Hepatitis B virus replication is regulated by the acetylation status of hepatitis B virus cccDNA-bound H3 and H4 histones.
OBJECTIVE
HBV covalently closed circular DNA (cccDNA), the replicative intermediate responsible for persistent HBV infection of hepatocytes, is the template for transcription of all viral mRNAs. Nuclear cccDNA accumulates as a stable episome organized into minichromosomes by histone and nonhistone proteins. In this study we investigated, by a newly developed sensitive and specific assay, the relationship between viral replication and HBV chromatin assembly, transcription, and interaction with viral and cellular regulatory proteins.


METHODS
To achieve this aim we coupled a quantitative chromatin immunoprecipitation (ChIP) technique to an established method that allows the amplification of virion-encapsidated HBV genomes after transfection of linear HBV DNA into human hepatoma HuH7 cells. The cccDNA-ChIP technique was also applied to study HBV minichromosome transcriptional regulation in liver tissue from HBV-infected patients.


RESULTS
The use of anti-acetyl-H4/-H3 specific antibodies to immunoprecipitate transcriptionally active chromatin revealed that HBV replication is regulated by the acetylation status of the cccDNA-bound H3/H4 histones. Class I histone deacetylases inhibitors induced an evident increase of both cccDNA-bound acetylated H4 and HBV replication. Finally, histones hypoacetylation and histone deacetylase 1 recruitment onto the cccDNA in liver tissue correlated with low HBV viremia in hepatitis B patients.


CONCLUSIONS
We developed a ChIP-based assay to analyze, in vitro and ex vivo, the transcriptional regulation of HBV cccDNA minichromosome. Our results provide new insights on the regulation of HBV replication and identify the enzymatic activities that modulate the acetylation of cccDNA-bound histones as new therapeutic targets for anti-HBV drugs.
Pollicino
Teresa
T
Laboratory of Gene Expression, Fondazione A. Cesalpino, University of Rome La Sapienza, Rome, Italy.
Belloni
Laura
L
Raffa
Giuseppina
G
Pediconi
Natalia
N
Squadrito
Giovanni
G
Raimondo
Giovanni
G
Levrero
Massimo
M
D000107:Acetylation; D000328:Adult; D000368:Aged; D004270:DNA, Circular / Q000378:metabolism*; D004279:DNA, Viral / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006515:Hepatitis B virus / Q000502:physiology*; D019694:Hepatitis B, Chronic / Q000378:metabolism; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D014766:Viremia / Q000378:metabolism; D014779:Virus Replication / Q000187:drug effects
D004270:DNA, Circular; D004279:DNA, Viral; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D006657:Histones