Insulin stimulates tyrosine phosphorylation of the proto-oncogene product of c-Cbl in 3T3-L1 adipocytes.
We report here that the product of the c-Cbl proto-oncogene is prominently tyrosine phosphorylated in response to insulin in 3T3-L1 adipocytes. The tyrosine phosphorylation of c-Cbl reaches a maximum within 1-2 min after stimulation by insulin and gradually declines thereafter. The tyrosine phosphorylation of c-Cbl was also observed after treatment of 3T3-L1 adipocytes with epidermal growth factor, whereas platelet-derived growth factor had no effect. After insulin-dependent tyrosine phosphorylation, c-Cbl specifically associates with fusion proteins containing the Src homology 2 (SH2) domains of Crk and the Fyn tyrosine kinase, but not with fusion proteins containing the SH2 domains of either the p85 subunit of phosphatidylinositol 3'-kinase or the tyrosine phosphatase SHPTP2/Syp. Furthermore insulin stimulates the association of c-Cbl with endogenous c-Crk and Fyn in intact 3T3-L1 adipocytes. The tyrosine phosphorylation of c-Cbl is regulated during adipocyte differentiation. Neither insulin-like growth factor 1 nor insulin stimulated the tyrosine phosphorylation of c-Cbl in 3T3-L1 fibroblasts. Moreover, c-Cbl is not tyrosine phosphorylated in response to insulin in cells expressing high levels of the human insulin receptor, or in hepatocytes, despite comparable levels of c-Cbl expression. These results suggest that c-Cbl might have a novel function in the regulation of insulin receptor intracellular signalling in 3T3-L1 adipocytes.
Ribon
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Department of Physiology, University of Michigan School of Medicine, Ann Arbor, Michigan 48109, USA.
Saltiel
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AR
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D051379:Mice; D010766:Phosphorylation; D011485:Protein Binding; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl; D050737:Proto-Oncogene Proteins c-crk; D051076:Proto-Oncogene Proteins c-fyn; D014443:Tyrosine / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases; D018909:src Homology Domains
D007328:Insulin; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D050737:Proto-Oncogene Proteins c-crk; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; C494957:FYN protein, human; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn; C067419:CBL protein, human; C493849:Cbl protein, mouse