Anti-KPNA4 (aa 471-521) polyclonal antibody

Interferon (IFN)-mediated antiviral response is an important part of host defense. Previous studies reported that porcine circovirus type 2 (PCV2) inhibits interferon production, but the mechanism is still poorly understood. In this study, PCV2 suppresses IFN-beta and IRF3 promoters and mRNA level of IFN-beta induced by ISD or Poly(I:C), but has no effect on the activation of AP-1 and NF-kB. Furthermore, PCV2 decreases the mRNA level of IFN-beta and IFN-beta promoter activity driven by STING, TBK1, IRF3, and IRF3/5D, and causes a reduction in the protein level of nuclear p-IRF3. In addition, PCV2 interrupts the interaction of KPNA3, rather than KPNA4, with p-IRF3. Overexpression of KPNA3 restores IFN-beta promoter activity. These results indicate that PCV2 disrupts the interaction of KPNA3 with p-IRF3 and blocks p-IRF3 translocation to the nucleus, thereby inhibiting IFN-beta induction in PK-15 cells.

The type I interferon (IFN) response is part of the first-line defense against viral infection. To initiate replication, viruses have developed powerful evasion strategies to counteract host IFN responses. In the present study, we found that the Japanese encephalitis virus (JEV) NS5 protein could inhibit double-stranded RNA (dsRNA)-induced IFN-beta expression in a dose-dependent manner. Our data further demonstrated that JEV NS5 suppressed the activation of the IFN transcriptional factors IFN regulatory factor 3 (IRF3) and NF-kappa B. However, there was no defect in the phosphorylation of IRF3 and degradation of I kappa B, an upstream inhibitor of NF-kappa B, upon NS5 expression, indicating a direct inhibition of the nuclear localization of IRF3 and NF-kappa B by NS5. Mechanistically, NS5 was shown to interact with the nuclear transport proteins KPNA2, KPNA3, and KPNA4, which competitively blocked the interaction of KPNA3 and KPNA4 with their cargo molecules, IRF3 and p65, a subunit of NF-kappa B, and thus inhibited the nuclear translocation of IRF3 and NF-kappa B. Furthermore, overexpression of KPNA3 and KPNA4 restored the activity of IRF3 and NF-kappa B and increased the production of IFN-kappa in NS5-expressing or JEV-infected cells. Additionally, an upregulated replication level of JEV was shown upon KPNA3 or KPNA4 overexpression. These results suggest that JEV NS5 inhibits the induction of type I IFN by targeting KPNA3 and KPNA4. IMPORTANCE JEV is the major cause of viral encephalitis in South and Southeast Asia, with high mortality. However, the molecular mechanisms contributing to the severe pathogenesis are poorly understood. The ability of JEV to counteract the host innate immune response is potentially one of the mechanisms responsible for JEV virulence. Here we demonstrate the ability of JEV NS5 to interfere with the dsRNA-induced nuclear translocation of IRF3 and NF-kappa B by competitively inhibiting the interaction of IRF3 and NF-kappa B with nuclear transport proteins. Via this mechanism, JEV NS5 suppresses the induction of type I IFN and the antiviral response in host cells. These findings reveal a novel strategy for JEV to escape the host innate immune response and provide new insights into the pathogenesis of JEV.