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

## TL;DR

GCN2 helps protect mice from mouse adenovirus type 1 infection by triggering a stress response and is more important than PKR in this process.

## Contribution

GCN2 is shown to be the primary driver of eIF2α phosphorylation during MAV-1 infection, and its absence increases host mortality.

## Key findings

- GCN2 is phosphorylated during MAV-1 infection and its activation depends on virus replication.
- Mice lacking GCN2 have higher mortality after MAV-1 infection, independent of increased viral replication.
- GCN2, not PKR, is the main inducer of eIF2α phosphorylation during MAV-1 infection.

## Abstract

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 Eif2ak4tm1.2Dron mice (designated here Gcn2−/− mice) had lower survival than wild-type (WT) mice, but results indicated that this was not due to increased viral replication. Both Gcn2−/− and WT mice developed multifocal brain parenchymal microhemorrhages during infection. While Gcn2−/− animals had more lesions, their higher mortality is likely not due to the microhemorrhages alone. Cytokine RNA and protein assays of WT and Gcn2−/− mice only showed a difference for IL- β levels, which were higher in Gcn2−/− 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.

Cells 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.