Goldberg Alexander A, Nkengfac Bernard, Sanchez Anthony M J, Moroz Nikolay, Qureshi Salman T, Koromilas Antonis E, Wang Shuo, Burelle Yan, Hussain Sabah N, Kristof Arnold S
From the Departments of Critical Care and Medicine, McGill University Health Centre and Meakins-Christie Laboratories, McGill University, Montreal, Quebec H4A 3J1, Canada.
the Lady Davis Institute for Medical Research, McGill University, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
J Biol Chem. 2017 Feb 3;292(5):1899-1909. doi: 10.1074/jbc.M116.771584. Epub 2016 Dec 23.
Autophagy involves the lysosomal degradation of cytoplasmic contents for regeneration of anabolic substrates during nutritional or inflammatory stress. Its initiation occurs rapidly after inactivation of the protein kinase mammalian target of rapamycin (mTOR) (or mechanistic target of rapamycin), leading to dephosphorylation of Unc-51-like kinase 1 (ULK1) and autophagosome formation. Recent studies indicate that mTOR can, in parallel, regulate the activity of stress transcription factors, including signal transducer and activator of transcription-1 (STAT1). The current study addresses the role of STAT1 as a transcriptional suppressor of autophagy genes and autophagic activity. We show that STAT1-deficient human fibrosarcoma cells exhibited enhanced autophagic flux as well as its induction by pharmacological inhibition of mTOR. Consistent with enhanced autophagy initiation, ULK1 mRNA and protein levels were increased in STAT1-deficient cells. By chromatin immunoprecipitation, STAT1 bound a putative regulatory sequence in the ULK1 5'-flanking region, the mutation of which increased ULK1 promoter activity, and rendered it unresponsive to mTOR inhibition. Consistent with an anti-apoptotic effect of autophagy, rapamycin-induced apoptosis and cytotoxicity were blocked in STAT1-deficient cells but restored in cells simultaneously exposed to the autophagy inhibitor ammonium chloride. In vivo, skeletal muscle ULK1 mRNA and protein levels as well as autophagic flux were significantly enhanced in STAT1-deficient mice. These results demonstrate a novel mechanism by which STAT1 negatively regulates ULK1 expression and autophagy.
自噬涉及在营养或炎症应激期间对细胞质内容物进行溶酶体降解，以再生合成代谢底物。自噬的起始在蛋白激酶哺乳动物雷帕霉素靶蛋白（mTOR）（或雷帕霉素作用机制靶蛋白）失活后迅速发生，导致Unc-51样激酶1（ULK1）去磷酸化并形成自噬体。最近的研究表明，mTOR可同时调节应激转录因子的活性，包括信号转导和转录激活因子1（STAT1）。本研究探讨了STAT1作为自噬基因转录抑制因子和自噬活性的作用。我们发现，STAT1缺陷的人纤维肉瘤细胞表现出自噬通量增强，以及通过mTOR的药理学抑制诱导自噬通量。与自噬起始增强一致，STAT1缺陷细胞中ULK1 mRNA和蛋白水平增加。通过染色质免疫沉淀，STAT1结合了ULK1 5'侧翼区域的一个假定调控序列，该序列的突变增加了ULK1启动子活性，并使其对mTOR抑制无反应。与自噬的抗凋亡作用一致，雷帕霉素诱导的凋亡和细胞毒性在STAT1缺陷细胞中被阻断，但在同时暴露于自噬抑制剂氯化铵的细胞中恢复。在体内，STAT1缺陷小鼠的骨骼肌ULK1 mRNA和蛋白水平以及自噬通量显著增强。这些结果证明了一种新机制，即STAT1负向调节ULK1表达和自噬。
