Dataset Information

Association of Hepatitis B Virus Covalently Closed Circular DNA and Human APOBEC3B in Hepatitis B Virus-Related Hepatocellular Carcinoma.

ABSTRACT: Chronic Hepatitis B Virus (HBV) infections can progresses to liver cirrhosis and hepatocellular carcinoma (HCC). The HBV covalently-closed circular DNA cccDNA is a key to HBV persistence, and its degradation can be induced by the cellular deaminase APOBEC3. This study aimed to measure the distribution of intrahepatic cccDNA levels and evaluate the association between levels of cccDNA and APOBEC3 in HCC patients. Among 49 HCC patients, 35 matched cancerous and contiguous noncancerous liver tissues had detectable cccDNA, and the median intrahepatic cccDNA in the cancerous tissues (CT) was significantly lower than in the contiguous noncancerous tissues (CNCT) (p = 0.0033). RCA (rolling circle amplification), followed by 3D-PCR identified positive amplification in 27 matched HCC patients. Sequence analysis indicated G to A mutations accumulated to higher levels in CT samples compared to CNCT samples, and the dinucleotide context showed preferred editing in the GpA context. Among 7 APOBEC3 genes, APOBEC3B was the only one up-regulated in cancerous tissues both at the transcriptional and protein levels (p < 0.05). This implies APOBEC3B may contribute to cccDNA editing and subsequent degradation in cancerous tissues.

SUBMITTER: Luo X

PROVIDER: S-EPMC4911053 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Publications

Association of Hepatitis B Virus Covalently Closed Circular DNA and Human APOBEC3B in Hepatitis B Virus-Related Hepatocellular Carcinoma.

Luo Xuan X Huang Yao Y Chen Yanmeng Y Tu Zeng Z Hu Jieli J Tavis John E JE Huang Ailong A Hu Yuan Y

PloS one 20160616 6

Chronic Hepatitis B Virus (HBV) infections can progresses to liver cirrhosis and hepatocellular carcinoma (HCC). The HBV covalently-closed circular DNA cccDNA is a key to HBV persistence, and its degradation can be induced by the cellular deaminase APOBEC3. This study aimed to measure the distribution of intrahepatic cccDNA levels and evaluate the association between levels of cccDNA and APOBEC3 in HCC patients. Among 49 HCC patients, 35 matched cancerous and contiguous noncancerous liver tissue ...[more]

PMID: 27310677

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Project description:Background & aimsHBV has a narrow host restriction, with humans and chimpanzees representing the only known natural hosts. The molecular correlates of resistance in species that are commonly used in biomedical research, such as mice, are currently incompletely understood. Expression of human NTCP (hNTCP) in mouse hepatocytes enables HBV entry, but subsequently covalently closed circular (cccDNA) does not form in most murine cells. It is unknown if this blockade in cccDNA formation is due to deficiency in repair of relaxed circular DNA (rcDNA) to cccDNA.MethodsHere, we deployed both in vivo and in vitro virological and biochemical approaches to investigate if murine cells contain a complete set of repair factors capable of converting HBV rcDNA to cccDNA.ResultsWe demonstrate that HBV cccDNA does form in murine cell culture or in mice when recombinant rcDNA without a protein adduct is directly introduced into cells. We further show that the murine orthologues of core components in DNA lagging strand synthesis, required for the repair of rcDNA to cccDNA in human cells, can support this crucial step in the HBV life cycle. It is worth noting that recombinant HBV rcDNA substrates, either without a protein adduct or containing neutravidin to mimic HBV polymerase, were used in our study; it remains unclear if the HBV polymerase removal processes are the same in mouse and human cells.ConclusionsCollectively, our data suggest that the HBV life cycle is blocked post entry and likely before the repair stage in mouse cells, which yields critical insights that will aid in the construction of a mouse model with inbred susceptibility to HBV infection.Lay summaryHepatitis B virus (HBV) is only known to infect humans and chimpanzees in nature. Mouse models are often used in modeling disease pathogenesis and preclinical research to assess the efficacy and safety of interventions before they are then tested in human participants. However, because mice are not susceptible to HBV infection it is difficult to accurately model human infection (and test potential treatments) in mouse models. Herein, we have shown that mice are able to perform a key step in the HBV life cycle, tightening the net around the possible reason why HBV can not efficiently infect and replicate in mice.

Project description:The covalently closed circular (CCC) DNA of hepatitis B virus (HBV) functions as the only viral transcriptional template capable of producing all viral RNA species and is essential to initiate and sustain viral replication. CCC DNA is converted from a relaxed circular (RC) DNA, in which neither of the two DNA strands is covalently closed. As RC DNA mimics damaged cellular DNA, the host cell DNA damage repair (DDR) system is thought to be responsible for HBV CCC DNA formation. The potential role of two major cellular DDR pathways, the ataxia telangiectasia mutated (ATM) pathway and the ATM and Rad3-related (ATR) pathway, in HBV CCC DNA formation was thus investigated. Inhibition, or expression knockdown, of ATR and its downstream signaling factor CHK1, but not of ATM, decreased CCC DNA formation during de novo HBV infection, as well as intracellular CCC DNA amplification, when RC DNA from extracellular virions and intracellular nucleocapsids, respectively, is converted to CCC DNA. Furthermore, a novel RC DNA processing product with 5' truncated minus strands was detected when the ATR-CHK1 pathway was inhibited, further indicating that this pathway controls RC DNA processing during its conversion to CCC DNA. These results provide new insights into how host cells recognize and process HBV RC DNA in order to produce CCC DNA and have implications for potential means to block CCC DNA production.IMPORTANCE Hepatitis B virus (HBV) chronically infects hundreds of millions of people and remains a major cause of viral hepatitis, cirrhosis, and liver cancer. HBV persistence is sustained by a viral nuclear episome that directs all viral gene expression needed to support viral replication. The episome is converted from an incomplete DNA precursor in viral particles in an ill-understood process. We report here that the incomplete DNA precursor is recognized by the host cell in a way similar to the sensing of damaged cellular DNA for subsequent repair to form the nuclear episome. Intense efforts are ongoing to develop novel antiviral strategies to eliminate CCC DNA so as to cure chronic HBV infection. Our results here provide novel insights into, and suggest novel ways of perturbing, the process of episome formation. Furthermore, our results inform mechanisms of cellular DNA damage recognition and repair, processes essential for normal cell growth.

Project description:It remains crucial to develop a laboratory model for studying hepatitis B virus (HBV) chronic infection. We hereby produced a recombinant covalently closed circular DNA (rcccDNA) in view of the key role of cccDNA in HBV persistence. A loxP-chimeric intron was engineered into a monomeric HBV genome in a precursor plasmid (prcccDNA), which was excised using Cre/loxP-mediated DNA recombination into a 3.3-kb rcccDNA in the nuclei of hepatocytes. The chimeric intron was spliced from RNA transcripts without interrupting the HBV life cycle. In cultured hepatoma cells, cotransfection of prcccDNA and pCMV-Cre (encoding Cre recombinase) resulted in accumulation of nuclear rcccDNA that was heat stable and epigenetically organized as a minichromosome. A mouse model of HBV infection was developed by hydrodynamic injection of prcccDNA. In the presence of Cre recombinase, rcccDNA was induced in the mouse liver with effective viral replication and expression, triggering a compromised T-cell response against HBV. Significant T-cell hyporesponsiveness occurred in mice receiving 4 μg prcccDNA, resulting in prolonged HBV antigenemia for up to 9 weeks. Persistent liver injury was observed as elevated alanine transaminase activity in serum and sustained inflammatory infiltration in the liver. Although a T-cell dysfunction was induced similarly, mice injected with a plasmid containing a linear HBV replicon showed rapid viral clearance within 2 weeks. Collectively, our study provides an innovative approach for producing a cccDNA surrogate that established HBV persistence in immunocompetent mice. It also represents a useful model system in vitro and in vivo for evaluating antiviral treatments against HBV cccDNA. Importance: (i) Unlike plasmids that contain a linear HBV replicon, rcccDNA established HBV persistence with sustained liver injury in immunocompetent mice. This method could be a prototype for developing a mouse model of chronic HBV infection. (ii) An exogenous intron was engineered into the HBV genome for functionally seamless DNA recombination. This original approach could be also extended to other viral studies. (iii) rcccDNA was substantially induced in the nuclei of hepatocytes and could be easily distinguished by its exogenous intron using PCR. This convenient model system affords the opportunity to test antivirals directly targeting HBV cccDNA.

Project description:Hepatitis B virus (HBV) infection is a major health burden worldwide, and currently there is no cure. The persistence of HBV covalently closed circular DNA (cccDNA) is the major obstacle for antiviral trement. HBV core protein (HBc) has emerged as a promising antiviral target, as it plays important roles in critical steps of the viral life cycle. However, whether HBc could regulate HBV cccDNA transcription remains under debate. In this study, different approaches were used to address this question. In synthesized HBV cccDNA and HBVcircle transfection assays, lack of HBc showed no effect on transcription of HBV RNA as well as HBV surface antigen (HBsAg) production in a hepatoma cell line and primary human hepatocytes. Reconstitution of HBc did not alter the expression of cccDNA-derived HBV markers. Similar results were obtained from an in vivo mouse model harboring cccDNA. Chromatin immunoprecipitation (ChIP) or ChIP sequencing assays revealed transcription regulation of HBc-deficient cccDNA chromatin similar to that of wild-type cccDNA. Furthermore, treatment with capsid assembly modulators (CAMs) dramatically reduced extracellular HBV DNA but could not alter viral RNA and HBsAg. Our results demonstrate that HBc neither affects histone modifications and transcription factor binding of cccDNA nor directly influences cccDNA transcription. Although CAMs could reduce HBc binding to cccDNA, they do not suppress cccDNA transcriptional activity. Thus, therapeutics targeting capsid or HBc should not be expected to sufficiently reduce cccDNA transcription. IMPORTANCE Hepatitis B virus (HBV) core protein (HBc) has emerged as a promising antiviral target. However, whether HBc can regulate HBV covalently closed circular DNA (cccDNA) transcription remains elusive. This study illustrated that HBc has no effect on epigenetic regulation of cccDNA, and it does not participate in cccDNA transcription. Given that HBc is dispensable for cccDNA transcription, novel cccDNA-targeting therapeutics are needed for an HBV cure.

Dataset Information

Association of Hepatitis B Virus Covalently Closed Circular DNA and Human APOBEC3B in Hepatitis B Virus-Related Hepatocellular Carcinoma.

Publications

Association of Hepatitis B Virus Covalently Closed Circular DNA and Human APOBEC3B in Hepatitis B Virus-Related Hepatocellular Carcinoma.

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