Hsp90 regulates a von Hippel Lindau-independent hypoxia-inducible factor-1 alpha-degradative pathway.
HIF-1 alpha is a normally labile proangiogenic transcription factor that is stabilized and activated in hypoxia. Although the von Hippel Lindau (VHL) gene product, the ubiquitin ligase responsible for regulating HIF-1 alpha protein levels, efficiently targets HIF-1 alpha for rapid proteasome-dependent degradation under normoxia, HIF-1 alpha is resistant to the destabilizing effects of VHL under hypoxia. HIF-1 alpha also associates with the molecular chaperone Hsp90. To examine the role of Hsp90 in HIF-1 alpha function, we used renal carcinoma cell (RCC) lines that lack functional VHL and express stable HIF-1 alpha protein under normoxia. Geldanamycin (GA), an Hsp90 antagonist, promoted efficient ubiquitination and proteasome-mediated degradation of HIF-1 alpha in RCC in both normoxia and hypoxia. Furthermore, HIF-1 alpha point mutations that block VHL association did not protect HIF-1 alpha from GA-induced destabilization. Hsp90 antagonists also inhibited HIF-1 alpha transcriptional activity and dramatically reduced both hypoxia-induced accumulation of VEGF mRNA and hypoxia-dependent angiogenic activity. These findings demonstrate that disruption of Hsp90 function 1) promotes HIF-1 alpha degradation via a novel, oxygen-independent E3 ubiquitin ligase and 2) diminishes HIF-1 alpha transcriptional activity. Existence of an Hsp90-dependent pathway for elimination of HIF-1 alpha predicts that Hsp90 antagonists may be hypoxic cell sensitizers and possess antiangiogenic activity in vivo, thus extending the utility of these drugs as therapeutic anticancer agents.
Isaacs
Jennifer S
JS
Cell and Cancer Biology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Rockville, Maryland 20850, USA.
Jung
Yun-Jin
YJ
Mimnaugh
Edward G
EG
Martinez
Alfredo
A
Cuttitta
Frank
F
Neckers
Leonard M
LM
D003546:Cysteine Endopeptidases / Q000378:metabolism; D015536:Down-Regulation; D018841:HSP90 Heat-Shock Proteins / Q000502:physiology*; D006868:Hydrolysis; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008025:Ligases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein
D018841:HSP90 Heat-Shock Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009097:Multienzyme Complexes; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008025:Ligases