Porcine reproductive and respiratory syndrome virus nsp2 protects viral RNA-dependent RNA polymerase from autophagic degradation

Porcine reproductive and respiratory syndrome virus (PRRSV) Infection induces Autophagy, a process that facilitates viral replication and involves multiple Viral Proteins. The nonstructural proteins (nsps) of PRRSV are crucial for viral replication, among which nsp9 is indispensable. Although Autophagy is closely linked to viral Infection, the specific interplay between nsp9 and Autophagy remains unclear. In this study, we found that nsp9 undergoes autophagic degradation in transfected cells. Through a series of experiments, we established that this degradation occurs via a ULK1-regulated, non-canonical Autophagy pathway independent of ATG5 and Atg7. Co-immunoprecipitation analysis revealed that both domains of nsp9 harbor autophagy-related ubiquitination sites and that nsp9 is modified by K63-linked polyubiquitination, which targets it for autophagic degradation. Notably, nsp9 escapes this degradation pathway during viral Infection. Further investigation demonstrated that the Deubiquitinase activity of nsp2 reduces nsp9 ubiquitination, thereby blocking its autophagic degradation in transfected cells. These findings reveal a novel mechanism by which PRRSV utilizes the nsp2-nsp9 interaction network to evade host autophagic clearance, providing fresh insights into viral immune evasion strategies.

Autophagic degradation; Nsp2; Nsp9; PRRSV; Ubiquitination.