title: Hypoxia-inducible factor 1alpha is regulated by the mammalian target of rapamycin (mTOR) via an mTOR signaling motif.
abstract: Tumors that form as a result of heightened mammalian target of rapamycin (mTOR) signaling are highly vascularized. This process of angiogenesis is regulated through hypoxia-inducible factor (HIF)-mediated transcription of angiogenic factors. It is recognized that inhibition of mTOR with rapamycin can diminish the process of angiogenesis. Our work shows that activation of mTOR by Ras homologue enriched in brain (Rheb) overexpression potently enhances the activity of HIF1alpha and vascular endothelial growth factor (VEGF)-A secretion during hypoxia, which is reversed with rapamycin. Mutants of Rheb, which do not bind guanine nucleotide (D60K, D60V, N119I, and D122N) and are unable to activate mTOR, inhibit the activity of HIF when overexpressed. We show that regulatory associated protein of mTOR (Raptor) interacts with HIF1alpha and requires an mTOR signaling (TOS) motif located in the N terminus of HIF1alpha. Furthermore, a mutant of HIF1alpha lacking this TOS motif dominantly impaired HIF activity during hypoxia and was unable to bind to the co-activator CBP/p300. Rapamycin treatments do not affect the stability of HIF1alpha and modulate HIF activity via a Von Hippel-Lindau (VHL)-independent mechanism. We demonstrate that the high levels of HIF activity in cells devoid of TSC2 can be reversed by treatments with rapamycin or the readdition of TSC2. Our work explains why human cancers with aberrant mTOR signaling are prone to angiogenesis and suggests that inhibition of mTOR with rapamycin might be a suitable therapeutic strategy.
authors.affiliation: Institute of Medical Genetics, Wales College of Medicine, Cardiff University, Heath Park, Cardiff, Wales, United Kingdom.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Land
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Tee
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D006150:Guanine Nucleotides / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D009369:Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000187:drug effects / Q000235:genetics; D000076205:Ras Homolog Enriched in Brain Protein; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics / Q000378:metabolism; D050880:p300-CBP Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D006150:Guanine Nucleotides; C497442:HIF1A protein, human; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009479:Neuropeptides; C490211:RHEB protein, human; D000076205:Ras Homolog Enriched in Brain Protein; C490213:Rheb protein, mouse; C000624653:TSC2 protein, human; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; D050880:p300-CBP Transcription Factors; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020123:Sirolimus