Natural variants of hepatitis B virus X protein have differential effects on the expression of cyclin-dependent kinase inhibitor p21 gene

Hepatitis B Virus X Protein Induces Reactive Oxygen Species Generation via Activation of p53 in Human Hepatoma Cells

Hepatitis B virus (HBV), particularly through the HBx protein, induces oxidative stress during liver infections. This study reveals that HBx increases reactive oxygen species (ROS) via two distinct mechanisms. The first mechanism is p53-independent, likely involving mitochondrial dysfunction, as demonstrated by elevated ROS levels in p53-deficient Hep3B cells and p53-knocked-down HepG2 cells after HBx expression or HBV infection. The increase in ROS persisted even when p53 transcriptional activity was inhibited by pifithrin-α (PFT-α), a p53 inhibitor. The second mechanism is p53-dependent, wherein HBx activates p53, which then amplifies ROS production through a feedback loop involving ROS and p53. The ability of HBx to elevate ROS levels was higher in HepG2 than in Hep3B cells. Knocking down p53 in HepG2 cells lowered ROS levels, while ectopic p53 expression in Hep3B cells raised ROS. HBx-activated p53 downregulated catalase and upregulated manganese-dependent superoxide dismutase, contributing to ROS amplification. The transcriptional activity of p53 was crucial for these effects, as cells with a p53 R175H mutation or those treated with PFT-α generated less ROS. Additionally, HBx variants with Ser-101 increased p53 and ROS levels, whereas variants with Pro-101 did not. These dual mechanisms of HBx-induced ROS generation are likely significant in the pathogenesis of HBV and may contribute to liver diseases, including hepatocellular carcinoma.

Reactive Oxygen Species Induction by Hepatitis B Virus: Implications for Viral Replication in p53-Positive Human Hepatoma Cells

Hepatitis B virus (HBV) infects approximately 300 million people worldwide, causing chronic infections. The HBV X protein (HBx) is crucial for viral replication and induces reactive oxygen species (ROS), leading to cellular damage. This study explores the relationship between HBx-induced ROS, p53 activation, and HBV replication. Using HepG2 and Hep3B cell lines that express the HBV receptor NTCP, we compared ROS generation and HBV replication relative to p53 status. Results indicated that HBV infection significantly increased ROS levels in p53-positive HepG2-NTCP cells compared to p53-deficient Hep3B-NTCP cells. Knockdown of p53 reduced ROS levels and enhanced HBV replication in HepG2-NTCP cells, whereas p53 overexpression increased ROS and inhibited HBV replication in Hep3B-NTCP cells. The ROS scavenger N-acetyl-L-cysteine (NAC) reversed these effects. The study also found that ROS-induced degradation of the HBx is mediated by the E3 ligase Siah-1, which is activated by p53. Mutations in p53 or inhibition of its transcriptional activity prevented ROS-mediated HBx degradation and HBV inhibition. These findings reveal a p53-dependent negative feedback loop where HBx-induced ROS increases p53 levels, leading to Siah-1-mediated HBx degradation and HBV replication inhibition. This study offers insights into the molecular mechanisms of HBV replication and identifies potential therapeutic targets involving ROS and p53 pathways.

All-trans retinoic acid downregulates HBx levels via E6-associated protein-mediated proteasomal degradation to suppress hepatitis B virus replication

All-trans retinoic acid (ATRA), recognized as the principal and most biologically potent metabolite of vitamin A, has been identified for its inhibitory effects on hepatitis B virus (HBV) replication. Nevertheless, the underlying mechanism remains elusive. The present study reveals that ATRA induces E6-associated protein (E6AP)-mediated proteasomal degradation of HBx to suppress HBV replication in human hepatoma cells in a p53-dependent pathway. For this effect, ATRA induced promoter hypomethylation of E6AP in the presence of HBx, which resulted in the upregulation of E6AP levels in HepG2 but not in Hep3B cells, emphasizing the p53-dependent nature of this effect. As a consequence, ATRA augmented the interaction between E6AP and HBx, resulting in substantial ubiquitination of HBx and consequent reduction in HBx protein levels in both the HBx overexpression system and the in vitro HBV replication model. Additionally, the knockdown of E6AP under ATRA treatment reduced the interaction between HBx and E6AP and decreased the ubiquitin-dependent proteasomal degradation of HBx, which prompted a recovery of HBV replication in the presence of ATRA, as confirmed by increased levels of intracellular HBV proteins and secreted HBV levels. This study not only contributes to the understanding of the complex interactions between ATRA, p53, E6AP, and HBx but also provides an academic basis for the clinical employment of ATRA in the treatment of HBV infection.

Hydrogen Peroxide Inhibits Hepatitis B Virus Replication by Downregulating HBx Levels via Siah-1-Mediated Proteasomal Degradation in Human Hepatoma Cells

The hepatitis B virus (HBV) is constantly exposed to significant oxidative stress characterized by elevated levels of reactive oxygen species (ROS), such as H2O2, during infection in hepatocytes of patients. In this study, we demonstrated that H2O2 inhibits HBV replication in a p53-dependent fashion in human hepatoma cell lines expressing sodium taurocholate cotransporting polypeptide. Interestingly, H2O2 failed to inhibit the replication of an HBV X protein (HBx)-null HBV mutant, but this defect was successfully complemented by ectopic expression of HBx. Additionally, H2O2 upregulated p53 levels, leading to increased expression of seven in absentia homolog 1 (Siah-1) levels. Siah-1, an E3 ligase, induced the ubiquitination-dependent proteasomal degradation of HBx. The inhibitory effect of H2O2 was nearly abolished not only by treatment with a representative antioxidant, N-acetyl-L-cysteine but also by knockdown of either p53 or Siah-1 using specific short hairpin RNA, confirming the role of p53 and Siah-1 in the inhibition of HBV replication by H2O2. The present study provides insights into the mechanism that regulates HBV replication under conditions of oxidative stress in patients.

All-trans Retinoic Acid Inhibits Hepatitis B Virus Replication by Downregulating HBx Levels via Siah-1-Mediated Proteasomal Degradation

All-trans retinoic acid (ATRA), the most biologically active metabolite of vitamin A, is known to abolish the potential of HBx to downregulate the levels of p14, p16, and p21 and to stimulate cell growth during hepatitis B virus (HBV) infection, contributing to its chemopreventive and therapeutic effects against HBV-associated hepatocellular carcinoma. Here, we demonstrated that ATRA antagonizes HBx to inhibit HBV replication. For this effect, ATRA individually or in combination with HBx upregulated p53 levels, resulting in upregulation of seven in absentia homolog 1 (Siah-1) levels. Siah-1, an E3 ligase, induces ubiquitination and proteasomal degradation of HBx in the presence of ATRA. The ability of ATRA to induce Siah-1-mediated HBx degradation and the subsequent inhibition of HBV replication was proven in an in vitro HBV replication model. The effects of ATRA became invalid when either p53 or Siah-1 was knocked down by a specific shRNA, providing direct evidence for the role of p53 and Siah-1 in the negative regulation of HBV replication by ATRA.

Hepatitis B Virus X Protein Stimulates Hepatitis C Virus (HCV) Replication by Protecting HCV Core Protein from E6AP-Mediated Proteasomal Degradation

Most clinical and experimental studies have suggested that hepatitis C virus (HCV) is dominant over hepatitis B virus (HBV) during coinfection, although the underlying mechanism remains unclear. In this study, we found that the HBV X protein (HBx) upregulates the levels of the HCV core protein to stimulate HCV replication during coinfection in human hepatoma cells. For this purpose, HBx upregulated both the protein levels and enzyme activities of cellular DNA methyltransferase 1 (DNMT1) and DNMT3b, and this subsequently reduced the expression levels of the E6-associated protein (E6AP), an E3 ligase of the HCV core protein, via DNA methylation. The ubiquitin-dependent proteasomal degradation of the HCV core protein was severely impaired in the presence of HBx, whereas this effect was not observed when E6AP was either ectopically expressed or restored by treatment with 5-aza-2'dC or DNMT1 knockdown. The effect of HBx on the HCV core protein was accurately reproduced in HBV/HCV coinfection systems, which were established by either monoinfection by HCV in Huh7D cells transfected with a 1.2-mer HBV replicon or coinfection by HBV and HCV in Huh7D-Na+-taurocholate cotransporting polypeptide cells, providing evidence for the stimulation of HCV replication by HBx. The present study may provide insights into understanding HCV dominance during HBV/HCV coinfection in patients. IMPORTANCE Hepatitis B virus (HBV) and hepatitis C virus (HCV) are major human pathogens that cause a substantial proportion of liver diseases worldwide. As the two hepatotropic viruses have the same modes of transmission, coinfection is often observed, especially in areas and populations where HBV is endemic. High-risk populations include people who inject drugs. Both clinical and experimental studies have shown that HCV is more dominant than HBV during coinfection, but the underlying mechanism remains unclear. In this study, we show that HBV X protein (HBx) stimulates HCV replication by inhibiting the expression of E6-associated protein (E6AP) via DNA methylation, thereby protecting the HCV core protein from proteasomal degradation, which can contribute to HCV dominance during HBV/HCV coinfection.

Tumor Suppressor p53 Inhibits Hepatitis B Virus Replication by Downregulating HBx via E6AP-Mediated Proteasomal Degradation in Human Hepatocellular Carcinoma Cell Lines

HBx, a multifunctional regulatory protein, plays an essential role in the replication and pathogenesis of the hepatitis B virus (HBV). In this study, we found that in human hepatoma cells, the tumor suppressor p53 downregulates HBx via ubiquitin-dependent proteasomal degradation. p53 transcriptional activity that results from HBV infection was not essential for this effect. This was shown by treatment with a potent p53 inhibitor, pifithrin-α. Instead, we found that p53 facilitated the binding of E6-associated protein (E6AP), which is an E3 ligase, to HBx and induced E6AP-mediated HBx ubiquitination in a ternary complex of p53, E6AP, and HBx. The ability of p53 to induce E6AP-mediated downregulation of HBx and inhibit HBV replication was demonstrated in an in vitro HBV infection system. This study may provide insights into the regulation of HBx and HBV replication, especially with respect to p53 status, which may also help in understanding HBV-associated tumorigenesis in patients.

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 C virus core protein inhibits hepatitis B virus replication by downregulating HBx levels via Siah-1-mediated proteasomal degradation during coinfection

Most clinical and experimental studies have suggested that hepatitis C virus (HCV) is dominant over hepatitis B virus (HBV) during coinfection, although the mechanism remains unclear. Here, we found that HCV core protein inhibits HBV replication by downregulating HBx levels during coinfection in human hepatoma cells. For this effect, HCV core protein increased reactive oxygen species levels in the mitochondria and activated the ataxia telangiectasia mutated-checkpoint kinase two pathway in the nucleus, resulting in an upregulation of p53 levels. Accordingly, HCV core protein induced p53-dependent activation of seven in absentia homolog one expression, an E3 ligase of HBx, resulting in the ubiquitination and proteasomal degradation of HBx. The effect of the HCV core protein on HBx levels was accurately reproduced in both a 1.2-mer HBV replicon and in vitro HBV infection systems, providing evidence for the inhibition of HBV replication by HCV core protein. The present study may provide insights into the mechanism of HCV dominance in HBV- and HCV-coinfected patients.

Proteasomal activator 28 gamma stabilizes hepatitis B virus X protein by competitively inhibiting the Siah-1-mediated proteasomal degradation

Proteasomal activator 28 gamma (PA28γ) upregulates the levels of HBx, a regulatory protein of hepatitis B virus (HBV) to stimulate HBV replication; however, the detailed mechanism remains unknown. Here, we found that PA28γ impaired the ability of seven in absentia homolog 1 (Siah-1) as an E3 ubiquitin ligase of HBx. PA28γ competitively inhibited the binding of Siah-1 to HBx in human hepatoma cells. Accordingly, PA28γ increased the stability of HBx and decreased HBx ubiquitination, abolishing the potential of Siah-1 to downregulate HBx levels. PA28γ also executed its role as an antagonist of Siah-1 during HBV replication, as demonstrated by an in vitro HBV replication system. The present study may provide insights into the mechanisms underlying the regulation of HBV replication.

Hepatitis B virus X protein stimulates cell growth by downregulating p16 levels via PA28γ-mediated proteasomal degradation

Proteasomal activator 28 gamma (PA28γ), an essential constituent of the 20S proteasome responsible for ubiquitin-independent degradation of target proteins, is frequently overexpressed in hepatocellular carcinoma. Recently, we have reported that hepatitis B virus (HBV) X protein (HBx) activates PA28γ expression in human hepatocytes via upregulation of p53 levels; however, its role in HBV tumorigenesis remains unknown. Here, we found that HBx-activated PA28γ downregulates p16 levels via ubiquitin-independent proteasomal degradation. As a result, HBx activated the Rb-E2F pathway and stimulated G₁/S cell cycle progression, resulting in an increase in cell proliferation. The potential of HBx to induce these effects was reproduced in a 1.2-mer HBV replicon and in in vitro HBV infection systems and was almost completely abolished by either PA28γ knockdown or p16 overexpression, demonstrating the critical role of the PA28γ-mediated p16 degradation in HBV tumorigenesis.

Mechanisms of Hepatitis B Virus-Induced Hepatocarcinogenesis

Hepatitis B virus (HBV) is a major cause of hepatocellular carcinoma (HCC). There are approximately 250 million people in the world that are chronically infected by this virus, resulting in nearly 1 million deaths every year. Many of these patients die from severe liver diseases, including HCC. HBV may induce HCC through the induction of chronic liver inflammation, which can cause oxidative stress and DNA damage. However, many studies also indicated that HBV could induce HCC via the alteration of hepatocellular physiology that may involve genetic and epigenetic changes of the host DNA, the alteration of cellular signaling pathways, and the inhibition of DNA repair mechanisms. This alteration of cellular physiology can lead to the accumulation of DNA damages and the promotion of cell cycles and predispose hepatocytes to oncogenic transformation.

Cyclin-dependent kinases and CDK inhibitors in virus-associated cancers

The role of several risk factors, such as pollution, consumption of alcohol, age, sex and obesity in cancer progression is undeniable. Human malignancies are mainly characterized by deregulation of cyclin-dependent kinases (CDK) and cyclin inhibitor kinases (CIK) activities. Viruses express some onco-proteins which could interfere with CDK and CIKs function, and induce some signals to replicate their genome into host's cells. By reviewing some studies about the function of CDK and CIKs in cells infected with oncoviruses, such as HPV, HTLV, HERV, EBV, KSHV, HBV and HCV, we reviewed the mechanisms of different onco-proteins which could deregulate the cell cycle proteins.

Acute hepatitis B virus infection model within the host incorporating immune cells and cytokine responses

We formulate and analyze a within-host hepatitis B viral mathematical model for hepatitis B in the acute phase of infection. The model incorporates hepatocytes, hepatitis B virus, immune system cells and cytokine dynamics using a system of ordinary differential equations. We use the model to demonstrate the trends of the hepatitis B infection qualitatively without the effects of immune cells and cytokines. Using these trends, we tested the effects of incorporating the immune cells only and immune cells with cytokine responses at low and high inhibitions on the hepatitis B virus infection. Our results showed that it is impossible to have the immune cells work independently from cytokines when there is an acute hepatitis B virus infection. Therefore, our results suggest that incorporating immune cells and cytokine dynamics in the acute hepatitis B virus infection stage delays infection in the hepatocytes and excluding such dynamics speeds up infection during this phase. Results from this study are useful in developing strategies for control of hepatocellular carcinoma which is caused by hepatitis B virus infection.

HBx natural variants containing Ser-101 instead of Pro-101 evade ubiquitin-dependent proteasomal degradation by activating proteasomal activator 28 gamma expression

Proteasomal activator 28 gamma (PA28γ) is frequently overexpressed in hepatocellular carcinoma; however, its underlying mechanism and role in hepatitis B virus (HBV) replication are largely unknown. Here, we found that HBV X protein (HBx) natural variants containing Ser-101 instead of Pro-101 increase reactive oxygen species levels in the mitochondria and activate the ataxia telangiectasia mutated/checkpoint kinase 2 pathway in the nucleus, resulting in the phosphorylation of p53 at Ser-15 and Ser-20 and the subsequent upregulation of its protein levels. Therefore, HBx variants containing Ser-101 induced p53-dependent activation of PA28γ expression in human hepatoma cells. The elevated PA28γ levels upregulated HBx levels through the inhibition of seven in absentia homologue 1-dependent proteasomal degradation. The self-amplifying ability of HBx variants containing Ser-101 via a positive feedback loop involving p53 and PA28γ was accurately reproduced in both a 1.2-mer HBV replicon and in vitro HBV infection systems, which also provided evidence for the stimulation of HBV replication by these HBx variants. In conclusion, the ability of HBx to upregulate PA28γ levels via p53 activation, in a Ser-101-dependent pathway, is critical for the stimulation of HBV replication.

Hepatitis B Virus X Protein Stimulates Virus Replication Via DNA Methylation of the C-1619 in Covalently Closed Circular DNA

Methylation of HBV cccDNA has been detected in vivo and in vitro; however, the mechanism and its effects on HBV replication remain unclear. HBx derived from a 1.2-mer HBV replicon upregulated protein levels and enzyme activities of DNA methyltransferase 1 (DNMT1), 3a, and 3b, resulting in methylation of the negative regulatory region (NRE) in cccDNA, while none of these effects were observed with an HBx-null mutant. The HBx-positive HBV cccDNA expressed higher levels of HBc and produced about 4-fold higher levels of HBV particles than those from the HBx-null counterpart. For these effects, HBx interrupted the action of NRE binding protein via methylation of the C-1619 within NRE, resulting in activation of the core promoter. Treatment with 5-Aza-2'dC or DNMT1 knock-down drastically impaired the ability of HBx to activate the core promoter and stimulate HBV replication in 1.2-mer HBV replicon and in vitro infection systems, indicating the positive role of HBx-mediated cccDNA methylation in HBV replication.

Molecular characterization of hepatitis B virus X gene in HIV-positive South Africans

Hepatitis B virus (HBV) infection is a major public health problem worldwide and the major cause of hepatocellular carcinoma (HCC) in South Africa. The role of HBV in HCC is not well understood, although the HBV X gene has been implicated as a critical factor. Data on the HBV X gene in HIV-positive South Africans are limited; thus, we investigated X gene variability in 24 HIV-infected treatment-naïve patients at Dr George Mukhari Academic Hospital. Quantitative and qualitative HBV DNA tests were conducted using real-time and in-house polymerase chain reaction (PCR) assays, respectively, targeting the complete HBV X gene. In-house PCR-positive samples were cloned using the P-Gem T-easy vector System II and sequenced. By phylogenetic analysis, X gene sequences were classified as subgenotype A1 (n = 15), A2 (n = 4), and D1 (n = 4), and one dual infection with subgenotypes as A1 and C. The basal core promoter mutations T1753C, A1762T, and G1764A were identified in the majority of sequences. Genotype D sequences had a 6-nucleotide insertion. In conclusion, subgenotype A1 was predominant, and a rare dual infection of HBV genotype A and C was detected. The 6-nucleotide insertion could represent a unique variant in the region and highlights the need for functional studies of HBV X gene variants, particularly from resource-limited settings.

Hepatitis B virus X protein suppresses all-trans retinoic acid-induced apoptosis in human hepatocytes by repressing p14 expression via DNA methylation

All-trans retinoic acid (ATRA), the most biologically active metabolite of vitamin A, is known to activate p14 expression via promoter hypermethylation to induce p53-dependent apoptosis in human hepatocytes. In this study, we found that the oncogenic hepatitis B virus (HBV) X protein (HBx) of HBV, derived from both overexpression and 1.2-mer replicon systems, suppresses ATRA-induced apoptosis in p53-positive human hepatocytes. For this effect, HBx upregulated both protein and enzyme activity levels of DNA methyltransferase 1, 3a and 3b, in the presence of ATRA and thereby inhibited p14 expression via promoter hypermethylation, resulting in inactivation of the p14-mouse double minute 2 pathway and subsequent downregulation of p53 levels. As a result, HBx was able to impair the potential of ATRA to activate apoptosis-related molecules, including Bax, p53-upregulated modulator of apoptosis, caspase-9, caspase-3 and poly (ADP-ribose) polymerase. In conclusion, the present study provides a new oncogenic action mechanism of HBx, namely by suppressing the anticancer potential of ATRA to induce p53-dependent apoptosis in HBV-infected hepatocytes.

Hepatitis B virus X protein activates E3 ubiquitin ligase Siah-1 to control virus propagation via a negative feedback loop

The seven in absentia homologue 1 (Siah-1) protein is an E3 ubiquitin ligase that induces ubiquitin-dependent proteasomal degradation of HBx, the principal regulatory protein of hepatitis B virus (HBV); however, its role in HBV propagation remains unknown. Here, we found that HBx upregulates Siah-1 levels in HepG2 but not in Hep3B cells, in which p53 is absent. For this effect, HBx sequentially activated ataxia telangiectasia mutated kinase and checkpoint kinase 2 via phosphorylation at the Ser-1981 and Thr-68 residues, respectively, which led to the activation of p53 via phosphorylation at the Ser-15 and Ser-20 residues. As a result, HBx was heavily ubiquitinated by Siah-1 and degraded by the ubiquitin-proteasome system in HepG2 cells, whereas this effect was marginal or undetectable in Hep3B cells. Knock-down of p53 in HepG2 cells downregulated Siah-1 levels and subsequently upregulated HBx levels, whereas ectopic p53 expression in Hep3B cells upregulated Siah-1 levels and subsequently downregulated HBx levels. In addition, Siah-1 knock-down impaired the ubiquitination and proteasomal degradation of HBx in HepG2 cells, whereas ectopic Siah-1 expression induced ubiquitin-dependent proteasomal degradation of HBx in Hep3B cells. The effects of HBx on p53 and Siah-1 were exactly reproduced in a 1.2-mer HBV replicon system, mimicking the natural course of HBV infection. In particular, Siah-1 knock-down upregulated the levels of HBx derived from the HBV replicon, resulting in an increase in HBV production. In conclusion, HBx modulates its own protein level via a negative feedback loop involving p53 and Siah-1 to control HBV propagation.

X region mutations of hepatitis B virus related to clinical severity

Chronic hepatitis B virus (HBV) infection remains a major health problem, with more than 240 million people chronically infected worldwide and potentially 650000 deaths per year due to advanced liver diseases including liver cirrhosis and hepatocellular carcinoma (HCC). HBV-X protein (HBx) contributes to the biology and pathogenesis of HBV via stimulating virus replication or altering host gene expression related to HCC. The HBV X region contains only 465 bp encoding the 16.5 kDa HBx protein, which also contains several critical cis-elements such as enhancer II, the core promoter and the microRNA-binding region. Thus, mutations in this region may affect not only the HBx open reading frame but also the overlapped cis-elements. Recently, several types of HBx mutations significantly associated with clinical severity have been described, although the functional mechanism in most of these cases remains unsolved. This review article will mainly focus on the HBx mutations proven to be significantly related to clinical severity via epidemiological studies.

Overview of hepatitis B viral replication and genetic variability

Chronic infection with hepatitis B virus (HBV) greatly increases the risk for liver cirrhosis and hepatocellular carcinoma (HCC). HBV isolates worldwide can be divided into ten genotypes. Moreover, the immune clearance phase selects for mutations in different parts of the viral genome. The outcome of HBV infection is shaped by the complex interplay of the mode of transmission, host genetic factors, viral genotype and adaptive mutations, as well as environmental factors. Core promoter mutations and mutations abolishing hepatitis B e antigen (HBeAg) expression have been implicated in acute liver failure, while genotypes B, C, subgenotype A1, core promoter mutations, preS deletions, C-terminal truncation of envelope proteins, and spliced pregenomic RNA are associated with HCC development. Our efforts to treat and prevent HBV infection are hampered by the emergence of drug resistant mutants and vaccine escape mutants. This paper provides an overview of the HBV life cycle, followed by review of HBV genotypes and mutants in terms of their biological properties and clinical significance.

Contributions of transgenic mouse studies on the research of hepatitis B virus and hepatitis C virus-induced hepatocarcinogenesis

Transgenic mouse technology has enabled the investigation of the pathogenic effects, including those on development, immunological reactions and carcinogenesis, of viral genes directly in living organism in a real-time manner. Although viral hepatocarcinogenesis comprises multiple sequences of pathological events, that is, chronic necroinflammation and the subsequent regeneration of hepatocytes that induces the accumulation of genetic alterations and hepatocellular carcinoma (HCC), the direct action of viral proteins also play significant roles. The pathogenesis of hepatitis B virus X and hepatitis C virus (HCV) core genes has been extensively studied by virtue of their functions as a transactivator and a steatosis inducer, respectively. In particular, the mechanism of steatosis in HCV infection and its possible association with HCC has been well studied using HCV core gene transgenic mouse models. Although transgenic mouse models have remarkable advantages, they are intrinsically accompanied by some drawbacks when used to study human diseases. Therefore, the results obtained from transgenic mouse studies should be carefully interpreted in the context of whether or not they are well associated with human pathogenesis.

Hepatitis B virus X protein induces epithelial-mesenchymal transition by repressing E-cadherin expression via upregulation of E12/E47

Previous reports have demonstrated that hepatitis B virus (HBV) X protein (HBx) represses E-cadherin expression to induce epithelial-mesenchymal transition (EMT), an essential component of cancer progression to more aggressive phenotypes characterized by tumour invasion, migration and metastasis; however, the underlying mechanism for this phenomenon is still unclear. In this study, we found that ectopic expression of HBx in human hepatocytes using overexpression and 1.2-mer WT HBV replicon systems upregulated levels of the transcriptional repressors E12 and E47, resulting in inactivation of the E-cadherin promoter, containing three E-box motifs, and subsequent repression of its expression. E12/E47 knockdown using a specific small interfering RNA almost completely abolished the potential of HBx to repress E-cadherin expression. HBx inhibited the ubiquitin-dependent proteasomal degradation of E12/E47 without affecting their expression at the transcriptional level. Upregulation of E12/E47 by HBx ultimately led to EMT in human hepatocytes, as demonstrated by morphological changes, altered protein levels of EMT markers, including E-cadherin, plakoglobin, fibronectin, vimentin and N-cadherin, and increased capacity for cell detachment and migration.

Hepatitis B Virus Core Promoter A1762T/G1764A (TA)/T1753A/T1768A Mutations Contribute to Hepatocarcinogenesis by Deregulating Skp2 and P53

BACKGROUND AND AIM

Hepatitis B virus core promoter (CP) mutations can increase risk of hepatocellular carcinoma. The CP region overlaps with the HBV X (HBx) gene, which has been associated with hepatocarcinogenesis. The cyclin kinase inhibitor P53 is an important regulator of cell cycle progression. We determined whether HBx mutants that result from mutations in the CP deregulate P53.

METHODS

A HBx combination (combo) mutant with changes in the CP region that corresponded to A1762T/G1764A (TA), T1753A, and T1768A was constructed and expressed in L-02 and Hep3B cells. The effects of CP mutations on expression and degradation of P53, and the effects on cell cycle progression and proliferation were analyzed.

RESULTS

The combo mutant decreased levels of P53 and increased cyclin D1 expression, accelerated P53 degradation in L-02 cells, accelerated cell cycle progression, and increased expression of S-phase kinase-associated protein 2 (Skp2) in L-02 and Hep3B cells. Silencing of Skp2 abrogated the effects of CP mutations on P53 expression. The kinetics of P53 expression correlated with changes in cell cycle distribution.

CONCLUSIONS

The HBx mutant with a combination of CP mutations can up-regulate Skp2, which then down-regulates P53 via ubiquitin-mediated proteasomal degradation, increasing the risk of hepatocellular carcinoma.

Mathematical models of the interrelated dynamics of hepatitis D and B

The hepatitis delta virus (HDV) is a rarest form of viral hepatitis, but has the worst outcomes for patients.It is a subviral satellite dependent on coinfection with hepatitis B (HBV) to replicate within the host liver.To date, there has been little to no modeling effort for HDV. Deriving and analyzing such a mathematical model poses difficulty as it requires the inclusion of (HBV). Here we begin with a well-studied HBV model from the literature and expand it to incorporate HDV. We investigate two models, one with and one without infected hepatocyte replication. Additionally, we consider treatment by the drug lamivudine. Comparison of model simulations with experimental results of lamivudine treatment indicate that infected cell proliferation may play a significant role in chronic HDV infection. Our results also shed light on several questions surrounding HDV and illustrate the need for more data.

All-trans retinoic acid induces p53-depenent apoptosis in human hepatocytes by activating p14 expression via promoter hypomethylation

All-trans retinoic acid (ATRA), the most biologically active metabolite of vitamin A, has been extensively studied for the prevention and treatment of cancer; however, the underlying mechanism of its anti-cancer potential is still unclear. Here we found that ATRA induces apoptosis in p53-positive HepG2 cells, but not in p53-negative Hep3B cells. For this effect, ATRA activated p14 expression via promoter hypomethylation, resulting in ubiquitin-dependent degradation of mouse double minute 2 (MDM2) and subsequent stabilization of p53. The potential of ATRA to stabilize p53 was almost completely abolished by knock-down of p14 in HepG2 cells and was not observed in p14-negative A549 cells. Upregulation of p14 also abolished the self-regulatory potential of p53 to repress p14 expression via DNA methylation and transcriptionally activate MDM2 expression. The accumulated p53 then activated several apoptosis-related molecules, including Bax, PUMA, caspase-9, Bid, caspase-8, caspase-3, and PARP. Ectopic expression of DNA methyltransferase 1 almost completely abolished the potential of ATRA to activate the p14-MDM2-p53 pathway and induce p53-dependent apoptosis. Therefore, we conclude that ATRA induces p14 promoter hypomethylation to trigger apoptosis.

Hepatitis B virus, HBx mutants and their role in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of death induced by cancer in the modern world and majority of the cases are related to chronic hepatitis B virus (HBV) infection. HBV-encoded X protein (HBx) is known to play a pivotal role in the pathogenesis of viral induced HCC. HBx is a multifunctional protein of 17 kDa which modulates several cellular processes by direct or indirect interaction with a repertoire of host factors resulting in HCC. HBX might interfere with several cellular processes such as oxidative stress, DNA repair, signal transduction, transcription, protein degradation, cell cycle progression and apoptosis. A number of reports have indicated that HBx is one of the most common viral ORFs that is often integrated into the host genome and its sequence variants play a crucial role in HCC. By mutational or deletion analysis it was shown that carboxy terminal of HBx has a likely role in protein-protein interactions, transcriptional transactivation, DNA repair, cell, signaling and pathogenesis of HCC. The accumulated evidence thus far suggests that it is difficult to understand the mechanistic nature of HBx associated HCC, and HBx mediated transcriptional transactivation and signaling pathways may be a major determinant. This article addresses the role of HBx in the development of HCC with particular emphasis on HBx mutants and their putative targets.

Hepatitis B virus X induces cell proliferation in the hepatocarcinogenesis via up-regulation of cytoplasmic p21 expression

BACKGROUND

Hepatitis B virus X protein (HBx) has been shown to induce hepatocarcinogenesis by disrupting the functions of intracellular molecules. Cyclin-dependent kinase inhibitor p21 (Cip1/WAF1), known as a tumour-suppressor gene, has been reported to have paradoxical function, that is, acting as an oncogene, particularly when expressed in the cytoplasm. The effects of HBx on the expression and function of p21 also remain controversial.

AIMS

We attempted to investigate the role of HBx in the hepatocarcinogenic process, focusing on the association with this paradoxical function of p21. The results obtained were further verified with experiments using the antihepatocarcinogenic action of interferon (IFN)-β.

METHODS

HBx transgenic mice (Xg) and HBx-transfected hepatoma cell lines were used. Intracellular localization of p21 was determined by Western blot analysis and immunofluorescence.

RESULTS

Xg and HBx-transfected cells exhibited increased expression of p21. Up-regulation of p21 was positively correlated with the expression of cyclin D1 and inactive phosphorylation of retinoblastoma protein (pRb). These HBx-induced cell proliferative responses were cancelled by knockdown of p21, which resulted in growth reduction in HBx-expressing cells, suggesting the oncogenic properties of HBx-induced p21. HBx induced accumulation of p21 in the cytoplasm, and activation of PKCα was involved. Finally, IFN-β-treated Xg liver, as well as hepatoma cells, showed a shift of cytoplasmic p21 to the nucleus, accompanied by the abrogation of HBx-induced oncogenic modulation.

CONCLUSIONS

Our results suggest that HBx induces hepatocarcinogenesis via PKCα-mediated overexpression of cytoplasmic p21 and IFN-β suppressed these molecular events by shifting p21 to the nucleus.

DNA methyltransferase inhibitor assay system based on the HBx-induced DNA methylation of E-cadherin

We here report a simple assay system for DNA methyltransferase (DNMT) inhibitors based on the HBx-induced DNA methylation of E-cadherin. A stable cell line named G1 was generated by co-transfecting E-cadherin luciferase reporter and HBx-expression plasmid into HepG2 cells. Treatment of G1 cells with DNMT inhibitors, 5-azacytidine, 5-aza-2'-deoxycytidine, and procainamaid, dose-dependently inhibited DNA methylation of E-cadherin promoter in the reporter, resulting in up-regulation of luciferase levels and its enzyme activity. Treatment with all-trans retinoic acid that is known to inhibit DNMT expression, also induced similar effects. Our system can be useful for development of epi-drugs targeting DNA methylation in malignancies.

Hepatitis B virus genetic variants: biological properties and clinical implications

Hepatitis B virus (HBV) causes a chronic infection in 350 million people worldwide and greatly increases the risk of liver cirrhosis and hepatocellular carcinoma. The majority of chronic HBV carriers live in Asia. HBV can be divided into eight genotypes with unique geographic distributions. Mutations accumulate during chronic infection or in response to external pressure. Because HBV is an RNA-DNA virus the emergence of drug resistance and vaccine escape mutants has become an important clinical and public health concern. Here, we provide an overview of the molecular biology of the HBV life cycle and an evaluation of the changing role of hepatitis B e antigen (HBeAg) at different stages of infection. The impact of viral genotypes and mutations/deletions in the precore, core promoter, preS, and S gene on the establishment of chronic infection, development of fulminant hepatitis and liver cancer is discussed. Because HBV is prone to mutations, the biological properties of drug-resistant and vaccine escape mutants are also explored.

Hepatitis B virus core promoter mutations contribute to hepatocarcinogenesis by deregulating SKP2 and its target, p21

BACKGROUND & AIMS

Clinical studies have associated hepatitis B virus core promoter (CP) mutations with an increased risk of hepatocellular carcinoma. The CP region overlaps with the HBV X (HBx) gene, which has been implicated in hepatocarcinogenesis. The cyclin kinase inhibitor p21WAF1/CIP1 is an important regulator of cell cycle progression and proliferation. We determined whether HBx mutants that result from mutations in the CP deregulate p21 and these processes.

METHODS

We constructed a series of HBx mutants with changes in the CP region that correspond to A1762T/G1764A (TA), T1753A, T1768A, or a combination of these (combo) and expressed them, along with wild-type HBx under control of its endogenous promoter, in primary human hepatocytes (PHHs) and HepG2 cells. We then analyzed the effects of CP mutations on expression and degradation of p21 and the effects on cell cycle progression and proliferation.

RESULTS

The combo mutant decreased levels of p21 and increased cyclin E expression in PHHs and HepG2 cells. The combo mutant, but not HBx with single or double CP mutations, accelerated p21 degradation in HepG2 cells. The combo mutant increased expression of S-phase kinase-associated protein 2 (SKP2) in PHHs and Huh7 cells. Silencing of SKP2 abrogated the effects of CP mutations on p21 expression. The kinetics of p21 expression correlated with changes in cell cycle distribution. The combo mutant accelerated cell cycle progression; p21 overexpression restored G1 arrest.

CONCLUSIONS

HBx mutants with changes that correspond to a combination of CP mutations up-regulate SKP2, which then down-regulates p21 via ubiquitin-mediated proteasomal degradation. CP mutations might increase the risk of hepatocellular carcinoma via this pathway.

Subversion of cellular autophagy machinery by hepatitis B virus for viral envelopment

Autophagy is a conserved eukaryotic mechanism that mediates the removal of long-lived cytoplasmic macromolecules and damaged organelles via a lysosomal degradative pathway. Recently, a multitude of studies have reported that viral infections may have complex interconnections with the autophagic process. The findings reported here demonstrate that hepatitis B virus (HBV) can enhance the autophagic process in hepatoma cells without promoting protein degradation by the lysosome. Mutation analysis showed that HBV small surface protein (SHBs) was required for HBV to induce autophagy. The overexpression of SHBs was sufficient to induce autophagy. Furthermore, SHBs could trigger unfolded protein responses (UPR), and the blockage of UPR signaling pathways abrogated the SHB-induced lipidation of LC3-I. Meanwhile, the role of the autophagosome in HBV replication was examined. The inhibition of autophagosome formation by the autophagy inhibitor 3-methyladenine (3-MA) or small interfering RNA duplexes targeting the genes critical for autophagosome formation (Beclin1 and ATG5 genes) markedly inhibited HBV production, and the induction of autophagy by rapamycin or starvation greatly contributed to HBV production. Furthermore, evidence was provided to suggest that the autophagy machinery was required for HBV envelopment but not for the efficiency of HBV release. Finally, SHBs partially colocalized and interacted with autophagy protein LC3. Taken together, these results suggest that the host's autophagy machinery is activated during HBV infection to enhance HBV replication.

Hepatitis B virus X protein overcomes all-trans retinoic acid-induced cellular senescence by downregulating levels of p16 and p21 via DNA methylation

Despite current molecular evidence suggesting that hepatitis B virus (HBV) X protein (HBx) plays an important role during HBV-mediated hepatocarcinogenesis, the detailed mechanism is still controversial. Here, it was shown that HBx overcomes cellular senescence provoked by all-trans retinoic acid (ATRA) in HepG2 cells, as demonstrated by the impaired induction of irreversible G(1) arrest and senescence-associated β-galactosidase activity by ATRA in the presence of HBx. The anti-senescence effect of HBx was also observed in another human hepatoma cell line, Hep3B, but not in Huh-7 cells in which the p16 and p21 proteins are absent. In addition, HBx suppressed ATRA-mediated induction of p16 and p21 in HepG2 cells via promoter hypermethylation, resulting in inactivation of retinoblastoma protein. Furthermore, the ability of HBx to overcome ATRA-induced cellular senescence almost completely disappeared when the levels of p16 and p21 in the HBx-expressing cells became similar to those in the control cells by complementation in the former by exogenous expression, knockdown of their expression in the latter using specific small interfering RNA or treatment with a DNA methylation inhibitor, 5-Aza-2'-deoxycytidine. These results suggest that HBx executes its potential by downregulating levels of p16 and p21 via DNA methylation. As cellular senescence is a tumour-suppression process, the present study provides a new strategy by which HBV promotes hepatocarcinogenesis.

Naturally occurring hepatitis B virus X deletions and insertions among Korean chronic patients

Deletions and insertions in the hepatitis B virus (HBV) X region have been associated with severe forms of liver disease, including hepatocellular carcinoma (HCC). However, the molecular epidemiologic features of this virus have been described rarely. Deletions and insertions in the X region were determined by direct sequencing in a Korean cohort of 267 patients with different clinical statuses. Deletions and insertions were observed in two sets of six patients each (2.2%, 6/267). The prevalence of deletions or insertions was significantly higher in patients with severe liver disease, HCC, or cirrhosis of the liver (7.2%, 10/132) compared to patients who were carriers or had chronic hepatitis (1.5%, 2/135) (P = 0.017). All deletions in six strains were concentrated at the C terminal end of HBx, encompassing the 113th to 154th codons. A total of four novel types of insertions (PKLL, GM, FFN, and tt) were observed in six patients. Of particular interest, all six strains with insertions were accompanied by double mutations in the basal core promoter (BCP). In conclusion, these results suggest that deletions or insertions in the X region may contribute to disease progression in Korean patients with genotype C infection.

Unique hepatitis B virus subgenotype in a primitive tribal community in eastern India

Hepatitis B virus (HBV) strains isolated from members of the primitive Paharia ethnic community of Eastern India were studied to gain insight into the genetic diversity and evolution of the virus. The Paharia tribe has remained quite separate from the rest of the Indians and differs culturally, genetically, and linguistically from the mainstream East Indian population, whose HBV strains were previously characterized. Full-length HBV DNA was PCR amplified, cloned, and sequenced. Phylogenetic relationships between the tribal sequences and reference sequences from the mainstream population were assessed, and divergence times of subgenotypes of HBV genotype D were estimated. HBV was found in 2% of the Paharias participating in the study. A predominance of hepatitis B e antigen-negative infection (73%) was observed among the Paharias, and the genome sequences of the HBV strains exhibited relative homogeneity, with a very low prevalence of mutations. The novel feature of Paharia HBV was the exclusive presence of the D5 subgenotype, which was recently identified in Eastern India. Analysis of the four open reading frames (ORFs) of these tribal HBV D5 sequences and comparison with previously reported D1 to D7 sequences enabled the identification of 27 specific amino acid residues, including 6 unique ones, that could be considered D5 signatures. The estimated divergence times among subgenotypes D1 to D5 suggest that D5 was the first to diverge and hence is the most ancient of the D subgenotypes. The presence of a specific, ancient subgenotype of HBV within an ethnically primitive, endogamous population highlights the importance of studies of HBV genetics in well-separated human populations to understand viral transmission between communities and genome evolution.

Cooperation of tumor-derived HBx mutants and p53-249(ser) mutant in regulating cell proliferation, anchorage-independent growth and aneuploidy in a telomerase-immortalized normal human hepatocyte-derived cell line

Hepatocellular carcinoma (HCC) is a common cancer, and hepatitis B virus (HBV) is a major etiological agent. Convincing epidemiological and experimental evidence also links HCC to aflatoxin, a naturally occurring mycotoxin that produces a signature p53-249(ser) mutation. Recently, we have reported that tumor-derived HBx variants encoded by HBV exhibited attenuated transactivation and proapoptotic functions but retained their ability to block p53-mediated apoptosis. These results indicate that mutations in HBx may contribute to the development of HCC. In this study, we determined whether tumor-derived HBx mutants along, or in cooperation with p53-249(ser), could alter cell proliferation and chromosome stability of normal human hepatocytes. To test this hypothesis, we established a telomerase immortalized normal human hepatocycte line HHT4 that exhibited a near diploid karyotype and expressed many hepatocyte-specific genes. We found that overexpression one of the tumor-derived HBx mutants, CT, significantly increased colony forming efficiency (CFE) while its corresponding wild-type allele CNT significantly decreased CFE in HHT4 cells. p53-249(ser) rescued CNT-mediated inhibition of colony formation. Although HHT4 cells lacked an anchorage independent growth capability as they did not form any colonies in soft agar, the CT-expressing HHT4 cells could form colonies, which could be significantly enhanced by p53-249(ser). Induction of aneuploidy could be observed in HHT4 cells expressing CT, but additionally recurring chromosome abnormalities could only be detected in cells coexpressing CT and p53-249(ser). Our results are consistent with the hypothesis that certain mutations in HBx and p53 at codon 249 may cooperate in contributing to liver carcinogenesis.

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.

Hepatitis B virus X protein overcomes the growth-inhibitory potential of retinoic acid by downregulating retinoic acid receptor-beta2 expression via DNA methylation

Aberrant promoter methylation of retinoic acid receptor-beta(2) (RAR-beta(2)) is frequently detected in hepatitis B virus (HBV)-positive hepatocellular carcinoma (HCC); however, the mechanism of methylation and its biological significance are unknown. This study showed that HBx, the principal oncogene product of HBV, induced promoter hypermethylation of RAR-beta(2) via upregulation of DNA methyltransferases 1 and 3a, resulting in downregulation of its expression in human HCC cells. In addition, HBx abolished the potential of retinoic acid (RA) to downregulate levels of G(1)-checkpoint regulators including p16, p21 and p27, resulting in activation of E2F1 in the presence of RA. As a consequence, HBx-expressing cells were less susceptible to RA-induced cell growth inhibition compared with control cells. These effects almost completely disappeared when levels of RAR-beta(2) in HBx-expressing cells were restored by treatment with a universal DNA methylation inhibitor, 5-aza-2'-deoxycytidine. As RAR-beta(2) is a major executor of the anti-tumour potential of RA, its epigenetic downregulation by HBx is likely to be an important step during HBV-mediated tumorigenesis.

Hepatitis B virus X protein overcomes stress-induced premature senescence by repressing p16(INK4a) expression via DNA methylation

Cellular senescence is an important tumor suppression process under diverse oncogenic conditions, entering a state of irreversible growth arrest to prevent damaged cells from undergoing aberrant proliferation. Developing a means of evading senescence thus seems to be a fundamental task that all cancer cells should solve early on. Here, we show that an oncogenic X protein of hepatitis B virus (HBx) overcomes cellular senescence provoked by a universal premature senescence inducer, H(2)O(2), in human hepatoma cells, as demonstrated by impaired induction of senescence-associated biomarkers, including morphological change, G(1) arrest, and beta-galactosidase activity, in the presence of HBx. HBx induced DNA hypermethylation of p16(INK4a) promoter and subsequently interfered action of transcription factors like Ets1 and Ets2 activated by H(2)O(2) through the p38(MAPK) pathway, resulting in inhibition of its transcription. Down-regulation of p16(INK4a) expression by HBx subsequently led to activation of G(1)-CDKs, phosphorylation of Rb, activation of E2F1, and finally evasion from G(1) arrest induced by H(2)O(2). Levels of another senescence regulator, p21(waf1), however, were not affected by HBx under our senescence-inducing conditions. In addition, the potentials of HBx to inactivate Rb and subsequently inhibit cellular senescence almost completely disappeared when levels of p16(INK4a) were recovered either by exogenous complementation or inhibition of the promoter hypermethylation. To our knowledge, our present study represents the first report that an oncogenic virus evades cellular senescence through epigenetic down-regulation of p16(INK4a) expression.

Rich dynamics of a hepatitis B viral infection model with logistic hepatocyte growth

Chronic hepatitis B virus (HBV) infection is a major cause of human suffering, and a number of mathematical models have examined within-host dynamics of the disease. Most previous HBV infection models have assumed that: (a) hepatocytes regenerate at a constant rate from a source outside the liver; and/or (b) the infection takes place via a mass action process. Assumption (a) contradicts experimental data showing that healthy hepatocytes proliferate at a rate that depends on current liver size relative to some equilibrium mass, while assumption (b) produces a problematic basic reproduction number. Here we replace the constant infusion of healthy hepatocytes with a logistic growth term and the mass action infection term by a standard incidence function; these modifications enrich the dynamics of a well-studied model of HBV pathogenesis. In particular, in addition to disease free and endemic steady states, the system also allows a stable periodic orbit and a steady state at the origin. Since the system is not differentiable at the origin, we use a ratio-dependent transformation to show that there is a region in parameter space where the origin is globally stable. When the basic reproduction number, R (0), is less than 1, the disease free steady state is stable. When R (0) > 1 the system can either converge to the chronic steady state, experience sustained oscillations, or approach the origin. We characterize parameter regions for all three situations, identify a Hopf and a homoclinic bifurcation point, and show how they depend on the basic reproduction number and the intrinsic growth rate of hepatocytes.

[Molecular mechanisms of hepatitis B virus-associated hepatocellular carcinoma]

Hepatocellular carcinoma (HCC) is one of the most common malignant diseases in the world. The hepatitis B virus (HBV) replicates non-cytopathically in hepatocytes, and most of the liver injury associated with this infection reflects the immune response. Epidemiological studies have clearly demonstrated that a chronic HBV infection is a major etiological factor in the development of HCC. The pathogenesis of HBV-associated HCC has been studied extensively, and the molecular changes during the malignant transformation have been identified. The main carcinogenic mechanism of HBV-associated HCC is related to the long term-inflammatory changes caused by a chronic hepatitis B infection, which might involve the integration of the HBV. Integration of the HBV DNA into the host genome occurs at the early steps of clonal tumorous expansion. The hepatitis B x protein (HBx) is a multifunctional regulatory protein that communicates directly or indirectly with a variety of host targets, and mediates many opposing cellular functions, including its function in cell cycle regulation, transcriptional regulation, signaling, encoding of the cytoskeleton and cell adhesion molecules, as well as oncogenes and tumor suppressor genes. Continued study of the mechanisms of hepatocarcinogenesis will refine our current understanding of the molecular and cellular basis for neoplastic transformations in the liver. This review summarizes the current knowledge of the mechanisms involved in HBV-associated hepatocarcinogenesis.

Analysis of hepatitis B virus X gene phylogeny, genetic variability and its impact on pathogenesis: implications in Eastern Indian HBV carriers

HBx genetic variability was explored in the Eastern Indian population with low HCC incidence. DNase I sensitive HBV DNA was detected in 53% samples, which differed significantly between clinical groups (P<0.001). HBV genotypes A (Aa/A1), C (Cs/C1) and D (D1, D2, D3, D5) were detected in 37.5%, 18.7% and 43.7% samples respectively. Population specific signature HBx residues A(36), V(88), S(101) in Aa/A1 and residues P(41), Q(110) in D5 were detected. Mutations T(127), M(130) and I(131) were detected in 66.7%, 91% and 75% of genotype A, C and D5 samples respectively. Very low occurrence of HCC associated mutations (V(5)M/L, P(38)S, and H(94)Y) and absence of C-terminal deletions were observed. Our study shows that HBV genotype associated clinically important HBx variations may evolve and act distinctly in different geo-ethnic populations. Further studies on HBx functions from the perspective of genetic variability are essential for the better understanding of the clinical significance of HBV.

Tumor-host interactions: the role of inflammation

It is well established that interactions between tumor cells and the host tissue stroma play a key role in determining whether and how any given solid malignancy will develop. In most cases, tumor cells hijack stromal cell functions for their own benefit and ultimately dictate the rules of engagement to the host tissue microenvironment. However, the contribution of the different stromal cell components to tumor growth remains to be clarified. Because most solid tumors are accompanied by a local inflammatory response, it has long been thought that inflammation and carcinogenesis are related. If formal proof that cancer can be initiated by inflammation in the absence of exogenous carcinogens is still lacking, there is abundant evidence that the inflammatory response can play a central role in modulating tumor growth and progression. This review will discuss some of the mechanisms whereby inflammation can both enhance and inhibit tumor growth.

The Molecular Diagnosis of Hepatitis B Virus-Associated Hepatocellular Carcinoma

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

Hepatitis B virus X mutations occurring naturally associated with clinical severity of liver disease among Korean patients with chronic genotype C infection

Few reports have detailed mutation frequencies and mutation patterns in the entire X region according to clinical status. The aims of this study were to elucidate the relationships between mutation patterns and their frequencies in the X region and clinical status in a Korean cohort and determine specific X mutation types, related closely with liver disease progression. All X mutations were determined by direct sequencing in 184 patients with different clinical features. Mutation rates in the X region in patients with more severe liver disease, hepatocellular carcinoma (HCC) (3.6%) or liver cirrhosis (4%) were always significantly higher than in patients with corresponding less severe forms, chronic hepatitis (2.9%) or asymptomatic carriers (2.1%), but no significant difference in mutation rates was found in terms of HBeAg serostatus. All five mutation types (V5M/L, P38S, H94Y, I127T/N, and K130M and V131I) affecting the six codons were found to be related significantly to clinical severity. Among these, two mutation types (V5M/L and K130M and V131I) were observed more frequently in HBeAg negative patients than in HBeAg positive patients. In conclusion, the results suggest that an accumulation of mutations in the X region contributes to disease progression in chronic patients, at least Korean patients with genotype C. Specific mutation types appears to be related more to severe liver diseases such as HCC or liver cirrhosis. In particular, a novel mutation type (V5M/L) discovered firstly during the present study was found to be associated significantly with HCC.

A new clade of hepatitis B virus subgenotype F1 from Peru with unusual properties

There are eight genotypes A-H of hepatitis B virus (HBV). Most genotypes are further divided into subgenotypes. Genotypes and subgenotypes influence the natural course of infection and therapy. We analysed nine sera from HBV carriers from Peru. Using the small hepatitis B surface protein HBs, all samples could be grouped to genotype F. Sequencing of three complete Peruvian genomes showed that HBV from Peru belongs to subgenotype F1. Two of the genomes from HBeAg positive carriers coded surprisingly for a stop codon in the polymerase-ORF leading to a translational stop after 213 and 214 aa, respectively. The third isolate from an HBe Ag positive carrier had three deletions: aa 1-53 and aa 111-142 in preS. In addition nt. 2002-2087 in the HBc-ORF were deleted, leading to an HBc starting at aa 66.