IFN-α inhibits HBV transcription and replication in cell culture and in humanized mice by targeting the epigenetic regulation of the nuclear cccDNA minichromosome
Laura Belloni, … , Maura Dandri, Massimo Levrero
Laura Belloni, … , Maura Dandri, Massimo Levrero
Published January 17, 2012
Citation Information: J Clin Invest. 2012;122(2):529-537. https://doi.org/10.1172/JCI58847.
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Research Article Virology

IFN-α inhibits HBV transcription and replication in cell culture and in humanized mice by targeting the epigenetic regulation of the nuclear cccDNA minichromosome

Abstract

HBV infection remains a leading cause of death worldwide. IFN-α inhibits viral replication in vitro and in vivo, and pegylated IFN-α is a commonly administered treatment for individuals infected with HBV. The HBV genome contains a typical IFN-stimulated response element (ISRE), but the molecular mechanisms by which IFN-α suppresses HBV replication have not been established in relevant experimental systems. Here, we show that IFN-α inhibits HBV replication by decreasing the transcription of pregenomic RNA (pgRNA) and subgenomic RNA from the HBV covalently closed circular DNA (cccDNA) minichromosome, both in cultured cells in which HBV is replicating and in mice whose livers have been repopulated with human hepatocytes and infected with HBV. Administration of IFN-α resulted in cccDNA-bound histone hypoacetylation as well as active recruitment to the cccDNA of transcriptional corepressors. IFN-α treatment also reduced binding of the STAT1 and STAT2 transcription factors to active cccDNA. The inhibitory activity of IFN-α was linked to the IRSE, as IRSE-mutant HBV transcribed less pgRNA and could not be repressed by IFN-α treatment. Our results identify a molecular mechanism whereby IFN-α mediates epigenetic repression of HBV cccDNA transcriptional activity, which may assist in the development of novel effective therapeutics.

Authors

Laura Belloni, Lena Allweiss, Francesca Guerrieri, Natalia Pediconi, Tassilo Volz, Teresa Pollicino, Joerg Petersen, Giovanni Raimondo, Maura Dandri, Massimo Levrero

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Figure 6

Schematic representation of cccDNA chromatin changes in response to IFN-α treatment.

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Schematic representation of cccDNA chromatin changes in response to IFN-...
cccDNA-bound histone acetylation status and the recruitment of chromatin-modifying enzymes onto the viral minichromosome change in relation to viral replication and IFN-α treatment. The drawings reflect what is observed in an in vitro replication system. The translation into the clinical scenario as it is observed in patients (lower boxes) is inferred, and it awaits to be confirmed by ex vivo experiments. In the context of high HBV replication and in the absence of IFN-α treatment, cccDNA-bound histones are hyperacetylated, cccDNA-associated chromatin is in an open configuration, pgRNA is actively transcribed, and HBV replication is unrestricted (left drawing). The clinical correlate is an active HBV carrier with high HBV viremia, reflecting high levels of intrahepatic viral replication and liver disease progression. In response to IFN-α, HDACs (HDAC1 and Sirt1) substitute HAT enzymes (p300, CBP, and P/CAF) on the cccDNA, and a PRC2-repressor complex is recruited. This leads to histone deacetylation/methylation at specific lysine residues, a “closed” chromatin configuration, and a striking reduction of pgRNA transcription, HBsAg synthesis, and HBV replication (middle drawing). In the clinical setting, this would translate into a rapid serum HBsAg decline and viral suppression (inactive carrier) with disease remission. When treatment is stopped, the chromatin changes imposed by IFN-α tend to persist (right drawing) resulting in the “off-therapy” maintenance of the virological suppression and clinical improvement (achieved in 30%–35% of HBeAg-positive patients and 20%–25% of HBeAg-negative patients). Darker forms in the middle and right drawings indicate components of the PRC2 complex whose recruitment has been directly investigated in this paper.