Oxidative stress induces NF-kappa B nuclear translocation without degradation of I kappa B alpha

Background - Rel/NF-kappa B, an oxidative stress-responsive transcription f actor, participates transiently in the control of gene expression. The cell ular mechanisms that mediate NF-KB activation during ischemia (and during r eperfusion in the course of treating ischemia) are not known. Methods and Results - To investigate the NF-kappa B activation induced duri ng oxidative stress, we examined human cardiac tissue obtained during surgi cal procedures requiring cardiopulmonary bypass. In vitro, we examined huma n umbilical vein endothelial cells (HUVECs) exposed to hypoxia, reoxygenati on after hypoxia, or a reactive oxygen intermediate (H2O2). Electrophoretic mobility shift assays performed on right atrial tissue revealed prominent NF-kappa B activation after hearts had been exposed to ischemia and reperfu sion. The assays also showed that NF-kappa B activation was observed in hyp oxic HUVECs after reoxygenation and in cultures treated with H2O2 (500 mu m ol/L). Pervanadate (200 mu mol/L) also induced marked NF-kappa B activation in HUVECs, indicating that H2O2-induced NF-kappa B activation is potentiat ed by the inhibition of tyrosine phosphatases. Western blotting of cytoplas mic I kappa B alpha demonstrated that NF-kappa B activation induced by oxid ative stress was not associated with I kappa B alpha degradation. In contra st, tumor necrosis factor-alpha-induced NF-kappa B activation occurred in c oncert with degradation of I kappa B alpha. Inhibition of I kappa B alpha d egradation with a proteasome inhibitor, MG-115, blocked NF-K kappa activati on induced by tumor necrosis factor-alpha; however, MG-115 had no effect on NF-kappa B activation during oxidative stress. Conclusions - This study demonstrated a stimulus-specific mechanism of NF-K kappa activation in endothelial cells that acts independently of I kappa B alpha degradation and may require tyrosine phosphorylation.