PTEN phosphorylation and nuclear export mediate free fatty acid-induced oxidative stress.
OBJECTIVE
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.


RESULTS
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.


METHODS
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.


CONCLUSIONS
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.
1 Department of Biochemistry, University of California , Riverside, California.
Yong
Y
Wu
Hillary
H
Zhou
Ke
K
Wu
Sangkyu
S
Lee
Ruijin
R
Li
Xuan
X
Liu
D021581:Active Transport, Cell Nucleus; D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D005979:Glutathione Peroxidase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D009569:Nitric Oxide / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D051059:PTEN Phosphohydrolase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019308:Palmitic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017382:Reactive Oxygen Species / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D054875:Ubiquitination; D000094765:Glutathione Peroxidase GPX1
D004791:Enzyme Inhibitors; D005230:Fatty Acids, Nonesterified; D017382:Reactive Oxygen Species; D016159:Tumor Suppressor Protein p53; D019308:Palmitic Acid; D009569:Nitric Oxide; D005979:Glutathione Peroxidase; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D051059:PTEN Phosphohydrolase; D000094765:Glutathione Peroxidase GPX1