Specific glucose-induced control of insulin receptor substrate-2 expression is mediated via Ca2+-dependent calcineurin/NFAT signaling in primary pancreatic islet β-cells.
Specific glucose-induced control of insulin receptor substrate-2 expression is mediated via Ca2+-dependent calcineurin/NFAT signaling in primary pancreatic islet β-cells.
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作者：
Demozay D;Tsunekawa S;Briaud I;Shah R;Rhodes CJ
胰岛素受体底物-2（IRS-2）通过促进生长和存活在胰岛β细胞中发挥着重要作用。IRS-2在原代β细胞中周转迅速，但其表达在转录水平上受到高度调节，尤其是葡萄糖。目的探讨葡萄糖对胰岛β细胞IRS-2基因表达调控的分子机制。将大鼠胰岛暴露于抑制剂或进行腺病毒载体介导的基因操作，然后通过实时PCR和免疫印迹分析葡萄糖诱导的IRS-2表达。用染色质免疫沉淀法分析活化T细胞转录因子核因子（NFAT）与IRS-2启动子的相互作用，用免疫组化法分析葡萄糖诱导的NFAT易位。在体内，葡萄糖诱导的IRS-2表达发生在胰岛β细胞中，而不是在肝脏中。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基因表达依赖于细胞外来源的细胞内钙浓度的升高。钙调磷酸酶抑制剂（FK 506，环孢素A，和肽钙调磷酸酶抑制剂[CAIN]）废除葡萄糖诱导的IRS-2的mRNA和蛋白质水平，而表达的组成性活性钙调磷酸酶增加他们。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。NFATc 1易位到细胞核中响应葡萄糖和协会的IRS-2启动子中的保守NFAT结合位点的NFATc 1被证明。葡萄糖诱导的胰岛β细胞特异性IRS-2基因表达的转录调控机制是由Ca 2 +/钙调神经磷酸酶/NFAT途径介导的。这种对IRS-2调节的洞察可以为2型糖尿病提供新的治疗手段，以维持足够的功能质量。
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 Ca2+ 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 Ca2+/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.