Chromosomal translocation and inverted duplication associated with integrated hepatitis B virus in hepatocellular carcinomas

HBV integrations reshaping genomic structures promote hepatocellular carcinoma

OBJECTIVE

Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC), mostly characterised by HBV integrations, is prevalent worldwide. Previous HBV studies mainly focused on a few hotspot integrations. However, the oncogenic role of the other HBV integrations remains unclear. This study aimed to elucidate HBV integration-induced tumourigenesis further.

DESIGN

Here, we illuminated the genomic structures encompassing HBV integrations in 124 HCCs across ages using whole genome sequencing and Nanopore long reads. We classified a repertoire of integration patterns featured by complex genomic rearrangement. We also conducted a clustered regularly interspaced short palindromic repeat (CRISPR)-based gain-of-function genetic screen in mouse hepatocytes. We individually activated each candidate gene in the mouse model to uncover HBV integration-mediated oncogenic aberration that elicits tumourigenesis in mice.

RESULTS

These HBV-mediated rearrangements are significantly enriched in a bridge-fusion-bridge pattern and interchromosomal translocations, and frequently led to a wide range of aberrations including driver copy number variations in chr 4q, 5p (TERT), 6q, 8p, 16q, 9p (CDKN2A/B), 17p (TP53) and 13q (RB1), and particularly, ultra-early amplifications in chr8q. Integrated HBV frequently contains complex structures correlated with the translocation distance. Paired breakpoints within each integration event usually exhibit different microhomology, likely mediated by different DNA repair mechanisms. HBV-mediated rearrangements significantly correlated with young age, higher HBV DNA level and TP53 mutations but were less prevalent in the patients subjected to prior antiviral therapies. Finally, we recapitulated the TONSL and TMEM65 amplification in chr8q led by HBV integration using CRISPR/Cas9 editing and demonstrated their tumourigenic potentials.

CONCLUSION

HBV integrations extensively reshape genomic structures and promote hepatocarcinogenesis (graphical abstract), which may occur early in a patient's life.

SurVirus: a repeat-aware virus integration caller

A significant portion of human cancers are due to viruses integrating into human genomes. Therefore, accurately predicting virus integrations can help uncover the mechanisms that lead to many devastating diseases. Virus integrations can be called by analysing second generation high-throughput sequencing datasets. Unfortunately, existing methods fail to report a significant portion of integrations, while predicting a large number of false positives. We observe that the inaccuracy is caused by incorrect alignment of reads in repetitive regions. False alignments create false positives, while missing alignments create false negatives. This paper proposes SurVirus, an improved virus integration caller that corrects the alignment of reads which are crucial for the discovery of integrations. We use publicly available datasets to show that existing methods predict hundreds of thousands of false positives; SurVirus, on the other hand, is significantly more precise while it also detects many novel integrations previously missed by other tools, most of which are in repetitive regions. We validate a subset of these novel integrations, and find that the majority are correct. Using SurVirus, we find that HPV and HBV integrations are enriched in LINE and Satellite regions which had been overlooked, as well as discover recurrent HBV and HPV breakpoints in human genome-virus fusion transcripts.

Nanomedicinal strategies as efficient therapeutic interventions for delivery of cancer vaccines

The applications of gene therapy-based treatment of cancers were started almost two decades back as a boon over the chemotherapeutic treatment strategies. Gene therapy helps in correcting the genetic sequences for treatment of cancers, thus also acts like a vaccine to induce the cellular and humoral immunity. However, the cancer vaccines typically suffer from a series of biopharmaceutical challenges due to poor solubility, low systemic availability and lack of targeting ability. Owing to these challenges, the physicians and pharmaceutical scientists have explored the applications of nanocarriers as quite promising systems for effective treatment against the tumors. A series of nanotherapeutic systems are available to date for diverse drug therapy applications. Systematic understanding on the preparation, evaluation and application of nanomedicines as a carrier system for delivering the cancer vaccines is highly important. The present review article provides an in-depth understanding on the challenges associated with cancer vaccine delivery and current opportunities with diverse nanomedicinal carriers being available for treatment of cancers.

Molecular Mechanisms Driving Progression of Liver Cirrhosis towards Hepatocellular Carcinoma in Chronic Hepatitis B and C Infections: A Review

Almost all patients with hepatocellular carcinoma (HCC), a major type of primary liver cancer, also have liver cirrhosis, the severity of which hampers effective treatment for HCC despite recent progress in the efficacy of anticancer drugs for advanced stages of HCC. Here, we review recent knowledge concerning the molecular mechanisms of liver cirrhosis and its progression to HCC from genetic and epigenomic points of view. Because ~70% of patients with HCC have hepatitis B virus (HBV) and/or hepatitis C virus (HCV) infection, we focused on HBV- and HCV-associated HCC. The literature suggests that genetic and epigenetic factors, such as microRNAs, play a role in liver cirrhosis and its progression to HCC, and that HBV- and HCV-encoded proteins appear to be involved in hepatocarcinogenesis. Further studies are needed to elucidate the mechanisms, including immune checkpoints and molecular targets of kinase inhibitors, associated with liver cirrhosis and its progression to HCC.

Molecular Mechanisms Driving Progression of Liver Cirrhosis towards Hepatocellular Carcinoma in Chronic Hepatitis B and C Infections: A Review

Almost all patients with hepatocellular carcinoma (HCC), a major type of primary liver cancer, also have liver cirrhosis, the severity of which hampers effective treatment for HCC despite recent progress in the efficacy of anticancer drugs for advanced stages of HCC. Here, we review recent knowledge concerning the molecular mechanisms of liver cirrhosis and its progression to HCC from genetic and epigenomic points of view. Because ~70% of patients with HCC have hepatitis B virus (HBV) and/or hepatitis C virus (HCV) infection, we focused on HBV- and HCV-associated HCC. The literature suggests that genetic and epigenetic factors, such as microRNAs, play a role in liver cirrhosis and its progression to HCC, and that HBV- and HCV-encoded proteins appear to be involved in hepatocarcinogenesis. Further studies are needed to elucidate the mechanisms, including immune checkpoints and molecular targets of kinase inhibitors, associated with liver cirrhosis and its progression to HCC.

Molecular pathogenesis of hepatocellular carcinoma and impact of therapeutic advances

Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality and has an increasing incidence worldwide. HCC can be induced by multiple etiologies, is influenced by many risk factors, and has a complex pathogenesis. Furthermore, HCCs exhibit substantial heterogeneity, which compounds the difficulties in developing effective therapies against this highly lethal cancer. With advances in cancer biology and molecular and genetic profiling, a number of different mechanisms involved in the development and progression of HCC have been identified. Despite the advances in this area, the molecular pathogenesis of hepatocellular carcinoma is still not completely understood. This review aims to elaborate our current understanding of the most relevant genetic alterations and molecular pathways involved in the development and progression of HCC, and anticipate the potential impact of future advances on therapeutic drug development.

Pathogenesis of hepatocellular carcinoma according to aetiology

Hepatocellular carcinoma is related to various etiologies including hepatitis B, hepatitis C, high alcohol intake, aflatoxin B1 and metabolic syndrome. Most of the time HCC developed on cirrhosis. Consequently, the mechanisms of carcinogenesis of these different risk factors are difficult to separate from the events leading to cirrhosis. In contrast, aflatoxin B1 and hepatitis B have a clear direct oncogenic role through point mutations in the TP53 tumour suppressor gene and insertional mutagenesis respectively. Finally, next-generation sequencing and transcriptome analysis will refine our knowledge of the relationship between aetiology and the genetic events that draw the mutational landscape of hepatocellular carcinoma.

Envelope proteins derived from naturally integrated hepatitis B virus DNA support assembly and release of infectious hepatitis delta virus particles

A natural subviral agent of human hepatitis B virus (HBV), hepatitis delta virus (HDV), requires only the envelope proteins from HBV in order to maintain persistent infection. HBV surface antigens (HBsAgs) can be produced either by HBV replication or from integrated HBV DNA regardless of replication. The functional properties of the integrant-generated HBsAgs were examined using two human hepatocellular carcinoma-derived cell lines, Hep3B and PLC/PRF/5, that contain HBV integrants but do not produce HBV virions and have no signs of HBV replication. Both cell lines were able to support HDV replication and assembly/egress of HDV virions. Neither of the cell lines was able to produce substantial amounts of the pre-S1-containing HDV particles. HDV virions assembled in PLC/PRF/5 cells were able to infect primary human hepatocytes, while Hep3B-derived HDV appeared to be noninfectious. These results correlate with the findings that the entire open reading frame (ORF) for the large (L) envelope protein that is essential for infectivity is present on HBV RNAs from PLC/PRF/5 cells, while an L protein ORF that was truncated and fused to inverted precore sequences was found using RNAs from Hep3B cells. This study demonstrates for the first time that at least some of the HBV DNA sequence naturally integrated during infection can produce functional small and large envelope proteins capable of the formation of infectious HDV virions. Our data indicate that in vivo chronic HDV infection can persist in the absence of HBV replication (or when HBV replication is profoundly suppressed) if functional envelope proteins are supplied from HBV integrants.

IMPORTANCE

The study addresses the unique mechanism of HDV persistence in the absence of ongoing HBV replication, advances our understanding of HDV-HBV interactions, and supports the implementation of treatments directly targeting HDV for HDV/HBV-infected individuals.

Structure and expression of integrated hepatitis B virus genes in an HBs antigen producing human cell line (huGK-14)

A human continuous cell line (huGK-14) within a lineage of passaged cultures was investigated in the mode of integration and expression of hepatitis B virus (HBV) genes. HBV DNA was integrated in eight different sites of the cellular DNA, in each of which HBV genome was rearranged, fragmented, and/or partly deleted. Complete HBV genome that may lead to production of infectious virus particles was not detected in the cells nor in the culture medium. Clones of cDNA containing a complete coding frame for small HBs antigen protein (type adr) were obtained from mRNA of the cells. The cells were stable over the period of six months of cultivation and more than 60 population doublings in the mode of HBV integration and HBs mRNA expression.These results provide substantial evidence for the absence of an ability for the integrated DNA to create an infectious product in the cell; for the stable production of HBs mRNA from the cells, and suggest the usefulness of this cell line as a substrate for HBV vaccine production.

Mechanisms of HBV-related hepatocarcinogenesis

The hepatitis B virus (HBV) is a small enveloped DNA virus, which primarily infects hepatocytes and causes acute and persistent liver disease. Epidemiological studies have provided overwhelming evidence for a causal role of chronic HBV infection in the development of hepatocellular carcinoma, but the molecular mechanisms underlying virally-induced tumourigenesis 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 cancer-related genes 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. Recent genetic studies indicate that HBV-related tumours display a distinctive profile with a high rate of chromosomal alterations and low frequency of beta-catenin mutations. This review will discuss the evidence implicating chronic HBV infection as a causal risk factor of primary liver cancer. It will also discuss the molecular mechanisms that are critical for the tumourigenic process due to long lasting infection with HBV.

A novel hepatitis B virus (HBV) subgenotype D (D8) strain, resulting from recombination between genotypes D and E, is circulating in Niger along with HBV/E strains

Niger is a west African country that is highly endemic for hepatitis B virus (HBV) infection. The seroprevalence for HBV surface antigen (HBsAg) is about 20%; however, there are no reports on the molecular epidemiology of HBV strains spreading in Niger. In the present study, HBV isolates from the sera of 58 consecutive, asymptomatic, HBsAg-positive blood donors were characterized. Genotype affiliation was determined by amplification, sequencing and phylogenetic analysis of the preS1, polymerase/reverse transcriptase (RT/Pol) and precore (preC)/C regions. The first series of results revealed that different genomic fragments clustered with different genotypes on phylogenetic trees, suggesting recombination events. Twenty-four complete genomic sequences were obtained by amplification and sequencing of seven overlapping regions covering the whole genome, and were studied by extensive phylogenetic analysis. Among them, 20 (83.3%) were classified unequivocally as genotype E (HBV/E). The remaining four (16.7%) clustered on a distinct branch within HBV/D with strong bootstrap and posterior probability values. Complete molecular characterization of these four strains was achieved by the Simplot program, bootscanning analysis and cloning experiments, and enabled us to identify an HBV/D-E recombinant that formed a new HBV/D subgenotype spreading in Niger, tentatively named D8. Moreover, 20 new complete HBV/E nucleotide sequences were determined that exhibited higher genetic variability than is generally described in Africa. One was found to be a recombinant containing HBV/D sequences in the preS2 and RT/Pol regions. Taken together, these data suggest that, in Niger, genetic variability of HBV strains is still evolving, probably reflecting ancient endemic HBV infection.

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.

The role of the woodchuck model in the treatment of hepatitis B virus infection

Experimental studies of animals with chronic hepadnavirus infection could provide valuable insight into optimal therapeutic strategies for individuals with chronic HBV infection. In this review, we focus on the contributions of the woodchuck model to our understanding of HBV biology and on its role in the development of antiviral drug. Furthermore, we consider the implications of studies focusing on the natural history of WHV infection for the management of HBV and the capacity of treatment to prevent complications of chronic hepatitis B infection.

Hepatitis B virus infection, the immune response and hepatocellular carcinoma

More than 250 million people worldwide are chronically infected with the hepatitis B virus (HBV) and have a 200-fold increased risk of developing hepatocellular carcinoma (HCC). This is one of the most common cancers in the world with a geographical distribution highest in areas where HBV is endemic. A number of molecular mechanisms have been proposed to explain this correlation including an acutely transforming viral oncogene; chromosomal aberrations due to HBV integration (i.e. deletions, translocations, duplications); activation of cellular proto-oncogenes; inactivation of cellular anti-oncogenes; and transactivation of cellular genes by HBV gene products. HCC usually develops only after 20-30 years of persistent HBV infection accompanied by hepatocyte necrosis, inflammation and regenerative hyperplasia. Because HBV is not directly cytopathic, liver injury must be immune mediated. Factors that predispose HBV-infected individuals to develop HCC are chronicity, an immune response and liver injury rather than a direct genetic event. Hepatic injury and continuous hepatocyte regeneration may allow an accumulation of multiple mutational events sufficient for the emergence of HCC. Pathways which lead to chronicity, the immune response during HBV infection, mechanisms of pathogenesis and methods to prevent HBV infection are all relevant to the development of HCC. Recent studies characterizing the humoral and cellular immune responses in patients chronically infected with HBV and transgenic mouse models of HBV-specific immune tolerance and pathogenesis are providing new insights into the complex association between HBV infection and HCC.

Pathogenesis of hepatitis B virus-associated hepatocellular carcinoma

Hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) remains the most common form of HCC in large areas of Asia and Africa. It remains common even in some countries where hepatitis C virus (HCV)-associated HCC has become the predominant form, such as Japan. Integration of HBV in HCC DNA is found at random sites in the host genome in nearly all patients with HBV-associated HCC. It is not clear how often this integration results in insertional mutagenesis, but previously unknown growth regulating genes and cancer-associated genes have been found frequently near HBV integration sites in HCC in recent studies. In addition, HBV encodes a transactivating protein, the X protein, which could enable the randomly integrated HBV to alter the function of host genes that are not near the integration site. Mutations at two adjacent codons in HBV (1762(T)/1764(A) mutations) within the X gene are frequently found in HCC patients, and may play a role in the mutagenic or transactivational role of HBV in HCC. The presence of cirrhosis in most patients with HBV-associated HCC, and the presence of mutations in tumor suppressor genes in many, suggests that these are also factors in hepatocarcinogenesis. Few studies have examined the mutations of more than one gene in the same HCC patients. Fewstudies have evaluated the interactions between HBV mutations, host gene mutations, cirrhosis, and other potentially mutagenic stresses at the cellular level, with progression to HCC, and few studies have been conducted to determine whether these changes must accumulate in succession to lead to HCC. The recent availability of rapid sequencing methods and DNA microarray technologies has permitted expression profiling and permutation analysis of an array of genes to explore the pattern and succession of molecular changes leading to HBV-associated HCC. To date, these methods have been used to show patterns of molecular changes that differ in HBV-associated HCC (compared to HCV-associated HCC or to HCC in patients lacking either virus) and patterns that can predict survival (and hence may directly indicate different mechanisms of disease), and may soon make possible a universally accepted clinical classification scheme for HCC.

Hepatitis B virus integration, fragile sites, and hepatocarcinogenesis

Chronic liver disease associated with long term hepatitis B virus (HBV) infection contributes importantly to the development of hepatocellular carcinoma (HCC). A salient feature of these chronic infections is the integration of subgenomic HBV DNA fragments into many different locations within the host DNA, suggesting that integration is random. Although this may promote genetic instability during liver regeneration which accompanies a bout of chronic liver disease, the actual role of integrated HBV DNA in hepatocarcinogenesis is uncertain. Importantly, most integration events retain the HBV open reading frame encoding the HBx antigen (HBxAg), which is the virus contribution to HCC. In addition, many integration events reported in the literature occur near or within fragile sites or other cancer associated regions of the human genome that are prone to instability in tumor development and progression. Genetic instability associated with integration potentially alters the expression of oncogenes, tumor suppressor genes, and microRNAs (miRNAs) that may contribute importantly to tumorigenesis. If so, then selected integration events may alter pathways that are rate limiting in hepatocarcinogenesis, thereby providing targets with diagnostic/prognostic potential and for therapeutic intervention.

Correction of chromosomal mutation and random integration in embryonic stem cells with helper-dependent adenoviral vectors

For gene therapy of inherited diseases, targeted integration/gene repair through homologous recombination (HR) between exogenous and chromosomal DNA would be an ideal strategy to avoid potentially serious problems of random integration such as cellular transformation and gene silencing. Efficient sequence-specific modification of chromosomes by HR would also advance both biological studies and therapeutic applications of a variety of stem cells. Toward these goals, we developed an improved strategy of adenoviral vector (AdV)-mediated HR and examined its ability to correct an insertional mutation in the hypoxanthine phosphoribosyl transferase (Hprt) locus in male mouse ES cells. The efficiency of HR was compared between four types of AdVs that contained various lengths of homologies at the Hprt locus and with various multiplicities of infections. The frequency of HR with helper-dependent AdVs (HD AdVs) with an 18.6-kb homology reached 0.2% per transduced cell at a multiplicity of infection of 10 genomes per cell. Detection of random integration at DNA levels by PCR revealed extremely high efficiency of 5% per cell. We also isolated and characterized chromosomal sites where HD AdVs integrated in a random manner. In contrast to retroviral, lentiviral, and adeno-associated viral vectors, which tend to integrate into genes, the integration sites of AdV was distributed randomly inside and outside genes. These findings suggest that HR mediated by HD AdVs is efficient and relatively safe and might be a new viable option for ex vivo gene therapy as well as a tool for chromosomal manipulation of a variety of stem cells.

Large scaled analysis of hepatitis B virus (HBV) DNA integration in HBV related hepatocellular carcinomas

BACKGROUND AND AIMS

Hepatitis B virus (HBV) DNA integration into or close to cellular genes is frequently detected in HBV positive hepatocellular carcinomas (HCC). We have previously shown that viral integration can lead to aberrant target gene transcription. In this study, we attempted to investigate common pathways to hepatocarcinogenesis.

METHODS

By using a modified Alu-polymerase chain reaction approach, we analysed 50 HCCs along with 10 previously published cases.

RESULTS

Sixty eight cellular flanking sequences (seven repetitive or unidentified sequences, 42 cellular genes, and 19 sequences potentially coding for unknown proteins) were obtained. Fifteen cancer related genes and 25 cellular genes were identified. HBV integration recurrently targeted the human telomerase reverse transcriptase gene (three cases) and genes belonging to distinct pathways: calcium signalling related genes, 60s ribosomal protein encoding genes, and platelet derived growth factor and mixed lineage leukaemia encoding genes. Two tumour suppressor genes and five genes involved in the control of apoptosis were also found at the integration site. The viral insertion site was distributed over all chromosomes except 13, X, and Y.

CONCLUSIONS

In 61/68 (89.7%) cases, HBV DNA was integrated into cellular genes potentially providing cell growth advantage. Identification of recurrent viral integration sites into genes of the same family allows recognition of common cell signalling pathways activated in hepatocarcinogenesis.

Integration of hepatitis B virus containing mutations in the core promoter/X gene in patients with hepatocellular carcinoma

Integration of hepatitis B virus is thought to be an essential step in hepatitis B virus associated hepatocarcinogenesis. Mutations at nucleotides 1762 and 1764 in the hepatitis B virus, within a sequence encoding both the core promoter gene and the X gene, have been found frequently in patients with hepatocellular carcinoma. However, integration of these mutant sequences has not been reported to date.

METHODS

A 228-base pair segment of the hepatitis B virus core promoter gene was amplified from hepatocellular carcinomas and adjacent non-tumourous liver tissue by nested PCR and sequenced. Integration of hepatitis B virus into human genomic DNA was investigated using the 'genome walking' method.

RESULTS

Point mutations were found in both hepatitis B virus nucleotides 1762 and 1764 in 8 of 14 hepatocellular carcinoma tissues (57%) and in 11 of 14 adjacent non-tumourous liver tissues (79%). Three patients were evaluated using the 'genome walking' method; all were found to have hepatitis B virus DNA integrated in their hepatocellular carcinoma (two patients) and/or in their non-tumourous liver tissue (three patients). Integration occurred in all tissues near host genomic sites that are prone to integration. Hepatitis B virus was integrated at or near the hepatitis B virus DR1 site in all samples, and all contained truncated X gene sequences that have been reported to be capable of producing fusion transcripts with transactivation potential.

CONCLUSIONS

Integrated hepatitis B virus DNA containing core promoter mutations at nucleotides 1762 and 1764 was found in hepatocellular carcinoma and/or adjacent non-tumourous liver tissue of three patients. These findings leave open the possibility that insertional mutagenesis or transactivation by fusion transcripts resulting from hepatitis B virus integration could play a role in hepatocarcinogenesis in some patients.

Analysis of risk factors for hepatocellular carcinoma in patients with HBs antigen- and anti-HCV antibody-negative alcoholic cirrhosis: clinical significance of prior hepatitis B virus infection

BACKGROUND

The hepatitis B virus (HBV) or hepatitis C virus (HCV) markers frequently are detected in alcoholic patients with hepatocellular carcinoma (HCC). However, risk factors for the development of HCC in patients with HBs antigen (Ag)- and anti-HCV antibody (anti-HCV)-negative alcoholic cirrhosis have not been clearly documented. The present study was conducted to elucidate the occurrence rates of HCC in HBs Ag- and anti-HCV-negative male alcoholic cirrhosis and to assess the risk factors for hepatocellular carcinogenesis.

METHOD

We prospectively studied 91 consecutive patients with HBs Ag- and anti-HCV-negative alcoholic cirrhosis for 0.5 to 12.5 years (median 5.9 years). Potential risk factors assessed for liver carcinogenesis included the following six variables: age, total alcohol intake, association of continuing alcohol intake after diagnosis, indocyanine green retention rate at 15 min, anti-HB core antibodies (anti-HBc), and association of diabetes mellitus.

RESULTS

Cumulative occurrence rates of HCC were 6.4%, 18.9%, and 28.7% at the end of the 5th, 7th and 10th years, respectively. When classified by anti-HBc, the occurrence rates of HCC in 31 patients with anti-HBc and 60 patients without anti-HBc were 15.6% and 2.9% at the 5th year, 28.4% and 13.5% at the 7th year, and 40.4% and 22.1% at the 10th year, respectively. The occurrence rates of HCC were also significantly related to the cumulative alcohol intake. Cox proportional hazard model identified that cumulative alcohol intake (p = 0.0047) and positive anti-HBc antibodies (p = 0.0598) were independently associated with the occurrence rates of HCC.

CONCLUSION

These epidemiologic results suggest that heavy cumulative alcohol intake and prior exposure to HBV infection are risk factors for the development of HCC in patients with HBs Ag- and anti-HCV-negative alcoholic cirrhosis.

Effects of hepatitis B virus infection on human sperm chromosomes

AIM: To evaluate the level of sperm chromosome aberrations in male patients with hepatitis B, and to directly detect whether there are HBV DNA integrations in sperm chromosomes of hepatitis B patients.

METHODS: Sperm chromosomes of 14 tested subjects (5 healthy controls, 9 patients with HBV infection, including 1 with acute hepatitis B, 2 with chronic active hepatitis B, 4 with chronic persistent hepatitis B, 2 chronic HBsAg carriers with no clinical symptoms) were prepared using interspecific in vitro fertilization between zona-free golden hamster ova and human spermatozoa, and the frequencies of aberration spermatozoa were compared between subjects of HBV infection and controls. Fluorescence in situ hybridization (FISH) to sperm chromosome spreads was carried out with biotin-labeled full length HBV DNA probe to detect the specific HBV DNA sequences in the sperm chromosomes.

RESULTS: The total frequency of sperm chromosome aberrations in HBV infection group (14.8%, 33/223) was significantly higher than that in the control group (4.3%, 5/116). Moreover, the sperm chromosomes in HBV infection patients commonly presented stickiness, clumping, failure to staining, etc, which would affect the analysis of sperm chromosomes. Specific fluorescent signal spots for HBV DNA were seen in sperm chromosomes of one patient with chronic persistent hepatitis. In 9 (9/42) sperm chromosome complements containing fluorescent signal spots, one presented 5 obvious FISH spots, others presented 2 to 4 signals. There was significant difference of fluorescence intensity among the signal spots. The distribution of signal sites among chromosomes was random.

CONCLUSION: HBV infection can bring about mutagenic effects on sperm chromosomes. Integrations of viral DNA into sperm chromosomes which are multisites and nonspecific, can further increase the instability of sperm chromosomes. This study suggested that HBV infection can create extensively hereditary effects by alteration genetic constituent and/or induction chromosome aberrations, as well as the possibility of vertical transmission of HBV via the germ line to the next generation.

Liver cancer

The prognosis of patients with HCC remains dismal. Even in the subgroups of patients who have the most favorable characteristics and are eligible for surgical resection, the 5-year survival rate is less than 25%. For patients with more advanced disease, the median survival time is less than 1 year. The good news in HCC research is that the disease can be prevented. In Taiwan, the rate of HCC in children aged 6 to 9 years decreased from 5.2 per million population before the neonatal vaccination program began in 1984 to 1.3 per million population in the first vaccinated cohort. Treatment of viral hepatitis with IFN may decrease the rates of long-term development of HCC. Other agents that may prevent second primary tumors following resection of HCC, such as polyprenoic acid and acylic retinoid, are also being investigated.

Interaction of Hepatitis B virus with cellular processes in liver carcinogenesis

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

Occult hepatitis B virus infection in HBs antigen-negative hepatocellular carcinoma in a Japanese population: involvement of HBx and p53

Hepatitis B virus (HBV) genome was reported to be detected in serum or liver tissues in hepatocellular carcinoma (HCC) patients negative for hepatitis B surface antigen (HBsAg). Hepatitis B x (HBx) and p53 protein were reported to play an important role in HBV-related hepatocarcinogenesis. To clarify latent HBV infection in HBsAg- and anti-hepatitis C virus (anti-HCV)-negative HCC in a Japanese population and involvement of HBx and p53 protein in these patients, we performed the sensitive and specific nested polymerase chain reaction (PCR) and immunohistochemical analysis. Of 1,024 HCC patients we saw between 1974 and 1998, 66 (6.4%) were negative for HBsAg and anti-HCV. Serum DNA was amplified by nested PCR by using specific primers of surface (S), core (C) and X regions in 26 patients negative for HBsAg and anti-HCV. Eighteen (69%) patients were positive for either S, C, or X region and the results of PCR were confirmed by Southern blotting. Of 18 PCR-positive patients, 3 were positive for anti-HBs and 9 were positive for anti-HBc, however, one was negative for any HBV markers. In HBsAg-negative and PCR-positive patients, the positive rates of expression of HBx and p53 were 8/13 (62%) and 7/13 (54%), being comparable to those in HBsAg-positive HCC patients. The results of the present study suggest that high prevalence of HBV infection is observed in HBsAg-negative HCC in a Japanese population and expression of HBx and p53 is consistent with a role, in these patients, for the transforming ability of these proteins.

Hepatitis B virus in hepatocarcinogenesis

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

Chromosomal aberrations in human hepatocellular carcinomas associated with hepatitis C virus infection detected by comparative genomic hybridization

Thirty-five hepatocellular carcinomas (HCCs) associated with hepatitis C virus (HCV) were analysed by comparative genomic hybridization (CGH), to screen for changes in copy-number of DNA sequences. Chromosomal losses were noted in 1p34-36 (37%), 4q12-21 (48%), 5q13-21 (35%), 6q13-16 (23%), 8p21-23 (28%), 13q (20%), 16q (33%) and 17p13 (37%). Gains were noted in 1q (46%), 6p (20%), 8q21-24 (31%) and 17q (43%). High level gains indicative of gene amplifications were found in 7q31 (3%), 11q13 (3%), 14q12 (6%) and 17q12 (3%); amplification at 14q12 may be characteristic for HCCs. No significant difference in chromosomal aberrations was noted between carcinomas associated with HCV-infection in our study and those reported earlier in HCCs infected with hepatitis B virus (HBV), indicating that both HBV- and HCV-related carcinomas may progress through a similar cascade of molecular events.

Possible contribution to hepatocarcinogenesis of X transcript of hepatitis B virus in Japanese patients with hepatitis C virus

Serological research suggests that hepatitis B virus (HBV) and hepatitis C virus (HCV) are associated with the development of hepatocellular carcinoma (HCC). It is unclear how genes of hepatitis viruses participate in hepatocarcinogenesis in patients infected with HCV. We investigated the expression of hepatitis virus-related RNAs in resected liver from 51 patients with HCV antibodies (Ab) and without hepatitis B surface antigen (HBsAg). mRNA transcripts of the genes HBx, HBc, HBs, nonstructural (NS) region 3 of HCV, the 5'-untranslated region (UTR) of HCV, and the 5'-UTR of hepatitis G virus (HGV) were amplified by reverse-transcription polymerase chain reaction (RT-PCR) with specific primers for each gene. The HBx transcript was detected in 19 (37%) tumors and in 8 (16%) specimens of noncancerous tissues (P =.014). The NS3 gene of HCV was detected in 35 (69%) tumors and 41 (80%) noncancerous tissues. HGV RNA was detected in 3 tumors (6%). Patients with HBx transcripts were younger than patients without HBx transcripts (P =.012). HBx transcripts were detected in 3 (33%) of 9 well-differentiated HCCs, in 8 (31%) of 26 moderately differentiated HCCs, and in 8 (50%) of 16 poorly differentiated HCCs. Codon 130 (AAG) and codon 131 (GTC) of HBx were changed to ATG and ATC, respectively, in all HCCs with HBx transcripts. In conclusion, we found that the HBx gene was expressed in many HCCs; the gene might promote hepatocarcinogenesis in patients with HCVAb and without HBsAg, but HGV is not closely related to hepatocarcinogenesis in such patients.

Accumulation of genetic alterations in a human hepatoma cell line transfected with hepatitis B virus

Chromosome and molecular analyses of the hepatitis B virus (HBV)-transfected HepG2T14.1 variant of the HepG2 cell line was conducted. In HepG2T14.1 cells several genetic alterations such as de novo aberrations of chromosomes 9, 14, 15, and 20 were identified that are not present in the parental HepG2 cell line. Furthermore, HepG2T14.1 cells showed loss of heterozygosity (LOH) in the q region of chromosome 14. The single HBV integration site in HepG2T14.1 cells mapped to the 2q35-36 region of one copy of chromosome 2 by fluorescence in situ hybridization (FISH). No genetic changes were identified at or near the HBV integration site at the level of these analyses. In addition, growth rates in vivo and in vitro were dramatically accelerated in HepG2T14.1 cells. These results document that a HBV-transfected hepatoma cell line has de novo genetic mutations at several sites of the host genome, one HBV integration site in an non-rearranged chromosome and an altered phenotype. These findings support our hypothesis that HBV might play a role in cellular transformation by interfering with cellular processes responsible for the stability of the genome.

Alteration of DNA ploidy and cell nuclearity in human hepatocellular carcinoma associated with HBV infection

BACKGROUND/AIMS

Hepatocellular carcinoma usually arises in cirrhotic livers as a complication of chronic liver disease, and may show a variable trend towards increasing ploidy. The aim of this study was to investigate possible associations between different etiological factors, particularly hepatitis B virus and hepatitis C virus infection, and alteration of DNA-ploidy and nuclearity of neoplastic hepatocytes.

METHODS

DNA-ploidy, the percentage of binucleated cells in the total cell population and the fraction of mononucleated hepatocytes in the polyploid compartment were assessed by image cytometry on cellular suspensions obtained by fine-needle biopsy from 60 hepatocellular carcinomas in patients whose viral status had previously been assessed.

RESULTS

Significantly higher DNA-ploidy values (p = 0.005), with a reduction in the percentage of binucleated hepatocytes (p = 0.003) and an increase in the fraction of mononucleated hepatocytes in the polyploid compartment (p < 0.0001), were found in hepatocellular carcinoma with actual or previous hepatitis B virus infection (including also HCV+ve patients) in comparison to those not associated with hepatitis B virus infection, but not when HCV+ve hepatocellular carcinomas were compared to HCV-ve ones. Statistically significant differences for ploidy values (p < 0.05), percentage of binucleated hepatocytes (p < 0.05) and fraction of mononucleated hepatocytes in the polyploid compartment (p = 0.003) were also found between hepatocellular carcinoma associated only to hepatitis B virus infection ("pure" hepatitis B virus cases) and those associated only to hepatitis C virus infection ("pure" hepatitis C virus cases).

CONCLUSIONS

Hepatocellular carcinoma associated with a previous or actual hepatitis B virus infection shows a peculiar phenotypical appearance, characterized by a trend towards increasing ploidy and reduction of binuclearity.

A t(3;8) chromosomal translocation associated with hepatitis B virus intergration involves the carboxypeptidase N locus

Integrated hepatitis B virus (HBV) DNA is found in the great majority of human hepatocellular carcinomas, suggesting that these viral integrations may be implicated in liver oncogenesis. Besides the insertional mutagenesis characterized in a few selected cases and the contribution of viral transactivators to cell transformation to malignancy, HBV has been shown to generate gross chromosomal rearrangements potentially involved in carcinogenesis. Here, we report a t(3;8) chromosomal translocation present in a hepatocellular carcinoma developed in noncirrhotic liver tissue. One side of the translocation, in 8p23, is shown to be in the vicinity of the carboxypeptidase N gene, a locus that is heavily transcribed in liver tissue and frequently deleted in hepatocellular carcinomas and other epithelial tumors. The other side of the translocation, in 3q27-29, is widely implicated in several types of translocations occurring in different malignancies, such as large-cell lymphomas. The present data strongly support a model in which HBV-induced chromosomal rearrangements play a key role during multistep liver oncogenesis.

Hepatitis B and C viruses and primary liver cancer

The data presented indicate that viral agents (namely, HBV and HCV) are major environmental aetiological factors for human primary liver cancer. It is important to elucidate the molecular mechanisms further because HCC is one of the few examples of virus-related human cancers. In addition, the available evidence points to the possibility of at least partial prevention of the tumour by large-scale vaccination.

The molecular pathogenesis of hepatocellular carcinoma

Some of the multiple factors involved in the molecular pathogenesis of hepatocellular carcinoma have been elucidated in recent years but no clear picture of how and in what sequence these factors interact at the molecular level has emerged yet. Transformation of hepatocytes to the malignant phenotype may occur irrespective of the aetiological agent through a pathway of chronic liver injury, regeneration and cirrhosis. The activation of cellular oncogenes, the inactivation of tumour suppressor genes and overexpression of certain growth factors contribute to the development of HCC. There is increasing evidence that the hepatitis B virus may play a direct role in the molecular pathogenesis of HCC. Aflatoxins have been shown to induce specific mutations of the p53 tumour suppressor gene thus providing a clue to how an environmental factor may contribute to tumour development at the molecular level.

Induction of cell cycle progression by hepatitis B virus HBx gene expression in quiescent mouse fibroblasts

The HBx gene of hepatitis B virus has been shown to induce hepatic tumors in transgenic mice and is implicated in hepatocarcinogenesis in human hepatitis B virus infection. To further characterize the role of HBx gene in carcinogenesis, we established mouse fibroblast cell lines in which the expression of HBx gene could be controlled by glucocorticoid hormone and examined the effect of HBx gene expression on cell growth in vitro. Along with the expression of HBx gene, most cells in the G0/G1 phase moved into the S phase in 24 h, and the cell cycle progressed further toward 48 h. Induction of DNA synthesis was also demonstrated by bromo-deoxyuridine labeling analysis. These results indicate that HBx gene has a function to trigger the synthesis of cellular DNA and suggest that HBx gene may play a role in hepatocarcinogenesis in human infection by driving deregulated cell cycle progression.

High-level expression of hepatitis B virus HBx gene and hepatocarcinogenesis in transgenic mice

We studied the development of liver tumors in male HBx gene transgenic mice. Of two lineages studied, in the lineage with the lowest HBx gene expression liver tumors developed only in an incidence comparable with that in normal CD-1 strain, whereas 84% of male mice with a high level of the HBx gene product succumbed to liver neoplasia, indicating that continued HBx gene expression higher than a certain threshold level may be necessary for the development of hepatic neoplasia. Sixty-five mice from a lineage with a high level of HBx expression were then followed throughout their 24-mo lifespan. The livers of transgenic mice showed foci of cellular alteration with cytoplasmic vacuolations around the central veins from the age of 2 mo, but these foci did not expand progressively by the age of 12 mo. Immunostaining demonstrated such hepatocytes had higher expression of HBx protein than surrounding cells. Neoplastic lesions including liver cell adenomas and hepatocellular carcinomas developed from the age of 13 mo. By bromodeoxyuridine labeling analysis, hepatocytes in altered foci were found to have increased DNA synthesis, whereas no labeling was observed in age- and sex-matched nontransgenic littermate controls. Furthermore, DNA content analysis revealed the existence of several small aneuploid peaks in the transgenic liver before the age of tumor development. These results suggest that the continued expression of HBx gene may initiate a complex process to hepatocellular carcinoma by inducing DNA synthesis and placing large numbers of hepatocytes subjective to secondary events for transformation.

Tumor suppressor genes, growth factor genes, and oncogenes in hepatitis B virus-associated hepatocellular carcinoma

A series of changes in the genes that control hepatocyte growth, or interference with the protein products of these genes, appears to have an important role in the etiology of hepatocellular carcinoma (HCC). Mutations of the p53 tumor suppressor gene have been identified in 30-50% of HCC patients in some geographic areas. Abnormalities of the RB tumor suppressor gene have been found in 20-25% of HCCs, including 80-86% of HCCs with p53 mutations. Overexpression of transforming growth factor alpha (TGF-alpha), insulin-like growth factor II (IGF-II), and the oncogenes N-ras, c-myc, and c-fos have been found in high percentages of HCC patients. The cumulative effect of these changes may be more important than the order in which they occur. Some of these changes may explain the mechanism(s) by which the hepatitis B virus participates in the development of HCC.

Analysis of integrated hepatitis B virus DNA and flanking cellular sequences in a childhood hepatocellular carcinoma

The DNA of tumor tissue K1 obtained at autopsy from a case of hepatocellular carcinoma (HCC) in a 9-year-old boy contained integrated hepatitis B virus (HBV) DNA at a single site in the chromosome (case 2, Chang et al.: Hepatology 13:316-320, 1991). To characterize further the integrated viral DNA sequences, a genomic library of the K1 DNA was constructed in the lambda L47.1 vector. One phage clone, designated KTM-1, containing integrated HBV DNA and cellular flanking sequences was obtained from this library. The restriction map and DNA sequence of this clone showed that the integrated HBV DNA was partially deleted and rearranged. The most conserved viral DNA sequences were surface and X genes and arranged in the opposite orientation. The viral core gene was not present. Using chloramphenicol acetyltransferase (CAT) assay, the C-terminal truncated X open reading frame was demonstrated to retain its trans-activating ability. The result suggested that the functional integrated X gene may play a role in hepatocarcinogenesis. The study also showed that the right cellular flanking sequences were human alphoid repetitive sequences.

Current pathogenetic and molecular concepts in viral liver carcinogenesis

Hepatocellular carcinoma (HCC) is one of the most frequent malignancies in humans and in most cases a consequence of chronic infection of the liver by hepatotropic viruses (Hepatitis B Virus (HBV) and possibly Hepatitis C Virus (HCV)). Formation of HCC results from a stepwise process involving different preneoplastic lesions that reflect multiple genetic events, like protooncogene activation, tumor suppressor gene inactivation, and growth factor over- or reexpression. Recent investigations have gained new insights into how these factors are activated and may interact. In addition, improved knowledge of the molecular biology of HBV has led to better understanding of its pleiotropic effects on induction and progression in hepatocarcinogenesis.

Transfected c-Ha-ras oncogene enhances karyotypic instability and integrates predominantly in aberrant chromosomes

A human colon tumor cell line, SW480, was transfected with the c-Ha-ras oncogene, the wild type c-Ha-ras gene, or the pSV2neo plasmid. Cytogenetic analysis and localization of chromosome integration sites were combined in an attempt to analyze the effects of transfection with the c-Ha-ras oncogene on the karyotype. All transfected cell lines showed new clonal chromosome abnormalities present in all cells, ranging from three new aberrations in pSV2neo-transfected SW480 cell lines to eight in c-Ha-ras oncogene-transfected SW480 cell lines. The level of expression of c-Ha-ras mRNA after transfection with the c-Ha-ras oncogene was positively correlated with increased genetic instability, reflected in enhanced karyotypic instability. A combination of banding and fluorescence in situ hybridization (FISH) was used to identify chromosome integration sites. Plasmids containing ras integrated predominantly in new structurally rearranged chromosomes (five of eight). Three of five integration sites in new structurally rearranged chromosomes were localized at or near translocation breakpoints situated in telomeric regions. Specific chromosomes were not involved in the chromosome rearrangements. The results indicate that 1) enhanced expression of c-Ha-ras mRNA correlates with an increase in genetic instability in c-Ha-ras oncogene-transfected SW480 cell lines, and 2) that no specific integration site was observed but ras-containing plasmids were located predominantly in aberrant chromosomes near or at translocation breakpoints involving telomeric bands.

The role of hepatitis B virus in the development of primary hepatocellular carcinoma: Part I

Chronic infections with hepatitis B virus (HBV) of humans and animal hepadnavirus infections in their natural hosts are strongly associated with primary hepatocellular carcinoma (HCC). Although viral integrations are found in cells of many HCC, no general viral-specific hepatocarcinogenic mechanism for hepadnaviruses has been identified. In approximately one half of HCC in woodchuck hepatitis virus (WHV) infected woodchucks, viral integrations near the c-myc or N-myc genes have been reported which result in enhanced expression of the respective gene. Such host gene-specific insertional mutagenesis has not been found in HCC of other hepadnavirus infected hosts. Thus in humans, ground squirrels and ducks hepadnaviral integrations appear to be at different host chromosomal DNA sites in each HCC and few integrations have been found within or near any cellular gene. Other possible hepadnavirus-specific carcinogenic mechanisms that are being investigated include transactivation of cellular gene expression by an hepadnavirus gene product (e.g. the X-gene), and mutation of host genes by unknown hepadnavirus-specific mechanisms. It should be noted, however, that chronic hepadnavirus infection is associated with chronic necroinflammatory liver disease with hepatocellular necrosis and regeneration (sometimes leading to cirrhosis in humans), a pathological process that is common to numerous other risk factors for HCC. This suggests the possibility that this pathological process is hepatocarcinogenic irrespective of the inciting agent and the role of hepadnavirus infection is no different from that of other risk factors in causing chronic necroinflammatory liver disease.