[Construction and biological activity assessment of core mutants of hepatitis B virus adr subtype]

OBJECTIVE

To construct the core mutant (L97 and V60) plasmids of hepatitis B virus (HBV) and assess their biological activity.

METHODS

Site-directed mutagenesis was performed to induce specific core point mutations in HBV adr suhtype 1.2 copy genome plasmid p3.8 II. The plasmids were transfected into HepG2 cells via liposome, and intracellular HBV DNA was analyzed by Southern hybridization, while extracellular HBV antigens (HBsAg and HBeAg) in the culture supernatant were assayed by enzyme-linked immunosorbent assay.

RESULTS

Sequence analysis of the constructed mutant plasmids p3.8 L97 and p3.8 V60 demonstrated mutations at 2 189 A C and 2 086 C HBV adr subtype genome core mutant (L97 and V60) plasmids we have constructed possess biological activity.G respectively. These mutant plasmids exhibited HBV DNA replication activity and gene expression in host cells.

CONCLUSION

HBV adr subtype genome core mutant (L97 and V60) plasmids we have constructed possess biological activity.

[Study on anti-HBV effects by antisense oligodeoxynucleotides in vitro]

OBJECTIVE

To study the inhibition effect of anti-HIV oligodeoxy-nucleotides on HBV X gene.

METHODS

Three antisense phosphorothioate oligodeoxy-nucleotides(AsON) complementary to the initiator of X, DR2, EN II respectively, were synthesized and tested for their anti-HBV activity on HepG2.2.15 cells with ELISA methods.

RESULTS

When the best effect concentration of AsON was 10 mumol/L, the inhibition rates on HBsAg of three AsON were 57%, 60% and 52% respectively, and on HBeAg were 56%, 45% and 56% respectively. There were two inhibition peaks at different times. There was no inhibition effect treated by random control (< 12%). Using the 3-(4,5-dimethythiazol-xyl)-2,5-diphnyl tetrazolium bromide method, there was no cytotoxicity at 40 mumol/L of AsON.

CONCLUSION

AsONs on three key region of X gene were effective drugs to inhibit the expression of HBV.

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.

Nuclear covalently closed circular viral genomic DNA in the liver of hepatocyte nuclear factor 1 alpha-null hepatitis B virus transgenic mice

The role of hepatocyte nuclear factor 1alpha (HNF1 alpha) in the regulation of hepatitis B virus (HBV) transcription and replication in vivo was investigated using a HNF1 alpha-null HBV transgenic mouse model. HBV transcription was not measurably affected by the absence of the HNF1 alpha transcription factor. However, intracellular viral replication intermediates were increased two- to fourfold in mice lacking functional HNF1 alpha protein. The increase in encapsidated cytoplasmic replication intermediates in HNF1 alpha-null HBV transgenic mice was associated with the appearance of nonencapsidated nuclear covalently closed circular (CCC) viral genomic DNA. Viral CCC DNA was not readily detected in HNF1 alpha-expressing HBV transgenic mice. This indicates the synthesis of nuclear HBV CCC DNA, the proposed viral transcriptional template found in natural infection, is regulated either by subtle alterations in the levels of viral transcripts or by changes in the physiological state of the hepatocyte in this in vivo model of HBV replication.

Hepatitis B virus X gene variability in French-born patients with chronic hepatitis and hepatocellular carcinoma

The polymorphism of the hepatitis B virus (HBV) X gene from patients born in Lorraine has been studied in serum samples from 22 HBV infected patients, 14 presenting with chronic hepatitis and 8 with hepatocellular carcinoma (HCC). Subtypes adw and ayw represented 21 of the 22 sequenced isolates. The sequence of the X gene of HBV strains from these patients differed from the ones of Far East origin by A to T(1678) and G to A(1759) changes for subtype ayw and C to T(1792) for adw. The expression of the preC region, as indicated by the detection of HBe antigen (HBeAg), was not observed in 11 patients. In 6 patients (3 HCC and 3 non HCC), the absence of HBeAg could be related to a stop codon at position 28. For the 5 remaining patients, the precore stop mutation at codon 28 was not evidenced but 3 out these 5 patients had mutations at nt 1764 and nt 1766 in the promoter of the preC/C gene. These two mutations were also observed in 2 patients with HBeAg, indicating that they are not implicated in the suppression of expression of this gene. Independently of the serotype, two main differences were noted between aminoacid (aa) sequences of chronic hepatitis and HCC related strains: first, twice as many aa changes were found in HCC patients than in chronic hepatitis B carriers (mean of aa changes per patient 4.1 vs. 2.0) and second, we found apparition of polar aa in HCC patients. Most mutations already described in patients from the Far East with HCC have been found in strains of patients from Lorraine. The changes K130M and V131I, considered as "hot spot mutations," were found in strains of HCC patients carrying an ayw subtype of the HBV genome but not in the ones of chronically infected patients. In contrast, strains of the adw subtype had these two changes in the two groups of patients. However when considering the 22 sequenced genes, these hot spot mutations were associated with HCC (P = 0.034).

Hepatocytes of double-transgenic mice expressing high levels of hepatitis B virus e antigen and interferon-gamma are not injured by HBeAg specific autoantibodies

Seroconversion from HBeAg to alphaHBe of persons chronically infected by HBV is usually associated with a transient exacerbation of liver disease and subsequent normalization of liver histology. It is speculated that these clinico-pathological features may be due to the activation of cytodestructive mechanisms by alphaHBe antibodies. The aim of the present study was to investigate the pathogenic potential of alphaHBe antibodies in a transgenic mouse model. Therefore, alphaHBe autoantibodies were elicited in double-transgenic mice expressing high amounts of HBeAg and interferon-gamma in the liver. Interferon-gamma has reviously been shown to play an important role in the development of hepatic necroinflammation associated with hepadnaviral infection, probably via tumor-necrosis-factor-alpha secreted by activated macrophages. We found no evidence that alphaHBe antibodies have the potential to destroy HBeAg-secreting hepatocytes even if the cells were predisposed to injury due to high-level interferon-gamma expression. We conclude that seroconversion from HBeAg to alphaHBe of persons chronically infected with HBV seems to be an immunological epiphenomenon without pathogenic significance.

Generation of MHC class I peptide antigens by protein processing in the secretory route by furin

Cytosolic degradation of endogenously synthesized proteins by the proteasome and translocation of processed peptides to the endoplasmic reticulum by the transporters associated with antigen presentation constitutes the classical route for antigen presentation by MHC class I proteins. We have previously defined an alternative pathway in the secretory route involving proteolytic maturation of precursor proproteins for chimeric hepatitis B virus secretory core protein HBe containing a class I epitope at its carboxy-terminus. We extend those results by demonstrating that intracellular delivery of the trans-Golgi network protease furin increases both proteolytic maturation and antigen presentation of the chimeric HBe proteins. An additional class I epitope from the HIV envelope gp160 protein was inserted into this COOH-terminal region of two different chimeric HBe proteins. This epitope was also presented to CTL in a transporter-independent manner involving furin, and protein maturation and antigen presentation were also enhanced by furin over-expression. Presentation of this second epitope was restricted by a different class I allele, thus suggesting that antigen presentation by this new pathway may apply to any antigenic epitope and class I molecule. These results define the furin proteolytic maturation pathway of HBe in the secretory route as a general antigen processing route for MHC class I presentation.

Anti-HBV effect of targeted antisense RNA against HBV C gene

OBJECTIVE

To investigate the anti-HBV effect of targeted antisense RNA to hepatic cells.

METHODS

pREP4-aC which would transcript antisense RNA against HBV C gene in eukaryotic cells were delivered into 2.2.15 cells by glactosylated poly-L-lisine (Gal-PLL), and the positive cells were selected. HBsAg, HBeAg and HBV DNA produced by 2. 2.15 cells were detected with ELISA or Southern blot during the experiment, and the cytotoxicity of targeted antisense on 2.2.15 cells was observed.

RESULTS

The inhibition effect on HBsAg, HBeAg and HBV DNA occurred at the 24th hour after delivery and reached the highest level at the 6th day, and kept at lest two months. No cytotoxicity on 2.2.15 cells was observed.

CONCLUSION

The targeted antisense against HBV C gene by delivery of Gal-PLL could effectively inhibit the antigen expression of HBV and DNA replication.

Sequential cleavage by metallopeptidases and proteasomes is involved in processing HIV-1 ENV epitope for endogenous MHC class I antigen presentation

Antigenic peptides derived from viral proteins by multiple proteolytic cleavages are bound by MHC class I molecules and recognized by CTL. Processing predominantly takes place in the cytosol of infected cells by the action of proteasomes. To identify other proteases involved in the endogenous generation of viral epitopes, specifically those derived from proteins routed to the secretory pathway, we investigated presentation of the HIV-1 ENV 10-mer epitope 318RGPGRAFVTI327 (p18) to specific CTL in the presence of diverse protease inhibitors. Both metalloproteinase and proteasome inhibitors decreased CTL recognition of the p18 epitope expressed from either native gp160 or from a chimera based on the hepatitis B virus secretory core protein as carrier protein. Processing of this epitope from both native ENV and the hepatitis B virus secretory core chimeric protein appeared to proceed by a TAP-dependent pathway that involved sequential cleavage by proteasomes and metallo-endopeptidases; however, other protease activities could replace the function of the lactacystin-sensitive proteasomes. By contrast, in a second TAP-independent pathway we detected no contribution of metallopeptidases for processing the ENV epitope from the chimeric protein. These results show that, in the classical TAP-dependent MHC class I pathway, endogenous Ag processing of viral proteins to yield the p18 10-mer epitope requires metallo-endopeptidases in addition to proteasomes.

A novel hepatitis B virus variant S 129 (Gln-->Leu): lack of correlation between antigenicity and immunogenicity

A point mutation has been detected in the "a" determinant of hepatitis B surface antigen (HBsAg) in an infant immunised with hepatitis B vaccine after exposure to hepatitis B virus (HBV). This A-to-T point mutation at nucleotide 540 resulted in a glutamine-to-leucine substitution at amino acid residue 129 (129L). The S gene fragment (nucleotide 58-1072) of this isolate was cloned and used to substitute the wild-type S gene in a plasmid (p3.8II), containing 1.2 copy of full-length HBV genome with expression and replication efficiency. This plasmid p3.8II-129L was used to transfect HepG2 cells. HBsAg expressed by p3.8II-129L showed higher binding efficiency compared with the original plasmid containing the wild-type clone. A panel of 24 anti-HBs monoclonal antibodies (MAbs) was used to characterise the binding efficiency of HBsAg expressed by p3.8II-129L. Eighteen showed higher binding to the antigen, whereas HBsAg expressed by p3.8II-145R gave a consistently lower absorbance or were negative. Surprisingly, when the immunogenicity of plasmid constructs was used for DNA immunisation in Balb/c mice, the anti-HBs response induced by p3.8II-129L was significantly lower than that of the wild-type p3.8II. The lack of correlation between the antigenicity profile (binding of expressed HBsAg to anti-HBs in vitro), and the immunogenicity (induction of anti-HBs by plasmid DNA in vivo) of HBsAg with leucine substitution at position 129 indicates that biological characteristics other than the binding efficiency of HBsAg to anti-HBs could occur in HBsAg variants. These different aspects of the biological characteristics of S mutants merit further investigation.

[Effects of the water-soluble extracts from the single herb of ganduqing against hepatitis B virus in vitro]

Comparing with Ara-Amp, the effects of the water-soluble extracts from the single herb of the formula for Ganduqing on HBeAg and HBsAg expression in 2.2.15 cells were studied. The results showed that the extracts of Serissa serissoides (DC) Druce, Hibiseus mutabilis Linn, Paedeuia scangens (Lour) Merr var tomentosa (BL) Hand-Mazz, Plumbago zeylanica L, Garcinia oblougifolia Champ and Begpnia edulia Levl had marked inhibition effects on HBeAg and HBsAg which expressed by 2.2.15 cells.

HBeAg immunostaining of liver tissue in various stages of chronic hepatitis B

AIMS

We studied the tissue expression of hepatitis B e antigen (HBeAg) in 29 liver biopsies from 27 HBV carriers.

METHODS

HBeAg expression was assessed in relation to HBeAg in serum, precore mutations, HBV DNA levels and liver damage as measured by histology activity index.

RESULTS

HBeAg in liver tissue was detected by immunostaining in 6 of 7 patients positive for HBeAg in serum. In patients negative for HBeAg in serum, HBeAg was detected in none of 11 specimens from patients infected exclusively with a precore mutant that disrupts HBeAg synthesis, as compared with 3 of 11 specimens from patients carrying HBV with an intact precore region. These 3 patients all showed high HBV DNA levels in serum and severe liver damage.

CONCLUSIONS

Overall, viral replication was strongly associated with the cytoplasmic HBeAg and nuclear HBcAg staining, but not with tissue staining for HBsAg. Because of the close relationship between tissue HBeAg expression and high viral load, the pathogenetic importance of HBeAg remains unclear.

Combinatorial screening and intracellular antiviral activity of hairpin ribozymes directed against hepatitis B virus

A combinatorial screening method has been used to identify hairpin ribozymes that inhibit hepatitis B virus (HBV) replication in transfected human hepatocellular carcinoma (HCC) cells. A hairpin ribozyme library (5 x 10(5) variants) containing a randomized substrate-binding domain was used to identify accessible target sites within 3.3 kb of full-length in vitro-transcribed HBV pregenomic RNA. Forty potential target sites were found within the HBV pregenomic RNA, and 17 sites conserved in all four subtypes of HBV were chosen for intracellular inhibition experiments. Polymerase II and III promoter expression constructs for corresponding hairpin ribozymes were generated and cotransfected into HCC cells together with a replication-competent dimer of HBV DNA. Four ribozymes inhibited HBV replication by 80, 69, 66, and 49%, respectively, while catalytically inactive mutant forms of these ribozymes affected HBV replication by 36, 28, 0, and 0%. These findings indicate that the inhibitory effects on HBV replication were largely mediated by the catalytic activity of the ribozymes. In conclusion, we have identified catalytically active RNAs by combinatorial screening that mediate intracellular antiviral effects on HBV.

Detection of mutations in the enhancer 2/core promoter region of hepatitis B virus in patients with chronic hepatitis B virus infection: comparison with mutations in precore and core regions in relation to clinical status

To investigate the meaning of the mutations in the enhancer 2/core promoter (Enh2/CP) region of hepatitis B virus (HBV) during the chronic HBV infection, mutations were examined in the Enh2/ CP region (carboxyl half of X region) and their correlation with mutations in the precore and core regions in relation to the presence of chronic liver disease. The entire nucleotide sequences of the Enh2/CP region were determined by direct sequencing of the amplified products derived from 30 cases with chronic HBV infection. The results were compared to the mutations in the precore and core regions. In the Enh2/CP region, 91 generally scattered nucleotide substitutions were detected. There were 11 substitutions in the 10 asymptomatic healthy carriers (mean, 1.1/case) and 80 in the 20 chronic liver disease patients (4.0/case). The most frequent substitutions from A to T at nucleotide 1764 and from G to A at nucleotide 1766 were seen in none of the 10 asymptomatic carriers and in 14 (70%) of the 20 chronic liver disease patients. Comparisons of mutations in the precore and core regions revealed that 14 of 16 patients with mutations in the core region had the mutations in the Enh2/CP region and/or a precore stop codon mutation. These data suggest that mutations in the Enh2/CP and precore regions may affect the expression of the core and HBeAg peptides and might be involved in the pathogenesis of chronic liver disease.

[Inhibiting effects of the ethanol-soluble extracts from the dried rhizoma of Garcinia oblougififolia on hepatitis B virus in vitro]

Comparing with Ara-Amp, the effects of the ethano-soluble extracts from the dried rhizoma of Garcinia oblougififolia Champ (GOC) on HBeAg and HBsAg expression in 2.2.15 cells, which came from transfected HepG2 cells with coloned HBV DNA, were studied. The results showed that the extracts of GOC had a marked inhibition effects on HBeAg adn HBsAg which expressed by 2.2.15 cells, the effective concentration was range from 195 to 780 micrograms/ml.

Major histocompatibility complex class I viral antigen processing in the secretory pathway defined by the trans-Golgi network protease furin

Classical antigen presentation by major histocompatibility complex class I molecules involves cytosolic processing of endogenously synthesized antigens by proteasomes and translocation of processed peptides into the endoplasmic reticulum (ER) by transporters associated with antigen presentation (TAP). Alternative pathways for processing of endogenous antigens, generally involving the ER, have been suggested but not fully proved. We analyzed the potential for class I presentation of proteolytic maturation of secretory antigens in the exocytic pathway. We found that hepatitis B (HB) virus secretory core protein HBe can efficiently deliver COOH-terminally located antigenic peptides for endogenous class I loading in the absence of TAP. Antigen presentation to specific cytotoxic T lymphocytes correlates with protein maturation at the COOH terminus, since modification of maturation and transport of HBe through the secretory pathway alters antigen presentation. Both maturation and a necessary processing step occur in the Golgi or post-Golgi compartment. Antigen presentation is independent of proteasome activity, but inhibitors of the trans-Golgi network resident protease furin inhibit both HBe maturation and antigen presentation. These results define a new antigen processing pathway located in the secretory route, with a central role for proteolytic maturation mediated by the subtilisin protease family member furin as an efficient source for antigen presentation.

The C terminus of the hepatitis B virus e antigen precursor is required for a tunicamycin-sensitive step that promotes efficient secretion of the antigen

The Hepatitis B virus encodes the secreted e antigen (HBe) whose function in the viral life cycle is unknown. HBe derives from a 25-kDa precursor that is directed to the secretory pathway. After cleavage of the signal sequence, the resulting 22-kDa protein (P22) is processed in a post-endoplasmic reticulum compartment to mature HBe by removal of the 34-amino acid C-terminal domain. The efficiency of HBe secretion is specifically decreased in cells grown in the presence of tunicamycin, an inhibitor of N-glycosylation. Inasmuch as HBe precursor is not N-glycosylated, our data suggest that a cellular tunicamycin-sensitive protein increases the intracellular transport through the HBe secretory pathway. The study of the secretion of HBe derived from C-terminal-truncated precursors demonstrates that the tunicamycin-sensitive secretion absolutely requires a part of the C-terminal region that is removed to form mature HBe, indicating that the cellular tunicamycin-sensitive protein increases the efficiency of the intracellular transport of P22. We have also shown that the Escherichia coli beta-galactosidase can be secreted when fused to the HBe precursor signal sequence and that the P22 C-terminal domain renders the secretion of this reporter protein also tunicamycin-sensitive.

[A molecular epidemiologic study on the mechanism of intrauterine transmission of hepatitis B virus]

A case-control study with examination of placentas using immunohistochemistry stain was reported in this paper. In the Maternal and Children Health Hospital of Shanxi Province, 242 consecutive HBsAg positive mothers and their babies were selected as subjects and 110 placentas of HBsAg positive mothers and 25 placentas of HBsAg negative mothers during the different period of pregnancy were collected for laboratory test. The results showed that maternal HBeAg positivity (OR = 32.63) and history of threatened premature labor (OR = 22.80) were important risk factors. Among full-term placentas with HBsAg positivity, HBsAg (biomarker of HBV infection) positive rates were 100% in decidual cell, 59.38% in trophoblastic cell, 65.50% in villous mesenchyme cell, and 39.38% in villous capillary endothelial cell (VCEC) with a decreasing trend (trend test, chi 2 = 30.5, P < 0.01) from mothers to fetus whereas HBsAg positive in VCEC was significantly related to intrauterine infection (OR = 20.86, P < 0.01). Results suggested that there might be two transmission routes on the mechanism of HBV intrauterine transmission, hemogenous by damage of placental vessels and cellular through placental cellular transfer of HBV.

[Synthesis and preliminary study on cleavage activity of ribozyme to hepatitis B virus preS2 gene in vitro]

In this paper, a multi-target hammerhead ribozyme gene was synthesized directed against 110, 122 and 132 sites of nucleotide of HBV preS2 gene. The target gene fragment was cut from HBV genome containing plasmid pCP10. Both of the ribozyme and the target gene fragments were cloned into pGEM3Zf(-) plasmid and sequenced by dideoxy chain termination method. The transcription of both gene fragments was performed in vitro utilizing T7 RNA promoter in pGEM3Zf (-) plasmid. The cleavage activity of ribozyme to substrate was confirmed in vitro. For further evaluating intracellular function of ribozyme, two ribozyme-retroviral recombinant plasmids with different promoter type pDOR-ripe and tRNA-ripe were constructed. Pseudo-virus was collected through routine packaging procedure and transduted into 2.2.15 cells. RIA data showed a stable inhibition of pHSA-R antigen expression to the lowest extent of 41.01% +/- 4.16 and the highest extent of 51.45% +/- 4.57 within 4 weeks after transduction. No influence, however, on HBsAg and HBeAg expression was demonstrated after ribozyme gene transfer.

Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial

Thymosin alpha1 (Talpha) is an immune modifier that has been shown in a pilot study to be effective for chronic hepatitis B; this requires confirmation. Ninety-eight patients with clinicopathologically proven chronic hepatitis B were randomly allocated to 3 groups: 1) group A received a 26-week course of Talpha with a 1.6-mg subcutaneous injection two times a week (T6 group); 2) group B received the same regimen as group A, but Talpha therapy extended for 52 weeks (T12 group); and 3) group C served as a control group and was followed up for 18 months without specific treatment (T0 group). The three groups were comparable in clinicohistological features at entry. The complete virological response rate (clearance of serum hepatitis B virus [HBV] DNA and hepatitis B e antigen [HBeAg]) was higher in group A (40.6%) and group B (26.5%) than in group C (9.4%) (group A vs. group C: P=.004; group B vs. group C: P=.068) when assessed 18 months after entry, although complete response rates among these three groups were similar when first assessed at the end of therapy. There was a trend for complete virological response to increase or accumulate gradually after the end of Talpha therapy. None of the responders lost hepatitis B surface antigen. Blinded histological assessment showed a significant improvement in treated patients, particularly in lobular necroinflammation and scores excluding fibrosis. No significant side effects were observed. These results suggest that a 26-week course of Talpha therapy is effective and safe in patients with chronic hepatitis B.

Hepatitis B virus mutants associated with 3TC and famciclovir administration are replication defective

Hepatitis B virus (HBV) variant strains may develop during therapy for chronic infection with the nucleoside analog 2',3'-dideoxy-3'-thiacytidine (3TC). HBV mutants result from isoleucine (I) or valine (V) substitutions in the methionine (M) of the YMDD motif in the viral reverse-transcriptase catalytic domain. In addition, other mutations in the reverse-transcriptase "B domain" involving either a phenylalanine (F)-to-leucine (L) at amino acid 501 (F501L) or an L-to-M substitution at amino acid 515 (L515M) have been observed during 3TC and Famciclovir therapy as well. To determine the biologic consequences of these mutations on viral replication, variant viral genomes were constructed and transiently transfected into hepatocellular carcinoma (HCC) and HEK 293 human embryo kidney-derived cell lines. In transiently transfected HCC cells, the viruses bearing the YI/VDD or F501L mutations had greatly impaired replication as compared to wild-type virus, whereas the virus carrying the L515M substitution showed the least defect. Double mutants with the L515M substitution showed intermediate defect between the YI/VDD or F501L and the L515M single-mutant strains. In contrast, when transfected into HEK 293 cells, the viruses bearing the YI/VDD or L515M mutation replicated as wild-type. However, under conditions of deoxynucleotide depletion produced by hydroxyurea treatment of HEK 293 cells, all mutants but not the wild-type virus exhibited a reduced replication phenotype similar to that observed in HCC cells. In both HCC and HEK 293 cells, the mutant viruses carrying the F501L substitution showed a decreased pregenomic RNA encapsidation level, suggesting that the defect in HBV DNA synthesis occurs at the RNA packaging level. These findings show that 3TC and Famciclovir selected mutations alter the properties of the HBV reverse transcriptase, resulting in impaired viral replication within the cell.

A monoclonal antibody against a hepatitis B e antigen epitope borne by six amino acids encoded by the precore region

Hepatitis B e antigen (HBeAg) polypeptide in the circulation (p17e) is composed of ten amino acids (aa) coded for by the precore region and 149 aa by the core gene of hepatitis B virus. A monoclonal antibody (Y0583A) was raised against the N-terminal ten amino acids (SKLCLGWLWG) encoded by the precore region. The binding of Y0583A with a panel of 203 decapeptides on multipins, which covered the precursor of HBeAg polypeptide made of 212 aa shifting by one aa, recognized an epitope sequenced LGWLWG representing the C-terminal six aa coded for by the precore region. This HBeAg epitope was not readily accessible on HBeAg in serum, but it became exposed and bound with Y0583A by treatment with 0.2 N NaOH. Using Y0583A, an enzyme-linked immunosorbent assay was developed for specific determination of HBeAg. The test sample was incubated with the monoclonal antibody to an HBeAg determinant encoded by the core gene (904) that had been immobilized on a solid support. Captured HBeAg was treated with 0.2 N NaOH, neutralized and released into the fluid phase. The reactant was then tested for a sandwich between monoclonal antibody (C33) to the C-terminus of the HBeAg polypeptide immobilized on a solid support and Y0583A labeled with horseradish peroxidase.

[The inhibitory effect of Chinese herb Phyllanthus on hepatitis B virus in vitro]

Seven preparations of different species of Chinese herb Phyllarthus with different formulations and additives were studied for their ability to inhibit hepatitis B virus DNA replication, that is the HBsAg and HBeAg expression in a HBV DNA-transfected cell line (2.2.15 cell). The results showed that all the drugs were effectively against HBV replication in vitro. Capsule 1 and tuo cha zhen zhu cao were found to be the most potent anti-HBV extracts of those examined. Both extracts decreased HBaAg expression by nearly 100% at the concentration of 500 mg/L without toxicity on cell growth. Southern blot showed that Capsule 1 inhibited HBV DNA replication in a dose-dependent manner. We observed further, that under similar dosage the drug inhibition to HBsAg and HBeAg expression was lower than that to HBV DNA replication, suggesting that the production of progeny virus particles not only were inhibited at the level of HBV DNA synthesis, but also was affected probably at the level of translation of viral mRNA.

Effects of a frequent double-nucleotide basal core promoter mutation and its putative single-nucleotide precursor mutations on hepatitis B virus gene expression and replication

The basal core promoter (BCP) of hepatitis B virus (HBV) directs the transcription of both precore RNA and core RNA which code for e antigen (HBeAg) and core antigen, respectively. A double mutation in the BCP which converts nucleotide (nt) 1762 from A to T and nt 1764 from G to A is frequently observed in patients with chronic hepatitis B. We recently demonstrated that this double mutation prevented the binding of a liver-enriched factor (LEF) to the BCP, suppressed only precore RNA transcription (and hence HBeAg expression), and enhanced progeny virus production. In order to understand the mechanism for the selection of this frequent double mutation, we have extended our previous studies to further characterize LEF and to compare the effects of this double-nucleotide mutation (M1) with each single-nucleotide mutation at nt 1762 (M2) and nt 1764 (M3). Our results indicate that LEF is likely composed of a heterodimer formed between the transcription factor chicken ovalbumin upstream promoter-transcription factor (COUP-TF) and an unidentified liver-enriched factor. Further studies reveal that both M1 and M2 prevent the binding of LEF to the BCP, suppress only precore RNA transcription, and increase the efficiency of progeny virus synthesis. In contrast, M3 retains some LEF binding activity, does not suppress HBV RNA transcription, and reduces slightly the efficiency of virus progeny synthesis. The reduced ability of M3 to replicate indicates that it has no selection advantage in itself at the level of the infected hepatocyte. In spite of its enhanced replication rate, M2 is rarely detected in HBV patients. This indicates the involvement of factors other than intracellular replication rates in the selection of these virus variants in the infected individual.