Wnt/β-catenin signaling pathway inhibits porcine reproductive and respiratory syndrome virus replication by enhancing the nuclear factor-κB-dependent innate immune response.

The Wnt/β-catenin signaling pathway is an evolutionarily highly conserved signaling pathway related to the replication of various viruses. However, the interaction between the Wnt/β-catenin pathway and porcine reproductive and respiratory syndrome virus (PRRSV) is unknown. In the present study, we showed that PRRSV-infected Marc-145 and PAM cells expressed high levels of c-myc and cyclinD1 mRNA and accumulation of β-catenin in the nucleus. PRRSV nonstructural proteins (Nsps) 1α, 1β, 3, 4, 7, 10, and 12, and proteins encoded by open reading frames (ORFs) 2b, 3, and 5 induced the activation of the Wnt pathway according to TOP/FOP luciferase reporter assay. But, Nsp5 inhibited the activation of the Wnt pathway. Pre-treatment with Wnt3a inhibited PRRSV replication in Marc-145 cells in a dose-dependent manner. Over-expression of β-catenin also inhibited PRRSV replication, while silencing of β-catenin by small hairpin RNA increased its replication in Marc-145 cells. Over-expression of β-catenin increased interferon regulatory factor (IRF)-3 expression and nuclear factor (NF)-κB phosphorylation, NF-κB and interferon-stimulated response element promoter activities, and interferon-β, DExD/H-box helicase 58 (DDX58), interferon-induced protein with tetratricopeptide repeats 1 (IFIT1), interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-8 mRNA expression. Conversely, silencing β-catenin decreased phosphorylated IRF-3 and NF-κB, NF-κB and IFIT1 promoter activities, and IFN-β, DDX58, IFIT1, IL-1β, TNF-α, and IL-8 mRNA levels in Marc-145 cells. Co-immunoprecipitation and immunofluorescence colocalization analyses confirmed that β-catenin interacted with NF-κB in Marc-145 cells. In conclusion, PRRSV infection activates the Wnt/β-catenin signaling pathway via Nsps 1α, 1β, 3, 4, 7, 10, and 12, and proteins encoded by ORFs 2b, 3, and 5. The Wnt/β-catenin pathway then inhibits PRRSV replication by enhancing the NF-κB-dependent innate immune response. These findings further our understanding of the role of the Wnt/β-catenin signaling pathway in regulating PRRSV replication and provide new insights into virus-host interactions.