) mice expressing a mutant SHP-1 with markedly deficient enzymes. These findings provide the first evidence that sst2 induces cell cycle arrest through the up-regulation of p27(Kip1) and demonstrate that SHP-1 is required for maintaining high inhibitory levels of p27(Kip1) and is a critical target of the insulin, and somatostatin signaling cascade, leading to the modulation of p27(Kip1).
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases; D016466:CHO Cells; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D006224:Cricetinae; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors; D016193:G1 Phase / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D017481:Receptors, Somatostatin / Q000502:physiology*; D016160:Retinoblastoma Protein / Q000378:metabolism; D016196:S Phase / Q000502:physiology*; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology; D025521:Tumor Suppressor Proteins; D018909:src Homology Domains