The RelA(p65) subunit of NF-kappa B is essential for inhibiting double-stranded RNA-induced cytotoxicity

Double-stranded RNA (dsRNA) molecules generated during virus infection can initiate a host antiviral response to limit further infection. Such a respo nse involves induction of antiviral gene expression by the dsRNA-activated protein kinase (PKR) and the NF-kappaB transcription factor. In addition, d sRNA can also induce apoptosis by an incompletely understood mechanism that may servo to further limit viral replication. Here we demonstrate a novel role for the RelA subunit of NF-KB in inhibiting dsRNA-induced cell death, dsRNA treatment resulted in caspase 3 activation and apoptotic morphologica l transformations in mouse embryonic fibroblasts (MEFs) derived from RelA-/ - mice but not from RelA+/- mice. Such dsRNA-induced killing could be inhib ited by expression of either a dominant-negative mutant of PKR or wild-type RelA Interestingly, caspase 3 activated following dsRNA treatment of RelA- /- MEFs was essential for apoptotic nuclear changes but dispensable for cyt otoxicity. A broader specificity caspase inhibitor was also unable to inhib it dsRNA-induced cytotoxicity, suggesting that caspase activation is not es sential for the induction of cell death by dsRNA in MEFs. However, combined inhibition of caspase 3 and reactive oxygen species production resulted in complete inhibition of dsRNA-induced cytotoxicity. These results demonstra te an essential role for NF-kappaB in protecting cells from dsRNA-induced a poptosis and suggest that NF-kappaB may inhibit both caspase-dependent and reactive oxygen species-dependent cytotoxic pathways.