Respiratory Syncytial Virus (RSV) optimizes the translational landscape during infection

Abstract

Viral infection often triggers eukaryotic initiator factor 2 (eIF2) phosphorylation, leading to global 5-cap-dependent translation inhibition. RSV encodes messenger RNAs (mRNAs) mimicking 5-cap structures of host mRNAs and thus inhibition of cap-dependent translation initiation would likely also reduce viral translation. We confirmed that RSV limits widespread translation initiation inhibition and unexpectedly found that the fraction of ribosomes within polysomes increases during infection, indicating higher ribosome loading on mRNAs during infection. We found that AU-rich host transcripts that are less efficiently translated under normal conditions become more efficient at recruiting ribosomes, similar to RSV transcripts. Viral transcripts are transcribed in cytoplasmic inclusion bodies, where the viral AU-rich binding protein M2-1 has been shown to bind viral transcripts and shuttle them into the cytoplasm. We further demonstrated that M2-1 is found on polysomes, and that M2-1 might deliver host AU-rich transcripts for translation. ImportanceViruses strongly rely on the hosts translational machinery to produce viral proteins required for replication. However, it is unknown how viruses that do not globally inhibit cap-dependent translation compete with abundant host transcripts for ribosomes. In this study, we found that respiratory syncytial virus (RSV) infection results in redistribution of 80S monosomes into the polysomes. High-throughput sequencing of translating transcripts revealed that low translation efficiency transcripts become more efficient at ribosome recruitment which are virus-resembling AU-rich host transcripts. Finally, we also uncover that AU-rich RNA binding protein RSV-M2-1 interacts with polysomes through contacts to mRNA. These findings revealed that RSV optimizes the translational landscape rather than inhibiting host translation.