College of Korean Medicine, Daegu Haany University, Gyeongsan, Gyeongsangbuk-do 38610, Republic of Korea.
College of Pharmacy, Chosun University, Gwangju 61452, Republic of Korea.
Biochim Biophys Acta Mol Cell Res. 2017 Jul;1864(7):1295-1307. doi: 10.1016/j.bbamcr.2017.04.010. Epub 2017 Apr 19.
Endoplasmic reticulum (ER) stress is characterized by an accumulation of misfolded proteins, and ER stress reduction is essential for maintaining tissue homeostasis. However, the molecular mechanisms that protect cells from ER stress are not completely understood. The present study investigated the role of sestrin 2 (SESN2) on ER stress and sought to elucidate the mechanism responsible for the hepatoprotective effect of SESN2 in vitro and in vivo. Treatment with tunicamycin (Tm) increased SESN2 protein and mRNA levels and reporter gene activity. Activating transcription factor 6 (ATF6) bound to unfolded protein response elements of SESN2 promoter, transactivated SESN2, and increased SESN2 protein expression. In addition, dominant negative mutant of ATF6α and siRNA against ATF6α blocked the ER stress-mediated SESN2 induction, whereas chemical inhibition of PERK or IRE1 did not affect SESN2 induction by Tm. Ectopic expression of SESN2 in HepG2 cells inhibited CHOP and GRP78 expressions by Tm. Moreover, SESN2 decreased the phosphorylations of JNK and p38 and PARP cleavage, and blocked the cytotoxic effect of excessive ER stress. In a Tm-induced liver injury model, adenoviral delivery of SESN2 in mice decreased serum ALT, AST and LDH activities and the mRNA levels of CHOP and GRP78 in hepatic tissues. Moreover, SESN2 reduced numbers of degenerating hepatocytes, and inhibited caspase 3 and PARP cleavages. These results suggest ATF6 is essential for ER stress-mediated SESN2 induction, and that SESN2 acts as a feedback regulator to protect liver from excess ER stress.
内质网（ER）应激的特征是错误折叠蛋白的积累，减少 ER 应激对于维持组织内稳态至关重要。然而，保护细胞免受 ER 应激的分子机制尚不完全清楚。本研究探讨了 sestrin 2（SESN2）在 ER 应激中的作用，并试图阐明 SESN2 在体外和体内发挥肝保护作用的机制。用衣霉素（Tm）处理可增加 SESN2 蛋白和 mRNA 水平以及报告基因活性。激活转录因子 6（ATF6）与 SESN2 启动子的未折叠蛋白反应元件结合，反式激活 SESN2，并增加 SESN2 蛋白表达。此外，ATF6α的显性失活突变体和针对 ATF6α 的 siRNA 阻断了 ER 应激介导的 SESN2 诱导，而 PERK 或 IRE1 的化学抑制并不影响 Tm 诱导的 SESN2 诱导。HepG2 细胞中 SESN2 的异位表达可抑制 Tm 诱导的 CHOP 和 GRP78 表达。此外，SESN2 降低了 JNK 和 p38 的磷酸化以及 PARP 裂解，并阻断了过度 ER 应激的细胞毒性作用。在 Tm 诱导的肝损伤模型中，小鼠中 SESN2 的腺病毒传递降低了血清 ALT、AST 和 LDH 活性以及肝组织中 CHOP 和 GRP78 的 mRNA 水平。此外，SESN2 减少了变性肝细胞的数量，并抑制了 caspase 3 和 PARP 的裂解。这些结果表明 ATF6 对于 ER 应激介导的 SESN2 诱导是必需的，并且 SESN2 作为一种反馈调节剂可保护肝脏免受过度的 ER 应激。
