Activation of NF-κB in cells productively infected with HSV-1 depends on activated protein kinase R and plays no apparent role in blocking apoptosis

Abstract

Microarray data reported elsewhere indicated that herpes simplex virus 1 induces the up-regulation of nuclear factor κB (NF-κB)-regulated genes, including that of its inhibitor, IκBα, consistent with the reports that wild-type virus induces the activation of NF-κB. In this report we show that activation of NF-κB in infected cells is linked to the activation of protein kinase R (PKR). Specifically: ( i ) PKR is activated in infected cells although the effects of the activated enzyme on protein synthesis are negated by the viral gene γ 1 34.5, which encodes a protein phosphatase 1α accessory factor that enables the dephosphorylation of the α subunit of eukaryotic translation initiation factor 2. NF-κB is activated in wild-type murine embryonic fibroblasts but not in related PKR-null cells. ( ii ) In cells infected with a replication-competent Δγ 1 34.5 mutant (R5104), but carrying a U S 11 gene expressed early in infection, eukaryotic translation initiation factor 2α is not phosphorylated, and in in vitro assays, PKR bound to the U S 11 protein is not phosphorylated on subsequent addition of double-stranded RNA. Here we report that this mutant does not activate PKR, has no effect on the accumulation of IκBα, and does not cause the translocation of NF-κB in infected cells. ( iii ) One hypothesis advanced for the activation of NF-κB is that it blocks apoptosis induced by viral gene products. The replication-competent R5104 mutant does not induce the programmed cell's death. We conclude that in herpes simplex virus 1-infected cells, activation of NF-κB depends on activation of PKR and that NF-κB is not required to block apoptosis in productively infected cells.