Hypoxia up-regulates the effects of prostaglandin E ₂ on tumor angiogenesis in ovarian cancer cells

Objective. Emerging evidence supports a role for prostaglandins (PG) and their synthesizing enzyme, cyclooxygenase (COX), in tumor angiogenesis. The objective of this study was to investigate the effects of prostaglandin E ₂ (PGE ₂) on the expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible transcription factor-1 alpha (HIF-1α) genes in epithelial ovarian cancer (EOC) cells. Methods. Two human EOC cell lines, MDAH-2774 and SKOV-3, were treated with exogenous dimethyl prostaglandin E ₂ (dmPGE ₂) at two doses of 10 and 50 μg/ml and cultured for 24 h under both normoxic and hypoxic conditions. Total RNA was extracted from EOC cells with the use of a monophasic solution of phenol and GITC/Trizol method. The levels of COX-2, VEGF, and HIF-1α mRNA were measured by quantitative reverse transcription PCR (RT-PCR). Results. Under normoxic conditions, treatment of both ovarian cancer cell lines with dmPGE ₂ resulted in a significant increase in VEGF expression but had no effect on HIF-1α. Culturing the cells under hypoxic conditions resulted in an increase in HIF-1α and VEGF mRNAs. The combination of hypoxia and dmPGE ₂ treatment resulted in the highest levels of VEGF and HIF-1α when compared to either individual treatment. Conclusion. PGE ₂ is a potent stimulator of VEGF expression in ovarian cancer cells. This effect of PG is further potentiated under hypoxic conditions where it is also associated with a significant increase in HIF-1α expression.