Polypeptide Hormone Laboratory, Department of Experimental Medicine, Research Institute of the McGill University Health Centre, McGill University, 3640 University Street, Montreal, QC, Canada.
Am J Physiol Endocrinol Metab. 2011 Mar;300(3):E423-34. doi: 10.1152/ajpendo.00088.2010. Epub 2010 Jun 29.
Obesity has been shown to create stress in the endoplasmic reticulum (ER), and that initiates the activation of the unfolded protein response (UPR). This has been reported to cause insulin resistance in selective tissues through activation of the inositol-requiring enzyme 1α (IRE1α)-c-Jun NH(2)-terminal kinase (JNK) pathway, which results in the phosphorylation of the insulin receptor substrate-1 (IRS-1) at an inhibitory site and blocks insulin receptor signaling. In this study, we report that the Src homology domain-containing adaptor protein Nck1, previously shown to modulate the UPR, is of functional importance in obesity-induced ER stress signaling and inhibition of insulin actions. We have examined obese Nck1(-/-) and Nck1(+/+) mice for glucose tolerance, insulin sensitivity, and signaling as well as for ER stress markers and IRS-1 phosphorylation at Ser(307). Our findings show that obese Nck1-deficient mice display improved glucose disposal accompanied by enhanced insulin signaling in liver. This correlates with attenuated IRE1α and JNK activation and IRS-1 phosphorylation at Ser(307) compared with obese wild-type mice. Consistent with our in vivo data, we report that downregulation of Nck1 using siRNA in HepG2 cells results in decreased thapsigargin-induced IRE1α activation and signaling and IRS-1 phosphorylation at Ser(307), whereas it markedly enhances insulin signaling. Overall, in liver and in cultured cells, we show that depletion of Nck1 attenuates the UPR signal and its inhibitory action on insulin signaling. Taken all together, our findings implicate Nck1 in regulating the UPR, which secondary to obesity impairs glucose homeostasis and insulin actions.
肥胖已被证明会在内质网（ER）中产生应激，从而引发未折叠蛋白反应（UPR）的激活。据报道，这会通过激活肌醇需求酶 1α（IRE1α）-c-Jun NH（2）-末端激酶（JNK）途径导致选择性组织中的胰岛素抵抗，这会导致胰岛素受体底物-1（IRS-1）在抑制性位点磷酸化并阻断胰岛素受体信号传导。在这项研究中，我们报告先前显示可调节 UPR 的含Src 同源结构域的衔接蛋白 Nck1 在肥胖诱导的 ER 应激信号传导和抑制胰岛素作用中具有功能重要性。我们已经检查了肥胖的 Nck1（-/-）和 Nck1（+/+）小鼠的葡萄糖耐量，胰岛素敏感性和信号传导以及 ER 应激标志物和 IRS-1 在 Ser（307）处的磷酸化。我们的发现表明，肥胖的 Nck1 缺乏小鼠显示出改善的葡萄糖处置能力，同时伴有肝脏中胰岛素信号的增强。这与 IRE1α和 JNK 激活以及 IRS-1 在 Ser（307）处的磷酸化减弱相关，与肥胖的野生型小鼠相比。与我们的体内数据一致，我们报告说，使用 siRNA 在 HepG2 细胞中下调 Nck1 会导致 thapsigargin 诱导的 IRE1α 激活和信号传导以及 IRS-1 在 Ser（307）处的磷酸化减少，而胰岛素信号传导明显增强。总的来说，在肝脏和培养的细胞中，我们表明 Nck1 的耗竭会减弱 UPR 信号及其对胰岛素信号的抑制作用。综上所述，我们的发现表明 Nck1 参与调节 UPR，肥胖会继发损害葡萄糖稳态和胰岛素作用。
