PRRSV suppresses ER-phagy through Nsp2- and Nsp5-mediated degradation of FAM134B.

Background: Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant pathogen in the swine industry that causes reproductive failure in sows and respiratory distress in pigs of all ages, leading to substantial economic losses globally. PRRSV manipulates host cellular processes, particularly those associated with endoplasmic reticulum (ER) function. ER-phagy plays a crucial role in maintaining ER homeostasis and enabling cellular adaptations to stress. Whether and how PRRSV modulates ER-phagy remains incompletely understood. Methods: ER-phagy was monitored by western blotting for free mCherry from the mCherry-Sec61B reporter. FAM134B mRNA and protein levels were examined by RT-qPCR and western blotting, respectively. All 12 PRRSV Nsps were screened for FAM134B-suppressing activity by co-transfection, followed by western blotting. Co-immunoprecipitation (Co-IP) was performed to assess interactions between candidate Nsps and FAM134B, as well as their impact on FAM134B- microtubule-associated proteins light chain 3 (LC3) binding. Viral replication was evaluated by RT-qPCR targeting ORF7 and TCID50 assays. Results: We investigated the interplay between PRRSV and ER-phagy and discovered that PRRSV suppresses ER-phagy during the late stages of infection. Further analysis revealed that PRRSV employs its Nsps to inhibit the expression of FAM134B. Specifically, PRRSV Nsp2 and Nsp5 interact with FAM134B, promote its degradation and disrupt its binding to microtubule-LC3, thereby impairing ER-phagy. Conclusions: Collectively, our findings uncover a novel viral strategy to subvert host ER-phagy and provide new insights into PRRSV pathogenesis.