SOS phosphorylation and disassociation of the Grb2-SOS complex by the ERK and JNK signaling pathways.
Insulin activation of Ras is mediated by the plasma membrane targeting of the guanylnucleotide exchange factor SOS associated with the small adapter protein Grb2. SOS also lies in an insulin-stimulated feedback pathway in which the serine/threonine phosphorylation of SOS results in disassociation of the Grb2-SOS complex thereby limiting the extent of Ras activation. To examine the relative role of the mitogen-activated protein kinases in the feedback phosphorylation of SOS we determined the signaling specificity of insulin, osmotic shock, and anisomycin to activate the ERK (extracellular-signal regulated kinase) and JNK (c-Jun kinase) pathways. In Chinese hamster ovary cells expressing the human insulin receptor and murine 3T3L1 adipocytes, insulin specifically activated ERK with no significant effect on JNK, whereas anisomycin specifically activated JNK but was unable to activate ERK. In contrast, osmotic shock was equally effective in the activation of both kinase pathways. Insulin and osmotic shock, but not anisomycin, resulted in SOS phosphorylation and disassociation of the Grb2-SOS complex, demonstrating that the JNK pathway was not involved in the insulin-stimulated feedback uncoupling of the Grb2- SOS complex. Both the insulin and osmotic shock-induced activation of ERK was prevented by treatment of cells with the specific MEK inhibitor (PD98059). However, expression of dominant-interfering Ras (N17Ras) inhibited the insulin- but not osmotic shock-stimulated phosphorylation of ERK and SOS. These data demonstrate that activation of the ERK pathway, but not JNK, is responsible for the feedback phosphorylation and disassociation of the Grb2-SOS complex.
Dong Chen
Program in Molecular Biology, University of Iowa, Iowa City 52242, USA.
Waters
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Holt
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Pessin
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D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D006224:Cricetinae; D005246:Feedback; D051380:GRB2 Adaptor Protein; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009997:Osmotic Pressure; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D007328:Insulin; D009419:Nerve Tissue Proteins; D011506:Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D000841:Anisomycin; D011972:Receptor, Insulin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins