Effects of ras and von Hippel-Lindau (VHL) gene mutations on hypoxia-inducible factor (HIF)-1 alpha, HIF-2 alpha, and vascular endothelial growth factor expression and their regulation by the phosphatidylinositol 3 '-kinase/Akt signaling pathway

Many oncogenes induce expression of vascular endothelial growth factor (VEG F), a key factor in tumor angiogenesis. Phosphatidylinositol 3'-kinase (PI3 K)/Akt is a common signaling pathway for oncogenes and tumor suppressor gen es and is involved in VEGF regulation. Because hypoxia is a major stimulus for VEGF production, we examined the effects of LY294002, a selective PI3K inhibitor, on hypoxia-inducible factor (EH)-1 alpha and HIF-2 alpha express ion and on endogenous VEGF responses to hypoxia. A panel of breast cancer c ell lines reflecting the different genetic changes occurring in human breas t cancer was analyzed. LY294002 inhibited HIF-1 alpha induction and phospho rylation under hypoxia. However, HIF-2a expression was not affected. Basal and hypoxia-inducible VEGF expression was reduced at both mRNA and protein levels by 50%. V12-ras overexpression resulted in an increase in hypoxia-in duced HIF-1 alpha and HIF-2 alpha expression. This effect was blocked by PI 3K inhibitor, demonstrating one mechanism for ras synergy with hypoxia-medi ated induction of genes. The decreased HT-1 alpha expression was not depend ent on VHL interaction because a renal carcinoma cell line with VHL mutatio n and constitutive high HIF-1a expression also showed down-regulation of HI F-1 alpha after treatment with LY294002. These results have implications fo r the use of PI3K inhibitors to inhibit synergistic effects of hypoxia with a wide range of common oncogenes.