Oxidation of IκBα at methionine 45 is one cause of taurine chloramine-induced inhibition of NF-κB activation

Abstract

A band shift of IκBα was observed in Western blots with Jurkat cells treated with 1 mM taurine chloramine (TauCl) for 1 h. TauCl treatment inhibited tumor necrosis factor α (TNFα)-initiated nuclear factorKB (NF-KB) activation. TauCl did not inhibit either the upstream of IKB kinase (IKK) activation or IKK itself but did inhibit NF-KB activation induced by IKK overexpression. Deletion experiments showed that a TauCl modification site causing the band shift of IκBα is Met45. High performance liquid chromatography and mass spectrometry analyses of a small peptide containing Met45 revealed that TauCl oxidizes Met45. A mutant of IκBα whose Met45 was converted to alanine did not generate a band shift upon TauCl treatment and degraded in response to TNFα stimulation. However, a reporter assay revealed that NF-KB-dependent luciferase expression was not fully recovered in cells transfected with this mutant. These results indicate that Met45 oxidation of IκBα is a molecular mechanism underlying the TauCl-induced inhibition of NF-KB activation. A similar band shift was observed when HL-60 cells expressing myeloperoxidase were treated with 100 μM hydrogen peroxide for 5 min. When rat neutrophils were incubated with bacteria, intracellular taurine decreased interleukin-8 production. Therefore, taurine may help suppress excessive inflammatory reaction in neutrophils.