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, p70S6K1, 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 p70S6K1 activation, and VEGF expression through HIF-1α expression. Forced expression of p70S6K1 and HIF-1α reversed catalase- and rapamycin-inhibited VEGF transcriptional activation. We also showed that rapamycin, p70S6K1 inhibitor and catalase overexpression inhibited tumor angiogenesis. This study demonstrates a novel mechanism of EGF-induced VEGF and HIF-1α expression through production of H₂O₂ and activation of AKT and p70S6K1 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.