title: Sustained activation of interferon regulatory factor 3 during infection by paramyxoviruses requires MDA5.
abstract: Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) are the main cytosolic sensors of single-stranded RNA viruses, including paramyxoviruses, and are required to initiate a quick and robust innate antiviral response. Despite different ligand-binding properties, the consensus view is that RIG-I and MDA5 trigger common signal(s) to activate interferon regulatory factor 3 (IRF-3) and NF-κB, and downstream antiviral and proinflammatory cytokine expression. Here, we performed a thorough analysis of the temporal involvement of RIG-I and MDA5 in the regulation of IRF-3 during respiratory syncytial virus (RSV) infection. Based on specific RNA interference-mediated knockdown of RIG-I and MDA5 in A549 cells, we confirmed that RIG-I is critical for the initiation of IRF-3 phosphorylation, dimerization and downstream gene expression. On the other hand, our experiments yielded the first evidence that knockdown of MDA5 leads to early ubiquitination and proteasomal degradation of active IRF-3. Conversely, ectopic expression of MDA5 prolonged RIG-I-induced IRF-3 activation. Altogether, we provide novel mechanistic insight into the temporal involvement of RIG-I and MDA5 in the innate antiviral response. While RIG-I is essential for initial IRF-3 activation, engagement of induced MDA5 is essential to prevent early degradation of IRF-3, thereby sustaining IRF-3-dependent antiviral gene expression. MDA5 plays a similar role during Sendai virus infection suggesting that this model is not restricted to RSV amongst paramyxoviruses.
authors.affiliation: CRCHUM - Centre Hospitalier de l'Université de Montréal, Montreal, Que., Canada.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Grandvaux
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Guan
authors.forename: Fabrice
authors.initials: F
authors.lastname: Yoboua
authors.forename: Nicolas
authors.initials: N
authors.lastname: Zucchini
authors.forename: Karin
authors.initials: K
authors.lastname: Fink
authors.forename: Priscilla
authors.initials: P
authors.lastname: Doyon
authors.forename: Lydie
authors.initials: L
authors.lastname: Martin
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Servant
authors.forename: Stéfany
authors.initials: S
authors.lastname: Chartier
mesh_terms: D002460:Cell Line; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000276:immunology* / Q000821:virology; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics; D050838:Interferon Regulatory Factor-3 / Q000235:genetics / Q000378:metabolism*; D000072640:Interferon-Induced Helicase, IFIH1; D010766:Phosphorylation / Q000235:genetics; D059748:Proteolysis; D034741:RNA, Small Interfering / Q000235:genetics; D011971:Receptors, Immunologic; D018357:Respiratory Syncytial Virus Infections / Q000276:immunology*; D018113:Respiratory Syncytial Virus, Human / Q000276:immunology*; D015398:Signal Transduction / Q000235:genetics; D054875:Ubiquitination / Q000235:genetics
chemical_list: C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D034741:RNA, Small Interfering; D011971:Receptors, Immunologic; C452820:RIGI protein, human; C452815:IFIH1 protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases; D000072640:Interferon-Induced Helicase, IFIH1