Hepatocellular carcinoma: role of hepatitis B and hepatitis C viruses proteins in hepatocarcinogenesis

Review article: pharmacological therapy for hepatocellular carcinoma with sorafenib and other oral agents

BACKGROUND

Hepatocellular carcinoma (HCC) is the fifth most common malignancy worldwide. Unresectable disease patients have median survival of few months. There is a substantial need for novel treatments for patients with advanced HCC.

AIM

To provide an update review of mechanism of hepatocarcinigenesis and systemic therapies for HCC and the relevant role of Sorafenib in patients with advanced disease.

METHODS

A Medline search was performed to identify pertinent original research and review articles. Selected references in these articles were also evaluated.

RESULTS

Systemic chemotherapy for HCC has been quite ineffective. Preclinical studies demonstrated that Raf/MAPK-ERK kinase (MEK)/Extracellular signal regulated kinase (ERK) pathway has a role in HCC. HCC tumours are highly vascularized and vascular endothelial growth factor (VEGF) augments HCC development and metastasis. Sorafenib blocks tumour cell proliferation by targeting Raf/MEK/ERK signalling and exerts an antiangiogenic effect by targeting VEGF receptors-2/3 and platelet derived growth factor receptor beta tyrosine kinases.

CONCLUSIONS

Currently available therapies are not effective for patients with advanced HCC. Sorafenib has demonstrated for the first time to prolong survival in patients with advanced HCC, and it is the new reference standard for systemic treatment in these patients.

Expression of p53 protein in liver and sera of patients with liver fibrosis, liver cirrhosis or hepatocellular carcinoma associated with chronic HCV infection

OBJECTIVES

Hepatitis C virus (HCV) is a major aetiological agent of chronic hepatitis and it leads to the development of liver cirrhosis and hepatocellular carcinoma (HCC). The significances of p53 protein and anti-p53 antibodies levels in HCV genotype IV infected patients with different liver pathology were evaluated.

DESIGN AND METHODS

Immunostaining and western blot based on monospecific anti-p53 antibody were used for the identification of p53 protein in liver tissues and serum samples. The serum levels of p53 protein and anti-p53 IgG antibodies were evaluated using enzyme linked immunosorbent assay (ELISA).

RESULTS

Mild and diffuse p53 cytoplasmic immunostaining was found in liver tissues of patients with liver fibrosis [F1-F3] and liver cirrhosis [F4] in comparison with strong and diffuse p53 cytoplasmic immunostaining in patients with HCC. The target p53 protein was identified in sera of patients with liver fibrosis, liver cirrhosis and HCC at 53-kDa. The detection rate of serum p53 protein increases significantly (p<0.05) with the progression of the liver pathology. However, a significant difference (p<0.05) was only shown between serum p53 protein level of HCC patients and those of other liver pathology. In contrast, anti-p53 IgG antibodies positive rates showed only a significant decrease (p<0.05) in HCC in comparison with liver cirrhosis.

CONCLUSIONS

The serum and cytoplasmic p53 protein expressions were more pronounced in patients with HCC more than liver cirrhosis, and in liver cirrhosis more than liver fibrosis. These results suggest that HCV genotype IV and p53 protein levels may have a role in the development of HCC among Egyptian patients.

Presence of hepatitis C virus DNA sequences in the DNA of infected patients

BACKGROUND

Hepatitis C virus (HCV) consists of a single positive RNA molecule. In the present study we investigated the possibility that HCV may undergo integration into the genomic DNA of infected cells.

MATERIALS AND METHODS

HCV(+) patients (n = 51) and 21 HCV(-) controls were investigated for HCV integration. RNase treated DNA samples of mononuclear cells (MNC) and liver biopsies of the patients were screened by PCR and seminested PCR processes for detection of integration. Positive results were further investigated by means of Southern analysis of patient's DNA as well as sequencing of PCR products of patient's DNA.

RESULTS

Positive PCR results were detected in 4/51 of the HCV(+) patients and in none of the control group. Southern analysis showed the presence of HCV sequence in a 23 kbp band of the patient which is much larger than the viral genome itself (9.646 kbp). Sequencing of cloned PCR products showed an identity of over 95.0% to HCV.

CONCLUSIONS

As much as we are aware this is the first demonstration of the possible integration of HCV sequences into the DNA of HCV(+) patients.

N-linked glycosylation of the liver cancer biomarker GP73

The association between elevated circulating levels of GP73 (and fucosylated GP73 in particular) and hepatocellular carcinoma suggests that a thorough analysis of the extent of GP73 glycosylation is warranted. Detailed analysis of the glycosylation patterns of such low abundance proteins are hampered by technical difficulties. Using conventional lectin affinity chromatography, we have established that three quarters of the GP73 secreted from a cell line derived from HCC is fucosylated. Using mass spectrometry, we have established that at least two of three potential sites of N-linked glycosylation are occupied on most molecules of GP73 secreted from cultured hepatoma cells. Furthermore, the oligosaccharides added to recombinant GP73 resemble those present in the bulk of secreted protein, mostly bi-antennary with core fucose, with a smaller fraction of tri- and tetra-antennary structures. The frequency of fucosylation observed on the recombinant protein agrees well with the pattern of lectin binding of the endogenous secreted protein. Finally, we have developed a method to interrogate the glycans added to either the near full length protein or at a particular sequon, providing proof of concept that a small peptide embedded in a heterologous context can preserve both fucosylation and a high level of branching of oligosaccharides added.

[Epidemiology, risk factors and molecular pathogenesis of primary liver cancer]

Primary liver cancer is the fifth most common cancer worldwide. Hepatocellular carcinoma accounts for 85-90% of primary liver cancers. Distribution of hepatocellular carcinoma shows variations among geographic regions and ethnic groups. Males have higher liver cancer rates than females. Hepatocellular carcinoma occurs within an established background of chronic liver disease and cirrhosis (70-90%). Major causes (80%) of hepatocellular carcinoma are hepatitis B, C virus infection, and aflatoxin exposition. Its development is a multistep process. We have a growing understanding on the molecular pathogenesis. Genetic and epigenetic changes activate oncogenes, inhibit tumorsuppressor genes, which result in autonomous cell proliferation. The chromosomal instability caused by telomere dysfunction, the growth-retrained environment and the alterations of the micro- and macroenvironment help the expansion of the malignant cells. Understanding the molecular mechanisms could improve the screening of patients with chronic liver disease, or cirrhosis, and the prevention as well as treatment of hepatocellular carcinoma.

Effects of hepatitis B virus X protein (HBx) on cell-growth inhibition in a CCL13-HBx stable cell line

OBJECTIVE

The known function of hepatitis B virus X protein (HBx) is to determine the fate of cells by modulating various signaling pathways. In our previous study, we demonstrated that HBx inhibits tumor formation in nude mice injected with CCL13-HBx stable cell lines; however, the mechanism underlying this inhibition is unclear.

METHODS

To investigate the possible mechanisms underlying HBx involvement in CCL13-HBx cells, gene profiles were initially analyzed by DNA microarray technology and subsequently confirmed by performing semiquantitative RT-PCR and Western blotting. Furthermore, the phenomenon of cell death via apoptosis was detected via DNA fragmentation, TUNEL staining, caspase-3 activity assay, and propidium iodide (PI) staining.

RESULTS

The results indicated that HBx induction downregulated Wnt-3 and beta-catenin that are involved in cell proliferation. Moreover, HBx induction repressed cell growth and downregulated the expressions of cyclin D1, CDK4, cyclin E, CDK2, and cyclin B1. Furthermore, HBx induction triggered cell death via apoptosis, as determined by DNA fragmentation, TUNEL staining, caspase-3 activity assay, and PI staining.

CONCLUSION

Most importantly, our results indicated that HBx induction in the CCL13-HBx stable cell line downregulated Wnt-3/beta-catenin expression and suppressed cell growth by repressing cell proliferation or triggering cell apoptosis.

Gene modulation associated with inhibition of liver regeneration in hepatitis B virus X transgenic mice

AIM: To analyze the modulation of gene expression profile associated with inhibition of liver regeneration in hepatitis B X (HBx)-expressing transgenic mice.

METHODS: Microarray technology was performed on liver tissue obtained from 4 control (LacZ) and 4 transgenic mice (HBx-LacZ), 48 h after partial hepatectomy. The significance of the normalized log-ratios was assessed for each gene, using robust t-tests under an empirical Bayes approach. Microarray hybridization data was verified on selected genes by quantitative PCR.

RESULTS: The comparison of gene expression patterns showed a consistent modulation of the expression of 26 genes, most of which are implicated in liver regeneration. Up-regulated genes included DNA repair proteins (Rad-52, MSH6) and transmembrane proteins (syndecan 4, tetraspanin), while down-regulated genes were connected to the regulation of transcription (histone deacetylase, Zfp90, MyoD1) and were involved in the cholesterol metabolic pathway and isoprenoid biosynthesis (farnesyl diphosphate synthase, Cyp7b1, geranylgeranyl diphosphate synthase, SAA3).

CONCLUSION: Our results provide a novel insight into the biological activities of HBx, implicated in the inhibition of liver regeneration.

Role of hepatitis C virus proteins (C, NS3, NS5A) in hepatic oncogenesis

In recent years, the effects of hepatitis C virus (HCV) proteins on hepatocarcinogenesis have undergone intense investigations. The potentially oncogenic proteins include at least three HCV proteins: core (C) protein, NS3, and NS5A. Several authors indicated relationships between subcellular localization, concentration, a specific molecular form of the proteins (full length, truncated, phosphorylated), the presence of specific domains (the nuclear localization signal homologous to e.g. Bcl-2) and their effects on the mechanisms linked to oncogenesis. The involvement of all the proteins has been described as being in control of the cell cycle, through interactions with key proteins of the process (p53, p21, cyclins, proliferating cell nuclear antigen), transcription factors, proto-oncogenes, growth factors/cytokines and their receptors, and proteins linked to the apoptotic process. Untilnow, the involvement of the core protein of HCV in liver carcinogenesis is the most recognized. One of the most common proteins affected by HCV proteins is the p53 tumor-suppressor protein. The p21/WAF1 gene is a major target of p53, and the effect of HCV proteins on the gene is frequently considered in parallel. The results of studies on the effects of HCV proteins on the apoptotic process are controversial. This work summarizes the information collected thus far in the field of HCV molecular virology and principal intracellular signaling pathways in which HCV oncogenic proteins are involved.

Hepatitis C virus: from oxygen free radicals to hepatocellular carcinoma

Epidemiological evidence clearly identifies chronic infection with hepatitis C virus (HCV) as a major risk factor for the development of hepatocellular carcinoma (HCC). Among the mechanisms that have been implicated in the pro-carcinogenic effect of HCV infection, an increased production of reactive oxygen species in the liver seems to have a major pathogenetic role in leading from chronic inflammation to cancer. Recent data have also demonstrated that HCV is capable of inducing this active production of free radicals per se, not just through inflammation, a feature peculiar to this virus and the specific activity of its core protein. This paper provides an overview of the inter-relationships between HCV, liver damage, free radical production and HCC, describing at least in part the complex network involving DNA oxidative damage, cytokine synthesis, proto-oncogene activation and oestrogen receptor expression, that may all be deeply involved in liver carcinogenesis.

Liver angiogenesis as a risk factor for hepatocellular carcinoma development in hepatitis C virus cirrhotic patients

AIM: To evaluate the predictive value of hepatocyte proliferation and hepatic angiogenesis for the occurrence of Hepatocellular carcinoma (HCC) in hepatitis C virus (HCV) cirrhotic patients.

METHODS: One hundred-five patients (69 males, 36 females; age range, 51-90 year; median 66 year) with biopsy proven HCV cirrhosis were prospectively monitored for HCC occurrence for a median time of 64 mo. Angiogenesis was assessed by using microvessel density (MVD), hepatocyte turnover by MIB1 and PCNA indexes at inclusion in liver biopsies.

RESULTS: Forty six patients (43.8%) developed HCC after a median time of 55 (6-120) mo while 59 (56.2%) did not. Patients were divided into two groups according to the median value of each index. The difference between patients with low (median MVD = 3; range 0-20) and high (median MVD = 7; range 1-24) MVD was statistically significant (χ² = 22.06; P < 0.0001) which was not the case for MIB1 or PCNA (MIB-1: χ² = 1.41; P = 0.2351; PCNA: χ² = 1.27; P = 0.2589). The median MVD was higher in patients who developed HCC than in those who did not. HCC-free interval was significantly longer in patients with the MVD ≤ 4 (P = 0.0006). No relationship was found between MIB₁ or PCNA and MVD (MIB-1 r² = 0.00007116, P = 0.9281; PCNA: r² = 0.001950; P = 0.6692). MVD only was able to predict the occurrence of HCC in these patients. Among other known risk factors for HCC, only male sex was statistically associated with an increased risk.

CONCLUSION: Liver angiogenesis has a role for in HCV-related liver carcinogenesis and for defining patients at higher risk.

Evolution of hepatitis C virus non-structural 5A gene in the progression of liver disease to hepatocellular carcinoma

BACKGROUND

The interaction between the hepatitis C virus (HCV) non-structural 5A (NS5A) protein of HCV and the protein kinase R (PKR), which is an effector of the cellular antiviral response and has been defined as a tumour suppressor, may affect the control of protein synthesis and cell growth.

AIM

We investigated the genetic evolution of the NS5A region in the NS5A PKR-binding domain (NS5A-PKRbd) of patients with HCV 1b-related cirrhosis who subsequently developed or not hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

The quasispecies composition of NS5A-PKRbd was inferred by sequencing an average of 15 clones per sample in specimens obtained from 26 patients with cirrhosis who developed or not HCC during a follow-up of 5 years.

RESULTS

At baseline, 13/17 patients with final HCC and six out of nine patients with cirrhosis who subsequently did not develop HCC harboured a wild-type (wt) strain master sequence. Over time, the prevalence of wt strain was higher in patients who developed HCC with respect to those who maintained the cirrhosis status (15/17 vs 4/9, respectively; P=0.0166).

CONCLUSION

The maintenance of or evolution to the wt strain of the NS5A domain in cirrhotic patients with final HCC highlights the central role of NS5A protein in the viral life cycle and in the progression of liver disease.

HIV-HBV and HIV-HCV coinfection and liver cancer development

Liver diseases caused by chronic HBV or HCV infection, including cirrhosis and HCC, are emerging as an increasingly important problem faced by millions of HIV-infected patients who are coinfected with HBV or HCV. On one hand, HIV-induced immune suppression enhances the risk of chronic viral hepatitis, increases HBV or HCV load, and may hasten the progression to cirrhosis and liver cancer. On the other hand, significant hepatotoxicity is associated with a number of antiretroviral drugs, further exacerbating liver damage associated with chronic viral hepatitis. The exact risk of HCC in HIV and HBV or HCV coinfected patients remains to be fully assessed. The elucidation of the multiple virus-virus and virus-host interactions that underlie viral hepatocarcinogenesis and potential HIV enhancement awaits the establishment of appropriate in vitro and in vivo model systems. As millions of HIV-infected patients in the developing countries are gaining access to HAART therapy for their HIV infections, endemic HBV and HCV infections and their associated liver diseases will only become more problematic on a global level. To ameliorate the suffering from HBV- and HCV-induced liver cancer in HIV patients, more effective treatment for chronic HBV and HCV infections are needed. The long time frame of viral hepatocarcinogenesis may afford a window of opportunity to develop and improve such treatment.

Association of p16INK4A hypermethylation with hepatitis B virus X protein expression in the early stage of HBV-associated hepatocarcinogenesis

The aim of the present study was to explore the relationship between methylation status of the p16(INK4A) promoter and some HBV-related factors, and the role of these factors in p16(INK4A) hypermethylation and hepatocellular carcinoma (HCC) progression. Twenty-three cases of surgically resected HBV-associated HCC and 25 fine-needle aspiration biopsy cases of chronic hepatitis B (CHB) were studied. The methylation status of the p16(INK4A) promoter was determined by methylation-specific polymerase chain reaction (PCR). Two-step immunohistochemical staining showed the expression of viral antigens in situ. Tissue HBV-DNA levels were determined by fluorescence quantitative real-time PCR. PCR and the direct sequencing method were used for mutation analysis. In peritumoral tissues (P = 0.025) and CHB samples (P = 0.029), the expression of hepatitis B virus X protein (HBx) was higher in methylated groups of p16(INK4A) promoter than in unmethylated groups. Other HBV factors including hepatitis B surface antigen and hepatitis B core antigen, tissue HBV-DNA levels and HBV x gene mutations had no relation to the methylation status of p16(INK4A) promoter. The data indicate that p16(INK4A) promoter hypermethylation correlated closely with higher HBx expression in the precancerous lesions, suggesting that HBx may play an important role in the early stage of HBV-associated hepatocarcinogenesis via induction of hypermethylation of p16(INK4A) promoter.

Tropolone and its derivatives as inhibitors of the helicase activity of hepatitis C virus nucleotide triphosphatase/helicase

In this report, we demonstrate the interaction of the non-structural protein 3 (NS3) of hepatitis C virus (HCV) with alkaloide tropolone (2-hydroxy-2,4,6-heptatriene-1-one) and its derivatives. The compounds were biochemically screened separately against the ATPase and helicase activities of HCV NS3. In the investigations presented, alkaIoide tropolone and its derivatives significantly inhibited the helicase activity of the viral protein when using a DNA substrate, with 50% inhibitory concentration values within a low micromolar range. The results using the RNA substrate were unexpected--none of the tropolone derivatives excerted any modulating influence towards the unwinding activity. Surprisingly, no influence of the nucleoside triphosphatase (NTPase) turnover was observed. Evidence is presented confirming that these compounds do not act by blocking the NTP-binding site, but by occupying an additional allosteric regulatory site. Further mechanisms of action, particularly of some of the derivatives, are discussed.

Hepatocellular Carcinoma and Non-Hodgkin's Lymphoma: The Roles of HIV, Hepatitis C Infection, and Alcohol Abuse

Purpose

To explore the relationship of HIV, hepatitis C (HCV), and alcohol abuse/dependence to risk for hepatocellular carcinoma and non-Hodgkin's lymphoma (NHL).

Patients and Methods

Male veterans (n = 14,018) with a first HIV diagnosis in the Veterans Affairs Healthcare System from October 1997 to September 2004; and 28,036 age-, race-, sex-, and location-matched HIV-negative veterans were identified. We examined the incidence of hepatocellular carcinoma and NHL and presence of HCV and alcohol abuse/dependence using International Classification of Diseases, ninth revision (ICD-9-CM) codes. HIV-positive to HIV-negative incident rate ratios (IRRs) and 95% CIs for the occurrence of hepatocellular carcinoma and NHL were calculated using Poisson regression models.

Results

HIV-positive veterans were at greater risk for hepatocellular carcinoma than HIV-negative veterans (IRR = 1.68; 95% CI, 1.02 to 2.77). After adjusting for HCV infection and alcohol abuse/dependence, HIV status was not independently associated with hepatocellular cancer (IRR = 0.96; 95% CI, 0.56 to 1.63). HIV-positive veterans had 9.71 times (95% CI, 6.99 to 13.49) greater risk of NHL than HIV-negative veterans. After adjusting for HCV and alcohol abuse/dependence, the IRR for NHL comparing HIV-positive with HIV-negative veterans is similar (IRR = 10.03, 95% CI, 7.19 to 13.97).

Conclusion

HIV-positive veterans have a higher relative incidence of hepatocellular carcinoma and NHL than HIV-negative veterans. For hepatocellular carcinoma, this association appears to be largely explained by the higher prevalence of HCV and alcohol abuse/dependence. Efforts to decrease hepatocellular carcinoma among persons with HIV should focus primarily on detecting and treating HCV and reducing heavy alcohol use.

Clinical features of hepatitis C virus-related hepatocellular carcinoma and their association with alpha-fetoprotein and protein induced by vitamin K absence or antagonist-II

PURPOSE

We investigated the differences in clinical features between alpha-fetoprotein (AFP)-predominant hepatocellular carcinoma (HCC) and protein induced by vitamin K absence or antagonist-II (PIVKA-II)-predominant HCC, especially regarding host factors thought to contribute to hepatocarcinogenesis in chronic hepatitis C virus (HCV) infection.

METHODS

HCV-related HCC patients (n=306) were divided into four groups according to median AFP (48.1 ng/ml) and PIVKA-II (60 mAU/ml). Host factors, tumor factors, survival, and risk factors affecting survival were compared.

RESULTS

Aspartate aminotransferase (AST; IU/L), alanine aminotransferase (ALT; IU/L), and platelet count (x 10(4)/ml) were, respectively, 81, 67, and 8.2 in AFP-predominant HCC (group A; n=66) vs. 50, 42, and 11.4 in PIVKA-II-predominant HCC (group P; n=52). Tumor sizes (mm) in groups A and P were 20 and 37, respectively. Significant differences were evident. Survival was identical between the two groups. Factors affecting survival were total bilirubin, portal tumor thrombus and number of nodule in group A, and albumin and tumor distribution in group P.

CONCLUSIONS

PIVKA-II-predominant HCC had a milder hepatitis and a better-preserved platelet count compared with AFP-predominant HCC. Considering the strong relation between hepatocarcinogenesis and hepatic inflammation with chronic HCV infection, these differences indicate that hepatocarcinogenic mechanisms in PIVKA-II-predominant HCC may differ from those in AFP-predominant HCC.

The role of cytokines in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a frequent malignancy worldwide with a high rate of metastasis. The hepatitis B and C viruses are considered major etiological factors associated with the development of HCC, particularly as a result of their induction of chronic inflammation. There is increasing evidence that the inflammatory process is inherently associated with many different cancer types, including HCC. Specifically, this review aims to cover evidence for the potential roles of cytokines, an important component of the immune system, in promoting HCC carcinogenesis and progression. A global summary of cytokine levels, functions, polymorphisms, and therapies with regard to HCC is presented. In particular, the role of proinflammatory Th1 and anti-inflammatory Th2 cytokine imbalances in the microenvironment of HCC patients with metastasis and the possible clinical significance of these findings are addressed. Overall, multiple studies, spanning many decades, have begun to elucidate the important role of cytokines in HCC.

State of hepatitis C viral replication enhances activation of NF-kB- and AP-1-signaling induced by hepatitis B virus X

We examined the effect of hepatitis B virus X (HBx) on NF-kB- and AP-1- mediated transcription in human hepatocellular carcinoma cell lines, Huh-7 with or without subgenomic hepatitis C virus (HCV) RNA. Expression of HBx in Huh-7 cells with HCV resulted in 4.9 times increased NF-kB-activation and 3.8 times AP-1-activation whereas that without HCV resulted in 2.4 times increased NF-kB-activation and 2.3 times AP-1-activation. Interestingly, the expression of the matured form of HCV core protein, Core173, did not activate NF-kB- or AP-1-transcription in either Huh7 with or without HCV replicon. HBx protein might play an important role in HCV-related hepatocarcinogenesis.

Prevalence of antibodies against hepatitis B virus and hepatitis C virus among blood donors in Lebanon, 1997-2003

The prevalence of hepatitis B virus (HBV) antigens (HBsAg) and antibody to hepatitis C virus (anti-HCV) was determined among 16,084 blood donors (14,993 males; mean age, 31.7 +/- 8.2 years and 1084 females; mean age, 31.4 +/- 8.2 years) in the period 1997-2003. Of the donors screened, 149 were HBsAg positive (0.926%), and 65 were anti-HCV positive (0.404%). There was a steady decline in HBsAg prevalence from 1.56% (1997) to 0.33% (2003) and in anti-HCV from 1.22% (1997) to 0.16% (2003). Females had a higher prevalence of anti-HCV (P = .031) and HBsAg (P = .047). Results obtained are of value in light of the occurrence of HBV and HCV transmission by nonparenteral routes.

Relationship between levels of DNA damage in lymphocytes and histopathological severity of chronic hepatitis C and various clinical forms of hepatitis B

BACKGROUND AND AIM

A significant proportion of cancer is attributable to DNA damage caused by chronic infection and inflammation. Because both hepatitis B and C viruses (HBV and HCV, respectively) cause chronic infection and inflammatory disease, the aim of the present study was to investigate whether there is a difference in peripheral DNA damage in patients with chronic HCV compared with patients with chronic HBV; and whether there is an association in the level of peripheral DNA damage with a natural history of HBV infection.

METHODS

Twenty patients with chronic hepatitis C, 20 patients with chronic hepatitis B, 11 patients with cirrhosis secondary to hepatitis B, 12 inactive hepatitis B s antigen (HBsAg) carriers and 21 healthy subjects were included in the study. The DNA damage in lymphocytes was determined using the alkaline comet assay.

RESULTS

Although the chronic hepatitis C group had similar levels of DNA damage compared with patients with cirrhosis due to hepatitis B (P > 0.05) and non-cirrhotic patients with chronic hepatitis B (P > 0.05), they had higher levels of DNA damage compared with inactive HBsAg carriers (P = 0.021) and controls (P = 0.001). Hepatitis B cirrhotic patients and patients with chronic hepatitis B had significantly higher levels of DNA damage than inactive HBsAg carriers (P = 0.002 and P = 0.012, respectively) and controls (both P = 0.001). Linear logistic regression analysis showed that chronic hepatitis C and HBV-related cirrhosis were discriminators in determining DNA damage in lymphocytes (beta 0.424 and P = 0.013, beta 0.393 and P = 0.016, respectively).

CONCLUSIONS

Chronic hepatitis C, based on the severity of liver disease, or cirrhosis as an advanced form of HBV infection increase DNA damage in lymphocytes independently of confounding factors such as age, gender, body mass index and smoking habits.

Construction of eukaryotic expression plasmid containing HCV NS3 segment and protein expression in human HL-7702 hepatocytes

AIM: To construct the eukaryotic expression plasmid containing HCV NS3 segment and to analyze the expression of NS3 protein in normal human hepatocyte HL-7702.

METHODS: We amplified HCV NS3 fragment from plasmid pBRTM/HCV 1-3011 containing the whole length of HCV genome, recombined it with expression vector pcDNA3.1(-) to form the eukaryotic expression vector pcDNA3.1(-)/NS3, and transfected human HL-7702 hepatocytes with the recombined plasmid by cationic polymers. The expressed HCV NS3 protein was detected and analyzed by immunohistochemical method and Western blot.

RESULTS: The amplified NS3 fragments had correct molecule weight and sequence. The successfully constructed eukaryotic expression plasmids were transfected to HL-7702 cells. The expressed NS3 proteins had correct molecular weight 70000.

CONCLUSION: Eukaryotic expression vector pcDNA3.1 (-)/NS3 containing NS3 segment of HCV can be constructed, the sequence of NS3 fragments is consistent with the template. Normal human HL-7702 hepatocytes can efficiently express specific HCV NS3 protein in vitro.

Hepatitis B virus X protein represses E-cadherin expression via activation of DNA methyltransferase 1

E-cadherin is a key cell adhesion molecule implicated as a tumor suppressor, which is frequently altered in hepatocellular carcinoma, especially in hepatitis B virus (HBV)-related tumors. Here, we report that HBV X protein (HBx) represses E-cadherin expression at the transcription level. Based on the differential effects of HBx natural variants, we determined that Lys-130 in the transactivation domain of HBx is critical for the E-cadherin repression. The repression effect of HBx was abolished after treatment with DNA methyltransferase inhibitor, 5'-Aza-2'dC. In addition, methylation-specific PCR analysis revealed that the CpG island 1 of E-cadherin promoter is hypermethylated by HBx. Furthermore, HBx induces DNA methyltransferase 1 expression by stimulating its transcription. Therefore, we conclude that HBx represses E-cadherin expression by inducing methylation-mediated promoter inactivation. The reduced E-cadherin expression results in dramatic morphological changes of the HBx-expressing cells. In addition, HBx-expressing cells aggregate poorly in suspension culture, reflecting their altered intercellular interactions. The biological significance was further demonstrated by the increased collagen invasion ability of HBx-expressing cells. Therefore, the present study suggests that HBx plays a role during hepatocellular carcinogenesis by favoring cell detachment from the surrounding cells and migration outside of the primary tumor site.

Targeting of host-cell ubiquitin pathways by viruses

The ability of viruses to co-opt cell signalling pathways has, over millions of years of co-evolution, come to pervade nearly every facet of cellular functions. Recognition of the extent to which the ubiquitin–proteasome system can be directed or subverted by viruses is relatively recent. Viral products interact with, and adjust, the ubiquitin–proteasome machinery precisely and at many levels, and they do so at distinct stages of viral life-cycles. The implications for both cells and viruses are fundamental, and understanding viral strategies in this context opens up fascinating new areas for research that span from basic cell biology to therapeutic interventions against both viruses and malignancies.

Upregulation of human telomerase reverse transcriptase mRNA expression by in vitro transfection of hepatitis B virus X gene into human hepatocarcinoma and cholangiocarcinoma cells

AIM: To study the changes of human telomerase reverse transcriptase (hTERT) mRNA expression in human hepatocarcinoma cell lines (HepG2) and cholangiocarcinoma cell lines (QBC939) after HBx gene transfection and to illustrate the significance of transcriptional regulation of hTERT gene by HBx gene in the carcinogenesis.

METHODS: HepG2 and QBC939 cell lines were cultured and co-transfected with eukaryotic expression vector containing the HBx coding region and cloning vector containing enhanced green fluorescent protein (EGFP) coding sequence using lipid-mediated gene transduction technique. Thirty-six hours after transfection, EGFP expression in cells was used as the indicator of successful transfection. Flow cytometry was performed to determine the transfection efficiency. Cells were harvested and total RNA was extracted using TRIzol^® reagent. The expression of hTERT mRNA in HepG2 and QBC939 cell lines was assayed by reverse transcription-polymerase chain reaction. The expression of HBx protein in both cell lines was detected by immunocytochemical staining and Western blotting.

RESULTS: Flow cytometry showed that the transfection efficiency was 46.4% in HepG2 cells and 29.6% in QBC939 cells for both HBx gene expression vector and blank vector. The expression of hTERT mRNA was meaningfully increased in HepG2 and QBC939 cell lines when transfected with HBx gene expression vector compared to those transfected with OPTI-MEM medium and blank vector. Immunocytochemical staining and Western blotting revealed HBx protein expression in HepG2 and QBC939 cells only when transfected with HBx gene.

CONCLUSION: HBx gene transfection can upregulate the transcriptional expression of hTERT mRNA. The transactiv-ation of hTERT gene by HBx gene is a newfound mechanism for pathogenesis of hepatocarcinomas and cholangioca-rcinomas after HBV infection.

Is the liver an important site for the development of immune tolerance to tumours?

Despite the enormous interest in the field of tumour immunology, and the development of vaccine based strategies for immunotherapy of tumours, results in patients with cancer have been disappointing. This is partly due to the lack of development of clearly defined anti-tumour immune responses. The basis for the induction of specific anti-tumour non-responsiveness is not known. Recently, the liver has been recognised as an important organ in the regulation of peripheral immunological responses. It is characterised by a remarkable ability to induce tolerance to antigens from a variety of sources. Oral tolerance to food antigens, antigens from gut flora and other antigens administered via the oral route is partly dependent upon local immunoregulation in the liver. Transplantation of liver tissue shows a remarkable ability to induce tolerance in some species, not only to liver tissue but also to other organs and tissues transplanted at the same time. This tolerance can be transferred by adoptive transfer of lymphocytes. It has been suggested that the establishment of persistent infection in the liver by hepatitis viruses, may partly depend on the tolerogenic environment of the liver, and that this may also play a role in the development of hepatocellular carcinoma in patients with chronic infections with these viruses. The liver is also a common and an important site for the development of metastases from many primary tumours. This is partly dependent upon the anatomic location and structure of the liver, but may also partly reflect the exploitation of the tolerogenic environment in the liver, allowing micrometastases to colonise and grow. This may account for the fact that the liver is such a common site for metastasis. Furthermore, once tolerance to tumour antigens is established in the liver, tolerated lymphocytes may migrate from the liver back to primary tumours and exacerbate immunological non-responsiveness at tumour sites. Indeed, if this happens early in tumour development, liver dependent tolerance to tumour antigens may play a significant role in tumour progression, and may partly determine impaired tumour responses in vaccine based immunotherapy strategies.

Plk4 haploinsufficiency causes mitotic infidelity and carcinogenesis

The polo-like kinase Plk4 (also called Sak) is required for late mitotic progression, cell survival and postgastrulation embryonic development. Here we identified a phenotype resulting from Plk4 haploinsufficiency in Plk4 heterozygous cells and mice. Plk4+/- embryonic fibroblasts had increased centrosomal amplification, multipolar spindle formation and aneuploidy compared with wild-type cells. The incidence of spontaneous liver and lung cancers was approximately 15 times high in elderly Plk4+/- mice than in Plk4+/+ littermates. Using the in vivo model of partial hepatectomy to induce synchronous cell cycle entry, we determined that the precise regulation of cyclins D1, E and B1 and of Cdk1 was impaired in Plk4+/- regenerating liver, and p53 activation and p21 and BubR1 expression were suppressed. These defects were associated with progressive cell cycle delays, increased spindle irregularities and accelerated hepatocellular carcinogenesis in Plk4+/- mice. Loss of heterozygosity occurs frequently (approximately 60%) at polymorphic markers adjacent to the PLK4 locus in human hepatoma. Reduced Plk4 gene dosage increases the probability of mitotic errors and cancer development.

Screening and identification of target genes differentially expressed in HepG2 cells treated with arsenic trioxide by suppression subtractive hybridization technique

AIM: To clone and identify human genes differentially expressed in human hepatocarcinoma HepG2 cells treated with arsenic trioxide by constructing a subtractive cDNA library with suppression subtractive hybridization (SSH) technique, and to elucidate the molecular mechanism of arsenic trioxide in the regulation of liver cells.

METHODS: The mRNA was isolated from HepG2 cells treated with arsenic trioxide and PBS, respectively, and then cDNA was synthesized. After digestion of restriction enzyme RsaI, small sizes cDNA were obtained. Then the tester cDNA was subdivided into two portions and each was ligated with a different cDNA adaptor. After the tester cDNA was hybridized with driver cDNA (twice) and underwent nested polymerase chain reaction (PCR) (twice), the DNA fragment was subcloned into T/A plasmid vectors to establish the subtractive cDNA library. Amplification of the library was performed in E. coli strain JM109. The amplified cDNA was sequenced and analyzed in GenBank with BLAST search after colony PCR.

RESULTS: The subtractive cDNA library of genes differentially expressed in HepG2 cells treated with arsenic trioxide was constructed successfully. The amplified library contained 109 positive clones. Colony PCR showed that these clones all contained 200-1 000 bp inserts. Thirty-six clones were analyzed by sequencing and bioinformatics. The results showed there were 15 coding sequences with known function and 6 novel ones with unknown function.

CONCLUSION: A subtractive cDNA library of genes differentially expressed in HepG2 cells treated with arsenic trioxide was constructed successfully using SSH technique.

In vivo hierarchy of immunodominant and subdominant HLA-A*0201-restricted T-cell epitopes of HBx antigen of hepatitis B virus

A polyepitopic CD8+ T-cell response is critical for the control of hepatitis B virus (HBV) infection. The HBV X protein (HBx) is a multifunctional protein that is important for the viral life cycle and for host-virus interactions. The aim of this study was to analyze the immunogenicity and dominance of various HLA-A*0201-restricted HBx-derived epitopes. For this purpose, we immunized HLA-A*0201-transgenic mice with HBx-derived peptides and DNA. This is a powerful model for studying the induction of HLA-A*0201-restricted immune responses in vivo, as these mice possess a cytotoxic T lymphocyte (CTL) repertoire representative of HLA-A2.1 individuals. We used cytotoxic tests and enzyme-linked immunosorbent spot (ELISPOT) assays to study the induction of specific cytotoxic and interferon (IFN)-gamma-secreting T cells. This allowed us to classify the HBx epitopes according to their T-cell activation capacity. After endogenous processing of the antigen synthesized in vivo after DNA-based immunization, we found that the HBx-specific T-cell response is targeted against one immunodominant epitope. Furthermore, following peptide immunization, we identified six additional novel subdominant T-cell epitopes. Inclusion of well-characterized epitopic sequences of HBx in a new vaccine for chronic HBV infections could help to broaden the T-cell response.