Hypoxia-induced up-regulation of vascular endothelial growth factor (VEGF) expression is a critical event leading to tumor neovascularization. Hypoxia stimulates hypoxia-inducible factor-1α (HIF-1α), a transcriptional activator of VEGF. Cyclooxygenase (COX)-2, an inducible enzyme that catalyzes the formation of prostaglandins (PGs) from arachidonic acid, is also induced by hypoxia. We reported previously that COX-2 inhibition prevents hypoxic up-regulation of VEGF in human prostate cancer cells and that prostaglandin E2 (PGE2) restores hypoxic effects on VEGF. We hypothesized that PGE2 mediates hypoxic effects on VEGF by modulating HIF-1α expression. Addition of PGE2 to PC-3ML human prostate cancer cells had no effect on HIF-1α mRNA levels. However, PGE2 significantly increased HIF-1α protein levels, particularly in the nucleus. This effect of PGE2 largely results from the promotion of HIF-1α translocation from the cytosol to the nucleus. PGE2 addition to PC-3 ML cells transfected with a GFP-HIF-1α vector induced a time-dependent nuclear accumulation of the HIF-1α protein. Two selective COX-2 inhibitors, meloxicam and NS398, decreased HIF-1α levels and nuclear localization, under both normoxic and hypoxic conditions. Of several prostaglandins tested, only PGE2 reversed the effects of a COX-2 inhibitor in hypoxic cells. Finally, PGE2 effects on HIF-1α were specifically inhibited by PD98059 (a MAPK inhibitor). These data demonstrate that PGE2 production via COX-2-catalyzed pathway plays a critical role in HIF-1α regulation by hypoxia and imply that COX-2 inhibitors can prevent hypoxic induction of HIF-mediated gene transcription in cancer cells.
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Published, JBC Papers in Press, October 24, 2002, DOI 10.1074/jbc.M201095200
This work was supported by Department of Defense Grant-in-aid DAMD 17-00-1-0090 and the T. J. Martell Foundation for Leukemia, Cancer, and Aids Research.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
