Differential roles of hypoxia-inducible factor 1alpha (HIF-1alpha) and HIF-2alpha in hypoxic gene regulation.
Transcriptional responses to hypoxia are primarily mediated by hypoxia-inducible factor (HIF), a heterodimer of HIF-alpha and the aryl hydrocarbon receptor nuclear translocator subunits. 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. Previous studies using Hif-1alpha(-/-) embryonic stem and mouse embryonic fibroblast cells show that loss of HIF-1alpha eliminates all oxygen-regulated transcriptional responses analyzed, suggesting that HIF-2alpha is dispensable for hypoxic gene regulation. In contrast, HIF-2alpha has been shown to regulate some hypoxia-inducible genes in transient transfection assays and during embryonic development in the lung and other tissues. To address this discrepancy, and to identify specific HIF-2alpha target genes, we used DNA microarray analysis to evaluate hypoxic gene induction in cells expressing HIF-2alpha but not HIF-1alpha. In addition, we engineered HEK293 cells to express stabilized forms of HIF-1alpha or HIF-2alpha via a tetracycline-regulated promoter. In this first comparative study of HIF-1alpha and HIF-2alpha target genes, we demonstrate that HIF-2alpha does regulate a variety of broadly expressed hypoxia-inducible genes, suggesting that its function is not restricted, as initially thought, to endothelial cell-specific gene expression. Importantly, HIF-1alpha (and not HIF-2alpha) stimulates glycolytic gene expression in both types of cells, clearly showing for the first time that HIF-1alpha and HIF-2alpha have unique targets.
Hu
Cheng-Jun
CJ
Abramson Family Cancer Research Institute. Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, 421 Curie Boulevard, Philadelphia, PA 19104, USA.
Wang
Li-Yi
LY
Chodosh
Lewis A
LA
Keith
Brian
B
Simon
M Celeste
MC
D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D015687:Cell Hypoxia / Q000235:genetics* / Q000502:physiology*; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006019:Glycolysis / Q000235:genetics; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D000099162:Endothelial PAS Domain-Containing Protein 1
D051792:Basic Helix-Loop-Helix Proteins; D018076:DNA, Complementary; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human