Hepadnaviral X Protein:Review of Recent Progress

Pathogenicity and virulence of Hepatitis B virus

Hepatitis B virus (HBV) is a hepatotropic virus and an important human pathogen. There are an estimated 296 million people in the world that are chronically infected by this virus, and many of them will develop severe liver diseases including hepatitis, cirrhosis and hepatocellular carcinoma (HCC). HBV is a small DNA virus that replicates via the reverse transcription pathway. In this review, we summarize the molecular pathways that govern the replication of HBV and its interactions with host cells. We also discuss viral and non-viral factors that are associated with HBV-induced carcinogenesis and pathogenesis, as well as the role of host immune responses in HBV persistence and liver pathogenesis.

Hepatitis B reactivation during or after direct acting antiviral therapy - implication for susceptible individuals

The FDA issued a warning following 24 cases of HBV reactivation during DAA therapy for HCV, including individuals with inactive, occult and past HBV infection. Clinical presentations ranged from asymptomatic fluctuations in HBV DNA to fulminant hepatic failure, liver transplantation and death. The mechanism is unknown. Areas covered: HCV/HBV coinfection is common, particularly in regions endemic for HBV. HCV and HBV utilize host factors to support replication; both viruses evade/impair host immunity. Clinical presentations of HBV reactivation during DAAs are summarized. Other causes of HBV reactivation are revisited and recent data regarding HBV reactivation are presented. Expert opinion: HBV reactivation during DAAs for HCV occurs, with life-threatening consequences in some individuals. The risk of HBV reactivation is observed in all HBV stages. The rapid removal of HCV likely alters and liberates host-viral ± viral-viral interactions that lead to increased HBV replication. As immune reconstitution occurs with HCV removal, host recognition of HBV DNA likely ensues followed by vigorous host immune responses leading to liver injury (HBV flare). These cases highlight the importance of HBV testing prior to initiating DAA therapy, the need for close monitoring of HBV during therapy and timely administration of anti-HBV therapy to prevent serious sequelae.

Inhibition of apoptosis by oncogenic hepatitis B virus X protein: Implications for the treatment of hepatocellular carcinoma

Hepatitis B virus X protein (HBx) plays an important role in the development of hepatocellular carcinoma (HCC). In addition, hepatoma upregulated protein (HURP) is a cellular oncogene that is upregulated in a majority of HCC cases. We highlight here recent findings demonstrating a link between HBx, HURP and anti-apoptosis effects observed in cisplatin-treated HCC cells. We observed that Hep3B cells overexpressing HBx display increased HURP mRNA and protein levels, and show resistance to cisplatin-induced apoptosis. Knockdown of HURP in HBx-expressing cells reverses this effect, and sensitizes cells to cisplatin. The anti-apoptotic effect of HBx requires activation of the p38/MAPK pathway as well as expression of SATB1, survivin and HURP. Furthermore, silencing of HURP using short-hairpin RNA promotes accumulation of p53 and reduces cell proliferation in SK-Hep-1 cells (p53^+/–), whereas these effects are not observed in p53-mutant Mahlavu cells. Similarly, HURP silencing does not affect the proliferation of H1299 lung carcinoma cells or Hep3B HCC cells which lack p53. Silencing of HURP sensitizes SK-Hep-1 cells to cisplatin. While HURP overexpression promotes p53 ubiquitination and degradation by the proteasome, HURP silencing reverses these effects. Inoculation of SK-Hep-1 cancer cells in which HURP has been silenced produces smaller tumors than control in nude mice. Besides, gankyrin, a positive regulator of the E3 ubiquitin ligase MDM2, is upregulated following HURP expression, and silencing of gankyrin reduces HURP-mediated downregulation of p53. In addition, we observed a positive correlation between HURP and gankyrin protein levels in HCC patients (r² = 0.778; n = 9). These findings suggest a role for the viral protein HBx and the host protein HURP in preventing p53-mediated apoptosis during cancer progression and establishment of chemoresistance.

Expression of B7-H4 and hepatitis B virus X in hepatitis B virus-related hepatocellular carcinoma

AIM: To investigate the expression and clinical significance of B7-H4 and hepatitis B virus X (HBx) protein in hepatitis B virus-related hepatocellular carcinoma (HBV-HCC).

METHODS: The expression of B7-H4 in the human HCC cell lines HepG2 and HepG2.2.15 were detected by western blot, flow cytometry, and immunofluorescence. The expression of B7-H4 and HBx in 83 HBV-HCC was detected by immunohistochemistry, and the relationship with clinicopathological features was analyzed. Paraffin sections were generated from 83 HBV-HCC patients (22 females and 61 males) enrolled in this study. The age of these patients ranged from 35 to 77 years, with an average of 52.5 ± 11.3 years. All experiments were approved by the Ethics Committees of the Second Affiliated Hospital, Zhejiang University School of Medicine.

RESULTS: B7-H4 was significantly upregulated in HepG2.2.15 cells compared to HepG2 cells. Specifically, the protein expression of B7-H4 in the lysates of HepG2 cells was more than that in HepG2.2.15 cells. In addition, HBx was expressed only in HepG2.2.15 cells. Similar data were obtained by flow cytometry. The positive rates of B7-H4 and HBx in the tissues of 83 HBV-HCC patients were 68.67% (57/83) and 59.04% (49/83), respectively. The expression of HBx was correlated with tumor node metastases (TNM) stage, and the expression of B7-H4 was positively correlated with HBx (r_s = 0.388; P < 0.01). The expression level of B7-H4 in HBx-positive HBV-HCC tissues was substantially higher than that in HBx-negative HBV-HCC tissues. The expression level of B7H4 was negatively related to tumor TNM stage.

CONCLUSION: Higher expression of HBx and B7-H4 was correlated with tumor progression of HBV-HCC, suggesting that B7-H4 may be involved in facilitating HBV-related hepatocarcinogenesis.

HBx interacted with Smad4 to deprive activin a growth inhibition function in hepatocyte HL7702 on CRM1 manner

Hepatitis B virus (HBV) is implicated in the pathogenesis of hepatocellular carcinoma, which has been found to be associated with TGF-beta signaling. Activin A is a TGF-β family cytokine that exhibits cell proliferation inhibition on normal hepatocyte. How HBV-encoded X oncoprotein play in activin's activity on hepatocyte has not been developed. In this study, a nontumor hepatic cell line HL7702 with HBX ectogenic expression has been established. MTT and BrdU assays showed that HBx promoted growth of HL7702 cells in vitro and downregulated activin signaling. Deregulated activin signaling pathway by HBX failed to activate target gene p21/waf1 and p15 transcription. In addition, mammalian two-hybrid and coimmunoprecipitation assays revealed that HBX could directly interact with activin signaling transduction protein Smad4, making activated Smad2/3/4 nucleus translocation suppressed. Furthermore, we detected that leptomycin B, the inhibitor of CRM1 protein, could recover nuclear translocation of endogenous Smads complex in HL7702 with HBX expression, indicating that HBX antagonized Smads nucleus translocation, at least partially, on CRM1-dependent manner. Leptomycin B was found to have antigrowth activity on HBX-expressed HL7702, according to its antitumor function in previous study. Above all, HBX antagonized activin signaling in normal human liver cells by interacting with Smad4 might one of the considerable causes of HBX-induced hepatocyte transformation, which deprived activin's cell growth inhibition function at an early stage of tumorigenesis.

Hepatitis B Virus X and Regulation of Viral Gene Expression

The efficient replication of hepatitis B virus (HBV) requires the HBV regulatory hepatitis B virus X (HBx) protein. The exact contributions of HBx are not fully understood, in part because of the limitations of the assays used for its study. When HBV replication is driven from a plasmid DNA, the contribution of HBx is modest. However, there is an absolute requirement for HBx in assays that recapitulate the infectious virus life cycle. There is much evidence that HBx can contribute directly to HBV replication by acting on viral promoters embedded within protein coding sequences. In addition, HBx may also contribute indirectly by modulating cellular pathways to benefit virus replication. Understanding the mechanism(s) of HBx action during virus replication may provide insight into novel ways to disrupt chronic HBV replication.

RPB5-Mediating Protein Suppresses Hepatitis B Virus (HBV) Transcription and Replication by Counteracting the Transcriptional Activation of Hepatitis B virus X Protein in HBV Replication Mouse Model

BACKGROUND

RPB5-Mediating protein (RMP) is associated with the RNA polymerase II subunit RPB5. This protein functionally counteracts the transcriptional activation of Hepatitis B Virus X protein (HBx) by competitively binding to the RPB5; however, the effects of RMP on Hepatitis B virus (HBV) transcription and replication remain unknown.

OBJECTIVES

The purpose of this study was to investigate the effect of RMP on viral transcription and replication in vivo by using the hydrodynamic-based HBV replication mouse model.

MATERIALS AND METHODS

Male balb/c mice were transfected with wild type (1.2 wt) or the HBx minus HBV plasmids (1.2x (-)) with or without HBx and RMP, to establish an HBV replication mouse model by hydrodynamic injection through the tail vein. The HBV RNA and HBV DNA replication intermediates (RI) were analyzed in the liver.

RESULTS

RPB5-Mediating protein could inhibit HBV transcription and replication in groups transfected with the 1.2 wt and HBx. The inhibitory effect disappeared in the 1.2x (-) groups, yet it reappeared in the groups co-transfected with 1.2x (-) and HBx. An inhibitory effect was indicated at a low dose of RMP (0.3 ug, 0.5 ug and 0.7 ug) compared to the control group and groups that had received high doses of RMP.

CONCLUSIONS

Our study demonstrated that a low dose of RMP could inhibit HBV transcription and replication, which is dependent on the appearance of HBx in vivo.

Hepatitis B and hepatitis C viruses: a review of viral genomes, viral induced host immune responses, genotypic distributions and worldwide epidemiology

Hepatitis B and hepatitis C viruses (HCV) are frequently propagating blood borne pathogens in global community. Viral hepatitis is primarily associated with severe health complications, such as liver cirrhosis, hepatocellular carcinoma, hepatic fibrosis and steatosis. A literature review was conducted on hepatitis B virus (HBV), HBV genome, genotypic distribution and global epidemiology of HBV, HCV, HCV genome, HCV and host immune responses, HCV genotypic distribution and global epidemiology. The valued information was subjected for review. HBV has strict tissue tropism to liver. The virus infecting hepatocytes produces large amount of hepatitis B surface antigen particles which lack the DNA. It has capability to integrate into host genome. It has been found that genotype C is most emerging genotype associated with more severe liver diseases (cirrhosis). The approximate prevalence rate of genotype C is 27.7% which represents a major threat to future generations. Approximately 8% of population is chronic carrier of HBV in developing countries. The chronic carrier rate of HBV is 2%-7% in Middle East, Eastern and Southern Europe, South America and Japan. Among HCV infected individuals, 15% usually have natural tendency to overcome acute viral infection, where as 85% of individuals were unable to control HCV infection. The internal ribosomal entry site contains highly conserved structures important for binding and appropriate positioning of viral genome inside the host cell. HCV infects only in 1%-10% of hepatocytes, but production of tumor necrosis factor alpha (from CD8+ cells) and interferon-gamma cause destruction of both infected cells and non-infected surrounding cells. Almost 11 genotypes and above 100 subtypes of HCV exists worldwide with different geographical distribution. Many efforts are still needed to minimize global burden of these infections. For the complete eradication of HBV (just like small pox and polio) via vaccination strategies, sincere efforts would be required from government and nongovernmental organizations.

Epigenetic regulation of MicroRNA-122 by peroxisome proliferator activated receptor-gamma and hepatitis b virus X protein in hepatocellular carcinoma cells

MicroRNA-122 (miR-122), a pivotal liver-specific miRNA, has been implicated in several liver diseases including hepatocellular carcinoma (HCC) and hepatitis C and B viral infection. This study aimed to explore epigenetic regulation of miR-122 in human HCC cells and to examine the effect of hepatitis C virus (HCV) and hepatitis B virus (HBV). We performed microRNA microarray analysis and identified miR-122 as the most up-regulated miRNA (6-fold) in human HCC cells treated with 5'aza-2'deoxycytidine (5-Aza-CdR, DNA methylation inhibitor) and 4-phenylbutyric acid (PBA, histone deacetylation inhibitor). Real-time polymerase chain reaction (PCR) analysis verified significant up-regulation of miR-122 by 5'aza and PBA in HCC cells, and to a lesser extent in primary hepatocytes. Peroxisome proliferator activated receptor-gamma (PPARγ) and retinoid X receptor alpha (RXRα) complex was found to be associated with the DR1 and DR2 consensus site in the miR-122 gene promoter which enhanced miR-122 gene transcription. 5-Aza-CdR and PBA treatment increased the association of PPARγ/RXRα, but decreased the association of its corepressors (N-CoR and SMRT), with the miR-122 DR1 and DR2 motifs. The aforementioned DNA-protein complex also contains SUV39H1, an H3K9 histone methyl transferase, which down-regulates miR-122 expression.

CONCLUSIONS

These findings establish a novel role of the PPARγ binding complex for epigenetic regulation of miR-122 in human HCC cells. Moreover, we show that hepatitis B virus X protein binds PPARγ and inhibits the transcription of miR-122, whereas hepatitis C viral particles exhibited no significant effect; these findings provide mechanistic insight into reduction of miR-122 in patients with HBV but not with HCV infection.

The DNA virus white spot syndrome virus uses an internal ribosome entry site for translation of the highly expressed nonstructural protein ICP35

Although shrimp white spot syndrome virus (WSSV) is a large double-stranded DNA virus (∼300 kbp), it expresses many polycistronic mRNAs that are likely to use internal ribosome entry site (IRES) elements for translation. A polycistronic mRNA encodes the gene of the highly expressed nonstructural protein ICP35, and here we use a dual-luciferase assay to demonstrate that this protein is translated cap independently by an IRES element located in the 5' untranslated region of icp35. A deletion analysis of this region showed that IRES activity was due to stem-loops VII and VIII. A promoterless assay, a reverse transcription-PCR together with quantitative real-time PCR analysis, and a stable stem-loop insertion upstream of the Renilla luciferase open reading frame were used, respectively, to rule out the possibility that cryptic promoter activity, abnormal splicing, or read-through was contributing to the IRES activity. In addition, a Northern blot analysis was used to confirm that only a single bicistronic mRNA was expressed. The importance of ICP35 to viral replication was demonstrated in a double-stranded RNA (dsRNA) interference knockdown experiment in which the mortality of the icp35 dsRNA group was significantly reduced. Tunicamycin was used to show that the α subunit of eukaryotic initiation factor 2 is required for icp35 IRES activity. We also found that the intercalating drug quinacrine significantly inhibited icp35 IRES activity in vitro and reduced the mortality rate and viral copy number in WSSV-challenged shrimp. Lastly, in Sf9 insect cells, we found that knockdown of the gene for the Spodoptera frugiperda 40S ribosomal protein RPS10 decreased icp35 IRES-regulated firefly luciferase activity but had no effect on cap-dependent translation.

Hepatitis B virus DNA integration in tumour tissue of a non-cirrhotic HFE-haemochromatosis patient with hepatocellular carcinoma

Co-existence of multiple causes of liver injury increases the risk of hepatocellular carcinoma (HCC) development. HCC usually develops in patients with cirrhosis although it may also occur in individuals with no or mild liver disease, in particular in cases with hepatitis B virus (HBV) infection. Here we report the case of a 43year-old man with HFE-haemochromatosis, seronegative for hepatitis B and C infections, who developed HCC in the absence of severe liver damage. Both tumoural and non-tumoural liver DNA extracts were tested by nested-PCR and primers specific for four different HBV genomic regions in order to evaluate the presence of occult HBV infection. Only X gene sequences were detected in tumour (but not in non-tumour) DNA extracts. HBV-Alu PCR showed a HBV integration involving a 5'-deleted X gene with an intact enhancer-II/basal-core promoter region. The viral-host junction sequencing revealed that this integrant was located upstream of the partitioning-defective-6-homolog-gamma gene (PARD6G) and real time-PCR quantification demonstrated that PARD6G was overexpressed in tumour compared to non-tumour liver tissues. In conclusion, the combination of HFE-haemochromatosis and occult HBV infection in this patient might have led to a sequel of cellular events that determined the development of HCC even in the absence of cirrhosis.

A comprehensive molecular interaction map for Hepatitis B virus and drug designing of a novel inhibitor for Hepatitis B X protein

Hepatitis B virus (HBV) infection is a leading source of liver diseases such as hepatitis, cirrhosis and hepatocellular carcinoma. In this study, we use computation methods in order to improve our understanding of the complex interactions that occur between molecules related to Hepatitis B virus (HBV). Due to the complexity of the disease and the numerous molecular players involved, we devised a method to construct a systemic network of interactions of the processes ongoing in patients affected by HBV. The network is based on high-throughput data, refined semi-automatically with carefully curated literature-based information. We find that some nodes in the network that prove to be topologically important, in particular HBx is also known to be important target protein used for the treatment of HBV. Therefore, HBx protein is the preferential choice for inhibition to stop the proteolytic processing. Hence, the 3D structure of HBx protein was downloaded from PDB. Ligands for the active site were designed using LIGBUILDER. The HBx protein's active site was explored to find out the critical interactions pattern for inhibitor binding using molecular docking methodology using AUTODOCK Vina. It should be noted that these predicted data should be validated using suitable assays for further consideration.

Hepatitis B and C virus hepatocarcinogenesis: lessons learned and future challenges

Worldwide, hepatocellular carcinoma (HCC) is one of the most common cancers. It is thought that 80% of hepatocellular carcinomas are linked to chronic infections with the hepatitis B (HBV) or hepatitis C (HCV) viruses. Chronic HBV and HCV infections can alter hepatocyte physiology in similar ways and may utilize similar mechanisms to influence the development of HCC. There has been significant progress towards understanding the molecular biology of HBV and HCV and identifying the cellular signal transduction pathways that are altered by HBV and HCV infections. Although the precise molecular mechanisms that link HBV and HCV infections to the development of HCC are not entirely understood, there is considerable evidence that both inflammatory responses to infections with these viruses, and associated destruction and regeneration of hepatocytes, as well as activities of HBV- or HCV-encoded proteins, contribute to hepatocyte transformation. In this review, we summarize progress in defining mechanisms that may link HBV and HCV infections to the development of HCC, discuss the challenges of directly defining the processes that underlie HBV- and HCV-associated HCC, and describe areas that remain to be explored.

Ubiquitin-independent proteasomal degradation during oncogenic viral infections

Most eukaryotic proteins destined for imminent destruction are first tagged with a chain of ubiquitin molecules and are subsequently dismantled by the proteasome. Ubiquitin-independent degradation of substrates by the proteasome, however, also occurs. The number of documented proteasome-dependent, ubiquitin-independent degradation events remains relatively small but continues to grow. Proteins involved in oncogenesis and tumor suppression make up the majority of the known cases for this type of protein destruction. Provocatively, viruses with confirmed or suspected oncogenic properties are also prominent participants in the pantheon of ubiquitin-independent proteasomal degradation events. In this review, we identify and describe examples of proteasome-dependent, ubiquitin-independent protein degradation that occur during tumor virus infections, speculate why this type of protein destruction may be preferred during oncogenesis, and argue that this uncommon type of protein turnover represents a prime target for antiviral and anticancer therapeutics.

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

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

Hepatoma cell line HepG2.2.15 demonstrates distinct biological features compared with parental HepG2

AIM: To investigate the biological features of hepatitis B virus (HBV)-transfected HepG2.2.15 cells.

METHODS: The cell ultrastructure, cell cycle and apoptosis, and the abilities of proliferation and invasion of HBV-transfected HepG2.2.15 and the parent HepG2 cells were examined by electron microscopy, flow cytometry, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and trans-well assay. Oncogenicity of the two cell lines was compared via subcutaneous injection and orthotopic injection or implantation in nude mice, and the pathological analysis of tumor formation was performed. Two cytoskeletal proteins were detected by Western blotting.

RESULTS: Compared with HepG2 cells, HepG2.2.15 cells showed organelle degeneration and filopodia disappearance under electron microscope. HepG2.2.15 cells proliferated and migrated slowly in vitro, and hardly formed tumor and lung metastasis in nude mice. Flow cytometry showed that the majority of HepG2.2.15 cells were arrested in G1 phase, and apoptosis was minor in both cell lines. Furthermore, the levels of cytoskeletal proteins F-actin and Ezrin were decreased in HepG2.2.15 cells.

CONCLUSION: HepG2.2.15 cells demonstrated a lower proliferation and invasion ability than the HepG2 cells due to HBV transfection.

Epidemiology and management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major world health problem because of the high incidence and case fatality rate. In most patients, the diagnosis of HCC is made at an advanced stage, which limits the application of curative treatments. Most HCCs develop in patients with underlying chronic liver disease. Chronic viral hepatitis B and C are the major causes of liver cirrhosis and HCC. Recent improvements in treatment of viral hepatitis and in methods for surveillance and therapy for HCC have contributed to better survival of patients with HCC. This article reviews the epidemiology, cause, prevention, clinical manifestations, surveillance, diagnosis, and treatment approach for HCC.

Cirrhosis is present in most patients with hepatitis B and hepatocellular carcinoma

BACKGROUND & AIMS

There are few data available about the prevalence or effects of cirrhosis in patients with hepatocellular carcinoma (HCC) from viral hepatitis. We compared patients with HCC and hepatitis B virus (HBV) or hepatitis C virus (HCV) infections to determine the proportions of cirrhosis in each group, virologic and tumor characteristics, and overall survival.

METHODS

This analysis included patients with HBV (n = 64) or HCV (n = 118) infection who were diagnosed with HCC at the Mayo Clinic in Rochester, Minnesota from 1994-2008; groups were matched for age and sex. The diagnosis of cirrhosis was based on histology and, if histologic information was insufficient or unavailable, clinical indicators that included ascites or varices, thrombocytopenia or splenomegaly, and radiographic configuration of cirrhosis. Virologic characteristics, tumor stage, and patient survival were also assessed.

RESULTS

The prevalence of histologic cirrhosis was 88% among patients with HBV infection and 93% among those with HCV infection (P = .46). When the most inclusive criteria for cirrhosis were applied, cirrhosis was present in 94% of patients with HBV and 97% with HCV (P = .24). Among HCV patients, 5.2% were negative for HCV RNA after antiviral treatment; 63.4% of HBV patients had HBV DNA <2000 IU/mL with or without treatment. Patients with HBV tended to have less surveillance and more advanced stages of HCC, without differences in survival from those with HCV infection (P = .75).

CONCLUSIONS

Most patients with HCC and chronic viral hepatitis had evidence of cirrhosis, including those with HBV infection and those without active viral replication.

Hepatitis B virus X protein prevents apoptosis of hepatocellular carcinoma cells by upregulating SATB1 and HURP expression

Protein X from hepatitis B virus (HBV) appears to play a critical role in the development of hepatocellular carcinoma (HCC). The hepatoma upregulated protein (HURP) is also upregulated in a majority of HCC cases, therefore suggesting that HURP represents an oncogene. In this study, we describe a link between the viral protein HBx, HURP, and the establishment of cisplatin chemoresistance in HCC cells. Hep3B cells which express HBx displayed increased levels of HURP mRNA and protein, and showed resistance to cisplatin-induced apoptosis. Knockdown of HURP in HBx-expressing cells reversed this effect and sensitized Hep3B cells to cisplatin. Interestingly, SATB1, a global gene regulator which is often overexpressed in malignant breast cancer, was also induced following expression of HBx. The anti-apoptotic effect of HBx was shown to require activation of the p38/MAPK pathway in Hep3B cells. In addition, the expression of survivin, an anti-apoptotic protein, was also upregulated by HBx in an HURP-dependent manner. Taken together, these results indicate that HBx activates the expression of HURP via the p38/MAPK pathway and the SATB1 protein, culminating with the accumulation of the anti-apoptotic protein survivin. Our findings illustrate the role of the viral protein HBx in preventing apoptosis during cancer progression and establishment of chemoresistance.

Molecular biology of the hepatitis B virus and role of the X gene

The hepatitis B virus (HBV) is a widespread human pathogen and a major health problem in many countries. Molecular cloning and sequencing of the viral DNA genome has demonstrated a small and compact structure organized into four overlapping reading frames that encode the viral proteins. Besides structural proteins of the core and the envelope, HBV encodes a DNA polymerase with reverse transcriptase activity, a secreted antigen of unknown function, and a transcriptional activator that is essential for viral replication. Major steps of the viral life cycle have been unraveled, including transcription of all viral RNAs from nuclear covalently closed circular DNA (cccDNA), followed by encapsidation of pregenomic RNA, a more-than-genome length transcript, and reverse transcription of pregenomic RNA leading to asymmetric synthesis of the DNA strands. Although HBV has been recognized as a human tumor virus, no direct transforming activity could be evidenced in different cellular and animal models. However, the transcriptional regulatory protein HBx encoded by the X gene is endowed with weak oncogenic activity. HBx harbors pleiotropic activities and plays a major role in HBV pathogenesis and in liver carcinogenesis.

Mechanisms of HBV-related hepatocarcinogenesis

The hepatitis B virus (HBV) is a small enveloped DNA virus, which primarily infects hepatocytes and causes acute and persistent liver disease. Epidemiological studies have provided overwhelming evidence for a causal role of chronic HBV infection in the development of hepatocellular carcinoma, but the molecular mechanisms underlying virally-induced tumourigenesis remain largely debated. In the absence of a dominant oncogene encoded by the HBV genome, indirect roles have been proposed, including insertional activation of cellular cancer-related genes by HBV DNA integration, induction of genetic instability by viral integration or by the regulatory protein HBx, and long-term effects of viral proteins in enhancing immune-mediated liver disease. Recent genetic studies indicate that HBV-related tumours display a distinctive profile with a high rate of chromosomal alterations and low frequency of beta-catenin mutations. This review will discuss the evidence implicating chronic HBV infection as a causal risk factor of primary liver cancer. It will also discuss the molecular mechanisms that are critical for the tumourigenic process due to long lasting infection with HBV.

Hepatitis B viral X protein alters the biological features and expressions of DNA repair enzymes in LO2 cells

OBJECTIVES

This study aimed at examining the effects of hepatitis B viral X protein (HBx) on the biological features and the expression of DNA repair enzymes in non-tumour human hepatic LO2 cells in vitro.

METHODS

The HBx gene was transfected into LO2 cells to establish stably HBx-expressing LO2/HBx cells. The morphological features, cell growth, cell cycle, apoptosis and colony formation of LO2/HBx cells, vector-transfected LO2/pcDNA3.1 cells and unmanipulated LO2 cells were studied. The expressions of DNA repair enzymes and DNA oxidative stress-related 8-hydroxydeoxyguanosine (8-OHdG) were determined by a real-time quantitative polymerase chain reaction assay and high-performance liquid chromatography coupled with electrochemical detection respectively.

RESULTS

In comparison with controls, significant morphological changes, faster growth, higher frequency of cells at the S phase, but lower at G0/G1 and M/G2 phases, a lower frequency of natural cell apoptosis and a higher percentage of colony formation were observed in the LO2/HBx cells. Furthermore, significantly higher levels of intracellular 8-OHdG and lower levels of human DNA glycosylase alpha (hMYHalpha) mRNA transcripts, but no significant change in human 8-oxoguanine DNA glycosylase 1 (hOGG1), were detected in the LO2/HBx cells.

CONCLUSIONS

Our data indicated that HBx promoted growth and malignant transformation of non-tumour hepatic LO2 cells in vitro, which was associated with the downregulation of hMYHalpha expression and accumulation of mutagenic DNA adduct 8-OHdG.

p53 Promotes proteasome-dependent degradation of oncogenic protein HBx by transcription of MDM2

Hepatitis B virus X protein (HBx) is closely involved in the development of hepatocellular carcinoma (HCC). Tumor suppressor p53 was reported to induce HBx degradation and repress its oncogenic function recently, but the molecular mechanism is unknown. In this study, we attempted to identify the underlying mechanism. We found that overexpression of p53 protein reduces the level of HBx protein and shortens its half-life, however, in MDM2 knock out cells, p53 has no effects on degradation of HBx, meanwhile, overexpression of MDM2 in absence of p53 can accelerate turnover of HBx protein. These indicate that p53-mediated HBx degradation is MDM2-dependent. MDM2 interacts with HBx in vitro and in vivo but does not promote its ubiquitination. In consistent with the results above, HCC tissue samples with wild-type p53 hardly detect HBx protein, whereas, HBx always accumulate in the tissues with mutant p53. Our data provide a possible mechanism on how p53 regulate HBx stability and also a new clue for the study of p53 mutation and HCC development.

The HCV ARFP/F/core+1 protein: production and functional analysis of an unconventional viral product

Hepatitis C virus (HCV) is an enveloped positive-strand RNA virus of the Flaviviridae family. It has a genome of about 9,600 nucleotides encoding a large polyprotein (about 3,000 amino acids) that is processed by cellular and viral proteases into at least 10 structural and nonstructural viral proteins. A novel HCV protein has also been identified by our laboratory and others. This protein--known as ARFP (alternative reading frame protein), F (for frameshift) or core+1 (to indicate the position) protein--is synthesized by an open reading frame overlapping the core gene at nucleotide +1 (core+1 ORF). However, almost 10 years after its discovery, we still know little of the biological role of the ARFP/F/core+1 protein. Abolishing core+1 protein production has no affect on HCV replication in cell culture or uPA-SCID mice, suggesting that core+1 protein is probably not important for the HCV reproductive cycle. However, the detection of specific anti-core+1 antibodies and T-cell responses in HCV-infected patients, as reported by many independent laboratories, provides strong evidence that this protein is produced in vivo. Furthermore, analyses of the HCV sequences isolated from patients with hepatocellular carcinoma and in vitro studies have provided strong preliminary evidence to suggest that core+1 protein plays a role in advanced liver disease and liver cancer. The available in vitro data also suggest that certain core function proteins may depend on production of the core+1 protein. We describe here the discovery of the various forms of the core+1 protein and what is currently known about the mechanisms of their production and their biochemical and functional properties. We also provide a detailed summary of the results of patient-based research.

Hepatitis B virus X gene is implicated in liver carcinogenesis

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

Human oncogenic viruses: hepatitis B and hepatitis C viruses and their role in hepatocarcinogenesis

Chronic infections caused by hepatitis B virus (HBV) and/or hepatitis C virus (HCV) are the main risk factors for the development of hepatocellular carcinoma (HCC) in humans. Both viruses cause a wide spectrum of clinical manifestations ranging from healthy carrier state to acute and chronic hepatitis, liver cirrhosis, and HCC. HBV and HCV belong to different viral families (Hepadnoviridae and Flaviviridae, respectively); they are characterized by different genetic structures. Clinical manifestations of these viral infections result from the interaction between these viruses and host hepatocytes (i.e. between viral and cell genomes). Proteins encoded by both viruses play an important role in processes responsible for immortalization and transformation of these cells. Chronic inflammation determined by host immune response to the viral infection, hepatocyte death and their compensatory proliferation, as well as modulation of expression of some regulatory proteins of the cell (growth factors, cytokines, etc.) are the processes that play the major role in liver cancer induced by HBV and HCV.

Application of a novel, rapid, and sensitive oligonucleotide ligation assay for detection of cancer-predicting mutations in the precore and basal core promoter of hepatitis B virus

Hepatocellular carcinoma (HCC) and cirrhosis are important causes of mortality worldwide. Persistent hepatitis B virus (HBV) infection is a major cause of these diseases. Double mutations in the basal core promoter (BCP) (A1762T and G1764A) and precore (pre-C) (G1896A) regions of the virus are associated with progression to HCC. The current study is aimed at developing a simple method for screening and detecting BCP and pre-C mutations in HBV carriers. We have developed and validated an oligonucleotide ligation assay (OLA) to detect point mutations in the HBV core gene. We have applied OLA methods to samples from HBV-infected carriers recruited from the Gambia Liver Cancer Study (GLCS) comprising asymptomatic HBsAg carriers, patients with cirrhosis, and patients with HCC. We observed an 89.3% and 95.8% concordance between the OLA and DNA sequencing for BCP and pre-C mutations, respectively. OLA detected the mutations in single-strain infections and in infections with mixtures of wild-type and mutant viruses under conditions where sequencing detected only the single dominant strains. BCP mutations were detected in 75.7% of patients with advanced liver disease (cirrhosis/HCC) compared to 47.6% of asymptomatic carriers, while pre-C mutations were detected in 34.5% of advanced liver disease patients and in 47.6% of asymptomatic HBsAg carriers. There was a significant association between the presence of BCP mutations and advanced liver disease. In conclusion, OLA is a simple, economical, and reliable assay for detection of pre-C and BCP mutations. Its application can lead to improvement in diagnosis and clinical care in regions where HBV is endemic.

Viruses associated with human cancer

It is estimated that viral infections contribute to 15-20% of all human cancers. As obligatory intracellular parasites, viruses encode proteins that reprogram host cellular signaling pathways that control proliferation, differentiation, cell death, genomic integrity, and recognition by the immune system. These cellular processes are governed by complex and redundant regulatory networks and are surveyed by sentinel mechanisms that ensure that aberrant cells are removed from the proliferative pool. Given that the genome size of a virus is highly restricted to ensure packaging within an infectious structure, viruses must target cellular regulatory nodes with limited redundancy and need to inactivate surveillance mechanisms that would normally recognize and extinguish such abnormal cells. In many cases, key proteins in these same regulatory networks are subject to mutation in non-virally associated diseases and cancers. Oncogenic viruses have thus served as important experimental models to identify and molecularly investigate such cellular networks. These include the discovery of oncogenes and tumor suppressors, identification of regulatory networks that are critical for maintenance of genomic integrity, and processes that govern immune surveillance.

siRNA pool targeting different sites of human hepatitis B surface antigen efficiently inhibits HBV infection

The main objective was to determine whether a pool of small interfering RNAs (siRNAs) targeting different regions of hepatitis B virus surface antigen (HBsAg) efficiently inhibits hepatitis B virus (HBV) infection. siRNAs targeting different regions of HBsAg were transfected into HBV-producing HepG2.2.15 cells and at 72 h post-transfection, the culture medium was collected for ELISA to determine HBsAg, while total RNA was isolated from the cells for real-time PCR. Three siRNA sequences that efficiently inhibited HBV infection were converted into small hairpin RNAs (shRNAs) and then cloned into a single plasmid psiSTRIKE driven by a single U6 promoter. These shRNA expressing plasmids were tested for HBsAg gene silencing in HepG2.2.15 cells. A pool of siRNAs targeting HBsAg efficiently inhibited HBV replication and antigen expression when transfected into HepG2.2.15 cells, compared with the use of single siRNA. Similarly, the plasmid encoding three different shRNAs driven by a single U6 promoter was more effective in silencing HBsAg at DNA, mRNA and protein levels compared with the plasmid encoding single shRNA. No apoptotic change was observed in the cells when the plasmid was transfected at a dose of 0.5-2 microg/1 x 10(6) cells after complex formation with Lipofectamine LTX. Furthermore, transfection with siRNA or shRNA did not increase interferon-gamma (IFNs-gamma) release, suggesting no induction of IFN response. In conclusion, a pool of chemically synthesised siRNAs as well as the shRNA expression plasmid encoding multiple shRNAs targeting different regions of HBsAg showed high gene silencing in HepG2.2.15 cells.

Ubiquitin-dependent and -independent proteasomal degradation of hepatitis B virus X protein

The hepatitis B virus X protein (HBX) plays key regulatory roles in viral replication and the development of hepatocellular carcinoma. HBX is an unstable protein; its instability is attributed to rapid degradation through the ubiquitin-proteasome pathway. Here, we show that the middle and carboxyl-terminal domains of HBX, independently fused to GFP, render the recombinant proteins susceptible to proteasomal degradation, while the amino-terminal domain has little effect on the ubiquitination or stability of HBX. Mutation of any single or combination of up to five of six lysine residues, all located in the middle and carboxyl-terminal domain, did not prevent HBX from being ubiquitinated, ruling out any specific lysine as the sole site of ubiquitination. Surprisingly, HBX in which all six lysines were mutated and showed no evidence of ubiquitination, was still susceptible to proteasomal degradation. These results suggest that both ubiquitin-dependent and -independent proteasomal degradation processes are operative in HBX turnover.

Analysis of the complete hepatitis B virus genome in patients with genotype C chronic hepatitis and hepatocellular carcinoma

Hepatitis B virus (HBV) genotype C and the basic core promoter (BCP) mutations were reported to be associated with the development of hepatocellular carcinoma (HCC). In this study the full sequences of HBV genomes were analyzed in order to find the other predictors of HCC development. We determined the full sequences of HBV genomes in 24 genotype C carriers who developed HCC (HCC group) at the beginning of follow-up and at the time of HCC diagnosis, and 20 patients who did not develop HCC (non-HCC group) served as a control. The number of nucleotide and amino acid substitutions in most regions was higher in the HCC group than in the non-HCC group, and the following substitutions and deletions were found more frequently in the HCC group than in the non-HCC group: G1317A and T1341C/A/G in the X promoter region were detected in 13 and six of the HCC cases, four and none of the non-HCC cases, respectively; and pre-S2 deletion was detected in eight HCC and none of the non-HCC cases. Compared with the wild type X promoter, the mutant type X promoters, M1 (G1317A), M2 (T1341C), and M4 (T1341G) showed increases in activity of 2.3, 3.8, and 1.4 times, respectively, in HepG2 cells. Substitutions and deletion of nucleotides of the HBV genome, especially the pre-S2 deletion and G1317A and T1341C/A/G mutations may be useful markers for predicting the development of HCC.

Rac1 GTPase is activated by hepatitis B virus replication--involvement of HBX

Hepatitis B virus (HBV) is a causative agent for liver diseases including hepatocellular carcinoma. Understanding its interactions with cellular proteins is critical in the elucidation of the mechanisms of disease progression. Using a cell-based HBV replication system, we showed that HBV replication in HepG2 cells resulted in a cellular morphological changes displaying membrane rufflings and lamellipodia like structures reminiscent of cells expressing constitutively activated Rac1. We also showed that activated Rac1 resulted in increased viral replication. HBV replication specifically activated wild type Rac1, but not Cdc42. The Rac1 activation by HBV replication also resulted in the phosphorylation of ERK1/2 and AKT, the downstream targets of Rac1 signaling cascade. The smallest HBV viral protein, HBX, was able to activate the endogenous Rac1 and induce membrane ruffling when transfected into cells. Significantly, HBX was found to directly interact with a Rac1 nucleotide exchange factor (betaPIX) through a SH3 binding motif. Taken together, we have shown the interaction of HBV with the Rho GTPase, affecting cell morphology through the Rac1 activation pathway. HBV may possibly make use of an activated Rac1 signaling pathway for increased replication and resultant metastatic effects.

Expression studies of the core+1 protein of the hepatitis C virus 1a in mammalian cells. The influence of the core protein and proteasomes on the intracellular levels of core+1

Recent studies have suggested the existence of a novel protein of hepatitis C virus (HCV) encoded by an ORF overlapping the core gene in the +1 frame (core+1 ORF). Two alternative translation mechanisms have been proposed for expression of the core+1 ORF of HCV-1a in cultured cells; a frameshift mechanism within codons 8-11, yielding a protein known as core+1/F, and/or translation initiation from internal codons in the core+1 ORF, yielding a shorter protein known as core+1/S. To date, the main evidence for the expression of this protein in vivo has been the specific humoral and cellular immune responses against the protein in HCV-infected patients, inasmuch as its detection in biopsies or the HCV infectious system remains elusive. In this study, we characterized the expression properties of the HCV-1a core+1 protein in mammalian cells in order to identify conditions that facilitate its detection. We showed that core+1/S is a very unstable protein, and that expression of the core protein in addition to proteosome activity can downregulate its intracellular levels. Also, we showed that in the Huh-7/T7 cytoplasmic expression system the core+1 ORF from the HCV-1 isolate supports the synthesis of both the core+1/S and core+1/F proteins. Finally, immunofluorescence and subcellular fractionation analyses indicated that core+1/S and core+1/F are cytoplasmic proteins with partial endoplasmic reticulum distribution in interphase cells, whereas in dividing cells they also localize to the microtubules of the mitotic spindle.

Enhancement of gene transactivation activity of androgen receptor by hepatitis B virus X protein

Hepatitis B virus (HBV) X protein (HBx) is a regulatory protein that is required for efficient replication of HBV in its natural host. In this report, we demonstrate by co-immunoprecipitation experiments that HBx can physically bind to the androgen receptor (AR), which is a nuclear hormone receptor that is expressed in many different tissues including the liver. This observation is further supported by confocal microscopy, which reveals that HBx can alter the subcellular localization of the AR both in the presence and in the absence of dihydrotestosterone (DHT). Further studies indicate that HBx can enhance the gene transactivation activity of AR by enhancing its DNA binding activity in a DHT-dependent manner. However, HBx does not remain associated with AR on the DNA. As AR can regulate the expression of a number of cellular genes, our results raise the possibility that HBV pathogenesis may be mediated in part via the interaction between HBx and AR.

Id-1 induces proteasome-dependent degradation of the HBX protein

Id-1 is a member of the HLH protein family that regulates a wide range of cellular processes such as cell proliferation, apoptosis, senescence and overexpression of Id-1 was recently suggested to play roles in the development and progression of different cancers. Previously, Id-1 was shown to physically interact with the viral protein E1A. Meanwhile, Id-1 expression was found to be regulated by several of the virus-encoded proteins, suggesting that Id-1 may be a common cellular target of the viral proteins. Here, we report that Id-1 interacts with the Hepatitis-B virus (HBV)-encoded protein HBX and regulates its stability in hepatocellular carcinoma (HCC) cells. We found that in HCC cells, ectopic Id-1 expression significantly decreased the half-life of the HBX protein, indicating that HBX is destabilized by Id-1. Meanwhile, the Id-1-induced HBX degradation was found to be inhibited by treatment with proteasome inhibitor, suggesting that this process is mediated through the proteasome pathway. Interestingly, while Id-1 did not induce HBX-ubiquitination, we found that removal of all the lysine residues of the HBX protein protects it from the effect of Id-1, indicating that ubiquitination is still required for the Id-1-mediated HBX degradation. Meanwhile, we found that Id-1 binds to the proteasome subunit C8 and facilitates its interaction with the HBX protein and disruption of this interaction completely abolishes the negative effect of Id-1 on HBX protein stability. Taken together, our results demonstrated a novel function of Id-1 in regulating HBX protein stability through interaction with the proteasome.

Hepatitis B virus X protein stimulates the mitochondrial translocation of Raf-1 via oxidative stress

The human hepatitis B virus (HBV) X protein (HBx) plays a crucial role(s) in the viral life cycle and contributes to the onset of hepatocellular carcinoma (HCC). HBx caused the mitochondrial translocation of Raf-1 kinase either alone or in the context of whole-viral-genome transfections. Mitochondrial translocation of Raf-1 is mediated by HBx-induced oxidative stress and was dependent upon the phosphorylation of Raf-1 at the serine338/339 and Y340/341 residues by p21-activated protein kinase 1 and Src kinase, respectively. These studies provide an insight into the mechanisms by which HBV induces intracellular events relevant to liver disease pathogenesis, including HCC.

The interaction of hepatitis B virus X protein and protein phosphatase type 2 Calpha and its effect on IL-6

HBx has been suggested as an important determinant mediating the pathological effects of HBV via interacting with various cellular proteins. To identify new HBx-interacting proteins and elucidate a possible mechanism associated with HBx and HBx-interacting proteins in hepatocellular carcinoma, yeast two-hybrid screening was performed. We identified a novel HBx-interacting protein, serine/threonine protein phosphatase PP2Calpha, and investigated the effects of PP2Calpha on HBx-mediated IL-6 regulation. The interaction between endogenous PP2Calpha, and HBx was confirmed by co-immunoprecipitation. Recombinant HBx dose-dependently reduced enzyme activity of recombinant PP2Calphain vitro. While ectopically expressed PP2Calpha in Cos-7 and Huh-7 cells reduced the expression of IL-6, overexpressed HBx with recombinant HBx-expressing adenovirus overcame PP2Calpha-mediated IL-6 downregulation. In the response of IL-6, HBx phosphorylated STAT3 and recovered PP2Calpha-mediated dephosphorylation of STAT3. These results supported that HBx might play a crucial role in HBV-associated hepatocarcinogenesis even in cases where cells express a negative regulator, PP2Calpha.

Differential effects on apoptosis induction in hepatocyte lines by stable expression of hepatitis B virus X protein

AIM: Hepatitis B virus protein X (HBx) has been shown to be weakly oncogenic in vitro. The transforming activities of HBx have been linked with the inhibition of several functions of the tumor suppressor p53. We have studied whether HBx may have different effects on p53 depending on the cell type.

METHODS: We used the human hepatoma cell line HepG2 and the immortalized murine hepatocyte line AML12 and analyzed stably transfected clones which expressed physiological amounts of HBx. P53 was induced by UV irradiation.

RESULTS: The p53 induction by UV irradiation was unaffected by stable expression of HBx. However, the expression of the cyclin kinase inhibitor p21^waf/cip/sdi which gets activated by p53 was affected in the HBx transformed cell line AML12-HBx9, but not in HepG2. In AML-HBx9 cells, p21^waf/cip/sdi-protein expression and p21^waf/cip/sdi transcription were deregulated. Furthermore, the process of apoptosis was affected in opposite ways in the two cell lines investigated. While stable expression of HBx enhanced apoptosis induced by UV irradiation in HepG2-cells, apoptosis was decreased in HBx transformed AML12-HBx9. P53 repressed transcription from the HBV enhancer I, when expressed from expression vectors or after induction of endogenous p53 by UV irradiation. Repression by endogenous p53 was partially reversible by stably expressed HBx in both cell lines.

CONCLUSION: Stable expression of HBx leads to deregulation of apoptosis induced by UV irradiation depending on the cell line used. In an immortalized hepatocyte line HBx acted anti-apoptotic whereas expression in a carcinoma derived hepatocyte line HBx enhanced apoptosis.

Functional switch of viral protein HBx on cell apoptosis, transformation, and tumorigenesis in association with oncoprotein Ras

The X protein (HBx) of hepatitis B virus (HBV) plays important roles in hepatitis, cirrhosis, and hepatocellular carcinoma (HCC) during viral infection. In this study, we demonstrated that co-transfection of mouse embryo fibroblasts (STO) with HBx and activated Ras triggered apoptotic cell death, while HBx or activated Ras individually failed to induce apoptosis. In addition, STO cells were able to form colonies on soft agar after transfected with HBx or Ras, and cells co-transfected with both genes failed to transform. Moreover, nude mice injected with STO cells carrying either HBx or Ras could develop tumor, but tumor growth was inhibited by the injection of both STO cells harboring HBx and carrying Ras. These results suggested that HBx plays a role as a tumor inducer and stimulates neoplastic transformation of normal cells, but shifts its function to the induction of apoptosis in association with Ras.

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.

Sequence-specific cleavage of hepatitis X RNA in cis and trans by novel monotarget and multitarget hammerhead motif-containing ribozymes

We constructed two monoribozymes and a diribozyme against the conserved region of the X RNA of hepatitis B virus (HBV). All the ribozymes (Rzs) possessed sequence-specific cleavage activities under standard and simulated physiologic conditions. Specific cleavage was also obtained when the same Rzs were placed in cis configuration with respect to X gene in multiple combinations. Rz-expressing cells were able to specifically interfere with the functional expression of X RNA and protein production in a liver-specific cell line HepG2. Potential applications of these novel Rzs are discussed.

Pathogenesis of hepatitis B virus-related hepatocellular carcinoma: old and new paradigms

Chronic infection with the hepatitis B virus (HBV) is a major risk factor for development of hepatocellular carcinoma (HCC). The pathogenesis of cancer in HBV infection has been extensively analyzed, and multiple factors appear to play a role. A major factor is chronic inflammation and the effects of cytokines in the development of fibrosis and liver cell proliferation. Also important is the role of integration of HBV DNA into host cellular DNA, which, in some situations, acts to disrupt or promote expression of cellular genes that are important in cell growth and differentiation. In addition, expression of HBV proteins may have a direct effect on cellular functions, and some of these gene products can favor malignant transformation. Several HBV genes have been found in infected tissues more frequently than others, including truncated pre-S2/S, hepatitis B X gene, and a novel spliced transcript of HBV, referred to as the hepatitis B spliced protein. The proteins expressed from these integrated genes have been shown to have intracellular activities that may account for their association with HCC, including effects on cellular growth and apoptosis. Finally, some patients with HCC have no detectable hepatitis B surface antigen in serum but do have low levels of HBV DNA in serum and integrated molecules of HBV DNA in tissue. Occult HBV infection may account for a proportion of cases of HCC that occur in patients without serologic markers for hepatitis B and C and may be a cofactor in HCC in patients with chronic hepatitis C who have coexistent occult HBV infection.

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

Hepatocellular carcinoma (HCC) is the most important primary hepatic cancer, being a common cancer type worldwide. Many aetiological factors have been related with HCC development, such as cirrhosis, hepatitis viruses and alcohol. Chronic infection with hepatitis B (HBV) and C viruses (HCV) often results in cirrhosis and enhances the probability of developing HCC. The underlying mechanisms that lead to malignant transformation of infected cells, however, remain unclear. HBV is a DNA virus that integrates into the host genome, and this integration is believed, in part, to be carcinogenic. Besides, the virus encodes a 17 kDa protein, HBx, which is known to be a causative agent in the formation of HCC. On the contrary, HCV is a RNA virus that does not integrate into the host genome but likely induces HCC through host protein interactions or via the inflammatory response to the virus. Products encoded in the HCV genome interfere with and disturb intracellular signal transduction. Some HCV proteins, such as the core protein, NS3 and NS5A, have seen to have a regulatory effect on cellular promoters, to interact with a number of cellular proteins, and to be involved in programmed-cell death modulation under certain conditions. The identification of these proteins functions in HCC development and the subsequent development of strategies to inhibit protein-protein interactions may be the first step towards reducing the chronicity and/or of the carcinogenicity of these two viruses.