Phosphatidylinositol 3-kinase signaling controls levels of hypoxia-inducible factor

The phosphatidylinositol 3-kinase (PI3K) signaling pathway has inherent onc ogenic potential. It is upregulated in diverse human cancers by either a ga in of function in PI3K itself or in its downstream target Akt or by a loss of function in the negative regulator PTEN, However, the complete consequen ces of this upregulation are not known. Here we show that insulin and epide rmal growth factor or an inactivating mutation in the tumor suppressor PTEN specifically increase the protein levels of hypoxia-inducible factor (HIF) 1 alpha but not of HIF-1 beta in human cancer cell lines. This specific el evation of HIF-1 alpha protein expression requires PI3K signaling. In the p rostate carcinoma-derived cell lines PC-3 and DU145, insulin- and epidermal growth factor-induced expression of HIF-1 alpha was inhibited by the PI3K- specific inhibitors LY294002 and wortmannin in a dose-dependent manner. HIF -1 beta expression was not affected by these inhibitors. Introduction of wi ld-type PTEN into the PTEN-negative PC-3 cell line specifically inhibited t he expression of HIF-1 alpha but not that of HIF-1 beta, In contrast to the HIF-1 alpha protein, the level of HIF-1 alpha mRNA was not significantly a ffected by PI3K signaling. Vascular endothelial growth factor reporter gene activity was induced by insulin in PC-3 cells and was inhibited by the PI3 K inhibitor LY294002 and by the coexpression of a HIF-1 dominant negative c onstruct. Vascular endothelial growth factor reporter gene activity was als o inhibited by expression of a dominant negative PI3K construct and by the tumor suppressor PTEN.