Zhang J, Ou J, Bashmakov Y, Horton J D, Brown M S, Goldstein J L
Department of Molecular Genetics, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9046, USA.
Proc Natl Acad Sci U S A. 2001 Mar 27;98(7):3756-61. doi: 10.1073/pnas.071054598. Epub 2001 Mar 20.
Recent data indicate that sustained elevations in plasma insulin suppress the mRNA for IRS-2, a component of the insulin signaling pathway in liver, and that this deficiency contributes to hepatic insulin resistance and inappropriate gluconeogenesis. Here, we use nuclear run-on assays to show that insulin inhibits transcription of the IRS-2 gene in the livers of intact rats. Insulin also inhibited transcription of a reporter gene driven by the human IRS-2 promoter that was transfected into freshly isolated rat hepatocytes. The human promoter contains a heptanucleotide sequence, TGTTTTG, that is identical to the insulin response element (IRE) identified previously in the promoters of insulin-repressed genes. Single base pair substitutions in this IRE decreased transcription of the IRS-2-driven reporter in the absence of insulin and abolished insulin-mediated repression. We conclude that insulin represses transcription of the IRS-2 gene by blocking the action of a positive factor that binds to the IRE. Sustained repression of IRS-2, as occurs in chronic hyperinsulinemia, contributes to hepatic insulin resistance and accelerates the development of the diabetic state.
近期数据表明，血浆胰岛素持续升高会抑制肝脏中胰岛素信号通路的一个组成部分——胰岛素受体底物-2（IRS-2）的信使核糖核酸（mRNA），且这种缺陷会导致肝脏胰岛素抵抗和不适当的糖异生。在此，我们使用核转录分析来表明胰岛素抑制完整大鼠肝脏中IRS-2基因的转录。胰岛素还抑制了由转染到新鲜分离的大鼠肝细胞中的人IRS-2启动子驱动的报告基因的转录。人启动子包含一个七核苷酸序列TGTTTTG，它与先前在胰岛素抑制基因启动子中鉴定出的胰岛素反应元件（IRE）相同。该IRE中的单碱基对替换在无胰岛素时降低了IRS-2驱动的报告基因的转录，并消除了胰岛素介导的抑制作用。我们得出结论，胰岛素通过阻断与IRE结合的正性因子的作用来抑制IRS-2基因的转录。如在慢性高胰岛素血症中发生的那样，IRS-2的持续抑制会导致肝脏胰岛素抵抗并加速糖尿病状态的发展。
