Suppression of Hypoxia-inducible Factor 2α Restores p53 Activity via Hdm2 and Reverses Chemoresistance of Renal Carcinoma Cells

p53 mutations are rarely detected in clear cell renal cell carcinoma (CCRCC), but, paradoxically, these tumors remain highly resistant to chemotherapy and death receptor-induced death. Here, we show that the accumulation of hypoxia-inducible factor 2 alpha (HIF2 alpha), a critical oncogenic event in CCRCC following the loss of von Hippel-Lindau (VHL) tumor suppressor protein, leads to Hdm2-mediated suppression of p53. Primary CCRCC specimens exhibiting strong hypoxic signatures show increased levels of activated nuclear phospho-Hdm2(Ser(166)), which is concomitant with low p53 expression. The abrogation of Hdm2-p53 interaction using the small-molecule Hdm2 inhibitor nutlin-3 or the downregulation of HIF2 alpha via HIF2 alpha-specific short hairpin RNA or wild-type VHL reconstitution restores p53 function and reverses the resistance of CCRCC cells to Fas-mediated and chemotherapy-induced cell death. These findings unveil a mechanistic link between HIF2 alpha and p53 and provide a rationale for combining Hdm2 antagonists with chemotherapy for the treatment of CCRCC. [Cancer Res 2009;69(23):9056-64]