Molecular functions and biological roles of hepatitis B virus x protein

Hepatitis B virus X protein specially regulates the sialyl lewis a synthesis among glycosylation events for metastasis

Background

The metastasis of hematogenous cancer cells is associated with abnormal glycosylation such as sialyl lewis antigens. Although the hepatitis B virus X protein (HBx) plays important role in liver disease, the precise function of HBx on aberrant glycosylation for metastasis remains unclear.

Methods

The human hepatocellular carcinoma tissues, HBx transgenic mice and HBx-transfected cells were used to check the correlation of expressions between HBx and Sialyl lewis antigen for cancer metastasis. To investigate whether expression levels of glycosyltransferases induced in HBx-transfected cells are specifically associated with sialyl lewis A (SLA) synthesis, which enhances metastasis by interaction of liver cancer cells with endothelial cells, ShRNA and siRNAs targeting specific glycosyltransferases were used.

Results

HBx expression in liver cancer region of HCC is associated with the specific synthesis of SLA. Furthermore, the SLA was specifically induced both in liver tissues from HBx-transgenic mice and in in vitro HBx-transfected cells. HBx increased transcription levels and activities of α2-3 sialyltransferases (ST3Gal III), α1-3/4 fucosyltransferases III and VII (FUT III and VII) genes, which were specific for SLA synthesis, allowing dramatic cell-cell adhesion for metastatic potential. Interestingly, HBx specifically induced expression of N-acetylglucosamine-β1-3 galactosyltransferase V (β1-3GalT 5) gene associated with the initial synthesis of sialyl lewis A, but not β1-4GalT I. The β1-3GalT 5 shRNA suppressed SLA expression by HBx, blocking the adhesion of HBx-transfected cells to the endothelial cells. Moreover, β1-3GalT 5 silencing suppressed lung metastasis of HBx-transfected cells in in vivo lung metastasis system.

Conclusion

HBx targets the specific glycosyltransferases for the SLA synthesis and this process regulates hematogenous cancer cell adhesion to endothelial cells for cancer metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-222) contains supplementary material, which is available to authorized users.

Sorafenib overcomes the chemoresistance in HBx-expressing hepatocellular carcinoma cells through down-regulation of HBx protein stability and suppresses HBV gene expression

Previous studies have revealed that HBx expression has anti-apoptotic effects, resulting in increased drug resistance in HCC cells. Thus, we examined if sorafenib efficiently induces apoptosis in HBx-overexpressing HCC cells. Noticeably, sorafenib efficiently induced apoptosis, even in HBx-expressing HepG2 cells, indicating that the HBx protein does not attenuate sorafenib-induced apoptosis. We next investigated if sorafenib modulates autophagy, allowing HCC cells to overcome the chemoresistance conferred by the HBx protein. Although autophagy plays a cytoprotective role against sorafenib-induced lethality, sorafenib was effective irrespective of HBx protein overexpression. We next examined if sorafenib exerts its cytotoxic effect via direct effects on the HBx protein. Importantly, sorafenib decreased HBx protein stability through a proteasome-dependent degradation pathway. Moreover, sorafenib decreased HBV gene expression and viral promoter activity. Taken together, sorafenib efficiently induces apoptotic cell death in HBx-expressing HCC cells via the downregulation of the HBx protein, a key factor in the anti-cancer drug resistance observed in HBV-induced HCC.

Key elements of the RNAi pathway are regulated by hepatitis B virus replication and HBx acts as a viral suppressor of RNA silencing

The host-mediated RNAi pathways restrict replication of viruses in plant, invertebrate and vertebrate systems. However, comparatively little is known about the interplay between RNAi and various viral infections in mammalian hosts. We show in the present study that the siRNA-mediated silencing of Drosha, Dicer and Ago2 [argonaute RISC (RNA-induced silencing complex) catalytic component 2] transcripts in Huh7 cells resulted in elevated levels of HBV (hepatitis B virus)-specific RNAs and, conversely, we observed a decrease in mRNA and protein levels of same RNAi components in HepG2 cells infected with HBV. Similar reductions were also detectable in CHB (chronic hepatitis B) patients. Analysis of CHB liver biopsy samples, with high serum HBV DNA load (>log108 IU/ml), revealed a reduced mRNA and protein levels of Drosha, Dicer and Ago2. The low expression levels of key RNAi pathway components in CHB patient samples as well as hepatic cells established a link between HBV replication and RNAi components. The HBV proteins were also examined for RSS (RNA-silencing suppressor) properties. Using GFP-based reversion of silencing assays, in the present study we found that HBx is an RSS protein. Through a series of deletions and substitution mutants, we found that the full-length HBx protein is required for optimum RSS activity. The in vitro dicing assays revealed that the HBx protein inhibited the human Dicer-mediated processing of dsRNAs into siRNAs. Together, our results suggest that the HBx protein might function as RSS to manipulate host RNAi defence, in particular by abrogating the function of Dicer. The present study may have implications in the development of newer strategies to combat HBV infection.

Hidden secret in hepatitis B viral X protein mutation and hypoxia-inducible factor-1α in hepatocarcinoma cancer

Hepatitis B type virus (HBV) is an old hepato oncogenic and hepatitis agent. Hepatitis B viral X protein (HBx)-induced malignant transformation requires the excess amounts of ATP level, inducing the extremely oxygen-deprived condition in the cancer tissues and vessels. To adapt, cells go to shift the hypoxic responsive state by altered hypoxia-responsive molecules such as HIF-1. In addition, tumors avoid or suppress immune recognition in the energy-deprived condition. The hypoxia-inducible factor-1α (HIF-1α) regulates MAP1, histone deacetylase and MAPK pathway. In the hypoxia, the HIF-1α interacts with HIF-1β, allowing DNA binding at the hypoxia response elements (HREs), while HBx binds with the nHLH/PAS domain of HIF-1α, preventing pVHL and HIF-1α binding capacity and degradation of HIF-1α protein. Recent work of Liu et al. [2013] demonstrated that HBx in hepatocellular carcinoma (HCC) tissues contained mutations, affecting the HBx transactivation capacity and C-terminal HBx mutation. In the HCC tissues, the HBx C-terminal mutation and HIF-1α expression were related and the different C-terminal mutations of HBx exhibit the different functionality of HIF-1α. The C-terminal region of amino acids 119-140 was important for the stability and transactivation, and the point mutations K130M/V131I enhance the functionality of HIF-1α, while C-terminal truncation diminish the HIF-1α function.

MicroRNAs as therapeutic strategy for hepatitis B virus-associated hepatocellular carcinoma: Current status and future prospects

Hepatocellular carcinoma (HCC) remains to be one of the top causing cancer-related deaths today. The majority of HCC cases are reported to be the result of chronic hepatitis B virus (HBV) infection. Current treatments for HBV-related HCC revolve around the use of drugs to inhibit viral replication, as a high level of viral load and antigen in circulation often presents a poor patient prognosis. However, existing therapies are inefficient in the complete eradication of HBV, often resulting in tumour recurrence. The involvement of microRNAs (miRNAs) in important processes in HBV-related HCC makes it an important player in the progression of HCC in chronic hepatitis B infected patients. In this review, we discuss the key aspects of HBV infection and the important viral products that may regulate cancer-related processes via their interaction with miRNAs or their closely related protein machinery. Conversely, we also look at how miRNAs may go about regulating the virus, especially in vital processes like viral replication. Apart from miRNAs acting as either oncogenes or tumour-suppressors, we also look at how miRNAs may function as biomarkers that may possibly serve as better candidates than those currently employed in the diagnosis of HBV infection or HBV-related HCC. A summary of the roles of miRNAs in HBV-related HCC will hopefully lead to a gain in understanding of the pathogenesis process and pave the way for new insights in medical therapy.

Peroxisome-localized hepatitis Bx protein increases the invasion property of hepatocellular carcinoma cells

HBx acts as a multifunctional regulator that modulates various cellular responses, which can lead to development and progression of hepatocellular carcinoma (HCC). Here, we show that the HBx protein is also localized to peroxisomes, and this increases cellular reactive oxygen species (ROS) to levels that are higher than when HBx is localized to other organelles. The elevated ROS strongly activated nuclear factor (NF)-κB. In addition, the peroxisome-localized HBx increased the expressions of matrix metalloproteinases and decreased the expression of E-cadherin, which increased the invasive ability of HCC cells. Thus, a specific distribution of HBx to peroxisomes may contribute to HCC progression by increasing the invasive ability of HCC cells through elevation of the cellular ROS level.

Potential mutations associated with occult hepatitis B virus status

CONTEXT

Occult hepatitis B virus (HBV) status (OHBS) is simply defined as the presence of HBV DNA in the liver (with or without detectable HBV DNA in the serum), in the absence of serum HBV surface antigen (HBsAg). Importance of OHBS is mostly clinical, related to its possible role in spreading through blood transfusion and liver transplantation; causing classic forms of HBV. Mechanisms underlying this entity are poorly defined. Several possibilities have been suggested, with major classification into two groups: defective host immune response and viral replication activity through mutations of HBV DNA sequence. Mutations are extensively investigated in all four overlapping open reading frames (ORFs) of HBV genome, to define their possible role in the pathogenesis of OHBS. Some of these mutations like S-escape mutants could not be detected by the routine available assays, making them difficult to diagnosis. Therefore, trying to detect this covert condition could be more helpful for defining better preventive and therapeutic strategies.

EVIDENCE ACQUISITION

In the present study we provided an in-depth review of the most important new data available on different mutations in HBV genome of patients with OHBS, which may play a role in the pathogenesis of OHBS. The data were collected through reviewing the full-text articles, identified by the PubMed search, using the following keywords and their different combinations: occult hepatitis B, HBV genome, "a" determinant, HBV open reading frames, S mutations, X mutations, P mutations and C mutations.

RESULTS

Variants within the major hydrophilic region (MHR) of the HBsAg, deletions in the pre-S1region, codon stop in the S open reading frames (ORF), sporadic non common mutations, some mutations affecting the posttranslational production of HBV proteins in the S ORF like deletion mutations, mutations in start codon and nucleotide changes in the X ORF, deletion and point mutations in P ORF and sometimes, nucleotide substitution in the C ORF are among the assumed mutations detected to have a role in OHBS appearance.

CONCLUSIONS

Studies mostly lacked a control group and the whole-length HBV sequencing was scant with conflicting results, suggesting that OHBS is often a result of multiple mechanisms. Additional studies on full-length HBV genomes from occult and non-occult HBV cases may shed more light on the interplay between different mechanisms involved in the pathogenesis of OHBS.

The unexpected roles of eukaryotic translation elongation factors in RNA virus replication and pathogenesis

The prokaryotic translation elongation factors were identified as essential cofactors for RNA-dependent RNA polymerase activity of the bacteriophage Qβ more than 40 years ago. A growing body of evidence now shows that eukaryotic translation elongation factors (eEFs), predominantly eEF1A, acting in partially characterized complexes sometimes involving additional eEFs, facilitate virus replication. The functions of eEF1A as a protein chaperone and an RNA- and actin-binding protein enable its "moonlighting" roles as a virus replication cofactor. A diverse group of viruses, from human immunodeficiency type 1 and West Nile virus to tomato bushy stunt virus, have adapted to use eEFs as cofactors for viral transcription, translation, assembly, and pathogenesis. Here we review the mechanisms used by viral pathogens to usurp these abundant cellular proteins for their replication.

Fatty acids increase hepatitis B virus X protein stabilization and HBx-induced inflammatory gene expression

The protein level of human hepatitis B virus (HBV) in infection is variable, depending on patient context. We previously reported that HBV X protein (HBx) induces hepatic lipid accumulation and inflammation. Here, we show that abnormal levels of hepatic fatty acids increase HBx protein stability during HBV expression, resulting in the potentiation of HBx-induced inflammation. Reactive oxygen species, Ca(2+) signaling and expression levels of various lipid metabolic genes were investigated in HBx-expressing cells and in HBx transgenic mice. Fatty acids, including palmitate, stearate and oleate, increased HBx protein stability by preventing proteasome-dependent degradation. Hepatic inflammation induced by a high fat diet (HFD) and HBx was measured based on the expression of interleukin-6 and tumor necrosis factor α. In addition, the protein level of HBx increased in HFD-HBx transgenic mice. Reactive oxygen species production and intracellular Ca(2+) signal activation play critical roles in fatty-acid-induced HBx stabilization. Abnormal levels of hepatic fatty acids resulted in synergistic induction of HBx protein and liver inflammatory gene expression through HBx protein stabilization. These results indicate that different fatty acid levels in the liver might affect HBV-induced pathogenesis.

Emerging role of insulin-like growth factor-binding protein 7 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a vicious and highly vascular cancer with a dismal prognosis. It is a life-threatening illness worldwide that ranks fifth in terms of cancer prevalence and third in cancer deaths. Most patients are diagnosed at an advanced stage by which time conventional therapies are no longer effective. Targeted molecular therapies, such as the multikinase inhibitor sorafenib, provide a modest increase in survival for advanced HCC patients and display significant toxicity. Thus, there is an immense need to identify novel regulators of HCC that might be targeted effectively. The insulin-like growth factor (IGF) axis is commonly abnormal in HCC. Upon activation, the IGF axis controls metabolism, tissue homeostasis, and survival. Insulin-like growth factor-binding protein 7 (IGFBP7) is a secreted protein of a family of low-affinity IGF-binding proteins termed “IGFBP-related proteins” that have been identified as a potential tumor suppressor in HCC. IGFBP7 has been implicated in regulating cellular proliferation, senescence, and angiogenesis. In this review, we provide a comprehensive discussion of the role of IGFBP7 in HCC and the potential use of IGFBP7 as a novel biomarker for drug resistance and as an effective therapeutic strategy.

15-Deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) promotes apoptosis of HBx-positive liver cells

This study aims to investigate the inflammatory response characteristics of liver cells caused by HBV x protein (HBx) and the unique function of the PGE2 inhibitor on HBx-positive liver cells. Tetrazolium blue colorimetric method, flow cytometry, and Western blot were performed to detect the proliferation, cycle, and apoptosis protein expression of HBx-positive HL7702 liver and control cells. The effect of the PGE2 inhibitor 15-Deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) on the growth of HL7702-HBx was also observed. HBx induces the PGE2 accumulation in HL7702 liver cells and promotes their growth and inhibits their apoptosis. HL7702-HBx and HL7702 cells showed increased apoptosis rate, increased apoptosis-promoting protein expression, and reduced apoptosis-inhibiting protein expression under the effect of 15d-PGJ2, and the changes in HL7702-HBx cells were more significant than in HL7702 cells. HBx expression causes liver cells to be more sensitive to the apoptosis-promoting function of 15d-PGJ2. Therefore, the use of 15d-PGJ2 may be a new method for the prevention or treatment of inflammatory changes to cancer caused by HBV infection in liver cells.

Hepatitis B virus X protein mutant HBxΔ127 promotes proliferation of hepatoma cells through up-regulating miR-215 targeting PTPRT

The mutant of virus is a frequent event. Hepatitis B virus X protein (HBx) plays a vital role in the development of hepatocellular carcinoma (HCC). Therefore, the identification of potent mutant of HBx in hepatocarcinogenesis is significant. Previously, we identified a natural mutant of the HBx gene (termed HBxΔ127). Relative to wild type HBx, HBxΔ127 strongly enhanced cell proliferation and migration in HCC. In this study, we aim to explore the mechanism of HBxΔ127 in promotion of proliferation of hepatoma cells. Our data showed that both wild type HBx and HBxΔ127 could increase the expression of miR-215 in hepatoma HepG2 and H7402 cells. However, HBxΔ127 was able to significantly increase miR-215 expression relative to wild type HBx in the cells. We identified that protein tyrosine phosphatase, receptor type T (PTPRT) was one of the target genes of miR-215 through targeting 3'UTR of PTPRT mRNA. In function, miR-215 was able to promote the proliferation of hepatoma cells. Meanwhile anti-miR-215 could partially abolish the enhancement of cell proliferation mediated by HBxΔ127 in vitro. Knockdown of PTPRT by siRNA could distinctly suppress the decrease of cell proliferation mediated by anti-miR-215 in HepG2-XΔ127/H7402-XΔ127 cells. Moreover, we found that anti-miR-215 remarkably inhibited the tumor growth of hepatoma cells in nude mice. Collectively, relative to wild type HBx, HBxΔ127 strongly enhances proliferation of hepatoma cells through up-regulating miR-215 targeting PTPRT. Our finding provides new insights into the mechanism of HBx mutant HBxΔ127 in promotion of proliferation of hepatoma cells.

Hepatitis B virus mutations related to liver disease progression of Korean patients

Hepatitis B virus (HBV) infection is a global health problem and more than 350 million people worldwide are chronic carriers of the virus. Despite the recent dramatic decline in HBV chronic patients through successful programs of hepatitis B surface antigen vaccination, South Korea is still recognized as an endemic area of HBV infection. HBV infections in South Korea exhibit several distinct features in epidemiologic and clinical aspects. In this review paper, we summarize the distinct HBV mutation patterns related to clinical severity and the molecular epidemiologic traits in Korean chronic patients based on previous reports. Generally, several lines of evidence, including our previous results, have led to the conclusion that a combination of the exclusive predominance of genotype C2, which is prone to mutations, the high prevalence of basal core promoter double mutations, and the presence of distinct immune responses against HBV proteins in the Korean population may generate the distinct HBV variants rarely or not encountered in other areas, which results in distinct clinical manifestations in Korean chronic patients. This may provide a novel insight into the relationships between clinical severity, HBV genotype distribution, and HBV naturally occurring variants.

The roles of hepatitis B virus-encoded X protein in virus replication and the pathogenesis of chronic liver disease

INTRODUCTION

Hepatitis B virus (HBV) is a major cause of chronic liver disease (CLD) and hepatocellular carcinoma (HCC) worldwide. More than 350 million people are at risk for HCC, and with few treatment options available, therapeutic approaches to targets other than the virus polymerase will be needed. This review suggests that the HBV-encoded X protein, HBx, would be an outstanding target because it contributes to the biology and pathogenesis of HBV in three fundamental ways.

AREAS COVERED

First, HBx is a trans-activating protein that stimulates virus gene expression and replication, thereby promoting the development and persistence of the carrier state. Second, HBx partially blocks the development of immune responses that would otherwise clear the virus, and protects infected hepatocytes from immune-mediated destruction. Thus, HBx contributes to the development of CLD without virus clearance. Third, HBx alters patterns of host gene expression that make possible the emergence of HCC. The selected literature cited is from the National Library of Medicine (Pubmed and Medline).

EXPERT OPINION

Understanding the mechanisms, whereby HBx supports virus replication and promotes pathogenesis, suggests that HBx will be an important therapeutic target against both virus replication and CLD aimed at the chemoprevention of HCC.

Hepatitis B virus X protein co-activates pregnane X receptor to induce the cytochrome P450 3A4 enzyme, a potential implication in hepatocarcinogenesis

BACKGROUND

Hepatitis B virus X protein is a key regulator of hepatocarcinogenesis. The pregnane X receptor is a xenobiotic nuclear receptor that plays a role in the regulation of drug-metabolizing enzymes including the cytochrome P450 3A4, an enzyme important for the bioactivation of the liver carcinogen aflatoxin B1.

AIMS

To identify novel host factor that interacts with hepatitis B virus X protein and the functional interaction between hepatitis B virus X protein and pregnane X receptor in hepatocarcinogenesis.

METHODS

Co-immunoprecipitation, glutathione S-transferase pull-down, and chromatin immunoprecipitation were utilized to assess the interaction between hepatitis B virus X protein and pregnane X receptor. The functional relevance of hepatitis B virus X protein-pregnane X receptor interaction was investigated in cell cultures and hepatocellular carcinoma samples.

RESULTS

We observed that hepatitis B virus X protein and pregnane X receptor co-localize in hepatic cells. Pregnane X receptor interacted with hepatitis B virus X protein via the ligand-binding domain of pregnane X receptor. Functionally, hepatitis B virus X protein increased the transcriptional activity of pregnane X receptor. Pregnane X receptor was able to recruit hepatitis B virus X protein to the CYP3A4 gene promoter. In clinic samples, the expression of pregnane X receptor was high in hepatitis B virus-associated liver cirrhosis and stage I hepatocellular carcinoma, but low in state II and stage III hepatocellular carcinoma.

CONCLUSION

We revealed a novel function of hepatitis B virus X protein in co-activating pregnane X receptor. The increased expression of pregnane X receptor and its target gene CYP3A4 are potential biomarkers for the early stage of hepatitis B virus-associated hepatocarcinogenesis.

Synergistic function of Kras mutation and HBx in initiation and progression of hepatocellular carcinoma in mice

Although the activation of Ras pathway is frequently observed in human hepatocellular carcinoma (HCC), the in vivo role of Ras activation in HCC initiation and progression is underdetermined. To test the consequence of Kras activation in hepatocyte, we generated a hepatocyte-specific Kras(G12D) transgenic mouse strain and observed spontaneous development of HCC in these mice. Remarkably, HBV X protein (HBx) expression significantly promotes the formation and malignant progression of Kras(G12D)-driven HCC as shown with the accelerated tumor onset, the increased tumor burden and the more poorly differentiated lesions. At the cellular level, concomitant expression of Kras(G12D) and HBx results in a robust increase in hepatocellular proliferation. We reveal that the Akt, MAPK, p53 and TGF-β pathways are deregulated in the Kras(G12D)-driven HCCs. Also, the dysregulation is more pronounced in the HCCs developed in Kras(G12D) and HBx double transgenic mice. In addition, the altered expressions of β-catenin, CD44 and E-cadherin are only observed in the Kras(G12D) and HBx double transgenic mice. These results demonstrate a crucial role of Ras activation in hepatocellular carcinogenesis and the functional synergy between Kras(G12D) and HBx in HCC initiation and progression. The novel genetic mouse models that closely recapitulate the histopathologic progression and molecular alterations of human HCC may potentially facilitate the future therapeutic studies.

Quasispecies structure, cornerstone of hepatitis B virus infection: Mass sequencing approach

Hepatitis B virus (HBV) is a DNA virus with complex replication, and high replication and mutation rates, leading to a heterogeneous viral population. The population is comprised of genomes that are closely related, but not identical; hence, HBV is considered a viral quasispecies. Quasispecies variability may be somewhat limited by the high degree of overlapping between the HBV coding regions, which is especially important in the P and S gene overlapping regions, but is less significant in the X and preCore/Core genes. Despite this restriction, several clinically and pathologically relevant variants have been characterized along the viral genome. Next-generation sequencing (NGS) approaches enable high-throughput analysis of thousands of clonally amplified regions and are powerful tools for characterizing genetic diversity in viral strains. In the present review, we update the information regarding HBV variability and present a summary of the various NGS approaches available for research in this virus. In addition, we provide an analysis of the clinical implications of HBV variants and their study by NGS.

Inhibition of hepatitis B virus (HBV) gene expression and replication by HBx gene silencing in a hydrodynamic injection mouse model with a new clone of HBV genotype B

Background

It has been suggested that different hepatitis B virus (HBV) genotypes may have distinct virological characteristics that correlate with clinical outcomes during antiviral therapy and the natural course of infection. Hydrodynamic injection (HI) of HBV in the mouse model is a useful tool for study of HBV replication in vivo. However, only HBV genotype A has been used for studies with HI.

Methods

We constructed 3 replication-competent clones containing 1.1, 1.2 and 1.3 fold overlength of a HBV genotype B genome and tested them both in vitro and in vivo. Moreover, A HBV genotype B clone based on the pAAV-MCS vector was constructed with the 1.3 fold HBV genome, resulting in the plasmid pAAV-HBV1.3_B and tested by HI in C57BL/6 mice. Application of siRNA against HBx gene was tested in HBV genotype B HI mouse model.

Results

The 1.3 fold HBV clone showed higher replication and gene expression than the 1.1 and 1.2 fold HBV clones. Compared with pAAV-HBV1.2 (genotype A), the mice HI with pAAV-HBV1.3_B showed higher HBsAg and HBeAg expression as well as HBV DNA replication level but a higher clearance rate. Application of two plasmids pSB-HBxi285 and pSR-HBxi285 expressing a small/short interfering RNA (siRNA) to the HBx gene in HBV genotype B HI mouse model, leading to an inhibition of HBV gene expression and replication. However, HBV gene expression may resume in some mice despite an initial delay, suggesting that transient suppression of HBV replication by siRNA may be insufficient to prevent viral spread, particularly if the gene silencing is not highly effective.

Conclusions

Taken together, the HI mouse model with a HBV genotype B genome was successfully established and showed different characteristics in vivo compared with the genotype A genome. The effectiveness of gene silencing against HBx gene determines whether HBV replication may be sustainably inhibited by siRNA in vivo.

Role and functional domain of hepatitis B virus X protein in regulating HBV transcription and replication in vitro and in vivo

The role of hepatitis B virus (HBV) X protein (HBx) in the regulation of HBV replication remains controversial. In the present study, the role of HBx in regulating HBV replication was initially investigated in both HepG2 and Huh7 in vitro cell lines with a transient transfection system. Next, the regions of HBx responsible for transcriptional transactivation and promotion of HBV replication were mapped in an HBV replication mouse model by in vivo transfection of a series of HBx expression plasmids. In an in vitro setting, HBx deficiency had little effect on HBV replication in Huh7 cells, but impaired HBV replication in HepG2 cells. In an in vivo setting, HBx had a strong enhancing effect on HBV transcription and replication. For the C-terminal two-thirds of the protein (amino acids [aa] 51 to 154) was required for this function of HBx, and the regions spanning aa 52 to 72 and 88 to 154 were found to be important for the stimulatory function of HBx on HBV replication. In conclusion, the role of HBx in HBV replication regulation is affected by host cell type, and HBx has an important role in stimulating HBV transcription and replication in hepatocytes in vivo. Further, the transcriptional transactivation function of HBx may be crucial for its stimulatory effect on HBV transcription and replication.

Hepatitis B viral RNA directly mediates down-regulation of the tumor suppressor microRNA miR-15a/miR-16-1 in hepatocytes

Hepatitis B virus (HBV) is a key risk factor for the development of hepatocellular carcinoma (HCC). Recent work suggests a functional link between HCC and microRNA expression, but the mechanism underlying the functional interaction between microRNA and HBV infection has remained largely elusive. Here we present evidence that the microRNA machinery serves as a defense system against HBV infection, which, in turn, reprograms the expression of specific microRNAs. We demonstrate a critical role of miR-15a/miR-16-1 in this functional interplay between microRNA and HBV infection, but in contrast to various indirect mechanisms mediated by viral proteins, we unexpectedly found that the HBx transcript directly triggers the down-regulation of miR-15a/miR-16-1 via the microRNA targeting sequences in the viral RNA. Because miR-15a and miR-16-1 are well known tumor suppressor microRNAs in multiple human cancers, our findings raise the intriguing possibility that viral RNA-mediated down-regulation of specific tumor suppressor microRNAs may contribute to HCC development in HBV-infected cells.

Hepatitis B virus X protein disrupts stress fiber formation and triggers apoptosis

Cytoskeletal proteins are key participants in the cellular progression to apoptosis. In a previous study we injected nude mice with CCL13-HBx cells and identified in contrast to non-HBx transfected cells a differentially phosphorylated myosin light chain (p-MLC) by two-dimensional PAGE and mass spectrometry of the tumor material. To investigate the role of HBx in myosin light chain kinase (MLCK) signaling pathways, we analyzed the key molecules, p-MLC and MLCK, by western blotting. Immunofluorescence staining analysis showed that HBx disrupted stress fiber formation and that focal adhesion kinase (FAK) and integrin-linked kinase (ILK) were regulated by HBx-mediated phosphatase and tensin homolog (PTEN). We also used pharmacological inhibitors to explore the correlation between cytoskeletal rearrangements and HBx-mediated cell apoptosis via an MLCK and a PTEN-dependent pathway. The results showed that both ML9 and bvp restored the effects caused by HBx induction. Our findings suggest that HBx disrupts stress fiber formation and triggers apoptosis via an MLCK and a PTEN-dependent pathway.

Efficacy of early treatment on 52 patients with preneoplastic hepatitis B virus-associated hepatocellular carcinoma by compound Phyllanthus Urinaria L

OBJECTIVE

To observe the change in the number of antibodies of preneoplastic hepatocellular carcinoma (HCC) using early treatment by Compound Phyllanthus Urinaria L. (CPUL) on patients with preneoplastic hepatitis B virus (HBV)-associated HCC.

METHODS

A total of 102 cirrhosis patients with regenerative or dysplastic nodules whose sera were tested positive for at least one of these six proteins (five up-regulated genes URG4, URG7, URG11, URG12 and URG19, and one down-regulated gene DRG2) were assigned randomly to two groups using continual random codes by SPSS software. Fifty-two patients were in the treatment group and 50 patients were in the control group. CPUL was used in the treatment group for 3 years, while the control group did not receive any treatment. The changes in HBV-DNA level, number of antibodies, and hepatocarcinogenesis occurred were observed. Patients who did not develop HCC were followed up for another 2 years.

RESULTS

HBV-DNA levels decreased ⩾2log in 22.2% (10/45) of patients in the treatment group in contrast to only 5.0% (2/40) of patients in the control group (P=0.0228). The number of antibodies that were tested positive in the treatment group (1.08±1.01) was significantly lower compared with the control group (2.11±1.12) after 24 months of drug treatment (P<0.01). Both the positive rates of anti-URG11 (33/52) and anti-URG19 (31/52) were over 60% at baseline in the two groups, and were decreased to 48.1% (25/52) and 46.2% (24/52) respectively at 36 months of drug treatment, while the rates increased to 68.0% (34/50) and 66.0% (33/50) respectively (P=0.0417, P=0.0436) in the control group. The positive rate of anti-DRG2 was increased to 55.8% (29/52) at 36 months of drug treatment, while in the control group was decreased to 36.0% (18/50, P=0.0452). Among the 102 patients who developed HCC, 2 were in the treatment group and 9 were in the control group, meaning that a significant difference between the two groups (P=0.0212). In 11 patients who developed HCC, anti-URG11 and anti-URG19 were always positive, while anti-DRG2 was negative. Patients newly developing HCC were 6 (20.0%) in the control group, and only one (2.5%) in the treatment group (P=0.0441) during 2-year follow-up after the end of the treatment.

CONCLUSIONS

Anti-URG11, anti-URG19 and anti-DRG2 could be used as early markers in the prediction of the therapeutic efficacy of CPUL in treating preneoplastic HCC. CPUL is useful in preventing or delaying the development of HBV-associated cirrhosis to HCC.

Hepatitis B virus X protein upregulates oncogene Rab18 to result in the dysregulation of lipogenesis and proliferation of hepatoma cells

Hepatitis B virus X protein (HBx) contributes to the development of hepatocellular carcinoma (HCC) through inducing dysregulation of lipogenesis. However, the mechanism by which HBx induces the abnormal lipogenesis is not well known. In this study, we report that the oncogene Rab18, a member of Ras family, enhances the HBx-induced hepatocarcinogenesis through inducing dysregulation of lipogenesis and proliferation. Our data showed that the expression levels of Rab18 were positively associated with those of HBx in clinical HCC tissues. HBx was able to upregulate the expression of Rab18 in p21-HBx transgenic mice and hepatoma cell lines. Next, we identified the mechanism by which HBx upregulated Rab18. The results demonstrated that cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) were able to stimulate Rab18 promoter through activating transcription factor activator protein 1 (AP-1) and cyclic adenosine 3',5'-monophosphate response element-binding (CREB). In addition, we identified another pathway that HBx activated Rab18. We found that miR-429 was able to directly target the 3' untranslated region of Rab18, suggesting that Rab18 is one of the target genes of miR-429. Then, we found that HBx was able to downregulate miR-429 in hepatoma cells. The oil red O staining showed that HBx resulted in the dysregulation of lipogenesis through Rab18. Moreover, Rab18 contributed to the HBx-enhanced proliferation of hepatoma cells in vitro and in vivo. HBx enhances hepatocarcinogenesis through leading to the dysregulation of lipogenesis and proliferation of hepatoma cells, involving two pathways such as HBx/COX-2/5-LOX/AP-1/CREB/Rab18 and HBx/miR-429/Rab18.

HBx-induced NF-κB signaling in liver cells is potentially mediated by the ternary complex of HBx with p22-FLIP and NEMO

Sustained activation of NF-κB is one of the causative factors for various liver diseases, including liver inflammation and hepatocellular carcinoma (HCC). It has been known that activating the NF-κB signal by hepatitis B virus X protein (HBx) is implicated in the development of HCC. However, despite numerous studies on HBx-induced NF-κB activation, the detailed mechanisms still remain unsolved. Recently, p22-FLIP, a cleavage product of c-FLIP_L, has been reported to induce NF-κB activation through interaction with the IκB kinase (IKK) complex in primary immune cells. Since our previous report on the interaction of HBx with c-FLIP_L, we explored whether p22-FLIP is involved in the modulation of HBx function. First, we identified the expression of endogenous p22-FLIP in liver cells. NF-κB reporter assay and electrophoretic mobility shift assay (EMSA) revealed that the expression of p22-FLIP synergistically enhances HBx-induced NF-κB activation. Moreover, we found that HBx physically interacts with p22-FLIP and NEMO and potentially forms a ternary complex. Knock-down of c-FLIP leading to the downregulation of p22-FLIP showed that endogenous p22-FLIP is involved in HBx-induced NF-κB activation, and the formation of a ternary complex is necessary to activate NF-κB signaling. In conclusion, we showed a novel mechanism of HBx-induced NF-κB activation in which ternary complex formation is involved among HBx, p22-FLIP and NEMO. Our findings will extend the understanding of HBx-induced NF-κB activation and provide a new target for intervention in HBV-associated liver diseases and in the development of HCC.

SREBP-1a activation by HBx and the effect on hepatitis B virus enhancer II/core promoter

Hepatitis B virus (HBV) X protein (HBx) plays an important role in HBV pathogenesis by regulating gene expression. Sterol regulatory element binding protein-1a (SREBP-1a) is a key transcriptional factor for modulating fatty acid and cholesterol synthesis. Here we demonstrated that HBx increased mature SREBP-1a protein level in the nucleus and its activity as a transcription factor. We further showed that the up-regulation of SREBP-1a by HBx occurred at the transcriptional level after ectopic expression and in the context of HBV replication. Deletional analysis using SREBP-1a promoter revealed that the sequence from -436 to -398 in the promoter was required for its activation by HBx. This promoter region possesses the binding sequences for two basic leucine zipper (b-ZIP) transcription factors, namely C/EBP and E4BP4. Mutagenesis of the binding sequences on the SREBP-1a promoter and ectopic expression experiments demonstrated that C/EBPα enhanced SREBP-1a activation by HBx, while E4BP4 had an inhibitory effect. C/EBPα was able to significantly reverse the inhibitory activity of E4BP4 on SREBP-1a promoter. These results demonstrated that HBx activates SREBP-1a activity at the transcription level through a complex mechanism involving two bZIP transcription factors C/EBP and E4BP4 with C/EBP being the dominant positive factor. Finally, we showed that knocking down SREBP-1 abolishes HBV enhancer II/core promoter activation by HBx.

Hepatitis B virus X protein protects hepatoma and hepatic cells from complement-dependent cytotoxicity by up-regulation of CD46

The involvement of hepatitis B virus X protein (HBx) in anti-complement-dependent cytotoxicity (CDC) activity during hepatocarcinogenesis is poorly understood. Here, we report that HBx is able to up-regulate membrane-bound complement regulatory protein CD46 in hepatoma cells and human immortalized liver cells through activating the promoter activity involving cAMP response element-binding protein (CREB)/cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2)/signal transducers and activators of transcription 3 (STAT3) signaling pathway. In contrast, the down-regulation of CD46 abolishes the resistance capability of hepatoma cells to CDC. Thus, we conclude that HBx contributes to the protection of hepatoma and hepatic cells from CDC by up-regulation of CD46.

Hepatitis B virus X protein upregulates Lin28A/Lin28B through Sp-1/c-Myc to enhance the proliferation of hepatoma cells

Hepatitis B virus X protein (HBx) plays critical roles in the pathogenesis of hepatocellular carcinoma (HCC). Here, we were interested in knowing whether the oncogene Lin28A and its homolog Lin28B are involved in the hepatocarcinogenesis mediated by HBx. We showed that the expression levels of Lin28A and Lin28B were increased in clinical HCC tissues, HepG2.2.15 cell line and liver tissues of p21-HBx transgenic mice. Interestingly, the expression levels of HBx were positively associated with those of Lin28A/Lin28B in clinical HCC tissues. Moreover, the overexpression of HBx resulted in the upregulation of Lin28A/Lin28B in hepatoma HepG2/H7402 cell lines by transient transfection, suggesting that HBx was able to upregulate Lin28A and Lin28B. Then, we examined the mechanism by which HBx upregulated Lin28A and Lin28B. We identified that the promoter region of Lin28A regulated by HBx was located at nt -235/-66 that contained Sp-1 binding element. Co-immunoprecipitation showed that HBx was able to interact with Sp-1 in HepG2-X cells. Moreover, chromatin immunoprecipitation (ChIP) demonstrated that HBx could bind to the promoter of Lin28A, which failed to work when Sp-1 was silenced. Electrophoretic mobility shift assay (EMSA) further identified that HBx was able to interact with Sp-1 element in Lin28A promoter via transcription factor Sp-1. In addition, we found that c-Myc was involved in the activation of Lin28B mediated by HBx. In function, Lin28A/Lin28B played important roles in HBx-enhanced proliferation of hepatoma cells in vitro and in vivo. In conclusion, HBx activates Lin28A/Lin28B through Sp-1/c-Myc in hepatoma cells. Lin28A/Lin28B serves as key driver genes in HBx-induced hepatocarcinogenesis.

Hepatitis B virus X gene differentially modulates cell cycle progression and apoptotic protein expression in hepatocyte versus hepatoma cell lines

The hepatitis B virus (HBV) X gene, which encodes the hepatitis B virus x protein (HBx), is essential for viral infection and genome replication, virus-associated liver disease, and development of hepatocellular carcinoma. However, the exact role(s) of HBx remain controversial. In this study, we focus on studying the role of HBx in the regulation of cell cycle and apoptosis in normal liver and hepatoma cell lines. We established the Huh7-X and Chang-X cell lines that constitutively express HBx. There were differences between the two cell lines in terms of cell cycle regulation and expression of p27 and transforming growth factor-β. Expression of HBx proteins dramatically increases expression of Bcl-2 and reduces levels of cleaved PARP protein in Chang-X cells, and it inhibits apoptosis under unfavourable conditions, such as serum starvation, in both cell lines. Our findings provide clues about the intracellular roles of HBx and demonstrate that expression of this protein is important for multiple cellular processes, that is, cell cycle progression and apoptosis, in hepatoma cells and normal liver cell lines.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

HSP72 and gp96 in gastroenterological cancers

Heat shock protein 72 (HSP72) and glycoprotein 96 (gp96) are highly expressed in cancer tissues. Recent studies indicate the possible roles of HSP72 and gp96 in the development and progression of gastrointestinal carcinomas but detailed mechanisms are still ambiguous. Human esophageal cancer, gastric cancer, colon cancer and liver cancer are common gastrointestinal malignant carcinomas in the world. The studies indicated that there existed a significant correlation between the expression of HSP72, gp96 and the development and progression of digestive carcinomas. HSP72 and gp96 expression were significantly associated with the presence of tumor infiltration, lymph node and remote metastasis. Interestingly, studies have found that HSP72 chaperoned alpha-fetoprotein (AFP), HBx in hepatocellular carcinoma, and CD44 in colonic carcinomas. The further researches demonstrated that HSP72-AFP or gp96-AFP recombined vaccine could elicit specific anti-tumor immunity. The high-level expression of HSP72 and gp96 may be not only used as diagnostic or prognostic markers for gastrointestinal carcinomas but also as better immunotherapeutic vaccines in the cancers.

Hepatitis B virus X protein modulates oncogene Yes-associated protein by CREB to promote growth of hepatoma cells

Hepatitis B virus X protein (HBx) plays critical roles in the development of hepatocellular carcinogenesis (HCC). Yes-associated protein (YAP), a downstream effector of the Hippo-signaling pathway, is an important human oncogene. In the present article, we report that YAP is involved in the hepatocarcinogenesis mediated by HBx. We demonstrated that the expression of YAP was dramatically elevated in clinical HCC samples, hepatitis B virus (HBV)-infected hepatoma HepG2.2.15 cell line, and liver cancer tissues of HBx-transgenic mice. Meanwhile, we found that overexpression of HBx resulted in the up-regulation of YAP in stably HBx-transfected HepG2/H7402 hepatoma cell lines, whereas HBx RNA interference reduced YAP expression in a dose-dependent manner in the above-mentioned cell lines, suggesting that HBx up-regulates YAP. Then, we investigated the mechanism underlying the up-regulation of YAP by HBx. Luciferase reporter gene assays revealed that the promoter region of YAP regulated by HBx was located at nt -232/+115 containing cyclic adenosine monophosphate response element-binding protein (CREB) element. Chromatin immunoprecipitation (ChIP) demonstrated that HBx was able to bind to the promoter of YAP, whereas it failed to work when CREB was silenced. Moreover, we confirmed that HBx activated the YAP promoter through CREB by electrophoretic mobility shift assay and luciferase reporter gene assays. Surprisingly, we found that YAP short interfering RNA was able to remarkably block the HBx-enhanced growth of hepatoma cells in vivo and in vitro.

CONCLUSION

YAP is a key driver gene in HBx-induced hepatocarcinogenesis in a CREB-dependent manner. YAP may serve as a novel target in HBV-associated HCC therapy.

Molecular biology of the hepatitis B virus for clinicians

Hepatitis B virus (HBV) infection is one of the major global health problems, especially in economically under-developed or developing countries. HBV infection can lead to a number of clinical outcomes including chronic infection, cirrhosis and liver cancer. It ranks among the top 10 causes of death, being responsible for around 1 million deaths every year. Despite the availability of a highly efficient vaccine and potent antiviral agents, HBV infection still remains a significant clinical problem, particularly in those high endemicity areas where vaccination of large populations has not been possible due to economic reasons. Although HBV is among the smallest viruses in terms of virion and genome size, it has numerous unique features that make it completely distinct from other DNA viruses. It has a partially double stranded DNA with highly complex genome organization, life cycle and natural history. Remarkably distinct from other DNA viruses, it uses an RNA intermediate called pregenomic RNA (pgRNA) and reverse transcriptase for its genome replication. Genome replication is accomplished by a complex mechanism of primer shifting facilitated by direct repeat sequences encoded in the genome. Further, the genome has evolved in such a manner that every single nucleotide of the genome is used for either coding viral proteins or used as regulatory regions or both. Moreover, it utilizes internal in-frame translation initiation codons, as well as different reading frames from the same RNA to generate different proteins with diverse functions. HBV also shows considerable genetic variability which has been related with clinical outcomes, replication potential, therapeutic response etc. This review aims at reviewing fundamental events of the viral life cycle including viral replication, transcription and translation, from the molecular standpoint, as well as, highlights the clinical relevance of genetic variability of HBV.

The viral transactivator HBx protein exhibits a high potential for regulation via phosphorylation through an evolutionarily conserved mechanism

BACKGROUND

Hepatitis B virus (HBV) encodes an oncogenic factor, HBx, which is a multifunctional protein that can induce dysfunctional regulation of signaling pathways, transcription, and cell cycle progression, among other processes, through interactions with target host factors. The subcellular localization of HBx is both cytoplasmic and nuclear. This dynamic distribution of HBx could be essential to the multiple roles of the protein at different stages during HBV infection. Transactivational functions of HBx may be exerted both in the nucleus, via interaction with host DNA-binding proteins, and in the cytoplasm, via signaling pathways. Although there have been many studies describing different pathways altered by HBx, and its innumerable binding partners, the molecular mechanism that regulates its different roles has been difficult to elucidate.

METHODS

In the current study, we took a bioinformatics approach to investigate whether the viral protein HBx might be regulated via phosphorylation by an evolutionarily conserved mechanism.

RESULTS

We found that the phylogenetically conserved residues Ser25 and Ser41 (both within the negative regulatory domain), and Thr81 (in the transactivation domain) are predicted to be phosphorylated. By molecular 3D modeling of HBx, we further show these residues are all predicted to be exposed on the surface of the protein, making them easily accesible to these types of modifications. Furthermore, we have also identified Yin Yang sites that might have the potential to be phosphorylated and O-β-GlcNAc interplay at the same residues.

CONCLUSIONS

Thus, we propose that the different roles of HBx displayed in different subcellular locations might be regulated by an evolutionarily conserved mechanism of posttranslational modification, via phosphorylation.

Hepatitis B virus encoded X protein suppresses apoptosis by inhibition of the caspase-independent pathway

Hepatitis B virus (HBV) encoded X protein (HBx) has been implicated in apoptotic and related pathogenic events during hepatocellular carcinoma. However, the underlying molecular mechanism through which HBx acts is largely unclear. We used tandem affinity purification under mild conditions to gain insight into the HBx interactome in HBV-producing HepG2.2.15 cells and identified 49 proteins by mass spectrometry that are potentially associated with HBx. Two of the key proteins of the caspase-independent apoptosis pathway were newly identified, apoptosis-inducing factor (AIF) and the homologous AMID (AIF-homologue mitochondrion-associated inducer of death). We confirmed the interactions of HBx with AIF and with AMID by reciprocal coimmunoprecipitation experiments, respectively. We observed the expression of HBx-reduced AIF-mediated apoptosis and HBx colocalization with AIF and AMID, principally in the cytoplasm. Furthermore, the elevated cytoplasmic levels of HBx could inhibit mitochondrion-to-nucleus translocation of AIF. Here, we present the first detailed molecular evidence that HBx can repress apoptosis via inhibition of the caspase-independent apoptosis pathway. This inhibition of apoptosis involves the repression of the mitochondrion-to-nucleus translocation of AIF, although tests with AMID were not conclusive. These findings provide important insights into the new mechanism of the apoptosis inhibition by HBV.

HBx induces HepG-2 cells autophagy through PI3K/Akt-mTOR pathway

Chronic hepatitis B virus infection is the dominant global cause of hepatocellular carcinoma (HCC), especially hepatitis B virus-X (HBx) plays a major role in this process. HBx protein promotes cell cycle progression, inactivates negative growth regulators, and binds to and inhibits the expression of p53 tumor suppressor gene and other tumor suppressor genes and senescence-related factors. However, the relationship between HBx and autophagy during the HCC development is poorly known. Previous studies found that autophagy functions as a survival mechanism in liver cancer cells. We suggest that autophagy plays a possible role in the pathogenesis of HBx-induced HCC. The present study showed that HBx transfection brought about an increase in the formation of autophagosomes and autolysosomes. Microtubule-associated protein light chain 3, Beclin 1, and lysosome-associated membrane protein 2a were up-regulated after HBx transfection. HBx-induced increase in the autophagic level was increased by mTOR inhibitor rapamycin and was blocked by treatment with the PI3K-Akt inhibitor LY294002. The same results can also be found in HepG2.2.15 cells. These results suggest that HBx activates the autophagic lysosome pathway in HepG-2 cells through the PI3K-Akt-mTOR pathway.

Hepatitis B virus X protein and c-Myc cooperate in the upregulation of ribosome biogenesis and in cellular transformation

Viral and cellular oncogenes are well known to enhance rRNA synthesis, leading to increased ribosome biogenesis and cell proliferation. Our study on the molecular underpinnings of the interaction between viral HBx and c-Myc, which is implicated in the development of hepatocellular carcinoma, showed a marked increase in the biosynthesis of rRNA, ribosomes and protein in hepatoma cells. A profound alteration in the nucleolar morphology and biochemical content of these cells was also observed. Increased biosynthetic activity was associated with increased cell proliferation and transformation of immortalized human hepatocytes. Furthermore, inhibition of RNA polymerase III activity impaired the proliferative advantage of hepatoma cells and transformation of immortalized hepatocytes as effectively as cisplatin treatment. These findings were corroborated in a transgenic HBx-myc microenvironment, in which an elevated hepatic level of rRNA was associated with conspicuous morphological and biochemical changes in the hepatocytic nucleoli. Thus, HBx and c-Myc seem to work cooperatively to support ribosome biogenesis and cellular transformation.

Hepatitis B virus X protein stabilizes amplified in breast cancer 1 protein and cooperates with it to promote human hepatocellular carcinoma cell invasiveness

Chronic infection of hepatitis B virus (HBV) is closely associated with the development of human hepatocellular carcinoma (HCC). HBV X protein (HBx) plays a key role in the progression of HCC. We recently found that amplified in breast cancer 1 (AIB1) protein is overexpressed in 68% of human HCC specimens and promotes HCC progression by enhancing cell proliferation and invasiveness. Given that both HBx and AIB1 play important oncogenic roles in HCC, we aimed to determine whether they could cooperatively promote human HCC development. Herein, we show that HBx-positive HCC tissues had a higher level of AIB1 protein, compared to HBx-negative HCC tissues. A positive correlation between HBx protein level and AIB1 protein level was established in HCC specimens. Without affecting its messenger RNA level, HBx induced a significant increase of the protein level of AIB1, which correlated with a significant extension of the half-life of AIB1 protein. Mechanistically, HBx could interact with AIB1 to prevent the interaction between envelope protein 3 ubiquitin ligase F-box and WD repeat domain containing 7 (Fbw7)α and AIB1, then inhibited the Fbw7α-mediated ubiquitination and degradation of AIB1. In addition, reporter assays and chromatin immunoprecipitation assays revealed that both HBx and AIB1 were recruited to matrix metalloproteinase-9 (MMP-9) promoter to enhance MMP-9 promoter activity cooperatively. Consistently, HBx and AIB1 cooperatively enhanced MMP-9 expression in HepG2 cells, which, in turn, increased cell-invasive ability.

CONCLUSION

Our study demonstrates that HBx can stabilize AIB1 protein and cooperate with it to promote human HCC cell invasiveness, highlighting the essential role of the cross-talk between HBx and AIB1 in HBV-related HCC progression.

Role of hepatitis B virus X protein in regulating LIM and SH3 protein 1 (LASP-1) expression to mediate proliferation and migration of hepatoma cells

BACKGROUND

Hepatitis B virus X protein (HBx) has been shown to be responsible for the development of hepatocellular carcinoma (HCC) caused by Hepatitis B virus infection. However, its potential effect on the progression of hepatocellular carcinoma remains yet unclear. LIM and SH3 protein 1 (LASP-1), a focal adhesion protein, is expressed in an up-regulation manner in the HCC tissues. LASP-1 plays an important role in the regulation of proliferation and migration of HCC. In this study, we investigated the effect of LASP-1 involved in HBx-related tumor progression.

METHODS

LASP-1 levels in the HBx stable transfected HepG2 and Huh-7 cells were detected by RT-PCR and western blot analysis. The cellular localization of LASP-1 was assessed by immunofluorescence analysis. The activity of phosphatidylinositol 3-kinase (PI3-K) pathway was demonstrated by western blot assay. The HBx-expressing cells were transfected with specific small interference RNA (siRNA) against LASP-1. The proliferation and migration ability of cells were evaluated by cell viability assay and plate clone formation assay. The migration ability of cells was detected by transwell assay and wound healing assay.

RESULTS

RT-PCR and western blot analysis indicated the expression of LASP-1 was increased in the stable HBx-expressing cells compared with the control cells. Immunofluorescence study revealed that the distributions of LASP-1 in HepG2-HBX cells were mainly in pseudopods and the cytoplasm while they were mainly localized in the cytoplasm of HepG2-Mock cells. The cellular localizations of LASP-1 in Huh-7-HBX cells were in the perinuclear fractions while they were mainly localized in the cytoplasm of Huh-7-Mock cells. The upregulation of LASP-1 was inhibited after treatment with LY294002, PI3-K pathway inhibitor. Overexpression of LASP-1 in the stable HBx-expressing cells enhanced the proliferation and migration ability of hepatocellular cells. siRNA-mediated LASP-1 knowdown in the stable HBx-expressing cells significantly suppressed hepatocellular cells proliferation and migration.

CONCLUSIONS

These results demonstrated that HBx could upregulate LASP-1 through PI3-K pathway to promote the proliferation and migration of hepatoma cells.

Variability in the precore and core promoter regions of HBV strains in Morocco: characterization and impact on liver disease progression

Background

Hepatitis B virus (HBV) is one of the most common human pathogens that cause aggressive hepatitis and advanced liver disease (AdLD), including liver cirrhosis and Hepatocellular Carcinoma. The persistence of active HBV replication and liver damage after the loss of hepatitis B e antigen (HBeAg) has been frequently associated with mutations in the pre-core (pre-C) and core promoter (CP) regions of HBV genome that abolish or reduce HBeAg expression. The purpose of this study was to assess the prevalence of pre-C and CP mutations and their impact on the subsequent course of liver disease in Morocco.

Methods/Principal Findings

A cohort of 186 patients with HBeAg-negative chronic HBV infection was studied (81 inactive carriers, 69 with active chronic hepatitis, 36 with AdLD). Pre-C and CP mutations were analyzed by PCR-direct sequencing method. The pre-C stop codon G1896A mutation was the most frequent (83.9%) and was associated with a lower risk of AdLD development (OR, 0.4; 95% CI, 0.15–1.04; p = 0.04). HBV-DNA levels in patients with G1896A were not significantly different from the other patients carrying wild-type strains (p = 0.84). CP mutations C1653T, T1753V, A1762T/G1764A, and C1766T/T1768A were associated with higher HBV-DNA level and increased liver disease severity. Multiple logistic regression analysis showed that older age (≥40 years), male sex, high viral load (>4.3 log₁₀ IU/mL) and CP mutations C1653T, T1753V, A1762T/G1764A, and C1766T/T1768A were independent risk factors for AdLD development. Combination of these mutations was significantly associated with AdLD (OR, 7.52; 95% CI, 4.8–8; p<0.0001).

Conclusions

This study shows for the first time the association of HBV viral load and CP mutations with the severity of liver disease in Moroccan HBV chronic carriers. The examination of CP mutations alone or in combination could be helpful for prediction of the clinical outcome.

Hepatitis B virus X protein blocks filamentous actin bundles by interaction with eukaryotic translation elongat ion factor 1 alpha 1

Hepatitis B virus (HBV)-encoded X protein (HBx protein) is a multi-functional regulatory protein. It functions by protein-protein interaction and plays a pivotal role in the pathogenesis of HBV-related diseases. However, the partners in hepatocytes interacting with HBx protein are far from understood fully. In this study, immunoprecipitation was employed to screen for binding partners for the HBx protein from huh-7 hepatoma cells infected with recombinant adenovirus expressing HBx protein, and five cellular proteins including eukaryotic translation elongation factor 1 alpha 1 (eEF1A1), were identified. The interaction between HBx protein and eEF1A1 was confirmed further using a GST pull-down assay and co-immunoprecipitation, respectively. In Huh-7 hepatoma cells, the HBx protein inhibits dimer formation of eEF1A1, hence blocks filamentous actin bundling. These findings provide new insights into the molecular mechanisms involved in the functions of the HBx protein.

Hepatitis B virus X protein regulates the mEZH2 promoter via the E2F1-binding site in AML12 cells

Histone lysine methyltransferase EZH2 has been reported to be frequently overexpressed in hepatocellular carcinoma (HCC) tissues and associated with hepatocarcinogenesis. However, the exact mechanism of EZH2 up-regulation in HCC has not been determined. In this study, we used murine hepatocyte AML12 cells to investigate the role of hepatitis B virus X protein (HBx) in regulating the expression of mEZH2. Western blot analysis demonstrated that the expression level of mEZH2 protein in AML12 cells was up-regulated by HBx in a dose-dependent manner. To further investigate the mechanism of mEZH2 overexpression, the 2500 bp regulatory sequence upstream from the first exon of the mEZH2 gene was amplified from AML12 genomic DNA and constructed into a luciferase reporter plasmid. The luciferase activity of the mEZH2 promoter significantly increased in AML12 cells co-transfected with HBx plasmid, and deleting the −486/−214 promoter region decreased HBx-induced mEZH2 promoter activation by nearly 50%. The −486/−214 region was then analyzed in the TRANSFAC 6.0 database and a typical E2F1-binding site was found. Mutation of this E2F1-binding site or knockdown of E2F1 expression by RNAi led to a dramatic decrease in HBx-induced activation of the mEZH2 promoter and mEZH2 overexpression in AML12 cells. These results provide evidence that HBx up-regulates mEZH2 expression by transactivating the mEZH2 promoter through E2F1 transcription factor, thereby providing new epigenetic evidence for the carcinogenic effect of HBx.

Local delivery of recombinant adenovirus expressing hepatitis B virus X protein and interleukin-12 results in antitumor effects via inhibition of hepatoma cell growth and intervention of tumor microenvironment

Hepatocellular carcinoma (HCC) is a typical hypervascular tumor. Our previous studies have demonstrated that hepatitis B virus X protein (HBx) was able to inhibit the growth of HCC cells via inducing apoptosis and inhibiting tumor angiogenesis. Interleukin-12 (IL-12) is a disulfide-linked heterodimeric cytokine with potent immunostimulatory activity and anti-angiogenic properties. In this study, to further investigate the regulatory effect of IL-12 on HBx-mediated intervention of hepatoma microenvironment especially on intervention of neovessels and immune microenvironment, we constructed the recombinant adenovirus expressing HBx and mouse IL-12 named Ad-HBx-mIL-12. HBx-mIL-12 could effectively suppress tumor growth and induce apoptosis in vivo. Moreover, treatment with Ad-HBx-mIL-12 not only induced a massive accumulation of immune cells (CD8(+) T leukocytes, macrophages and dendritic cells) in tumors in situ, also apparently reduced the number of angiogenic blood vessels within tumor tissues. These results suggest that HBx-mIL-12 can not only induce cell cycle arrest and apoptosis in HCC cells, but also effectively shift the tumor microenvironment from pro-oncogenic to antitumor through recruitment of immune cells and inhibiting stromal cell growth, such as vascular endothelial cells.

Role of miR-148a in hepatitis B associated hepatocellular carcinoma

Hepatitis B virus encoded X antigen (HBx) is a trans-regulatory protein that alters the activity of selected transcription factors and cytoplasmic signal transduction pathways. HBx transcriptionally up-regulates the expression of a unique gene, URG11, which in turn transcriptionally up-regulates β-catenin, thereby contributing importantly to hepatocarcinogenesis. HBx and URG11 also alter the expression of multiple microRNAs, and by miRNA array analysis, both were shown to promote the expression of miR-148a. Elevated miR-148a was also seen in HBx positive liver samples from infected patients. To study the function of miR-148a, anti-148a was introduced into HepG2 and Hep3B cells stably expressing HBx or stably over-expressing URG11. Anti-miR-148a suppressed cell proliferation, cell cycle progression, cell migration, anchorage independent growth in soft agar and subcutaneous tumor formation in SCID mice. Introduction of anti-miR-148a increased PTEN protein and mRNA expression, suggesting that PTEN was targeted by miR-148a. Anti-miR-148a failed to suppress PTEN expression when co-transfected with reporter gene mutants in the 3′UTR of PTEN mRNA. Introduction of anti-miR-148a also resulted in depressed Akt signaling by HBx and URG11, resulting in decreased expression of β-catenin. Thus, miR-148a may play a central role in HBx/URG11 mediated HCC, and may be an early diagnostic marker and/or therapeutic target associated with this tumor type.

HBx activates FasL and mediates HepG2 cell apoptosis through MLK3-MKK7-JNKs signal module

AIM

To investigate the possible mechanism by which hepatitis B virus X protein (HBx) mediates apoptosis of HepG2 cells.

METHODS

HBx expression vector pcDNA3.1-X was transfected into HepG2 cells to establish an HBx high-expression cellular model as pcDNA3.1-X transfected group. The pcDNA3.1-X and pSilencer3.1-shHBX (HBx antagonist) were cotransfected into HepG2 cells to establish an HBx low-expression model as RNAi group. Untransfected HepG2 cells and HepG2 cells transfected with negative control plasmid were used as controls. Apoptosis rate, the expression of Fas/FasL signaling pathway-related proteins and the phosphorylation levels of MLK3, MKK7 and JNKs, which are upstream molecules of death receptor pathways and belong to the family of mitogen-activated protein kinases (MAPKs), were measured in each group.

RESULTS

Compared with HepG2 cell group and RNAi group, apoptosis rate, the expression of Fas and FasL proteins, and the activation of MLK3, MKK7 and JNKs were increased in the pcDNA3.1-X transfected group. The activation of JNKs and expression of FasL protein were inhibited in the pcDNA3.1-X transfected group when treated with a known JNK inhibitor, SP600125. When authors treated pcDNA3.1-X transfected group with K252a, a known MLK3 inhibitor, the activation of MLK3, MKK7 and JNKs as well as expression of FasL protein was inhibited. Furthermore, cell apoptosis rate was also significantly declined in the presence of K252a in the pcDNA3.1-X transfected group.

CONCLUSION

HBx can induce HepG2 cell apoptosis via a novel active MLK3-MKK7-JNKs signaling module to upregulate FasL protein expression.

Establishment of a HepG2 cell line stably transduced with a lentivirus expressing the HBV X gene

AIM: To establish a HepG2 cell line stably transduced with a lentivirus expressing the HBV X (HBx) gene for studying the biological function of HBx and its role in hepatocarcinogenesis.

METHODS: The HBV X gene was amplified from plasmid pIERES2-EGFP-HBV by PCR. The purified HBx gene fragment was inserted into a lentivirus vector (pZac2.1), and the insertion was identified by PCR, restriction endonuclease analysis and DNA sequencing. HepG2 cells were then transfected with the packaged recombinant lentivirus, and resistant cell clones were selected with puromycin. The expression of HBx was examined using RT-PCR, immunohistochemistry, and Western blot.

RESULTS: Restriction enzyme digestion and DNA sequencing showed that the full-length HBx (489 bp) gene had been successfully subcloned into the lentiviral vector to result in the recombinant vector pZac2.1-HBx. The titre of purified recombinant lentivirus was 1×10⁸ TU/mL. Monoclonal cell line HepG2-HBx was produced 8-10 d after transfection with the recombinant lentivirus and selected with puromycin. HBx mRNA could be detected on days 3, 14, 30 and at 2 mo after cell colony formation. Meanwhile, stable expression of HBx protein was verified by immunohistochemistry and Western blot.

CONCLUSION: A HepG2 cell line stably transduced with a lentivirus expressing the HBx gene has been successfully generated.