Hepatitis C virus core protein abrogates the DDX3 function that enhances IPS-1-mediated IFN-beta induction

PLoS One. 2010 Dec 8;5(12):e14258. doi: 10.1371/journal.pone.0014258.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism*
  • Cytoplasm / metabolism
  • DEAD-box RNA Helicases / metabolism*
  • Gene Expression Regulation, Viral*
  • Hepacivirus / metabolism*
  • Hepatitis C / metabolism*
  • Hepatocytes / cytology
  • Humans
  • Interferon-beta / metabolism*
  • Microscopy, Confocal
  • Mitochondria / metabolism
  • Protein Structure, Tertiary
  • RNA Interference
  • Signal Transduction
  • Viral Core Proteins / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • MAVS protein, human
  • Viral Core Proteins
  • nucleocapsid protein, Hepatitis C virus
  • Interferon-beta
  • DDX3X protein, human
  • DEAD-box RNA Helicases