Regulation of transforming growth factor-beta 1 expression by the hepatitis B virus (HBV) X transactivator. Role in HBV pathogenesis

Viral hepatocarcinogenesis

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

The etiology of liver damage imparts cytokines transforming growth factor beta1 or interleukin-13 as driving forces in fibrogenesis

It is unknown whether transforming growth factor beta1 (TGF-beta1) signaling uniformly participates in fibrogenic chronic liver diseases, irrespective of the underlying origin, or if other cytokines such as interleukin (IL)-13 share in fibrogenesis (e.g., due to regulatory effects on type I pro-collagen expression). TGF-beta1 signaling events were scored in 396 liver tissue samples from patients with diverse chronic liver diseases, including hepatitis B virus (HBV), hepatitis C virus (HCV), Schistosoma japonicum infection, and steatosis/steatohepatitis. Phospho-Smad2 staining correlated significantly with fibrotic stage in patients with HBV infection (n = 112, P < 0.001) and steatosis/steatohepatitis (n = 120, P < 0.01), but not in patients with HCV infection (n = 77, P > 0.05). In tissue with HBx protein expression, phospho-Smad2 was detectable, suggesting a functional link between viral protein expression and TGF-beta1 signaling. For IL-13, immunostaining correlated with fibrotic stage in patients with HCV infection and steatosis/steatohepatitis. IL-13 protein was more abundant in liver tissue lysates from three HCV patients compared with controls, as were IL-13 serum levels in 68 patients with chronic HCV infection compared with 20 healthy volunteers (72.87 +/- 26.38 versus 45.41 +/- 3.73, P < 0.001). Immunohistochemistry results suggest that IL-13-mediated liver fibrogenesis may take place in the absence of phospho-signal transducer and activator of transcription protein 6 signaling. In a subgroup of patients with advanced liver fibrosis (stage > or =3), neither TGF-beta nor IL-13 signaling was detectable.

CONCLUSION

Depending on the cause of liver damage, a predominance of TGF-beta or IL-13 signaling is found. TGF-beta1 predominance is detected in HBV-related liver fibrogenesis and IL-13 predominance in chronic HCV infection. In some instances, the underlying fibrogenic mediator remains enigmatic.

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

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

CONCLUSION

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

Putative roles of hepatitis B x antigen in the pathogenesis of chronic liver disease

Under most circumstances, hepatitis B virus (HBV) is noncytopathic. However, hepatocellular regeneration that accompanies each bout of hepatitis appears to be associated with increased integration of HBV DNA fragments expressing the virus encoded hepatitis B x antigen (HBxAg). Intrahepatic HBxAg staining correlates with the intensity and progression of chronic liver disease (CLD), and additional work has shown that HBxAg blocks immune mediated killing by Fas and by tumor necrosis factor alpha (TNFalpha). This is not only associated with the blockage of caspase activities by HBxAg, but also by the constitutive stimulation of hepatoprotective pathways, such as nuclear factor kappa B (NF-kappaB), phosphoinositol 3-kinase (PI3K), and beta-catenin (beta-catenin). HBxAg also appears to promote fibrogenesis, by stimulating the production of fibronectin. HBxAg also stimulates the production and activity of transforming growth factor beta1 (TGFbeta1) by several mechanisms, thereby promoting the profibrogenic and tumorigenic properties of this important cytokine. In addition, HBxAg appears to remodel the extracellular matrix (ECM) by altering the expression of several matrix metalloproteinases (MMPs), which may promote tumor metastasis. Hence, HBxAg appears to promote chronic infection by preventing immune mediated apoptosis of infected hepatocytes, by promoting the establishment and persistence of fibrosis and cirrhosis preceding the development of HCC, and by promoting the remodeling of EMC during tumor progression.

Genetic profile of Egyptian hepatocellular-carcinoma associated with hepatitis C virus Genotype 4 by 15 K cDNA microarray: preliminary study

Background

Hepatocellular carcinoma (HCC) is a preventable disease rather than a curable one, since there is no well-documented effective treatment modality until now, making the molecular study of this disease mandatory.

Findings

We studied gene expression profile of 17 Egyptian HCC patients associated with HCV genotype-4 infection by c-DNA microarray. Out of the 15,660 studied genes, 446 were differentially expressed; 180 of them were up regulated and 134 were down regulated. Seventeen genes out of the 180 up-regulated genes are involved in 28 different pathways. Protein phosphatase 3 (PPP3R1) is involved in 10 different pathways followed by fibroblast growth factor receptor 1 (FGFR1), Cas-Br-M ecotropic retroviral transforming sequence b (CBLB), spleen tyrosine kinase (SYK) involved in three pathways; bone morphogenetic protein 8a (BMP8A), laminin alpha 3 (LAMA3), cell division cycle 23 (CDC23) involved in 2 pathways and NOTCH4 which regulate Notch signaling pathway. On the other hand, 25 out of the 134 down-regulated genes are involved in 20 different pathways. Integrin alpha V alpha polypeptide antigen CD51 (ITGVA) is involved in 4 pathways followed by lymphotoxin alpha (TNF superfamily, member 1) (LTA) involved in 3 pathways and alpha-2-macroglobulin (A2M), phosphorylase kinase alpha 2-liver (PHKA2) and MAGI1 membrane associated guanylate kinase 1 (MAGI1) involved in 2 pathways. In addition, 22 genes showed significantly differential expression between HCC cases with cirrhosis and without cirrhosis. Confirmation analysis was performed on subsets of these genes by RT-PCR, including some up-regulated genes such as CDK4, Bax, NOTCH4 and some down-regulated genes such as ISGF3G, TNF, and VISA.

Conclusion

This is the first preliminary study on gene expression profile in Egyptian HCC patients associated with HCV-Genotype-4 using the cDNA microarray. The identified genes could provide a new gate for prognostic and diagnostic markers for HCC associated with HCV. They could also be used to identify candidate genes for molecular target therapy.

The Molecular Diagnosis of Hepatitis B Virus-Associated Hepatocellular Carcinoma

Hepatitis B virus (HBV) infection is the major cause of hepatocellular carcinoma (HCC) worldwide. The pathogenesis of HBV-associated HCC has been studied extensively, and molecular changes during malignant transformation have been identified. It has been proposed that the insertion of HBV DNA into the human genome results in chromosomal instability and inactivation of tumor suppressor genes. Transactivation of oncogenes, inactivation of tumor suppressor genes, and alteration of the cell cycle by HBV proteins are also involved in the progression of hepatocellular carcinogenesis. Traditional clinical examinations of HCC, such as biopsy, computer tomography, ultrasonic imaging, and detection of such biomarkers as a-fetoprotein, are currently the "gold standard" in diagnosis. These tests diagnose HCC only in the late stages of disease. This limitation has greatly reduced the chance of survival of HCC patients. To resolve this problem, new biomarkers that can diagnose HCC in earlier stages are necessary. Based on recent molecular studies of the effects of HBV on cellular transformation, differentially expressed biomarkers of HBV infection have been elucidated. With the analyses of the HBV replication profile, the viral load (HBV DNA levels) of patients, and the viral protein expression, the severity of hepatitis in the preneoplastic stages can be assessed. In the future, with the molecular profiles identified by genomic and proteomic approaches, stage-specific biomarkers should be identified to monitor the progression and prognosis of HCC.

HBV X protein: elucidating a role in oncogenesis

Chronic HBV infection is associated with the development of hepatocellular carcinoma (HCC). HBV contributes to tumorigenesis by encoding hepatitis B x antigen (HBxAg), which is a trans-regulatory protein that appears to contribute to HCC by altering patterns of host gene expression. In this review, recent data is presented that outlines some of the putative mechanisms whereby HBxAg contributes to HCC. With the development of animal models of HBxAg-mediated HCC, the relevance and temporal order of putative steps in this process can now be dissected to elucidate what is rate limiting and when. This will have a profound impact on the design of novel and specific therapeutics for HCC.

Transforming growth factor-beta gene expression signature in mouse hepatocytes predicts clinical outcome in human cancer

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world. The clinical heterogeneity of HCC, and the lack of good diagnostic markers and treatment strategies, has rendered the disease a major challenge. Patients with HCC have a highly variable clinical course, indicating that HCC comprises several biologically distinctive subgroups reflecting a molecular heterogeneity of the tumors. Transforming growth factor beta (TGF-beta) is known to exhibit tumor stage dependent suppressive (that is, growth inhibition) and oncogenic (that is, invasiveness) properties. Here, we asked if a TGF-beta specific gene expression signature could refine the classification and prognostic predictions for HCC patients. Applying a comparative functional genomics approach we demonstrated that a temporal TGF-beta gene expression signature established in mouse primary hepatocytes successfully discriminated distinct subgroups of HCC. The TGF-beta positive cluster included two novel homogeneous groups of HCC associated with early and late TGF-beta signatures. Kaplan-Meier plots and log-rank statistics indicated that the patients with a late TGF-beta signature showed significantly (P < 0.005) shortened mean survival time (16.2 +/- 5.3 months) compared to the patients with an early (60.7 +/- 16.1 months) TGF-beta signature. Also, tumors expressing late TGF-beta-responsive genes displayed invasive phenotype and increased tumor recurrence. We also showed that the late TGF-beta signature accurately predicted liver metastasis and discriminated HCC cell lines by degree of invasiveness. Finally, we established that the TGF-beta gene expression signature possessed a predictive value for tumors other than HCC.

CONCLUSION

These data demonstrate the clinical significance of the genes embedded in TGF-beta expression signature for the molecular classification of HCC.

The hepatitis B virus X protein induces paracrine activation of human hepatic stellate cells

Chronic hepatitis B virus (HBV) infection is a major cause of liver fibrosis, eventually leading to cirrhosis and hepatocellular carcinoma. Although the involvement of the X protein of HBV (HBx) in viral replication and tumor development has been extensively studied, little is known about its possible role in the development of fibrosis. In this work we show that expression of HBx in hepatocytes results in paracrine activation and proliferation of hepatic stellate cells (HSCs), the main producers of extracellular matrix proteins in the fibrotic liver. Both human primary HSCs and rat HSCs exposed to conditioned medium from HBx-expressing hepatocytes showed increased expression of collagen I, connective tissue growth factor, alpha smooth muscle actin, matrix metalloproteinase-2, and transforming growth factor-beta (TGF-beta), together with an enhanced proliferation rate. We found that HBx induced TGF-beta secretion in hepatocytes and that the activation of HSCs by conditioned medium from HBx-expressing hepatocytes was prevented by a neutralizing anti-TGF-beta antibody, indicating the involvement of this profibrotic factor in the process.

CONCLUSION

Our results propose a direct role for HBx in the development of liver fibrosis by the paracrine activation of stellate cells and reinforce the indication of antiviral treatment in patients with advanced HBV-related chronic liver disease and persistent liver replication.

Whole genome expression profiling of hepatitis B virus-transfected cell line reveals the potential targets of anti-HBV drugs

Hepatitis B virus (HBV) infection is a major health concern world wide, and few effective treatments have been developed. It has recently been reported that inhibiting host-cell proteins can prevent viral infection. The human genome may contain more genes required for HBV infection and replication than the viral genome. A systematic approach to find these potential antiviral targets is by host gene expression analysis using DNA microarrays. The aim of this study was to identify and validate novel cellular anti-HBV targets. The Human Whole Genome Bioarray was used to analyze differentially expressed genes in HepG2.2.15 cells and HepG2 cells. Altered gene expression in HepG2.2.15 cells was studied following treatment with the anti-HBV drug, lamivudine. Genes that were differentially expressed during HBV infection and reversed with anti-HBV drugs were validated by semiquantitative reverse transcription-PCR. Bioinformatics analysis revealed ABHD2, EREG, ACVR2B, CDC34, KHDRBS3 and RORA as potential cellular anti-HBV targets. Antisense oligodeoxynucleotides were used to test the antiviral activity of these potential targets. Results strongly suggested that inhibition of ABHD2 or EREG significantly blocked HBV propagation in HepG2.2.15 cells. This study demonstrates that ABHD2 and EREG are essential for HBV propagation and provides strong evidence that these proteins could be used as potential targets for anti-HBV drugs.

Hepatitis B virus X protein sensitizes UV-induced apoptosis by transcriptional transactivation of Fas ligand gene expression

Hepatitis B virus X protein (HBx) is a promiscuous transcriptional transactivator of many viral and cellular promoters. HBx plays an important role in hepatitis B virus pathogenesis related with liver diseases including hepatocellular carcinoma (HCC). HBx is also involved in the signal transduction and the apoptosis of HBV-infected cells. However, the exact mechanism of apoptosis by HBx is still controversial. To demonstrate the mechanism of apoptosis by HBx, we induced the apoptosis of HBx-expressing liver cells, HepG2-X, by UV irradiation. We found that HepG2-X was much more sensitive to the UV-induced apoptosis than normal liver cells by analyzing the DNA fragmentation and the cell viability. Very interestingly, when the Fas-associated death domain (FADD)-dominant negative mutant protein was present in HepG2-X, the sensitized apoptotic response of HepG2-X to UV was completely abolished suggesting that there is a close relationship between HBx and Fas pathway in apoptosis. Therefore we examined the transactivation of Fas receptor (Fas) promoter and Fas ligand (FasL) promoter by HBx. We found that HBx strongly transcriptionally transactivated FasL promoter, but not Fas promoter. In addition, it also turned out that the mRNA levels of FasL are higher than those of Fas in HepG2-X. Taken together, HBx sensitizes the apoptosis of UV-irradiated liver cells by transcriptional transactivation of FasL gene.

Effect of pegylated interferon alpha 2b plus ribavirin treatment on plasma transforming growth factor-β1, metalloproteinase-1, and tissue metalloproteinase inhibitor-1 in patients with chronic hepatitis C

AIM: To evaluate the effect of antiviral treatment on plasma levels of transforming growth factor-β1 (TGF-β1), metalloproteinase 1 (MMP-1), and tissue inhibitor of metalloproteinase-1 (TIMP-1) in patients with chronic hepatitis C.

METHODS: TGF-β1, MMP-1, and TIMP-1 plasma concentrations were measured by an enzyme immunoassay in 28 patients, during 48 wk of treatment with pegylated interferon-alpha 2b (PEG-IFN-α2b) plus ribavirin (RBV) and after 24 wk of follow-up. Patients were divided into two groups: responders (R) and non-responders (NR) related to achieved sustained virologic response. Normal values were evaluated in plasma samples of 13 healthy volunteers.

RESULTS: Baseline plasma concentrations of TGF-β1 and TIMP-1 (30.9±3.7 and 1 506±61 ng/mL respectively) measured in all subjects significantly exceeded the normal values (TGF-β1: 18.3±1.6 ng/mL and TIMP-1: 1 102±67 ng/mL). In contrast, pretreatment MMP-1 mean level (6.5±0.9 ng/mL) was significantly lower than normal values (11.9±0.9 ng/mL). Response to the treatment was observed in 12 patients (43%). TGF-β1 mean concentration measured during the treatment phase decreased to the control level in both groups. However at wk 72, values of NR patients increased and became significantly higher than in R group. TIMP-1 concentrations in R group decreased during the treatment to the level similar to normal. In NR group, TIMP-1 remained significantly elevated during treatment and follow-up phase and significant difference between both groups was demonstrated at wk 48 and 72. MMP-1 levels were significantly decreased in both groups at baseline. Treatment caused rise of its concentration only in the R group, whereas values in NR group remained on the level similar to baseline. Statistically significant difference between groups was noted at wk 48 and 72.

CONCLUSION: These findings support the usefulness of TGF-β1, TIMP-1, and MMP-1 in the management of chronic hepatitis C. Elevated TIMP-1 and low MMP-1 plasma concentrations during antiviral therapy may indicate medication failure.

Therapeutic inhibition of hepatitis B virus surface antigen expression by RNA interference

RNA interference (RNAi) mediated inhibition of virus-specific genes has emerged as a potential therapeutic strategy against virus induced diseases. Human hepatitis B virus (HBV) surface antigen (HBsAg) has proven to be a significant risk factor in HBV induced liver diseases, and an increasing number of mutations in HBsAg are known to enhance the difficulty in therapeutic interventions. The key challenge for achieving effective gene silencing in particular for the purpose of the therapeutics is primarily based on the effectiveness and specificity of the RNAi targeting sequence. To explore the therapeutic potential of RNAi on HBV induced diseases in particular resulted from aberrant or persistent expression of HBsAg, we have especially screened and identified the most potent and specific RNAi targeting sequence that directly mediated inhibition of the HBsAg expression. Using an effective DNA vector-based shRNA expression system, we have screened 10 RNAi targeting sequences (HBsAg-1 to 10) that were chosen from HBsAg coding region, in particular the major S region, and have identified four targeting sequences that could mediate sequence specific inhibition of the HBsAg expression. Among these four shRNAs, an extremely potent and highly sequence specific HBsAg-3 shRNA was found to inhibit HBsAg expression in mouse HBV model. The inhibition was not only preventive in cotransfection experiments, but also had therapeutic effect as assessed by post-treatment protocols. Moreover, this HBsAg-3 shRNA also exhibited a great potency of inhibition in transgenic mice that constitutively expressed HBsAg. These results indicate that HBsAg-3 shRNA can be considered as a powerful therapeutic agent on HBsAg induced diseases.

Early growth response proteins EGR-4 and EGR-3 interact with immune inflammatory mediators NF-κB p50 and p65

Here, we characterize the basis for the T-cell-specific activity of the human zinc-finger protein early growth response factor 4 (EGR-4). A yeast two-hybrid screen showed interaction of EGR-4 with NF-κB p50. Using recombinant proteins, stable physical complex formation was confirmed for EGR-4 and EGR-3 with p50 and with p65 using glutathione-S-transferase pull-down assays and surface-plasmon-resonance and peptide-spot analyses. In vivo interaction of EGR-4 and EGR-3 with NF-κB p65 was demonstrated by immunoprecipitation experiments and fluorescence-resonance-energy transfer (FRET) analysis showing interaction in the nucleus of transfected Jurkat T cells. In transfection assays, EGR-p50 complexes were transcriptionally inactive and EGR-p65 complexes strongly activated transcription of the promoters of the human genes encoding the cytokines interleukin 2, tissue necrosis factor α and ICAM-1. The EGR-p65 complexes increased reporter-gene activity about 100-fold and thus exceeded the transcriptional activities of the p65 homodimer and the p65/p50 heterodimers. The major interaction domain for p65 was localized within the third zinc finger of EGR-4 using deletion mutants for pull-down assays and peptide-spot assays. By computer modeling, this interaction domain was localized to an α-helical region and shown to have the central amino acids surface exposed and thus accessible for interaction. In summary, in T cells, the two zinc-finger proteins EGR-4 and EGR-3 interact with the specific nuclear mediator NF-κB and control transcription of genes encoding inflammatory cytokines.

Viral hepatitis and hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in the world. The incidence of HCC varies considerably with the geographic area because of differences in the major causative factors. Chronic hepatitis B and C, mostly in the cirrhotic stage, are responsible for the great majority of cases of HCC worldwide. The geographic areas at the highest risk are South-East Asia and sub-Saharan Africa, here hepatitis B is highly endemic and is the main cause of HCC. In areas with an intermediate rate of HCC such as Southern Europe and Japan, hepatitis C is the predominant cause, whereas in low rate areas such as Northern Europe and the USA, HCC is often related to other factors as alcoholic liver disease. There is a rising incidence in HCC in developed countries during the last two decades, due to the increasing rate of hepatitis C infection and improvement of the clinical management of cirrhosis.

METHODS

This article reviews the literature on hepatitis and hepatocellular carcinoma. The Medline search was carried out using these key words and articles were selected on epidemiology, risk factors, screening, and prevention of hepatocellular carcinoma.

RESULTS

Screening of patients with advanced chronic hepatitis B and C with hepatic ultrasound and determination of serum alfa-fetoprotein may improve the detection of HCC, but further studies are needed whether screening improves clinical outcome. Hepatitis B and C viruses (HBV/HCV) can be implicated in the development of HCC in an indirect way, through induction of chronic inflammation, or directly by means of viral proteins or, in the case of HBV, by creation of mutations by integration into the genome of the hepatocyte.

CONCLUSION

The most effective tool to prevent HCC is avoidance of the risk factors such as viral infection. For HBV, a very effective vaccine is available. Preliminary data from Taiwan indicate a protective effect of universal vaccination on the development of HCC. Vaccination against HBV should therefore be a health priority. In patients with chronic hepatitis B or C, interferon-alfa treatment in a noncirrhotic stage is protective for HCC development in responders, probably by prevention of cirrhosis development. When cirrhosis is already present, the protective effect is less clear. For cirrhosis due to hepatitis B, a protective effect was demonstrated in Oriental, but not in European patients. For cirrhosis due to hepatitis C, interferon-alfa treatment showed to be protective in some studies, especially in Japan with a high incidence of HCC in untreated patients. Virological, but also merely biochemical response, seems to be associated with a lower risk of development of HCC. As most studies are not randomized controlled trials, no definitive conclusions on the long-term effects of interferon-alfa in HBV or HCV cirrhosis can be established. Especially in hepatitis C, prospective studies should be performed using the more potent reference treatments for cirrhotics, namely the combination of peginterferon and ribavirin.

Molecular mechanisms in hepatocellular carcinoma development

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world. It usually develops in patients with chronic viral hepatitis, aflatoxin exposure, or excessive alcohol use. Most patients with HCC present with advanced disease and have a poor prognosis. The implementation of antiviral drugs and the availability of a vaccine for hepatitis B should help reduce the incidence of HCC. Considerable effort has now focused on unraveling the molecular pathogenesis of HCC in order to design better treatments, or to prevent the disease altogether. However, so far, the pathogenesis of HCC appears to be quite heterogeneous among patients. In particular, several mechanisms of tumorigenesis seem to be involved, including loss of tumor suppressor gene function, oncogene activation, direct viral effects, DNA methylation, and angiogenesis. It is not clear which events are critical in tumor initiation versus tumor progression. RNA expression arrays and proteomics hold promise to provide further clues about this common and complex cancer.

Preneoplastic markers of hepatitis B virus-associated hepatocellular carcinoma

Hepatitis B virus (HBV) carriers are at high risk for the development of hepatocellular carcinoma (HCC), but there are no reliable markers that will identify such high-risk carriers. The objective of this work is to identify serologic markers that may indicate the early presence of HCC. Since HBV-encoded X antigen (HBxAg) likely contributes to HCC by up- or down-regulation of host gene expression, X positive and negative HepG2 cells were made and subjected to cDNA subtraction. When specific ELISAs were constructed measuring differentially expressed antigens and corresponding antibodies, antibodies to several differentially expressed genes were detected. In cross-sectional and longitudinal studies, antibodies were predominantly present in patients with HBV-associated cirrhosis and HCC, but not in most carriers with hepatic inflammation alone or without active liver disease. Antibodies were also present in patients with hepatitis C virus (HCV)-related HCC, but rarely detected in sera from uninfected individuals, those with tumors other than HCC, or those with drug-induced hepatitis. Statistical analysis showed that HCC patients with four or more antibodies detectable before the appearance of HCC had decreased survival, suggesting that these markers may reflect stepwise hepatocarcinogenesis. Hence, these antibodies may serve as preneoplastic markers for HCC in HBV carriers with chronic liver disease, and may be identified by a simple blood test.

N/A

N/A

The conserved amino-terminal region (amino acids 1–20) of the hepatitis B virus X protein shows a transrepression function

The X protein of hepatitis B virus or HBx is a multifunctional regulatory protein that carries the fame of a promiscuous transactivator. Although, the N-terminal 'A' region of HBx (amino acids 1-20) is the most conserved region among mammalian hepadnavirus genomes, it has been found to be dispensable for transactivation function [Proc. Natl. Acad. Sci. U.S.A. 93, 1996, 5647]. To elucidate its biological role, DNA sequence corresponding to the A region of X gene was amplified by polymerase chain reaction and cloned as a 72 base pair HBx mutant X17. In order to augment the intracellular biochemical stability of the expressed protein, the monomeric X17 was multimerized and 2-10 units long tandem repeats of the A region (X17-n) were cloned in a mammalian expression vector. Expression of the X17 constructs was confirmed by in vitro transcription and translation, as well as by RT-PCR after transfection in hepatoma cells. The function of X17 was investigated using the chloramphenicol acetyl transferase reporter constructs of viral (RSV-LTR, HIV1-LTR and HBx) and cellular gene promoters (c-Jun and epidermal growth receptor). Not only did the X17 multimers inhibit the HBx-mediated transactivation of all the reporter genes, but also their basal activities. The inhibition was dependent on the amount of X17 plasmid transfected in cells as well as on the number of repeat units present in the X17 expression vectors. Further, the X17-related inhibition of transactivation was not a cytotoxic effect. Thus, our data suggests that the N-terminal 'A' domain of HBx has a negative regulatory function.

Effect of lamivudine treatment on plasma levels of transforming growth factor β1, tissue inhibitor of metalloproteinases-1 and metalloproteinase-1 in patients with chronic hepatitis B

AIM: Transforming growth factor (TGF)-β₁, metalloproteinase (MMP)-1 and its tissue inhibitor (TIMP)-1 are considered predictive biomarkers of chronic hepatitis activity and fibrosis. The aim of this study was to evaluate the effect of lamivudine treatment on the plasma levels of these peptides in patients with chronic hepatitis B.

METHODS: TGF-β₁, MMP-1 and TIMP-1 plasma concentrations were measured with an enzyme immunoassay in 40 patients treated with lamivudine for 48 wk. Elimination of HBV-DNA and HBV antigens was evaluated 24 wk after treatment completion.

RESULTS: Baseline TGF-β₁ (29.6 ± 2.2 ng/mL) and TIMP-1 (1578 ± 93 ng/mL) significantly exceeded normal values (18.3 ± 1.6 ng/mL and 1102 ± 67 ng/mL respectively). Lamivudine treatment resulted in a significant decrease of TGF-β₁ and TIMP-1 during treatment with an increase after 24 wk of treatment. Pretreatment MMP-1 levels (6.7 ± 0.7 ng/mL) were significantly lower than normal values (11.9 ± 0.9 ng/mL) and increased during treatment and follow-up. A significant correlation was noted between TGF-β₁ or TIMP-1 and aminotransferases as well as fibrosis scored in liver biopsy specimens. There were no statistically significant differences of TGF-β₁, TIMP-1 and MMP-1 between four groups at baseline, 24 and 48 wk of treatment. TGF-β₁ and TIMP-1 levels increased significantly in non-responders and normalized in responders at wk 72. MMP-1 also normalized in responders and decreased to values significantly lower than normal in non-responders.

CONCLUSION: These findings support the role of TGF-β₁, TIMP-1 and MMP-1 in the pathogenesis of chronic hepatitis B. Because of their association with hepatic injury and antiviral treatment efficacy, determination of these peptides may be useful in disease management.

Early molecular and genetic determinants of primary liver malignancy

Although the overview above provides a partial molecular picture of the early stages of stepwise hepatocarcinogenesis. it should be emphasized that tumor and nontumor liver contain multiple changes, and that there is variability in their profile among different patients even within single studies. Variability in the number and types of genetic changes has also been observed geographically, and may be dependent upon the etiology of the tumor (viral, chemical or both). Interestingly, HBxAg inactivates tumor suppressors (such as p53 [by direct binding] and Rb [by stimulating its phosphorylation]) early in carcinogenesis that are mutated later during tumor progression. HBxAg also constitutively activates signal transduction pathways, such as those involving c-jun and ras, and activates oncogenes,such as c-nloc, that are otherwise activated by 3-catenin mutations. These findings suggest common molecular targets in hepatocarcinogenesis, despite different mechanisms of activation or inactivation. These observations need to be exploited in future drug discovery and in the development of new therapeutics. Heterogeneity in the mechanisms of tumor development, evidenced by the differences in the up- and down regulated genes reported in micro array analyses, as well as in the genetic loci that undergo mutation or LOH indifferent reports, has now been well documented. This suggests that there are multiple pathways to HCC, and that there is redundancy in the pathways that regulate cell growth and survival. These findings also reflect that,although hepatocarcinogenesis is multistep, the molecular changes that underpin histopathological changes in tumor development are likely to be different or only partially overlapping in individual tumors. Overall, the consequences of these changes suggest that the pathogenesis of HCC is accompanied by a progressive loss of differentiation, loss of normal cell adhesion, loss of the ECM, and constitutive activation of selected signal transduction pathways that promote cell growth and survival. Although mechanisms are important, attention also has to be paid to the target genes whose altered expression actually mediate the neoplastic phenotype. Other key avenues of work need to be explored. For example, it will be important to try to identify germline mutations in HBV-infected patients that are passed on to their children, resulting in the development of HCC in childhood. Clinical materials will also be important for the validation of new markers with diagnostic or prognostic potential. In this context, there is an urgent need to establish simple and low-cost tests based upon molecular changes that are hallmarks of HCC development. Identification of patients with early HCC will also significantly increase survival through its impact upon treatment. The discovery and validation of HCC markers may permit accurate staging of lesions, determine the proximity of such lesions to malignancy, and determine whether lesions with a particular genetic profile are still capable of remodeling through appropriate therapeutic intervention. The efficient reintroduction of the relevant tumor suppressors, or the inhibition of oncogene expression by siRNA, provide just some of the additional opportunities that will ultimately be useful in patient treatment. Together, these approaches will go far in reducing the very high morbidity and mortality associated with HCC.

Hepatitis B virus X protein induces expression of Fas ligand gene through enhancing transcriptional activity of early growth response factor

FasL expressed in tumor cells plays an important role in the escape from immune surveillance by inducing apoptosis in T-cells bearing Fas. Since the Fas/FasL signaling pathway requires transcriptional induction of the FasL gene, elucidation of the precise mechanisms underlying regulation of FasL gene expression may provide useful molecular insights on tumor progression. We and others (Shin, E. C., Shin, J. S., Park, J. H., Kim, H., and Kim, S. J. (1999) Int. J. Cancer 82, 587-591; Lee, M. O., Kang, H. J., Cho, H., Shin, E. C., Park, J. H., and Kim, S. J. (2001) Biochem. Biophys. Res. Commun. 288, 1162-1168) have previously reported that hepatitis B virus X protein (HBx) plays a role in the induction of FasL expression in hepatitis B virus-associated hepatoma. In the present study, we analyzed the potential cis- and trans-acting factors that regulate FasL promoter. We found that HBx induced activity of the reporter containing FasL promoter through binding site for Egr but not through NFAT or SP-1, which are known as strong activators of the FasL promoter in T-cells. Transient expression of antisense Egr-2 and antisense Egr-3 abolished expression of FasL, which further confirmed the role of Egr in the HBx-mediated FasL expression. Also we observed that HBx increased the transcriptional activity of Egr-2 and Egr-3 by enhancing expression as well as the transactivation function of these proteins. HBx interacted with Egr-2 and Egr-3 in vivo and enhanced binding of Egr to the co-activator, cAMP-response element-binding protein-binding protein, which may explain the molecular mechanism by which HBx induced the transactivation function of Egr. Finally, we found that the carboxyl terminus of HBx was necessary and sufficient for FasL induction as well as activation of Egr. Taken together, our results show a novel mechanism by which HBx induces FasL gene expression that is mediated by enhancing transcriptional activity of Egr-2 and Egr-3.

Hepatitis B viral HBx induces matrix metalloproteinase-9 gene expression through activation of ERK and PI-3K/AKT pathways: involvement of invasive potential

Hepatitis B virus (HBV) X protein (HBx) has been shown to be essential for the development of hepatocellular carcinoma (HCC). Recently, we have found that HBx causes the progression of liver cancer through down-expression of PTEN, known as a tumor suppressor gene (1). The prognosis for HCC depends mainly on the clinicopathological characteristic regarding invasion and metastasis. The expression of matrix metalloproteinase (MMP)-9 has been implicated as playing an important role in HCC invasion and metastasis. We previously reported that HBV infection increased the invasiveness of hepatocytes and HCC cells through the transcriptional activation of MMP-9 (2). The HBx was shown to activate the mitogen-activated protein (MAP) kinase and phosphatidylinositol 3-kinase (PI-3K) signal cascade, which is essential for activation of transcription factors such as activating protein (AP)-1 and nuclear factor (NF)-kappaB. In this study, we show that the HBx protein stimulates the activities of the PI-3K-Akt/ protein kinase B (PKB) as well as extracellular signal-regulated kinase 1/2 (ERK 1/2) in HBx-transfected cells. Furthermore, we have shown that enhanced expression of MMP-9 in HBx-transfected cells mediated by not only activation of AP-1 transcriptional activity through ERKs pathway but also activation of NF-kappaB transcriptional activity through PI-3K-AKT/PKB pathway, and was associated with the invasive potential. However, treatment with U0126 (known as the ERKs inhibitor) or wortmannin (known as the PI-3K inhibitor), but not SB203580 (known as the p38 MAPK inhibitor), markedly inhibited the expression of MMP-9 induced by HBx in HBx-transfected cells. Seemingly, the invasiveness of HBx-transfected cells was decreased by treating with U0126 or wortmannin, but not SB203580. These results clearly suggest that the HBx contributed to the transcriptional regulation of MMP-9 through the ERKs and PI-3K-AKT/PKB pathway, and increased an invasive potential of cells.

Human S15a expression is upregulated by hepatitis B virus X protein

The hepatitis B virus (HBV)-encoded X antigen (HBxAg) may contribute to the development of hepatocellular carcinoma (HCC) through the upregulated expression of selected cellular genes. To identify these genes, RNAs isolated from HBxAg-positive and -negative HepG2 cells were compared by PCR select cDNA subtraction. One gene overexpressed in HBxAg-positive cells by Northern and Western blotting is the ribosomal protein S15a. The S15a mRNA is 535 base pairs, encoding a protein 130 amino acids long with a molecular weight of 14.3 kDa. S15a expression was upregulated in HBV-infected livers, where it costained with HBxAg. Overexpression of S15a stimulated cell growth, colony formation in soft agar, and tumor formation in SCID mice. Hence, HBxAg upregulated the expression of S15a, the latter of which participates in the development of HCC, perhaps by altering the integrity of translation.

Hepatitis B virus X antigen promotes transforming growth factor-beta1 (TGF-beta1) activity by up-regulation of TGF-beta1 and down-regulation of alpha2-macroglobulin

Hepatitis B virus (HBV) X antigen (HBxAg) may contribute to the development of hepatocellular carcinoma (HCC) by activation of signalling pathways such as NF-kappaB. To identify NF-kappaB target genes differentially expressed in HBxAg-positive compared to -negative cells, HepG2 cells consistently expressing HBxAg (HepG2X cells) were stably transfected with pZeoSV2 or pZeoSV2-IkappaBalpha. mRNA from each culture was isolated and compared by PCR select cDNA subtraction. The results showed lower levels of alpha(2)-macroglobulin (alpha(2)-M) in HepG2X-pZeoSV2 compared to HepG2X-pZeoSV2-IkappaBalpha cells. This was confirmed by Northern and Western blotting, and by measurement of extracellular alpha(2)-M levels. Elevated transforming growth factor-beta1 (TGF-beta1) levels were also seen in HepG2X compared to control cells. Serum-free conditioned medium (SFCM) from HepG2X cells suppressed DNA synthesis in a TGF-beta-sensitive cell line, Mv1Lu. The latter was reversed when the SFCM was pretreated with exogenous, activated alpha(2)-M or with anti-TGF-beta. Since elevated TGF-beta1 promotes the development of many tumour types, these observations suggest that the HBxAg-mediated alteration in TGF-beta1 and alpha(2)-M production may contribute importantly to the pathogenesis of HCC.

N/A

N/A

Transforming growth factor beta/Smad3 signaling regulates IRF-7 function and transcriptional activation of the beta interferon promoter

The rapid induction of alpha interferon (IFN-alpha) and IFN-beta expression plays a critical role in the innate immune response against viral infection. We studied the effects of transforming growth factor beta (TGF-beta) and its intracellular effectors, the Smads, on the function of IRF-7, an essential transcription factor for IFN-alpha and -beta induction. IRF-7 interacted with Smads, and IRF-7, but not IRF-3, cooperated with Smad3 to activate IFN-beta transcription. This transcriptional cooperation occurred at the IRF-binding sequences in the IFN-beta promoter, and dominant-negative interference with TGF-beta receptor signaling and Smad3 function decreased IRF-7-mediated transcription. Furthermore, elimination of Smad3 expression in Smad3(-/-) fibroblasts delayed and decreased double-stranded RNA-induced expression of endogenous IFN-beta, whereas restoration of Smad3 expression enhanced IFN-beta induction. The IRF-7-Smad3 cooperativity resulted from the regulation of the transactivation activity of IRF-7 by Smad3, and dominant-negative interference with Smad3 function decreased IRF-7 activity. Consistent with the regulation by Smad3, the transcriptional activity of IRF-7 depended on and was regulated by TGF-beta signaling. Our studies underscore a role of TGF-beta/Smad3 signaling in IRF-7-mediated induction of IFN-beta expression.

Hepatitis C virus core protein upregulates transforming growth factor-beta 1 transcription

The majority of persons with chronic hepatitis C virus (HCV) infection develop liver fibrosis. Transforming growth factor (TGF)-beta 1 plays a pivotal role in the pathogenesis of post-inflammatory liver scarring. To clarify the influence of HCV infection on liver fibrosis, a reporter assay was used to investigate the effect of viral proteins on TGF-beta 1 expression in human hepatoma cells. Of all HCV proteins investigated (core, E1/E2/p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B), only the core protein activated the TGF-beta 1 promoter and upregulated TGF-beta 1 expression measured by an RNase protection assay. Bases -376 to -331 bp in the promoter region of TGF-beta 1 are responsible for upregulation by HCV core protein, and the nuclear protein that binds to this region increased with the stimulation of HCV core protein. Blocking the mitogen-activated protein kinase pathway prevented upregulation of TGF-beta 1 by HCV core protein. The immunological response is supposed to be a major factor to cause the secretion of TGF-beta 1 from non-parenchymal cells, but the results suggest that the HCV core protein expression may upregulate directly TGF-beta 1 transcription in parenchymal cells and suggest a new paradigm for exacerbation of liver fibrosis by HCV infection.

Hepatitis B virus X protein activates a survival signaling by linking SRC to phosphatidylinositol 3-kinase

We have previously shown that transactivation-proficient hepatitis virus B X protein (HBx) protects Hep 3B cells from transforming growth factor-beta (TGF-beta)-induced apoptosis via activation of the phosphatidylinositol 3-kinase (PI 3-kinase)/Akt signaling pathway. This work further investigated how HBx activates PI 3-kinase. Src activity was elevated in Hep 3B cells following expression of transactivation-proficient HBx or HBx-GFP fusion proteins. The Src family kinase inhibitor PP2 and C-terminal Src kinase (Csk) both alleviated HBx-mediated PI 3-kinase activation and protection from TGF-beta-induced apoptosis. Therefore, HBx activated a survival signal by linking Src to PI 3-kinase. Systemic subcellular fractionation and membrane flotation assays indicated that approximately 1.5% of ectopically expressed HBxGFP was associated with periplasmic membrane where Src was located. However, neither nucleus-targeted nor periplasmic membrane-targeted HBxGFP was able to upregulate Src activity or to augment PI 3-kinase survival signaling pathway.

Early growth response proteins (EGR) and nuclear factors of activated T cells (NFAT) form heterodimers and regulate proinflammatory cytokine gene expression

Activation of transcription factors by receptor mediated signaling is an essential step for T lymphocyte effector function. Following antigenic stimulation of T cells the two central cytokines IL-2 and TNFalpha are co-expressed and co-regulated. Two important transcription factors, i.e., early growth response (EGR) protein EGR-1 and nuclear factors of activated T cells (NFAT) protein NFATc, regulate transcription of the human IL-2 cytokine and the same combination of EGR and NFAT proteins seems relevant for coordinated cytokine expression. Here we demonstrate that the zinc finger protein EGR-1 and two members of the NFAT protein family bind simultaneously to adjacent elements position -168 to -150 within the TNFalpha promoter. Both promoter sites are important for TNFalpha gene transcription as shown by transfection assays having the IL-2 and TNFalpha promoters linked to a luciferase reporter. The use of promoter deletion constructs with the zinc finger protein (ZIP), the NFAT binding element or a combination of both deleted show a functional cooperation of these elements and of their binding factors. These experiments demonstrate that EGR-1 as well as EGR-4 functionally cooperate with NFAT proteins and induce expression of both cytokine genes. Using tagged NFATc and NFATp in glutathione S-transferase pull down assays showed interaction and physical complex formation of each NFAT protein with recombinant, as well as native, EGR-1 and EGR-4 proteins. Thus EGR-NFAT interaction and complex formation seems essential for human cytokine expression as adjacent ZIP and NFAT elements are conserved in the IL-2 and TNFalpha gene promoters. Binding of regulatory EGR and NFAT factors to these sites and the functional interaction and formation of stable heterodimeric complexes indicate an important role of these factors for gene transcription.

The hepatitis B virus X protein promotes tumor cell invasion by inducing membrane-type matrix metalloproteinase-1 and cyclooxygenase-2 expression

Hepatocellular carcinoma is strongly associated with chronic infection by the hepatitis B virus (HBV) and has poor prognosis due to intrahepatic metastasis. HBx is often the only HBV protein detected in hepatic tumor cells; however, its contribution to tumor invasion and metastasis has not been established so far. In this work, we show that HBx enhances tumor cell invasion, both in vivo and in vitro. The increased invasive capacity induced by HBx is mediated by an upregulation of membrane-type 1 matrix metalloproteinase (MT1-MMP) expression, which in turn activates matrix metalloproteinase-2. Induction of both MT1-MMP expression and cell invasion by HBx is dependent on cyclooxygenase-2 (COX-2) activity. In addition, HBx upregulates the expression of COX-2, which is mediated by the transcriptional activation of the COX-2 gene promoter in a nuclear factor of activated T cell-dependent (NF-AT-dependent) manner. These results demonstrate the ability of HBx to promote tumor cell invasion by a mechanism involving the upregulation of MT1-MMP and COX-2 and provide new insights into the mechanism of action of this viral protein and its involvement in tumor metastasis and recurrence of hepatocellular carcinoma.

The hepatitis B virus X protein promotes tumor cell invasion by inducing membrane-type matrix metalloproteinase-1 and cyclooxygenase-2 expression

Hepatocellular carcinoma is strongly associated with chronic infection by the hepatitis B virus (HBV) and has poor prognosis due to intrahepatic metastasis. HBx is often the only HBV protein detected in hepatic tumor cells; however, its contribution to tumor invasion and metastasis has not been established so far. In this work, we show that HBx enhances tumor cell invasion, both in vivo and in vitro. The increased invasive capacity induced by HBx is mediated by an upregulation of membrane-type 1 matrix metalloproteinase (MT1-MMP) expression, which in turn activates matrix metalloproteinase-2. Induction of both MT1-MMP expression and cell invasion by HBx is dependent on cyclooxygenase-2 (COX-2) activity. In addition, HBx upregulates the expression of COX-2, which is mediated by the transcriptional activation of the COX-2 gene promoter in a nuclear factor of activated T cell-dependent (NF-AT-dependent) manner. These results demonstrate the ability of HBx to promote tumor cell invasion by a mechanism involving the upregulation of MT1-MMP and COX-2 and provide new insights into the mechanism of action of this viral protein and its involvement in tumor metastasis and recurrence of hepatocellular carcinoma.

Expression of hepatitis B virus X (HBx) gene is up-regulated by adriamycin at the post-transcriptional level

Hepatitis B virus (HBV) X protein (HBx) is thought to be involved in the development of liver cancer and alteration of cellular HBx level may influence the pathological progression of HBV-induced liver diseases. We found that the cellular levels of HBx mRNA transcript and protein in cells were greatly enhanced by adriamycin, a topoisomerase II inhibitor. Up-regulation of HBx mRNA by adriamycin was also observed in HBx transgenic mice, which was accompanied with a significant increase of VEGF mRNA, the downstream target of HBx. When we investigated the underlying mechanism, we found that half-life of HBx mRNA in HBx-expressing Chang cells was about 3h, but was prolonged to >6h in the presence of adriamycin. Moreover, half-life of rapidly degrading HBx protein was determined as about 15min however, it remained almost constant until 60min in the presence of adriamycin. These results provide the first evidence that the cellular level of HBx gene can be increased at the post-transcriptional level.

Hepatitis B virus X protein induced expression of interleukin 18 (IL-18): a potential mechanism for liver injury caused by hepatitis B virus (HBV) infection

BACKGROUND/AIMS

The hepatitis B virus X protein (HBx), a major viral transactivator, is implicated in hepatic inflammation, since it induces many pro-inflammatory cytokines at transcriptional level. The aim of this study was to investigate role of HBx in expression of interleukin 18 (IL-18), a newly identified cytokine that up-regulates Fas ligand (FasL) expression.

METHODS

Chang X-34 that expressing HBx under the control of a doxycycline-inducible promoter, and hepatitis B virus (HBV)-integrated hepatoma cell lines were examined for IL-18 expression by Northern and Western blotting analysis. To test the role of IL-18 produced by hepatoma cells, FasL expression was examined by flow cytometry after treatment with neutralizing anti-IL-18 antibodies. Further, IL-18 expression was examined in the liver tissues of HBx-transgenic mice.

RESULTS

Induction of IL-18 following HBx expression in Chang X-34 and the pattern of IL-18 expression in HBV-integrated cell lines, implicated that HBx transcriptionally induces IL-18 expression. Neutralizing anti-IL-18 antibodies blocked the expression of FasL, suggesting that IL-18 plays a critical role in FasL expression. Further, IL-18 expression in the HBx-transgenic liver, was correlated with the degree of hepatitis.

CONCLUSIONS

Our results demonstrated that HBx induces IL-18 expression in liver, which may be associated with hepatic injury by amplifying FasL expression during HBV infection.

The hepatitis B virus X protein binds to and activates the NH(2)-terminal trans-activation domain of nuclear factor of activated T cells-1

We have previously reported that the hepatitis B virus X protein (HBx) activates nuclear factor of activated T cells (NF-AT), a key regulator of the immune system, by a calcium/calcineurin-dependent pathway, involving dephosphorylation and nuclear translocation of this transcription factor. In addition, we showed that HBx synergizes with potent calcium-mobilizing stimuli to activate NF-AT-dependent transcription, suggesting that additional mechanisms might also be operative in the activation of NF-AT by HBx. Here we demonstrate that HBx activates the NH(2)-terminal transcription activation domain (TAD) of NF-AT1 by a mechanism involving protein-protein interaction. Targeting of HBx to the nucleus did not affect its ability to induce the transcriptional activity of NF-AT1. In contrast, mutations of HBx affecting its functional interaction with general transcription factors abrogated the HBx-induced activity of NF-AT1. Together these results indicate that HBx may exert its function by acting as a nuclear coactivator of NF-AT1.

Disruption of transforming growth factor beta signaling by a novel ligand-dependent mechanism

Transforming growth factor (TGF)-beta is the prototype in a family of secreted proteins that act in autocrine and paracrine pathways to regulate cell development and function. Normal cells typically coexpress TGF-beta receptors and one or more isoforms of TGF-beta, thus the synthesis and secretion of TGF-beta as an inactive latent complex is considered an essential step in regula-ting the activity of this pathway. To determine whether intracellular activation of TGF-beta results in TGF-beta ligand-receptor interactions within the cell, we studied pristane-induced plasma cell tumors (PCTs). We now demonstrate that active TGF-beta1 in the PCT binds to intracellular TGF-beta type II receptor (TbetaRII). Disruption of the expression of TGF-beta1 by antisense TGF-beta1 mRNA restores localization of TbetaRII at the PCT cell surface, indicating a ligand-induced impediment in receptor trafficking. We also show that retroviral expression of a truncated, dominant-negative TbetaRII (dnTbetaRII) effectively competes for intracellular binding of active ligand in the PCT and restores cell surface expression of the endogenous TbetaRII. Analysis of TGF-beta receptor-activated Smad2 suggests the intracellular ligand-receptor complex is not capable of signaling. These data are the first to demonstrate the formation of an intracellular TGF-beta-receptor complex, and define a novel mechanism for modulating the TGF-beta signaling pathway.

Genetic mechanisms of hepatocarcinogenesis

The development of hepatocellular carcinoma (HCC) is a multistep process associated with changes in host gene expression, some of which correlate with the appearance and progression of tumor. Preneoplastic changes in gene expression result from altered DNA methylation, the actions of hepatitis B and C viruses, and point mutations or loss of heterozygosity (LOH) in selected cellular genes. Tumor progression is characterized by LOH involving tumor suppressor genes on many chromosomes and by gene amplification of selected oncogenes. The changes observed in different HCC nodules are often distinct, suggesting heterogeneity on the molecular level. These observations suggest that there are multiple, perhaps redundant negative growth regulatory pathways that protect cells against transformation. An understanding of the molecular pathogenesis of HCC may provide new markers for tumor staging, for assessment of the relative risk of tumor formation, and open new opportunities for therapeutic intervention.

Mitochondrially associated hepatitis B virus X protein constitutively activates transcription factors STAT-3 and NF-kappa B via oxidative stress

The hepatitis B virus X protein (HBx) plays essential roles in viral replication and the generation of hepatocellular carcinoma. In spite of a large number of suggestive cellular targets and functions, a clear picture of its mechanism(s) of action has remained elusive. In this report, we continue to characterize its recently described mitochondrial association and further examine its impact on mitochondrial functions. HBx was previously shown to bind to a voltage-dependent anion channel (VDAC3) and alter the mitochondrial transmembrane potential (Delta Psi(m)). Here we show that, as a consequence of association with mitochondria, HBx constitutively induces activation of transcription factors, which include STAT-3 and NF-kappa B. This induction of activation was sensitive to the antioxidants N-acetyl L-cysteine and pyrrolidine dithiocarbamate, as well as to overexpression of Mn-superoxide dismutase. These results therefore implicate a potential role of reactive oxygen species (ROS) in a process that ultimately leads to the activation of STAT-3 and NF-kappa B. Evidence is also presented for the HBx-induced generation of ROS. The ability of HBx to induce the activation of STAT-3 and NF-kappa B was demonstrated by mobility shift and reporter gene expression assays with lysates from HBx-transfected HepG2 cells. A C-terminal HBx deletion mutant, HBx Delta 99, failed to bind VDAC3 and activate STAT-3 and NF-kappa B. These studies shed new light on the physiological significance of HBx's mitochondrial association and its role in inducing oxidative stress which can contribute to the liver disease pathogenesis associated with the hepatitis B virus infection.

New animal models of hepatitis B and C

The narrow host range of infection and lack of suitable tissue culture systems for the propagation of hepatitis B and C viruses are limitations that have prevented a more thorough understanding of persistent infection and the pathogenesis of chronic liver disease. With hepatitis B virus (HBV), this lack of knowledge has been partially overcome by the discovery and characterization of HBV-like viruses in wild animals. With hepatitis C virus (HCV), related flaviviruses have been used as surrogate systems for such studies. Other laboratories have developed transgenic mice that express virus gene products and/or support virus replication. Some HBV transgenic mouse models develop fulminant hepatitis, acute hepatitis, or chronic liver disease after adoptive transfer, and others spontaneously develop hepatocellular carcinoma (HCC), as in human infections. Among HCV transgenic mice, most develop no disease, but acute hepatitis has been observed in one model, and HCC in another. Although mice are not susceptible to HBV and HCV, their ability to replicate these viruses and to develop liver diseases characteristic of human infections provides new opportunities to study pathogenesis and develop novel therapeutics.

Hepatitis B and hepatitis C co-infection in patients with HIV

HAART has increased the life expectancy of patients with HIV. However, as their life expectancy increases, it becomes increasingly important to focus on the management of concurrent illnesses such as chronic HBV and HCV infections which have the potential to increase mid to long term morbidity and mortality. Shared epidemiological risks have resulted in the HIV infected population having a higher incidence of both HBV and HCV than those uninfected with HIV. Co-infection with HIV modifies the natural history of HBV infection, increasing the rate of viral replication, risk of carriage and chronic hepatitis but without increasing liver necroinflammatory processes. In chronic HCV infection, the presence of HIV enhances the risk of severe liver disease. There is no evidence as yet that HBV directly impacts on HIV disease progression but HCV infection increases the risk of death or an AIDS defining illness and impairs CD4+ T cell recovery during antiretroviral therapy. Treatment of either hepatitis virus is complex because of pharmacokinetic interactions with components of HAART regimens.

Transforming growth factor-beta signal transduction in epithelial cells

Transforming growth factor (TGF)-beta is a natural and potent growth inhibitor of a variety of cell types, including epithelial, endothelial, and hematopoietic cells. The ability of TGF-beta to potently inhibit the growth of many solid tumors of epithelial origin, including breast and colon carcinomas, is of particular interest. However, many solid tumor cells become refractory to the growth inhibitory effects of TGF-beta due to defects in TGF-beta signaling pathways. In addition, TGF-beta may stimulate the invasiveness of tumor cells via the paracrine effects of TGF-beta. Accordingly, in order to develop more effective anticancer therapeutics, it is necessary to determine the TGF-beta signal transduction pathways underlying the growth inhibitory effects and other cellular effects of TGF-beta in normal epithelial cells. Thus far, two primary signaling cascades downstream of the TGF-beta receptors have been elucidated, the Sma and mothers against decapentaplegic homologues and the Ras/mitogen-activated protein kinase pathways. The major objective of this review is to summarize TGF-beta signaling in epithelial cells, focusing on recent advances involving the Sma and mothers against decapentaplegic homologues and Ras/mitogen-activated protein kinase pathways. This review is particularly timely in that it provides a comprehensive summary of both signal transduction mechanisms and the cell cycle effects of TGF-beta.

Characterization of serum activin-A and follistatin and their relation to virological and histological determinants in chronic viral hepatitis

BACKGROUND/METHODS

Hepatocyte proliferation in viral hepatitis is regulated by a number of growth factors. Activin-A inhibits hepatocyte DNA synthesis while follistatin, a potent activin-A antagonist, promotes liver regeneration. We report the first study of activin-A and follistatin in human viral hepatitis. Sera from 15 normal subjects, 22 hepatitis B and 47 hepatitis C patients were analysed for activin-A and follistatin and correlated with serological and histological markers of liver injury and with specific immunohistochemistry.

RESULTS

All groups showed immunoreactivity for activin with hepatocyte localisation. Serum activin-A was significantly increased in viral hepatitis patients compared to controls, was greater in hepatitis B compared to hepatitis C, and correlated with serum aminotransferase and hepatitis B viral replication. A concurrent rise in serum follistatin was not observed in either group, but serum follistatin correlated inversely with hepatitis B DNA levels. Although hepatocyte apoptosis in hepatitis C and proliferation in both groups was significantly elevated compared to controls, there was no correlation with serum activin-A or follistatin.

CONCLUSIONS

Activin-A and follistatin are constitutively expressed in human liver and serum concentrations are increased in viral hepatitis. Dysregulation of the activin/follistatin axis may be linked to hepatitis B replication but does not correlate with hepatocyte apoptosis.

Molecular pathways in virus-induced cytokine production

Virus infections induce a proinflammatory response including expression of cytokines and chemokines. The subsequent leukocyte recruitment and antiviral effector functions contribute to the first line of defense against viruses. The molecular virus-cell interactions initiating these events have been studied intensively, and it appears that viral surface glycoproteins, double-stranded RNA, and intracellular viral proteins all have the capacity to activate signal transduction pathways leading to the expression of cytokines and chemokines. The signaling pathways activated by viral infections include the major proinflammatory pathways, with the transcription factor NF-kappaB having received special attention. These transcription factors in turn promote the expression of specific inducible host proteins and participate in the expression of some viral genes. Here we review the current knowledge of virus-induced signal transduction by seven human pathogenic viruses and the most widely used experimental models for viral infections. The molecular mechanisms of virus-induced expression of cytokines and chemokines is also analyzed.

The hepatitis B virus encoded oncoprotein pX amplifies TGF-beta family signaling through direct interaction with Smad4: potential mechanism of hepatitis B virus-induced liver fibrosis

Hepatitis B, one of the most common infectious diseases in the world, is closely associated with acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Many clinical investigations have revealed that hepatic fibrosis is an important component of these liver diseases caused by chronic hepatitis B. TGF-beta signaling plays an important role in the pathogenesis of fibrosis in chronic hepatitis and cirrhosis. As these diseases are associated with hepatitis B virus (HBV) infection, we examined the possibility that the HBV-encoded pX oncoprotein regulates TGF-beta signaling. We show that pX enhances transcriptional activity in response to TGF-beta, BMP-2, and activin by stabilizing the complex of Smad4 with components of the basic transcriptional machinery. Additionally, confocal microscopic studies suggest that pX facilitates and potentiates the nuclear translocation of Smads, further enhancing TGF-beta signaling. Our studies suggest a new paradigm for amplification of Smad-mediated signaling by an oncoprotein and suggest that enhanced Smad-mediated signaling may contribute to HBV-associated liver fibrosis.

Transforming growth factor-beta1 as a surrogate marker of hepatic dysfunction in chronic liver diseases

The aim of the study was to evaluate the possible association between plasma concentrations of transforming growth factor-beta1 (TGF-beta1) and the degree of hepatic dysfunction in patients with chronic liver diseases. TGF-beta1 was measured with an enzyme immunoassay in plasma from 21 patients with chronic active hepatitis and 40 patients with liver cirrhosis. Normal values were obtained from a group of 13 healthy volunteers. Results were analysed with respect to aetiology and the degree of liver insufficiency as evaluated by the Child-Pugh classification. The mean plasma concentration of TGF-beta1 in patients (36.9+/-2.8 ng/ml) was twice that found in normal volunteers (18.3+/-1.6 ng/ml). The highest values were observed in patients with alcoholic liver cirrhosis (44.4+/-4.7 ng/ml). Plasma TGF-beta1 showed a statistically significant positive correlation with the degree of liver insufficiency. These results indicate the possible use of plasma TGF-beta1 measurement as a good marker of liver function impairment. Further observation of patients involved in this study may help to evaluate its possible prognostic value in chronic liver diseases.

Chemotherapeutic drug, adriamycin, restores the function of p53 protein in hepatitis B virus X (HBx) protein-expressing liver cells

Hepatitis B virus X (HBx) protein implicated in the development of liver cancer may inhibit the function of p53 tumor suppressor protein through cytoplasmic retention of p53 protein. Here, we attempt to investigate whether the functional inhibition of p53 protein by HBx protein is reversible. First, we provide the evidence for the association of endogenous p53 protein with HBx by co-immunoprecipitation in stable Chang cells that express HBx protein in an inducible manner (ChangX-34). By immunofluorescence microscopy, the major location of p53 protein of ChangX-34 cells was confirmed at the nuclear periphery as well as in the cytoplasm where HBx protein is mainly expressed. Surprisingly, anticancer drug, adriamycin induces the nuclear translocation of p53 protein sequestered in the cytoplasm. This change is accompanied by the restoration of p53 activity, which results in increased transcriptional activity at the p53-responsive DNA elements as well as increase of p21WAF1 mRNA expression. Further, we observed the induction of cell death and G1 arrest in these cells upon adriamycin treatment regardless of HBx expression. Together, we demonstrate that functional inhibition of p53 protein through its cytoplasmic retention by HBx protein is reversible. These results may be extended into other tumors of which p53 activity is modulated by viral oncoproteins.

Expression of integrated hepatitis B virus X variants in human hepatocellular carcinomas and its significance

Hepatitis B virus X protein (HBX) has been implicated in the transactivation of diverse cellular genes and possibly also the pathogenesis of human hepatocellular carcinoma (HCC). We report the characterization of HBX variants from HBV-related human hepatocellular carcinoma (HCC). These HBX variants were integrated into the host chromosomes and also expressed in the HCC tissues. In addition, we report a novel in vitro HBX activity assay based on color changes that were indicative of the beta-galactosidase enzyme activity. Conducted in wheat germ lysates, the transactivating function of either wild type or mutant HBX protein was measured through their interaction with the Early Growth Response factor 1 (Egr-1) that controls the beta-galactosidase gene. Further analysis of these HBX deletion mutants using this assay may shed new insights on the significance of various mutations occurring in HCC-associated HBX.

Interaction of Hepatitis B virus with cellular processes in liver carcinogenesis

Hepatitis B infection is strongly linked epidemiologically to hepatocellular carcinoma development. This article reviews the molecular mechanisms by which hepatitis B encoded proteins such as hepatitis B x and hepatitis B surface transactivators may interact with gene transcription, tumor suppression, apoptosis, and signalling pathways of the liver cell with the possible consequence of tumor induction. Data on the interaction between hepatitis B proteins and cellular processes are often conflicting indicating a non-specific simultaneous interaction with antagonistic cellular processes that result in the formation of escape mutants that are not subject to these selective pressures.