Virus-induced translational arrest through 4EBP1/2-dependent decay of 5'-TOP mRNAs restricts viral infection.

The mosquito-transmitted bunyavirus, Rift Valley fever virus (RVFV), is a highly successful pathogen for which there are no vaccines or therapeutics. Translational arrest is a common antiviral strategy used by hosts. In response, RVFV inhibits two well-known antiviral pathways that attenuate translation during infection, PKR and type I IFN signaling. Despite this, translational arrest occurs during RVFV infection by unknown mechanisms. Here, we find that RVFV infection triggers the decay of core translation machinery mRNAs that possess a 5'-terminal oligopyrimidine (5'-TOP) motif in their 5'-UTR, including mRNAs encoding ribosomal proteins, which leads to a decrease in overall ribosomal protein levels. We find that the RNA decapping enzyme NUDT16 selectively degrades 5'-TOP mRNAs during RVFV infection and this decay is triggered in response to mTOR attenuation via the translational repressor 4EBP1/2 axis. Translational arrest of 5'-TOPs via 4EBP1/2 restricts RVFV replication, and this increased RNA decay results in the loss of visible RNA granules, including P bodies and stress granules. Because RVFV cap-snatches in RNA granules, the increased level of 5'-TOP mRNAs in this compartment leads to snatching of these targets, which are translationally suppressed during infection. Therefore, translation of RVFV mRNAs is compromised by multiple mechanisms during infection. Together, these data present a previously unknown mechanism for translational shutdown in response to viral infection and identify mTOR attenuation as a potential therapeutic avenue against bunyaviral infection.