Identification of neutralizing epitopes in the preS2 domain of the hepatitis B virus.

Hepatitis B virus (HBV) infection is a major public health problem. The sodium taurocholate cotransporting polypeptide (NTCP) has been identified as an essential HBV receptor. Human hepatocytes are infected with HBV via binding between the preS1 region of the HBV large envelope protein and the NTCP. However, the role of preS2 in HBV entry is not well understood. In this study, we induced anti-preS2 serum in mice by DNA immunization, and showed that the resulting antiserum neutralized HBV infectivity. Competition assays using overlapping peptides suggested that the neutralizing epitope is located in the N-terminal region of preS2. In addition, monoclonal antibodies targeting the N-terminal region of preS2 neutralized HBV infectivity, indicating that these domains are critical epitopes for viral neutralization. These findings provide new insights into the HBV entry machinery while suggesting a novel modality for the prevention and treatment of HBV infection.

Novel Neplanocin A Derivatives as Selective Inhibitors of Hepatitis B Virus with a Unique Mechanism of Action.

Novel neplanocin A derivatives have been identified as potent and selective inhibitors of hepatitis B virus (HBV) replication in vitro. These include (1S,2R,5R)-5-(5-bromo-4-methyl-7H-pyrrolo[2,3-d]-pyrimidin-7-yl)-3-(hydroxymethyl)cyclopent-3-ene-1,2-diol (AR-II-04-26) and (1S,2R,5R)-5-(4-amino-3-iodo-1H-pyrazolo[3,4-d]pyrimidin-1-yl)-3-(hydroxylmethyl)cyclopent-3-ene-1,2-diol (MK-III-02-03). The 50% effective concentrations of AR-II-04-26 and MK-III-02-03 were 0.77 ± 0.23 and 0.83 ± 0.36 µM in HepG2.2.15.7 cells, respectively. These compounds reduced intracellular HBV RNA levels in HepG2.2.15.7 cells and infected primary human hepatocytes. Accordingly, they could reduce HBs and HBe antigen production in the culture supernatants, which was not observed with clinically approved anti-HBV nucleosides and nucleotides (reverse transcriptase inhibitors). The neplanocin A derivatives also inhibited HBV RNA derived from cccDNA. In addition, unlike neplanocin A itself, the compounds did not inhibit S-adenosyl-l-homocysteine hydrolase activity. Thus, it appears that the mechanism of action of AR-II-04-26 and MK-III-02-03 differs from that of the clinically approved anti-HBV agents. Although their exact mechanism (target molecule) remains to be elucidated, the novel neplanocin A derivatives are considered promising candidate drugs for inhibition of HBV replication.

Inhibitory effect of a novel thiazolidinedione derivative on hepatitis B virus entry.

The development of novel antivirals to treat hepatitis B virus (HBV) infection is still needed because currently available drugs do not completely eradicate chronic HBV in some patients. Recently, troglitazone and ciglitazone, classified among the compounds including the thiazolidinedione (TZD) moiety, were found to inhibit HBV infection, but these compounds are not clinically available. In this study, we synthesized 11 TZD derivatives, compounds 1-11, and examined the effect of each compound on HBV infection in HepG2 cells expressing NTCP (HepG2/NTCP cells). Among the derivatives, (Z)-5-((4'-(naphthalen-1-yl)-[1,1'-biphenyl]-4-yl)methylene)thiazolidine-2,4-dione (compound 6) showed the highest antiviral activity, with an IC50 value of 0.3 µM and a selectivity index (SI) of 85, but compound 6 did not affect HCV infection. Treatment with compound 6 inhibited HBV infection in primary human hepatocytes (PHHs) but did not inhibit viral replication in HepG2.2.15 cells or HBV DNA-transfected Huh7 cells. Moreover, treatment with compound 6 significantly impaired hepatitis delta virus (HDV) infection and inhibited a step in HBV particle internalization but did not inhibit attachment of the preS1 lipopeptide or viral particles to the cell surface. These findings suggest that compound 6 interferes with HBV infection via inhibition of the internalization process.

Hepatitis C virus modulates signal peptide peptidase to alter host protein processing.

Immunoevasins are viral proteins that prevent antigen presentation on major histocompatibility complex (MHC) class I, thus evading host immune recognition. Hepatitis C virus (HCV) evades immune surveillance to induce chronic infection; however, how HCV-infected hepatocytes affect immune cells and evade immune recognition remains unclear. Herein, we demonstrate that HCV core protein functions as an immunoevasin. Its expression interfered with the maturation of MHC class I molecules catalyzed by the signal peptide peptidase (SPP) and induced their degradation via HMG-CoA reductase degradation 1 homolog, thereby impairing antigen presentation to CD8+ T cells. The expression of MHC class I in the livers of HCV core transgenic mice and chronic hepatitis C patients was impaired but was restored in patients achieving sustained virological response. Finally, we show that the human cytomegalovirus US2 protein, possessing a transmembrane region structurally similar to the HCV core protein, targets SPP to impair MHC class I molecule expression. Thus, SPP represents a potential target for the impairment of MHC class I molecules by DNA and RNA viruses.

Establishment of a Cell Culture Model Permissive for Infection by Hepatitis B and C Viruses.

Compared with each monoinfection, coinfection with hepatitis B virus (HBV) and hepatitis C virus (HCV) is well known to increase the risks of developing liver cirrhosis and hepatocellular carcinoma. However, the mechanism by which HBV/HCV coinfection is established in hepatocytes is not well understood. Common cell culture models for coinfection are required to examine viral propagation. In this study, we aimed to establish a cell line permissive for both HBV and HCV infection. We first prepared a HepG2 cell line expressing sodium taurocholate cotransporting polypeptide, an HBV receptor, and then selected a cell line highly permissive for HBV infection, G2/NT18-B. After transduction with a lentivirus-encoding microRNA-122, the cell line harboring the highest level of replicon RNA was selected and then treated with anti-HCV compounds to eliminate the replicon RNA. The resulting cured cell line was transduced with a plasmid-encoding CD81. The cell line permissive for HCV infection was cloned and then designated the G2BC-C2 cell line, which exhibited permissiveness for HBV and HCV propagation. JAK inhibitor I potentiated the HCV superinfection of HBV-infected cells, and fluorescence-activated cell-sorting analysis indicated that HBV/HCV double-positive cells accounted for approximately 30% of the coinfected cells. Among several host genes tested, cyclooxygenase-2 showed synergistic induction by coinfection compared with each monoinfection. Conclusion: These data indicate that our in vitro HBV/HCV coinfection system provides an easy-to-use platform for the study of host and viral responses against coinfection and the development of antiviral agents targeting HBV and HCV.

N-Terminal PreS1 Sequence Regulates Efficient Infection of Cell-Culture-Generated Hepatitis B Virus.

BACKGROUND AND AIMS: An efficient cell-culture system for hepatitis B virus (HBV) is indispensable for research on viral characteristics and antiviral reagents. Currently, for the HBV infection assay in cell culture, viruses derived from HBV genome-integrated cell lines of HepG2.2.15 or HepAD-38 are commonly used. However, these viruses are not suitable for the evaluation of polymorphism-dependent viral characteristics or resistant mutations against antiviral reagents. HBV obtained by the transient transfection of the ordinary HBV molecular clone has limited infection efficiencies in cell culture. APPROACH AND RESULTS: We found that an 11-amino-acid deletion (d11) in the preS1 region enhances the infectivity of cell-culture-generated HBV (HBVcc) to sodium taurocholate cotransporting polypeptide-transduced HepG2 (HepG2/NTCP) cells. Infection of HBVcc derived from a d11-introduced genotype C strain (GTC-d11) was ~10-fold more efficient than infection of wild-type GTC (GTC-wt), and the number of infected cells was comparable between GTC-d11- and HepG2.2.15-derived viruses when inoculated with the same genome equivalents. A time-dependent increase in pregenomic RNA and efficient synthesis of covalently closed circular DNA were detected after infection with the GTC-d11 virus. The involvement of d11 in the HBV large surface protein in the enhanced infectivity was confirmed by an HBV reporter virus and hepatitis D virus infection system. The binding step of the GTC-d11 virus onto the cell surface was responsible for this efficient infection. CONCLUSIONS: This system provides a powerful tool for studying the infection and propagation of HBV in cell culture and also for developing the antiviral strategy against HBV infection.

Identification of Two Critical Neutralizing Epitopes in the Receptor Binding Domain of Hepatitis B Virus preS1.

Hepatitis B virus (HBV) infection is a major public health problem. Human hepatocytes are infected with HBV via binding between the preS1 region in the large envelope protein of HBV and sodium taurocholate cotransporting polypeptide. Although several monoclonal antibodies (MAbs) that recognize the receptor binding domain in preS1 and neutralize HBV infection have been isolated, details of neutralizing epitopes are not understood. In this study, we generated 13 MAbs targeting the preS1 receptor binding domain from preS1-specific memory B cells derived from DNA immunized mice. The MAbs were classified into three groups according to the epitope regions, designated epitopes I-III. A virus neutralization assay revealed that MAbs recognizing epitopes I and III neutralized HBV infection, suggesting that these domains are critical epitopes for viral neutralization. In addition, a neutralization assay against multiple genotypes of HBV revealed that epitope I is a semi-pangenotypic neutralizing epitope, whereas epitope III is a genotype-specific epitope. We also showed that neutralizing MAbs against preS1 could neutralize HBV bearing vaccine-induced escape mutation. These findings provide insight into novel immunoprophylaxis for the prevention and treatment of HBV infection.IMPORTANCE The HBV preS1 2-47 aa region (preS1/2-47) is essential for virus binding with sodium taurocholate cotransporting polypeptide. Several MAbs targeting preS1/2-47 have been reported to neutralize HBV infection; however, which region in preS1/2-47 contains the critical neutralizing epitope for HBV infection is unclear. Here, we generated several MAbs targeting preS1/2-47 and found that MAbs recognizing the N- or C-terminus of preS1/2-47 remarkably neutralized HBV infection. We further confirmed the neutralizing activity of anti-preS1 MAbs against HBV with vaccine escape mutation. These data clarified the relationship between the antibody epitope and the virus neutralizing activity and also suggested the potential ability of a vaccine antigen containing the preS1 region to overcome the weakness of current HB vaccines comprising the small S protein.

Induction of HOX Genes by Hepatitis C Virus Infection via Impairment of Histone H2A Monoubiquitination.

Hepatitis C virus (HCV) infection causes liver pathologies, including hepatocellular carcinoma (HCC). Homeobox (HOX) gene products regulate embryonic development and are associated with tumorigenesis, although the regulation of HOX genes by HCV infection has not been clarified in detail. We examined the effect of HCV infection on HOX gene expression. In this study, HCV infection induced more than half of the HOX genes and reduced the level of histone H2A monoubiquitination on lysine 119 (K119) (H2Aub), which represses HOX gene promoter activity. HCV infection also promoted proteasome-dependent degradation of RNF2, which is an E3 ligase mediating H2A monoubiquitination as a component of polycomb repressive complex 1. Since full-genomic replicon cells but not subgenomic replicon cells exhibited reduced RNF2 and H2Aub levels and induction of HOX genes, we focused on the core protein. Expression of the core protein reduced the amounts of RNF2 and H2Aub and induced HOX genes. Treatment with LY-411575, which can reduce HCV core protein expression via signal peptide peptidase (SPP) inhibition without affecting other viral proteins, dose-dependently restored the amounts of RNF2 and H2Aub in HCV-infected cells and impaired the induction of HOX genes and production of viral particles but not viral replication. The chromatin immunoprecipitation assay results also indicated infection- and proteasome-dependent reductions in H2Aub located in HOX gene promoters. These results suggest that HCV infection or core protein induces HOX genes by impairing histone H2A monoubiquitination via a reduction in the RNF2 level.IMPORTANCE Recently sustained virologic response can be achieved by direct-acting antiviral (DAA) therapy in most hepatitis C patients. Unfortunately, DAA therapy does not completely eliminate a risk of hepatocellular carcinoma (HCC). Several epigenetic factors, including histone modifications, are well known to contribute to hepatitis C virus (HCV)-associated HCC. However, the regulation of histone modifications by HCV infection has not been clarified in detail. In this study, our data suggest that HCV infection or HCV core protein expression impairs monoubiquitination of histone H2A K119 in the homeobox (HOX) gene promoter via destabilization of RNF2 and then induces HOX genes. Several lines of evidence suggest that the expression of several HOX genes is dysregulated in certain types of tumors. These findings reveal a novel mechanism of HCV-related histone modification and may provide information about new targets for diagnosis and prevention of HCC occurrence.

Establishment of a novel hepatitis B virus culture system using immortalized human hepatocytes.

Recent development of hepatitis B virus (HBV) culture systems has made it possible to analyze the almost all steps of the viral life cycle. However, the reproducibility of interaction between HBV and host cells seemed inaccurate in those systems because of utilization of cancer cell lines with a difference from hepatocytes in the majority of cases. In this study, in order to resolve this point, a novel HBV culture system using non-cancer-derived immortalized human hepatocytes derived cell lines, producing exogenous human sodium taurocholate cotransporting polypeptide, was developed. One of the cell clones, E/NtG8 cells, was permissive to both blood-borne HBV (HBVbb) and culture-derived recombinant HBV when cultured in the three-dimensional condition. Furthermore, the production of infectious HBV particles, which showed the similar physicochemical properties to HBVbb, was observed for about a month after HBVbb infection in this system, suggesting that it may reproduce whole steps of the HBV lifecycle under the condition analogous to human liver cells infected with HBV. This system seemed to contribute not only to find novel interactions between HBV and host cells but also to understand mechanism of HBV pathogenesis.

Cancer-related genetic changes in multistep hepatocarcinogenesis and their correlation with imaging and histological findings.

AIM: The landscape of cancer-related genetic aberrations in hepatocellular carcinoma (HCC) has gradually become clear through recent next-generation sequencing studies. However, it remains unclear how genetic aberrations correlate with imaging and histological findings. METHODS: Using 117 formalin-fixed paraffin-embedded specimens of primary liver tumors, we undertook targeted next-generation sequencing of 50 cancer-related genes and digital polymerase chain reaction of hTERT. After classifying tumors into several imaging groups by hierarchal clustering with the information from gadoxetic acid enhanced magnetic resonance imaging, contrast-enhanced computed tomography, contrast-enhanced ultrasound, and diffusion-weighted imaging magnetic resonance imaging, the correlation between genetic aberrations and imaging and histology were investigated. RESULTS: Most frequent mutations were hTERT (61.5%), followed by TP53 (42.7%), RB1 (24.8%), and CTNNB1 (18.8%). Liver tumors were classified into six imaging groups/grades, and the prevalence of hTERT mutations tended to increase with the advancement of imaging/histological grades (P = 0.026 and 0.13, respectively), whereas no such tendency was evident for TP53 mutation (P = 0.78 and 1.00, respectively). Focusing on the mutations in each tumor, although the variant frequency (VF) of hTERT did not change (P = 0.36 and 0.14, respectively) in association with imaging/histological grades, TP53 VF increased significantly (P = 0.004 and <0.001, respectively). In multivariate analysis, stage III or IV (hazard ratio, 3.64; P = 0.003), TP53 VF ≥ 50% (hazard ratio, 3.79; P = 0.020) was extracted as an independent risk for recurrence in primary HCC patients. CONCLUSIONS: Increased prevalence of hTERT mutation and increased TP53 mutation VF are characteristic features of HCC progression, diagnosed with imaging/histological studies.

Anti-viral effects of interferon-λ3 on hepatitis B virus infection in cell culture.

AIM: Interferon (IFN)-λ3 is known to have antiviral effects against various pathogens. Recently, it has been reported that the production of IFN-λ3 in colon cells after the administration of nucleotide analogs is expected to reduce hepatitis B surface antigen in chronic hepatitis B patients. Here, we aimed to prove the antiviral effects of IFN-λ3 on hepatitis B virus (HBV) by using an in vitro HBV production and infection system. METHODS: We used HepG2.2.15-derived HBV as an inoculum and the replication-competent molecular clone of HBV as a replication model. RESULTS: By administering IFN-λ3 to HepG2 cells transfected with the HBV molecular clone, the production of hepatitis B surface antigen and hepatitis B core-related antigen was reduced dose-dependently. IFN-λ3 treatment also reduced the number of HBV-positive cells and the synthesis of covalently closed circular DNA after infection of HepG2.2.15-derived HBV to sodium taurocholate cotransporting polypeptide-transduced HepG2 cells. The inhibitory effect on HBV infection by IFN-λ3 was confirmed by using a recombinant a HBV reporter virus system. To elucidate the underlying mechanisms of the anti-HBV effect of IFN-λ3, we assessed the transcription of HBV RNA and the production of core-associated HBV DNA in HBV molecular clone-transfected HepG2 cells, and found that both parameters were reduced by IFN-λ3. CONCLUSIONS: We observed that the administration of IFN-λ3 inhibits HBV infection and the production of HBV proteins at the HBV RNA transcription level. This finding provides novel insight into the treatment of chronic hepatitis B patients with the administration or induction of IFN-λ3.

C-terminal α Domain of p63 Binds to p300 to Coactivate ß-Catenin.

TP63 (p63), a member of the tumor suppressor TP53 (p53) gene family, is essential for ectodermal tissue development and suppresses malignant progression of carcinomas. The most abundant isoform, ΔNp63α (referred to as p63), lacks the N-terminal transactivation (TA) domain, and was originally characterized as a dominant-negative type suppressor against p53 family proteins. It also binds to TCF/LEF to inhibit ß-catenin. Nevertheless, transcriptional activation by p63 has also been observed in varied systems. To understand the puzzling results, we analyzed the structure-function relationship of p63 in the control of ß-catenin-dependent transcription. p63 acted as a suppressor of moderately induced ß-catenin. However, when nuclear targeted S33Y ß-catenin was applied to cause the maximum enhancer activation, p63 displayed a ß-catenin-coactivating function. The DNA-binding domain of p63 and the target sequence facilitated it. Importantly, we newly found that, despite the absence of TA domain, p63 was associated with p300, a general adaptor protein and chromatin modifier causing transcriptional activation. C-terminal α domain of p63 was essential for p300-binding and for the coactivator function. These results were related to endogenous p63-p300 complex formation and Wnt/ß-catenin-responsive gene regulation by p63 in squamous cell carcinoma lines. The novel p63-p300 interaction may be involved in positive regulation of gene expression in tissue development and carcinogenesis.

USP15 Participates in Hepatitis C Virus Propagation through Regulation of Viral RNA Translation and Lipid Droplet Formation.

Hepatitis C virus (HCV) utilizes cellular factors for efficient propagation. Ubiquitin is covalently conjugated to the substrate to alter its stability or to modulate signal transduction. In this study, we examined the importance of ubiquitination for HCV propagation. We found that inhibition of deubiquitinating enzymes (DUBs) or overexpression of nonspecific DUBs impaired HCV replication, suggesting that ubiquitination regulates HCV replication. To identify specific DUBs involved in HCV propagation, we set up RNA interference (RNAi) screening against DUBs and successfully identified ubiquitin-specific protease 15 (USP15) as a novel host factor for HCV propagation. Our studies showed that USP15 is involved in translation of HCV RNA and production of infectious HCV particles. In addition, deficiency of USP15 in human hepatic cell lines (Huh7 and Hep3B/miR-122 cells) but not in a nonhepatic cell line (293T cells) impaired HCV propagation, suggesting that USP15 participates in HCV propagation through the regulation of hepatocyte-specific functions. Moreover, we showed that loss of USP15 had no effect on innate immune responses in vitro and in vivo We also found that USP15-deficient Huh7 cells showed reductions in the amounts of lipid droplets (LDs), and the addition of palmitic acids restored the production of infectious HCV particles. Taken together, these data suggest that USP15 participates in HCV propagation by regulating the translation of HCV RNA and the formation of LDs.IMPORTANCE Although ubiquitination has been shown to play important roles in the HCV life cycle, the roles of deubiquitinating enzymes (DUBs), which cleave ubiquitin chains from their substrates, in HCV propagation have not been investigated. Here, we identified USP15 as a DUB regulating HCV propagation. USP15 showed no interaction with viral proteins and no participation in innate immune responses. Deficiency of USP15 in Huh7 cells resulted in suppression of the translation of HCV RNA and reduction in the amounts of lipid droplets, and the addition of fatty acids partially restored the production of infectious HCV particles. These data suggest that USP15 participates in HCV propagation in hepatic cells through the regulation of viral RNA translation and lipid metabolism.

Hepatitis B virus (HBV)-infected patients with low hepatitis B surface antigen and high hepatitis B core-related antigen titers have a high risk of HBV-related hepatocellular carcinoma.

AIM: Although the viral markers hepatitis B surface antigen (HBsAg) and hepatitis B core-related antigen (HbcrAg) could reflect intrahepatic hepatitis B virus (HBV) replication activity and constitute important biomarkers for hepatocellular carcinoma (HCC), the value of using these two markers in combination for assessing HCC risk has not been clarified in detail. METHODS: Four hundred and forty-nine consecutive patients with chronic HBV infection were included in the study and the association of HBsAg and HBcrAg with HCC risk was investigated cross-sectionally, as well as longitudinally. RESULTS: When the high value cut-offs of HBsAg and HBcrAg were defined as 3.0 log IU/mL and 3.0 log U/mL, respectively, patients with a history of HCC were found frequently in the low HBsAg group (P = 0.002) and high HBcrAg group (P < 0.001). When HBsAg and HBcrAg were combined, an HCC history was most frequent in the subset with low HBsAg and high HBcrAg, among the HBeAg-negative patients (odds ratio [OR], 7.83; P < 0.001), irrespective of nucleos(t) ide analogue (NA) therapy (NA: OR, 4.76; P < 0.001; non-NA: OR, 9.60; P < 0.001). In a longitudinal analysis of the subsequent development of HCC, carried out on the 338 patients without an HCC history at enrollment, HCC developed significantly more frequently in the low HBsAg/high HBcrAg group (P = 0.005). CONCLUSIONS: Patients with low HBsAg/high HBcrAg values are at high risk of developing HBV-related HCC, according to this cross-sectional and longitudinal analysis, indicating that the combination of HBsAg and HBcrAg values is an excellent biomarker for assessing HCC risk.

Characterization of SPP inhibitors suppressing propagation of HCV and protozoa.

Signal peptide peptidase (SPP) is an intramembrane aspartic protease involved in the maturation of the core protein of hepatitis C virus (HCV). The processing of HCV core protein by SPP has been reported to be critical for the propagation and pathogenesis of HCV. Here we examined the inhibitory activity of inhibitors for γ-secretase, another intramembrane cleaving protease, against SPP, and our findings revealed that the dibenzoazepine-type structure in the γ-secretase inhibitors is critical for the inhibition of SPP. The spatial distribution showed that the γ-secretase inhibitor compound YO-01027 with the dibenzoazepine structure exhibits potent inhibiting activity against SPP in vitro and in vivo through the interaction of Val223 in SPP. Treatment with this SPP inhibitor suppressed the maturation of core proteins of all HCV genotypes without the emergence of drug-resistant viruses, in contrast to the treatment with direct-acting antivirals. YO-01027 also efficiently inhibited the propagation of protozoa such as Plasmodium falciparum and Toxoplasma gondii These data suggest that SPP is an ideal target for the development of therapeutics not only against chronic hepatitis C but also against protozoiasis.

Insights into the mechanism of isoenzyme-specific signal peptide peptidase-mediated translocation of heme oxygenase.

It has recently been shown that signal peptide peptidase (SPP) can catalyze the intramembrane cleavage of heme oxygenase-1 (HO-1) that leads to translocation of HO-1 into the cytosol and nucleus. While there is consensus that translocated HO-1 promotes tumor progression and drug resistance, the physiological signals leading to SPP-mediated intramembrane cleavage of HO-1 and the specificity of the process remain unclear. In this study, we used co-immunoprecipitation and confocal laser scanning microscopy to investigate the translocation mechanism of HO-1 and its regulation by SPP. We show that HO-1 and the closely related HO-2 isoenzyme bind to SPP under normoxic conditions. Under hypoxic conditions SPP mediates intramembrane cleavage of HO-1, but not HO-2. In experiments with an inactive HO-1 mutant (H25A) we show that translocation is independent of the catalytic activity of HO-1. Studies with HO-1 / HO-2 chimeras indicate that the membrane anchor, the PEST-domain and the nuclear shuttle sequence of HO-1 are necessary for full cleavage and subsequent translocation under hypoxic conditions. In the presence of co-expressed exogenous SPP, the anchor and the PEST-domain are sufficient for translocation. Taken together, we identified the domains involved in HO-1 translocation and showed that SPP-mediated cleavage is isoform-specific and independent of HO-activity. A closer understanding of the translocation mechanism of HO-1 is of particular importance because nuclear HO-1 seems to lead to tumor progression and drug resistance.

Cinnamic acid derivatives inhibit hepatitis C virus replication via the induction of oxidative stress.

Several cinnamic acid derivatives have been reported to exhibit antiviral activity. In this study, we prepared 17 synthetic cinnamic acid derivatives and screened them to identify an effective antiviral compound against hepatitis C virus (HCV). Compound 6, one of two hit compounds, suppressed the viral replications of genotypes 1b, 2a, 3a, and 4a with EC50 values of 1.5-8.1 µM and SI values of 16.2-94.2. The effect of compound 6 on the phosphorylation of Tyr705 in signal transducer and activator of transcription 3 (STAT3) was investigated because a cinnamic acid derivative AG490 was reported to suppress HCV replication and the activity of Janus kinase (JAK) 2. Compound 6 potently suppressed HCV replication, but it did not inhibit the JAK1/2-dependent phosphorylation of STAT3 Tyr705 at the same concentration. Furthermore, a pan-JAK inhibitor tofacitinib potently impaired phosphorylation of STAT3 Tyr 705, but it did not inhibit HCV replication in the replicon cells and HCV-infected cells at the same concentration, supporting the notion that the phosphorylated state of STAT3 Tyr705 is not necessarily correlated with HCV replication. The production of reactive oxygen species (ROS) was induced by treatment with compound 6, whereas N-acetyl-cysteine restored HCV replication and impaired ROS production in the replicon cells treated with compound 6. These data suggest that compound 6 inhibits HCV replication via the induction of oxidative stress.

Inhibitory effects of metachromin A on hepatitis B virus production via impairment of the viral promoter activity.

The currently available antiviral agents for chronic infection with hepatitis B virus (HBV) are pegylated interferon-α and nucleoside/nucleotide analogues, although it has been difficult to completely eliminate covalently closed circular DNA (cccDNA) from patients. To identify an antiviral compound targeting HBV core promoter, 15 terpenes originating from marine organisms were screened using a cell line expressing firefly luciferase under the control of the HBV core promoter. Metachromin A, which is a merosesquiterpene isolated from the marine sponge Dactylospongia metachromia, inhibited the viral promoter activity at the highest level among the tested compounds, and suppressed HBV production with an EC50 value of 0.8 µM regardless of interferon signaling and cytotoxicity. The analysis on the structure-activity relationship revealed that the hydroquinone moiety, and the double bonds at carbon numbers-5 and -9 in metachromin A are crucial for anti-HBV activity. Furthermore, metachromin A reduced the protein level but not the RNA level of hepatic nuclear factor 4α, which mainly upregulates the activities of enhancer I/X promoter and enhancer II/core promoter. These results suggest that metachromin A can inhibit HBV production via impairment of the viral promoter activity. Antiviral agents targeting the viral promoter may ameliorate HBV-related disorders regardless of remaining cccDNA.

The potential of signal peptide peptidase as a therapeutic target for hepatitis C.

INTRODUCTION: Chronic infection with hepatitis C virus (HCV) causes liver steatosis, cirrhosis, metabolic syndrome with inflammation, and eventually leads to hepatocellular carcinoma. HCV core protein is a well-known capsid protein and pathogenic factor related to lipid accumulation, type 2 diabetes mellitus, and carcinogenesis. Cleavage of the C-terminal transmembrane region by signal peptide peptidase (SPP) is required for maturation of the core protein. Areas covered: Herein, this review details the general aspects of the structure, lifecycle, pathogenesis, and maturation of the HCV core protein, the function of SPP, and clinically available direct-acting antivirals (DAAs). SPP is classified into a group of GXGD-type intramembrane proteases including presenilin-1, which is a component of γ-secretase complex. Several SPP inhibitors were previously identified from γ-secretase inhibitors, but have not yet been improved based on specificity to SPP. Finally, the author discusses the potential of SPP inhibitors for hepatitis C therapy. Expert opinion: Currently available DAAs therapies are limited because of different viral genotypes and underlying conditions in each patient. DAA-resistant viruses have also been reported. Development of SPP-selective inhibitors may improve current HCV therapies by decreasing in the emergence of DAA-resistant viruses irrespective of viral genotype.

Hepatitis B virus prevents excessive viral production via reduction of cell death-inducing DFF45-like effectors.

The relationship between hepatitis B virus (HBV) infection and lipid accumulation remains largely unknown. In this study, we investigated the effect of HBV propagation on lipid droplet growth in HBV-infected cells and HBV-producing cell lines, HepG2.2.15 and HBV-inducible Hep38.7-Tet. The amount of intracellular triglycerides was significantly reduced in HBV-infected and HBV-producing cells compared with HBV-lacking control cells. Electron and immunofluorescent microscopic analyses showed that the average size of a single lipid droplet (LD) was significantly less in the HBV-infected and HBV-producing cells than in the HBV-lacking control cells. Cell death-inducing DFF45-like effectors (CIDEs) B and C (CIDEB and CIDEC), which are involved in LD expansion for the improvement of lipid storage, were expressed at a significantly lower level in HBV-infected or HBV-producing cells than in HBV-lacking control cells, while CIDEA was not detected in those cells regardless of HBV production. The activity of the CIDEB and CIDEC gene promoters was impaired in HBV-infected or HBV-producing cells compared to HBV-lacking control cells, while CIDEs potentiated HBV core promoter activity. The amount of HNF4α, that can promote the transcription of CIDEB was significantly lower in HBV-producing cells than in HBV-lacking control cells. Knockout of CIDEB or CIDEC significantly reduced the amount of supernatant HBV DNA, intracellular viral RNA and nucleocapsid-associated viral DNA, while the expression of CIDEB or CIDEC recovered HBV production in CIDEB- or CIDEC-knockout cells. These results suggest that HBV regulates its own viral replication via CIDEB and CIDEC.