The hepatitis B virus (HBV) precore protein inhibits HBV replication in transgenic mice

Characterization of Intracellular Precore-Derived Proteins and Their Functions in Hepatitis B Virus-Infected Human Hepatocytes

Hepatitis B virus (HBV) precore protein is not essential for viral replication but is thought to facilitate chronic infection. In addition to the secreted precore products, including the hepatitis B e antigen (HBeAg) and PreC protein, intracellular precore-derived proteins in HBV-infected human hepatocytes remain poorly characterized, and their roles, if any, remain largely unknown. Here, we detected multiple precore derivatives, including the nonprocessed precursor p25 and the processing intermediate p22, in HBV-infected human hepatocytes as well as human hepatoma cells overexpressing the HBV precore protein. Both p25 and p22 showed phosphorylated and unphosphorylated forms, which were located in different intracellular compartments. Interestingly, precore expression was associated with decreases in intracellular HBV core protein (HBc) and secreted DNA-containing virions but was also associated with an increase in secreted empty virions. The decrease in HBc by precore could be attributed to cytosolic p22, which caused HBc degradation, at least in part by the proteasome, and consequently decreased HBV pregenomic RNA packaging and DNA synthesis. In addition, cytosolic p22 formed chimeric capsids with HBc in the cell, which were further secreted in virions. In contrast, the PreC antigen, like HBeAg, was secreted via the endoplasmic reticulum (ER)-Golgi secretory pathway and was thus unable to form capsids in the cell or be secreted in virions. Furthermore, p25, as well as p22, were secreted in virions from HBV-infected human hepatocytes and were detected in the sera of HBV-infected chimpanzees. In summary, we have detected multiple intracellular precore-derived proteins in HBV-infected human hepatocytes and revealed novel precore functions in the viral life cycle. IMPORTANCE Chronic hepatitis B remains a worldwide public health issue. The hepatitis B virus (HBV) precore protein is not essential for HBV replication but may facilitate viral persistence. In this study, we have detected multiple precore protein species in HBV-infected human hepatocytes and studied their functions in the HBV life cycle. We found that the HBV precore proteins decreased intracellular HBV core protein and reduced secretion of complete virions but enhanced secretion of empty virions. Interestingly, the cytosolic precore protein species formed chimeric capsids with the core protein and were secreted in virions. Our results shed new light on the functions of intracellular precore protein species in the HBV life cycle and have implications for the roles of precore proteins in HBV persistence and pathogenesis.

Pathogenicity and virulence of Hepatitis B virus

Hepatitis B virus (HBV) is a hepatotropic virus and an important human pathogen. There are an estimated 296 million people in the world that are chronically infected by this virus, and many of them will develop severe liver diseases including hepatitis, cirrhosis and hepatocellular carcinoma (HCC). HBV is a small DNA virus that replicates via the reverse transcription pathway. In this review, we summarize the molecular pathways that govern the replication of HBV and its interactions with host cells. We also discuss viral and non-viral factors that are associated with HBV-induced carcinogenesis and pathogenesis, as well as the role of host immune responses in HBV persistence and liver pathogenesis.

Amino acid residues at core protein dimer-dimer interface modulate multiple steps of hepatitis B virus replication and HBeAg biogenesis

The core protein (Cp) of hepatitis B virus (HBV) assembles pregenomic RNA (pgRNA) and viral DNA polymerase to form nucleocapsids where the reverse transcriptional viral DNA replication takes place. Core protein allosteric modulators (CpAMs) inhibit HBV replication by binding to a hydrophobic "HAP" pocket at Cp dimer-dimer interfaces to misdirect the assembly of Cp dimers into aberrant or morphologically "normal" capsids devoid of pgRNA. We report herein that a panel of CpAM-resistant Cp with single amino acid substitution of residues at the dimer-dimer interface not only disrupted pgRNA packaging, but also compromised nucleocapsid envelopment, virion infectivity and covalently closed circular (ccc) DNA biosynthesis. Interestingly, these mutations also significantly reduced the secretion of HBeAg. Biochemical analysis revealed that the CpAM-resistant mutations in the context of precore protein (p25) did not affect the levels of p22 produced by signal peptidase removal of N-terminal 19 amino acid residues, but significantly reduced p17, which is produced by furin cleavage of C-terminal arginine-rich domain of p22 and secreted as HBeAg. Interestingly, p22 existed as both unphosphorylated and phosphorylated forms. While the unphosphorylated p22 is in the membranous secretary organelles and the precursor of HBeAg, p22 in the cytosol and nuclei is hyperphosphorylated at the C-terminal arginine-rich domain and interacts with Cp to disrupt capsid assembly and viral DNA replication. The results thus indicate that in addition to nucleocapsid assembly, interaction of Cp at dimer-dimer interface also plays important roles in the production and infectivity of progeny virions through modulation of nucleocapsid envelopment and uncoating. Similar interaction at reduced p17 dimer-dimer interface appears to be important for its metabolic stability and sensitivity to CpAM suppression of HBeAg secretion.

Hepatitis B virus envelope proteins can serve as therapeutic targets embedded in the host cell plasma membrane

Hepatitis B virus (HBV) infection is a major health threat causing 880,000 deaths each year. Available therapies control viral replication but do not cure HBV, leaving patients at risk to develop hepatocellular carcinoma. Here, we show that HBV envelope proteins (HBs)-besides their integration into endosomal membranes-become embedded in the plasma membrane where they can be targeted by redirected T-cells. HBs was detected on the surface of HBV-infected cells, in livers of mice replicating HBV and in HBV-induced hepatocellular carcinoma. Staining with HBs-specific recombinant antibody MoMab recognising a conformational epitope indicated that membrane-associated HBs remains correctly folded in HBV-replicating cells in cell culture and in livers of HBV-transgenic mice in vivo. MoMab coated onto superparamagnetic iron oxide nanoparticles allowed to detect membrane-associated HBs after HBV infection by electron microscopy in distinct stretches of the hepatocyte plasma membrane. Last but not least, we demonstrate that HBs located on the cell surface allow therapeutic targeting of HBV-positive cells by T-cells either engrafted with a chimeric antigen receptor or redirected by bispecific, T-cell engager antibodies. TAKE AWAYS: HBs become translocated to the plasma membrane. Novel, recombinant antibody confirmed proper conformation of HBs on the membrane. HBs provide an interesting target by T-cell-based, potentially curative therapies.

In vitro expression of precore proteins of hepatitis B virus subgenotype A1 is affected by HBcAg, and can affect HBsAg secretion

HBeAg, a non-particulate protein of hepatitis B virus (HBV), is translated from the precore/core region as a precursor, which is post-translationally modified. Subgenotype A1 of HBV, which is a risk factor for hepatocellular carcinoma (HCC), has unique molecular characteristics in the basic core promoter/precore regions. Carriers of A1 exhibit early HBeAg loss. We sought to further characterize the precore proteins of A1 in vitro. HuH-7 cells were transfected with subgenomic constructs expressing individual precore proteins. Western blot analysis using DAKO anti-core antibody showed the expected sizes and a 1 kDa larger band for P22, P20 and P17. Using confocal microscopy, a cytoplasmic accumulation of HBeAg and precursors was observed with P25-expressing plasmid, whereas P22 localized both in the cytoplasm and nucleus. P20 and P17, which lack the carboxy end of P22 showed strong nuclear accumulation, implicating a nuclear localization signal in the N-terminal 10 amino acids. G1862T, unique to subgenotype A1, is frequently found in HBV from HCC patients. P25 with G1862T showed delayed and reduced HBeAg expression/secretion. Knock-out of core in the replication competent clones led to precore protein accumulation in the cytoplasm/perinuclear region, and decreased HBeAg secretion. Knock-out of precore proteins increased HBsAg secretion but intracellular HBsAg expression was unaffected. Over-expression of precore proteins in trans led to decreased HBsAg expression and secretion. Intracellular trafficking of HBV A1 precore proteins was followed. This was unaffected by the CMV promoter and different cell types. In the viral context, precore protein expression was affected by absence of core, and affected HBsAg expression, suggesting an interrelationship between precore proteins, HBcAg and HBsAg. This modulatory role of HBeAg and its precursors may be important in viral persistence and ultimate development of HCC.

Targeting the multifunctional HBV core protein as a potential cure for chronic hepatitis B

The core (capsid) protein of hepatitis B virus (HBV) is the building block of nucleocapsids where viral DNA reverse transcriptional replication takes place and mediates virus-host cell interaction important for the persistence of HBV infection. The pleiotropic role of core protein (Cp) in HBV replication makes it an attractive target for antiviral therapies of chronic hepatitis B, a disease that affects more than 257 million people worldwide without a cure. Recent clinical studies indicate that core protein allosteric modulators (CpAMs) have a great promise as a key component of hepatitis B curative therapies. Particularly, it has been demonstrated that modulation of Cp dimer-dimer interactions by several chemical series of CpAMs not only inhibit nucleocapsid assembly and viral DNA replication, but also induce the disassembly of double-stranded DNA-containing nucleocapsids to prevent the synthesis of cccDNA. Moreover, the different chemotypes of CpAMs modulate Cp assembly by interaction with distinct amino acid residues at the HAP pocket between Cp dimer-dimer interfaces, which results in the assembly of Cp dimers into either non-capsid Cp polymers (type I CpAMs) or empty capsids with distinct physical property (type II CpAMs). The different CpAMs also differentially modulate Cp metabolism and subcellular distribution, which may impact cccDNA metabolism and host antiviral immune responses, the critical factors for the cure of chronic HBV infection. This review article highlights the recent research progress on the structure and function of core protein in HBV replication cycle, the mode of action of CpAMs, as well as the current status and perspectives on the discovery and development of core protein-targeting antivirals. This article forms part of a symposium in Antiviral Research on "Wide-ranging immune and direct-acting antiviral approaches to curing HBV and HDV infections."

Biological features of hepatitis B virus strains associated with fulminant hepatitis

Accumulating evidence suggests that hepatitis B virus (HBV) biological features may influence the course and clinical manifestations of infection and possibly the development of fulminant hepatitis (FH). Since HBV is not a cytocidal virus, virus-induced liver damage results from an interplay between the virus replication and the host's defense. Therefore, viral factors contributing to enhanced replication, induction of a stronger immune attack or apoptosis of hepatocytes could be crucial in development of FH. Numerous mutations in basal core promoter, pre-C, C and S regions of the HBV genome contribute to development of FH by different mechanisms, including enhanced viral replication, the loss of a decoy for immune response, unbalanced expression of viral proteins and retention of unprocessed cytotoxic proteins in hepatocytes.

The Hepatitis B Virus Envelope Proteins: Molecular Gymnastics Throughout the Viral Life Cycle

New hepatitis B virions released from infected hepatocytes are the result of an intricate maturation process that starts with the formation of the nucleocapsid providing a confined space where the viral DNA genome is synthesized via reverse transcription. Virion assembly is finalized by the enclosure of the icosahedral nucleocapsid within a heterogeneous envelope. The latter contains integral membrane proteins of three sizes, collectively known as hepatitis B surface antigen, and adopts multiple conformations in the course of the viral life cycle. The nucleocapsid conformation depends on the reverse transcription status of the genome, which in turn controls nucleocapsid interaction with the envelope proteins for virus exit. In addition, after secretion the virions undergo a distinct maturation step during which a topological switch of the large envelope protein confers infectivity. Here we review molecular determinants for envelopment and models that postulate molecular signals encoded in the capsid scaffold conducive or adverse to the recruitment of envelope proteins.

Designing a therapeutic hepatitis B vaccine to circumvent immune tolerance

An effective prophylactic hepatitis B virus (HBV) vaccine has long been available but is ineffective for chronic infection. The primary cause of chronic hepatitis B (CHB) and greatest impediment for a therapeutic vaccine is the direct and indirect effects of immune tolerance to HBV antigens. The resulting defective CD4⁺/CD8⁺ T cell response, poor cytokine production, insufficient neutralizing antibody (nAb) and poor response to HBsAg vaccination characterize CHB infection. The objective of this study was to develop virus-like-particles (VLPs) that elicit nAb to prevent viral spread and prime CD4⁺/CD8⁺ T cells to eradicate intracellular HBV. Eight neutralizing B cell epitopes from the envelope PreS1 region were consolidated onto a species-variant of the HBV core protein, the woodchuck hepatitis core antigen (WHcAg). PreS1-specific B cell epitopes were chosen because of preferential expression on HBV virions. Because WHcAg and HBcAg are not crossreactive at the B cell level and only partially cross-reactive at the CD4⁺/CD8⁺ T cell level, CD4⁺ T cells specific for WHcAg-unique T cell sites can provide cognate T-B cell help for anti-PreS1 Ab production that is not curtailed by immune tolerance. Immunization of immune tolerant HBV transgenic (Tg) mice with PreS1-WHc VLPs elicited levels of high titer anti-PreS1 nAbs equivalent to wildtype mice. Passive transfer of PreS1 nAbs into human-liver chimeric mice prevented acute infection and cleared serum HBV from mice previously infected with HBV in a model of CHB. At the T cell level, PreS1-WHc VLPs and hybrid WHcAg/HBcAg DNA immunogens elicited HBcAg-specific CD4⁺ Th and CD8⁺ CTL responses.

Immune-Escape Hepatitis B Virus Mutations Associated with Viral Reactivation upon Immunosuppression

Hepatitis B virus (HBV) reactivation occurs as a major complication of immunosuppressive therapy among persons who have recovered from acute hepatitis and those who have controlled chronic infection. Recent literature data emphasize the presence of a high degree of S gene variability in HBV isolates from patients who developed reactivation. In reactivated HBV, the most frequently detected mutations belong to the second loop of “a” determinant in HBsAg. These mutations were identified to be immune escape and responsible for vaccine- and diagnostic-escape phenomena. Their emergence clearly provides survival in the presence of a developed humoral immune response and is often associated with impaired serological diagnosis of HBV reactivation. The knowledge of their existence and roles can elucidate the process of reactivation and strongly highlights the importance of HBV DNA detection in monitoring all patients with a history of HBV infection who are undergoing immunosuppression. This review discusses the possible influence of the most frequently found immune-escape mutations on HBV reactivation.

Hepatitis B e Antigen Inhibits NF-κB Activity by Interrupting K63-Linked Ubiquitination of NEMO

Viruses have adopted diverse strategies to suppress antiviral responses. Hepatitis B virus (HBV), a virus that is prevalent worldwide, manipulates the host's innate immune system to evade scavenging. It is reported that the hepatitis B e antigen (HBeAg) can interfere with NF-κB activity, which then leads to high viral loads, while HBV with the G1896A mutation remains infectious without the production of HBeAg but can induce more severe proinflammatory response and liver damage. The aim of current work was to study the molecular mechanism by which HBeAg suppresses interleukin-1β (IL-1β)-stimulated NF-κB activity, which leads to the suppression of the innate immune responses to HBV infection. Our study revealed that HBeAg could interact with NEMO, a regulatory subunit associated with IκB kinase, which regulates the activation of NF-κB. HBeAg suppressed the IL-1β-induced tumor necrosis factor (TNF)-associated factor 6 (TRAF6)-dependent K63-linked ubiquitination of NEMO, thereby downregulating NF-κB activity and promoting virus replication. We further demonstrated the inhibitory effect of HBeAg on the NF-κB signaling pathway using primary human hepatocytes, HBV-infected HepG2-NTCP cells, and clinical liver samples. Our study reveals a molecular mechanism whereby HBeAg suppresses IL-1β-induced NF-κB activation by decreasing the TRAF6-dependent K63-linked ubiquitination of NEMO, which may thereby enhance HBV replication and promote a persistent infection.IMPORTANCE The role of HBeAg in inflammatory responses during the infection of hepatitis B virus (HBV) is not fully understood, and several previous reports with regard to the NF-κB pathway are controversial. In this study, we showed that HBeAg could suppress both Toll-like receptor 2 (TLR2)- and IL-1β-induced activation of NF-κB in cells and clinical samples, and we further revealed novel molecular mechanisms. We found that HBeAg can associate with NEMO, the regulatory subunit for IκB kinase (IKK) that controls the NF-κB signaling pathway, and thereby inhibits TRAF6-mediated K63-linked ubiquitination of NEMO, resulting in downregulation of NF-κB activity and promotion of virus replication. In contrast, the HBeAg-negative HBV mutant can induce higher levels of NF-κB activity. These results are important for understanding the HBV-induced pathogenesis of chronic hepatitis and indicate that different clinical measures should be considered to treat HBeAg-positive and HBeAg-negative infections. Our findings represent a conceptual advance in HBV-related suppression of NF-κB signaling.

Therapeutic vaccination for chronic hepatitis B

A therapeutic vaccine is meant to activate the patient's immune system to fight and finally control or ideally eliminate an already established infectious pathogen. Whereas the success of prophylactic vaccination is based on rapid antibody-mediated neutralization of an invading pathogen, control and elimination of persistent viruses such as hepatitis, herpes or papilloma viruses requires multi-specific and polyfunctional effector T cell responses. These are ideally directed against continuously expressed viral antigens to keep the pathogen in check. Activation of a humoral immune response in order to lower viral antigen load and to limit virus spread, however, confers an additional benefit. Therapeutic vaccines are under development for a number of chronic infections and require an intelligent vaccine design. Hepatitis B virus (HBV) infection may serve as a prime example since a spontaneous, immune-mediated recovery of chronic hepatitis B and an elimination of the virus is possible even if it is observed only in very rare cases. In this review, we summarize the current knowledge and potential improvements of therapeutic vaccines for chronic hepatitis B.

Sustained Inhibition of HBV Replication In Vivo after Systemic Injection of AAVs Encoding Artificial Antiviral Primary MicroRNAs

Chronic infection with hepatitis B virus (HBV) remains a problem of global significance and improving available treatment is important to prevent life-threatening complications arising in persistently infected individuals. HBV is susceptible to silencing by exogenous artificial intermediates of the RNA interference (RNAi) pathway. However, toxicity of Pol III cassettes and short duration of silencing by effectors of the RNAi pathway may limit anti-HBV therapeutic utility. To advance RNAi-based HBV gene silencing, mono- and trimeric artificial primary microRNAs (pri-miRs) derived from pri-miR-31 were placed under control of the liver-specific modified murine transthyretin promoter. The sequences, which target the X sequence of HBV, were incorporated into recombinant hepatotropic self-complementary adeno-associated viruses (scAAVs). Systemic intravenous injection of the vectors into HBV transgenic mice at a dose of 1 × 10¹¹ per animal effected significant suppression of markers of HBV replication for at least 32 weeks. The pri-miRs were processed according to the intended design, and intrahepatic antiviral guide sequences were detectable for 40 weeks after the injection. There was no evidence of toxicity, and innate immunostimulation was not detectable following the injections. This efficacy is an improvement on previously reported RNAi-based inhibition of HBV replication and is important to clinical translation of the technology.

Hepatitis B e antigen and its precursors promote the progress of hepatocellular carcinoma by interacting with NUMB and decreasing p53 activity

Hepatitis B viral infection is one of the leading causes of hepatocellular carcinoma (HCC) worldwide. Although several viral factors have been identified that may increase the risk for HCC development, the molecular mechanisms leading to the transformation of normal hepatocytes into cancer cells remain elusive. In this study, we demonstrated that the intracellular hepatitis B e antigen (HBeAg) and its precore precursors, but not their homologous core protein, could associate with NUMB and thereby impair the stability and transcriptional activity of tumor suppressor p53. HBeAg and its precursors could disrupt p53-NUMB and HDM2-NUMB interactions and tricomplex p53-HDM2-NUMB formation, inhibit the acetylation and translocation of p53 from cytosol to the nucleus, promote HDM2-mediated ubiquitination and degradation of p53, and suppress p53-dependent apoptosis. A xenograft tumorigenicity assay showed that expression of HBeAg and its precursors promoted carcinogenesis in a mouse model. Immunohistochemical analysis of the bioptic liver samples of HCC patients revealed that HBeAg positivity was associated with reduced transcriptional activity of p53. Taken together, the results suggest a role of intracellular HBeAg and its precursors in HCC development.

CONCLUSION

HBeAg and its precursors promote HDM2-mediated degradation and impair transcriptional activity of p53 by interacting with NUMB, consequently contributing to HCC development. (Hepatology 2016;64:390-404).

High Functional Stability of a Low-cost HBV DNA qPCR Primer Pair and Plasmid Standard

Aim

We studied the functional stability of a primer pair and the standard curve based on a plasmid carrying full-length HBV genome, from a novel low-cost real-time quantitative polymerase chain reaction (qPCR) assay. The assay was developed at the Center for Genetic Engineering and Biotechnology (CIGB) in Havana, to quantify the serum hepatitis B virus (HBV) DNA from chronic HBV-infected (CHB) patients.

Materials and methods

In-house generated oligonucleotides and plasmids were incubated at 37°C during 1 month and compared with the same materials incubated at –20, 4, and 25°C during the same time in qPCR experiments.

Results

This work shows that the oligonucleotide pair and the plasmid for the quantitative standard curve are functionally stable in severe temperature conditions during 1 month. Polymerase chain reaction amplification with both materials after its incubation 30 days at 37°C produced similar cycle threshold (CT) values and similar degree of sample quantifications compared with the same materials preserved using the conventional storage conditions at –20°C.

Conclusion

These results are indicative of the robustness of this low-cost qPCR system for HBV DNA quantification. These results also support that this qPCR assay can be used as a low-cost technology in clinical studies to monitor the viral load changes of serum HBV DNA of CHB patients, which could be used by poor people of third world countries, where there are frequent blackouts and temperature changes that can hinder the primer and plasmid stability.

How to cite this article

Aguiar J, García G, León Y, Canales E, Silva JA, Gell O, Estrada R, Morán I, Muzio V, Guillén G, Pentón E, Aguilar JC. High Functional Stability of a Low-cost HBV DNA qPCR Primer Pair and Plasmid Standard. Euroasian J Hepato-Gastroenterol 2016;6(1):19-24.

Hepatitis mouse models: from acute-to-chronic autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease associated with interface hepatitis, raised plasma liver enzymes, the presence of autoantibodies and regulatory T-cell (Tregs) dysfunction. The clinical course is heterogeneous, manifested by a fulminant or indolent course. Although genetic predisposition is well accepted, the combination with currently undefined environmental factors is crucial for the development of the disease. Progress in the development of reliable animal models provides added understanding of the pathophysiology of AIH, and these will be very useful in evaluating potential therapeutics. It appears that artificially breaking tolerance in the liver is easy. However, maintaining this state of tolerance breakdown, to get chronic hepatitis, is difficult because liver immune homeostasis is strongly regulated by several immune response inhibitory mechanisms. For example, Tregs are crucial regulators in acute and chronic hepatitis, and C57BL/6 mice are most prone to experimental AIH. Immunization of C57BL/6 mice with liver (AIH) autoantigens (CYP2D6/FTCD or IL-4R) and the disturbance of liver regulatory mechanism(s), leading to experimental AIH, are likely to be most representative of human AIH pathology.

Conserved aromatic residues of the hepatitis B virus Precore propeptide are involved in a switch between distinct dimeric conformations and essential in the formation of heterocapsids

The Hepatitis B virus Precore protein, present in the secretory pathway as the HBeAg precursor, can associate in the cytoplasm with the Core protein to form heterocapsids, likely to favor viral persistence. Core and Precore proteins share their primary sequence except for ten additional aminoacids at the N-terminus of Precore. To address the role of this propeptide sequence in the formation of Precore heterocapsids, we designed a Precore mutant in which the two propeptide tryptophans are replaced by glycines. This mutant retains the properties of the wild-type Precore, notably cell trafficking and ability to interact with Core. However, it is not incorporated into heterocapsids and forms stable dimers distinct from the labile HBe dimers and the presumably Core-like dimers assembled into heterocapsids. Our data highlights the essential role of Precore׳s propeptide in switching between different conformations for different functions and pinpoint the propeptide Tryptophan residues as central in these properties.

Mouse models of hepatitis B and delta virus infection

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. Therapeutic regimens currently available can efficiently suppress HBV replication; however, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. Among the HBV chronically infected patients, more than 15million patients are estimated to be co-infected with the hepatitis delta virus (HDV), a defective satellite virus that needs the HBV envelope for propagation. No specific drugs are currently available against HDV, while nucleos(t)ide analogs are not effective against HDV replication. Since chronic HBV/HDV co-infection leads to the most severe form of chronic viral hepatitis in men, a better understanding of the molecular mechanisms of HDV-mediated pathogenesis and the development of improved therapeutic approaches is urgently needed. The obvious limitations imposed by the use of great apes and the paucity of robust experimental models of HBV infection have hindered progresses in understanding the complex network of virus-host interactions that are established in the course of HBV and HDV infections. This review focuses on summarizing recent advances obtained with well-established and more innovative experimental mouse models, giving emphasis on the strength of infection systems based on the reconstitution of the murine liver with human hepatocytes, as tools for elucidating the whole life cycle of HBV and HDV, as well as for studies on interactions with the infected human hepatocytes and for preclinical drug evaluation.

Susceptibility of different hepatitis B virus isolates to interferon-alpha in a mouse model based on hydrodynamic injection

Interferon alpha (IFN-α) is commonly used for the treatment of chronic hepatitis B (CHB) patients. Many factors including viral genetics may determine the outcome of IFN-α therapy. In this study, we tested whether the expression of IFN-α directly in the liver inhibits HBV gene expression and replication using a HBV hydrodynamic injection (HI) mouse model. Two replication-competent clones from different HBV isolates that belonging to HBV genotype A and B based on a pAAV vector (pAAV-HBV-A and pAAV-HBV-B) were compared for their susceptibility to IFN-α. HBV clones were injected into mice either alone or in combination with a murine (m) IFN-α expression plasmid (pmIFN-α). HBsAg and HBeAg concentrations and HBV DNA levels in mice differed after injection of these two HBV clones. Co-application of pmIFN-α together with the two distinct isolates resulted in markedly different kinetics of decline of HBsAg, HBeAg, and HBV DNA levels in the mice. Immunohistochemical staining of liver sections with anti-HBc showed that mIFN-α application completely inhibited the expression of HBcAg in mice inoculated with pAAV-HBV-B, whereas the expression of HBcAg was only reduced in mice with pAAV-HBV-A. Consistently, mice injected with pAAV-HBV-B and pmIFN-α showed higher expression levels of the IFN-stimulated genes (ISGs) ISG15, OAS, PKR as well as proinflammatory cytokine IL-6 in the liver. In addition, expression levels of anti-inflammatory cytokine IL-10 was down-regulated significantly in liver of the mice injected with pAAV-HBV-B and pmIFN-α. Our data demonstrate that IFN-α exerts antiviral activity in HBV mouse model, but different HBV isolates may have diverse susceptibility to IFN-α.

Role of proinflammatory cytokines (interferon gamma) and anti-inflammatory cytokine (interleukin-10) gene polymorphisms in chronic hepatitis B infection: an Indian scenario

Immune-mediated mechanisms have been found to play an important role in the progression of hepatitis B virus (HBV) infection. The outcomes of infection do not appear to be determined by viral strains. Instead, allelic variants in human genome are likely to affect the disease progression. Allelic variation of proinflammatory cytokines such as interferon gamma (IFN-γ) participates in the elimination of HBV, and interleukin-10 (IL-10) helps in inhibition of Th1 effector mechanisms for host defense. The aim of this study was to determine the influence of host genetic factors in chronic HBV infection and gene promoter polymorphism or single-nucleotide polymorphism analysis of IFN-γ+874 and IL-10 (-1082, -592, and -819) on disease progression and persistence. A total of 232 patients along with 76 healthy controls were included. Allele-specific primers for IFN-γ and restriction fragment length polymorphism for IL-10 were used. The study indicated that low IFN-γ expression probably impairs host immune response to HBV, rendering these subjects more prone to HBV infection. No significant differences were detected between the 2 groups in the distributions of IL-10 genotype at the -1082, -819, and -592 positions. Odds ratio indicated that heterozygosity of genotypes -819 CT and -592 AC was more strongly associated with liver chronicity. Significantly, AA homozygous genotype was dominant in chronic hepatitis B cases in IFN-γ+874 and IL-10 (-1082 and -592) and is associated with increased risk of persistent infection.

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.

Identification of a unique double-negative regulatory T-cell population

Regulatory T (Treg) cells represent one of the main mechanisms of regulating self-reactive immune cells. Treg cells are thought to play a role in down-regulating immune responses to self or allogeneic antigens in the periphery. Although the function of Treg cells has been demonstrated in many experimental settings, the precise mechanisms and antigen specificity often remain unclear. In a hepatitis B e antigen-T-cell receptor (HBeAg-TCR) double transgenic mouse model, we observed a phenotypically unique (TCR+)  CD4- /CD8-  CD25(+/-)  GITR(high)  PD-1(high)  FoxP3-) HBeAg-specific population that demonstrates immune regulatory function. This HBeAg-specific double-negative regulatory cell population proliferates vigorously in vitro, in contrast to any other known regulatory population, in an interleukin-2-independent manner.

Viral adaptation to host immune responses occurs in chronic hepatitis B virus (HBV) infection, and adaptation is greatest in HBV e antigen-negative disease

Hepatitis B virus (HBV)-specific T-cell responses are important in the natural history of HBV infection. The number of known HBV-specific T-cell epitopes is limited, and it is not clear whether viral evolution occurs in chronic HBV infection. We aimed to identify novel HBV T-cell epitopes by examining the relationship between HBV sequence variation and the human leukocyte antigen (HLA) type in a large prospective clinic-based cohort of Asian patients with chronic HBV infection recruited in Australia and China (n = 119). High-resolution 4-digit HLA class I and II typing and full-length HBV sequencing were undertaken for treatment-naïve individuals (52% with genotype B, 48% with genotype C, 63% HBV e antigen [HBeAg] positive). Statistically significant associations between HLA types and HBV sequence variation were identified (n = 49) at 41 sites in the HBV genome. Using prediction programs, we determined scores for binding between peptides containing these polymorphisms and associated HLA types. Among the regions that could be tested, HLA binding was predicted for 14/18 (78%). We identified several HLA-associated polymorphisms involving likely known anchor residues that resulted in altered predicted binding scores. Some HLA-associated polymorphisms fell within known T-cell epitopes with matching HLA restriction. Enhanced viral adaptation (defined as the presence of the relevant HLA and the escaped amino acid) was independently associated with HBeAg-negative disease (P = 0.003). Thus, HBV appears to be under immune pressure in chronic HBV infection, particularly in HBeAg-negative disease.

The hepatitis B e antigen (HBeAg) targets and suppresses activation of the toll-like receptor signaling pathway

BACKGROUND & AIMS

Viruses target innate immune pathways to evade host antiviral responses. Recent studies demonstrate a relationship between hepatitis B disease states and the host's innate immune response, although the mechanism of immunomodulation is unknown. In humans, the innate immune system recognizes pathogens via pattern recognition receptors such as the Toll-like receptors (TLR), initiating anti-inflammatory responses. TLR expression and pro-inflammatory cytokine production is reduced in hepatitis B e antigen (HBeAg)-positive patients following TLR stimulation. The aim of this study was to investigate interactions between TLR signaling pathways and the mature HBeAg protein localized in the cytosol.

METHODS

The ability of HBeAg to inhibit TLR signaling and association with TLR adapters was evaluated by immunoprecipitation, immunostaining, and reporter studies.

RESULTS

Our findings show that HBeAg co-localizes with Toll/IL-1 receptor (TIR)-containing proteins TRAM, Mal, and TLR2 at the sub-cellular level, which was not observed for Hepatitis B core antigen. Co-immunoprecipitation analysis demonstrated HBeAg interacted with TIR proteins Mal and TRAM, while a mutated HBeAg ablated interaction between Mal and MyD88. Importantly, HBeAg also disrupted homotypic TIR:TIR interaction critical for TLR-mediated signaling. Finally, HBeAg suppressed TIR-mediated activation of the inflammatory transcription factors, NF-κB and Interferon-β promoter activity.

CONCLUSIONS

Our study provides the first molecular mechanism describing HBeAg immunomodulation of innate immune signal transduction pathways via interaction and targeting of TLR-mediated signaling pathways. These finding suggest the mechanism as to how HBeAg evades innate immune responses contributing to the pathogenesis of chronic hepatitis B infection and the establishment of viral persistence.

The YMDD and rtA194T mutations result in decreased replication capacity in wild-type HBV as well as in HBV with precore and basal core promoter mutations

BACKGROUND

A recent study indicated that addition of the hepatitis B e antigen (HBeAg) precore (PC) or basal core promoter (BCP) mutations to wild-type HBV offset the reduced replication of the HBV polymerase rtA194T±rtL180M+rtM204V mutations. rtA194T was reportedly associated with tenofovir resistance. We investigated these findings in genotype D HBV, where both PC and BCP naturally occur in vivo.

METHODS

A plasmid containing a wild-type 1.3 genome length genotype D HBV laboratory strain was used as a parent for PC, BCP, rtA194T±rtL180M+rtM204V, rtL180M+rtM204V and rtM204I mutants. Viral replication was evaluated by Southern blot analysis of intracellular HBV core DNA following transient transfection of HepG2 cells. Drug susceptibility was evaluated by quantitative PCR of intracellular HBV DNA.

RESULTS

PC and BCP mutations each increased HBV DNA replication by approximately 200% over wild-type. rtA194T reduced replication by <40%, whereas rtL180M+rtM204V, rtL180M+rtA194T+rtM204V or rtM204I each reduced by >75% from their respective wild-type, PC or BCP genome backbone (P<0.05). The enhanced replication by PC or BCP offset the reduction by rtA194T; however, the other reverse transcriptase (RT) mutations in PC or BCP backbones remained significantly lower than wild-type (P<0.05). Regardless of the backbone, rtA194T±rtL180M+rtM204V remained susceptible to tenofovir in vitro. rtA194T alone remained susceptible to lamivudine, while rtL180M+rtM204V and rtL180M+rtA194T+rtM204V were resistant.

CONCLUSIONS

PC or BCP mutations increased HBV DNA replication, offset the decreased replication by rtA194T alone, but they did not fully rescue the impaired replication conferred by other RT mutations as compared with wild-type. rtA194T±rtL180M+rtM204V did not confer tenofovir resistance.

Clinical efficacy of a 24-months course of lamivudine therapy in patients with HBeAg negative chronic hepatitis B: a long-term prospective study

The optimal duration of oral nucleos(t)ide analogue therapy for HBeAg negative chronic hepatitis B (CHB) has not been defined. The aim of this study was to investigate the clinical efficacy of 24-months course of lamivudine therapy in patients with HBeAg negative CHB in Korea. A total of 50 Korean patients with HBeAg negative CHB were prospectively enrolled. The patients received 100 mg/day of lamivudine orally for 24 months. Patients who showed complete response at 24 months to lamivudine therapy stopped treatment, and regular follow-up was done thereafter. The mean follow-up duration after cessation of therapy was 40.8+/-22.7 (range 12-96) months. The complete response rate at months 12 and 24 were 86.0% (43/50) and 86.0% (43/50), respectively, and the clinical breakthrough at months 12 and 24 were 4.0% (2/50) and 14.0% (7/50), respectively. The expected durability of responses at months 12, 24, and 36 after cessation of lamivudine therapy in 43 complete responders was 79.1%, 64.0%, and 56.9%, respectively. In conclusion, a 24-months course of lamivudine therapy shows high end-treatment response rate and substantial durability of initial response after cessation of therapy in HBeAg negative CHB patients in Korea.

The correlation of hepatocyte nuclear factor 4 alpha and 3 beta with hepatitis B virus replication in the liver of chronic hepatitis B patients

Hepatocyte nuclear factors 4 alpha (HNF4alpha) and 3 beta (HNF3beta) are members of a group of liver-enriched transcription factors (LETFs) that play important roles in regulating the replication of hepatitis B virus (HBV). Using cell culture and animal models, we showed that HNF4alpha supports HBV replication in nonhepatic cells and HNF3beta inhibits HBV replication. However, the expression of HNF4alpha and HNF3beta in the liver tissue of chronic HBV-infected patients and the relationship between the levels of HNF4alpha and HNF3beta and HBV replication are unclear. In this study, liver biopsy specimens from 86 chronic HBV-infected patients were collected. The expression levels of HNF4alpha, HNF3beta, hepatitis B surface antigen (HBsAg) and hepatitis B core antigen (HBcAg) were detected by an immunohistochemical technique and the level of HBV DNA was checked by in situ hybridization with serial sections from liver biopsy tissue samples. We show here that samples with higher levels of HNF4alpha expression also have higher levels of HBsAg, HBcAg and HBV DNA. In contrast, in samples with higher levels of HNF3beta expression, levels of HBsAg, HBcAg and HBV DNA were lower. There was a positive correlation between HNF4alpha expression and HBV replication, and a negative correlation between HNF3beta expression and HBV replication, in the liver of chronic HBV-infected patients. This suggests that HNF4alpha and HNF3beta likely participate in HBV replication in patients with HBV infection, or that HBV replication may somehow influence the expression of HNF4alpha and HNF3beta in the liver.

The rtA194T polymerase mutation impacts viral replication and susceptibility to tenofovir in hepatitis B e antigen-positive and hepatitis B e antigen-negative hepatitis B virus strains

Tenofovir is a new effective treatment option for patients with chronic hepatitis B, but could be potentially hampered by mutations in the hepatitis B virus (HBV) polymerase conferring drug resistance. Drug resistance may occur preferentially if long-term administration is required, for example, in patients with hepatitis B e antigen (HBeAg)-negative HBV infection bearing precore (PC) and basal core promoter (BCP) mutations. The rtA194T polymerase mutation has been found in HBV/HIV coinfected patients during tenofovir treatment and may be associated with tenofovir resistance. We generated replication-competent HBV constructs harboring rtA194T alone or in addition to lamivudine (LAM) resistance (rt180M + rtM204V), PC mutations, and BCP mutations and assessed their replicative capacity after transient transfection in human hepatoma cells. The rtA194T polymerase mutation alone or in conjunction with LAM resistance reduced the replication efficiency as compared with wild-type (WT) HBV. In contrast, combination of rtA194T (+/- LAM resistance) with HBeAg-negative PC or BCP mutants increased the replication capacity of the drug-resistant polymerase mutants, thereby restoring the viral replication to similar levels as WT clones. Clones harboring rtA194T showed partial resistance to tenofovir in vitro and also to LAM but remained susceptible to telbivudine and entecavir.

CONCLUSION

The rtA194T polymerase mutation is associated with partial tenofovir drug resistance and negatively impacts replication competence of HBV constructs. Viral replication, however, can be restored to WT levels, if these polymerase mutations occur together with precore or basic core promoter substitutions as found in HBeAg-negative hepatitis B. Patients with HBeAg-negative chronic HBV infection may therefore be at particular risk when developing drug resistance to tenofovir. Telbivudine or entecavir should be considered as effective alternative treatment options for these patients.

Molecular analysis of an HBsAg-negative hepatitis B virus mutant selected in a tenofovir-treated HIV-hepatitis B virus co-infected patient

The molecular analysis performed in an HIV-hepatitis B virus (HBV) coinfected patient revealed selection of an unusual HBV polymerase mutation (rtV191I) during tenofovir-containing therapy, conferring simultaneously immune escape by HBsAg negativity and resistance to lamivudine but not tenofovir. Phenotypic analysis revealed impaired replicative capacity of mutants, which could be restored by concomitant precore or basal core promoter mutations (HBe-antigen-negativity). HBV mutants carrying drug and vaccine resistance may represent a considerable individual risk and public health concern.

A mechanism to explain the selection of the hepatitis e antigen-negative mutant during chronic hepatitis B virus infection

Hepatitis B virus (HBV) expresses two structural forms of the nucleoprotein, the intracellular nucleocapsid (hepatitis core antigen [HBcAg]) and the secreted nonparticulate form (hepatitis e antigen [HBeAg]). The aim of this study was to evaluate the ability of HBcAg- and HBeAg-specific genetic immunogens to induce HBc/HBeAg-specific CD4(+)/CD8(+) T-cell immune responses and the potential to induce liver injury in HBV-transgenic (Tg) mice. Both the HBcAg- and HBeAg-specific plasmids primed comparable immune responses. Both CD4(+) and CD8(+) T cells were important for priming/effector functions of HBc/HBeAg-specific cytotoxic T-lymphocyte (CTL) responses. However, a unique two-step immunization protocol was necessary to elicit maximal CTL priming. Genetic vaccination did not prime CTLs in HBe- or HBc/HBeAg-dbl-Tg mice but elicited a weak CTL response in HBcAg-Tg mice. When HBc/HBeAg-specific CTLs were adoptively transferred into HBc-, HBe-, and HBc/HBeAg-dbl-Tg mice, the durations of the liver injury and inflammation were significantly greater in HBeAg-Tg recipient mice than in HBcAg-Tg mice. Importantly, liver injury in HBc/HBeAg-dbl-Tg mice was similar to the injury observed in HBeAg-Tg mice. Loss of HBeAg synthesis commonly occurs during chronic HBV infection; however, the mechanism of selection of HBeAg-negative variants is unknown. The finding that hepatocytes expressing wild-type HBV (containing both HBcAg and HBeAg) are more susceptible to CTL-mediated clearance than hepatocytes expressing only HBcAg suggest that the HBeAg-negative variant may have a selective advantage over wild-type HBV within the livers of patients with chronic infection during an immune response and may represent a CTL escape mutant.

The hepatitis B virus precore protein is retrotransported from endoplasmic reticulum (ER) to cytosol through the ER-associated degradation pathway

The hepatitis B virus precore protein is closely related to the nucleocapsid core protein but is processed distinctly in the cell and plays a different role in the viral cycle. Precore is addressed to the endoplasmic reticulum (ER) through a signal peptide, and the form present in the ER is the P22 protein. P22 is then cleaved in its C-terminal part to be secreted as HBe antigen. In addition, a cytosolic form of 22 kDa less characterized has been observed. Precore gene was shown to be implicated in viral persistence, but until now, the actual protein species involved has not been determined. Our work focuses on the cytosolic form of precore. Using human cells expressing precore and a convenient fractionation assay, we demonstrated that the cytosolic form is identical to the ER form and retrotransported in the cytoplasm through the ER-associated degradation pathway. This cellular machinery translocates misfolded proteins to the cytoplasm, where they are ubiquitinated on lysine residues and degraded by proteasome. We showed that precore escapes proteasome due to its low lysine content and accumulates in the cytosol. The role of this retrotransport was investigated. In the presence of precore, we found a specific redistribution of the Grp78/BiP chaperone protein to cytosol and demonstrated a specific interaction between precore and Grp78/BiP. Altogether, these data support the idea that the hepatitis B virus develops a strategy to take advantage of the ER-associated degradation pathway, allowing distinct subcellular localization and probably distinct roles for the viral precore protein.

Establishment and primary application of a mouse model with hepatitis B virus replication

AIM: To establish a rapid and convenient animal model with hepatitis B virus (HBV) replication.

METHODS: A naked DNA solution of HBV-replication-competent plasmid was transferred to BALB/C mice via the tail vein, using a hydrodynamic in vivo transfection procedure. After injection, these mice were sacrificed on d 1, 3, 4, 5, 7 and 10. HBV DNA replication intermediates in the liver were analyzed by Southern blot hybridization. The expression of hepatitis B core antigen (HBcAg) and hepatitis B surface antigen (HBsAg) in the liver was checked by immunohistochemistry. Serum HBsAg and hepatitis B e antigen (HBeAg) was detected by enzyme-linked immunosorbent assay (ELISA). Inhibition of HBV replication was compared in HBV replication model mice treated intraperitoneally with polyinosinic-polytidylin acid (polyIC) or phosphate-buffered saline (PBS).

RESULTS: After hydrodynamic in vivo transfection, HBV DNA replication intermediates in the mouse liver were detectable on d 1 and abundant on d 3 and 4, the levels were slightly decreased and remained relatively stable between d 5 and 7, and were almost undetectable on d 10. The expression patterns of HBcAg and HBsAg were similar to that of HBV replication intermediate DNA, except that they reached a peak on d 1 after injection. No obvious differences in HBV DNA replication intermediates were observed in the left, right and middle lobes of the liver. After treatment with polyIC, the level of HBV intermediate DNA in the liver was lower than that in the control mice injected with PBS.

CONCLUSION: A rapid and convenient mouse model with a high level of HBV replication was developed and used to investigate the inhibitory effect of polyIC on HBV replication, which provides a useful tool for future functional studies of the HBV genome.

Molecular testing in the diagnosis and management of chronic hepatitis B

Hepatitis B virus (HBV) is an enveloped virus with a small (3.2-kb) partially double-stranded DNA genome that causes acute and chronic infections. The impact of these infections on public health worldwide is enormous, with an estimated prevalence of 2 billion acute infections and 360 million chronic infections globally. This review focuses on chronic hepatitis B and the molecular assays used in its diagnosis and management. Background information, including that about features of the hepatitis B virion, viral replication, and epidemiology of infection, that is important for understanding chronic hepatitis B and molecular diagnostic tests for HBV is provided. To facilitate an understanding of the utility of molecular testing for chronic hepatitis B, the four stages of chronic hepatitis B infection that are currently recognized, as well as an additional entity, occult hepatitis B, that can be diagnosed only by sensitive nucleic acid amplification methods, are reviewed in detail, including available therapeutic agents. The molecular diagnostic content focuses on tests for HBV DNA quantification, genotyping, and mutation detection (including precore/core promoter and antiviral resistance mutations). The discussion of these tests encompasses their current utility and performance characteristics, drawing from current clinical guidelines and other studies from the literature. In recognition of the continual evolution of this field, the final section describes emerging molecular markers with future diagnostic potential.

HBV pathogenesis in animal models: recent advances on the role of platelets

Hepatitis B virus (HBV) causes acute and chronic necroinflammatory liver diseases and hepatocellular carcinoma (HCC). HBV replicates noncytopathically in the hepatocyte, and most of the liver injury associated with this infection reflects the immune response. While the innate immune response may not contribute significantly to the pathogenesis of liver disease or viral clearance, the adaptive immune response, particularly the cytotoxic T lymphocyte (CTL) response, contributes to both. Recent observations also reveal that antigen-nonspecific inflammatory cells enhance CTL-induced liver pathology and, more surprisingly, that platelets facilitate the intrahepatic accumulation of CTLs, suggesting that the host response to HBV infection is a highly complex but coordinated process. The notion that platelets contribute to liver disease and viral clearance by promoting the recruitment of virus-specific CTLs into the liver is a new concept in viral pathogenesis, which may prove useful to implement treatments of chronic HBV infection in man.

In vitro resistance to interferon-alpha of hepatitis B virus with basic core promoter double mutation

The hepatitis B virus (HBV) genome basic core promoter (BCP) modulates HBeAg secretion at the transcriptional level. In addition to pre-core mutations, variations in the BCP are related to hepatitis B e antigen (HBeAg)-negative chronic hepatitis B. HBeAg-negative chronic hepatitis B patients show a lower sustained response to interferon (IFN). The aim of this study was to determine if there is a relationship between HBV BCP mutation and sensitivity of HBV to IFN-alpha in vitro. BCP mutations were introduced by site-directed mutagenesis and the entire genomes of wild-type and mutant HBV were transiently transferred into Huh7 cells by calcium phosphate transfection. With or without IFN-alpha, viral products in the culture medium and viral replication intermediates in the cytoplasm were detected 3 days after transfection. The amount of hepatitis B surface antigen (HBsAg) secreted by wild-type HBV and the BCP mutant was similar, while HBeAg secreted by the mutant was decreased by 35.4%. HBV particles and replication intermediates of the BCP mutant were increased. After IFN-alpha was added, HBeAg, HBV DNA and HBV replication intermediates decreased for both the wild-type HBV (by 25.7%, 31.8%, 29.8%, respectively) and the BCP mutant (by 8.4%, 27.4%, 10.1%, respectively). These data indicate that HBV harboring the BCP double mutation has stronger replication competence and lower sensitivity to IFN-alpha than wild-type.

Altered proteolysis and global gene expression in hepatitis B virus X transgenic mouse liver

Hepatitis B virus X (HBX) is essential for the productive infection of hepatitis B virus (HBV) in vivo and has a pleiotropic effect on host cells. We have previously demonstrated that the proteasome complex is a cellular target of HBX, that HBX alters the proteolytic activity of proteasome in vitro, and that inhibition of proteasome leads to enhanced viral replication, suggesting that HBX and proteasome interaction plays a crucial role in the life cycle and pathogenesis of HBV. In the present study, we tested the effect of HBX on the proteasome activities in vivo in a transgenic mouse model in which HBX expression is developmentally regulated by the mouse major urinary promoter in the liver. In addition, microarray analysis was performed to examine the effect of HBX expression on the global gene expression profile of the liver. The results showed that the peptidase activities of the proteasome were reduced in the HBX transgenic mouse liver, whereas the activity of another cellular protease was elevated, suggesting a compensatory mechanism in protein degradation. In the microarray analysis, diverse genes were altered in the HBX mouse livers and the number of genes with significant changes increased progressively with age. Functional clustering showed that a number of genes involved in transcription and cell growth were significantly affected in the HBX mice, possibly accounting for the observed pleiotropic effect of HBX. In particular, insulin-like growth factor-binding protein 1 was down-regulated in the HBX mouse liver. The down-regulation was similarly observed during acute woodchuck hepatitis virus infection. Other changes including up-regulation of proteolysis-related genes may also contribute to the profound alterations of liver functions in HBV infection.

Cellular cIAP2 gene expression associated with anti-HBV activity of TNF-alpha in hepatoblastoma cells

Hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTLs) can abolish HBV gene expression and replication through a noncytopathic mechanism mediated by tumor necrosis factor-alpha (TNF-alpha). However, the molecular mechanisms of TNF-alpha antiviral activity are not completely understood. To examine TNF-alpha-induced cellular responses and identify genes involved in anti-HBV activity, cDNA microarrays dotted with 14, 112 human genes were used to examine the transcriptional changes in HepG2 after treatment with TNF-alpha for 6 h. The results showed that many genes related to ligands and receptors, signal transduction including the TNF-alpha signaling pathway, mitochondrial and ribosomal proteins, and transcription regulation were induced by TNF-alpha. Interestingly, the TNF-alpha-inducible gene cIAP2 was found to inhibit HBV protein synthesis, viral replication, and transcription. Taken together, our results revealed the global effects of TNF-alpha treatment on hepatocellular gene expression. The antiviral genes identified by microarray could be developed as potential new anti-HBV drugs or for other novel therapies.

Animal models for the study of HBV replication and its variants

Enormous progresses in hepatitis B virus research have been made through the identification of avian and mammalian HBV related viruses, which offer ample opportunities for studies in naturally occurring hosts. However, none of these natural hosts belongs to the commonly used laboratory animals, and the development of various mouse strains carrying HBV transgenes offered unique opportunities to investigate some mechanisms of viral pathogenesis. Furthermore, the need to perform infection studies in a system harbouring HBV-permissive hepatocytes has lately led researchers to create new challenging human mouse chimera models of HBV infection. In this review, we will overview the type of animal models currently available in hepadnavirus research.

Hepatitis B virus DNA-negative dane particles lack core protein but contain a 22-kDa precore protein without C-terminal arginine-rich domain

DNA-negative Dane particles have been observed in hepatitis B virus (HBV)-infected sera. The capsids of the empty particles are thought to be composed of core protein but have not been studied in detail. In the present study, the protein composition of the particles was examined using new enzyme immunoassays for the HBV core antigen (HBcAg) and for the HBV precore/core proteins (core-related antigens, HBcrAg). HBcrAg were abundant in fractions slightly less dense than HBcAg and HBV DNA. Three times more Dane-like particles were observed in the HBcrAg-rich fraction than in the HBV DNA-rich fraction by electron microscopy. Western blots and mass spectrometry identified the HBcrAg as a 22-kDa precore protein (p22cr) containing the uncleaved signal peptide and lacking the arginine-rich domain that is involved in binding the RNA pregenome or the DNA genome. In sera from 30 HBV-infected patients, HBcAg represented only a median 10.5% of the precore/core proteins in enveloped particles. These data suggest that most of the Dane particles lack viral DNA and core capsid but contain p22cr. This study provides a model for the formation of the DNA-negative Dane particles. The precore proteins, which lack the arginine-rich nucleotide-binding domain, form viral RNA/DNA-negative capsid-like particles and are enveloped and released as empty particles.

Cellular response to conditional expression of the hepatitis B virus precore and core proteins in cultured hepatoma (Huh-7) cells

BACKGROUND

The expression of the hepatitis Be antigen (HBeAg) is one of several strategies used by hepatitis B virus (HBV) to ensure persistence. The HBeAg may function as a toleragen in utero and has been shown to regulate the host's immune response.

AIM

The aim of this study was to examine the effect of the HBV precore and core protein on cellular gene expression in the hepatoma cell line Huh-7.

STUDY DESIGN

Huh-7 cells with tight regulated expression of the HBV core or precore protein were produced using the Tet-Off tetracycline gene expression system. Changes in cellular gene expression in response to core/precore expression compared to Huh-7 cells not expressing the proteins were determined using a commercial high-density oligonucleotide array (Affymetrix Hu95A GeneChip) containing probes for 12,626 full-length human genes.

RESULTS

Analysis of differential mRNA gene expression profiles at 7 days post precore and core expression revealed 45 and 5 genes, respectively, with mRNA changes greater than three-fold. The most striking feature was in Huh-7 cells expressing the precore protein in which 43/45 genes were downregulated 3-11-fold. These included genes that encoded products that regulate transcription/DNA binding proteins, cell surface receptors, cell-cycle/nucleic acid biosynthesis and intracellular signalling and trafficking. The only known gene, which was upregulated encoded a cytoskeletal protein. For the core cell line, 4/5 genes were downregulated 3-15-fold upon core induction and included genes that encoded products that affect intermediary metabolism, cell surface receptors and intracellular signalling. The one gene, which was upregulated was a cytokine gene.

CONCLUSION

The results of this study show that HBV precore protein has a much greater effect on cellular gene expression in comparison to the core protein, suggesting that core and precore proteins may have diverse effects on cellular functions and equally different roles in modulating HBV pathogenesis.

The precore mutation is associated with severity of liver damage in Brazilian patients with chronic hepatitis B

BACKGROUND

The clinical relevance of the G1896A precore mutation in chronic hepatitis B is still poorly understood.

OBJECTIVES

To assess the frequency of G1896A precore mutation in Brazilian patients with chronic hepatitis B, as well as its relation to the viral genotype, serum HBV-DNA levels and liver damage.

STUDY DESIGN

Fifty chronic hepatitis B patients (29 HBeAg-negative and 21 HBeAg-positive) were studied. HBV-DNA was quantified by the Amplicor HBV Monitor test and precore region and S gene were amplified and submitted to automatic sequencing. The histological activity index (HAI), degrees of hepatic fibrosis and distribution of core antigen (HBcAg) in hepatocytes were determined.

RESULTS

Precore mutation occurred in 1/21 (4.8%) HBeAg-positive patients and in 17/29 (58.6%) HBeAg-negative (p < 0.0001). Genotype D was identified in 56.5%, genotype A in 41.3%, and genotype F in 2.2%. The frequency of genotypes D and A, as well as serum levels of ALT and HBV-DNA were similar in patients infected with wild type and with precore mutant. Patients infected with precore mutant presented a higher frequency of moderate/severe HAI (p: 0.03) and moderate/severe fibrosis and cirrhosis (p: 0.03) than those infected with wild type. There was no association between G1896A mutation and cytoplasmic expression of HBcAg.

CONCLUSIONS

Precore mutation was frequent among Brazilian subjects with chronic hepatitis B and its presence was associated with greater severity of liver disease.

Immune Tolerance Split between Hepatitis B Virus Precore and Core Proteins

The function of the hepatitis B virus (HBV) precore or HBeAg is largely unknown because it is not required for viral assembly, infection, or replication. However, the HBeAg does appear to play a role in viral persistence. It has been suggested that the HBeAg may promote HBV chronicity by functioning as an immunoregulatory protein. As a model of chronic HBeAg exposure and to examine the tolerogenic potential of the HBV precore and core (HBcAg) proteins, HBc/HBeAg-transgenic (Tg) mice crossed with T cell receptor (TCR)-Tg mice expressing receptors for the HBc/HBeAgs (i.e., TCR-antigen double-Tg pairs) were produced. This study revealed three phenotypes of HBe/HBcAg-specific T-cell tolerance: (i) profound T-cell tolerance most likely mediated by clonal deletion, (ii) T-cell clonal ignorance, and (iii) nondeletional T-cell tolerance mediated by clonal anergy and dependent on the structure, location, and concentration of the tolerogen. The secreted HBeAg is significantly more efficient than the intracellular HBcAg at eliciting T-cell tolerance. The split T-cell tolerance between the HBeAg and the HBcAg and the clonal heterogeneity of HBc/HBeAg-specific T-cell tolerance may have significant implications for natural HBV infection and especially for precore-negative chronic hepatitis.

A function of the hepatitis B virus precore protein is to regulate the immune response to the core antigen

A unique characteristic of the hepatitis B virus is the production of a secreted form (precore or HBeAg) of the structural nucleocapsid (core or HBcAg). By using T cell receptor (TCR) transgenic (Tg) and TCR x HBc/HBeAg double- and triple-Tg pairs, we demonstrate that HBeAg elicits T cell tolerance, whereas HBcAg is nontolerogenic in this system. In fact, TCR x HBc double-Tg mice spontaneously seroconvert to IgG anti-HBc positivity at an early age. However, the presence of HBeAg in the serum of TCR x HBc x HBe triple-Tg mice prevents anti-HBc seroconversion. HBeAg mediates its immunoregulatory effect by eliciting tolerance in HBc/HBeAg-specific T cells. The results suggest that hepadnaviruses have retained a secretory form of the nucleoprotein because it functions as a T cell tolerogen and regulates the immune response to the intracellular nucleocapsid. This HBeAg-mediated immune regulation may predispose to chronicity during perinatal infections and prevent severe liver injury during adult infections.

Basal core promoter and precore mutations in the hepatitis B virus genome enhance replication efficacy of Lamivudine-resistant mutants

During chronic hepatitis B virus (HBV) infection, mutations in the precore (PC) or basal core promoter (BCP) region affecting HBV e antigen (HBeAg) expression occur commonly and represent the predominant virus species in patients with HBeAg-negative chronic hepatitis B. The PC mutation (G1896A+C1858T) creates a translational stop codon resulting in absent HBeAg expression, whereas BCP mutations (A1762T/G1764A) reduce HBeAg expression by transcriptional mechanisms. Treatment of chronic HBV infection with lamivudine (LMV) often selects drug-resistant strains with single (rtM204I) or double (rtL180M+rtM204V) point mutations in the YMDD motif of HBV reverse transcriptase. We cloned replication-competent HBV vectors (genotype A, adw2) combining mutations in the core (wild type [wt], PC, and BCP) and polymerase gene (wt, rtM204I, and rtL180M/M204V) and analyzed virus replication and drug sensitivity in vitro. Resistance to LMV (rtM204I/rtL180M+rtM204V) was accompanied by a reduced replication efficacy as evidenced by reduced pregenomic RNA, encapsidated progeny DNA, polymerase activity, and virion release. PC mutations alone did not alter virus replication but restored replication efficacy of the LMV-resistant mutants without affecting drug resistance. BCP mutants had higher replication capacities than did the wt, also in combination with LMV resistance mutations. All nine HBV constructs showed similar sensitivities to adefovir. In conclusion, BCP-PC mutations directly impact the replication capacity of LMV-resistant mutants. PC mutations compensated for replication inefficiency of LMV-resistant mutants, whereas BCP mutations increased viral replication levels to above the wt baseline values, even in LMV-resistant mutants, without affecting drug sensitivity in vitro. Adefovir may be an effective treatment when combinations of core and polymerase mutations occur.

Regulation of hepatitis B virus core promoter by transcription factors HNF1 and HNF4 and the viral X protein

Hepatitis B virus (HBV) core promoter contains a binding site for nuclear receptors. A natural double mutation in this binding site, which changes nucleotide (nt) 1765 from A to T and nt 1767 from G to A, selectively abolishes the binding of several nuclear receptors without affecting that of HNF4. This double mutation also creates a binding site for the transcription factor HNF1 and changes two amino acids in the overlapping X protein sequence. In this study, we have examined the roles of HNF1, HNF4, and the X protein in the regulation of the core promoter activities in Huh7 hepatoma cells. Our results indicate that HNF4 could stimulate the expression of the precore RNA and the core RNA from the core promoter of both the wild-type (WT) HBV and the double mutant, although its effect on the former was more prominent. In contrast, HNF1, which did not affect the WT core promoter, suppressed the precore RNA expression of the double mutant. Further analysis using HBV genomic constructs, with and without the ability to express the X protein, indicates that the X protein did not affect the HNF4 activity on the core promoter and affected the HNF1 activity on the core promoter of only the double mutant. Thus, our results indicate that the phenotypic differences of HBV WT and double-mutant core promoters are at least partially due to the differential activities of HNF1, HNF4, and the X protein on these two promoters.

Complete hepatitis B virus genome analysis in HBsAg positive mothers and their infants with fulminant hepatitis B

Background

After perinatal transmission of hepatitis B virus, infants of anti-HBe positive HBsAg carrier mothers may develop fulminant hepatitis B. Previously it has been suggested, that fulminant hepatitis B in adults was associated with specific mutations in the HBV-genome. The aim of this study was to investigate, whether specific viral variants are associated with fulminant hepatitis B in young infants.

Methods

The complete HBV-genomes of five mothers and their infants with fulminant hepatitis were isolated from the sera, amplified and directly sequenced.

Results

Between 6 and 43 base pair exchanges between the HBV genomes of the infants and their mothers were identified. The mutations spread over the entire virus genome. Nucleotide exchanges in the basic core promotor and precore region were identified in all cases. A heterogeneous virus population was detected in four mothers.

Conclusions

Many new mutations were proved to emerge during fulminant hepatitis B in infants, who had been perinatally infected. HBeAg negative variants were the predominant population in all children, whereas these mutants could only be detected as subpopulations in four mothers. The data suggest that the selection of a specific HBeAg negative viral strain may be associated with the development of fulminant hepatitis B in children.

In vitro and in vivo interactions between the hepatitis B virus protein P22 and the cellular protein gC1qR

gC1qR, a mitochondrial matrix protein, was identified as the main cellular partner of the hepatitis B virus P22 protein. We demonstrated by immunofluorescence studies that some P22 molecules were colocalized with the endogenous gC1qR in both the cytoplasm and the nucleus but never in the mitochondria. We also showed that the last 34 amino acids of P22 were involved in the association with gC1qR.