The value of hepatitis B x antigen as a prognostic marker in the development of hepatocellular carcinoma

Short chain fatty acids delay the development of hepatocellular carcinoma in HBx transgenic mice

Chronic infection with hepatitis B virus (HBV) is a major risk factor for the development of hepatocellular carcinoma (HCC). The HBV encoded oncoprotein, HBx, alters the expression of host genes and the activity of multiple signal transduction pathways that contribute to the pathogenesis of HCC by multiple mechanisms independent of HBV replication. However, it is not clear which pathways are the most relevant therapeutic targets in hepatocarcinogenesis. Short chain fatty acids (SCFAs) have strong anti-inflammatory and anti-neoplastic properties, suggesting that they may block the progression of chronic liver disease (CLD) to HCC, thereby identifying the mechanisms relevant to HCC development. This hypothesis was tested in HBx transgenic (HBxTg) mice fed SCFAs. Groups of HBxTg mice were fed with SCFAs or vehicle from 6 to 9 months of age and then assessed for dysplasia, and from 9 to 12 months of age and then assessed for HCC. Livers from 12 month old mice were then analyzed for changes in gene expression by mass spectrometry-based proteomics. SCFA-fed mice had significantly fewer dysplastic and HCC nodules compared to controls at 9 and 12 months, respectively. Pathway analysis of SCFA-fed mice showed down-regulation of signaling pathways altered by HBx in human CLD and HCC, including those involved in inflammation, phosphatidylinositol 3-kinase, epidermal growth factor, and Ras. SCFA treatment promoted increased expression of the tumor suppressor, disabled homolog 2 (DAB2). DAB2 depresses Ras pathway activity, which is constitutively activated by HBx. SCFAs also reduced cell viability in HBx-transfected cell lines in a dose-dependent manner while the viability of primary human hepatocytes was unaffected. These unique findings demonstrate that SCFAs delay the pathogenesis of CLD and development of HCC, and provide insight into some of the underlying mechanisms that are relevant to pathogenesis in that they are responsive to treatment.

HBV-Integration Studies in the Clinic: Role in the Natural History of Infection

Hepatitis B virus (HBV) infection is a major global health problem causing acute and chronic liver disease that can lead to liver cirrhosis and hepatocellular carcinoma (HCC). HBV covalently closed circular DNA (cccDNA) is essential for viral replication and the establishment of a persistent infection. Integrated HBV DNA represents another stable form of viral DNA regularly observed in the livers of infected patients. HBV DNA integration into the host genome occurs early after HBV infection. It is a common occurrence during the HBV life cycle, and it has been detected in all the phases of chronic infection. HBV DNA integration has long been considered to be the main contributor to liver tumorigenesis. The recent development of highly sensitive detection methods and research models has led to the clarification of some molecular and pathogenic aspects of HBV integration. Though HBV integration does not lead to replication-competent transcripts, it can act as a stable source of viral RNA and proteins, which may contribute in determining HBV-specific T-cell exhaustion and favoring virus persistence. The relationship between HBV DNA integration and the immune response in the liver microenvironment might be closely related to the development and progression of HBV-related diseases. While many new antiviral agents aimed at cccDNA elimination or silencing have been developed, integrated HBV DNA remains a difficult therapeutic challenge.

Profiling of LINE-1-Related Genes in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a prime public health concern that accounts for most of the primary liver malignancies in humans. The most common etiological factor of HCC is hepatitis B virus (HBV). Despite recent advances in treatment strategies, there has been little success in improving the survival of HCC patients. To develop a novel therapeutic approach, evaluation of a working hypothesis based on different viewpoints might be important. Long interspersed element 1 (L1) retrotransposons have been suggested to play a role in HCC. However, the molecular machineries that can modulate L1 biology in HBV-related HCC have not been well-evaluated. Here, we summarize the profiles of expression and/or activation status of L1-related genes in HBV-related HCC, and HBV- and HCC-related genes that may impact L1-mediated tumorigenesis. L1 restriction factors appear to be suppressed by HBV infection. Since some of the L1 restriction factors also limit HBV, these factors may be exhausted in HBV-infected cells, which causes de-suppression of L1. Several HBV- and HCC-related genes that interact with L1 can affect oncogenic processes. Thus, L1 may be a novel prime therapeutic target for HBV-related HCC. Studies in this area will provide insights into HCC and other types of cancers.

Nuclear Expression of Hepatitis B Virus X Protein Is Associated with Recurrence of Early-Stage Hepatocellular Carcinomas: Role of Viral Protein in Tumor Recurrence

Background:

Hepatitis B virus (HBV) plays well-known roles in tumorigenesis of hepatocellular carcinoma (HCC) in infected patients. However, HBV-associated protein status in tumor tissues and the relevance to tumor behavior has not been reported. Our study aimed to examine the expression of HBV-associated proteins in HCC and adjacent nontumorous tissue and their clinicopathologic implication in HCC patients.

Methods:

HBV surface antigen (HBsAg), HBV core antigen (HBcAg), and HBV X protein (HBx) were assessed in 328 HBV-associated HCCs and in 155 matched nontumorous tissues by immunohistochemistry staining.

Results:

The positive rates of HBsAg and cytoplasmic HBx staining in tumor tissue were lower than those in nontumorous tissue (7.3% vs. 57.4%, p < .001; 43.4% vs. 81.3%, p < .001). Conversely, nuclear HBx was detected more frequently in tumors than in nontumorous tissue (52.1% vs. 30.3%, p < .001). HCCs expressing HBsAg, HBcAg, or cytoplasmic HBx had smaller size; lower Edmondson-Steiner (ES) nuclear grade, pT stage, and serum alpha-fetoprotein, and less angioinvasion than HCCs not expressing HBV-associated proteins. Exceptionally, nuclear HBx-positive HCCs showed higher ES nuclear grade and more frequent large-vessel invasion than did nuclear HBx-negative HCCs. In survival analysis, only nuclear HBx-positive HCCs had shorter disease-free survival than nuclear HBx-negative HCCs in pT1 and ES nuclear grade 1–2 HCC subgroup (median, 126 months vs. 35 months; p = .015).

Conclusions:

Our data confirmed that expression of normal HBV-associated proteins generally decreases in tumor cells in comparison to nontumorous hepatocytes, with the exception of nuclear HBx, which suggests that nuclear HBx plays a role in recurrence of well-differentiated and early-stage HCCs.

Hepatitis B viral X protein alters the biological features and expressions of DNA repair enzymes in LO2 cells

OBJECTIVES

This study aimed at examining the effects of hepatitis B viral X protein (HBx) on the biological features and the expression of DNA repair enzymes in non-tumour human hepatic LO2 cells in vitro.

METHODS

The HBx gene was transfected into LO2 cells to establish stably HBx-expressing LO2/HBx cells. The morphological features, cell growth, cell cycle, apoptosis and colony formation of LO2/HBx cells, vector-transfected LO2/pcDNA3.1 cells and unmanipulated LO2 cells were studied. The expressions of DNA repair enzymes and DNA oxidative stress-related 8-hydroxydeoxyguanosine (8-OHdG) were determined by a real-time quantitative polymerase chain reaction assay and high-performance liquid chromatography coupled with electrochemical detection respectively.

RESULTS

In comparison with controls, significant morphological changes, faster growth, higher frequency of cells at the S phase, but lower at G0/G1 and M/G2 phases, a lower frequency of natural cell apoptosis and a higher percentage of colony formation were observed in the LO2/HBx cells. Furthermore, significantly higher levels of intracellular 8-OHdG and lower levels of human DNA glycosylase alpha (hMYHalpha) mRNA transcripts, but no significant change in human 8-oxoguanine DNA glycosylase 1 (hOGG1), were detected in the LO2/HBx cells.

CONCLUSIONS

Our data indicated that HBx promoted growth and malignant transformation of non-tumour hepatic LO2 cells in vitro, which was associated with the downregulation of hMYHalpha expression and accumulation of mutagenic DNA adduct 8-OHdG.

High prevalence of hepatitis B virus infection in patients with B-cell non-Hodgkin's lymphoma in Korea

This study assessed the association of hepatitis B virus (HBV) and hepatitis C virus (HCV) infection with non-Hodgkin's lymphoma in a highly HBV-endemic area. The prevalence of either HBV or HCV infection in 235 patients with non-Hodgkin's lymphoma was compared with that of an age- and sex-matched hospital control group of 235 patients. The prevalence of HBV infection was higher in B-cell non-Hodgkin's lymphoma (15.5%) than control (8.1%), but the prevalence of HCV infection in the non-Hodgkin's lymphoma patients (2.1%) and control group (3%) was similar. HBV prevalence increased significantly with age in the B-cell non-Hodgkin's lymphoma patients. The presence of HBV proteins and DNA in lymphoma tissues and peripheral blood mononuclear cells (PBMCs) from HBV-infected non-Hodgkin's lymphoma patients was also investigated using immunohistochemistry and PCR. HBV DNA was frequently detected in PBMCs from HBV-infected non-Hodgkin's lymphoma patients, but HBV antigens were not. Therefore, HBV infection, but not HCV infection, was associated with B-cell non-Hodgkin's lymphoma in Korea, suggesting a possible role for HBV in the development of non-Hodgkin's lymphoma.

COOH-terminal deletion of HBx gene is a frequent event in HBV-associated hepatocellular carcinoma

AIM: To investigate the hepatitis B virus (HBV) x gene (HBx) state in the tissues of HBV-related hepatocellular carcinoma (HCC) in Chinese patients and whether there were particular HBx mutations.

METHODS: HBx gene was amplified and direct sequencing was used in genomic DNA samples from 20 HCC and corresponding non-cancerous liver tissues from HBsAg-positive patients. HBV DNA integration and HBx deleted mutation were validated in 45 HCC patients at different stages by Southern blot analysis and polymerase chain reaction methods.

RESULTS: The frequencies of HBx point mutations were significantly lower in HCC than their corresponding non-cancerous liver tissues (11/19 vs 18/19, P = 0.019). In contrast, deletions in HBx gene were significantly higher in HCC than their non-cancerous liver tissues (16/19 vs 4/19, P < 0.001). The deletion of HBx COOH-terminal was detected in 14 HCC tissues. A specific integration of HBx at 17p13 locus was also found in 8 of 16 HCC, and all of them also exhibited full-length HBx deletions. Integrated or integrated coexistence with replicated pattern was obtained in 45.5% (20/45) - 56.8% (25/45) tumors and 40.9% (18/45) - 52.3% (23/45) non-tumor tissues.

CONCLUSION: HBx deletion, especially the COOH-terminal deletion of HBx is a frequent event in HBV-associated HCC tissues in China. HBV integration had also taken place in partial HCC tissues. This supporting the hypothesis that deletion and probably integrated forms of the HBx gene may be implicated in liver carcinogenesis.

Development of PCR-ELISA for the detection of hepatitis B virus x gene expression and clinical application

The presence of hepatitis B virus x (HBx) antigen/antibody is known to correlate with the well-established serological markers of ongoing viral replication in the chronic phase of HBV infection, and strongly suggests that the level and duration of HBx expression may influence the outcome of the chronic infection. In this research, we developed a polymerase chain reaction enzyme-linked immunosorbent assay (PCR-ELISA) method for the detection of HBx gene expression. We also investigated its relationship to the progress of the disease in HBV-related patients. Peripheral blood mononuclear cells (PBMCs) were purely isolated, and reverse transcription-PCR (RT-PCR) was performed for improved sensitivity. The PCR products were determined by ELISA, and we investigated the relationship of the proposed method to the clinical status of the patients. The PCR-ELISA used in this work was found to be at least 100 times more sensitive than the conventional PCR method, and even 8,000-fold diluted PCR products could be detected. The HBx concentrations significantly differed among control subjects (0.36+/-0.09, [P<0.01] and patients with chronic hepatitis (1.13+/-0.34 [P<0.01 compared to control]), liver cirrhosis (LC; 1.37+/-0.28 [P<0.01 compared to control]), and hepatocellular carcinoma (HCC; 1.48+/-0.95 [P<0.01 compared to control]). These findings suggest that monitoring of HBx could be useful for early diagnosis and prognosis in patients with chronic HBV infection, LC, and HCC.

Polymorphism analyses of hepatitis B virus X gene in hepatocellular carcinoma patients from southern China

Chronic hepatitis B virus (HBV) infection is one of the major causes of hepatocellular carcinoma (HCC), and the HBV X (HBx) gene plays a critical role in the molecular pathogenesis of HBV-related HCC. We have investigated whether there are particular HBx gene mutations associated with HCC in patients from southern China. The HBx gene was examined in 51 paraffin-embedded tumor tissue samples from patients with HCC and 25 serum samples from the HBV carrier by nested polymerase chain reaction (PCR), single-stranded conformational polymorphism and heteroduplex analysis. The HBx genes with potentially important mutations from tumor tissue samples were cloned, sequenced and aligned with the published HBx gene sequence. HBV genotypes in tumor tissue samples were analyzed by nested PCR. Analyses of HBx gene polymorphism showed that 31.3% of HBx gene fragments in tumor tissue samples had a special pattern. A common deletion at nt 382-400 of the HBx gene accompanied by 29 point mutations was detected in four randomly selected tumor tissue samples with this pattern which caused a frame-shift in the HBx open reading frame with a new stop codon at nt 1818, resulting in an HBx polypeptide chain truncated at the C end in these cases. Among the four randomly selected samples, three were HBV genotype B, and one was not detected by our present assay. In another tumor tissue sample, amplification of the full-length HBx gene yielded a shorter fragment. Sequencing of this fragment revealed a 264 bp deletion between nt 1577 and 1840 of the HBV gene. These results suggest that HBx gene mutation occurs frequently in HCC samples, and the deletion at nt 382-400 of the HBx gene might play a role in carcinogenesis of HCC in southern China.

Knock-down of hepatitis B virus X protein reduces the tumorigenicity of hepatocellular carcinoma cells

Hepatitis B virus (HBV) infection is a major cause of hepatocellular carcinoma (HCC) in Southeast Asia and Hong Kong. Among the four proteins that are encoded by the HBV genome, HBV X (HBx) is the most potentially oncogenic factor. It is known that HBx plays an important role in hepatocarcinogenesis, but the exact functions and molecular mechanisms of HBx in HCC are not well understood. In this study, we constructed expression vectors for small hairpin RNAs (shRNA) against HBx and investigated their regulatory effects in PLC/PRF/5 HCC cells, which constitutively produce HBx. Our data show that this tool of RNA interference (RNAi) could successfully reduce the HBx mRNA and protein levels by 50-95%. RNAi targeting HBx in PLC/PRF/5 cells demonstrated significant reduction in cell proliferation, cell growth, anchorage-independent growth in soft agar, and tumour development in nude mice. In addition, depletion of HBx expression increased cell sensitivity to TNFalpha-mediated and serum-free-induced apoptosis, and reduced the expression levels of C-myc and Bcl-X(L). These findings suggest that HBx plays an important role in tumorigenicity and anti-apoptotic mechanisms in HCC.

Sequence-specific cleavage of hepatitis X RNA in cis and trans by novel monotarget and multitarget hammerhead motif-containing ribozymes

We constructed two monoribozymes and a diribozyme against the conserved region of the X RNA of hepatitis B virus (HBV). All the ribozymes (Rzs) possessed sequence-specific cleavage activities under standard and simulated physiologic conditions. Specific cleavage was also obtained when the same Rzs were placed in cis configuration with respect to X gene in multiple combinations. Rz-expressing cells were able to specifically interfere with the functional expression of X RNA and protein production in a liver-specific cell line HepG2. Potential applications of these novel Rzs are discussed.

The carboxy-terminus of the hepatitis B virus X protein is necessary and sufficient for the activation of hypoxia-inducible factor-1alpha

Hepatitis B virus X protein (HBx) of the hepatitis B virus is strongly implicated in angiogenesis and metastasis during hepatocarcinogenesis. Previously, we reported that HBx enhances activity of hypoxia-inducible factor-1alpha (HIF-1alpha), a potent transactivator that induces angiogenic factors. Here, we delineate the structural region of HBx that potentiates HIF-1alpha. The carboxy-terminus of HBx increased the stability of HIF-1alpha protein, probably through inhibiting interaction with von Hippel-Lindau protein. Further, the carboxy-terminus of HBx enhanced the transactivation function of HIF-1alpha by enhancing its association with CREB binding protein (CBP). Finally, we demonstrated the physical association of HBx with the basic helix-loop-helix/PER-ARNT-SIM domain, the inhibitory domain, and the carboxy-terminal transactivation domain of HIF-1alpha in vivo.

Significant correlation between expression level of HSP gp96 and progression of hepatitis B virus induced diseases

AIM: Gp96, also known as Grp94, is a member of heat shock protein (HSP) family and binds repertoires of peptides thereof eliciting peptide-specific T cell immune responses. It predominantly locates inside the endoplasmic reticulum (ER) with some cell surface expression in certain cancerous cells. Previous studies have shown that gp96 expression level was up-regulated in tumor cells, including hepatocellular carcinoma (HCC). However, relationship between the extent of gp96 expression and disease progression especially HBV-induced chronic infection, cirrhosis and hepatocellular carcinoma, has not been addressed before. As primary HCC can be induced and progressed from chronic hepatitis B virus (HBV) infection and HBV-induced cirrhosis, we designed an immunohistochemical experiment to test the correlation between gp96 expression level and HBV-induced disease progression, from chronic HBV infection, cirrhosis to HCC.

METHODS: We chose liver samples from different patients of hepatitis B virus induced diseases, including chronic hepatitis B (77 patients), cirrhosis (27 patients) and primary HCC (30 patients), to test the expression level of gp96 in different affected groups. Formalin-fixed, and paraffin-embedded liver tissues taken from these patients were immuno-stained by using an anti-gp96 monoclonal antibody for the expression level of gp96 protein in the sections. In addition, Western blotting of whole cell lysates derived from established human embryonic liver cell lines and several human HCC cell lines (Huh7, HepG2, SSMC-7721) was compared with the expression of gp96.

RESULTS: We found that the extent of elevated gp96 expression was significantly correlated with the disease progression, and was the highest in HCC patients, lowest in chronic HBV infection and was that of the cirrhosis in the middle.

CONCLUSION: Increased expression of gp96 might be used as a diagnostic or prognostic bio-marker for the HBV infection and HBV-induced diseases.

Detection of the hepatitis B virus X protein (HBx) antigen and anti-HBx antibodies in cases of human hepatocellular carcinoma

Hepatitis B virus X protein (HBx) expressed in Escherichia coli DH5alpha by recombinant DNA technology was purified to homogeneity by use of glutathione-Sepharose beads. Immunological characterization of the recombinant HBx protein was performed. Specific binding between the anti-HBx monoclonal antibody and HBx protein showed the specificity of the recombinant HBx protein. The intact HBx protein of the factor Xa-digested glutathione S-transferase-HBx fusion protein was further purified and was used as an antigen for screening the titers of anti-HBx antibodies in sera. Titers of anti-HBx in sera from 20 patients with hepatocellular carcinoma (HCC), 20 patients with chronic hepatitis (CH), and 20 healthy individuals were evaluated by Western blotting and a quantitative enzyme-linked immunosorbent assay. The results indicated that 70% of sera from HCC patients and 5% of sera from CH patients contained antibodies with significant binding to the HBx protein. Western blotting of HBx protein in liver extracts from 20 HCC patients was also performed by using the anti-HBx monoclonal antibody. Results showed that 85% of HCC patients' liver tissues contained a specific HBx protein with the same molecular size as the purified intact HBx. Full correlation was found between anti-HBx antibody positivity in serum and HBx protein positivity in HCC tissues. The data demonstrated that the etiology of HCC is involved with hepatitis B virus (HBV) infection and that HBx in particular plays a role in the development of HBV-related HCC.

Rising incidence of hepatocellular carcinoma: the role of hepatitis B and C; the impact on transplantation and outcomes

Hepatocellular carcinoma caused by hepatitis B and hepatitis C are global scourges but are likely to peak in incidence in the next 2 decades and then decline. Universal vaccination has been effective in stemming the incidence of chronic hepatitis B and early-onset HCC in regions of high endemicity where implemented, but preventive measures in HCV are not yet available. After the attrition of older affected generations, the incidence of HCC will likely decline rapidly. While no vaccine is currently available for hepatitis C, cases are projected to peak and decline because of a marked reduction in transmission as a result of behavioral modification and safeguarding of blood supplies. Until these epidemiologic projections come to pass, management of hepatocellular carcinoma will continue to become a progressively more frequently encountered clinical challenge. Therapy for chronic hepatitis may ameliorate but will not eliminate the development of tumors. The demand for orthotopic liver transplantation will continue to climb, and palliative therapies for non-resectable cases will require studies aimed at optimization of benefit. LDLT may remain an option for high-risk patients affording tumor-free survival for some otherwise terminal patients.

Regulation of p21 and p27 expression by the hepatitis B virus X protein and the alternate initiation site X proteins, AUG2 and AUG3

BACKGROUND

The hepatitis B virus X gene has three in-frame start codons encoding the pX, AUG2 and AUG3 proteins. The AUG2 and AUG3 genes are 5'-truncated in respect to the full-length pX gene; however, all three genes terminate at the same stop codon. The activity of pX as an oncogene is well characterized; however, less is known about the AUG2 and AUG3 proteins.

METHODS

The effects of pX, AUG2 and AUG3 on p21Cip,1/WAF,1/MDA6 and p27Kip-1 cyclin kinase inhibitor (CKI) protein expression, and the impact they have on proliferation, were investigated in CHO K-1 cells. CHO K-1 cells were chosen because they can be transfected at 100% efficiency.

RESULTS

p21- and p27-luciferase reporter expression is modulated by increasing doses of the hepatitis B X proteins. At low concentrations of pX or AUG2, p21- and p27-luciferase activity was increased, and at high concentrations, p21- and p27-luciferase activity was decreased. Expression of the AUG3 gene showed a different profile: it was increasingly stimulatory with dose for both promoters. Western blot analyses demonstrated that p21 and p27 protein levels were modulated as predicted based on data generated in the promoter-luciferase experiments. Tritiated thymidine labeling of DNA showed biphasic kinetics of incorporation in the presence of varying pX and AUG2 concentrations, whereas labeling decreased with AUG3 concentration. The growth inhibitory effect of pX expression was reduced by antisense ablation of either p21 or p27.

CONCLUSIONS

The relative expression level of pX, AUG2, and AUG3 impacts on CKI expression and cell proliferation. Our findings may explain why divergent effects of pX expression on growth have been observed by different groups, which may be related to relative pX expression levels.

Dominant mutations of hepatitis B virus variants in hepatoma accumulate in B-cell and T-cell epitopes of the HBx antigen

Hepatitis B virus (HBV) X gene, encoding a pleotropic transactivator of HBx protein, has been associated with the development of hepatocellular carcinoma (HCC). Molecular information on liver-derived HBV variants isolated from HCC among Taiwanese population was studied. Amplification of the HBV X genes of 20 HCC patients in high stringency with HBV specific primers was observed. The resulting amplified HBV X genes were purified and individually-cloned into pUC-T vector. Sequences of the eight liver-derived X gene were aligned and compared with the wild type, the ayw HBV serotype. Results indicate that the HBx protein of variants were found predominantly within the regions of amino acid positions 26-45 in N-terminus, and positions 87, 88, 116, 118, 119, 127 and 144. Sequences from six out of the eight variants were found to be identical. These accumulated sequence mutations among the eight HBx variants were found to coincide within the B-cell epitopes (positions 29-48), particularly in the HBx proline and serine rich (PSR) domain, and the T-cell epitopes regions (positions 116-127). These frequent mutations of HBV variants, rather than subtype-specific polymorphic sites, may be involved in immunoevasion.

Woodchuck hepatitis virus replication and antigen expression gradually decrease in preneoplastic hepatocellular lineages

BACKGROUND/AIMS

Hepatocellular carcinomas elicited in woodchucks by the woodchuck hepatitis virus (WHV) emerge gradually from parenchymal areas of minimal structural deviation via two predominant preneoplastic hepatocellular lineages, composed of either glycogenotic/basophilic or amphophilic/basophilic cell foci. In this study we analyzed WHV replication during neoplastic development in both lineages.

METHODS

In minimal deviation areas, preneoplastic hepatocellular foci, and hepatocellular neoplasms, developing in 16 WHV-carriers 31-38 months after WHV-inoculation, the proportion of hepatocytes containing WHV replicative intermediates (as detected by in situ hybridization for WHV DNA) and immunoreactive for WHV core and surface antigens was assessed.

RESULTS

Appearance of WHV replicative intermediates and expression of antigens were limited to the cytoplasm of hepatocytes and were strongly correlated (P<0.0001), both showing high levels in minimal deviation areas, but markedly reduced amounts in all types of preneoplastic hepatic focus (P<0.0001), and in hepatocellular adenomas. Most hepatocellular carcinomas were negative for WHV replicative intermediates and antigens.

CONCLUSIONS

In both the glycogenotic-basophilic and the amphophilic-basophilic preneoplastic hepatocellular lineage, WHV replication and antigen expression gradually decrease early during the preneoplastic phase. The close correlation of these changes with metabolic aberrations characterizing preneoplastic hepatocellular lineages suggests that oncogenic effects mimicking insulin/glucagon imbalances may be responsible for the repression of hepadnaviral replication.

Immunohistochemical assessment and prognostic value of hepatitis B virus X protein in chronic hepatitis and primary hepatocellular carcinomas using anti-HBxAg monoclonal antibody

Hepatitis B virus (HBV) is the most meaningful risk factor in chronic hepatitis, cirrhosis and primary hepatocellular carcinoma (PHC). The hepatitis B virus X protein (HBxAg) is a multifunctional protein with many important functions in hepatocellular carcinogenesis. A monoclonal anti-HBxAg antibody was developed in our laboratory and characterized by different methods. Using this antibody HBxAg was detected in formaldehyde fixed paraffin embedded tissue sections of 72 liver biopsies from patients with acute hepatitis, chronic hepatitis, cirrhosis and primary hepatocellular carcinoma. The co-expression of hepatitis B surface antigen (HBsAg), hepatitis B core antigen (HBcAg) and HBxAg was compared. The histological and cytological localization of the detected HBxAg showed a characteristic distribution in different stages of HBV infection. Strong and diffuse nuclear reaction was detected in PHC cases in contrast to the focal, cytoplasmic and nuclear labeling in the acute and chronic B hepatitis cases. Our antibody seems to be a suitable prognostic marker for routine pathohistological diagnosis and for comparative pathological and epidemiological research on the development of PHC.

Modulation of glutathione S-transferase alpha by hepatitis B virus and the chemopreventive drug oltipraz

Persistent infection by hepatitis B virus (HBV) and exposure to chemical carcinogens correlates with the prevalence of hepatocellular carcinoma in endemic areas. The precise nature of the interaction between these factors is not known. Glutathione S-transferases (GST) are responsible for the cellular metabolism and detoxification of a variety of cytotoxic and carcinogenic compounds by catalysis of their conjugation with glutathione. Diminished GST activity could enhance cellular sensitivity to chemical carcinogens. We have investigated GST isozyme expression in hepatocellular HepG2 cells and in an HBV-transfected subline. Total GST activity and selenium-independent glutathione peroxidase activity are significantly decreased in HBV transfected cells. On immunoblotting, HBV transfected cells demonstrate a significant decrease in the level of GST Alpha class. Cytotoxicity assays reveal that the HBV transfected cells are more sensitive to a wide range of compounds known to be detoxified by GST Alpha conjugation. Although no significant difference in protein half-life between the two cell lines was found, semi-quantitative reverse transcription-polymerase chain reaction shows a reduced amount of GST Alpha mRNA in the transfected cells. Because the HBV x protein (HBx) seems to play a role in HBV transfection, we also demonstrated that expression of the HBx gene into HepG2 cells decreased the amount of GST Alpha protein. Transient transfection experiments using both rat and human GST Alpha (rGSTA5 and hGSTA1) promoters in HepG2 cells show a decreased CAT activity upon HBx expression, supporting a transcriptional regulation of both genes by HBx. This effect is independent of HBx interaction with Sp1. Treatment with oltipraz, an inducer of GST Alpha, partially overcomes the effect of HBx on both promoters. Promoter deletion studies indicate that oltipraz works through responsive elements distinct from AP1 or NF-kappaB transcription factors. Thus, HBV infection alters phase II metabolizing enzymes via different mechanisms than those modulated by treatment with oltipraz.

The translation initiation factor, hu-Sui1 may be a target of hepatitis B X antigen in hepatocarcinogenesis

The role of hepatitis B virus X antigen in the development of hepatocellular carcinoma was explored by stably transfecting HepG2 cells with an X antigen expression vector, and identifying the differences in gene expression that distinguish X positive from X negative cells by subtractive PCR. One differentially expressed gene, the human homolog of sui1 (hu-sui1), encodes a translation initiation factor whose expression was suppressed by X antigen in HepG2 cells. Hu-Sui1 was also expressed in nontumor liver but not in tumor cells from patients with hepatocellular carcinoma. Introduction of hu-sui1 into HepG2 cells inhibited cell growth in culture, in soft agar, and partially inhibited tumor formation in nude mice. Hence, the suppression of hu-sui1 by X antigen may result in the abrogation of negative growth regulation and contribute to the development of hepatocellular carcinoma.

Downregulation of DNA excision repair by the hepatitis B virus-x protein occurs in p53-proficient and p53-deficient cells

Synergism between exposure to chemical carcinogens and infection with the hepatitis B virus (HBV) has been implicated in the high incidence of hepatocellular carcinoma. In this study we report that the HBV protein HBx, inhibits cellular DNA repair capacity in a p53-independent manner. Two alternative assays were used: the host cell reactivation assay, which measures the cell's capacity to repair DNA damage in a reporter plasmid, and unscheduled DNA synthesis, which measures the overall DNA repair capacity in damaged cells. Two p53-proficient cell lines, the hepatocellular carcinoma cell line HepG2 and liver epithelial cell line CCL13, were co-transfected with the pCMV-HBx reporter plasmid and the pCMV-CAT plasmid damaged with UVC radiation. Compared with cells transfected with control plasmid, the presence of HBx resulted in approximately 50% inhibition of the cell's capacity to reactivate CAT activity of UVC-damaged plasmid, and approximately 25% inhibition of unscheduled DNA synthesis in cells treated with either aflatoxin B1 epoxide or UVC radiation. Using the p53-deficient cell line Saos-2, we demonstrated that expression of HBx also resulted in diminished overall cellular DNA repair of damage induced by both aflatoxin B1 epoxide and UVC radiation, using both the host cell reactivation and unscheduled DNA synthesis assays. In summary, this study provides evidence for p53-independent regulation of DNA repair by HBx.

Expression of mutated hepatitis B virus X genes in human hepatocellular carcinomas

To explore the role of hepatitis B virus (HBV) X protein in liver carcinogenesis, independently from its role in viral replication, we have analyzed X gene structure and expression in tumorous and non-tumorous tissues obtained from 9 hepatitis B surface antigen (HBsAg)-negative, HBV DNA-positive patients. HBV replication was undetectable in tumorous tissues. HBV X gene was truncated at its 3' end in 5 of 9 tumorous tissues and 1 of 8 non-tumorous livers. Sequence analysis performed on uninterrupted X genes from 3 tumors and 3 surrounding non-tumorous tissues showed a high rate of mutations, selectively in the tumorous livers. In 1 of the 3 tumors, a frameshift mutation induced a new stop at codon 129. HBV RNAs were tested by reverse transcriptase-polymerase chain reaction (RT-PCR) with surface (S), core (C) and X specific primers. X, but not S and C, RNA expression was found in 6 of 8 tumors and in 6 of 7 non-tumorous tissues. This finding was consistent with immunohistochemical detection of X, but not S and C, antigens in all tumors also expressing X RNA. Our results provide evidence for selective expression of HBV X, but not S and C, RNA and protein in the tumorous and non-tumorous tissue of HBsAg-negative, HBV DNA-positive patients. It also shows that the structure of the X gene is modified (interrupted or highly mutated) in the majority of tumorous livers. Taken together, our findings are consistent with a potential role of mutated X proteins in HBV-related liver oncogenesis.

Compensatory apoptosis in preneoplastic liver of a transgenic mouse model for viral hepatocarcinogenesis

The HBx protein of hepatitis B virus has been shown to induce hepatocellular carcinoma in transgenic mice as direct evidence for its involvement in hepatocarcinogenesis. In these transgenic mice, however, it is not clear why hepatocytes do not acquire a neoplastic phenotype by 13 months old despite the continuous growth stimulation by the HBx protein from 2 months old. In this study, we show that the accelerated proliferation of hepatocytes is counterbalanced by apoptosis, which maintains liver homeostasis. A decrease in the extent of apoptosis seems to precede the emergence of neoplasia in the transgenic mouse liver. The disappearance or block of apoptotic signals, which may be the result of additional genetic or epigenetic aberrations, may result in the preneoplastic hepatocytes becoming neoplastic.

A monoclonal antibody against the X protein of hepatitis B virus: fine mapping of its epitope and application in a quantitative ELISA of the X protein in sera of hepatitis B patients

A HBx-specific mouse monoclonal antibody was developed and its epitope mapped to a hydrophilic segment 94HKRTLGL100 using the multipin peptide synthesis technique. A sensitive ELISA with a threshold of 5 to 10 ng was developed to identify the HBx-positive hepatitis B cases and measure the levels of HBx in sera. The same patient sera were also analyzed for the presence of anti-HBx using the purified recombinant antigen. HBx was present in 23% of the cases (15/65) whereas only 14% of the cases (9/65) were positive for anti-HBx. The mean value of HBx in acute hepatitis sera was higher (522 ng/ml) than in cirrhosis cases (48 ng/ml). PCR amplification of the S gene showed that all 15 HBx-positive cases were also positive for the viral DNA.

Expression of hepatitis B virus X protein in HBV-infected human livers and hepatocellular carcinomas

Transactivation of cellular genes and functional inactivation of p53 by the hepatitis B virus (HBV) X gene-encoded protein (HBx) are proposed as alternative mechanisms for induction of hepatocellular carcinomas (HCCs) in chronic HBV infection. Using an immunohistochemical approach, we studied the expression of HBx in 39 explanted livers with HBV-associated disease. Because the data reported previously have been inconsistent, possibly due to the application of different antibodies, we compared results with 5 polyclonal and 6 monoclonal anti-HBx antibodies from five laboratories. Ten of the 11 antibodies reacted with recombinant HBx by Western blotting, but only 1 polyclonal and 2 monoclonal antibodies reacted specifically with HBx in tissue, and were thus suitable for immunohistochemistry. Three other polyclonal antibodies reacted with tissue components in addition to HBx. One polyclonal and 4 monoclonal antibodies did not recognize the HBx in the tissue. HBx was demonstrated in 16 of 30 (53.3%) cirrhotic livers and 10 of 18 (58.8%) HCCs by all specific antibodies. The expression of HBx, among three HBV antigens examined, was found to be preferentially maintained in HCC and the surrounding liver parenchyma, including focal or nodular preneoplastic lesions. However, the immunoreactivity was always limited to the cytoplasm of a small number of parenchymal and neoplastic cells. The role of X gene expression in HBV-associated human hepatocarcinogenesis remains to be established.

An alternative purification protocol for producing hepatitis B virus X antigen on a preparative scale in Escherichia coli

A truncated variant of the hepatitis B virus X gene (HBx) was cloned into the fusion expression vector of pGEX-3X (Pharmacia), resulting in a GST-HBx fusion gene construction (pGEX-3XXBF). This plasmid was transformed into and expressed by the Escherichia coli strain DH5. More than 80% of the expressed fusion protein was found in the insoluble fraction (inclusion body) of the cell lysate. The fusion protein was selectively extracted from the inclusion bodies with 8 M urea at pH 6.5, and it was refolded by diluting 3-fold with deionized distilled water at 4 degrees C. The in vitro cleavage of the refolded fusion protein by factor Xa at about 2-3 mg ml-1 in the presence of 2.66 M urea at pH 6.5 was complete. The final steps of purification involved precipitation of the cleaved proteins with ammonium sulphate, solubilization in guanidine hydrochloride and separation on a Superdex 75 FPLC column. With this approach, following an inclusion body strategy and a beneficial in vitro refolding, a predominantly hydrophobic and highly disulphide-bonded protein was produced in preparative scale for subsequent diagnostic use.

Hepatitis B virus-induced hepatocellular carcinoma: possible roles for HBx

The hepatitis B virus-encoded protein, HBx, may contribute to carcinogenesis by perturbing cell growth and differentiation. There is some evidence indicating that HBx represses the nuclear import of the tumour repressor p53 and p53-dependent trans-activation and that HBx activates members of the basic region-leucine zipper (bZIP) family.

Differential expression of transforming growth factor alpha and insulin-like growth factor II in chronic active hepatitis B, cirrhosis and hepatocellular carcinoma

In the present study we investigated the expression of transforming growth factor alpha and insulin-like growth factor II to explain the role of these growth factors in the development of hepatocellular carcinoma from chronic active hepatitis B and cirrhosis. The expression of transforming growth factor alpha and insulin-like growth factor II was tested in 38 tissue samples from patients with chronic active hepatitis B, 32 cirrhosis and 31 hepatocellular carcinoma, by immunohistochemical staining using monoclonal anti-transforming growth factor alpha and anti-insulin-like growth factor II. All patients were seropositive for HBsAg. Transforming growth factor alpha was expressed in 26 (68.4%) of 38 chronic active hepatitis B, 18 (56.3%) of 32 cirrhosis and 16 (51.6%) of 31 hepatocellular carcinoma tissue samples. Transforming growth factor alpha was found in the periportal hepatocytes of chronic active hepatitis B and in regenerating hepatocytes of cirrhotic nodules. In hepatocellular carcinoma tissues, transforming growth factor alpha-containing tumor cells were evenly distributed within the tumor tissues but focal distribution limited to a part of tumor tissues was also observed. The expression of insulin-like growth factor II was observed in 30 (93.8%) of 32 cirrhosis and all the 31 hepatocellular carcinoma tissue samples tested, but not in chronic active hepatitis B samples. Insulin-like growth factor II was expressed in most hepatocytes of regenerating nodules and in tumorous as well as non-tumorous hepatocytes of hepatocellular carcinoma tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct interaction of the hepatitis B virus HBx protein with p53 leads to inhibition by HBx of p53 response element-directed transactivation

Hepatitis B virus is a major risk factor in human hepatocellular carcinomas. We have used protein affinity chromatography to show that the 17-kDa hepatitis B virus gene product, HBx, binds directly to the human tumor suppressor gene product, p53. Interaction of HBx with p53 did not prevent p53 from specifically binding DNA. Instead, HBx enhanced p53's oligomerization state on a DNA oligonucleotide containing a p53 response element. Optimal binding of HBx to p53 required intact p53, but weaker binding to both the N-terminal activation domain of p53 and a protein fragment containing the C-terminal DNA-binding and oligomerization domains of p53 was observed. In transient transfection experiments with human Calu-6 cells, HBx inhibited transactivation by p53 of a reporter gene containing a p53 response element. Also, HBx inhibited p53-stimulated transcription in vitro even when added to the reaction mixture after the formation of the preinitiation complex. Interaction of HBx with p53 did not prevent the activation domain of p53 from binding two general initiation factors, the TATA-box binding protein subunit of TFIID and the p62 subunit of TFIIH. To explain these results, we propose that localization of HBx to a promoter by interaction with DNA-bound p53 enables a repression domain in HBx to directly contact the basal transcription machinery and thereby repress transcription.