Molecular biology of hepatitis B virus e antigen

HBV PreC interacts with SUV39H1 to induce viral replication by blocking the proteasomal degradation of viral polymerase

Hepatitis B e antigen (HBeAg) seropositivity during the natural history of chronic hepatitis B (CHB) is known to coincide with significant increases in serum and intrahepatic HBV DNA levels. However, the precise underlying mechanism remains unclear. In this study, we found that PreC (HBeAg precursor) genetic ablation leads to reduced viral replication both in vitro and in vivo. Furthermore, PreC impedes the proteasomal degradation of HBV polymerase, promoting viral replication. We discovered that PreC interacts with SUV39H1, a histone methyltransferase, resulting in a reduction in the expression of Cdt2, an adaptor protein of CRL4 E3 ligase targeting HBV polymerase. SUV39H1 induces H3K9 trimethylation of the Cdt2 promoter in a PreC-induced manner. CRISPR-mediated knockout of endogenous SUV39H1 or pharmaceutical inhibition of SUV39H1 decreases HBV loads in the mouse liver. Additionally, genetic depletion of Cdt2 in the mouse liver abrogates PreC-related HBV replication. Interestingly, a negative correlation of intrahepatic Cdt2 with serum HBeAg and HBV DNA load was observed in CHB patient samples. Our study thus sheds light on the mechanistic role of PreC in inducing HBV replication and identifies potential therapeutic targets for HBV treatment.

Cross-Reactivity of HBe Antigen-Specific Polyclonal Antibody with HBc Antigen

Hepatitis B virus (HBV) infection is a major health problem worldwide and causes almost one million deaths annually. The HBV core gene codes for two related antigens, known as core antigen (HBcAg) and e-antigen (HBeAg), sharing 149 residues but having different amino- and carboxy-terminals. HBeAg is a soluble variant of HBcAg and a clinical marker for determining the disease severity and patients' screening. Currently available HBeAg assays have a shortcoming of showing cross-reactivity with HBcAg. In this study, for the first time, we evaluated whether HBcAg-adsorbed anti-HBe polyclonal antibodies could specifically recognize HBeAg or still show cross-reactivity with HBcAg. Recombinant HBeAg was cloned in pCold1 vector and successfully expressed in Escherichia coli and after purification by Ni-NTA resin was used to generate polyclonal anti-HBe antibodies in rabbit. Purified HBeAg was further characterized by assessing its reactivity with anti-HBe in the sera of chronically infected patients and HBeAg-immunized rabbit. Sera from patients with chronic HBV infection, containing anti-HBe, specifically reacted with recombinant HBeAg, implying antigenic similarity between the prokaryotic and native HBeAg in the serum of HBV-infected patients. In addition, the designed enzyme-linked immunosorbent assay (ELISA) with rabbit anti-HBe polyclonal antibodies could detect recombinant HBeAg with high sensitivity, while high cross-reactivity with HBcAg was observed. It is noteworthy that HBcAg-adsorbed anti-HBe polyclonal antibodies still showed high cross-reactivity with HBcAg, implying that due to the presence of highly similar epitopes in both antigens, HBcAg-adsorbed polyclonal antibodies cannot differentiate between the two antigens.

Clinical isolates of hepatitis B virus genotype C have higher in vitro transmission efficiency than genotype B isolates

Serum samples were collected from 54 hepatitis B e antigen (HBeAg)-positive Chinese patients infected with hepatitis B virus (HBV) subgenotype B2 or C2. They were compared for transmission efficiency using same volume of samples or infectivity using same genome copy number. Adding polyethylene glycol (PEG) during inoculation did not increase infectivity of fresh samples but markedly increased infectivity following prolonged sample storage. Differentiated HepaRG cells infected without PEG produced more hepatitis B surface antigen (HBsAg) and higher HBsAg/HBeAg ratio than sodium taurocholate cotransporting polypeptide (NTCP)-reconstituted HepG2 cells infected with PEG. They better supported replication of core promoter mutant in contrast to wild-type (WT) virus by HepG2/NTCP cells. Overall, subgenotype C2 samples had higher viral load than B2 samples, and in general produced more HBeAg, HBsAg, and replicative DNA following same-volume inoculation. Precore mutant was more prevalent in subgenotype B2 and had reduced transmission efficiency. When same genome copy number of viral particles was inoculated, viral signals were not necessarily higher for three WT C2 isolates than four WT B2 isolates. Using viral particles generated from cloned HBV genome, three WT C2 isolates showed slightly reduced infectivity than three B2 isolates. In conclusion, subgenotype C2 serum samples had higher transmission efficiency than B2 isolates in association with higher viral load and lower prevalence of precore mutant, but not necessarily higher infectivity. PEG-independent infection by HBV viremic serum samples is probably attributed to a labile host factor.

Surrogate Markers for Hepatitis B Virus Covalently Closed Circular DNA

Chronic infection with the hepatitis B virus (HBV) is one of the most common causes of liver disease worldwide. Chronic HBV infection is currently incurable because of the persistence of the viral template for the viral transcripts, covalently closed circular deoxyribonucleic acid (cccDNA). Detecting changes in cccDNA transcriptional activity is key to understanding fundamental virology, determining the efficacy of new therapies, and deciding the optimal clinical management of HBV patients. In this review, we summarize surrogate circulating biomarkers that have been used to infer cccDNA levels and activity in people with chronic hepatitis B. Moreover, we outline the current shortcomings of the current biomarkers and highlight the clinical importance in improving them and expanding their use.

A Systematic Review of T Cell Epitopes Defined from the Proteome of Hepatitis B Virus

Hepatitis B virus (HBV) infection remains a worldwide health problem and no eradicative therapy is currently available. Host T cell immune responses have crucial influences on the outcome of HBV infection, however the development of therapeutic vaccines, T cell therapies and the clinical evaluation of HBV-specific T cell responses are hampered markedly by the lack of validated T cell epitopes. This review presented a map of T cell epitopes functionally validated from HBV antigens during the past 33 years; the human leukocyte antigen (HLA) supertypes to present these epitopes, and the methods to screen and identify T cell epitopes. To the best of our knowledge, a total of 205 CD8⁺ T cell epitopes and 79 CD4⁺ T cell epitopes have been defined from HBV antigens by cellular functional experiments thus far, but most are restricted to several common HLA supertypes, such as HLA-A0201, A2402, B0702, DR04, and DR12 molecules. Therefore, the currently defined T cell epitope repertoire cannot cover the major populations with HLA diversity in an indicated geographic region. More researches are needed to dissect a more comprehensive map of T cell epitopes, which covers overall HBV proteome and global patients.

Biogenesis of hepatitis B virus e antigen is driven by translocon-associated protein complex and regulated by conserved cysteine residues within its signal peptide sequence

Hepatitis B virus uses e antigen (HBe), which is dispensable for virus infectivity, to modulate host immune responses and achieve viral persistence in human hepatocytes. The HBe precursor (p25) is directed to the endoplasmic reticulum (ER), where cleavage of the signal peptide (sp) gives rise to the first processing product, p22. P22 can be retro-translocated back to the cytosol or enter the secretory pathway and undergo a second cleavage event, resulting in secreted p17 (HBe). Here, we report that translocation of p25 to the ER is promoted by translocon-associated protein complex. We have found that p25 is not completely translocated into the ER; a fraction of p25 is phosphorylated and remains in the cytoplasm and nucleus. Within the p25 sp sequence, we have identified three cysteine residues that control the efficiency of sp cleavage and contribute to proper subcellular distribution of the precore pool.

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.

Effect of intestinal microbiota imbalance associated with chronic hepatitis B virus infection on the expression of microRNA‑192 and GLP‑1

It has been reported that hepatitis B virus (HBV) infection has an impact on intestinal microbiota imbalance to induce diabetes mellitus (DM), but the underlying mechanisms still remain to be explored. The present study aimed to investigate the regulatory role of microRNA‑192 (miR‑192‑5p) and glucagon‑like peptide‑1 (GLP‑1) in intestinal microbiota imbalance by recruiting patients with DM infected with HBV. In the present study, patients with HBV infection and different levels of alanine transaminase (ALT) were recruited and divided into three groups. Intestinal microbiota analysis was performed to evaluate the fecal bacterial composition of patients in various groups. Quantitative PCR was performed to explore the differential expression of miR‑192‑5p and GLP‑1 in the feces, peripheral blood and intestinal mucosal tissue samples of each patient. Immunohistochemistry was used to assess the expression of GLP‑1 protein in the intestinal mucosal tissue samples. Luciferase assays were performed by cell transfection of miR‑192‑5p mimics/precursors/inhibitors to study the inhibitory effect of miR‑192‑5p on GLP‑1 expression. Intestinal microbiota imbalance was observed in hepatitis B surface antigen (HBsAg)‑positive patients with high ALT. The expression of miR‑192‑5p was significantly elevated in the feces, peripheral blood and intestinal mucosal tissue samples of HBsAg‑positive patients with high ALT along with decreased GLP‑1 mRNA and protein expression. Luciferase activity of GLP‑1 vector was inhibited by miR‑192‑5p mimics and promoted by miR‑192‑5p inhibitors. Transfection of miR‑192‑5p precursors resulted in upregulation of miR‑192‑5p and downregulation of GLP‑1, while miR‑192‑5p inhibitors remarkably suppressed the expression of miR‑192‑5p and notably induced the expression of GLP‑1. These results showed a regulatory network involving HBV infection, intestinal microbiota imbalance, and miR‑192‑5p and GLP‑1 expression.

Lost Small Envelope Protein Expression from Naturally Occurring PreS1 Deletion Mutants of Hepatitis B Virus Is Often Accompanied by Increased HBx and Core Protein Expression as Well as Genome Replication

Hepatitis B virus (HBV) transcribes coterminal mRNAs of 0.7 to 3.5 kb from the 3.2-kb covalently closed circular DNA, with the 2.1-kb RNA being most abundant. The 0.7-kb RNA produces HBx protein, a transcriptional transactivator, while the 3.5-kb pregenomic RNA (pgRNA) drives core and P protein translation as well as genome replication. The large (L) and small (S) envelope proteins are translated from the 2.4-kb and 2.1-kb RNAs, respectively, with the majority of the S protein being secreted as noninfectious subviral particles and detected as hepatitis B surface antigen (HBsAg). pgRNA transcription could inhibit transcription of subgenomic RNAs. The present study characterized naturally occurring in-frame deletions in the 3' preS1 region, which not only codes for L protein but also serves as the promoter for 2.1-kb RNA. The human hepatoma cell line Huh7 was transiently transfected with subgenomic expression constructs for envelope (and HBx) proteins, dimeric constructs, or constructs mimicking covalently closed circular DNA. The results confirmed lost 2.1-kb RNA transcription and HBsAg production from many deletion mutants, accompanied by increases in other (especially 2.4-kb) RNAs, intracellular HBx and core proteins, and replicative DNA but impaired virion and L protein secretion. The highest intracellular L protein levels were achieved by mutants that had residual S protein expression or retained the matrix domain in L protein. Site-directed mutagenesis of a high replicating deletion mutant suggested that increased HBx protein expression and blocked virion secretion both contributed to the high replication phenotype. Our findings could help explain why such deletions are selected at a late stage of chronic HBV infection and how they contribute to viral pathogenesis. IMPORTANCE Expression of hepatitis B e antigen (HBeAg) and overproduction of HBsAg by wild-type HBV are implicated in the induction of immune tolerance to achieve chronic infection. How HBV survives the subsequent immune clearance phase remains incompletely understood. Our previous characterization of core promoter mutations to reduce HBeAg production revealed the ability of the 3.5-kb pgRNA to diminish transcription of coterminal RNAs of 2.4 kb, 2.1 kb, and 0.7 kb. The later stage of chronic HBV infection often selects for in-frame deletions in the preS region. Here, we found that many 3' preS1 deletions prevented transcription of the 2.1-kb RNA for HBsAg production, which was often accompanied by increases in intracellular 3.5-, 0.7-, and especially 2.4-kb RNAs, HBx and core proteins, and replicative DNA but lost virion secretion. These findings established the biological consequences of preS1 deletions, thus shedding light on why they are selected and how they contribute to hepatocarcinogenesis.

Role of core protein mutations in the development of occult HBV infection

BACKGROUND & AIMS

Occult HBV infection (OBI) is associated with transfusion-transmitted HBV infection and hepatocellular carcinoma. Studies on OBI genesis have concentrated on mutations in the S region and the regulatory elements. Herein, we aimed to determine the role of mutations in the core region on OBIs.

METHODS

An OBI strain (SZA) carrying 9 amino acid (aa) substitutions in the core protein/capsid (Cp) was selected by sequence alignment and Western blot analysis from 26 genotype B OBI samples to extensively explore the impact of Cp mutations on viral antigen production in vitro and in vivo.

RESULTS

A large panel of 30 Cp replicons were generated by a replication-competent pHBV1.3 carrying SZA or wild-type (WT) Cp in a 1.3-fold over-length of HBV genome, in which the various Cp mutants were individually introduced by repairing site mutations of SZA-Cp or creating site mutations of WT-Cp by site-directed mutagenesis. The expression of HBcAg, HBeAg, and HBsAg and viral RNA was quantified from individual SZA and WT Cp mutant replicons in transfected Huh7 cells or infected mice, respectively. An analysis of the effect of Cp mutants on intracellular or extracellular viral protein production indicated that the W62R mutation in Cp had a critical impact on the reduction of HBcAg and HBeAg production during HBV replication, whereas P50H and/or S74G mutations played a limited role in influencing viral protein production invivo.

CONCLUSIONS

W62R and its combination mutations in HBV Cp might massively affect HBcAg and HBeAg production during viral replication, which, in turn, might contribute to the occurrence of OBI.

LAY SUMMARY

Occult hepatitis B virus infections (OBIs) have been found to be associated with amino acid mutations in the S region of the HBV, but the role of mutations in the core protein (Cp) remains unclear. In this study, an OBI strain (SZA) carrying 9 amino acid substitutions in Cp has been examined comprehensively in vitro and in vivo. The W62R mutation in Cp majorly reduces HBcAg and HBeAg production during HBV replication, potentially contributing to the occurrence of OBI.

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.

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.

TIMM29 interacts with hepatitis B virus preS1 to modulate the HBV life cycle

Hepatitis B virus (HBV), a major global health problem, can cause chronic hepatitis, liver cirrhosis, and hepatocellular carcinomas in chronically infected patients. However, before HBV infection can be adequately controlled, many mysteries about the HBV life cycle must be solved. In this study, TIMM29, an inner mitochondrial membrane protein, was identified as an interaction partner of the preS1 region of the HBV large S protein. The interaction was verified by both an immunoprecipitation with preS1 peptides and a GST-pulldown assay. Immunofluorescence studies also showed colocalization of preS1 and TIMM29. Moreover, it was determined that the preS1 bound with amino acids 92-189 of the TIMM29 protein. Infection of HBV in TIMM29-overexpressing NTCP/G2 cells resulted in a significant decrease of HBeAg and both extracellular particle-associated and core particle-associated HBV DNA without affecting cccDNA formation. Comparable results were obtained with TIMM29-overexpressing HB611 cells, which constitutively produce HBV. In contrast, knockout of TIMM29 in NTCP/G2 cells led to a higher production of HBV including HBeAg expression, as did knockout of TIMM29 in HB611. Collectively, these results suggested that TIMM29 interacts with the preS1 region of the HBV large S protein and modulates HBV amplification.

Capsids of hepatitis B virus e antigen with authentic C termini are stabilized by electrostatic interactions

The hepatitis B virus e antigen, an alternative transcript of the core gene, is a secreted protein that maintains viral persistence. The physiological form has extended C termini relative to Cp(-10)149, the construct used in many studies. To examine the role of the C termini, we expressed the constructs Cp(-10)151 and Cp(-10)154, which have additional arginine residues. Both constructs when treated with reductant formed capsids more efficiently than Cp(-10)149. These capsids were also substantially more stable, as measured by thermal denaturation and resistance to urea dissociation. Mutagenesis suggests that electrostatic interactions between the additional arginine residues and glutamate residues on adjacent subunits play a role in the extra stabilization. These findings have implications for the physiological role and biotechnological potential of this protein.

Hepatitis B Virus Precore Protein p22 Inhibits Alpha Interferon Signaling by Blocking STAT Nuclear Translocation

Antagonism of host immune defenses against hepatitis B virus (HBV) infection by the viral proteins is speculated to cause HBV persistence and the development of chronic hepatitis. The circulating hepatitis B e antigen (HBeAg, p17) is known to manipulate host immune responses to assist in the establishment of persistent viral infection, and HBeAg-positive (HBeAg+) patients respond less effectively to IFN-α therapy than do HBeAg-negative (HBeAg-) patients in clinical practice. However, the function(s) of the intracellular form of HBeAg, previously reported as the precore protein intermediate (p22) without the N-terminal signal peptide, remains elusive. Here, we report that the cytosolic p22 protein, but not the secreted HBeAg, significantly reduces interferon-stimulated response element (ISRE) activity and the expression of interferon-stimulated genes (ISGs) upon alpha interferon (IFN-α) stimulation in cell cultures. In line with this, HBeAg+ patients exhibit weaker induction of ISGs in their livers than do HBeAg- patients upon IFN-α therapy. Mechanistically, while p22 does not alter the total STAT1 or pSTAT1 levels in cells treated with IFN-α, it blocks the nuclear translocation of pSTAT1 by interacting with the nuclear transport factor karyopherin α1 through its C-terminal arginine-rich domain. In summary, our study suggests that HBV precore protein, specifically the p22 form, impedes JAK-STAT signaling to help the virus evade the host innate immune response and, thus, causes resistance to IFN therapy.IMPORTANCE Chronic hepatitis B virus (HBV) infection continues to be a major global health concern, and patients who fail to mount an efficient immune response to clear the virus will develop a life-long chronic infection that can progress to chronic active hepatitis, cirrhosis, and primary hepatocellular carcinoma. There is no definite cure for chronic hepatitis B, and alpha interferon (IFN-α) is the only available immunomodulatory drug, to which only a minority of chronic patients are responsive, with hepatitis B e antigen (HBeAg)-negative patients responding better than HBeAg-positive patients. We herein report that the intracellular HBeAg, also known as precore or p22, inhibits the antiviral signaling of IFN-α, which sheds light on the enigmatic function of precore protein in shaping HBV chronicity and provides a perspective toward areas that need to be further studied to make the current therapy better until a cure is achieved.

Hepatitis B e antigen induces the expansion of monocytic myeloid-derived suppressor cells to dampen T-cell function in chronic hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is associated with functionally impaired virus-specific T cell responses. Although the myeloid-derived suppressor cells (MDSCs) are known to play a critical role in impairing antiviral T cell responses, viral factors responsible for the expansion of MDSCs in chronic hepatitis B (CHB) remain obscure. In order to elucidate the mechanism of monocytic MDSCs (mMDSCs) expansion and T cell function suppression during persistent HBV infection, we analyzed the circulation frequency of mMDSCs in 164 CHB patients and 70 healthy donors, and found that the proportion of mMDSCs in HBeAg (+) CHB patients was significantly increased compared to that in HBeAg (-) patients, which positively correlated with the level of HBeAg. Furthermore, exposure of peripheral blood mononuclear cells (PBMCs) isolated from healthy donors to HBeAg led to mMDSCs expansion and significant upregulation of IL-1β, IL-6 and indoleamine-2, 3-dioxygenase (IDO), and depletion of the cytokines abrogated HBeAg-induced mMDSCs expansion. Moreover, HBeAg-induced mMDSCs suppressed the autologous T-cell proliferation in vitro, and the purified mMDSCs from HBeAg (+) subjects markedly reduced the proliferation of CD4⁺ and CD8⁺ T cells and IFN-γ production, which could be efficiently restored by inhibiting IDO. In summary, HBeAg-induced mMDSCs expansion impairs T cell function through IDO pathway and favors the establishment of a persistent HBV infection, suggesting a mechanism behind the development of HBeAg-induced immune tolerance.

HBeAg is not a structural component of HBV and is not essential for viral DNA replication, however, HBeAg positivity is associated with high levels of viremia in patients. HBeAg may represent a viral strategy to establish persistent infection, but the mechanism remains largely ambiguous. Growing evidence suggests that chronic HBV infection may be shaped by MDSCs-mediated T-cell exhaustion. Here, we report that the frequency of circulating mMDSCs in HBeAg (+) patients is higher than HBeAg (-) patients and positively correlates with serum HBeAg levels. The correlation is further demonstrated by in vitro HBeAg stimulation of PBMCs, which induced mMDSCs expansion. Furthermore, HBeAg-induced expansion of mMDSCs is dependent upon cytokine IL-6 and IL-1β, and the indoleamine-2, 3-dioxynase (IDO) plays a critical role in the suppression of T cell proliferation and IFN-γ production by HBeAg-activated mMDSCs. Therefore, our findings demonstrate a novel mechanism responsible for mMDSCs expansion in HBeAg (+) patients, and suggest that the HBeAg-mMDSC-IDO axis may serve as an immunotherapeutic target of chronic hepatitis B.

Mechanisms of Hepatitis B Virus Persistence

Hepatitis B virus (HBV) chronically infects 250 million people worldwide, resulting in nearly one million deaths annually. Studies in recent years have significantly improved our knowledge on the mechanisms of HBV persistence. HBV uses multiple pathways to harness host innate immunity to enhance its replication. It can also take advantage of the developing immune system and the not-yet-stabilized gut microbiota of young children to facilitate its persistence, and use maternal viral e antigen to educate immunity of the offspring to support its persistence after vertical transmission. The knowledge gained from these recent studies paves the way for the development of new therapies for the treatment of chronic HBV infection, which has so far been very challenging.

Maternal-Derived Hepatitis B Virus e Antigen Alters Macrophage Function in Offspring to Drive Viral Persistence after Vertical Transmission

In contrast to horizontal transmission of hepatitis B virus (HBV) between adults, which often leads to self-limited acute infection, vertical transmission of HBV from mother to child often leads to chronic infection. However, the mechanisms linking vertical transmission with chronic infection are not known. We developed a mouse model to study the effect of maternal HBV infection on HBV persistence in offspring and found that HBV carried by the mother impaired CD8(+) T cell responses to HBV in her offspring, resulting in HBV persistence. This impairment of CD8(+) T cell responses was mediated by hepatic macrophages, which were predisposed by maternal HBV e antigen (HBeAg) to support HBV persistence by upregulation of inhibitory ligand PD-L1 and altered polarization upon restimulation with HBeAg. Depletion of hepatic macrophages led to CD8(+) T cell activation and HBV clearance in the offspring, raising the possibility of targeting macrophages to treat chronic HBV patients.

Nuclear export of human hepatitis B virus core protein and pregenomic RNA depends on the cellular NXF1-p15 machinery

Hepatitis B virus (HBV) core protein (HBc) can shuttle between nucleus and cytoplasm. Cytoplasm-predominant HBc is clinically associated with severe liver inflammation. Previously, we found that HBc arginine-rich domain (ARD) can associate with a host factor NXF1 (TAP) by coimmunoprecipitation. It is well known that NXF1-p15 heterodimer can serve as a major export receptor of nuclear mRNA as a ribonucleoprotein complex (RNP). In the NXF1-p15 pathway, TREX (transcription/export) complex plays an important role in coupling nuclear pre-mRNA processing with mRNA export in mammalian cells. Here, we tested the hypothesis whether HBc and HBV specific RNA can be exported via the TREX and NXF1-p15 mediated pathway. We demonstrated here that HBc can physically and specifically associate with TREX components, and the NXF1-p15 export receptor by coimmunoprecipitation. Accumulation of HBc protein in the nucleus can be induced by the interference with TREX and NXF1-p15 mediated RNA export machinery. HBV transcripts encodes a non-spliced 3.5 kb pregenomic RNA (pgRNA) which can serve as a template for reverse transcription. Cytoplasmic HBV pgRNA appeared to be reduced by siRNA treatment specific for the NXF1-p15 complex by quantitative RT-qPCR and Northern blot analyses. This result suggests that the pgRNA was also exported via the NXF1-p15 machinery. We entertain the hypothesis that HBc protein can be exported as an RNP cargo via the mRNA export pathway by hijacking the TREX and NXF1-p15 complex. In our current and previous studies, HBc is not required for pgRNA accumulation in the cytoplasm. Furthermore, HBc ARD can mediate nuclear export of a chimeric protein containing HBc ARD in a pgRNA-independent manner. Taken together, it suggests that while both pgRNA and HBc protein exports are dependent on NXF1-p15, they are using the same export machinery in a manner independent of each other.

Potential mechanisms of hepatitis B virus induced liver injury

Chronic active hepatitis (CAH) is acknowledged as an imperative risk factor for the development of liver injury and hepatocellular carcinoma. The histological end points of CAH are chronic inflammation, fibrosis and cirrhosis which are coupled with increased DNA synthesis in cirrhotic vs healthy normal livers. The potential mechanism involved in CAH includes a combination of processes leading to liver cell necrosis, inflammation and cytokine production and liver scaring (fibrosis). The severity of liver damage is regulated by Hepatitis B virus genotypes and viral components. The viral and cellular factors that contribute to liver injury are discussed in this article. Liver injury caused by the viral infection affects many cellular processes such as cell signaling, apoptosis, transcription, DNA repair which in turn induce radical effects on cell survival, growth, transformation and maintenance. The consequence of such perturbations is resulted in the alteration of bile secretion, gluconeogenesis, glycolysis, detoxification and metabolism of carbohydrates, proteins, fat and balance of nutrients. The identification and elucidation of the molecular pathways perturbed by the viral proteins are important in order to design effective strategy to minimize and/or restore the hepatocytes injury.

The hepatitis B virus e antigen suppresses the respiratory burst and mobility of human monocytes and neutrophils

The Hepatitis B virus (HBV) e antigen (HBeAg) is a secretory, non-structural protein, and associated with persistent infection of HBV. Previous studies indicate that HBeAg is able to regulate T cell-mediated responses, however, the interaction between HBeAg and the innate immune system is poorly understood. In this study, we demonstrated that recombinant HBeAg (rHBe) bound to human peripheral blood monocytes, neutrophils, and B lymphocytes but not to T lymphocytes. We focused on investigating the effects of HBeAg on monocytes and neutrophils and found that rHBe decreased the respiratory burst in both types of cells. Furthermore, we observed that cell migration in monocytes and neutrophils was suppressed by rHBe in a transwell assay. The attenuation of rHBe was not caused by a general cytotoxic effect because rHBe treatment stimulated low levels of cytokine and chemokine production by monocytes and it promoted neutrophil survival. Since the recruitment of monocytes and neutrophils to the infected site is crucial for the initiation of inflammation, HBeAg may modulate innate immune responses by diminishing the respiratory burst and migration of monocytes and neutrophils, which might interfere with the subsequent innate and adaptive immune responses against HBV, leading to the establishment of chronic infection.

Assessment of differences in the conformational flexibility of hepatitis B virus core-antigen and e-antigen by hydrogen deuterium exchange-mass spectrometry

Hepatitis B virus core-antigen (capsid protein) and e-antigen (an immune regulator) have almost complete sequence identity, yet the dimeric proteins (termed Cp149d and Cp(-10)149d , respectively) adopt quite distinct quaternary structures. Here we use hydrogen deuterium exchange-mass spectrometry (HDX-MS) to study their structural properties. We detect many regions that differ substantially in their HDX dynamics. Significantly, whilst all regions in Cp(-10)149d exchange by EX2-type kinetics, a number of regions in Cp149d were shown to exhibit a mixture of EX2- and EX1-type kinetics, hinting at conformational heterogeneity in these regions. Comparison of the HDX of the free Cp149d with that in assembled capsids (Cp149c ) indicated increased resistance to exchange at the C-terminus where the inter-dimer contacts occur. Furthermore, evidence of mixed exchange kinetics were not observed in Cp149c , implying a reduction in flexibility upon capsid formation. Cp(-10)149d undergoes a drastic structural change when the intermolecular disulphide bridge is reduced, adopting a Cp149d -like structure, as evidenced by the detected HDX dynamics being more consistent with Cp149d in many, albeit not all, regions. These results demonstrate the highly dynamic nature of these similar proteins. To probe the effect of these structural differences on the resulting antigenicity, we investigated binding of the antibody fragment (Fab E1) that is known to bind a conformational epitope on the four-helix bundle. Whilst Fab E1 binds to Cp149c and Cp149d , it does not bind non-reduced and reduced Cp(-10)149d , despite unhindered access to the epitope. These results imply a remarkable sensitivity of this epitope to its structural context.

Antigenic switching of hepatitis B virus by alternative dimerization of the capsid protein

Chronic hepatitis B virus (HBV) infection afflicts millions worldwide with cirrhosis and liver cancer. HBV e-antigen (HBeAg), a clinical marker for disease severity, is a nonparticulate variant of the protein (core antigen, HBcAg) that forms the building-blocks of capsids. HBeAg is not required for virion production, but is implicated in establishing immune tolerance and chronic infection. Here, we report the crystal structure of HBeAg, which clarifies how the short N-terminal propeptide of HBeAg induces a radically altered mode of dimerization relative to HBcAg (∼140° rotation), locked into place through formation of intramolecular disulfide bridges. This structural switch precludes capsid assembly and engenders a distinct antigenic repertoire, explaining why the two antigens are cross-reactive at the T cell level (through sequence identity) but not at the B cell level (through conformation). The structure offers insight into how HBeAg may establish immune tolerance for HBcAg while evading its robust immunogenicity.

Hepatitis B precore protein: pathogenic potential and therapeutic promise

Hepatitis B virus (HBV), a small and economically packaged double-stranded DNA virus, represents an enormous global health care burden. In spite of an effective vaccine, HBV is endemic in many countries. Chronic hepatitis B (CHB) results in the development of significant clinical outcomes such as liver disease and hepatocellular carcinoma (HCC), which are associated with high mortality rates. HBV is a non-cytopathic virus, with the host's immune response responsible for the associated liver damage. Indeed, HBV appears to be a master of manipulating and modulating the immune response to achieve persistent and chronic infection. The HBV precore protein or hepatitis B e antigen (HBeAg) is a key viral protein involved in these processes, for instance though the down-regulation of the innate immune response. The development of new therapies that target viral proteins, such as HBeAg, which regulates of the immune system, may offer a new wave of potential therapeutics to circumvent progression to CHB and liver disease.

Role of the propeptide in controlling conformation and assembly state of hepatitis B virus e-antigen

Hepatitis B virus "e-antigen" (HBeAg) is thought to be a soluble dimeric protein that is associated with chronic infection. It shares 149 residues with the viral capsid protein "core-antigen" (HBcAg), but has an additional 10-residue, hydrophobic, cysteine-containing amino-terminal propeptide whose presence correlates with physical, serological, and immunological differences between the two proteins. In HBcAg dimers, the subunits pair by forming a four-helix bundle stabilized by an intermolecular disulfide bond. The structure of HBeAg is probably similar but, instead, has two intramolecular disulfide bonds involving the propeptide. To compare the proteins directly and thereby clarify the role of the propeptide, we identified mutations and solution conditions that render both proteins as either soluble dimers or assembled capsids. Thermally induced unfolding monitored by circular dichroism, and electrophoresis of oxidized and reduced dimers, showed that the propeptide has a destabilizing effect and that the intramolecular disulfide bond forms preferentially and blocks the formation of the intermolecular disulfide bond that otherwise stabilizes the dimer. The HBeAg capsids are less regular than the HBcAg capsids; nevertheless, cryo-electron microscopy reconstructions confirm that they are constructed of dimers resembling those of HBcAg capsids. In them, a portion of the propeptide is visible near the dimer interface, suggesting that it intercalates there, consistent with the known formation of a disulfide bond between C(-7) in the propeptide and C61 in the dimer interface. However, this intercalation distorts the dimer into an assembly-reluctant conformation.

Overview of expression of hepatitis B surface antigen in transgenic plants

Hepatitis B virus (HBV), a pathogen for chronic liver infection, afflicts more than 350 million people world-wide. The effective way to control the virus is to take HBV vaccine. Hepatitis B surface antigen (HBsAg) is an effective protective antigen suitable for vaccine development. At present, "edible" vaccine based on transgenic plants is one of the most promising directions in novel types of vaccines. HBsAg production from transgenic plants has been carried out, and the transgenic plant expression systems have developed from model plants (such as tobacco, potato and tomato) to other various plant platforms. Crude or purified extracts of transformed plants have been found to conduct immunological responses and clinical trials for hepatitis B, which gave the researches of plant-based HBsAg production a big boost. The aim of this review was to summarize the recent data about plant-based HBsAg development including molecular biology of HBsAg gene, selection of expression vector, the expression of HBsAg gene in plants, as well as corresponding immunological responses in animal models or human.

Molecular basis for the high degree of antigenic cross-reactivity between hepatitis B virus capsids (HBcAg) and dimeric capsid-related protein (HBeAg): insights into the enigmatic nature of the e-antigen

The hepatitis B virus core gene codes for two closely related antigens: a 21-kDa protein that forms dimers that assemble as multimegadalton capsids, and a 17-kDa protein that also forms dimers but that do not assemble. The proteins, respectively referred to as core antigen (HBcAg) and e-antigen (HBeAg), share a sequence of 149 residues but have different amino- and carboxy-termini. Their structural and serological relationship has long been unclear. With insights gained from recent structural studies on immune complexes of the capsids, the relationship was reassessed using recombinant forms of the antigens and a panel of monoclonal antibodies (mAbs) commonly believed to discriminate between core and e-antigen. Surface plasmon resonance (SPR) was used to measure the affinities, in contrast to previous studies that used more error-prone and less sensitive plate-type assays. Four of the six mAbs did not discriminate between core and e-antigen, nor did they discriminate between e-antigen and dimers of dissociated core antigen capsids. One mAb (3120) was specific for assembled capsids and one (e6) was specific for unassembled dimers. Epitope valency of the e-antigen was also studied, using a sandwich SPR assay where e-antigen was captured with one mAb and probed with a second. The e-antigen is often considered to be a monomeric protein on the basis of monovalent reactivity with antibody pairs specific for either an alpha or beta epitope (in a prior nomenclature for e-antigen specificity). This model, however, is incorrect, because recombinant e-antigen is a stable dimer and its apparent monovalency is due to steric blockage. This was proven by the formation of a 2:1 Fab e6-e-antigen complex. These results suggest new approaches for the isolation of the authentic e-antigen, its biological assay, and its stabilization as an immune complex for structural studies.

Ribosome can resume the translation in both +1 or -1 frames after encountering an AGA cluster in Escherichia coli

In Escherichia coli the rare codons AGG, AGA and CGA are reported to have a detrimental effect on protein synthesis, especially during the expression of heterologous proteins. In the present work, we have studied the impact of successive clusters of these rare codons on the accuracy of mRNA translation in E. coli. For this purpose, we have analyzed the expression of an mRNA which contains in its 3' region a triplet and a tandem of AGA codons. This mRNA is derived from the human hepatitis B virus (HBV) preC gene. Both in eukaryotic cells and in eukaryotic cell-free translation system, this mRNA, directs the synthesis of a single 25 kDa protein. However, in a conventional E. coli strain BL 21 (DE3), transformed with a plasmid expressing this protein the synthesis of four polypeptides ranging from 30 to 21.5 kDa can be observed. Using different approaches, notably expression of i) precore mutated proteins or ii) chimeric proteins containing HA- and Myc-tags downstream of the AGA clusters (respectively in the -1 or +1 frame), we have found that when the ribosome encounters the AGA clusters, it can then resume the translation in both +1 and -1 frames. This result is in agreement with the model proposed recently by Baranov et al. (Baranov, P.V., Gesteland, R.F., Atkins, J.F., 2004. P-site tRNA is a crucial initiator of ribosomal frameshifting. RNA 10, 221-230), thus confirming that AGA/AGG codons can serve as sites for -1 frameshifting events. Only +1 frameshifting was suggested previously to occur at the AGA/AGG clusters.

Molecular virology of hepatitis B virus for clinicians

This article reviews the molecular biology of the hepatitis B virus in an effort to explain its natural history from a molecular perspective. The life cycle of the virus, with special attention to virus replication, polypeptide production, and morphogenesis, is described. The way in which these steps may influence the natural history of viral pathogenesis, as well as the effectiveness of interventions, receives special consideration.

A substituted tetrahydro-tetrazolo-pyrimidine is a specific and novel inhibitor of hepatitis B virus surface antigen secretion

The high levels of hepatitis B virus (HBV) surface antigen (HBsAg)-bearing subviral particles in the serum of chronically infected individuals are thought to play a role in suppressing the HBV-specific immune response. Current therapeutics are not directed at reducing this viral antigenemia; thus, our group has focused on identifying inhibitors of HBsAg secretion. By using the HBV-expressing cell line HepG2.2.15, high-throughput screening of an 80,288-compound synthetic small-molecule library identified HBF-0259, an aromatically substituted tetrahydro-tetrazolo-(1, 5-a)-pyrimidine. Following resynthesis, HBF-0259 had a 50% effective concentration of approximately 1.5 microM in a secondary, HBV-expressing cell line, with a concentration that exhibited 50% cytotoxicity of >50 microM. The equilibrium concentration of HBF-0259 in aqueous solution at physiological pH was 15 to 16 microM; the selective index was thus >9. As intended by our screening paradigm, HBF-0259 is a selective, potent inhibitor of secretion of both subviral and DNA-containing viral particles, while the secretion of alpha-1-acid glycoprotein and alpha-1-antitrypsin was unaffected. The HBV e antigen, which is not a constituent of HBV particles, was also unaffected, suggesting that the secretion of particles bearing HBV structural glycoproteins is targeted directly. Inhibitory activity was also confirmed by transfection of HBsAg, indicating that the action of the compound is independent of those of other viral proteins. HBF-0259 had no effect on HBV DNA synthesis, demonstrating that inhibition is independent of viral genomic replication. Finally, HBF-0259 had little or no effect on the cell-to-cell spread of two unrelated viruses, suggesting that it is a specific inhibitor of secretion of HBsAg. Possible mechanisms of action and the implications for its development are discussed.

Human hepatitis B viral e antigen interacts with cellular interleukin-1 receptor accessory protein and triggers interleukin-1 response

Human hepatitis B virus (HBV) can cause acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. HBV e antigen (HBeAg), a secreted protein and not required for viral replication, is thought to play an immunoregulatory role during viral infection. However, the functional involvement of HBeAg in host immune response has not been fully elucidated. We report in this study that HBeAg can bind to interleukin-1 receptor accessory protein (IL-1RAcP). Interleukin-1 (IL-1) plays an important role in inflammation and regulation of immune response, and membrane form of IL-1RAcP (mIL-1RAcP) is an essential component of trimeric IL-1/IL-1 receptor/mIL-1RAcP complex. We show that glutathione S-transferase- or polyhistidine-tagged recombinant HBeAg can interact with endogenous mIL-1RAcP in vitro. Purified (His)6-HBeAg added in the culture medium can interact with overexpressed FLAG-tagged mIL-1RAcP in vivo. Indirect immunofluorescence and confocal microscopy show that HBeAg colocalizes with mIL-1RAcP on the cell surface. Furthermore, HBeAg is able to induce the interaction of IL-1 receptor I (IL-1RI) with mIL-1RAcP and trigger the recruitment of adaptor protein myeloid differentiation factor 88 (MyD88) to the IL-1RI/mIL-1RAcP complex. Assembly and activation of IL-1RI/mIL-1RAcP signaling complex by HBeAg can activate downstream NF-kappaB pathway through IkappaB degradation, induce NF-kappaB-dependent luciferase expression, and induce the expression of IL-1-responsive genes. Silencing of IL-1RAcP by small interfering RNA dramatically abolishes HBeAg-mediated NF-kappaB activation. These results demonstrate that HBeAg can trigger host IL-1 response by binding to mIL-1RAcP. The interaction of HBeAg with mIL-1RAcP may play an important role in modulating host immune response in acute and chronic HBV infection.

Cloning of spliced variant HBeBP4A of hepatitis B virus e antigen binding protein 4

AIM: To clone a new gene, binding protein 4 spliced variant HBeBP4A of hepatitis B virus e antigen (HBeAg), and to explore its function and structure by bioinformatical analysis.

METHODS: HBeBP4A was amplified by reverse transcription-polymerase chain reaction (RT-PCR) using HepG2 cDNA as template and inserted into pGEM-T easy vector by TA cloning. Recombinant eukaryotic expression vector (pcDNA^TM3.1/myc-HisA-HBeBP4A) was constructed by subcloning followed by restriction enzyme digestion analysis and sequencing. Bioinformatical methods were used to analyze its possible physical and chemical characteristics, structure, and function.

RESULTS: Spliced form of HBeBP4, named HBeBP4A, was amplified successfully by RT-PCR from HepG2 cDNA. Bioinformatical analysis showed that its new open reading frame (ORF) is 1104 bp in length and translated a protein containing 367 amino acid residues.

CONCLUSION: A new gene, spliced variant HBeBP4A of HBeAg binding protein 4, is recognized, and its recombinant eukaryotic expression vector is constructed.

Clinical Significance of the Genotype and Core Promoter/Pre-Core Mutations in Hepatitis B Virus Carriers

It has been shown that clinical and virological characteristics vary among hepatitis B virus (HBV) genotypes. In this study, we measured the virus level, disease severity, and presence or absence of core promoter (CP)/pre-core (PC) mutations in 241 HBV carriers, and investigated the clinical significance of measuring the HBV genotype. In genotype C HBV carriers, the proportion of hepatitis B e antigen (HBeAg)-positive patients was significantly higher than that in genotype B HBV carriers (0 vs. 34.4%, p < 0.05), and the virus level was higher (4.9 vs. 4.05 LGE/ml). In the genotype B HBV carriers, the incidence of PC mutation was significantly higher (69 vs. 34%, p < 0.05). In the genotype C HBV carriers, the incidence of CP mutation was significantly higher (13 vs. 78%, p < 0.05). We compared patients with the wild (W)/mutant (M) pattern in the CP/PC regions to those with the M/W pattern in the CP/PC regions among the genotype C HBV carriers. Both the proportion of HBeAg-positive patients (65.8 vs. 15.4%, p < 0.05) and the alanine aminotransferase (ALT) level (48 vs. 21.5 IU, p < 0.05) were higher in the patients with the M/W pattern in the CP/PC regions, and the disease severity was deteriorated. In conclusion, genotype B HBV may more frequently induce HBe seroconversion via PC mutation compared to genotype C HBV. Among the genotype C HBV carriers, hepatitis activity and the deterioration of the disease severity were significantly inhibited in the group in which PC mutation initially occurred, in comparison to the group in which CP mutation initially occurred.

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.

Screening and identification of genes trans-regulated by a novel HBeAg binding protein E-18 with microarray assay

AIM: To investigate the biological functions of a novel hepatitis B virus e antigen (HBeAg) binding protein E-18, and to use cDNA microarray technique to screen genes regulated by E-18.

METHODS: A novel gene E-18 coding for HBeAg was screened and identified by using yeast two-hybrid system 3 and co-immunoprecipitation technique. The E-18 coding DNA fragment was amplified by reverse transcription polymerase chain reaction (RT-PCR) technique from HepG2 cell. The expressive vector of pcDNA3.1-E-18 was constructed by routine molecular biological methods. The HepG2 cells were transfected with pcDNA3.1(-) and pcDNA3.1-E-18, respectively by using lipofectamine. The total RNA was isolated and reverse transcribed. The cDNA of each sample were subjected to microarray screening with 1 152 cDNA probes and analyzed by bioinformatics.

RESULTS: E-18 cDNA sequence was obtained and identified by yeast two-hybrid screening and bioinformatics analysis. The expressive vector was constructed and confirmed by DNA sequencing analysis and restriction enzyme digestion. High quality mRNA and cDNA of transfected HepG2 cells had been prepared and successful microarray screening conducted. From the scanning results, there were 52 differential expression genes, of which 36 genes were down-regulated, and 16 genes were up-regulated.

CONCLUSION: Microarray technique is successfully used to screen the genes trans-regulated by E-18. The expression of E-18 protein affects the expression spectrum of HepG2 cell.

Identification and sequence analysis of a Macaca fascicularis homologous gene to human hepatitis B viruse antigen binding protein E-19

AIM: To explore the biological and immunoregulatory functions of hepatitis B e antigen (HBeAg) which is a secreted nonparticulate version of the viral nucleocapsid hepatitis B core antigen (HBcAg), yeast-two hybrid technique was performed to seek proteins in hepatocytes interacting with HBeAg and a novel gene named as E-19 was identified. To clone E-19 homologous gene from different species, a Macaca fascicularis homologous gene E-19 was identified by bioinformatics.

METHODS: HBeAg bait plasmid was constructed and transformed into yeast AH109 (a type). AH109 was mated with yeast cells Y187 (type) containing liver cDNA library plasmid pCAT2 in 2×YPDA medium. Plasmid of true positive blue colonies were extracted and analyzed by DNA sequencing and a new human gene E-19 was identified. A Macaca fascicularis homologous gene E-19 was identified by bioinformatics methods.

RESULTS: A Macaca fascicularis homologous gene E-19 was identified by bioinformatics. The Macaca fascicularis homologous gene E-19 was consisted of 378 nt and encoded a protein of 125 aa.

CONCLUSION: Human gene E-19, a HBeAg interacting proteins in hepatocytes, is successfully cloned by yeast-two hybrid technique and a Macaca fascicularis homologous gene E-19 is identified by bioinformatics.

Screening and identification of genes trans-regulated by a novel HBeAg binding protein E-36 with cDNA microarray assay

AIM: To investigate the biological functions of a novel hepatitis B virus e antigen (HBeAg) binding protein E-36, and to screen genes regulated by E-36.

METHODS: The E-36 coding DNA fragment was amplified by reverse transcription polymerase chain reaction (RT-PCR) technique from HepG2 cell. The expressive vector of pcDNA 3.1-E-36 was constructed by routine molecular biological methods. The HepG2 cells were transfected by pcDNA3.1(-) and pcDNA3.1-E-36, respectively by using lipofectamine. The total RNA was isolated and reverse transcribed. The cDNAs were subjected to microarray screening with 1 152 cDNA probes.

RESULTS: The expressive vector was constructed and confirmed by restriction enzyme digestion and DNA sequencing analysis. High quality mRNA and cDNA of transfected HepG2 cells were prepared and successful microarray screening conducted. From the scanning results, 20 genes were found to be up-regulated, including PTH-responsive osteosarcoma B1 protein, slit homolog 2, nuclear factor of kappa light polypeptide gene enhancer in B-cells 1, interleukin 3 receptor, caspase 2, angiotensin I converting enzyme, Low density lipoprotein 1, interkeukin 6, T-cell receptor rearranged beta chain gene V-region, activator of NFB, tumor suppressing subtransferable candidate 1, cyclin-dependent kinase-like 2, sialyltransferase 8, glutamate receptor, metabotropic 7, and 5 novel genes. Expression of the gene of eukaryotic translation elongation factor 2 could be down-regulated by E-36 protein.

CONCLUSION: The expression of E-36 protein affects the expression spectrum of HepG2 cell. The microarray is an important technique for the study of transactivating effects for viral proteins.

Stability and morphology comparisons of self-assembled virus-like particles from wild-type and mutant human hepatitis B virus capsid proteins

Instead of displaying the wild-type selective export of virions containing mature genomes, human hepatitis B virus (HBV) mutant I97L, changing from an isoleucine to a leucine at amino acid 97 of HBV core antigen (HBcAg), lost the high stringency of selectivity in genome maturity during virion export. To understand the structural basis of this so-called "immature secretion" phenomenon, we compared the stability and morphology of self-assembled capsid particles from the wild-type and mutant I97L HBV, in either full-length (HBcAg1-183) or truncated core protein contexts (HBcAg1-149 and HBcAg1-140). Using negative staining and electron microscopy, full-length particles appear as "thick-walled" spherical particles with little interior space, whereas truncated particles appear as "thin-walled" spherical particles with a much larger inner space. We found no significant differences in capsid stability between wild-type and mutant I97L particles under denaturing pH and temperature in either full-length or truncated core protein contexts. In general, HBV capsid particles (HBcAg1-183, HBcAg1-149, and HBcAg1-140) are very robust but will dissociate at pH 2 or 14, at temperatures higher than 75 degrees C, or in 0.1% sodium dodecyl sulfate (SDS). An unexpected upshift banding pattern of the SDS-treated full-length particles during agarose gel electrophoresis is most likely caused by disulfide bonding of the last cysteine of HBcAg. HBV capsids are known to exist in natural infection as dimorphic T=3 or T=4 icosahedral particles. No difference in the ratio between T=3 (78%) and T=4 particles (20.3%) are found between wild-type HBV and mutant I97L in the context of HBcAg1-140. In addition, we found no difference in capsid stability between T=3 and T=4 particles successfully separated by using a novel agarose gel electrophoresis procedure.

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.

Screening and identification of a novel hepatitis B virus e antigen binding protein E-19 in hepatocytes by yeast two-hybrid technique

AIM

The hepatitis B precore Ag (HBeAg) is a secreted nonparticulate version of the viral nucleocapsid hepatitis B core Ag (HBcAg), and its function is unknown. Some researchers have proposed that the HBeAg may have an immunoregulatory function in promoting viral persistence and is associated with immunologic tolerance. To investigate biological functions of hepatitis B virus e protein(HBeAg), yeast two-hybrid technique was employed to seek proteins in hepatocytes interacting with HBeAg.

METHODS

HBeAg bait plasmid was constructed by ligating HBeAg gene with yeast expression vector pGBKT7, then transformed into yeast AH109 (a type). The transformed yeast cells were amplified and mated with yeast cells Y187(α type) containing liver cDNA library plasmid pCAT2 in 2×YPDA medium. Diploid yeast cells were plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) and synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing x-α-gal for selection twice. Plasmid of true positive blue colonies were extracted and analysed by DNA sequencing and blast in GenBank. After the complete sequence of new gene E-19 was amplified from the mRNA of HepG2 cell by RT-PCR and cloned into pGADT7 vector, the recombined plasmid was translated by using reticulocyte lysate and analysed by immunoprecipitation technique in vitro together with HBeAg.

RESULTS

Twenty genes in thirty nine positive colonies were obtained, there were five new genes.The complete sequence of new gene E-19 was successfully amplified from the mRNA of HepG2 cell by RT-PCR. The interaction between HBeAg and expression products of new gene E-19 was further confirmed by immunoprecipitation technique.

CONCLUSION

Genes of HBeAg interacting proteins in hepatocytes were successfully cloned and HBeAg could bind with the protein expressed by new gene E-19.

Coexistence of two distinct secretion mutations (P5T and I97L) in hepatitis B virus core produces a wild-type pattern of secretion

Unlike a Tokyo isolate of hepatitis B virus variants, we found a Shanghai isolate that secretes few virions with an immature genome despite its core I97L mutation. Core mutations P5T and I97L were found to be mutually compensatory in offsetting their respective distinct effects on virion secretion.

Proteolytic processing of the hepatitis B virus e antigen precursor. Cleavage at two furin consensus sequences

The Hepatitis B virus P22 protein is a nonstructural protein that is the precursor of the 17-kDa secreted e antigen (HBeAg). The mature HBeAg is obtained after the removal of the C-terminal region of P22, a process which involves a proprotein convertase. Our studies show first that the protease could cleave P22 at the C-terminal side of Arg(167) or Arg(154) and second, that the maturation process can be either done in one step or in two steps with the generation of a processing intermediate (P20). Our data also demonstrate that the removal of the P22 C terminus, which occurs mainly in the trans-Golgi network, can also be achieved after exocytosis. Keeping in mind this characteristic and the amino acid sequence of the cleavage sites, we concluded that furin is involved in the maturation of the HBeAg. In addition, we show that in our experimental system, the HBeAg is a 164-amino acid protein and not a 159-amino acid protein as previously reported.

Overexpression and purification of the hepatitis B e antigen precursor

Circumstantial evidence suggests that the secreted hepatitis B virus (HBV) e antigen (HBeAg) and/or its 22 kDa precursor (P22) have an essential role in the establishment of persistent infection. In order to identify cellular proteins that could interact with P22, large amounts of this protein are required to perform pull-down assays. A plasmid was constructed encoding a recombinant P22 with a Histidine-tag at its N-terminal extremity (P22r). The initial attempts to overexpress P22r in a conventional Escherichia coli strain failed, most likely due to the presence of rare AGA/AGG codon clusters in the 3' part of the gene. To overcome this difficulty, P22r was overexpressed in the Epicurian coli BL21-codonplus (DE3)-RIL strain, which possesses extra copies of the ArgU gene that encodes the tRNA(AGA/AGG). In this strain, P22r was overexpressed successfully and then purified in milligram quantities by metal affinity chromatography on Ni2+-chelated His-Bind resin. The purified recombinant protein P22r was able to interact with a cellular protein (P32), which had previously been shown to co-immunoprecipitate with native P22, indicating that at least some of the P22r molecules were folded correctly.

Correlation of HBV DNA levels in serum and liver of chronic hepatitis B patients with cirrhosis

AIM

We sought to evaluate whether serum HBV DNA levels correlates with the liver free HBV DNA levels in chronic hepatitis B.

METHODS

Thirty-three consecutive chronic hepatitis B patients with cirrhosis were included in this study. Twenty cases had detectable serum HBV DNA (> 1.8 pg/ml). All had detectable free liver HBV DNA.

RESULTS

There was a strong correlation between the serum and liver HBV DNA levels (P = 0.0018, r = 0.717). Thirteen cases had undetectable serum HBV DNA. Among them, six cases still had detectable liver free HBV DNA. Eight cases were HBeAg-positive. Among them, seven cases were positive for both serum and liver HBV DNA, and one case was negative for both serum and liver HBV DNA. Twenty-five cases were HBeAg-negative and anti-HBe-positive. Among them, 13 cases were positive for serum HBV DNA, and 19 cases were positive for liver HBV DNA. No significant difference was noted for positivity of serum HBV DNA or liver free HBV DNA between HBeAg-positive and HBeAg-negative groups. The level of serum HBV DNA(491 +/- 772 pg/ml versus 203 +/- 447 pg/ml, p = 0.07) and liver free HBV DNA (33 +/- 81 pg/microg versus 6 +/- 15 pg/microg, p = 0.13) was also not statistically different.

CONCLUSION

In conclusion, serum HBV DNA levels is strongly correlated with liver HBV DNA levels in chronic hepatitis B with cirrhosis. Liver free HBV DNA can still be detected in about half of the cirrhotic patients with undetectable serum HBV DNA. Serum HBeAg is not a good predictor of serum or liver HBV DNA levels in cirrhotic patients.

Out-of-frame versus in-frame core internal deletion variants of human and woodchuck hepatitis B viruses

Human hepatitis B virus (HBV) variants containing in-frame core internal deletion (CID) have been demonstrated to contain all the functional features of defective interfering (DI) particles (Yuan, T. T.-T., M.-H. Lin, D. S. Chen, and C. Shih, 1998, J. Virol. 72, 578-584). Here, we report that out-of-frame HBV CID variants exhibit defective interfering property similar to in-frame CID variants characterized previously. This result raises the possibility that it may be the deleted pregenomic RNA product, rather than the deleted core protein product, that is responsible for interference. Furthermore, a genomic deletion elsewhere does not cause interference since preS2 deletion variants exhibit no influence on wild-type HBV replication. Consistent with the natural occurrence of HBV CID variants, we recently identified CID variants of woodchuck hepatitis virus (WHV) in natural infection. However, unlike HBV CID variants, functional characterization of WHV CID variants using a human hepatoma cell line has not revealed any interference in tissue culture. In summary, defective interference is a general phenomenon for both in-frame and out-of-frame HBV CID variants.

Differential regulation of hepatitis B virus gene expression by the Sp1 transcription factor

The expression of hepatitis B virus (HBV) genes is regulated by a number of transcription factors. One such factor, Sp1, has two binding sites in the core promoter and one in its upstream regulatory element, which is also known as the ENII enhancer. In this study, we have analyzed the effects of these three Sp1 binding sites on the expression of HBV genes. Our results indicate that both Sp1 binding sites in the core promoter are important for the transcription of the core RNA and the precore RNA. Moreover, while the downstream Sp1 site (the Sp1-1 site) in the core promoter did not affect the transcription of the S gene and the X gene, the upstream Sp1 site (the Sp1-2 site) in the core promoter was found to negatively regulate the transcription of the S gene and the X gene, as removal of the latter led to enhancement of transcription of these two genes. The Sp1 binding site in the ENII enhancer (the Sp1-3 site) positively regulates the expression of all of the HBV genes, as its removal by mutation suppressed the expression of all of the HBV genes. However, the suppressive effect of the Sp1-3 site mutation on the expression of the S gene and the X gene was abolished if the two Sp1 sites in the core promoter were also mutated. These results indicate that Sp1 can serve both as a positive regulator and as a negative regulator for the expression of HBV genes. This dual activity may be important for the differential regulation of HBV gene expression.

Identification of a cellular protein specifically interacting with the precursor of the hepatitis B e antigen

In hepatitis B virus (HBV) the precore gene encodes a protein from which derives P22, the precursor of the mature secreted hepatitis B virus e antigen (HBeAg). Circumstantial evidences suggest that HBeAg and/or its precursor P22 are important for establishing persistent infection. Although P22 is essentially present in the secretory pathway, a substantial fraction has been found in the cytosol. In order to get new insights into the biological function of P22, we looked for cellular proteins which could strongly associate with this protein. Using immunoprecipitation studies on human cell extracts, we found that a non-secreted cellular protein of about 32 kDa (P32) bound with a high specificity to P22. P32 associated neither with HBeAg nor with the viral core protein P21 which exhibits the same amino acids sequence as P22 but is N-terminally shorter by 10 residues. We also demonstrated that this interaction depended on the presence of the P22 C-terminal domain. Our data argues for a potential biological function of P22.