Hepatitis B viruses and hepatocellular carcinoma

Adenovirus Vectors Expressing Eight Multiplex Guide RNAs of CRISPR/Cas9 Efficiently Disrupted Diverse Hepatitis B Virus Gene Derived from Heterogeneous Patient

Hepatitis B virus (HBV) chronically infects more than 240 million people worldwide, causing chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Genome editing using CRISPR/Cas9 could provide new therapies because it can directly disrupt HBV genomes. However, because HBV genome sequences are highly diverse, the identical target sequence of guide RNA (gRNA), 20 nucleotides in length, is not necessarily present intact in the target HBV DNA in heterogeneous patients. Consequently, possible genome-editing drugs would be effective only for limited numbers of patients. Here, we show that an adenovirus vector (AdV) bearing eight multiplex gRNA expression units could be constructed in one step and amplified to a level sufficient for in vivo study with lack of deletion. Using this AdV, HBV X gene integrated in HepG2 cell chromosome derived from a heterogeneous patient was cleaved at multiple sites and disrupted. Indeed, four targets out of eight could not be cleaved due to sequence mismatches, but the remaining four targets were cleaved, producing irreversible deletions. Accordingly, the diverse X gene was disrupted at more than 90% efficiency. AdV containing eight multiplex gRNA units not only offers multiple knockouts of genes, but could also solve the problems of heterogeneous targets and escape mutants in genome-editing therapy.

Hepatitis B Virus DNA Integration Occurs Early in the Viral Life Cycle in an In Vitro Infection Model via Sodium Taurocholate Cotransporting Polypeptide-Dependent Uptake of Enveloped Virus Particles

Chronic infection by hepatitis B virus (HBV) is the major contributor to liver disease worldwide. Though HBV replicates via a nuclear episomal DNA (covalently closed circular DNA [cccDNA]), integration of HBV DNA into the host cell genome is regularly observed in the liver in infected patients. While reported as a prooncogenic alteration, the mechanism(s) and timing of HBV DNA integration are not well understood, chiefly due to the lack of in vitro infection models that have detectable integration events. In this study, we have established an in vitro system in which integration can be reliably detected following HBV infection. We measured HBV DNA integration using inverse nested PCR in primary human hepatocytes, HepaRG-NTCP, HepG2-NTCP, and Huh7-NTCP cells after HBV infection. Integration was detected in all cell types at a rate of >1 per 10,000 cells, with the most consistent detection in Huh7-NTCP cells. The integration rate remained stable between 3 and 9 days postinfection. HBV DNA integration was efficiently blocked by treatment with a 200 nM concentration of the HBV entry inhibitor Myrcludex B, but not with 10 μM tenofovir, 100 U of interferon alpha, or a 1 μM concentration of the capsid assembly inhibitor GLS4. This suggests that integration of HBV DNA occurs immediately after infection of hepatocytes and is likely independent of de novo HBV genome replication in this model. Site analysis revealed that HBV DNA integrations were distributed over the entire human genome. Further, integrated HBV DNA sequences were consistent with double-stranded linear HBV DNA being the major precursor. Thus, we have established an in vitro system to interrogate the mechanisms of HBV DNA integration.IMPORTANCE Hepatitis B virus (HBV) is a common blood-borne pathogen and, following a chronic infection, can cause liver cancer and liver cirrhosis. Integration of HBV DNA into the host genome occurs in all known members of the Hepadnaviridae family, despite this form not being necessary for viral replication. HBV DNA integration has been reported to drive liver cancer formation and persistence of virus infection. However, when and the mechanism(s) by which HBV DNA integration occurs are not clear. In this study, we have developed and characterized an in vitro system to reliably detect HBV DNA integrations that result from a true HBV infection event and that closely resemble those found in patient tissues. Using this model, we showed that integration occurs when the infection is first established. Importantly, we provide here a system to analyze molecular factors involved in HBV integration, which can be used to develop strategies to halt its formation.

Hit-And-Run Mechanism of HBV-Mediated Progression to Hepatocellular Carcinoma

Aim and background

Hepatitis B virus is implicated in the development of hepatocellular caracinoma. No oncogenes have been identified within the viral genome. Furthermore, it frequently fragments after integration into the hepatocyte genome. Simultaneous investigations of hepatitis B virus integration patterns and genetic changes in precancerous tissues are important to understand the role played by hepatitis B virus integration in hepatocellular caracinoma.

Method

We used a combination approach of dual characterization of highly polymorphic loci and the change in hepatitis B virus-DNA integration pattern. Large regenerative nodules were dissected from 6 explanted hepatitis B virus infected cirrhotic livers. Nodules within each liver segment were schematically mapped and histopathologically analyzed. Genomic DNA from each nodule was analyzed for hepatitis B virus integration and the genetic stability of 12 microsatellite loci including D3S2321, D8S1022, D17S1159, D4S2281, D5S1/2, D16S675, D16S685, D16S490, D16S526, D16S673, D16S677 and D16S690.

Results

Data from different liver segments revealed few viral integrations and average allele loss. The most exciting results came from a segment containing a set of clonally and spatially related nodules having similar histologic features, a progressive lineage of allele loss, HBV integration and loss of integration.

Conclusions

This model portrait, a scenario of genetic events that precede tumor formation where the acquisition and loss of hepatitis B virus integrations in clonally related regenerative nodules, might explain how the virus acts as a hit-and-run mutagen.

Luteolin-7-O-Glucoside Present in Lettuce Extracts Inhibits Hepatitis B Surface Antigen Production and Viral Replication by Human Hepatoma Cells in Vitro

Hepatitis B virus (HBV) infection is endemic in Asia and chronic hepatitis B (CHB) is a major public health issue worldwide. Current treatment strategies for CHB are not satisfactory as they induce a low rate of hepatitis B surface antigen (HBsAg) loss. Extracts were prepared from lettuce hydroponically cultivated in solutions containing glycine or nitrate as nitrogen sources. The lettuce extracts exerted potent anti-HBV effects in HepG2 cell lines in vitro, including significant HBsAg inhibition, HBV replication and transcription inhibition, without exerting cytotoxic effects. When used in combination interferon-alpha 2b (IFNα-2b) or lamivudine (3TC), the lettuce extracts synergistically inhibited HBsAg expression and HBV replication. By using differential metabolomics analysis, Luteolin-7-O-glucoside was identified and confirmed as a functional component of the lettuce extracts and exhibited similar anti-HBV activity as the lettuce extracts in vitro. The inhibition rate on HBsAg was up to 77.4%. Moreover, both the lettuce extracts and luteolin-7-O-glucoside functioned as organic antioxidants and, significantly attenuated HBV-induced intracellular reactive oxygen species (ROS) accumulation. Luteolin-7-O-glucoside also normalized ROS-induced mitochondrial membrane potential damage, which suggests luteolin-7-O-glucoside inhibits HBsAg and HBV replication via a mechanism involving the mitochondria. Our findings suggest luteolin-7-O-glucoside may have potential value for clinical application in CHB and may enhance HBsAg and HBV clearance when used as a combination therapy.

Historical review of the causes of cancer

In the early 1900s, numerous seminal publications reported that high rates of cancer occurred in certain occupations. During this period, work with infectious agents produced only meager results which seemed irrelevant to humans. Then in the 1980s ground breaking evidence began to emerge that a variety of viruses also cause cancer in humans. There is now sufficient evidence of carcinogenicity in humans for human T-cell lymphotrophic virus, human immunodeficiency virus, hepatitis B virus, hepatitis C virus, human papillomavirus, Epstein-Barr virus, and human herpes virus 8 according to the International Agency for Research on Cancer (IARC). Many other causes of cancer have also been identified by the IARC, which include: Sunlight, tobacco, pharmaceuticals, hormones, alcohol, parasites, fungi, bacteria, salted fish, wood dust, and herbs. The World Cancer Research Fund and the American Institute for Cancer Research have determined additional causes of cancer, which include beta carotene, red meat, processed meats, low fibre diets, not breast feeding, obesity, increased adult height and sedentary lifestyles. In brief, a historical review of the discoveries of the causes of human cancer is presented with extended discussions of the difficulties encountered in identifying viral causes of cancer.

Oncogenic viruses and hepatocellular carcinoma

About 80% of hepatocellular carcinoma (HCC) is caused by hepatitis B virus (HBV) and/or hepatitis C virus (HCV) infections especially in the setting of established cirrhosis or advanced fibrosis, making HCC prevention a major goal of antiviral therapy. HCC tumors are highly complex and heterogeneous resulting from the aberrant function of multiple molecular pathways. The roles of HCV or HBV in promoting HCC development are still either directly or indirectly are still speculative, but the evidence for both effects is compelling. In patients with chronic hepatitis viral infection, cirrhosis is not a prerequisite for tumorigenesis.

Patients with chronic hepatitis C without advanced fibrosis and hepatocellular carcinoma: a retrospective clinical-pathological study

BACKGROUND

There are very few studies on the incidence and risk factors of hepatitis C virus (HCV)-induced hepatocellular carcinoma (HCC) in the absence of advanced fibrosis. Our objective was to identify the clinical-pathological features of these patients.

METHODS

We retrospectively reviewed 162 patients admitted to our hospital for HCV-related HCC between 2000 and 2010. Patients with hepatitis of other aetiologies, human immunodeficiency virus co-infection, or treated with interferon were excluded. We compared demographic, laboratory, clinical and outcome parameters of patients with and without advanced fibrosis.

RESULTS

137 patients had advanced fibrosis (85%). Median age was higher in the advanced fibrosis vs. the non-advanced fibrosis group (62 vs. 65 years, respectively; p = 0.025). Steatosis was significantly more frequent in patients with advanced fibrosis compared to those without advanced fibrosis (43% vs. 20%, respectively; p = 0.032). Independent predictors associated to the occurrence of HCC in patients without advanced fibrosis were hepatitis B core antigen (odds ratio: 3.86; p = 0.044) and duration of hepatitis C infection (odds ratio: 1.21; p = 0.003).

CONCLUSIONS

Risk factors such as steatosis or diabetes were not frequent in patients without advanced fibrosis. Further studies are needed to evaluate the role of occult hepatitis B and the duration of hepatitis infection in patients with HCC and chronic hepatitis C without advanced fibrosis.

Role of hepatitis B virus DNA integration in human hepatocarcinogenesis

Liver cancer ranks sixth in cancer incidence, and is the third leading cause of cancer-related deaths worldwide. Hepatocellular carcinoma (HCC) is the most common type of liver cancer, which arises from hepatocytes and accounts for approximately 70%-85% of cases. Hepatitis B virus (HBV) frequently causes liver inflammation, hepatic damage and subsequent cirrhosis. Integrated viral DNA is found in 85%-90% of HBV-related HCCs. Its presence in tumors from non-cirrhotic livers of children or young adults further supports the role of viral DNA integration in hepatocarcinogenesis. Integration of subgenomic HBV DNA fragments into different locations within the host DNA is a significant feature of chronic HBV infection. Integration has two potential consequences: (1) the host genome becomes altered (“cis” effect); and (2) the HBV genome becomes altered (“trans” effect). The cis effect includes insertional mutagenesis, which can potentially disrupt host gene function or alter host gene regulation. Tumor progression is frequently associated with rearrangement and partial gain or loss of both viral and host sequences. However, the role of integrated HBV DNA in hepatocarcinogenesis remains controversial. Modern technology has provided a new paradigm to further our understanding of disease mechanisms. This review summarizes the role of HBV DNA integration in human carcinogenesis.

Contributory role of viral infection in congenital tumour development

Congenital tumours are a group of distinct infrequent disorders whose exact aetiologies have not clearly been understood so far. Viral infection seems to be one of the key factors involved in the carcinogenesis of certain tumours. This study was performed to assess whether viral DNAs are present in the congenital tumours or not. Nucleic acid from 31 congenital tumours was extracted. Detection of Epstein–Barr virus, Cytomegalovirus (CMV), adenovirus, Herpes simplex virus 1 (HSV1) and 2, Human herpes virus 6 (HHV6), and BK virus was performed using polymerase chain reaction. Viral nucleic acid was detected in eight subjects (25.8%), mostly adenovirus, CMV, and HHV6. Despite their low frequencies, a possible role could be identified for viral infections in tumour development or progression.

Animal Models of Human Viral Diseases

As the threat of exposure to emerging and reemerging viruses within a naive population increases, it is vital that the basic mechanisms of pathogenesis and immune response be thoroughly investigated. By using animal models in this endeavor, the response to viruses can be studied in a more natural context to identify novel drug targets, and assess the efficacy and safety of new products. This is especially true in the advent of the Food and Drug Administration's animal rule. Although no one animal model is able to recapitulate all the aspects of human disease, understanding the current limitations allows for a more targeted experimental design. Important facets to be considered before an animal study are the route of challenge, species of animals, biomarkers of disease, and a humane endpoint. This chapter covers the current animal models for medically important human viruses, and demonstrates where the gaps in knowledge exist.

Deep sequencing of the hepatitis B virus in hepatocellular carcinoma patients reveals enriched integration events, structural alterations and sequence variations

Chronic hepatitis B virus (HBV) infection is epidemiologically associated with hepatocellular carcinoma (HCC), but its role in HCC remains poorly understood due to technological limitations. In this study, we systematically characterize HBV in HCC patients. HBV sequences were enriched from 48 HCC patients using an oligo-bead-based strategy, pooled together and sequenced using the FLX-Genome-Sequencer. In the tumors, preferential integration of HBV into promoters of genes (P < 0.001) and significant enrichment of integration into chromosome 10 (P < 0.01) were observed. Integration into chromosome 10 was significantly associated with poorly differentiated tumors (P < 0.05). Notably, in the tumors, recurrent integration into the promoter of the human telomerase reverse transcriptase (TERT) gene was found to correlate with increased TERT expression. The preferred region within the HBV genome involved in integration and viral structural alteration is at the 3'-end of hepatitis B virus X protein (HBx), where viral replication/transcription initiates. Upon integration, the 3'-end of the HBx is often deleted. HBx-human chimeric transcripts, the most common type of chimeric transcripts, can be expressed as chimeric proteins. Sequence variation resulting in non-conservative amino acid substitutions are commonly observed in HBV genome. This study highlights HBV as highly mutable in HCC patients with preferential regions within the host and virus genome for HBV integration/structural alterations.

Relative telomere length: a novel non-invasive biomarker for the risk of non-cirrhotic hepatocellular carcinoma in patients with chronic hepatitis B infection

BACKGROUND AND AIMS

Telomere length has emerged as a promising risk predictor of various cancers including hepatocellular carcinoma (HCC). However, the majority of studies in this area measured telomere length in hepatocytes and one in lymphocytes with conflicting results. Moreover, no studies have been reported on using circulating DNA telomere length as a non-invasive HCC biomarker.

METHODS

We conducted a nested case-control study to determine the relative telomere length (RTL) in serum DNA from 140 hepatitis B virus (HBV)-related HCC cases and 280 frequency-matched cancer-free HBV controls.

RESULTS

Cases had a significantly longer RTL (median, 0.31; range, 0.02-2.31) than controls (median, 0.20; range, 0.01-1.60) (P = 0.003). Consistently, longer RTLs conferred a significantly increased HCC risk compared to short RTLs in a univariate logistic regression analysis (odds ratio [OR] = 1.55, 95% confidence interval [CI] = 1.02-2.33, P = 0.038). This association attenuated after multivariate adjustment (OR = 1.40, 95% CI = 0.90-2.19, P = 0.132). In a quartile analysis, a significant dose-response relationship was noted in univariate analysis (P(trend) = 0.017) which was again attenuated in multivariate analysis (P(trend) = 0.079). Further analyses revealed that the significant association between serum RTL and HCC risk was evident in non-cirrhotic (OR = 3.54, 95% CI 1.58-7.93 P = 0.002), but not cirrhotic (OR = 0.95, 95% CI 0.55-1.64, P = 0.860) HBV patients. Moreover, the significantly increased HCC risk conferred by cirrhosis was modulated by RTL with a significant interaction effect (P(interaction) = 0.013).

CONCLUSIONS

RTL in circulating cell-free serum DNA could potentially be used as a novel non-invasive biomarker for non-cirrhotic HCC. Prospective cohort studies are warranted to validate this finding and assess its clinical significance in HCC prevention.

Enhancement of canonical Wnt/β-catenin signaling activity by HCV core protein promotes cell growth of hepatocellular carcinoma cells

BACKGROUND

The Hepatitis C virus (HCV) core protein has been implicated as a potential oncogene or a cofactor in HCV-related hepatocellular carcinoma (HCC), but the underlying mechanisms are unknown. Overactivation of the Wnt/β-catenin signaling is a major factor in oncogenesis of HCC. However, the pathogenesis of HCV core-associated Wnt/β-catenin activation remains to be further characterized. Therefore, we attempted to determine whether HCV core protein plays an important role in regulating Wnt/β-catenin signaling in HCC cells.

METHODOLOGY

Wnt/β-catenin signaling activity was investigated in core-expressing hepatoma cells. Protein and gene expression were examined by Western blot, immunofluorescence staining, RT-qPCR, and reporter assay.

PRINCIPAL FINDINGS

HCV core protein significantly enhances Tcf-dependent transcriptional activity induced by Wnt3A in HCC cell lines. Additionally, core protein increases and stabilizes β-catenin levels in hepatoma cell line Huh7 through inactivation of GSK-3β, which contributes to the up-regulation of downstream target genes, such as c-Myc, cyclin D1, WISP2 and CTGF. Also, core protein increases cell proliferation rate and promotes Wnt3A-induced tumor growth in the xenograft tumor model of human HCC.

CONCLUSIONS/SIGNIFICANCE

HCV core protein enhances Wnt/β-catenin signaling activity, hence playing an important role in HCV-associated carcinogenesis.

Models of hepatocellular carcinoma and biomarker strategy

The overwhelming need to improve preclinical models in oncology has stimulated research efforts to refine and validate robust orthotopic models that closely mimic the disease population and therefore have the potential to better predict clinical outcome with novel therapies. Sophisticated technologies including bioluminescence, contrast enhanced ultrasound imaging, positron emission tomography, computed tomography and magnetic resonance imaging have been added to existing serum- and histology-based biomarkers to assist with patient selection and the design of clinical trials. The rationale for the use of human hepatocellular carcinoma (HCC) cell lines, implementation of xenograft and orthotopic animal models and utilization of available biomarkers have been discussed, providing guidelines to facilitate preclinical research for the development of treatments for HCC patients.

Hepatitis B and C virus-related carcinogenesis

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection are the most important causes of hepatocellular carcinoma (HCC), accounting for the majority of the cases worldwide. The geographical distribution of HCC therefore coincides with the distribution of HBV and HCV infections in those areas. Similar to nonviral liver diseases, HBV and HCV infection can cause chronic injury to the liver, with subsequent progression to severe fibrosis and cirrhosis. The presence of cirrhosis is a major risk factor for the development of HCC. However, HCC can occur in the absence of cirrhosis, suggesting that both HBV and HCV may be directly involved in hepatocarcinogenesis. Several HBV factors have been implicated in hepatocarcinogenesis, including the HBx gene, the pre-S2/S gene and the HBV spliced protein. Furthermore, HBV can be integrated into the host genome, leading to changes in genomic function or chromosomal instability. By contrast to HBV, HCV cannot integrate into the host genome. Various HCV proteins, including the core, envelope and nonstructural proteins, have been shown to have oncogenic properties. For HBV infection, antiviral therapy and vaccination have been shown to decrease the risk of HCC. Antiviral therapy for HCV can also reduce the risk of HCC.

Hepatitis C-associated hepatocellular carcinomas in non-cirrhotic livers

Chronic hepatitis C viral infection can lead to cirrhosis and hepatocellular carcinoma. It is generally believed that hepatitis C infection is not oncogeneic per se, but that the presence of cirrhosis determines the increased risk for hepatocellular carcinoma. However, a search of surgical pathology files from two large tertiary care centers for the years 2001-2008 identified a total of 18 hepatocellular carcinomas in non-cirrhotic livers with chronic hepatitis C infection. In six cases the background livers showed bridging fibrosis, while the remainder showed lower stages of fibrosis. Cases were negative for clinical and serological evidence of hepatitis B co-infection, and occult hepatitis B test was negative by PCR of formalin-fixed, paraffin embedded tissues. The tumors were also negative for TP53, exon 7, codon 249 mutations, a characteristic mutation strongly linked to aflatoxin exposure. The hepatocellular carcinomas had typical histology with no enrichment for unusual growth patterns or histological features. Among all resected hepatocellular carcinomas in non-cirrhotic livers over this time period, the prevalence of 16% with HCV infection was significantly greater than that expected by chance. In conclusion, these results demonstrate that hepatocellular carcinomas can arise in livers chronically infected with hepatitis C but without cirrhosis. These findings raise the possibility that in some cases hepatitis C infection and inflammation can be directly oncogeneic. It is also possible that established cirrhosis may have regressed in some cases. Regardless of the mechanism, these findings highlight an important and previously under-recognized risk for hepatocellular carcinoma in HCV-infected individuals who do not have cirrhosis.

Liver cell transformation in chronic HBV infection

Epidemiological studies have provided overwhelming evidence for a causal role of chronic HBV infection in the development of hepatocellular carcinoma (HCC), but the molecular mechanisms underlying virally-induced tumorigenesis remain largely debated. In the absence of a dominant oncogene encoded by the HBV genome, indirect roles have been proposed, including insertional activation of cellular oncogenes by HBV DNA integration, induction of genetic instability by viral integration or by the regulatory protein HBx, and long term effects of viral proteins in enhancing immune-mediated liver disease. In this chapter, we discuss different models of HBV-mediated liver cell transformation based on animal systems of hepadnavirus infection as well as functional studies in hepatocyte and hepatoma cell lines. These studies might help identifying the cellular effectors connecting HBV infection and liver cell transformation.

Human oncogenic viruses: hepatitis B and hepatitis C viruses and their role in hepatocarcinogenesis

Chronic infections caused by hepatitis B virus (HBV) and/or hepatitis C virus (HCV) are the main risk factors for the development of hepatocellular carcinoma (HCC) in humans. Both viruses cause a wide spectrum of clinical manifestations ranging from healthy carrier state to acute and chronic hepatitis, liver cirrhosis, and HCC. HBV and HCV belong to different viral families (Hepadnoviridae and Flaviviridae, respectively); they are characterized by different genetic structures. Clinical manifestations of these viral infections result from the interaction between these viruses and host hepatocytes (i.e. between viral and cell genomes). Proteins encoded by both viruses play an important role in processes responsible for immortalization and transformation of these cells. Chronic inflammation determined by host immune response to the viral infection, hepatocyte death and their compensatory proliferation, as well as modulation of expression of some regulatory proteins of the cell (growth factors, cytokines, etc.) are the processes that play the major role in liver cancer induced by HBV and HCV.

Inhibition of hepadnavirus reverse transcriptase-epsilon RNA interaction by porphyrin compounds

The hepatitis B virus (HBV) reverse transcriptase (RT) plays a multitude of fundamental roles in the viral life cycle and is the key target in the development of anti-HBV chemotherapy. We report here that the endogenous small molecule iron protoporphyrin IX (hemin) and several related porphyrin compounds potently blocked a critical RT interaction with the viral RNA packaging signal/origin of replication, called epsilon. As RT-epsilon interaction is essential for the initiation of viral reverse transcription, which is primed by RT itself (protein priming), the porphyrin compounds dramatically suppressed the protein-priming reaction. Further studies demonstrated that these compounds could target the unique N-terminal domain of the RT protein, the so-called terminal protein. Hemin and related porphyrin compounds thus represent a novel class of agents that can block HBV RT functions through a mechanism and target that are completely distinct from those of existing anti-HBV drugs.

Non-cytolytic antigen clearance in DNA-vaccinated mice with electroporation

AIM

To explore the potential of electroporation (EP)-mediated hepatitis B virus (HBV) DNA vaccination for the treatment of chronic HBV infection.

METHODS

BALB/c mice were vaccinated with HBV DNA vaccine encoding for the HBV preS(2)-S antigen, combined with or without EP. HBV surface antigen expression plasmid was administered into mice liver via a hydrodynamic injection to mimic HBV infection. The clearance of antigen in the serum and liver was detected by ELISA assay and immunohistochemical staining. The histopathology of the liver tissues was examined by HE staining and serum alanine aminotransferase assay.

RESULTS

The immunogenicity of HBV DNA vaccine encoding for the HBV preS(2)- S antigen can be improved by EP-mediated vaccine delivery. The elicited immune responses can indeed reduce the expression of HBV surface antigen (HBsAg) in hepatocytes of the mouse model that was transfected to express HBsAg using the hydrodynamic injection method. The antigen clearance process did not cause significant toxicity to liver tissue, suggesting a non-cytolytic mechanism.

CONCLUSION

The EP-aided DNA vaccination may have potential in mediating viral clearance in chronic hepatitis B patients.

Thermodynamics and NMR studies on Duck, Heron and Human HBV encapsidation signals

Hepatitis B virus (HBV) replication is initiated by binding of its reverse transcriptase (P) to the apical stem-loop (AL) and primer loop (PL) of epsilon, a highly conserved RNA element at the 5'-end of the RNA pregenome. Mutation studies on duck/heron and human in vitro systems have shown similarities but also differences between their P-epsilon interaction. Here, NMR and UV thermodynamic data on AL (and PL) from these three species are presented. The stabilities of the duck and heron ALs were found to be similar, and much lower than that of human. NMR data show that this low stability stems from an 11-nt internal bulge destabilizing the stem of heron AL. In duck, although structured at low temperature, this region also forms a weak point as its imino resonances broaden to disappearance between 30 and 35 degrees C well below the overall AL melting temperature. Surprisingly, the duck- and heron ALs were both found to be capped by a stable well-structured UGUU tetraloop. All avian ALs are expected to adhere to this because of their conserved sequence. Duck PL is stable and structured and, in view of sequence similarities, the same is expected for heron - and human PL.

Solution structure of the apical stem-loop of the human hepatitis B virus encapsidation signal

Hepatitis B virus (HBV) replication is initiated by HBV RT binding to the highly conserved encapsidation signal, epsilon, at the 5′ end of the RNA pregenome. Epsilon contains an apical stem–loop, whose residues are either totally conserved or show rare non-disruptive mutations. Here we present the structure of the apical stem–loop based on NOE, RDC and ¹H chemical shift NMR data. The ¹H chemical shifts proved to be crucial to define the loop conformation. The loop sequence 5′-CUGUGC-3′ folds into a UGU triloop with a CG closing base pair and a bulged out C and hence forms a pseudo-triloop, a proposed protein recognition motif. In the UGU loop conformations most consistent with experimental data, the guanine nucleobase is located on the minor groove face and the two uracil bases on the major groove face. The underlying helix is disrupted by a conserved non-paired U bulge. This U bulge adopts multiple conformations, with the nucleobase being located either in the major groove or partially intercalated in the helix from the minor groove side, and bends the helical stem. The pseudo-triloop motif, together with the U bulge, may represent important anchor points for the initial recognition of epsilon by the viral RT.

Hepatitis B virus reverse transcriptase and epsilon RNA sequences required for specific interaction in vitro

Initiation of reverse transcription and nucleocapsid assembly in hepatitis B virus (HBV) depends on the specific recognition of an RNA signal (the packaging signal, epsilon) on the pregenomic RNA by the viral reverse transcriptase (RT). Using an in vitro reconstitution system whereby the cellular heat shock protein 90 chaperone system activates recombinant HBV RT for specific epsilon binding, we have defined the protein and RNA sequences required for specific HBV RT-epsilon interaction in vitro. Our results indicated that approximately 150 amino acid residues from the terminal protein domain and 230 from the RT domain were necessary and sufficient for epsilon binding. With respect to the epsilon RNA sequence, its internal bulge and, in particular, the first nucleotide (C) of the bulge were specifically required for RT binding. Sequences from the upper portion of the lower stem and the lower portion of the upper stem also contributed to RT binding, as did the base pairing of the upper portion and the single unpaired U residue of the upper stem. Surprisingly, the apical loop of epsilon, known to be required for RNA packaging, was entirely dispensable for RT binding. A comparison of the requirements for in vitro RT-epsilon interaction with those for in vivo pregenomic RNA (pgRNA) packaging clearly indicated that RT-epsilon interaction was necessary but not sufficient for pgRNA packaging. In addition, our results suggest that recognition of some epsilon sequences by the RT may be required specifically for viral DNA synthesis.

Animal models for the study of HBV replication and its variants

Enormous progresses in hepatitis B virus research have been made through the identification of avian and mammalian HBV related viruses, which offer ample opportunities for studies in naturally occurring hosts. However, none of these natural hosts belongs to the commonly used laboratory animals, and the development of various mouse strains carrying HBV transgenes offered unique opportunities to investigate some mechanisms of viral pathogenesis. Furthermore, the need to perform infection studies in a system harbouring HBV-permissive hepatocytes has lately led researchers to create new challenging human mouse chimera models of HBV infection. In this review, we will overview the type of animal models currently available in hepadnavirus research.

Lack of WHV integration nearby N-myc2 and in the downstream b3n and win loci in a considerable fraction of liver tumors with activated N-myc2 from naturally infected wild woodchucks

In liver tumors induced by chronic WHV infection in the WHV/woodchuck model of HBV infection, activation of genes of the myc family by WHV insertion has been well documented. Several studies have shown that N-myc2 is by far the most frequently involved, and in most cases, its transcriptional activation is due to WHV insertion nearby the gene. N-myc2 has been shown to be also activated by WHV insertion in two downstream loci, b3n and win. Although the extent of insertion in these latter loci in woodchuck tumors has not been investigated, their discovery has led to the notion that therein WHV insertion accounts for N-myc2 activation in the remaining tumors expressing the proto-oncogene in absence of any detectable alteration nearby the gene, a notion remained unproved and not further investigated yet. In the majority of cases, the above observations were derived from tumors developed in colony born laboratory bred woodchucks experimentally infected with standardized viral inocula, mostly of the same lineage. In the present work, we investigated a survey of liver tumors naturally developed in wild woodchucks with naturally acquired chronic WHV infection. Tumors had histological features of well to moderately differentiated HCCs. In most animals, multiple tumor nodules were observed; in the great majority of cases, they were shown to be independent tumors because their WHV integration patterns were not clonally related. 53 independent tumors were investigated for N-myc activation and WHV integration nearby N-myc genes and in the b3n and win loci. Comparison of our results with data from previous studies revealed that, in tumors from naturally infected wild woodchucks, the frequency of WHV integration nearby N-myc2 has a tendency to be lower and, in addition, N-myc2 activation is due to WHV integration nearby the gene significantly less frequently than in tumors from experimentally infected colony born animals (12/28, 43% vs. 15/20, 75%, P = 0.0397). These findings are likely related to the less uniform conditions as to infecting virus and host genetic background in naturally infected wild woodchucks with respect to experimentally infected colony born woodchucks and suggest that viral and/or host factors may influence the site of viral insertion finally detected in overt tumors. In addition, more than one third (11/28, 39%) tumors with activated N-myc2 transcription did not show rearrangement either nearby the gene, or in b3n or in win. These findings challenge the notion that integration in the downstream b3n and win loci is responsible for N-myc2 activation in tumors lacking insertion nearby N-myc2 and suggest that in a considerable fraction of liver tumors, at least from wild woodchucks, N-myc2 activation might be due either to WHV integration in further regions of the N-myc2 chromosomal domain or to other mechanisms related or unrelated to viral insertion.

Infectious agents and cancer: criteria for a causal relation

Infectious agents, mainly viruses, are among the few known causes of cancer and contribute to a variety of malignancies worldwide. The agents and cancers considered here are human papillomaviruses (cervical carcinoma); human polyomaviruses (mesotheliomas, brain tumors); Epstein-Barr virus (B-cell lymphoproliferative diseases and nasopharyngeal carcinoma); Kaposi's Sarcoma Herpesvirus (Kaposi's Sarcoma and primary effusion lymphomas); hepatitis B and hepatitis C viruses (hepatocellular carcinoma); Human T-cell Leukemia Virus-1 (T-cell leukemias); and helicobacter pylori (gastric carcinoma), which account for up to 20% of malignancies around the globe. The criteria most often used in determining causality are consistency of the association, either epidemiologic or on the molecular level, and oncogenicity of the agent in animal models or cell cultures. However use of these generally applied criteria in deciding on causality is selective, and the criteria may be weighted differently. Whereas for most of the tumor viruses the viral genome persists in an integrated or episomal form with a subset of viral genes expressed in the tumor cells, some agents (HBV, HCV, helicobacter) are not inherently oncogenic, but infection leads to transformation of cells by indirect means. For some malignancies the viral agent appears to serve as a cofactor (Burkitt's lymphoma-EBV; mesothelioma - SV(40)). For others the association is inconsistent (Hodgkin's Disease, gastric carcinomas, breast cancer-EBV) and may either define subsets of these malignancies, or the virus may act to modify phenotype of an established tumor, contributing to tumor progression rather than causing the tumor. In these cases and for the human polyomaviruses the association with malignancy is less consistent or still emerging. In contrast despite the potent oncogenic properties of some strains of human adenovirus in tissue culture and animals the virus has not been linked with any human cancers. Finally it is likely that more agents, most likely viruses, both known and unidentified, have yet to be implicated in human cancer. In the meantime study of tumorigenic infectious agents will continue to illuminate molecular oncogenic processes.

Requirement of heat shock protein 90 for human hepatitis B virus reverse transcriptase function

The initiation of reverse transcription and nucleocapsid assembly in hepatitis B virus (HBV) depends on the specific recognition of an RNA signal (the packaging signal, epsilon) on the pregenomic RNA (pgRNA) by the viral reverse transcriptase (RT). RT-epsilon interaction in the duck hepatitis B virus (DHBV) was recently shown to require the molecular chaperone complex, the heat shock protein 90 (Hsp90). However, the requirement for RT-epsilon interaction in the human HBV has remained unknown due to the inability to obtain a purified RT protein active in specific epsilon binding. We now report that Hsp90 is also required for HBV RT-epsilon interaction. Inhibition of Hsp90 led to diminished HBV pgRNA packaging into nucleocapsids in cells, which depends on RT-epsilon interaction. Furthermore, using truncated HBV RT proteins purified from bacteria and five purified Hsp90 chaperone factors, we have developed an in vitro RT-epsilon binding assay. Our results demonstrate that Hsp90, in a dynamic process that was dependent on ATP hydrolysis, facilitated RT-epsilon interaction in HBV, as in DHBV. Specific epsilon binding required sequences from both the amino-terminal terminal protein and the carboxy-terminal RT domain. Only the cognate HBV epsilon, but not the DHBV epsilon, could bind the HBV RT proteins. Furthermore, the internal bulge, but not the apical loop, of epsilon was required for RT binding. The establishment of a defined in vitro reconstitution system has now paved the way for future biochemical and structural studies to elucidate the mechanisms of RT-epsilon interaction and chaperone activation.

Expression profiling and differential screening between hepatoblastomas and the corresponding normal livers: identification of high expression of the PLK1 oncogene as a poor-prognostic indicator of hepatoblastomas

Hepatoblastoma is one of the most common malignant liver tumors in young children. Recent evidences have suggested that the abnormalities in Wnt signaling pathway, as seen in frequent mutation of the beta-catenin gene, may play a role in the genesis of hepatoblastoma. However, the precise mechanism to cause the tumor has been elusive. To identify novel hepatoblastoma-related genes for unveiling the molecular mechanism of the tumorigenesis, a large-scale cloning of cDNAs and differential screening of their expression between hepatoblastomas and the corresponding normal livers were performed. We constructed four full-length-enriched cDNA libraries using an oligo-capping method from the primary tissues which included two hepatoblastomas with high levels of alpha-fetoprotein (AFP), a hepatoblastoma without production of AFP, and a normal liver tissue corresponded to the tumor. Among the 10,431 cDNAs randomly picked up and successfully sequenced, 847 (8.1%) were the genes with unknown function. Of interest, the expression profile among the two subsets of hepatoblastoma and a normal liver was extremely different. A semiquantitative RT-PCR analysis showed that 86 out of 1188 genes tested were differentially expressed between hepatoblastomas and the corresponding normal livers, but that only 11 of those were expressed at high levels in the tumors. Notably, PLK1 oncogene was expressed at very high levels in hepatoblastomas as compared to the normal infant's livers. Quantitative real-time RT-PCR analysis for the PLK1 mRNA levels in 74 primary hepatoblastomas and 29 corresponding nontumorous livers indicated that the patients with hepatoblastoma with high expression of PLK1 represented significantly poorer outcome than those with its low expression (5-year survival rate: 55.9 vs 87.0%, respectively, p=0.042), suggesting that the level of PLK1 expression is a novel marker to predict the prognosis of hepatoblastoma. Thus, the differentially expressed genes we have identified may become a useful tool to develop new diagnostic as well as therapeutic strategies of hepatoblastoma.

Genomic DNA double-strand breaks are targets for hepadnaviral DNA integration

Integrated hepadnaviral DNA in livers and tumors of chronic hepatitis B patients has been reported for many years. In this study, we investigated whether hepatitis B virus DNA integration occurs preferentially at sites of cell DNA damage. A single I-SceI homing endonuclease recognition site was introduced into the DNA of the chicken hepatoma cell line LMH by stable DNA transfection, and double-strand breaks were induced by transient expression of I-SceI after transfection of an I-SceI expression vector. Alteration of the target cleavage site by imprecise nonhomologous end joining occurred at a frequency of approximately 10(-3) per transfected cell. When replication of an avian hepadnavirus, duck hepatitis B virus, occurred at the time of double-strand break repair, we observed integration of viral DNA at the site of the break with a frequency of approximately 10(-4) per transfected cell. Integration depended on the production of viral double-stranded linear DNA and the expression of I-SceI, and integrated DNA was stable through at least 17 cell divisions. Integration appeared to occur through nonhomologous end joining between the viral linear DNA ends and the I-SceI-induced break, because small deletions or insertions were observed at the sites of end joining. The results suggest that integration of hepadnaviral DNA in infected livers occurs at sites of DNA damage and may indicate the presence of more widespread genetic changes beyond that caused by viral DNA integration itself [corrected].

Integration of woodchuck hepatitis and N-myc rearrangement determine size and histologic grade of hepatic tumors

Integrations of woodchuck hepatitis virus (WHV) DNA and rearrangements of the N-myc 2 gene have been detected frequently in hepatocellular carcinoma (HCC) of Eastern woodchucks (Marmota monax) chronically infected with WHV. Fifty-five hepatocellular neoplasms and matched nontumor hepatic tissue specimens obtained postmortem from 13 chronic WHV carriers were analyzed and the frequency of WHV DNA integrations and of N-myc rearrangements compared in tumors of different size and histologic grade. Four small tumor nodules were classified histologically as adenomas and integrated sequences of WHV DNA were detected in two of the four tumor nodules. In one of the two nodules, there was evidence of N-myc rearrangement. Fifty-one neoplasms were classified as HCC. Seven were grade 1 HCCs. WHV DNA integrations were demonstrated in 43% but none had N-myc rearrangements. Twenty grade 2 HCCs had WHV DNA integrations in 80% and in 38% N-myc rearrangements were present. Twenty-four grade 3 HCCs had integrations of WHV DNA in 79% and N-myc rearrangements in 74%. In two other grade 3 HCCs, rearrangements of N-myc were detected in the absence of WHV DNA integrations. The 12 largest tumors in the series all were grade 2 or 3 HCCs, and in 83%, both WHV DNA integrations and N-myc rearrangements were demonstrated. In conclusion, molecular changes observed in this study suggest a progression of genetic alterations providing either a significant proliferative stimulation and/or a growth advantage in hepatocarcinogenesis of woodchucks with chronic WHV infection.

Characterization of HBV integrants in 14 hepatocellular carcinomas: association of truncated X gene and hepatocellular carcinogenesis

Although the integration of hepatitis B virus (HBV) into human DNA has been found to be associated with the development of hepatocellular carcinoma (HCC), the molecular mechanism remains unclear. In order to obtain additional insight into the correlation of HBV integration and HCC development, integrated HBV in 14 primary HCC cases was isolated and characterized by sequencing analysis. Our findings in this study showed that: (1) none of the known cellular oncogene or tumor suppressor gene was affected by the HBV integration; (2) although the integration of HBV is random, the integration site was often within or close to human repetitive sequences; (3) integrated HBV may possess the capacity to transpose to another chromosome region through reintegration; (4) rearrangements of HBV sequence were observed in all the 14 integrants, involving (most frequently) X (12/14 integrants), P (8/14), S (7/14), and C (7/14) genes; and (5) 3'-deleted X gene and consequent C-terminal truncated X protein caused by HBV integration was observed in 10 cases. These deletions cause the losses of p53-dependent transcriptional repression binding site, transcription factor Sp1 binding site, and growth-suppressive effect domain, leading to cell proliferation and transformation. This finding suggests that 3'-deleted X gene caused by the HBV integration may play an important role in the HCC development.

Reactive oxygen species modulates the intracellular level of HBx viral oncoprotein

HBx (hepatitis B virus X) viral oncoprotein is a multifunctional protein of which the cellular level may be one of the important factors in determining HBV-mediated pathological progression of liver diseases, chronic hepatitis, and hepatocellular carcinoma. Our previous work revealed that adriamycin, a chemotherapeutic agent, caused a marked increase in the intracellular level of HBx by retarding its rapid degradation. In the present study, modulation of HBx expression was found to be confined to adriamycin but not to other chemotherapeutic agents, cisplatin and 5-fluorouracil. Interestingly, adriamycin caused a rapid increase of reactive oxygen species (ROS) and its accumulation continued until 24h. In contrast, two other agents had little effect on ROS generation, suggesting the possible involvement of ROS in the HBx regulation. In fact, direct addition of H(2)O(2) to the cells significantly increased the level of HBx protein in HBx-expressing ChangX-34 cells as well as in hepatitis B virus-related hepatoma cells, PLC/PRF/5 and HepG2.2.15 cells. Furthermore, antioxidants, N-acetyl-cysteine and pyrrolidinedithiocarbamate (PDTC), completely abolished the increase of HBx protein induced by adriamycin, indicating that adriamycin modulates the intracellular HBx level via ROS generation. Together, these findings provide a novel aspect of HBx regulation by cellular ROS level. Therefore, intracellular microenvironments generating ROS such as severe inflammation may aggravate the pathogenesis of liver disease by accumulating the HBx level.

Expression of hepatoma-derived growth factor in hepatocarcinogenesis

BACKGROUND AND AIM

The present study investigated the expression of hepatoma-derived growth factor (HDGF) in human hepatocellular carcinoma (HCC) and in the liver during hepatocarcinogenesis in two rodent models.

METHODS

Expression of HDGF was analyzed using northern blotting and immunohistochemistry in the human and rodent models.

RESULTS

Hepatoma-derived growth factor was more highly expressed in HCC than in the adjacent liver in humans with hepatitis, as shown by northern blotting. Using immunohistochemistry with the specific anti-HDGF antibody, HDGF was more strongly and frequently expressed in the nucleus and cytoplasm of HCC cells than in the adjacent normal hepatocytes. Hepatoma-derived growth factor was also more strongly expressed in the tumors than in the adjacent fatty liver of fatty liver Shionogi (FLS) mice, than in the cirrhotic liver of choline-deficient amino acid feeding rats, as shown by northern blotting and immunohistochemistry. In the liver of FLS mice, HDGF expression increased gradually from the age of 24 weeks through to 52 weeks after birth, showing that HDGF expression was already increased at an early stage before tumor development. In the non-tumorous liver with fatty change, the foci expressing HDGF appeared at 24 weeks of age, which were the activated macrophage clusters with enhanced DNA synthesis and fat droplets. It is suggested that HDGF was secreted or released from these foci and stimulated hepatocyte proliferation in a paracrine manner in FLS mice, and stimulated the proliferation of hepatic tumor cells in an autocrine manner.

CONCLUSIONS

The present findings suggest that HDGF plays an important role in the development or progression of HCC in humans and rodents.

Beta-catenin mutations in liver tumors induced by 2-amino-3,4-dimethylimidazo[4,5-f]quinoline in CDF1 mice

Heterocyclic amines are potent mutagens and carcinogens formed in cooked protein rich foods. In this study, we screened liver tumors induced by 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) in CDF1 mice for beta-catenin and APC mutations and other genetic alterations shown to occur in human hepatocellular carcinomas (HCC), including mutations in the p53 and H-ras genes, c-myc amplification and E-cadherin promoter methylation. SSCP followed by direct DNA sequencing revealed mutations in exon 2 of the beta-catenin gene in 2 of 16 liver tumors (12.5%). Promoter methylation of the E-cadherin gene was detected in one liver tumor induced by MeIQ. There were no mutations in the mutation cluster region of the APC gene, in exons 5-8 of the p53 gene, or in codons 12, 13 and 61 of the H-ras gene, nor c-myc amplification in any of liver tumors induced by MeIQ. These data indicate that except for the occasional disruption of the Wnt pathway through beta-catenin mutations, the genetic pathways involved in the development of HCC differ significantly between human liver cancer and tumors induced in mice by MeIQ, but do not rule out the possibility that heterocyclic amines constitute a carcinogenic risk factor in humans.

Infection and cancer: the common vein

The role of infectious agents in the development of cancer is well documented. The pathogenesis of various human neoplasms ranging from non-Hodgkin lymphoma (NHL) to cervical carcinoma frequently involves a chronic, most often viral, infection. At the same time, there is compelling evidence that certain acute infections result in the inhibition of neoplastic growth. The basis for this phenomenon is often thought to be concomitant anti-tumor immunity. Yet, experimental data supporting this hypothesis are scarce, and other non-immune anti-tumor factors could be involved. For instance, since virtually all aggressive tumors outstrip their blood supply, development of new vessels, or angiogenesis, is a limiting factor during neoplastic growth. In this review, we will discuss recent studies that implicate anti-angiogenesis in infection-mediated tumor suppression and suggest that this mechanism could also complement cytotoxic immunity arising from the use of cancer vaccines.

Molecular aspects of hepatitis B viral infection and the viral carcinogenesis

Of many viral causes of human cancer, few are of greater global importance than the hepatitis B virus (HBV). Over 250 million people worldwide are persistently infected with HBV. A significant minority of these develop severe pathologic consequences, including chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Earlier epidemiological evidence suggested a link between chronic HBV infection and HCC. Further, the existence of related animal viruses that induce acute and chronic infections of the liver, and eventually HCC, confirms the concept that HBV belongs to one of the few human oncogenic viruses. Although it is clear that chronic HBV infections are major risk factors, relatively little is understood about how the viral factors contribute to hepatocarcinogenesis. This review will introduce molecular aspects of the viral infection, and highlight recent findings on the viral contribution to hepatocarcinogenesis.

A critical evaluation of DNA adducts as biological markers for human exposure to polycyclic aromatic compounds

The causative role of polycyclic aromatic hydrocarbons (PAH) in human carcinogenesis is undisputed. Measurements of PAH-DNA adduct levels in easily accessible white blood cells therefore represent useful early endpoints in exposure intervention or chemoprevention studies. The successful applicability of DNA adducts as early endpoints depends on several criteria: i. adduct levels in easily accessible surrogate tissues should reflect adduct levels in target-tissues, ii. toxicokinetics and the temporal relevance should be properly defined. iii. sources of interand intra-individual variability must be known and controllable, and finally iv. adduct analyses must have advantages as compared to other markers of PAHexposure. In general, higher DNA adduct levels or a higher proportion of subjects with detectable DNA adduct levels were found in exposed individuals as compared with nonexposed subjects, but saturation may occur at high exposures. Furthermore, DNA adduct levels varied according to changes in exposure, for example smoking cessation resulted in lower DNA adduct levels and adduct levels paralleled seasonal variations of air-pollution. Intraindividual variation during continuous exposure was low over a short period of time (weeks), but varied significantly when longer time periods (months) were investigated. Inter-individual variation is currently only partly explained by genetic polymorphisms in genes involved in PAH-metabolism and deserves further investigation. DNA adduct measurements may have three advantages over traditional exposure assessment: i. they can smooth the extreme variability in exposure which is typical for environmental toxicants and may integrate exposure over a longer period of time. Therefore, DNA adduct assessment may reduce the monitoring effort. ii. biological monitoring of DNA adducts accounts for all exposure routes. iii. DNA adducts may account for inter-individual differences in uptake, elimination, distribution, metabolism and repair amongst exposed individuals. In conclusion, there is now a sufficiently large scientific basis to justify the application of DNA adduct measurements as biomarkers in exposure assessment and intervention studies. Their use in risk-assessment, however, requires further investigation.

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.

Increased chromosomal alterations and micronuclei formation in human hepatoma HepG2 cells transfected with the hepatitis B virus HBX gene

The protein encoded by the hepatitis B virus (HBV)-X gene, HBX, has been implicated to be involved in the development of HBV-associated liver cancer. HBX is a multifunctional regulatory protein that has been identified as a potential oncogene but its exact function remains unclear. HBX was documented to interact with several factors involved in cellular DNA repair as well as compromise the cell's ability to repair damaged DNA. We previously documented an accumulation of genetic alterations in two HepG2 cell lines independently transfected with HBV. In this report, we investigate the effect of the HBV-X gene (HBX) on the stability of the host genome using HepG2 stable transfectants (HepG2-HBX) and vector controls (HepG2-neo). We document that all HepG2-HBX clones analyzed contain HBX gene integrated and HBX transcript. Our data demonstrate that HepG2-HBX cells have an increased number of chromosome alterations and micronuclei formation compared to vector controls. A total of 10 de novo chromosomal rearrangements involving nine different chromosomes were detected in the HepG2-HBX clones, while no new rearrangements were found in vector controls. Each HepG2-HBX clone contained independently occurring de novo alterations not found in other HBX or vector clones. A three-fold increase of micronuclei formation was detected in HepG2-HBX cells compared to vector controls. Micronuclei originated from all chromosomes, however, preliminary data indicated that micronuclei originating from chromosomes 2, 3, 7, 18 and 20 were found in a greater amount in cells expressing the HBX gene. Interestingly, chromosomes 2, 18 and 20 were three of the chromosomes found rearranged in HepG2-HBX clones. These data provide evidence that genomic integrity was affected in cells expressing the HBX gene. De novo cytogenetic alterations identified in HepG2-HBX clones implicate the involvement of HBX in the process and support the hypothesis that HBX may interfere with normal cellular processes responsible for genomic integrity, increasing the risk for acquiring genetic mutations in infected hepatocytes.

The hepatitis B virus X protein abrogates Bcl-2-mediated protection against Fas apoptosis in the liver

The role of the hepatitis B virus protein HBx in liver cell proliferation and apoptosis remains controversial. Using a transgenic mouse model, we have recently shown that HBx stimulates the apoptotic turnover of hepatocytes, independently of p53. In this paper, we tested whether the proapoptotic function of HBx can interfere with Bcl-2 during hepatic apoptosis in vivo. HBx transgenic mice were crossed with PK-hBcl-2 mice that are protected against Fas killing by constitutive overexpression of Bcl-2 in hepatocytes. In a lethal challenge with Fas antibodies, HBx expressed at low levels restored sensitivity to Fas-mediated apoptosis and fulminant hepatic failure in mice overexpressing Bcl-2. Furthermore, cytochrome c release from mitochondria and caspase 3 activation were restored to normal levels in HBx/Bcl-2 mice during transduction of the Fas signal. Thus, the proapoptotic activity of HBx overcomes or bypasses the inhibitory effect of Bcl-2 against Fas cytotoxicity. This effect was not apparently mediated through downregulation of the PK-hBcl-2 transgene or via delocalization of the Bcl-2 protein, and a direct interaction of HBx with Bcl-2, Bcl-X(L) or Bax could not be evidenced in yeast two-hybrid assays. We further show that apoptosis induced by ectopic expression of HBx is associated with mitochondrial membrane alterations and caspase 3 activation. Our data indicate that the dominant function of HBx upon Bcl-2-regulated control of apoptosis might play an important role in the pathogenesis of chronic hepatitis B.

Analysis of chromosomal aberrations in large hepatocellular carcinomas by comparative genomic hybridization

Hepatocellular carcinoma (HCC) is a very common and highly malignant tumor, associated mainly with chronic viral hepatitis, cirrhosis of any cause, aflatoxin exposure and ethanol consumption. The aim of this study was to map genomic aberrations in HCC by a recently developed technique: comparative genomic hybridization (CGH). We applied CGH on 17 liver specimens, of which seven were HCCs. The rest were benign liver tumors, cirrhotic and normal livers, and other liver malignancies. Our study included mainly large tumors (mean size 10.5 cm) unrelated to viral hepatitis or cirrhosis. Our CGH analysis detected genomic imbalances in 42% of HCCs. The common aberrations included DNA gains of 1q, 9p, and 8q and DNA losses of 17p, 13q, 9q, 4q, and 11q. Also, we detected trisomies 8, 9, 18 and 21, which have not been reported previously. Gains and losses of DNA found in this study probably involve oncogenes and tumor suppressor genes that play a role in the puzzle of hepatocarcinogenesis. This study also suggests a possible link between the size of the tumor and the burden of genetic changes.

Hepatitis B virus X protein acts as a tumor promoter in development of diethylnitrosamine-induced preneoplastic lesions

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 and to influence cell cycle progression suggests two possible pathways. To investigate these possibilities in vivo, we treated double-transgenic mice that both express HBx (ATX mice) and possess a bacteriophage lambda transgene with the hepatocarcinogen diethylnitrosamine (DEN). Histological examination of liver tissue confirmed that DEN-treated ATX mice developed approximately twice as many focal lesions of basophilic hepatocytes as treated wild-type littermates. Treatment of mice with DEN resulted in a six- to eightfold increase in the mutation frequency (MF), as measured by a functional analysis of the lambda transgene. HBx expression was confirmed by immunoprecipitation and Western blotting and was associated with a modest 23% increase in the MF. Importantly, the extent of hepatocellular proliferation in 14-day-old mice, as measured by the detection of proliferating cell nuclear antigen and by the incorporation of 5-bromo-2'-deoxyuridine, was determined to be approximately twofold higher in ATX livers than in wild-type livers. These results are consistent with a model in which HBx expression contributes to the development of DEN-mediated carcinogenesis by promoting the proliferation of altered hepatocytes rather than by directly interfering with the repair of DNA lesions.

Activated ras oncogene collaborates with HBx gene of hepatitis B virus to transform cells by suppressing HBx-mediated apoptosis

The hepatitis B virus HBx protein is a promiscuous transactivator implicated in the development of hepatocellular carcinoma. The ectopic expression of HBx fails to transform both primary and immortalized rodent cells, but rather induces apoptosis. Furthermore, most transgenic mice harboring HBx do not develop liver tumors. Thus, it remains unclear whether and how HBx contributes to oncogenesis. Here, we show that HBx collaborates with activated H-ras to transform immortalized rodent cells. Indeed, REF52 cells transfected by both HBx and activated H-ras were morphologically transformed and were able to grow in soft agar. Remarkably, nude mice injected with REF52 cells transfected by both HBx and activated H-ras developed tumors, whereas the mice injected with REF52 cells transfected by either gene alone did not. Thus, we concluded that HBx could contribute to neoplastic transformation of cells in collaboration with other oncogenes, such as H-ras, that renders cells to overcome the HBx-mediated apoptosis. Further, we found that HBx mediated apoptosis was suppressed by activated H-ras through activation of the phosphatidylinositol-3 kinase and Akt pathway. Data presented here firmly established the oncogenic potential of HBx during multistage carcinogenesis. Oncogene (2001) 20, 16 - 23.

Hepatitis viruses and hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is among the most frequent malignancies worldwide. Hepatitis viruses, such as the hepatitis B virus (HBV) and hepatitis C virus (HCV) are undoubtedly listed in the etiology of HCC. Studies show that, in the near future, viral hepatitis will carry increasing weight in the etiology of HCC. This review briefly discusses the known carcinogenic effects of HBV and HCV in the light of experimental and human studies. The data show that viral proteins may directly interfere with gene products responsible for cell proliferation and cell growth. Many other signal transduction cascades may be affected as well. Direct integration of HBV viral sequences into the host genome increases the genomic instability. The genomic imbalance allows the development and survival of malignant clones bearing defected genomic information. HBV and HCV infection induces indirect and direct mechanisms through cellular damage, increased regeneration and cell proliferation, therefore enhancing the development of HCC.

In vitro reconstitution of a functional duck hepatitis B virus reverse transcriptase: posttranslational activation by Hsp90

Reverse transcription in hepatitis B viruses is initiated through a unique protein priming mechanism whereby the viral reverse transcriptase (RT) first assembles into a ribonucleoprotein (RNP) complex with its RNA template and then initiates DNA synthesis de novo using the RT itself as a protein primer. RNP formation and protein priming require the assistance of host cell factors, including the molecular chaperone heat shock protein 90 (Hsp90). To better understand the mechanism of RT activation by Hsp90, we have now mapped the minimal RT sequences of the duck hepatitis B virus that are required for chaperone binding, RNP formation, and protein priming. Furthermore, we have reconstituted in vitro both RNP formation and protein priming using purified RT proteins and host factors. Our results show that (i) Hsp90 recognizes two independent domains of the RT, both of which are necessary for RNP formation and protein priming; (ii) Hsp90 function is required not only to establish, but also to maintain, the RT in a state competent for RNA binding; and (iii) Hsp90 is not required during RT synthesis and can activate the RT posttranslationally. Based on these findings, we propose a model for Hsp90 function whereby the chaperone acts as an active interdomain bridge to bring the two RT domains into a poised but labile conformation competent for RNP formation. It is anticipated that the reconstitution system established here will facilitate the isolation of additional host factors required for RT functions and further elucidation of the mechanisms of RT activation.

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.

Hepatitis B virus-transfected Hep G2 cells demonstrate genetic alterations and de novo viral integration in cells replicating HBV

Hepatitis B virus (HBV) is a major etiological factor associated with hepatocarcinogenesis, but its role in the transformation process remains unclear. We previously documented the accumulation of genetic alterations in a HBV-transfected cell line. In the present study, we addressed the effect of HBV and its replication on the genome and phenotype of the host cell. Parental HBV-free Hep G2 cells and two HBV-transfected variant lines Hep G2215 and Hep G2T14. 1, which do and do not replicate HBV, respectively, were used to monitor genetic alterations in conjunction with HBV profile in vitro and in vivo. Comparison of in vitro growth rates showed that Hep G2T14.1 cells grew more rapidly, while Hep G2215 cells, replicating HBV, grew slower than parental Hep G2 cells. Molecular analysis confirmed an HBV integration site (s) in both variants, and reverse trancriptase-polymerase chain reaction (RT-PCR) amplification documented expression of transcript for the HBX protein, which has recently been implicated in the compromised efficiency of cellular DNA repair. Tumorigenisity testing indicate a comparable rate of tumor formation in nude mice of both HBV-transfected variants, giving rise to tumors in 3 weeks; parental Hep G2 cells did not form tumors in nude mice. Tumor tissue from nude mice injected with Hep G2T14.1 cells showed no change in HBV status. However, a new HBV integration site was detected in tumor tissue from Hep G2215-injected mice. Two cell lines derived from the respective tumor tissue grew in vitro at rates compatible to those observe before passage in nude mice. The Hep G2215 tumor-derived line continued to replicate HBV, while HBV status remained unchanged in the Hep G2T14.1 tumor-derived line. Unique genetic alterations were detected in both transfected cell lines, and Hep G2215 cells particularly showed cellular mosaicism and clonal selection when analyzed after the passage in nude mice. Further genetic alterations were detected in tumor-derived cell lines. Interestingly, the de novo genetic alterations in the Hep G2215 cells, which maintain the ability to replicate HBV, included a new HBV integration site, several chromosome rearrangements and loss of heterozygosity (LOH) of one p53 allele. Western analyses of p21/Waf1 protein indicate an upregulation of the protein in cells that replicate HBV. Based on the combined data, we hypothesize that the genetic alterations in the cellular genome could also be generated as a function in the presence of HBV and HBV replication. Possible mechanisms that could be implicated in cumulative mutagenetic events are discussed.