title: Evidence that hepatitis B virus replication in mouse cells is limited by the lack of a host cell dependency factor.
abstract: OBJECTIVE
  Hepatitis B virus (HBV) is a major human pathogen restricted to hepatocytes. Expression of the specific receptor human sodium taurocholate cotransporting polypeptide (hNTCP) in mouse hepatocytes renders them susceptible to hepatitis delta virus (HDV), a satellite of HBV; however, HBV remains restricted at an early stage of replication. This study aims at clarifying whether this restriction is caused by the lack of a dependency factor or the activity of a restriction factor.
  
  
  METHODS
  Six hNTCP-expressing mouse and human cell lines were generated and functionally characterized. By fusion with replication-supporting but non-infectable HepG2 cells, we analysed the ability of these heterokaryonic cells to fully support HBV replication by HBcAg expression and HBsAg/HBeAg secretion.
  
  
  RESULTS
  While hNTCP expression in three mouse cell lines and the non-hepatic human HeLa cells conferred susceptibility to HDV, HBV replication was still restricted. Upon fusion of refractive cells to HepG2 cells, all heterokaryonic cells supported receptor-mediated infection with HBV. hNTCP was provided by the mouse cells and replication competence came from the HepG2 cell line. Transfection of a covalently closed circular DNA (cccDNA)-like molecule into non-susceptible cells promoted gene expression, indicating that the limiting step is upstream of cccDNA formation.
  
  
  CONCLUSIONS
  In addition to the expression of hNTCP, establishment of HBV infection in mouse and non-hepatocytic human cell lines requires supplementation with a dependency factor and is not limited by a restriction factor. This result opens new avenues for the development of a fully permissive immunocompetent HBV mouse model.
authors.affiliation: Department of Infectious Diseases, Molecular Virology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Florian A
authors.initials: FA
authors.lastname: Lempp
authors.affiliation: Department of Infectious Diseases, Molecular Virology, University Hospital Heidelberg, Heidelberg, Germany; Division of Virus-Associated Carcinogenesis, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Pascal
authors.initials: P
authors.lastname: Mutz
authors.affiliation: Model Systems for Infection and Immunity, Helmholtz Centre for Infection Research, Braunschweig, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Lipps
authors.affiliation: Model Systems for Infection and Immunity, Helmholtz Centre for Infection Research, Braunschweig, Germany.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Wirth
authors.affiliation: Department of Infectious Diseases, Molecular Virology, University Hospital Heidelberg, Heidelberg, Germany; Division of Virus-Associated Carcinogenesis, German Cancer Research Center (DKFZ), Heidelberg, Germany; German Centre for Infection Research, Heidelberg University, Heidelberg, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Bartenschlager
authors.affiliation: Department of Infectious Diseases, Molecular Virology, University Hospital Heidelberg, Heidelberg, Germany; German Centre for Infection Research, Heidelberg University, Heidelberg, Germany. Electronic address: Stephan.Urban@med.uni-heidelberg.de.
authors.forename: Stephan
authors.initials: S
authors.lastname: Urban
mesh_terms: D000818:Animals; D002460:Cell Line; D056945:Hep G2 Cells; D006515:Hepatitis B virus / Q000502:physiology*; D003698:Hepatitis Delta Virus / Q000502:physiology; D022781:Hepatocytes / Q000821:virology; D006801:Humans; D051379:Mice; D029363:Organic Anion Transporters, Sodium-Dependent / Q000235:genetics / Q000502:physiology*; D027981:Symporters / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication
chemical_list: D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter
keywords: Cell fusion; HBV; HDV; Hepatitis B virus; Hepatitis D virus; Mouse model; NTCP