Hepatitis B Virus Gene Research Articles

Krüppel-like factor 15 activates hepatitis B virus gene expression and replication

Hepatitis B virus (HBV) is a small DNA virus that requires cellular transcription factors for the expression of its genes. To understand the molecular mechanisms that regulate HBV gene expression, we conducted a yeast one-hybrid screen to identify novel cellular transcription factors that may control HBV gene expression. Here, we demonstrate that Krüppel-like factor 15 (KLF15), a liver-enriched transcription factor, can robustly activate HBV surface and core promoters. Mutations in the putative KLF15 binding site in the HBV core promoter abolished the ability of KLF15 to activate the core promoter in luciferase assays. Furthermore, the overexpression of KLF15 stimulated the expression of HBV surface antigen (HBsAg) and the core protein and enhanced viral replication. Conversely, small interfering RNA knockdown of the endogenous KLF15 in Huh7 cells resulted in a reduction in HBV surface- and core-promoter activities. In electrophoretic mobility shift and chromatin immunoprecipitation assays, KLF15 binds to DNA probes derived from the core promoter and the surface promoter. Introduction of an expression vector for KLF15 short hairpin RNA, together with the HBV genome into the mouse liver using hydrodynamic injection, resulted in a significant reduction in viral gene expression and DNA replication. Additionally, mutations in the KLF15 response element in the HBV core promoter significantly reduced viral DNA levels in the mouse serum. KLF15 is a novel transcriptional activator for HBV core and surface promoters. It is possible that KLF15 may serve as a potential therapeutic target to reduce HBV gene expression and viral replication.

Use of RNA interference to modulate liver adenoma development in a murine model transgenic for hepatitis B virus

Chronic hepatitis B virus (HBV) infection is closely related to the development of severe liver complications, including hepatocellular carcinoma. In previous studies, we reported that in vivo long-term HBV suppression in transgenic mice can be achieved without apparent toxicity by short hairpin RNA sequentially delivered using adeno-associated viral (AAV) vectors of different serotypes. Our goal herein was to address the clinical utility of this delivery system and, in particular, to determine whether RNA interference (RNAi) and its ability to induce long-term HBV suppression will modulate the development of HBV-associated liver pathology. As a model system, we used a unique HBV transgenic mouse model, containing a 1.3 times over length of the HBV genome, on the ICR mouse background. These transgenic mice produce high serum HBV titers comparable with human chronic HBV patients, and, importantly, manifest characteristic HBV-associated pathology, including progressive hepatocellular injury and the development of hepatocellular adenoma. Using this system, we injected animals with AAV vectors expressing either HBV-specific or a control luciferase-specific short hairpin RNA and followed animals for a total of 18 months. We report herein that AAV-mediated RNAi therapy profoundly inhibits HBV replication and gene expression, with a significant reduction in hepatic regeneration, liver enzymes and, importantly, the appearance of liver adenomas. Indeed, the therapeutic effect of RNAi correlated with the reduction in HBV titers. Our data demonstrate that appropriately designed RNAi therapy has the potential to prevent formation of HBV-associated hepatocellular adenoma.

The X Protein of Hepatitis B Virus Inhibits Apoptosis in Hepatoma Cells through Enhancing the Methionine Adenosyltransferase 2A Gene Expression and Reducing S-Adenosylmethionine Production

The X protein (HBx) of hepatitis B virus (HBV) is involved in the development of hepatocellular carcinoma (HCC), and methionine adenosyltransferase 2A (MAT2A) promotes the growth of liver cancer cells through altering S-adenosylmethionine homeostasis. Thus, we speculated that a link between HBx and MAT2A may contribute to HCC development. In this study, the effects of HBx on MAT2A expression and cell apoptosis were investigated, and the molecular mechanism by which HBx and MAT2A regulate tumorigenesis was evaluated. Results from immunohistochemistry analyses of 37 pairs of HBV-associated liver cancer tissues/corresponding peritumor tissues showed that HBx and MAT2A are highly expressed in most liver tumor tissues. Our in vitro results revealed that HBx activates MAT2A expression in a dose-dependent manner in hepatoma cells, and such regulation requires the cis-regulatory elements NF-κB and CREB on the MAT2A gene promoter. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) further demonstrated that HBx facilitates the binding of NF-κB and CREB to MAT2A gene promoter. In addition, overexpression of HBx or MAT2A inhibits cell apoptosis, whereas knockdown of MAT2A expression stimulates apoptosis in hepatoma cells. Furthermore, we demonstrated that HBx reduces MAT1A expression and AdoMet production but enhances MAT2β expression. Thus, we proposed that HBx activates MAT2A expression through NF-κB and CREB signaling pathways to reduce AdoMet production, inhibit hepatoma cell apoptosis, and perhaps enhance HCC development. These findings should provide new insights into our understanding how the molecular mechanisms underline the effects of HBV infection on the production of MAT2A and the development of HCC.

Distribution of hepatitis B virus genotypes and serotypes in people who had a physical examination in Yunnan Province

To know genotypes and serotypes of hepatitis B virus (HBV) detected from hepatitis B infected people in Yunnan Province. Serum samples were collected from HBsAg carriers detected from people who had a physical examination at Yunnan Provincial Center for Disease Control and Prevention. The S genes of HBV were amplified by nested PCR and the PCR products were sequenced. The viral genotype was identified by phylogenetic analysis. 27 reference sequences corresponding to HBV genotype A to I were obtained from GenBank. According to the amino acid sequences deduced from the nucleotide sequences of S gene, the dominant serotype of HBV detected from these people were confirmed. 39 HBsAg positive serum samples were detected from 2216 people who had a physical examination. The results shows that 76.9% were C genotype; 15.4% were B genotype; 5.1% were D genotype; 2.5% were I genotype. Three serotypes were found. The rates of adw2, adrq+ and ayr serotypes are 71.8%, 17.9% and 10.3% respectively. All of adw2 subtype specimens are C genotype. Among the serum specimens in which both HBsAg and HBeAg are positive, 75% were C genotype and adw2 subtype. It is determined that the main genotype and subtype of HBV prevailed in Yunnan province is C genotype and adw2 subtype.

Oxygenated derivatives of cholesterol promote hepatitis B virus gene expression through nuclear receptor LXRα activation

Hepatitis B virus (HBV) gene expression and replication are regulated by the activation of a number of liver-enriched transcription factors dependent on intracellular and extracellular stimuli. However, the association between the metabolic events and HBV gene expression remains unclear. In this study, we assessed the effects of cholesterol metabolism on HBV viral replication and gene expression. Exposure of oxygenated derivatives of cholesterol (oxysterols) increased HBV gene expression and viral promoter activity. This increase in HBV transcription and replication was directed by nuclear receptor LXRα induction in the presence of oxysterols. In addition, HBV viral expression by oxysterol was inhibited through small heterodimer partner and sterol regulatory element-binding protein 2, key regulators of cholesterol synthesis. When IFNα and oxysterols were co-incubated, oxysterols and LXRα significantly reduced the anti-HBV effects of IFNα. These results point to a novel mechanism of oxysterol-mediated gene regulation in HBV replication and a potent mechanism underlying the failure of IFNα-based treatment.

Hepatocyte metabolic signalling pathways and regulation of hepatitis B virus expression

Hepatitis B virus (HBV) is a small DNA virus responsible for significant morbidity and mortality worldwide. The liver, which is the main target organ for HBV infection, provides the virus with the machinery necessary for persistent infection and propagation, a process that might ultimately lead to severe liver pathologies such as chronic hepatitis, cirrhosis and liver cancer. HBV gene expression is regulated mainly at the transcriptional level by recruitment of a whole set of cellular transcription factors (TFs) and co-activators to support transcription. Over the years, many of these TFs were identified and interestingly enough most are associated with the body's nutritional state. These include the hepatocyte nuclear factors, forkhead Box O1, Farnesoid X receptor, cyclic-AMP response element-binding (CREB), CCAAT/enhancer-binding protein (C/EBP) and glucocorticoid receptor TFs and the transcription coactivator PPARγ coactivator-1α. Consequently, HBV gene expression is linked to hepatic metabolic processes such as glucose and fat production and utilization as well as bile acids' production and secretion. Furthermore, recent evidence indicates that HBV actively interferes with some of these hepatic metabolic processes by manipulating key TFs, such as CREB and C/EBP, to meet its requirements. The discovery of the mechanisms by which HBV is controlled by the hepatic metabolic milieu may broaden our understanding of the unique regulation of HBV expression and may also explain the mechanisms by which HBV induces liver pathologies. The emerging principle of the intimate link between HBV and liver metabolism can be further exploited for host-targeted therapeutic strategies.

Effect of hepatitis B virus X gene on the expression of spastic paraplegia 21

To investigate the effect of hepatitis B virus(HBV) X gene on the expression of SPG21. The expressions of SPG21 mRNA and protein in HepG2 and HepG2.2.15 cells were tested by RT-PCR and western blot. HepG2 cells were co-transfected with reporter plasmid pGL3-SPG21 and plasmids carrying individual genes of HBV, the luciferase activity was measured and the expressions of SPG21 were detected by RT-PCR and western blot. The expressions of SPG21 mRNA and protein were higher in HepG2.2.15 cells than in HepG2 cells (0.36+/-0.06 vs 0.21+/-0.05, P value is less than 0.05). The activity of SPG21 in HepG2 cells transfected with pCMV-X was higher (875+/-27 vs 67+/-12, P value is less than 0.01) as compared to blank control group (transfected with pCMV-tag2B). HBV X gene enhanced SPG21 gene promoter activity, SPG21 mRNA expression and SPG21 protein production in HepG2 cells in a dose-dependent manner. HBV X gene can specially activate SPG21 expression.

Targets for human encoded microRNAs in HBV genes

MicroRNAs (miRNAs) are increasingly being shown to play vital roles in development, apoptosis, and oncogenesis by interfering with gene expression at the post-transcriptional level. miRNAs, in principle, can contribute to the repertoire of host-pathogen interactions during infection by the Hepatitis B virus (HBV). Using a consensus-scoring approach, high-scoring miRNA-target pairs were selected, which were identified by four well-established target-prediction softwares. The miRNAs miR-7, miR196b, miR433, and miR511 target the polymerase or S gene of HBV, miR205 targets the X gene, and miR345 targets the preC gene. The minimum free-energy values for the bound complexes were the lowest, and the rules so far observed for miRNA-target pairing, namely, (1) pairing at a continuous stretch of 6-7 bases toward the 5'-end of the miRNA and (2) incomplete complementarity with the target sequence, were found to be valid. The target regions were highly conserved across the various clades of HBV. miRNA expression profiles from previously reported Solexa-sequencing based experiments showed that the four human miRNAs are expressed in the liver. This is the first report of human miRNAs that can target crucial HBV genes.

High Conservation of Hepatitis B Virus Surface Genes during Maternal Vertical Transmission despite Active and Passive Vaccination

Objective: Our purpose was to explore the relationship between hepatitis B virus (HBV) gene heterogeneity and maternal vertical transmission. Methods: HBsAg-positive mothers and their neonates were selected and classified into a vertical infection neonate group (group N), a vertical infection mother group (group M) and a control group (group C). Serum HBsAg and HBeAg were examined. HBV gene fragments, including the pre-S1, and pre-S2 and S coding regions, were amplified and sequenced, and the genotype and serotype of the sequences were identified. Mutation sites and frequency of mutations were then compared between group N and group C. Results: A total of 104 HBV clone sequences were obtained. All obtained sequences belonged to genotype C and serotype adr. Upon comparing sequences between group N and group C, 4 nonsynonymous mutations were found with significant difference in mutation frequency (p < 0.05). When the mothers were both HBsAg and HBeAg positive, 10 nonsynonymous mutations were found. The frequencies of these mutations were significantly lower in group N than in group C (p < 0.05). Conclusion: The 10 HBV mutations were negatively associated with vertical transmission when maternal HBeAg was positive. Furthermore, the species that were vertically transmitted to the fetus were mainly wild-type.

Suppression of hepatitis B virus replication by microRNA-199a-3p and microRNA-210

Accumulating evidence suggests that microRNAs (miRNAs) control the replication of both RNA and DNA viruses. In order to determine whether host-encoded miRNAs affect hepatitis B virus (HBV) replication, antisense oligonucleotides (ASOs) of 328 identified human miRNAs were transfected into HepG2 2.2.15 cells, respectively. ELISA and MTS assay were used to measure the expression level of HBV S protein (HBsAg), HBV e antigen (HBeAg) and cell proliferation. Compared to experimental controls, miR-199a-3p and miR-210 efficiently reduced HBsAg expression without affecting HepG2 2.2.15 cell proliferation. Quantification of HBV DNA by real-time PCR showed that both miRNAs suppressed viral replication. Bioinformatics analysis indicated a putative binding site for miR-199a-3p in the HBsAg coding region and a putative binding site for miR-210 in the HBV pre-S1 region. The direct effect of miRNAs on the target region in HBV transcripts was validated by a fluorescent reporter assay, and the suppression of HBs gene expression by both miRNAs was measured by real-time PCR and Western blot. These results suggest that up-regulation of miR-199a-3p and miR-210 in HepG2 2.2.15 cells compared to HepG2 cells may play a role in regulating HBV replication and maintenance of a suitable level of virion production in persistent infection by targeting crucial HBV genes.

Control of hepatitis B virus at the level of transcription

Hepatitis B virus (HBV) is tightly controlled by a number of noncytotoxic mechanisms. This control occurs within the host hepatocyte at different steps of the HBV replication cycle. HBV persists by establishing a nuclear minichromosome, HBV cccDNA, serving as a transcription template for the viral pregenome and viral mRNAs. Nucleoside/nucleotide analogues widely used for antiviral therapy as well as most antiviral cytokines act at steps after transcription of HBV RNAs and thus can control virus replication but do not directly affect its gene expression. Control of HBV at the level of transcription in contrast is able to restrict both, HBV replication and gene expression. In the review, we focus on how HBV is controlled at the level of transcription. We discuss how the composition of transcription factors determines HBV gene expression and replication and how this may be influenced by antivirally active substances, e.g. the cytokine IL-6 or helioxanthin analogues, or by the differentiation state of the hepatocyte.

Inhibition of hepatitis B virus replication in vivo using lipoplexes containing altritol-modified antiviral siRNAs

Chronic infection with the hepatitis B virus (HBV) occurs in approximately 6% of the world's population and carriers of the virus are at risk for complicating hepatocellular carcinoma. Current treatment options have limited efficacy and chronic HBV infection is likely to remain a significant global medical problem for many years to come. Silencing HBV gene expression by harnessing RNA interference (RNAi) presents an attractive option for development of novel and effective anti HBV agents. However, despite significant and rapid progress, further refinement of existing technologies is necessary before clinical application of RNAi-based HBV therapies is realized. Limiting off target effects, improvement of delivery efficiency, dose regulation and preventing reactivation of viral replication are some of the hurdles that need to be overcome. To address this, we assessed the usefulness of the recently described class of altritol-containing synthetic siRNAs (ANA siRNAs), which were administered as lipoplexes and tested in vivo in a stringent HBV transgenic mouse model. Our observations show that ANA siRNAs are capable of silencing of HBV replication in vivo. Importantly, non specific immunostimulation was observed with unmodified siRNAs and this undesirable effect was significantly attenuated by ANA modification. Inhibition of HBV replication of approximately 50% was achieved without evidence for induction of toxicity. These results augur well for future application of ANA siRNA therapeutic lipoplexes.

Bile acids increase hepatitis B virus gene expression and inhibit interferon‐α activity

Hepatitis B virus (HBV) is a 3.2 kb DNA virus that preferentially replicates in the liver. A number of transcription factors, including nuclear receptors, regulate the activities of HBV promoters and enhancers. However, the association between these metabolic events and HBV replication remains to be clearly elucidated. In the present study, we assessed the effects of bile acid metabolism on HBV gene expression. Conditions associated with elevated bile acid levels within the liver include choleostatic liver diseases and an increased dietary cholesterol uptake. The results obtained in the present study demonstrate that bile acids promote the transcription and expression of the gene for HBV in hepatic cell lines; in addition, farnesoid X receptor alpha and the c-Jun N-terminal kinase/c-Jun signal transduction pathway mediate the regulatory effect of bile acids. Furthermore, an orphan nuclear receptor, small heterodimer partner protein, is also involved in the bile acid-mediated regulation of HBV gene expression. The bile acid-mediated promotion of HBV gene expression counteracts the antiviral effect of interferon-alpha.

Hepatitis B virus core antigen determines viral persistence in a C57BL/6 mouse model

We recently developed a mouse model of hepatitis B virus (HBV) persistence, in which a single i.v. hydrodynamic injection of HBV DNA to C57BL/6 mice allows HBV replication and induces a partial immune response, so that about 20-30% of the mice carry HBV for more than 6 months. The model was used to identify the viral antigen crucial for HBV persistence. We knocked out individual HBV genes by introducing a premature termination codon to the HBV core, HBeAg, HBx, and polymerase ORFs. The specific-gene-deficient HBV mutants were hydrodynamically injected into mice and the HBV profiles of the mice were monitored. About 90% of the mice that received the HBcAg-mutated HBV plasmid exhibited high levels of hepatitis B surface antigenemia and maintained HBsAg expression for more than 6 months after injection. To map the region of HBcAg essential for viral clearance, we constructed a set of serial HBcAg deletion mutants for hydrodynamic injection. We localized the essential region of HBcAg to the carboxyl terminus, specifically to the 10 terminal amino acids (HBcAg176-185). The majority of mice receiving this HBV mutant DNA did not elicit a proper HBcAg-specific IFN-gamma response and expressed HBV virions for 6 months. These results indicate that the immune response triggered in mice by HBcAg during exposure to HBV is important in determining HBV persistence.

Curcumin inhibits hepatitis B virus via down-regulation of the metabolic coactivator PGC-1α

Hepatitis B virus (HBV) infects the liver and uses its cell host for gene expression and propagation. Therefore, targeting host factors essential for HBV gene expression is a potential anti-viral strategy. Here we show that treating HBV expressing cells with the natural phenolic compound curcumin inhibits HBV gene expression and replication. This inhibition is mediated via down-regulation of PGC-1α, a starvation-induced protein that initiates the gluconeogenesis cascade and that has been shown to robustly coactivate HBV transcription. We suggest curcumin as a host targeted therapy for HBV infection that may complement current virus-specific therapies.

Differential inhibition of lamivudine-resistant hepatitis B virus by allele-specific RNAi

Drug-resistant hepatitis B virus (HBV) is a serious problem affecting antiviral therapy. In this study, two long-term eukaryotic cell lines with full-length HBV were constructed and contained either lamivudine-resistant mutants (HBV-YIDD) or wild-type virus (HBV-wt). High levels of intracellular viral DNA replication were observed continuously after transfecting the plasmids into HepG2 cells, and HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) were secreted into the cell culture supernatant. A series of experiments showed differential inhibition of HBV gene expression and replication by four specific siRNAs, according to the principles of allele-specific RNAi technology. The results showed that the designed siRNAs with a mismatch in the sixteenth nucleotide of the guide strands could effectively discriminate the HBV-YIDD mutants from the wild-type alleles, thus providing a new insight into the development of antiviral therapy with differing or complementary patterns characteristic of lamivudine-resistant HBV.

Hepatitis B Virus Replication Induces Methylation of both Host and Viral DNA

Control of viral replication is a major therapeutic goal to reduce morbidity and mortality from chronic hepatitis B virus (HBV) infection. Recently, methylation has been identified as a novel host defense mechanism, and methylation of viral DNA leads to downregulation of HBV gene expression. To better understand the mechanisms of HBV methylation, cell lines were exposed to HBV using a model system that mimics natural infection and the expression of host DNA methyltransferase genes (DNMTs) was measured. DNMT1, DNMT2, and DNMT3 were all significantly upregulated in response to HBV. DNMT3 was further studied because of its known role in the de novo methylation of DNA. Cotransfection experiments with full-length HBV and DNMT3 led to the downregulation of viral protein and pregenomic RNA production. To investigate whether the upregulation of DNMTs could also have an effect on the methylation of host DNA, cell lines were exposed to HBV in two independent model systems, one that mimics natural infection and a second model with temporary transfection. Host DNA methylation was measured by DNA microarray analysis. Increased methylation of host CpG islands was detected in both experimental systems. Two CpG islands, corresponding to genes SUFU and TIRAP, were selected, and the downregulation of these genes in hepatocellular carcinomas was confirmed. In conclusion, hepatocytes respond to HBV infection by upregulating DNMTs. The DNMTs methylate viral DNA, leading to decreased viral gene expression and decreased viral replication. However, virus-induced overexpression of DNMTs also leads to methylation of host CpG islands.

QDs-DNA nanosensor for the detection of hepatitis B virus DNA and the single-base mutants

We report here a quantum dots-DNA (QDs-DNA) nanosensor based on fluorescence resonance energy transfer (FRET) for the detection of the target DNA and single mismatch in hepatitis B virus (HBV) gene. The proposed one-pot DNA detection method is simple, rapid and efficient due to the elimination of the washing and separation steps. In this study, the water-soluble CdSe/ZnS QDs were prepared by replacing the trioctylphosphine oxide (TOPO) on the surface of QDs with 3-mercaptopropionic acid (MPA). Subsequently, oligonucleotides were attached to the QDs surface to form functional QDs-DNA conjugates. Along with the addition of DNA targets and Cy5-modified signal DNAs into the QDs-DNA conjugates, sandwiched hybrids were formed. The resulting assembly brings the Cy5 fluorophore, the acceptor, and the QDs, the donor, into proximity, leading to fluorescence emission from the acceptor by means of FRET on illumination of the donor. In order to efficiently detect single-base mutants in HBV gene, oligonucleotide ligation assay was employed. If there existed a single-base mismatch, which could be recognized by the ligase, the detection probe was not ligated and no Cy5 emission was produced due to the lack of FRET. The feasibility of the proposed method was also demonstrated in the detection of synthetic 30-mer oliginucleotide targets derived from the HBV with a sensitivity of 4.0 nM by using a multilabel counter. The method enables a simple and efficient detection that could be potentially used for high throughput and multiplex detections of target DNA and the mutants.

Progress in the use of RNA interference as a therapy for chronic hepatitis B virus infection

Chronic infection with hepatitis B virus (HBV) occurs in approximately 6% of the world's population and carriers of the virus are at risk for hepatocellular carcinoma and cirrhosis. Current treatment regimens, which include interferon-α and nucleoside/nucleotide analogs, are only partially effective and new treatment methods remain an important objective. Harnessing the RNA interference (RNAi) pathway to achieve post-transcriptional silencing of rogue genetic elements is an exciting avenue for development of novel therapeutic strategies. The specific and potent suppression of HBV gene expression and replication is an attractive option as a novel and effective approach for the treatment of chronic HBV infection. However, despite significant and rapid progress, existing RNAi technologies require further refinement before clinical applications can be realized. Here, we review current efforts aimed at improving the efficiency of anti-HBV RNAi-based delivery systems, at limiting the toxicities associated with RNAi modalities and at preventing reactivation of viral replication. We discuss the progress towards clinical implementation of anti-HBV RNAi therapies.

The “Trojan horse” model-delivery of anti-HBV small interfering RNAs by a recombinant HBV vector

Hepatitis B virus (HBV) is a small virus that infects the liver. The major obstacle in applying the RNA interference method as an anti-HBV weapon is the challenge to deliver the small interfering RNA molecules to the liver efficiently and specifically. Here we show that HBV-specific short hairpin RNAs (shRNAs) are efficiently expressed from a recombinant HBV into which an shRNA-expressing cassette was inserted, resulting in a significant knock-down of HBV gene expression. Notably, this recombinant HBV still expresses the HBV Core protein, which is targeted by the shRNAs produced by the same vector. Our results set the stage for further use of this recombinant HBV virus with the potential to function as a “Trojan horse”; one that specifically targets the liver and uses the resident virus as an helper for its own propagation, and at the same time eliminate itself and the resident HBV by knocking-down their gene expression.