Reactive oxygen species regulate epidermal growth factor-induced vascular endothelial growth factor and hypoxia-inducible factor-1α expression through activation of AKT and P70S6K1 in human ovarian cancer cells

The epidermal growth factor (EGF) and EGF receptor (EGFR) family are often overexpressed in various human cancers including ovarian cancer. While it is generally believed that reactive oxygen species (ROS) are involved in the intracellular signaling events, the role of ROS in EGF-induced angiogenesis and carcinogenesis remains to be elucidated. The present study investigated the role of ROS in the regulation of AKT, p70S6KI, vascular endothelial growth factor (VEGF), and hypoxia-inducible factor 1(HIF-1) in ovarian cancer cells. In this study, OVCAR-3 cells were treated with EGF and catalase, an H2O2 scavenger. EGF treatment increases H2O2 production, leading to activation of the AKT/p70S6K1 pathway, resulting in increased VEGF expression at the transcriptional level. The inhibition of H2O2 production by catalase abolished EGF-induced AKT and p70S6KI activation, and VEGF expression through HIF-1 alpha expression. Forced expression of p70S6KI and HIF-1 alpha reversed catalase- and rapamycin-inhibited VEGF transcriptional activation. We also showed that rapamycin, p70S6KI inhibitor and catalase overexpression inhibited tumor angiogenesis. This study demonstrates a novel mechanism of EGF-induced VEGF and HIF-1 alpha expression through production of H2O2 and activation of AKT and p70S6KI in human ovarian cancer cells. This study also indicates that p70S6K1 and H2O2 are important in tumor angiogenesis. The results of the study could have an important implication in ovarian cancer therapy. (c) 2006 Elsevier Inc. All rights reserved.