<b>PRRSV Nucleocapsid Protein Suppresses Pyroptosis by Recruiting OTUD4 to Degrade Caspase-1 via K48 Linked Ubiquitination</b>

Pyroptosis mediated by Caspase-1/GSDMD is a crucial antiviral defense. We reveal that PRRSV nucleocapsid protein (N) subverts this pathway by recruiting host ubiquitination machinery. PRRSV N binds Caspase-1 via its N-terminal domain (residues 1-57), driving K48-linked ubiquitination and proteasomal degradation. This suppresses GSDMD cleavage (p30 generation), LDH release, and IL-1β maturation. PRRSV N hijacks deubiquitinase OTUD4 to remove Caspase-1 ubiquitin chains while stabilizing itself through reciprocal feedback. OTUD4 catalytic mutant (C45A) still disrupted Caspase-1 stability, indicating non-enzymatic scaffolding roles. Caspase-1 overexpression inhibited PRRSV replication in 3D4+CD163 and Marc-145 cells, reversed by inhibitor VX765. Thus, PRRSV N exploits OTUD4 to destabilize Caspase-1 and evade pyroptosis. The OTUD4-Caspase-1 axis represents a therapeutic target against PRRSV immunosuppression.