Liver-specific enhancer II is the target for the p53-mediated inhibition of hepatitis B viral gene expression

Forkhead O Transcription Factor 4 Restricts HBV Covalently Closed Circular DNA Transcription and HBV Replication through Genetic Downregulation of Hepatocyte Nuclear Factor 4 Alpha and Epigenetic Suppression of Covalently Closed Circular DNA via Interacting with Promyelocytic Leukemia Protein

Nuclear located hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) remains the key obstacle to cure chronic hepatitis B (CHB). In our previous investigation, it was found that FoxO4 could inhibit HBV core promoter activity through downregulating the expression of HNF4α. However, the exact mechanisms whereby FoxO4 inhibits HBV replication, especially its effect on cccDNA, remain unclear. Here, our data further revealed that FoxO4 could effectively inhibit cccDNA mediated transcription and HBV replication without affecting cccDNA level. Mechanistic study showed that FoxO4 could cause epigenetic suppression of cccDNA. Although FoxO4-mediated downregulation of HNF4α contributed to inhibiting HBV core promoter activity, it had little effect on cccDNA epigenetic regulation. Further, it was found that FoxO4 could colocalize within promyelocytic leukemia protein (PML) nuclear bodies and interact with PML. Of note, PML was revealed to be critical for FoxO4-mediated inhibition of cccDNA epigenetic modification and of the following cccDNA transcription and HBV replication. Furthermore, FoxO4 was found to be downregulated in HBV-infected hepatocytes and human liver tissues, and it was negatively correlated with cccDNA transcriptional activity in CHB patients. Together, these findings highlight the role of FoxO4 in suppressing cccDNA transcription and HBV replication via genetic downregulation of HNF4α and epigenetic suppression of cccDNA through interacting with PML. Targeting FoxO4 may present as a new therapeutic strategy against chronic HBV infection.

IMPORTANCE HBV cccDNA is a determining factor for viral persistence and the main obstacle for a cure of chronic hepatitis B. Strategies that target cccDNA directly are therefore of great importance in controlling persistent HBV infection. In present investigation, we found that FoxO4 could efficiently suppress cccDNA transcription and HBV replication without affecting the level of cccDNA itself. Further, our data revealed that FoxO4 might inhibit cccDNA function via a two-part mechanism: one is to epigenetically suppress cccDNA transcription via interacting with PML, and the other is to inhibit HBV core promoter activity via the genetic downregulation of HNF4α. Of note, HBV might dampen the expression of FoxO4 for its own persistent infection. We propose that manipulation of FoxO4 may present as a potential therapeutic strategy against chronic HBV infection.

Host Transcription Factors in Hepatitis B Virus RNA Synthesis

The hepatitis B virus (HBV) chronically infects over 250 million people worldwide and is one of the leading causes of liver cancer and hepatocellular carcinoma. HBV persistence is due in part to the highly stable HBV minichromosome or HBV covalently closed circular DNA (cccDNA) that resides in the nucleus. As HBV replication requires the help of host transcription factors to replicate, focusing on host protein–HBV genome interactions may reveal insights into new drug targets against cccDNA. The structural details on such complexes, however, remain poorly defined. In this review, the current literature regarding host transcription factors’ interactions with HBV cccDNA is discussed.

Sodium selenite suppresses hepatitis B virus transcription and replication in human hepatoma cell lines

Hepatitis B virus (HBV) infection is one of the most serious and prevalent health problems worldwide. Current anti‐HBV medications have a number of drawbacks, such as adverse effects and drug resistance; thus, novel potential anti‐HBV reagents are needed. Selenium (Se) has been shown to be involved in both human immunodeficiency virus and hepatitis C virus infections, but its role in HBV infection remains unclear. To address this, sodium selenite (Na₂SeO₃) was applied to three HBV cell models: HepG2.2.15 cells, and HuH‐7 cells transfected with either 1.1 or 1.3× HBV plasmids. Cytotoxicity of Na₂SeO₃ was examined by Cell Counting Kit‐8. Levels of viral antigen expression, transcripts, and encapsidated viral DNA were measured by enzyme‐linked immunosorbent assay, northern blot, and Southern blot, respectively. There was no obvious cytotoxicity in either HepG2.2.15 or HuH‐7 cells with <2.5 µM Na₂SeO₃. Below this concentration, Na₂SeO₃ suppressed HBsAg and HBeAg production, HBV transcript level, and amount of genomic DNA in all three tested models, and suppression level was enhanced in line with increases in Na₂SeO₃ concentration or treatment time. Moreover, the inhibitory effect of Na₂SeO₃ on HBV replication can be further enhanced by combined treatment with lamivudine, entecavir, or adefovir. Thus, the present study clearly proves that Na₂SeO₃ suppresses HBV protein expression, transcription, and genome replication in hepatoma cell models in a dose‐ and time‐dependent manner. J. Med. Virol. 88:653–663, 2016. © 2015 Wiley Periodicals, Inc.

Possible role of tocopherols in the modulation of host microRNA with potential antiviral activity in patients with hepatitis B virus-related persistent infection: a systematic review

Hepatitis B virus (HBV) infection represents a serious global health problem and persistent HBV infection is associated with an increased risk of cirrhosis, hepatocellular carcinoma and liver failure. Recently, the study of the role of microRNA (miRNA) in the pathogenesis of HBV has gained considerable interest as well as new treatments against this pathogen have been approved. A few studies have investigated the antiviral activity of vitamin E (VE) in chronic HBV carriers. Herein, we review the possible role of tocopherols in the modulation of host miRNA with potential anti-HBV activity. A systematic research of the scientific literature was performed by searching the MEDLINE, Cochrane Library and EMBASE databases. The keywords used were 'HBV therapy', 'HBV treatment', 'VE antiviral effects', 'tocopherol antiviral activity', 'miRNA antiviral activity' and 'VE microRNA'. Reports describing the role of miRNA in the regulation of HBV life cycle, in vitro and in vivo available studies reporting the effects of VE on miRNA expression profiles and epigenetic networks, and clinical trials reporting the use of VE in patients with HBV-related chronic hepatitis were identified and examined. Based on the clinical results obtained in VE-treated chronic HBV carriers, we provide a reliable hypothesis for the possible role of this vitamin in the modulation of host miRNA profiles perturbed by this viral pathogen and in the regulation of some cellular miRNA with a suggested potential anti-HBV activity. This approach may contribute to the improvement of our understanding of pathogenetic mechanisms involved in HBV infection and increase the possibility of its management and treatment.

Virus associated malignancies: the role of viral hepatitis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading fatal cancer worldwide and its incidence continues to increase. Chronic viral hepatitis involving either hepatitis B virus (HBV) or hepatitis C virus (HCV) infection is the leading etiology for HCC, making HCC prevention a major goal of antiviral therapy. While recent clinical observations and translational research have enhanced our understanding of the molecular mechanisms driving the initiation and progression of HCC, much remains unknown. Current data indicates that HCC tumors are highly complex and heterogeneous resulting from the aberrant function of multiple molecular pathways. This complex biology is responsible, at least in part, for the absence of highly efficient target-directed therapies for this deadly cancer. Additionally, the direct or indirect effect of HBV and HCV infection on the development of HCC is still a contentious issue. Thus, the question remains whether viral hepatitis-associated HCC stems from virus-specific factors, and/or from a general mechanism involving inflammation and tissue regeneration. In this review we summarize general mechanisms implicated in HCC, emphasizing data generated by new technologies available today. We also highlight specific pathways by which HBV and HCV could be involved in HCC pathogenesis. However, improvements to current in vitro and in vivo systems for both viruses will be needed to rigorously define the temporal sequence and specific pathway dysregulations that drive the strong clinical link between chronic hepatitis virus infection and HCC.

The p53-microRNA-34a axis regulates cellular entry receptors for tumor-associated human herpes viruses

A growing number of reports indicate the frequent presence of DNA sequences and gene products of human cytomegalovirus in various tumors as compared to adjacent normal tissues, the brain tumors being studied most intensely. The mechanisms underlying the tropism of human cytomegalovirus to the tumor cells or to the cells of tumor origin, as well as the role of the host's genetic background in virus-associated oncogenesis are not well understood. It is also not clear why cytomegalovirus can be detected in many but not in all tumor specimens. Our in silico prediction results indicate that microRNA-34a may be involved in replication of some human DNA viruses by targeting and downregulating the genes encoding a diverse group of proteins, such as platelet-derived growth factor receptor-alpha, complement component receptor 2, herpes simplex virus entry mediators A, B, and C, and CD46. Notably, while their functions vary, these surface molecules have one feature in common: they serve as cellular entry receptors for human DNA viruses (cytomegalovirus, Epstein-Barr virus, human herpes virus 6, herpes simplex viruses 1 and 2, and adenoviruses) that are either proven or suspected to be linked with malignancies. MicroRNA-34a is strictly dependent on its transcriptional activator tumor suppressor protein p53, and both p53 and microRNA-34a are frequently mutated or downregulated in various cancers. We hypothesize that p53-microRNA-34a axis may alter susceptibility of cells to infection with some viruses that are detected in tumors and either proven or suspected to be associated with tumor initiation and progression.

Hepatitis B virus core promoter mutations G1613A and C1653T are significantly associated with hepatocellular carcinoma in genotype C HBV-infected patients

BACKGROUND

Hepatitis B virus (HBV) is a major cause of hepatocarcinogenesis.To identify mutations relevant to hepatocellular carcinoma (HCC) development, we compared the full genome sequences of HBV from the sera of patients with and without HCC.

METHODS

We compared the full genome sequences of HBV isolates from 37 HCC patients (HCC group 1) and 38 patients without HCC (non-HCC group 1). We also investigated part of the core promoter region sequences from 40 HCC patients (HCC group 2) and 68 patients without HCC. Of the 68 patients who initially did not have HCC, 52 patients remained HCC-free during the follow-up period (non-HCC group 2), and 16 patients eventually developed HCC (pre-HCC group 2). Serum samples collected from patients were subjected to PCR, and the HBV DNA was directly sequenced.

RESULTS

All patients had genotype C. A comparison of the nucleotide sequences of the HBV genome between HCC group 1 and non-HCC group 1 revealed that the prevalence of G1613A and C1653T mutations in the core promoter region was significantly higher in the HCC group. These mutations tended to occur simultaneously in HCC patients. Multivariate analysis with group 2 revealed that the presence of HCC was associated with aging and the double mutation. Future emergence of HCC was associated with aging and the presence of a single G1613A mutation.

CONCLUSIONS

G1613A and C1653T double mutations were frequently found in patients with HCC. A single G1613A mutation was associated with future emergence of HCC. These mutations may serve as useful markers in predicting HCC development.

Association between Hepatitis B Virus X Gene Mutations and Clinical Status in Patients with Chronic Hepatitis B Infection

BACKGROUND/AIMS

Few reports have described the association between mutations in the entire X gene of the hepatitis B virus (HBV) and the clinical status of HBV-infected patients. We studied the association between HBV X gene mutations and the disease status of patients infected with HBV genotype C.

METHODS

Mutations in the HBV X genes of 194 patients were determined by direct sequencing. The subject population consisted of patients with chronic hepatitis (n=60), liver cirrhosis (n=65), and hepatocellular carcinoma (HCC) (n=69). The sequencing results of these 3 groups were compared.

RESULTS

Each of the mutations G1386M, C1485T, C1653T, T1753V, A1762T, and G1764A was significantly associated with the patient's clinical status. The T1753V (p<0.001) and A1762T/G1764A (p<0.001) mutations were found more frequently in Hepatitis B e antigen (HBeAg)-negative than in HBeAg-positive patients. Specific X gene mutations (G1386M, C1653T, and A1762T/G1764A) were more prevalent in patients with liver cirrhosis and HCC than in chronic hepatitis patients (p<0.005 for all). In addition, the T1753V (p<0.001) and C1485T (p<0.001) mutations were significantly more prevalent in HCC patients than in chronic hepatitis patients. Only the prevalence of the T1753V mutation increased as the HBV infection progressed from liver cirrhosis to HCC (p=0.023).

CONCLUSIONS

Our findings show a difference in the pattern of X gene mutations that were associated with the clinical status of patients with chronic HBV infection.

Molecular mechanism of p73-mediated regulation of hepatitis B virus core promoter/enhancer II: implications for hepatocarcinogenesis

Hepatitis B virus (HBV) is a causative agent of chronic hepatitis and hepatocellular carcinoma. Recent findings demonstrating p73 and specifically N-terminally truncated p73 (DeltaTAp73) accumulation in hepatocellular carcinoma suggest that p73 plays a role in the malignant phenotype. Here, we investigated the mechanism of HBV pregenomic core promoter/enhancer II (cp/EII) regulation by full-length TAp73 and its oncogenic counterpart DeltaTAp73. Ectopic and endogenous expression of TAp73 leads to a significant downregulation of cp/EII activity in p53-deficient hepatoma cell lines. In contrast, overexpression of DeltaTAp73 results in significant cp/EII activation and increased HBV core (HBc) expression. TAp73-mediated repression of HBV transcription was substantially abolished by DeltaTAp73. We show that both TAp73 and DeltaTAp73 proteins directly bind to the Sp1 transcription factor, a key stimulator of HBV gene expression. However, only TAp73 abolishes Sp1 binding to cp/EII, whereas the DeltaTAp73-Sp1 complex further persists on the DNA. The inhibitory effect of p53/p73 on HBc expression is associated with the inhibition of viral replication, while DeltaTAp73 is not. These data strongly support the fact that the p73-isoform-related interaction with Sp1 is the underlying mechanism of the diverse outcome on HBc expression, suggesting a new mechanism by which oncogenic DeltaTAp73 could enhance the carcinogenic process in liver cells.

Molecular biology of hepatitis B virus: effect of nucleotide substitutions on the clinical features of chronic hepatitis B

Hepatitis B virus (HBV) is a major cause of liver disease worldwide. It is covered with envelope (surface antigen) proteins with the nucleocapsid (core antigen) inside. In the nucleocapsid, there is an incomplete double-stranded DNA and a DNA polymerase. Four genes, S, C, X, and P, are encoded, and these partially overlap. Mutations have been reported in each gene and in their promoter regions, and these mutations can change the efficiency of HBV replication and the clinical course of patients. In this article, we review the relationship between the molecular biology of HBV and its clinical outcome.

Merlin Neutralizes the Inhibitory Effect of Mdm2 on p53

The stability of p53 tumor suppressor is regulated by Mdm2 via the ubiquitination and proteasome-mediated proteolysis pathway. The c-Abl and PTEN tumor suppressors are known to stabilize p53 by blocking the Mdm2-mediated p53 degradation. This study investigated the correlation between p53 and merlin, a neurofibromatosis 2 (NF2)-related tumor suppressor, in association with the Mdm2 function. The results showed that merlin increased the p53 stability by inhibiting the Mdm2-mediated degradation of p53, which accompanied the increase in the p53-dependent transcriptional activity. The stabilization of p53 by merlin appeared to be accomplished through Mdm2 degradation, and the N-terminal region of merlin was responsible for this novel activity. This study also showed that overexpression of merlin-induced apoptosis of cells depending preferentially on p53 in response to the serum starvation or a chemotherapeutic agent. These results suggest that merlin could be a positive regulator of p53 in terms of tumor suppressor activity, and provide the promising therapeutic means for treating tumors with non-functional merlin or Mdm2 overexpression.

Characterization of HBV integrants in 14 hepatocellular carcinomas: association of truncated X gene and hepatocellular carcinogenesis

Although the integration of hepatitis B virus (HBV) into human DNA has been found to be associated with the development of hepatocellular carcinoma (HCC), the molecular mechanism remains unclear. In order to obtain additional insight into the correlation of HBV integration and HCC development, integrated HBV in 14 primary HCC cases was isolated and characterized by sequencing analysis. Our findings in this study showed that: (1) none of the known cellular oncogene or tumor suppressor gene was affected by the HBV integration; (2) although the integration of HBV is random, the integration site was often within or close to human repetitive sequences; (3) integrated HBV may possess the capacity to transpose to another chromosome region through reintegration; (4) rearrangements of HBV sequence were observed in all the 14 integrants, involving (most frequently) X (12/14 integrants), P (8/14), S (7/14), and C (7/14) genes; and (5) 3'-deleted X gene and consequent C-terminal truncated X protein caused by HBV integration was observed in 10 cases. These deletions cause the losses of p53-dependent transcriptional repression binding site, transcription factor Sp1 binding site, and growth-suppressive effect domain, leading to cell proliferation and transformation. This finding suggests that 3'-deleted X gene caused by the HBV integration may play an important role in the HCC development.

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p73β inhibits transcriptional activities of enhancer I and X promoter in hepatitis B virus more efficiently than p73α

AIM: p73, as a novel member of a family of p53-related transcription factors, shares redundant functions with p53, such as the abilities of inducing apoptosis and suppressing growth. It is well known that p53 can repress HBV expression and transcription efficiently. The aim of this paper is to investigate the transcriptional effect of p73α and p73β on hepatitis B virus (HBV) and to understand the correlation between HBV and p73.

METHODS: To construct an x-gene inactivated HBV plasmid which was cotransfected with p73α or p73β expression vectors into HepG2 cells. After transiently transfection, HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) were detected by ELISA. Viral transcripts synthesized by HBV were evaluated by Northern blotting analysis. The activities of HBV regulatory elements, including enhancer I/X promoter (ENI/Xp) and enhancer II/core promoter (ENII/Cp) were monitored by luciferase assays.

RESULTS: Both p73α and p73β could repress HBsAg and HBeAg expression by downregulating the ENI/Xp and ENII/ Cp activities. But p73β exerted stronger inhibition on the activity of ENI/Xp than p73α, resulting in much lower level of viral transcripts and the antigens expression.

CONCLUSION: p73β as a novel member of p53 family can efficiently inhibit HBV transcription mainly through downregulating the activities of the HBV ENI/Xp regulatory elements.

A dominant-negative form of p63 is required for epidermal proliferation in zebrafish

Epidermal stem cells play a critical role in producing the multilayered vertebrate skin. Products of the p63 gene not only mark the epidermal stem cells, but also are absolutely required for the formation of mammalian epidermis. We find that early zebrafish embryos express a dominant-negative form of p63 (DeltaNp63), which accumulates in the nucleus just as epidermal growth begins. Using antisense morpholino oligonucleotides, we show that DeltaNp63 is needed for epidermal growth and limb development and is specifically required for the proliferation of epidermal cells by inhibiting p53 activity. While the structure of fish epidermis is very different from that of higher vertebrates, our study shows that DeltaNp63 has essential and ancient role in the development of skin.

Seek protein which can interact with hepatitis B virus X protein from human liver cDNA library by yeast two-hybrid system

AIM: To seek the X associated protein (XAP) with the constructed bait vector pAS2-1X from normal human liver cDNA library.

METHODS: The X region of the HBV gene was amplied by PCR and cloned into the eukaryotic expression vector pAS2-1.The reconstituted plasmid pAS2-1X was transformed into the yeast cells and the expression of X protein (pX) was confirmed by Western blot analysis. Yeast cells were cotransformed with pAS2-1X and the normal human liver cDNA library and were grown in selective SC/-trp-leu-his-ade medium, the second screen was performed with the LacZ report gene. Furthermore, segregation analysis and mating experiment were performed to eliminate the false positive and the true positive clones were selected for PCR and sequencing.

RESULTS: Reconstituted plasmid pAS2-1X including the anticipated fragment of X gene was proved by auto-sequencing assay. Western blot analysis showed that reconstituted plasmid pAS2-1X expressed BD:X fusion protein in yeast cells. Of 5 × 10⁶ transformed colonies screened, 65 grew in the selective SC/-trp-leu-his-ade medium, 5 scored positive for β-gal activity, and only 2 remaining clones passed through the segregation analysis and mating experiment. Sequence analysis identified that two clones contained similar cDNA fragment: GAACTTGCG.

CONCLUSION: The short peptide (glutacid-leucine-alanine)is a possible required site for XAP binding to pX. Normal human liver cDNA library has difficulties in expressing the integrated XAP on yeast cells.

Through induction of juxtaposition and tyrosine kinase activity of Jak1, X-gene product of hepatitis B virus stimulates Ras and the transcriptional activation through AP-1, NF-kappaB, and SRE enhancers

Here, based on the recent finding of HBx (X-gene product of hepatitis B virus) as the inducer of Jak1, we investigated the mechanism for the HBx-mediated host cell regulation and found that (i) HBx associates specifically with Jak1 in vivo; (ii) HBx itself forms a dimer which leads to juxtaposition of associated Jak1 and subsequent activation of the tyrosine kinase activity of Jak1; (iii) HBx-mediated activation of the promoters containing AP-1-, NF-kappaB-, SRE-, and SIE-sites is dependent on the activation of Jak1; (iv) Jak1, once activated by HBx, induces Ras activity through recruitment of Grb2 and induces tyrosine phosphorylation of Raf1, but not shc. These findings show that previously reported functions of HBx, such as activation of multiple signaling pathways and transcriptional activation are attributable to HBx-mediated Jak1 activation.

Hepatitis B viral transactivator HBx alleviates p53-mediated repression of alpha-fetoprotein gene expression

Chronic infection with hepatitis B virus (HBV) is associated with development of hepatocellular carcinoma (HCC). The exact mechanism by which chronic infection with HBV contributes to onset of HCC is unknown. However, previous studies have implicated the HBV transactivator protein, HBx, in progression of HCC through its ability to bind the human tumor suppressor protein, p53. In this study, we have examined the ability of HBx to modify p53 regulation of the HCC tumor marker gene, alpha-fetoprotein (AFP). By utilizing in vitro chromatin assembly of DNA templates prior to transcription analysis, we have demonstrated that HBx functionally disrupts p53-mediated repression of AFP transcription through protein-protein interaction. HBx modification of p53 gene regulation is both tissue-specific and dependent upon the p53 binding element. Our data suggest that the mechanism by which HBx alleviates p53 repression of AFP transcription is through an association with DNA-bound p53, resulting in a loss of p53 interaction with liver-specific transcriptional co-repressors.

Induction of hepatitis B virus gene expression at low temperature

There is a limited understanding of the cellular regulation of HBV gene expression in differentiated hepatocytes. We previously demonstrated that HBV replication inversely correlates with cell proliferation and DNA synthesis. In this report, temperature-induced modulation of cell growth was used as a novel approach to study HBV gene expression in the absence of indirect effects from drugs or serum deprivation. We observed markedly elevated levels of hepatic HBV mRNA expression from integrated and episomal HBV DNA at 32 degrees C. Additionally, hepatoblastoma cells cultured at 32 degrees C expressed increased levels of albumin mRNA and decreased levels of c-myc mRNA, which demonstrates that liver-derived cells cultured at low temperature exhibit characteristics of functional and differentiated hepatocytes. In transiently transfected HepG2 cells cultured at 32 degrees C, the HBV enhancer 1 activated the X promoter and core/pregenomic promoter by 7.3- and 28-fold, respectively. In the absence of enhancer 1, core/pregenomic promoter activity was 2.4-fold higher than the X promoter in HepG2 cells at 32 degrees C. In contrast, enhancer 1 exclusively activated the X promoter in transfected non-liver cells at 32 degrees C. Therefore, the core/pregenomic promoter exhibits strict liver-specificity at low temperature. This work supports the hypothesis that HBV replication and gene expression are optimal in non-activated hepatocytes, and provides a novel system for delineating molecular aspects of the HBV replication process.