The Large Form of ADAR 1 Is Responsible for Enhanced Hepatitis Delta Virus RNA Editing in Interferon-Alpha-Stimulated Host Cells

J Viral Hepat. 2006 Mar;13(3):150-7. doi: 10.1111/j.1365-2893.2005.00663.x.

Abstract

Hepatitis delta virus (HDV) RNA editing controls the formation of hepatitis-delta-antigen-S and -L and therefore indirectly regulates HDV replication. Editing is thought to be catalysed by the adenosine deaminase acting on RNA1 (ADAR1) of which two different forms exist, interferon (IFN)-alpha-inducible ADAR1-L and constitutively expressed ADAR1-S. ADAR1-L is hypothesized to be a part of the innate cellular immune system, responsible for deaminating adenosines in viral dsRNAs. We examined the influence of both forms on HDV RNA editing in IFN-alpha-stimulated and unstimulated hepatoma cells. For gene silencing, an antisense oligodeoxyribonucleotide against a common sequence of both forms of ADAR1 and another one specific for ADAR1-L alone were used. IFN-alpha treatment of host cells led to approximately twofold increase of RNA editing compared with unstimulated controls. If ADAR1-L expression was inhibited, this substantial increase in editing could no longer be observed. In unstimulated cells, ADAR1-L suppression had only minor effects on editing. Inhibition of both forms of ADAR1 simultaneously led to a substantial decrease of edited RNA independently of IFN-alpha-stimulation. In conclusion, the two forms of ADAR1 are responsible almost alone for HDV editing. In unstimulated cells, ADAR1-S is the main editing activity. The increase of edited RNA under IFN-alpha-stimulation is because of induction of ADAR1-L, showing for the first time that this IFN-inducible protein is involved in the base modification of replicating HDV RNA. Thus, induction of ADAR1-L may at least partially cause the antiviral effect of IFN-alpha in natural immune response to HDV as well as in case of therapeutic administration of IFN.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Deaminase / physiology*
  • Carcinoma, Hepatocellular
  • Cell Line, Tumor
  • Electrophoresis, Polyacrylamide Gel
  • Gene Silencing
  • Hepatitis Delta Virus / genetics
  • Hepatitis Delta Virus / immunology
  • Hepatitis Delta Virus / physiology*
  • Humans
  • Immunoblotting
  • Interferon-alpha / immunology*
  • Oligoribonucleotides, Antisense / pharmacology
  • RNA Editing / physiology*
  • RNA, Messenger / analysis
  • RNA, Viral / metabolism*
  • RNA-Binding Proteins
  • Reverse Transcriptase Polymerase Chain Reaction

Substances

  • Interferon-alpha
  • Oligoribonucleotides, Antisense
  • RNA, Messenger
  • RNA, Viral
  • RNA-Binding Proteins
  • ADARB1 protein, human
  • Adenosine Deaminase