GCN2 enhances host survival and drives eIF2α phosphorylation during mouse adenovirus type 1 infection.

The integrated stress response (ISR) is a cellular signaling pathway that reduces protein synthesis in the face of cellular stress, including viral infection. Two eukaryotic initiation factor 2α (eIF2α) kinases, protein kinase R (PKR) and general control nonderepressible 2 (GCN2), are commonly activated during viral infections. Mouse adenovirus type 1 (MAV-1) infection leads to a steep reduction of PKR levels by proteasomal degradation. We assayed whether GCN2, a sensor of amino acid starvation and UV damage, plays a role in the ISR to MAV-1 infection. There was more phosphorylated GCN2 in MAV-1-infected cells, and its activation was dependent on virus replication since UV-inactivated virus was not able to increase the phosphorylation of GCN2. Infected mice (designated here mice) had lower survival than wild-type (WT) mice, but results indicated that this was not due to increased viral replication. Both and WT mice developed multifocal brain parenchymal microhemorrhages during infection. While animals had more lesions, their higher mortality is likely not due to the microhemorrhages alone. Cytokine RNA and protein assays of WT and mice only showed a difference for IL- β levels, which were higher in mice. Our results also indicate that of the two eIF2α kinases, PKR and GCN2, GCN2 is the primary inducer of phosphorylated-eIF2α during MAV-1 infection. GCN2 is thus antiviral and contributes to the host response to MAV-1 infection.IMPORTANCECells often respond to viral infection by activation of the host protein kinase R (PKR), part of the integrated stress response (ISR). We show that a second host protein kinase, general control nonderepressible 2 (GCN2), is activated by phosphorylation in response to mouse adenovirus type 1 (MAV-1) infection. Our results indicate GCN2 is antiviral: without it, the mortality in MAV-1-infected mouse is higher. Furthermore, the data show that GCN2, rather than PKR, is the main inducer of eIf2α phosphorylation (and thus the ISR) upon MAV-1 infection. This is consistent with PKR exerting antiviral effects in MAV-1 infections through a pathway independent of eIf2α phosphorylation.