Cytokine-induced Activation of Nuclear Factor-γB is Inhibited by Hydrogen Peroxide through Oxidative Inactivation of IκB Kinase

Abstract

Rapid activation of the IκB kinase (IKK) complex is considered an obligatory step in the activation of nuclear factor-κB (NF-κB) in response to diverse stimuli. Since oxidants have been implicated in the regulation of NF-κB, the focus of the present study was the activation of IKK by tumor necrosis factor α (TNFα) in the presence or absence of hydrogen peroxide (H2O2). Exposure of mouse alveolar epithelial cells to H2O2 was not sufficient to activate IKK, degrade IκBα, or activate NF-κB. In contrast, TNFα induced IKK activity rapidly and transiently resulting in IκBα degradation and NF-κB activation. Importantly, in the presence of H 2O2, the ability of TNFα to induce IKK activity was markedly decreased and resulted in prevention of IκBα degradation and NF-κB activation. Neither tyrosine kinases nor phosphatidylinositol 3-kinases, known regulators of NF-κB by oxidants, were involved in IKK inhibition by H2O2. Direct addition of H2O 2 to the immunoprecipitated IKK complex inhibited enzyme activity. Inhibition of IKK activity by H2O2 was associated with direct oxidation of cysteine residues present in the IKK complex and occurred only in enzymatically active IKK. In contrast to previously published observations, our findings demonstrate that the oxidant H2O 2 reduces NF-κB activation by inhibiting activated IKK activity.