title: Enterovirus 2Apro targets MDA5 and MAVS in infected cells.
abstract: 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 caspase- and proteasome-mediated degradation during poliovirus infection. Additionally, MAVS is reported to be cleaved during infection with coxsackievirus B3 (CVB3) by the CVB3 proteinase 3C(pro), whereas MAVS cleavage by enterovirus 71 has been attributed to 2A(pro). 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 caspase- and proteasome-independent manner. We convincingly show that MDA5 and MAVS cleavages are both mediated by CVB3 2A(pro), while RIG-I is cleaved by 3C(pro). Moreover, we show that proteinases 2A(pro) and 3C(pro) of poliovirus (HEV-C) and enterovirus 71 (HEV-A) exert the same functions. This study identifies a critical role of 2A(pro) by cleaving MDA5 and MAVS and shows that enteroviruses use a common strategy to counteract the interferon response in infected cells.
  
  
  OBJECTIVE
  Human enteroviruses (HEVs) are important pathogens that cause a variety of diseases in humans, including poliomyelitis, hand, foot, and mouth disease, viral meningitis, cardiomyopathy, and more. Like many other viruses, enteroviruses target the host immune pathways to gain replication advantage. The MDA5/MAVS pathway is responsible for recognizing enterovirus infections in the host cell and leads to expression of type I interferons (IFN-I), crucial antiviral signaling molecules. Here we show that three species of HEVs all employ the viral proteinase 2A (2A(pro)) to proteolytically target MDA5 and MAVS, leading to an efficient blockade upstream of IFN-I transcription. These observations suggest that MDA5/MAVS antagonization is an evolutionarily conserved and beneficial mechanism of enteroviruses. Understanding the molecular mechanisms of enterovirus immune evasion strategies will help to develop countermeasures to control infections with these viruses in the future.
authors.affiliation: Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
authors.forename: Qian
authors.initials: Q
authors.lastname: Feng
authors.forename: Martijn A
authors.initials: MA
authors.lastname: Langereis
authors.forename: Marie
authors.initials: M
authors.lastname: Lork
authors.forename: Mai
authors.initials: M
authors.lastname: Nguyen
authors.forename: Stanleyson V
authors.initials: SV
authors.lastname: Hato
authors.forename: Kjerstin
authors.initials: K
authors.lastname: Lanke
authors.forename: Luni
authors.initials: L
authors.lastname: Emdad
authors.forename: Praveen
authors.initials: P
authors.lastname: Bhoopathi
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fisher
authors.forename: Richard E
authors.initials: RE
authors.lastname: Lloyd
authors.forename: Frank J M
authors.initials: FJ
authors.lastname: van Kuppeveld
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D029822:Enterovirus B, Human / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D004769:Enterovirus Infections / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D054884:Host-Pathogen Interactions; D006801:Humans; D000072640:Interferon-Induced Helicase, IFIH1; D010766:Phosphorylation; D059748:Proteolysis; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C505371:MAVS protein, human; C437968:PLAAT4 protein, human; D018168:Receptors, Retinoic Acid; D014764:Viral Proteins; D003546:Cysteine Endopeptidases; C057400:picornain 2A, Picornavirus; C452815:IFIH1 protein, human; D053487:DEAD-box RNA Helicases; D000072640:Interferon-Induced Helicase, IFIH1