Two signals downstream of PKR had been detected before: a kinase-independent activation of NF-κB and a kinase-dependent inactivation of the translation factor eIF-2α, leading to apoptosis. But the previous studies focused on one pathway at a time.
Donzé induced PKR production and saw that NF-κB activation preceded eIF-2α phosphorylation by several hours. The same was true after virus infection. NF-κB induced numerous downstream genes including several anti-apoptotic factors. Sure enough, cells lacking the NF-κB response died more quickly.
Precedent exists for NF-κB induction downstream of virus binding to a receptor. But activation of PKR's kinase activity, and thus phosphorylation of eIF-2α, is delayed until later, when the virus starts replicating. The double-stranded RNA of the replicated virus activates PKR. Presumably eIF-2α phosphorylation inhibits the translation of anti-apoptotic mRNAs (such as those induced by NF-κB), while sparing translation of the pro-apoptotic proteins that kill off the cell. ▪