Hypoxia-inducible factor 1 alpha mediates epidermal growth factor-induced down-regulation of E-cadherin expression and cell invasion in human ovarian cancer cells

Hypoxia-inducible factor 1α (HIF-1α) regulates the transcription of a number of genes under hypoxia and other extracellular stimulations. It has been shown that E-cadherin is down-regulated by epidermal growth factor receptor (EGF) stimulation, and that cells with low E-cadherin expression are more invasive. Our recent study demonstrated a novel mechanism by which EGF down-regulates E-cadherin expression through production of hydrogen peroxide (H2O2) and the activation of p38 MAPK in human ovarian cancer cells. In this study, we were interested in examining the potential role of HIF-1α in cell invasion under normoxic conditions, specifically when cells are treated with EGF, which is known to down-regulate E-cadherin and increase invasiveness. We show that EGF treatment induces HIF-1α expression in two human ovarian cancer cell lines (SKOV3 and OVCAR5), and that this effect is diminished by treatment with a membrane-permeable H2O2 scavenger, PEG-catalase. However, the induction of HIF-1α by EGF did not require the activation of p38 MAPK. Treatment with siRNA targeting HIF-1α reduces both basal and EGF-induced HIF-1α levels. Importantly, treatment with HIF-1α siRNA diminishes the up-regulation of Snail and Slug as well as the down-regulation of E-cadherin by EGF. The involvement of HIF-1α in the down-regulation of E-cadherin was confirmed with cobalt chloride (CoCl2), a hypoxia-mimetic reagent. Finally, we also show that EGF-induced cell invasion is attenuated by treatment with HIF-1α siRNA. This study demonstrates an important role for HIF-1α in mediating the effects of EGF on Snail, Slug and E-cadherin expression as well as invasiveness in human ovarian cancer cells.