title: FOXO3a is activated in response to hypoxic stress and inhibits HIF1-induced apoptosis via regulation of CITED2.
abstract: FOXO transcription factors are important regulators of cell survival in response to a variety of stress stimuli, among which are oxidative stress, DNA damage, and nutrient deprivation. Here we report a role for FOXO3a under conditions of hypoxic stress. In response to hypoxia, FOXO3a transcript levels accumulate in an HIF1-dependent way, resulting in enhanced FOXO3a activity. We show that transcription of CITED2, a transcriptional cofactor that functions in a negative feedback loop to control HIF1 activity, is induced by FOXO3a during hypoxia. In fibroblasts as well as in breast cancer cells, FOXO3a inhibits HIF1-induced apoptosis by stimulating the transcription of CITED2, which results in reduced expression of the proapoptotic HIF1 target genes NIX and RTP801. Thus, by fine-tuning HIF1 activity, FOXO3a plays an important role in the survival response of normal and cancer cells in response to hypoxic stress.
authors.affiliation: Campbell Family Institute for Breast Cancer Research, University Health Network, Ontario Cancer Institute and Princess Margaret Hospital, Toronto, ON M5G 2C1, Canada.
authors.forename: Walbert J
authors.initials: WJ
authors.lastname: Bakker
authors.forename: Isaac S
authors.initials: IS
authors.lastname: Harris
authors.forename: Tak W
authors.initials: TW
authors.lastname: Mak
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D015687:Cell Hypoxia; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D002867:Chromones / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D053595:Embryonic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005434:Flow Cytometry; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D041681:NIH 3T3 Cells; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D002867:Chromones; C110087:Cited2 protein, mouse; D004268:DNA-Binding Proteins; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D051793:Hypoxia-Inducible Factor 1; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D015534:Trans-Activators; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one