The Foot-and-Mouth Disease Virus Lb Protease Cleaves Intracellular Transcription Factors STAT1 and STAT2 to Antagonize IFN-ß-Induced Signaling.

Foot-and-mouth disease virus (FMDV) is the causative agent of foot-and-mouth disease, one of the most highly infectious animal viruses throughout the world. The JAK-STAT signaling pathway is a highly conserved pathway for IFN-ß-induced antiviral gene expression. Previous studies have shown that FMDV can strongly suppress the innate immune response. Moreover, although STAT1 and STAT2 (STAT1/2) have been well established in JAK-STAT signaling-induced antiviral gene expression, whether FMDV proteins inhibit IFN-ß-induced JAK-STAT signaling remains poorly understood. In this study, we described the Lb leader protease (Lbpro) of FMDV as a candidate for inhibiting IFN-ß-induced signaling transduction via directly interacting with STAT1/2. We further showed that Lbpro colocalized with STAT1/2 to inhibit their nuclear translocation. Importantly, Lbpro cleaved STAT1/2 to inhibit IFN-ß-induced signal transduction, whereas the catalytically inactive mutant of LC51A (Lbpro with cysteine substituted with alanine at amino acid residue 51) had no effect on the stability of STAT1/2 proteins. The cleavage of the STAT1/2 proteins was also determined during FMDV infection in vitro. Lbpro could cleave the residues between 252 and 502 aa for STAT1 and the site spanning residues 140 - 150 aa (QQHEIESRIL) for STAT2. The in vivo results showed that Lbpro can cleave STAT1/2 in pigs. Overall, our findings suggest that FMDV Lbpro-mediated targeting of STAT1/2 may reveal a novel mechanism for viral immune evasion.

Senecavirus a 3D Interacts with NLRP3 to Induce IL-1ß Production by Activating NF-κB and Ion Channel Signals.

Senecavirus A (SVA) infection induces inflammation in animals, such as fever, diarrhea, vesicles and erosions, and even death. The inflammatory cytokine interleukin-1ß (IL-1ß) plays a pivotal role in inflammatory responses to combat microbes. Although SVA infection can produce inflammatory clinical symptoms, the modulation of IL-1ß production by SVA infection remains unknown at present. Here, both in vitro and in vivo, SVA robustly induced IL-1ß production in macrophages and pigs. Infection performed in NOD-, LRR-, and pyrin domain-containing three (NLRP3) knockdown cells indicated that NLRP3 is essential for SVA-induced IL-1ß secretion. Importantly, we identified that the 1 to 154 amino acid (aa) portion of SVA 3D binds to the NLRP3 NACHT domain to activate NLRP3 inflammasome assembly and IL-1ß secretion. In addition, the SVA 3D protein interacts with IKKα and IKKß to induce NF-κB activation, which facilitates pro-IL-1ß transcription. Meanwhile, 3D induces p65 nucleus entry. Moreover, SVA 3D induces calcium influx and potassium efflux, which triggers IL-1ß secretion. Ion channels might be related to 3D binding with NLRP3, resulting in NLRP3-ASC complex assembly. We found that 3D protein expression induced tissue hemorrhage and swelling in the mice model. Consistently, expression of 3D in mice caused IL-1ß maturation and secretion. In the natural host of pigs, we confirmed that 3D also induced IL-1ß production. Our data reveal a novel mechanism underlying the activation of the NLRP3 inflammasome after SVA 3D expression, which provides clues for controlling pig's inflammation during the SVA infection. IMPORTANCE Inflammation refers to the response of the immune system to viral, bacterial, and fungal infections or other foreign particles in the body, which can involve the production of a wide array of soluble inflammatory mediators. The NLRP3 inflammasome is one of the best-characterized inflammasome leading to IL-1ß production and maturation. Senecavirus A (SVA) is an oncolytic virus that can cause fever, vesicles and erosions, severe fatal diarrhea, and even the sudden death of piglets. In this study, we demonstrated that 1 to 154 aa of SVA polymerase protein 3D interacts with the NACHT domain of NLRP3 to induce IL-1ß production via the NF-κB signaling pathway and ion channel signal. Our study unveils the mechanism underlying the regulation of inflammasome assembly and production of IL-1ß in response to SVA infection that will help better understand the modulation of host inflammation in pathogens invasion and development of the vaccine.