Peroxynitrite Induces an Alternative NF-κB Activation Pathway in L8 Rat Myoblasts

Abstract

The role of peroxynitrite in NF-κB activation remains controversial. This study investigated NF-κB activation by peroxynitrite in skeletal myocytes. Myocytes were treated with NO and peroxynitrite donors. Both NO and peroxynitrite caused NF-κB activation (measured by p65 nuclear translocation and luciferase expression). NO donor-induced NF-κB activation was transient, dependent on I-κB α degradation, and was decreased in the presence of I-κB α super-repressor. Conversely, peroxynitrite donors induced NF-κB activation that was dependent on tyrosine nitration of I-κB α, but independent of its serine phosphorylation and degradation. This activation did not decrease in the presence of I-κB α super-repressor. Prolonged exposure to peroxynitrite resulted in nontransient NF-κB activation and high iNOS expression. Proteasome inhibitor MG-132 did not diminish SIN-1-induced NF-κB activation. Tyrosine nitration inhibitor EGCG re-established transient NF-κB activation with I-κB α degradation after SIN-1 treatment. EGCG, but not MG-132 decreased SIN-1- dependent iNOS expression. Peroxynitrite activates NF-κB in skeletal myocytes through an alternative mechanism, in which I-κB α is nitrated on tyrosine and dissociated from NF-κB, thus enabling its nontransient activation. This resulted in prolonged iNOS expression. Hence, peroxynitrite may exacerbate inflammatory responses mediated by NF-κB.