The Alpha Subunit of Eukaryotic Initiation Factor 2B (eIF2B) Is Required for eIF2-Mediated Translational Suppression of Vesicular Stomatitis Virus

Eukaryotic translation initiation factor 2B (eIF2B) is a heteropentameric guanine nucleotide exchange factor that converts protein synthesis initiation factor 2 (eIF2) from a GDP-bound form to the active eIF2-GTP complex. Cellular stress can repress translation initiation by activating kinases capable of phosphorylating the alpha subunit of eIF2 (eIF2 alpha), which sequesters eIF2B to prevent exchange activity. Previously, we demonstrated that tumor cells are sensitive to viral replication, possibly due to the occurrence of defects in eIF2B that overcome the inhibitory effects of eIF2 alpha phosphorylation. To extend this analysis, we have investigated the importance of eIF2B alpha function and report that this subunit can functionally substitute for its counterpart, GCN3, in yeast. In addition, a variant of mammalian eIF2B alpha harboring a point mutation (T41A) was able overcome translational inhibition invoked by amino acid depravation, which activates Saccharomyces cerevisiae GCN2 to phosphorylate the yeast eIF2 alpha homolog SUI2. Significantly, we also demonstrate that the loss of eIF2B alpha, or the expression of the T41A variant in mammalian cells, is sufficient to neutralize the consequences of eIF2 alpha phosphorylation and render normal cells susceptible to virus infection. Our data emphasize the importance of eIF2B alpha in mediating the eIF2 kinase translation-inhibitory activity and may provide insight into the complex nature of viral oncolysis.