Serine / Threonine Phosphorylation and IRS1 Degradation

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DESCRIPTION (provided by applicant): Type 2 diabetes is characterized by systemic insulin resistance that cannot be corrected by increased insulin secretion. IRS proteins, important insulin receptor-signaling propagators, represent a potential point of signal breakdown that could lead to insulin resistance. Low IRS protein expression has been observed in humans who have advanced T2 diabetes. Low expression could be due to a number of reasons including increased protein degradation by the 26S proteosome. This study aims at understanding the molecular cues needed to trigger IRS-1 degradation. MS analysis has revealed new S/T phosphorylation sites that are present in IRS-1, only when it is isolated in the presence of proteosome inhibitors (e.g. MG132). Using site- specific mutagenesis and phospho-specific mAbs, each of these sites will be examined for its impact on IRS- 1 protein degradation. Potential kinases that regulate IRS-1 degradation will be investigated using MS analysis as well. This work will highlight previously unappreciated regulatory sites among the numerous S/T residues contained within IRS-1, a key suspect in the development of insulin resistance, and it will identify new IRS-1 regulatory proteins that could be potential drug targets for the treatment of T2 diabetes.