Oxidative modification of IκB by monochloramine inhibits tumor necrosis factor α-induced NF-κB activation

We have previously reported that monochloramine (NH2Cl), a neutrophil-derived oxidant, inhibited tumor necrosis factor α (TNFα)-induced expression of cell adhesion molecules and nuclear factor-κB (NF-κB) activation (Free Radical Research 36 (2002) 845-852). Here, we studied the mechanism how NH2Cl inhibited TNFα-induced NF-κB activation, and compared the effects with taurine chloramine (Tau-NHCl). Pretreatment of Jurkat cells with NH2Cl at 70 μM resulted in suppression of TNFα-induced IκB phosphorylation and degradation, and inhibited NF-κB activation. In addition, a slow-moving IκB band appeared on SDS-PAGE. By contrast, Tau-NHCl for up to 200 μM had no effects. Interestingly, NH2Cl did not inhibit IκB kinase activation by TNFα. Protein phosphatase activity did not show apparent change. When recombinant IκB was oxidized by NH2Cl in vitro and phosphorylated by TNFα-stimulated Jurkat cell lysate, its phosphorylation occurred less effectively than non-oxidized IκB. In addition, when NF-κB-IκB complex was immunoprecipitated from NH2Cl-treated cells and phosphorylated in vitro by recombinant active IκB kinase, native IκB but not oxidized IκB was phosphorylated. Amino acid analysis of the in vitro oxidized IκB showed methionine oxidation to methionine sulfoxide. Although Tau-NHCl alone had little effects on TNFα-induced NF-κB activation, simultaneous presence of Tau-NHCl and ammonium ion significantly inhibited the NF-κB activation, probably through the conversion of Tau-NHCl to NH2Cl. These results indicated that NH2Cl inhibited TNFα-induced NF-κB activation through the oxidation of IκB, and that NH2Cl is physiologically more relevant than Tau-NHCl in modifying NF-κB-mediated cellular responses.