BmSNX20 restricts Bombyx mori nucleopolyhedrovirus infection and is associated with autophagy-mediated antiviral immunity.

Abstract

Sorting nexins (SNXs) are phosphoinositide-binding proteins that play critical roles in membrane trafficking and have been implicated in antiviral immunity. However, the function of SNX20 in insect antiviral immunity remains poorly defined. In this study, we investigated the role of Bombyx mori SNX20 (BmSNX20) during infection with Bombyx mori nucleopolyhedrovirus (BmNPV). Phylogenetic and domain analyses revealed that SNX20 is evolutionarily conserved across insect species and contains a canonical phox homology (PX) domain. Expression profiling showed that BmSNX20 is highly expressed in the midgut and fat body and is significantly upregulated upon BmNPV infection in both larvae and BmN cells. Functional analyses demonstrated that BmSNX20 knockdown significantly enhanced viral replication, whereas its overexpression suppressed viral gene expression, reduced viral titers, and improved host survival, indicating a clear antiviral role. Mechanistically, BmSNX20 overexpression activated multiple immune pathways, including Imd, JAK/STAT signaling, RNA interference, STING and notably promoted autophagy, as indicated by upregulated expression of ATG5 and ATG8, enhanced MDC fluorescence, increased conversion of ATG8 to its lipidated form ATG8-PE, and strong colocalization between BmSNX20 and ATG8. These demonstrate that BmSNX20 overexpression triggers an autophagic response, which may contribute to its antiviral activity, in addition to the activation of multiple other immune pathways. In conclusion, this study identified BmSNX20 as a novel antiviral factor in silkworms and highlighted its role in linking membrane trafficking to autophagy and innate immunity. These findings expand our understanding of SNX protein functions in insect antiviral defense and provide novel insights into host-virus interactions in invertebrates.