RNA-dependent protein kinase PKR is required for activation of NF-κB by INF-γ in a STAT1-independent pathway

The IFN-inducible dsRNA-activated protein kinase PKR regulates protein synthesis through phosphorylation of eukaryotic initiation factor-2α. It also acts as a signal transducer for transcription factors NF-κB, IFN regulatory factor-1, and activating transcription factor-2. IFN-γ, a pleiotropic cytokine, elicits gene expression by activating the Janus kinase-STAT signaling pathway. IFN-γ can synergize with TNF-α to activate NF-κB in a number of cell lines. Here we show that IFN-γ alone can activate NF-κB, by a Janus kinase-1-mediated, but Stat1-independent, mechanism. NF-κB activation by IFN-γ is associated with degradation of IκB β. The IFN-γ response can be blocked by 2′,5′-oligoadenylate-linked antisense chimeras against PKR mRNA. There was no activation of NF-κB by IFN in PKR-null cells, indicating that PKR is required for IFN-γ signaling to NF-κB.