DEAD box RNA helicases 5 and 17 are new host factors for Sindbis virus infection

Abstract The DEAD-box ATP-dependent RNA helicases DDX5 and DDX17 play an important role in many aspects of cellular RNA biology, including metabolism, translation, splicing, transcriptional regulation, ribosome biogenesis and mRNA nuclear export. Both RNA helicases were also found to either promote or inhibit viral replication upon infection with several RNA viruses. Here we show that DDX5 depletion by RNAi or CRISPR/Cas9 has a negative impact on Sindbis virus (SINV) infection at the viral protein, RNA and infectious particle accumulation level, indicating a pro-viral role. We also demonstrate that DDX5 interacts with the SINV RNA in infected conditions. Furthermore, proteomic analysis of the DDX5 interactome in mock and SINV-infected HCT116 cells identified new cellular and viral partners and confirmed the interaction between DDX5 and DDX17. Of note, while DDX5 and DDX17 are mostly nuclear in uninfected cells, they both re-localize to the cytoplasm upon SINV infection and interact with the viral capsid protein. Finally, we show that DDX17 depletion has a negative impact on SINV and further reduces viral infection in a DDX5-depleted background, suggesting a cumulative pro-viral effect of the DDX5 and DDX17 proteins on SINV. These results not only expand our understanding of the roles played by DDX5 and DDX17 as regulators of viral infections, but also highlight their critical contributions to the SINV life cycle.