Molecular pathogenesis of hepatocellular carcinoma in hepatitis B virus transgenic mice

Increase in de novo HBV DNA integrations in response to oxidative DNA damage or inhibition of poly(ADP-ribosyl)ation

Chronic infection with hepatitis B virus (HBV) is associated with an increased risk for the development of cirrhosis and hepatocellular carcinoma (HCC). Although clonal HBV DNA integrations are detected in nearly all HCCs the role of these integrations in hepatocarcinogenesis is poorly understood. We have used a cloning protocol that allows studying the frequency and the natural history of HBV DNA integrations in cell culture. Southern blot analysis of the genomic DNA of HepG2 2.2.15 subclones, which replicate HBV, enabled us to detect new HBV DNA integrations in approximately 10% of the HepG 2.2.15 subclones over 4 rounds of sequential subcloning, whereas no loss of any preexisting HBV DNA integrations was observed. Treatments of HepG2 cells with H(2)O(2), designed to increase DNA damage, increased the frequency of HBV integrations to approximately 50% of the subclones and treatments designed to inhibit DNA repair, by inhibiting Poly(ADP-ribosyl)ation, also increased the frequency of HBV integration to 50%. These findings suggest that DNA strand breaks induced by oxidative stress during persistent HBV infection in humans may increase HBV DNA integration events, whereas PARP-1 activity may function to limit the occurrence of de novo HBV DNA integrations.

Hepatocarcinogenesis in hepatitis viral infection: lessons from transgenic mouse studies

Over the past decade, genetically engineered mouse models have been used for studies of the mechanisms underlying human diseases. One advantage of these models is that the targeted protein executes its function in normal cells in their natural tissue microenvironments. Transgenic mouse models for human viral hepatitis have also been established and have provided new insights into the pathogenesis of hepatitis and hepatocellular carcinoma (HCC). In the search for the mechanism of hepatocarcinogenesis in hepatitis viral infection, two viral proteins, the core protein of hepatitis C virus (HCV) and the HBx protein of hepatitis B virus (HBV), have been shown to possess oncogenic potential through transgenic mouse studies, indicating the direct involvement of the hepatitis viruses in hepatocarcinogenesis. The presence of the hepatitis C virus core or HBx protein, which has an oncogenic potential, may allow some of the steps in multistep hepatocarcinogenesis to be skipped. This may explain the very high frequency of HCC in patients with HCV or HBV infection.

Molecular analysis of hepatitis B virus genomes isolated from black African patients with fulminant hepatitis B

To investigate further the possible role of mutant hepatitis B viruses in the pathogenesis of fulminant hepatitis B, the genomic sequence of hepatitis B virus isolates from 9 South African blacks with this disease, including 5 entire genomes, was analysed. Seven of the isolates were genotype A. The mutation most often reported in patients with fulminant hepatitis B, the G1896A precore stop-codon substitution, was, as expected, not present in the genotype A isolates with the exception of one in which it was accompanied by a compensatory C1858T substitution. G1896A was, however, present in the one genotype D isolate. No other precore-defective mutants were detected. The other mutation commonly found in patients with fulminant hepatitis B, the paired A1762T, G1764A substitution in the basic core promoter, was present in only one patient and G1764A in one other. The pre-surface initiation-codon mutation documented in a number of patients with fulminant hepatitis B was not found in our isolates. An 18-amino acid deletion present in the pre-surface region of one isolate has not previously been described in fulminant hepatitis B. Variations within the surface region were mainly genotype specific and not previously described. A relatively large number of mutations were present in the middle region of the core gene in those isolates without G1896A or A1762T, G1764A mutations, although the pattern was not consistent with those in published studies. Thus, as in other published series in which the entire genome of hepatitis B virus responsible for fulminant hepatitis was sequenced, we detected many mutations in different genes, but none was common to all the reported isolates.

Possible role of retinoids in hepatitis B virus-associated liver damage

Liver damage following hepatitis B virus (HBV) infection may be due to the action of retinoids as modulators of viral replication. The reduced rate of survival of liver grafts in patients with HBV infection could also be due to the continued presence of the virus, stimulated by retinoids in the graft tissue. Subject to obtaining empirical support for this hypothesis, the use of retinoid-blocking agents could be explored to reduce the risk of liver damage in HBV infection and to enhance the survival of liver grafts. Continued use of such agents may need to be used in conjunction with anti-viral modalities such as HBV hyperimmune globulin and lamivudine to prevent recurrent liver damage and to increase the long-term viability of the graft.

Hepatitis B virus and hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is a major global cause of hepatocellular carcinoma (HCC). Individuals who are chronic carriers have a greater than 100-fold increased relative risk of developing the tumour. Several mechanisms of HBV-induced HCC have been proposed. Integration of HBV DNA into the genome of hepatocytes occurs commonly, although integration at cellular sites that are important for regulation of hepatocyte proliferation appears to be a rare event. Functions of the HBx protein are also potentially oncogenic. These include transcriptional activation of cellular growth regulatory genes, modulation of apoptosis and inhibition of nucleotide excision repair of damaged cellular DNA. The effects of HBx are mediated by interaction with cellular proteins and activation of cell signalling pathways. Variations in HBV genome sequences may be important in hepatocarcinogenesis, although their significance has not yet been completely elucidated. Necroinflammatory hepatic disease, which often accompanies chronic HBV infection, may contribute indirectly to hepatocyte transformation in a number of ways, including by facilitating HBV DNA integration, predisposing to the acquisition of cellular mutations and generating mutagenic oxygen reactive species. Although HCC is a malignancy with a poor prognosis, the availability of an effective vaccine against HBV infection, and its inclusion in the Expanded Programme of Immunization of many countries, augurs well for the eventual elimination of HBV-associated HCC.

Activating immunity in the liver. I. Liver dendritic cells (but not hepatocytes) are potent activators of IFN-gamma release by liver NKT cells

A prominent subset of the hepatic innate immune system is alpha-galactosylceramide (alphaGalCer)-reactive, (CD4(+) and CD4(-)CD8(-)) CD1d-restricted NKT cells. We investigated in C57BL/6 (B6) mice which hepatic cell type stimulates hepatic NKT cell activation. Surface expression of CD1d but not CD40, CD80, or CD86 costimulator molecules was detected in hepatocytes. Pulsed in vitro or in vivo with alphaGalCer, hepatocytes triggered IL-4 release by liver NKT cells but required exogenous IL-12 to trigger IFN-gamma release by NKT cells. Liver dendritic cells (DC) isolated from nontreated mice showed low surface expression of MHC, CD1d, and CD40, CD80, or CD86 costimulator molecules that were strikingly up-regulated after alphaGalCer injection. Although liver CD11c(+) DC displayed lower CD1d surface expression than hepatocytes, they were potent stimulators of IFN-gamma and IL-4 release by liver NKT when pulsed with alphaGalCer in vitro or in vivo. Liver DC are thus potent stimulators of proinflammatory cytokine release by NKT cells, are activated themselves in the process of NKT cell activation, and express an activated phenotype after the NKT cell population is eliminated following alphaGalCer stimulation.

The woodchuck model of hepatitis B virus infection

The woodchuck hepatitis virus (WHV) was the first of the mammalian and avian hepadnaviruses described after discovery of the virus of hepatitis B (HBV). Woodchucks chronically infected with WHV develop progressively severe hepatitis and hepatocellular carcinoma, which present as lesions that are remarkably similar to those associated with HBV infection in humans. The initial virological studies and studies of pathogenesis utilized woodchucks that had been trapped in the wild and had acquired WHV infection naturally. Research with wild woodchucks was complicated by lack of knowledge of their backgrounds (e.g., dietary history, exposure to parasites or environmental toxins, and source and duration of WHV infection). Breeding colonies of woodchucks have been established and maintained in laboratory animal facilities, and laboratory-reared woodchucks are superior for experimental studies of pathogenesis or hepatocarcinogenesis. It is possible to infect neonatal woodchucks born in the laboratory with standardized inocula and produce a high rate of chronic WHV carriers that are useful for controlled investigations. WHV has been shown experimentally to cause hepatocellular carcinoma, supporting conclusions based on epidemiological and molecular virological studies that HBV is an important etiological factor in human hepatocarcinogenesis. Chronic WHV carrier woodchucks have become a valuable animal model for the preclinical evaluation of antiviral therapy for HBV infection, providing useful pharmacokinetic and pharmacodynamic results in a relevant animal disease model. It also has been shown that the pattern of toxicity and hepatic injury observed in woodchucks treated with certain fluorinated pyrimidines is remarkably similar to that observed in humans that were treated with the same drugs, suggesting the woodchuck has significant potential for the preclincial assessment of antiviral drug toxicity.

New animal models of hepatitis B and C

The narrow host range of infection and lack of suitable tissue culture systems for the propagation of hepatitis B and C viruses are limitations that have prevented a more thorough understanding of persistent infection and the pathogenesis of chronic liver disease. With hepatitis B virus (HBV), this lack of knowledge has been partially overcome by the discovery and characterization of HBV-like viruses in wild animals. With hepatitis C virus (HCV), related flaviviruses have been used as surrogate systems for such studies. Other laboratories have developed transgenic mice that express virus gene products and/or support virus replication. Some HBV transgenic mouse models develop fulminant hepatitis, acute hepatitis, or chronic liver disease after adoptive transfer, and others spontaneously develop hepatocellular carcinoma (HCC), as in human infections. Among HCV transgenic mice, most develop no disease, but acute hepatitis has been observed in one model, and HCC in another. Although mice are not susceptible to HBV and HCV, their ability to replicate these viruses and to develop liver diseases characteristic of human infections provides new opportunities to study pathogenesis and develop novel therapeutics.

Hepatitis B and hepatitis C co-infection in patients with HIV

HAART has increased the life expectancy of patients with HIV. However, as their life expectancy increases, it becomes increasingly important to focus on the management of concurrent illnesses such as chronic HBV and HCV infections which have the potential to increase mid to long term morbidity and mortality. Shared epidemiological risks have resulted in the HIV infected population having a higher incidence of both HBV and HCV than those uninfected with HIV. Co-infection with HIV modifies the natural history of HBV infection, increasing the rate of viral replication, risk of carriage and chronic hepatitis but without increasing liver necroinflammatory processes. In chronic HCV infection, the presence of HIV enhances the risk of severe liver disease. There is no evidence as yet that HBV directly impacts on HIV disease progression but HCV infection increases the risk of death or an AIDS defining illness and impairs CD4+ T cell recovery during antiretroviral therapy. Treatment of either hepatitis virus is complex because of pharmacokinetic interactions with components of HAART regimens.

CpG oligodeoxynucleotides with hepatitis B surface antigen (HBsAg) for vaccination in HBsAg-transgenic mice

DNA motifs containing unmethylated CpG dinucleotides within the context of certain flanking sequences enhance both innate and antigen-specific immune responses, due in part to the enhanced production of Th1-type cytokines. Here we explored the ability of CpG-containing oligodeoxynucleotides combined with recombinant hepatitis B surface antigen (HBsAg) to induce Th1 responses in mice that are transgenic for this antigen and that represent a model for asymptomatic hepatitis B virus chronic carriers. This was compared to hepatitis B virus-specific DNA-mediated immunization, which we have previously shown to induce the clearance of the transgene expression product and the down-regulation of hepatitis B virus mRNA in this transgenic mouse lineage. In control nontransgenic C57BL/6 mice, three immunizations with HBsAg and CpG triggered the production of anti-HBs antibodies and of HBs-specific T cells that secrete gamma interferon but do not display any HBsAg-specific cytotoxic activity. In the HBsAg-transgenic mice, immunization with HBsAg and CpG oligodeoxynucleotides, but not with CpG alone, induced the clearance of HBsAg circulating in the sera, with a concomitant appearance of specific antibodies, and was able to regulate the hepatitis B virus mRNA constitutively expressed in the liver. Finally, adoptive transfer experiments with CD8(+) T cells primed in C57BL/6 mice with HBsAg and CpG oligodeoxynucleotide-based immunization show that these cells were able to partially control transgene expression in the liver and to clear the HBsAg from the sera of recipient transgenic mice without an antibody requirement. CpG oligodeoxynucleotides motifs combined with HBsAg could therefore represent a potential therapeutic approach with which to treat chronically infected patients.

Profile of hepatocellular carcinoma in India: an insight into the possible etiologic associations

BACKGROUND

Several etiologic factors including hepatitis viruses, alcohol and aflatoxin have been implicated in the pathogenesis of hepatocellular carcinoma (HCC). There is, however, limited information from the Indian subcontinent.

METHODS

Seventy-four consecutive cases of HCC were studied. A detailed history, tests for hepatitis B virus (HBV; HBsAg, HBeAg, anti-HBe, IgG anti-HBc, anti-HBs and HBV-DNA), hepatitis C virus (HCV; anti-HCV and HCV-RNA) infection, liver histopathology and HBV-DNA integration by using Southern blot hybridization were studied. A p53 gene mutation was also studied by using PCR and single-strand conformation polymorphism.

RESULTS

Hepatocellular carcinoma patients were predominantly males (mean age 49.5 +/- 14.0 years). Portal hypertension and cirrhosis were seen in 56 (76%) patients, more often (P < 0.05) in viral marker positive cases. Forty-five percent of patients had features of hepatic decompensation at presentation. Evidence of HBV infection was present in 53 (71%) patients. Twenty-six (49%) of these patients had either HBeAg + ve, HBV-DNA + ve (n = 12), or HBsAg - ve, HBV-DNA + ve (n = 14) forms of HBV infection. Hepatitis B virus DNA integration in the liver tissue was seen in 10 of 17 (59%) patients. Infection with HCV alone was detected in three (4%) and dual HBV and HCV infection in six (8%) patients. A majority (78.5%) of the chronic alcoholics had associated viral infection. The etiology of HCC remained undetermined in 15 (20%) patients. The p53 gene mutations were detected only in three of 21 (14%) liver tissues. Aflatoxin toxicity, oral contraceptive use or metabolic disorder were not seen.

CONCLUSIONS

In India: (i) HBV infection is the predominant factor for the development of HCC, often related to mutant forms of HBV; (ii) a majority of the HCC patients have overt cirrhosis of the liver; and (iii) HCV and alcohol per se are uncommonly associated.

Abnormal liver function associated with occupational exposure to dimethylformamide and hepatitis B virus

N,N-Dimethylformamide (DMF) has excellent solvent properties and is used intensively in the production of synthetic leather and resins. It has caused hepatoxicity in human and animal studies. Hepatitis B virus (HBV) and hepatitis C virus infections are reported to be the major causes of chronic liver diseases (including liver cirrhosis and liver cancer) in Taiwan. This study examined the dose-response relationship of the observed abnormal liver function among the DMF-exposed workers and the interactions among DMF, other chemical exposures, HBV infection, and potential confounders on liver abnormalities. The average DMF exposure concentration was 11.6 ppm (median, 5.9 ppm; range, 0.1 to 86.6 ppm); 65 of 176 workers (36.9%) had high (> 10 ppm) DMF exposure, 37 (21%) had middle (> 5 ppm, < or = 10 ppm) exposure, and 74 (42%) had low (< or = 5 ppm) exposure. There were 24 of 65 abnormal liver function test results (LFTs) (36.9%) (elevations of either glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, or gamma-glutamyl transpeptidase) among the workers with high DMF exposure, 10 of 37 abnormal LFTs (27%) among workers with middle DMF exposure, and 11 of 74 abnormal LFTs (22%) among workers with low DMF exposure. Compared with the workers having low DMF exposure, the HBV, drinking, body mass index (BMI), sex, duration of employment, epichlorohydrin, and toluene exposure adjusted odds ratios (ORs) (and 95% confidence intervals [CIs]) for abnormal LFTs were 1.62 (0.61, 4.28) for workers with middle DMF exposure and 2.93 (1.27, 6.8) for those with high DMF exposure, and there was a significant dose response between DMF exposure and the prevalence of abnormal LFTs (P = 0.006). There were significant associations between abnormal LFTs and HBV carriers (adjusted OR: 3.11; 95% CI: 1.29, 7.5; P = 0.01) and between abnormal LFTs and increased BMI (adjusted OR: 2.2; 95% CI: 1.02, 4.72; P = 0.041). Ultrasonography showed significant associations between chronic liver diseases and HBV carrier status, increased BMI, and high cumulative (> 100 ppm-years) DMF exposure (respectively, adjusted OR: 9.58, 95% CI: 1.79, 51.4, P = 0.007; adjusted OR: 13.2, 95% CI: 1.32, 132, P = 0.025; and adjusted OR: 6.2, 95% CI: 1.14, 34.1, P = 0.032). Drinking and BMI were significantly associated with fatty liver (respectively, adjusted OR: 4.9, 95% CI: 1.39, 17.3, P = 0.012; and adjusted OR: 7.93, 95% CI: 1.6, 39.3, P = 0.01). In conclusion, this study demonstrated that (1) a significant dose-response relationship existed between liver function abnormalities and DMF exposure among workers in Taiwan, (2) HBV carrier status or increased BMI had synergistic effects with DMF in causing liver abnormalities (abnormal LFTs and clinical chronic liver diseases).

Transcriptional regulation of the TFIIH transcription repair components XPB and XPD by the hepatitis B virus x protein in liver cells and transgenic liver tissue

Human hepatitis B virus is a risk factor for the development of hepatocellular carcinoma. The hepatitis B virus x protein (HBx) has been shown to inactivate the p53 tumor suppressor protein and impair DNA repair, cell cycle, and apoptosis mechanisms. Herein we report that HBx represses two components of the transcription-repair factor TFIIH, XPB (p89), and XPD (p80), both in p53-proficient and p53-deficient liver cells. This inhibition is observed while HBx maintains its transactivation function. Expression of HBx in liver cells results in down-regulation of endogenous XPB and XPD mRNAs and proteins; this inhibition is not observed with other TFIIH subunits, XPA or PCNA. In liver tissue from HBx transgenics, XPB and XPD proteins are down-regulated in comparison to matched normal liver tissue. HBx has been shown to interact with Sp1 transcription factor and affects its DNA binding activity. Sp1 is essential for the basal promoter activity of XPB in liver cells and Drosophila SL2 cells. In the Sp1-deficient SL2 cells, HBx-induced XPB and XPD inhibition is Sp1-dependent. In summary, our results provide evidence that HBx represses the expression of key TFIIH proteins at least in part through Sp1 elements; this repression may impair TFIIH function in DNA repair mechanisms.

Hepatitis B virus and hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is a major global cause of hepatocellular carcinoma (HCC). Individuals who are chronic carriers have a greater than 100-fold increased relative risk of developing the tumour. Several mechanisms of HBV-induced HCC have been proposed. Integration of HBV DNA into the genome of hepatocytes occurs commonly, although integration at cellular sites that are important for regulation of hepatocyte proliferation appears to be a rare event. Functions of the HBx protein are also potentially oncogenic. These include transcriptional activation of cellular growth regulatory genes, modulation of apoptosis and inhibition of nucleotide excision repair of damaged cellular DNA. The effects of HBx are mediated by interaction with cellular proteins and activation of cell signalling pathways. Variations in HBV genome sequences may be important in hepatocarcinogenesis, although their significance has not yet been completely elucidated. Necroinflammatory hepatic disease, which often accompanies chronic HBV infection, may contribute indirectly to hepatocyte transformation in a number of ways, including by facilitating HBV DNA integration, predisposing to the acquisition of cellular mutations and generating mutagenic oxygen reactive species. Although HCC is a malignancy with a poor prognosis, the availability of an effective vaccine against HBV infection, and its inclusion in the Expanded Programme of Immunization of many countries, augurs well for the eventual elimination of HBV-associated HCC.

The hepatitis B virus encoded oncoprotein pX amplifies TGF-beta family signaling through direct interaction with Smad4: potential mechanism of hepatitis B virus-induced liver fibrosis

Hepatitis B, one of the most common infectious diseases in the world, is closely associated with acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Many clinical investigations have revealed that hepatic fibrosis is an important component of these liver diseases caused by chronic hepatitis B. TGF-beta signaling plays an important role in the pathogenesis of fibrosis in chronic hepatitis and cirrhosis. As these diseases are associated with hepatitis B virus (HBV) infection, we examined the possibility that the HBV-encoded pX oncoprotein regulates TGF-beta signaling. We show that pX enhances transcriptional activity in response to TGF-beta, BMP-2, and activin by stabilizing the complex of Smad4 with components of the basic transcriptional machinery. Additionally, confocal microscopic studies suggest that pX facilitates and potentiates the nuclear translocation of Smads, further enhancing TGF-beta signaling. Our studies suggest a new paradigm for amplification of Smad-mediated signaling by an oncoprotein and suggest that enhanced Smad-mediated signaling may contribute to HBV-associated liver fibrosis.

Animal models of hepadnavirus-associated hepatocellular carcinoma

Animal models of hepatitis B virus infection have been valuable for determining the mechanisms of hepadnavirus replication, for studies of pathogenesis, and for investigations of viral hepatocarcinogenesis. The woodchuck model also seems to be useful in the discovery and development of antiviral drugs to treat HBV infection and for testing new forms of immunotherapy. In particular, the woodchuck seems to be ideal for studying the effect of antiviral treatment and immunotherapy on the outcome of hepadnavirus infection and on survival. The median life expectancy of experimentally infected, chronic WHV carriers is approximately 29 months, and almost all develop HCC. New types of prophylaxis or therapy can be evaluated under controlled experimental conditions, in a relevant animal model, and within a reasonable time frame.

Targeting murine immune responses to selected T cell- or antibody-defined determinants of the hepatitis B surface antigen by plasmid DNA vaccines encoding chimeric antigen

By exchanging sequences from the middle-surface (MS) and small-surface (S) Ag of hepatitis B virus (HBV) with corresponding sequences of the MS Ag of woodchuck hepatitis virus, we constructed chimeric MS variants. Using these constructs as DNA vaccines in mice, we selectively primed highly specific (non-cross-reactive) Ab responses to pre-S2 of the HBV MS Ag and the "a" determinant of the HBV S Ag, as well as L(d)- or K(b)-restricted CTL responses to HBV S epitopes. In transgenic mice that constitutively express large amounts of HBV surface Ag in the liver we could successfully suppress serum antigenemia (but not Ag production in the liver) by adoptive transfer of anti-pre-S2 or anti-"a" immunity but not CTL immunity. DNA vaccines greatly facilitate construction of chimeric fusion Ags that efficiently prime specific, high-affinity Ab and CTL responses. Such vaccines, in which sequences of an Ag of interest are exchanged between different but related viruses, are interesting tools for focusing humoral or cellular immunity on selected antigenic determinants and elucidating their biological role.

Identification and characterization of a prevalent hepatitis B virus X protein mutant in Taiwanese patients with hepatocellular carcinoma

The aim of this study was to investigate whether there was a particular hepatitis B virus (HBV) X protein (HBx) mutant associated with Taiwanese patients with hepatocellular carcinoma (HCC). Initially, the entire coding region of HBx gene from the serum samples of 14 Taiwanese patients were sequenced. A novel mutant, HBx-A31, was preferentially found in patients with HCC. Sera from 67 patients with HCC and 100 patients with chronic hepatitis B were thus subjected for codon 31 analysis using a dual amplification created restriction site method. HBx-A31 was detected more frequently in patients with HCC (52% versus 12%; P<0.001) and in patients with liver cirrhosis (44% versus 6%; P<0.001). Site directed mutagenesis experiment revealed that HBx-A31 was less effective in transactivating HBV enhancer I-X promoter complex, less efficient in supporting HBV replication, and less potent in enhancing TNF-alpha induced increment of CPP32/caspase 3 activities in HepG2 cells. In conclusion, a prevalent HBx mutant was identified in Taiwanese patients with hepatocellular carcinoma. Development of this mutant might represent a strategy of the virus to escape immune surveillance and thus contribute to the process of multiple-step hepatocarcinogenesis.

Elevated expression of hepatic proliferative markers during early hepatocarcinogenesis in hepatitis-B virus transgenic mice lacking mdr1a-encoded P-glycoprotein

Recent studies have shown that expression levels of the multidrug resistance gene MDR1, which encodes the drug transporter P-glycoprotein, correlate with prognostic outcomes of certain tumor types. These findings suggest that expression of MDR1 may affect tumor behaviors. To address this issue further, we investigated the expression of mdr1a, a human MDR1 homolog, on the development of hepatocellular carcinoma in a transgenic mouse model carrying the liver-targeted expression of human hepatitis-B virus (HBV) surface antigen. The pathogenetic program was compared in HBV mice carrying either mdr1a(+/+) or mdr1a(-/-). We found that the expressions of proliferative activity markers, Ki67 nuclear antigen, and proliferating cell nuclear antigen were elevated in mdr1a(-/-) mice younger than 10 wk in comparison with those in the same age group of wild-type animals. Replication in the hepatic population as determined by bromodeoxyuridine incorporation tended to support observation that mdr1a(-/-) mice exhibited elevated labeling indices in this age group. Moreover, histologic staining and flow-cytometric analysis showed that the mdr1a(-/-) animals exhibited a higher cell population with polyploidy than did the mdr1a(+/+) counterparts of the same age. However, no significant differences in the expression of the liver-injury markers serum alanine transaminase and aspartate transaminase were observed. Although our results showed that absence of mdr1a expression is correlated with modest enhanced proliferative characteristics in the livers at stage before the development of hepatocellular carcinoma, the overall life spans between these two strains of mice were not significantly different. The implication of these findings to the role of P-glycoprotein in tumor development and cancer chemotherapy is discussed.

Interaction of Hepatitis B virus with cellular processes in liver carcinogenesis

Hepatitis B infection is strongly linked epidemiologically to hepatocellular carcinoma development. This article reviews the molecular mechanisms by which hepatitis B encoded proteins such as hepatitis B x and hepatitis B surface transactivators may interact with gene transcription, tumor suppression, apoptosis, and signalling pathways of the liver cell with the possible consequence of tumor induction. Data on the interaction between hepatitis B proteins and cellular processes are often conflicting indicating a non-specific simultaneous interaction with antagonistic cellular processes that result in the formation of escape mutants that are not subject to these selective pressures.

Clinical features and etiology of hepatocellular carcinoma arising in patients with membranous obstruction of the inferior vena cava: in reference to hepatitis viral infection

BACKGROUND AND AIMS

Budd-Chiari syndrome (BCS) comprises hepatic vein thrombosis and inferior vena cava (IVC) obstruction known as membranous obstruction of the IVC (MOVC). The latter is frequently complicated by hepatocellular carcinoma (HCC). The etiology of MOVC-associated HCC in relation to hepatitis viral infection is not known. In this study, we investigated the clinical features and etiology of HCC in MOVC.

METHODS

Membranous obstruction of IVC and HCC were diagnosed and studied by using imaging techniques. Sera from patients with MOVC, complicated by HCC, were examined for hepatitis viral antigens and antibodies (hepatitis B surface antigen (HBsAg), antibody to HBsAg (anti-HBs), antibody to hepatitis B core antigen (anti-HBc) and third generation antibody to hepatitis C virus (anti-HCV)) and for hepatitis viral nucleic acids (hepatitis B virus (HBV)-DNA, hepatitis C virus (HCV)-RNA, hepatitis G virus (HGV)-RNA and TT virus DNA).

RESULTS

We studied 12 patients with BCS who were seen between April 1968 and February 1999. All of them had MOVC. Hepatocellular carcinoma developed in three (25%) of them. There were no obvious differences in the clinical features and imaging findings concerning MOVC between patients with and without HCC. Hepatocellular carcinoma in these three patients showed no clear trend in clinical features and imaging findings. Of the hepatitis viral markers examined, HBsAg, anti-HBc and HBV-DNA were positive in only one of three patients with HCC and all of the viral markers were negative in the other two patients.

CONCLUSIONS

Chronic congestion in the liver, caused by an outflow block of hepatic veins and subsequent histopathologic change, must have led to HCC in two patients without any hepatitis viral markers. Patients with MOVC should be followed closely as a high-risk group for HCC.

Hepadnaviral hepatocarcinogenesis: in situ visualization of viral antigens, cytoplasmic compartmentation, enzymic patterns, and cellular proliferation in preneoplastic hepatocellular lineages in woodchucks

BACKGROUND/AIMS

Hepadnaviral hepatocarcinogenesis induced in woodchucks with and without dietary aflatoxin B1 has been established as an appropriate animal model for studying the pathogenesis of human hepatocellular carcinoma in high-risk areas. Our aim in this study was the elucidation of phenotypic cellular changes in early stages of this process.

METHODS

Woodchucks were inoculated as newborns with woodchuck hepatitis virus (WHV), and partly also exposed to aflatoxin B1. Sequential hepatocellular changes in the expression of viral antigens, ultrastructural organization, cellular proliferation and apoptosis were studied in situ by electron microscopy, enzyme and immunohistochemistry.

RESULTS

A characteristic finding in WHV-infected animals (with and without aflatoxin B1) was proliferative areas of minimal structural deviation, which predominated periportally, comprised glycogen-rich, amphophilic, and ground-glass hepatocytes, and expressed the woodchuck hepatitis core and surface antigens. Two main types of proliferative foci emerged from minimal deviation areas, glycogenotic clear cell foci and amphophilic cell foci (being poor in glycogen but rich in mitochondria), giving rise to the glycogenotic-basophilic and the amphophilic preneoplastic hepatocellular lineages. A gradual loss in the expression of viral antigens appeared in both lineages, particularly early in the glycogenotic-basophilic cell lineage. Whereas glycogenosis was associated with an enzymic pattern suggesting an early activation of the insulin-signaling pathway, amphophilic cells showed changes in enzyme activities mimicking a response of the hepatocytes to thyroid hormone, which may also result from early changes in signal transduction.

CONCLUSION

Preneoplastic hepatocellular lineages in hepadnaviral and chemical hepatocarcinognesis show striking phenotypic similarities, indicating concordant and possibly synergistic early changes in signaling.

Viral hepatitis in the liver transplant recipient

Understanding and management of HBV and HCV infection in the OLT recipient has evolved rapidly in the last decade. The spontaneous risk for viral recurrence after transplantation is high, but has been decreased effectively in hepatitis B-positive recipients with the use of HBIG and lamivudine. HCV recurrence as defined by histologic injury is almost universal, although graft or patient outcomes for the first 8 years after OLT do not appear to be limited by HCV serostatus. However, effective prophylactic regimens that alter the natural history of HCV reinfection do not currently exist, and with longer follow-up into the second decade, the prevalence of HCV-related graft failure is likely to increase.

Genes and viruses in hepatobiliary neoplasia

Hepatobiliary neoplasms comprise a significant portion of the worldwide cancer burden. Advances in basic science research have led to rapid progress in our understanding of the molecular events responsible for these dreaded diseases. The genetic changes associated with hepatocellular carcinoma (HCC) have received the most attention. Aflatoxin B1 exposure leads to mutations in the p53 tumor suppressor gene, most commonly a transversion in codon 249 that leads to a substitution of serine for arginine in the p53 protein. Numerous other tumor suppressor genes, oncogenes, and tumor gene pathways are altered in HCC. Hepatitis B virus (HBV) infection is strongly associated with HCC. HBV may cause HCC either directly via the HBV X protein, or indirectly by causing liver inflammation and cirrhosis. Hepatitis C virus (HCV) infection is also associated with HCC. Recent evidence suggests that the HCV core protein may play a role in hepatocarcinogenesis. Several inherited metabolic diseases are associated with HCC. It is likely that these diseases cause HCC indirectly by causing cirrhosis. The molecular pathogenesis of cholangiocarcinoma and gallbladder cancer has not been well defined. However, multiple tumor suppressor genes and oncogenes, including p53 and K-ras, are altered in these tumors. Further molecular characterization of hepatobiliary tumors may lead to earlier diagnosis, better staging, improved treatment planning, and the development of more effective therapies.

Effects of carcinogen-induced transcription factors on the activation of hepatitis B virus expression in human hepatoblastoma HepG2 cells and its implication on hepatocellular carcinomas

To elucidate the molecular mechanisms involved in the action of common carcinogens, which can act as important cofactors in modulating hepatitis B virus-mediated hepatocellular carcinogenesis, we have investigated the influence of aflatoxin B(1) (AFB), a potent liver carcinogen, as well as benzo[a]pyrene (BP) and 4-aminobiphenyl (4-ABP), carcinogens in cigarette smoke, on the induction of various transcription factors in human hepatoblastoma HepG2 cells. DNA electrophoretic mobility shift assays were performed with nuclear extracts from HepG2 cells treated with 10 micromol/L AFB, 40 micromol/L BP, or 300 micromol/L 4-ABP for 6 and 24 hours. Eight- and 6-fold increases in nuclear transcription factor kappaB (NF-kappaB), and 5- and 10-fold increases in activated protein (AP-1) transcription factor were observed with 24 hours AFB and BP treatments, respectively, whereas 4-ABP treatment resulted in an approximately 4-fold induction of both NF-kappaB and AP-1. Moreover, 4-ABP gave the strongest NF-kappaB activation in 6 hours of treatment. Four- and 10-fold activation of stress protein was detected by a consensus heat shock factor (HSF) sequence binding probe, with AFB and BP treatments, respectively. DNA adducts were observed by immunoassays in HepG2 cells treated with AFB and BP but not with 4-ABP. Increased human hepatitis B virus (HBV) surface antigen (HBsAg) synthesis was detected in AFB- and BP-treated HepG2 cells following transfection with recircularized HBV DNA. These data suggest that certain carcinogen-induced transcription factors may influence viral carcinogenesis and initiate hepatocellular carcinomas (HCC).

Molecular analysis of hepatitis B virus DNA in serum and peripheral blood mononuclear cells from hepatitis B surface antigen-negative cases

We have analyzed the molecular bases of the persistence of hepatitis B virus (HBV) DNA in serum and peripheral blood mononuclear cells (PBMC) in the absence of detectable hepatitis B surface antigen (HBsAg) in hemodialysis patients and dialysis-unit staff members who had suffered acute hepatitis B that resolved previously. HBV DNA was found in both compartments by polymerase chain reaction (PCR) using primers of the pre-S/S region. Viral DNA was transcriptionally active in PBMC, because the covalently closed circular (ccc) HBV DNA, the template for the viral RNA transcription, was detected in 47% of the samples. Furthermore, all PBMC had HBV RNA. HBsAg-negative cases had statistically lower levels of HBV DNA in serum and PBMC than a control group of chronic HBsAg carriers. We have also studied the presence of immune complexes and the existence of mutations in the pre-S/S gene to explain the lack of detection of HBsAg in these cases. No serum HBsAg/hepatitis B surface antigen antibody (anti-HBs) immune complexes or mutations in the "a determinant of the S gene were found. However, we have observed that all HBsAg-negative cases were infected by a mixture of the wild-type virus and a deletion mutant in the pre-S1 region. This deletion (amino acids 58-118) affects the S gene promoter, and previous in vitro studies have shown that it produces a reduction of the HBsAg synthesis. In conclusion, this work shows that the lack of detection of HBsAg in the presence of low viral levels of replication may be caused by the existence of viral genomes harboring deletions in the pre-S1 region that affect the S promoter.

Hepatitis B virus-related insertional mutagenesis implicates SERCA1 gene in the control of apoptosis

We have used the Hepatitis B Virus DNA genome as a probe to identify genes clonally mutated in vivo, in human liver cancers. In a tumor, HBV-DNA was found to be integrated into the gene encoding Sarco/Endoplasmic Reticulum Calcium ATPase (SERCA), which pumps calcium, an important intracellular messenger for cell viability and growth, from the cytosol to the endoplasmic reticulum. The HBV X gene promoter cis-activates chimeric HBV X/SERCA1 transcripts, with splicing of SERCA1 exon 11, encoding C-terminally truncated SERCA1 proteins. Two chimeric HBV X/SERCA1 proteins accumulate in the tumor and form dimers. In vitro analyses have demonstrated that these proteins localize to the ER, determine its calcium depletion and induce cell death. We have also shown that these biological effects are related to expression of the SERCA, rather than of the viral moiety. This report involves for the first time the expression of mutated SERCA proteins in vivo in a tumor cell proliferation and in vitro in the control of cell viability. Oncogene (2000).

Expression of hepatitis B virus X protein does not alter the accumulation of spontaneous mutations in transgenic mice

Chronic infection with hepatitis B virus (HBV) is one of the major etiological factors in the development of human hepatocellular carcinoma. Transgenic mice that express the HBV X protein (HBx) have previously been shown to be more sensitive to the effects of hepatocarcinogens, although the mechanism for this cofactor role remains unknown. The ability of HBx to inhibit DNA repair in transiently transfected cell lines suggests one possible pathway. In the present study, primary hepatocytes isolated from transgenic mice that possess the HBV X gene under the control of the human alpha-1-antitrypsin regulatory region (ATX mice) were found to be deficient in their ability to conduct unscheduled DNA synthesis in response to UV-induced DNA damage. In order to measure the impact of HBx expression on DNA repair in vivo, double-transgenic mice that express HBx and possess a bacteriophage lambda transgene were sacrificed at 30, 90, and 240 days of age. Mutation frequency was determined for high-molecular-weight liver DNA of ATX and control mice by functional analysis of the lambda transgene. Expression of HBx did not significantly increase the accumulation of spontaneous mutations. These results are consistent with previous studies of HBx transgenic mice in which no effect of HBx on liver histology was apparent. This new animal model provides a powerful system in which to investigate the in vivo cooperation between HBx expression and environmental carcinogens.

Hepatitis B virus surface (S) transactivator with DNA-binding properties

Chronic infection with hepatitis B virus (HBV) in humans is strongly linked to the development of hepatocellular carcinoma (HCC). Activation of growth-regulatory genes may play a crucial role in carcinogenesis. Proto-oncogene expression has been shown to be higher in HCC tissue with integrated HBV DNA than in the normal liver. Earlier, we showed that the 3' end of the HBV major surface gene (S) (426-855 nucleotides of the S region) is a transactivator of the X promoter-enhancer regulatory element in co-transfection experiments. This region expresses a truncated carboxy terminal S protein extending from amino acid residues 102 to 226. In this study, the truncated S protein (trc-S) was examined for its enhancing activity on several viral and cellular regulatory elements. The results indicate that trc-S activates rous sarcoma virus long terminal repeat (LTR), human T-lymphotropic virus 2 LTR, human immunodeficiency virus 1 LTR, and the c-jun and c-fos promoters. Electrophoretic mobility shift assays carried out to investigate its DNA-binding properties established that trc-S binds to HBV X promoter and oligonucleotides representing binding sites for the AP1 and TFIID transcription factors. The specificity of this interaction was confirmed by using competition experiments and supershift assays. These experiments suggest that trc-S is a transactivator of several cellular and viral promoters and that this activity is mediated by direct interaction with DNA.

Identification of a pre-S2 mutant in hepatocytes expressing a novel marginal pattern of surface antigen in advanced diseases of chronic hepatitis B virus infection

BACKGROUND AND AIMS

The expression of hepatitis B viral (HBV) antigens in liver tissue reflects the replicative status of chronic HBV infection. We have previously recognized a novel marginal pattern of hepatitis B surface antigen (HBsAg) in hepatocytes, which usually clusters in groups and emerges at the late non-replicative phase. This study was designed to investigate whether the marginal-type HBsAg represented the gene product of a specific HBV-surface mutant.

METHODS

Microdissection of cirrhotic nodules homogeneously expressing marginal HBsAg was performed on two of 12 resected livers from HBsAg-seropositive patients with hepatocellular carcinoma. The gene presumably encoding marginal HBsAg was polymerase chain reaction (PCR)-cloned, sequenced and analysed. In vitro transfection and expression of the cloned surface mutant plasmids were performed on the Huh7 cell line to illustrate intrahepatic HBsAg expression.

RESULTS

Immunohistochemical staining revealed that the marginal HBsAg was positive for pre-S1 and thus contained large surface proteins. The PCR cloning and sequencing of the genes presumably encoding marginal-type HBsAg in both cases revealed the same deletion at the 5' terminus (nt 2-55) of pre-S2. A point mutation on the small-surface (S) antigen was also found in one case. The pre-S2 deletion sequence and the mutation sites of the S gene coincide with human lymphocyte antigen-restricted T- and/or B-cell epitopes. In vitro transfection of the mutant plasmid revealed a blot-like retention or accumulation of HBsAg in the cytoplasm or at the periphery of hepatocytes, accompanied by a decreased secretion of HBsAg in the culture supernatant, mimicking intrahepatic expression.

CONCLUSION

A natural pre-S2 deletion mutant was identified in hepatocytes expressing a novel marginal pattern of HBsAg, which probably contains mutant, large, surface proteins. The biological significance of the pre-S2 deletion mutant should be interesting in view of the clustering proliferation of hepatocytes expressing marginal HBsAg.

Ongoing murine T1 or T2 immune responses to the hepatitis B surface antigen are excluded from the liver that expresses transgene-encoded hepatitis B surface antigen

Different protein- or DNA-based vaccination techniques are available that prime potent humoral and cellular, T1 or T2 immune responses to the hepatitis B surface Ag (HBsAg) in mice. T1 and T2 are immune responses with isotype profile indicating Th1 and Th2 immunoregulation. We tested whether HBsAg-specific immune responses can be established in transgenic mice that express HBsAg in the liver (HBs-tg mice) using either these different vaccination techniques or an adoptive transfer system. HBsAg-specific responses could not be primed in HBs-tg mice with the established, potent vaccine delivery techniques. In contrast, adoptive transfers of T1- and T2-type HBsAg-immune spleen cells into congenic HBs-tg hosts (that were not conditioned by pretreatment) suppressed HBsAg antigenemia and gave rise to HBsAg-specific serum Ab titers. The establishment of continuously rising anti-HBsAg serum Ab levels with alternative isotype profiles (reflecting T1 or T2 polarization) in transplanted HBs-tg hosts required donor CD4+ T cell-dependent restimulation of adoptively transferred immune cells by transgene-derived HBsAg. Injections of HBsAg-specific Abs into HBs-tg mice did not establish stable humoral immunity. The expanding T1 or T2 immune responses to HBsAg in HBs-tg hosts did not suppress transgene-directed HBsAg expression in the liver and did not induce liver injury. In addition to priming functional antiviral effector cells, the conditioning of the liver microenvironment to enable delivery of antiviral effector functions to this organ are therefore critical for effective antiviral defense. A major challenge in the development of a therapeutic vaccine against chronic hepatitis B or C virus infection is thus the efficient targeting of specifically induced immune effector specificities to the liver.

Hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is increasing in many countries as a result of an increase in hepatitis C virus (HCV) infection since World War II. The epidemiology of HCC varies with the global region. There have been conflicting observations from different parts of the world concerning the frequency of HCC in patients who in the distant past had post-transfusion non-A, non-B hepatitis. The genetic basis of hepatocarcinogenesis is still poorly understood. In hepatitis B virus (HVB) associated HCC, codon 249 mutation in the p 53 gene seems more related to exposure to aflatoxin B1 than to hepatocarcinogenesis itself. HCC that occurs in children in high HBV endemic regions could be associated with germ-line mutations, but little information is available; not much is known about chemical hepatocarcinogens in the environment other than aflatoxins. The X gene of HBV seems to play an important role in HBV-associated hepatocarcinogenesis. There are preliminary observations on the molecular mechanism of HCV-associated HCC, such as HCV core protein inducing HCC in transgenic mice and the NS3 genome transforming NIH 3T3 cells. Pathological distinction between preneoplastic and very early transformed lesions still depends on classical morphology, and a more genetically oriented differential diagnosis is required. Clinical diagnosis based on modern imaging has improved greatly, but is still unsatisfactory in the differential diagnosis of preneoplastic and early transformed nodules, because the vasculature changes that occur within the nodule are not accurately discerned with the current imaging. Use of sensitive des-gamma-carboxy prothrombin (PIVKA II) assay, and lectin affinity chromatography separating HCC specific subspecies of AFP molecules with a more practical biochemical technique will further improve diagnosis. Early diagnosis and transplantation are the best treatment at the moment, but transplantation is not widely available because of the donor shortage. Despite successful resection, the remnant cirrhotic liver frequently develops new HCC lesions, seriously curtailing long-term survival. All-out efforts should be directed to the prevention of HCC, through prevention of viral hepatitis, prevention of acute hepatitis from becoming chronic, prevention of chronic hepatitis from progressing to cirrhosis, and prevention of the cirrhotic liver from developing HCC (chemoprevention). At the moment, very few such studies exist.

Hepatitis B virus biology

Hepadnaviruses (hepatitis B viruses) cause transient and chronic infections of the liver. Transient infections run a course of several months, and chronic infections are often lifelong. Chronic infections can lead to liver failure with cirrhosis and hepatocellular carcinoma. The replication strategy of these viruses has been described in great detail, but virus-host interactions leading to acute and chronic disease are still poorly understood. Studies on how the virus evades the immune response to cause prolonged transient infections with high-titer viremia and lifelong infections with an ongoing inflammation of the liver are still at an early stage, and the role of the virus in liver cancer is still elusive. The state of knowledge in this very active field is therefore reviewed with an emphasis on past accomplishments as well as goals for the future.

The enhancer I core region contributes to the replication level of hepatitis B virus in vivo and in vitro

Chronic hepatitis B virus (HBV) infection can lead to liver cirrhosis and hepatocellular carcinoma. Long-term interaction of the immune system with the virus results in the selection of escape mutants and viral persistence. In this work we characterize mutations in the enhancer I region isolated prior to liver transplantation from the HBV genomes of 10 patients with chronic HBV infection. The HBV-genomes were sequenced, and the enhancer I region was cloned into luciferase reporter constructs to determine the transcriptional activity. Functional studies were performed by transfecting HBV replication-competent plasmids into hepatoma cells. Analyses of the replication fitness of the mutant strains were conducted by biochemical analysis. In all HBV genomes the enhancer I region was mutated. Most of these mutations resulted in decreased transcriptional activity. The strongest effects were detectable in strains with mutations in the hepatocyte nuclear factor 3 and 4 (HNF3 and HNF4) binding sites of the enhancer I core domain. Replication-competent HBV constructs containing these mutations demonstrated up to 10-fold-reduced levels of virus replication. Before liver transplantation, when the mutant strains were detected in the patients' sera, low HBV DNA levels were found. After transplantation and reinfection with a wild-type virus, the levels of replication were up to 240-fold higher. Our results show that mutations in the enhancer I region of HBV have a major impact on HBV replication. These mutations may also determine the switch from high to low levels of viral replication which is frequently observed during chronic HBV infection.

Hepatitis B infection: pathogenesis and management

Although hepatitis B is an ancient disease, most of the advances in our knowledge of its epidemiology, prevention, pathogenesis, natural history and treatment were made in the last 30 years. The prospect of global eradication of HBV infection within the next 50 years is technologically possible but implementation of worldwide vaccination against hepatitis B will require significantly more time to overcome the social and economic hurdles. While there is reasonable optimism that HBV infection will be eradicated, there are currently 300 million HBV carriers worldwide who are at risk of dying from liver failure or hepatocellular carcinoma, and there will continue to be new cases of HBV infection for many more years. Thus, HBV infection cannot be considered to be a health problem of the past. The focus of hepatitis B research at the turn of the millenium will be the development of more effective therapies that can be applied to all patients with chronic HBV infection. These treatments need to be effective in inhibiting HBV DNA synthesis and in eliminating ccc DNA. They may involve monotherapy with more potent antiviral agents that do not induce resistance, but are more likely to require a combination of antiviral agents or antiviral and immunomodulatory agents. These treatments must be safe, convenient to administer, and affordable. It is likely that new therapies with increasing efficacy will be available in the next one to two decades and combination therapy will be used widely by 2010. These treatments will induce sustained remission in the majority of patients who can afford them but provision of treatment to all those who need them will be more difficult. Other areas of hepatitis B that need to be addressed are the prevalence of occult HBV infection, the changing epidemiology and clinical significance of HBV variants, in particular the A1896 mutant, and the mechanisms of immune clearance and pathogenesis.

Hepatitis C virus structural proteins induce liver cell injury in transgenic mice

To develop an animal model of hepatitis C virus (HCV) infection, transgenic mice carrying part of the HCV cDNA (C980) encoding HCV-core and envelope proteins under control of the mouse class I major histocompatibility complex gene (H-2K) regulatory region were produced. HCV-C980 RNA and HCV-core protein were present in livers from line H36 as determined by RNase protection assay and immunostaining, respectively. More than 40 animals from line H36 were examined histologically. Most of these H36 mice after 10 months of age developed spontaneous focal infiltration of lymphocytes, hepatocyte necrosis, degeneration, and altered foci with mitotic hepatocytes. These pathological lesions were absent in livers from the age-matched control littermates. Liver cells from these H36 mice were sensitive to damage induced by intravenous administration of an anti-Fas antibody. It is suggested that HCV-C980 proteins by themselves may be one causative agent of liver cell injury in subjects with HCV infection.

Hepatitis B virus in hepatocarcinogenesis

Hepatitis B virus (HBV) is an important etiologic agent of chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Although the mechanism whereby HBV causes HCC is not fully understood, it is likely that there are many relevant molecular pathways that contribute to the development of HBV-associated HCC. This review provides an overview of some of these proposed pathways and their relative importance. It also raises questions on basic and translational research that will signficantly contribute to the better understanding of underlying mechanisms, prevention, and treatment of this tumor type.

Activation of c-Raf-1 kinase signal transduction pathway in alpha(7) integrin-deficient mice

Integrin alpha(7)-deficient mice develop a novel form of muscular dystrophy. Here we report that deficiency of alpha(7) integrin causes an activation of the c-Raf-1/mitogen-activated protein (MAP) 2 kinase signal transduction pathway in muscle cells. The observed activation of c-Raf-1/MAP2 kinases is a specific effect, because the alpha(7) integrin deficiency does not cause unspecific stress as determined by measurement of the Hsp72/73 level and activity of the JNK2 kinase. Because an increased level of activated FAK was found in muscle of alpha(7) integrin-deficient mice, the activation of c-Raf-1 kinase is triggered most likely by an integrin-dependent pathway. In accordance with this, in the integrin alpha(7)-deficient mice, part of the integrin beta(1D) variant in muscle is replaced by the beta(1A) variant, which permits the FAK activation. A recent report describes that integrin activity can be down-modulated by the c-Raf-1/MAP2 kinase pathway. Specific activation of the c-Raf-1/MAP2 kinases by cell-permeable peptides in skeletal muscle of rabbits causes degeneration of muscle fibers. Therefore, we conclude that in alpha(7) integrin-deficient mice, the continuous activation of c-Raf-1 kinase causes a permanent reduction of integrin activity diminishing integrin-dependent cell-matrix interactions and thereby contributing to the development of the dystrophic phenotype.

Establishment and characterization of four human hepatocellular carcinoma cell lines containing hepatitis B virus DNA

AIM: To investigate the characteristics of newly established f our hepatocellular carcinoma cell lines (SNU-739, SNU-761, SNU-878 and SNU-886) from Korean hepatocellular cancer patients.

METHODS: Morphologic and genetic studies were done.

RESULTS: All four lines grew as a monolayer with an adherent pat tern, and their doubling times ranged from 20 to 29 h. The viability rate was relatively high (88%-94%). Neither mycoplasmal nor bacterial contamination was present. The lines showed different patterns in fingerprinting analysis. The hepatitis B virus (HBV) DNA was integrated in the genomes of all four lines, and in all of them HBx, HBc and HBs transcripts were detected by reverse transcriptase-PCR methods. Among the three cell lines used as control (Hep 3B, SK Hep1 and Hep G2), only Hep 3B showed HBx expression, and this line was used as a HBV integrated control. The RNA of albumin was detected in three lines (SNU-761, SNU- 878 and SNU-886), that of transferrin in two lines (SNU-878, SNU-886), and that of IGF- II was detected in none of the cell lines.

CONCLUSION: These well characterized cell lines may be very useful for studying the biology of hepatocellular carcinoma in association with the hepatitis B virus.

Interactions between hepatitis B virus infection and exposure to aflatoxins in the development of hepatocellular carcinoma: a molecular epidemiological approach

Aflatoxins and hepatitis B virus (HBV) are major risk factors for hepatocellular carcinoma (HCC) in high incidence areas for this cancer, namely southeast Asia and parts of Africa. There is evidence from both epidemiological studies and animal models that the two factors can act synergistically to increase the risk of HCC. The cellular and molecular mechanism of the interaction between these two factors is as yet undefined. However, one possible mechanism attested to by studies in HBV transgenic mice is that chronic liver injury alters the expression of specific carcinogen metabolising enzymes thus modulating the binding of aflatoxin to DNA in hepatocytes. The high levels of aflatoxin exposure which occur in many areas of the world where chronic HBV infection is endemic indicate that measures to reduce aflatoxin exposure would contribute to reducing HCC incidence. In preliminary studies, Guinea-Conakry have established baseline data for the implementation of a community-based intervention study to evaluate the effectiveness of improved post-harvest processing and storage of the groundnut crop, a major source of aflatoxins. Aflatoxin-albumin adducts were measured in 423 sera from individuals living in the four natural geographic zones of Guinea. More than 95% of the serum samples were positive for this biomarker and highest exposures were found in Lower Guinea where groundnuts are consumed as a dietary staple. Variations in mean levels between villages within a geographic region did not vary greatly. HBV infection was endemic in all regions with an overall prevalence of 16.7% chronic carriers. Thus in this population both HBV vaccination and reduction in aflatoxin exposure would be beneficial in decreasing morbidity and mortality from liver disease.

High, persistent hepatocellular proliferation and apoptosis precede hepatocarcinogenesis in growth hormone transgenic mice

AIMS/BACKGROUND

Growth hormone (GH) transgenic mice are known to develop hepatocellular adenomas and carcinomas. In order to understand more about hepatocarcinogenesis in the GH-transgenic mouse model we quantitated the rates of hepatocellular proliferation and apoptosis in these mice.

METHODS

Two lines of GH-transgenic mice and non-transgenic control mice were generated and sacrificed at regular intervals between one and nine months. Hepatocellular replication was measured by in vivo incorporation of bromodeoxyuridine (BrdU) and counting BrdU-positive nuclei in histological liver sections. Serial sections taken from these mouse livers were also assessed for rates of hepatocellular apoptosis using the in situ end-labelling of fragmented DNA (TUNEL) method.

RESULTS

High levels of hepatocellular replication were sustained life-long in this model. Increased rates of hepatocellular proliferation preceded the onset of hepatic inflammation, a prominent feature in the liver pathology of GH-transgenic mice. In tumour tissue, cellular proliferation was up to 17-fold greater than in surrounding non-tumour tissue. Apoptosis rates were also elevated in non-tumour regions of GH-transgenic mouse livers compared to controls. Interestingly, large dysplastic hepatocytes were common in the fraction of cells undergoing apoptosis, especially in older mice with inflamed livers. The increase in the rate of hepatocellular apoptosis in GH-transgenic animals largely balanced the augmented levels of proliferation seen in these mice. In tumour tissue, however, the profound increase in the number of proliferating tumour cells outstripped the increase in apoptosis.

CONCLUSION

Relatively high and enduring levels of hepatocellular replication and apoptosis precede hepatocarcinogenesis in GH-transgenic mice. Increased cellular proliferation and resistance to apoptosis were evident in tumour growth in older animals.

Cell-based and animal models for hepatitis B and C viruses

Reliable cell-based assays and animal models have been developed for evaluating agents against hepatitis B virus. Although much progress has been made, in vitro and in vivo assays for hepatitis C virus are still on the horizon. Advances towards establishing inexpensive and reliable experimental models have accelerated the development of therapeutic modalities for these life-threatening viral infections. The characterization of well-defined viral targets coupled with improved molecular diagnostic technologies have illuminated this field.

Repression of hepatitis B virus X gene expression by hammerhead ribozymes

The X protein (HBx) of human hepatitis B virus (HBV) is a transcriptional activator protein. The HBx protein plays an important role in viral replication in HBV infected cells and the liver diseases including hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Therefore, the repression of HBx gene expression by hammerhead ribozymes may be a good way to inhibit HBV replication and cure HBV-related liver diseases. We designed two hammerhead ribozymes, RzA and RzB, to cleave target sites at nucleotides 114 and 309 in the HBx open reading frame (ORF), respectively. In vitro, RzA and RzB cleaved HBx RNAs at their target sites up to 52 and 75%, respectively; however, the disabled ribozymes (dRzs) which have mutations in the catalytic site did not cleave the target RNAs at all. When each of the ribozymes were cotransfected into HepG2 cells with HBx expression plasmid, RzA and RzB reduced the level of HBx mRNA to 40 and 57%, respectively. The transactivation activity of HBx protein was also reduced dramatically by the ribozymes. These results suggest that the hammerhead ribozymes, RzA and RzB, can be used for the gene therapy of liver diseases caused by HBV.

Altered expression of hepatic carcinogen metabolizing enzymes with liver injury in HBV transgenic mouse lineages expressing various amounts of hepatitis B surface antigen

AIMS/BACKGROUND

The objective of this work was to evaluate the possible modulation of carcinogen metabolizing enzymes in relation to chronic infection by hepatitis B virus (HBV). This was to test whether enzyme level is altered in association with HBV gene expression per se or only when that expression was associated with an induction of liver injury.

METHODS

For this purpose, we studied four different HBV transgenic mouse lineages (23.3, 45.2, 50.4 and 107.5) that express the transgene encoding for the large envelope protein (HBsAg) at different levels. These lineages exhibit an associated liver injury which progresses with age and is positively correlated with the degree of accumulation of HBsAg in the hepatocytes. The modulation of levels of cytochrome P450 (1a, 2a-5, 2b, 2c, 3A4 and 2E1) and glutathione S-transferases (GST alpha and pi) involved in carcinogen metabolism was examined by immunohistochemistry in these lineages.

RESULTS

While we observed an increase in staining intensity of P450s 1-a and 2a-5 in lineages expressing cytopathic amounts of HBsAg (lineages 50.4 and 45.2), we only observed minor changes or no changes at all for the other lineages (23.3 and 107.5). Staining with antibodies to cytosolic pi class GST demonstrated an increase in older mice, although no major alterations were observed for GST alpha.

CONCLUSIONS

These results suggest that liver cell injury induced by accumulation of HBV antigens can result in the induction of some carcinogen metabolizing enzymes and this may be one mechanism of chemical-viral interaction in hepatocarcinogenesis.

Enhanced duck hepatitis B virus gene expression following aflatoxin B1 exposure

Epidemiological studies have suggested synergistic interactions between chronic hepatitis B virus (HBV) infection and aflatoxin B1 (AFB1) exposure in the etiology of hepatocellular carcinoma (HCC), although the molecular mechanisms of their interactions are still not understood. The aim of this study was to use the Pekin duck model to investigate the impact of AFB1 exposure on duck hepatitis B virus (DHBV) replication during the early stages of virus-carcinogen interactions. Six-week-old chronic DHBV-carrier or uninfected ducks were exposed to AFB1 for 5 weeks or treated with dimethylsulfoxide (DMSO) as a control. Animals were observed for 6 to 13 weeks after AFB1 treatment to study the influence of AFB1 exposure on DHBV replication and liver pathologies. Histological analysis showed more marked changes in the livers of AFB1-treated ducks, and these were enhanced by DHBV infection. A significant increase in serum and liver DHBV DNA level was observed in AFB1-treated ducks as compared with DMSO-treated controls. In addition, viral RNAs, in particular the pregenomic RNA that is the template of viral replication, and intrahepatic DHBV DNA replicative intermediates, were significantly increased by AFB1 treatment. Moreover, an overexpression and accumulation of DHBV large envelope (L) protein was observed in the hepatocytes of AFB1-exposed animals. The in vitro study has further confirmed an increase in intracellular viral DNA and in virus release in AFB1-treated primary duck hepatocytes. Taken together, our results indicate that AFB1 exposure leads to an increase in virus gene expression associated with intrahepatic accumulation of DHBV L protein and enhanced liver pathology.