Involvement of double-stranded RNA-activated protein kinase in the synergistic activation of nuclear factor-κB by tumor necrosis factor-α and γ-interferon in preneuronal cells

Tumor necrosis factor-alpha (TNF-alpha) and gamma-interferon (IFN-gamma) cooperate during a variety of biological responses and ultimately synergistically enhance the expression of genes involved in immune and inflammatory responses. Recently, we demonstrated that IFN-gamma can significantly potentiate TNF-alpha-induced nuclear factor (NF)-kappa B nuclear translocation in neuronal derived and endothelial cell lines. The mechanism by which these two cytokines exert their synergistic effect on NF-kappa B involves the de novo degradation of the NF-kappa B inhibitor, I kappa B beta. The double-stranded RNA-dependent kinase PKR is IFN-inducible and has been implicated in the activation of NF-kappa B; therefore, we examined the possibility that PKR may play a role in the synergistic activation of NF-kappa B during TNF-alpha/IFN-gamma cotreatment. The PKR inhibitor 2-aminopurine (2-AP) inhibited TNF-alpha/IFN-gamma-induced NF-kappa B nuclear translocation in neuronal derived cells but not in endothelial cells. The induced degradation of I kappa B beta, which is normally observed upon TNF-alpha/IFN-gamma cotreatment, was blocked completely by 2-AP in neuronal derived cells. Also, 2-AP treatment or overexpression of a catalytically inactive PKR inhibited the TNF-alpha/IFN-gamma-induced synergistic activation of kappa B-dependent gene expression. Our results suggest that the signal generated by IFN-gamma during TNF-alpha/IFN-gamma cotreatment may require PKR to elicit enhanced NF-kappa B activity, and this signal may affect the stability of the I kappa B beta protein.