Effect of deficiency of the double-stranded RNA-dependent protein kinase, PKR, on antiviral resistance in the presence or absence of ribonuclease L: HSV-1 replication is particularly sensitive to deficiency of the major IFN-mediated enzymes

Control of viral replication by interferon (IFN) is thought to be principal ly mediated by the 2',5'-oligoadenylate synthetase (OAS)/RNAse L, double-st randed dependent protein kinase (PKR), and myxovirus resistance protein (Mx ) pathways. In this study, we monitored the constitutive and IFN-induced an tiviral activity in mouse embryo fibroblasts lines derived from mice with t argeted disruption of either PKR or PKR/RNAse L genes. At high multiplicity of infection (moi = 10), the absence of PKR had no effect on replication o f vesicular stomatitis virus (VSV) but moderately enhanced encephalomyocard itis virus (EMCV) growth and greatly increased replication of herpes simple x virus-1 (HSV-1), Replication of EMCV, HSV-1, and VSV was modestly higher in PKR-/- RNAse L-/- fibroblasts when compared with control cells. Although the antiviral action of IFN-alpha was unaffected by the absence of PKR, IF N action was significantly impaired in the double knockout cells but was de pendent on the stage of the virus cycle. At early stages, it appeared that anti-EMCV and anti-HSV-1 action of IFN-alpha was significantly compromised, although weak residual antiviral activity was seen. The action of IFN-alph a against VSV was specifically compromised at a late stage of virus replica tion. The results showed that PKR is an important mediator in constitutive resistance against HSV-1 and that RNAse L is also necessary for the full an tiviral activity of IFN against a variety of viruses. These results support ed the existence of novel pathways aimed toward specific stages of the viru s life cycle.