Activation in vitro of somatostatin receptor subtypes 2, 3, or 4 stimulates protein tyrosine phosphatase activity in membranes from transfected Ras-transformed NIH 3T3 cells: coexpression with catalytically inactive SHP-2 blocks responsiveness.
Somatostatin receptors (sstr) subtypes 1-5 were transiently expressed in NIH 3T3 cells stably transformed with Ha-Ras(G12V) to assess the ability of each receptor to stimulate protein tyrosine phosphatase (PTPase) activity in vitro. Treatment of membranes from sstr2-, sstr3-, or sstr4-expressing cells with somatostatin-14 plus guanyl-5'-yl imidodiphosphate (GMPPNP) increased PTPase activity, and this stimulation was pertussis toxin-sensitive. Somatostatin alone, GMPPNP alone, or somatostatin plus GDP were ineffective under these conditions. sstr1 and sstr5 failed to increase PTPase activity although both receptors were expressed, as assessed by appearance of high-affinity binding sites for [125I-Tyr11]somatostatin-14. Somatostatin plus GMPPNP stimulated PTPase activity in vitro when sstr2 was coexpressed with wild type PTP1B or a Cys to Ser (C/S), catalytically inactive PTP1B or with wild type SH2-domain containing PTPase SHP-2. However, coexpression with catalytically inactive C/S SHP-2 abrogated this response. Thus, three of the five cloned sstr's can couple to activate PTPase in this cellular background. Abrogation of the response by C/S SHP-2 strongly suggests, but does not prove, a role for SHP-2 in the mechanism.
Reardon
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Center for Cell Signaling, Department of Internal Medicine, University of Virginia, Charlottesville 22908, USA.
Dent
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Wood
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Kong
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Sturgill
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D016475:3T3 Cells / Q000187:drug effects; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D011905:Genes, ras; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D051379:Mice; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000187:drug effects / Q000378:metabolism*; D017481:Receptors, Somatostatin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases; D013004:Somatostatin / Q000494:pharmacology; D014162:Transfection; D014170:Transformation, Genetic
D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D017481:Receptors, Somatostatin; D011994:Recombinant Proteins; C103631:somatostatin receptor 3; C098681:somatostatin receptor subtype-4; D006165:Guanylyl Imidodiphosphate; D013004:Somatostatin; C093733:somatostatin receptor 2; 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; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases