The binding site of transcription factor YY1 is required for intramolecular recombination between terminally repeated sequences of linear replicative hepatitis B virus DNA

miR-HCC2 suppresses hepatitis B virus replication by inhibiting the activity of the enhancer I/X promoter

miR-HCC2 has been reported to markedly promote the growth, metastasis, and stemness of hepatocellular carcinoma (HCC) cells in vitro and in vivo. Deep sequencing showed that miR-HCC2 was significantly upregulated in hepatitis B virus (HBV)-positive (HBV+) HCC tissue samples compared with HBV-negative (HBV-) HCC tissue samples. miR-HCC2 expression was further evaluated in HCC tissues and cells, and the expression of miR-HCC2 was found to be significantly higher in HBV+ HCC tissues and cells than in HBV- HCC tissues and cells, suggesting that high miR-HCC2 expression could be induced by HBV infection. To explore the relationship between miR-HCC2 and HBV, we investigated the effect of miR-HCC2 on HBV antigen expression, transcription, and replication. We found that miR-HCC2 was involved in the negative feedback regulation of HBV replication. Further mechanistic studies revealed that miR-HCC2 suppressed HBV replication by inhibiting the activity of the enhancer I/X promoter. Our study demonstrates the effect of the inhibition of miR-HCC2 on HBV gene expression and replication, which can help to illustrate the complex regulatory network involving host miRNAs and HBV.

Yin-Yang 1 and HBx protein activate HBV transcription by mediating the spatial interaction of cccDNA minichromosome with cellular chromosome 19p13.11

HBV cccDNA stably exists in the nuclei of infected cells as an episomal munichromosome which is responsible for viral persistence and failure of current antiviral treatments. However, the regulatory mechanism of cccDNA transcription by viral and host cellular factors is not well understood. In this study, we investigated whether cccDNA could be recruited into a specific region of the nucleus via specific interaction with a cellular chromatin to regulate its transcription activity. To investigate this hypothesis, we used chromosome conformation capture (3C) technology to search for the potential interaction of cccDNA and cellular chromatin through rcccDNA transfection in hepatoma cells and found that cccDNA is specifically associated with human chromosome 19p13.11 region, which contains a highly active enhancer element. We also confirmed that cellular transcription factor Yin-Yang 1 (YY1) and viral protein HBx mediated the spatial regulation of HBV cccDNA transcription by 19p13.11 enhancer. Thus, These findings indicate that YY1 and HBx mediate the recruitment of HBV cccDNA minichromosomes to 19p13.11 region for transcription activation, and YY1 may present as a novel therapeutic target against HBV infection.

Hepatitis B virus cccDNA: Formation, regulation and therapeutic potential

Hepatitis B virus (HBV) infection remains a major public health concern worldwide with about 257 million individuals chronically infected. Current therapies can effectively control HBV replication and slow down disease progress, but cannot cure HBV infection. Upon infection, HBV establishes a pool of covalently closed circular DNA (cccDNA) in the nucleus of infected hepatocytes. The cccDNA exists as a minichromosome and resists to antivirals, thus a therapeutic eradication of cccDNA from the infected cells remains unattainable. In this review, we summarize the state of knowledge on the mechanisms underlying cccDNA formation and regulation, and discuss the possible strategies that may contribute to the eradication of HBV through targeting cccDNA.

Host Transcription Factors in Hepatitis B Virus RNA Synthesis

The hepatitis B virus (HBV) chronically infects over 250 million people worldwide and is one of the leading causes of liver cancer and hepatocellular carcinoma. HBV persistence is due in part to the highly stable HBV minichromosome or HBV covalently closed circular DNA (cccDNA) that resides in the nucleus. As HBV replication requires the help of host transcription factors to replicate, focusing on host protein–HBV genome interactions may reveal insights into new drug targets against cccDNA. The structural details on such complexes, however, remain poorly defined. In this review, the current literature regarding host transcription factors’ interactions with HBV cccDNA is discussed.

Development of Direct-acting Antiviral and Host-targeting Agents for Treatment of Hepatitis B Virus Infection

Hepatitis B virus (HBV) infection affects approximately 300 million people worldwide. Although antiviral therapies have improved the long-term outcomes, patients often require life-long treatment and there is no cure for HBV infection. New technologies can help us learn more about the pathogenesis of HBV infection and develop therapeutic agents to reduce its burden. We review recent advances in development of direct-acting antiviral and host-targeting agents, some of which have entered clinical trials. We also discuss strategies for unbiased high-throughput screens to identify compounds that inhibit HBV and for repurposing existing drugs.

YY1-dependent transcriptional regulation of the human GDAP1 gene

Charcot-Marie-Tooth disease (CMT) is a heritable neurodegenerative condition, some types of which (notably CMT4A) are caused by mutations in the GDAP1 gene that encodes a protein of unknown molecular function implicated in regulation of mitochondrial fission. Here we present for the first time a functional analysis of the GDAP1 gene promoter which we found to be transcriptionally regulated by YY1, a broadly studied factor that seems to be involved in regulating many of the same cellular phenomena as GDAP1. We show that GDAP1 is broadly expressed in cancer cell lines of different tissue origin, contrasting with the restricted neuronal distribution reported by some authors. There is a consensus YY1 binding site in the GDAP1 core promoter which we show to be functional in both in vitro binding assays and in living cells. Overexpression of YY1 activated the GDAP1 promoter in a reporter gene system as well as increased the level of endogenous mRNA. RNAi-mediated knockdown of YY1 in HEK293 cells led to decreased GDAP1 expression. While YY1 is known to exert both positive and negative regulatory influences on nuclear-encoded mitochondrial proteins, as well as on neurodegeneration-related genes, in all cell lines we studied (including neuroblastoma) the effect of YY1 on GDAP1 expression is activatory. This leads to interesting conclusions about the possible clinical role of this interaction and suggests a broader regulatory network.

The gene encoding the major viral structural protein stimulates recombination in polyomavirus DNA

RmI is a chimeric DNA molecule consisting of a polyoma genome in which a partly duplicated VP1-coding region brackets an insert of murine DNA (Ins); when transfected into mouse cells, RmI recombines intramolecularly to yield infectious, unit-length, polyoma DNA. We report here that RmI encodes a polypeptide of 337 amino acids (designated VmP1) which includes the N-terminal 328 amino acids of VP1 and 9 amino acids specified by Ins. Mutating the VmP1-coding sequence strongly reduces the ability of RmI to yield polyoma DNA. In contrast, mutating the portion of the VP1-coding sequence which is not part of the VmP1-coding sequence has little or no impact on the ability of RmI to yield polyoma DNA, even though it renders such DNA noninfectious. Thus, release of polyoma DNA from RmI involves a function of VP1 distinct from that ensuring virus assembly and propagation; since VP1 can arise only after recombination has occurred, VmP1, but not VP1, could carry such a function. We suggest that VmP1 acts in concert with VP2, which we have already reported to stimulate recombination in RmI.