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Rolling circle amplification, a powerful tool for genetic and functional studies of complete hepatitis B virus genomes from low-level infections and for directly probing covalently closed circular DNA. Antimicrob Agents Chemother 2008; 52:3068-73. [PMID: 18606836 DOI: 10.1128/aac.01318-07] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Complete characterization of the biological properties of hepatitis B virus (HBV) variants requires the generation of full-length genomes. The aim of this study was to develop new tools for the efficient full-length genome amplification of virus from samples with low viral loads. Rolling circle amplification (RCA) was used to amplify full-length HBV genomes from both sera and liver biopsy samples from chronic HBV carriers. Serum-derived relaxed circular HBV DNA could be amplified only after completion and ligation of plus-strand DNA. Covalently closed circular DNA (cccDNA) from liver biopsies could be amplified directly from as few as 13 copies, using RCA, followed by a full-length HBV PCR. Three serial liver biopsy samples were obtained from a lamivudine-resistant patient who cleared detectable serum HBV after adefovir dipivoxil was added to the lamivudine therapy and then seroconverted to anti-HBs. Only the genomes from the last biopsy specimen obtained after the emergence of lamivudine resistance contained the lamivudine resistance-associated mutations rtL180M and rtM204V ("rt" indicates reverse transcriptase domain). Defective genomes were also found in this biopsy sample. Genomes cloned from the liver biopsy specimens were transfected into HuH7 cells to study their replication competence and their susceptibility to lamivudine. RCA is a powerful tool for amplifying full-length HBV genomes and will be especially useful for the study of occult or inactive HBV infections and patients undergoing antiviral treatment. It can also be used to probe HBV cccDNA, the crucial intermediate in viral persistence and the archive of resistance mutations.
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2
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Gao W, Hu J. Formation of hepatitis B virus covalently closed circular DNA: removal of genome-linked protein. J Virol 2007; 81:6164-74. [PMID: 17409153 PMCID: PMC1900077 DOI: 10.1128/jvi.02721-06] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Hepatitis B virus (HBV) contains a small, partially double-stranded, relaxed circular (RC) DNA genome. RC DNA needs to be converted to covalently closed circular (CCC) DNA, which serves as the template for all viral RNA transcription. As a first step toward understanding how CCC DNA is formed, we analyzed the viral and host factors that may be involved in CCC DNA formation, using transient and stable DNA transfections of HBV and the related avian hepadnavirus, duck hepatitis B virus (DHBV). Our results show that HBV CCC DNA formed in hepatoma cells was derived predominantly from RC DNA with a precise junction sequence. In contrast to that of DHBV, HBV CCC DNA formation in cultured cells was accompanied by the accumulation of a RC DNA species from which the covalently attached viral reverse transcriptase (RT) protein was removed (protein-free or PF-RC DNA). Furthermore, whereas envelope deficiency led to increased CCC DNA formation in DHBV, it resulted mainly in increased PF-RC, but not CCC, DNA in HBV, suggesting that the envelope protein(s) may negatively regulate a step in CCC DNA formation that precedes deproteination in both HBV and DHBV. Interestingly, PF-RC DNA, in contrast to RT-linked RC DNA, contained, almost exclusively, mature plus-strand DNA, suggesting that the RT protein was removed preferentially from mature RC DNA.
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Affiliation(s)
- Weifan Gao
- Department of Microbiology and Immunology-H107, The Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA
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3
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Basagoudanavar SH, Perlman DH, Hu J. Regulation of hepadnavirus reverse transcription by dynamic nucleocapsid phosphorylation. J Virol 2006; 81:1641-9. [PMID: 17135319 PMCID: PMC1797568 DOI: 10.1128/jvi.01671-06] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Reverse transcription, an essential step in the life cycle of all retroelements, is a complex, multistep process whose regulation is not yet clearly understood. We have recently shown that reverse transcription in the pararetrovirus duck hepatitis B virus is associated with complete dephosphorylation of the viral core protein, which forms the nucleocapsid wherein reverse transcription takes place. Here we present a genetic study of the role of this dynamic nucleocapsid phosphorylation in regulating viral reverse transcription. Detailed analyses of the reverse transcription products synthesized within nucleocapsids composed of core phosphorylation site mutants revealed that alanine substitutions, mimicking the nonphosphorylated state, completely blocked reverse transcription at a very early stage. In contrast, aspartate substitutions, mimicking the phosphorylated state, allowed complete first-strand DNA synthesis but were severely defective in accumulating mature double-stranded DNA. The latter defect was due to a combination of mutant nucleocapsid instability during maturation and a block in mature second-strand DNA synthesis. Thus, the reversible phosphorylation of the nucleocapsids regulates the ordered progression of reverse transcription.
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Affiliation(s)
- Suresh H Basagoudanavar
- Department of Microbiology and Immunology-H107, The Penn State University College of Medicine, 500 University Dr., Hershey, PA 17033, USA
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4
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Faure E. Multiple sclerosis and hepatitis B vaccination: Could minute contamination of the vaccine by partial Hepatitis B virus polymerase play a role through molecular mimicry? Med Hypotheses 2005; 65:509-20. [PMID: 15908138 DOI: 10.1016/j.mehy.2005.02.044] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Accepted: 02/17/2005] [Indexed: 11/20/2022]
Abstract
Reports of multiple sclerosis developing after hepatitis B vaccination have led to the concern that this vaccine might be a cause of multiple sclerosis in previously healthy subjects. Some articles evidenced that minor Hepatitis B virus (HBV) polymerase proteins could be produced by alternative transcriptional or translational strategies. Their detection is very difficult because they are in minute concentration and probably enzymatically inactive, however, it was shown that they could be exposed on the outside of the virus particles and also be immunogenic. In addition, HBV polymerase shares significant amino acid similarities with the human myelin basic protein. We hypothesise that some of the apparent adverse reactions to the vaccine could be due to a process called of molecular mimicry, the HBV polymerase, which could be a contaminant in the recombinant or plasma-derived vaccines, could act as autoantigens and induce autoimmune demyelinating diseases such as multiple sclerosis.
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Affiliation(s)
- E Faure
- E.R. Biodiversity and Environment, case 5, University of Provence, Place Victor Hugo, 13331 Marseilles cedex 3, France.
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5
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Chen SY, Kao CF, Chen CM, Shih CM, Hsu MJ, Chao CH, Wang SH, You LR, Lee YHW. Mechanisms for inhibition of hepatitis B virus gene expression and replication by hepatitis C virus core protein. J Biol Chem 2003; 278:591-607. [PMID: 12401801 DOI: 10.1074/jbc.m204241200] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
We have demonstrated previously that the core protein of hepatitis C virus (HCV) exhibits suppression activity on gene expression and replication of hepatitis B virus (HBV). Here we further elucidated the suppression mechanism of HCV core protein. We demonstrated that HCV core protein retained the inhibitory effect on HBV gene expression and replication when expressed as part of the full length of HCV polyprotein. Based on the substitution mutational analysis, our results suggested that mutation introduced into the bipartite nuclear localization signal of the HCV core protein resulted in the cytoplasmic localization of core protein but did not affect its suppression ability on HBV gene expression. Mutational studies also indicated that almost all dibasic residue mutations within the N-terminal 101-amino acid segment of the HCV core protein (except Arg(39)-Arg(40)) impaired the suppression activity on HBV replication but not HBV gene expression. The integrity of Arg residues at positions 101, 113, 114, and 115 was found to be essential for both suppressive effects, whereas the Arg residue at position 104 was important only in the suppression of HBV gene expression. Moreover, our results indicated that the suppression on HBV gene expression was mediated through the direct interaction of HCV core protein with the trans-activator HBx protein, whereas the suppression of HBV replication involved the complex formation between HBV polymerase (pol) and the HCV core protein, resulting in the structural incompetence for the HBV pol to bind the package signal and consequently abolished the formation of the HBV virion. Altogether, this study suggests that these two suppression effects on HBV elicited by the HCV core protein likely depend on different structural context but not on nuclear localization of the core protein, and the two effects can be decoupled as revealed by its differential targets (HBx or HBV pol) on these two processes of the HBV life cycle.
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Affiliation(s)
- Shiow-Yi Chen
- Institute of Biochemistry and Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan 112, Republic of China
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6
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Abstract
The cellular chaperone Hsp90 has been shown to associate with the reverse transcriptase (RT) of the duck hepatitis B virus and is required for RT functions. However, the molecular basis for the specific interaction between the RT and Hsp90 remains unknown. Comparison of protein compositional properties suggests that the RT is highly related to the protein kinase c-Raf, which interacts with Hsp90 via the cochaperone p50 (CDC37). We tested whether the RT, like c-Raf, is specifically recognized by p50. Immunoprecipitation and pull-down assays showed that p50 or p50deltaC, a p50 mutant defective in Hsp90 binding, could interact specifically with the RT both in vitro and in vivo, indicating that p50 can bind the RT independently of Hsp90. Furthermore, purified p50 and p50deltaC interacted directly with purified RT. The importance of p50-RT interaction for RT functions was underscored by 1) inhibition of protein-primed initiation of reverse transcription by p50deltaC in vitro and 2) stimulation of viral DNA replication and RNA packaging by p50 and their inhibition by p50deltaC in transfected cells. These results suggest that p50 can function as a cellular cofactor for the hepadnavirus RT by mediating the interaction between the RT and Hsp90.
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Affiliation(s)
- Xingtai Wang
- Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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7
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Barrasa MI, Guo JT, Saputelli J, Mason WS, Seeger C. Does a cdc2 kinase-like recognition motif on the core protein of hepadnaviruses regulate assembly and disintegration of capsids? J Virol 2001; 75:2024-8. [PMID: 11160705 PMCID: PMC115152 DOI: 10.1128/jvi.75.4.2024-2028.2001] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hepadnaviruses are enveloped viruses, each with a DNA genome packaged in an icosahedral nucleocapsid, which is the site of viral DNA synthesis. In the presence of envelope proteins, DNA-containing nucleocapsids are assembled into virions and secreted, but in the absence of these proteins, nucleocapsids deliver viral DNA into the cell nucleus. Presumably, this step is identical to the delivery of viral DNA during the initiation of an infection. Unfortunately, the mechanisms triggering the disintegration of subviral core particles and delivery of viral DNA into the nucleus are not yet understood. We now report the identification of a sequence motif resembling a serine- or threonine-proline kinase recognition site in the core protein at a location that is required for the assembly of core polypeptides into capsids. Using duck hepatitis B virus, we demonstrated that mutations at this sequence motif can have profound consequences for RNA packaging, DNA replication, and core protein stability. Furthermore, we found a mutant with a conditional phenotype that depended on the cell type used for virus replication. Our results support the hypothesis predicting that this motif plays a role in assembly and disassembly of viral capsids.
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Affiliation(s)
- M I Barrasa
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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8
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Zoulim F, Trépo C. Drug therapy for chronic hepatitis B: antiviral efficacy and influence of hepatitis B virus polymerase mutations on the outcome of therapy. J Hepatol 1998; 29:151-68. [PMID: 9696505 DOI: 10.1016/s0168-8278(98)80191-8] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- F Zoulim
- Inserm Unit 271, Hôtel Dieu Hospital, Lyon, France.
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9
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Seifer M, Hamatake R, Bifano M, Standring DN. Generation of replication-competent hepatitis B virus nucleocapsids in insect cells. J Virol 1998; 72:2765-76. [PMID: 9525596 PMCID: PMC109721 DOI: 10.1128/jvi.72.4.2765-2776.1998] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The double-stranded DNA genome of human hepatitis B virus (HBV) and related hepadnaviruses is reverse transcribed from a pregenomic RNA by a viral polymerase (Pol) harboring both priming and RNA- and DNA-dependent elongation activities. Although hepadnavirus replication occurs inside viral nucleocapsids, or cores, biochemical systems for analyzing this reaction are currently limited to unencapsidated Pols expressed in heterologous systems. Here, we describe cis and trans classes of replicative HBV cores, produced in the recombinant baculovirus system via coexpression of HBV core and Pol proteins from either a single RNA (i.e., in cis) or two distinct RNAs (in trans). Upon isolation from insect cells, cis and trans cores contained Pol-linked HBV minus-strand DNA with 5' ends mapping to the authentic elongation origin DR1 and also plus-strand DNA species. Only trans cores, however, were highly active for the de novo priming and reverse transcription of authentic HBV minus strands in in vitro endogenous polymerase assays. This reaction strictly required HBV Pol but not the epsilon stem-loop element, although the presence of one epsilon, or better, two epsilons, enhanced minus-strand synthesis up to 10-fold. Compared to unencapsidated Pol enzymes, encapsidated Pol appeared to be (i) highly processive, able to extend minus-strand DNAs of 400 nucleotides from DR1 in vitro, and (ii) more active for HBV plus-strand synthesis. These observations suggest possible contributions to the replication process from the HBV core protein. These novel core reagents should facilitate the analysis of HBV replication in its natural environment, the interior of the capsid, and also fuel the development of new anti-HBV drug screens.
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Affiliation(s)
- M Seifer
- Pharmaceutical Research Institute, Bristol-Myers Squibb, Wallingford, Connecticut 06492, USA
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10
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Lanford RE, Notvall L, Lee H, Beames B. Transcomplementation of nucleotide priming and reverse transcription between independently expressed TP and RT domains of the hepatitis B virus reverse transcriptase. J Virol 1997; 71:2996-3004. [PMID: 9060659 PMCID: PMC191428 DOI: 10.1128/jvi.71.4.2996-3004.1997] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Hepadnavirus polymerases initiate reverse transcription in a protein-primed reaction that involves the covalent linkage of the first deoxyribonucleotide to the polymerase polypeptide. We recently expressed human hepatitis B virus (HBV) reverse transcriptase (pol) in insect cells by using the recombinant baculovirus system. The purified protein is active in nucleotide priming and reverse transcription reactions. In this report, we demonstrate that the tyrosine residue at amino acid number 63 within the TP (terminal protein) domain of the polymerase is the site of covalent linkage of the first nucleotide of minus-strand DNA. Analysis of pol polypeptides with mutations in the TP and RT (reverse transcriptase) domains indicated that both domains were required for in vitro nucleotide priming activity. Polymerase proteins with mutations in the TP and RT domains were not capable of complementing each other in the nucleotide priming reaction, suggesting that transcomplementation between full-length polypeptides was not possible. However, when the TP and RT domains were expressed as separate polypeptides, they formed a highly stable complex that was active in nucleotide priming and reverse transcription. The presence of an epsilon stem-loop dramatically increased the nucleotide priming activity in transcomplementation assays, even though full-length pol displayed similar activities in the absence and presence of epsilon. These data raise the possibility that in the transcomplementation assay, epsilon may play a role in the formation of a functional complex between TP and RT, rather than being required only as the template for nucleotide priming. The results indicate that using the baculovirus system, it is possible to dissect the protein-protein and protein-RNA interactions required for HBV genome replication.
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Affiliation(s)
- R E Lanford
- Department of Virology and Immunology, Southwest Foundation for Biomedical Research, San Antonio, Texas 78227, USA.
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11
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Hu J, Seeger C. Hsp90 is required for the activity of a hepatitis B virus reverse transcriptase. Proc Natl Acad Sci U S A 1996; 93:1060-4. [PMID: 8577714 PMCID: PMC40030 DOI: 10.1073/pnas.93.3.1060] [Citation(s) in RCA: 268] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The heat shock protein Hsp90 is known as an essential component of several signal transduction pathways and has now been identified as an essential host factor for hepatitis B virus replication. Hsp90 interacts with the viral reverse transcriptase to facilitate the formation of a ribonucleoprotein (RNP) complex between the polymerase and an RNA ligand. This RNP complex is required early in replication for viral assembly and initiation of DNA synthesis through a protein-priming mechanism. These results thus invoke a role for the Hsp90 pathway in the formation of an RNP.
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Affiliation(s)
- J Hu
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
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12
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Fallows DA, Goff SP. Hepadnaviruses: current models of RNA encapsidation and reverse transcription. Adv Virus Res 1996; 46:165-94. [PMID: 8824700 DOI: 10.1016/s0065-3527(08)60072-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- D A Fallows
- Howard Hughes Medical Institute, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA
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13
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Liu C, Mason WS, Burch JB. Identification of factor-binding sites in the duck hepatitis B virus enhancer and in vivo effects of enhancer mutations. J Virol 1994; 68:2286-96. [PMID: 8139013 PMCID: PMC236704 DOI: 10.1128/jvi.68.4.2286-2296.1994] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Hepatitis B viruses (hepadnaviruses) can cause chronic, productive infections of hepatocytes. Analyses of the enhancers and promoters of these viruses in cell lines have suggested a requirement of these elements for liver-enriched transcription factors. In this study, a minimum of seven factor-binding sites on the duck hepatitis B virus enhancer were detected by DNase I footprinting using duck liver nuclear extracts. Among the sites that were tentatively identified were one C/EBP-, one HNF1-, and two HNF3-binding sites. Mutations of the HNF1- and HNF3-like sites, which eliminated factor binding, as assessed by both DNase I footprinting and competitive gel shift assays, were evaluated for their effects on enhancer activity. Using a construct in which human growth hormone was expressed from the viral enhancer and core gene promoter, we found that all of the mutations, either alone or in combination, reduced expression two- to fourfold in LMH chicken hepatoma cells. The mutations in the HNF1 site and one of the HNF3 sites, when inserted into the intact viral genome, also suppressed virus RNA synthesis in primary hepatocyte cultures. Virus carrying the latter HNF3 mutation was also examined for its ability to infect and replicate in ducks. No significant inhibition of virus replication was observed in a short-term assay; however, virus with the HNF3 mutation was apparently unable to grow in the pancreas, a second site of duck hepatitis B virus replication in the duck.
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Affiliation(s)
- C Liu
- Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111
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14
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Mason WS, Cullen J, Saputelli J, Wu TT, Liu C, London WT, Lustbader E, Schaffer P, O'Connell AP, Fourel I, Aldrich CE, Jilbert AR. Characterization of the antiviral effects of 2' carbodeoxyguanosine in ducks chronically infected with duck hepatitis B virus. Hepatology 1994. [PMID: 8294097 DOI: 10.1002/hep.1840190219] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
This study was carried out to evaluate benefits and limitations of long-term therapy of hepatitis B virus infections with a nucleoside analog inhibitor of virus replication. The model we used was the domestic duck chronically infected with duck hepatitis B virus by in ovo infection. 2' Carbodeoxyguanosine was used as an inhibitor of viral DNA synthesis. In all animals examined there was a reduction in virus production during therapy. A dose of 2' carbodeoxyguanosine of 10 micrograms/kg every other day reduced the number of infected hepatocytes from greater than 95% to 25% to 50% in less than 3 mo, whereas a 10-fold higher dose produced a decline to less than 10%. Histological evaluation revealed mild to moderate liver injury in ducks receiving the higher dose of 2' carbodeoxyguanosine, suggesting that disappearance of infected hepatocytes may have been accelerated by a toxic effect of the drug. Drug treatment did not completely eliminate duck hepatitis B virus from any duck, and replication was restored in all hepatocytes within a few weeks to several months after antiviral therapy was terminated. Our results suggest that elimination of a chronic infection with a single inhibitor of replication may be difficult in a host that lacks an antiviral immune response capable of eliminating at least a portion of the infected hepatocytes and of ultimately producing antibodies capable of neutralizing residual virus.
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Affiliation(s)
- W S Mason
- Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111
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15
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Oberhaus SM, Newbold JE. Detection of DNA polymerase activities associated with purified duck hepatitis B virus core particles by using an activity gel assay. J Virol 1993; 67:6558-66. [PMID: 8411359 PMCID: PMC238093 DOI: 10.1128/jvi.67.11.6558-6566.1993] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Replication of hepadnaviruses involves reverse transcription of an intermediate RNA molecule. It is generally accepted that this replication scheme is carried out by a virally encoded, multifunctional polymerase which has DNA-dependent DNA polymerase, reverse transcriptase, and RNase H activities. Biochemical studies of the polymerase protein(s) have been limited by the inability to purify useful quantities of functional enzyme from virus particles and, until recently, to express enzymatically active polymerase proteins in heterologous systems. An activity gel assay which detects in situ catalytic activities of DNA polymerases after electrophoresis in partially denaturing polyacrylamide gels was used by M.R. Bavand and O. Laub (J. Virol. 62:626-628, 1988) to show the presence of DNA- and RNA-dependent DNA polymerase activities associated with hepatitis B virus particles produced in vitro. This assay has provided the only means by which hepadnavirus polymerase proteins have been detected in association with enzymatic activities. Since conventional methods have not allowed purification of useful quantities of enzymatically active polymerase protein(s), we have devised a protocol for purifying large quantities of duck hepatitis B virus (DHBV) core particles to near homogeneity. These immature virus particles contain DNA- and RNA-dependent DNA polymerase activities, as shown in the endogenous DNA polymerase assay. We have used the activity gel assay to detect multiple DNA- and RNA-dependent DNA polymerase proteins associated with these purified DHBV core particles. These enzymatically active proteins appear larger than, approximately the same size as, and smaller than an unmodified DHBV polymerase protein predicted from the polymerase open reading frame. This is the first report of the detection of active hepadnavirus core-associated DNA polymerase proteins derived from a natural host.
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Affiliation(s)
- S M Oberhaus
- Department of Microbiology and Immunology, School of Medicine, University of North Carolina at Chapel Hill 27599
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16
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Abstract
Reverse transcription of all retroviruses and most retroid elements requires tRNA as a primer for DNA synthesis. However, in hepatitis B viruses the viral polymerase itself acts as a primer for reverse transcription (G.-H. Wang and C. Seeger, Cell 71:663-670, 1992). We have now demonstrated that in order to prime DNA synthesis, the polymerase binds to an RNA hairpin, which then serves as a template for the formation of a short DNA primer that is covalently linked to protein. Following its synthesis, the nascent DNA strand apparently dissociates from its template and reanneals with complementary sequences at the 3' end of the RNA genome, where DNA synthesis continues. Since this RNA hairpin also functions as a packaging signal for viral RNA, hepadnaviruses have adopted a replication strategy that relies on the same signal for two biochemically distinct events, RNA packaging and reverse transcription. This mechanism is without precedent among all known retroid elements and among other viruses and bacteriophages that use protein as a primer for RNA or DNA synthesis. It could provide an effective target for antiviral therapy, which is required for the treatment of more than 300 million carriers of hepatitis B virus.
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Affiliation(s)
- G H Wang
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111
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17
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Moraleda G, Wu TT, Jilbert AR, Aldrich CE, Condreay LD, Larsen SH, Tang JC, Colacino JM, Mason WS. Inhibition of duck hepatitis B virus replication by hypericin. Antiviral Res 1993; 20:235-47. [PMID: 8470884 DOI: 10.1016/0166-3542(93)90023-c] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Hypericin was found to be active against a member of the hepatitis B virus family, duck hepatitis B virus (DHBV). After a single 1 h incubation with hypericin, cells stably-transfected with a clone of DHBV stopped producing infectious virus for several days, though virus-like particles continued to be released into the culture medium. Characterization of these virions revealed a buoyant density characteristic of infectious virus preparations and lower than that of virus cores, suggesting that the particles were enveloped. Western blot analysis suggested, however, that the viral preS protein in surface antigen particles and, by inference, in virions, was present in covalently cross-linked aggregates. Evidence of a similar level of aggregation of the core subunit of virion nucleocapsids was not found, nor was there evidence of a similar high level of aggregation of cell-associated core and preS proteins. Hypericin was only slightly virucidal against DHBV and culture medium from treated cultures did not block initiation of infection when added to DHBV susceptible cultures prior to a challenge with infectious DHBV. Thus, the primary antiviral activity of hypericin against DHBV replication appears to be exerted at a late step in viral morphogenesis.
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Affiliation(s)
- G Moraleda
- Fox Chase Cancer Center, Philadelphia, PA 19111
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18
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Wang GH, Seeger C. The reverse transcriptase of hepatitis B virus acts as a protein primer for viral DNA synthesis. Cell 1992; 71:663-70. [PMID: 1384989 DOI: 10.1016/0092-8674(92)90599-8] [Citation(s) in RCA: 300] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Hepatitis B viruses (hepadnaviruses) replicate their DNA genomes by reverse transcription of an RNA intermediate. Efforts to examine the biochemical mechanism for viral DNA synthesis have been hampered by the failure to solubilize the reverse transcriptase from virions and to express the polymerase in heterologous systems in an enzymatically active form. Here, we demonstrate that the polymerase of a hepadnavirus synthesized in an in vitro translation reaction exhibits reverse transcriptase activity. Furthermore, our results show that the polymerase acts as a primer for DNA synthesis and remains covalently linked to nascent DNA, a feature that is not known to exist in any other RNA-directed DNA polymerases. Priming of DNA synthesis requires viral RNA but occurs independently of other viral components. The ability to express the hepadnavirus reverse transcriptase in an enzymatically active form will allow detailed biochemical and functional analyses of this complex enzyme, and may facilitate the identification of inhibitors required for antiviral therapy.
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Affiliation(s)
- G H Wang
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111
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19
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Hantz O, Baginski I, Fourel I, Chemin I, Trepo C. Viral spliced RNA are produced, encapsidated and reverse transcribed during in vivo woodchuck hepatitis virus infection. Virology 1992; 190:193-200. [PMID: 1382340 DOI: 10.1016/0042-6822(92)91205-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
By the use of reverse transcription followed by polymerase chain reaction (RT-PCR), we have identified one shorter than full-length, pregenomic viral RNA species in liver samples of woodchucks chronically infected with the woodchuck hepatitis virus (WHV). The spliced WHV RNA of about 2.4 kb in length was cloned and partially sequenced. The splicing donor and acceptor sites of this novel RNA are located, respectively, 130 nucleotides downstream of the ATG initiation codon of the core gene and 21 nucleotides upstream of the initiation codon of the pre-S2 surface gene. The splicing event generates a new core-polymerase fusion protein and removes the terminal protein domain and the spacer region of the polymerase gene. A nucleotide probe specific for the splice junction was used following RT-PCR, to further confirm the existence of this spliced RNA in the liver of seven WHV-infected woodchucks. Deleted viral DNA molecules corresponding to the 2.4 kb spliced RNA were also detected in the liver and, to a lesser extent, in the serum of infected woodchucks, suggesting that this spliced RNA can be encapsidated and reverse-transcribed during the course of natural WHV infection.
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Abstract
We describe experiments demonstrating that after transfection into permissive cells, the RNA pregenome of an avian hepadnavirus, the duck hepatitis B virus, is infectious. Using a Sindbis virus expression vector, we showed that cytoplasmic synthesis of the pregenome resulted in hepadnaviral DNA synthesis. Moreover, complete infectious virus was produced from cells transfected with hepadnaviral pregenomic RNA. We conclude that the pregenome of hepadnaviruses can express all the proteins required for DNA synthesis as well as serve as a template for reverse transcription and that DNA resulting from pregenome expression can be utilized to establish a productive infection in pregenome-transfected cells.
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Affiliation(s)
- M J Huang
- Department of Cell Biology, University of New Mexico School of Medicine, Albuquerque 87131
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