Three envelope proteins of hepatitis B virus: large S, middle S, and major S proteins needed for the formation of Dane particles

Viral Hepatitis: Host Immune Interaction, Pathogenesis and New Therapeutic Strategies

Viral hepatitis is a major cause of liver illness worldwide. Despite advances in the understanding of these infections, the pathogenesis of hepatitis remains a complex process driven by intricate interactions between hepatitis viruses and host cells at the molecular level. This paper will examine in detail the dynamics of these host-pathogen interactions, highlighting the key mechanisms that regulate virus entry into the hepatocyte, their replication, evasion of immune responses, and induction of hepatocellular damage. The unique strategies employed by different hepatitis viruses, such as hepatitis B, C, D, and E viruses, to exploit metabolic and cell signaling pathways to their advantage will be discussed. At the same time, the innate and adaptive immune responses put in place by the host to counter viral infection will be analyzed. Special attention will be paid to genetic, epigenetic, and environmental factors that modulate individual susceptibility to different forms of viral hepatitis. In addition, this work will highlight the latest findings on the mechanisms of viral persistence leading to the chronic hepatitis state and the potential implications for the development of new therapeutic strategies. Fully understanding the complex host-pathogen interactions in viral hepatitis is crucial to identifying new therapeutic targets, developing more effective approaches for treatment, and shedding light on the mechanisms underlying progression to more advanced stages of liver damage.

Regulation of Hepatitis B Virus Replication by Modulating Endoplasmic Reticulum Stress (ER-Stress)

Hepatitis B virus (HBV), resistant to several antiviral drugs due to viral genomic mutations, has been reported, which aggravates chronic infection and leads to hepatocellular carcinoma. Therefore, host cellular factors/signaling modulation might be an alternative way of treatment for drug-resistant HBV. Here, we investigated the viral protein expression, replication, and virion production using endoplasmic reticulum (ER) stress-modulating chemicals, tunicamycin (an ER-stress inducer), and salubrinal (an ER-stress inhibitor). We found that ER-stress could be induced by HBV replication in transfected HepG2 cells as well as by tunicamycin as demonstrated by dual luciferase assay. HBV intracellular core-associated DNA quantified by qPCR has been significantly increased by tunicamycin in transfected HepG2 cells. Inversely, intracellular core associated and extracellular particle DNA has been significantly decreased in a dose-dependent manner in salubrinal-treated HepG2 cells transfected with HBV-replicating plasmid pHBI. Similar results were found in stably HBV-expressing hepatoblastoma (HB611) cells treated with salubrinal. However, increased or decreased ER-stress by tunicamycin or salubrinal treatment, respectively, has been confirmed by expression analysis of grp78 using Western blot. In addition, Western blot results demonstrated that the expression of HBV core protein and large HBsAg is increased and decreased by tunicamycin and salubrinal, respectively. In conclusion, the sal-mediated inhibition of the HBV replication and virion production might be due to the simultaneous reduction of core and large HBsAg expression and maintaining the ER homeostasis. These results of HBV replication regulation by modulation of ER-stress dynamics would be useful for designing/identifying anti-HBV drugs targeting cellular signaling pathways.

Evolution and diversity of the hepatitis B virus genome: Clinical implications

Hepatitis B virus (HBV) infection remains a significant global health burden. The genetic variation of HBV is complex. HBV can be divided into nine genotypes, which show significant differences in geographical distribution, clinical manifestations, transmission routes and treatment response. In recent years, substantial progress has been made through various research methods in understanding the development, pathogenesis, and antiviral treatment response of clinical disease associated with HBV genetic variants. This progress provides important theoretical support for a deeper understanding of the natural history of HBV infection, virus detection, drug treatment, vaccine development, mother-to-child transmission, and surveillance management. This review summarizes the mechanisms of HBV diversity, discusses methods used to detect viral diversity in current studies, and the impact of viral genome variation during infection on the development of clinical disease.

Comprehensive analysis of antigenic variations and genomic properties of hepatitis B virus in clinical samples in the mid-north east region of Bangladesh

This investigation delineates an exhaustive analysis of the clinical, immunological, and genomic landscapes of hepatitis B virus (HBV) infection across a cohort of 22 verified patients. The demographic analysis unveiled a pronounced male bias (77.27%), with patient ages spanning 20 to 85 years and durations of illness ranging from 10 days to 4 years. Predominant clinical manifestations included fever, fatigue, anorexia, abdominal discomfort, and arthralgia, alongside observed co-morbidities such as chronic renal disorders and hepatocellular carcinoma. Antigenic profiling of the HBV envelope proteins elucidated significant heterogeneity among the infected subjects, particularly highlighted by discordances in the detection capabilities of small and large HBsAg assays, suggesting antigenic diversity. Quantitative assessment of viral loads unveiled a broad spectrum, accompanied by atypical HBeAg reactivity patterns, challenging the reliability of existing serological markers. Correlative studies between viral burden and antigenicity of the envelope proteins unearthed phenomena indicative of diagnostic evasion. Notably, samples demonstrating robust viral replication were paradoxically undetectable by the large HBsAg ELISA kit, advocating for more sophisticated diagnostic methodologies. Genotypic examination of three HBV isolates classified them as genotype D (D2), with phylogenetic alignment to strains from various global origins. Mutational profiling identified pivotal mutations within the basic core promoter and preS2/S1 regions, associated with an augmented risk of hepatocellular carcinoma. Further, mutations discerned in the small HBsAg and RT/overlap regions were recognized as contributors to vaccine and/or diagnostic escape mechanisms. In summation, this scholarly discourse elucidates the intricate interplay of clinical presentations, antigenic diversity, and genomic attributes in HBV infection, accentuating the imperative for ongoing investigative endeavors to refine diagnostic and therapeutic modalities.

[Neutralization of hepatitis B virus with vaccine-escape mutations by novel hepatitis B vaccine with large-HBs antigen]

Although the current hepatitis B (HB) vaccine comprising yeast-derived small hepatitis B surface antigen (HBsAg) is potent and safe and used worldwide, specific concerns should not be ignored, such as the attenuated prophylaxis against hepatitis B virus (HBV) infection with specific amino acid polymorphisms, called vaccine-escape mutations (VEMs). We investigated a novel HB vaccine consisting of large-HBsAg that covers the shortcomings of the current HB vaccine in a nonhuman primate model. The yeast-derived large-HBsAg was mixed with the adjuvant and used to immunize rhesus macaques, and the induction of antibodies to HBsAg was compared with that of the current HB vaccine. The current HB vaccine predominantly induced antibodies to small-HBsAg, whereas immunization with the large-HBsAg vaccine mainly induced antibodies to the preS1 region. Although the antibodies induced by the current HB vaccine could not prevent infection of HBV with VEMs, the large-HBsAg vaccine-induced antibodies neutralized infection of HBV with VEMs at levels similar to those of the wild type. The HBV genotypes that exhibited attenuated neutralization by induced antibodies differed between these vaccines. In conclusion, the novel HB vaccine consisting of large-HBsAg was revealed to be useful to compensate for shortcomings of the current HB vaccine. The combined use of these HB vaccines may be able to induce antibodies that can neutralize HBV strains with VEMs or multiple HBV genotypes.

Establishment of monoclonal antibodies broadly neutralize infection of hepatitis B virus

Antibodies against hepatitis B virus S protein can protect against hepatitis B virus (HBV) infection. Therefore, hepatitis B immunoglobulin (HBIG), which contains HBsAb, is used clinically as a therapy for HBV infection. In this study, we obtained a series of monoclonal antibodies that recognize multiple HBV genotypes. All the antibodies recognized conformational epitopes of S protein, but not linear epitopes. Several antibodies neutralized HBV infection and exhibited strong affinities and neutralizing activities. Antigenic epitope analysis demonstrated that they recognized residue Ile152 of S protein_, which is localized outside the "a" determinant. Ile152 is highly conserved, and a mutation in this residue resulted in reduced expression of large hepatitis B surface proteins (L protein), suggesting that the amino acid at this position is involved in the expression of L protein. In addition, the antibodies neutralized the infection of hepatitis D virus possessing a Gly145 mutation to Arg in S protein, which is a well-known escape mutation against HBIG treatment. Using mouse monoclonal antibodies, we successfully established a humanized antibody possessing affinities and neutralizing activities similar to those of the original mouse antibody. The antibodies generated in this study may have potential for use in alternative antibody therapies for HBV infection. This article is protected by copyright. All rights reserved.

Human hepatitis B virus-derived virus-like particle as a drug and DNA delivery carrier

The controlled release of medications using nanoparticle-based drug delivery carriers is a promising method to increase the efficacy of pharmacotherapy and gene therapy. One critical issue that needs to be overcome with these drug delivery carriers is their target specificity. We focused on the cell tropism of a virus to solve this issue, i.e., we attempted to apply hepatitis B virus-like particle (HBV-VLP) as a novel hepatic cell-selective carrier for medication and DNA. To prepare HBV-VLP, 293T cells were transfected with expression plasmids carrying HBV envelope surface proteins, large envelope protein (L), and small envelope protein (S). After 72 h post-transfection, VLP-containing culture supernatants were harvested, and HBV-VLP was labeled with red fluorescent dye (DiI) and was purified by sucrose gradient ultracentrifugation. An anticancer drugs (geldanamycin or doxorubicin) and GFP-expressing plasmid DNA were incorporated into HBV-VLP, and medication- and plasmid DNA-loaded VLPs were prepared. We evaluated their delivery capabilities into hepatocytes, other organ-derived cells, and hepatocytes expressing sodium taurocholate cotransporting polypeptide (NTCP), which functions as the cellular receptor for HBV by binding to HBV L protein. HBV-VLP selectively delivered both anticancer drugs and plasmid DNA not into HepG2, Huh7, and other organ cells but into HepG2 cells expressing NTCP. In summary, we developed a novel delivery nanocarrier using HBV-VLP that could be used as a hepatitis selective drug- and DNA-carrier for cancer treatment and gene therapy.

Analysis of the Physicochemical Properties, Replication and Pathophysiology of a Massively Glycosylated Hepatitis B Virus HBsAg Escape Mutant

Mutations in HBsAg, the surface antigen of the hepatitis B virus (HBV), might affect the serum HBV DNA level of HBV-infected patients, since the reverse transcriptase (RT) domain of HBV polymerase overlaps with the HBsAg-coding region. We previously identified a diagnostic escape mutant (W3S) HBV that produces massively glycosylated HBsAg. In this study, we constructed an HBV-producing vector that expresses W3S HBs (pHB-W3S) along with a wild-type HBV-producing plasmid (pHB-WT) in order to analyze the physicochemical properties, replication, and antiviral drug response of the mutant. Transfection of either pHB-WT or W3S into HepG2 cells yielded similar CsCl density profiles and eAg expression, as did transfection of a glycosylation defective mutant, pHB-W3S (N146G), in which a glycosylation site at the 146aa asparagine (N) site of HBs was mutated to glycine (G). Virion secretion, however, seemed to be severely impaired in cases of pHB-W3S and pHB-W3S (N146G), compared with pHB-WT, as determined by qPCR and Southern blot analysis. Furthermore, inhibition of glycosylation using tunicamycin^TM on wild-type HBV production also reduced the virion secretion. These results suggested that the HBV core and Dane particle could be formed either by massively glycosylated or glycosylation-defective HBsAg, but reduced and/or almost completely blocked the virion secretion efficiency, indicating that balanced glycosylation of HBsAg is required for efficient release of HBV, and mutations inducing an imbalanced glycosylation of HBs would cause the virion to become stuck in the cells, which might be associated with various pathogeneses due to HBV infection.

Amino Acid Polymorphism in Hepatitis B Virus Associated With Functional Cure

BACKGROUND & AIMS

To provide an adequate treatment strategy for chronic hepatitis B, it is essential to know which patients are expected to have a good prognosis and which patients do not require therapeutic intervention. Previously, we identified the substitution of isoleucine to leucine at amino acid 97 (I97L) in the hepatitis B core region as a key predictor among patients with stable hepatitis. In this study, we attempted to identify the point at which I97L affects the hepatitis B virus (HBV) life cycle and to elucidate the underlying mechanisms governing the stabilization of hepatitis.

METHODS

To confirm the clinical features of I97L, we used a cohort of hepatitis B e antigen-negative patients with chronic hepatitis B infected with HBV-I97 wild-type (wt) or HBV-I97L. The effects of I97L on viral characteristics were evaluated by in vitro HBV production and infection systems with the HBV reporter virus and cell culture-generated HBV.

RESULTS

The ratios of reduction in hepatitis B surface antigen and HBV DNA were higher in patients with HBV-I97L than in those with HBV-I97wt. HBV-I97L exhibited lower infectivity than HBV-I97wt in both infection systems with reporter HBV and cell culture-generated HBV. HBV-I97L virions exhibiting low infectivity primarily contained a single-stranded HBV genome. The lower efficiency of cccDNA synthesis was demonstrated after infection of HBV-I97L or transfection of the molecular clone of HBV-I97L.

CONCLUSIONS

The I97L substitution reduces the level of cccDNA through the generation of immature virions with single-stranded genomes. This I97L-associated low efficiency of cccDNA synthesis may be involved in the stabilization of hepatitis.

HBsAg, Subviral Particles, and Their Clearance in Establishing a Functional Cure of Chronic Hepatitis B Virus Infection

In diverse viral infections, the production of excess viral particles containing only viral glycoproteins (subviral particles or SVP) is commonly observed and is a commonly evolved mechanism for immune evasion. In hepatitis B virus (HBV) infection, spherical particles contain the hepatitis B surface antigen, outnumber infectious virus 10 000-100 000 to 1, and have diverse inhibitory effects on the innate and adaptive immune response, playing a major role in the chronic nature of HBV infection. The current goal of therapies in development for HBV infection is a clinical outcome called functional cure, which signals a persistent and effective immune control of the infection. Although removal of spherical SVP (and the HBsAg they carry) is an important milestone in achieving functional cure, this outcome is rarely achieved with current therapies due to distinct mechanisms for assembly, secretion, and persistence of SVP, which are poorly targeted by direct acting antivirals or immunotherapies. In this Review, the current understanding of the distinct mechanisms involved in the production and persistence of spherical SVP in chronic HBV infection and their immunoinhibitory activity will be reviewed as well as current therapies in development with the goal of clearing spherical SVP and achieving functional cure.

Functional roles of GRP78 in hepatitis B virus infectivity and antigen secretion

Viruses utilize cellular proteins to mediate their life cycle. However, the hepatitis B virus (HBV) life cycle is still mysterious and remains to be elucidated. Here, GRP78/BiP/HSPA5, a 78 kDa glucose-regulated protein, was identified as a preS2 interacting protein. Pulldown assay showed the interaction of glucose-regulated protein 78 (GRP78) with both the preS2 domain-containing large S and middle S proteins expressed in a human hepatocellular cell line. The immunofluorescence studies revealed that the preS2 colocalized with GRP78. Interestingly, it was found that preS2 specifically bound to the ATPase domain of GRP78. To understand how GRP78 plays a role in HBV infection, stably GRP78-expressing cells were established, which promoted HBV infectivity and replication. In contrast, knockdown of GRP78 changed the HBV antigen secretion but not the viral DNA amplification. Taken together, these results suggest that GRP78 should interact with preS2 via the ATPase domain and modulate both the HBV infectivity and HBV antigen secretion.

Mechanisms of Hepatitis B Virus-Induced Hepatocarcinogenesis

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.

Hepatitis B surface antigen seroclearance: Immune mechanisms, clinical impact, importance for drug development

HBsAg seroclearance occurs rarely in the natural history of chronic hepatitis B (CHB) infection and is associated with improved clinical outcomes. Many factors are associated with HBsAg seroconversion, including immune and viral factors. However, the immune mechanisms associated with HBsAg seroclearance are still difficult to elucidate. HBsAg seroclearance is the ideal aim of HBV treatment. Unfortunately, this goal is rarely achieved with current treatments. Understanding the mechanisms of HBsAg loss appears to be important for the development of curative HBV treatments. While studies from animal models give insights into the potential immune mechanisms and interactions occurring between the immune system and HBsAg, they do not recapitulate all features of CHB in humans and are subject to variability due to their complexity. In this article, we review recent studies on these immune factors, focusing on their influence on CHB progression and HBsAg seroconversion. These data provide new insights for the development of therapeutic approaches to partially restore the anti-HBV immune response. Targeting HBsAg will ideally relieve the immunosuppressive effects on the immune system and help to restore anti-HBV immune responses.

Mechanism and Complex Roles of HSC70 in Viral Infections

Heat shock cognate 71-kDa protein (HSC70), a constitutively expressed molecular chaperon within the heat shock protein 70 family, plays crucial roles in maintaining cellular environmental homeostasis through implicating in a wide variety of physiological processes, such as ATP metabolism, protein folding and transporting, antigen processing and presentation, endocytosis, and autophagy. Notably, HSC70 also participates in multiple non-communicable diseases and some pathogen-caused infectious diseases. It is known that virus is an obligatory intracellular parasite and heavily relies on host machineries to self-replication. Undoubtedly, HSC70 is a striking target manipulated by virus to ensure the successful propagation. In this review, we summarize the recent advances of the regulatory mechanisms of HSC70 during viral infections, which will be conducive to further study viral pathogenesis.

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.

Targeting Host Innate and Adaptive Immunity to Achieve the Functional Cure of Chronic Hepatitis B

Despite the availability of an effective preventive vaccine for hepatitis B virus (HBV) for over 38 years, chronic HBV (CHB) infection remains a global health burden with around 257 million patients. The ideal treatment goal for CHB infection would be to achieve complete cure; however, current therapies such as peg-interferon and nucleos(t)ide analogs are unable to achieve the functional cure, the newly set target for HBV chronic infection. Considering the fact functional cure has been accepted as an endpoint in the treatment of chronic hepatitis B by scientific committee, the development of alternative therapeutic strategies is urgently needed to functionally cure CHB infection. A promising target for future therapeutic strategies is immune modulation to restore dysfunctional HBV-specific immunity. In this review, we provide an overview of the progress in alternative therapeutic strategies, including immune-based therapeutic approaches that enhance host innate and adaptive immunity to achieve and increase the functional cure from CHB infection.

SERINC5 Inhibits the Secretion of Complete and Genome-Free Hepatitis B Virions Through Interfering With the Glycosylation of the HBV Envelope

Serine incorporator 3 (SERINC3) and SERINC5 were recently identified as host intrinsic factors against human immunodeficiency virus (HIV)-1 and counteracted by HIV-1 Nef. However, whether they inhibit hepatitis B virus (HBV), which is a severe health problem worldwide, is unknown. Here, we demonstrate that SERINC5 potently inhibited HBV virion secretion in the supernatant without affecting intracellular core particle-associated DNA and the total RNA, but SERINC3 and SERINC1 did not. Further investigation discovered that SERINC5 increased the non-glycosylation of LHB, MHB, and SHB proteins of HBV and slightly decreased HBs proteins levels, which led to the decreased HBV secretion. Importantly, SERINC5 co-localized with LHB proteins in the Golgi apparatus, which is important for glycan processing and transport. In addition, we determined the functional domain in SERINC5 required for HBV inhibition, which was completely different from that required for HIV-1 restriction, whereas phosphorylation and glycosylation sites in SERINC5 were dispensable for HBV restriction. Taken together, our results demonstrate that SERINC5 suppresses HBV virion secretion through interfering with the glycosylation of HBV proteins, suggesting that SERINC5 might possess broad-spectrum antiviral activity.

Impact of the Interaction of Hepatitis B Virus with Mitochondria and Associated Proteins

Around 350 million people are living with hepatitis B virus (HBV), which can lead to death due to liver cirrhosis and hepatocellular carcinoma (HCC). Various antiviral drugs/nucleot(s)ide analogues are currently used to reduce or arrest the replication of this virus. However, many studies have reported that nucleot(s)ide analogue-resistant HBV is circulating. Cellular signaling pathways could be one of the targets against the viral replication. Several studies reported that viral proteins interacted with mitochondrial proteins and localized in the mitochondria, the powerhouse of the cell. And a recent study showed that mitochondrial turnover induced by thyroid hormones protected hepatocytes from hepatocarcinogenesis mediated by HBV. Strong downregulation of numerous cellular signaling pathways has also been reported to be accompanied by profound mitochondrial alteration, as confirmed by transcriptome profiling of HBV-specific CD8 T cells from chronic and acute HBV patients. In this review, we summarize the ongoing research into mitochondrial proteins and/or signaling involved with HBV proteins, which will continue to provide insight into the relationship between mitochondria and HBV and ultimately lead to advances in viral pathobiology and mitochondria-targeted antiviral therapy.

The modulation of HBsAg level by sI126T is affected by additional amino acid substitutions in the S region of HBV

The hepatitis B surface antigen (HBsAg) is a vital serum marker for hepatitis B virus (HBV) infection. Amino acid (AA) substitutions in small hepatitis B surface protein (SHBs) are known to affect HBsAg level. However, how the genetic backbones of SHBs sequences would affect the roles of a specific AA substitution on HBsAg level remains unclear. In this study, we found that sI126 had a very high substitution detection rate of 17.54% (40/228) in untreated chronic hepatitis B cohort with subgenotype C2 HBV infection. Among different substitution types at sI126, the sI126T (N = 28) was found to be associated with significantly lower serum HBsAg level. Clone sequencing revealed that sI126T-harboring SHBs sequences had varied genetic backbones with zero to nine additional AA substitutions. Thus, we constructed 24 HBsAg expression plasmids harboring sI126T without (plasmid 1, P1) or with (P2-P24) additional AA substitution(s) and studied them in the HepG2 cells. The HBsAg levels were determined by both ELISA and Western blot. In vitro experiments showed that P1 significantly reduced HBsAg level and its secretion (p < .05), however, P2-P24 showed various extracellular and intracellular HBsAg levels. No significant differences were detected among the HBsAg mRNA levels of nine representative mutant plasmids. Our findings suggest that the modulation of HBsAg level by sI126T is affected by additional AA substitution(s) in the S region of HBV. The effects of AA combination substitutions in SHBs sequences on HBsAg levels are worthwhile for more attentions in terms of HBV biology and its clinical application.

MiR-185-5p suppresses HBV gene expression by targeting ELK1 in hepatoma carcinoma cells

AIMS

To investigate the role and underlying mechanism of miR-185-5p in hepatitis B virus (HBV) expression and replication.

MAIN METHODS

The relative levels of hepatitis B surface antigen and hepatitis B e antigen were detected by enzyme-linked immunosorbent assay (ELISA). The HBV DNA copies in the cultures medium were measured by RT-qPCR. The HBV large surface antigen promoter (S1p) activity was analyzed by luciferase reporter assay. The target relationship between miR-185-5p and ELK1 was identified by bioinformatics analysis and EGFP fluorescent reporter assay. The ELK1 expression was determined by RT-qPCR and Western blot.

KEY FINDINGS

miR-185-5p significantly decreased HBV large surface antigen promoter activity and subsequently the production of HBV proteins and HBV DNA copies in vitro. Further, we identified the ETS transcription factor ELK1 is a target of miR-185-5p. Overexpression and knockdown experiments showed overexpression of ELK1 stimulated HBV large surface antigen promoter activity and promoted the production of HBV proteins and HBV DNA copies, whereas knockdown of ELK1 has the opposite effects. Moreover, the rescue of ELK1 expression reversed the suppression of miR-185-5p on HBV replication and gene expression. Further mechanistic study showed that the ETS binding sites within the HBV large surface antigen promoter are required for the repression effect of miR-185-5p on HBV.

SIGNIFICANCE

There are few reports about the interaction between miRNAs and the transcription from HBV S1p, we found that miR-185-5p decreases HBV S1p activity by targeting ELK1, which may provide a promising therapeutic strategy for HBV infection.

A G-quadruplex motif in an envelope gene promoter regulates transcription and virion secretion in HBV genotype B

HBV genotypes differ in pathogenicity. In addition, genotype-specific differences in the regulation of transcription and virus replication exist in HBV, but the underlying mechanisms are unknown. Here, we show the presence of a G-quadruplex motif in the promoter of the preS2/S gene; this G-quadruplex is highly conserved only in HBV genotype B but not in other HBV genotypes. We demonstrate that this G-quadruplex motif forms a hybrid intramolecular G-quadruplex structure. Interestingly, mutations disrupting the G-quadruplex in HBV genotype B reduced the preS2/S promoter activity, leading to reduced hepatitis B surface antigen (HBsAg) levels. G-quadruplex ligands stabilized the G-quadruplex in genotype B and enhanced the preS2/S promoter activity. Furthermore, mutations disrupting the G-quadruplex in the full-length HBV genotype B constructs were associated with impaired virion secretion. In contrast to typical G-quadruplexes within promoters which are negative regulators of transcription the G-quadruplex in the preS2/S promoter of HBV represents an unconventional positive regulatory element. Our findings highlight (a) G-quadruplex mediated enhancement of transcription and virion secretion in HBV and (b) a yet unknown role for DNA secondary structures in complex genotype-specific regulatory mechanisms in virus genomes.

Viral mechanisms for docking and delivering at nuclear pore complexes

Some viruses possess the remarkable ability to transport their genomes across nuclear pore complexes (NPCs) for replication inside the host cell's intact nuclear compartment. Viral mechanisms for crossing the restrictive NPC passageway are highly complex and astonishingly diverse, requiring in each case stepwise interaction between incoming virus particles and components of the nuclear transport machinery. Exactly how a large viral genome loaded with accessory proteins is able to pass through the relatively narrow central channel of the NPC without causing catastrophic structural damage is not yet fully understood. It appears likely, however, that the overall structure of the NPC changes in response to the cargo. Translocation may result in nucleic acids being misdelivered to the cytoplasm. Here we consider in detail the diverse strategies that viruses have evolved to target and subvert NPCs during infection. For decades, this process has both captivated and confounded researchers in the fields of virology, cell biology, and structural biology.

Investigation of a Novel Hepatitis B Virus Surface Antigen (HBsAg) Escape Mutant Affecting Immunogenicity

Mutation in the hepatitis B virus surface antigen (HBsAg) may affect the efficiency of diagnostic immunoassays or success of vaccinations using HBsAg. Thus, antigenicity and immunogenicity analyses of the mutated HBsAg are necessary to develop novel diagnostic tools and efficient vaccinations. Here, the in vitro antigenicity of three wild-type HBsAg open reading frames (ORFs) (adr4, W1S [subtype adr] and W3S [subtype adr]) isolated from clinically infected patients and nineteen synthesized single/double/multiple amino acid-substituted mutants were tested with commercial ELISA kits. Immunofluorescence staining of transfected cells and Western blot analysis confirmed that these ORFs were expressed at comparable levels in HEK-293 cells. W1S and adr4 were clearly detected, whereas W3S could not be detected. Using the same commercial immunoassay kit, we found that the single mutants, K120P and D123T, were marginally reactive, whereas W3S-aW1S and the double mutant, K120P/D123T, exhibited antigenicity roughly equivalent to the wild-type wako1S. On the other hand, the single mutants of W1S, P120K and T123D, significantly impaired the reactivity, while W1S-aW3S and the double mutant of W1S, P120K/T123D, resulted in a complete loss of antigenicity. In addition, ELISA revealed reduced HBs antigenicity of two mutants, W1S N146G and W1S Q129R/G145R. These commercial ELISA-based antigenic reactivities of HBsAg were also strongly correlated with the predicted Ai alterations of affected amino acids due to the specific mutation. In conclusion, this study showed for the first time that lysine (K120) and aspartate (D123) simultaneously affected HBsAg antigenicity, leading to diagnostic failure. These findings will improve diagnostic assays and vaccine development.

The intracellular dynamics of hepatitis B virus (HBV) replication with reproduced virion "re-cycling"

Hepatitis B virus (HBV) is a causative agent of hepatitis. Clinical outcome of hepatitis type B depends on the viral titer observed in the peripheral blood of the patient. In the chronic hepatitis patient, production of HBV virion remains low level. On the other hand, the viral load prominently increases in fulminant hepatitis patient as compared with that in the chronic hepatitis patient. We previously proposed a mathematical model describing the intracellular dynamics of HBV replication. Our model clarified that there are two distinguishable replication patterns of HBV named "arrested" and "explosive" replication. In the arrested replication, the amount of virion newly reproduced from an infected cell remains low level, while the amount of virion extremely increases in the explosive replication. Viral load is drastically changed by slight alteration of expression ratio of 3.5kb RNA to 2.4kb mRNA of HBV. Though our model provided the switching mechanism determining the replication pattern of HBV, HBV dynamics is determined by not only the expression pattern of viral genes. In this study, "recycling" of HBV virion in the replication cycle is investigated as a new factor affecting the intracellular dynamics of HBV replication. A part of newly produced virion of HBV is reused as a core particle that is a resource of HBV replication. This recycling of HBV virion lowers the threshold for the explosive replication when waiting time for the next cycle of the replication is large. It is seemingly contradicting that prominent production of HBV is caused by large recycling rate and small release rate of HBV virion from infected cell to extracellular space. But the recycling of HBV virion can contribute to the positive feedback cycle of HBV replication for the explosive replication to accumulate the core particle as a resource of HBV replication in an infected cell. Accumulation of core particle in the infected cell can be risk factor for the exacerbation of hepatitis rather than rapid release of HBV virion from the infected cell.

Molecular mechanisms underlying HBsAg negativity in occult HBV infection

Although genomic detection is considered the gold standard test on HBV infection identification, the HBsAg investigation is still the most frequent clinical laboratory request to diagnose HBV infection in activity. However, the non-detection of HBsAg in the bloodstream of chronic or acutely infected individuals has been a phenomenon often observed in clinical practice, despite the high sensitivity and specificity of screening assays standardized commercially and adopted in routine. The expansion of knowledge about the hepatitis B virus biology (replication/life cycle, genetic variability/mutability/heterogeneity), their biochemical and immunological properties (antigenicity and immunogenicity), in turn, has allowed to elucidate some mechanisms that may explain the occurrence of this phenomenon. Therefore, the negativity for HBsAg during the acute or chronic infection course may become a fragile or at least questionable result. This manuscript discusses some mechanisms that could explain the negativity for HBsAg in a serological profile of individuals with HBV infection in activity, or factors that could compromise its detection in the bloodstream during HBV infection.

A Human Monoclonal Antibody against Hepatitis B Surface Antigen with Potent Neutralizing Activity

We describe the production and characterization of human monoclonal antibodies (mAb) specific for the major hepatitis B virus (HBV) S protein. The mAbs, two IgG1κ and one IgG1λ, were secreted by B-cell clones obtained from peripheral blood mononuclear cells (PBMC) of one person convalescent from acute hepatitis B and one vaccinated individual. The former recognized a denaturation-insensitive epitope within the p24 protein whereas the latter recognized a denaturation-sensitive, conformational epitope located within the HBsAg common "a" determinant. This mAb, denominated ADRI-2F3, displayed a very high protective titer of over 43,000 IU/mg mAb and showed an extremely potent neutralizing activity in the in vitro model of HBV infection using primary hepatocytes from Tupaia belangeri as target. Recombinant variable heavy and light domain sequences derived from mAb ADRI-2F3 were cloned into eukaryotic expression vectors and showed identical fine specificity and 1 log10 higher titer than the original IgG1λ. It is envisaged that such mAb will be able to efficiently prevent HBV reinfection after liver transplantation for end-stage chronic HBV infection or infection after needle-stick exposure, providing an unlimited source of valuable protective anti-HBs antibody.

Hepatitis B core-based virus-like particles to present heterologous epitopes

Since the first effort to recombinantly express the hepatitis B core protein (HBc) in bacteria, the remarkable virion-like structure has fuelled interest in unraveling the structural and antigenic properties of this protein. Initial studies proved HBc virus-like particles to possess strong immunogenic properties, which can be conveyed to linked antigens. More than 35 years later, numerous studies have been performed using HBc as a carrier protein for antigens derived from over a dozen different pathogens and diseases. In this review, the authors highlight the intriguing features of HBc as carrier and antigen, illustrated by some examples and experimental results that underscore the value of HBc as an antigen-presenting platform. Two of these HBc fusions, targeting influenza A and malaria, have even progressed into clinical testing. In the future, the HBc-based virus-like particles platform will probably continue to be used for the display of poorly immunogenic antigens, mainly because virus-like particle formation by HBc capsomers is compatible with nearly any available recombinant gene expression system.

[Reverse genetics of Hepatitis B virus]

A global expansion of Hepatitis B virus (HBV) infection continues still now, and it poses a still big problem. Since the Australia antigen was discovered, HBV research has been continued by various methods, such as clinical medicine and epidemiology. However, the simple and efficient infection experimental systems (in vitro and in vivo) have not been established, because the host range of HBV is narrow. Therefore, the techniques of reverse genetics have contributed to HBV research greatly. We have established the HBV clones of various genotypes from the chronic hepatitis B patients, and have analyzed using the techniques of reverse genetics. Based on our results, it has become clear gradually how HBV pathogenesis related to the genotypes. In this paper, we would like to introduce the outline of research analyzed by reverse genetics about HBV.

HBV-related hepatocellular carcinoma: the role of integration, viral proteins and miRNA

The development of hepatocellular carcinoma during chronic hepatitis B infection is a multifactorial process thought to be a consequence of several direct and indirect mechanisms. In this review we discuss how viral proteins and cycles of ongoing liver damage and regeneration, coupled with HBV DNA integration and aberrant miRNA expression may enhance the risk for the development of hepatocellular carcinoma.

Significance of K(L/V)WX(I/L/V)P Epitope of the B2Gpi in Its (Patho)Physiologic Function

β2-glycoprotein I (β2GPI) is a major autoantigen of autoimmune thrombophilia, known as the antiphospholipid syndrome. The exact mechanism underlying the β2GPI's involvement in the disease is not fully elucidated, as it is not its physiological role. We used random phage peptide library to identify sequences binding to β2GPI. Obtained K(L/V)WX(I/L/V)P motif, primarily designated as target unrelated, was confirmed as the selective binder of β2GPI. Based on this motif we confirmed the previously suggested role of polar residues in β2GPI interactions, and identified some already known and some new putative β2GPI binding proteins. The latter can help to further elucidate β2GPI's (patho)physiological role.

Roles of the envelope proteins in the amplification of covalently closed circular DNA and completion of synthesis of the plus-strand DNA in hepatitis B virus

Covalently closed circular DNA (cccDNA), the nuclear form of hepatitis B virus (HBV), is synthesized by repair of the relaxed circular (RC) DNA genome. Initially, cccDNA is derived from RC DNA from the infecting virion, but additional copies of cccDNA are derived from newly synthesized RC DNA molecules in a process termed intracellular amplification. It has been shown that the large viral envelope protein limits the intracellular amplification of cccDNA for duck hepatitis B virus. The role of the envelope proteins in regulating the amplification of cccDNA in HBV is not well characterized. The present report demonstrates regulation of synthesis of cccDNA by the envelope proteins of HBV. Ablation of expression of the envelope proteins led to an increase (>6-fold) in the level of cccDNA. Subsequent restoration of envelope protein expression led to a decrease (>50%) in the level of cccDNA, which inversely correlated with the level of the envelope proteins. We found that the expression of L protein alone or in combination with M and/or S proteins led to a decrease in cccDNA levels, indicating that L contributes to the regulation of cccDNA. Coexpression of L and M led to greater regulation than either L alone or L and S. Coexpression of all three envelope proteins was also found to limit completion of plus-strand DNA synthesis, and the degree of this effect correlated with the level of the proteins and virion secretion.

Quantification of HBsAg: Basic virology for clinical practice

Hepatitis B surface antigen (HBsAg) is produced and secreted through a complex mechanism that is still not fully understood. In clinical fields, HBsAg has long served as a qualitative diagnostic marker for hepatitis B virus infection. Notably, advances have been made in the development of quantitative HBsAg assays, which have allowed viral replication monitoring, and there is an opportunity to make maximal use of quantitative HBsAg to elucidate its role in clinical fields. Yet, it needs to be underscored that a further understanding of HBsAg, not only from clinical point of view but also from a virologic point of view, would enable us to deepen our insights, so that we could more widely expand and apply its utility. It is also important to be familiar with HBsAg variants and their clinical consequences in terms of immune escape mutants, issues resulting from overlap with corresponding mutation in the P gene, and detection problems for the HBsAg variants. In this article, we review current concepts and issues on the quantification of HBsAg titers with respect to their biologic nature, method principles, and clinically relevant topics.

A mathematical model of the intracellular replication and within host evolution of hepatitis type B virus: Understanding the long time course of chronic hepatitis

Hepatitis B virus (HBV) causes acute and chronic liver disease. Especially, chronic hepatitis is a major risk factor of liver cirrhosis and hepatocellular carcinoma. Viral kinetics of HBV observed in peripheral blood is quite different depending on the clinical course of hepatitis. But the relationship between the intracellular replication dynamics and clinical course of HBV infection is unclear. Further it is very difficult to predict the long time course of hepatitis because the nature of HBV is changed by mutation within host with high mutation rate. We investigate the intracellular replication dynamics and within host evolution of HBV by using a mathematical model. Two different intracellular replication patterns of HBV, "explosive" and "arrested", are switched depending on the viral gene expression pattern. In the explosive replication, prominent growth of HBV is observed. On the other hand, the virion production is restricted in the arrested replication. It is suggested that the arrested and explosive replication is associated with chronic hepatitis and exacerbation of hepatitis respectively. It is shown by our evolutionary simulation that the exacerbation of hepatitis is caused by the emergence of explosive genotype of HBV from arrested genotype by mutation during chronic hepatitis. It is also shown that chronic infection without exacerbation is maintained by short waiting time for virion release and superinfection with arrested genotype. It is suggested that extension of waiting time for virion release and existence of uninfected hepatocyte in the liver may become risk factors for the exacerbation of hepatitis.

HBV life cycle: entry and morphogenesis

Hepatitis B virus (HBV) is a major cause of liver disease. HBV primarily infects hepatocytes by a still poorly understood mechanism. After an endocytotic process, the nucleocapsids are released into the cytoplasm and the relaxed circular rcDNA genome is transported towards the nucleus where it is converted into covalently closed circular cccDNA. Replication of the viral genome occurs via an RNA pregenome (pgRNA) that binds to HBV polymerase (P). P initiates pgRNA encapsidation and reverse transcription inside the capsid. Matured, rcDNA containing nucleocapsids can re-deliver the RC-DNA to the nucleus, or be secreted via interaction with the envelope proteins as progeny virions.

Involvement of GRP78 in inhibition of HBV secretion by Boehmeria nivea extract in human HepG2 2.2.15 cells

Previous studies showed that the root extract of Boehmeria nivea (BNE) can significantly suppress the production of hepatitis B virus (HBV) in vitro and in vivo. In this study, viral core and large-surface proteins accompanied with their encapsidated viral DNA were observed to accumulate within the cells. Notably, 78-kDa glucose-regulated protein (GRP78) was found to be suppressed by BNE, and stimulation of the GRP78 expression by thapsigargin could rescue virus production initially inhibited by BNE. The antiviral effect of BNE was reversible, which also coincided with the level of GRP78. Furthermore, we synthesized the GRP78 siRNA to knockdown the expression of GRP78 protein, and the production of supernatant HBV DNA was reduced simultaneously. Moreover, combined treatment of BNE and 3TC exhibited an additive anti-hepatitis B virus effect. In conclusion, the inhibitory effect of BNE on blocking assembled virion secretion might be via the reduction of GRP78.

Hepatitis B virus morphogenesis

The hepatitis B virus (HBV) particle consists of an envelope containing three related surface proteins and probably lipid and an icosahedral nucleocapsid of approximately 30 nm diameter enclosing the viral DNA genome and DNA polymerase. The capsid is formed in the cytosol of the infected cell during packaging of an RNA pregenome replication complex by multiple copies of a 21-kDa C protein. The capsid gains the ability to bud during synthesis of the viral DNA genome by reverse transcription of the pregenome in the lumen of the particle. The three envelope proteins S, M, and L shape a complex transmembrane fold at the endoplasmic reticulum, and form disulfide-linked homo- and heterodimers. The transmembrane topology of a fraction of the large envelope protein L changes post-translationally, therefore, the N terminal domain of L (preS) finally appears on both sides of the membrane. During budding at an intracellular membrane, a short linear domain in the cytosolic preS region interacts with binding sites on the capsid surface. The virions are subsequently secreted into the blood. In addition, the surface proteins can bud in the absence of capsids and form subviral lipoprotein particles of 20 nm diameter which are also secreted.

In Vitro Antiviral Activity of 1,2,3,4,6-Penta-O-galloyl-.BETA.-D-glucose against Hepatitis B Virus

This study examined the antiviral activity of the root of Paeonia lactiflora PALL. Among the solvent fractions of the crude drug, the ethyl acetate fraction showed anti-hepatitis B virus (HBV) activity (IC50, 8.1 microg/ml) in an HBV-producing HepG2.2.15 cell culture system. The active anti-HBV principle was isolated and identified as 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG) from the crude drug by activity-guided fractionation. PGG isolated from P. lactiflora was examined for the inhibition of HBV multiplication by measurement of HBV DNA and hepatitis B surface antigen (HBsAg) levels in the extracellular medium of HepG2.2.15 cells after 8-d treatment. PGG decreased the level of extracellular HBV (IC50, 1.0 microg/ml) in a dose-dependent manner. PGG also reduced the HBsAg level by 25% at a concentration of 4 microg/ml. The gallate structure of PGG may play a critical role in the inhibition of anti-HBV activity. These results suggest that PGG could be a candidate for developing an anti-HBV agent.

Reduced secretion of virions and hepatitis B virus (HBV) surface antigen of a naturally occurring HBV variant correlates with the accumulation of the small S envelope protein in the endoplasmic reticulum and Golgi apparatus

We identified two novel naturally occurring mutations (W74L and L77R) in the small S envelope protein of hepatitis B virus (HBV). Mutation L77R alone resulted in >10-fold-reduced secretion of virions. In addition, the 2.8-fold reduction of the extracellular HBV surface antigen (HBsAg) of mutant L77R from transfected Huh7 cells appeared to be correlated with a 1.7-fold reduction of intracellular HBsAg, as measured by enzyme-linked immunosorbent assay (ELISA). Surprisingly, opposite to the ELISA results, Western blot analysis revealed a near-10-fold-increased level of the intracellular mutant small S envelope protein. The discrepancy between ELISA and Western blot data was due to significant accumulation of the mutant L77R HBsAg in the intracellular pellet fraction. In contrast to HBsAg, the secretion of HBeAg was normal in L77R-transfected cells. The wild-type HBsAg was usually more diffuse and evenly distributed in the cytoplasm, often outside the perinuclear endoplasmic reticulum (ER) and Golgi apparatus, as observed by immunofluorescence assay. In contrast, the L77R mutant HBsAg tends to be highly restricted within the ER and Golgi, often accumulated in the Golgi compartments distal from the nucleus. The almost exclusive retention in the ER-Golgi of L77R HBsAg was similar to what was observed when the large envelope protein was overexpressed. These multiple aberrant phenotypes of mutant L77R can be corrected by a second naturally occurring S envelope mutation, W74L. Despite the accumulation of L77R HBsAg in ER-Golgi of transfected Huh7 cells, we detected no increase in Grp78 mRNA and proteins, which are common markers for ER stress response.

Formation of vesicular stomatitis virus pseudotypes bearing surface proteins of hepatitis B virus

It has been difficult to propagate and titrate hepatitis B virus (HBV) in tissue culture. We examined whether vesicular stomatitis virus (VSV) pseudotypes bearing HBV surface (HBs) proteins infectious for human cell lines could be prepared. For this, expression plasmids for three surface proteins, L, M, and S, of HBV were made. 293T cells were then transfected with these plasmids either individually or in different combinations. 293T cells expressing HBs proteins were infected with VSVdeltaG*-G, a recombinant VSV expressing green fluorescent protein (GFP), to make VSV pseudotypes. Culture supernatants together with cells were harvested and sonicated for a short time. The infectivities of freshly harvested supernatants were determined by quantifying the number of cells expressing GFP after neutralization with anti-VSV serum and mouse monoclonal antibodies (MAbs) against HBs protein. Among 14 cell lines tested for susceptibility to HBV pseudotype samples, HepG2, JHH-7, and 293T cells were judged to be the most susceptible. Namely, the infectious units (IU) of the culture supernatant samples neutralized with anti-VSV in the absence and presence of anti-HBs S MAbs and titrated on HepG2 cells ranged from 1,000 to 4,000 IU/ml and 200 to 400 IU/ml, respectively, suggesting the presence of VSVdeltaG*(HBV) pseudotypes. This infectivity was inhibited by treatment with lactoferrin or dextran sulfate. Pretreatment of the cells with trypsin or tunicamycin inhibited plating of the pseudotype samples. The HBV pseudotypes can be used to analyze early steps of HBV infection, including the entry mechanism of HBV.

Envelopment of the hepatitis B virus nucleocapsid

The hepatitis B virus (HBV) is an enveloped DNA virus with an icosahedral capsid replicating via reverse transcription. The crystal structure of the capsid is known. It has a diameter of 36 nm and is formed by one protein species (C protein). The viral envelope contains three different coterminal proteins (S, M, and L proteins) spanning the membrane several times. These proteins are not only released from infected cells as components of the viral envelope but in 10,000-fold excess as subviral lipoprotein particles with a diameter of 22 nm containing no capsid. Assembly of the capsid occurs in the cytosol and results in packaging of a 3.5 kb RNA molecule together with viral and cellular factors. This newly formed capsid cannot be enveloped. Rather, synthesis of the viral DNA genome in the lumen of the capsid by reverse transcription is required to induce a budding competent state. Envelopment then takes place at an intracellular membrane of the pre-Golgi compartment. The S and the L protein, but not the M protein, is required for this process. The L protein forms two different transmembrane topologies. The isoform exposing the N-terminal part at the cytosolic side of the membrane is essential for budding. In this domain, a 22 amino acid (aa) long linear stretch has been mapped genetically to play a vital role in the morphogenetic process. This domain probably mediates the contact to the capsid. A second matrix domain was mapped to the cytosolic loop of the S protein. A similar genetic approach identified two small areas on the capsid surface, which might interact with the envelope proteins during envelopment.

Quantitative analysis of the interaction between the envelope protein domains and the core protein of human hepatitis B virus

Interaction between preformed nucleocapsids and viral envelope proteins is critical for the assembly of virus particles in infected cells. The pre-S1 and pre-S2 and cytosolic regions of the human hepatitis B virus envelope protein had been implicated in the interaction with the core protein of nucleocapsids. The binding affinities of specific subdomains of the envelope protein to the core protein were quantitatively measured by both ELISA and BIAcore assay. While a marginal binding was detected with the pre-S1 or pre-S2, the core protein showed high affinities to pre-S with apparent dissociation constants (K(D)(app)) of 7.3+/-0.9 and 8.2+/-0.4microM by ELISA and BIAcore assay, respectively. The circular dichroism analysis suggested that conformational change occurs in pre-S through interaction with core protein. These results substantiate the importance of specific envelope domains in virion assembly, and demonstrate that the interaction between viral proteins can be quantitatively measured in vitro.

Study of the early steps of the Hepatitis B Virus life cycle

Hepatitis B virus (HBV) is a human pathogen, causing the serious liver disease. Despite considerable advances in the understanding of the natural history of HBV disease, most of the early steps in the virus life cycle remain unclear. Virus attachment to permissive cells, fusion and penetration through cell membranes and subsequent genome release, are largely a mystery. Current knowledge on the early steps of HBV life cycle has mostly come from molecular cloning, expression of individual genes and studies of the infection of duck hepatitis B virus (DHBV) with duck primary duck hepatocytes. However, considering of the difference of the surface protein of HBV and DHBV both in the composition and sequence, the degree to which information from DHBV applies to human HBV attachment and entry may be limited. A major obstacle to the study HBV infection is the lack of a reliable and sensitive in vitro infection system. We have found that the digestion of HBV and woodchuck hepatitis virus (WHBV) by protease V8 led to the infection of HepG2 cell, a cell line generally is refractory for their infection [Lu et al. J Virol. 1996. 70. 2277-2285 . Lu et al. Virus Research. 2001. 73(1): 27-4].. Further studies showed that a serine protease inhibitor Kazal (SPIK) was over expressed in the HepG2 cells. Therefore, it is possible that to silence the over expressed SPIK and thus to reinstate the activity of indispensable cellular proteases can result in the restoration of the susceptibility of HepG2 cells for HBV infection. The establishing a stable cell line for study of the early steps of HBV life cycle by silencing of SPIK is discussed.

Selection of a secretion-incompetent mutant in the serum of a patient with severe hepatitis B

BACKGROUND AND AIMS

A secretion-incompetent, highly replicating hepatitis B variant was previously found as the dominant viral population in the serum of a liver transplant recipient with severe hepatitis B reinfection. The secretion block resulted from mutations in the S protein, including the Gly145Arg substitution known to emerge under antibody to hepatitis B surface antigen immunoglobulin treatment. Here we investigated the mechanisms that allow selection of a secretion-incompetent virus as the predominant strain in the serum.

METHODS

To reproduce the interaction of viral quasispecies occurring in vivo, cotransfection experiments were performed with full-length genomes containing wild-type or mutant sequences. In addition, the relevance of mutations in the common S part of the surface proteins for the competence of L and S protein to support viral secretion was studied.

RESULTS

A small amount of wild-type virus or of a wild-type S protein-expressing variant rescued secretion of the defective mutant. In the secreted virions, the high-replicating mutant genome was predominant. Selection of the defective mutant was further supported by a transdominant negative effect of mutant S protein on wild-type virion secretion. In contrast, mutant L protein with the same c-terminal mutations as mutant S protein efficiently supported virion formation and secretion.

CONCLUSIONS

Interaction of the variant with a small amount of wild-type virus can reverse its secretion-defective phenotype. Mutations in the common region of S and L protein have different consequences for the ability of the envelope proteins to support virion assembly and secretion.

Molecular chaperone GRP78/BiP interacts with the large surface protein of hepatitis B virus in vitro and in vivo

The proper folding and assembly of viral envelope proteins are mediated by host chaperones. In this study, we demonstrated that an endoplasmic reticulum luminal chaperone GRP78/BiP bound specifically to the pre-S1 domain of the L protein in vitro and in vivo where complete viral particles were secreted, suggesting that GRP78/BiP plays an essential role in the proper folding of the L protein and/or assembly of viral envelope proteins.

Bacterial expression, purification, and in vitro N-myristoylation of fusion hepatitis B virus preS1 with the native-type N-terminus

Very low-level expression of hepatitis B virus (HBV) preS1 with the native-type N-terminus hampered the biochemical and functional studies on its myristoylation. In the present study, the fusion HBV preS1 with the native-type N-terminus and a His6-Tag fused to C-terminus (HBV preS1-HT) was highly expressed in Escherichia coli. This was due to an introduced mutation of the rare codon GGA found in the HBV preS1 to the codon preferred by E. coli, GGU. The protein was rapidly purified from bacterial lysate by Ni-IDA affinity chromatography. The experimental assays using 3H-labeled substrate demonstrate that the purified HBV preS1-HT can be effectively N-myristoylated by recombinant human protein N-myristoyltransferase (NMT) in vitro.

Antiviral therapy for hepatitis B virus infections: new targets and technical challenges

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.

Influence of a putative intermolecular interaction between core and the pre-S1 domain of the large envelope protein on hepatitis B virus secretion

Virion release of hepatitis B virus (HBV) from hepatocytes is a tightly regulated event. It is a dogma that only the mature HBV genome is preferentially allowed to export from the intracellular compartment (J. Summers and W. S. Mason, Cell 29:403-415, 1982). Recently, an "immature secretion" phenotype of a highly frequent naturally occurring HBV variant containing a leucine residue at amino acid 97 of the core protein was identified. Unlike wild-type HBV, this variant secretes almost equal amounts of mature and immature genomes. This phenomenon is not caused by any instability of core particles or by any deficiency in viral reverse transcription (T. T. Yuan, P. C. Tai, and C. Shih, J. Virol. 73:10122-10128, 1999). In this study, our kinetic analysis of virion secretion of the mutant F97L (phenylalanine to leucine) indicates that the secretion of its immature genome does not occur earlier than that of its mature genome. In addition, the secretion kinetics of the mature genomes are comparable between the wild-type HBV and the mutant F97L. Therefore, the immature secretion phenomenon of mutant F97L is not caused by premature secretion or more efficient secretion. Previously, we hypothesized that the immature secretion phenotype is probably caused by the aberrant interaction between its mutant core and wild-type envelope proteins. Here, we further demonstrated that a pre-S1 envelope mutation at position 119, changing an alanine (A) to a phenylalanine (F), can offset the immature secretion phenotype of the mutant I97L (isoleucine to leucine) and successfully restore the wild-type-like selective export of the mature genome of the double mutant pre-S1-A119F/core-I97L.

Hypermodification and immune escape of an internally deleted middle-envelope (M) protein of frequent and predominant hepatitis B virus variants

Naturally occurring deletions within the human hepatitis B virus (HBV) preS2 region have frequently been identified in patients with hepatocellular carcinoma (HCC), while chronic carriers without cirrhosis and HCC contain no detectable preS2 deletion variants. We have characterized two different preS2 internal deletion variants from two patients. In addition to several weak phenotypes, our study revealed three unexpected strong phenotypes: (1) a paradoxical "hypermodification" phenomenon was observed with significantly increased size heterogeneity and molecular weights of the secreted middle (M) envelope proteins containing a preS2 internal deletion. This phenomenon was observed in transient transfection with a human hepatoma Huh7 cell line as well as in stable transfection with a rodent hepatoma cell line 7777. (2) A significantly increased intracellular accumulation of all three envelope proteins (large, middle, and small) was detected by both Western blot analysis and immunofluorescence microscopy. (3) The middle envelope proteins with a preS2 internal deletion were not recognized in vitro by a putative neutralizing antiserum, suggesting that these variants can evade immune recognition in vivo. To our knowledge, this is the first identification and characterization of the M deletion variant protein in HBV natural infection.