The Molecular Mechaniam Underlying FMDV VP1-induced Suppression Of Type Ⅰ Interferon Expression

Foot-and-mouth disease (FMD) is an acute, febrile, highly contagious animal disease caused by FMD virus (FMDV), and has been recognized as the most important constraint to international trade in animals and animal products. An outstanding feature for FMDV infection is that the FMDV infected animals may remain as a carrier state, some of the animals exposed to FMDV may have a long term asymptomatic infection. Viruses can evade host immune surveillance and exploit the host response to provide favorable intracellular conditions for long-term persistence. FMDV VP1is the major structural protein, which plays an important role in the process of viral infection and immune evasion, but the underlying mechanism has not yet been elucidated. Here we showed the critical role of VP1in FMDV-induced persistent infection.In this study, we found that the FMDV VP1was transfected into HEK293T cells and the effects of expression of the viral proteins on expression of type I interferon and the transcription activation of NF-κB were examined by the qRT-PCR and dual-luciferase reporter gene assay. To further investigate the molecular mechanism underlying VP1-induced immunosuppression, we performed the Yeast Two-hybrid assay using FMDV protein VP1as the bait and the PK15cDNA library as the prey to screen the VP1-interacting proteins. Among the positive clones, we focus on soluble resistance-related calcium-binding protein (Sorcin). The interaction between VP1and Sorcin was confirmed by Co-IP and Confocal assay. Importantly, we found that knockdown of Sorcin abolished the inhibitory effects of the activation of Type I interferon and NF-κB promoters. These results indicate that Sorcin is required for VP1-induced suppression of type I interferon response. In addition, over-expression or down-expression of Sorcin can also affect the transcriptional activation of type I interferons and NF-κB, it is speculated that the Sorcin is a negative regulator of immune signaling pathway. To further validate the role of Sorcin in vivo, constructing Sorcin knockout mice, preliminary experimental results showed that: knockout mice exhibited more severe inflammation.To explore the mechanism of action of Sorcin and the pathways in which Sorcin is involved, yeast two hybrid screens, co-immunoprecipitation and confocal assay unambiguously identified signal transducer and activator of transcription3(STAT3) as a Sorcin-interacting protein. More interesting, knocking down of the STAT3abolished the ability of Sorcin to inhibit NF-κB signaling, suggesting that STAT3functions downstream of Sorcin in NF-κB signaling pathway.In summary, by yeast two-hybrid screening and immunoprecipitation approaches, we found that FMDV VP1interacted with Sorcin in the cytoplasm, and that VP1inhibited type I IFN response via interacting with Sorcin. Importantly, we found that Sorcin interacts with STAT3, and that STAT3act as an downstream adaptor protein of Sorcin in the negative regulation of NF-κB signaling pathway. These data further our understandings and provide new insights into the molecular mechanisms of the persistent infection of FMDV.