Enterovirus 2A Targets MDA5 and MAVS in Infected Cells

RIG-I-like receptors (RLRs) MDA5 and RIG-I are key players in the innate antiviral response. Upon recognition of viral RNA, they interact with MAVS, eventually inducing type I interferon production. The interferon induction pathway is commonly targeted by viruses. How enteroviruses suppress interferon production is incompletely understood. MDA5 has been suggested to undergo caspaseand proteasome-mediated degradation during poliovirus infection. Additionally, MAVS is reported to be cleaved during infection with coxsackievirus B3 (CVB3) by the CVB3 proteinase 3C, whereas MAVS cleavage by enterovirus 71 has been attributed to 2A. As yet, a detailed examination of the RLR pathway as a whole during any enterovirus infection is lacking. We performed a comprehensive analysis of crucial factors of the RLR pathway, including MDA5, RIG-I, LGP2, MAVS, TBK1, and IRF3, during infection of CVB3, a human enterovirus B (HEV-B) species member. We show that CVB3 inhibits the RLR pathway upstream of TBK1 activation, as demonstrated by limited phosphorylation of TBK1 and a lack of IRF3 phosphorylation. Furthermore, we show that MDA5, MAVS, and RIG-I all undergo proteolytic degradation in CVB3-infected cells through a caspaseand proteasome-independent manner. We convincingly show that MDA5 and MAVS cleavages are both mediated by CVB3 2A, while RIG-I is cleaved by 3C. Moreover, we show that proteinases 2A and 3C of poliovirus (HEV-C) and enterovirus 71 (HEV-A) exert the same functions. This study identifies a critical role of 2A by cleaving MDA5 and MAVS and shows that enteroviruses use a common strategy to counteract the interferon response in infected cells.