title: Proteasomal inhibition attenuates transcriptional activity of hypoxia-inducible factor 1 (HIF-1) via specific effect on the HIF-1alpha C-terminal activation domain.
abstract: The ubiquitin-proteasome pathway (UPP) is involved in regulation of multiple cellular processes. Hypoxia-inducible factor 1 alpha (HIF-1 alpha) is a prototypic target of the UPP and, as such, is stabilized under conditions of proteasomal inhibition. Using carbonic anhydrase IX (CAIX) and vascular endothelial growth factor (VEGF) expression as paradigmatic markers of HIF-1 activity, we found that proteasomal inhibitors (PI) abrogated hypoxia-induced CAIX expression in all cell lines tested and VEGF expression in two out of three. Mapping of the inhibitory effect identified the C-terminal activation domain (CAD) of HIF-1 alpha as the primary target of PI. PI specifically inhibited the HIF-1 alpha CAD despite activating the HIF-1 alpha coactivator p300 and another p300 cysteine/histidine-rich domain 1-dependent transcription factor, STAT-2. Coimmunoprecipitation and glutathione S-transferase pull downs indicated that PI does not disrupt interactions between HIF-1 alpha and p300. Mutational analysis failed to confirm involvement of sites of known or putative posttranslational modifications in regulation of HIF-1 alpha CAD function by PI. Our data provide evidence for the counterintuitive hypothesis that inhibition of HIF-1 function could be responsible for at least some of the antitumor effects of proteasomal inhibition. Further studies of the mechanism of the PI-induced attenuation of HIF-1alpha will provide important, potentially novel insight into regulation of HIF-1 activity and possibly identify new targets for HIF-directed therapy.
authors.affiliation: Department of Microbiology and Molecular Genetics, Medical Science I B210, University of California at Irvine, College of Medicine, Irvine, CA 92697-4025, USA. skaluz@uci.edu
authors.forename: Stefan
authors.initials: S
authors.lastname: Kaluz
authors.forename: Milota
authors.initials: M
authors.lastname: Kaluzová
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Stanbridge
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001897:Boronic Acids / Q000378:metabolism; D000069286:Bortezomib; D002256:Carbonic Anhydrases / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D011480:Protease Inhibitors / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D017434:Protein Structure, Tertiary; D011719:Pyrazines / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D050880:p300-CBP Transcription Factors / Q000378:metabolism
chemical_list: D015415:Biomarkers; D001897:Boronic Acids; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007527:Isoenzymes; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D011993:Recombinant Fusion Proteins; D042461:Vascular Endothelial Growth Factor A; D000069286:Bortezomib; D050880:p300-CBP Transcription Factors; D046988:Proteasome Endopeptidase Complex; D002256:Carbonic Anhydrases