title: Cobalt stimulates HIF-1-dependent but inhibits HIF-2-dependent gene expression in liver cancer cells.
abstract: Hypoxia-inducible factors (HIFs) are transcriptional regulators that mediate the cellular response to low oxygen. Although HIF-1 is usually considered as the principal mediator of hypoxic adaptation, several tissues and different cell types express both HIF-1 and HIF-2 isoforms under hypoxia or when treated with hypoxia mimetic chemicals such as cobalt. However, the similarities or differences between HIF-1 and HIF-2, in terms of their tissue- and inducer-specific activation and function, are not adequately characterized. To address this issue, we investigated the effects of true hypoxia and hypoxia mimetics on HIF-1 and HIF-2 induction and specific gene transcriptional activity in two hepatic cancer cell lines, Huh7 and HepG2. Both hypoxia and cobalt caused rapid induction of both HIF-1α and HIF-2α proteins. Hypoxia induced erythropoietin (EPO) expression and secretion in a HIF-2-dependent way. Surprisingly, however, EPO expression was not induced when cells were treated with cobalt. In agreement, both HIF-1- and HIF-2-dependent promoters (of PGK and SOD2 genes, respectively) were activated by hypoxia while cobalt only activated the HIF-1-dependent PGK promoter. Unlike cobalt, other hypoxia mimetics such as DFO and DMOG activated both types of promoters. Furthermore, cobalt impaired the hypoxic stimulation of HIF-2, but not HIF-1, activity and cobalt-induced HIF-2α interacted poorly with USF-2, a HIF-2-specific co-activator. These data show that, despite similar induction of HIF-1α and HIF-2α protein expression, HIF-1 and HIF-2 specific gene activating functions respond differently to different stimuli and suggest the operation of oxygen-independent and gene- or tissue-specific regulatory mechanisms involving additional transcription factors or co-activators.
authors: Laboratory of Biochemistry, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Larissa 41110, Greece.
authors: Christina
authors: C
authors: Befani
authors: Ilias
authors: I
authors: Mylonis
authors: Ioanna-Maria
authors: IM
authors: Gkotinakou
authors: Panagiotis
authors: P
authors: Georgoulias
authors: Cheng-Jun
authors: CJ
authors: Hu
authors: George
authors: G
authors: Simos
authors: Panagiotis
authors: P
authors: Liakos
mesh_terms: D000600:Amino Acids, Dicarboxylic / Q000494:pharmacology; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology*; D003676:Deferoxamine / Q000494:pharmacology; D004921:Erythropoietin / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D008113:Liver Neoplasms / Q000235:genetics* / Q000473:pathology; D010735:Phosphoglycerate Kinase / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011412:Propanolamines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D011759:Pyrrolidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D051720:Upstream Stimulatory Factors / Q000378:metabolism; D000099162:Endothelial PAS Domain-Containing Protein 1; D000099156:Superoxide Dismutase 2
chemical_list: D000600:Amino Acids, Dicarboxylic; D051792:Basic Helix-Loop-Helix Proteins; D003035:Cobalt; D003676:Deferoxamine; D004921:Erythropoietin; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D010735:Phosphoglycerate Kinase; D011412:Propanolamines; D011759:Pyrrolidines; D012333:RNA, Messenger; D013482:Superoxide Dismutase; D051720:Upstream Stimulatory Factors; D000099162:Endothelial PAS Domain-Containing Protein 1; D000099156:Superoxide Dismutase 2; C401299:1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol; C497442:HIF1A protein, human; C497184:USF2 protein, human; C577282:PGK1 protein, human; C018021:cobaltous chloride; C040947:oxalylglycine
keywords: Cobalt; EPO; HIF-2α; Hypoxia; SOD2; USF2
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