Importance of eIF2 alpha phosphorylation assembly in alphavirus translation and stress granule regulation

摘要

Alphavirus infection results in the shutoff of host protein synthesis in favor of viral translation. Here, we show that during Semliki Forest virus (SFV) infection, the translation inhibition is largely due to the activation of the cellular stress response via phosphorylation of eukaryotic translation initiation factor 2 alpha subunit (eIF2 alpha). Infection of mouse embryo fibroblasts (MEFs) expressing a nonphosphorylatable mutant of eIF2a does not result in efficient shutoff, despite efficient viral protein production. Furthermore, we show that the SFV translation enhancer element counteracts the translation inhibition imposed by eIF2a phosphorylation. In wild-type MEFs, viral infection induces the transient formation of stress granules (SGs) containing the cellular TIA-1/R proteins. These SGs are disassembled in the vicinity of viral RNA replication, synchronously with the switch from cellular to viral gene expression. We propose that phosphorylation of eIF2a and the consequent SG assembly is important for shutoff to occur and that the localized SG disassembly and the presence of the enhancer aid the SFV mRNAs to elude general translational arrest.