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

Occult Hepatitis B Virus Infection: An Update

Occult hepatitis B virus (HBV) infection (OBI) refers to a condition in which replication-competent viral DNA is present in the liver (with detectable or undetectable HBV DNA in the serum) of individuals testing negative for the HBV surface antigen (HBsAg). In this peculiar phase of HBV infection, the covalently closed circular DNA (cccDNA) is in a low state of replication. Many advances have been made in clarifying the mechanisms involved in such a suppression of viral activity, which seems to be mainly related to the host's immune control and epigenetic factors. OBI is diffused worldwide, but its prevalence is highly variable among patient populations. This depends on different geographic areas, risk factors for parenteral infections, and assays used for HBsAg and HBV DNA detection. OBI has an impact in several clinical contexts: (a) it can be transmitted, causing a classic form of hepatitis B, through blood transfusion or liver transplantation; (b) it may reactivate in the case of immunosuppression, leading to the possible development of even fulminant hepatitis; (c) it may accelerate the progression of chronic liver disease due to different causes toward cirrhosis; (d) it maintains the pro-oncogenic properties of the "overt" infection, favoring the development of hepatocellular carcinoma.

Calcium signaling in hepatitis B virus infection and its potential as a therapeutic target

As a ubiquitous second messenger, calcium (Ca2+) can interact with numerous cellular proteins to regulate multiple physiological processes and participate in a variety of diseases, including hepatitis B virus (HBV) infection, which is a major cause of hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. In recent years, several studies have demonstrated that depends on the distinct Ca2+ channels on the plasma membrane, endoplasmic reticulum, as well as mitochondria, HBV can elevate cytosolic Ca2+ levels. Moreover, within HBV-infected cells, the activation of intracellular Ca2+ signaling contributes to viral replication via multiple molecular mechanisms. Besides, the available evidence indicates that targeting Ca2+ signaling by suitable pharmaceuticals is a potent approach for the treatment of HBV infection. In the present review, we summarized the molecular mechanisms related to the elevation of Ca2+ signaling induced by HBV to modulate viral propagation and the recent advances in Ca2+ signaling as a potential therapeutic target for HBV infection. Video Abstract.

DeepHBV: a deep learning model to predict hepatitis B virus (HBV) integration sites

Background

The hepatitis B virus (HBV) is one of the main causes of viral hepatitis and liver cancer. HBV integration is one of the key steps in the virus-promoted malignant transformation.

Results

An attention-based deep learning model, DeepHBV, was developed to predict HBV integration sites. By learning local genomic features automatically, DeepHBV was trained and tested using HBV integration site data from the dsVIS database. Initially, DeepHBV showed an AUROC of 0.6363 and an AUPR of 0.5471 for the dataset. The integration of genomic features of repeat peaks and TCGA Pan-Cancer peaks significantly improved model performance, with AUROCs of 0.8378 and 0.9430 and AUPRs of 0.7535 and 0.9310, respectively. The transcription factor binding sites (TFBS) were significantly enriched near the genomic positions that were considered. The binding sites of the AR-halfsite, Arnt, Atf1, bHLHE40, bHLHE41, BMAL1, CLOCK, c-Myc, COUP-TFII, E2A, EBF1, Erra, and Foxo3 were highlighted by DeepHBV in both the dsVIS and VISDB datasets, revealing a novel integration preference for HBV.

Conclusions

DeepHBV is a useful tool for predicting HBV integration sites, revealing novel insights into HBV integration-related carcinogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01869-8.

DeepVISP: Deep Learning for Virus Site Integration Prediction and Motif Discovery

Approximately 15% of human cancers are estimated to be attributed to viruses. Virus sequences can be integrated into the host genome, leading to genomic instability and carcinogenesis. Here, a new deep convolutional neural network (CNN) model is developed with attention architecture, namely DeepVISP, for accurately predicting oncogenic virus integration sites (VISs) in the human genome. Using the curated benchmark integration data of three viruses, hepatitis B virus (HBV), human herpesvirus (HPV), and Epstein-Barr virus (EBV), DeepVISP achieves high accuracy and robust performance for all three viruses through automatically learning informative features and essential genomic positions only from the DNA sequences. In comparison, DeepVISP outperforms conventional machine learning methods by 8.43-34.33% measured by area under curve (AUC) value enhancement in three viruses. Moreover, DeepVISP can decode cis-regulatory factors that are potentially involved in virus integration and tumorigenesis, such as HOXB7, IKZF1, and LHX6. These findings are supported by multiple lines of evidence in literature. The clustering analysis of the informative motifs reveales that the representative k-mers in clusters could help guide virus recognition of the host genes. A user-friendly web server is developed for predicting putative oncogenic VISs in the human genome using DeepVISP.

Calcium transfer between endoplasmic reticulum and mitochondria in liver diseases

Calcium (Ca²⁺ ) is a second messenger essential for cellular homeostasis. Inside the cell, Ca²⁺ is compartmentalized and exchanged among organelles in response to both external and internal stimuli. Mitochondria-associated membranes (MAMs) provide a platform for proteins and channels involved in Ca²⁺ transfer between the endoplasmic reticulum (ER) and mitochondria. Deregulated Ca²⁺ signaling and proteins regulating ER-mitochondria interactions have been linked to liver diseases and intensively investigated in recent years. In this review, we summarize the role of MAM-resident proteins in Ca²⁺ transfer and their association with different liver diseases.

HBV-Integration Studies in the Clinic: Role in the Natural History of Infection

Hepatitis B virus (HBV) infection is a major global health problem causing acute and chronic liver disease that can lead to liver cirrhosis and hepatocellular carcinoma (HCC). HBV covalently closed circular DNA (cccDNA) is essential for viral replication and the establishment of a persistent infection. Integrated HBV DNA represents another stable form of viral DNA regularly observed in the livers of infected patients. HBV DNA integration into the host genome occurs early after HBV infection. It is a common occurrence during the HBV life cycle, and it has been detected in all the phases of chronic infection. HBV DNA integration has long been considered to be the main contributor to liver tumorigenesis. The recent development of highly sensitive detection methods and research models has led to the clarification of some molecular and pathogenic aspects of HBV integration. Though HBV integration does not lead to replication-competent transcripts, it can act as a stable source of viral RNA and proteins, which may contribute in determining HBV-specific T-cell exhaustion and favoring virus persistence. The relationship between HBV DNA integration and the immune response in the liver microenvironment might be closely related to the development and progression of HBV-related diseases. While many new antiviral agents aimed at cccDNA elimination or silencing have been developed, integrated HBV DNA remains a difficult therapeutic challenge.

Molecular Dysfunctions of Mitochondria-Associated Membranes (MAMs) in Alzheimer's Disease

Alzheimer’s disease (AD) is a multifactorial neurodegenerative pathology characterized by a progressive decline of cognitive functions. Alteration of various signaling cascades affecting distinct subcellular compartment functions and their communication likely contribute to AD progression. Among others, the alteration of the physical association between the endoplasmic reticulum (ER) and mitochondria, also referred as mitochondria-associated membranes (MAMs), impacts various cellular housekeeping functions such as phospholipids-, glucose-, cholesterol-, and fatty-acid-metabolism, as well as calcium signaling, which are all altered in AD. Our review describes the physical and functional proteome crosstalk between the ER and mitochondria and highlights the contribution of distinct molecular components of MAMs to mitochondrial and ER dysfunctions in AD progression. We also discuss potential strategies targeting MAMs to improve mitochondria and ER functions in AD.

Occult hepatitis B infection and hepatocellular carcinoma: Epidemiology, virology, hepatocarcinogenesis and clinical significance

Occult hepatitis B infection (OBI) refers to a condition where replication-competent HBV DNA is present in the liver, with or without HBV DNA in the blood, in individuals with serum HBsAg negativity assessed by currently available assays. The episomal covalently closed circular DNA (cccDNA) in OBI is in a low replicative state. Viral gene expression is mediated by epigenetic control of HBV transcription, including the HBV CpG island methylation pathway and post-translational modification of cccDNA-bound histone, with a different pattern from patients with chronic HBV infection. The prevalence of OBI varies tremendously across patient populations owing to numerous factors, such as geographic location, assay characteristics, host immune response, coinfection with other viruses, and vaccination status. Apart from the risk of viral reactivation upon immunosuppression and the risk of transmission of HBV, OBI has been implicated in hepatocellular carcinoma (HCC) development in patients with chronic HCV infection, those with cryptogenic or known liver disease, and in patients with HBsAg seroclearance after chronic HBV infection. An increasing number of prospective studies and meta-analyses have reported a higher incidence of HCC in patients with HCV and OBI, as well as more advanced tumour histological grades and earlier age of HCC diagnosis, compared with patients without OBI. The proposed pathogenetic mechanisms of OBI-related HCC include the influence of HBV DNA integration on the hepatocyte cell cycle, the production of pro-oncogenic proteins (HBx protein and mutated surface proteins), and persistent low-grade necroinflammation (contributing to the development of fibrosis and cirrhosis). There remain uncertainties about exactly how, and in what order, these mechanisms drive the development of tumours in patients with OBI.

Insights into Hepatitis B Virus DNA Integration-55 Years after Virus Discovery

Hepatitis B virus (HBV), which was discovered in 1965, is a threat to global public health. HBV infects human hepatocytes and leads to acute and chronic liver diseases, and there is no cure. In cells infected by HBV, viral DNA can be integrated into the cellular genome. HBV DNA integration is a complicated process during the HBV life cycle. Although HBV integration normally results in replication-incompetent transcripts, it can still act as a template for viral protein expression. Of note, it is a primary driver of hepatocellular carcinoma (HCC). Recently, with the development of detection methods and research models, the molecular biology and the pathogenicity of HBV DNA integration have been better revealed. Here, we review the advances in the research of HBV DNA integration, including molecular mechanisms, detection methods, research models, the effects on host and viral gene expression, the role of HBV integrations in the pathogenesis of HCC, and potential treatment strategies. Finally, we discuss possible future research prospects of HBV DNA integration.

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HBV DNA integration is associated with hepatocarcinogenesis via multiple mechanisms

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HBV double-stranded linear DNA (dslDNA) is the dominant substrate for integration into the host genome

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The insertion sites of HBV DNA integration occur throughout the whole host genome using the NHEJ or MMEJ DNA repair pathway

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HBV DNA integration should be used as a clinical indicator for disease monitoring and treatment of patients with HBV infection

Oncogenic HBV variants and integration are present in hepatic and lymphoid cells derived from chronic HBV patients

The hepatitis B virus (HBV) is a major cause of hepatocellular carcinoma (HCC), partly driven by viral integration and specific oncogenic HBV variants. However, the biological significance of HBV genomes within lymphoid cells (i.e., peripheral blood mononuclear cells, PBMCs) is unclear. Here, we collected available plasma, PBMC, liver, and tumor from 52 chronic HBV (CHB) carriers: 32 with HCC, 19 without HCC, and one with dendritic cell sarcoma, DCS. Using highly sensitive sequencing techniques, next generation sequencing, and AluPCR, we demonstrate that viral genomes (i.e., HBV DNA, RNA, and cccDNA), oncogenic variants, and HBV-host integration are often found in all sample types collected from 52 patients (including lymphoid cells and a DCS tumor). Viral integration was recurrently identified (n = 90 such hits) in genes associated with oncogenic consequences in lymphoid and liver cells. Further, HBV genomes increased in PBMCs derived from 7 additional (treated or untreated) CHB carriers after extracellular mitogen stimulation. Our study shows novel HBV molecular data and replication not only liver, but also within 63.8% of lymphoid cells analysed (including a representative lymphoid cell malignancy), that was enhanced in ex vivo stimulated PBMC.

VISDB: a manually curated database of viral integration sites in the human genome

Virus integration into the human genome occurs frequently and represents a key driving event in human disease. Many studies have reported viral integration sites (VISs) proximal to structural or functional regions of the human genome. Here, we systematically collected and manually curated all VISs reported in the literature and publicly available data resources to construct the Viral Integration Site DataBase (VISDB, https://bioinfo.uth.edu/VISDB). Genomic information including target genes, nearby genes, nearest transcription start site, chromosome fragile sites, CpG islands, viral sequences and target sequences were integrated to annotate VISs. We further curated VIS-involved oncogenes and tumor suppressor genes, virus–host interactions involved in non-coding RNA (ncRNA), target gene and microRNA expression in five cancers, among others. Moreover, we developed tools to visualize single integration events, VIS clusters, DNA elements proximal to VISs and virus–host interactions involved in ncRNA. The current version of VISDB contains a total of 77 632 integration sites of five DNA viruses and four RNA retroviruses. VISDB is currently the only active comprehensive VIS database, which provides broad usability for the study of disease, virus related pathophysiology, virus biology, host–pathogen interactions, sequence motif discovery and pattern recognition, molecular evolution and adaption, among others.

HBV Integration-mediated Cell Apoptosis in HepG2.2.15

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and the second leading cause of cancer deaths in the word. Hepatitis B virus (HBV) infection plays an important role in the development of HCC. However, the mechanisms by which HBV integration affects host cells remain poorly understood. HepG2.2.15 cell line is derived from HCC cell line HepG2 with stable transfection HBV expression. In this study, HepG2.2.15 cells showed decreased proliferation, G1 cell cycle arrest and increased apoptosis, when compared to HepG2 cells. HBV capture sequencing was conducted in both genome and transcriptome level, followed by RNA expression sequencing in HepG2.2.15. Here, CAMSAP2/CCDC12/DPP7/OR4F3 were found to be targets for HBV integration in both genome and transcriptome level, accompanied by alteration in their expression when compared to HepG2. Among these genes, DPP7 was the only one gene with HBV integration into its exon, meanwhile DPP7 expression level was also downregulated in HepG2.2.15 as compared to HepG2. Furthermore, DPP7 knockdown resulted in increased apoptosis through upregulation of the Bax/Bcl2 ratio in HepG2 cells. Our results suggest that HBV integration of DPP7 was involved in cell apoptosis.

Cellular Genomic Sites of Hepatitis B Virus DNA Integration

Infection with the Hepatitis B Virus (HBV) is one of the strongest risk-factors for liver cancer (hepatocellular carcinoma, HCC). One of the reported drivers of HCC is the integration of HBV DNA into the host cell genome, which may induce pro-carcinogenic pathways. These reported pathways include: induction of chromosomal instability; generation of insertional mutagenesis in key cancer-associated genes; transcription of downstream cancer-associated cellular genes; and/or formation of a persistent source of viral protein expression (particularly HBV surface and X proteins). The contribution of each of these specific mechanisms towards carcinogenesis is currently unclear. Here, we review the current knowledge of specific sites of HBV DNA integration into the host genome, which sheds light on these mechanisms. We give an overview of previously-used methods to detect HBV DNA integration and the enrichment of integration events in specific functional and structural cellular genomic sites. Finally, we posit a theoretical model of HBV DNA integration during disease progression and highlight open questions in the field.

Reduced SERCA activity underlies dysregulation of Ca2+ homeostasis under atmospheric O2 levels

Unregulated increases in cellular Ca²⁺ homeostasis are a hallmark of pathophysiological conditions and a key trigger of cell death. Endothelial cells cultured under physiologic O₂ conditions (5% O₂) exhibit a reduced cytosolic Ca²⁺ response to stimulation. The mechanism for reduced plateau [Ca²⁺]_i upon stimulation was due to increased sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA)-mediated reuptake rather than changes in Ca²⁺ influx capacity. Agonist-stimulated phosphorylation of the SERCA regulatory protein phospholamban was increased in cells cultured under 5% O₂. Elevation of cytosolic and mitochondrial [Ca²⁺] and cell death after prolonged ionomycin treatment, as a model of Ca²⁺ overload, were lower when cells were cultured long-term under 5% compared with 18% O₂. This protection was abolished by cotreatment with the SERCA inhibitor cyclopiazonic acid. Taken together, these results demonstrate that culturing cells under hyperoxic conditions reduces their ability to efficiently regulate [Ca²⁺]_i, resulting in greater sensitivity to cytotoxic stimuli.-Keeley, T. P., Siow, R. C. M., Jacob, R., Mann, G. E. Reduced SERCA activity underlies dysregulation of Ca²⁺ homeostasis under atmospheric O₂ levels.

SERCA control of cell death and survival

Intracellular calcium (Ca²⁺⁾ is a critical coordinator of various aspects of cellular physiology. It is increasingly apparent that changes in cellular Ca²⁺ dynamics contribute to the regulation of normal and pathological signal transduction that controls cell growth and survival. Aberrant perturbations in Ca²⁺ homeostasis have been implicated in a range of pathological conditions, such as cardiovascular diseases, diabetes, tumorigenesis and steatosis hepatitis. Intracellular Ca²⁺ concentrations are therefore tightly regulated by a number of Ca²⁺ handling enzymes, proteins, channels and transporters located in the plasma membrane and in Ca²⁺ storage organelles, which work in concert to fine tune a temporally and spatially precise Ca²⁺ signal. Chief amongst them is the sarco/endoplasmic reticulum (SR/ER) Ca²⁺ ATPase pump (SERCA) which actively re-accumulates released Ca²⁺ back into the SR/ER, therefore maintaining Ca²⁺ homeostasis. There are at least 14 different SERCA isoforms encoded by three ATP2A1-3 genes whose expressions are species- and tissue-specific. Altered SERCA expression and activity results in cellular malignancy and induction of ER stress and ER stress-associated apoptosis. The role of SERCA misregulation in the control of apoptosis in various cell types and disease setting with prospective therapeutic implications is the focus of this review. Ca²⁺ is a double edge sword for both life as well as death, and current experimental evidence supports a model in which Ca²⁺ homeostasis and SERCA activity represent a nodal point that controls cell survival. Pharmacological or genetic targeting of this axis constitutes an incredible therapeutic potential to treat different diseases sharing similar biological disorders.

Hepatitis B virus PreS1 facilitates hepatocellular carcinoma development by promoting appearance and self-renewal of liver cancer stem cells

Hepatitis B virus (HBV) is a major etiologic agent of hepatocellular carcinoma (HCC). However, the molecular mechanism by which HBV infection contributes to HCC development is not fully understood. Here, we initially showed that HBV stimulates the production of cancer stem cells (CSCs)-related markers (CD133, CD117 and CD90) and CSCs-related genes (Klf4, Sox2, Nanog, c-Myc and Oct4) and facilitates the self-renewal of CSCs in human hepatoma cells. Cellular and clinical studies revealed that HBV facilitates hepatoma cell growth and migration, enhances white blood cell (WBC) production in the sera of patients, stimulates CD133 and CD117 expression in HCC tissues, and promotes the CSCs generation of human hepatoma cells and clinical cancer tissues. Detailed studies revealed that PreS1 protein of HBV is required for HBV-mediated CSCs generation. PreS1 activates CD133, CD117 and CD90 expression in normal hepatocyte derived cell line (L02) and human hepatoma cell line (HepG2 and Huh-7); facilitates L02 cells migration, growth and sphere formation; and finally enhances the abilities of L02 cells and HepG2 cells to induce tumorigeneses in nude mice. Thus, PreS1 acts as a new oncoprotein to play a key role in the appearance and self-renewal of CSCs during HCC development.

The function of targeted host genes determines the oncogenicity of HBV integration in hepatocellular carcinoma

BACKGROUND & AIMS

Although hepatitis B virus (HBV) integration into the human genome has been considered as one of the major causative factors to hepatocarcinogenesis, the underlying mechanism(s) was still elusive. Here we investigate the essential difference(s) of HBV integration between HCC tumor and adjacent non-tumor tissues and explore the factor(s) that determine the oncogenicity of HBV integration.

METHODS

1115 HBV integration sites were collected from four recent studies. Functional annotation analysis of integration targeted host genes (ITGs) was performed using DAVID based on Gene Ontology and KEGG pathway databases. Array-based expression profiles, real-time qPCR and western blot were used to detect the expression of recurrent integration targeted genes (RTGs). The biological consequences of the overexpression of UBXN8 in 8 HCC cell lines were studied in vitro.

RESULTS

HBV is prone to integrate in genic regions (exons, introns, and promoters) and gene-dense regions. Functional annotation analysis reveals that, compared to those in adjacent non-tumor tissues, ITGs in HCC tumor tissues were significantly enriched in functional terms related to negative regulation of cell death, transcription regulation, development and differentiation, and cancer related pathways. 32% of the 75 RTGs identified in this analysis expressed abnormally in HCC tissues. UBXN8, one of the RTGs, was identified as a new tumor suppressor candidate which functions in a TP53 dependent manner.

CONCLUSIONS

The oncogenicity of HBV integration was determined, to some extend by the function of HBV integration targeted host genes in HCC.

Virus associated malignancies: the role of viral hepatitis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading fatal cancer worldwide and its incidence continues to increase. Chronic viral hepatitis involving either hepatitis B virus (HBV) or hepatitis C virus (HCV) infection is the leading etiology for HCC, making HCC prevention a major goal of antiviral therapy. While recent clinical observations and translational research have enhanced our understanding of the molecular mechanisms driving the initiation and progression of HCC, much remains unknown. Current data indicates that HCC tumors are highly complex and heterogeneous resulting from the aberrant function of multiple molecular pathways. This complex biology is responsible, at least in part, for the absence of highly efficient target-directed therapies for this deadly cancer. Additionally, the direct or indirect effect of HBV and HCV infection on the development of HCC is still a contentious issue. Thus, the question remains whether viral hepatitis-associated HCC stems from virus-specific factors, and/or from a general mechanism involving inflammation and tissue regeneration. In this review we summarize general mechanisms implicated in HCC, emphasizing data generated by new technologies available today. We also highlight specific pathways by which HBV and HCV could be involved in HCC pathogenesis. However, improvements to current in vitro and in vivo systems for both viruses will be needed to rigorously define the temporal sequence and specific pathway dysregulations that drive the strong clinical link between chronic hepatitis virus infection and HCC.

The oncogenic role of hepatitis B virus

The hepatitis B virus (HBV) is a small enveloped DNA virus that causes acute and chronic hepatitis. HBV infection is a world health problem, with 350 million chronically infected people at increased risk of developing liver disease and hepatocellular carcinoma (HCC). HBV has been classified among human tumor viruses by virtue of a robust epidemiologic association between chronic HBV carriage and HCC occurrence. In the absence of cytopathic effect in infected hepatocytes, the oncogenic role of HBV might involve a combination of direct and indirect effects of the virus during the multistep process of liver carcinogenesis. Liver inflammation and hepatocyte proliferation driven by host immune responses are recognized driving forces of liver cell transformation. Genetic and epigenetic alterations can also result from viral DNA integration into host chromosomes and from prolonged expression of viral gene products. Notably, the transcriptional regulatory protein HBx encoded by the X gene is endowed with tumor promoter activity. HBx has pleiotropic activities and plays a major role in HBV pathogenesis and in liver carcinogenesis. Because hepatic tumors carry a dismal prognosis, there is urgent need to develop early diagnostic markers of HCC and effective therapies against chronic hepatitis B. Deciphering the oncogenic mechanisms that underlie HBV-related tumorigenesis might help developing adapted therapeutic strategies.

Effects of hepatitis B virus X protein on human T cell cytokines

Chronic infection with hepatitis B virus (HBV) plays a significant role in hepatocellular carcinoma development. To investigate the effect of hepatitis B virus X protein (HBx) on inflammatory cytokines of human T cell, a eukaryotic expression vector, HBx-pEGFP-C1, was constructed and transfected into the Jurkat human T-cell line. Jurkat cells were transfected transiently using Lipofectamine 2000 and activated by phytohemagglutinin (PHA). Interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), IL-4, IL-10, IL-13, and IL-14 mRNA was measured. The results showed that the vector HBx-pEGFP-C1 was successfully constructed, and HBx was expressed in Jurkat cells. Compared with a control group, mRNA of IL-1β and TNF-α was significantly elevated in the HBx-pEGFP-C1 group (p < 0.05), while IL-4, IL-10, IL-13, and IL-14 mRNA was decreased (p < 0.05). Therefore, transient overexpression of HBx promoted PHA-induced pro-inflammatory cytokine secretion and repressed anti-inflammatory cytokine secretion in human T cells.

Recurrent targeted genes of hepatitis B virus in the liver cancer genomes identified by a next-generation sequencing-based approach

Integration of the viral DNA into host chromosomes was found in most of the hepatitis B virus (HBV)–related hepatocellular carcinomas (HCCs). Here we devised a massive anchored parallel sequencing (MAPS) method using next-generation sequencing to isolate and sequence HBV integrants. Applying MAPS to 40 pairs of HBV–related HCC tissues (cancer and adjacent tissues), we identified 296 HBV integration events corresponding to 286 unique integration sites (UISs) with precise HBV–Human DNA junctions. HBV integration favored chromosome 17 and preferentially integrated into human transcript units. HBV targeted genes were enriched in GO terms: cAMP metabolic processes, T cell differentiation and activation, TGF beta receptor pathway, ncRNA catabolic process, and dsRNA fragmentation and cellular response to dsRNA. The HBV targeted genes include 7 genes (PTPRJ, CNTN6, IL12B, MYOM1, FNDC3B, LRFN2, FN1) containing IPR003961 (Fibronectin, type III domain), 7 genes (NRG3, MASP2, NELL1, LRP1B, ADAM21, NRXN1, FN1) containing IPR013032 (EGF-like region, conserved site), and three genes (PDE7A, PDE4B, PDE11A) containing IPR002073 (3′, 5′-cyclic-nucleotide phosphodiesterase). Enriched pathways include hsa04512 (ECM-receptor interaction), hsa04510 (Focal adhesion), and hsa04012 (ErbB signaling pathway). Fewer integration events were found in cancers compared to cancer-adjacent tissues, suggesting a clonal expansion model in HCC development. Finally, we identified 8 genes that were recurrent target genes by HBV integration including fibronectin 1 (FN1) and telomerase reverse transcriptase (TERT1), two known recurrent target genes, and additional novel target genes such as SMAD family member 5 (SMAD5), phosphatase and actin regulator 4 (PHACTR4), and RNA binding protein fox-1 homolog (C. elegans) 1 (RBFOX1). Integrating analysis with recently published whole-genome sequencing analysis, we identified 14 additional recurrent HBV target genes, greatly expanding the HBV recurrent target list. This global survey of HBV integration events, together with recently published whole-genome sequencing analyses, furthered our understanding of the HBV–related HCC.

Integration of the hepatitis B virus (HBV) into the human liver cells was found in most of the related hepatocellular carcinomas (HCCs). Here, taking the recent advances in high-throughput sequencing, we devised an efficient and cost-effective method that we named massive anchored parallel sequencing (MAPS) method, to conduct a global survey of HBV integration events in 40 pairs of HBV–related HCC tissues (cancer and adjacent tissues). We identified 286 unique integration sites (UISs) with precise HBV–Human DNA junctions. We identified a higher number of HBV integration events in cancer adjacent tissues than in HCC tissues, suggesting a clonal expansion process during HCC development. We also found that fibronectin and its related genes (fibronectin type III-like fold domain containing genes) were frequently targeted by HBV. Fibronectin is a protein produced abundantly by the liver cells and also serves as a linker in the extracellular matrix. Our findings might suggest a role for the disruption of fibronectin and associated cellular matrix in HBV related liver cancers. We also identified 14 additional recurrent HBV target genes, greatly expanding the HBV recurrent target list. This study would add significantly to our understanding of HCC development.

Mitochondrial Ca(2+) and apoptosis

Mitochondria are key decoding stations of the apoptotic process. In support of this view, a large body of experimental evidence has unambiguously revealed that, in addition to the well-established function of producing most of the cellular ATP, mitochondria play a fundamental role in triggering apoptotic cell death. Various apoptotic stimuli cause the release of specific mitochondrial pro-apoptotic factors into the cytosol. The molecular mechanism of this release is still controversial, but there is no doubt that mitochondrial calcium (Ca(2+)) overload is one of the pro-apoptotic ways to induce the swelling of mitochondria, with perturbation or rupture of the outer membrane, and in turn the release of mitochondrial apoptotic factors into the cytosol. Here, we review as different proteins that participate in mitochondrial Ca(2+) homeostasis and in turn modulate the effectiveness of Ca(2+)-dependent apoptotic stimuli. Strikingly, the final outcome at the cellular level is similar, albeit through completely different molecular mechanisms: a reduced mitochondrial Ca(2+) overload upon pro-apoptotic stimuli that dramatically blunts the apoptotic response.

Viral Integration and Consequences on Host Gene Expression

Upon cell infection, some viruses integrate their genome into the host chromosome, either as part of their life cycle (such as retroviruses), or incidentally. While possibly promoting long-term persistence of the virus into the cell, viral genome integration may also lead to drastic consequences for the host cell, including gene disruption, insertional mutagenesis and cell death, as well as contributing to species evolution. This review summarizes the current knowledge on viruses integrating their genome into the host genome and the consequences for the host cell.

Hepatitis B virus X gene and hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection has been identified as a major risk factor in hepatocellular carcinoma (HCC), which is one of the most common cancers worldwide. The pathogenesis of HBV-mediated hepatocarcinogenesis is, however, incompletely understood. Evidence suggests that the HBV X protein (HBx) plays a crucial role in HCC development. HBx is a multifunctional regulator that modulates transcription, signal transduction, cell cycle progression, apoptosis, protein degradation pathways, and genetic stability through interaction with host factors. This review describes the current state of knowledge of the molecular pathogenesis of HBV-induced HCC, with a focus on the role of HBx in hepatocarcinogenesis.

Endoplasmic-reticulum calcium depletion and disease

The endoplasmic reticulum (ER) as an intracellular Ca(2+) store not only sets up cytosolic Ca(2+) signals, but, among other functions, also assembles and folds newly synthesized proteins. Alterations in ER homeostasis, including severe Ca(2+) depletion, are an upstream event in the pathophysiology of many diseases. On the one hand, insufficient release of activator Ca(2+) may no longer sustain essential cell functions. On the other hand, loss of luminal Ca(2+) causes ER stress and activates an unfolded protein response, which, depending on the duration and severity of the stress, can reestablish normal ER function or lead to cell death. We will review these various diseases by mainly focusing on the mechanisms that cause ER Ca(2+) depletion.

The Ca2+ pumps of the endoplasmic reticulum and Golgi apparatus

The various splice variants of the three SERCA- and the two SPCA-pump genes in higher vertebrates encode P-type ATPases of the P(2A) group found respectively in the membranes of the endoplasmic reticulum and the secretory pathway. Of these, SERCA2b and SPCA1a represent the housekeeping isoforms. The SERCA2b form is characterized by a luminal carboxy terminus imposing a higher affinity for cytosolic Ca(2+) compared to the other SERCAs. This is mediated by intramembrane and luminal interactions of this extension with the pump. Other known affinity modulators like phospholamban and sarcolipin decrease the affinity for Ca(2+). The number of proteins reported to interact with SERCA is rapidly growing. Here, we limit the discussion to those for which the interaction site with the ATPase is specified: HAX-1, calumenin, histidine-rich Ca(2+)-binding protein, and indirectly calreticulin, calnexin, and ERp57. The role of the phylogenetically older and structurally simpler SPCAs as transporters of Ca(2+), but also of Mn(2+), is also addressed.

From chronic liver disorders to hepatocellular carcinoma: Molecular and genetic pathways

Hepatocarcinogenesis is a process attributed to progressive genomic changes that alter the hepatocellular phenotype producing cellular intermediates that evolve into hepatocellular carcinoma (HCC). During the preneoplastic phase, the liver is often the site of chronic hepatitis and/or cirrhosis, and these conditions induce liver regeneration with accelerated hepatocyte cycling in an organ that is otherwise proliferatively at rest. Hepatocyte regeneration is accelerated by upregulation of mitogenic pathways involving molecular and genetic mechanisms. Hepatic growth factors, inhibitors and triggers may also play a role. This process leads to the production of monoclonal populations of aberrant and dysplastic hepatocytes that have telomerase re-expression, microsatellite instability, and occasionally structural aberrations in genes and chromosomes. Development of dysplastic hepatocytes in foci and nodules and the emergence of HCC are associated with the accumulation of irreversible structural alterations in genes and chromosomes even if the genomic basis of the malignant phenotype is largely heterogeneous. Therefore, a malignant hepatocyte phenotype may be produced by changes in genes acting through different regulatory pathways, thus producing several molecular variants of HCC. On these bases, a key point for future research will be to determine whether the deletions are specific, due to particular loci in the minimally deleted regions of affected chromosome arms, or whether they are non-specific with loss of large portions of chromosomes or entire chromosome arms leading to passive deletion of loci. The final aim is the possibility of identifying a step where carcinogenetic processes could be terminated.

Calcium Pumps in Health and Disease

Ca2+-ATPases (pumps) are key actors in the regulation of Ca2+ in eukaryotic cells and are thus essential to the correct functioning of the cell machinery. They have high affinity for Ca2+ and can efficiently regulate it down to very low concentration levels. Two of the pumps have been known for decades (the SERCA and PMCA pumps); one (the SPCA pump) has only become known recently. Each pump is the product of a multigene family, the number of isoforms being further increased by alternative splicing of the primary transcripts. The three pumps share the basic features of the catalytic mechanism but differ in a number of properties related to tissue distribution, regulation, and role in the cellular homeostasis of Ca2+. The molecular understanding of the function of the pumps has received great impetus from the solution of the three-dimensional structure of one of them, the SERCA pump. These spectacular advances in the structure and molecular mechanism of the pumps have been accompanied by the emergence and rapid expansion of the topic of pump malfunction, which has paralleled the rapid expansion of knowledge in the topic of Ca2+-signaling dysfunction. Most of the pump defects described so far are genetic: when they are very severe, they produce gross and global disturbances of Ca2+ homeostasis that are incompatible with cell life. However, pump defects may also be of a type that produce subtler, often tissue-specific disturbances that affect individual components of the Ca2+-controlling and/or processing machinery. They do not bring cells to immediate death but seriously compromise their normal functioning.

Calcium and apoptosis: ER-mitochondria Ca2+ transfer in the control of apoptosis

There is a growing consensus that the various forms of cell death (necrosis, apoptosis and autophagy) are not separated by strict boundaries, but rather share molecular effectors and signaling routes. Among the latter, a clear role is played by calcium (Ca(2+)), the ubiquitous second messenger involved in the control of a broad variety of physiological events. Fine tuning of intracellular Ca(2+) homeostasis by anti- and proapoptotic proteins shapes the Ca(2+) signal to which mitochondria and other cellular effectors are exposed, and hence the efficiency of various cell death inducers. Here, we will review: (i) the evidence linking calcium homeostasis to the regulation of apoptotic, and more recently autophagic cell death, (ii) the discussion of mitochondria as a critical, although not unique checkpoint and (iii) the molecular and functional elucidation of ER/mitochondria contacts, corresponding to the mitochondria-associated membrane (MAM) subfraction and proposed to be a specialized signaling microdomain.

Integration of hepatitis B virus DNA into the myeloid/lymphoid or mixed-lineage leukemia (MLL4) gene and rearrangements of MLL4 in human hepatocellular carcinoma

Integration of hepatitis B virus (HBV) DNA into host DNA is detected in about 90% of HBV-related hepatocellular carcinoma (HCC), but the preferential sites of the viral integration etiologically relevant to oncogenesis have been controversial. By using an adaptor-ligation/suppression-PCR, we identified four integrations into the myeloid/lymphoid or mixed-lineage leukemia 4 (MLL4) gene from 10 HCC patients with positive HBV surface antigen (HBsAg). Determination of the cellular-virus DNA junction demonstrated that various lengths of the virus were integrated within 300 bp of intron 3 flanked by the Alu element of MLL4. Chimeric hepatitis B virus X gene (HBx)/MLL4 transcripts and the HBx fusion proteins were detected. DNA microarray revealed that HBx/MLL4 fusion proteins suppressed unique genes in HepG2 cells. Finally, chromosomal translocations of intron 3 of MLL4 to the specific region of chromosome 17p11.2 in 22 out of 32 HCC patients were observed, showing that the intron 3 region of MLL4 gene would be a target of translocation breakpoint. In conclusion, the present data suggest that the translocation breakpoint of MLL4 gene is one of the preferential targets for HBV DNA integration into the MLL4 gene and the HBV DNA integration may be involved in liver oncogenesis.

Future of molecular profiling of human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a fatal disease occurring worldwide and developing mainly in chronic liver diseased patients. Despite routine screening of individuals at high risk, most of the patients are diagnosed at late stages of HCC. In addition, the recurrence rate after surgical resection of small tumors is high. Molecular profiling, including expression analysis, comparative genomics and proteomics, provides powerful tools to gain insight into the molecular mechanisms underlying carcinogenesis. Advances in bioinformatics have also allowed for the evaluation of large data sets. Therefore, molecular profiling of HCC using a Biological Expression Network Discovery (BLEND) strategy that integrates global molecular profiling data, including mRNA, miRNA, DNA methylation and DNA copy numbers from both the tumor and the surrounding microenvironment, along with mechanistic studies, may improve the diagnosis, treatment and prognosis of HCC patients. Such an approach will provide mechanistic insight into the pathogenesis of HCC, potentially leading to personalized medicine and the identification of new therapeutic targets.

Activation of the androgen receptor alters the intracellular calcium response to glutamate in primary hippocampal neurons and modulates sarco/endoplasmic reticulum calcium ATPase 2 transcription

Androgens have been shown to have a number of effects on hippocampal function. Although androgen receptors (AR) are found at high levels in hippocampal neurons, the intracellular mechanisms responsible for androgen's actions are unknown. If androgens were capable of altering internal calcium concentration ([Ca(2+)](i)), they could influence a variety of intracellular signaling pathways, maintain neuronal homeostasis and Ca(2+) induced excitotoxicity. In the present study, calcium imaging was used to measure the [Ca(2+)](i) in rat primary hippocampal neurons treated with either the AR agonist dihydrotestosterone (DHT), DHT+flutamide (AR antagonist), flutamide alone, or vehicle for 24 h and subsequently presented with an excitatory glutamate stimulus. In the absence of glutamate stimulation, DHT treatment caused a significant upward shift in baseline [Ca(2+)](i) when compared with neurons from all other groups. Glutamate had a greater effect on [Ca(2+)](i) in DHT-treated neurons and DHT-treated neurons returned to baseline levels significantly faster than all other groups. Cyclopiazonic acid, an inhibitor of sarco/endoplasmic reticulum calcium ATPase (SERCA) had a larger response in DHT-treated neurons compared with controls, suggesting increased Ca(2+) stores in DHT-treated neurons. In all cases the effects of DHT were blocked by treatment with flutamide indicating an AR-mediated mechanism. To determine a possible mechanism by which AR activation could be influencing [Ca(2+)](i), SERCA2 mRNA levels were measured in primary hippocampal neurons. SERCA2 is inserted into the endoplasmic reticulum (ER) membrane and functions to rapidly pump [Ca(2+)](i) into the ER. Following treatment of primary hippocampal neurons with DHT, SERCA2 mRNA was increased, an effect that was blocked in the presence of flutamide. Taken together these results indicate that DHT, working through AR, causes an up-regulation of SERCA2, which increases the sequestering of [Ca(2+)](i) in the endoplasmic reticulum of hippocampal neurons. Such changes may allow the neurons to respond more robustly to a stimulus and recover more quickly following a highly stimulatory challenge.

Calcium signalling and cancer cell growth

Cancer is caused by defects in the mechanisms underlying cell proliferation and cell death. Calcium ions are central to both phenomena, serving as major signalling agents with spatial localization, magnitude and temporal characteristics of calcium signals ultimately determining cell's fate. There are four primary compartments: extracellular space, cytoplasm, endoplasmic reticulum and mitochondria that participate in the cellular Ca2+ circulation. They are separated by own membranes incorporating divers Ca2(+)-handling proteins whose concerted action provides for Ca2+ signals with the spatial and temporal characteristics necessary to account for specific cellular response. The transformation of a normal cell into a cancer cell is associated with a major re-arrangement of Ca2+ pumps, Na/Ca exchangers and Ca2+ channels, which leads to the enhanced proliferation and impaired ability to die. In the present chapter we examine what changes in Ca+ signalling and the mechanisms that support it underlie the passage from normal to pathological cell growth and death control. Understanding this changes and identifying molecular players involved provides new prospects for cancers treatment.

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.

Hepatitis B virus-related hepatocellular carcinoma: paradigms for viral-related human carcinogenesis

As discussed in detail in other chapters of this review, chronic hepatitis B (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC). Most HCCs complicate the evolution of an active or inactive cirrhosis. However, some tumors occur on livers with minimal histological changes; the prevalence of such cases varies from one geographical region to the other, being much higher in the southern half of Africa (around 40% of HCCs) than in Asia, America and Europe, where at least 90% of HCCs are associated with the cirrhosis. This heterogeneity is probably a reflection of different environmental and genetic factors. This review will summarize the current knowledge on the mechanisms involved in HBV-related liver carcinogenesis. It will show in particular how viruses can be viewed as tools to discover and dissect new cellular pathways involved in cancer development and emphasize the potential synergistic effects between HBV and hepatitis C virus, as well as between viral infections and other environmental factors, such as alcohol.

Expression des pompes calciques de type SERCA au cours de la différenciation cellulaire et de la tumorigenèse: application à la carcinogenèse colique

Calcium homeostasis of the endoplasmic reticulum (ER) is involved in intracellular signaling pathways and is implicated in major cell functions such as cell growth, differentiation, protein synthesis and apoptosis. The accumulation of calcium in the ER is performed by specific sarco/endoplasmic reticulum calcium transport ATPases (SERCA iso-enzymes). The expression of biochemically distinct SERCA isoforms is cell type dependent and developmentally regulated. This review summarizes pertinent data about the modulation of the expression of SERCA enzymes during the differentiation of normal and tumor cells. These data support the implication of SERCA pumps and especially SERCA3 in the differentiation program of cancer and leukemia cells. During the multi-step process of colon carcinogenesis, the decrease of SERCA3 expression seems to be linked to enhanced APC/ss-catenin/TCF4 signaling and deficient Sp1-like factor-dependent transcription.

Bcl-2 and Ca2+ homeostasis in the endoplasmic reticulum

Recent data have revealed an unexpected role of Bcl-2 in modulating the steady-state levels and agonist-dependent fluxes of Ca(2+) ions. Direct monitoring of endoplasmic reticulum (ER) Ca(2+) concentration with recombinant probes reveals a lower state of filling in Bcl-2-overexpressing cells and a higher leak rate from the organelle. The broader set of indirect data using cytosolic probes reveals a more complex scenario, as in many cases no difference was detected in the Ca(2+) content of the intracellular pools. At the same time, Ca(2+) signals have been shown to affect important checkpoints of the apoptotic process, such as mitochondria, thus tuning the sensitivity of cells to various challenges. In this contribution, we will review (i) the data on the effect of Bcl-2 on [Ca(2+)](er), (ii) the functional significance of the Ca(2+)-signalling alteration and (iii) the current insight into the possible mechanisms of this effect.

Hepatocellular carcinoma: role of hepatitis B and hepatitis C viruses proteins in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the most important primary hepatic cancer, being a common cancer type worldwide. Many aetiological factors have been related with HCC development, such as cirrhosis, hepatitis viruses and alcohol. Chronic infection with hepatitis B (HBV) and C viruses (HCV) often results in cirrhosis and enhances the probability of developing HCC. The underlying mechanisms that lead to malignant transformation of infected cells, however, remain unclear. HBV is a DNA virus that integrates into the host genome, and this integration is believed, in part, to be carcinogenic. Besides, the virus encodes a 17 kDa protein, HBx, which is known to be a causative agent in the formation of HCC. On the contrary, HCV is a RNA virus that does not integrate into the host genome but likely induces HCC through host protein interactions or via the inflammatory response to the virus. Products encoded in the HCV genome interfere with and disturb intracellular signal transduction. Some HCV proteins, such as the core protein, NS3 and NS5A, have seen to have a regulatory effect on cellular promoters, to interact with a number of cellular proteins, and to be involved in programmed-cell death modulation under certain conditions. The identification of these proteins functions in HCC development and the subsequent development of strategies to inhibit protein-protein interactions may be the first step towards reducing the chronicity and/or of the carcinogenicity of these two viruses.

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

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

Caspase-dependent alterations of Ca2+ signaling in the induction of apoptosis by hepatitis B virus X protein

The hepatitis B virus X protein (HBx) is a multifunctional protein, acting on different targets (e.g. transcription factors, cytoplasmic kinases, and mitochondrial proteins) and exerting cellular effects as diverse as stimulation of cell proliferation and apoptosis. In its biological effects, the modulation of cellular Ca2+ signals has been proposed to be involved, but the direct assessment of Ca2+ homeostasis in HBx-transfected cells has not been carried out yet. In this work, we have employed for this purpose aequorin-based recombinant probes specifically targeted to intracellular organelles and microdomains. Using these probes, we observed that overexpression of HBx enhanced agonist-evoked cytosolic Ca2+ signals in HepG2 and HeLa cells, without affecting either the steady state of endoplasmic reticulum Ca2+ concentration or the kinetics of Ca2+ release. Rather, caspase-3-dependent cleavage of the plasma membrane Ca2+ ATPase could be demonstrated, and larger rises were detected in the cytoplasmic rim beneath the plasma membrane. In mitochondria, major morphological (fragmentation and swelling) and functional (reduced Ca2+ uptake) alterations were detected in HBx-expressing cells. As to the cellular consequences, we observed that HBx-induced apoptosis was markedly reduced when the alterations in Ca2+ signaling (e.g. by loading a Ca2+ chelator or preventing PMCA cleavage) or the downstream effects (e.g. by inhibiting mitochondrial permeability transition) were prevented. Overall, these results indicate that HBx perturbs intracellular Ca2+ homeostasis, acting on the extrusion mechanisms, and that this effect plays an important role in the control of HBx-related apoptosis.

Rising incidence of hepatocellular carcinoma: the role of hepatitis B and C; the impact on transplantation and outcomes

Hepatocellular carcinoma caused by hepatitis B and hepatitis C are global scourges but are likely to peak in incidence in the next 2 decades and then decline. Universal vaccination has been effective in stemming the incidence of chronic hepatitis B and early-onset HCC in regions of high endemicity where implemented, but preventive measures in HCV are not yet available. After the attrition of older affected generations, the incidence of HCC will likely decline rapidly. While no vaccine is currently available for hepatitis C, cases are projected to peak and decline because of a marked reduction in transmission as a result of behavioral modification and safeguarding of blood supplies. Until these epidemiologic projections come to pass, management of hepatocellular carcinoma will continue to become a progressively more frequently encountered clinical challenge. Therapy for chronic hepatitis may ameliorate but will not eliminate the development of tumors. The demand for orthotopic liver transplantation will continue to climb, and palliative therapies for non-resectable cases will require studies aimed at optimization of benefit. LDLT may remain an option for high-risk patients affording tumor-free survival for some otherwise terminal patients.

Hepatitis B virus-related insertional mutagenesis occurs frequently in human liver cancers and recurrently targets human telomerase gene

Integration of Hepatitis B Virus (HBV) DNA into liver cell DNA has been well established, but its implication in liver carcinogenesis is still being debated. In particular, insertion of the viral genome into cellular genes has been viewed as a rare event. By using HBV-Alu PCR, we have now isolated, from nine hepatocellular carcinomas, nine HBV-DNA integration sites showing that the viral genome mutates key regulatory cellular genes: neurotropic tyrosin receptor kinase 2 (NTRK2) gene, IL-1R-associated kinase 2 (IRAK2) gene, p42 mitogen-activated protein kinase 1 (p42MAPK1) gene, inositol 1,4,5-triphosphate receptor type 2 (IP3R2) gene, inositol 1,4,5-triphosphate receptor (IP3R) type 1 (IP3R1) gene, alpha 2,3 sialyltransferase (ST3GAL VI or SITA) gene, thyroid hormone uncoupling protein (TRUP) gene, EMX2-like gene, and human telomerase reverse transcriptase (hTERT) gene. This result brings to 15 the total number of genes targeted by HBV in a study of 22 human liver cancers. Overall, we found that both the inositol 1,4,5-triphosphate receptor gene and the telomerase gene were targeted by HBV in two different tumors. Thus, HBV frequently targets cellular genes involved in cell signalling and some of them may be preferential targets of the viral integration.

Integrations of the hepatitis B virus (HBV) and human papillomavirus (HPV) into the human telomerase reverse transcriptase (hTERT) gene in liver and cervical cancers

Chronic infections with the hepatitis B virus (HBV) and high-risk human papillomaviruses (HPVs) are important risk factors for hepatocellular carcinoma (HCC) and cervical cancer (CC), respectively. HBV and HPV are DNA viruses that almost invariably integrate into the host genome in invasive tumors. The viral integration sites occur throughout the genome, leading to the presumption that there are no preferred sites of integration. A number of viral integrations have been shown to occur within the vicinity of important cancer-related genes. In studies of HBV-induced HCC and HPV-induced CC, we have identified two HBV and three HPV integrations into the human telomerase reverse transcriptase (hTERT) gene. Detailed characterization of the integrations revealed that four integrations occurred within the hTERT promoter and upstream region and the fifth integration occurred in intron 3 of the hTERT gene. None of the integrations altered the hTERT coding sequence and all resulted in juxtaposition of viral enhancers near hTERT, with potential activation of hTERT expression. Our work supports the hypothesis that the sites of oncogenic viral integration are nonrandom and that genes at the sites of viral integration may play important roles in carcinogenesis.

Sequencing of human-viral DNA junctions in hepatocellular carcinoma from patients with HCV and occult HBV infection

DNA of free hepatitis B viruses (HBV) has been detected in the liver of patients infected with hepatitis C virus (HCV). It is unknown whether HBV DNA is integrated into such livers; if so, it may affect hepatocarcinogenesis. Hepatocellular carcinomas (HCCs) from 34 patients without HBV surface antigen (HBsAg) and with anti-HCV, and from 7 patients with HBsAg and without anti-HCV as controls, were examined, using the cassette-ligation-mediated polymerase chain reaction and primers based on HBV DNA sequence. In the controls, HBV DNA had been integrated into human DNA of all HCCs. On the basis of HBV DNA in tumor tissue, 23 of the 34 patients with anti-HCV had occult infection. Junctions between human DNA and HBV DNA were detected in 10 of the 34 patients without HBsAg and with anti-HCV. HBV DNA was integrated into chromosome 11q in 4 of the 10 HCCs with junctions. The DNA to either side of the human-viral junctions was sequenced. Clinically, the mean tumor size of these 10 HCCs was 39 mm; that of the 24 HCCs without integrated HBV was 25 mm. The surrounding tissue was cirrhotic in 2 of the 10 former HCCs and in 16 of the latter 24 HCCs. In conclusion, integrated HBV was detected in some patients with HCV infection; in these patients, the integrated DNA was associated with accelerated hepatocarcinogenesis.

Paracrine in vivo inhibitory effects of hepatitis B virus X protein (HBx) on liver cell proliferation: an alternative mechanism of HBx-related pathogenesis

The role of the hepatitis B virus X protein (HBx) in the pathogenesis of hepatitis B virus (HBV) infection remains unclear. HBx exhibits pleiotropic biological effects, whose in vivo relevance is a matter for debate. In the present report, we have used a combination of HBx-expressing transgenic mice and liver cell transplantation to investigate the in vivo impact of HBx expression on liver cell proliferation and viability in a regenerative context. We show that moderate HBx expression inhibits liver regeneration after partial hepatectomy in HBx-expressing transgenic mice. We also demonstrate that the transplantation of HBx-expressing liver cells, isolated from HBx transgenic mice, is sufficient to inhibit overall recipient liver regeneration after partial hepatectomy. Moreover, the injection of serum samples drawn from HBx-expressing transgenic mice mimicked the inhibitory effect of HBx on liver regeneration. Finally, the incubation of primary rat hepatocytes with the supernatant of HBx-expressing liver cells inhibits cellular DNA synthesis. Taken together, our results demonstrate a paracrine inhibitory effect of HBx on liver cell proliferation and lead us to propose HBV as one of the few viruses implicated in human cancer which act, at least in part, through paracrine biological pathways.