Expression of Variant Forms of Insulin Receptor Substrate-1 Identified in Patients with Noninsulin-Dependent Diabetes Mellitus1

Several polymorphisms have been identified in the amino acid sequence of human insulin receptor substrate-1 (IRS-1). Some of the variant sequences have been reported to be increased in prevalence among patients with noninsulin-dependent diabetes mellitus (NIDDM). This observation led to the hypothesis that these amino acid substitutions may impair the function of IRS-1, thereby causing the insulin resistance seen in patients with NIDDM. To address this question, we have designed studies to evaluate the effects of three variant sequences identified in our laboratory: Gly819→Arg, Gly972→Arg, and Arg1221→Cys. We constructed four IRS-1 expression vectors for transfection in COS-7 cells: wild-type, single mutant (Gly819→Arg), double mutant (Gly819→Arg; Gly972→Arg), and triple mutant (Gly819→Arg; Gly972→Arg; Arg1221→Cys) IRS-1. The mutations did not alter the level of expression or the extent of insulin receptor-mediated tyrosine phosphorylation of recombinant IRS-1. Moreover, the mutations did not lead to a de...