Porcine hemagglutinating encephalomyelitis virus nucleocapsid protein targets RIG-I and IRF3 to evade IFN immunity

The neurotropic betacoronavirus porcine hemagglutinating encephalomyelitis virus (PHEV) subverts early innate defenses to establish persistent neuronal infection. We show that PHEV activates RIG-I-MAVS signaling but hijacks this pathway to induce a delayed IRF7-dependent interferon (IFN-I) response (>12 h post-infection), permitting unchecked replication prior to late-phase immunity. Mechanistically, the viral nucleocapsid (N) protein directly engages RIG-I's caspase activation and recruitment domain (CARD) via its C-terminal domain (CTD), competitively blocking TRIM25-mediated K63-linked ubiquitination and silencing RIG-I activation. Concurrently, N protein disrupts IRF3 activation by disrupting homodimerization, phosphorylation, and nuclear translocation, abrogating its function as the dominant early antiviral mediator. Consequently, inadequate IRF7-driven IFN induction (<3-fold at mRNA level) fails to compensate for IRF3 inactivation, creating an immune-permissive window. Pharmacological blockade of replication (Remdesivir or Lopinavir) abolished RIG-I-IRF7 activation and IFN induction, confirming replication-derived dsRNA as the essential immune trigger. Thus, PHEV deploys its N protein to simultaneously sabotage RIG-I sensing and IRF3 effector functions, enabling covert immune evasion critical for neurotropic pathogenesis.IMPORTANCEPorcine hemagglutinating encephalomyelitis virus (PHEV) causes lethal encephalomyelitis in piglets by exploiting neuronal immune vulnerabilities. We reveal that PHEV nucleocapsid (N) protein directly binds RIG-I to block its antiviral activation signal (K63-ubiquitination) and concurrently disabling IRF3-the master regulator of early interferon defense. This unique strategy, distinct from nonstructural protein-mediated evasion in other coronaviruses, allows unchecked viral replication during critical early infection. Our work identifies the N protein as a central immunosuppressor evolved for neurotropism and exposes the RIG-I-IRF3 interface as a druggable target. These findings provide a blueprint for countermeasures against PHEV and related neuroinvasive coronaviruses threatening human and animal health.