title: Hepatitis C virus core protein abrogates the DDX3 function that enhances IPS-1-mediated IFN-beta induction.
abstract: The DEAD box helicase DDX3 assembles IPS-1 (also called Cardif, MAVS, or VISA) in non-infected human cells where minimal amounts of the RIG-I-like receptor (RLR) protein are expressed. DDX3 C-terminal regions directly bind the IPS-1 CARD-like domain as well as the N-terminal hepatitis C virus (HCV) core protein. DDX3 physically binds viral RNA to form IPS-1-containing spots, that are visible by confocal microscopy. HCV polyU/UC induced IPS-1-mediated interferon (IFN)-beta promoter activation, which was augmented by co-transfected DDX3. DDX3 spots localized near the lipid droplets (LDs) where HCV particles were generated. Here, we report that HCV core protein interferes with DDX3-enhanced IPS-1 signaling in HEK293 cells and in hepatocyte Oc cells. Unlike the DEAD box helicases RIG-I and MDA5, DDX3 was constitutively expressed and colocalized with IPS-1 around mitochondria. In hepatocytes (O cells) with the HCV replicon, however, DDX3/IPS-1-enhanced IFN-beta-induction was largely abrogated even when DDX3 was co-expressed. DDX3 spots barely merged with IPS-1, and partly assembled in the HCV core protein located near the LD in O cells, though in some O cells IPS-1 was diminished or disseminated apart from mitochondria. Expression of DDX3 in replicon-negative or core-less replicon-positive cells failed to cause complex formation or LD association. HCV core protein and DDX3 partially colocalized only in replicon-expressing cells. Since the HCV core protein has been reported to promote HCV replication through binding to DDX3, the core protein appears to switch DDX3 from an IFN-inducing mode to an HCV-replication mode. The results enable us to conclude that HCV infection is promoted by modulating the dual function of DDX3.
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oshiumi
authors.forename: Masanori
authors.initials: M
authors.lastname: Ikeda
authors.forename: Misako
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Ayako
authors.initials: A
authors.lastname: Watanabe
authors.forename: Osamu
authors.initials: O
authors.lastname: Takeuchi
authors.forename: Shizuo
authors.initials: S
authors.lastname: Akira
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kato
authors.forename: Kunitada
authors.initials: K
authors.lastname: Shimotohno
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Seya
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D016174:Hepacivirus / Q000378:metabolism*; D006526:Hepatitis C / Q000378:metabolism*; D022781:Hepatocytes / Q000166:cytology; D006801:Humans; D016899:Interferon-beta / Q000378:metabolism*; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D015398:Signal Transduction; D014758:Viral Core Proteins / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C505371:MAVS protein, human; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus; D016899:Interferon-beta; C119332:DDX3X protein, human; D053487:DEAD-box RNA Helicases