| Extensive research has identified increased serine phosphorylation of IRS1 as a central molecular mechanism in the inhibition of insulin signaling by numerous mediators of acute and chronic insulin resistance, including Tumor necrosis factor α. Identification of negative regulatory serine residues in the IRS proteins and the kinases that phosphorylate them are important goals for learning how to reverse the insulin resistance that perturbs metabolic homeostasis and contributes to the progression of type 2 diabetes. The work in this thesis demonstrates that Serine 307 of rat IRS1 is phosphorylated in cell culture, mice, rats, and humans in response to potential mediators of acute and chronic insulin resistance. Using reverse phase high performance liquid chromatography and manual radio-sequencing, Serine 307 was determined to be phosphorylated in vivo, by an IRS1-associated kinase activity, and by the c-Jun N-terminal kinase in vitro. The function of this phosphorylation is to inhibit generation of the insulin signal through abrogation of the IR/IRS1 interaction. The results from this work suggest that chronic accumulation of IRS1 molecules unresponsive to subsequent insulin stimulation may result in the progressive insulin resistance characteristic of the pre-diabetic state. |
