Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, Kovler Diabetes Center, University of Chicago, Chicago, Illinois, USA.
Diabetes. 2011 Nov;60(11):2892-902. doi: 10.2337/db11-0341. Epub 2011 Sep 22.
Insulin receptor substrate-2 (IRS-2) plays an essential role in pancreatic islet β-cells by promoting growth and survival. IRS-2 turnover is rapid in primary β-cells, but its expression is highly regulated at the transcriptional level, especially by glucose. The aim was to investigate the molecular mechanism on how glucose regulates IRS-2 gene expression in β-cells.
Rat islets were exposed to inhibitors or subjected to adenoviral vector-mediated gene manipulations and then to glucose-induced IRS-2 expression analyzed by real-time PCR and immunoblotting. Transcription factor nuclear factor of activated T cells (NFAT) interaction with IRS-2 promoter was analyzed by chromatin immunoprecipitation assay and glucose-induced NFAT translocation by immunohistochemistry.
Glucose-induced IRS-2 expression occurred in pancreatic islet β-cells in vivo but not in liver. Modulating rat islet β-cell Ca(2+) influx with nifedipine or depolarization demonstrated that glucose-induced IRS-2 gene expression was dependent on a rise in intracellular calcium concentration derived from extracellular sources. Calcineurin inhibitors (FK506, cyclosporin A, and a peptide calcineurin inhibitor [CAIN]) abolished glucose-induced IRS-2 mRNA and protein levels, whereas expression of a constitutively active calcineurin increased them. Specific inhibition of NFAT with the peptide inhibitor VIVIT prevented a glucose-induced IRS-2 transcription. NFATc1 translocation to the nucleus in response to glucose and association of NFATc1 to conserved NFAT binding sites in the IRS-2 promoter were demonstrated.
The mechanism behind glucose-induced transcriptional control of IRS-2 gene expression specific to the islet β-cell is mediated by the Ca(2+)/calcineurin/NFAT pathway. This insight into the IRS-2 regulation could provide novel therapeutic means in type 2 diabetes to maintain an adequate functional mass.
胰岛素受体底物-2（IRS-2）在胰腺胰岛β细胞中发挥着重要作用，促进其生长和存活。在原代β细胞中，IRS-2 的周转率很快，但它的表达在转录水平上受到高度调控，特别是受到葡萄糖的调控。本研究旨在探讨葡萄糖调节β细胞中 IRS-2 基因表达的分子机制。
用抑制剂处理大鼠胰岛或用腺病毒载体介导的基因操作处理大鼠胰岛，然后通过实时 PCR 和免疫印迹分析葡萄糖诱导的 IRS-2 表达。用染色质免疫沉淀检测法分析核因子活化 T 细胞（NFAT）与 IRS-2 启动子的相互作用，用免疫组化检测葡萄糖诱导的 NFAT 易位。
体内葡萄糖诱导的 IRS-2 表达发生在胰腺胰岛β细胞中，但不在肝脏中。用硝苯地平或去极化调节大鼠胰岛β细胞 Ca(2+)内流表明，葡萄糖诱导的 IRS-2 基因表达依赖于来源于细胞外的细胞内 Ca(2+)浓度升高。钙调神经磷酸酶抑制剂（FK506、环孢菌素 A 和钙调神经磷酸酶肽抑制剂[CAIN]）可使葡萄糖诱导的 IRS-2 mRNA 和蛋白水平降低，而组成型激活的钙调神经磷酸酶则使其升高。用肽抑制剂 VIVIT 特异性抑制 NFAT 可阻止葡萄糖诱导的 IRS-2 转录。证明了 NFATc1 在葡萄糖刺激下向核内易位以及 NFATc1 与 IRS-2 启动子中保守的 NFAT 结合位点结合。
胰岛β细胞中葡萄糖诱导的 IRS-2 基因表达的转录控制机制是由 Ca(2+)/钙调神经磷酸酶/NFAT 途径介导的。对 IRS-2 调控的这一深入了解可能为 2 型糖尿病提供新的治疗手段，以维持足够的功能质量。
