Upregulation of vascular endothelial growth factor by cobalt chloride-simulated hypoxia is mediated by persistent induction of cyclooxygenase-2 in a metastatic human prostate cancer cell line

Upregulation of vascular endothelial growth factor (VEGF) expression induce d by hypoxia is crucial event leading to neovascularization. Cyclooxygenase -2, an inducible enzyme that catalyzes the formation of prostaglandins (PGs ) from arachidonic acid, has been demonstrated to be induced by hypoxia and play role in angiogenesis and metastasis. To investigate the potential eff ect of COX-2 on hypoxia-induced VEGF expression in prostate cancer. We exam ined the relationship between COX-2 expression and VEGF induction in respon se to cobalt chloride (CoCl2)-simulated hypoxia in three human prostate can cer cell lines with differing biological phenotypes. Northern blotting and ELISA revealed that all three tested cell lines constitutively expressed VE GF mRNA, and secreted VEGF protein to different degrees (LNCaP > PC-3 > PC3 ML). However, these cell lines differed in the ability to produce VEGF in t he presence of CoCl2-simulated hypoxia. CoCl2 treatment resulted in 40% and 75% increases in VEGF mRNA, and 50% and 95% in protein secretion by LNCaP and PC-3 cell lines, respectively. In contrast, PC-3ML cell line, a PC-3 su bline with highly invasive, metastatic phenotype, exhibits a dramatic upreg ulation of VEGF, 5.6-fold in mRNA and 6.3-fold in protein secretion after t reatment with CoCl2. The upregulation of VEGF in PC-3ML cells is accompanie d by a persistent induction of COX-2 mRNA (6.5-fold) and protein (5-fold). Whereas COX-2 expression is only transiently induced in PC-3 cells and not affected by CoCl2 in LNCaP cells. Moreover, the increases in VEGF mRNA and protein secretion induced by CoCl2 in PC-3ML cells were significantly suppr essed following exposure to NS398, a selective COX-2 inhibitor. Finally, th e effect of COX-2 inhibition on CoCl2-induced VEGF production was reversed by the treatment with exogenous PGE(2). Our data demonstrate that VEGF indu ction by cobalt chloride-simulated hypoxia is maintained by a concomitant, persistent induction of COX-2 expression and sustained elevation of PGE(2) synthesis in a human metastatic prostate cancer cell line, and suggest that COX-2 activity, reflected by PGE(2) production, is involved in hypoxia-ind uced VEGF expression, and thus, modulates prostatic tumor angiogenesis.