Porzio O, Federici M, Hribal M L, Lauro D, Accili D, Lauro R, Borboni P, Sesti G
Laboratory of Molecular Medicine, Department of Internal Medicine, University of Rome Tor Vergata, Rome, Italy.
J Clin Invest. 1999 Aug;104(3):357-64. doi: 10.1172/JCI5870.
Recent studies have identified several polymorphisms in the human insulin receptor substrate-1 (IRS-1) gene. The most prevalent IRS-1 variant, a Gly-->Arg change at the codon 972, has been reported to be increased in prevalence among patients with type 2 diabetes. Carriers of the Arg(972) substitution are characterized by lower fasting insulin and C-peptide levels compared with non-carriers, suggesting that the Arg(972) IRS-1 variant may contribute to impairment of insulin secretion. In this study, we stably overexpressed both wild-type IRS-1 (RIN-WT) and Arg(972) IRS-1 variant (RIN-Arg(972)) in RIN beta cells to investigate directly whether the polymorphism in codon 972 of IRS-1 impairs insulin secretion. The Arg(972) IRS-1 variant did not affect expression or function of endogenous IRS-2. RIN-WT showed a marked increase in both glucose- and insulin-stimulated tyrosine phosphorylation of IRS-1 compared with control RIN cells. The Arg(972) IRS-1 variant did not alter the extent of either glucose- or insulin-stimulated tyrosine phosphorylation of recombinant IRS-1. However, RIN-Arg(972) showed a significant decrease in binding of the p85 subunit of phosphatidylinositol-3-kinase (PI 3-kinase) with IRS-1, compared with RIN-WT. Compared with control RIN cells, insulin content was reduced to the same extent in RIN-WT or RIN-Arg(972) at both the protein and mRNA levels. Both glucose- and sulfonylurea-induced insulin secretion was increased in RIN-WT compared with control RIN cells. By contrast, RIN cells expressing Arg(972) IRS-1 exhibited a marked decrease in both glucose- and sulfonylurea-stimulated insulin secretion compared with RIN-WT. These data suggest that the insulin signaling pathway involving the IRS-1/PI 3-kinase may play an important role in the insulin secretory process in pancreatic beta cells. More importantly, the results suggest that the common Arg(972) IRS-1 polymorphism may impair glucose-stimulated insulin secretion, thus contributing to the relative insulin deficiency observed in carriers of this variant.
最近的研究已确定人类胰岛素受体底物-1（IRS-1）基因存在几种多态性。最常见的IRS-1变体是密码子972处的甘氨酸（Gly）替换为精氨酸（Arg），据报道在2型糖尿病患者中的发生率有所增加。与非携带者相比，携带精氨酸（972）替换的个体空腹胰岛素和C肽水平较低，这表明精氨酸（972）IRS-1变体可能导致胰岛素分泌受损。在本研究中，我们在RINβ细胞中稳定过表达野生型IRS-1（RIN-WT）和精氨酸（972）IRS-1变体（RIN-Arg(972)），以直接研究IRS-1密码子972处的多态性是否会损害胰岛素分泌。精氨酸（972）IRS-1变体不影响内源性IRS-2的表达或功能。与对照RIN细胞相比，RIN-WT在葡萄糖和胰岛素刺激下IRS-1的酪氨酸磷酸化均显著增加。精氨酸（972）IRS-1变体未改变重组IRS-1在葡萄糖或胰岛素刺激下的酪氨酸磷酸化程度。然而，与RIN-WT相比，RIN-Arg(972)显示磷脂酰肌醇-3激酶（PI 3激酶）的p85亚基与IRS-1的结合显著减少。与对照RIN细胞相比，RIN-WT和RIN-Arg(972)的胰岛素含量在蛋白质和mRNA水平上均降低到相同程度。与对照RIN细胞相比，RIN-WT中葡萄糖和磺脲类药物诱导的胰岛素分泌均增加。相比之下，与RIN-WT相比，表达精氨酸（972）IRS-1的RIN细胞在葡萄糖和磺脲类药物刺激下的胰岛素分泌均显著减少。这些数据表明，涉及IRS-1/PI 3激酶的胰岛素信号通路可能在胰腺β细胞的胰岛素分泌过程中起重要作用。更重要的是，结果表明常见的精氨酸（972）IRS-1多态性可能损害葡萄糖刺激的胰岛素分泌，从而导致该变体携带者出现相对胰岛素缺乏。
