Wu Yong, Zhou Hillary, Wu Ke, Lee Sangkyu, Li Ruijin, Liu Xuan
1 Department of Biochemistry, University of California , Riverside, California.
Antioxid Redox Signal. 2014 Mar 20;20(9):1382-95. doi: 10.1089/ars.2013.5498. Epub 2013 Nov 13.
Oxidative stress induced by free fatty acids (FFA) contributes to metabolic syndrome-associated development of cardiovascular diseases, yet molecular mechanisms remain poorly understood. This study aimed at establishing whether phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and its subcellular location play a role in FFA-induced endothelial oxidative stress.
Exposing human endothelial cells (ECs) with FFA activated mammalian target of rapamycin (mTOR)/S6K pathway, and upon activation, S6K directly phosphorylated PTEN at S380. Phosphorylation of PTEN increased its interaction with its deubiquitinase USP7 in the nucleus, leading to PTEN deubiquitination and nuclear export. The reduction of PTEN in the nucleus, in turn, decreased p53 acetylation and transcription, reduced the expression of the p53 target gene glutathione peroxidase-1 (GPX1), resulting in reactive oxygen species (ROS) accumulation and endothelial damage. Finally, C57BL/6J mice fed with high-fat atherogenic diet (HFAD) showed PTEN nuclear export, decreased p53 and GPX1 protein expressions, elevated levels of ROS, and significant lesions in aortas. Importantly, inhibition of mTOR or S6K effectively blocked these effects, suggesting that mTOR/S6K pathway mediates HFAD-induced oxidative stress and vascular damage via PTEN/p53/GPX1 inhibition in vivo.
Our study demonstrated for the first time that S6K directly phosphorylated PTEN at S380 under high FFA conditions, and this phosphorylation mediated FFA-induced endothelial oxidative stress. Furthermore, we showed that S380 phosphorylation affected PTEN monoubiquitination and nuclear localization, providing the first example of coordinated regulation of PTEN nuclear localization via phosphorylation and ubiquitination.
Our studies provide a novel mechanism by which hyperlipidemia causes vascular oxidative damage through the phosphorylation of PTEN, blocking of PTEN nuclear function, and inhibition of p53/GPX1 activity.
游离脂肪酸（FFA）诱导的氧化应激促成了与代谢综合征相关的心血管疾病发展，但其分子机制仍知之甚少。本研究旨在确定10号染色体缺失的磷酸酶和张力蛋白同源物（PTEN）及其亚细胞定位是否在FFA诱导的内皮氧化应激中起作用。
用FFA处理人内皮细胞（ECs）可激活雷帕霉素靶蛋白（mTOR）/S6K通路，激活后，S6K直接在S380位点磷酸化PTEN。PTEN的磷酸化增加了其与细胞核中去泛素化酶USP7的相互作用，导致PTEN去泛素化和核输出。细胞核中PTEN的减少进而降低了p53的乙酰化和转录，降低了p53靶基因谷胱甘肽过氧化物酶-1（GPX1）的表达，导致活性氧（ROS）积累和内皮损伤。最后，喂食高脂致动脉粥样硬化饮食（HFAD）的C57BL/6J小鼠表现出PTEN核输出、p53和GPX1蛋白表达降低、ROS水平升高以及主动脉明显病变。重要的是，抑制mTOR或S6K可有效阻断这些效应，表明mTOR/S6K通路在体内通过抑制PTEN/p53/GPX1介导HFAD诱导的氧化应激和血管损伤。
我们的研究首次证明，在高FFA条件下，S6K直接在S380位点磷酸化PTEN，这种磷酸化介导了FFA诱导的内皮氧化应激。此外，我们表明S380磷酸化影响PTEN单泛素化和核定位，提供了通过磷酸化和泛素化协同调节PTEN核定位的首个实例。
我们的研究提供了一种新机制，即高脂血症通过PTEN磷酸化、PTEN核功能阻断和p53/GPX1活性抑制导致血管氧化损伤。
