Temporal dynamics of tyrosine phosphorylation in insulin signaling

The insulin-signaling network regulates blood glucose levels, controls metabolism, and when dysregulated, may lead to the development of type 2 diabetes. Although the role of tyrosine phosphorylation in this network is clear, only a limited number of insulin-induced tyrosine phosphorylation sites have been identified. To address this issue and establish temporal response, we have, for the first time, carried out an extensive, quantitative, mass spectrometry-based analysis of tyrosine phosphorylation in response to insulin. The study was performed with 3T3-L1 adipocytes stimulated with insulin for 0, 5, 15, and 45 min. It has resulted in the identification and relative temporal quantification of 122 tyrosine phosphorylation sites on 89 proteins. Insulin treatment caused a change of at least 1.3-fold in tyrosine phosphorylation on 89 of these sites. Among the responsive sites, 20 were previously known to be tyrosine phosphorylated with insulin treatment, including sites on the insulin receptor and insulin receptor substrate-1. The remaining 69 responsive sites have not previously been shown to be altered by insulin treatment. They were on proteins with a wide variety of functions, including components of the trafficking machinery for the insulin-responsive glucose transporter GLUT4. These results show that insulin-elicited tyrosine phosphorylation is extensive and implicate a number of hitherto unrecognized proteins in insulin action.