IFIT3 mediated the type I interferon antiviral response by targeting Senecavirus A entry, assembly and release pathways

Senecavirus A (SVA) is a newly emerging etiological agent of vesicular disease associated with sow abortion and acute piglet death, causing devastating economic consequences to global pig industry. IFN-induced protein with tetratricopeptide repeats (IFIT) genes are versatile in combating a variety of viruses, but the detailed mechanisms-of-action against SVA is unexplored. Transcriptomic analysis and immunoblot revealed high abundance of IFIT transcripts and proteins following SVA infection, initially implying the correlation between IFITs and SVA. Type I IFNs restricted SVA replication accompanied with substantial elevation of IFIT expression, potentializing IFITs as anti-SVA effectors downstream of IFN signaling. Gain-of-function assay demonstrated that IFIT3 rather than IFIT1/2 potently inhibited SVA replication, which was consistently verified by SVA strain SVV CH-FJ-2017 by TCID50 titration and an eGFP-tagged recombinant SVA using fluorescent microscopy. Afterwards, IFIT3 disrupted SVA life cycle at the early stage of virus binding and internalization, and at the late stage of virus assembly and release, as quantified by copy number and transmission electron microscopy, respectively. Directly transfecting SVA infectious RNA in IFIT3-overexpressed cells bypassed its antiviral activity, further suggesting that IFIT3 targeted viral life cycle beyond RNA replication. Further investigations showed that IFIT3 overexpression was incapable of regulating host immune responses against pathogens. Those results identified IFIT3 as a potent inhibitor of SVA and implicated IFIT3 pathway in the regulation of virus entry/assembly. In short, IFIT3 exerted significant inhibitory effects on the replication and spread of SVA, and played different functions in the life cycle of SVA.