title: DEAD/H BOX 3 (DDX3) helicase binds the RIG-I adaptor IPS-1 to up-regulate IFN-beta-inducing potential.
abstract: Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLR) are members of the DEAD box helicases, and recognize viral RNA in the cytoplasm, leading to IFN-beta induction through the adaptor IFN-beta promoter stimulator-1 (IPS-1) (also known as Cardif, mitochondrial antiviral signaling protein or virus-induced signaling adaptor). Since uninfected cells usually harbor a trace of RIG-I, other RNA-binding proteins may participate in assembling viral RNA into the IPS-1 pathway during the initial response to infection. We searched for proteins coupling with human IPS-1 by yeast two-hybrid and identified another DEAD (Asp-Glu-Ala-Asp) box helicase, DDX3 (DEAD/H BOX 3). DDX3 can bind viral RNA to join it in the IPS-1 complex. Unlike RIG-I, DDX3 was constitutively expressed in cells, and some fraction of DDX3 is colocalized with IPS-1 around mitochondria. The 622-662 a.a DDX3 C-terminal region (DDX3-C) directly bound to the IPS-1 CARD-like domain, and the whole DDX3 protein also associated with RLR. By reporter assay, DDX3 helped IPS-1 up-regulate IFN-beta promoter activation and knockdown of DDX3 by siRNA resulted in reduced IFN-beta induction. This activity was conserved on the DDX3-C fragment. DDX3 only marginally enhanced IFN-beta promoter activation induced by transfected TANK-binding kinase 1 (TBK1) or I-kappa-B kinase-epsilon (IKKepsilon). Forced expression of DDX3 augmented virus-mediated IFN-beta induction and host cell protection against virus infection. Hence, DDX3 is an antiviral IPS-1 enhancer.
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oshiumi
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sakai
authors.forename: Misako
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Seya
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000276:immunology* / Q000378:metabolism; D000818:Animals; D002460:Cell Line / Q000187:drug effects / Q000276:immunology; D002522:Chlorocebus aethiops; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D007369:Interferon Inducers / Q000494:pharmacology; D000072640:Interferon-Induced Helicase, IFIH1; D016899:Interferon-beta / Q000096:biosynthesis* / Q000235:genetics; D046912:Multiprotein Complexes; D017955:Poliovirus / Q000276:immunology; D011070:Poly I-C / Q000494:pharmacology; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D012367:RNA, Viral / Q000276:immunology*; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins / Q000276:immunology; D015398:Signal Transduction; D014709:Vero Cells; D014721:Vesicular stomatitis Indiana virus / Q000276:immunology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D007369:Interferon Inducers; C505371:MAVS protein, human; D046912:Multiprotein Complexes; D034741:RNA, Small Interfering; D012367:RNA, Viral; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; D016899:Interferon-beta; C119332:DDX3X protein, human; C452820:RIGI protein, human; C452815:IFIH1 protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases; D000072640:Interferon-Induced Helicase, IFIH1; D011070:Poly I-C