Duck Hepatitis B Virus: An Invaluable Model System for HBV Infection
Introduction
Hepatitis B virus (HBV) is the causative agent of acute and chronic hepatitis B in humans. More than 350 million people worldwide are chronic virus carriers and face a significantly increased risk of developing liver cirrhosis and primary hepatocellular carcinoma (Blumberg, 1997). Effective prophylactic vaccines based on noninfectious empty envelopes (termed S particles or subviral particles), originally purified from the plasma of carriers and later produced in recombinant form in yeast or mammalian cell lines, have been available since the 1980s; for a comprehensive review on clinical aspects, including various vaccines, see Hollinger and Liang (2001). Nonetheless, for many developing countries, large-scale vaccination programs were hardly affordable. This situation is improving, but an enormous number of chronic HBV carriers will be in need of better medication for decades to come. Current therapies are based on the systemic administration of high doses of interferon-α (IFN-α) or, more recently, on nucleoside analogs, such as 3-thiacytidine (lamivudine) and adefovir. However, both therapies have a sustained response rate of only about 30%, combinations exert no clear synergism, and lamivudine therapy leads to the rapid emergence of resistant virus variants (Pumpens 2002, Zoulim 2001).
A full understanding of the molecular biology of HBV and its infectious cycle is hampered by experimental limitations: as of yet there is no feasible small animal infection model, and only a few aspects of its replication cycle are amenable to biochemical methods. The focus of this review is on one of two established animal virus models, namely duck hepatitis B virus (DHBV). Although humans and ducks are only distantly related hosts, HBV and DHBV, which are the type members of the orthohepadnaviruses and avihepadnaviruses (hepatotropic DNA viruses), share fundamental common features. In fact, many of the principles of hepadnavirus replication have been established using DHBV. Its major advantages are the ready availability of ducks, allowing experimental infections with wild-type and mutant viruses in vivo as well as in cultured primary hepatocytes, and the recent development of in vitro systems to study biochemically the intricate mechanism of hepadnaviral replication. Thus, unlike other hepadnaviruses DHBV offers the full range of experimental approaches, from the test tube to animal studies, to investigate fundamental as well as selected medical aspects of hepadnavirus biology.
The emphasis here is on the value of DHBV as a model for HBV, but the differences between the human and the duck viruses should not be neglected. DHBV can cause acute and chronic infections but is at variance with HBV and mammalian viruses in several aspects: (i) DHBV does not appear to be pathogenic for its host; (ii) DHBV probably lacks a regulatory protein comparable to the mammalian virus HBx gene product, a promiscuous transactivator that, by acting on the host cell, appears to be essential for establishment of infection and has been implicated in carcinogenesis; and (iii) a host-cell encoded glycoprotein, carboxypeptidase D (CPD), appears to be critical for DHBV infection, yet no evidence supports a similar role for its human homologue. This chapter will address these differences as well as peculiarities concerning the structure and function of individual viral proteins. Additional information on DHBV can be found in several recent reviews describing the general features of hepadnavirus biology (Ganem 2001, Nassal 1999, Nassal 2000, Seeger 2000) and describing DHBV-specific immunological aspects (Jilbert and Kotlarski, 2000).
Section snippets
Animal Models of HBV
Two salient features of hepadnaviruses are their pronounced liver tropism and their narrow host range. In general, therefore, the closer the hosts are related, the closer the respective viruses are related. Overall, however, the mammalian orthohepadnaviruses and the avian avihepadnaviruses share a very similar genome organization and replication characteristics (Section III); hence, numerous aspects of one type of hepadnavirus are also applicable to the other types.
The Hepadnaviral Infectious Cycle: An Overview
All hepadnaviruses are DNA viruses (i.e., infectious virions contain DNA). Summers and Mason were the first to demonstrate, using DHBV, that this DNA is generated by reverse transcription (Summers and Mason, 1982). Hence, hepadnaviruses are related to retroviruses although the latter, based on the genome form present in infectious virions, are RNA viruses. Retroviral RNA is reverse transcribed upon infection of a new cell (i.e., as an early event of the cycle), whereas in hepadnaviruses,
DHBV Proteins and Their Basic Functions in Replication and Morphogenesis
All hepadnaviruses produce three types of particles (reviewed in Nassal, 1996): complete enveloped virions (diameter about 42 nm); nucleocapsids which, in vivo, are found only intracellularly (core particles; diameter about 30 to 34 nm in cryo-electron micrographs but only about 27 nm upon negative staining); and empty envelopes (S particles, or subviral particles, SVPs) that are secreted in vast excess over virions. Orthohepadnaviruses produce two morphologically distinct forms: 22-nm diameter
In Vitro Infection of Primary Duck Hepatocytes
The in vitro experimental infection of primary duck hepatocytes (Tuttleman et al., 1986b) provided, for the first time, a manageable system for the study of the hepadnaviral infectious cycle. The system has been instrumental in the description of all the key steps of replication and has enabled the identification and characterization of the attachment receptor for virion internalization. This being said, it is not a system without limitations and inefficiencies. These largely stem from two
Cytokines and Their Role in Controlling Hepadnaviral Infection
During infection with hepatitis B or C viruses, cytotoxic T lymphocytes (CTL) are thought to contribute to both liver cell injury and virus clearance (reviewed in Bertoletti 2000, Rehermann 2000). It is generally accepted that clearance of intracellular pathogens requires the destruction of infected cells by major histocompatibility complex (MHC) class I-restricted CD8+ CTLs that kill their target cells via Perforin- or Fas-dependent mechanisms (Chisari and Ferrari, 1995). It has also been
DHBV and the Development of Hepadnaviral Transduction Vectors
It has been previously reported that hepatitis B virus (HBV) replication and gene expression are inhibited by the hepatic induction of certain proinflammatory cytokines (reviewed in Guidotti and Chisari, 1999). This implied that expression of cytokines in the liver of chronically HBV-infected patients might be of therapeutic value. The application of gene therapy, however, requires an appropriate gene-delivery system that allows for selectively targeting the liver and efficiently infecting
Conclusions and Perspectives
Despite substantial progress in the development of surrogate infection systems for HBV and a few other orthohepdnaviruses, none comes anywhere close to the experimental opportunities offered by DHBV. As outlined in this chapter, the unique potential of the DHBV system has, in the past, allowed the prototypical derivation of many mechanistic principles underlying hepadnaviral infection on the genetic level. At present, the DHBV system remains the only system allowing for a true biochemical
Acknowledgements
The authors thank many of their colleagues for providing unpublished data. They acknowledge support of their own research by grants from the Deutsche Forschungsgemeinschaft (DFG), the German Bundesministerium für Bildung and Forschung (BMBF), the Fonds der Chemischen Industrie (FCI), the Landesstiftung Baden-Württemberg, the National Health and Medical Research Council grant (ID 111710), and the research fund of the Burnet Institute.
References (275)
- et al.
Experimental confirmation of a hepatitis B virus (HBV) epsilon-like bulge-and-loop structure in avian HBV RNA encapsidation signals
Virology
(1997) - et al.
Efficient Hsp90-independent in vitro activation by Hsc70 and Hsp40 of duck hepatitis B virus reverse transcriptase, an assumed Hsp90 client protein
J. Biol. Chem
(2003) - et al.
Different cytokine profiles of intraphepatic T cells in chronic hepatitis B and hepatitis C virus infections
Gastroenterology
(1997) - et al.
Protection or damage: A dual role for the virus-specific cytotoxic T lymphocyte response in hepatitis B and C infection?
Curr. Opin. Microbiol
(2000) - et al.
Endothelial cell-mediated uptake of a hepatitis B virus: A new concept of liver targeting of hepatotropic microorganisms
Hepatology
(2001) - et al.
Transcripts and the putative RNA pregenome of duck hepatitis B virus: Implications for reverse transcription
Cell
(1985) - et al.
Mutation preventing formation of hepatitis B e antigen in patients with chronic hepatitis B infection
Lancet
(1989) - et al.
A new avian hepadnavirus infecting snow geese (Anser caerulescens) produces a significant fraction of virions containing single-stranded DNA
Virology
(1999) - et al.
Human T cell leukemia virus type 1 Tax associates with a molecular chaperone complex containing hTid-1 and Hsp70
Curr. Biol
(2001) - et al.
Epitope-specific antibody response to the surface antigen of duck hepatitis B virus in infected ducks
Virology
(1990)
Woodchuck hepatocytes remain permissive for hepadnavirus infection and mouse liver repopulation after cryopreservation
Hepatology
Repopulation of mouse liver with human hepatocytes and in vivo infection with hepatitis B virus
Hepatology
Virus-like particles in serum of patients with Australia-antigen-associated hepatitis
Lancet
IL-18: A TH1-inducing, proinflammatory cytokine and new member of the IL-1 family
J. Allergy Clin. Immunol
gp180, a protein that binds duck hepatitis B virus particles, has metallocarboxypeptidase D-like enzymatic activity
J. Biol. Chem
Minor envelope proteins of duck hepatitis B virus are initiated at internal pre-S AUG codons but are not essential for infectivity
Virology
Stable association of hsp90 and p23, but Not hsp70, with active human telomerase
J. Biol. Chem
Structure of hepatitis B surface antigen. Characterization of the lipid components and their association with the viral proteins
J. Biol. Chem
Intracellular inactivation of the hepatitis B virus by cytotoxic T lymphocytes
Immunity
Structural and functional homology between duck and chicken interferon-gamma
Dev. Comp. Immunol
Characterization of age- and dose-related outcomes of duck hepatitis B virus infection
Virology
Virus-liver cell interactions in duck hepatitis B virus infection. A study of virus dissemination within the liver
Gastroenterology
Adding the third dimension to virus life cycles: Three-dimensional reconstruction of icosahedral viruses from cryo-electron micrographs
Microbiol. Mol. Biol. Rev
Does a cdc2 kinase-like recognition motif on the core protein of hepadnaviruses regulate assembly and disintegration of capsids?
J. Virol
The P gene product of hepatitis B virus is required as a structural component for genomic RNA encapsidation
J. Virol
Sequence- and structure-specific determinants in the interaction between the RNA encapsidation signal and reverse transcriptase of avian hepatitis B viruses
J. Virol
Formation of a functional hepatitis B virus replication initiation complex involves a major structural alteration in the RNA template
Mol. Cell. Biol
Reconstitution of a functional duck hepatitis B virus replication initiation complex from separate reverse transcriptase domains expressed in Escherichia coli
J. Virol
Hepatitis B virus nucleocapsid assembly: Primary structure requirements in the core protein
J. Virol
Hepatitis B virus the vaccine, and the control of primary cancer of the liver
Proc. Natl. Acad. Sci. USA
Transcytosis of infectious human immunodeficiency virus across a tight human epithelial cell line barrier
Nat. Med
Determination of the fold of the core protein of hepatitis B virus by electron cryomicroscopy
Nature
Calcium signaling by HBx protein in hepatitis B virus DNA replication
Science
Cellular receptor traffic is essential for productive duck hepatitis B virus infection
J. Virol
Carboxypeptidase D (gp180), a Golgi-resident protein, functions in the attachment and entry of avian hepatitis B viruses
J. Virol
Enhancement of hepatitis B virus infection by noninfectious subviral particles
J. Virol
Mutational analysis of hepatitis B surface antigen particle assembly and secretion
J. Virol
Post-translational alterations in transmembrane topology of the hepatitis B virus large envelope protein
EMBO J
Mapping a region of the large envelope protein required for hepatitis B virion maturation
J. Virol
Functions of the internal pre-S domain of the large surface protein in hepatitis B virus particle morphogenesis
J. Virol
Two regions of an avian hepadnavirus RNA pregenome are required in cis for encapsidation
J. Virol
Interleukin-12 inhibits hepatitis B virus replication in transgenic mice
J. Virol
Inhibition of hepatitis B virus replication during adenovirus and cytomegalovirus infections in transgenic mice
J. Virol
Effects of insertional and point mutations on the functions of the duck hepatitis B virus polymerase
J. Virol
Duck hepatitis B virus expresses a regulatory HBx-like protein from a hidden open reading frame
J. Virol
Selected mutations of the duck hepatitis B virus P gene RNase H domain affect both RNA packaging and priming of minus-strand DNA synthesis
J. Virol
Epitope mapping of neutralizing monoclonal antibodies against duck hepatitis B virus
J. Virol
Hepatitis B virus transgenic mice: Models of viral immunobiology and pathogenesis
Curr. Top. Microbiol. Immunol
Hepatitis B virus immunopathogenesis
Annu. Rev. Immunol
A short N-proximal region in the large envelope protein harbors a determinant that contributes to the species specificity of human hepatitis B virus
J. Virol
Cited by (78)
iPSCs for modeling hepatotropic pathogen infections
2021, iPSCs for Studying Infectious DiseasesThe Pekin duck programmed death ligand-2: cDNA cloning, genomic structure, molecular characterization and expression analysis
2018, Biochemistry and Biophysics ReportsCitation Excerpt :However, induction of duPD-L2 expression by LPS was only observed in adherent PBMC suggesting a TLR-mediated up-regulation of PD-L2 mRNA expression in duck PBMC enriched for monocytes/macrophages. In contrast mitogen activation of freshly isolated duck PBMC that constitute mainly lymphocytes [18] did not induce duPD-L2 expression (data not shown). In future studies it will be of interest to study duPD-L2 expression in response to other TLR-ligands and viral infections.
Hepatocarcinogenesis associated with hepatitis B, delta and C viruses
2016, Current Opinion in Virology