Peroxynitrite induces an alternative NF-κB activation pathway in L8 rat myoblasts

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