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HBV X protein mutations affect HBV transcription and association of histone-modifying enzymes with covalently closed circular DNA.

ABSTRACT: The hepatitis B X protein (HBx) plays a role in the epigenetic regulation of hepatitis B virus (HBV) replication. This study investigated the effects of HBx mutations on HBV transcription and the recruitment of HBx, histone acetyl-transferase P300 and histone deacetylase 1 (HDAC1) to circularized HBV DNA (which resembles covalently closed circular DNA [cccDNA]). Compared with wild type, majority of mutants had lower levels of intracellular HBV RNA (44-77% reduction) and secretory HBsAg (25-81% reduction), and 12 mutants had a reduction in intracellular encapsidated HBV DNA (33-64% reduction). Eight mutants with >70% reduction in HBV RNA and/or HBsAg were selected for chromatin immunoprecipitation analysis. Four HBx mutants with mutations in amino acid residues 55-60 and 121-126 had a lower degree of HBx-cccDNA association than wild type HBx (mean % input: 0.02-0.64% vs. 3.08% in wild type). A reduced association between cccDNA and P300 (mean % input: 0.69-1.81% vs. 3.48% in wild type) and an augmented association with HDAC1 (mean % input: 4.01-14.0% vs. 1.53% in wild type) were detected. HBx amino acid residues 55-60 and 121-126 may play an important role in HBV transcription regulation, via their impeded interaction with cccDNA and altered recruitment of histone modifying enzymes to cccDNA.

SUBMITTER: Chong CK

PROVIDER: S-EPMC6972884 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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HBV X protein mutations affect HBV transcription and association of histone-modifying enzymes with covalently closed circular DNA.

Chong Chun Kong CK Cheng Ching Yan Serene CYS Tsoi Sin Yi Jasmine SYJ Huang Fung-Yu FY Liu Fen F Fung James J Seto Wai-Kay WK Lai Keane K-Y KK Lai Ching-Lung CL Yuen Man-Fung MF Wong Danny Ka-Ho DK

Scientific reports 20200121 1

The hepatitis B X protein (HBx) plays a role in the epigenetic regulation of hepatitis B virus (HBV) replication. This study investigated the effects of HBx mutations on HBV transcription and the recruitment of HBx, histone acetyl-transferase P300 and histone deacetylase 1 (HDAC1) to circularized HBV DNA (which resembles covalently closed circular DNA [cccDNA]). Compared with wild type, majority of mutants had lower levels of intracellular HBV RNA (44-77% reduction) and secretory HBsAg (25-81% r ...[more]

PMID: 31964944

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Project description:Covalently closed circular DNA (cccDNA) of hepadnaviruses exists as an episomal minichromosome in the nucleus of an infected hepatocyte and serves as the template for the transcription of viral mRNAs. It had been demonstrated by others and us that interferon alpha (IFN-α) treatment of hepatocytes induced a prolonged suppression of human and duck hepatitis B virus cccDNA transcription, which is associated with the reduction of cccDNA-associated histone modifications specifying active transcription (H3K9ac or H3K27ac), but not the histone modifications marking constitutive (H3K9me3) or facultative (H3K27me3) heterochromatin formation. In our efforts to identify IFN-induced cellular proteins that mediate the suppression of cccDNA transcription by the cytokine, we found that downregulating the expression of signal transducer and activator of transcription 1 (STAT1), structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1), or promyelocytic leukemia (PML) protein increased basal level of cccDNA transcription activity and partially attenuated IFN-α suppression of cccDNA transcription. In contrast, ectopic expression of STAT1, SMCHD1, or PML significantly reduced cccDNA transcription activity. SMCHD1 is a noncanonical SMC family protein and implicated in epigenetic silencing of gene expression. PML is a component of nuclear domain 10 (ND10) and is involved in suppressing the replication of many DNA viruses. Mechanistic analyses demonstrated that STAT1, SMCHD1, and PML were recruited to cccDNA minichromosomes and phenocopied the IFN-α-induced posttranslational modifications of cccDNA-associated histones. We thus conclude that STAT1, SMCHD1, and PML may partly mediate the suppressive effect of IFN-α on hepadnaviral cccDNA transcription.IMPORTANCE Pegylated IFN-α is the only therapeutic regimen that can induce a functional cure of chronic hepatitis B in a small, but significant, fraction of treated patients. Understanding the mechanisms underlying the antiviral functions of IFN-α in hepadnaviral infection may reveal molecular targets for development of novel antiviral agents to improve the therapeutic efficacy of IFN-α. By a loss-of-function genetic screening of individual IFN-stimulated genes (ISGs) on hepadnaviral mRNAs transcribed from cccDNA, we found that downregulating the expression of STAT1, SMCHD1, or PML significantly increased the level of viral RNAs without altering the level of cccDNA. Mechanistic analyses indicated that those cellular proteins are recruited to cccDNA minichromosomes and induce the posttranslational modifications of cccDNA-associated histones similar to those induced by IFN-α treatment. We have thus identified three IFN-α-induced cellular proteins that suppress cccDNA transcription and may partly mediate IFN-α silencing of hepadnaviral cccDNA transcription.

Dataset Information

HBV X protein mutations affect HBV transcription and association of histone-modifying enzymes with covalently closed circular DNA.

Publications

HBV X protein mutations affect HBV transcription and association of histone-modifying enzymes with covalently closed circular DNA.

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