Alpha-Interferon Suppresses Hepadnavirus Transcription by Altering Epigenetic Modification of cccDNA Minichromosomes
Open Access
- 12 September 2013
- journal article
- research article
- Published by Public Library of Science (PLoS) in PLoS Pathogens
- Vol. 9 (9), e1003613
- https://doi.org/10.1371/journal.ppat.1003613
Abstract
Covalently closed circular DNA (cccDNA) of hepadnaviruses exists as an episomal minichromosome in the nucleus of infected hepatocyte and serves as the transcriptional template for viral mRNA synthesis. Elimination of cccDNA is the prerequisite for either a therapeutic cure or immunological resolution of HBV infection. Although accumulating evidence suggests that inflammatory cytokines-mediated cure of virally infected hepatocytes does occur and plays an essential role in the resolution of an acute HBV infection, the molecular mechanism by which the cytokines eliminate cccDNA and/or suppress its transcription remains elusive. This is largely due to the lack of convenient cell culture systems supporting efficient HBV infection and cccDNA formation to allow detailed molecular analyses. In this study, we took the advantage of a chicken hepatoma cell line that supports tetracycline-inducible duck hepatitis B virus (DHBV) replication and established an experimental condition mimicking the virally infected hepatocytes in which DHBV pregenomic (pg) RNA transcription and DNA replication are solely dependent on cccDNA. This cell culture system allowed us to demonstrate that cccDNA transcription required histone deacetylase activity and IFN-α induced a profound and long-lasting suppression of cccDNA transcription, which required protein synthesis and was associated with the reduction of acetylated histone H3 lysine 9 (H3K9) and 27 (H3K27) in cccDNA minichromosomes. Moreover, IFN-α treatment also induced a delayed response that appeared to accelerate the decay of cccDNA. Our studies have thus shed light on the molecular mechanism by which IFN-α noncytolytically controls hepadnavirus infection. Hepatitis B virus (HBV) infection affects approximately one-third of the world population and more than 350 million people are chronically infected by the virus, for which the currently available antiviral therapies fail to provide a cure. This is because the HBV DNA polymerase inhibitors have no direct effect on the nuclear form of HBV genome, the covalently closed circular (ccc) DNA. Elimination or transcriptional silencing of cccDNA is the prerequisite for either a therapeutic cure or immunological resolution of HBV infection. However, due to the lack of proper experimental systems, the molecular mechanism of cccDNA biosynthesis, maintenance and transcription regulation remains to be elucidated. We report herein the establishment of a cell-based assay where the replication of duck hepatitis B virus (DHBV), a close relative of HBV, is supported by cccDNA. This experimental system not only allows us to demonstrate the unique property of alpha-interferon suppression of cccDNA transcription, but also shows for the first time that DHBV cccDNA transcription requires histone deacetylase activity. It is conceivable that the principles revealed by studying DHBV cccDNA metabolism and transcription regulation should provide valuable insight in HBV cccDNA biology and clues for the development of therapeutics to control chronic hepatitis B.Keywords
This publication has 69 references indexed in Scilit:
- An integrated encyclopedia of DNA elements in the human genomeNature, 2012
- MuLV IN mutants responsive to HDAC inhibitors enhance transcription from unintegrated retroviral DNAVirology, 2012
- Chromatin-targeting small molecules cause class-specific transcriptional changes in pancreatic endocrine cellsProceedings of the National Academy of Sciences of the United States of America, 2012
- Activator-dependent p300 Acetylation of Chromatin in Vitro: ENHANCEMENT OF TRANSCRIPTION BY DISRUPTION OF REPRESSIVE NUCLEOSOME-NUCLEOSOME INTERACTIONSJournal of Biological Chemistry, 2010
- Nuclear HBx binds the HBV minichromosome and modifies the epigenetic regulation of cccDNA functionProceedings of the National Academy of Sciences of the United States of America, 2009
- Epigenetic activation of unintegrated HIV-1 genomes by gut-associated short chain fatty acids and its implications for HIV infectionProceedings of the National Academy of Sciences of the United States of America, 2009
- Inhibition of the histone demethylase LSD1 blocks α-herpesvirus lytic replication and reactivation from latencyNature Medicine, 2009
- Interferon-inducible antiviral effectorsNature Reviews Immunology, 2008
- High-Resolution Profiling of Histone Methylations in the Human GenomeCell, 2007
- Chromatin Modifications and Their FunctionCell, 2007