Abstract

In this study, the role of the double-stranded (ds) RNA-dependent protein kinase (PKR) in macrophage activation was examined. dsRNA [polyinosinic:polycytidylic acid (poly IC)]-stimulated inducible nitric oxide synthase, interleukin (IL)-1 and IL-1 mRNA expression, nitrite formation and IL-1 release are attenuated in RAW264.7 cells stably expressing dominant negative (dn) mutants of PKR. The transcriptional regulator nuclear factor (NF)-B is activated by dsRNA, and appears to be required for dsRNA-induced macrophage activation. While dnPKR mutants prevent macrophage activation, they fail to attenuate dsRNA-induced IB degradation or NF-B nuclear localization. The inhibitory actions of dnPKR on dsRNA-induced macrophage activation can be overcome by treatment with interferon (IFN)-, an event associated with PKR degradation. Furthermore, dsRNA + IFN- stimulate inducible nitric oxide synthase expression, IB degradation and NF-B nuclear localization to similar levels in macrophages isolated from PKR^-/- and PKR^+/+ mice. These findings indicate that both NF-B and PKR are required for dsRNA-induced macrophage activation; however, dsRNA-induced NF-B activation occurs by PKR-independent mechanisms in macrophages. In addition, the PKR dependence of dsRNA-induced macrophage activation can be overcome by IFN-.