Hepatitis B virus transactivator HBx uses a tumour promoter signalling pathway

Immunological pathways in viral hepatitis-induced hepato-cellular carcinoma

Hepatocellular carcinoma (HCC) is a serious neoplastic disease with increasing incidence and mortality, accounting for 90% of all liver cancers. Hepatitis viruses are the major causative agents in the development of HCC. Hepatitis A virus (HAV) primarily causes acute infections, which is associated with HCC to a certain extent, as shown by clinicopathological studies. Chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infections lead to persistent liver inflammation and cirrhosis, disrupt multiple pathways associated with cellular apoptosis and proliferation, and are the most common viral precursors of HCC. Mutations in the HBV X protein (HBx) gene are closely associated with the incidence of HCC, while the expression of HCV core proteins contributes to hepatocellular lipid accumulation, thereby promoting tumorigenesis. In the clinical setting, hepatitis D virus (HDV) frequently co-infects with HBV, increasing the risk of chronic hepatitis. Hepatitis E virus (HEV) usually causes acute infections. However, chronic infections of HEV have been increasing recently, particularly in immuno-compromised patients and organ transplant recipients, which may increase the risk of progression to cirrhosis and the occurrence of HCC. Early detection, effective intervention and vaccination against these viruses may significantly reduce the incidence of liver cancer, while mechanistic insights into the interplay between hepatitis viruses and HCC may facilitate the development of more effective intervention strategies. This article provides a comprehensive overview of hepatitis viruses and reviews recent advances in research on aberrant hepatic immune responses and the pathogenesis of HCC due to viral infection.

Identification of Estradiol Benzoate as an Inhibitor of HBx Using Inducible Stably Transfected HepG2 Cells Expressing HiBiT Tagged HBx

HBx plays a significant role in the cccDNA epigenetic modification regulating the hepatitis B virus (HBV) life cycle and in hepatocyte proliferation and carcinogenesis. By using the sleeping-beauty transposon system, we constructed a tetracycline-induced HBx-expressing stable cell line, SBHX21. HBx with a HiBiT tag can be quickly detected utilizing a NanoLuc-based HiBiT detection system. By screening a drug library using SBHX21 cells, we identified estradiol benzoate as a novel anti-HBx agent. Estradiol benzoate also markedly reduced the production of HBeAg, HBsAg, HBV pgRNA, and HBV DNA in a dose-dependent manner, suggesting that estradiol benzoate could be an anti-HBV agent. Docking model results revealed that estradiol benzoate binds to HBx at TRP87 and TRP107. Collectively, our results suggest that estradiol benzoate inhibits the HBx protein and HBV transcription and replication, which may serve as a novel anti-HBV molecular compound for investigating new treatment strategies for HBV infection.

Novel protein kinase C phosphorylated kinase inhibitor-matrine suppresses replication of hepatitis B virus via modulating the mitogen-activated protein kinase signal

HBV (hepatitis B virus) infection still threatens human health. Therefore, it is essential to find new effective anti-HBV compounds. Here, we identified matrine as a novel inhibitor of PKC (protein kinase C) phosphorylated kinase by screening a natural compound library. After HepG2.215 cells were treated with matrine, we carried out a phosphorylated proteomics sequence study and analyzed the prediction of related kinase expression level. In the case of HBV infection, it was found that PKC kinase mediates the activation of mitogen-activated protein kinase (MAPK) signaling pathway known as son of sevenless (SOS) activation. It was also found that PKC kinase inhibits the expression of C-X-C Motif Chemokine Ligand 8 (CXCL8) by inhibiting the activity of activating transcription factor 2/ cAMP response element binding protein (ATF2/CREB), and this effect is independent of its activated MAPK signaling pathway. Finally, Western blot was used to detect the expression of MAPK, ATF2, CREB3 phosphorylation and nonphosphorylation in matrine-treated cells and PKC-treated cells. PKC phosphorylated kinase inhibitor-matrine suppresses the replication of HBV via modulating the MAPK/ATF2 signal. Matrine is a good clinical drug to enhance the autoimmunity in the adjuvant treatment of chronic HBV infection.

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

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

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

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

Dynamic expression of ZNF382 and its tumor-suppressor role in hepatitis B virus-related hepatocellular carcinogenesis

Hepatitis B virus (HBV) infection is the primary cause of hepatocellular carcinoma (HCC). Zinc-finger protein 382 (ZNF382), which belongs to zinc-finger protein family, has been documented to be downregulated in certain types of cancer. However, its role in HCC remains largely unknown. In this study, we demonstrated that ZNF382 expression was significantly elevated in HBV-infected liver cirrhosis tissues relative to HBV-negative normal liver tissues at protein levels, but not at mRNA levels, and was positively correlated with the levels of HBV DNA and hepatitis B virus X protein (HBx). Further studies revealed that ZNF382 was a target of miR-6867, and HBx promoted the translation of ZNF382 during HBV chronic infection through Erk-mediated miR-6867 inhibition. In addition, our data showed that ZNF382 was frequently downregulated by promoter methylation in HBV-related HCCs relative to HBV-infected liver cirrhosis tissues, and decreased expression of ZNF382 was strongly correlated with poor survival in early-stage HCC patients. Functional studies demonstrated that ZNF382 was a potent tumor suppressor in HCC cells through inhibiting cell proliferation, colony formation, migration, invasion, and tumorigenic potential in nude mice, and inducing cell apoptosis. Mechanistically, ZNF382 exerted its tumor-suppressor functions in HCC through transcriptionally repressing its downstream targets such as Fos proto-oncogene (FOS), Jun proto-oncogene (JUN), disheveled segment polarity protein 2 (DVL2), and frizzled class receptor 1 (FZD1), thereby impairing the activities of activating protein 1 (AP-1) and Wnt/β-catenin pathways and activating p53 signaling. Altogether, our data show that ZNF382 acts as a tumor suppressor, and is co-regulated by HBx and epigenetic mechanism in HBV-related hepatocellular carcinogenesis.

MicroRNA Profile in Peripheral Blood Mononuclear Cells from Hepatitis B Virus Infected Patients

INTRODUCTION AND AIM

The pathogenesis of hepatitis B virus (HBV)-related liver diseases remains not fully understood. Here, we aim to explore the potential roles of dysregulated miRNAs in chronic hepatitis B (CHB) and HBV-related acute-on-chronic liver failure (ACLF).

MATERIAL AND METHODS

MiRNA microarray was conducted in peripheral blood mononuclear cells (PBMCs) obtained from healthy donors or patients with CHB or ACLF. Altered expression of miRNAs was further confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Finally, the differentially expressed miRNAs and their target genes were subjected to bioinformatics analysis.

RESULTS

The miRNA microarray identified 45 up-regulated and 62 down-regulated miRNAs with a fold change ≥ 1.5. Expression of eight miRNAs was validated using qRT-PCR analysis, which was consistent with miRNA microarray analysis. Bioinformatics analysis indicated that multiple biological processes and signaling pathways were affected by these miRNAs and a miRNA-gene regulatory network was generated with Cytoscape.

CONCLUSION

The current study provided a global view of miRNA expression in PBMCs from CHB and ACLF patients. Functional analysis showed that multiple biological processes and signaling pathways were modulated by these miRNAs. These data provide intriguing insights into the molecular pathogenesis of HBVrelated liver diseases, which deserve further investigation.

EVI1 promotes cell proliferation in HBx-induced hepatocarcinogenesis as a critical transcription factor regulating lncRNAs

The involvement of the hepatitis B virus X (HBx) protein in epigenetic modifications during hepatocarcinogenesis has been previously characterized. Long noncoding RNAs (lncRNAs), a kind of epigenetic regulator molecules, have also been shown to play crucial roles in HBx-related hepatocellular carcinoma (HCC). In this study, we analyzed the key transcription factors of aberrantly expressed lncRNAs in the livers of HBx transgenic mice by bioinformatics prediction, and found that ecotropic viral integration site 1 (Evi1) was a potential main transcription regulator. Further investigation showed that EVI1 was positively correlated to HBx expression and was frequently up-regulated in HBV-related HCC tissues. The forced expression of HBx in liver cell lines resulted in a significant increase of the expression of EVI1. Furthermore, suppression of EVI1 expression decreased the proliferation of HCC cells overexpressing HBx in vitro and in vivo.

Conclusion: Our findings suggest that EVI1 is frequently up-regulated and regulates a cluster of lncRNAs in HBV-related hepatocellular carcinoma (HCC). These findings highlight a novel mechanism for HBx-induced hepatocarcinogenesis through transcription factor EVI1 and its target lncRNAs, and provide a potential new approach to predict the functions of lncRNAs.

HBx drives alpha fetoprotein expression to promote initiation of liver cancer stem cells through activating PI3K/AKT signal pathway

Hepatitis B virus (HBV)-X protein (HBx) plays critical role in inducing the malignant transformation of liver cells. Alpha fetoprotein (AFP) expression is closely related to hepatocarcinogenesis. We report that Oct4, Klf4, Sox2 and c-myc expression positively associated with AFP(+)/HBV(+) hepatocellular carcinoma(HCC) tissues, and the expression of the stemness markers CD44, CD133 and EpCAM was significantly higher in AFP(+)/HBV(+) HCC tissues compared to normal liver tissues or AFP (-)/HBV(-) HCC tissues. AFP expression turned on prior to expression of Oct4, Klf4, Sox2 and c-myc, and the stemness markers CD44, CD133 and EpCAM in the normal human liver L-02 cell line or CHL cell lines upon transfection with MCV-HBx vectors. Stem-like cells generated more tumour colonies compared to primary cells, and xenografts induced tumourigenesis in nude mice. Expression of reprogramming-related proteins was significantly enhanced in HLE cells while transfected with pcDNA3.1-afp vectors. The specific PI3K inhibitor Ly294002 inhibited the effects of pcDNA3.1-afp vectors. AFP-siRNA vectors were able to inhibit tumour colony formation and reprogramming-related gene expression. Altogether, HBx stimulates AFP expression to induce natural reprogramming of liver cells, and AFP plays a critical role in promoting the initiation of HCC progenitor/stem cells. AFP may be a potential novel biotarget for combating HBV-induced hepatocarcinogenesis.

Hepatitis B virus X protein induces expression of alpha-fetoprotein and activates PI3K/mTOR signaling pathway in liver cells

The hepatitis B virus (HBV)-X protein (HBx) induces malignant transformation of liver cells, and elevated expression of alpha-fetoprotein (AFP) is a significant biomarker of hepatocarcinogenesis. However, the role of AFP in HBV-related hepatocarcinogenesis is unclear. In this study, we investigated the regulatory impact of AFP expression on HBx-mediated malignant transformation of human hepatocytes. We found that HBV induced the expression of AFP before that of oncogenes, e.g., Src, Ras and chemokine (C-X-C motif) receptor 4 (CXCR4), and AFP activated protein kinase B (AKT) and mammalian target of rapamycin (mTOR) in HBV-related HCC tissues and in human liver cells transfected with HBx. Cytoplasmic AFP interacted with and inhibited phosphatase and tensin homolog deleted on chromosome 10 (PTEN), activating the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway and promoting mTOR-mediated stimulation of the transcription factor hypoxia inducible factor-1α (HIF-1α), and therefore led to the activation of the promoters of Src, CXCR4, and Ras genes. On the contrary, reduced expression of AFP by siRNA resulted in the repression of p-mTOR, pAKT, Src, CXCR4, and Ras in human malignant liver cells. Taken together, for the first time our study indicates that HBx-induced AFP expression critically promote malignant transformation in liver cells through the activation of PI3K/mTOR signaling.

Hepatitis B Virus X Protein Upregulates hELG1/ ATAD5 Expression through E2F1 in Hepatocellular Carcinoma

The precise mechanism by which HBx protein of hepatitis B virus (HBV) impacts on hepato-carcinogenesis remain largely elusive despite strong evidences for its' involvement in the process. Here, we have investigated the role of HBx on expression of a novel gene hELG1/ATAD5, which is required for genome maintenance and its' importance in hepatocarcinogenesis. This study has for the first time showed that the expression of this gene was significantly higher in human cancer such as HBV-associated hepatocellular carcinoma (HCC) and in different HCC cell lines compared to normal liver. In addition, a significant elevation in ATAD5 expression was also found in HBx transfected HCC cell lines implicating HBx mediated transcriptional regulation on ATAD5. Using different deletion mutant constructs of putative promoter, the active promoter region was first identified here and subsequently the regulatory region of HBx was mapped by promoter-luciferase assay. But ChIP assay with anti-HBx antibody revealed that HBx was not physically present in ATAD5 transcription machinery whereas anti-E2F1 antibody showed the presence of E2F1 in the complex. Luciferase assay with E2F1 binding site mutant had further confirmed it. Moreover, both loss-and gain-of-function studies of ATAD5 showed that ATAD5 could enhance HBV production in transfected cells whereas knock down of ATAD5 increased the sensitivity of HCC cell line to chemotherapeutics 5-fluorouracil. Overall, this data suggests that a positive feedback loop regulation between ATAD5 and HBV contributed to both viral replication and chemo-resistance of HCC cells.

A novel mutant 10Ala/Arg together with mutant 144Ser/Arg of hepatitis B virus X protein involved in hepatitis B virus-related hepatocarcinogenesis in HepG2 cell lines

Hepatitis B virus (HBV) infection-related hepatocellular carcinoma (HCC) represents a major health problem worldwide. HBV X (HBx) protein is the most common open reading frame that may undergo mutations, resulting in the development of HCC. This study aimed to determine specific HBx mutations that differentiate the central- and para-tumor tissues, and identify their association with HCC development. HBx gene from HCC tumor and para-tumor tissues of 47 HCC patients was amplified, sequenced and statistically analyzed. A novel combination of 2 mutations at residues 10 and 144 was identified which might play a significant role in HCC development. Expression vectors carrying HBx with the specific mutations were constructed and transfected into HepG2 and p53-null HepG2 cells. Compared to wild type (WT) and single mutation of HBx at residue 10 or 144, the 10/144 double mutations strongly up-regulated p21 expression and prolonged G1/S transition in WT- and p53-null HepG2 cells. Apoptosis was also inhibited by HBx harboring 10/44 double-mutation. Binding of 10/144 double-mutant HBx to p53 was lower than WT HBx. Conclusively, the 10/144 double mutation of HBx might play a crucial role in HCC formation.

Hepatitis B virus X protein activates Notch signaling by its effects on Notch1 and Notch4 in human hepatocellular carcinoma

Deregulated expression of Notch receptors and abnormal activity of Notch signaling have been observed in a growing number of malignant tumors, however, the expression and activity of Notch in hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) and their relationship with HBV X protein (HBx) are still not fully elucidated. To address this, we examined the overall expression of Notch receptors in HBV-associated HCC tissues, analyzed their relationship with HBx, and further investigated the role of Notch signaling in HBx stable transfected HepG2 cells (HepG2X). The results showed that Notch signaling could be activated by HBx in HepG2 cells. The expression of cytoplasmic Notch1 or nuclear Notch4 was correlated with the expression of HBx in HBV-associated HCC tissues. The expression of cytoplasmic Notch1 or nuclear Notch4 could also be upregulated by HBx in HepG2X cells. The upregulation of Notch1 by HBx was through p38 MAPK pathway. Moreover, HBx was found to directly interact with Notch1, whereas, not with Notch4 in HepG2X cells. Suppression of Notch signaling by γ-secretase inhibitor (GSI) decreased cell growth, blocked cell cycle progression and induced cell apoptosis in HepG2X cells. The present study indicates that HBx activates Notch signaling by its effects on Notch1 and Notch4, and therefore, recruits Notch signaling as a downstream pathway contributing to its carcinogenic role in HBV-associated HCC.

The Chinese medicine Sini-San inhibits HBx-induced migration and invasiveness of human hepatocellular carcinoma cells

Background

Sini-San (SNS) is a formulation of four Traditional Chinese Drugs that exhibits beneficial therapeutic effects in liver injury and hepatitis. However, there are no reports describing its effects on the hepatitis B X-protein (HBx)-induced invasion and metastasis in hepatoma cells, and the detailed molecular mechanisms of its actions are still unclear.

Methods

In this study, we investigated the mechanisms underlying SNS-mediated inhibition of HBx-induced cell invasion and the inhibition of secreted and cytosolic MMP-9 production, using gelatin zymography and Western blot analysis in a human hepatoma cell line (HepG2). Relative luciferase activity was assessed for MMP-9, NF-κB, or AP-1 reporter plasmid-transfected cells.

Results

SNS suppressed MMP-9 transcription by inhibiting activator protein (AP)-1 and nuclear factor-κ B (NF-κB) activity. SNS suppressed HBx-induced AP-1 activity through inhibition of phosphorylation in the extracellular signal-related kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways. SNS also suppressed HBx-induced inhibition of NF-κB nuclear translocation through IκB and suppressed HBx-induced activation of ERK/phosphatidylinositol 3-kinase/Akt upstream of NF-κB and AP-1.

Conclusions

SNS suppresses the invasiveness and metastatic potential of hepatocellular carcinoma cells by inhibiting multiple signal transduction pathways.

HBx induced expression of alpha fetoprotein drives malignant transformation of liver cells

The development of hepatocellular carcinoma (HCC) is closely related to hepatitis B virus (HBV) infection, and HBV-X protein (HBx) plays a critical role in the malignant transformation of liver cells. HBx stimulates the expression of alpha fetoprotein (AFP) via restraining the transcription activity of P53 in the early stage of HCC genesis. Recently, studies have indicated that HBx preferentially promotes AFP expression during the malignant transformation of hepatic cells, and AFP accelerates the expression of malignant behavior related molecules through activating the phosphatidylinositol-3 kinase (PI3K)/protein kinas A (AKT) signaling pathway. These results suggest that AFP may be an important factor for HBx driven hepatocarcinogenesis. The discovery of novel function of AFP implicates that AFP can be used not only as a tumor marker for HBV-related HCC but also as a target for HCC therapy.

Hepatitis B virus X protein inhibits tumor suppressor miR-205 through inducing hypermethylation of miR-205 promoter to enhance carcinogenesis

The infection of hepatitis B virus (HBV) is closely associated with the development of hepatocellular carcinoma (HCC), in which HBV X protein (HBx) plays crucial roles. MicroRNAs are involved in diverse biologic functions and in carcinogenesis by regulating gene expression. In the present study, we aim to investigate the underlying mechanism by which HBx enhances hepatocarcinogenesis. We found that miR-205 was downregulated in 33 clinical HCC tissues in comparison with adjacent noncancerous hepatic tissues. The expression levels of miR-205 were inversely correlated with those of HBx in abovementioned tissues. Then, we demonstrated that HBx was able to suppress miR-205 expression in hepatoma and liver cells. We validated that miR-205 directly targeted HBx mRNA. Ectopic expression of miR-205 downregulated HBx, whereas depletion of endogenous miR-205 upregulated HBx in hepatoma cells. Notably, our data revealed that HBx downregulated miR-205 through inducing hypermethylation of miR-205 promoter in the cells. In terms of function, the forced miR-205 expression remarkably inhibited the HBx-enhanced proliferation of hepatoma cells in vitro and in vivo, suggesting that miR-205 is a potential tumor-suppressive gene in HCC. HBx-transgenic mice showed that miR-205 was downregulated in the liver. Importantly, HBx was able to abrogate the effect of miR-205 on tumor suppression in carcinogenesis. Therefore, we conclude that HBx is able to inhibit tumor suppressor miR-205 to enhance hepatocarcinogenesis through inducing hypermethylation of miR-205 promoter during their interaction. Therapeutically, miR-205 may be useful in the treatment of HCC.

Alpha fetoprotein can induce malignant transformation of liver cells and be used as a therapeutic target for hepatocellular carcinoma

Alpha-fetoprotein (AFP) is associated with the development of hepatocellular carcinoma (HCC) and widely used as a golden tumor marker for diagnosing HCC since the AFP gene is activated in the early stage of malignant transformation of liver cells. However, the molecular mechanisms responsible for the role of AFP in hepatocarcinogenesis remain poorly understood. Recently, we found that hepatitis B virus (HBV) preferentially induces the expression of AFP when triggering malignant transformation of hepatocytes, and AFP activates phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT) signaling by inhibiting the activity of phosphatase and tensin homolog deleted on chromosome ten (PTEN). Our results also indicated that AFP not only impedes all-trans retinoid acid receptor-β (RAR-β) regulated expression of target genes, but also blocks the transduction of apoptotic signaling by suppressing the activity of Caspase3. Inhibited expression of AFP is able to augment HCC sensitivity to tumor necrosis factor-related apoptosis-induced ligand (TRAIL) and all-trans retinoid acid. These data indicate that AFP can drive the malignant transformation of liver cells and antagonize apoptosis induced by agents for HCC. Taken together, these findings suggest that AFP may drive the malignant transformation of liver cells and can be used as a target for therapy of HCC.

Viruses as modulators of mitochondrial functions

Mitochondria are multifunctional organelles with diverse roles including energy production and distribution, apoptosis, eliciting host immune response, and causing diseases and aging. Mitochondria-mediated immune responses might be an evolutionary adaptation by which mitochondria might have prevented the entry of invading microorganisms thus establishing them as an integral part of the cell. This makes them a target for all the invading pathogens including viruses. Viruses either induce or inhibit various mitochondrial processes in a highly specific manner so that they can replicate and produce progeny. Some viruses encode the Bcl2 homologues to counter the proapoptotic functions of the cellular and mitochondrial proteins. Others modulate the permeability transition pore and either prevent or induce the release of the apoptotic proteins from the mitochondria. Viruses like Herpes simplex virus 1 deplete the host mitochondrial DNA and some, like human immunodeficiency virus, hijack the host mitochondrial proteins to function fully inside the host cell. All these processes involve the participation of cellular proteins, mitochondrial proteins, and virus specific proteins. This review will summarize the strategies employed by viruses to utilize cellular mitochondria for successful multiplication and production of progeny virus.

Hepatitis B virus X induces cell proliferation in the hepatocarcinogenesis via up-regulation of cytoplasmic p21 expression

BACKGROUND

Hepatitis B virus X protein (HBx) has been shown to induce hepatocarcinogenesis by disrupting the functions of intracellular molecules. Cyclin-dependent kinase inhibitor p21 (Cip1/WAF1), known as a tumour-suppressor gene, has been reported to have paradoxical function, that is, acting as an oncogene, particularly when expressed in the cytoplasm. The effects of HBx on the expression and function of p21 also remain controversial.

AIMS

We attempted to investigate the role of HBx in the hepatocarcinogenic process, focusing on the association with this paradoxical function of p21. The results obtained were further verified with experiments using the antihepatocarcinogenic action of interferon (IFN)-β.

METHODS

HBx transgenic mice (Xg) and HBx-transfected hepatoma cell lines were used. Intracellular localization of p21 was determined by Western blot analysis and immunofluorescence.

RESULTS

Xg and HBx-transfected cells exhibited increased expression of p21. Up-regulation of p21 was positively correlated with the expression of cyclin D1 and inactive phosphorylation of retinoblastoma protein (pRb). These HBx-induced cell proliferative responses were cancelled by knockdown of p21, which resulted in growth reduction in HBx-expressing cells, suggesting the oncogenic properties of HBx-induced p21. HBx induced accumulation of p21 in the cytoplasm, and activation of PKCα was involved. Finally, IFN-β-treated Xg liver, as well as hepatoma cells, showed a shift of cytoplasmic p21 to the nucleus, accompanied by the abrogation of HBx-induced oncogenic modulation.

CONCLUSIONS

Our results suggest that HBx induces hepatocarcinogenesis via PKCα-mediated overexpression of cytoplasmic p21 and IFN-β suppressed these molecular events by shifting p21 to the nucleus.

HBV induced HCC: major risk factors from genetic to molecular level

Hepatocellular carcinoma (HCC) is a deadly and emerging disease leading to death in Asian countries. High hepatitis B virus (HBV) load and chronic hepatitis B (CHB) infection increase the risk of developing HCC. HBV is a DNA virus that can integrate DNA into host genome thereby increase the yield of transactivator protein HBxAg that may deregulate many pathways involving in metabolism of cells. Several monogenic and polygenic risk factors are also involved in HCC development. This review summarizes the mechanism involved in HCC development and discusses some promising therapies to make HCC curative.

Hepatitis B virus regulation of Raf1 promoter activity through activation of transcription factor AP-2α

The X protein of hepatitis B virus (HBx) is one of the important factors in the development of hepatocellular carcinoma. Raf1 kinase is a central component of many signaling pathways that are involved in normal cell growth and oncogenic transformation. We previously demonstrated that hepatitis B virus regulates Raf1 expression in HepG2.2.15 cells by enhancing its promoter activity and that HBx and HBs might play an important role in this process. However, the underlying molecular mechanisms remain unclear. In this study, we show that nucleotides -209 to -133 of the Raf1 promoter sequence constitute the core region where hepatitis B virus is regulated. This regulation was found to require the involvement of cis-regulatory element AP-2α. We further demonstrated that AP-2α expression was higher in HepG2.2.15 cells (HBV-expressing cells) than in HepG2 cells in vitro. Silencing AP-2α expression by siRNA significantly inhibited the Raf1 promoter activity in HepG2.2.15 cells. These findings indicated that HBV regulates Raf1 promoter activity, possibly through AP-2α.

Modulation of apoptotic signaling by the hepatitis B virus X protein

Worldwide, an estimated 350 million people are chronically infected with the Hepatitis B Virus (HBV); chronic infection with HBV is associated with the development of severe liver diseases including hepatitis and cirrhosis. Individuals who are chronically infected with HBV also have a significantly higher risk of developing hepatocellular carcinoma (HCC) than uninfected individuals. The HBV X protein (HBx) is a key regulatory HBV protein that is important for HBV replication, and likely plays a cofactor role in the development of HCC in chronically HBV-infected individuals. Although some of the functions of HBx that may contribute to the development of HCC have been characterized, many HBx activities, and their putative roles during the development of HBV-associated HCC, remain incompletely understood. HBx is a multifunctional protein that localizes to the cytoplasm, nucleus, and mitochondria of HBV‑infected hepatocytes. HBx regulates numerous cellular signal transduction pathways and transcription factors as well as cell cycle progression and apoptosis. In this review, we will summarize reports in which the impact of HBx expression on cellular apoptotic pathways has been analyzed. Although various effects of HBx on apoptotic pathways have been observed in different model systems, studies of HBx activities in biologically relevant hepatocyte systems have begun to clarify apoptotic effects of HBx and suggest mechanisms that could link HBx modulation of apoptotic pathways to the development of HBV-associated HCC.

Potential role of signal transducer and activator of transcription (STAT)3 signaling pathway in inflammation, survival, proliferation and invasion of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies, and is also the fourth most common cancer worldwide with around 700,000 new cases each year. Currently, first line chemotherapeutic drugs used for HCC include fluorouracil, cisplatin, doxorubicin, paclitaxel and mitomycin, but most of these are non-selective cytotoxic molecules with significant side effects. Sorafenib is the only approved targeted therapy by the U.S. Food and Drug Administration for HCC treatment, but patients suffer from various kinds of adverse effects, including hypertension. The signal-transducer-and-activator-of-transcription 3 (STAT3) protein, one of the members of STATs transcription factor family, has been implicated in signal transduction by different cytokines, growth factors and oncogenes. In normal cells, STAT3 activation is tightly controlled to prevent dysregulated gene transcription, whereas constitutively activated STAT3 plays an important role in tumorigenesis through the upregulation of genes involved in anti-apoptosis, proliferation and angiogenesis. Thus, pharmacologically safe and effective agents that can block STAT3 activation have the potential both for the prevention and treatment of HCC. In the present review, we discuss the possible role of STAT3 signaling cascade and its interacting partners in the initiation of HCC and also analyze the role of various STAT3 regulated genes in HCC progression, inflammation, survival, invasion and angiogenesis.

Hepatitis B virus X protein stabilizes amplified in breast cancer 1 protein and cooperates with it to promote human hepatocellular carcinoma cell invasiveness

Chronic infection of hepatitis B virus (HBV) is closely associated with the development of human hepatocellular carcinoma (HCC). HBV X protein (HBx) plays a key role in the progression of HCC. We recently found that amplified in breast cancer 1 (AIB1) protein is overexpressed in 68% of human HCC specimens and promotes HCC progression by enhancing cell proliferation and invasiveness. Given that both HBx and AIB1 play important oncogenic roles in HCC, we aimed to determine whether they could cooperatively promote human HCC development. Herein, we show that HBx-positive HCC tissues had a higher level of AIB1 protein, compared to HBx-negative HCC tissues. A positive correlation between HBx protein level and AIB1 protein level was established in HCC specimens. Without affecting its messenger RNA level, HBx induced a significant increase of the protein level of AIB1, which correlated with a significant extension of the half-life of AIB1 protein. Mechanistically, HBx could interact with AIB1 to prevent the interaction between envelope protein 3 ubiquitin ligase F-box and WD repeat domain containing 7 (Fbw7)α and AIB1, then inhibited the Fbw7α-mediated ubiquitination and degradation of AIB1. In addition, reporter assays and chromatin immunoprecipitation assays revealed that both HBx and AIB1 were recruited to matrix metalloproteinase-9 (MMP-9) promoter to enhance MMP-9 promoter activity cooperatively. Consistently, HBx and AIB1 cooperatively enhanced MMP-9 expression in HepG2 cells, which, in turn, increased cell-invasive ability.

CONCLUSION

Our study demonstrates that HBx can stabilize AIB1 protein and cooperate with it to promote human HCC cell invasiveness, highlighting the essential role of the cross-talk between HBx and AIB1 in HBV-related HCC progression.

Hepatitis B virus X protein upregulates mTOR signaling through IKKβ to increase cell proliferation and VEGF production in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), a major cause of cancer-related death in Southeast Asia, is frequently associated with hepatitis B virus (HBV) infection. HBV X protein (HBx), encoded by a viral non-structural gene, is a multifunctional regulator in HBV-associated tumor development. We investigated novel signaling pathways underlying HBx-induced liver tumorigenesis and found that the signaling pathway involving IκB kinase β (IKKβ), tuberous sclerosis complex 1 (TSC1), and mammalian target of rapamycin (mTOR) downstream effector S6 kinase (S6K1), was upregulated when HBx was overexpressed in hepatoma cells. HBx-induced S6K1 activation was reversed by IKKβ inhibitor Bay 11-7082 or silencing IKKβ expression using siRNA. HBx upregulated cell proliferation and vascular endothelial growth factor (VEGF) production, and these HBx-upregulated phenotypes were abolished by treatment with IKKβ inhibitor Bay 11-7082 or mTOR inhibitor rapamycin. The association of HBx-modulated IKKβ/mTOR/S6K1 signaling with liver tumorigenesis was verified in a HBx transgenic mouse model in which pIKKβ, pS6K1, and VEGF expression was found to be higher in cancerous than non-cancerous liver tissues. Furthermore, we also found that pIKKβ levels were strongly correlated with pTSC1 and pS6K1 levels in HBV-associated hepatoma tissue specimens taken from 95 patients, and that higher pIKKβ, pTSC1, and pS6K1 levels were correlated with a poor prognosis in these patients. Taken together, our findings demonstrate that HBx deregulates TSC1/mTOR signaling through IKKβ, which is crucially linked to HBV-associated HCC development.

Hepatitis B virus X protein upregulates mTOR signaling through IKKβ to increase cell proliferation and VEGF production in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), a major cause of cancer-related death in Southeast Asia, is frequently associated with hepatitis B virus (HBV) infection. HBV X protein (HBx), encoded by a viral non-structural gene, is a multifunctional regulator in HBV-associated tumor development. We investigated novel signaling pathways underlying HBx-induced liver tumorigenesis and found that the signaling pathway involving IκB kinase β (IKKβ), tuberous sclerosis complex 1 (TSC1), and mammalian target of rapamycin (mTOR) downstream effector S6 kinase (S6K1), was upregulated when HBx was overexpressed in hepatoma cells. HBx-induced S6K1 activation was reversed by IKKβ inhibitor Bay 11-7082 or silencing IKKβ expression using siRNA. HBx upregulated cell proliferation and vascular endothelial growth factor (VEGF) production, and these HBx-upregulated phenotypes were abolished by treatment with IKKβ inhibitor Bay 11-7082 or mTOR inhibitor rapamycin. The association of HBx-modulated IKKβ/mTOR/S6K1 signaling with liver tumorigenesis was verified in a HBx transgenic mouse model in which pIKKβ, pS6K1, and VEGF expression was found to be higher in cancerous than non-cancerous liver tissues. Furthermore, we also found that pIKKβ levels were strongly correlated with pTSC1 and pS6K1 levels in HBV-associated hepatoma tissue specimens taken from 95 patients, and that higher pIKKβ, pTSC1, and pS6K1 levels were correlated with a poor prognosis in these patients. Taken together, our findings demonstrate that HBx deregulates TSC1/mTOR signaling through IKKβ, which is crucially linked to HBV-associated HCC development.

Establishment of a HepG2 cell line stably transduced with a lentivirus expressing the HBV X gene

AIM: To establish a HepG2 cell line stably transduced with a lentivirus expressing the HBV X (HBx) gene for studying the biological function of HBx and its role in hepatocarcinogenesis.

METHODS: The HBV X gene was amplified from plasmid pIERES2-EGFP-HBV by PCR. The purified HBx gene fragment was inserted into a lentivirus vector (pZac2.1), and the insertion was identified by PCR, restriction endonuclease analysis and DNA sequencing. HepG2 cells were then transfected with the packaged recombinant lentivirus, and resistant cell clones were selected with puromycin. The expression of HBx was examined using RT-PCR, immunohistochemistry, and Western blot.

RESULTS: Restriction enzyme digestion and DNA sequencing showed that the full-length HBx (489 bp) gene had been successfully subcloned into the lentiviral vector to result in the recombinant vector pZac2.1-HBx. The titre of purified recombinant lentivirus was 1×10⁸ TU/mL. Monoclonal cell line HepG2-HBx was produced 8-10 d after transfection with the recombinant lentivirus and selected with puromycin. HBx mRNA could be detected on days 3, 14, 30 and at 2 mo after cell colony formation. Meanwhile, stable expression of HBx protein was verified by immunohistochemistry and Western blot.

CONCLUSION: A HepG2 cell line stably transduced with a lentivirus expressing the HBx gene has been successfully generated.

Hepatitis B virus X protein inhibits extracellular IFN-α-mediated signal transduction by downregulation of type I IFN receptor

We have previously shown that hepatitis B virus (HBV) protein X (HBX), a regulatory protein of HBV, activates Stat1, leading to type I interferon (IFN) production. Type I IFN secreted from HBX-expressing hepatic cells enforces antiviral signals through its binding to the cognate type I IFN receptor. We therefore investigated how cells handle this detrimental situation. Interestingly, compared to Chang cells stably expressing an empty vector (Chang-Vec), Chang cells stably expressing HBX (Chang-HBX) showed lower levels of IFN-α receptor 1 (IFNAR1) protein, a subunit of type I IFN receptor. The levels of IFNAR1 transcripts detected in Chang-HBX cells were lower than the levels in Chang-Vec cells, indicating that HBX regulates IFNAR1 at the transcriptional level. Moreover, we observed that HBX induced the translocation of IFNAR1 to the cytoplasm. Consistent with these observations, HBX also downregulated Tyk2, which is required for the stable expression of IFNAR1 on the cell surface. Eventually, Chang-HBX cells consistently maintained a lower level of IFNAR1 expression and displayed no proper response to IFN-α, while Chang-Vec cells exhibited a proper response to IFN-α treatment. Taken together, we propose that HBX downregulates IFNAR1, leading to the avoidance of extracellular IFN-α signal transduction.

Hepatitis B virus X protein promotes the growth of hepatocellular carcinoma by modulation of the Notch signaling pathway

Hepatitis B virus X protein (HBx) plays a crucial role in the development of hepatocellular carcinoma (HCC), however, little is known about the mechanism. Here, we investigated the relationship between HBx and Notch signaling in HepG2 cells after they were transfected with the HBx gene. It was found that HBx upregulated the expression of Notch-1, Jagged-1 and Hes-1 at the transcriptional level by binding to the Notch-1 intracellular domain, which is congruent with the observations of enhanced malignant biological activities of HBx-transfected HepG2 cells compared with normal HepG2 cells. However, while Notch signaling was blocked, the HBx-induced abnormalities were partially reversed. These findings suggest that HBx may promote the progression of HCC via the activated Notch pathway.

Identification of the common regulators for hepatocellular carcinoma induced by hepatitis B virus X antigen in a mouse model

Hepatitis B virus X antigen plays an important role in the development of human hepatocellular carcinoma (HCC). The key regulators controlling the temporal downstream gene expression for HCC progression remains unknown. In this study, we took advantage of systems biology approach and analyzed the microarray data of the HBx transgenic mouse as a screening process to identify the differentially expressed genes and applied the software Pathway Studio to identify potential pathways and regulators involved in HCC. Using subnetwork enrichment analysis, we identified five common regulator genes: EDN1, BMP7, BMP4, SPIB and SRC. Upregulation of the common regulators was validated in the other independent HBx transgenic mouse lines. Furthermore, we verified the correlation of their RNA expression levels by using the human HCC samples, and their protein levels by using the human liver disease tissue arrays. EDN1, bone morphogenetic protein (BMP) 4 and BMP7 were upregulated in cirrhosis, BMP4, BMP7 and SRC were further upregulated in hepatocellular or cholangiocellular carcinoma samples. The trend of increasing expression of the common regulators correlates well with the progression of human liver cancer. Overexpression of the common regulators increases the cell viability, promotes migration and invasiveness and enhances the colony formation ability in Hep3B cells. Our approach allows us to identify the critical genes in hepatocarcinogenesis in an HBx-induced mouse model. The validation of the gene expressions in the liver cancer of human patients and their cellular function assays suggests that the identified common regulators may serve as useful molecular targets for the early-stage diagnosis or therapy for HCC.

Hepatitis B virus X protein promotes hepatoma cell proliferation via upregulation of MEKK2

AIM

To investigate the mechanism underlying the increase of hepatoma cell proliferation by hepatitis B virus X protein (HBx).

METHODS

HepG2, H7402 and HepG2.2.15 cells, which constitutively replicated hepatitis B virus were used. The effects of HBx on hepatoma cell proliferation were examined using 5-ethynyl-2-deoxyuridine (EdU) incorporation assay and MTT assay. The expression level of MEKK2 was measured using RT-PCR, Western blot and luciferase reporter gene assay. The activity of activator protein 1 (AP-1) was detected using luciferase reporter gene assay. The phosphorylation levels of JNK and c-Jun were measured using Western blot. The expression levels of HBx and MEKK2 in 11 clinical hepatocellular carcinoma (HCC) tissues were measured using real time PCR and Western blot. In addition, the expression of MEKK2 in 95 clinical HCC tissues was examined using immunohistochemistry.

RESULTS

HBx significantly enhanced HepG2-X cell proliferation. In HepG2-X, H7402-X and HepG2.2.15 cells, the expression level of MEKK2 was remarkably increased. In HepG2.2.15 cells, HBx was found to activate JNK and AP-1, which were the downstream effectors of MEKK2 in HepG2-X and HepG2.2.15 cells. In 11 clinical HCC tissues, both HBx and MEKK2 expression levels were remarkably increased, as compared to those in the corresponding peritumor tissues. In 95 clinical HCC tissues, the rate of detection of MEKK2 was 85.3%.

CONCLUSION

HBx promotes hepatoma cell proliferation via upregulating MEKK2, which may be involved in hepatocarcinogenesis.

The novel immunosuppressive protein kinase C inhibitor sotrastaurin has no pro-viral effects on the replication cycle of hepatitis B or C virus

The pan-protein kinase C (PKC) inhibitor sotrastaurin (AEB071) is a novel immunosuppressant currently in phase II trials for immunosuppression after solid organ transplantation. Besides T-cell activation, PKC affects numerous cellular processes that are potentially important for the replication of hepatitis B virus (HBV) and hepatitis C virus (HCV), major blood-borne pathogens prevalent in solid organ transplant recipients. This study uses state of the art virological assays to assess the direct, non-immune mediated effects of sotrastaurin on HBV and HCV. Most importantly, sotrastaurin had no pro-viral effect on either HBV or HCV. In the presence of high concentrations of sotrastaurin, well above those used clinically and close to levels where cytotoxic effects become detectable, there was a reduction of HCV and HBV replication. This reduction is very likely due to cytotoxic and/or anti-proliferative effects rather than direct anti-viral activity of the drug. Replication cycle stages other than genome replication such as viral cell entry and spread of HCV infection directly between adjacent cells was clearly unaffected by sotrastaurin. These data support the evaluation of sotrastaurin in HBV and/or HCV infected transplant recipients.

The role of hepatitis B virus X protein is related to its differential intracellular localization

Chronic hepatitis B virus (HBV) infection has been strongly associated with hepatocellular carcinoma. HBV encodes an oncogenic hepatitis B virus X protein (HBx), which is a multifunctional regulator that modulates signal transduction, transcription, cell cycle progress, protein degradation, apoptosis, and genetic stability through direct and indirect interaction with host factors. The subcellular localization of HBx is primarily cytoplasmic, with a small fraction in the nucleus. In addition, high levels of HBx expression lead to an abnormal mitochondrial distribution. The dynamic distribution of HBx could be important to the multiple functions of HBx at different stages of the HBV life cycle. This short review presents an overview of the differential roles of HBx as a function of its intracellular localization.

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.

Proteomic analysis of the interleukin-4 (IL-4) response in hepatitis B virus-positive human hepatocelluar carcinoma cell line HepG2.2.15

Hepatitis B virus (HBV) infection is the leading cause of liver cirrhosis and hepatocellular carcinoma worldwide. In recent decades, significant progress toward understanding the molecular virology and pathogenesis of HBV infection has been made. In addition, multiple treatment modalities have been developed for persons with HBV infection. In the present study, we demonstrated that IL-4 inhibits the expression of hepatitis B surface antigen and hepatitis B e antigen in a HBV stably transfected hepatocellular carcinoma cell line (HepG2.2.15). To reveal the anti-HBV mechanism of IL-4 by proteomics, 2-DE and MS technology were utilized to profile global changes in protein expression in HepG2.2.15 cells after IL-4 treatment. A total of 56 differentially expressed proteins were identified in IL-4-treated HepG2.2.15 cells. To find out the interaction of these changed proteins by bioinformatics, signaling network analysis with the STRING tool showed that the identified proteins are primarily involved in transcription and proteolysis. Taken together, these results offer valuable clues for understanding the molecular mechanisms of the IL-4-mediated anti-HBV response.

Epigenetic repression of E-cadherin expression by hepatitis B virus x antigen in liver cancer

Loss of E-cadherin is associated with acquisition of metastatic capacity. Numerous studies suggest histone deacetylation and/or hypermethylation of CpG islands in E-cadherin gene (CDH1) are major mechanisms responsible for E-cadherin silencing in different tumors and cancer cell lines. The Hepatitis B virus (HBV) encoded X antigen, HBx, contributes importantly to the development of hepatocellular carcinoma (HCC) using multiple mechanisms. Experiments were designed to test if in addition to CDH1 hypermethylation HBx promotes epigenetic modulation of E-cadherin transcriptional activity through histone deacetylation and miR-373. The relationships between HBx, E-cadherin, mSin3A, Snail-1 and miR-373 were evaluated in HBx expressing (HepG2X) and control (HepG2CAT) cells by western blotting, immunoprecipitation, chromatin immunoprecipitation as well as by immunohistochemical staining of liver and tumor tissue sections from HBV infected patients. In HepG2X cells, decreased levels of E-cadherin and elevated levels of mSin3A and Snail-1 were detected. Reciprocal immunoprecipitation with anti-HBx and anti-mSin3A demonstrated mutual binding. Further, HBx-mSin3A co-localization was detected by immunofluorescent staining. HBx down-regulated E-cadherin expression by the recruitment of the mSin3A/HDAC complex to the Snail-binding sites in human CDH1. Histone deacetylation inhibition by Trichostatin A treatment restored E-cadherin expression. Mir-373, a positive regulator of E-cadherin expression, was down-regulated by HBx in HepG2X cells and tissue sections from HBV infected patients. Thus, histone deacetylation of CDH1 and down-regulation of miR-373, together with the previously demonstrated hyper-methylation of CDH1 by HBx, may be important for the understanding of HBV-related carcinogenesis.

Stimulation of B7-H1 in hepatocarcinoma cells by hepatitis B virus X antigen

The cross-talk between the hepatitis B virus X protein (HBx) and B7-H1 in hepatocarcinoma (HCC) is unclear. This study analyzed the potential relationships between HBx and B7-H1 in hepatocarcinogenesis. One of human HCC cell lines, HepG2 cells, was transfected to stably express HBx protein (HBx(+)-HepG2). The transcription of B7-H1 mRNA was increased significantly in these cells compared to cells transfected with control vector (HBx(-)-HepG2), as confirmed by a comparative genome-wide microarray analysis (Capitalbio) and real time quantitative PCR (qPCR). Flow cytometry and western-blot further demonstrated that B7-H1 protein synthesis was enhanced in HBx(+)-HepG2 cells. Site-directed mutagenesis of promoter constructs revealed that the transcription factor (NF)-κB binding site between 128 and 137 bp upstream of B7-H1 gene transcriptional start site is primarily responsible for HBx-mediated B7-H1 expression. Co-culture experiments with HBx(+)-HepG2/T cells showed that the number of apoptotic T cells increased profoundly, and this effect could be partially prevented when a neutralizing mAb against B7-H1 was added to the culture, demonstrating that B7-H1 signaling can promote T cell apoptosis. Our results suggest that the expression of B7-H1 in hepatocarcimona cells can be initiated by HBx antigen, thus inducing T cell apoptosis and finally potentially facilitates the genesis of HCC.

Hepatitis B virus X protein impedes the DNA repair via its association with transcription factor, TFIIH

Background

Hepatitis B virus (HBV) infections play an important role in the development of hepatocellular carcinoma (HCC). HBV X protein (HBx) is a multifunctional protein that can modulate various cellular processes and plays a crucial role in the pathogenesis of HCC. HBx is known to interact with DNA helicase components of TFIIH, a basal transcriptional factor and an integral component of DNA excision repair.

Results

In this study, the functional relevance of this association was further investigated in the context to DNA repair. By site-directed mutagenesis HBx's critical residues for interaction with TFIIH were identified. Similarly, TFIIH mutants lacking ATPase domain and the conserved carboxyl-terminal domain failed to interact with HBx. Yeast and mammalian cells expressing HBx^wt conferred hypersensitivity to UV irradiation, which is interpreted as a basic deficiency in nucleotide excision repair. HBx^mut120 (Glu to Val) was defective in binding to TFIIH and failed to respond to UV.

Conclusions

We conclude that HBx may act as the promoting factor by inhibiting DNA repair causing DNA damage and accumulation of errors, thereby contributing to HCC development.

Hepatitis B virus e antigen downregulates cytokine production in human hepatoma cell lines

Disease activities of hepatitis B are affected by the status of hepatitis B e antigen (HBeAg). The function of the hepatitis B virus (HBV) precore or HBeAg is unknown. We assumed that HBeAg blocks aberrant immune responses, although HBeAg is not required for viral assembly, infection, or replication. We examined the interaction of HBeAg and the immune system, including cytokine production. The inflammatory cytokine TNF, IL-6, IL-8, IL-12A, IFN-α1, and IFN-ß mRNA were downregulated in HBeAg-positive HepG2, which stably expresses HBeAg, compared to HBeAg-negative HepG2 cells. The results of real-time RT-PCR-based cytokine-related gene arrays showed the downregulation of cytokine and IFN production. We also observed inhibition of the activation of NF-κB- and IFN-ß-promoter in HBeAg-positive HepG2, as well as inhibition of IFN and IL-6 production in HBeAg-positive HepG2 cell culture fluids. HBeAg might modify disease progression by inhibiting inflammatory cytokine and IFN gene expression, while simultaneously suppressing NF-κB-signaling- and IFNß-promoter activation.

Ageing, telomeres, senescence, and liver injury

Populations in developed countries continue to grow older and an understanding of the ageing process to allow healthy ageing carries important medical implications. Older individuals are more susceptible to most acquired liver disorders and more vulnerable to the consequences of liver disease. Accordingly, age is a critical determinant of outcome for hepatitis C virus infection and liver transplantation. In this review we describe changes in the ageing liver and discuss mechanisms of senescence at the cellular level. In particular, we focus on mechanisms by which inflammation, oxidative stress, and oncogenic stress accelerate cellular senescence. In the setting of chronic hepatic injury and inflammation, cellular senescence functions as an essential stress-response mechanism to limit the proliferation of damaged cells and reduce the risk of malignancy, but this benefit is achieved at the expense of senescence-related organ dysfunction. The dual role of cell senescence in chronic liver disease will make this an intriguing but challenging area for future clinical interventions.

Hepatitis B virus BCP, Precore/core, X gene mutations/genotypes and the risk of hepatocellular carcinoma in India

The study aims to characterize mutations of the HBV genome involving BCP, Precore/core and X regions and also defines HBV genotypes in patients of hepatocellular carcinoma (HCC). The study involved 150 HBV-related HCC cases and 136 HBV-related chronic liver disease patients without HCC as controls. HBV DNA was subjected to mutational analysis using SSCP technique, genotyping by RFLP, and direct nucleotide sequencing. HBV DNA was found in 58.7% (88/150) of the HCC cases and 74.3% (101/136) of controls. HBV mutants were observed in 44.3% of HCC cases and 43.2% of controls. HBV/D was prevalent amongst the patients and controls, followed by HBV/A. The prevalence of the TT1504 mutation in the X gene, the V1753 and T1762/A1764 mutations in the BCP region, and G1914 mutation in the core gene were significantly higher in the HCC group than in the non-HCC group. Multivariate analyses showed that the TT1504, V1753, A1762T/G1764A, and the G1914 mutations and the patient's age, sex, and HBeAg status increased the risk of HCC development significantly. Also, patients with HCC had lower levels of serum albumin, viral load, and platelet counts but higher values of alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, bilirubin, and Alpha feto-protein than those of controls (P < 0.001 for all comparisons). HBV/D was the predominant genotype associated with HCC cases seen in India. The presence of different types of HBV mutations, age, sex, HBeAg status, and viral load was found to increase significantly the risk of HCC development in India.

[Pro-apoptotic function of hepatitis B virus X protein]

Infection of hepatitis B virus (HBV) is a main cause of liver diseases including hepatitis, cirrhosis and hepatocellular carcinoma (HCC). Among the HBV-encoded proteins, the HBV X protein (HBx) has been suspected to be strongly involved in HBV-associated liver pathogenesis. HBx, a virally encoded multifunctional regulator, has been shown to induce apoptosis, anti-apoptosis, proliferation, and transformation of cells depending on the cell lines, model systems used, assay protocols, and research groups. Among the several activities of HBx, the pro-apoptotic function of HBx will be discussed in this review. Given that the disruption of apoptosis pathway by HBx contributes to the liver pathogenesis, a better understanding of the molecular interference in the cellular pro-apoptotic networks by HBx will provide useful clues for the intervention in HBV-mediated liver diseases.

Hepatitis B virus protein X-induced expression of the CXC chemokine IP-10 is mediated through activation of NF-kappaB and increases migration of leukocytes

Interferon-gamma inducible protein 10 (IP-10) involves inflammatory cell recruitment and cellular immune damage during virus infection. Although an increase of the peripheral IP-10 level is known in HBV-infected patients, the molecular basis of HBV infection inducing IP-10 expression has remained elusive. In the present study, we demonstrate that hepatitis B virus protein X (HBx) increases IP-10 expression in a dose-dependent manner. Transfection of the HBx-expressing vector into HepG2 cells results in nuclear translocation of NF-kappaB, which directly binds the promoter of IP-10 at positions from -122 to -113, thus facilitating transcription. The addition of the NF-kappaB inhibitor blocks the effect of HBx on IP-10 induction. In parallel, increase of NF-kappaB subunits p65 and p50 in HepG2 cells also augments IP-10 expression. Furthermore, we show that HBx induces activation of NF-kappaB through the TRAF2/TAK1 signaling pathway, leading to up-regulation of IP-10 expression. As a consequence, up-regulation of IP-10 may mediate the migration of peripheral blood leukocytes in a NF-kappaB-dependent manner. In conclusion, we report a novel molecular mechanism of HBV infection inducing IP-10 expression, which involves viral protein HBx affecting NF-kappaB pathway, leading to transactivation of the IP-10 promoter. Our study provides insight into the migration of leukocytes in response to HBV infection, thus causing immune pathological injury of liver.

Pathogenesis of hepatitis B virus infection

The adaptive immune response is thought to be responsible for viral clearance and disease pathogenesis during hepatitis B virus infection. It is generally acknowledged that the humoral antibody response contributes to the clearance of circulating virus particles and the prevention of viral spread within the host while the cellular immune response eliminates infected cells. The T cell response to the hepatitis B virus (HBV) is vigorous, polyclonal and multispecific in acutely infected patients who successfully clear the virus and relatively weak and narrowly focussed in chronically infected patients, suggesting that clearance of HBV is T cell dependent. The pathogenetic and antiviral potential of the cytotoxic T lymphocyte (CTL) response to HBV has been proven by the induction of a severe necroinflammatory liver disease following the adoptive transfer of HBsAg specific CTL into HBV transgenic mice. Remarkably, the CTLs also purge HBV replicative intermediates from the liver by secreting type 1 inflammatory cytokines thereby limiting virus spread to uninfected cells and reducing the degree of immunopathology required to terminate the infection. Persistent HBV infection is characterized by a weak adaptive immune response, thought to be due to inefficient CD4+ T cell priming early in the infection and subsequent development of a quantitatively and qualitatively ineffective CD8+ T cell response. Other factors that could contribute to viral persistence are immunological tolerance, mutational epitope inactivation, T cell receptor antagonism, incomplete down-regulation of viral replication and infection of immunologically privileged tissues. However, these pathways become apparent only in the setting of an ineffective immune response, which is, therefore, the fundamental underlying cause. Persistent infection is characterized by chronic liver cell injury, regeneration, inflammation, widespread DNA damage and insertional deregulation of cellular growth control genes, which, collectively, lead to cirrhosis of the liver and hepatocellular carcinoma.

Hepatitis B virus X gene is implicated in liver carcinogenesis

Hepatitis B virus (HBV) is a small hepatotropic and highly species-specific enveloped DNA virus. The carcinogenicity of this virus has become focused on the X gene and its coded X protein. The X protein itself is unable to bind to DNA directly, but works as a potent transcriptional activator through multiple cis-acting elements and mediates several signal transduction cascades. Two regions of the X protein, aa.61-69 and aa.105-140, are found essential for the viral replication and expression as well. These functions interacting with transcription factors and signaling cascades are acting cooperatively to cause cell proliferation. Furthermore, the association of X protein with mitochondria causes loss of the mitochondrial membrane potential and subsequently causes cell death, the function of which is attributed to the aa.68-104 region of X protein. As a result, the X protein has two independent proliferative and cell death-promoting activities. Liver cancer has been shown to result from a series of mutations in specific oncogenes and tumor suppressor genes. In a recent study, X protein stimulates ROS generation in the mitochondria due to collapse of the membrane potential and increases the mutation frequency, that evokes malignant transformation. Inflammation as a result of HBV infection is concerned to cause DNA damage. In the past 10years, the possibility that several viral proteins directly engaged in the DNA damage has increased to some extent. From an evolutionary viewpoint, it is noteworthy that several arrangement proteins have been found in viruses. Thus, there is some clue that a small amount of X protein acts as an arrangement protein for HBV replication dependent upon cellular DNA damage due to generated ROS as an amplified signal.