The RelA(p65) subunit of NF-κB is essential for inhibiting double-stranded RNA-incluced cytotoxicity

Abstract

Double-stranded RNA (dsRNA) molecules generated during virus infection can initiate a host antlviral response to limit further infection. Such a response involves induction of antiviral gene expression by the dsRNA-activated protein kinase (PKR) and the NF-κB transcription factor. In addition, dsRNA can also induce apoptosis by an incompletely understood mechanism that may serve to further limit viral replication. Here we demonstrate a novel role for the RElA subunit of NF-κB in inhibiting dsRNA-induced cell death. dsRNA treatment resulted in caspase 3 activation and apoptotic morphological transformations in mouse embryonic fibroblasts (MEFs) derived from RElA-/- mice but not from RElA+/+ mice. Such dsRNA-induced killing could be inhibited 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 cytotoxicity. A broader specificity caspase inhibitor was also unable to inhibit dsRNA-induced cytotoxicity, suggesting that caspase activation is not essential 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 demonstrate an essential role for NF-κB in protecting cells from dsRNA-induced apoptosis and suggest thai NF-κB may inhibit both caspase-de-pendent and reactive oxygen species-dependent cytotoxic pathways.