Common host factors for internal ribosomal entry site-mediated translation of viral genomic RNA: An investigation in foot-and-mouth disease and classical swine fever viruses.

We previously proposed polycystic kidney disease1-like 3 (PKD1L3) and ubiquitin-specific peptidase 31 (USP31) as potential common host factors for IRES-mediated RNA translation in infections with foot-and-mouth disease virus (FMDV) and classical swine fever virus (CSFV). However, those findings required substantiation, and the specific roles of these factors in the IRES-mediated translation remained unclear. Accordingly, in this study, we aimed to confirm the roles of PKD1L3 and USP31 as host factors associated with IRES activity in bi-cistronic reporter assays, and to investigate the interactions of these host proteins during IRES activity. PKD1L3 and USP31 silencing suppressed IRES activity in both FMDV and CSFV RNAs. PKD1L3 and USP31 overexpression had no significant effects. PKD1L3 and USP31 silencing also suppressed viral RNA replication for CSFV and infection with another picornavirus (from the same family as FMDV), encephalomyocarditis virus. Immunoprecipitation assays revealed that PKD1L3 and USP31 can interact with each other. We also examined their interaction with a eukaryotic translation factor involved in the IRES of hepatitis C virus (HCV), eIF3c. PKD1L3 and more pronouncedly USP31 can interact with eIF3c. Immunofluorescent assays revealed partial, cytoplasmic co-localization of USP31 with PKD1L3, eIF3c, and Hsp90β. Moreover, silencing of eIF3c and Hsp90β suppressed FMDV- and CSFV-IRES activity. Our results indicate the possibility that PKD1L3 and USP31 can participate in IRES activity by interacting with eIF3c and Hsp90β.