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Background & Aims To provide an adequate treatment strategy for chronic hepatitis B, it is essential to know which patients are expected to have a good prognosis and which patients do not require therapeutic intervention. Previously, we identified the substitution of isoleucine to leucine at amino acid 97 (I97L) in the hepatitis B core region as a key predictor among patients with stable hepatitis. In this study, we attempted to identify the point at which I97L affects the hepatitis B virus (HBV) life cycle and to elucidate the underlying mechanisms governing the stabilization of hepatitis. Methods To confirm the clinical features of I97L, we used a cohort of hepatitis B e antigen–negative patients with chronic hepatitis B infected with HBV-I97 wild-type (wt) or HBV-I97L. The effects of I97L on viral characteristics were evaluated by in vitro HBV production and infection systems with the HBV reporter virus and cell culture-generated HBV. Results The ratios of reduction in hepatitis B surface antigen and HBV DNA were higher in patients with HBV-I97L than in those with HBV-I97wt. HBV-I97L exhibited lower infectivity than HBV-I97wt in both infection systems with reporter HBV and cell culture-generated HBV. HBV-I97L virions exhibiting low infectivity primarily contained a single-stranded HBV genome. The lower efficiency of cccDNA synthesis was demonstrated after infection of HBV-I97L or transfection of the molecular clone of HBV-I97L. Conclusions The I97L substitution reduces the level of cccDNA through the generation of immature virions with single-stranded genomes. This I97L-associated low efficiency of cccDNA synthesis may be involved in the stabilization of hepatitis., Graphical abstract

Autophagy has been linked to a wide range of functions, including a degradative process that defends host cells against pathogens. Although the involvement of autophagy in HBV infection has become apparent, it remains unknown whether selective autophagy plays a critical role in HBV restriction. Here, we report that a member of the galectin family, GAL9, directs the autophagic degradation of HBV HBc. BRET screening revealed that GAL9 interacts with HBc in living cells. Ectopic expression of GAL9 induces the formation of HBc-containing cytoplasmic puncta through interaction with another antiviral factor viperin, which co-localized with the autophagosome marker LC3. Mechanistically, GAL9 associates with HBc via viperin at the cytoplasmic puncta and enhanced the auto-ubiquitination of RNF13, resulting in p62 recruitment to form LC3-positive autophagosomes. Notably, both GAL9 and viperin are type I IFN-stimulated genes that act synergistically for the IFN-dependent proteolysis of HBc in HBV-infected hepatocytes. Collectively, these results reveal a previously undescribed antiviral mechanism against HBV in infected cells and a form of crosstalk between the innate immune system and selective autophagy in viral infection., In human cells, invading pathogens trigger an innate immune response that helps prevent viral replication and spread. Here, the authors reveal a mechanism of innate immunity that selectively leads to the autophagic degradation of hepatitis B virus core protein.

Hepatitis B virus (HBV), a highly persistent pathogen causing hepatocellular carcinoma (HCC), takes full advantage of host machinery, presenting therapeutic targets. Here we aimed to identify novel druggable host cellular factors using the reporter HBV we have recently generated. In an RNAi screen of G protein-coupled receptors (GPCRs), GPCR39 (GPR39) appeared as the top hit to facilitate HBV proliferation. Lentiviral overexpression of active GPR39 proteins and an agonist enhanced HBV replication and transcriptional activities of viral promoters, inducing the expression of CCAAT/enhancer binding protein (CEBP)-&beta, (CEBPB). Meanwhile, GPR39 was uncovered to activate the heat shock response, upregulating the expression of proviral heat shock proteins (HSPs). In addition, glioma-associated oncogene homologue signaling, a recently reported target of GPR39, was suggested to inhibit HBV replication and eventually suppress expression of CEBPB and HSPs. Thus, GPR39 provirally governed intracellular circuits simultaneously affecting the carcinopathogenetic gene functions. GPR39 and the regulated signaling networks would serve as antiviral targets, and strategies with selective inhibitors of GPR39 functions can develop host-targeted antiviral therapies preventing HCC.

Chronic infection with Hepatitis B virus (HBV) increases the risk of developing fibrosis, cirrhosis, or hepatocellular carcinoma. Current therapies are limited to type-I interferons and/or nucleos(t)ide analogues; however, these are only partially effective. The development of novel anti-HBV agents for new treatment strategies has been hampered by the lack of a suitable system that allows the in vitro replication of HBV. Studies of virus infection/replication at the molecular level using wild-type HBV are labor-intensive and time-consuming. To overcome these problems, we previously constructed a recombinant reporter HBV bearing the NanoLuc gene and showed its usefulness to identify factors that affect HBV proliferation. Because this system mimics the early stage of HBV life cycle faithfully, we conducted a quantitative analysis of HBV infectivity to several human hepatocyte cell lines as well as the effect of dimethyl sulfoxide and HBV protein X on the early stage of HBV proliferation using this system. Furthermore, we developed a system to produce a reporter HBV expressing a pol gene. These reporter HBVs may provide an opportunity to enhance our understanding of the HBV life cycle and aid strategies for the development of new anti-HBV agents. This article is protected by copyright. All rights reserved.

Antiviral therapies for chronic hepatitis B virus (HBV) infection that are currently applicable for clinical use are limited to nucleos(t)ide analogs targeting HBV polymerase activity and pegylated interferon alpha (PEG-IFN). Towards establishing an effective therapy for HBV related diseases, it is important to develop a new anti-HBV agent that suppresses and eradicates HBV. This study used recombinant HBV encoding NanoLuc to screen anti-HBV compounds from 1827 US Food and Drug Administration approved compounds and identified several compounds that suppressed HBV infection. Among them, KX2-391, a non-ATP-competitive inhibitor of SRC kinase and tubulin polymerization, was identified as a lead candidate for an anti-HBV drug. Treatment of sodium taurocholate cotransporting polypeptide (NTCP) transduced-HepG2 (HepG2-NTCP) or primary human hepatocytes with KX2-391 suppressed HBV replication in a dose-dependent manner. The anti-HBV activity of KX2-391 appeared not to depend on SRC kinase activity because siRNA for SRC mRNA did not impair the HBV infection/replication. The anti-HBV activity of KX2-391 depended on the inhibitory effect of tubulin polymerization similar to other tubulin polymerization inhibitors, some of which were shown to inhibit HBV replication. KX2-391 inhibited HBV transcription driven by a HBV precore promoter in an HBV X protein-independent manner but did not inhibit the activity of HBV-S1, -S2, -X or cytomegalovirus promoters. Treatment with KX2-391 reduced the expression of several various factors including hepatocyte nuclear factor-4a.

Here, we identify ATP1B3 and fibrillin-1 as novel BST-2-binding proteins. ATP1B3 depletion in HeLa cells (BST-2-positive cells), but not 293T cells (BST-2-negative cells), induced the restriction of HIV-1 production in a BST-2-dependent manner. In contrast, fibrillin-1 knockdown reduced HIV-1 production in 293T and HeLa cells in a BST-2-independent manner. Moreover, NF-κB activation was enhanced by siATP1B3 treatment in HIV-1- and HIV-1ΔVpu-infected HeLa cells. In addition, ATP1B3 silencing induced high level BST-2 expression on the surface of HeLa cells. These results indicate that ATP1B3 is a co-factor that accelerates BST-2 degradation and reduces BST-2-mediated restriction of HIV-1 production and NF-κB activation.

Hepatitis B virus (HBV) is a global major health problem, with over one million deaths annually caused by chronic liver damage. Understanding host factors that modulate HBV replication may aid the development of anti-HBV therapies. Our recent genome-wide small interfering RNA screen using recombinant HBV demonstrated that TIP60 inhibited HBV infection. Here, we show that TIP60 complex contributes to anti-HBV defense. The TIP60 complex bound to the HBV promoter and suppressed HBV transcription driven by the precore/core promoter. The silencing of EP400, TRRAP, BAF53a, RUVBL1, and RUVBL2, which form the TIP60 complex, also resulted in increased HBV transcription. These results contribute to our enhanced understanding of the molecular mechanism of HBV transcription associated with the chromatin structure of HBV covalently closed circular DNA (cccDNA). Exploiting these intrinsic cellular defenses might help develop new anti-HBV agents. IMPORTANCE Investigating the molecular mechanism of HBV replication is important to understand the persistent nature of HBV infection and to aid the development of new HBV agents, which are currently limited to HBV polymerase inhibitors. Previously, we developed a new reporter HBV. By screening host factors using this recombinant virus, we identified several gene products that regulate HBV infection, including TIP60. Here, we showed that TIP60, a catalytic subunit of the NuA4 complex, inhibited HBV replication. Depletion of TIP60 increased the level of HBV mRNA. Moreover, TIP60 localized in the HBV cccDNA chromatin complex catalyzed the acetylation of histone H4 to recruit Brd4. These results suggest that TIP60, in concert with other cellular factors, plays an important role in the regulation of the HBV chromatin structure by acting as a critical component of the intrinsic antiviral defense, which sheds new light on the regulation of HBV replication.

Hepatitis B virus (HBV) is the major cause of liver cirrhosis and hepatocellular carcinoma. After entering a hepatocyte, HBV forms a nuclear viral episome and produces pregenomic (pg) RNA with a stem-loop structure called an epsilon, which acts to signal encapsidation. We previously demonstrated that TGF-β upregulates activation-induced cytidine deaminase (AID) expression in hepatocytes, which in turn downregulates HBV transcripts by recruiting the RNA exosome complex. The molecular mechanism underlying AID-mediated HBV RNA reduction remains largely unclear. Here we used a pgRNA reporter system having a reporter gene within pgRNA to identify sis- and trans-acting elements in AID-mediated HBV RNA reduction. We found that the epsilon RNA and C-terminus of AID are required for AID-mediated HBV RNA reduction. Importantly, this reduction was reproduced in a hydrodynamic HBV transfection mouse model. The molecular mechanism of AID-mediated HBV RNA reduction is discussed.

Currently, it is possible to construct recombinant forms of various viruses, such as human immunodeficiency virus 1 (HIV-1) and hepatitis C virus (HCV), that carry foreign genes such as a reporter or marker protein in their genomes. These recombinant viruses usually faithfully mimic the life cycle of the original virus in infected cells and exhibit the same host range dependence. The development of a recombinant virus enables the efficient screening of inhibitors and the identification of specific host factors. However, to date the construction of recombinant hepatitis B virus (HBV) has been difficult because of various experimental limitations. The main limitation is the compact genome size of HBV, and a fairly strict genome size that does not exceed 1.3 genome sizes, that must be packaged into virions. Thus, the size of a foreign gene to be inserted should be smaller than 0.4 kb if no deletion of the genome DNA is to be performed. Therefore, to overcome this size limitation, the deletion of some HBV DNA is required. Here, we report the construction of recombinant HBV encoding a reporter gene to monitor the early stage of the HBV replication cycle by replacing part of the HBV core-coding region with the reporter gene by deleting part of the HBV pol coding region. Detection of recombinant HBV infection, monitored by the reporter activity, was highly sensitive and less expensive than detection using the currently available conventional methods to evaluate HBV infection. This system will be useful for a number of applications including high-throughput screening for the identification of anti-HBV inhibitors, host factors and virus-susceptible cells.

Despite the breadth of knowledge that exists regarding the function of long noncoding RNAs (lncRNAs) in biological phenomena, the role of lncRNAs in host antiviral responses is poorly understood. Here, we report that lncRNA#32 is associated with type I IFN signaling. The silencing of lncRNA#32 dramatically reduced the level of IFN-stimulated gene (ISG) expression, resulting in sensitivity to encephalomyocarditis virus (EMCV) infection. In contrast, the ectopic expression of lncRNA#32 significantly suppressed EMCV replication, suggesting that lncRNA#32 positively regulates the host antiviral response. We further demonstrated the suppressive function of lncRNA#32 in hepatitis B virus and hepatitis C virus infection. lncRNA#32 bound to activating transcription factor 2 (ATF2) and regulated ISG expression. Our results reveal a role for lncRNA#32 in host antiviral responses.

Hepatitis B virus (HBV) is not eradicated by current antiviral therapies due to persistence of HBV covalently closed circular DNA (cccDNA) in host cells and thus development of novel culture models for productive HBV infection is urgently needed, which will allow the study of HBV cccDNA eradication. To meet this need, we developed culture models of HBV infection using human induced pluripotent stem cell-derived hepatocyte lineages, including immature proliferating hepatic progenitor-like cell lines (iPS-HPCs) and differentiated hepatocyte-like cells (iPS-Heps). These cells were susceptible to HBV infection, produced HBV particles and maintained innate immune responses. The infection efficiency of HBV in iPS-HPCs predominantly depended on the expression levels of sodium taurocholate cotransporting polypeptide (NTCP) and was low relative to iPS-Heps: however, long-term culture of iPS-Heps was difficult. To provide a model for HBV persistence, iPS-HPCs overexpressing NTCP were established. The long-term persistence of HBV cccDNA was detected in iPS-HPCs overexpressing NTCP and depended on the inhibition of the Janus-kinase signaling pathway. In conclusion, this study provides evidence that iPS-derived hepatic cell lines can be utilized for novel HBV culture models with genetic variation to investigate the interactions between HBV and host cells and the development of anti-HBV strategies.

Pattern recognition receptors (PRRs) play a pivotal role in host innate immune responses against microbial infection. Viruses are primarily recognized by PRRs such as Toll-like receptor 3, 7, 8 and 9, and RIG-I-like receptors. Recent studies have demonstrated that DNA-dependent activator of IFN-regulatory factors (DAI) is a cytosolic sensor molecule for dsDNA, and is implicated in antiviral responses to some DNA viruses. Soon after infection, human immunodeficiency virus type-1 (HIV-1) synthesizes viral dsDNA in the cytoplasm by reverse transcriptase. In addition, an immune compromised state due to chronic HIV-1 infection results in opportunistic infection with some microbes that potentially activate DAI. However, it has not been elucidated whether DAI affects HIV-1 replication, or its possible mechanisms. Here, we showed that forced expression of DAI markedly enhanced HIV-1 replication, which was largely impaired by mutations at κB sites in HIV-1 LTR or by suppressing activation of NF-κB. Moreover, intact structure around the D3 region (174-232 aa) and two RIP homotypic interaction motifs (198-214 aa and 256-272 aa) within DAI were critical for its activity. These results suggest that activation of DAI might contribute to augment HIV-1 replication through DAI- NF-κB pathway.

Gene targeting in mammalian cells through the use of short-hairpin RNAs (shRNAs) has been advanced by the development of vector systems for efficient delivery and stable expression of shRNA sequences (4, 7, 22, 30). Upon delivery into cells, shRNAs are converted into short double-stranded RNAs, termed small interfering RNAs (siRNAs), that mediate a sequence-specific RNA degradation process termed RNA interference (RNAi) (12, 14, 42). Antiviral therapy based on siRNA has been proposed as a new method for intracellular immunization against human immunodeficiency virus type 1 (HIV-1) (16, 31, 32) and hepatitis C virus (HCV) (34). When viral genes are targeted, viruses can escape from RNAi-mediated inhibition due to their high mutation rate (6, 11, 39). An alternative approach that shows promise is the use of siRNAs targeting cellular genes essential for virus replication. In the case of HIV-1, siRNAs against the cell surface CD4 receptor (31) or CXCR4 and CCR5 coreceptors for HIV-1 entry conferred viral resistance (2, 3, 33). However, CD4 and CXCR4 are essential for T-cell development and proper immunologic function. In addition, although CCR5 might be nonessential for normal function (23), not all HIV-1 strains require CCR5. Downregulation of an essential cellular coreceptor could potentially result in the emergence of HIV-1 variants that use another coreceptor(s) for viral entry into the cell. To achieve long-term control of viral replication by siRNA and prevent the emergence of escape variants, it is important to target highly conserved and/or essential HIV-1 sequences. For example, many sites in the cis-regulatory regions, as well as the protein-coding regions, of HIV-1 have been examined as potential targets for siRNA. These regions include the primer-binding site, the polypurine tract, the long terminal repeat, and the gag, pol, env, tat, rev, vif, and nef genes (6, 10, 11, 16, 18, 21, 30, 39). The degree to which siRNAs inhibited HIV-1 replication and the underlying mechanisms varied considerably, depending on the target sequence (10, 11). For example, RNAi-resistant HIV-1 variants can emerge not only through mutations in the siRNA target sequence but also through mutations that alter the local RNA structure (39). These results emphasize the need for empirical studies to determine effective siRNA target sites within the HIV-1 genome. In the present study, we selected several sequences for lentivirus-mediated shRNA expression based on a preliminary screening of HIV-1 RNAi target sites using synthetic siRNA duplexes. These sequences mapped within the integrase (IN) gene (int) and the attachment site (att), which are essential for HIV-1 integration. We evaluated the anti-HIV-1 activity of these expressed shRNAs using a highly susceptible CD4+ T-cell line. Genetic analysis of HIV-1 escape mutants that emerged after treatment with combinations of shRNAs revealed that two or more shRNAs targeting different essential sequences had the strongest impact on antiviral activity. The results also suggest that shRNAs or long-hairpin RNA (lhRNA) that targets incoming viral RNA before proviral DNA formation is more efficient at mediating RNAi antiviral therapy.

We investigated the effects of signaling through CD28 family molecules on human immunodeficiency virus type 1 (HIV-1) replication in vitro. A monoclonal antibody (mAb) specific for inducible costimulator (ICOS) suppressed both X4 and R5 HIV-1 replication in CD4+ peripheral blood mononuclear cells (PBMC). This suppression was not attributable to reduced cell growth or viability. CD28 mAb showed variable effects and also suppressed HIV-1 replication when immobilized. Replication of pseudotype viruses with HIV-1-but not with vesicular stomatitis virus G-envelope was efficiently suppressed in CD4+ PBMC treated with ICOS or CD28 mAbs. However, CD4, CXCR4, and CCR5 expression on the surface was not down-regulated. Moreover, HIV-1 replication in CD4+ PBMC was suppressed by a soluble form of human B7-H2, a ligand of ICOS, but was enhanced by soluble B7-1, a ligand for CD28. These findings suggest that natural or artificial ligands for ICOS potentially suppress HIV-1 replication mainly at the entry stages.

Previous studies have demonstrated that cyclopentenone prostaglandins (cyPGs) inhibit human immunodeficiency virus type 1 (HIV-1) replication in various cell types. This antiviral activity has been associated with the induction of heat-shock protein 70 (HSP70) in infected cells. We investigated a new role of prostaglandin A₁ (PGA₁) in the replication of HIV-1 in non-permissive cells. Because overexpression of HSP70 blocks the viral infectivity factor (Vif)-mediated degradation of APOBEC3G (A3G) via the ubiquitin-proteasome pathway, we examined the effects of PGA₁ on A3G and HIV-1 replication. The induction of HSP70 synthesis by PGA₁ blocked Vif-mediated A3G degradation and enhanced the incorporation of A3G into both wild-type and Vif-deficient viruses. Furthermore, we determined the viral titer of HIV-1 particles produced from PGA₁-treated 293T cells. The induction of HSP70 synthesis by PGA₁ significantly reduced the viral titer in the presence of A3G. Additionally, the p24 Gag antigen levels were dramatically reduced in non-permissive cells treated once or repeatedly with PGA₁. Thus, we showed that PGA₁ inhibits HIV-1 replication, at least in part, by blocking Vif-mediated A3G degradation.

The cytidine deaminase APOBEC3G, which is incorporated into nascent virus particles, possesses potent antiviral activity and restricts Vif-deficient HIV-1 replication at the reverse transcription step through deamination-dependent and -independent effects. HIV-1 Vif counteracts the antiviral activity of APOBEC3G by inducing APOBEC3G polyubiquitination and its subsequent proteasomal degradation. In this study, we show that overexpression of heat shock protein 70 (HSP70) blocked the degradation of APOBEC3G in the ubiquitin-proteasome pathway by HIV-1 Vif, rendering the viral particles non-infectious. In addition, siRNA targeted knock-down of HSP70 expression enhanced the Vif-mediated degradation of APOBEC3G. A co-immunoprecipitation study revealed that overexpression of HSP70 inhibited APOBEC3G binding to HIV-1 Vif. Thus, we provide evidence for a host protein-mediated suppression of HIV-1 replication in an APOBEC3G-dependent manner.

It was found previously that human immunodeficiency virus type 1 (HIV-1)-irrelevant CD8+ cytotoxic T lymphocytes (CTLs) from uninfected donors suppressed HIV-1 replication in a cell-contact-dependent manner. However, one of these CTL lines (CTL-3) also significantly suppressed HIV-1 replication through its supernatant. Here, the suppressive fraction from CTL-3 supernatant was purified and analysed by mass spectrometry. A protein band specific for the suppressive fraction was identified as arginine deiminase from Mycoplasma arginini, which catalyses the hydrolysis of arginine to citrulline. Addition of l-arginine or the use of antibiotics against mycoplasma restored supernatant-mediated but not cell-contact-dependent suppression of HIV-1 replication by CTL-3, clearly indicating that arginine deiminase of M. arginini in the supernatants suppressed HIV-1 replication, which is independent of CD8+ T-cell-mediated HIV-1 suppression via cell contact. Arginine deiminase is known to be a chemotherapeutic agent against arginine-requiring tumours and these results suggest that it also has potential application in antiviral therapy.

RNA interference (RNAi) is a sequence-specific RNA degradation process mediated by short double-stranded RNAs termed small interfering RNAs. Here, we describe the lentivirus-based vector small interfering RNA system expressing. As a pilot study, we generated constructs expressing small hairpin RNA (shRNA) specific for luciferase gene (shLuc) or green fluorescence protein (shGFP) under the control of human H1 RNA polymerase III promoter. The effect of the shRNA was evaluated against HIV-1 infection in a single-round or multiple-round infectious system using an HIV-1 molecular clone carrying the luc or GFP gene. In the single-round infectious system, cells transduced with shLuc by lentiviral vector significantly reduced (approximately 90% reduction) viral gene expression after challenge infection at a multiplicity of infection of 10. These transduced cells continued to resist against at least four sequentially repeated challenge infections. Importantly, this efficient antiviral activity persisted over 35 days in culture. In a multiple-round infectious system using a replication-competent HIV-1 molecular clone carrying the GFP gene, we also observed that a lentiviral vector expressing shGFP could inhibit HIV-1 replication for at least 1 week. The profound effect of lentiviral shRNA was also observed in human primary monocyte-derived macrophages. Thus, shRNA introduced through the lentiviral vector can be useful for efficient and stable gene suppression in human cells including primary non-dividing cells. Moreover, quantitative analysis of viral cDNA synthesis on challenge infection showed that viral genomic RNAs packaged in incoming virus core might not be targeted by shLuc. Instead, the degradation of transcripts from integrated proviral DNAs might be a major cause of the profound reduction in HIV-1 gene expression by shRNA in our system.

Long terminal repeats (5'-LTR) contain essential enhancer and promoter elements that act as targets for cellular and viral regulatory proteins. The interplay of these cis-acting sequences with specific transcription factors (NF kappa B, Ap1, and Sp1) present in infected cells determines the rate of transcription initiation from the 5'-LTR promoter element, and thus strongly influences the level of viral replication. Furthermore, Tat functions to enhance transcriptional elongation by binding to the trans-activation response element (TAR). These transcriptional factors enhance the transcriptional elongation from the HIV-1 promoter. HIV-1 genomic RNA packaging is a highly specific process involving interactions between the viral Gag precursor and cis acting packaging signals in the 5' leader sequence of HIV-1 genomic RNA. We examined the suppression effect of HIV-1 expression by the decoy RNAs targeted to these HIV-1 transcriptional and packaging regulatory regions. HIV-1 expression was inhibited by the 5'-LTR decoy RNA, and measured by the amount of HIV-1 gag p24 protein, but no inhibition of HIV-1 packaging could be detected.

The efficient processing of human immunodeficiency virus type 1 Gag–Pol requires not only protease activity but also specific reverse transcriptase (RT) and integrase sequences. However, the critical amino acid residues of the HIV-1 Pol gene involved in protease-mediated Gag–Pol processing have not been precisely defined. Here, we found that the substitution of Thr-128 or Tyr-146 with Ala markedly impaired the proteolytic processing of the MA/CA, p66/p51 and RT/IN sites but did not affect the normal processing of other sites. Moreover, a Thr-128 or Tyr-146 mutation in RT abolished RT dimerization in vitro. These results suggest that Thr-128 and Tyr-146 within the RT region play important roles in protease-mediated Gag–Pol processing.Structured summary of protein interactionsRT and RT physically interact by cross-linking study (View interaction: 1, 2, 3).CK2 alpha phosphorylates RT by protein kinase assay (View interaction).