Expression of the hepatitis B virus genome in chronic hepatitis B carriers and patients with hepatocellular carcinoma

In situ analysis of hepatitis B virus (HBV) antigen and DNA in HBV-induced hepatocellular carcinoma

Aims

Hepatitis B Virus (HBV) infection is the major risk factor for hepatocellular carcinoma (HCC) in East Asia. Here we aimed to further investigate the abundance of viral antigen and DNA within HBV-related HCC and surrounding tissues at histological level.

Method

In addition to routine histopathology, in situ hybridization (ISH) of HBV DNA and immunohistochemistry (IHC) of HBsAg were performed in tissues from 131 HBsAg-positive HCC patients undergoing liver resection. Serum α-fetoprotein together with basic biochemical and immunological parameter was also measured.

Results

Overall, the ISH of HBV DNA and IHC of HBsAg showed 31.3% and 92.9% positive rate respectively (p < 0.0001). The level of correlation between these two markers was much more significant in tumor (p < 0.0001) than in tumor-surrounding tissue (p = 0.01). HBsAg exhibited a much higher positive rate in tumor-adjacent tissue than in tumor tissue (86.6% versus 29.9%, p < 0.0001) with significantly different staining pattern. By contrast, the positive rate of HBV DNA ISH was comparable in tumor and surrounding tissue (17.6% versus 22.9%, p = 0.36). Yet the HBV DNA signal in tumor tissue showed predominant nuclear localization (87.0%) whereas staining pattern in adjacent tissue was mixed (43.3% nuclear localization, p = 0.0015). Finally, no significant association between intra-tumor HBV DNA/HBsAg positivity and major histological markers (microvascular invasion, tumor differentiation, etc.) or recurrence after surgery was observed.

Conclusions

These data confirmed the largely integrated state of HBV DNA, weaker expression and altered localization of surface antigen in tumor compared with surrounding tissue. The strikingly different prevalence and localization of HBsAg and HBV DNA reflected the complex and heterogeneous mechanisms leading to HBV-induced tumorigenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13000-022-01194-8.

Mechanisms of DNA Methylation in Virus-Host Interaction in Hepatitis B Infection: Pathogenesis and Oncogenetic Properties

Hepatitis B virus (HBV), the well-studied oncovirus that contributes to the majority of hepatocellular carcinomas (HCC) worldwide, can cause a severe inflammatory microenvironment leading to genetic and epigenetic changes in hepatocyte clones. HBV replication contributes to the regulation of DNA methyltransferase gene expression, particularly by X protein (HBx), and subsequent methylation changes may lead to abnormal transcription activation of adjacent genes and genomic instability. Undoubtedly, the altered expression of these genes has been known to cause diverse aspects of infected hepatocytes, including apoptosis, proliferation, reactive oxygen species (ROS) accumulation, and immune responses. Additionally, pollutant-induced DNA methylation changes and aberrant methylation of imprinted genes in hepatocytes also complicate the process of tumorigenesis. Meanwhile, hepatocytes also contribute to epigenetic modification of the viral genome to affect HBV replication or viral protein production. Meanwhile, methylation levels of HBV integrants and surrounding host regions also play crucial roles in their ability to produce viral proteins in affected hepatocytes. Both host and viral changes can provide novel insights into tumorigenesis, individualized responses to therapeutic intervention, disease progress, and early diagnosis. As such, DNA methylation-mediated epigenetic silencing of cancer-related genes and viral replication is a compelling therapeutic goal to reduce morbidity and mortality from liver cancer caused by chronic HBV infection. In this review, we summarize the most recent research on aberrant DNA methylation associated with HBV infection, which is involved in HCC development, and provide an outlook on the future direction of the research.

Proportion of transcriptionally active DNA virus integrants: a meta-analysis

Oncoviruses are collectively responsible for over 1,000,000 new cases of cancer per year; some can integrate into the host's chromosomes. The present work was aimed at assessing the proportion of transcriptionally active viral integrants through a systematic review of the scientific publications present on the MedLine database. From the articles screened, 628 viral integrants overall were retrieved, of which 530.84 were transcriptionally active (84.53%); among the clinical samples, 264 of 323 integrants were active (81.73%). The causes for the silencing were not addressed in the articles analyzed. These findings might highlight a possible risk factor for the insurgence of cancer since some oncovirus integrants could be reactivated by stimuli of disparate nature. Further studies should address such possibility.

Wild type HBx and truncated HBx: Pleiotropic regulators driving sequential genetic and epigenetic steps of hepatocarcinogenesis and progression of HBV-associated neoplasms

Hepatitis B virus (HBV) is one of the causative agents of hepatocellular carcinoma. The molecular mechanisms of tumorigenesis are complex. One of the host factors involved is apparently the long-lasting inflammatory reaction which accompanies chronic HBV infection. Although HBV lacks a typical viral oncogene, the HBx gene encoding a pleiotropic regulatory protein emerged as a major player in liver carcinogenesis. Here we review the tumorigenic functions of HBx with an emphasis on wild type and truncated HBx variants, and their role in the transcriptional dysregulation and epigenetic reprogramming of the host cell genome. We suggest that HBx acquired by the HBV genome during evolution acts like a cellular proto-onc gene that is activated by deletion during hepatocarcinogenesis. The resulting viral oncogene (v-onc gene) codes for a truncated HBx protein that facilitates tumor progression. Copyright © 2015 John Wiley & Sons, Ltd.

Global DNA methylation levels in white blood cells as a biomarker for hepatocellular carcinoma risk: a nested case-control study

Global DNA hypomethylation is associated with genomic instability and human cancer and blood DNAs collected at the time of cancer diagnosis have been used to examine the relationship between global methylation and cancer risk. To test the hypothesis that global hypomethylation is associated with increased risk of hepatocellular carcinoma (HCC), we conducted a prospective case-control study nested within a community-based cohort with 16 years of follow-up. We measured methylation levels in Satellite 2 (Sat2) by MethyLight and LINE-1 by pyrosequencing using baseline white blood cell DNA from 305 HCC cases and 1254 matched controls. We found that Sat2 hypomethylation was associated with HCC risk [odds ratio (OR) per unit decrease in natural log Sat2 methylation = 1.77, 95% confidence interval (CI) = 1.06-2.95]. The association was significant among individuals diagnosed with HCC before age 62 (OR per unit decrease in natural log Sat2 methylation = 2.47, 95% CI = 1.06-5.73) but not after (OR = 1.67, 95% CI = 0.84-3.32). We did not observe an association of LINE-1 with HCC overall risk by age at diagnosis. Among carriers of hepatitis B virus surface antigen (HBsAg), with each 1U decrease in natural log Sat2 methylation level, the OR for HCC increased by 2.19 (95% CI = 1.00-4.89). LINE-1 hypomethylation was associated with about a 2-fold increased risk of HCC, with ORs (95% CI) of 2.39 (1.06-5.39), 2.09 (0.91-4.77) and 2.28 (0.95-5.51, P(trend) = 0.14) for HBsAg carriers in the third, second and lowest quartile of LINE-1 methylation, respectively compared with carriers in the fourth. These results suggest that global hypomethylation may be a useful biomarker of HCC susceptibility.

Replicative activity of hepatitis B virus is negatively associated with methylation of covalently closed circular DNA in advanced hepatitis B virus infection

OBJECTIVES

The aim of this study was to examine the methylation status of intrahepatic hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) and to elucidate the possible relationship between the cccDNA methylation and viral replicative activity in patients with HBV-related liver cirrhosis (HBV-LC).

METHODS

The methylation status of HBV cccDNA was investigated by bisulfite sequencing in nonneoplastic tissues from 12 patients with HBV-LC who underwent surgical resection for combined hepatocellular carcinoma. Clinical, biochemical and virologic factors were evaluated with respect to the degrees of cccDNA methylation. We also examined the effect of methylation of cccDNA on viral transcription by an in vitro transcription assay.

RESULTS

Variable degrees of CpG methylation were present in the HBV cccDNA from patients with HBV-LC. Old age, low serum HBV DNA levels and low virion productivity were significantly associated with elevated cccDNA methylation. Virion productivity of cccDNA was also lower in HepAD38 cells with a higher degree of cccDNA methylation. In vitro transcription assays showed that the transcriptional activity of HBV cccDNA was suppressed by increased methylation of cccDNA.

CONCLUSIONS

Increased CpG methylation of cccDNA is associated with old age, low serum HBV DNA levels and suppressed replicative activity in HBV-LC.

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

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

Stimulation of human lymphocyte proliferation and CD40 antigen expression by phosphorothioate oligonucleotides complementary to hepatitis B virus genome

We have studied the proliferation and CD40 antigen expression of lymphocytes, and the cytotoxicity to monocytes, of antisense phosphorothioate oligodeoxynucleotides complementary to the SP II promoter of HBV mRNA (sequence I) and the X gene (sequence II) in patients with chronic hepatitis B. The oligo sequence I stimulated proliferation of both T and, to a lesser extent, B cells. The percentage of cells expressing CD40 in T and B cell co-cultures increased from 4.2% to 13.8% after oligo stimulation in patients, while it increased form 4.7% to 48.6% in healthy controls. The sense sequence (sequence III) of the X gene also enhanced the expression of CD40 antigen in patients with hepatitis B. The proportion of CD40 cells (26%) in a resting B-cell preparation from hepatitis B patients decreased to zero after a 5-day culture with sequence I, but IgG levels in the culture supernatant increased. The cytotoxic properties of monocytes were not influenced by the oligos. These findings indicate that antisense oligos against hepatitis B virus (HBV) have mitogenic effects on the proliferation of human lymphocytes in a non-specific manner and may activate T cells to express CD40 antigen.

Inhibition of hepatitis B virus surface antigen gene expression in carcinogen-induced liver tumors from transgenic mice

We previously showed that hepatitis B surface antigen (HBsAg)-producing transgenic mice were more sensitive to hepatocarcinogens than their normal littermates were. We have now investigated the regulation of hepatitis B virus (HBV) gene expression in carcinogen-induced liver tumors of HBV-carrier transgenic mice and in three cell lines derived from tumor samples. Transcription of the S gene was repressed in 17 tumors even though they had normal levels of liver-specific mRNAs such as albumin and transferrin. Three hepatoma cell lines, derived from independent tumor samples, were analyzed for their capacity to express the S gene after transfection of cloned DNA. Although they no longer expressed the endogenous S gene, they were still able to express it from transfected viral DNA both transiently and stably. The loss of HBsAg expression in tumors and in the cell lines was accompanied by de novo methylation of the S region, which is a way to permanently repress gene expression. Our data confirm in an animal model previous observations of S-gene expression in human hepatocarcinoma and suggest a role for its downregulation in tumor progression.

Identification and characterization of intrahepatic hepatitis B virus DNA in HBsAg-seronegative patients with chronic liver disease and hepatocellular carcinoma in Taiwan

To clarify the role of hepatitis B virus infection in HBsAg-seronegative patients with chronic liver disease and hepatocellular carcinoma in Taiwan, we examined the hepatitis B virus DNA in liver biopsy tissues of 112 patients by Southern blot analysis. The patients studied included 43 patients with nonalcoholic chronic liver disease, 21 patients with hepatocellular carcinoma and 48 control patients with other hepatobiliary and gastrointestinal diseases. To confirm the specificity of the intrahepatic hepatitis B virus DNA signal and to understand the structure of the integrated viral sequences, molecular cloning and DNA sequencing of an integrated hepatitis B virus DNA were done in one patient. Among 13 patients without serological evidence of previous hepatitis B virus infection, no hepatitis B virus sequences were found in the liver. In other HBsAg-negative patients with evidence of previous hepatitis B virus exposure, a substantial positive rate of intrahepatic hepatitis B virus DNA was found (7%). The intrahepatic hepatitis B virus DNA was all in integrated form. The positive rate among patients with nonalcoholic chronic hepatitis and cirrhosis (2%) was not different from that of the control group with other hepatobiliary and gastrointestinal diseases (4%). However, the positive rate of integrated hepatitis B virus DNA between hepatocellular carcinoma patients and nonhepatocellular carcinoma patients was statistically significant (19% vs. 3%, p less than 0.05). Molecular cloning and sequencing of a 3.0 kb EcoRI fragment of an integrated hepatitis B virus DNA from an anti-HBs-positive patient revealed that it was a partial copy of the hepatitis B virus genome.(ABSTRACT TRUNCATED AT 250 WORDS)

Malignant transformation of immortalized transgenic hepatocytes after transfection with hepatitis B virus DNA

Persistent infection by hepatitis B virus (HBV) is epidemiologically correlated with the prevalence of hepatocellular carcinoma, but its role in tumor development is not yet understood. To study the putative oncogenic potential of HBV, a non-malignant immortal mouse hepatocyte line FMH202 harboring metallothionein promoter-driven simian virus 40 large tumor antigen was transfected with HBV DNA. All stably transfected clones which replicated HBV displayed malignant growth characteristics in soft agar and were tumorigenic upon inoculation in nude mice. The nude mice tumors were histologically classified as differentiated or anaplastic hepatocellular carcinomas. As with human liver carcinomas, rearrangements of in vitro integrated HBV sequences were observed in the nude mouse tumors, and in tumor-derived cell lines. In one case, expression of viral core and surface antigens was blocked in the tumors, correlating with hypermethylation of the HBV genome. However, the expression of X gene was maintained in most tumors and tumor-derived cell lines. X protein was detected in nuclei by immune fluorescence and by immune blot. These results provide the first demonstration that HBV displays oncogenic potential in an experimental system. This system could be useful to functionally identify HBV genes which convey a tumorigenic phenotype.

Hepatocellular carcinoma: molecular biology of its growth and relationship to hepatitis B virus infection

Hepatocellular carcinoma is a very common tumor worldwide and is associated with high mortality rates. Evidence that the development of hepatocellular carcinoma is related to chronic HBV infection has accumulated from epidemiologic studies, information from animal and cell culture models, and molecular biologic evidence that HBV components can be found within hepatocellular carcinoma tissue. Integration of HBV DNA within host liver cell chromosomes may be a crucial step in the development of hepatocellular carcinoma. Integration is associated with disruption of both structure and function of DNA at the site of integration. The study of individual examples of HBV DNA integration in hepatocellular carcinoma tissue illustrates possible mechanisms of hepatocarcinogenesis by HBV. In many cases, activation of various growth factors has been found in association with HBV DNA integration including IGF II, oncogenes such as c-myc, and novel growth factors such as the retinoic acid receptor. A clearer understanding of the mechanisms involved may allow for possible therapeutic interventions in the future, or perhaps even the prevention of hepatocellular carcinoma.