Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine, Imperial College London, London, UK.
Diabetes. 2012 Mar;61(3):574-85. doi: 10.2337/db10-1329. Epub 2012 Feb 14.
Carbohydrate-responsive element-binding protein (ChREBP) is a regulator of pancreatic β-cell gene expression and an important mediator of glucotoxicity. Glucose increases the activity and nuclear localization of ChREBP by still ill-defined mechanisms. Here we reveal, using both MIN6 and primary mouse β-cells, a unique mechanism behind ChREBP nuclear translocation. At low glucose concentrations, ChREBP interacts with sorcin, a penta EF hand Ca(2+) binding protein, and is sequestered in the cytosol. Sorcin overexpression inhibits ChREBP nuclear accumulation at high glucose and reduced the activity of L-type pyruvate kinase (L-PK) and TxNIP promoters, two well-characterized ChREBP target genes. Sorcin inactivation by RNA interference increases ChREBP nuclear localization and in vivo binding to the L-PK promoter at low glucose concentrations. Ca(2+) influx was essential for this process since Ca(2+) chelation with EGTA, or pharmacological inhibition with diazoxide and nifedipine, blocked the effects of glucose. Conversely, mobilization of intracellular Ca(2+) with ATP caused the nuclear accumulation of ChREBP. Finally, sorcin silencing inhibited ATP-induced increases in intracellular Ca(2+) and glucose-stimulated insulin secretion. We therefore conclude that sorcin retains ChREBP in the cytosol at low glucose concentrations and may act as a Ca(2+) sensor for glucose-induced nuclear translocation and the activation of ChREBP-dependent genes.
碳水化合物反应元件结合蛋白（ChREBP）是胰腺β细胞基因表达的调节剂，也是葡萄糖毒性的重要介质。葡萄糖通过仍未明确的机制增加 ChREBP 的活性和核定位。在这里，我们使用 MIN6 和原代小鼠β细胞揭示了 ChREBP 核易位背后的独特机制。在低葡萄糖浓度下，ChREBP 与 sorcin（一种五 EF 手 Ca(2+)结合蛋白）相互作用，并被隔离在细胞质中。sorcin 的过表达抑制高葡萄糖时 ChREBP 的核积累，并降低 L 型丙酮酸激酶（L-PK）和 TxNIP 启动子的活性，这两个是 ChREBP 的典型靶基因。sorcin 通过 RNA 干扰失活增加 ChREBP 在低葡萄糖浓度下的核定位和体内与 L-PK 启动子的结合。Ca(2+)内流对于这个过程是必不可少的，因为 EGTA 螯合 Ca(2+)或 diazoxide 和 nifedipine 的药理学抑制作用阻断了葡萄糖的作用。相反，用 ATP 动员细胞内 Ca(2+)会导致 ChREBP 的核积累。最后，sorcin 沉默抑制了 ATP 诱导的细胞内 Ca(2+)增加和葡萄糖刺激的胰岛素分泌。因此，我们得出结论，sorcin 在低葡萄糖浓度下将 ChREBP 保留在细胞质中，并可能作为葡萄糖诱导的核易位和 ChREBP 依赖性基因激活的 Ca(2+)传感器。
