Hypoxia-induced gene expression occurs solely through the action of hypoxia-inducible factor 1alpha (HIF-1alpha): role of cytoplasmic trapping of HIF-2alpha.
The hypoxia-inducible factors 1alpha (HIF-1alpha) and 2alpha (HIF-2alpha) have extensive structural homology and have been identified as key transcription factors responsible for gene expression in response to hypoxia. They play critical roles not only in normal development, but also in tumor progression. Here we report on the differential regulation of protein expression and transcriptional activity of HIF-1alpha and -2alpha by hypoxia in immortalized mouse embryo fibroblasts (MEFs). We show that oxygen-dependent protein degradation is restricted to HIF-1alpha, as HIF-2alpha protein is detected in MEFs regardless of oxygenation and is localized primarily to the cytoplasm. Endogenous HIF-2alpha remained transcriptionally inactive under hypoxic conditions; however, ectopically overexpressed HIF-2alpha translocated into the nucleus and could stimulate expression of hypoxia-inducible genes. We show that the factor inhibiting HIF-1 can selectively inhibit the transcriptional activity of HIF-1alpha but has no effect on HIF-2alpha-mediated transcription in MEFs. We propose that HIF-2alpha is not a redundant transcription factor of HIF-1alpha for hypoxia-induced gene expression and show evidence that there is a cell type-specific modulator(s) that enables selective activation of HIF-1alpha but not HIF-2alpha in response to low-oxygen stress.
Park
Sang-Ki
SK
Molecular Biology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, California 92093-0366, USA.
Dadak
Agnes M
AM
Haase
Volker H
VH
Fontana
Lucrezia
L
Giaccia
Amato J
AJ
Johnson
Randall S
RS
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D002451:Cell Compartmentation; D015687:Cell Hypoxia / Q000502:physiology*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D016228:Endothelial Growth Factors / Q000235:genetics; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D051272:Glucose Transporter Type 1; D007003:Hypoglycemia / Q000235:genetics / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008222:Lymphokines / Q000235:genetics; D051379:Mice; D008817:Mice, Mutant Strains; D006899:Mixed Function Oxygenases; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D010100:Oxygen / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D010735:Phosphoglycerate Kinase / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1
D051792:Basic Helix-Loop-Helix Proteins; D016228:Endothelial Growth Factors; D051272:Glucose Transporter Type 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D036341:Intercellular Signaling Peptides and Proteins; D008025:Ligases; D008222:Lymphokines; D006899:Mixed Function Oxygenases; D009004:Monosaccharide Transport Proteins; D010100:Oxygen; D010447:Peptide Hydrolases; D010735:Phosphoglycerate Kinase; D046988:Proteasome Endopeptidase Complex; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1; C439790:HIF1AN protein, human; C061553:ATP dependent 26S protease