Porcine reproductive and respiratory syndrome virus increases SOCS3 production via activation of p38/AP-1 signaling pathway to promote viral replication

SOCS3 belongs to the suppressor of cytokine signaling (SOCS) family, which function as negative factors in host immune responses. Prior studies have noted the importance of SOCS family proteins in immunosuppression induced by some viruses. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important swine-borne viruses and has threatened the global swine industry with huge economic losses since it was first described in the 1980s. PRRSV is the etiological agent of PRRS, which causes reproductive failure and respiratory disorders. PRRSV causes immunosuppression thus establishing persistent infection. In this study, it was observed that SOCS3 was upregulated in PRRSV-infected primary porcine alveolar macrophages (PAMs) and Marc-145 cells with dose-dependent effects, which depends on virus replication. Deletion of AP-1 binding motif located in SOCS3 promoter inhibited promoter activities, which indicates that AP-1 is essential for PRRSV-induced SOCS3. This result was confirmed by experiments using AP-1 inhibitor, whose pretreatment suppressed SOCS3 mRNA and protein expression. Further research showed that p38 was crucial for PRRSV-induced SOCS3 production. Importantly, SOCS3 enhanced PRRSV replication during infection. Taken together, this study indicates that PRRSV infection induced SOCS3 expression through p38/AP-1 signaling pathway. These results revealed the molecular basis of SOCS3 upregulation and would advance further understanding of the strategy for viral immune evasion.