title: Differential regulation of the transcriptional activities of hypoxia-inducible factor 1 alpha (HIF-1alpha) and HIF-2alpha in stem cells.
abstract: Transcriptional responses to hypoxia are primarily mediated by hypoxia-inducible factors (HIFs), HIF-1alpha and HIF-2alpha. The HIF-1alpha and HIF-2alpha subunits are structurally similar in their DNA binding and dimerization domains but differ in their transactivation domains, implying they may have unique target genes and require distinct transcriptional cofactors. Our previous results demonstrated that HIF-1alpha and HIF-2alpha regulate distinct target genes. Here, we report that HIF-2alpha is not transcriptionally active in embryonic stem (ES) cells, as well as possible inhibition by a HIF-2alpha-specific transcriptional repressor. Using DNA microarray analysis of hypoxia-inducible genes in wild-type (WT), Hif-1alpha(-)(/)(-), and Hif-2alpha(-)(/)(-) ES cells, we show that HIF-1alpha induces a large number of both confirmed and novel hypoxia-inducible genes, while HIF-2alpha does not activate any of its previously described targets. We further demonstrate that inhibition of HIF-2alpha function occurs at the level of transcription cofactor recruitment to endogenous target gene promoters. Overexpression of WT and, notably, a DNA-binding-defective HIF-2alpha mutant restores endogenous HIF-2alpha protein activity, suggesting that ES cells express a HIF-2alpha-specific corepressor that can be titrated by overexpressed HIF-2alpha protein. HIF-2alpha repression may explain why patients with mutations in the VHL tumor suppressor gene display cancerous lesions in specific tissue types.
authors.affiliation: Howard Hughes Medical Institute and Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, 421 Curie Boulevard, Philadelphia, PA 19104, USA.
authors.forename: Cheng-Jun
authors.initials: CJ
authors.lastname: Hu
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Iyer
authors.forename: Aneesa
authors.initials: A
authors.lastname: Sataur
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Covello
authors.forename: Lewis A
authors.initials: LA
authors.lastname: Chodosh
authors.forename: M Celeste
authors.initials: MC
authors.lastname: Simon
mesh_terms: D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D000860:Hypoxia / Q000235:genetics*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D013234:Stem Cells / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D015533:Transcriptional Activation; D015854:Up-Regulation / Q000235:genetics; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D014157:Transcription Factors; D000099162:Endothelial PAS Domain-Containing Protein 1; C497397:Arnt protein, mouse