Inhibition of phosphatidylinositol-3-kinase enhances insulin stimulation of insulin receptor substrate 1 tyrosine phosphorylation and extracellular signal-regulated kinases in mouse R- fibroblasts.
Insulin stimulates phosphatidylinositol-3-kinase (PI3K) and extracellular signal-regulated kinases (ERK) in various mammalian cells. To study the role of PI3K in insulin stimulation of ERK, we employed PI3K inhibitor LY294002 and mouse embryonic R- fibroblasts lacking IGF-1 receptors. In these R- cells, PI3K inhibition by LY294002 enhanced insulin stimulation of ERK phosphorylation whereas LY294002 inhibited insulin stimulation of Akt phosphorylation. The enhanced insulin stimulation of ERK phosphorylation was accompanied by increased IRS-1 tyrosine phosphorylation. Insulin stimulation of insulin receptor tyrosine phosphorylation was not altered. PI3K inhibition increased IRS-1-Grb2 complex formation and ras activity following insulin treatment of cells. Increased insulin stimulation of ERK by PI3K inhibition was mediated by the MEK/ERK pathway, but did not involve inhibitory Ser259 phosphorylation of raf that was reported to be mediated by Akt. In summary, PI3K inhibition in R- cells enhanced insulin stimulation of ERK phosphorylation by mechanisms involving enhancement of IRS-1 tyrosine phosphorylation, IRS-1-Grb2 complex formation and the ras/MEK/ERK pathway.
Choi
Woo S
WS
Department of Physiology and Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, California 90089-9141, USA.
Sung
Chin K
CK
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D006160:Guanosine Triphosphate / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002867:Chromones; D004791:Enzyme Inhibitors; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D009025:Morpholines; D010750:Phosphoproteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014443:Tyrosine; D012694:Serine; D006160:Guanosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1; D048052:Mitogen-Activated Protein Kinase 3; D018631:ras Proteins