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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Cell Hypoxia
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Chromones / pharmacology
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Cobalt / pharmacology
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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DNA-Binding Proteins / physiology
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Enzyme Inhibitors / pharmacology
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Glucose Transporter Type 1
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Helix-Loop-Helix Motifs*
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Humans
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Hypoxia-Inducible Factor 1
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Hypoxia-Inducible Factor 1, alpha Subunit
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Leupeptins / pharmacology
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Monosaccharide Transport Proteins / genetics
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Morpholines / pharmacology
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Nuclear Proteins / physiology
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Phosphoinositide-3 Kinase Inhibitors
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Protein Kinase Inhibitors
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Protein Kinases / genetics
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Protein Kinases / metabolism*
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Recombinant Fusion Proteins / physiology
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Sirolimus / pharmacology
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TOR Serine-Threonine Kinases
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Transcription Factors / genetics
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Transcription Factors / metabolism*
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Transcription Factors / physiology
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Transcription, Genetic / drug effects
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Transcriptional Activation*
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Tumor Cells, Cultured
Substances
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Chromones
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DNA-Binding Proteins
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Enzyme Inhibitors
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Glucose Transporter Type 1
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HIF1A protein, human
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Hypoxia-Inducible Factor 1
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Hypoxia-Inducible Factor 1, alpha Subunit
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Leupeptins
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Monosaccharide Transport Proteins
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Morpholines
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Nuclear Proteins
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Phosphoinositide-3 Kinase Inhibitors
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Protein Kinase Inhibitors
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Recombinant Fusion Proteins
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SLC2A1 protein, human
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Transcription Factors
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carbobenzoxy-leucyl-leucyl-norvalinal
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2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
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Cobalt
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Protein Kinases
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MTOR protein, human
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TOR Serine-Threonine Kinases
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cobaltous chloride
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Sirolimus