Reactive oxygen species modulates the intracellular level of HBx viral oncoprotein

ALR inhibits HBV replication and autophagosome formation by ameliorating HBV-induced ROS production in hepatic cells

HBV has a small genome and thrives in the infected hepatocytes by hijacking the cellular machinery and cellular pathways. HBV induces incomplete autophagy for its replication and survival. This study showed that HBV replication induces Reactive oxygen species (ROS) production, which in turn augments the formation of autophagosomes. Augmenter of liver regeneration (ALR) is a sufhydryl oxidase and has an anti-oxidative property. We sought to determine the interplay between HBV and antioxidant protein ALR. We showed that HBV downregulated ALR expression in hepatic cells. There was increased ROS production in HBV-infected cells while ALR downregulated ROS levels and expression of NADPH oxidase NOX4. N-acetyl cysteine, a ROS scavenger, downregulated ROS level and autophagosome formation in HBV-expressing cells. ALR overexpression in HBV-expressing cells downregulated the expression of autophagy marker proteins while upregulated the expression of p-MTOR. ALR overexpression decreased the expression of HBx, HBsAg, and total HBV load. This study showed that HBx relieved ALR-mediated inhibition by upregulating the miR-181a expression in HBV-infected cells, which in turn downregulated ALR expression.

The Abnormal Proliferation of Hepatocytes is Associated with MC-LR and C-Terminal Truncated HBX Synergistic Disturbance of the Redox Balance

Background

Microcystin-LR (MC-LR) and hepatitis B virus (HBV) are associated with hepatocellular carcinoma (HCC). However, the concentrations of MC-LR in drinking water and the synergistic effect of MC-LR and HBV on hepatocellular carcinogenesis through their disturbance of redox balance have not been fully elucidated.

Methods

We measured the MC-LR concentrations in 168 drinking water samples of areas with a high incidence of HCC. The relationships between MC-LR and both redox status and liver diseases in 177 local residents were analyzed. The hepatoma cell line HepG2 transfected with C-terminal truncated hepatitis B virus X gene (Ct-HBX) were treated with MC-LR. Reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) were measured. Cell proliferation, migration, invasion, and apoptosis were assessed with cell activity assays, scratch and transwell assays, and flow cytometry, respectively. The mRNA and protein expression-related redox status genes were analyzed with qPCR and Western blotting.

Results

The average concentration of MC-LR in well water, river water and reservoir water were 57.55 ng/L, 76.74 ng/L and 132.86 ng/L respectively, and the differences were statistically significant (P < 0.05). The MC-LR levels in drinking water were correlated with liver health status, including hepatitis, clonorchiasis, glutamic pyruvic transaminase abnormalities and hepatitis B surface antigen carriage (all P values < 0.05). The serum MDA increased in subjects who drank reservoir water and were infected with HBV (P < 0.05). In the cell experiment, ROS increased when Ct-HBX-transfected HepG2 cells were treated with MC-LR, followed by a decrease in SOD and GSH and an increase in MDA. MC-LR combined with Ct-HBX promoted the proliferation, migration and invasion of HepG2 cells, upregulated the mRNA and protein expression of MAOA gene, and downregulated UCP2 and GPX1 genes.

Conclusion

MC-LR and HBV may synergistically affect redox status and play an important role in hepatocarcinoma genesis.

Immunoenhancement and antioxidative damage effects of Polygonum Cillinerve polysaccharide on RAW264.7 cells

OBJECTIVES

The effects of Polygonum Cillinerve polysaccharide (PCP) on the immune and antioxidant activity were studied.

METHODS

The effects of PCP on cell proliferation, phagocytic activity, cell uptake, the secretion of NO, iNOS, IL-6, IL-12, CAT and POD, intracellular ROS, cell apoptosis and antioxidative mechanism were measured by MTT, ELISA, fluorescence staining, flow cytometry and western blot.

KEY FINDINGS

The results showed that PCP had no toxic effect at 31.25-1.95 µg/ml, could improve the uptake of neutral red and fluorescein isothiocyanate-labelled ovalbumin and promote the release of nitric oxide and nitric oxide synthase. Moreover, PCP also could promote the secretion of IL-6 and IL-12. The damage of RAW264.7 cells induced by hydrogen peroxide was significantly alleviated by PCP at 15.63-0.975 µg/ml. The mechanism of antioxidative damage might be that PCP inhibited the upstream p38 and the phosphorylation of JNK and ERK proteins, and down-regulated caspase 3 and up-regulated the protein expressions of cytochrome C and Bcl-2, finally PCP improved the antioxidative capacity and protected the oxidative damage of cells.

CONCLUSIONS

These results indicated that PCP had the better immunopotentiation and antioxidative damage activity.

Short chain fatty acids delay the development of hepatocellular carcinoma in HBx transgenic mice

Chronic infection with hepatitis B virus (HBV) is a major risk factor for the development of hepatocellular carcinoma (HCC). The HBV encoded oncoprotein, HBx, alters the expression of host genes and the activity of multiple signal transduction pathways that contribute to the pathogenesis of HCC by multiple mechanisms independent of HBV replication. However, it is not clear which pathways are the most relevant therapeutic targets in hepatocarcinogenesis. Short chain fatty acids (SCFAs) have strong anti-inflammatory and anti-neoplastic properties, suggesting that they may block the progression of chronic liver disease (CLD) to HCC, thereby identifying the mechanisms relevant to HCC development. This hypothesis was tested in HBx transgenic (HBxTg) mice fed SCFAs. Groups of HBxTg mice were fed with SCFAs or vehicle from 6 to 9 months of age and then assessed for dysplasia, and from 9 to 12 months of age and then assessed for HCC. Livers from 12 month old mice were then analyzed for changes in gene expression by mass spectrometry-based proteomics. SCFA-fed mice had significantly fewer dysplastic and HCC nodules compared to controls at 9 and 12 months, respectively. Pathway analysis of SCFA-fed mice showed down-regulation of signaling pathways altered by HBx in human CLD and HCC, including those involved in inflammation, phosphatidylinositol 3-kinase, epidermal growth factor, and Ras. SCFA treatment promoted increased expression of the tumor suppressor, disabled homolog 2 (DAB2). DAB2 depresses Ras pathway activity, which is constitutively activated by HBx. SCFAs also reduced cell viability in HBx-transfected cell lines in a dose-dependent manner while the viability of primary human hepatocytes was unaffected. These unique findings demonstrate that SCFAs delay the pathogenesis of CLD and development of HCC, and provide insight into some of the underlying mechanisms that are relevant to pathogenesis in that they are responsive to treatment.

Effect of HBx on inflammation and mitochondrial oxidative stress in mouse hepatocytes

Hepatitis B virus × protein (HBx) serves an important role in the pathogenesis of the hepatitis B virus infection. Previous studies have reported that the interaction between HBx and hepatocyte mitochondria is an important factor leading to liver cell injury and apoptosis, ultimately inducing the formation of liver cancer. In the present study, a mouse model expressing HBx was constructed using hydrodynamic in vivo transfection based on the interaction between HBx and cytochrome c oxidase (COX) subunit III. The specific mechanism of HBx-induced oxidative stress in mouse hepatocytes and the subsequent effect on mitochondrial function and inflammatory injury was assessed. The results demonstrated that HBx reduced the activity of COX and the expression of superoxide dismutase and upregulated the expression of malondialdehyde, NF-κB and phospho-AKT, thus increasing oxidative stress. In addition, HBx induced an increase in interleukin (IL)-6, IL-1β and IL-18 expression levels, which created an inflammatory microenvironment in the liver, further promoting hepatocyte inflammatory injury. Therefore, it was proposed that HBx may affect hepatocyte mitochondrial respiration by reducing the activity of cytochrome c oxidase, leading to mitochondrial dysfunction and inducing hepatocyte inflammation and injury.

Kinetics of DNA damage repair response accompanying initial hepadnavirus-host genomic integration in woodchuck hepatitis virus infection of hepatocyte

Mechanism of initial hepatitis B virus (HBV) integrations and kinetics of DNA repair immediately after infection remain essentially unknown impairing understanding of hepadnaviral oncogenesis. WCM260 hepatocytes susceptible to HBV-compatible woodchuck hepatitis virus (WHV) were examined from 15 min to 72 h post-infection (p.i.). WHV strongly induced reactive oxygen species (ROS), transiently inducible nitric oxide (iNOS) and DNA damage from 15 min p.i. All initial WHV-host fusions had the head-to-tail format indicating their formation by non-homologous end joining (NHEJ). Transcription of poly(ADP-ribose) polymerase 1 (PARP1) and X-ray repair cross-complementing protein 1 (XRCC1), the PARP1 binding partner, were induced in 30 min p.i. and that of 8-oxyguanine DNA glycosylse (OGG1) responding to oxidative DNA damage at 12 h p.i. Nicotinamide adenine dinucleotide (NAD⁺), a marker of PARP1 activation, and heme oxygenase-1 (HO1), an indicator of pro-oxidative stress, were significantly augmented from 15-30 min p.i. Additionally, PARP1 cleavage activity was evident from 30 min p.i. confirming that PARP1-mediated DNA repair became operational almost instatly after hepatocyte contact with virus. By applying complementary approaches, the study showed that initial WHV integration was due to virus-induced oxidative DNA damage and implied that the NHEJ PARP1-dependent repair pathway determined format of the first virus-host DNA junctions.

Oxidative stress, a trigger of hepatitis C and B virus-induced liver carcinogenesis

Virally induced liver cancer usually evolves over long periods of time in the context of a strongly oxidative microenvironment, characterized by chronic liver inflammation and regeneration processes. They ultimately lead to oncogenic mutations in many cellular signaling cascades that drive cell growth and proliferation. Oxidative stress, induced by hepatitis viruses, therefore is one of the factors that drives the neoplastic transformation process in the liver. This review summarizes current knowledge on oxidative stress and oxidative stress responses induced by human hepatitis B and C viruses. It focuses on the molecular mechanisms by which these viruses activate cellular enzymes/systems that generate or scavenge reactive oxygen species (ROS) and control cellular redox homeostasis. The impact of an altered cellular redox homeostasis on the initiation and establishment of chronic viral infection, as well as on the course and outcome of liver fibrosis and hepatocarcinogenesis will be discussed The review neither discusses reactive nitrogen species, although their metabolism is interferes with that of ROS, nor antioxidants as potential therapeutic remedies against viral infections, both subjects meriting an independent review.

Mitochondrial Proteins Coded by Human Tumor Viruses

Viruses must exploit the cellular biosynthetic machinery and evade cellular defense systems to complete their life cycles. Due to their crucial roles in cellular bioenergetics, apoptosis, innate immunity and redox balance, mitochondria are important functional targets of many viruses, including tumor viruses. The present review describes the interactions between mitochondria and proteins coded by the human tumor viruses human T-cell leukemia virus type 1, Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus, human hepatitis viruses B and C, and human papillomavirus, and highlights how these interactions contribute to viral replication, persistence and transformation.

Hepatitis B virus X protein sensitizes HL-7702 cells to oxidative stress-induced apoptosis through modulation of the mitochondrial permeability transition pore

Chronic hepatitis B virus (HBV) infection is a leading cause of liver cirrhosis and cancer. Among the pathogenic factors of HBV, HBV X protein (HBx) is attracting increased attention. Although it is documented that HBx is a multifunctional regulator that modulates cell inflammation and apoptosis, the exact mechanism remains controversial. In the present study, we explored the effect of HBx on oxidative stress-induced apoptosis in normal liver cell line, HL-7702. Our results showed that the existence of HBx affected mitochondrial biogenesis by modulating the opening of the mitochondrial permeability transition pore (MPTP). Notably, this phenomenon was associated with a pronounced translocation of Bax from the cytosol to the mitochondria during the period of exposure to oxidative stress with a release of cytochrome c and activation of cleaved caspase-3 and PARP. Moreover, MPTP blockage with cyclosporin A prevented the translocation of Bax, and inhibited oxidative stress-induced apoptotic killing in the HBx-expressing HL-7702 cells. Our findings suggest that HBx exhibits pro-apoptotic effects upon normal liver cells following exposure to oxidative stress by modulating the MPTP gateway.

Prognostic significance of catalase expression and its regulatory effects on hepatitis B virus X protein (HBx) in HBV-related advanced hepatocellular carcinomas

Hepatitis B virus X protein (HBx) plays a role in liver cancer development. We previously showed that ROS increased HBx levels and here, we investigated the role of antioxidants in the regulation of HBx expression and their clinical relevance. We found that overexpression of catalase induced a significant loss in HBx levels. The cysteine null mutant of HBx (Cys-) showed a dramatic reduction in its protein stability. In clonogenic proliferation assays, Huh7-X cells produced a significant number of colonies whereas Huh7-Cys- cells failed to generate them. The Cys at position 69 of HBx was crucial to maintain its protein stability and transactivation function in response to ROS. Among 50 HBV-related hepatocellular carcinoma (HCC) specimens, 72% of HCCs showed lower catalase levels than those of surrounding non-tumor tissues. In advanced stage IV, catalase levels in non-tumor tissues were increased whereas those in tumors were further reduced. Accordingly, patients with a high T/N ratio for catalase showed significantly longer survival than those with a low T/N ratio. Together, catalase expression in HCC patients can be clinically useful for prediction of patient survival, and restoration of catalase expression in HCCs could be an important strategy for intervention in HBV-induced liver diseases.

Hepatitis B virus X protein activates the ATM-Chk2 pathway and delays cell cycle progression

Genetic instability is intimately associated with tumour development. In particular, liver cancers associated with hepatitis B virus (HBV) exhibit high genetic instability; however, our understanding of the underlying molecular mechanisms remains limited. In this study, we found that γ-H2AX, a marker of DNA double-strand breaks (DSBs), and the levels of phospho-Chk2 (p-Chk2, the activated form) were significantly elevated in HBV-associated hepatocellular carcinomas and neighbouring regenerating nodules. Likewise, introduction of the pHBV or pMyc-HBx plasmids into cells induced accumulation of γ-H2AX foci and increased the p-Chk2 level. In these cells, inhibitory phosphorylation of Cdc25C phosphatase (Ser(216)) and CDK1 (Tyr(15)) was elevated; consequently, cell-cycle progression was delayed at G2/M phase, suggesting that activation of the ATM-Chk2 pathway by the HBV X protein (HBx) induces cell-cycle delay. Accordingly, inhibition of ataxia telangiectasia mutated (ATM) by caffeine or siRNA abolished the increase in the p-Chk2 level and restored the delayed CDK1 kinase activity in ChangX cells. We also found that cytoplasmic HBx, but not nuclear HBx, induced reactive oxygen species (ROS) production and led to the accumulation of γ-H2AX foci and the increased p-Chk2 level. Together, these data indicate that HBx-induced ROS accumulation induces DNA damage that activates the ATM-Chk2 pathway. Our findings provide insight into the mechanisms of HBV pathogenesis.

Fatty acids increase hepatitis B virus X protein stabilization and HBx-induced inflammatory gene expression

The protein level of human hepatitis B virus (HBV) in infection is variable, depending on patient context. We previously reported that HBV X protein (HBx) induces hepatic lipid accumulation and inflammation. Here, we show that abnormal levels of hepatic fatty acids increase HBx protein stability during HBV expression, resulting in the potentiation of HBx-induced inflammation. Reactive oxygen species, Ca(2+) signaling and expression levels of various lipid metabolic genes were investigated in HBx-expressing cells and in HBx transgenic mice. Fatty acids, including palmitate, stearate and oleate, increased HBx protein stability by preventing proteasome-dependent degradation. Hepatic inflammation induced by a high fat diet (HFD) and HBx was measured based on the expression of interleukin-6 and tumor necrosis factor α. In addition, the protein level of HBx increased in HFD-HBx transgenic mice. Reactive oxygen species production and intracellular Ca(2+) signal activation play critical roles in fatty-acid-induced HBx stabilization. Abnormal levels of hepatic fatty acids resulted in synergistic induction of HBx protein and liver inflammatory gene expression through HBx protein stabilization. These results indicate that different fatty acid levels in the liver might affect HBV-induced pathogenesis.

Oxidative stress and epigenetic instability in human hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a major cause of cancer death, and its development is influenced by the status of inflammation and oxidative stress in the liver. Although oxidative stress might induce genetic changes and play a role in HCC development, many epigenetic alterations have also been reported in this type of tumor, suggesting the importance of epigenetic instability in hepatocarcinogenesis. Epigenetic instability results in 2 types of DNA alterations: hypermethylation of the promoter of tumor suppressor genes (TSGs), and hypomethylation of nonpromoter CpG, such as repetitive elements and satellite DNA. The former causes transcriptional inactivation of TSGs, while the latter reportedly induces chromosomal instability and an abnormal activation of oncogenes as well as mobile genetic elements. Oxidative stress could induce epigenetic instability and inactivate TSGs through the recruitment of the polycomb repressive complex to the promoter sequence carrying DNA damage induced by oxidation. Inflammatory cytokines from immune cells also reportedly induce expression of several histone and DNA modulators. On the other hand, DNA oxidation could lead to activation of DNA repair pathways and affect the binding of methyl cytosine-binding protein to DNA, which could cause DNA hypomethylation. The decrease of the level of methyl group donors also contributes to the alteration in the methylation status. These mechanisms should act in concert and induce epigenetic instability, leading to HCC.

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.

Vitamins in the treatment of chronic viral hepatitis

Hepatitis B virus (HBV)- and hepatitis C virus (HCV)-related chronic infections represent a major health problem worldwide. Although the efficacy of HBV and HCV treatment has improved, several important problems remain. Current recommended antiviral treatments are associated with considerable expense, adverse effects and poor efficacy in some patients. Thus, several alternative approaches have been attempted. To review the clinical experiences investigating the use of lipid- and water-soluble vitamins in the treatment of HBV- and HCV-related chronic infections, PubMed, the Cochrane Library, MEDLINE and EMBASE were searched for clinical studies on the use of vitamins in the treatment of HBV- and HCV-related hepatitis, alone or in combination with other antiviral options. Different randomised clinical trials and small case series have evaluated the potential virological and/or biochemical effects of several vitamins. The heterogeneous study designs and populations, the small number of patients enrolled, the weakness of endpoints and the different treatment schedules and follow-up periods make the results largely inconclusive. Only well-designed randomised controlled trials with well-selected endpoints will ascertain whether vitamins have any role in chronic viral hepatitis. Until such time, the use of vitamins cannot be recommended as a therapy for patients with chronic hepatitis B or C.

Reactivation of p53 in cells expressing hepatitis B virus X-protein involves p53 phosphorylation and a reduction of Hdm2

Multifunctional activities of the hepatitis B virus X-protein (HBx) in cells have been largely implicated in the development of liver cancer; one of these activities is the loss of p53 function by sequestering p53 in the cytoplasm. We have previously found that doxorubicin increased the p53 levels in cells containing p53-binding HBx protein and restored the p53-mediated transcriptional activity that was suppressed by HBx. Here, we investigated the mechanism underlying p53 reactivation. We found that six phosphorylation sites of the Serine residues of p53 were efficiently phosphorylated in HBx-expressing ChangX-34 cells, suggesting that the binding of HBx to the p53 protein does not interfere with the phosphorylation of p53 by signaling kinases. In addition, doxorubicin caused a dramatic reduction of Hdm2 mRNA and protein levels in cells expressing HBx. Intriguingly, reactivation of p53 was accompanied with a nuclear accumulation of p53 and the phosphorylated p53 at Serine15 was only detected in nuclear fraction, but not in cytosolic fraction of doxorubicin-treated ChangX-34 cells. Functional restoration of the p53 protein in HBx-expressing cells occurs according to the dual effects of doxorubicin: a significant reduction of Hdm2 expression and a nuclear accumulation of the phosphorylated p53 protein. Thus, proper usage of doxorubicin as an effective antitumor agent may be reevaluated and can be extended to tumors primarily caused by infection of DNA tumor viruses.

The upregulation of expressed proteins in HepG2 cells transfected by the recombinant plasmid-containing HBx gene

It is known that the hepatitis B virus X protein (HBx) plays a crucial role in the pathogenesis of HCC, but the exact functions and molecular mechanisms of HBx in HCC are not well understood. In the present study, HepG2 cell lines were cultured and transfected with pEGFP-N1 and pEGFP-N1-X. Twenty-four hours after transfection, cells were harvested and total RNA was extracted using TRIzol reagent. The expression of HBx in HepG2 cell line was assayed by real-time polymerase chain reaction and was detected by Western blotting. Moreover, proteomic analysis was performed for the HepG2-pEGFP-X cells and HepG2-pEGFP control cells. The combination of 2DE and MALDI-TOF-MS/MS revealed that SEC13L1 (SEC13-like 1 isoform b), PA28 alpha (proteasome activator REG alpha), serine-threonine kinase receptor-associated protein (STRAP) and nm23/nucleoside diphosphate kinase (NME) were upregulated in HepG2-pEGFP-X cells. STRAP is known to be a WD40 domain-containing protein, which interacts with TbetaR-I and TbetaR-II and negatively regulates TGF-beta signalling, was also found increased in human cancers. NME is known to be involved in the regulation of cancer cell progression and metastasis. These results would help the understanding of how HBx maintains tumorigenicity and progression of HCC.

Knock-down of hepatitis B virus X protein reduces the tumorigenicity of hepatocellular carcinoma cells

Hepatitis B virus (HBV) infection is a major cause of hepatocellular carcinoma (HCC) in Southeast Asia and Hong Kong. Among the four proteins that are encoded by the HBV genome, HBV X (HBx) is the most potentially oncogenic factor. It is known that HBx plays an important role in hepatocarcinogenesis, but the exact functions and molecular mechanisms of HBx in HCC are not well understood. In this study, we constructed expression vectors for small hairpin RNAs (shRNA) against HBx and investigated their regulatory effects in PLC/PRF/5 HCC cells, which constitutively produce HBx. Our data show that this tool of RNA interference (RNAi) could successfully reduce the HBx mRNA and protein levels by 50-95%. RNAi targeting HBx in PLC/PRF/5 cells demonstrated significant reduction in cell proliferation, cell growth, anchorage-independent growth in soft agar, and tumour development in nude mice. In addition, depletion of HBx expression increased cell sensitivity to TNFalpha-mediated and serum-free-induced apoptosis, and reduced the expression levels of C-myc and Bcl-X(L). These findings suggest that HBx plays an important role in tumorigenicity and anti-apoptotic mechanisms in HCC.

Effects of antioxidants and caspase-3 inhibitor on the phenylethyl isothiocyanate-induced apoptotic signaling pathways in human PLC/PRF/5 cells

Phenylethyl isothiocyanate (PEITC) is a well recognized potential chemopreventive compound against human cancers. In this study, the molecular mechanism of PEITC-induced apoptosis was examined with two antioxidants (N-acetyl-cysteine and vitamin E) and a caspase-3 inhibitor (z-DEVD-fmk). Results demonstrated that PEITC significantly induced human hepatoma PLC/PRF/5 (CD95-negative) cells undergoing apoptosis. Treatment with 0 approximately 10 microM PEITC-triggered cell apoptosis as revealed by the externalization of annexin V-targeted phosphatidylserine and the subsequent appearance of sub-G1 population. Results also displayed that PEITC-induced apoptosis involves the up-regulation of p53 and Bax protein, down-regulation of the XIAP, Bcl-2, Bcl-(XL) and Mcl-1 proteins, cleavage of Bid, and the release of cytochrome c and Smac/Diablo, which were accompanied by the activation of caspases -9, -3 and -8. PEITC-induced the generation of reactive oxygen species and the decrease of mitochondrial membrane potential (Deltapsim) in a time-dependent pattern. N-acetyl-cysteine and vitamin E at 100 microM, and z-DEVD-fmk at 50 microM markedly blocked PEITC-induced apoptosis, which was demonstrated by a decline in the reactive oxygen species generation and the release of the cytochrome c and Smac/Diablo from mitochondria to the cytosol. N-acetyl-cysteine, vitamin E and z-DEVD-fmk also prevented the PEITC in inducing the loss of Deltapsim. They also affected the activity of XIAP and Bax proteins. Taken together, these studies suggest that PEITC is an apoptotic inducer that acts on the mitochondria and the feedback amplification loop of caspase-8/Bid pathways in PLC/PRF/5 cells.

Hepatitis B virus X protein is essential for the activation of Wnt/beta-catenin signaling in hepatoma cells

Wnt/beta-catenin signaling contributes to diverse cellular functions, such as Drosophila wing development and colon carcinogenesis. Recently, stabilizing mutations of beta-catenin, a hallmark of Wnt signaling, were documented in significant numbers of primary hepatocellular carcinomas (HCC). However, whether the beta-catenin mutation leads to the activation of Wnt/beta-catenin signaling in hepatoma cells has not been established. We found that Wnt/beta-catenin signaling could be activated by ectopic expression of Wnt-1 in some hepatoma cells, such as Hep3B and PLC/PRF/5 cells, but not in others, such as Huh7 and Chang cells. Importantly, we noted that the former were derived from hepatitis B virus (HBV)-infected livers, whereas the latter were derived from HBV-negative livers. It was then speculated that HBx, a viral regulatory protein of HBV, is involved in activating Wnt/beta-catenin signaling in hepatoma cells. In agreement with this notion, ectopic expression of HBx along with Wnt-1 activated Wnt/beta-catenin signaling in Huh7 cells by stabilizing cytoplasmic beta-catenin. Further, we showed that such stabilization of beta-catenin by HBx was achieved by suppressing glycogen synthase kinase 3 activity via the activation of Src kinase. In conclusion, the data suggest that Wnt-1 is necessary but insufficient to activate Wnt/beta-catenin signaling in hepatoma cells and the enhanced stabilization of beta-catenin by HBx, in addition to Wnt-1, is essential for the activation of Wnt/beta-catenin signaling in hepatoma cells.