Highly pathogenic porcine reproductive and respiratory syndrome virus nonstructural protein 1 interacts with TRAF6 to activate the TAK1/p38/JNK/AP-1 signaling and induce IL-1β

ABSTRACT Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) is a highly contagious disease that severely threatens the global pig industry. A significant symptom of PRRS is severe pneumonia. At present, studies have shown that IL-1β is upregulated by PRRSV infection in vivo and in vitro , while the underlying mechanism remains unknown. Here, we explored how PRRSV regulated IL-1β production. We found that HP-PRRSV nsp1 upregulated the expression of IL-1β. Overexpression of nsp1 induced IL-1β production in a dose-dependent manner. Subsequently, we demonstrated that nsp1 enhanced IL-1β expression by activating JNK/p38 signaling pathways, as the addition of p38 and JNK inhibitors reduced IL-1β production induced by nsp1. Moreover, deleting the AP-1 binding motif in porcine IL-1β promoter impaired IL-1β expression induced by nsp1, suggesting that AP-1 is essential for IL-1β production. In addition, we showed that TRAF6 was required for nsp1 to activate the TAK1/JNK/p38/AP-1 signaling pathway by interacting with each other. Truncation and deletion mutation analysis indicated that R308 and R375 amino acids were important for nsp1 to interact with TRAF6 and induce IL-1β production. Finally, we constructed the recombinant viruses mutated at R308 and R375 and found that the mutated virus PRRSV-R308/375A exhibited a significantly reduced replication rate and impaired the ability to induce IL-1β compared to the wild-type strain. These findings provide new insights into the molecular mechanisms of IL-1β production induced by PRRSV and help us further understand the pathogenesis of PRRSV infection. IMPORTANCE Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has been prevalent in China since 2006, causing severe pneumonia in pigs. IL-1β is a proinflammatory cytokine secreted by various cells. In this study, we demonstrated that PRRSV protein nsp1 interacted with TRAF6 to activate the TAK1/JNK/p38/AP-1 signaling pathway, consequently inducing the expression of IL-1β. Additionally, our findings revealed that R308 and R375 in nsp1 were critical amino acid residues for nsp1 to interact with TRAF6 and induce IL-1β production. Notably, the recombinant virus PRRSV-R308/375A exhibited a significantly reduced replication rate and impaired ability to induce proinflammatory cytokines in vitro compared to the wild-type strain HP-PRRSV. This study helps us further understand HP-PRRSV pathogenesis and provides a new idea for the development of PRRSV vaccines.