Molecular pathogenesis of hepatocellular carcinoma in hepatitis B virus transgenic mice

Hepatitis C virus antibody in patients with primary liver cancer (hepatocellular carcinoma, cholangiocarcinoma, and combined hepatocellular-cholangiocarcinoma) in Japan

BACKGROUND

In hepatocellular carcinoma (HCC), a high prevalence of hepatitis C virus antibody (anti-HCV) has been reported, indicating that it may be an important etiologic factor in the pathogenesis of HCC. In this study, the authors investigated the prevalence of anti-HCV in HCC patients, as well as the same prevalence in patients with cholangiocarcinoma (CC) and combined hepatocellular-cholangiocarcinoma (combined HCC-CC), to study the clinicopathologic features of anti-HCV-positive cases.

METHODS

The authors examined 141 patients with primary liver cancer who were pathologically diagnosed as having HCC (121 cases), CC (13 cases), or combined HCC-CC (7 cases). Hepatitis B surface antigen (HBsAg) and anti-HCV were measured in these patients.

RESULTS

Of 121 HCC cases, 85 (70.3%) were found to be anti-HCV positive, 16 (13.2%) were HBsAg positive, and 5 (4.1%) were both anti-HCV and HBsAg positive. In 13 cases with CC and in 7 with combined HCC-CC examined, 4 (30.8%) and 5 (71.4%), respectively, were anti-HCV positive.

CONCLUSIONS

The anti-HCV-positive rate was high in combined HCC-CC as well as in HCC. These three types of primary liver cancer, which were anti-HCV positive, shared two common features: male dominance and high incidences of complication with liver cirrhosis.

p53 gene mutations and 17p allelic deletions in hepatocellular carcinoma from Japan

BACKGROUND

p53 gene mutations at codon 249 have been reported in hepatocellular carcinoma (HCC) from China and South Africa, a phenomenon shown to be closely associated with food contamination by aflatoxin. There have been few reports, however, in regard to p53 gene mutations in HCC from other geographic areas.

METHODS

The authors analyzed 20 HCC from Japan for alteration of the p53 gene by restriction fragment length polymorphisms and for nucleic acid mutations by polymerase chain reaction with direct sequencing.

RESULTS

Alterations associated with the p53 gene were found in 6 of 20 HCC (30%). Allelic loss of chromosome 17p occurred in 5 of 14 informative (heterozygous) cases (36%). Mutations in the p53 gene were detected in three cases (15%), at codons 176 (exon 5), 236 (exon 7), and 294 (exon 8). These cases were different from the HCC cases from China and South Africa, where point mutations in the p53 gene were reported at the same codon 249 in half of the cases and where aflatoxin food contamination and hepatitis B virus infection are recognized risk factors of HCC. No p53 gene alterations were found in smaller HCC (< 3 cm) or at earlier stages.

CONCLUSIONS

In Japan, p53 gene alterations seem to be a late event in the progression of hepatocarcinogenesis, which is often associated with persistent infection by the hepatitis C or B virus, but not usually with exposure to aflatoxin.

Proliferative activity of hepatocytes in chronic viral hepatitis as revealed by immunohistochemistry for proliferating cell nuclear antigen

Liver biopsy specimens of 65 cases of chronic viral hepatitis, including 29 cases of type B, 34 cases of type C, and two cases of non-A, non-B, non-C type, were immunohistochemically stained for proliferating cell nuclear antigen (PCNA) to evaluate the proliferative activity of hepatocytes. According to a histopathologic evaluation using the histology activity index (HAI) scoring system, chronic persistent hepatitis and chronic active hepatitis were clearly differentiated with no overlapping of the score. The labeling indices of PCNA of hepatocytes in chronic persistent hepatitis had a significant relationship with HAI scores (r = .54), suggestive of a contribution of lobular hepatocyte necrosis and/or portal inflammation to the regenerative rate of hepatocytes, but did not exceed 3.0%. On the other hand, 11 of 47 cases of chronic active hepatitis showed PCNA labeling indices higher than 3.5% without any significant relationship with the HAI scores. There was no significant difference, however, of distribution of HAI scores or PCNA labeling indices between hepatitis types B and C. Based on current concepts of the role of hepatocyte proliferation in the development of liver cirrhosis and hepatocellular carcinoma, the present results suggest that the high proliferative rate of hepatocytes subject to the persistent liver cell injury in chronic active hepatitis may be related to a reconstruction pattern of the liver in cases of progression to cirrhosis and development of hepatocellular carcinoma.

Experimental transmission of human hepatitis delta virus to the laboratory mouse

Human hepatitis delta virus (HDV), obtained from the serum of an experimentally infected woodchuck, was injected into either the peritoneal cavity or the tail vein of both adult CB17 mice and mice with a severe combined immunodeficiency (CB17-scid mice). Three lines of evidence indicated that the virus was able to reach the liver and infect hepatocytes: (i) the amount of HDV genomic RNA detected in the liver by Northern (RNA) analysis increased during the first 5 to 10 days postinoculation, reaching a peak that was about threefold the amount in the original inoculum; (ii) also detected in the liver was the viral antigenomic RNA, which is complementary to the genomic RNA found in virions, and is diagnostic for virus replication; and (iii) by immunoperoxidase staining of liver sections, the delta antigen was detected in the nuclei of scattered cells identifiable as hepatocytes. In all of the mice, clearance of the infection occurred between 10 and 20 days after inoculation. The half-life for clearance was about 3 days in CB17-scid mice, indicating that clearance of infection did not involve a T- and B-cell-dependent immune response. Cell-to-cell spread of the initial infection was not detected. One possible interpretation of our results is that HDV infection of hepatocytes is directly cytopathic. Also, the results imply that chronic infection of the liver in humans may require continuous spread of virus within the liver. Alternatively, HDV in the absence of helper virus may be unable to cause a chronic infection of hepatocytes in vivo.

A role for the nucleotype in the pathogenesis of primary hepatocellular carcinoma

The risk of developing primary hepatocellular carcinoma (HCC) is 200 times higher for chronic carriers of hepatitis B virus antigen (HBsAg) than for the rest of the population. There is experimental evidence which suggests that the expression of viral DNA sequences integrated into the host's genome directly contributes to HCC development. However, most evidence available suggests that development of HCC requires a second genetic event that results from the chronic hepatitis and cirrhosis observed in symptomatic HBsAg chronic carriers. Here it is argued that the nucleotype, defined as those non-genic characters of nuclear DNA that affect or control the phenotype, is the element that links the viral, cellular and host factors involved in the genesis of HCC.

Exploring pathogenetic mechanisms using transgenic animals

Molecular technologies for the permanent germ-line transformation of animals are now well established and routine. These new strains of animals, called transgenic, offer an unprecedented opportunity to gain a basic understanding of human genetic disorders. In this brief review we discuss the role of transgenic animals in the creation of new models of human disease and their experimental use in biomedical research. Models are now available for the study of the genetic processes involved in the pathogenesis of neoplasia, diabetes, atherosclerosis, and developmental abnormalities. Many others are available and new ones are being produced at a great rate. Principles of gene replacement therapy are amenable to analysis with transgenic animals and the information gained will be important for the development of rational therapy.

Rodent models for targeted oncogenesis of the prostate gland

Currently, prostate cancer ranks as the most frequent non-skin malignancy detected in males. Yet, of the major human cancers, it remains one of the least understood in terms of its molecular and genetic basis. Research on prostate cancer has been limited by the paucity of tissues available for study. Much of the tissue obtained through surgery for localized prostate cancer will be required for pathological staging and grading. The more aggressive forms of prostate cancer are usually detected subsequent to metastatic involvement at which point there is little reason to surgically remove the prostate tumor(s). A final complication is the propensity of prostate cancer to metastasize to the bone, a site extremely difficult to obtain suitable biopsies for study. Further hindering research efforts on prostate cancer is the lack of suitable animal models for study. In contrast to its frequent occurrence in humans, prostate cancer is a rare event in most other mammalian species, particularly laboratory rodents. Therefore, in order to make this disease more amenable for study, there is a growing effort to identify or develop a means to target oncogenesis to the prostate gland of rodents. As will be reviewed here, this goal is being approached with the use of 3 different methods; one that takes advantage of the unique androgenic hormone requirement for prostate growth to exaggerate the effects of carcinogens at that site and two methods (recombinant retrovirus transduction prior to organ reconstitution and transgenic targeting) that allow direct genetic manipulation of cells in the prostate gland leading to the development of prostatic malignancy.

Increasing titers and changing specificities of antinuclear antibodies in patients with chronic liver disease who develop hepatocellular carcinoma

BACKGROUND

Patients with liver cirrhosis and chronic hepatitis are at high risk for development of hepatocellular carcinoma (HCC). In HCC and other malignant neoplasms, antinuclear antibodies (ANA) have been detected, but the clinical and biologic significance of these autoantibodies has not been established. This study documents changing ANA manifested as seroconversion from a negative to positive ANA status, increasing titers, and changing antibody specificities in patients in whom chronic liver disease has progressed to HCC.

METHODS

Sera were collected from patients with chronic liver diseases and HCC in Japan. Indirect immunofluorescence was used to detect ANA, and Western blotting, two-dimensional immunoblotting, and enzyme-linked immunosorbent assay were used to characterize nuclear antigen-antibody systems.

RESULTS

ANA were detected in 57 of 183 (31%) patients with HCC, a statistically higher frequency than in patients with the most common antecedent clinical conditions, liver cirrhosis (9 of 64 patients [14%]; P < 0.05) or chronic hepatitis (16 of 123 patients [13%]; P < 0.001). One patient with autoimmune hepatitis observed for 9 years had a decrease in ANA titer after therapy with corticosteroid and azathioprine and had a rebound increase in ANA titer associated with development of HCC. Immunologic assays demonstrated dramatic decreases in levels of autoantibodies to histones during therapy and the appearance of new autoantibodies coincident with HCC. Changes in ANA associated with the appearance of auto-antibodies of new specificities were documented in four other patients with chronic liver disease in whom HCC developed.

CONCLUSIONS

Changes in ANA, especially alterations in autoantibody specificities, are seen infrequently in systemic autoimmune diseases. It is possible that in HCC such changes in ANA might reflect autoimmune responses to intranuclear antigens that are perturbed in cellular transformation.

Distribution of glucose-6-phosphatase activity in normal, hyperplastic, and preneoplastic rat liver

The significance of glucose-6-phosphatase (G6P) expression by bile duct-like cells proliferating during hepatocarcinogenesis in the histogenesis of hepatocellular carcinoma is not clear. To this end, we measured the histochemical and biochemical activity of G6P in normal rat liver, and in rat livers in which bile duct-like proliferation was induced by either hyperplastic (bile duct ligation for 14 days or feeding alpha-naphthylisothiocyanate for 28 days) or neoplastic (feeding a choline-devoid diet containing 0.1% ethionine for 60 days) regimens. In normal, hyperplastic, and preneoplastic livers, G6P histochemical activity was confined to the hepatocytes; proliferated bile duct-like cells, like normal bile ducts, did not display visible G6P staining. When the enzyme activity was determined biochemically, however, hydrolysis of glucose-6-phosphate was observed in both parenchymal and nonparenchymal liver cells isolated from all experimental animals. In elutriated nonparenchymal fractions, G6P activity was directly proportional to the number of cells positive for gamma-glutamyl transpeptidase and cytokeratin no. 19 (markers of bile duct cells) and inversely proportional to the number of cells positive for vimentin (marker of mesenchymal cells). These results indicate that, while by light microscopy hepatic G6P histochemical activity is detectable only in the hepatocytes, the biochemical activity is also expressed in proliferating bile duct-like cells. However, the nonparenchymal activity is observed during both neoplastic and hyperplastic liver growth, thus indicating that the presence of this enzyme in bile duct-like cells proliferating during hepatocarcinogenesis should not necessarily be construed as supporting their stem cell nature nor their neoplastic commitment.

A novel transgenic mouse model for the in vivo evaluation of anti-human immunodeficiency virus type 1 drugs

We have developed a binary transgenic mouse system that allows easy in vivo evaluation of new anti-human immunodeficiency virus type 1 (HIV-1) drugs or therapies specifically designed to target the viral transactivator protein (TAT) or long terminal repeat (LTR) functions. This approach consists of a simple genetic cross between an "activator" transgenic mouse expressing the HIV-1-tat gene exclusively to T lymphocytes and a "target" transgenic mouse bearing a silent reporter gene whose expression is under the control of the HIV-1-LTR. As expected, most of the target transgenic animals did not express the reporter gene; on the contrary, all the double-transgenic mice bearing both the activator and target transgenes strongly expressed the TAT-induced reporter gene. The choice of a secreted human alpha 1-antitrypsin variant (alpha 1-AT) as reporter gene readily permits in a single animal the quantitative determination of the plasma level of alpha 1-AT protein before and after anti-LTR or anti-TAT treatments. Such mice may be valuable as new laboratory models for the in vivo evaluation of agents with potential anti-HIV-1 activity.

DNA rearrangement causes hepatocarcinogenesis in albumin-plasminogen activator transgenic mice

Hepatocyte-directed production of urokinase-type plasminogen activator (uPA) in transgenic mice is hepatotoxic. Infrequently, hepatocytes arise that do not express uPA, due to physical loss of transgene DNA, and these cells clonally repopulate the entire liver within 3 months of birth. Surprisingly, hepatic tumors appear in these mice beginning at 8 months of age despite the fact that uPA is not oncogenic or genotoxic. Analysis of the transgene locus reveals that tumors arise only from a particular subclass of transgene-deficient cells in which the entire transgene array, and possibly a significant amount of flanking DNA, is deleted. Considering that all transgene-deficient regenerative nodules undergo extensive replication but only a subset gives rise to tumors, we propose that loss of genomic DNA, not mitogenesis per se, is a primary carcinogenic determinant in this model of hepatocarcinogenesis.

Repression of liver-specific hepatitis B virus enhancer 2 activity by adenovirus E1A proteins

Two regions of the hepatitis B virus (HBV) genome have been shown to display properties of a transcriptional enhancer. Enhancer 1 is active in most hepatoma lines examined as well as in some non-hepatocyte-derived cell lines. In contrast, enhancer 2 activity is strictly liver specific. In this study, we show that adenovirus E1A expression in the highly differentiated human hepatoma line Huh6 strongly inhibits HBV enhancer 2-stimulated transcription while having no effect on HBV enhancer 1 activity. A sequence motif in HBV enhancer 2 which is essential for its enhancer function is the target for E1A-mediated repression. The repression of HBV enhancer 2 activity is mediated through the N-terminal region of the E1A proteins known to bind a 300-kDa cellular protein. Our results suggest that HBV enhancer function may be modulated by a cellular mechanism similar to E1A-mediated transcriptional repression.

Analysis of a cellular model to account for the natural history of infection by the hepatitis B virus and its role in the development of primary hepatocellular carcinoma

Infection with the hepatitis B virus (HBV) can have many different outcomes. Transient infection may result in acute hepatitis or may remain subclinical. Persistent infection may also be subclinical, or may involve chronic active hepatitis, and can finally lead to the development of primary hepatocellular carcinoma. A mathematical model is given to account for the many different outcomes of HBV pathogenesis. The model is based on the assumption that the liver contains two cell populations with differing abilities to support active HBV replication and/or viral integration into the genome. The model helps account for the relationship of the different clinical courses of HBV infection to the age when the disease is acquired, together with the state of the immune system of the patient.

Hepatitis B virus, alpha-fetoprotein synthesis, and hepatocellular carcinoma in Zaire

We investigated the epidemiology of hepatocellular carcinoma (HCC) in Zaire, and evaluated the association between exposure to hepatitis B virus (HBV) and the development of HCC. Two hundred and twenty-three consecutive cases of HCC diagnosed over 19 years (1966-1985) were reviewed. HCC represented 8.32% of all carcinomas and 5.56% of all cancers. Frequency was higher in males (75.7%) than in females (24.3%); a sex ratio of 3/1. The majority (82.1%) of patients were aged 14 to 55 years with a peak occurrence in the fourth decade (28.6%). The mean age in males (41.27 +/- 17.5 years) and females (37.40 +/- 15.16 years) was significantly different (p < 0.02). Sera from 40 patients and 68 age and sex-matched controls were analyzed for markers of HBV infection: patients and controls had comparable rates of exposure (96% vs 72.1%, respectively). However, patients had significantly higher HBsAg carrier rates (56.7% vs 7.35%; p < 0.001), and lower anti-HBsAg seroconversion rates (25% vs 63.2%, p < 0.05). Using immunohistochemical analysis, the livers of patients were evaluated for HBsAg and HBcAg. These HBV antigens were more frequent in non-tumourous hepatocytes (53.3% vs 23.3%, respectively) than in HCC cells (13.3% vs 3.3%). Serum alpha-fetoprotein (AFP) was abnormal (> 20 ng/ml) in 90% of patients. The geometric mean (GM) AFP was 7273.8 ng/ml. AFP levels were significantly higher in HBsAg-positive HCC cases (GM: 19,322.6 ng/ml; 95% confidence interval (CI): [3639.2, 102,565.2]) than in antigen negative cases (GM: 1939.5 ng/ml; 95% CI: [182.8, 19,952.6]), but did not correlate with HBV replication. Immunohistochemical detection of AFP revealed a similar correlation between AFP and HBsAg. Neither AFP level nor HBsAg production correlated with cellular atypia or tumor grade.

Transforming growth factor-alpha in human hepatocellular carcinoma and coexpression with hepatitis B surface antigen in adjacent liver

BACKGROUND

Hepatitis B virus (HBV) infection is closely associated with the development of hepatocellular carcinoma (HCC) in many patients, but the mechanisms by which HBV contributes to HCC are not known. Transforming growth factor-alpha (TGF-alpha), a regulator of growth and regeneration in rat liver that can be found in high levels in some human cancers, theoretically could play such an intermediate role in the development of HCC.

METHODS

The expression of TGF-alpha and its relation to the HBV antigens were evaluated in human HCC and adjacent nontumorous livers from 33 patients from the United States and China using immunoperoxidase staining of paraffin-embedded sections.

RESULTS

TGF-alpha was detected in HCC from 27 of 33 (82%) patients; the frequencies were similar in patients from the United States and China. TGF-alpha was detected in HCC more frequently in patients whose adjacent nontumorous livers had detectable hepatitis B surface antigen (HBsAg) and/or hepatitis B core antigen (HBcAg) than in those whose adjacent livers lacked HBsAg and HBcAg. Detection of TGF-alpha was not affected by tumor size, histologic type, or grade. TGF-alpha was detected in adjacent nontumorous livers from 31 of 33 patients (94%). Coexpression at a high intensity of TGF-alpha and HBsAg in the same hepatocytes could be demonstrated by specific staining of consecutively cut sections for 17 of 33 patients (52%).

CONCLUSIONS

TGF-alpha is expressed at a high level in 82% of human HCC. Localization of HBsAg within the same hepatocytes as TGF-alpha suggests a possible interaction between HBV and TGF-alpha during hepatocarcinogenesis in humans. Stimulation of TGF-alpha expression could be part of a chain of events by which HBV contributes to the development of HCC in some patients.

HBsAg retention sensitizes the hepatocyte to injury by physiological concentrations of interferon-gamma

The role that inflammatory cytokines may play in the life cycle of the hepatitis B virus and in the pathogenesis of its associated liver disease has not been carefully delineated. In this report, we demonstrate that bacterial lipopolysaccharide, a potent inducer of inflammatory cytokines in vivo, causes a severe acute liver disease in transgenic mice whose hepatocytes produce the hepatitis B virus large envelope polypeptide and retain HBsAg within the endoplasmic reticulum. In contrast, 100-fold higher doses of bacterial lipopolysaccharide do not induce liver cell injury in nontransgenic littermate controls or in transgenic mice whose hepatocytes secrete HBsAg rather than retain it. Coincident with the hepatocellular injury and the influx of inflammatory cells into the liver, a marked reduction occurs in the intrahepatic content of hepatitis B virus steady-state messenger RNA, thereby confirming the selectivity of this process for the HBsAg-positive hepatocyte. Bacterial lipopolysaccharide-induced hepatocellular injury appears to be principally mediated by interferon-gamma because it can be markedly reduced by the prior administration of neutralizing interferon-gamma-specific monoclonal antibodies and because recombinant interferon-gamma is also selectively cytotoxic for the HBsAg-positive transgenic hepatocyte in vivo. Tumor necrosis factor-alpha is also involved in this process because bacterial lipopolysaccharide-induced liver cell injury is significantly reduced by tumor necrosis factor-alpha specific monoclonal antibodies. The role of tumor necrosis factor-alpha in bacterial lipopolysaccharide-induced liver cell injury is less clear than interferon-gamma, however, because unlike interferon-gamma it is also toxic for nontransgenic hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Transgenic animals in the evaluation of compound efficacy and toxicity: will they be as useful as they are novel?

1. Construction of transgenic mice is predicated upon inserting foreign DNA into native host DNA and having this expressed in the germline. This may be accomplished by nuclear injection, retroviral vectors or use of embryonic stem (ES) cells. 2. Expression of novel structural genes may be reasonably directed by the judicious use of an accompanying promoter/enhancer sequence. Insertion of foreign genes may be designed to result in phenotypic expression of a novel trait or ablation of a native gene or gene product. 3. Resulting transgenic mice offer significant utility as models of human diseases and a unique opportunity for investigating immune and metabolic pathways as well as for exploring mechanisms of development, mutagenesis and teratogenesis. 4. Use of transgenic animals in drug development has considerable potential although realization of this potential will take time. Constructing transgenics is only the first step in a complex series of events culminating in understanding the consequences of imposing novel genetic material on an intact, highly integrated living system. Practical use of transgenic animals will depend upon substantial effort being spent in investigating and validating the phenotypic consequences of gene transfer.

Hepatitis B virus infection and primary hepatocellular carcinoma

For many years, epidemiological studies have demonstrated a strong link between chronic hepatitis B virus (HBV) infection and the development of primary hepatocellular carcinoma (PHC). Other hepatocarcinogens such as hepatitis C virus and aflatoxin also contribute to hepatocarcinogenesis either in conjunction with HBV infection or alone. Cellular and molecular biological studies are providing explanations for the HBV-PHC relationship, and models are now being formulated to further test the relative importance of various factors such as viral DNA integration, activation of oncogenes, genetic instability, loss of tumor suppressor genes, and trans-activating properties of HBV to the pathogenesis of PHC. Further research will probably define more than a single mechanism whereby chronic HBV infection results in PHC.

Molecular biology of hepatocellular carcinoma and hepatitis B virus association

The involvement of the hepatitis B virus in the pathogenesis of hepatocellular carcinoma was initially suggested on the basis of epidemiological studies. In recent years several kinds of experimental evidence have supported this hypothesis; however, the role played by hepatitis B virus in hepatocarcinogenesis still needs to be elucidated. Several groups of researchers are presently involved in establishing whether hepatitis B virus makes a specific genetic contribution to carcinogenesis or predisposes to neoplastic transformation by causing chronic inflammation and cell regeneration. A comprehensive examination of the data available in the literature suggests that the two hypotheses may not be mutually exclusive.

Frequent amplification of c-myc in ground squirrel liver tumors associated with past or ongoing infection with a hepadnavirus

Persistent infection with hepatitis B virus (HBV) is a major cause of hepatocellular carcinoma (HCC) in humans. HCC has also been observed in animals chronically infected with two other hepadnaviruses: ground squirrel hepatitis virus (GSHV) and woodchuck hepatitis virus (WHV). A distinctive feature of WHV is the early onset of woodchuck tumors, which may be correlated with a direct role of the virus as an insertional mutagen of myc genes: c-myc, N-myc, and predominantly the woodchuck N-myc2 retroposon. In the present study, we searched for integrated GSHV DNA and genetic alterations of myc genes in ground squirrel HCCs. Viral integration into host DNA was detected in only 3/14 squirrel tumors and did not result in insertional activation of myc genes, despite the presence of a squirrel locus homologous to the woodchuck N-myc2 gene. This suggests that GSHV may differ from WHV in its reduced ability to induce mutagenic integration events. However, the high frequency of c-myc amplification (6/14) observed in ground squirrel HCCs indicates that myc genes might be preferential effectors in the tumorigenic processes associated with rodent hepadnaviruses, a feature not reported so far in HBV-induced carcinogenesis. Together with previous observations, our results suggest that hepadnaviruses, despite close genetic and biological properties, may use different pathways in the genesis of liver cancer.

Regulation of hepatitis B virus gene expression by its two enhancers

Hepatitis B virus (HBV) infection causes acute and chronic hepatitis and is closely associated with the development of hepatocellular carcinoma. The principal site of HBV infection is liver, and HBV actively replicates in hepatocytes. Two regions of the HBV genome have been shown previously to display properties of a transcriptional enhancer. In this study, we show that either of the two HBV enhancers can activate all three major HBV promoters in several human hepatoma lines, and the cooperative action of the two enhancers ultimately affects overall activity of the three promoters. In addition, our data suggest that HBV gene expression may be differentially regulated by its enhancers. HBV infection causes chronic liver inflammation and hepatocyte regeneration. It has been proposed that progressive accumulation of mutations during the regenerative hyperplasia may lead to alterations in the differentiation state of hepatocytes. Thus, the development of two differentially regulated enhancers may reflect a strategy of HBV to replicate efficiently in less differentiated hepatocytes during hepatocyte regeneration or hepatocarcinogenesis.

Increased growth of permanent mouse fibroblasts in soft agar after transfection with hepatitis B virus DNA

Previously we have shown that a nontumorigenic mouse hepatocyte line harboring simian virus 40 large tumor antigen (SV 40 TAg) could be converted to a full-malignant phenotype by transfection with HBV DNA. Using a permanent SV 40 TAg-negative mouse fibroblast cell line (LTK-), we studied whether the in vitro-oncogenicity of HBV was dependent on simultaneous expression of SV 40 TAg or not. Three fibroblast lines stably transfected by full-length HBV DNA formed four times more colonies of large size in soft agar than nontransfected LTK- cells. All three clones expressed high levels of HBx protein, but variable levels of other HBV proteins. A second type of clone that was transfected by a partial HBV genome and that expressed HBV surface but no HBx proteins, did not acquire increased growth in soft agar. These data reveal that HBV DNA can enhance malignant growth independent of SV 40 TAg and suggest that HBx protein may act as an HBV oncogene at least in vitro.

Hepatitis B virus X protein activates transcription factor NF-kappa B without a requirement for protein kinase C

The hepatitis B virus X protein stimulates transcription from a variety of promoter elements, including those activated by transcription factor NF-kappa B. A diverse group of extra- and intracellular agents, including growth factors and the human immunodeficiency virus tat protein, have been shown to require a functional protein kinase C (PKC) system to achieve activation of NF-kappa B. In this study we have investigated the molecular mechanism by which X protein activates NF-kappa B. We demonstrate that in hepatocytes, X protein induces a maximal activation of NF-kappa B corresponding to the sequestered pool of factor, which is also activated by phorbol esters. To determine whether X protein requires activation of PKC to stimulate transcription by NF-kappa B, we attempted to prevent transactivation by X protein in the presence of the PKC inhibitors calphostin C and H7. We show that PKC inhibitors do not block X protein activation of NF-kappa B, whereas they largely impair activation by phorbol esters. In addition, activation of PKC is correlated with its translocation from the cytoplasm to the plasma membrane. The subcellular distribution of PKC was investigated by introducing X protein from a replication-defective adenovirus vector, followed by immunochemical detection of PKC in cell fractions. These data also indicate that X protein stimulates transcription by NF-kappa B without the activation and translocation of PKC.

Tumours of the liver

One of the major debates in hepatocellular carcinogenesis at present is whether the hepatitis-B and -C viruses are directly carcinogenic or exert their effect indirectly by causing chronic necro-inflammatory hepatic disease, which in turn is responsible for malignant transformation of hepatocytes. This debate has been fueled by the observation that hepatitis C virus is a single-stranded RNA virus with no precedent for inducing cancer but with a marked propensity to cause chronic necro-inflammatory hepatic disease and by the findings in Chisari's transgenic mouse model, which suggest that severe and prolonged hepatocellular injury per se induces a proliferative response that progresses to tumour formation. Recent reports of a guanine to thymine mutation of the third base of codon 249 of the tumour suppressor gene, p53, in 50% of patients with hepatocellular carcinoma in regions of high aflatoxin exposure, and mutagenic experiments showing that aflatoxin B1 binds particularly to guanine residues in G-C-rich domains and that codon 249 is a preferred target have suggested a mechanism whereby aflatoxin might induce malignant transformation.

Hepatitis B virus. New and evolving issues

Recent developments in molecular biology have advanced our understanding of the pathogenesis of HBV-induced disease. New data derived from the molecular analysis of clinical material have begun to bridge the gap between bench research and the clinical arena. In this review, we consider topics that have relevance to clinical management and that have not been summarized in the recent literature. The recent advances that have been made in the areas of HBV variants, in vitro cell culture systems, and extrahepatic infection are discussed in greater detail.

Long-term survival following treatment of hepatocellular carcinoma in Singapore: evaluation of Wellferon in the prophylaxis of high-risk pre-cancerous conditions

The present paper reviews several studies performed between 1977 and 1986 in Singapore on the 10-year survival outcome of treatment for stage I and II hepatocellular carcinoma (HCC). Of 801 HCC patients evaluated, only 2 survivors (0.3%) remained in complete remission for 13 and 14 years, respectively. One had received four weekly cycles of prednisolone, Adriamycin, vincristine and 5-fluorouracil for an inoperable HCC with a 10-cm diameter, and the other had received localised synchronised hepatic irradiation and Adriamycin. As follow-up, the use of localised hepatic irradiation consisting of 131I-labeled (30 mCi) iodised oil in lipiodol infused via the hepatic artery appeared to benefit patients with small residual tumours but did not affect larger tumours measuring 2 cm in diameter. Prophylactic, intermittent long-term administration of lymphoblastoid interferon-alpha (Wellferon) was carried out in pre-cancerous, high-risk hepatitis B surface antigen (HBsAg)-positive patients with cirrhosis, in immediate male relatives of liver cancer patients, and in persons who had undergone hepatic resection. In the untreated group, 10/162 (6%) cirrhotics, 3/18 (17%) male family members, and 6/10 (60%) post-resection cases developed single or multiple HCCs within 1 year of screening done at 3-month intervals on the basis of alpha-fetoprotein (AFP) levels and real-time hepatic ultrasonography. In contrast, none of the Wellferon-treated group consisting of 518 cirrhotic patients, 82 male relatives of HCC patients and 20 post-resection cases developed HCC. Two HBsAg-positive individuals who had not been treated with interferon (IFN) developed hepatic nodules which that showed dysplasia, AFP elevation and chromosomal changes. These studies demonstrate the poor results of late diagnosis and show that early intervention and prophylaxis with Wellferon can reduce the incidence of HCC in high-risk persons. In addition, transhepatic chemoembolisation and liver resection are suitable methods for treating small HCCs (single or multiple) that are detected by screening. However, some of these early-detected HCCs remain highly malignant. Prophylactic treatment of pre-cancerous conditions appears to be a better option as a long-term programme for HCC.

Clinical aspects and epidemiology of hepatitis B and C viruses in hepatocellular carcinoma in Japan

The incidence of hepatocellular carcinoma (HCC) in Japan has increased over the past two decades. Of the 379 patients with HCC treated at Shinshu University Hospital over the past 20 years, 112 underwent treatment between 1971 and 1980 and 267 were treated between 1981 and 1990. The prevalence of hepatitis B virus-associated HCC and hepatitis C virus-associated HCC was 54% and 34%, respectively, during the first decade and 31% and 60%, respectively, during the second decade. Major factors contributing to the increased incidence of HCC include an increase in the incidence of type C chronic hepatitis and an increase in the incidence of cirrhosis of the liver, which in turn are the result of blood transfusions received about 30 years ago. Donated blood testing positive for hepatitis C virus antibody is currently rejected from the blood supply. However, the occurrence of post-transfusion hepatitis with the potential to develop into HCC has not been entirely eliminated. In addition, there is an as yet unelucidated route of horizontal transmission of hepatitis C virus.

Transgenic models of tumor development

Numerous cancer-prone strains of mice have been created by the introduction of candidate tumor-promoting genes into fertilized eggs. Each transgenic strain is predisposed to develop specific types of tumors, but they usually arise stochastically because of the need for spontaneous mutation of genes that collaborate with the introduced oncogene. These mice are providing insights into the effects of individual oncogenes on cellular proliferation, differentiation, and viability, as well as on oncogene cooperativity. Their predisposed state imposes sensitivity to viral and chemical carcinogenesis, and the mice should prove valuable in tests of potential carcinogens, therapies, and preventive measures.

Hepatocarcinogenesis in transgenic mice carrying albumin-promoted SV40 T antigen gene

We have developed transgenic mice that inherit albumin promoter-regulated simian virus 40 (SV40) large T antigen gene, expressed specifically in hepatocytes. These mice all develop multifocal hepatocellular carcinomas at around 5 months and die of liver insufficiency by 7 months. Sequential morphological observation of hepatocarcinogenesis revealed 5 distinct stages: (I) newborn to 2 weeks of age, neither recognizable histological changes nor cellular replication in spite of T antigen expression; (II) between 3 and 7 weeks, diffuse cytomegalic change of hepatocytes with numerous abnormal mitoses, usually resulting in cell death; (III) from 7 weeks onwards, quasi-regenerative small hepatocyte foci with a decreased tendency for cytomegaly in spite of T antigen expression, rapidly replacing the hepatic tissue; (IV) 11 weeks of age and thereafter, neoplastic foci and nodules with enzymatic alteration; (V) 20 weeks of age and thereafter, gross hepatocellular carcinomas with occasional pulmonary metastases. Considerable variation existed both in morphological and enzymatic features and T antigen expression among neoplastic lesions, including carcinomas. Thus, these transgenic mice clearly show a multistep process in hepatocarcinogenesis with remarkable synchrony and provide a promising model for analyzing the essential events of carcinogenesis at different stages.

Evidence for increased in vitro recombination with insertion of human hepatitis B virus DNA

Chromosomal translocation, deletion, and inversion/duplication directly linked to hepatitis B virus (HBV) DNA integration occur frequently in host DNA of human hepatocellular carcinomas. To test the possible recombinogenic effect of HBV DNA, we have utilized an in vitro recombination assay. Fragments containing the region spanning DR1, which is believed to be the origin of viral replication and a preferred site in the viral genome for integration, increased the recombination events reproducibly in the presence of extracts from actively dividing cells (e.g., hepatocellular carcinoma) but not resting cells (e.g., normal liver). Moreover, in these extracts we have found a protein(s) that specifically binds to these HBV DNA fragments. These results support the notion that in some instances integrated HBV DNAs cause further genomic instability, possibly involving specific cellular protein(s). The fact that extracts from nondividing, normal liver did not increase recombination events suggests that genomic instability depends upon active cellular growth, a feature more commonly found subsequent to HBV-induced hepatocellular injury than in healthy liver. Our results offer an explanation for the high incidence of liver cancer that accompanies chronic hepatitis and add HBV to the list of agents that can cause genetic recombination.

Hepatitis B defective virus with rearrangements in the preS gene during chronic HBV infection

We have found a defective form of HBV2 in a HBsAg- and anti-HBe-positive patient with liver cancer. Viral deletions were identified in the preS coding region using PCR. The presence of deleted HBV forms was observed in serum, PBMC, and liver samples. After sequencing 12 clones were analyzed (subtype adr). In 9 out of 12 clones a 183-bp in-frame deletion was recorded in the preS1 region (2995 to 3177). Three out of 9 clones also yielded rearrangements of the preS2 N-terminal part. Four out of 9 showed numerous point mutations in the preS1 and preS2 sequence. In addition, 3 out of 12 clones, which did not show the 183-bp preS1 deletion were found to have small deletions and insertions in the same part of the preS1 gene. Immunological mapping using monoclonal anti-preS antibodies showed loss of preS epitopes located at the 3'-part of preS1 and the 5'-part of preS2. On the other hand, epitopes mapped to the 5'-part of preS1 and 3' of preS2 were conserved. PBMC were also tested and solely PCR showed the major form of defective HBV with preS1 183-bp deletion. However, viral deletions in the preS gene eliminated the preS2 promotor region and B- and T-cell recognition sites. In contrast to this, the preS1 binding site to hepatocytes was conserved. Therefore, such deletions would potentially lead to an impairment in viral clearance without affecting viral penetration in liver cells, possibly accounting for chronic HBV infection.

Complete hepatic regeneration after somatic deletion of an albumin-plasminogen activator transgene

We previously demonstrated that expression of an albumin-urokinase-type plasminogen activator (Alb-uPA) fusion construct in transgenic mice resulted in elevated plasma uPA concentration, hypofibrinogenemia, and neonatal hemorrhaging. Two lines of Alb-uPA mice were established in which only one half of the transgenic pups died at birth; surprisingly, plasma uPA concentrations in survivors gradually returned to normal by 2 months of age. The basis for this phenomenon is DNA rearrangement within hepatocytes that affects the transgene tandem array and abolishes transgene expression. Transgene-deficient cells selectively proliferate relative to surrounding liver, and this process culminates in replacement of the entire liver by clonal hepatic nodules derived from transgene-deficient progenitor cells. In some cases as few as two nodules can reconstitute over 90% of liver mass, highlighting the remarkable regenerative capacity of individual liver cells.

Myristylation is involved in intracellular retention of hepatitis B virus envelope proteins

The envelope of hepatitis B virus contains three related proteins, one of which is myristylated. The nonmyristylated small and middle protein are assembled into empty envelope particles which are secreted from cells, whereas the myristylated large envelope protein is mainly found in complete virions and is not secreted in the absence of the nucleocapsid. The block to secretion can be partially overcome by mutation or deletion of the myristylation site. Creation of a myristyl attachment site in the small protein impairs the secretion of empty envelope particles but not their intracellular assembly. Myristylation may therefore play a crucial role in hepatitis B virus replication by channeling the envelope proteins into complete viral particles.

A hepatitis B virus mutant associated with an epidemic of fulminant hepatitis

BACKGROUND

A nosocomial outbreak of fulminant hepatitis B occurred in five patients in Haifa, Israel. Previous investigations identified the suspected source as a carrier of hepatitis B surface antigen who was positive for antibodies to hepatitis B e antigen and had chronic liver disease. We examined the strain of hepatitis B virus (HBV) that caused this epidemic, in order to identify specific mutations in the precore or core region.

METHODS

The presence of HBV was identified by polymerase-chain-reaction amplification of viral DNA in serum from the source patient, the five patients with fulminant hepatitis B, and five controls with acute, self-limited hepatitis B. The amplified viral HBV DNA samples were then cloned and sequenced.

RESULTS

Sequence analysis of viral DNA established that the same HBV mutant with two mutations in the precore region was present in the source patient and the five patients with fulminant hepatic failure. This HBV mutant had significant sequence divergence from other known HBV subtypes in the X, precore, and core regions. Cloned HBV DNA derived from a hospitalized patient who had subclinical hepatitis B at the same time as the outbreak and from four other control subjects with acute, self-limited hepatitis B all contained the wild-type sequence in the precore region.

CONCLUSIONS

In the outbreak we studied, a mutant hepatitis B viral strain was transmitted from a common source to five patients who subsequently died of fulminant hepatitis B infection. Naturally occurring viral mutations hepatitis B infection. Naturally occurring viral mutations in the HBV genome may predispose the infected host to more severe liver injury.

HBx gene of hepatitis B virus induces liver cancer in transgenic mice

The exact role of hepatitis B virus in the development of liver cancer is not known. The recent identification of a viral regulatory gene HBx suggests a possible direct involvement of the virus whereby the HBx protein, acting as a transcriptional transactivator of viral genes, may alter host gene expression and lead to the development of hepatocellular carcinoma. We have tested this possibility of placing the entire HBx gene under its own regulatory elements directly into the germline of mice. Transgenic animals harbouring this viral gene succumbed to progressive histopathological changes specifically in the liver, beginning with multifocal areas of altered hepatocytes, followed by the appearance of benign adenomas, and proceeding to the development of malignant carcinomas. Male mice developed disease and died much earlier than females. This transgenic animal model appears ideal for defining the molecular events that follow the expression of the viral HBx gene and are responsible for the development of liver cancer.