title: The heterogeneous ribonuclear protein C interacts with the hepatitis delta virus small antigen.
abstract: BACKGROUND
  Hepatitis delta virus (HDV) is considered to be a satellite virus of the Hepatitis B virus. The genome consists of a 1679 nt ssRNA molecule in which a single ORF was identified. This ORF codes for a unique protein, the Delta antigen (HDAg). During transcription, two forms, small (S-HDAg; p24) and large (L-HDAg; p27) of this antigen are derived as a result of an editing mechanism catalyzed by cellular adenosine deaminase 1. Despite its simplicity, little is still known about the host factors that interact with the virus RNA and antigens being to modulate virus replication.
  
  
  METHODS
  A yeast two-hybrid screening of a human liver cDNA library, using the hepatitis delta virus (HDV) small antigen (S-HDAg) as bait, was performed. Blot overlay and co-immunoprecipitation assays were used in an attempt to confirm the interaction of hnRNPC and S-HDAg. siRNA knockdown assays of hnRNPC were performed to assess the effect on HDV antigen expression.
  
  
  RESULTS
  Thirty known proteins were identified as S-HDAg interactors in the yeast two-hybrid screening. One of the identified proteins, hnRNPC, was found to interact with S-HDAg in vitro and in vivo in human liver cells. The interaction of the two proteins is mediated by the C-terminal half of the S-HDAg which contains a RNA-binding domain (aa 98-195). HDV RNA, S-HDAg, and hnRNPC, were also found to co-localize in the nucleus of human liver cells. Knockdown of hnRNPC mRNA using siRNAs resulted in a marked decreased expression of HDV antigens.
  
  
  CONCLUSIONS
  S-HDAg was found to interact with human liver proteins previously assigned to different functional categories. Among those involved in nucleic acid metabolism, hnRNPC was found to interact in vitro and in vivo in human liver cells. Similar to other RNA viruses, it seems plausible that hnRNPC may also be involved in HDV replication. However, further investigation is mandatory to clarify this question.
authors.affiliation: Unidade de Microbiologia Médica, Centro de Malária e outras Doenças Tropicais, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Lisboa, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Casaca
authors.forename: Margarida
authors.initials: M
authors.lastname: Fardilha
authors.forename: Edgar
authors.initials: E
authors.lastname: da Cruz e Silva
authors.forename: Celso
authors.initials: C
authors.lastname: Cunha
mesh_terms: D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry / Q000821:virology; D055785:Gene Knockdown Techniques; D003698:Hepatitis Delta Virus / Q000472:pathogenicity*; D035923:Hepatitis delta Antigens / Q000378:metabolism*; D022781:Hepatocytes / Q000821:virology; D034482:Heterogeneous-Nuclear Ribonucleoprotein Group C / Q000235:genetics / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D025941:Protein Interaction Mapping; D020798:Two-Hybrid System Techniques
chemical_list: C503635:HNRNPC protein, human; D035923:Hepatitis delta Antigens; D034482:Heterogeneous-Nuclear Ribonucleoprotein Group C