Abstract
Background/Aims: To investigate the roles of hypoxia-inducible factor 1α (HIF-1α), cyclooxygenase-2 (Cox-2) and its product, Prostaglandin E2 (PGE<sub>2</sub>), in the mechanisms underlying hypoxia-induced survivin expression in human umbilical vein endothelial cells (HUVECs) and to examine the effect of celecoxib, a selective Cox-2 inhibitor, on survivin expression. Methods: HUVECs were exposed to a normal (95% O<sub>2</sub>) or hypoxic (3% O<sub>2</sub>) environment for 24 hrs. We observed the localized expression of survivin, Cox-2 and HIF-1α in HUVECs using immunocytochemistry and detected the inhibitory effects of celecoxib on the growth of HUVECs using an MTT assay. mRNA and protein levels of Cox-2, HIF-1α and survivin were determined by real-time PCR and Western blot analysis under hypoxic conditions for 0, 6, 12, or 24 hrs. The time course changes of HIF-1α and survivin protein expression induced by cobalt chloride (CoCl<sub>2</sub>) were studied using Western blot analysis. We then treated HUVECs under hypoxia for 24 hrs with celecoxib (a Cox-2 selective inhibitor), genistein (a HIF-1α inhibitor) or exogenous PGE<sub>2</sub> to further investigate the changes in hypoxia-induced survivin expression. Results: Following 24 hrs of hypoxic treatment, cells exhibited strongly positive survivin, HIF-1α and Cox-2 cytoplasmic staining. Celecoxib (65 μM) effectively inhibited cell proliferation under hypoxic conditions. The protein and mRNA levels of Cox-2, HIF-1α and survivin were increased under hypoxia. The patterns of HIF-1α and survivin expression induced by CoCl<sub>2</sub> were similar to those induced by exposure to hypoxia. Genistein partially blocked survivin expression. Celecoxib reversed the hypoxia-induced survivin expression, whereas the addition of PGE<sub>2</sub> partially restored this effect. Conclusions: Hypoxia-induced survivin expression in HUVECs may be mediated by dual interdependent mechanisms directly involving HIF-1α and indirectly involving the Cox-2/PGE<sub>2</sub> pathways. Celecoxib may offset hypoxia-induced survivin expression.
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