Key role of a CCAAT element in regulating hepatitis B virus surface protein expression

Pathogenicity and virulence of Hepatitis B virus

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

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.

Characterization of contrasting features between hepatitis B virus genotype A and genotype D in small envelope protein expression and surface antigen secretion

Hepatitis B virus (HBV) genotypes A and D are prevalent in many parts of the world and show overlapping geographic distributions. We amplified the entire HBV genome from sera of patients with genotypes A and D and generated overlength constructs for transient transfection into Huh7 or HepG2 cells. Genotype D clones were associated with less HBsAg in culture supernatant and even less intracellular HBsAg. They produced less 2.1-kb RNA due to a weaker SPII promoter. Chimeric promoter constructs identified three divergent positions as most critical, and their exchange reversed extracellular HBsAg phenotype. The S protein of genotype D was more efficient at secretion, while its L protein possessed greater inhibitory effect. Swapping the S gene diminished genotypic difference in intracellular S protein but widened the difference in secreted HBsAg. In conclusion, HBV genotypes A and D differ in S protein expression, secretion and modulation by L protein.

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.

Synthesis and antiviral effects of isosteviol-derived analogues against the hepatitis B virus

Among several isosteviol-derived analogues, NC-8 (ent-16-oxobeyeran-19-N-methylureido) showed inhibitory potency against the hepatitis B virus (HBV) in HepG2 2.2.15 cells. Its anti-HBV mechanism was then next investigated in a human hepatoma cell culture system. Results showed that it specifically inhibited viral gene expression and reduced the level of encapsidated viral DNA intermediates in Huh7 cells that expressed replicating HBV. It also potently attenuated all viral promoter activity in HBV-expressing Huh7 cells, but not in cells lacking HBV expression. By examining its antiviral mechanism in cellular signaling pathways, NC-8 was found to inhibit the activity of the nuclear factor (NF)-κB element-containing promoter, but only slightly enhanced activities of activator protein (AP)-1- and interferon-sensitive response element (ISRE)-containing promoters in HBV-expressing cells. NC-8 also significantly eliminated NF-κB (p65/p50) and Toll-like receptor (TLR)2 proteins, but increased the IκBα protein level in a dose-dependent manner in HBV-transfected Huh7 cells, while these protein levels were apparently unchanged in non-transfected cells. Meanwhile, NC-8-treated nuclear extracts that co-expressed HBV inhibited the binding of NF-κB to the CS1 site of HBV major surface gene and specifically attenuated CS1-containing promoter activity. Taken together, this study suggests that the antiviral mechanism of NC-8 appears to be mediated by disturbing replication and gene expression of HBV and by inhibiting the host TLR2/NF-κB signaling pathway.

Functional analysis of hepatitis B virus pre-s deletion variants associated with hepatocellular carcinoma

BACKGROUND

Naturally occurring pre-S deletion mutants have been identified in hepatitis B carriers and shown to be associated with the development of hepatocellular carcinoma. The phenotypes of these pre-S deletion genomes remain unclear, and they were investigated in this study.

METHODS

The pre-S deletion genomes: (1) pre-S1 deletion, (2) deletion spanning pre-S1 and pre-S2, (3) pre-S2 N-terminal deletion, and (4) pre-S2 internal deletion were constructed and analyzed by transfection into Huh-7 cells.

RESULTS

Functional analyses reveal that these mutants were divided into two groups: S promoter deletion and non-S promoter deletion variants. Compared with the wild-type genome, S promoter deletion variants led to an inverse ratio of pre-S1 mRNA and pre-S2/S mRNA, and intracellular accumulation of surface proteins. An interesting finding is that a small amount of L proteins was detected in the medium from S promoter deletion variant-transfected cells. Non-S promoter deletion variants conversely displayed a wild-type like mRNA and protein pattern. The secretion of surface proteins from non-S promoter deletion variants was inhibited less than from S promoter deletion variant. Immunofluorescence analysis showed mutant surface proteins colocalized with ER and exhibited an atypical distribution: granular staining pattern in the S-promoter deletion variants and perinuclear staining pattern in the non-S promoter deletion variants.

CONCLUSION

This study shows that these pre-S deletion genomes exhibit two different phenotypes in mRNA transcription, surface protein expression and secretion. This diversity seems to result from the deletion of S promoter rather than result from the deletion of pre-S1 or pre-S2.

Krüppel-like factor 15 activates hepatitis B virus gene expression and replication

Hepatitis B virus (HBV) is a small DNA virus that requires cellular transcription factors for the expression of its genes. To understand the molecular mechanisms that regulate HBV gene expression, we conducted a yeast one-hybrid screen to identify novel cellular transcription factors that may control HBV gene expression. Here, we demonstrate that Krüppel-like factor 15 (KLF15), a liver-enriched transcription factor, can robustly activate HBV surface and core promoters. Mutations in the putative KLF15 binding site in the HBV core promoter abolished the ability of KLF15 to activate the core promoter in luciferase assays. Furthermore, the overexpression of KLF15 stimulated the expression of HBV surface antigen (HBsAg) and the core protein and enhanced viral replication. Conversely, small interfering RNA knockdown of the endogenous KLF15 in Huh7 cells resulted in a reduction in HBV surface- and core-promoter activities. In electrophoretic mobility shift and chromatin immunoprecipitation assays, KLF15 binds to DNA probes derived from the core promoter and the surface promoter. Introduction of an expression vector for KLF15 short hairpin RNA, together with the HBV genome into the mouse liver using hydrodynamic injection, resulted in a significant reduction in viral gene expression and DNA replication. Additionally, mutations in the KLF15 response element in the HBV core promoter significantly reduced viral DNA levels in the mouse serum.

CONCLUSION

KLF15 is a novel transcriptional activator for HBV core and surface promoters. It is possible that KLF15 may serve as a potential therapeutic target to reduce HBV gene expression and viral replication.

Identification of a novel negative regulatory element on the hepatitis B virus S-(+)-strand

In this study, we scanned the whole hepatitis B virus (HBV) genome for the identification of potential regulatory elements located on the S-(+)-strand. With pCDNA3.1-HBV1.3 as template which contains 1.3-fold HBV whole genome, HBV fragments were amplified by PCR methods, and then inserted into the upstream of a heterologous luciferase reporter vector (pGL3control) in antisense orientation, allowing the HBV expression from the S-(+)-strand. We found that the reporter plasmid containing nt 509-1(3182)-2639 of HBV inhibited luciferase gene transcription and expression in HepG2 cells. Our results strongly suggested that nt 453-250 of HBV may act as a novel negative regulatory element, which has not been reported before. Serial deletion analyses further indicated that nt 453-250 sequence of HBV genome would be the minimal sequence essential for the inhibitory effect of the novel negative regulatory element.

The prevalence of hepatitis B virus preS deletions occurring naturally in Korean patients infected chronically with genotype C

Although Korea is one of the endemic areas for hepatitis B virus infection (HBV), the prevalence of deletions in HBV preS region occurring naturally have not been determined. In the present study, the prevalence of preS deletions was determined in terms of clinical state and HBeAg serostatus in 120 patients with different clinical features [59 HBeAg positive, 61 HBeAg negative; 38 asymptomatic carriers, 21 patients with chronic hepatitis, 21 patients with liver cirrhosis, 40 patients with hepatocellular carcinoma (HCC)]. A total of 37 strains (30.8%) harbored deletions in the preS region. Overall, the frequencies of preS deletions tended to increase gradually according to the degree of the clinical severity of liver disease. The prevalence of preS1 deletions in HCC patients tended to be higher than in patients with liver cirrhosis (32.5% vs. 19%). The prevalence of preS2 deletions in HBeAg negative patients was significantly higher than in HBeAg positive patients (23% vs. 6.8%). The type of deletion encountered most frequently was one disrupting the preS1 start codon [14/37 strains (37.8%)], which showed a very high prevalence in HCC patients (9/40, 22.5%; HCC vs. asymptomatic carriers, P=0.048). These results suggest that there might be the discrepancy between preS1 and preS2 mutations in the mechanism of enhancing the progression of chronic liver disease, especially the development of HCC and to maintain tolerance during the stage of immune tolerance. Specific deletion of the type disrupting preS1 start codon may play important roles in hepatocarcinogenesis, at least in Korean patients with chronic HBV infection.

Mutations in preS genes of genotype C hepatitis B virus in patients with chronic hepatitis B and hepatocellular carcinoma

BACKGROUND

Hepatitis B virus (HBV) preS mutations are frequently isolated from patients with severe forms of liver disease. Meanwhile, genotype C has been shown to cause more serious liver disease than genotype B. This study assesses the frequency of preS mutation in Chinese patients with genotype C chronic HBV infection and its relation to liver damage.

METHODS

Seventy-nine persistently infected patients (25 asymptomatic carriers, 28 with chronic hepatitis, and 26 with hepatocellular carcinoma) with genotype C HBV were analyzed. Levels of HBV DNA, hepatitis B e antigen (HBeAg), alanine aminotransferase, and aspartate transaminase and mutations in the preS region were determined.

RESULTS

The correlations of preS deletion with disease progression were distinct: preS deletion mutations were more commonly found in the hepatocellular carcinoma (HCC) group than in the chronic hepatitis B (CHB) or asymptomatic carrier (ASC) groups, with the frequencies of 38.46% (10/26) in the HCC, 7.14% (2/28) in the CHB, and 4.00% (1/25) in the ASC (P = 0.001) groups. The HBeAg-positive rate and HBV DNA levels were comparable between patients with the preS mutation and those without.

CONCLUSIONS

PreS deletion mutations of genotype C HBV might play a role in HBV-related hepatocarcinogenesis.

Role of surface promoter mutations in hepatitis B surface antigen production and secretion in occult hepatitis B virus infection

The production, secretion, and localization of surface proteins of hepatitis B virus (HBV) and the ratio of large to small surface protein S was studied in HepG2 cells transfected with the wild-type and mutant pre-S1 and pre-S2/S promoters of HBV molecular clones 313.1 (GenBank accession no. AY161147) and 761.1 (GenBank accession no. AY161159) from two patients with occult HBV infection. Fusion constructs were made by in frame fusion of the wild-type surface gene to the mutant pre-S1 and pre-S2/S promoters and wild-type promoter so that the structural part of the small surface protein remains identical. HepG2 cells transfected transiently were used for analysis. HBV surface proteins production and secretion was determined by enzyme linked immuno assay (ELISA) and localization by immunofluorescence. Immunoprecipitation of the large, middle, and small surface protein was carried out in transient transfected and metabolically labeled cells to determine the ratio of the large to small surface protein. The results indicate that HepG2 cells transfected with mutant HBV promoters had reduced HBV surface proteins secretion compared to wild-type HBV. HepG2 cells transfected with mutant HBV pre-S1 and pre-S2/S promoters showed cytoplasmic aggregation of HBV surface proteins compared to wild-type HBV promoters, which showed diffuse cytoplasmic localization. In all cases, the HBV surface proteins localized to the endoplasmic reticulum. The ratio between the large and small surface protein was 1.89 and 0.56 with mutant HBV 313.1 and 761.1 pre-S1 and pre-S2/S promoters, respectively, compared to 0.17 in wild-type. Thus, the aggregation of surface proteins, altered ratio and secretion of surface proteins were possibly the causes of occult hepatitis B infection.

Clinical significance of pre-S mutations in patients with genotype C hepatitis B virus infection

We investigated the overall and site-specific prevalence of pre-S mutations and its clinical significance in patients with genotype C hepatitis B virus (HBV) infection. Three hundred subjects were included: 50 asymptomatic carriers (AC), 87 chronic hepatitis (CH), 91 liver cirrhosis (LC) and 72 hepatocellular carcinoma (HCC). Pre-S mutations were determined by nucleotide sequence analysis. Possible correlations between pre-S mutations and clinical/virological parameters were examined. Pre-S mutations were detected in 82 cases (27.3%); it was more frequently found in HCC (43.1%) and LC (35.2%) group than in the CH (20.7%) and AC (2.0%) group. Pre-S2 deletion was the most commonly found mutation (10.7%), followed by pre-S2 start codon mutation (9.7%), pre-S1-S2 deletion (3.0%) and both pre-S2 deletion and start codon mutation (2.7%). Pre-S2 deletion and pre-S2 start codon mutation were more frequently detected in advanced diseases (LC and HCC). Pre-S mutations were associated with older age and higher rates of positive HBV DNA (>/=0.5 pg/mL). Advanced disease and positive HBV DNA were shown to be independent predictors of pre-S mutations by logistic regression analysis. These findings suggest that pre-S mutations, especially pre-S2 deletions and pre-S2 start codon mutations, are common in patients with genotype C HBV infection and are associated with advanced liver disease and active viral replication.

Hepatocyte-like cells transdifferentiated from a pancreatic origin can support replication of hepatitis B virus

Recently, a rat pancreatic cell line (AR42J-B13) was shown to transdifferentiate to hepatocyte-like cells upon induction with dexamethasone (Dex). The aim of this study is to determine whether transdifferentiated hepatocytes can indeed function like bona fide liver cells and support replication of hepatotropic hepatitis B virus (HBV). We stably transfected AR42J-B13 cells with HBV DNA and examined the expression of hepatocyte markers and viral activities in control and transdifferentiated cells. A full spectrum of HBV replicative intermediates, including covalently closed circular DNA (cccDNA) and Dane particles, were detected only after induction with Dex and oncostatin M. Strikingly, the small envelope protein and RNA of HBV were increased by 40- to 100-fold upon induction. When HBV RNAs were examined by primer extension analysis, novel core- and precore-specific transcripts were induced by Dex which initiated at nucleotide (nt) 1820 and nt 1789, respectively. Most surprisingly, another species of core-specific RNA, which initiates at nt 1825, is always present at almost equal intensity before and after Dex treatment, a result consistent with Northern blot analysis. The fact that HBV core protein is dramatically produced only after transdifferentiation suggests the possibility of both transcriptional and translational regulation of HBV core antigen in HBV-transfected AR42J-B13 cells. Upon withdrawal of Dex, HBV replication and gene expression decreased rapidly-less than 50% of the cccDNA remained detectable in 1.5 days. Our studies demonstrate that the transdifferentiated AR42J-B13 cells can function like bona fide hepatocytes. This system offers a new opportunity for basic research of virus-host interactions and pancreatic transdifferentiation.

Activation of hepatitis B virus S promoter by a cell type-restricted IRE1-dependent pathway induced by endoplasmic reticulum stress

IRE1-alpha is an integral membrane protein of the endoplasmic reticulum (ER) that is a key sensor in the cellular transcriptional response to stress in the ER. Upon induction of ER stress, IRE1-alpha is activated, resulting in the synthesis of the active form of the transcription factor XBP1 via IRE1-mediated splicing of its mRNA. In this report, we have examined the role of IRE1-alpha and XBP1 in activation of the hepatitis B virus S promoter by ER stress. Cotransfection experiments revealed that overexpression of either IRE1-alpha or XBP1 activated this promoter. Conversely, cotransfected dominant-negative IRE1-alpha or small interfering RNA directed against XBP1 decreased the activation of the S promoter by ER stress, confirming an important role for the IRE1-alpha/XBP1 signaling pathway in activation of the S promoter. However, XBP1 does not bind directly to the S promoter; rather, a novel S promoter-binding complex that does not contain XBP1 is induced in cells undergoing ER stress in an XBP1-dependent manner. This complex, as well as transcriptional activation of the S promoter, is induced by ER stress in hepatocytes but not in fibroblasts, despite the presence of active XBP1 in the latter. Thus, the hepatitis B virus S promoter responds to a novel, cell type-restricted transcriptional pathway downstream of IRE1-alpha and XBP1.

Novel Autoregulatory Function of Hepatitis B Virus M Protein on Surface Gene Expression

The hepatitis B virus surface gene consists of a single open reading frame divided into three coding regions: pre-S1, pre-S2, and S. By alternate translation at each of the three initiation codons, L, M, and S proteins can be synthesized. Studies have shown that M protein is not essential for viral replication, virion morphogenesis, or in vitro infectivity. In this study, we show that native M protein can regulate surface gene expression at the transcriptional level. The regulatory effect of M protein is mediated through the CCAAT box within the S promoter. Deletion mapping analysis indicated that the transactivating effect of M protein is mediated through amino acids 1-57 of M protein (the MHBs(au) domain), although its maximal transactivation activity coincides with that of the pre-S2 domain. This conclusion is supported by the fact that disruption of the putative V8 protease site at the pre-S2/S domain junction not only rendered M protein incapable of transactivating the S promoter but also inactivated its nuclear translocation potential. Immunoprecipitation and immunoblot experiments demonstrated that pre-S2 interacts with the three subunits of the CCAAT box-binding factor/nuclear factor Y, the cognate binding protein of the CCAAT box. These results demonstrate and define a novel regulatory role of M protein, which, under natural conditions, may undergo a proteolytic process to generate an MHBs(au) species that will be translocated inside the nucleus, where it will interact with the CCAAT box-binding factor to regulate surface gene expression. Because the CCAAT box is located at a fixed position within numerous promoters, these observations might provide a plausible explanation for hepatitis B virus-associated hepatocarcinogenesis.

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

Background

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

Methods

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

Results

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

Conclusions

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

Unusual life style of giant chlorella viruses

Paramecium bursaria chlorella virus (PBCV-1) is the prototype of a family of large, icosahedral, plaque-forming, dsDNA viruses that replicate in certain unicellular, eukaryotic chlorella-like green algae. Its 330-kb genome contains approximately 373 protein-encoding genes and 11 tRNA genes. The predicted gene products of approximately 50% of these genes resemble proteins of known function, including many that are unexpected for a virus, e.g., ornithine decarboxylase, hyaluronan synthase, GDP-D-mannose 4,6 dehydratase, and a potassium ion channel protein. In addition to their large genome size, the chlorella viruses have other features that distinguish them from most viruses. These features include: (a) The viruses encode multiple DNA methyltransferases and DNA site-specific endonucleases. (b) The viruses encode at least some, if not all, of the enzymes required to glycosylate their proteins. (c) PBCV-1 has at least three types of introns, a self-splicing intron in a transcription factor-like gene, a spliceosomal processed intron in its DNA polymerase gene, and a small intron in one of its tRNA genes. (d) Many chlorella virus-encoded proteins are either the smallest or among the smallest proteins of their class. (e) Accumulating evidence indicates that the chlorella viruses have a very long evolutionary history.

Study on definition of pre-x region in hepatitis B virus genome

AIM

To identify the pre-X gene in HBV strains of Chinese patients.

METHODS

The whole HBV genome was amplified by long-distance and accurate polymerase chain reaction (LA-PCR) method from the serum of 2 patients with chronic HBV infection, and then the PCR products were cloned into pGEM Teasy vectors. Five clones of HBV genome were sequenced. Sequences of our finding were compared with other HBV genome sequence deposited in GenBank.

RESULTS

Pre-X region was found in the HBV genome of these 5 clones, just upstream to the X gene. The pre-X gene is 168 bp long, and can be translated with X gene in frame. The amino acids sequence of pre-X gene was as the following: MGLGYWPSPPAWNLCGSSADPYCGTPSSLFCS QPVWSETYRNRQLCCPLSQIHLLS.

CONCLUSION

Pre-X region may be a serotype-specific coding gene.

Study on definition of pre-pre-S region in hepatitis B virus genome

AIM

To investigate the new open reading frame (ORF) in hepatitis B virus (HBV) genome.

METHODS

The whole HBV genome was amplified by long-distance and accurate polymerase chain reaction (LA-PCR) method from the serum of 2 patients with chronic HBV infection, and then the PCR products were ligased into pGEM Teasy vectors. Five clones of HBV genome were sequenced. Sequences of our finding were compared with other HBV genome sequence deposited in GenBank.

RESULTS

A new ORF was found in HBV genome, just before Pre-S1 region. It was defined as pre-pre-S region. The pre-pre-S ORF was deduced to be translated with Pre-S1, Pre-S2 and S gene in frame. Its amino acids sequence was as the following: MQLIITSKLGIIYILCGRLVFYIREKLHAV PHFVGHHILGNKSYS. There was a TA-rich region before the ATG of pre-pre-S ORF, indicating a possible promoter for its transcription.

CONCLUSION

There is a new ORF pre-pre-S located upstream to pre-S1 region.

Influence of hepatitis B virus genotypes on the development of preS deletions and advanced liver disease

Hepatitis B virus (HBV) mutants with deletions in the preS region have not been evaluated for association with viral genotypes. In a case-control study, HBV DNA samples collected from 80 each of carriers infected with HBV genotype B or C were examined for preS deletions. PreS deletion mutants were found in a total of 37 of 160 (23%) HBV carriers. Carriers with preS deletion mutants were older (56.0 +/- 12.7 vs 49.3 +/- 16.9 years, P < 0.05), were infected more frequently with HBV genotype C (84% vs 40%, P < 0.05), and had more advanced disease, such as liver cirrhosis and hepatocellular carcinoma (54% vs 31%; P < 0.05), than did those without such mutants. In a multivariate analysis, genotype C (odds ratio [OR] = 9.3, P < 0.001) and advanced liver disease (OR = 3.1, P < 0.01) were the most significant variables in association with preS deletions. A direct repeat sequence (TCAGG) was found at the start or at the end of preS1 deletions in 6 of the 20 (30%) cases examined, and preS2 deletions in these cases were clustered over the 5'-terminal half of this region. These results indicate that the development of preS deletion mutants depends on HBV genotypes and that it may be associated with progressive liver disease.

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Overexpression of hepatitis B virus surface antigens including the preS1 region in a serum-free Chinese hamster ovary cell line

Current hepatitis B virus (HBV) vaccines consist of preparations of recombinant HBV major surface antigen (sAg) and are protective in about 90-95% of vaccinated subjects. In improved vaccines, the frequency of nonresponders to the classical vaccine could be reduced by including additional epitopes from the preS-domains of the middle and large surface antigens. In this report, the development and characterization of a CHO cell line for HBsAg, expressing major, middle, and large antigens are described. Despite the previously reported retention of secreted proteins by the preS1 domain, cell lines could be amplified that secreted large amounts of the complete set of antigens. A producer line was established that expressed 1mg HBsAg per 100ml suspension culture per week during exponential growth. The productivity per cell increased further by at least threefold when the culture reached the stationary phase at high cell densities. In the production cell line, several hundred copies of the HBV vector were integrated at two adjacent sites into chromosome 2. The cell line was adapted to growth in a defined protein-free medium minimizing the risk of adventitious agents introduced by animal derived supplements. The cell line stably produced antigen over several months. In the candidate vaccine, both preS2 and preS1 domains were present at ratios similar to HBsAg from human sera. In summary, a production cell line for an improved HBV vaccine is presented with properties such as high productivity, long term stability of expression, and growth in protein-free media.

Regulatory elements of hepatitis B virus transcription

The precise modulation of hepatitis B virus (HBV) gene expression is essential for replication of the virus. HBV sequences are transcribed under the control of the preC/pregenomic, S1, S2 and X promoters. With the exception of S1, all the HBV promoters lack the orthodox TATA box motifs required for the formation of the transcription initiation complex, and as such they represent a unique model of transcription initiation elements. The presence of two enhancer sequences and negative regulatory elements in the HBV genome further augments the controlled synthesis of HBV- RNA. All these transcription cis-elements are embedded within protein coding regions of the genome. This feature demonstrates the remarkable ability of the virus to maximize the function of its small genome. HBV transcription control elements also display a preference for liver-specific or liver-enriched trans-factors, which contributes to the liver tropism of the virus. This review outlines the major HBV transcription regulatory elements and highlights the reliance of accurate HBV gene modulation on the complex interplay between several trans-acting factors and their corresponding cis- motifs in the viral genome.

Characterization of two hepatitis B virus populations isolated from a hepatitis B surface antigen-negative patient

In a study of surface antigen-negative, but weakly hepatitis B virus (HBV) DNA-positive, patients, we were able to amplify and clone whole HBV genomes from the serum of a cirrhotic patient. Sequencing showed that the patient harbored two different HBV populations, one of genotype A and the other of genotype D, with the genotype D genome apparently predominating. The surface antigen of the genotype A virus is heavily mutated, especially in the extracellular << determinant a >> region, with several mutations that have not been previously described. The genotype D virus is a precore mutant. Both genomes possess the common A1762T-G1764A double mutation of the basal core promoter (BCP), and the genotype D virus is also mutated in the << TATA box >> of the large surface antigen promoter. Biological characterization showed that the genotype A genome was fully replication-competent, whereas the genotype D genome replicated poorly. The small surface antigen of the genotype A virus was only very weakly recognized by commercial tests. The small surface antigen of the genotype D virus could be recognized by the tests, but it was mainly retained within transfected cells, probably because of an excess of large surface antigen. In conclusion, the cryptic nature of this double HBV infection is characterized by the predominance of the replication-deficient genotype D virus over the replication-competent genotype A virus.

Hepatitis B surface antigen variants in vaccinees, blood donors and an interferon-treated patient

Variants of hepatitis B virus (HBV), with amino acid substitutions in the major antigenic "a" determinant of hepatitis B surface antigen (HBsAg), have been described mainly in vaccinated children. In the present study in addition to vaccinated children, we have investigated Chinese blood donors positive for anti-HBc alone, and a patient with continuing liver disease after interferon-induced seroconversion to anti-HBs. Variants were detected in two of four children with break-through infections. One child had a double mutation (P142S and G145R) and the other a G145A substitution. Three of seven anti-HBc positive Chinese blood donors had a T131I substitution, whilst the interferon-treated patient had a treble amino acid substitution (P142S, G145R and N146D). The present results indicate that HBsAg variants may exist in individuals other than vaccinated children.

Activation of promoters for cellular lipogenic genes by hepatitis B virus large surface protein

Hepatitis B virus large surface protein has the unusual property of accumulating in a particulate form within a preGolgi compartment, leading to marked proliferation of intracellular membranes. We show here that large surface protein activates the promoters for two lipogenic genes that code for farnesyl diphosphate synthase and fatty acid synthase. This activation is transduced, in part, by the transcription factor NF-Y. Although NF-Y is also necessary for the transcriptional induction of chaperone proteins residing in the endoplasmic reticulum by unfolded proteins, other inducers of chaperone synthesis do not activate the promoters for farnesyl diphosphate synthase and fatty acid synthase. Our results suggest the presence of a novel signaling pathway from the endoplasmic reticulum to the nucleus that causes the intracellular membrane proliferation seen in the hepatocytes of persons with accumulated large surface protein particles.

The pre-S region determines the intracellular localization and appearance of hepatitis B virus

The functional role of the hepatitis B virus (HBV) pre-S region for assembly and appearance of the virus is not completely understood. In this study, 3 natural-occurring mutants were investigated. Three mutants of the pre-S region-a point mutation in the CCAAT box (MUT1), a 6-bp deletion (MUT2) 3' of the CCAAT box, and a 153-bp deletion (MUT3) in the preS2 domain-were cloned alone or in combinations in replication-competent HBV plasmids and transfected in hepatoma cells. The impact on HBV assembly and appearance was studied by Northern Blot, primer extension analysis, immunofluorescence studies, enzyme-linked immunosorbent assay, and electron microscopy. An inversed ratio of pre-S/S mRNA transcripts compared with wild-type (wt) HBV was found when either MUT1 or -2 were included into the plasmid. Intracellular localization with both mutants showed retention of large S-protein in the endoplasmic reticulum and nuclear accumulation of core protein. The extracellular amount of S-protein was reduced with MUT1 and -2 or combinations in which 1 of the mutants was included. However, the extracellular appearance of viral products was comparable with wtHBV. In contrast, MUT3 showed major changes. Virion-like particles had a fried-egg, and filaments a screw-like appearance. The S-promoter mutations MUT1 and MUT2 correlated with viral retention. MUT3 leads to malformed viral particles. Therefore, different regions in the pre-S domain are essential to determine the intracellular localization and extracellular appearance of HBV, and might contribute to the prognosis of chronic HBV infection.

Two control elements in the hepatitis B virus S-promoter are important for full promoter activity mediated by CCAAT-binding factor

Natural occurring mutations in the preS-region are frequently found during chronic hepatitis B virus (HBV) infection. Here we used the mutated preS-region from a patient to study the transcriptional regulation of the S-promoter. The mutations were a CCAAT-box (MUT1) point mutation, a 6-base pair (bp) deletion (MUT2) 3' of the CCAAT-box, and a 153 bp deletion (MUT3) in the preS2 genome. Transfection experiments revealed for MUT1 and 2 30% to 40% and MUT3 75% of the wildtype (wt) S-promoter activity. In electro-mobility shift assays experiments, binding of a nuclear protein was impaired with MUT1. Ultraviolet cross-linking, South-Western, and gel shift experiments revealed a 30- to 40-kd protein interacting with the wt CCAAT-motif. Computer-assisted analysis and supershift experiments showed that CCAAT-binding factor (CBF) is the CCAAT-box binding protein. Cotransfection experiments with expression vectors for dominant-negative CBF or wt CBF showed that the wt S-promoter but not MUT1 could be regulated through CBF. Additionally, the CBF constructs did not modulate the basal activity of MUT2 but changes the activity of MUT3 like wt HBV. Artificial mutations were introduced in the MUT2 reporter constructs. Transfection experiments revealed that wt promoter activity could not be reconstituted. Therefore these experiments indicated the sterical position of CBF being essential for full S-promoter activity. Our study shows that the CCAAT-box and a second region is essential to mediate full S-promoter activity dependent on CBF. As these mutations also lead to retention of S-protein in the endoplasmic reticulum our results indicate that mutational changes in the preS-region might be linked to the progression of HBV-related liver disease.

Giant viruses infecting algae

Paramecium bursaria chlorella virus (PBCV-1) is the prototype of a family of large, icosahedral, plaque-forming, double-stranded-DNA-containing viruses that replicate in certain unicellular, eukaryotic chlorella-like green algae. DNA sequence analysis of its 330, 742-bp genome leads to the prediction that this phycodnavirus has 376 protein-encoding genes and 10 transfer RNA genes. The predicted gene products of approximately 40% of these genes resemble proteins of known function. The chlorella viruses have other features that distinguish them from most viruses, in addition to their large genome size. These features include the following: (a) The viruses encode multiple DNA methyltransferases and DNA site-specific endonucleases; (b) PBCV-1 encodes at least part, if not the entire machinery to glycosylate its proteins; (c) PBCV-1 has at least two types of introns--a self-splicing intron in a transcription factor-like gene and a splicesomal processed type of intron in its DNA polymerase gene. Unlike the chlorella viruses, large double-stranded-DNA-containing viruses that infect marine, filamentous brown algae have a circular genome and a lysogenic phase in their life cycle.

Functional analysis of HBV genomes from patients with fulminant hepatitis

Two previous case reports suggest that hepatitis B virus (HBV) core promoter variants with a high replication competence contribute to the pathogenesis of fulminant hepatitis B (FHB). We recently found in HBV genomes from patients with FHB an accumulation of mutations within the core promoter region. Therefore, the aim of this study was to investigate the phenotype of these HBV variants. Replication competence and expression of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) of viral genomes from seven patients with FHB and one patient with fulminant recurrent hepatitis after liver transplantation were analyzed by transfection experiments in human hepatoma cells. Compared with wild-type virus, the HBV variants from the seven patients with FHB produced similar or slightly lower levels of intracellular replicative intermediates and extracellular viral particles. In contrast, the HBV genomes from the patient with fulminant recurrent hepatitis synthesized and secreted significantly more HBV DNA. All genomes tested expressed similar or even higher levels of HBeAg compared with wild-type virus, except for those from four patients with a precore stop codon mutation in the respective dominant viral populations. The level of HBsAg produced by all variant genomes was similar or reduced compared with wild-type virus. These data indicate that in some cases HBV variants with enhanced replication competence and/or a defect in HBeAg expression may contribute to the development of FHB. However, neither phenotype is an essential prerequisite; thus, an additional role of other viral or host factors in the pathogenesis of FHB is suggested.

Activation of hepatitis B virus S promoter by the viral large surface protein via induction of stress in the endoplasmic reticulum

Hepatitis B virus (HBV) codes for three forms of surface protein. The minor, large form is translated from transcripts specified by the preS1 promoter, while the middle and small forms are translated from transcripts specified by the downstream S promoter. When the large surface protein is overexpressed, the secretion of both subviral and virion particles is blocked within the secretory pathway. We show here that overexpression of the large surface protein leads to up to a 10-fold activation of the S promoter but not of an unrelated promoter. Neither the middle nor the small surface protein, nor a secretable form of the large surface protein, activates the S promoter, but agents that induce endoplasmic reticulum (ER) stress have an effect similar to that of the large surface protein. The large surface protein also activates the S promoter in the context of the entire viral genome. Therefore, it appears that HBV has evolved a feedback mechanism, such that ER stress induced by accumulation of the large surface protein increases the synthesis of the middle and small surface proteins, which in combination with the large surface protein can form mixed, secretable particles. In addition, like other agents that induce ER stress, the large surface protein can activate the cellular grp78 and grp94 promoters, raising the possibility that it may alter the physiology of the host cell.

Hepatitis B virus sequence changes evolving in liver transplant recipients with fulminant hepatitis

BACKGROUND/AIMS

Patients undergoing liver transplantation for hepatitis B virus (HBV) related liver cirrhosis are at major risk of developing HBV recurrence, and occasionally fulminant hepatitis. Here we tested in a longitudinal study whether specific viral variants are associated with fulminant HBV infection in the graft.

METHODS

The complete HBV genomes isolated from the sera of three patients with HBV and HBV and hepatitis delta virus (HDV) coinfection during chronic infection before and during fulminant reinfection after transplantation were amplified and directly sequenced.

RESULTS

Twenty, 25 and 19 mutations, distributed over the entire genome, were identified which differed between the HBV genomes isolated from each patient during chronic and fulminant infection, respectively. This reflects a much higher rate of nucleotide sequence changes than expected from the natural variation of HBV. No common HBV mutation emerged in any of the three cases during fulminant infection. However, precore defective viruses were found to be present in all three patients at the time of fulminant infection and in two of the patients before fulminant infection. Two of the patients had preS2-defective HBVs both before and after transplantation. A point mutation in the 'a'-determinant of the surface protein emerged in one case after transplantation under treatment with polyclonal HBV specific immunoglobulins.

CONCLUSIONS

Many new, but no specific common mutations emerged during fulminant HBV reinfection. Although HBeAg defective variants were found in all cases studied, the presence of these variants also during chronic infection in two cases demonstrates that they are not sufficient to cause fulminant hepatitis. Thus, other factors than the emergence of a specific viral strain seem to contribute to the development of fulminant reinfection in a liver graft.

Hepatitis B virus mutations in the pre-S genome before and after liver transplantation

Mutational changes in the pre-S region of hepatitis B virus (HBV) were analyzed in 20 patients who experienced HBV reinfection after orthotopic liver transplantation (OLT). HBV DNA was extracted from patient sera before and after OLT. The pre-S sequence was amplified via polymerase chain reaction, subcloned, sequenced, and analyzed. In 18 of 20 patients, mutational changes were found in the pre-S region pre- or post- OLT; 11 showed point mutations (1-10) and 7 cases major changes (insertions/deletions). For the point mutations, there was no trend in the selection of wild-type (wt) HBV before or after OLT in the pre-S region. Additional HBV reinfection during hepatitis B surface antigen antibody (anti-HBS) administration had no influence on selection pressure in the pre-S region. In contrast, insertions/deletions were more frequently found before OLT. In the 7 patients with deletions/insertions, changes in the hepatocyte attachment site were not seen after OLT. Interestingly, the only patient with changes in a major virus population after OLT had changes in the CCAAT-box of the S-promoter. As shown by gel shift analysis, this mutation was associated with loss of specific binding to this element and thus probably led to dysregulation of S-gene transcription. Major changes in the pre-S genome are mainly seen before OLT, and HBV reinfection does occur with the intact hepatocyte attachment sites after OLT. Anti-HBs (hepatitis B immune globulin [HBIg]) creates no selection pressure on the pre-S region. The mutation in the CCAAT-box of the S-promoter potentially leads to its dysregulation and may be associated with the occurrence of fibrosing cholestatic hepatitis after OLT.

Intracellular retention of surface protein by a hepatitis B virus mutant that releases virion particles

In the course of chronic infection, hepatitis B virus mutants can sometimes be found circulating in the serum as the predominant species. One class of such mutants contains in-frame deletions in the S promoter region. By transfecting hepatoma cells with wild-type or mutant viral genomic DNA, we have shown that one such mutant gives rise to extremely small amounts of S transcripts, as expected, and therefore expresses very little of the middle and small surface (viral envelope) proteins that are translated from these transcripts. In addition, this mutant gives rise to greater-than-wild-type levels of the preS1 transcripts, which are translated into the large surface protein. Because the large surface protein, unlike the other forms of surface protein, is incompetent for secretion, cells transfected with the mutant viral DNA contain large amounts of 20-nm particles within dilated perinuclear vesicles. Therefore, this and similar S promoter mutants may be one contributing factor in the pathogenesis of ground-glass cells, which are hepatocytes containing nonsecretable viral surface proteins within dilated vesicles and are commonly found during chronic hepatitis B. Interestingly, DNA-containing virion particles are secreted into the medium by cells transfected with the mutant DNA, in amounts that are slightly larger than those secreted from wild-type-transfected cells, apparently because the amount of large surface protein is insufficient to block virion secretion. This finding may explain how such mutants can become the predominant circulating species in the serum, especially if there are selection pressures against the wild-type virus.