The PreS2 activator MHBs(t) of hepatitis B virus activates c-raf-1/Erk2 signaling in transgenic mice

Modeling human liver cancer heterogeneity: virally induced transgenic models and mouse genetic models of chronic liver inflammation

In addition to being the most common primary liver cancer, hepatocellular carcinoma (HCC) is the second most common cause of cancer-related death in humans. Treatment options are limited for this chemoresistant cancer, with liver transplantation and surgical intervention in early stages being the most successful treatments. Drug development over the past 15 years has focused on generating mouse models that mimic the human pathology for HCC. This has enabled the laboratory testing of potentially new human therapeutics. Described in this unit are the classification of HCC and an overview of hepatitis virus-related transgenic and genetically engineered mouse models (GEMMs) that are employed for elucidating the mechanism(s) responsible for the development of HCC, with particular emphasis on genetic, dietary, and environmental factors.

Potential mechanisms of hepatitis B virus induced liver injury

Chronic active hepatitis (CAH) is acknowledged as an imperative risk factor for the development of liver injury and hepatocellular carcinoma. The histological end points of CAH are chronic inflammation, fibrosis and cirrhosis which are coupled with increased DNA synthesis in cirrhotic vs healthy normal livers. The potential mechanism involved in CAH includes a combination of processes leading to liver cell necrosis, inflammation and cytokine production and liver scaring (fibrosis). The severity of liver damage is regulated by Hepatitis B virus genotypes and viral components. The viral and cellular factors that contribute to liver injury are discussed in this article. Liver injury caused by the viral infection affects many cellular processes such as cell signaling, apoptosis, transcription, DNA repair which in turn induce radical effects on cell survival, growth, transformation and maintenance. The consequence of such perturbations is resulted in the alteration of bile secretion, gluconeogenesis, glycolysis, detoxification and metabolism of carbohydrates, proteins, fat and balance of nutrients. The identification and elucidation of the molecular pathways perturbed by the viral proteins are important in order to design effective strategy to minimize and/or restore the hepatocytes injury.

Hepatitis B virus PreS/S gene variants: pathobiology and clinical implications

The emergence and takeover of hepatitis B virus (HBV) variants carrying mutation(s) in the preS/S genomic region is a fairly frequent event that may occur spontaneously or may be the consequence of immunoprophylaxis or antiviral treatments. Selection of preS/S mutants may have relevant pathobiological and clinical implications. Both experimental data and studies in humans show that several specific mutations in the preS/S gene may induce an imbalance in the synthesis of the surface proteins and their consequent retention within the endoplasmic reticulum (ER) of the hepatocytes. The accumulation of mutated surface proteins may cause ER stress with the consequent induction of oxidative DNA damage and genomic instability. Viral mutants with antigenically modified surface antigen may be potentially infectious to immune-prophylaxed patients and may account for cases of occult HBV infection. In addition, preS/S variants were reported to be associated with cases of fulminant hepatitis as well as of fibrosing cholestatic hepatitis, and they are associated with cirrhosis and hepatocellular carcinoma development.

Screening of hepatocyte proteins binding with C‑terminally truncated surface antigen middle protein of hepatitis B virus (MHBst167) by a yeast two‑hybrid system

The function of middle hepatitis B surface protein C‑terminally truncated at amino acid position 167 (MHBst167) is not currently clear. This study aimed to screen and identify the proteins that interact with MHBst167 in hepatocytes using a yeast two‑hybrid system, and to explore the effects of MHBst167 in the development of hepatocellular carcinoma and precancerous diseases of the liver. The MHBst167 gene was amplified by polymerase chain reaction (PCR) and cloned into a pGEM‑T vector. The target region was sequenced and the constructed bait plasmid, pGBKT7‑MHBst167, was transformed into AH109 yeast cells. The transformed AH109 cells were then mated with Y187 yeast cells containing the fetal liver cDNA library plasmid using a yeast two‑hybrid system. The false positives were eliminated and the true positive clones were selected by PCR and sequencing analysis. The pGBKT7‑MHBst167 bait plasmid was successfully constructed and 66 clones grew in the selective synthetic defined media lacking leucine, tryptophan, histidine and adenine. Fifty‑two clones were identified following X‑α‑Gal selection and segregation analysis. Seven proteins were found to be expressed that could interact with MHBst167 in hepatocytes by the yeast two‑hybrid system. These results have provided novel insights into the biological functions of MHBst167.

Transactivation of proto-oncogene c-Myc by hepatitis B virus transactivator MHBst167

C-terminally truncated hepatitis B virus (HBV) middle size surface proteins (MHBs^t) has been shown to be a transcriptional activator and may be relevant to hepatocarcinogenesis by transactivating gene expression. In the present study, a pcDNA3.1(-)-MHBs^t167 vector coding for MHBs^t truncated at amino acid 167 (MHBs^t167) was constructed and transfected into the HepG2 hepatoma cell line. mRNA and protein expression of MHBs^t167 in the cells was detected by reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis. A cDNA library of genes transactivated by the truncated protein in HepG2 cells was made in pGEM-T Easy using suppression subtractive hybridization. The cDNAs were sequenced and analyzed with BLAST searching against the sequences in GenBank. The results showed that certain sequences, such as that of human proto-oncogene c-Myc, may be involved in tumor development. An expression vector pCAT3/c-Myc containing the chloramphenicol acetyltransferase (CAT) gene under the control of a c-Myc promoter was generated, and the transcriptional transactivating effect of MHBs^t167 on the c-Myc promoter was investigated by RT-PCR and western blotting. MHBs^t167 was found to upregulate the transcriptional activity of the promoter, as well as transcription and translation of c-Myc. MHBs^t167 was also shown to transactivate SV40 immediate early promoter, and transcriptionally transactivate the expression of human c-Myc. These findings provide new directions for studying the biological functions of MHBs^t167, and for a better understanding of the tumor development mechanisms of HBV infection.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

Programmed hepatocytes cell death associated with FLIP downregulation in response to extracellular preS1/2

Chronic hepatitis B virus (HBV) infection involves liver damage resulting in continuous cell injury and death. During HBV infection, hepatocytes exhibit changes in death receptor expression and in their susceptibility to death. These changes are observed not only in infected cells but also in bystander cells. Because excess viral surface protein (HBsAg) is secreted in large amounts as soluble particles containing preS proteins, the role of soluble preS1/2 in hepatocyte (HepG2) death modulation is an important issue to be explored. An increase of cell death induced by preS1/2 was observed. Also, cell death was associated with the down-regulation of FLIP and activation of caspase 8, caspase 9, and BID. Additionally, hepatocytes exhibited a sensitization to death mediated by the Fas receptor. These results, may contribute to understanding the role of envelope proteins (preS1/2) in the pathogenesis of HBV infection.

Identification of α-taxilin as an essential factor for the life cycle of hepatitis B virus

BACKGROUND & AIMS

α-taxilin was identified as binding partner of syntaxins and is supposed to regulate vesicular trafficking. However, the physiological functions of α-taxilin and its potential relevance for the life cycle of hepatitis B virus (HBV) are still poorly understood.

METHODS

Transfected hepatoma cells, infected primary human hepatocytes, and liver tissue of HBV-infected patients were used to study the expression of α-taxilin. Subcellular localization and colocalization were analyzed by confocal laser scanning microscopy (CLSM). Protein-protein interactions were further investigated by co-immunoprecipitations. Silencing of α-taxilin expression was performed by lentiviral gene transfer.

RESULTS

HBV producing cells show a significant higher level of α-taxilin. HBV induces α-taxilin expression, by its regulatory proteins HBx and LHBs via c-Raf. This indicates that α-taxilin is essential for the release of HBV particles. CLSM and co-immunoprecipitations demonstrated that the PreS1PreS2 domain of LHBs interacts with α-taxilin. α-taxilin harbors a YXXL motif that represents a classic late domain. In accordance with this, it was found by co-immunoprecipitations that α-taxilin interacts with the ESCRT I component tsg101. CLSM revealed that a fraction of α-taxilin colocalizes with LHBs and tsg101.

CONCLUSIONS

α-taxilin plays an essential role for release of HBV-DNA containing particles. It might act as an adapter that binds, on the one hand, to LHBs and, on the other hand, to tsg101 and thereby helps recruit the ESCRT machinery to the viral envelope proteins.

Hepatitis B virus (HBV) induces the expression of interleukin-8 that in turn reduces HBV sensitivity to interferon-alpha

High levels of serum interleukin-8 (IL-8) have been detected in chronic hepatitis B (CHB) patients during episodes of hepatitis flares. We investigated whether hepatitis B virus (HBV) may directly induce IL-8 production and whether IL-8 may antagonize interferon-alpha (IFN-α) antiviral activity against HBV. We showed that CHB patients had significantly higher IL-8 levels both in serum and in liver tissue than controls. In HBV-replicating HepG2 cells, IL-8 transcription was significantly activated. AP-1, C/EBP and NF-kB transcription factors were concurrently necessary for maximum IL-8 induction. Moreover, HBx viral protein was recruited onto the IL-8 promoter and this was paralleled by IL8-bound histone hyperacetylation and by active recruitment of transcriptional coactivators. Inhibition of IL-8 increases the antiviral activity of IFN-α against HBV. Our results indicate that HBV activates IL-8 gene expression by targeting the epigenetic regulation of the IL-8 promoter and that IL-8 may contribute to reduce HBV sensitivity to IFN-α.

Direct effects of hepatitis B virus-encoded proteins and chronic infection in liver cancer development

Hepatocellular carcinoma (HCC) ranks as the third leading cause of cancer-related death worldwide with currently limited treatment options. Chronic hepatitis B virus (HBV) infection accounts for HCC development in more than 50% of cases. The lifetime risk of HBV carriers to develop cirrhosis, liver failure or HCC is estimated to be as high as 15-40%. Although several pathways and triggers contributing to HCC development have been described, many features of hepatocellular carcinogenesis and the attributed direct role of viral factors remain elusive. Host genetic factors, the geographic area and epidemiologic factors, as well as the direct risk related to chronic HBV and hepatitis C virus (HCV) infections, account for geographical and gender differences of HCC prevalence. There is growing evidence that hepatocarcinogenesis is a multistep process. Human HCC is typically preceded by chronic inflammation and apoptotic and nonapoptotic cell death with compensatory liver proliferation. However, we still lack a thorough understanding of the common underlying molecular mechanisms. High levels of HBV replication and chronicity of inflammation are known to independently increase the risk for HCC. A direct carcinogenic role of viral factors is very likely to contribute to liver cancer since HCC is known to also occur in noncirrhotic livers of individuals with an inactive chronic or even with occult HBV infection with no significant histological signs of inflammation or cytopathic effects. Furthermore, synergistic or independent viral risk factors for primary liver cancer development have been described, such as HBV genotype, integration of viral DNA into the host genome and direct effects of viral proteins. A broader understanding of these viral factors in hepatocarcinogenesis might give rise to new diagnostic and therapeutic means in the future. We review the current state of research in liver cancer development and focus on the role of direct viral factors in HBV infection.

Pre-s mutation is a significant risk factor for hepatocellular carcinoma development: a long-term retrospective cohort study

BACKGROUND

Several cross-sectional studies have shown an association between pre-S mutation and hepatocellular carcinoma (HCC).

AIMS

We aim to verify whether pre-S mutation represents a risk for HCC development in a longitudinal way.

METHODS

A total of 195 patients with chronic HBV infection [age: 43.7 ± 10.8 years, males: 141 (72.3 %), genotype C: 195 (100 %), hepatitis B e antigen (HBeAg) positive: 109 (55.9 %), cirrhosis: 79 (40.5 %), and pre-S mutation positive: 44 (22.6 %)] were followed up for a median of 7.2 years (range 1.0-7.8 years).

RESULTS

HCC developed in 24 patients during follow-up. The 1-, 3-, and 5-year cumulative incidences of HCC were 0.5, 4.9, and 10.4 %, respectively. Patients with pre-S mutation had significantly higher 5-year cumulative incidences of HCC than those without (26.5 vs. 5.7 %, p < 0.001) and showed higher hazard ratio for HCC [3.04 (95 % CI 1.24-7.42), p = 0.015, adjusted for age, gender, HBeAg, cirrhosis and baseline HBV DNA level]. Notably, in patients aged ≥50 years, the 5-year cumulative incidences of HCC in patients with pre-S mutation were considerably high (58.3 %), compared to those without (16.1 %, p < 0.001).

CONCLUSIONS

Patients with pre-S mutations had higher incidence of HCC during follow-up, especially in aged patients. Patients with pre-S mutations, especially older ones, may require careful attention to HCC development.

Hepatocellular carcinoma: high hepatitis B viral load and mortality in patients treated with transarterial chemoembolization

PURPOSE

To determine the relationship between hepatitis B virus (HBV) DNA level and the survival of patients with hepatocellular carcinoma treated by means of transarterial chemoembolization (TACE).

MATERIALS AND METHODS

This study was approved by the institutional review board, and the requirement to obtain informed consent was waived. From January 2005 to March 2007, 183 patients with HBV-related hepatocellular carcinoma who underwent TACE but never received antiviral therapy were consecutively enrolled in our cohort. All patients were tested for pre-TACE serum level of HBV DNA, and overall survival was measured from date of enrollment until death from any cause. Radiologic progression was evaluated by using the modified response evaluation criteria in solid tumors by means of independent radiologic assessment.

RESULTS

The median overall survival was 19 months (95% confidence interval: 13.7, 24.3) and median time to progression was 4 months (95% confidence interval: 3.03, 4.97). Multivariate analysis revealed that a high pre-TACE serum level of HBV DNA (> 2000 IU/L) was an independent risk factor for reduced overall survival (P = .021; hazard ratio [HR], 1.725), high cancer progression-related mortality (P = .014; HR, 1.936), and hepatic failure-related mortality associated with cancer progression (P = .005, HR, 3.908). Pre-TACE level of HBV DNA did not significantly affect hepatic failure-related mortality that was not caused by cancer progression.

CONCLUSION

A high pre-TACE serum level of HBV DNA was associated with poor overall survival and rapid progression of hepatocellular carcinoma after TACE, and the cause of mortality was not hepatitis exacerbation but cancer progression.

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

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

HBV-related hepatocellular carcinoma: the role of integration, viral proteins and miRNA

The development of hepatocellular carcinoma during chronic hepatitis B infection is a multifactorial process thought to be a consequence of several direct and indirect mechanisms. In this review we discuss how viral proteins and cycles of ongoing liver damage and regeneration, coupled with HBV DNA integration and aberrant miRNA expression may enhance the risk for the development of hepatocellular carcinoma.

ECHS1 acts as a novel HBsAg-binding protein enhancing apoptosis through the mitochondrial pathway in HepG2 cells

We aimed to confirm the role of ECHS1 as a binding protein of HBsAg (HBs) and investigate its function during the development of hepatocellular carcinoma (HCC). Our results show that both exogenous and endogenous ECHS1 proteins bind to HBs and co-localize in the cytoplasm in vitro. The coexistence of HBs and ECHS1 enhances HepG2 cell apoptosis, affects ECHS1 localization in the mitochondria and induces apoptosis by decreasing the mitochondrial membrane potential (MMP). These findings suggest that ECHS1 may be applied as a potential therapeutic target during the treatment of HBV-related hepatitis or HCC.

Modulation of autophagy-like processes by tumor viruses

Autophagy is an intracellular degradation pathway for long-lived proteins and organelles. This process is activated above basal levels upon cell intrinsic or environmental stress and dysregulation of autophagy has been linked to various human diseases, including those caused by viral infection. Many viruses have evolved strategies to directly interfere with autophagy, presumably to facilitate their replication or to escape immune detection. However, in some cases, modulation of autophagy appears to be a consequence of the virus disturbing the cell’s metabolic signaling networks. Here, we summarize recent advances in research at the interface of autophagy and viral infection, paying special attention to strategies that human tumor viruses have evolved.

Aberrant cyclin A expression and centrosome overduplication induced by hepatitis B virus pre-S2 mutants and its implication in hepatocarcinogenesis

Ground glass hepatocytes harboring hepatitis B virus (HBV) pre-S2 mutants have been recognized as pre-neoplastic lesions of hepatocellular carcinoma (HCC). The pre-S2 mutants accumulated in endoplasmic reticulum (ER) can induce ER stress, upregulate cyclin A and promote hepatocyte proliferation. Notably, cyclin A was aberrantly detected in the cytoplasm, instead of nucleus, of pre-S2 mutant-transgenic mice livers, thereby raising the potential role of cytoplasmic cyclin A in HBV hepatocarcinogenesis. In this study, we confirmed that cyclin A was detected in the cytoplasm in the majority of HBV-related HCC tissues. In vitro, the pre-S2 mutant-initiated ER stress could induce cytoplasmic cyclin A mediated via cleavage by the calcium-dependent protease μ-calpain, resulting in an N-terminal truncated product which was preferentially located in the cytoplasm. The aberrant cyclin A expression subsequently induced centrosome overduplication, and this effect was abolished by calpain-specific inhibitors or RNA interference targeting to cyclin A. Overall, our data indicate that HBV pre-S2 mutant may elicit aberrant cyclin A expression and centrosome overduplication through ER stress induction and thereby represent a potential mechanism for the chromosome instability in HBV hepatocarcinogenesis.

Hepatitis B virus large surface antigen promotes liver carcinogenesis by activating the Src/PI3K/Akt pathway

Of the three envelope glycoproteins encoded by hepatitis B virus (HBV) that are collectively referred to as HBV surface antigen (HBsAg), the large HBsAg (LHBs) glycoprotein is expressed preferentially in HBV-associated hepatocellular carcinoma. LHBs can act as an oncogene in transgenic mice, but how it contributes functionally to hepatocarcinogenesis remains unclear. In this study, we determined the molecular and functional roles of LHBs during HBV-associated hepatocarcinogenesis. LHBs increased tumor formation of hepatoma cells. Moreover, expression of LHBs but not other HBV envelope glycoproteins specifically promoted proliferation of hepatoma and hepatic cells in vitro. Mechanistic investigations revealed that these effects were caused by activation of the Src/PI3K/Akt pathway through proximal stimulation of PKCα/Raf1 signaling by LHBs. Proliferation induced by stable LHBs expression was associated with increased G(1)-S cell-cycle progression and apoptosis resistance mediated by Src kinase activation, as established in hepatocellular carcinoma clinical specimens. Importantly, LHBs-induced cellular proliferation and tumor formation were reversed by administration of the Src inhibitor saracatinib. Together, our findings suggest that LHBs promotes tumorigenesis of hepatoma cells by triggering a PKCα/Raf1 to Src/PI3K/Akt signaling pathway, revealing novel insights into the underlying mechanisms of HBV-associated hepatocarcinogenesis.

Novel feedback inhibition of surface antigen synthesis by mammalian target of rapamycin (mTOR) signal and its implication for hepatitis B virus tumorigenesis and therapy

Ground glass hepatocytes (GGHs) harboring hepatitis B virus (HBV) pre-S mutants have been recognized as precursor lesions of hepatocellular carcinoma (HCC). Previously, we observed the activation of mammalian target of rapamycin (mTOR) in GGHs and HCCs, together with a decreased expression of HBV surface antigen (HBsAg) in HCC tissues. It is, therefore, hypothesized that the activation of mTOR during HBV tumorigenesis may potentially down-regulate HBsAg expression. In this study, we verified an inverse relationship between the expression of HBsAg and phosphorylated mTOR (p-mTOR) in 13 of 20 paired nontumorous liver and HCC tissues. In vitro, wild-type or mutant pre-S proteins could activate mTOR in the HuH-7 cell line. Interestingly, the up-regulated mTOR, in turn, suppressed HBsAg synthesis at the transcriptional level via the transcription factor, Yin Yang 1 (YY1), which bound to nucleotide 2812-2816 of the pre-S1 promoter. This inhibitory effect by the mTOR signal could be abolished by the knockdown of histone deacetylase 1 (HDAC1). Furthermore, YY1 was physically associated with HDAC1 in a manner dependent on mTOR activation. Collectively, pre-S protein-induced mTOR activation may recruit the YY1-HDAC1 complex to feedback suppress transcription from the pre-S1 promoter.

CONCLUSION

The activation of mTOR signal in GGHs may feedback suppress HBsAg synthesis during HBV tumorigenesis and explain the observed decrease or absence of HBsAg in HCC tissues. Therapy using mTOR inhibitors for HCCs may potentially activate HBV replication in patients with chronic HBV infection.

Knockdown of HBV surface antigen gene expression by a lentiviral microRNA-based system inhibits HBV replication and HCC growth

Current options for the treatment of hepatitis B virus (HBV) infections, a common liver cancer risk factor, are limited. While RNA interference (RNAi) technologies have been shown to inhibit HBV replication, the consequent effects on hepatocellular carcinoma (HCC) cell growth are not fully understood. The aim of this study was to evaluate the effect of RNAi-mediated decrease in the HBV surface antigen (HBsAg) gene on HBV replication and HCC growth. A lentiviral microRNA-based system expressing siRNAs targeting the HBsAg gene (LVshHBS) was developed and transfected into HepG2.2.15 cells (HBV stably expressing line). We found that LVshHBS significantly inhibited the HBsAg mRNA and protein levels in the HepG2.2.15 cells, while HBsAg secretion into the culture supernatant decreased by 70%. BALB/c (nu/nu) mice were injected with HepG2.2.15 cells transduced with LVshHBS or control vectors to investigate the effect of inhibiting the HBsAg on the development of tumour growth in a human HCC nude mice model. Compared with the control, the tumour growth in nude mice was significantly decreased after injection with LVshHBS. Microarray analysis of tumour-related genes in LVshHBS-transduced HepG2.2.15 cells showed that the expressions of genes involved in cell cycle, differentiation and oncogenesis such as ACP2, BHLHB2, CLK3, CTSC, FOS, NR1D1, PIM1 and SEPT6 genes were downregulated, while that of the E2F3 gene was upregulated. In conclusion, lentiviral microRNA-based RNAi against the HBsAg gene not only inhibits HBV replication but also inhibits the growth of HCC. Downregulation of growth-related genes is implicated in this mechanism of inhibition.

Evolution of Hepatitis B Virus in a Chronic HBV-Infected Patient over 2 Years

Mutations in full-length HBV isolates obtained from a chronic HBV-infected patient were evaluated at three time points: 1 day, 6 months, and 31 months. While 5 nucleotides variation, and an 18 bp deletion of preS1 have been kept in during at least the first two years, C339T mutation occurring in the hydrophilic region of HBsAg and T770C that caused polymerase V560A substitution were the new point mutations found existing in sequenced clones of the 3rd time point. Internal deletion of coding region obviously appeared in the 3rd time point. The splicers included two new 5′-splice donors and three new 3′-splice acceptors besides the reported donors and acceptors and may have produced presumptive HBV-spliced proteins or truncated preS proteins. ALT, HBeAg and viral DNA load varied during the follow-up years. These data demonstrated the diversity of genomes in HBV-infected patient during evolution. Combined with clinical data, the HBV variants discovered in this patient may contribute to viral persistence of infection or liver pathogenesis.

Oxidative stress and antioxidants in hepatic pathogenesis

Long term hepatitis B virus (HBV) infection is a major risk factor in pathogenesis of chronic liver diseases, including hepatocellular carcinoma (HCC). The HBV encoded proteins, hepatitis B virus X protein and preS, appear to contribute importantly to the pathogenesis of HCC. Both are associated with oxidative stress, which can damage cellular molecules like lipids, proteins, and DNA during chronic infection. Chronic alcohol use is another important factor that contributes to oxidative stress in the liver. Previous studies reported that treatment with antioxidants, such as curcumin, silymarin, green tea, and vitamins C and E, can protect DNA from damage and regulate liver pathogenesis-related cascades by reducing reactive oxygen species. This review summarizes some of the relationships between oxidative stress and liver pathogenesis, focusing upon HBV and alcohol, and suggests antioxidant therapeutic approaches.

Hepatitis B virus induces expression of antioxidant response element-regulated genes by activation of Nrf2

The expression of a variety of cytoprotective genes is regulated by short cis-acting elements in their promoters, called antioxidant response elements (AREs). A central regulator of ARE-mediated gene expression is the NF-E2-related factor 2 (Nrf2). Human hepatitis B virus (HBV) induces a strong activation of Nrf2/ARE-regulated genes in vitro and in vivo. This is triggered by the HBV-regulatory proteins (HBx and LHBs) via c-Raf and MEK. The Nrf2/ARE-mediated induction of cytoprotective genes by HBV results in a better protection of HBV-positive cells against oxidative damage as compared with control cells. Furthermore, there is a significantly increased expression of the Nrf2/ARE-regulated proteasomal subunit PSMB5 in HBV-positive cells that is associated with a decreased level of the immunoproteasome subunit PSMB5i. In accordance with this finding, HBV-positive cells display a higher constitutive proteasome activity and a decreased activity of the immunoproteasome as compared with control cells even after interferon α/γ treatment. The HBV-dependent induction of Nrf2/ARE-regulated genes might ensure survival of the infected cell, shape the immune response to HBV, and thereby promote establishment of the infection.

Hepatitis B doubly spliced protein, generated by a 2.2 kb doubly spliced hepatitis B virus RNA, is a pleiotropic activator protein mediating its effects via activator protein-1- and CCAAT/enhancer-binding protein-binding sites

The 2.2 kb doubly spliced defective hepatitis B virus (HBV) genome is frequently detected in the serum of patients with chronic hepatitis B. However, the biological significance of this type of defective genome is not well understood. In this study, expression of the hepatitis B doubly spliced protein (HBDSP) was confirmed from the 2.2 kb doubly spliced defective HBV genome, which was isolated and transfected into Huh-7 hepatoma cells. To explore the potential pathogenicity of HBDSP, hepatocellular proteins interacting with HBDSP were screened by a yeast two-hybrid assay. Unexpectedly, HBDSP could transactivate the GAL4-responsive element, and deletion mapping revealed that the fragment located between residues Leu-48 and Gln-75 of HBDSP was crucial for transactivation activity. In Huh-7 hepatoma cells, HBDSP localized predominantly to the cytoplasm and showed transactivating effects on the cytomegalovirus immediate-early promoter, simian virus 40 enhancer/promoter and HBV regulatory elements including the S1 promoter, S2 promoter, Enhancer I and core upstream regulatory sequences. Further studies revealed that the transactivating activities were mediated by activator protein-1- and CCAAT/enhancer-binding protein-binding sites. These findings suggest that HBDSP is a pleiotropic activator protein that can potentially serve as an HBV virulence factor.

Viral hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the fifth most common cancer and the third leading cause of cancer death worldwide. Despite recent advances in the diagnosis and treatment of HCC, its prognosis remains dismal. Infection with hepatitis B virus (HBV) and hepatitis C virus (HCV) are the major risk factors for HCC. Although both are hepatotropic viral infections, there are important differences between the oncogenic mechanisms of these two viruses. In addition to the oncogenic potential of its viral proteins, HBV, as a DNA virus, can integrate into host DNA and directly transform hepatocytes. In contrast, HCV, an RNA virus, is unable to integrate into the host genome, and viral protein expression has a more critical function in hepatocarcinogenesis. Both HBV and HCV proteins have been implicated in disrupting cellular signal transduction pathways that lead to unchecked cell growth. Most HCC develops in the cirrhotic liver, but the linkage between cirrhosis and HCC is likely multifactorial. In this review, we summarize current knowledge regarding the pathogenetic mechanisms of viral HCC.

HBV life cycle: entry and morphogenesis

Hepatitis B virus (HBV) is a major cause of liver disease. HBV primarily infects hepatocytes by a still poorly understood mechanism. After an endocytotic process, the nucleocapsids are released into the cytoplasm and the relaxed circular rcDNA genome is transported towards the nucleus where it is converted into covalently closed circular cccDNA. Replication of the viral genome occurs via an RNA pregenome (pgRNA) that binds to HBV polymerase (P). P initiates pgRNA encapsidation and reverse transcription inside the capsid. Matured, rcDNA containing nucleocapsids can re-deliver the RC-DNA to the nucleus, or be secreted via interaction with the envelope proteins as progeny virions.

The hepatitis C virus non-structural NS5A protein impairs both the innate and adaptive hepatic immune response in vivo

The role of hepatitis C virus (HCV) protein non-structural (NS) 5A in HCV-associated pathogenesis is still enigmatic. To investigate the in vivo role of NS5A for viral persistence and virus-associated pathogenesis a transgenic (Tg) mouse model was established. Mice with liver-targeted NS5A transgene expression were generated using the albumin promoter. Alterations in the hepatic immune response were determined by Western blot, infection by lymphocytic choriomeningitis virus (LCMV), and using transient NS3/4A Tg mice generated by hydrodynamic injection. Cytotoxic T lymphocyte (CTL) activity was investigated by the Cr-release assay. The stable NS5A Tg mice did not reveal signs of spontaneous liver disease. The intrahepatic immunity was disrupted in the NS5A Tg mice as determined by clearance of LCMV infection or transiently NS3/4A Tg hepatocytes in vivo. This impaired immunity was explained by a reduced induction of interferon beta, 2',5'-OAS, and PKR after LCMV infection and an impairment of the CTL-mediated elimination of NS3-expressing hepatocytes. In conclusion, these data indicate that in the present transgenic mouse model, NS5A does not cause spontaneous liver disease. However, we discovered that NS5A could impair both the innate and the adaptive immune response to promote chronic HCV infection.

Enhanced expression of vascular endothelial growth factor-A in ground glass hepatocytes and its implication in hepatitis B virus hepatocarcinogenesis

Ground glass hepatocytes (GGH) in chronic hepatitis B virus (HBV) infection harbor HBV pre-S deletion mutants in endoplasmic reticulum (ER) and exhibit complex biologic features such as ER stress, DNA damage, and growth advantage. The presence of pre-S mutants in serum has been shown to predict the development of hepatocellular carcinoma (HCC) in HBV carriers. GGHs hence represent a potentially preneoplastic lesion. Whether a specific growth factor is overexpressed and activated in GGHs remains to be clarified. In this study, growth factor(s) up-regulated by pre-S mutants was identified using a growth factor array in HuH-7 cells. Immunohistochemistry, reverse-transcriptase polymerase chain reaction, and Western blot analysis were performed to study the participation of these genes and their signal pathways in HuH-7 cells and liver tissues. We demonstrate that vascular endothelial growth factor-A (VEGF-A) was up-regulated by pre-S mutants in HuH-7 cells and further confirmed in GGHs by immunostaining. The VEGF-A up-regulation by pre-S mutants could be suppressed by vomitoxin, an ER stress inhibitor. Furthermore, pre-S mutants-expressed HuH-7 cells exhibited activation of Akt/mTOR (mammalian target of rapamycin) signaling and increased growth advantage, which could be inhibited by VEGF-A neutralization. Consistent with this notion, enhanced expression of VEGF-A and activation of Akt/mTOR signaling, comparable to the levels of paired HCC tissues, were also detected in HBV-related nontumorous livers.

CONCLUSION

The enhanced expression of VEGF-A in GGHs provides potential mechanism to explain the progression from preneoplastic GGHs to HCC in chronic HBV infection.

Interacting with HBsAg compromises resistance of jumping translocation breakpoint protein to ultraviolet radiation-induced apoptosis in 293FT cells

Jumping translocation breakpoint protein (JTB) is suppressed in many cancers, implying it plays a role in the neoplastic transformation of cells. In order to explore the role of JTB in the carcinogenesis of liver, we used mammalian two-hybrid, co-immunoprecipitation, GST pull-down and laser scanning confocal to verify the interaction between HBs and JTB. According to the results, HBs interacts with JTB. In addition, we further determined that S region within HBs is sufficient for binding JTB. Overexpression of JTB conferred resistance to apoptosis induced by ultraviolet radiation, whereas this effect was compromised by the co-overexpression of HBs.

Proteome responses to stable hepatitis B virus transfection and following interferon alpha treatment in human liver cell line HepG2

Hepatitis B virus (HBV) infection is a worldwide health problem and may develop to liver fibrosis, cirrhosis, and even hepatocellular carcinoma. To investigate the global proteome responses of liver-derived cells to HBV infection and IFNalpha treatment, 2-DE and MS-based analysis were performed to compare the proteome changes between HBV stably transfected cell line HepG2.2.15 and its parental cell line HepG2, as well as HepG2.2.15 before and after IFNalpha treatment (5000 IU/mL for 72 h). Compared to HepG2, 12 of 18 down-regulated and 27 of 32 up-regulated proteins were identified in HepG2.2.15. After IFNalpha treatment, 6 of 7 down-regulated and 11 of 14 up-regulated proteins were identified. Differentially expressed proteins caused by HBV infection were involved with cytoskeletal matrix, heat shock stress, kinases/signal transduction, protease/proteasome components, etc. Prohibitin showed a dose-dependent up-regulation during IFNalpha treatment and might play a potent role in anti-HBV activities of IFNalpha by enhancing the crossbinding p53 expression to achieve the apoptosis of HBV infected liver cells. Down-regulation of interferon-stimulated gene 15 (ISG15) in HepG2.2.15 and recovery by IFNalpha suggested its relationship with IFNalpha's anti-HBV effect.

Role of hepatitis B surface antigen in the development of hepatocellular carcinoma: regulation of lymphoid enhancer-binding factor 1

Background

There are around 350 million of hepatitis B surface antigen (HBsAg) carriers worldwide, and among them, high risk of developing hepatocellular carcinoma (HCC) has been identified by epidemiological studies. To date, the molecular role of HBsAg in HCC development has not been fully studied. We have previously reported that in cell cultures, HBsAg up-regulated the expression of lymphoid enhancer-binding factor 1 (LEF-1), a key component of the Wnt pathway. In this study we aimed to study this effect of HBsAg on LEF-1 in the development of HCC.

Methods

Expression of HBsAg, LEF-1 and its downstream effector genes were compared among 30 HCCs, their peritumor tissue counterparts and 9 normal control liver tissues by quantitative real-time PCR. In addition, immunohistochemical staining studies on HBsAg and LEF-1 expression were conducted among these samples.

Results

The expression of LEF-1 was compared between 13 HBsAg positive HCC tissues and 17 HBsAg negative HCC tissues. Simultaneous detection of LEF-1 and HBsAg was observed in HBsAg positive HCC tissues and, additionally, the simultaneous detection of HBsAg and LEF-1 was more pronounced in peritumor tissues, compared to that in the tumor tissues. The distribution of cellular LEF-1 in peritumor tissues was predominantly in the cytoplasm; while LEF-1 in the tumor tissues was located either exclusively in the nucleus or both in the nucleus and cytoplasm. By real-time PCR, the expression levels of LEF-1 downstream effector genes cyclin D1 and c-myc were higher in peritumor cells compared to that of the tumor cells. However, a 38 kDa truncated isoform of LEF-1, rather than the 55 kDa wild-type LEF-1, was significantly elevated in the HBsAg positive tumor cells.

Conclusion

Data indicate that deregulation of the Wnt pathway by HBsAg occurred in HBV-associated HCCs, but was more pronounced in the peritumor cells. It is speculated that HBsAg could stimulate proliferation and functional modification of hepatocytes via LEF-1 through the Wnt pathway at the pre-malignant stage.

Hepatitis B virus induced hepatocellular carcinoma

A number of risk factors appear to play a role in Hepatocellularcinoma (HCC), HBV infection being one of the most important. Chronic inflammation and cytokines are key determinants in the development of fibrosis and liver cell proliferation. HBV DNA integration and/or expression of HBV proteins may have a direct effect on cellular functions. Occult hepatitis B virus infection is characterized by persistence of HBV DNA in hepatitis B surface antigen-negative individuals. There are evidences that occult HBV is a risk factor for the development of HCC and that the potential mechanisms whereby overt HBV might induce tumour formation are mostly maintained.

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

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

Suppression of p38 mitogen-activated protein kinase inhibits hepatitis B virus replication in human hepatoma cell: the antiviral role of nitric oxide

The role of the p38 mitogen-activated protein kinase (MAPK) pathway in hepatitis B virus (HBV) replication was investigated in this study. After transient transfection with HBV plasmid, p38 MAPK, but not JNK or ERK1/2, was significantly phosphorylated in human hepatoma cell Huh7. Interestingly, HBV proteins and RNA synthesis were significantly inhibited by a specific inhibitor of p38 MAPK, SB203580, in a dose-dependent manner. Intracellular core-associated DNA, extracellular virion-associated DNA and covalently closed circular DNA were also significantly inhibited by SB203580. Further results showed the antiviral role of nitric oxide (NO) on the suppression of HBV replication and downregulation of p38 MAPK phosphorylation. In conclusion, these results suggested that suppression of phosphorylation of p38 MAPK by inhibitor or NO could inhibit intracellular HBV replication.

Screening of hepatocyte proteins interacting with the small surface protein of hepatitis B virus using yeast-two hybrid technique

AIM: To screen candidate hepatocyte binding proteins interacting with the surface antigen protein (SHBs) of hepatitis B virus.

METHODS: Polymerase chain reaction (PCR) was used to amplify SHBs gene. The target gene of SHBs was cloned into the yeast expression plasmid pDEST32 to construct bait plasmid pDEST32-SHBs. Western blot was employed to test SHBs expression after pDEST32-SHBs was transformed into the yeast cell MaV203 by Liac-mediated method. Both pDEST32-SHBs and pDEST22-cDNA were contemporarily transformed into MaV203 cells to screen the binding protein of SHBs. MaV203 cells were plated on synthetic dropout nutrient media (SC/-Trp-Leu-His-Ura) and X-gal containing media for selection and screening. After that, the prey plasmids from true positive colonies were extracted and sequenced. The partial cDNA sequences in prey plasmids were analyzed by bioinformatics software.

RESULTS: The yeast expression vector pDEST32-SHBs was successfully constructed. After screening, 3 pieces of cDNA in prey plasmids from true positive blue colonies were sequenced. The cDNA sequences were alpha-2-macroglobulin, tubulin alpha 1a and ribosomal protein L3.

CONCLUSION: Yeast-two hybrid method is successfully used for screening out alpha-2-macroglobulin, tubulin alpha 1a and ribosomal protein L3 as candidate binding proteins of SHBs.

New insights into hepatitis B and hepatitis delta virus entry

Notwithstanding the medical importance of the HBV infection, our understanding of how this pathogen enters hepatocytes is incomplete. This reflects a long-lasting dependence of in vitro infection studies solely on primary human hepatocytes, which are difficult to obtain and maintain in a susceptible state. The establishment of a polarizable HBV-susceptible human hepatoma cell line (HepaRG) and the utilization of Tupaia belangeri hepatocytes (PTHs) resolved this issue. Since then, important insight into viral and cellular determinants participating in HBV binding and infection have been achieved. We now know that the large viral surface protein (L) plays a pivotal role in HBV entry. It mediates diverse functions, commencing binding of virions to heparan sulfate proteoglycans at the hepatocytes surface as a prerequisite for entry. Subsequently, (a) highly specific event(s) involving the myristoylated N-terminal preS1 subdomain of L, as well as the cytosolic and antigenic loops of the S-domain, initiates a series of less well understood steps, resulting in a pH independent, reduction-sensitive fusion of the viral membrane with a cellular membrane. One of these steps is highly sensitive to synthetic N-acylated preS1 lipopeptides and can be blocked in vitro and in vivo at picomolar concentrations. This opens novel therapeutic options addressing virus entry. Future approaches aiming at the elucidation of HBV hepatotropism, the identification of (a) specific receptor(s), the clarification of the endocytic entry pathway and imaging of fluorescently-labeled virions will allow us to decipher more precisely the HBV entry pathway in the near future. Furthermore, clinical efficacy studies with HBV–preS-derived lipopeptides will tell us whether entry inhibition is a passable way to defend acute and chronic HBV and hepatitis delta virus infections.

Viruses associated with human cancer

It is estimated that viral infections contribute to 15-20% of all human cancers. As obligatory intracellular parasites, viruses encode proteins that reprogram host cellular signaling pathways that control proliferation, differentiation, cell death, genomic integrity, and recognition by the immune system. These cellular processes are governed by complex and redundant regulatory networks and are surveyed by sentinel mechanisms that ensure that aberrant cells are removed from the proliferative pool. Given that the genome size of a virus is highly restricted to ensure packaging within an infectious structure, viruses must target cellular regulatory nodes with limited redundancy and need to inactivate surveillance mechanisms that would normally recognize and extinguish such abnormal cells. In many cases, key proteins in these same regulatory networks are subject to mutation in non-virally associated diseases and cancers. Oncogenic viruses have thus served as important experimental models to identify and molecularly investigate such cellular networks. These include the discovery of oncogenes and tumor suppressors, identification of regulatory networks that are critical for maintenance of genomic integrity, and processes that govern immune surveillance.