Enhancer I predominance in hepatitis B virus gene expression

The dual-specificity kinase DYRK1A interacts with the Hepatitis B virus genome and regulates the production of viral RNA

The genome of Hepatitis B virus (HBV) persists in infected hepatocytes as a nuclear episome (cccDNA) that is responsible for the transcription of viral genes and viral rebound, following antiviral treatment arrest in chronically infected patients. There is currently no clinically approved therapeutic strategy able to efficiently target cccDNA (Lucifora J 2016). The development of alternative strategies aiming at permanently abrogating HBV RNA production requires a thorough understanding of cccDNA transcriptional and post-transcriptional regulation. In a previous study, we discovered that 1C8, a compound that inhibits the phosphorylation of some cellular RNA-binding proteins, could decrease the level of HBV RNAs. Here, we aimed at identifying kinases responsible for this effect. Among the kinases targeted by 1C8, we focused on DYRK1A, a dual-specificity kinase that controls the transcription of cellular genes by phosphorylating transcription factors, histones, chromatin regulators as well as RNA polymerase II. The results of a combination of genetic and chemical approaches using HBV-infected hepatocytes, indicated that DYRK1A positively regulates the production of HBV RNAs. In addition, we found that DYRK1A associates with cccDNA, and stimulates the production of HBV nascent RNAs. Finally, reporter gene assays showed that DYRK1A up-regulates the activity of the HBV enhancer 1/X promoter in a sequence-dependent manner. Altogether, these results indicate that DYRK1A is a proviral factor that may participate in the HBV life cycle by stimulating the production of HBx, a viral factor absolutely required to trigger the complete cccDNA transcriptional program.

Hepatitis B Viral Protein HBx: Roles in Viral Replication and Hepatocarcinogenesis

Hepatitis B virus (HBV) infection remains a major public health concern worldwide, with approximately 296 million individuals chronically infected. The HBV-encoded X protein (HBx) is a regulatory protein of 17 kDa, reportedly responsible for a broad range of functions, including viral replication and oncogenic processes. In this review, we summarize the state of knowledge on the mechanisms underlying HBx functions in viral replication, the antiviral effect of therapeutics directed against HBx, and the role of HBx in liver cancer development (including a hypothetical model of hepatocarcinogenesis). We conclude by highlighting major unanswered questions in the field and the implications of their answers.

Co-Transcriptional Regulation of HBV Replication: RNA Quality Also Matters

Chronic hepatitis B (CHB) virus infection is a major public health burden and the leading cause of hepatocellular carcinoma. Despite the efficacy of current treatments, hepatitis B virus (HBV) cannot be fully eradicated due to the persistence of its minichromosome, or covalently closed circular DNA (cccDNA). The HBV community is investing large human and financial resources to develop new therapeutic strategies that either silence or ideally degrade cccDNA, to cure HBV completely or functionally. cccDNA transcription is considered to be the key step for HBV replication. Transcription not only influences the levels of viral RNA produced, but also directly impacts their quality, generating multiple variants. Growing evidence advocates for the role of the co-transcriptional regulation of HBV RNAs during CHB and viral replication, paving the way for the development of novel therapies targeting these processes. This review focuses on the mechanisms controlling the different co-transcriptional processes that HBV RNAs undergo, and their contribution to both viral replication and HBV-induced liver pathogenesis.

G-quadruplexes control hepatitis B virus replication by promoting cccDNA transcription and phase separation in hepatocytes

Phase separation regulates fundamental processes in gene expression and is mediated by the local concentration of proteins and nucleic acids, as well as nucleic acid secondary structures such as G-quadruplexes (G4s). These structures play fundamental roles in both host gene expression and in viral replication due to their peculiar localisation in regulatory sequences. Hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) is an episomal minichromosome whose persistence is at the basis of chronic infection. Identifying the mechanisms controlling its transcriptional activity is indispensable to develop new therapeutic strategies against chronic hepatitis B. The aim of this study was to determine whether G4s are formed in cccDNA and regulate viral replication. Combining biochemistry and functional studies, we demonstrate that cccDNA indeed contains ten G4s structures. Furthermore, mutations disrupting two G4s located in the enhancer I HBV regulatory region altered cccDNA transcription and viral replication. Finally, we showed for the first time that cccDNA undergoes phase separation in a G4-dependent manner to promote its transcription in infected hepatocytes. Altogether, our data give new insight in the transcriptional regulation of the HBV minichromosome that might pave the way for the identification of novel targets to destabilize or silence cccDNA.

SKI complex: A multifaceted cytoplasmic RNA exosome cofactor in mRNA metabolism with links to disease, developmental processes, and antiviral responses

RNA stability and quality control are integral parts of gene expression regulation. A key factor shaping eukaryotic transcriptomes, mainly via 3'-5' exoribonucleolytic trimming or degradation of diverse transcripts in nuclear and cytoplasmic compartments, is the RNA exosome. Precise exosome targeting to various RNA molecules requires strict collaboration with specialized auxiliary factors, which facilitate interactions with its substrates. The predominant class of cytoplasmic RNA targeted by the exosome are protein-coding transcripts, which are carefully scrutinized for errors during translation. Normal, functional mRNAs are turned over following protein synthesis by the exosome or by Xrn1 5'-3'-exonuclease, acting in concert with Dcp1/2 decapping complex. In turn, aberrant transcripts are eliminated by dedicated surveillance pathways, triggered whenever ribosome translocation is impaired. Cytoplasmic 3'-5' mRNA decay and surveillance are dependent on the tight cooperation between the exosome and its evolutionary conserved co-factor-the SKI (superkiller) complex (SKIc). Here, we summarize recent findings from structural, biochemical, and functional studies of SKIc roles in controlling cytoplasmic RNA metabolism, including links to various cellular processes. Mechanism of SKIc action is illuminated by presentation of its spatial structure and details of its interactions with exosome and ribosome. Furthermore, contribution of SKIc and exosome to various mRNA decay pathways, usually converging on recycling of ribosomal subunits, is delineated. A crucial physiological role of SKIc is emphasized by describing association between its dysfunction and devastating human disease-a trichohepatoenteric syndrome (THES). Eventually, we discuss SKIc functions in the regulation of antiviral defense systems, cell signaling and developmental transitions, emerging from interdisciplinary investigations. This article is categorized under: RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms RNA Turnover and Surveillance > Regulation of RNA Stability RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Peptide YY inhibits transcription and replication of hepatitis B virus by suppressing promoter/enhancer activity

Hepatitis B virus (HBV) infection is a noteworthy cause of liver diseases, especially cirrhosis and hepatocellular carcinomas. However, the interaction between the host and HBV has not been fully elucidated. Peptide YY (PYY) is a 36-amino-acid gastrointestinal hormone that is mainly involved in the regulation of the human digestive system. This study found that PYY expression was reduced in HBV-expressing hepatocytes and HBV patients. Overexpression of PYY could significantly inhibit HBV RNA, DNA levels, and the secretion of HBsAg. In addition, PYY inhibits HBV RNA dependent on transcription through reducing the activities of CP/Enh I/II, SP1 and SP2. Meanwhile, PYY blocks HBV replication independent on core, polymerase protein and ε structure of pregenomic RNA. These results suggest that PYY can impair HBV replication by suppressing viral promoters/enhancers in hepatocytes. Our data shed light on a novel role for PYY as anti-HBV restriction factor.

Cellular Factors Involved in the Hepatitis D Virus Life Cycle

Hepatitis D virus (HDV) is a defective RNA virus with a negative-strand RNA genome encompassing less than 1700 nucleotides. The HDV genome encodes only for one protein, the hepatitis delta antigen (HDAg), which exists in two forms acting as nucleoproteins. HDV depends on the envelope proteins of the hepatitis B virus as a helper virus for packaging its ribonucleoprotein complex (RNP). HDV is considered the causative agent for the most severe form of viral hepatitis leading to liver fibrosis/cirrhosis and hepatocellular carcinoma. Many steps of the life cycle of HDV are still enigmatic. This review gives an overview of the complete life cycle of HDV and identifies gaps in knowledge. The focus is on the description of cellular factors being involved in the life cycle of HDV and the deregulation of cellular pathways by HDV with respect to their relevance for viral replication, morphogenesis and HDV-associated pathogenesis. Moreover, recent progress in antiviral strategies targeting cellular structures is summarized in this article.

Evidence for a Hepatitis B Virus Short RNA Fragment Directly Targeting the Cellular RRM2 Gene

The hepatitis B virus (HBV) is one of the smallest but most highly infectious human pathogens. With a DNA genome of only 3.2 kb and only four genes, HBV successfully completes its life cycle by using intricate processes to hijack the host machinery. HBV infects non-dividing liver cells in which dNTPs are limited. As a DNA virus, HBV requires dNTPs for its replication. HBV induces the ATR-mediated cellular DNA damage response pathway to overcome this constraint. This pathway upregulates R2 (RRM2) expression in generating an active RNR holoenzyme catalyzing de novo dNTP synthesis. Previously we reported that ERE, a small RNA fragment within the HBx ORF, is sufficient to induce R2 upregulation. Interestingly, there is high sequence similarity between ERE and a region within the R2 5′UTR that we named R2-box. Here, we established a mutant cell line in the R2-box region of the R2 gene using CRISPR-Cas9 technology to investigate the R2 regulation by ERE. This cell line expresses a much lower R2 level than the parental cell line. Interestingly, the HBV infection and life cycle were severely impaired. These cells became permissive to HBV infection upon ectopically R2 expression. These results validate the requirement of the R2 gene expression for HBV replication. Remarkably, the R2-box mutated cells became ERE refractory, suggesting that the homology region between ERE and R2 gene is critical for ERE-mediated R2 upregulation. Thus, along with the induction of the ATR pathway of the DNA damage response, ERE might also directly target the R2 gene via the R2-box.

Pathogenicity and virulence of Hepatitis B virus

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

Hepatocyte Growth Factor-Dependent Antiviral Activity of Activated cdc42-Associated Kinase 1 Against Hepatitis B Virus

Activated cdc42-associated kinase 1 (ACK1) is a well-known non-receptor tyrosine kinase that regulates cell proliferation and growth through activation of cellular signaling pathways, including mitogen-activated protein kinase (MAPK). However, the anti-HBV activity of ACK1 has not been elucidated. This study aimed to investigate the role of ACK1 in the HBV life cycle and the mechanism underlying the anti-HBV activity of ACK1. To examine the antiviral activity of ACK1, we established HepG2-ACK1 cells stably overexpressing ACK1. The HBV life cycle, including HBeAg/HBsAg secretion, HBV DNA/transcription, and enhancer activity, was analyzed in HepG2 and HepG2-ACK1 cells with HBV replication-competent HBV 1.2mer (HBV 1.2). Finally, the anti-HBV activity of ACK1 was examined in an HBV infection system. ACK1 suppressed HBV gene expression and transcription in HepG2 and HepG2-ACK1 cells. Furthermore, ACK1 inhibited HBV replication by decreasing viral enhancer activity. ACK1 exhibited its anti-HBV activity via activation of Erk1/2, which consequently downregulated the expression of HNF4α binding to HBV enhancers. Furthermore, hepatocyte growth factor (HGF) induced ACK1 expression at an early stage. Finally, ACK1 mediated the antiviral effect of HGF in the HBV infection system. These results indicated that ACK1 induced by HGF inhibited HBV replication at the transcriptional level by activating the MAPK-HNF signaling pathway. Our findings suggest that ACK1 is a potentially novel upstream molecule of MAPK-mediated anti-HBV activity.

RNR-R2 Upregulation by a Short Non-Coding Viral Transcript

DNA viruses require dNTPs for replication and have developed different strategies to increase intracellular dNTP pools. Hepatitis B virus (HBV) infects non-dividing cells in which dNTPs are scarce and the question is how viral replication takes place. Previously we reported that the virus induces the DNA damage response (DDR) pathway culminating in RNR-R2 expression and the generation of an active RNR holoenzyme, the key regulator of dNTP levels, leading to an increase in dNTPs. How the virus induces DDR and RNR-R2 upregulation is not completely known. The viral HBx open reading frame (ORF) was believed to trigger this pathway. Unexpectedly, however, we report here that the production of HBx protein is dispensable. We found that a small conserved region of 125 bases within the HBx ORF is sufficient to upregulate RNR-R2 expression in growth-arrested HepG2 cells and primary human hepatocytes. The observed HBV mRNA embedded regulatory element is named ERE. ERE in isolation is sufficient to activate the ATR-Chk1-E2F1-RNR-R2 DDR pathway. These findings demonstrate a non-coding function of HBV transcripts to support its propagation in non-cycling cells.

Hepatitis B virus middle surface antigen loss promotes clinical variant persistence in mouse models

Hepatitis B virus (HBV) middle surface antigen (MHBs) mutation or deletion occurs in patients with chronic HBV infection. However, the functional role of MHBs in HBV infection is still an enigma. Here, we reported that 7.33% (11/150) isolates of CHB patients had MHBs start codon mutations compared with 0.00% (0/146) in acute hepatitis B (AHB) patients. Interestingly, MHBs loss accounted for 11.88% (126/1061) isolates from NCBI GenBank, compared with 0.09% (1/1061) and 0.00% (0/1061) for HBV large surface antigen (LHBs) loss and HBV small surface antigen (SHBs) loss, respectively. One persistent HBV clone of genotype B (B56, MHBs loss) from a CHB patient was hydrodynamically injected into BALB/c mice. B56 persisted for >70 weeks in BALB/c mice, whereas B56 with restored MHBs (B56^M+) was quickly cleared within 28 days. Serum cytokine assays demonstrated that CXCL1, CXCL2, IL-6 and IL-33 were significantly increased during rapid HBV clearance in B56^M+ mice. Furthermore, the enhancers and promoters of B56 were proved to be required for B56 persistence in mice. Ablating MHBs expression improved the persistence of a new clone (HBV1.3, genotype B) which was recreated by using enhancers and promoters of B56. These data demonstrated that MHBs deletion can promote the persistence of specific HBV variants in a hydrodynamic mouse model. MHBs re-expression restored a rapid clearance of HBV, which was accompanied by cytokine responses including the elevation of CXCL1, CXCL2, IL-6 and IL-33.

Translatomic profiling reveals novel self-restricting virus-host interactions during HBV infection

BACKGROUND & AIMS

HBV remains a global threat to human health. It remains incompletely understood how HBV self-restricts in the host during most adult infections. Thus, we performed multi-omics analyses to systematically interrogate HBV-host interactions and the life cycle of HBV.

METHODS

RNA-sequencing and ribosome profiling were conducted with cell-based models for HBV replication and gene expression. The novel translational events or products hereby detected were then characterized, and functionally assessed in both cell and mouse models. Moreover, quasi-species analyses of HBV subpopulations were conducted with patients at immune tolerance or activation phases, using next- or third-generation sequencing.

RESULTS

We identified EnhI-SL (Enhancer I-stem loop) as a new cis element in the HBV genome; mutations disrupting EnhI-SL were found to elevate viral polymerase expression. Furthermore, while re-discovering HpZ/P', a previously under-explored isoform of HBV polymerase, we also identified HBxZ, a novel short isoform of HBX. Having confirmed their existence, we functionally characterized them as potent suppressors of HBV gene expression and genome replication. Mechanistically, HpZ/P' was found to repress HBV gene expression partially by interacting with, and sequestering SUPV3L1. Activation of the host immune system seemed to reduce the abundance of HBV mutants deficient in HpZ/P' or with disruptions in EnhI-SL. Finally, SRSF2, a host RNA spliceosome protein that is downregulated by HBV, was found to promote the splicing of viral pre-genomic RNA and HpZ/P' biogenesis.

CONCLUSION

This study has identified multiple self-restricting HBV-host interactions. In particular, SRSF2-HpZ/P' appeared to constitute another negative feedback mechanism in the HBV life cycle. Targeting host splicing machinery might thus represent a strategy to intervene in HBV-host interactions.

LAY SUMMARY

There remain many unknowns about the natural history of HBV infection in adults. Herein, we identified new HBV-host mechanisms which could be responsible for self-restricting infections. Targeting these mechanisms could be a promising strategy for the treatment of HBV infections.

A3G-induced mutations show a low prevalence and exhibit plus-strand regional distribution in hepatitis B virus DNA from patients with non-hepatocellular carcinoma (HCC) and HCC

APOBEC3G (A3G) cytidine deaminase is an innate immune restriction factor that can edit and inhibit hepatitis B virus (HBV) replication. The preferred target of A3G is deamination of the third cytosine of 5'CCC to form a mutant marker 5'CC C → K. However, the distribution of A3G-induced mutations on HBV DNA during infection is not well characterized. To provide clarity, we obtained the HBV DNA sequences from HBV infected individuals with and without hepatocellular carcinoma (HCC and non-HCC, respectively), from the NCBI database, and calculated the r values of A3G-induced 5'CC C → K mutation prevalence in HBV DNA. A3G-induced mutations were weakly prevalent and mainly distributed in the plus strand of HBV DNA (r = 1.407). The mutations on the minus strand were weaker (r = .8189). There were A3G-induced mutation regions in the 1200 to 2000 nt region of the plus strand and the 1600 to 1500 nt region of the minus strand. There was no significant difference in the r values of A3G-induced mutations in HBV DNA between the HCC and non-HCC groups. However, the rvalue of the plus strand 2400 to 2800 nt regions of HCC derived HBV DNA (r = 4.2) was significantly higher than that of the same regions of non-HCC derived HBV DNA (r = 1.21). These findings clarify the weak prevalence and preferred plus-strand distribution of A3G-induced mutations on HBV DNA from HCC and non-HCC. These findings may provide valuable clues regarding the interaction mechanism between A3G and HBV DNA and inform HCC screening.

Phosphorylation of CREB-Specific Coactivator CRTC2 at Ser238 Promotes Proliferation, Migration, and Invasion of Colorectal Cancer Cells

cAMP response element binding protein (CREB)-regulated transcription coactivator 2 (CRTC2), a member of the novel CRTC family of transcriptional coactivators that activates basic leucine zipper transcription factors, including CREB, is overexpressed in many carcinomas, including colon cancer. Phosphorylation of CRTC2 protein at different residues is important for its subcellular localization and activity. However, the functions of some of the serine phosphorylation sites have not been elucidated. This study aimed to investigate the effects of phosphorylation of Ser127, Ser238, and Ser245 sites of CRTC2 in colorectal cancer (CRC) cells. Recombinant lentiviral particles with a CRTC2-targeting small hairpin RNA (shRNA) sequence were transfected into CRC cells to obtained shCRTC2 cell lines. Site-directed mutagenesis of Ser127, Ser238, and Ser245 cells were constructed by transfecting CRTC2 cDNA containing S127A, S238A, and S245A mutations into shCRTC2. Cell proliferation was measured by cell counting kit-8. Cell migration and invasion were examined by transwell assay. mRNA expression was assayed by qRT-PCR, and protein expression was determined by Western blot. Our results indicate that CRTC2 is overexpressed in CRC cells. Knockdown of CRTC2 inhibits the proliferation, migration, and invasion of CRC cells. When the phosphorylation of CRTC2 Ser238 decreases due to the lack of ERK2, the phosphorylation of Ser171 site increases. The proliferation, migration and invasion of CRC cells were inhibited, the nuclear aggregation of CRTC2 in the nucleus was reduced, and the interaction between CRTC2 and CREB was weaken. It is shown that the phosphorylation of CRTC2 Ser238 is important for CREB transcriptional activity. These findings may help in the identification of potentially new targets for CRC therapy.

Insights into Hepatitis B Virus DNA Integration-55 Years after Virus Discovery

Hepatitis B virus (HBV), which was discovered in 1965, is a threat to global public health. HBV infects human hepatocytes and leads to acute and chronic liver diseases, and there is no cure. In cells infected by HBV, viral DNA can be integrated into the cellular genome. HBV DNA integration is a complicated process during the HBV life cycle. Although HBV integration normally results in replication-incompetent transcripts, it can still act as a template for viral protein expression. Of note, it is a primary driver of hepatocellular carcinoma (HCC). Recently, with the development of detection methods and research models, the molecular biology and the pathogenicity of HBV DNA integration have been better revealed. Here, we review the advances in the research of HBV DNA integration, including molecular mechanisms, detection methods, research models, the effects on host and viral gene expression, the role of HBV integrations in the pathogenesis of HCC, and potential treatment strategies. Finally, we discuss possible future research prospects of HBV DNA integration.

Hepatitis B virus cccDNA: Formation, regulation and therapeutic potential

Hepatitis B virus (HBV) infection remains a major public health concern worldwide with about 257 million individuals chronically infected. Current therapies can effectively control HBV replication and slow down disease progress, but cannot cure HBV infection. Upon infection, HBV establishes a pool of covalently closed circular DNA (cccDNA) in the nucleus of infected hepatocytes. The cccDNA exists as a minichromosome and resists to antivirals, thus a therapeutic eradication of cccDNA from the infected cells remains unattainable. In this review, we summarize the state of knowledge on the mechanisms underlying cccDNA formation and regulation, and discuss the possible strategies that may contribute to the eradication of HBV through targeting cccDNA.

A short note on HBV infection

HBV-related liver sickness or hepatocellular carcinoma is common worldwide. Therefore, it is of interest to document the current trends in hepatitis prevention, diagnosis, treatment and care.

Defined host factors support HBV infection in non-hepatic 293T cells

Hepatitis B virus (HBV) is a human hepatotropic virus. However, HBV infection also occurs at extrahepatic sites, but the relevant host factors required for HBV infection in non-hepatic cells are only partially understood. In this article, a non-hepatic cell culture model is constructed by exogenous expression of four host genes (NTCP, HNF4α, RXRα and PPARα) in human non-hepatic 293T cells. This cell culture model supports HBV entry, transcription and replication, as evidenced by the detection of HBV pgRNA, HBV cccDNA, HBsAg, HBeAg, HBcAg and HBVDNA. Our results suggest that the above cellular factors may play a key role in HBV infection of non-hepatic cells. This model will facilitate the identification of host genes that support extrahepatic HBV infection.

The Regulation of HBV Transcription and Replication

Hepatitis B virus (HBV) is a major human pathogen lacking a reliable curative therapy. Current therapeutics target the viral reverse transcriptase/DNA polymerase to inhibit viral replication but generally fail to resolve chronic HBV infections. Due to the limited coding potential of the HBV genome, alternative approaches for the treatment of chronic infections are desperately needed. An alternative approach to the development of antiviral therapeutics is to target cellular gene products that are critical to the viral life cycle. As transcription of the viral genome is an essential step in the viral life cycle, the selective inhibition of viral RNA synthesis is a possible approach for the development of additional therapeutic modalities that might be used in combination with currently available therapies. To address this possibility, a molecular understanding of the relationship between viral transcription and replication is required. The first step is to identify the transcription factors that are the most critical in controlling the levels of HBV RNA synthesis and to determine their in vivo role in viral biosynthesis. Mapping studies in cell culture utilizing reporter gene constructs permitted the identification of both ubiquitous and liver-enriched transcription factors capable of modulating transcription from the four HBV promoters. However, it was challenging to determine their relative importance for viral biosynthesis in the available human hepatoma replication systems. This technical limitation was addressed, in part, by the development of non-hepatoma HBV replication systems where viral biosynthesis was dependent on complementation with exogenously expressed transcription factors. These systems revealed the importance of specific nuclear receptors and hepatocyte nuclear factor 3 (HNF3)/forkhead box A (FoxA) transcription factors for HBV biosynthesis. Furthermore, using the HBV transgenic mouse model of chronic viral infection, the importance of various nuclear receptors and FoxA isoforms could be established in vivo. The availability of this combination of systems now permits a rational approach toward the development of selective host transcription factor inhibitors. This might permit the development of a new class of therapeutics to aid in the treatment and resolution of chronic HBV infections, which currently affects approximately 1 in 30 individuals worldwide and kills up to a million people annually.

HBV-encoded miR-2 functions as an oncogene by downregulating TRIM35 but upregulating RAN in liver cancer cells

BACKGROUND

Hepatitis B virus (HBV) infection has been well established as a high-risk factor for the carcinogenesis of hepatocellular carcinoma (HCC). Cellular microRNA (miRNA) is involved in tumorigenesis by accelerating the malignant phenotype in HCC. However, whether HBV can encode miRNAs that contribute to HCC is not entirely clear.

METHODS

In this study, an miRNA encoded by HBV (HBV-miR-2) was identified by Solexa sequencing in HBV-positive HCC specimens and further verified in serum samples from HCC patients with HBV infection and in HBV-positive HCC cell lines. To evaluate the roles of HBV-miR-2 in liver cancer cells, we determined cell viability and migration/invasion ability by gain-of-function experiment in HBV(-) liver cancer cells (HepG2 and Huh7) and loss-of-function experiments in Huh7 cells stably expressing HBV-miR-2 (Huh7/HBV-miR-2 cells) and HepG2.2.15 cells. Furthermore, to elucidate the mechanism by which HBV-miR-2 work on cell malignancy, we identified and studied the effect of two target genes (TRIM35 and RAN) of HBV-miR-2 in liver cancer cells.

FINDINGS

We revealed that HBV-miR-2 promoted HCC cell growth ability by suppressing apoptosis and promoting migration and invasion by enhancing the epithelial-mesenchymal transition (EMT), functioning as an oncogene in the development of HBV-related HCC. Furthermore, we demonstrated that HBV-miR-2 suppresses the expression of TRIM35 but enhances RAN expression by targeting their 3'-untranslated regions (3'UTR) and that the ectopic expression of TRIM35 or knockdown of RAN counteracted the malignant phenotypes induced by HBV-miR-2.

INTERPRETATION

Our findings indicate that an HBV-encoded miRNA, HBV-miR-2, promotes oncogenic activity by downregulating TRIM35 expression and upregulating RAN expression in liver cancer cells, likely providing insight into tumorigenesis in HBV-related liver cancer. FUND: This work was supported in part by the National Natural Science Foundation of China (No: 81830094; 91629302; 31270818) and the Natural Science Foundation of Tianjin (No: 12JCZDJC25100).

Distribution and difference of APOBEC-induced mutations in the TpCpW context of HBV DNA between HCC and non-HCC

Hepatitis B virus (HBV) DNA is vulnerable to editing by human apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like (APOBEC) cytidine deaminases. However, the distribution of APOBEC-induced mutations on HBV DNA is not well characterized. To this end, we obtained the HBV DNA sequence of HBV-infected individuals with and without hepatocellular carcinoma (HCC and non-HCC groups, respectively) from NCBI database and calculated the r_apo values of APOBEC-induced TpCpW→TpKpW mutation prevalence in HBV DNA. The results showed that the APOBEC-induced mutations were mainly distributed in the minus strand of non-HCC-derived HBV DNA (r_apo  = 2.04), while the mutation on the plus-strand was weaker (r_apo  = 0.99). There were high APOBEC-induced mutation regions in the minus strand of HBV DNA 1 to 1000 nucleotides (nts) region and in the plus-strand of HBV DNA 1000 to 1500 nts region; the mutations in the 1 to 1000 nts region were mainly TpCpW→TpTpW mutation types (total T/G: 111/18) and a number of these were missense mutations (missense/synonymous: 35/94 in P gene, 17/15 in S gene, and 5/10 in X gene). The difference between minus to plus-strand r_apo of HCC-derived HBV DNA (1.96) was greater than that of the non-HCC group (1.05). The minus-strand r_apo of HCC-derived HBV DNA regions 1000 to1500nts and 1500 to 2000 nts (r_apo = 4.2 and 4.2) was also higher than that of the same regions of non-HCC-derived HBV DNA (r_apo  = 1.2 and 1.1). Finally, the ratio of minus to plus-strand r_apo was used to distinguish HCC-derived HBV DNA from non-HCC-derived HBV DNA. This study unraveled the distribution characteristics of APOBEC-induced mutations on double strands of HBV DNA from HCC and non-HCC samples. Our findings would help understand the mechanism of APOBECs on HBV DNA and may provide important insights for the screening of HCC.

Characterization of Novel Splice Variants of Zinc Finger Antiviral Protein (ZAP)

Given the unprecedented scale of the recent Ebola and Zika viral epidemics, it is crucial to understand the biology of host factors with broad antiviral action in order to develop novel therapeutic approaches. Here, we look into one such factor: zinc finger antiviral protein (ZAP) inhibits a variety of RNA and DNA viruses. Alternative splicing results in two isoforms that differ at their C termini: ZAPL (long) encodes a poly(ADP-ribose) polymerase (PARP)-like domain that is missing in ZAPS (short). Previously, it has been shown that ZAPL is more antiviral than ZAPS, while the latter is more induced by interferon (IFN). In this study, we discovered and confirmed the expression of two additional splice variants of human ZAP: ZAPXL (extralong) and ZAPM (medium). We also found two haplotypes of human ZAP. Since ZAPL and ZAPS have differential activities, we hypothesize that all four ZAP isoforms have evolved to mediate distinct antiviral and/or cellular functions. By taking a gene-knockout-and-reconstitution approach, we have characterized the antiviral, translational inhibition, and IFN activation activities of individual ZAP isoforms. Our work demonstrates that ZAPL and ZAPXL are more active against alphaviruses and hepatitis B virus (HBV) than ZAPS and ZAPM and elucidates the effects of splice variants on the action of a broad-spectrum antiviral factor.IMPORTANCE ZAP is an IFN-induced host factor that can inhibit a wide range of viruses, and there is great interest in fully characterizing its antiviral mechanism. This is the first study that defines the antiviral capacities of individual ZAP isoforms in the absence of endogenous ZAP expression and, hence, cross talk with other isoforms. Our data demonstrate that ZAP is expressed as four different forms: ZAPS, ZAPM, ZAPL, and ZAPXL. The longer ZAP isoforms better inhibit alphaviruses and HBV, while all isoforms equally inhibit Ebola virus transcription and replication. In addition, there is no difference in the abilities of ZAP isoforms to enhance the induction of type I IFN expression. Our results show that the full spectrum of ZAP activities can change depending on the virus target and the relative levels of basal expression and induction by IFN or infection.

HoxA10 Facilitates SHP-1-Catalyzed Dephosphorylation of p38 MAPK/STAT3 To Repress Hepatitis B Virus Replication by a Feedback Regulatory Mechanism

Hepatitis B virus (HBV) infection is the leading cause of chronic hepatitis B (CHB), liver cirrhosis (LC), and hepatocellular carcinoma (HCC). This study reveals a distinct mechanism underlying the regulation of HBV replication. HBV activates homeobox A10 (HoxA10) in human hepatocytes, leukocytes, peripheral blood mononuclear cells (PBMCs), HepG2-NTCP cells, leukocytes isolated from CHB patients, and HBV-associated HCC tissues. HoxA10 in turn represses HBV replication in human hepatocytes, HepG2-NTCP cells, and BALB/c mice. Interestingly, we show that during early HBV infection, p38 mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) were activated to facilitate HBV replication; however, during late HBV infection, HoxA10 was induced to attenuate HBV replication. Detailed studies reveal that HoxA10 binds to p38 MAPK, recruits SH2-containing protein tyrosine phosphatase 1 (SHP-1) to facilitate SHP-1 in catalyzing dephosphorylation of p38 MAPK/STAT3, and thereby attenuates p38 MAPK/STAT3 activation and HBV replication. Furthermore, HoxA10 binds to the HBV enhancer element I (EnhI)/X promoter, competes with STAT3 for binding of the promoter, and thereby represses HBV transcription. Taken together, these results show that HoxA10 attenuates HBV replication through repressing the p38 MAPK/STAT3 pathway by two approaches: HoxA10 interacts with p38 MAPK and recruits SHP-1 to repress HBV replication, and HoxA10 binds to the EnhI/X promoter and competes with STAT3 to attenuate HBV transcription. Thus, the function of HoxA10 is similar to the action of interferon (IFN) in terms of inhibition of HBV infection; however, the mechanism of HoxA10-mediated repression of HBV replication is different from the mechanism underlying IFN-induced inhibition of HBV infection.IMPORTANCE Two billion people have been infected with HBV worldwide; about 240 million infected patients developed chronic hepatitis B (CHB), and 650,000 die each year from liver cirrhosis (LC) or hepatocellular carcinoma (HCC). This work elucidates a mechanism underlying the control of HBV replication. HBV infection activates HoxA10, a regulator of cell differentiation and cancer progression, in human cells and patients with CHB and HCC. HoxA10 subsequently inhibits HBV replication in human tissue culture cells and mice. Additionally, HoxA10 interacts with p38 MAPK to repress the activation of p38 MAPK and STAT3 and recruits and facilitates SHP-1 to catalyze the dephosphorylation of p38 MAPK and STAT3. Moreover, HoxA10 competes with STAT3 for binding of the HBV X promoter to repress HBV transcription. Thus, this work reveals a negative regulatory mechanism underlying the control of HBV replication and provides new insights into the development of potential agents to control HBV infection.

Development of Direct-acting Antiviral and Host-targeting Agents for Treatment of Hepatitis B Virus Infection

Hepatitis B virus (HBV) infection affects approximately 300 million people worldwide. Although antiviral therapies have improved the long-term outcomes, patients often require life-long treatment and there is no cure for HBV infection. New technologies can help us learn more about the pathogenesis of HBV infection and develop therapeutic agents to reduce its burden. We review recent advances in development of direct-acting antiviral and host-targeting agents, some of which have entered clinical trials. We also discuss strategies for unbiased high-throughput screens to identify compounds that inhibit HBV and for repurposing existing drugs.

Hepatitis B virus pathogenesis: Fresh insights into hepatitis B virus RNA

Hepatitis B virus (HBV) is still a worldwide health concern. While divergent factors are involved in its pathogenesis, it is now clear that HBV RNAs, principally templates for viral proteins and viral DNAs, have diverse biological functions involved in HBV pathogenesis. These functions include viral replication, hepatic fibrosis and hepatocarcinogenesis. Depending on the sequence similarities, HBV RNAs may act as sponges for host miRNAs and may deregulate miRNA functions, possibly leading to pathological consequences. Some parts of the HBV RNA molecule may function as viral-derived miRNA, which regulates viral replication. HBV DNA can integrate into the host genomic DNA and produce novel viral-host fusion RNA, which may have pathological functions. To date, elimination of HBV-derived covalently closed circular DNA has not been achieved. However, RNA transcription silencing may be an alternative practical approach to treat HBV-induced pathogenesis. A full understanding of HBV RNA transcription and the biological functions of HBV RNA may open a new avenue for the development of novel HBV therapeutics.

Silencing Retinoid X Receptor Alpha Expression Enhances Early-Stage Hepatitis B Virus Infection In Cell Cultures

Multiple steps of the life cycle of hepatitis B virus (HBV) are known to be coupled to hepatic metabolism. However, the details of involvement of the hepatic metabolic milieu in HBV infection remain incompletely understood. Hepatic lipid metabolism is controlled by a complicated transcription factor network centered on retinoid X receptor alpha (RXRα). Here, we report that RXRα negatively regulates HBV infection at an early stage in cell cultures. The RXR-specific agonist bexarotene inhibits HBV in HepG2 cells expressing the sodium taurocholate cotransporting polypeptide (NTCP) (HepG2-NTCP), HepaRG cells, and primary Tupaia hepatocytes (PTHs); reducing RXRα expression significantly enhanced HBV infection in the cells. Transcriptome sequencing (RNA-seq) analysis of HepG2-NTCP cells with a disrupted RXRα gene revealed that reduced gene expression in arachidonic acid (AA)/eicosanoid biosynthesis pathways, including the AA synthases phospholipase A2 group IIA (PLA2G2A), is associated with increased HBV infection. Moreover, exogenous treatment of AA inhibits HBV infection in HepG2-NTCP cells. These data demonstrate that RXRα is an important cellular factor in modulating HBV infection and implicate the participation of AA/eicosanoid biosynthesis pathways in the regulation of HBV infection.IMPORTANCE Understanding how HBV infection is connected with hepatic lipid metabolism may provide new insights into virus infection and its pathogenesis. By a series of genetic studies in combination with transcriptome analysis and pharmacological assays, we here investigated the role of cellular retinoid X receptor alpha (RXRα), a crucial transcription factor for controlling hepatic lipid metabolism, in de novo HBV infection in cell cultures. We found that silencing of RXRα resulted in elevated HBV covalently closed circular DNA (cccDNA) formation and viral antigen production, while activation of RXRα reduced HBV infection efficiency. Our results also showed that silencing phospholipase A2 group IIA (PLA2G2A), a key enzyme of arachidonic acid (AA) synthases, enhanced HBV infection efficiency in HepG2-NTCP cells and that exogenous AA treatment reduced de novo HBV infection in the cells. These findings unveil RXRα as an important cellular factor in modulating HBV infection and may point to a new strategy for host-targeted therapies against HBV.

Engineered zinc-finger transcription factors inhibit the replication and transcription of HBV in vitro and in vivo

In the present study, an artificial zinc-finger transcription factor eukaryotic expression vector specifically recognizing and binding to the hepatitis B virus (HBV) enhancer (Enh) was constructed, which inhibited the replication and expression of HBV DNA. The HBV EnhI‑specific pcDNA3.1‑artificial transcription factor (ATF) vector was successfully constructed, and then transformed or injected into HepG2.2.15 cells and HBV transgenic mice, respectively. The results demonstrated that the HBV EnhI (1,070‑1,234 bp)‑specific ATF significantly inhibited the replication and transcription of HBV DNA in vivo and in vitro. The HBV EnhI‑specific ATF may be a meritorious component of progressive combination therapies for eliminating HBV DNA in infected patients. A radical cure for chronic HBV infection may become feasible by using this bioengineering technology.

Identification of Slug and SOX7 as transcriptional repressors binding to the hepatitis B virus core promoter

BACKGROUND & AIMS

The Hepatitis B Virus (HBV) may gain entry into non-liver cells but does not actively replicate in them. We investigated the possibility that these cells possess mechanisms that block HBV core promoter (HBVCP) transcription, specifically absent in liver cells, which together with other liver-specific mechanisms, such as sodium-taurocholate cotransporting polypeptide-mediated entry, enable liver cells to effectively produce HBV.

METHODS

Liver and non-liver cell lines were screened for their capacity to activate the HBVCP and synthesize pre-genomic RNA (pgRNA). Transcription regulators differentially expressed between cells with active or inactive HBVCP were determined by human transcriptome array. Slug (SNAI2) and SRY-related HMG box 7 (SOX7) transcriptional repressors were identified and shown to bind specifically to the HBVCP by electrophoretic mobility shift assay. The resultant inhibitory effect on HBVCP transcription was validated using luciferase reporter and assays for pgRNA, HBcAg and cccDNA accumulation in cells with HBV replicon and HBV infection models. To further confirm their specific activity, short peptide mimetics generated from Slug zinc-finger domains and SOX7 HMG-box were generated.

RESULTS

The HBVCP was found to be active in liver and selected non-liver cells. These cells have low/negligible expression of Slug and SOX7, which inhibit HBVCP transcription specifically by binding at the pgRNA initiator site and competitively displacing hepatocyte nuclear factor 4α, respectively. Overexpression of Slug and/or SOX7 specifically reduced HBVCP transcription, significantly diminishing pgRNA synthesis, HBcAg and cccDNA accumulation in HBV-infected primary human hepatocytes. Similar results were obtained with Slug and SOX7 stapled peptides individually, which were even more potent in combination.

CONCLUSIONS

Slug and SOX7 are transcriptional repressors that bind specifically to the HBVCP. Their absence or weak expression in liver cells contribute to the favorable host environment for the active and efficient production of HBV.

LAY SUMMARY

Hepatitis B virus (HBV) replication occurs efficiently in human liver because of the specificity of viral uptake receptors and presence of numerous liver-enriched transcription activators. Herein, we show that the specific lack of transcriptional inhibitory mechanisms in liver cells also contribute to effective HBV production. HBV replication is kept low in non-liver cells as transcriptional repressors Slug and SRY-related HMG box 7 (SOX7) actively bind to the transcriptional initiator and displace transcription activators, respectively, within the HBV core promoter.

Virus-host interplay in hepatitis B virus infection and epigenetic treatment strategies

Worldwide, chronic hepatitis B virus (HBV) infection is a major health problem and no cure exists. Importantly, hepatocyte intrusion by HBV particles results in a complex deregulation of both viral and host cellular genetic and epigenetic processes. Among the attempts to develop novel therapeutic approaches against HBV infection, several options targeting the epigenomic regulation of HBV replication are gaining attention. These include the experimental treatment with 'epidrugs'. Moreover, as a targeted approach, the principle of 'epigenetic editing' recently is being exploited to control viral replication. Silencing of HBV by specific rewriting of epigenetic marks might diminish viral replication, viremia, and infectivity, eventually controlling the disease and its complications. Additionally, epigenetic editing can be used as an experimental tool to increase our limited understanding regarding the role of epigenetic modifications in viral infections. Aiming for permanent epigenetic reprogramming of the viral genome without unspecific side effects, this breakthrough may pave the roads for an ambitious technological pursuit: to start designing a curative approach utilizing manipulative molecular therapies for viral infections in vivo.

A Broad RNA Virus Survey Reveals Both miRNA Dependence and Functional Sequestration

Small non-coding RNAs have emerged as key modulators of viral infection. However, with the exception of hepatitis C virus, which requires the liver-specific microRNA (miRNA)-122, the interactions of RNA viruses with host miRNAs remain poorly characterized. Here, we used crosslinking immunoprecipitation (CLIP) of the Argonaute (AGO) proteins to characterize strengths and specificities of miRNA interactions in the context of 15 different RNA virus infections, including several clinically relevant pathogens. Notably, replication of pestiviruses, a major threat to milk and meat industries, critically depended on the interaction of cellular miR-17 and let-7 with the viral 3' UTR. Unlike canonical miRNA interactions, miR-17 and let-7 binding enhanced pestivirus translation and RNA stability. miR-17 sequestration by pestiviruses conferred reduced AGO binding and functional de-repression of cellular miR-17 targets, thereby altering the host transcriptome. These findings generalize the concept of RNA virus dependence on cellular miRNAs and connect virus-induced miRNA sequestration to host transcriptome regulation.

Hepatitis B virus molecular biology and pathogenesis

As obligate intracellular parasites, viruses need a host cell to provide a milieu favorable to viral replication. Consequently, viruses often adopt mechanisms to subvert host cellular signaling processes. While beneficial for the viral replication cycle, virus-induced deregulation of host cellular signaling processes can be detrimental to host cell physiology and can lead to virus-associated pathogenesis, including, for oncogenic viruses, cell transformation and cancer progression. Included among these oncogenic viruses is the hepatitis B virus (HBV). Despite the availability of an HBV vaccine, 350-500 million people worldwide are chronically infected with HBV, and a significant number of these chronically infected individuals will develop hepatocellular carcinoma (HCC). Epidemiological studies indicate that chronic infection with HBV is the leading risk factor for the development of HCC. Globally, HCC is the second highest cause of cancer-associated deaths, underscoring the need for understanding mechanisms that regulate HBV replication and the development of HBV-associated HCC. HBV is the prototype member of the Hepadnaviridae family; members of this family of viruses have a narrow host range and predominately infect hepatocytes in their respective hosts. The extremely small and compact hepadnaviral genome, the unique arrangement of open reading frames, and a replication strategy utilizing reverse transcription of an RNA intermediate to generate the DNA genome are distinguishing features of the Hepadnaviridae. In this review, we provide a comprehensive description of HBV biology, summarize the model systems used for studying HBV infections, and highlight potential mechanisms that link a chronic HBV-infection to the development of HCC. For example, the HBV X protein (HBx), a key regulatory HBV protein that is important for HBV replication, is thought to play a cofactor role in the development of HBV-induced HCC, and we highlight the functions of HBx that may contribute to the development of HBV-associated HCC.

HBx-induced MiR-1269b in NF-κB dependent manner upregulates cell division cycle 40 homolog (CDC40) to promote proliferation and migration in hepatoma cells

BACKGROUND

Occurrence and progression of hepatocellular carcinoma (HCC) are associated with hepatitis B virus (HBV) infection. miR-1269b is up-regulated in HCC cells and tissues. However, the regulation of miR-1269b expression by HBV and the mechanism underlying the oncogenic activity of miR-1269b in HCC are unclear.

METHODS

Reverse transcription quantitative PCR (RT-qPCR) was used to measure the expression of miR-1269b and target genes in HCC tissues and cell lines. Western blot analysis was used to assess the expression of miR-1269b target genes and related proteins. Using luciferase reporter assays and EMSA, we identified the factors regulating the transcriptional level of miR-1269b. Colony formation, flow cytometry and cell migration assays were performed to evaluate the phenotypic changes caused by miR-1269b and its target in HCC cells.

RESULTS

We demonstrated that the expression levels of pre-miR-1269b and miR-1269b in HBV-positive HepG2.2.15 cells were dramatically increased compared with HBV-negative HepG2 cells. HBx was shown to facilitate translocation of NF-κB from the cytoplasm to the nucleus, and NF-κB binds to the promoter of miR-1269b to enhance its transcription. miR-1269b targets and up-regulates CDC40, a cell division cycle 40 homolog. CDC40 increases cell cycle progression, cell proliferation and migration. Rescue experiment indicated that CDC40 promotes malignancy induced by miR-1269b in HCC cells.

CONCLUSION

We found that HBx activates NF-κB to promote the expression of miR1269b, which augments CDC40 expression, contributing to malignancy in HCC. Our findings provide insights into the mechanisms underlying HBV-induced hepatocarcinogenesis.

Cleaved c-FLIP mediates the antiviral effect of TNF-α against hepatitis B virus by dysregulating hepatocyte nuclear factors

BACKGROUND & AIMS

Cytokines are key molecules implicated in the defense against virus infection. Tumor necrosis factor-alpha (TNF-α) is well known to block the replication of hepatitis B virus (HBV). However, the molecular mechanism and the downstream effector molecules remain largely unknown.

METHODS

In this study, we investigated the antiviral effect and mechanism of p22-FLIP (FLICE-inhibitory protein) by ectopic expression in vitro and in vivo. In addition, to provide the biological relevance of our study, we examined that the p22-FLIP is involved in TNF-α-mediated suppression of HBV in primary human hepatocytes.

RESULTS

We found that p22-FLIP, a newly discovered c-FLIP cleavage product, inhibited HBV replication at the transcriptional level in both hepatoma cells and primary human hepatocytes, and that c-FLIP conversion to p22-FLIP was stimulated by the TNF-α/NF-κB pathway. p22-FLIP inhibited HBV replication through the upregulation of HNF3β but downregulation of HNF4α, thus inhibiting both HBV enhancer elements. Finally, p22-FLIP potently inhibited HBV DNA replication in a mouse model of HBV replication.

CONCLUSIONS

Taken together, these findings suggest that the anti-apoptotic p22-FLIP serves a novel function of inhibiting HBV transcription, and mediates the antiviral effect of TNF-α against HBV replication.

Wild type HBx and truncated HBx: Pleiotropic regulators driving sequential genetic and epigenetic steps of hepatocarcinogenesis and progression of HBV-associated neoplasms

Hepatitis B virus (HBV) is one of the causative agents of hepatocellular carcinoma. The molecular mechanisms of tumorigenesis are complex. One of the host factors involved is apparently the long-lasting inflammatory reaction which accompanies chronic HBV infection. Although HBV lacks a typical viral oncogene, the HBx gene encoding a pleiotropic regulatory protein emerged as a major player in liver carcinogenesis. Here we review the tumorigenic functions of HBx with an emphasis on wild type and truncated HBx variants, and their role in the transcriptional dysregulation and epigenetic reprogramming of the host cell genome. We suggest that HBx acquired by the HBV genome during evolution acts like a cellular proto-onc gene that is activated by deletion during hepatocarcinogenesis. The resulting viral oncogene (v-onc gene) codes for a truncated HBx protein that facilitates tumor progression. Copyright © 2015 John Wiley & Sons, Ltd.

CRISPR/Cas9 cleavage of viral DNA efficiently suppresses hepatitis B virus

Chronic hepatitis B virus (HBV) infection is prevalent, deadly, and seldom cured due to the persistence of viral episomal DNA (cccDNA) in infected cells. Newly developed genome engineering tools may offer the ability to directly cleave viral DNA, thereby promoting viral clearance. Here, we show that the CRISPR/Cas9 system can specifically target and cleave conserved regions in the HBV genome, resulting in robust suppression of viral gene expression and replication. Upon sustained expression of Cas9 and appropriately chosen guide RNAs, we demonstrate cleavage of cccDNA by Cas9 and a dramatic reduction in both cccDNA and other parameters of viral gene expression and replication. Thus, we show that directly targeting viral episomal DNA is a novel therapeutic approach to control the virus and possibly cure patients.

The hepatitis B virus (HBV) core protein enhances the transcription activation of CRE via the CRE/CREB/CBP pathway

We previously reported that hepatitis B virus core protein (HBc) can bind to the Enhancer I (Enh I) domain and can accumulate with transcription coactivator cAMP response element (CRE). This raises the possibility that HBc may interact with CRE/CREB and regulate CRE transcription activation. In this study, we investigated the function and mechanisms of HBc in regulating CRE transcriptional activation using the HepG2 cell line. Our results showed the following: (1) HBc expression significantly increases HBV CRE transcriptional activation; (2) phosphorylation of the serine residues in the arginine-rich domain (ARD) of HBc protein impacts the function of transcriptional activation by the CRE; (3) HBc protein significantly increases HBV CRE transcriptional activation following forskolin treatment; (4) HBc nonspecifically binds to CRE and enhances the binding of the cAMP response element-binding protein (CREB) to CRE; and (5) HBc increases the concurrent accumulation of CREB and CBP at the CRE region. HBc activates Enh I through its binding to CRE, increasing the concurrent accumulation of CREB/CBP on CRE, and thus increases CRE transcriptional activation.

Transbody against hepatitis B virus core protein inhibits hepatitis B virus replication in vitro

Hepatitis B virus (HBV) infection is one of the major causes of chronic liver diseases. The current therapeutics show limited efficacy. In the HBV life cycle, virus core antigen (HBcAg) plays important multiple roles. Blocking the pleiotropic functions of HBcAg may thus represent a promising strategy for anti-HBV replication. In this study, monoclonal antibody (MAb) against core antigen of human HBV was coupled with TAT protein transduction domain (TAT PTD) to form transbody, and the effect on virus replication was evaluated in vitro. The HBV transbody, HBcMAb-TAT PTD conjugate, recognized HBcAg and retained cell-penetrating activity in living cells. In HBV-transfected liver cell line HepG2.2.15, HBV transbody suppressed not only the extracellular HBsAg, HBeAg and HBV DNA, but also the intracellular HBsAg, HBeAg, HBcAg and HBV DNA in a dose-dependent manner. These results indicate that the transbody prepared possesses readily cell-penetrating ability and potent antiviral activity, providing a novel approach, a cell-permeable antibody against HBcAg, for the treatment of HBV infection.

The inhibitory effect of the hepatitis B virus singly-spliced RNA-encoded p21.5 protein on HBV nucleocapsid formation

Hepatitis B virus (HBV) is the smallest DNA virus and the major cause of acute and chronic hepatitis. The 3.2 kb HBV viral genome generates four major species of unspliced viral transcript as well as several alternatively spliced RNAs. A 2.2 kb singly-spliced RNA is the most abundant spliced RNA and is widely expressed among all HBV genotypes. The expression of the singly-spliced RNA, as well as that of its encoded protein HBSP, is strongly associated with hepatopathology during HBV infection. Here, we report a novel inhibitory role of a p21.5 protein, which is encoded by a 2.2 kb singly-spliced RNA, in the modulation of HBV replication. We show that overexpression of the singly-spliced RNA is able to efficiently inhibit HBV replication. Furthermore, a mutation in the ATG start codon of the precore region completely abolishes the inhibitory effect of the singly-spliced RNA, indicating that a viral protein (p21.5) derived from the singly-spliced RNA is the mediator of the inhibition. Furthermore, p21.5 is able to form a homodimer that interacts with core dimers forming hybrid viral assembly components. Sucrose gradient fractionation revealed that co-expression of p21.5 resulted in a spread distribution pattern of core proteins ranging from low to high sucrose densities. When compared with p22, p21.5 is almost ten times more efficient at destabilizing HBV nucleocapsid assembly in Huh7 cells overexpressing either p21.5 or p22 protein. Moreover, in vivo expression of p21.5 protein by tail vein injection was found to decrease the amount of nucleocapsid in the livers of HBV-expressing BALB/c mice. In conclusion, our study reveals that the HBV 2.2 kb singly-spliced RNA encodes a 21.5 kDa viral protein that significantly interferes with the assembly of nucleocapsids during HBV nucleocapsid formation. These findings provide a possible strategy for elimination of HBV particles inside cells.

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.

MicroRNA-26b inhibits hepatitis B virus transcription and replication by targeting the host factor CHORDC1 protein

Hepatitis B virus (HBV) causes acute and chronic hepatitis in humans, and HBV infection is a major threat to global health. HBV replication is regulated by a series of host factors, including microRNAs (miRNAs), which are highly conserved small noncoding RNAs that participate in a variety of physiological and pathological processes. Here, we report that a chemically synthesized mimic of miR-26b inhibited HBV antigen expression, transcription, and replication, whereas antisense knockdown of endogenous miR-26b enhanced HBV replication in HepG2 cells. Overexpression and knockdown experiments showed that miR-26b significantly decreased HBV enhancer/promoter activities. We identified the cysteine- and histidine-rich domain containing 1 (CHORDC1) as a novel host factor target of miR-26b. CHORDC1 protein but not mRNA was markedly decreased by miR-26b overexpression via base-pairing with complementary sequences in the 3'UTR of its mRNA. Overexpression and knockdown studies showed that CHORDC1 increased viral antigen expression, transcription, and replication by elevating HBV enhancer/promoter activities. Conversely, HBV infection suppressed miR-26b expression and increased CHORDC1 protein levels in human liver cells. Another mature miRNA of the hsa-miR-26 family, miR-26a, had a similar function as miR-26b in targeting CHORDC1 and affecting HBV production. These results suggest that suppression of miR-26b expression up-regulates its target gene CHORDC1, which increases HBV enhancer/promoter activities and promotes viral transcription, gene expression, and replication. Our study could provide new insights into miRNA expression and the persistence of HBV infection.

Modulation of HBV replication by microRNA-15b through targeting hepatocyte nuclear factor 1α

Hepatitis B virus (HBV) infection remains a major health problem worldwide. The role played by microRNAs (miRNAs) in HBV replication and pathogenesis is being increasingly recognized. In this study, we found that miR-15b, an important miRNA during HBV infection and hepatocellular carcinoma development, directly binds hepatocyte nuclear factor 1α (HNF1α) mRNA, a negative regulator of HBV Enhancer I, to attenuate HNF1α expression, resulting in transactivation of HBV Enhancer I, in turn causing the enhancement of HBV replication and expression of HBV antigens, including HBx protein, finally leading to the down-regulated expression of miR-15b in both cell lines and mice in a long cascade of events. Our research showed that miR-15b promotes HBV replication by augmenting HBV Enhancer I activity via direct targeting HNF1α, while HBV replication and antigens expression, particularly the HBx protein, then repress the expression of miR-15b. The reciprocal regulation between miR-15b and HBV controls the level of HBV replication and might play a role in persistent HBV infection. This work adds to the body of knowledge concerning the complex interactions between HBV and host miRNAs.

CRTC2 enhances HBV transcription and replication by inducing PGC1α expression

Background

Hepatitis B virus (HBV) transcription and replication are essentially restricted to hepatocytes. Based on the HBV enhancer and promoter complex that links hepatic glucose metabolism to its transcription and replication, HBV adopts a regulatory system that is unique to the hepatic gluconeogenic genes. CRTC2, the CREB-regulated transcription coactivator 2, is a critical switch modulating the gluconeogenic program in response to both hormonal and intracellular signals. However, the relationship between CRTC2 and HBV transcription and replication remains unclear.

Methods

To analyze the influence of CRTC2 on HBV transcription and replication, CRTC2 expression construct or siRNA was cotransfected with plasmids containing enhancer II/core promoter complex-controlled luciferase or 1.3× wtHBV genome in Huh-7 cells. Luciferase activity, HBV core protein expression, HBV transcripts, and DNA replication intermediates were measured by luciferase assays, western blots, real-time polymerase chain reaction (PCR), and Southern blots, respectively. Forskolin (FSK) or phosphorylation-defective CRTC2 mutants were further utilized to elucidate the potential mechanism. siRNA against peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) was also used to examine the mediator involved in CRTC2-regulated HBV biosynthesis in Huh-7 cells.

Results

CRTC2 overexpression increased HBV transcription and replication in Huh-7 cells, including levels of core protein expression, mRNA, and DNA replication intermediates. Correspondingly, CRTC2 knock down by siRNA reduced HBV biosynthesis. FSK treatment strongly enhanced the effect of CRTC2 through triggering the dephosphorylation and nuclear entry of CRTC2. The phosphorylation-defective mutant (S171A/S275A) of CRTC2 localized in the nucleus and was constitutively active, which dramatically promoted HBV transcription and replication similar to FSK-treated wild-type CRTC2. Knock down of PGC1α, whose expression was induced by CRTC2, greatly compromised the enhancing effect of CRTC2 on HBV transcription and replication.

Conclusions

Our results clearly indicate that non-phosphorylated CRTC2 strongly enhances HBV biosynthesis through inducing PGC1α expression. Further study of the mechanisms will elucidate the importance of metabolic signals on HBV transcription and replication, and offer insight into potential targets for developing anti-HBV agents.

The oncogenic role of hepatitis B virus

The hepatitis B virus (HBV) is a small enveloped DNA virus that causes acute and chronic hepatitis. HBV infection is a world health problem, with 350 million chronically infected people at increased risk of developing liver disease and hepatocellular carcinoma (HCC). HBV has been classified among human tumor viruses by virtue of a robust epidemiologic association between chronic HBV carriage and HCC occurrence. In the absence of cytopathic effect in infected hepatocytes, the oncogenic role of HBV might involve a combination of direct and indirect effects of the virus during the multistep process of liver carcinogenesis. Liver inflammation and hepatocyte proliferation driven by host immune responses are recognized driving forces of liver cell transformation. Genetic and epigenetic alterations can also result from viral DNA integration into host chromosomes and from prolonged expression of viral gene products. Notably, the transcriptional regulatory protein HBx encoded by the X gene is endowed with tumor promoter activity. HBx has pleiotropic activities and plays a major role in HBV pathogenesis and in liver carcinogenesis. Because hepatic tumors carry a dismal prognosis, there is urgent need to develop early diagnostic markers of HCC and effective therapies against chronic hepatitis B. Deciphering the oncogenic mechanisms that underlie HBV-related tumorigenesis might help developing adapted therapeutic strategies.

The metabolic sensors FXRα, PGC-1α, and SIRT1 cooperatively regulate hepatitis B virus transcription

Hepatitis B virus (HBV) genome transcription is highly dependent on liver-enriched, metabolic nuclear receptors (NRs). Among others, NR farnesoid X receptor α (FXRα) enhances HBV core promoter activity and pregenomic RNA synthesis. Interestingly, two food-withdrawal-induced FXRα modulators, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) and deacetylase SIRT1, have been found to be associated with HBV genomes ex vivo. Whereas PGC-1α induction was shown to increase HBV replication, the effect of SIRT1 on HBV transcription remains unknown. Here, we showed that, in hepatocarcinoma-derived Huh-7 cells, combined activation of FXRα by GW4064 and SIRT1 by activator 3 increased HBV core promoter-controlled luciferase expression by 25-fold, compared with a 10-fold increase with GW4064 alone. Using cell lines differentially expressing FXRα in overexpression and silencing experiments, we demonstrated that SIRT1 activated the core promoter in an FXRα- and PGC-1α-dependent manner. Maximal activation (>150-fold) was observed in FXRα- and PGC-1α-overexpressing Huh-7 cells treated with FXRα and SIRT1 activators. Similarly, in cells transfected with full-length HBV genomes, maximal induction (3.5-fold) of core promoter-controlled synthesis of 3.5-kb RNA was observed in the same conditions of transfection and treatments. Thus, we identified a subnetwork of metabolic factors regulating HBV replication, strengthening the hypothesis that transcription of HBV and metabolic genes is similarly controlled.

Polypyrimidine tract binding protein (PTB) associates with intronic and exonic domains to squelch nuclear export of unspliced RNA

Retention of unspliced pre-messenger RNA (pre-mRNA) in the nucleus is essential for cell survival. Available nuclear factors must recognize and discern between diverse export signals present in pre-mRNA to establish an export inhibitory complex. We found that polypyrimidine domains present in both intron and exon were important for export inhibition of a minigene transcript based on hepatitis B virus pregenomic RNA. Overexpression of PTB drastically reduced export and presence of RRM4 domain seemed critical. This inhibitory network overrode stimulation from an exonic export-facilitating element. We posit that binding of PTB to multiple loci on pre-mRNA regulates nuclear retention.

Role of hepatitis B virus genotype D & its mutants in occult hepatitis B infection

BACKGROUND & OBJECTIVES

Non-detection of hepatitis B virus (HBV) envelope protein (hepatitis B surface antigen, HBsAg) in a chronically HBV infected individual has been described as occult infection. One possible reason for this phenotype is alteration in large (L-HBsAg) to small (S-HBsAg) envelope protein ratio associated with reduced or non secretion of HBsAg. This results in quantitative levels of serum HBsAg below the detection limit of enzyme immunoassays. Genotype D of HBV has a characteristic 33 nucleotide (nt) deletion upstream of the pre-S2/S promoter. This deletion may reduce HBsAg secretion in occult infection patients infected with genotype D HBV. Additional deletions in the pre-S2/S promoter may further aggravate reduced HBsAg secretion in patients infected with genotype D HBV. Thus, the aim of the present study was to determine the role of genotype D specific 33nt deletion and additional pre-S2/S promoter deletions in causing reduced or no secretion of HBsAg, in occult infection. Since these deletions overlap virus polymerase, their effect on virus replication was also investigated.

METHODS

We examined the in vitro expression of HBsAg, ratio of cure and 'e' antigen (HBcAg/HBeAg), their secretion and virus replication, using overlength 1.3 mer/1.86 mer genotype A replicons, and genotype D replicons with and without additional pre-S2/S promoter deletions from cases of occult infection.

RESULTS

Genotype D replicon showed a decrease in HBsAg secretion compared to the wild-type genotype A. Genotype D replicons carrying additional pre-S2/S promoter deletions, showed further reduction in HBsAg secretion, demonstrated presence of intracellular HBcAg/HBeAg, virus replication intermediates and 'e' antigen secretion.

INTERPRETATION & CONCLUSIONS

The characteristic 33 nt deletion of genotype D HBV reduces HBsAg secretion. Additional pre-S2/S promoter deletions may further diminish HBsAg secretion, leading to occult infection. Pre-S2/S promoter deletions do not affect HBV replication.

GCN5 acetyltransferase inhibits PGC1α-induced hepatitis B virus biosynthesis

Hepatitis B virus (HBV) biosynthesis is primarily restricted to hepatocytes due to the governing of liver-enriched nuclear receptors (NRs) on viral RNA synthesis. The liver-enriched NR hepatocyte nuclear factor 4α (HNF4α), the key regulator of genes implicated in hepatic glucose metabolism, is also a primary determinant of HBV pregenomic RNA synthesis and HBV replication. Peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) coactivates and further enhances the effect of HNF4α on HBV biosynthesis. Here, we showed that the acetyltransferase General Control Non-repressed Protein 5 (GCN5) acetylated PGC1α, leading to alteration of PGC1α from a transcriptionally active state into an inactive state. As a result, the coactivation activity of PGC1α on HBV transcription and replication was suppressed. Apparently, an acetylation site mutant of PGC1α (PGC1αR13) still had coactivation activity as GCN5 could not suppress the coactivation activity of the mutant. Moreover, a catalytically inactive acetyltransferase mutant GCN5m, due to the loss of acetylation activity, failed to inhibit the coactivation function of PGC1α in HBV biosynthesis. Our results demonstrate that GCN5, through its acetyltransferase activity, inhibits PGC1α-induced enhancement of HBV transcription and replication both in vitro and in vivo.