title: sst2 Somatostatin receptor inhibits cell proliferation through Ras-, Rap1-, and B-Raf-dependent ERK2 activation.
abstract: The G protein-coupled sst2 somatostatin receptor is a critical negative regulator of cell proliferation. sstII prevents growth factor-induced cell proliferation through activation of the tyrosine phosphatase SHP-1 leading to induction of the cyclin-dependent kinase inhibitor p27Kip1. Here, we investigate the signaling molecules linking sst2 to p27Kip1. In Chinese hamster ovary-DG-44 cells stably expressing sst2 (CHO/sst2), the somatostatin analogue RC-160 transiently stimulates ERK2 activity and potentiates insulin-stimulated ERK2 activity. RC-160 also stimulates ERK2 activity in pancreatic acini isolated from normal mice, which endogenously express sst2, but has no effect in pancreatic acini derived from sst2 knock-out mice. RC-160-induced p27Kip1 up-regulation and inhibition of insulin-dependent cell proliferation are both prevented by pretreatment of CHO/sst2 cells with the MEK1/2 inhibitor PD98059. In addition, using dominant negative mutants, we show that sst2-mediated ERK2 stimulation is dependent on the pertussis toxin-sensitive Gi/o protein, the tyrosine kinase Src, both small G proteins Ras and Rap1, and the MEK kinase B-Raf but is independent of Raf-1. Phosphatidylinositol 3-kinase (PI3K) and both tyrosine phosphatases, SHP-1 and SHP-2, are required upstream of Ras and Rap1. Taken together, our results identify a novel mechanism whereby a Gi/o protein-coupled receptor inhibits cell proliferation by stimulating ERK signaling via a SHP-1-SHP-2-PI3K/Ras-Rap1/B-Raf/MEK pathway.
authors.affiliation: INSERM U531, IFR31, Centre Hospitalier Universitaire Rangueil, 1 avenue Jean Poulhès, 31403 Toulouse Cedex and CNRS Unité Mixte de Recherche 146, Institut Curie, Centre Universitaire, 91405 Orsay Cedex, France.
authors.forename: Hicham
authors.initials: H
authors.lastname: Lahlou
authors.forename: Nathalie
authors.initials: N
authors.lastname: Saint-Laurent
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Estève
authors.forename: Alain
authors.initials: A
authors.lastname: Eychène
authors.forename: Lucien
authors.initials: L
authors.lastname: Pradayrol
authors.forename: Stéphane
authors.initials: S
authors.lastname: Pyronnet
authors.forename: Christiane
authors.initials: C
authors.lastname: Susini
mesh_terms: D000818:Animals; D016466:CHO Cells; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D006224:Cricetinae; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004789:Enzyme Activation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D020935:MAP Kinase Signaling System; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D017481:Receptors, Somatostatin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000494:pharmacology; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D017481:Receptors, Somatostatin; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C051458:vapreotide; D013004:Somatostatin; C093733:somatostatin receptor 2; C482120:Braf protein, mouse; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C516725:Ptpn11 protein, mouse; C509248:Ptpn6 protein, mouse; D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins