STRUCTURE OF IRS PROTEINS IN INSULIN RESISTANCE

Joslin Diabetes Center, Boston MA

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Abstract

DESCRIPTION(Adapted from applicant's abstract): Insulin controls systemic metabolism by regulating glucose uptake, the synthesis and storage of glycogen and fat, and protein and DNA synthesis. Insulin=s cellular effects are mediate by the insulin receptor (IR) and its substrates. The known number of insulin receptor substrates (IRS proteins) has recently expanded to four, IRS-1, -2, -3, and -4. The activated IR phosphorylates IRS proteins directly. Tyrosine-phosphorylated IRS proteins bind and activate SH2 domain enzymes, including the PI 3-kinase, the phosphatase SHP-2, and the Grb2/Sos complex, to amplify and propagate insulin signals into cells. Insulin resistance- the ability of key targets (muscle and fat) to respond to insulin- is considered t be the initiating step in the pathogenesis of non-insulin dependent diabetes mellitus (NIDDM). Insulin resistance is also associated with common disease states such as hypertension, atherosclerosis, aging, obesity, and polycystic ovarian disease. Recent findings suggest that Ser/threonine phosphorylation of IRS proteins may cause insulin resistance in cells and in vivo. Hyperglycemia, hyperinsulinemia, TNF and leptin could influence insulin sensitivity through this mechanism. The proposed studies will provide a structural basis for understanding the early events in insulin action and test hypotheses that relate insulin resistance and Ser/Thr phosphorylation of IRS proteins. Specifically, we will (1) Determine high resolution structures of IRS protein homology domains (the approximately 270 residue region common to IRS proteins that encompasses the PH and PTB domains), (2) Determine physiological binding partners for the IRS-1, -2, -3, and -4 PH and PTB domains, (3) Determine high resolution structures of full-length IRS proteins (IRS-3 is being attempted first, but IRS-1 is planned, as well), and (4) Use IRS structures to analyze potential mechanisms of insulin resistance.