Reovirus Induces and Benefits from an Integrated Cellular Stress Response

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Abstract
Following infection with most reovirus strains, viral protein synthesis is robust, even when cellular translation is inhibited. To gain further insight into pathways that regulate translation in reovirus-infected cells, we performed a comparative microarray analysis of cellular gene expression following infection with two strains of reovirus that inhibit host translation (clone 8 and clone 87) and one strain that does not (Dearing). Infection with clone 8 and clone 87 significantly increased the expression of cellular genes characteristic of stress responses, including the integrated stress response. Infection with these same strains decreased transcript and protein levels of P58IPK, the cellular inhibitor of the eukaryotic initiation factor 2α (eIF2α) kinases PKR and PERK. Since infection with host shutoff-inducing strains of reovirus impacted cellular pathways that control eIF2α phosphorylation and unphosphorylated eIF2α is required for translation initiation, we examined reovirus replication in a variety of cell lines with mutations that impact eIF2α phosphorylation. Our results revealed that reovirus replication is more efficient in the presence of eIF2α kinases and phosphorylatable eIF2α. When eIF2α is phosphorylated, it promotes the synthesis of ATF4, a transcription factor that controls cellular recovery from stress. We found that the presence of this transcription factor increased reovirus yields 10- to 100-fold. eIF2α phosphorylation also led to the formation of stress granules in reovirus-infected cells. Based on these results, we hypothesize that eIF2α phosphorylation facilitates reovirus replication in two ways—first, by inducing ATF4 synthesis, and second, by creating an environment that places abundant reovirus transcripts at a competitive advantage for limited translational components.