In this study, the role of the double-stranded (ds) RNA-dependent protein k
inase (PKR) in macrophage activation was examined. dsRNA [polyinosinic:poly
cytidylic acid (poly IC)]-stimulated inducible nitric oxide synthase, inter
leukin (IL)-1 alpha and IL-1 beta mRNA expression, nitrite formation and IL
-1 release are attenuated in RAW264.7 cells stably expressing dominant nega
tive (dn) mutants of PKR. The transcriptional regulator nuclear factor (NF)
-kappa B is activated by dsRNA, and appears to be required for dsRNA-induce
d macrophage activation. While dnPKR mutants prevent macrophage activation,
they fail to attenuate dsRNA-induced I kappa B degradation or NF-kappa B n
uclear localization. The inhibitory actions of dnPKR on dsRNA-induced macro
phage activation can be overcome by treatment with interferon (IPN)-gamma,
an event associated with PKR degradation. Furthermore, dsRNA + IFN-gamma st
imulate inducible nitric oxide synthase expression, I kappa B degradation a
nd NF-kappa B nuclear localization to similar levels in macrophages isolate
d from PKR-/- and PKR+/+ mice. These findings indicate that both NF-kappa B
and PKR are required for dsRNA-induced macrophage activation; however, dsR
NA-induced NF-kappa B activation occurs by PKR-independent mechanisms in ma
crophages, In addition, the PKR dependence of dsRNA-induced macrophage acti
vation can be overcome by IFN-gamma.