Objective— Reactive oxygen species have been implicated as signaling molecules modulating the activity of redox-sensitive transcription factors such as nuclear factor kappa B (NF-κB). Recently, the transcription factor hypoxia-inducible factor-1 (HIF-1), known to mediate gene expression by hypoxia, has been found to be also activated by nonhypoxic factors in a redox-sensitive manner. We therefore aimed to elucidate the link between these 2 important redox-sensitive transcription factors.

Methods and Results— In pulmonary artery smooth muscle cells, reactive oxygen species generated either by exogenous H₂O₂ or by a NOX4-containing NADPH oxidase stimulated by thrombin activated or induced NF-κB and HIF-1α. The reactive oxygen species-mediated HIF-1α induction occurred on the transcriptional level and was dependent on NF-κB. Transfection experiments with wild-type or mutant HIF-1α promoter constructs revealed the presence of a yet unidentified NF-κB binding element. Gel shift analyses and chromatin immunoprecipitation verified binding of NF-κB to this site. Furthermore, reactive oxygen species enhanced expression of plasminogen activator inhibitor-1, which was prevented by dominant-negative IκB or mutation of the HIF-1 binding site within the plasminogen activator inhibitor-1 promoter.

Conclusion— These findings show for the first time to our knowledge that reactive oxygen species directly link HIF-1α and NF-κB, implicating an important pathophysiological role of this novel pathway in disorders associated with elevated levels of reactive oxygen species.