title: Regulation of hypoxia-inducible factor 1alpha expression and function by the mammalian target of rapamycin.
abstract: Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor containing an inducibly expressed HIF-1alpha subunit and a constititutively expressed HIF-1beta subunit. Under hypoxic conditions, the HIF-1alpha subunit accumulates due to a decrease in the rate of proteolytic degradation, and the resulting HIF-1alpha-HIF-1beta heterodimers undergo posttranslational modifications that promote transactivation. Recent studies suggest that amplified signaling through phosphoinositide 3-kinase, and its downstream target, mTOR, enhances HIF-1-dependent gene expression in certain cell types. In the present study, we have explored further the linkage between mTOR and HIF-1 in PC-3 prostate cancer cells treated with hypoxia or the hypoxia mimetic agent, CoCl(2). Pretreatment of PC-3 cells with the mTOR inhibitor, rapamycin, inhibited both the accumulation of HIF-1alpha and HIF-1-dependent transcription induced by hypoxia or CoCl(2). Transfection of these cells with wild-type mTOR enhanced HIF-1 activation by hypoxia or CoCl(2), while expression of a rapamycin-resistant mTOR mutant rendered both HIF-1alpha stabilization and HIF-1 transactivating function refractory to inhibition by rapamycin. Studies with GAL4-HIF-1alpha fusion proteins pinpointed the oxygen-dependent degradation domain as a critical target for the rapamycin-sensitive, mTOR-dependent signaling pathway leading to HIF-1alpha stabilization by CoCl(2). These studies position mTOR as an upstream activator of HIF-1 function in cancer cells and suggest that the antitumor activity of rapamycin is mediated, in part, through the inhibition of cellular responses to hypoxic stress.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Christine C
authors.initials: CC
authors.lastname: Hudson
authors.forename: Mei
authors.initials: M
authors.lastname: Liu
authors.forename: Gary G
authors.initials: GG
authors.lastname: Chiang
authors.forename: Diane M
authors.initials: DM
authors.lastname: Otterness
authors.forename: Dawn C
authors.initials: DC
authors.lastname: Loomis
authors.forename: Fiona
authors.initials: F
authors.lastname: Kaper
authors.forename: Amato J
authors.initials: AJ
authors.lastname: Giaccia
authors.forename: Robert T
authors.initials: RT
authors.lastname: Abraham
mesh_terms: D015687:Cell Hypoxia; D002867:Chromones / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051272:Glucose Transporter Type 1; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007976:Leupeptins / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D009025:Morpholines / Q000494:pharmacology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
chemical_list: D002867:Chromones; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D051272:Glucose Transporter Type 1; C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007976:Leupeptins; D009004:Monosaccharide Transport Proteins; D009025:Morpholines; D009687:Nuclear Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011993:Recombinant Fusion Proteins; C495677:SLC2A1 protein, human; D014157:Transcription Factors; C089486:carbobenzoxy-leucyl-leucyl-norvalinal; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D003035:Cobalt; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; C018021:cobaltous chloride; D020123:Sirolimus