Porcine reproductive and respiratory syndrome virus antagonizes the host restriction factor SHFL to sustain viral programmed ribosomal frameshifting and replication.

The global pandemic of porcine reproductive and respiratory syndrome virus (PRRSV) and its continuous evolution pose a sustained threat to the swine industry, underscoring the urgent need for a broad-spectrum antiviral strategy. Programmed ribosomal frameshifting (PRF) is an essential mechanism in PRRSV that directs the synthesis of viral nonstructural proteins (nsps) and represents an attractive antiviral target. Here, we show that SHFL, an interferon-stimulated gene (ISG), restricts PRRSV infection by specifically targeting viral biosynthesis steps. Mechanistically, SHFL inhibits the canonical programmed -1 ribosomal frameshifting (-1 PRF) of PRRSV, thereby suppressing RNA replication. SHFL also effectively blocks PRRSV -2 PRF, demonstrating its broad-spectrum activity against different frameshifting mechanisms. To sustain viral replication, PRRSV employs its nsp12 and nucleocapsid (N) proteins to counteract the expression of SHFL transcriptionally, thereby attenuating this host antiviral defense. These findings identify SHFL as a broad-spectrum PRF inhibitor against PRRSV, further elucidating its antiviral mechanisms of SHFL. The discovery that PRRSV proteins antagonize SHFL not only deepens our understanding of PRRSV pathogenesis but also highlights the dynamic interplay between virus and host.