Hepatitis C virus targets over-expression of arginase I in hepatocarcinogenesis

Hepatitis C virus (HCV) infection is often associated with chronic liver disease, which is a major risk factor for the development of hepatocellular carcinoma (HCC). To study the HCV host-cell relationship on the molecular level, HepG2 and Huh7 cells were stably transfected with an infectious cDNA clone of HCV or with empty vector. Evidence for HCV replication was obtained in both culture systems. HCV also stimulated growth in vitro. To identify genes whose altered expression by HCV are important to the pathogenesis of infection, RNAs were isolated from HepG2-HCV and HepG2-vector cells and subjected to microarray analysis. The results showed that arginase 1 mRNA and protein were elevated about threefold in HCV positive compared with negative cells (p < 0.01). Arginase 1 expression was elevated in more than 75% of HCV infected liver samples compared with paired HCC from the same patients (>33% positive) and to uninfected liver tissues (0% positive). Arginase 1 specific siRNA inhibited the ability of HCV to stimulate hepatocellular growth in culture by >70%, suggesting that the metabolism of arginine to ornithine may contribute to HCV mediated stimulation of hepatocellular growth. Introduction of arginase specific siRNA also resulted in increased nitric oxide synthase (iNOS) (>1.2-fold), nitric oxide (NO) production (>3-fold) and increased cell death (>2.5-fold) in HCV positive compared with negative cells, suggesting that these molecules potentially contribute to hepatocellular damage. Hence, an important part of the mechanism whereby HCV regulates hepatocellular growth and survival may be through altering arginine metabolism.

Mitochondria-associated HBV x antigen: what is going on?

Evaluation of: Clippinger AJ, Bouchard MJ: Hepatitis B virus HBx protein localizes to mitochondria in primary rat hepatocytes and modulates mitochrondrial membrane potential. J. Virol. 82(14), 6798–6811 (2008). Over 350 million people are chronically infected with HBV, and a significant number of these individuals develop primary liver cancer. HBV encodes seven viral proteins, including the nonstructural Hepatitis B x (HBx) protein. The results of studies with immortalized or transformed cells and with HBx transgenic mice demonstrated that HBx can interact with mitochondria. However, no studies with normal hepatocytes have characterized the precise mitochondrial localization of HBx or the effect of HBx on mitochondrial physiology. We have used cultured primary rat hepatocytes as a model system to characterize the mitochondrial localization of HBx and the effect of HBx expression on mitochondrial physiology. We now show that a fraction of HBx co-localizes with density gradient-purified mitochondria and associates with the outer mitochondrial membrane. We also demonstrate that HBx regulates mitochondrial membrane potential in hepatocytes, and that this function of HBx varies depending upon the status of NF-κB activity. In primary rat hepatocytes, HBx activation of NF-κB prevented mitochondrial membrane depolarization; however, when NF-κB activity was inhibited, HBx induced membrane depolarization through modulation of the mitochondrial permeability transition pore. Collectively, these results define potential pathways through which HBx may act in order to modulate mitochondrial physiology, thereby altering many cellular activities and ultimately contributing to the development of HBV-associated liver cancer.

Pharmacotherapy of chronic viral hepatitis and hepatocellular carcinoma

BACKGROUND

Hepatitis B virus (HBV) is a major etiologic agent of chronic liver disease (CLD) and hepatocellular carcinoma. Drugs have been developed and shown to be effective against HBV replication. These treatments are often associated with the resolution of CLD. However, they are too expensive, not well tolerated, and result in the development of resistance when given as mono or salvage therapies. In addition, most of these drugs target only the virus polymerase.

OBJECTIVE

To revitalize the field, drugs with other targets and combination therapies need to be developed.

METHODS

Major advances in HBV and liver cancer drug development over the past decade, focusing on Phase III trials and FDA-approved compounds, are presented.

RESULTS/DISCUSSION

A number of potent nucleoside/nucleotide analogs are now available for treatment, but for the long-term management of CLD, the development of combination therapies will probably be required. Development of compounds with new virus targets will enhance the utility of combination therapies. Development of compounds to host targets altered prior to or after the development of liver cancer, as demonstrated by sorafenib, need to be developed. The goal is to devise drug cocktails that will yield sustained virus responses and halt disease progression and tumor development.

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.

Hepatitis B virus X protein mutants exhibit distinct biological activities in hepatoma Huh7 cells

The role of the hepatitis B virus X protein (HBx) in hepatocarcinogenesis remains controversial. To investigate the biological impact of hepatitis B virus x gene (HBx) mutation on hepatoma cells, plasmids expressing the full-length HBx or HBx deletion mutants were constructed. The biological activities in these transfectants were analyzed by a series of assays. Results showed that HBx3'-20 and HBx3'-40 amino acid deletion mutants exhibited an increase in cellular proliferation, focus formation, tumorigenicity, and invasive growth and metastasis through promotion of the cell cycle from G0/G1 to the S phase, when compared with the full-length HBx. In contrast, HBx3'-30 amino acid deletion mutant repressed cell proliferation by blocking in G1 phase. The expression of P53, p21(WAF1), p14(ARF), and MDM2 proteins was regulated by expression of HBx mutants. In conclusions, HBx variants showed different effects and functions on cell proliferation and invasion by regulation of the cell cycle progression and its associated proteins expression.

Mutations in the C-terminus of the X protein of hepatitis B virus regulate Wnt-5a expression in hepatoma Huh7 cells: cDNA microarray and proteomic analyses

Background: The hepatitis B virus x gene (HBx) is a promiscuous transactivator implicated in the development of hepatocellular carcinoma (HCC). The present study was designed to investigate the molecular events regulated by HBx. Methods: Genomic and proteomic expression profiling was performed in Huh7 HCC cells transfected with HBx mutants with a C-terminal deletion. The gene and protein expression of wingless-type murine-mammary-tumour virus (MMTV) integration site family, member 5A (Wnt-5a) was validated by analyses of reverse transcription–polymerase chain reaction (RT–PCR), real-time RT–PCR, western blot and immunohistochemistry. Results: Differentially expressed genes and proteins were found in the transfected Huh7 HCC cells; most of them were involved in transcriptional regulation, although others including oncogenes or tumor suppressor genes, and molecules involved in cell junctions, signal transduction pathways, metabolism or the immune response were also observed. The expression of the Wnt-5a gene was elevated >10-fold in Huh7 cells transfected with the HBx3′-30 amino acid deletion mutant. However, the expression was downregulated by the transfection with the HBx3′-40 amino acid deletion mutant. The changes in Wnt-5a expression were also observed in human HCC tissues, compared with corresponding non-cancerous liver tissues. A negative correlation was found between the expression of Wnt-5a and HBx COOH mutations in HCC tissues. Conclusions: HBx mutants may participate in the development and progression of HCC, at least in part through the Wnt-5a pathway.

Development of a novel mouse model to evaluate drug candidates against hepatitis B virus

Woodchuck hepatitis virus (WHV)-infected woodchucks have been used for preclinical development of drugs against hepatitis B virus (HBV). However, there is no simple in vivo model to evaluate small amounts of compounds against HBV. To develop such a model, HepAD38 cells, in which HBV replication is regulated by tetracycline (tet), were grown as subcutaneous tumours in nude mice. Mice developing viraemia were then left untreated or given tet in the drinking water. In some of the mice given tet, it was removed and the mice were injected intraperitoneally with phosphate buffer saline (PBS), lamivudine (3TC), clevudine (CLV) or tenofovir dipivoxil fumarate (TDF). Virus DNA titres were measured by real-time PCR during and after drug treatment. In water-fed and PBS-injected mice, virus titres reached approximately 10(9) copies/ml serum within 35 days of HepAD38 injection, whereas in tet-treated mice, virus titres remained at 10(4)-10(5) copies/ml. HBV DNA levels were suppressed by 3TC, TDF and CLV, with the latter two drugs showing more sustained virus suppression compared with 3TC. Combination therapy with CLV plus TDF was much more effective than either drug alone in suppressing virus titre for at least 3 weeks after the end of treatment. There was no demonstrable toxicity to HepAD38 cells in drug-treated mice. Hence, a robust tet-controlled system for HBV replication in vivo was demonstrated, validated with monotherapies against HBV and shown to be useful in assessing combination therapy. This system will be useful for preclinical assessment of small amounts of single or multiple compounds against HBV in vivo.

COOH-terminal deletion of HBx gene is a frequent event in HBV-associated hepatocellular carcinoma

AIM: To investigate the hepatitis B virus (HBV) x gene (HBx) state in the tissues of HBV-related hepatocellular carcinoma (HCC) in Chinese patients and whether there were particular HBx mutations.

METHODS: HBx gene was amplified and direct sequencing was used in genomic DNA samples from 20 HCC and corresponding non-cancerous liver tissues from HBsAg-positive patients. HBV DNA integration and HBx deleted mutation were validated in 45 HCC patients at different stages by Southern blot analysis and polymerase chain reaction methods.

RESULTS: The frequencies of HBx point mutations were significantly lower in HCC than their corresponding non-cancerous liver tissues (11/19 vs 18/19, P = 0.019). In contrast, deletions in HBx gene were significantly higher in HCC than their non-cancerous liver tissues (16/19 vs 4/19, P < 0.001). The deletion of HBx COOH-terminal was detected in 14 HCC tissues. A specific integration of HBx at 17p13 locus was also found in 8 of 16 HCC, and all of them also exhibited full-length HBx deletions. Integrated or integrated coexistence with replicated pattern was obtained in 45.5% (20/45) - 56.8% (25/45) tumors and 40.9% (18/45) - 52.3% (23/45) non-tumor tissues.

CONCLUSION: HBx deletion, especially the COOH-terminal deletion of HBx is a frequent event in HBV-associated HCC tissues in China. HBV integration had also taken place in partial HCC tissues. This supporting the hypothesis that deletion and probably integrated forms of the HBx gene may be implicated in liver carcinogenesis.

[Preneoplastic markers of hepatitis B virus-associated hepatocellular carcinoma and their significance in clinical settings]

OBJECTIVES

To identify serologic markers that may indicate the early presence of hepatocellular carcinoma (HCC), and analyze their significance in the pathogenesis of chronic hepatitis B.

METHODS

Hepatitis B x antigen (HBxAg) positive and negative HepG2 cells were subjected to PCR select cDNA subtraction to identify differentially expressed genes that may precede the development of HCC. These included the up-regulated genes URG4, URG7, URG11, and VEGFR3, and the down-regulated gene, Sui1. Specific ELISAs were constructed to measure differentially expressed antigens and their corresponding antibodies to determine whether they had prognostic and/or diagnostic value. The study population consisted of 730 people. Among them, 416 were HBsAg(-) and 298 were HBV carriers with chronic liver disease and/or HCC. In addition, 16 patients had non-viral hepatitis. Among these, serial serum samples from 53 HBsAg(+) patients with cirrhosis were collected and studied.

RESULTS

Antibodies to multiple differentially regulated genes were detectable in serum samples from patients with HBV associated cirrhosis and HCC, but not in serum samples from uninfected individuals (P < 0.01). Antibodies were undetectable in serum samples from HBV patients without liver disease and in serum samples from patients with other tumor types, and among those with non viral hepatitis. Among patients at high risk of developing HCC, these antibodies were found to be independent of nationality and ethnicity. Statistical analysis of the 28 HBsAg(+) patients with HCC showed that anti-URG11 and anti-VEGFR3 were the most frequently detected antibodies. These antibodies were found to coexist in 16 (P < 0.05). In contrast, among the 25 HBsAg(+) patients without HCC, anti-Sui1 and anti-URG7 were the most prevalent antibodies. These antibodies coexisted in 11 (P < 0.05). In addition, HCC patients with four or more antibodies detected before the appearance of HCC had a poorer survival outcome.

CONCLUSION

These antibodies can be detected in serum samples several months to several years before the appearance of HCC. This suggests that they may be preneoplastic markers that may help to distinguish which HBV carriers with cirrhosis are most likely to progress and develop HCC.

Hepatitis B x antigen up-regulates vascular endothelial growth factor receptor 3 in hepatocarcinogenesis

Hepatitis B x antigen (HBxAg) is a trans-activating protein that contributes to liver cancer, in part, by altering the expression of cellular genes. However, few natural effectors of HBxAg have been identified. Hence, HBxAg positive and negative HepG2 cells were prepared and analyzed by PCR select cDNA subtraction. The results identified elevated vascular endothelial growth factor receptor-3 short form splice variant (VEGFR-3(S)) expression in HBxAg positive compared to negative cells. Normally, VEGFR-3 activates Akt signaling in lymphatic endothelial cells, resulting in lymphangiogenesis. In contrast, the results here show that the expression of VEGFR-3(S) is up-regulated in >75% of HBxAg positive hepatocellular carcinoma (HCC) nodules. VEGFR-3(S) up-regulation correlates with the expression of HBxAg, is associated with decreased survival in tumor bearing patients, and when over-expressed in HepG2 cells, strongly stimulated cell growth in culture, in soft agar, and accelerated tumor formation in a ligand independent manner. VEGFR-3(S) siRNA partially blocked the ability of HBxAg to promote hepatocellular growth. In conclusion, HBxAg may short circuit VEGFR-3(S) signaling in liver cancer. Blocking VEGFR-3(S) signaling may be effective in preventing tumor development and/or prolonging survival in tumor bearing patients.

Hepatitis B virus integration, fragile sites, and hepatocarcinogenesis

Chronic liver disease associated with long term hepatitis B virus (HBV) infection contributes importantly to the development of hepatocellular carcinoma (HCC). A salient feature of these chronic infections is the integration of subgenomic HBV DNA fragments into many different locations within the host DNA, suggesting that integration is random. Although this may promote genetic instability during liver regeneration which accompanies a bout of chronic liver disease, the actual role of integrated HBV DNA in hepatocarcinogenesis is uncertain. Importantly, most integration events retain the HBV open reading frame encoding the HBx antigen (HBxAg), which is the virus contribution to HCC. In addition, many integration events reported in the literature occur near or within fragile sites or other cancer associated regions of the human genome that are prone to instability in tumor development and progression. Genetic instability associated with integration potentially alters the expression of oncogenes, tumor suppressor genes, and microRNAs (miRNAs) that may contribute importantly to tumorigenesis. If so, then selected integration events may alter pathways that are rate limiting in hepatocarcinogenesis, thereby providing targets with diagnostic/prognostic potential and for therapeutic intervention.

Transient inhibition of Th1-type cytokine production by CD4 T cells in hepatitis B core antigen immunized mice is mediated by regulatory T cells

The non-cytopathic hepatitis B virus (HBV) can induce chronic infections characterized by weak and limited T cell responses against the virus. The factors contributing to the failure to clear HBV and subsequent development of chronic HBV infections are not clearly understood, but a strong interferon-gamma (IFN-gamma) response by CD4+ T cells against the nucleocapsid hepatitis B core antigen (HBcAg) of the virus appears to be important for viral clearance. The present study documents depressed numbers of CD4+ T cells secreting IFN-gamma and interleukin-2 (IL-2) in enzyme-linked immunospot assay (ELISPOT) assays restimulated for 24 hr with antigen following both primary and secondary immunizations of mice with recombinant hepatitis B core antigen (rHBcAg). The kinetics of these responses showed that the depression occurred following a peak response and lasted approximately 2 weeks before returning to the previous peak levels. The depression was abrogated by depletion of CD25+ cells prior to culture in the ELISPOT assay, suggesting inhibition by regulatory T cells. This inhibition of IFN-gamma and IL-2 production was also reversed by in vitro restimulation of the test cells for 48 hr rather than 24 hr in the assay. No such transient, reversible inhibition was detected in the production of IL-5, a Th2-type cytokine. The inhibition in cytokine production did not appear to correlate with the number of antibody-secreting cells or the isotypes produced. This delay by regulatory T cells of Th1-type cytokine production could contribute to viral persistence in chronic HBV infection by interfering with the critical role IFN-gamma plays in protection against viral infections.

Downregulation of E-cadherin by hepatitis B virus X antigen in hepatocellullar carcinoma

Hepatitis B virus (HBV)-encoded X antigen (HBxAg) contributes to the development of hepatocellular carcinoma (HCC). A frequent characteristic of HCC is reduced or absent expression of the cell adhesion protein, E-cadherin, although it is not known whether HBxAg plays a role. To address this, the levels of E-cadherin were determined in HBxAg-positive and -negative HepG2 cells in culture, and in tumor and surrounding nontumor liver from a panel of HBV carriers. The results showed an inverse relationship between HBxAg and E-cadherin expression both in tissue culture and in vivo. In HBxAg-positive cells, E-cadherin was suppressed at both the mRNA and protein levels. This was associated with hypermethylation of the E-cadherin promoter. Depressed E-cadherin correlated with HBxAg trans-activation function, as did the migration of HepG2 cells in vitro. Decreased expression of E-cadherin was also associated with the accumulation of beta-catenin in the cytoplasm and/or nuclei in tissues and cell lines, which is characteristic of activated beta-catenin. Additional work showed that HBxAg-activated beta-catenin. Together, these results suggest that the HBxAg is associated with decreased expression of E-cadherin, accumulation of beta-catenin in the cytoplasm and nucleus, and increased cell migration, which may contribute importantly to hepatocarcinogenesis.

Downregulation of E-cadherin by hepatitis B virus X antigen in hepatocellullar carcinoma

Hepatitis B virus (HBV)-encoded X antigen (HBxAg) contributes to the development of hepatocellular carcinoma (HCC). A frequent characteristic of HCC is reduced or absent expression of the cell adhesion protein, E-cadherin, although it is not known whether HBxAg plays a role. To address this, the levels of E-cadherin were determined in HBxAg-positive and -negative HepG2 cells in culture, and in tumor and surrounding nontumor liver from a panel of HBV carriers. The results showed an inverse relationship between HBxAg and E-cadherin expression both in tissue culture and in vivo. In HBxAg-positive cells, E-cadherin was suppressed at both the mRNA and protein levels. This was associated with hypermethylation of the E-cadherin promoter. Depressed E-cadherin correlated with HBxAg trans-activation function, as did the migration of HepG2 cells in vitro. Decreased expression of E-cadherin was also associated with the accumulation of beta-catenin in the cytoplasm and/or nuclei in tissues and cell lines, which is characteristic of activated beta-catenin. Additional work showed that HBxAg-activated beta-catenin. Together, these results suggest that the HBxAg is associated with decreased expression of E-cadherin, accumulation of beta-catenin in the cytoplasm and nucleus, and increased cell migration, which may contribute importantly to hepatocarcinogenesis.

Enhanced cell survival of Hep3B cells by the hepatitis B x antigen effector, URG11, is associated with upregulation of beta-catenin

Intrahepatic expression of hepatitis B x antigen (HBxAg) is associated with the development of hepatocellular carcinoma (HCC), perhaps through trans-activation of selected cellular genes. When this was examined by PowerBlot analysis, upregulated levels of beta-catenin and several known beta-catenin effectors were observed in HBxAg-positive compared with HBxAg-negative HepG2 cells. When HBxAg was introduced into Hep3B cells, upregulated expression of wild-type beta-catenin was observed. This was also observed in Hep3B cells overexpressing the HBxAg upregulated gene, URG11. Upregulated expression of URG11 and beta-catenin correlated with HBxAg trans-activation function. Transient transfection assays with fragments of the beta-catenin promoter showed that it was activated by both HBxAg and URG11 and inhibited by URG11-specific small inhibitory RNA. The latter also inhibited the growth of Hep3BX cells in a serum-free medium, which correlated with depressed levels of beta-catenin. Activation of beta-catenin effector genes was observed in cells stably expressing HBxAg or overexpressing URG11 compared with control cells transfected with the pTOPFLASH reporter plasmid. Extensive costaining between HBxAg, URG11, and beta-catenin was observed in infected liver and HCC nodules, suggesting a close relationship in vivo. In conclusion, wild-type beta-catenin is activated by HBxAg, in part, through the upregulated expression of the HBxAg effector URG11. URG11 stimulates the beta-catenin promoter and hepatocellular growth and survival. These observations also suggest that URG11 may be a regulatory element in the beta-catenin signaling pathway and may be a target for chemoprevention of HCC.

Different response requirements for IFNgamma production in ELISPOT assays by CD4+ T cells from mice early and late after immunization

Antigen specific immune responses that occur early after antigen exposure differ from those that are present late in the response. The present study focused on detecting changes in production of IFNgamma by CD4+ T cells over time during chronic antigen exposure. (C3HxCB17)F1 mice were primed with recombinant hepatitis B core antigen (rHBcAg) in incomplete Freund's adjuvant to allow persistent antigen exposure. To assay the CD4+ T cell response to HBcAg, splenocytes from immunized mice were restimulated with rHBcAg for 24 or 48 h in vitro and tested for IFNgamma and IL-5 secreting cells by ELISPOT. Results showed that early after antigen exposure (7 days for primary and 3 days for secondary exposures), the maximal number of IFNgamma secreting cells was detected in the ELISPOT after 24 h of restimulation. However, late after antigen exposure (28 days for primary and 14 days for secondary exposures), the maximum number of IFNgamma secreting cells was not detected until 48 h of restimulation in this assay. This delay in IFNgamma production was related to the availability of IL-2, since addition of IL-2 allowed the delayed cells from late responses to develop peak IFNgamma production in vitro by 24 h, equivalent to that of cells from early responses. This IL-2 dependent delay occurred in Th1-type IFNgamma responses but not in Th2-type IL-5 responses. These observations indicate that, when detecting IFNgamma secreting cells it is important to screen responses at different times of restimulation or in the presence and absence of IL-2 to ensure optimal detection. This approach should prove critical, particularly when evaluating patients with chronic infections and in determining the effectiveness of vaccines since these deal with both early and late responses.

Parallel epigenetic and genetic changes in the pathogenesis of hepatitis virus-associated hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent tumor types in the world, with short survival times and few treatment options. Hepatitis B virus (HBV) and hepatitis C virus (HCV) are major etiologic agents of HCC, although the associated mechanisms are incompletely understood. The available evidence suggests that both viruses promote tumorigenesis by up-regulating genes that promote hepatocellular growth and survival, and by down-regulating other genes that act as tumor suppressors and negative growth regulatory molecules. Significantly, a number of the pathways that are altered by these viruses are the same ones that accumulate genetic alterations during tumor progression. This suggests that the pathways that promote virus persistence and replication may also promote cell growth and survival. From the perspective of the virus, this promotes chronic infection, while from the perspective of the host, this promotes tumorigenesis.

Hepatitis C virus replication in stably transfected HepG2 cells promotes hepatocellular growth and tumorigenesis

HepG2 cells stably transfected with a full-length, infectious hepatitis C virus (HCV) cDNA demonstrated consistent replication of HCV for more than 3 years. Intracellular minus strand HCV RNA was present. Minus strand synthesis was NS5B dependent, and was sensitive to interferon alpha (IFN alpha) treatment. NS5B and HCV core protein were detectable. HCV stimulated HepG2 cell growth and survival in culture, in soft agar, and accelerated tumor growth in SCID mice. These mice became HCV RNA positive in blood, where the virus was also sensitive to IFN alpha. The RNA banded at the density of HCV, and was resistant to RNase prior to extraction. Hence, HCV stably replicates in HepG2 cells, stimulates hepatocellular growth and tumorigenesis, and is susceptible to IFN alpha both in vitro and in vivo.

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.

Activation of fibronectin gene expression by hepatitis B virus x antigen

The development of fibrosis and cirrhosis during chronic hepatitis B virus (HBV) infection correlates with the persistent expression of HBV x antigen (HBxAg), which acts in part, by stimulating selected signal transduction pathways, including nuclear factor kappa B (NF-kappa B). To identify NF-kappa B responsive genes that are differentially expressed in HBxAg-positive cells, HepG2 cells were stably transfected with HBxAg, and then with pZeoSV2 or pZeoSV2-I kappa B alpha. When RNAs from each culture were compared by PCR-select cDNA subtraction, fibronectin (FN) mRNA was shown to be strongly down-regulated by I kappa B alpha. Up-regulated expression of FN and co-expression between FN and HBxAg were observed in liver sections from HBV carriers that were stained for HBxAg and analysed for FN mRNA by in situ hybridization (ISH). In liver cell cultures, HBxAg increased the levels of FN mRNA and protein. This was because of the HBxAg-mediated trans-activation of the FN promoter, which was NF-kappa B-dependent. HBxAg also antagonized the repression of the FN promoter by the tumour suppressor, p53. Hence, the FN gene may be a natural target for HBxAg trans-activation, perhaps through activation of NF-kappa B and inactivation of p53, thereby contributing to the accumulation of FN in the liver over the course of chronic HBV infection.

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.