Increased tyrosine phosphorylation of the insulin receptor, the insulin receptor substrate-1 and a 73 kDa protein associated with insulin-induced mitogenesis in SV40-transformed 3T3T cells.
Insulin selectively induces mitogenesis in quiescent SV40 large T antigen-transformed murine 3T3T (CSV3-1) cells but not in quiescent nontransformed 3T3T cells. This mitogenic effect induced by insulin in CSV3-1 cells requires an induction of AP-1 activity associated with c-Jun and JunB. To further investigate the mechanisms that are involved in insulin-induced mitogenesis in CSV3-1 cells, the current experiments were performed. The results show that following insulin stimulation, the insulin receptor beta-subunit and the insulin receptor substrate-1 undergo a much more significant tyrosine phosphorylation in CSV3-1 cells than in 3T3T cells. Insulin also induces tyrosine phosphorylation of a 73 kDa protein that is coprecipitated with the tyrosine-phosphorylated insulin receptor in CSV3-1 cells but not in 3T3T cells. The increased tyrosine phosphorylation in response to insulin stimulation in CSV3-1 cells does not appear to be due to an increase in the level of expression of the insulin receptor and does not appear to result from a significant change in tyrosine phosphatase activity compared to nontransformed cells. The results also show that the insulin effect in CSV3-1 cells is not mediated by insulin-like growth factor 1 receptor because insulin at the concentrations that induce mitogenesis does not increase the tyrosine phosphorylation of the insulin-like growth factor 1 receptor and the expression level of the receptor is not significantly changed in CSV3-1 cells compared to nontransformed cells. These data together indicate that the selective mitogenic effect of insulin on CSV3-1 cells involves increased tyrosine phosphorylation of the insulin receptor, the insulin receptor substrate-1 and the 73 kDa protein, although the underlying mechanisms need to be further elucidated.
Wang
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Department of Pathology, The University of Chicago Hospitals, Illinois 60637, USA.
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D008938:Mitosis / Q000187:drug effects*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D017451:Receptors, Somatomedin / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013539:Simian virus 40 / Q000502:physiology; D014443:Tyrosine / Q000378:metabolism*
D017931:DNA Primers; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D011506:Proteins; D012333:RNA, Messenger; D017451:Receptors, Somatomedin; D014443:Tyrosine; D011972:Receptor, Insulin; D017027:Protein Tyrosine Phosphatases