Abstract 53: PTEN Nuclear Export and p53 Inhibition Mediate Free Fatty Acid-Induced Oxidative Stress in Endothelial Cells
Oxidative stress induced by free fatty acids (FFA) contributes to metabolic syndrome-associated development of cardiovascular diseases. In this study, we investigated the mechanisms involved in the p53-mediated regulation of antioxidant enzyme glutathione peroxidase-1 (GPx-1) expression and induction of intracellular ROS levels by palmitic acid (PA). The p53 pathway plays a very important role in regulating ROS production. We exposed human umbilical vein endothelial cells (HUVEC) to PA and demonstrated that p53 acetylation and protein levels decrease in a dose-dependent manner. The p53 downregulation correlated with a decrease in its downstream target GPx-1 and increase in the production of intracellular ROS. Nuclear PTEN was previously identified as an important factor involved in the upregulation of p53 acetylation, transcription activity and protein stability. Here, we show treatment of HUVEC with PA induced increase in PTEN phosphorylation at Ser380 and in interaction between PTEN and HAUSP, a deubiquitylating enzyme that cleaves ubiquitin from its substrates. The increased PTEN-HAUSP interaction leads to a dramatic decrease in PTEN mono-ubiquitination and increase in PTEN nuclear export, which prevents p53 acetylation. Pharmacologic inhibition or genetic ablation of mammalian target of rapamycin (mTOR) or S6K abolished PA-induced PTEN phosphorylation, PTEN-HAUSP interaction and PTEN nuclear export, suggesting that mTOR/S6K pathway is responsible for nuclear PTEN phosphorylation. Importantly, inhibition of mTOR/S6K pathway significantly blocks PA-induced PTEN nuclear export, p53-mediated GPx-1 expression, and increase in ROS production in HUVEC cells. These results demonstrate that PA treatment elevates PTEN-Ser380 phosphorylation through mTOR/S6K pathway. Once phosphorylated, PTEN in turn binds to HAUSP, reduces its mono-ubiquitination and nuclear localization, which prevents p53 from activating GPx-1 to compromise the most important antioxidant defense system and cause oxidative damage to human vascular endothelium.
- © 2012 by American Heart Association, Inc.