Oxidative stress induces NF-kappaB nuclear translocation without degradation of IkappaBalpha.

Rel/NF-kappaB, an oxidative stress-responsive transcription factor, participates transiently in the control of gene expression. The cellular mechanisms that mediate NF-kappaB activation during ischemia (and during reperfusion in the course of treating ischemia) are not known. To investigate the NF-kappaB activation induced during oxidative stress, we examined human cardiac tissue obtained during surgical procedures requiring cardiopulmonary bypass. In vitro, we examined human umbilical vein endothelial cells (HUVECs) exposed to hypoxia, reoxygenation after hypoxia, or a reactive oxygen intermediate (H(2)O(2)). Electrophoretic mobility shift assays performed on right atrial tissue revealed prominent NF-kappaB activation after hearts had been exposed to ischemia and reperfusion. The assays also showed that NF-kappaB activation was observed in hypoxic HUVECs after reoxygenation and in cultures treated with H(2)O(2) (500 micromol/L). Pervanadate (200 micromol/L) also induced marked NF-kappaB activation in HUVECs, indicating that H(2)O(2)-induced NF-kappaB activation is potentiated by the inhibition of tyrosine phosphatases. Western blotting of cytoplasmic IkappaBalpha demonstrated that NF-kappaB activation induced by oxidative stress was not associated with IkappaBalpha degradation. In contrast, tumor necrosis factor-alpha-induced NF-kappaB activation occurred in concert with degradation of IkappaBalpha. Inhibition of IkappaBalpha degradation with a proteasome inhibitor, MG-115, blocked NF-kappaB activation induced by tumor necrosis factor-alpha; however, MG-115 had no effect on NF-kappaB activation during oxidative stress. This study demonstrated a stimulus-specific mechanism of NF-kappaB activation in endothelial cells that acts independently of IkappaBalpha degradation and may require tyrosine phosphorylation.