Hepatitis B virus X protein modulates remodelling of minichromosomes related to hepatitis B virus replication in HepG2 cells

Abstract

Abstract. Hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) is organised into minichromosomes by histone and non-histone proteins. Remodelling of minichromosomes is crucial for the regulation of HBV replication, which is dependent on the presence of the hepatitis B virus X protein (HBx). However, the mechanisms of HBx-dependent HBV replication remain obscure. The objective of this study was to investigate the mechanism of HBx-dependent HBV replication through the pathway of chromatin remodelling. The role of HBx was investigated by transfecting human HepG2 cells with the linear full-length HBV genome (wild-type) or HBx-deficient mutant HBV DNA (HBx mutant). Our results showed that although the formation of cccDNA was not affected by HBx, HBV replication, transcription and antigen secretion were all significantly reduced, resulting from the absence of HBx. The acetylation, mono-methylation and phosphorylation of cccDNA-bound histone H3 were associated with HBV replication. In addition, the levels of cccDNA-bound methylated, phosphorylated and acetylated histone H3 decreased sharply in HBx mutant HBV DNA. HBx modulated not only the status of acetylation but also the methylation and phosphorylation of histone H3 bound to the cccDNA during HBV replication in HepG2 cells. These findings suggest that HBx plays an important role in modulating the remodelling of minichromosomes related to HBV replication and it may regulate viral replication through the pathway of chromatin remodelling.

Inhibition of Histone Deacetylases Stimulates HBV Replication Independent of Protein X

“…A hallmark of this silencing is the deacetylation of the HBV cccDNA associated histones [11,1,3,2]. Here, we investigated whether the HBV X protein stimulates HBV replication by preventing the deacetylation of the cccDNA-associated histones.…”

“…This episomal cccDNA is wrapped around histones and thus forms a minichromosome that is subject to various epigenetic modifications to both the cccDNA and the associated histones [1]. It has been shown that these epigenetic modifications regulate the transcription of the viral RNAs [2,3].…”

“…This episomal cccDNA is wrapped around histones and thus forms a minichromosome that is subject to various epigenetic modifications to both the cccDNA and the associated histones [1]. It has been shown that these epigenetic modifications regulate the transcription of the viral RNAs [2,3].The HBV protein called X (HBx) is essential for HBV replication in vivo [4]. In vitro, HBx acts as a transcriptional transactivator [4][5][6][7][8] that increases transcription from episomal DNA templates independent of promoter sequences [9].…”

“…The capacity of HBx to transactivate transcription in vitro is related to its in vivo function and can therefore be used to study HBx functionality [10]. It has been shown that HBx expression critically affects the epigenetic status of the cccDNA [3,11,1,3,2]. In the absence of HBx, the cccDNA-associated histones undergo modifications that effectively abrogate HBV RNA transcription.…”

Hepatitis B Virus Protein X Induces Degradation of Talin-1

“…HBx expression affects various processes such as apoptosis, the cell cycle, and DNA repair [5,6,7,8,9]. In the absence of HBx, viral RNA transcription from the HBV cccDNA is epigenetically silenced [10,11,12]. In most hepatoma-derived cell lines, such as HepG2 cells, HBx expression stimulates HBV transcription but is not essential [11,13,14,15].…”