ZFP91 restricts RSV replication by driving K48-linked ubiquitination and proteasomal degradation of M2-1.

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in children. Among viral components, the M2-1 protein is essential for efficient transcription and replication. Given its pivotal role in the viral life cycle, host factors that regulate this process may represent potential therapeutic targets against RSV. In this study, we identified the E3 ubiquitin ligase ZFP91 as a host factor that restricts RSV replication. Notably, RSV infection upregulated ZFP91 expression; ZFP91 overexpression significantly suppressed viral replication, whereas ZFP91 knockdown increased viral titers and viral gene expression, including that of M2-1 and N. Importantly, in an RSV-infected mouse model, epithelial-specific loss of ZFP91 increased viral burden and M2-1 protein levels in lung tissues, confirming its antiviral function in vivo. Mechanistically, ZFP91 directly interacted with M2-1 and promoted its degradation by catalyzing K48-linked polyubiquitination at lysine residues 8, 48, and 52. Collectively, these findings identify ZFP91 as a key regulator of RSV replication and reveal a novel antiviral mechanism mediated by its E3 ubiquitin ligase activity. This work thus provides new insights into RSV pathogenesis and host-virus interactions.