title: Hepatitis C Virus nonstructural 5A protein inhibits lipopolysaccharide-mediated apoptosis of hepatocytes by decreasing expression of Toll-like receptor 4.
abstract: BACKGROUND
  Hepatitis C virus (HCV) nonstructural protein 5A (NS5A) has been shown to modulate multiple cellular processes, including apoptosis. The aim of this study was to assess the effects of HCV NS5A on apoptosis induced by Toll-like receptor (TLR) 4 ligand, lipopolysaccharide (LPS).
  
  
  METHODS
  Apoptotic responses to TLR4 ligands and the expression of molecules involved in TLR signaling pathways in human hepatocytes were examined with or without expression of HCV NS5A.
  
  
  RESULTS
  HCV NS5A protected HepG2 hepatocytes against LPS-induced apoptosis, an effect linked to reduced TLR4 expression. A similar downregulation of TLR4 expression was observed in Huh-7-expressing genotype 1b and 2a. In agreement with these findings, NS5A inhibited the expression of numerous genes encoding for molecules involved in TLR4 signaling, such as CD14, MD-2, myeloid differentiation primary response gene 88, interferon regulatory factor 3, and nuclear factor-κB2. Consistent with a conferred prosurvival advantage, NS5A diminished the poly(adenosine diphosphate-ribose) polymerase cleavage and the activation of caspases 3, 7, 8, and 9 and increased the expression of anti-apoptotic molecules Bcl-2 and c-FLIP.
  
  
  CONCLUSIONS
  HCV NS5A downregulates TLR4 signaling and LPS-induced apoptotic pathways in human hepatocytes, suggesting that disruption of TLR4-mediated apoptosis may play a role in the pathogenesis of HCV infection.
authors.affiliation: Department of Medicine and Clinical Oncology, Chiba University, Graduate School of Medicine, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Tamura
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kanda
authors.forename: Fumio
authors.initials: F
authors.lastname: Imazeki
authors.forename: Shuang
authors.initials: S
authors.lastname: Wu
authors.forename: Shingo
authors.initials: S
authors.lastname: Nakamoto
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Makoto
authors.initials: M
authors.lastname: Arai
authors.forename: Keiichi
authors.initials: K
authors.lastname: Fujiwara
authors.forename: Kengo
authors.initials: K
authors.lastname: Saito
authors.forename: Thierry
authors.initials: T
authors.lastname: Roger
authors.forename: Takaji
authors.initials: T
authors.lastname: Wakita
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shirasawa
authors.forename: Osamu
authors.initials: O
authors.lastname: Yokosuka
mesh_terms: D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D020169:Caspases / Q000378:metabolism; D015536:Down-Regulation; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D016174:Hepacivirus / Q000235:genetics* / Q000472:pathogenicity; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D008024:Ligands; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008070:Lipopolysaccharides / Q000502:physiology; D051218:Lymphocyte Antigen 96 / Q000378:metabolism; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D011485:Protein Binding; D015398:Signal Transduction / Q000235:genetics*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000235:genetics* / Q000378:metabolism; D012324:RNA-Dependent RNA Polymerase
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D020169:Caspases; D050838:Interferon Regulatory Factor-3; D008024:Ligands; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D051218:Lymphocyte Antigen 96; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D051197:Toll-Like Receptor 4; D017361:Viral Nonstructural Proteins; C506386:CFLAR protein, human; C494232:IRF3 protein, human; C495377:LY96 protein, human; C507779:MYD88 protein, human; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase