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Elpek GO. Molecular pathways in viral hepatitis-associated liver carcinogenesis: An update. World J Clin Cases 2021; 9:4890-4917. [PMID: 34307543 PMCID: PMC8283590 DOI: 10.12998/wjcc.v9.i19.4890] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2021] [Revised: 03/14/2021] [Accepted: 05/26/2021] [Indexed: 02/06/2023] Open
Abstract
Hepatocellular carcinoma (HCC) is the most common type of cancer among primary malignant tumors of the liver and is a consequential cause of cancer-related deaths worldwide. In recent years, uncovering the molecular mechanisms involved in the development and behavior of this tumor has led to the identification of multiple potential treatment targets. Despite the vast amount of data on this topic, HCC remains a challenging tumor to treat due to its aggressive behavior and complex molecular profile. Therefore, the number of studies aiming to elucidate the mechanisms involved in both carcinogenesis and tumor progression in HCC continues to increase. In this context, the close association of HCC with viral hepatitis has led to numerous studies focusing on the direct or indirect involvement of viruses in the mechanisms contributing to tumor development and behavior. In line with these efforts, this review was undertaken to highlight the current understanding of the molecular mechanisms by which hepatitis B virus (HBV) and hepatitis C virus (HCV) participate in oncogenesis and tumor progression in HCC and summarize new findings. Cumulative evidence indicates that HBV DNA integration promotes genomic instability, resulting in the overexpression of genes related to cancer development, metastasis, and angiogenesis or inactivation of tumor suppressor genes. In addition, genetic variations in HBV itself, especially preS2 deletions, may play a role in malignant transformation. Epigenetic dysregulation caused by both viruses might also contribute to tumor formation and metastasis by modifying the methylation of DNA and histones or altering the expression of microRNAs. Similarly, viral proteins of both HBV and HCV can affect pathways that are important anticancer targets. The effects of these two viruses on the Hippo-Yap-Taz pathway in HCC development and behavior need to be investigated. Additional, comprehensive studies are also needed to determine these viruses' interaction with integrins, farnesoid X, and the apelin system in malignant transformation and tumor progression. Although the relationship of persistent inflammation caused by HBV and HCV hepatitis with carcinogenesis is well defined, further studies are warranted to decipher the relationship among inflammasomes and viruses in carcinogenesis and elucidate the role of virus-microbiota interactions in HCC development and progression.
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Affiliation(s)
- Gulsum Ozlem Elpek
- Department of Pathology, Akdeniz University Medical School, Antalya 07070, Turkey
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2
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Abstract
Hepatitis B virus (HBV) is a major cause of hepatocellular carcinoma (HCC). There are approximately 250 million people in the world that are chronically infected by this virus, resulting in nearly 1 million deaths every year. Many of these patients die from severe liver diseases, including HCC. HBV may induce HCC through the induction of chronic liver inflammation, which can cause oxidative stress and DNA damage. However, many studies also indicated that HBV could induce HCC via the alteration of hepatocellular physiology that may involve genetic and epigenetic changes of the host DNA, the alteration of cellular signaling pathways, and the inhibition of DNA repair mechanisms. This alteration of cellular physiology can lead to the accumulation of DNA damages and the promotion of cell cycles and predispose hepatocytes to oncogenic transformation.
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Affiliation(s)
- Jiyoung Lee
- Department of Molecular Microbiology and Immunology, University of Southern California Keck School of Medicine, 2011 Zonal Avenue, HMR-401, Los Angeles, CA, 90033, USA
| | - Kuen-Nan Tsai
- Department of Molecular Microbiology and Immunology, University of Southern California Keck School of Medicine, 2011 Zonal Avenue, HMR-401, Los Angeles, CA, 90033, USA
| | - Jing-Hsiung James Ou
- Department of Molecular Microbiology and Immunology, University of Southern California Keck School of Medicine, 2011 Zonal Avenue, HMR-401, Los Angeles, CA, 90033, USA.
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3
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A Cell-Free Assembly System for Generating Infectious Human Papillomavirus 16 Capsids Implicates a Size Discrimination Mechanism for Preferential Viral Genome Packaging. J Virol 2015; 90:1096-107. [PMID: 26559838 DOI: 10.1128/jvi.02497-15] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 11/03/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED We have established a cell-free in vitro system to study human papillomavirus type 16 (HPV16) assembly, a poorly understood process. L1/L2 capsomers, obtained from the disassembly of virus-like particles (VLPs), were incubated with nuclear extracts to provide access to the range of cellular proteins that would be available during assembly within the host cell. Incorporation of a reporter plasmid "pseudogenome" was dependent on the presence of both nuclear extract and ATP. Unexpectedly, L1/L2 VLPs that were not disassembled prior to incubation with a reassembly mixture containing nuclear extract also encapsidated a reporter plasmid. As with HPV pseudoviruses (PsV) generated intracellularly, infection by cell-free particles assembled in vitro required the presence of L2 and was susceptible to the same biochemical inhibitors, implying the cell-free assembled particles use the infectious pathway previously described for HPV16 produced in cell culture. Using biochemical and electron microscopy analyses, we observed that, in the presence of nuclear extract, intact VLPs partially disassemble, providing a mechanistic explanation to how the exogenous plasmid was packaged by these particles. Further, we provide evidence that capsids containing an <8-kb pseudogenome are resistant to the disassembly/reassembly reaction. Our results suggest a novel size discrimination mechanism for papillomavirus genome packaging in which particles undergo iterative rounds of disassembly/reassembly, seemingly sampling DNA until a suitably sized DNA is encountered, resulting in the formation of a stable virion structure. IMPORTANCE Little is known about papillomavirus assembly biology due to the difficulties in propagating virus in vitro. The cell-free assembly method established in this paper reveals a new mechanism for viral genome packaging and will provide a tractable system for further dissecting papillomavirus assembly. The knowledge gained will increase our understanding of virus-host interactions, help to identify new targets for antiviral therapy, and allow for the development of new gene delivery systems based on in vitro-generated papillomavirus vectors.
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Zlotnick A, Venkatakrishnan B, Tan Z, Lewellyn E, Turner W, Francis S. Core protein: A pleiotropic keystone in the HBV lifecycle. Antiviral Res 2015; 121:82-93. [PMID: 26129969 DOI: 10.1016/j.antiviral.2015.06.020] [Citation(s) in RCA: 179] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Revised: 06/22/2015] [Accepted: 06/26/2015] [Indexed: 12/21/2022]
Abstract
Hepatitis B Virus (HBV) is a small virus whose genome has only four open reading frames. We argue that the simplicity of the virion correlates with a complexity of functions for viral proteins. We focus on the HBV core protein (Cp), a small (183 residue) protein that self-assembles to form the viral capsid. However, its functions are a little more complicated than that. In an infected cell Cp modulates almost every step of the viral lifecycle. Cp is bound to nuclear viral DNA and affects its epigenetics. Cp correlates with RNA specificity. Cp assembles specifically on a reverse transcriptase-viral RNA complex or, apparently, nothing at all. Indeed Cp has been one of the model systems for investigation of virus self-assembly. Cp participates in regulation of reverse transcription. Cp signals completion of reverse transcription to support virus secretion. Cp carries both nuclear localization signals and HBV surface antigen (HBsAg) binding sites; both of these functions appear to be regulated by contents of the capsid. Cp can be targeted by antivirals - while self-assembly is the most accessible of Cp activities, we argue that it makes sense to engage the broader spectrum of Cp function. This article forms part of a symposium in Antiviral Research on "From the discovery of the Australia antigen to the development of new curative therapies for hepatitis B: an unfinished story."
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Affiliation(s)
- Adam Zlotnick
- Molecular & Cellular Biology, Indiana University, Bloomington, IN, United States.
| | | | - Zhenning Tan
- Assembly BioSciences, Bloomington, IN, United States; Assembly BioSciences, San Francisco, CA, United States
| | - Eric Lewellyn
- Assembly BioSciences, Bloomington, IN, United States; Assembly BioSciences, San Francisco, CA, United States
| | - William Turner
- Assembly BioSciences, Bloomington, IN, United States; Assembly BioSciences, San Francisco, CA, United States
| | - Samson Francis
- Molecular & Cellular Biology, Indiana University, Bloomington, IN, United States; Assembly BioSciences, Bloomington, IN, United States; Assembly BioSciences, San Francisco, CA, United States
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5
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Serine phosphoacceptor sites within the core protein of hepatitis B virus contribute to genome replication pleiotropically. PLoS One 2011; 6:e17202. [PMID: 21358805 PMCID: PMC3039676 DOI: 10.1371/journal.pone.0017202] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Accepted: 01/25/2011] [Indexed: 01/29/2023] Open
Abstract
The core protein of hepatitis B virus can be phosphorylated at serines 155, 162, and 170. The contribution of these serine residues to DNA synthesis was investigated. Core protein mutants were generated in which each serine was replaced with either alanine or aspartate. Aspartates can mimic constitutively phosphorylated serines while alanines can mimic constitutively dephosphorylated serines. The ability of these mutants to carry out each step of DNA synthesis was determined. Alanine substitutions decreased the efficiency of minus-strand DNA elongation, primer translocation, circularization, and plus-strand DNA elongation. Aspartate substitutions also reduced the efficiency of these steps, but the magnitude of the reduction was less. Our findings suggest that phosphorylated serines are required for multiple steps during DNA synthesis. It has been proposed that generation of mature DNA requires serine dephosphorylation. Our results suggest that completion of rcDNA synthesis requires phosphorylated serines.
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The arginine clusters of the carboxy-terminal domain of the core protein of hepatitis B virus make pleiotropic contributions to genome replication. J Virol 2010; 85:1298-309. [PMID: 21084467 DOI: 10.1128/jvi.01957-10] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The carboxy-terminal domain (CTD) of the core protein of hepatitis B virus is not necessary for capsid assembly. However, the CTD does contribute to encapsidation of pregenomic RNA (pgRNA). The contribution of the CTD to DNA synthesis is less clear. This is the case because some mutations within the CTD increase the proportion of spliced RNA to pgRNA that are encapsidated and reverse transcribed. The CTD contains four clusters of consecutive arginine residues. The contributions of the individual arginine clusters to genome replication are unknown. We analyzed core protein variants in which the individual arginine clusters were substituted with either alanine or lysine residues. We developed assays to analyze these variants at specific steps throughout genome replication. We used a replication template that was not spliced in order to study the replication of only pgRNA. We found that alanine substitutions caused defects at both early and late steps in genome replication. Lysine substitutions also caused defects, but primarily during later steps. These findings demonstrate that the CTD contributes to DNA synthesis pleiotropically and that preserving the charge within the CTD is not sufficient to preserve function.
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Feld J, Locarnini S. Antiviral therapy for hepatitis B virus infections: new targets and technical challenges. J Clin Virol 2002; 25:267-83. [PMID: 12423691 DOI: 10.1016/s1386-6532(02)00107-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
There are presently only two licensed therapies for treating liver disease caused by infection with the hepatitis B virus (HBV). These are interferon-alpha and lamivudine. Neither agent was specifically developed as an antiviral compound for treating patients infected with HBV. Both therapies are limited in the clinic by a low response rate and in the case of lamivudine, selection of drug-resistant mutants, whilst troublesome side effects limit the use of interferon-alpha. Several promising nucleoside/nucleotide analogues are undergoing clinical trials, including adefovir dipivoxil and entecavir, both of which appear to be active against lamivudine- resistant HBV. In addition to these nucleoside/nucleotide analogues, it will be important to develop new agents with different modes of action, which can be added to the antiviral cocktails that will be required to adequately suppress and hopefully eliminate HBV replication.
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Affiliation(s)
- Jordan Feld
- Research and Molecular Development, Victorian Infectious Diseases Reference Laboratory, 10 Wreckyn Street, 3051 North Melbourne, Victoria, Australia
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8
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François G, Kew M, Van Damme P, Mphahlele MJ, Meheus A. Mutant hepatitis B viruses: a matter of academic interest only or a problem with far-reaching implications? Vaccine 2001; 19:3799-815. [PMID: 11427251 DOI: 10.1016/s0264-410x(01)00108-6] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- G François
- WHO Collaborating Centre for Prevention and Control of Viral Hepatitis, Department of Epidemiology and Social Medicine, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, Belgium.
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9
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Ho TC, Jeng KS, Hu CP, Chang C. Effects of genomic length on translocation of hepatitis B virus polymerase-linked oligomer. J Virol 2000; 74:9010-8. [PMID: 10982345 PMCID: PMC102097 DOI: 10.1128/jvi.74.19.9010-9018.2000] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Accurate translocation of the polymerase-linked oligomer to the acceptor site (DR1*) in reverse transcription is crucial for maintaining the correct size of the hepatitis B virus (HBV) genome. Various sizes of foreign sequences were inserted at different sites of the HBV genome, and their effects on accurate translocation of polymerase-linked oligomer to DR1* were tested. Three types of replicate DNA products were observed in these insertion mutants: RC (relaxed circle) and type I and type II DL (duplex linear) DNA. Our results indicated that the minus strand of RC and type I DL form was elongated from DR1*, while the minus strand of the type II DL form was elongated from multiple internal acceptor sites (IAS), such as IAS2. These IASs were also found to be used by wild-type HBV but with a very low frequency. Mutation of IAS2 by base substitution abrogated polymerase-linked oligomer transferring to IAS2, demonstrating that base pairing also plays an important role in the function of IAS2 as a polymerase-linked oligomer acceptor site. Data obtained from our insertion mutants also demonstrate that the distance between the polymerase-linked oligomer priming site and the acceptor is important. The polymerase-linked oligomer prefers to translocate to an acceptor, DR1* or IAS2, which are ca. 3.2 kb apart. However, it will translocate to both DR1* and IAS2 if they are not located 3.2 kb apart. These results suggest that the polymerase-linked oligomer may be able to scan bidirectionally for appropriate acceptor sites at a distance of 3.2 kb. A model is proposed to discuss the possible mechanism of polymerase-linked oligomer translocation.
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Affiliation(s)
- T C Ho
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University
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10
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Jeong JK, Yoon GS, Ryu WS. Evidence that the 5'-end cap structure is essential for encapsidation of hepatitis B virus pregenomic RNA. J Virol 2000; 74:5502-8. [PMID: 10823855 PMCID: PMC112035 DOI: 10.1128/jvi.74.12.5502-5508.2000] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Hepatitis B virus (HBV) replicates by reverse transcription of an RNA intermediate, the pregenomic RNA. The first step of HBV genome replication is the encapsidation of the pregenomic RNA encoding the encapsidation signal, termed epsilon, into the core particles, which is preceded by recognition and binding of HBV DNA polymerase to epsilon. The pregenomic RNA contains two identical epsilon elements due to its terminal redundancy: one near the 5' end and another near the 3' end. Despite the fact that both epsilon elements have an identical sequence, only the 5' epsilon, but not the 3' epsilon, is functional for encapsidation. To understand the molecular nature of this position effect, we made a series of lacZ RNA expression plasmids which contain the epsilon element at various positions from the 5' end of the transcripts. Following transfection, the lacZ RNAs in cytoplasmic core particles were measured by RNase protection assay for encapsidation. The results indicated that the lacZ RNAs with epsilon positioned up to 65 nucleotides from the 5' end were encapsidated, whereas the lacZ RNAs with epsilon positioned further downstream were not. Interestingly, the cap-free lacZ RNA transcribed by T7 RNA polymerase was not encapsidated, implying that the 5' cap structure is required for encapsidation of the pregenomic RNA. We hypothesized that HBV DNA polymerase must somehow recognize the cap structure and/or its associated factors, as well as the 5' epsilon, for encapsidation to occur.
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Affiliation(s)
- J K Jeong
- Department of Biochemistry and Institute of Bioscience and Biotechnology, Yonsei University, Seoul, Korea 120-749
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11
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Hui EKW, Chen KL, Lo SJ. Hepatitis B virus maturation is affected by the incorporation of core proteins having a C-terminal substitution of arginine or lysine stretches. J Gen Virol 1999; 80 ( Pt 10):2661-2671. [PMID: 10573159 DOI: 10.1099/0022-1317-80-10-2661] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Assembly of replication-competent hepadnavirus nucleocapsids requires interaction of core protein, polymerase and encapsidation signal (epsilon) with viral pregenomic RNA. The N-terminal portion (aa 1-149) of the core protein is able to self-assemble into nucleocapsids, whereas the C-terminal portion (aa 150-183) is known to interact with pregenomic RNA. In this study, two hepatitis B virus (HBV) core mutants (C144Arg and C144Lys) in which the C-terminal SPRRR (Ser-Pro-Arg-Arg-Arg) motif was replaced by a stretch of arginine or lysine residues were generated to test their role in pregenome encapsidation and virus maturation. Mutant or wild-type core-expression plasmids were co-transfected with a core-negative plasmid into human hepatoma HuH-7 cells to compare trans-complementation efficiency for virus replication. Both low- and high-density capsids were present in -the cytoplasm and culture medium of HuH-7 cells in all transfections. Nucleocapsids formed by C144Arg and C144Lys, however, lost the endogenous polymerase activity to repair HBV DNA. Furthermore, in co-transfection of pHBVC144Arg or pHBVC144Lys with a plasmid which produces replication-competent nucleocapsids, the HBV DNA repairing signal was reduced 40- to 80-fold. This is probably due to formation of mosaic particles of wild-type and mutant cores. Results indicated that the SPRRR motif at the core protein C terminus is important for HBV DNA replication and maturation. Additionally, triple-plasmid transfection experiments showed that nucleocapsids containing various amounts of C144Arg and wild-type core proteins exhibited a bias in selecting a shorter pregenome for encapsidation and DNA replication. It is therefore suggested that unknown factors are also involved in HBV pregenome packaging.
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Affiliation(s)
- Eric Ka-Wai Hui
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1
| | - Kun-Lin Chen
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1
| | - Szecheng J Lo
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1
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12
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Hanafusa T, Yumoto Y, Hada H, Shinji T, Koide N, Tsuji T. Replication of hepatitis B virus which carries foreign DNA in vitro. Biochem Biophys Res Commun 1999; 262:530-3. [PMID: 10462508 DOI: 10.1006/bbrc.1999.1224] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Targeting a specific DNA sequence to the desired tissues is an important step in gene therapy. The hepatitis B virus (HBV) is the only DNA virus that has hepatocyte specificity. We attempted to construct an HBV-based vector for targeting the liver. We observed the replication and secretion of virus particles in an HBV construct that lacks X gene and carries an extra 63 bp DNA fragment in vitro. Replication was observed in the cell line HuH-7 but not HepG2. From this construct, we designed an HBV-based vector that could carry foreign DNA. HBV based vectors provide for the possibilities of generating therapeutic agents for individual patients. Our host vector system may be used to clear out the HBV from the HBV carrier or chronic hepatitis B patients by introducing a genetically engineered HBV into these patients.
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Affiliation(s)
- T Hanafusa
- Isotope Center, Okayama University, Okayama, Japan
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13
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Abstract
The hepatitis B virus (HBV) and other members of the hepadnaviridae replicate by reverse transcription of an RNA intermediate, pregenomic RNA (pgRNA). pgRNA is also translated into core protein and polymerase (reverse transcriptase) protein. Before being reverse transcribed, pgRNA is sequestrated from the cytoplasm by being packaged, together with polymerase, into subviral particles composed of core protein. For pgRNA to be encapsidated, its 5' end is folded into a stem-loop structure, known as the encapsidation signal or epsilon (epsilon). This stable bipartite stem-loop structure contains a bulge and an apical loop. Besides encapsidation, epsilon is involved in the activation of polymerase, in template restriction and in the initiation of DNA synthesis by reverse transcription. HBV DNA encoding epsilon forms part of the template that is translated into the precore/core fusion protein that is in turn post-translationally modified to produce hepatitis B e antigen (HBeAg). The DNA encoding epsilon may be recombinogenic. Mutations within epsilon can affect its function and sequence conservation within epsilon in natural isolates is therefore high. epsilon could provide a practical target for antiviral therapy.
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Affiliation(s)
- A Kramvis
- Department of Medicine, University of the Witwatersrand, Johannesburg, South Africa
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14
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Liou J, Jeng K, Lin C, Hu C, Chang C. A novel regulator inhibits HBV gene expression. J Biomed Sci 1998; 5:343-54. [PMID: 9758908 DOI: 10.1007/bf02253444] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Affiliation(s)
- J Liou
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Shih-Pai, Taipei, Taiwan, ROC
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15
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Blum HE. Hepatitis viruses: genetic variants and clinical significance. INTERNATIONAL JOURNAL OF CLINICAL & LABORATORY RESEARCH 1998; 27:213-24. [PMID: 9506264 DOI: 10.1007/bf02912461] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Variants of hepatitis B, C, and delta virus have been identified in patients both with acute and chronic infections. In the hepatitis B virus genome, naturally occurring mutations have been found in all viral genes, most notably in the genes coding for the structural envelope and nucleocapsid proteins. In the hepatitis C virus genome, the regions coding for the structural envelope proteins E1 and E2, as well as the 3'-contiguous non-structural region NS1, were found to be hypervariable. Viral variants may be associated with a specific clinical course of the infection, e.g., acute, fulminant or chronic hepatitis. Specific mutations may reduce viral clearance by immune mechanisms ('vaccine escape' and 'immune escape'), response to antiviral therapy ('therapy escape'), as well as detection ('diagnosis escape'). The exact contribution, however, of specific mutations to the pathogenesis and natural course of hepatitis B, C, or delta virus infection, including hepatocellular carcinoma development, and the response to antiviral treatment remains to be established.
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Affiliation(s)
- H E Blum
- Department of Internal Medicine II, University of Freiburg, Germany
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16
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Yuan TT, Lin MH, Qiu SM, Shih C. Functional characterization of naturally occurring variants of human hepatitis B virus containing the core internal deletion mutation. J Virol 1998; 72:2168-76. [PMID: 9499073 PMCID: PMC109512 DOI: 10.1128/jvi.72.3.2168-2176.1998] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/1997] [Accepted: 11/12/1997] [Indexed: 02/06/2023] Open
Abstract
Naturally occurring variants of human hepatitis B virus (HBV) containing the core internal deletion (CID) mutation have been found frequently in HBV carriers worldwide. Despite numerous sequence analysis reports of CID variants in patients, in the past decade, CID variants have not been characterized functionally, and thus their biological significance to HBV infection remains unclear. We report here two different CID variants identified from two patients that are replication defective, most likely due to the absence of detectable core protein. In addition, we were unable to detect the presence of the precore protein and e antigen from CID variants. However, the production of polymerase appeared to be normal. The replication defect of the CID variants can be rescued in trans by complementation with wild-type core protein. The rescued CID variant particles, which utilize the wild-type core protein, presumably are enveloped properly since they can be secreted into the medium and band at a position similar to that of mature wild-type Dane particles, as determined by gradient centrifugation analysis. Our results also provide an explanation for the association of CID variants with helper or wild-type HBV in nature. The significance of CID variants in HBV infection and pathogenesis is discussed.
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Affiliation(s)
- T T Yuan
- Department of Pathology, Center for Tropical Diseases, University of Texas Medical Branch, Galveston 77555-0609, USA
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17
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Howe AY, Tyrrell DL. Duck hepatitis B virus polymerase acts as a suppressor of core protein translation. J Virol 1996; 70:5035-42. [PMID: 8764010 PMCID: PMC190457 DOI: 10.1128/jvi.70.8.5035-5042.1996] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Nucleocapsid assembly in hepadnavirus replication requires selective encapsidation of the pregenomic RNA template and the viral polymerase by the core proteins. It has been shown that an encapsidation signal located at the 5' end of the pregenomic RNA is responsible for its interaction with the polymerase. In the present study, we have shown that a region located at the 3' periphery of the core open reading frame may interact with the viral polymerase in duck hepatitis B virus. By using an in vitro rabbit reticulocyte lysate translation system, we found that interaction of the polymerase with this region resulted in selective suppression of core mRNA translation. Insertion of this putative inhibitory sequence into the CD4 gene also led to a selective inhibition of CD4 mRNA translation in the presence of polymerase. Specific inhibition of core protein synthesis was observed in a chicken hepatoma cell line (LMH) cotransfected with core and polymerase plasmid DNA.
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Affiliation(s)
- A Y Howe
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Canada
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18
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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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19
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Fallows DA, Goff SP. Mutations in the epsilon sequences of human hepatitis B virus affect both RNA encapsidation and reverse transcription. J Virol 1995; 69:3067-73. [PMID: 7707534 PMCID: PMC189007 DOI: 10.1128/jvi.69.5.3067-3073.1995] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Hepadnaviruses replicate by reverse transcription of an RNA intermediate within subviral core particles in the cytoplasm of infected hepatocytes. Recognition of the epsilon encapsidation signal located on the 5' end of the pregenomic RNA by the viral polymerase occurs early in core particle assembly. The epsilon sequences contain a set of nested inverted repeats which form a stable stem-loop structure shown to play a role in RNA packaging and recently implicated as the site of initiation of minus-strand DNA synthesis. We have introduced a variety of site-directed mutations into the epsilon sequences of human hepatitis B virus to study their effects on viral replication in transfected HuH7 cells. We have identified two classes of mutations: those which adversely affect packaging and those which package RNA but adversely affect DNA synthesis. Analysis of these mutants has allowed us to identify separate features of the epsilon cis-acting signal which function in the processes of RNA packaging and reverse transcription.
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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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Feitelson MA, Duan LX, Guo J, Horiike N, McIntyre G, Blumberg BS, Thomas HC, Carman W. Precore and X region mutants in hepatitis B virus infections among renal dialysis patients. J Viral Hepat 1995; 2:19-31. [PMID: 7493291 DOI: 10.1111/j.1365-2893.1995.tb00068.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Hepatitis B virus (HBV) variants containing mutations within the X and the precore regions of the viral genome were demonstrated by polymerase chain reaction (PCR) amplification and DNA sequencing in renal dialysis patients with different serological patterns of HBV infection. Among carriers, X region deletion mutants predominated in patients who lost hepatitis B e antigen (HBeAg), or developed anti-HBe, but not in persistently HBeAg-positive patients. The precore region remained wild type in all carriers whether or not they seroconverted from HBeAg to anti-HBe. The frequency of precore and X region mutants was greatest among non-carrier patients with viral antibodies as the only indication of infection and among patients with non-A, non-B hepatitis (NANBH), suggesting an inverse relationship between the presence of wild type HBV markers and the presence of HBV mutants. Furthermore, the detection of one but not the other mutation in many serum samples suggests that these mutations are independently selected for during infection. Finally, the absence of HBV DNA in 21 'uninfected' dialysis patients with normal transaminases and no viral serology, suggests that replication of these mutants is associated with hepatitis. These results have important implications for HBV screening and treatment, as well as for the pathogenesis of chronic infection.
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Affiliation(s)
- M A Feitelson
- Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA
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Pollack JR, Ganem D. Site-specific RNA binding by a hepatitis B virus reverse transcriptase initiates two distinct reactions: RNA packaging and DNA synthesis. J Virol 1994; 68:5579-87. [PMID: 7520092 PMCID: PMC236958 DOI: 10.1128/jvi.68.9.5579-5587.1994] [Citation(s) in RCA: 150] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Hepatitis B viruses encode a polymerase (P) protein with key roles in both reverse transcription and genomic RNA encapsidation. Genetic analysis of cis-acting signals required for viral replication implicates an RNA stem-loop structure in both RNA packaging and the initiation of reverse transcription, a process in which P protein also serves as the primer. We now show that duck hepatitis B virus (DHBV) polymerase binds specifically and with high affinity to this RNA stem-loop structure. Mutational analysis indicates that all mutations in the RNA target that inhibit the P protein-RNA interaction inhibit both in vivo RNA packaging and in vitro DNA priming to comparable extents. However, certain mutations in the loop region of the RNA have minimal impact on P protein-RNA binding but are nonetheless severely defective for packaging and DNA synthesis. Thus, P protein-RNA complex formation is necessary but not sufficient to initiate these activities. In addition, examination of RNA binding by truncated P proteins indicates that the C terminus of the polymerase, although required for RNA encapsidation in vivo, is dispensable for RNA binding and DNA priming.
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Affiliation(s)
- J R Pollack
- Department of Biochemistry and Biophysics, University of California Medical Center, San Francisco 94143-0502
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Abstract
Selective encapsidation of hepatitis B virus (HBV) genomic RNA within cytoplasmic core particles requires recognition of the cis-encapsidation signal, (termed epsilon) located at the 5' end of genomic RNA. By transfecting plasmids expressing chimeric RNAs bearing HBV sequences fused to lacZ, we have mapped the minimal region of epsilon to the 5' 94 nucleotides (nt) of genomic RNA. Enzymatic probing of the RNA secondary structure in this region (by using either in vitro transcripts or RNA extracted from HBV core particles) reveals a stem-loop structure containing a lower stem, a 6-nt bulge, an upper stem with a single unpaired U residue, and a 6-nt loop. The functional role of this structure in encapsidation was explored by examining the effects of mutations in epsilon on encapsidation of RNA in vivo. These studies reveal that (i) in the lower stem, base pairing but not specific primary sequence is required for function; (ii) there is no requirement for base pairing in the lower portion of the upper stem, but base pairing elsewhere in this stem contributes to packaging efficiency; (iii) the presence of the 6-nt bulge, but not its primary sequence, is important for function; and (iv) specific nucleotide sequences in the loop and in regions of the upper stem are critical for RNA encapsidation.
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Affiliation(s)
- J R Pollack
- Department of Biochemistry and Biophysics, University of California Medical Center, San Francisco 94143-0502
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