Lando, D.Pongratz, I.Poellinger, L.Whitelaw, M.2007-05-112007-05-112000Journal of Biological Chemistry, 2000; 275(7):4618-46270021-92581083-351Xhttp://hdl.handle.net/2440/27998Hypoxia-inducible factor 1α (HIF-1α) and the HIF-like factor (HLF) are two highly related basic Helix-Loop-Helix/Per-Arnt-Sim (bHLH/PAS) homology transcription factors that undergo dramatically increased function at low oxygen levels. Despite strong similarities in their activation mechanisms (e.g. they both undergo rapid hypoxia-induced protein stabilization, bind identical target DNA sequences, and induce synthetic reporter genes to similar degrees), they are both essential for embryo survival via distinct functions during vascularization (HIF-1α) or catecholamine production (HLF). It is currently unknown how such specificity of action is achieved. We report here that DNA binding by HLF, but not by HIF-1α, is dependent upon reducing redox conditions. In vitro DNA binding and mammalian two-hybrid assays showed that a unique cysteine in the DNA-binding basic region of HLF is a target for the reducing activity of redox factor Ref-1. Although the N-terminal DNA-binding domain of HIF-1α can function in the absence of Ref-1, we found that the C-terminal region containing the transactivation domain requires Ref-1 for full activity. Our data reveal that the hypoxia-inducible factors are subject to complex redox control mechanisms that can target discrete regions of the proteins and are the first to establish a discriminating control mechanism for differential regulation of HIF-1α and HLF activity.enHela CellsHumansCysteineDNA-(Apurinic or Apyrimidinic Site) LyaseCarbon-Oxygen LyasesSerineDNA-Binding ProteinsNuclear ProteinsRecombinant ProteinsTranscription FactorsOligonucleotides, AntisenseDNAMutagenesis, Site-DirectedGene Expression RegulationAmino Acid SequenceHelix-Loop-Helix MotifsSequence Homology, Amino AcidOxidation-ReductionMolecular Sequence DataHypoxia-Inducible Factor 1Hypoxia-Inducible Factor 1, alpha SubunitJournal article000100040310.1074/jbc.275.7.46182-s2.0-003468137863768