title: Prolonged hypoxia differentially regulates hypoxia-inducible factor (HIF)-1alpha and HIF-2alpha expression in lung epithelial cells: implication of natural antisense HIF-1alpha.
abstract: Transcriptional adaptations to hypoxia are mediated by hypoxia-inducible factor (HIF)-1, a heterodimer of HIF-alpha and aryl hydrocarbon receptor nuclear translocator subunits. The HIF-1alpha and HIF-2alpha subunits both undergo rapid hypoxia-induced protein stabilization and bind identical target DNA sequences. When coexpressed in similar cell types, discriminating control mechanisms may exist for their regulation, explaining why HIF-1alpha and HIF-2alpha do not substitute during embryogenesis. We report that, in a human lung epithelial cell line (A549), HIF-1alpha and HIF-2alpha proteins were similarly induced by acute hypoxia (4 h, 0.5% O(2)) at the translational or posttranslational level. However, HIF-1alpha and HIF-2alpha were differentially regulated by prolonged hypoxia (12 h, 0.5% O(2)) since HIF-1alpha protein stimulation disappeared because of a reduction in its mRNA stability, whereas HIF-2alpha protein stimulation remained high and stable. Prolonged hypoxia also induced an increase in the quantity of natural antisense HIF-1alpha (aHIF), whose gene promoter contains several putative hypoxia response elements to which (as we confirm here) the HIF-1alpha or HIF-2alpha protein can bind. Finally, transient transfection of A549 cells by dominant-negative HIF-2alpha, also acting as a dominant-negative for HIF-1alpha, prevented both the decrease in the HIF-1alpha protein and the increase in the aHIF transcript. Taken together, these data indicate that, during prolonged hypoxia, HIF-alpha proteins negatively regulate HIF-1alpha expression through an increase in aHIF and destabilization of HIF-1alpha mRNA. This trans-regulation between HIF-1alpha and HIF-2alpha during hypoxia likely conveys target gene specificity.
authors.affiliation: Department of Physiology, INSERM U426, Faculté de Médecine Xavier Bichat, Université Paris 7, 75870 Paris, Cedex 18, France. christine.clerici@lmr.ac-hop-paris.fr
authors.forename: Tokujiro
authors.initials: T
authors.lastname: Uchida
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rossignol
authors.forename: Michael A
authors.initials: MA
authors.lastname: Matthay
authors.forename: Rémi
authors.initials: R
authors.lastname: Mounier
authors.forename: Sylvianne
authors.initials: S
authors.lastname: Couette
authors.forename: Eric
authors.initials: E
authors.lastname: Clottes
authors.forename: Christine
authors.initials: C
authors.lastname: Clerici
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D003676:Deferoxamine / Q000494:pharmacology; D019281:Dimerization; D004847:Epithelial Cells / Q000378:metabolism*; D005799:Genes, Dominant; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D015151:Immunoblotting; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012260:Ribonucleases / Q000378:metabolism; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D003035:Cobalt; D004247:DNA; D003676:Deferoxamine; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D010100:Oxygen; D012333:RNA, Messenger; D012260:Ribonucleases; D015534:Trans-Activators; D014157:Transcription Factors; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C018021:cobaltous chloride