Ribonucleotide reductase M2 promotes RNA replication of hepatitis C virus by protecting NS5B protein from hPLIC1-dependent proteasomal degradation

Hepatitis C virus (HCV) establishes a chronic infection that can lead to cirrhosis and hepatocellular carcinoma. The HCV life cycle is closely associated with host factors that promote or restrict viral replication, the characterization of which could help to identify potential therapeutic targets. To this end, here we performed a genome-wide microarray analysis and identified ribonucleotide reductase M2 (RRM2) as a cellular factor essential for HCV replication. We found that RRM2 is up-regulated in response to HCV infection in quiescent hepatocytes from humanized chimeric mouse livers. To elucidate the molecular basis of RRM2 expression in HCV-infected cells, we used HCV-infected hepatocytes from chimeric mice and hepatoma cells infected with the HCV strain JFH1. Both models exhibited increased RRM2 mRNA and protein expression levels. Moreover, siRNA-mediated silencing of RRM2 suppressed HCV replication and infection. Of note, RRM2 and RNA polymerase nonstructural protein 5B (NS5B) partially co-localized in cells and co-immunoprecipitated, suggesting that they might interact. RRM2 knockdown reduced NS5B expression, which depended on the protein degradation pathway, as NS5B RNA levels did not decrease and NS5B protein stability correlated with RRM2 protein levels. We also found that RRM2 silencing decreased levels of hPLIC1 (human homolog 1 of protein linking integrin-associated protein and cytoskeleton), a ubiquitin-like protein that interacts with NS5B and promotes its degradation. This finding suggests that there is a dynamic interplay between RRM2 and the NS5B-hPLIC1 complex that has an important function in HCV replication. Together, these results identify a role of host RRM2 in viral RNA replication.

Avian H5N1 influenza virus infection causes severe pneumonia in the Northern tree shrew (Tupaia belangeri)

Avian-origin influenza viruses like H5N1 and H7N9 often cause severe symptoms with high mortality in humans. Animal models are useful for clarification of the mechanisms of pathogenicity of these infections. In this study, to expand the potential utility of the Northern tree shrew (Tupaia belangeri) for influenza virus infection, we assessed the pathogenicity of H5N1 and H7N9 avian influenza viruses in tupaia. Infectious virus was detected continuously from nasal, oral, tracheal, and conjunctival swab samples in the animals infected with these viruses. H5N1 influenza virus infection of tupaia caused severe diffuse pneumonia with fever and weight loss. In contrast, H7N9 influenza virus infection caused focal pneumonia. The severity of pneumonia was correlated with proinflammatory cytokine transcript levels. These results indicated that tupaia can be another suitable animal model for avian influenza virus research.

Hepatitis C Virus: Viral Quasispecies and Genotypes

Hepatitis C virus (HCV) mainly replicates in the cytoplasm, where it easily establishes persistent infection, resulting in chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Due to its high rate of mutation, HCV forms viral quasispecies, categorized based on the highly variable regions in the envelope protein and nonstructural 5A protein. HCV possesses seven major genotypes, among which genotype 1 is the most prevalent globally. The distribution of HCV genotypes varies based on geography, and each genotype has a different sensitivity to interferon treatment. Recently-developed direct-acting antivirals (DAAs), which target viral proteases or polymerases, mediate drastically better antiviral effects than previous therapeutics. Although treatment with DAAs has led to the development of drug-resistant HCV mutants, the most recently approved DAAs show improved pan-genomic activity, with a higher barrier to viral resistance.

Interferon-β response is impaired by hepatitis B virus infection in Tupaia belangeri

To date, the chimpanzee has been used as the natural infection model for hepatitis B virus (HBV). However, as this model is very costly and difficult to use because of ethical and animal welfare issues, we aimed to establish the tupaia (Tupaia belangeri) as a new model for HBV infection and characterized its intrahepatic innate immune response upon HBV infection. First, we compared the propagation of HBV genotypes A2 and C in vivo in tupaia hepatocytes. At 8-10days post infection (dpi), the level of HBV-A2 propagation in the tupaia liver was found to be higher than that of HBV-C. Abnormal architecture of liver cell cords and mitotic figures were also observed at 8 dpi with HBV-A2. Moreover, we found that HBV-A2 established chronic infection in some tupaias. We then aimed to characterize the intrahepatic innate immune response in this model. First, we infected six tupaias with HBV-A2 (strains JP1 and JP4). At 28 dpi, intrahepatic HBV-DNA and serum hepatitis B surface antigens (HBsAg) were detected in all tupaias. The levels of interferon (IFN)-β were found to be significantly suppressed in the three tupaias infected with HBV A2_JP4, while no significant change was observed in the three infected with HBV A2_JP1. Expression of toll-like receptor (TLR) 1 was suppressed, while that of TLR3 and TLR9 were induced, in HBV A2_JP1-infected tupaias. Expression of TLR8 was induced in all tupaias. Next, we infected nine tupaias with HBV-A2 (JP1, JP2, and JP4), and characterized the infected animals after 31 weeks. Serum HBsAg levels were detected at 31 weeks post-infection (wpi) and IFN-β was found to be significantly suppressed in all tupaias. TLR3 was not induced, except in tupaia #93 and #96. Suppression of TLR9 was observed in all tupaias, except tupaia #93. Also, we investigated the expression levels of cyclic GMP-AMP synthase, which was found to be induced in all tupaias at 28 dpi and in four tupaias at 31 wpi. Additionally, we evaluated the expression levels of sodium-taurocholate cotransporting polypeptide, which was found to be suppressed during chronic HBV infection. Thus, the tupaia infection model of HBV clearly indicated the suppression of IFN-β at 31 wpi, which might have contributed to the establishment of chronic HBV infection.

Identification and molecular characterization of novel primate bocaparvoviruses from wild western lowland gorillas of Moukalaba-Doudou National Park, Gabon

Bocaparvoviruses have been studied extensively owing to their ability to cause respiratory illness or gastroenteritis in humans. Some bocaparvoviruses have been detected in non-human primates (gorillas and chimpanzees), but the diversity and evolution of these viruses are not fully understood. In this study, we collected 107 fecal samples from wild western lowland gorillas in Moukalaba-Doudou National Park in Gabon to investigate the presence of bocaparvoviruses. Using a combination of pan-bocaparvovirus PCR and individual identification by microsatellite genotyping, we found that two samples from two apparently healthy infant gorillas were positive for bocaparvovirus. Sequencing and phylogenetic analyses revealed that the two gorilla bocaparvovirus strains are nearly identical and are closely related to viruses in the species Primate bocaparvovirus 2 (with 86.0% nucleotide identity to a human bocavirus 2 isolate). To our knowledge, this is the first report showing the presence of a non-human primate bocaparovirus within Primate bocaparvovirus 2. Our findings provide novel insights into the diversity and evolution of bocaparvoviruses and highlight the importance of surveying these viruses for the safe management of gorilla-based ecotourism.

Susceptibility and initial immune response of Tupaia belangeri cells to dengue virus infection

Dengue is an emerging disease of great public health significance worldwide. The lack of a suitable infection model has hampered dengue virus (DENV) pathogenesis study, and developing a suitable small animal model has been a long-standing challenge. The aim of this study was to develop a feasible experimental model of DENV infection using Tupaia belangeri. The susceptibility of tupaia to DENV infection and characteristics of its innate immune response were examined in vitro. We found that tupaia fibroblast cells support replication of DENV serotypes 1-4 with a linear increase in viral load 24-96h post-infection in both cells and culture supernatants. DENV-2 resulted in the highest viral growth among all serotypes. To characterize the innate immune response in tupaia cells during the early phase of DENV infection, we first evaluated the evolutionary relationship between tupaia Toll-like receptors (TLR1-9) and those of other mammalian species. Phylogenetic analysis showed that tupaia TLRs are evolutionarily much closer to human than they are to rodent. We next established an innate immune response measurement system by assessing the mRNA expression of TLR1-9 and four cytokines in DENV-infected tupaia cells. All serotypes induced the upregulation of TLR8 mRNA expression in infected tupaia cells. Silencing of TLR8 led to an increase in viral replication, indicating the existence of antiviral response through TLR8 on DENV infection. Although upregulation of IFN-β and IL-6 expression was only observed in DENV-1 infected cells and a significant suppression of TNF-α was observed in DENV-2 infected cells alone, IL-8 was upregulated in all DENV-1-4. Thus, this study demonstrates for the first time the susceptibility of tupaia cells to DENV infections and the role of TLR8 in the anti-viral response of tupaia cells to DENV. These findings demonstrate the potential utility of tupaia as a model for DENV research in the future.

Molecular epidemiological study of adenovirus infecting western lowland gorillas and humans in and around Moukalaba-Doudou National Park (Gabon)

Adenoviruses are widespread in human population as well as in great apes, although the data about the naturally occurring adenovirus infections remain rare. We conducted the surveillance of adenovirus infection in wild western lowland gorillas in Moukalaba-Doudou National Park (Gabon), in order to investigate naturally occurring adenovirus in target gorillas and tested specifically a possible zoonotic transmission with local people inhabiting the vicinity of the park. Fecal samples were collected from western lowland gorillas and humans, and analyzed by PCR. We detected adenoviral genes in samples from both gorillas and the local people living around the national park, respectively: the overall prevalence rates of adenovirus were 24.1 and 35.0 % in gorillas and humans, respectively. Sequencing revealed that the adenoviruses detected in the gorillas were members of Human mastadenovirus B (HAdV-B), HAdV-C, or HAdV-E, and those in the humans belonged to HAdV-C or HAdV-D. Although HAdV-C members were detected in both gorillas and humans, phylogenetic analysis revealed that the virus detected in gorillas are genetically distinct from those detected in humans. The HAdV-C constitutes a single host lineage which is compatible with the host-pathogen divergence. However, HAdV-B and HAdV-E are constituted by multiple host lineages. Moreover, there is no evidence of zoonotic transmission thus far. Since the gorilla-to-human transmission of adenovirus has been shown before, the current monitoring should be continued in a broader scale for getting more insights in the natural history of naturally occurring adenoviruses and for the safe management of gorillas' populations.

Supplementing Conventional Treatment with Pycnogenol® May Improve Hepatitis C Virus-Associated Type 2 Diabetes: A Mini Review

Hepatitis C virus (HCV) infection and type 2 diabetes mellitus (T2DM) present a significant health burden, with increasing complications and mortality rates worldwide. Pycnogenol® (PYC), a natural product, possesses antidiabetic and antiviral properties that may improve HCV-associated T2DM. In this review, we present previously published data on the effectiveness of PYC against HCV replication and T2DM. We believe that supplementing conventional treatment with PYC may improve the current HCV therapy, attenuate HCV-associated T2DM, and reduce the risk of complications such as cirrhosis or hepatocellular carcinoma and cardiovascular disease.

Extracellular Vesicles Including Exosomes Regulate Innate Immune Responses to Hepatitis B Virus Infection

The innate immune system is essential for controlling viral infection. Hepatitis B virus (HBV) persistently infects human hepatocytes and causes hepatocellular carcinoma. However, the innate immune response to HBV infection in vivo remains unclear. Using a tree shrew animal model, we showed that HBV infection induced hepatic interferon (IFN)-γ expression during early infection. Our in vitro study demonstrated that hepatic NK cells produced IFN-γ in response to HBV only in the presence of hepatic F4/80⁺ cells. Moreover, extracellular vesicles (EVs) released from HBV-infected hepatocytes contained viral nucleic acids and induced NKG2D ligand expression in macrophages by stimulating MyD88, TICAM-1, and MAVS-dependent pathways. In addition, depletion of exosomes from EVs markedly reduced NKG2D ligand expression, suggesting the importance of exosomes for NK cell activation. In contrast, infection of hepatocytes with HBV increased immunoregulatory microRNA levels in EVs and exosomes, which were transferred to macrophages, thereby suppressing IL-12p35 mRNA expression in macrophages to counteract the host innate immune response. IFN-γ increased the hepatic expression of DDX60 and augmented the DDX60-dependent degradation of cytoplasmic HBV RNA. Our results elucidated the crucial role of exosomes in antiviral innate immune response against HBV.

Establishment of an intermittent cold stress model using Tupaia belangeri and evaluation of compound C737 targeting neuron-restrictive silencer factor

Previous studies have shown that intermittent cold stress (ICS) induces depression-like behaviors in mammals. Tupaia belangeri (the tree shrew) is the only experimental animal other than the chimpanzee that has been shown to be susceptible to infection by hepatitis B and C viruses. Moreover, full genome sequence analysis has revealed strong homology between host proteins in Tupaia and in humans and other primates. Tupaia neuromodulator receptor proteins are also known to have a high degree of homology with their corresponding primate proteins. Based on these similarities, we hypothesized that induction of ICS in Tupaia would provide a useful animal model of stress responses. We exposed young adult Tupaia to ICS and observed decreases in body temperature and body weight in both female and male Tupaia, suggesting that Tupaia are an appropriate animal model for ICS studies. We further examined the efficacy of a new small-molecule compound, C737, against the effects of ICS. C737 mimics the helical structure of neuron-restrictive silencer factor (NRSF/REST), which regulates a wide range of target genes involved in neuronal function and pain modulation. Treatment with C737 significantly reduced stress-induced weight loss in female Tupaia; these effects were stronger than those elicited by the antidepressant agomelatine. These results suggest that Tupaia represents a useful non-rodent ICS model. Our data also provide new insights into the function of NRSF/REST in stress-induced depression and other disorders with epigenetic influences or those with high prevalence in women.

IRES-mediated translation of foot-and-mouth disease virus (FMDV) in cultured cells derived from FMDV-susceptible and -insusceptible animals

BACKGROUND

Foot-and-mouth disease virus (FMDV) possess a positive sense, single stranded RNA genome. Internal ribosomal entry site (IRES) element exists within its 5' untranslated region (5'UTR) of the viral RNA. Translation of the viral RNA is initiated by internal entry of the 40S ribosome within the IRES element. This process is facilitated by cellular factors known as IRES trans-acting factors (ITAFs). Foot-and-mouth disease (FMD) is host-restricted disease for cloven-hoofed animals such as cattle and pigs, but the factors determining the host range have not been identified yet. Although, ITAFs are known to promote IRES-mediated translation, these findings were confirmed only in cells derived from FMDV-insusceptible animals so far. We evaluated and compared the IRES-mediated translation activities among cell lines derived from four different animal species using bicistronic luciferase reporter plasmid, which possesses an FMDV-IRES element between Renilla and Firefly luciferase genes. Furthermore, we analyzed the effect of the cellular factors on IRES-mediated translation by silencing the cellular factors using siRNA in both FMDV-susceptible and -insusceptible animal cells.

RESULTS

Our data indicated that IRES-mediated translational activity was not linked to FMDV host range. ITAF45 promoted IRES-mediated translation in all cell lines, and the effects of poly-pyrimidine tract binding protein (PTB) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) were observed only in FMDV-susceptible cells. Thus, PTB and 4E-BP1 may influence the host range of FMDV.

CONCLUSIONS

IRES-mediated translation activity of FMDV was not predictive of its host range. ITAF45 promoted IRES-mediated translation in all cells, and the effects of PTB and 4E-BP1 were observed only in FMDV-susceptible cells.

Contribution of the interaction between the rabies virus P protein and I-kappa B kinase ϵ to the inhibition of type I IFN induction signalling

The P protein of rabies virus (RABV) is known to interfere with the phosphorylation of the host IFN regulatory factor 3 (IRF-3) and to consequently inhibit type I IFN induction. Previous studies, however, have only tested P proteins from laboratory-adapted fixed virus strains, and to the best of our knowledge there is no report about the effect of P proteins from street RABV strains or other lyssaviruses on the IRF-3-mediated type I IFN induction system. In this study, we evaluated the inhibitory effect of P proteins from several RABV strains, including fixed and street virus strains and other lyssaviruses (Lagos bat, Mokola and Duvenhage viruses), on IRF-3 signalling. All P proteins tested inhibited retinoic acid-inducible gene-1 (RIG-I)- and TANK binding kinase 1 (TBK1)-mediated IRF-3-dependent IFN-β promoter activities. On the other hand, the P proteins from the RABV street strains 1088 and HCM-9, but not from fixed strains Nishigahara (Ni) and CVS-11 and other lyssaviruses tested, significantly inhibited I-kappa B kinase ϵ (IKKϵ)-inducible IRF-3-dependent IFN-β promoter activity. Importantly, we revealed that the P proteins from the 1088 and HCM-9 strains, but not from the remaining viruses, interacted with IKKϵ. By using expression plasmids encoding chimeric P proteins from the 1088 strain and Ni strain, we found that the C-terminal region of the P protein is important for the interaction with IKKϵ. These findings suggest that the P protein of RABV street strains may contribute to efficient evasion of host innate immunity.

Isolation and characterization of influenza A viruses from environmental water at an overwintering site of migratory birds in Japan

The Izumi plain in Kagoshima prefecture, Japan, is an overwintering site of more than 10,000 cranes. The wet paddy areas are artificially created to provide roosting sites for the cranes every winter. Since wild ducks, known to be a natural reservoir of influenza A viruses, also overwinter in this area, the cranes' roost water likely serves as a source of influenza A virus infection. To assess this potential risk, we collected 126 water samples from the cranes' roost in the 2012/2013 winter season for virus isolation. We isolated six influenza viruses of three subtypes (H3N8, H4N6, and H4N8) from the water samples collected in the months of November and December. Genetic analysis of our isolates indicated that these viruses were genetically similar to the low-pathogenic avian influenza viruses circulating among Eurasian waterfowl. These findings suggest the possibility of the cranes becoming infected with the avian influenza viruses that are present in their roost water.

Efficacy of Recombinant Canine Distemper Virus Expressing Leishmania Antigen against Leishmania Challenge in Dogs

Canine distemper virus (CDV) vaccination confers long-term protection against CDV reinfection. To investigate the utility of CDV as a polyvalent vaccine vector for Leishmania, we generated recombinant CDVs, based on an avirulent Yanaka strain, that expressed Leishmania antigens: LACK, TSA, or LmSTI1 (rCDV-LACK, rCDV-TSA, and rCDV-LmSTI1, respectively). Dogs immunized with rCDV-LACK were protected against challenge with lethal doses of virulent CDV, in the same way as the parental Yanaka strain. To evaluate the protective effects of the recombinant CDVs against cutaneous leishmaniasis in dogs, dogs were immunized with one recombinant CDV or a cocktail of three recombinant CDVs, before intradermal challenge (in the ears) with infective-stage promastigotes of Leishmania major. Unvaccinated dogs showed increased nodules with ulcer formation after 3 weeks, whereas dogs immunized with rCDV-LACK showed markedly smaller nodules without ulceration. Although the rCDV-TSA- and rCDV-LmSTI1-immunized dogs showed little protection against L. major, the cocktail of three recombinant CDVs more effectively suppressed the progression of nodule formation than immunization with rCDV-LACK alone. These results indicate that recombinant CDV is suitable for use as a polyvalent live attenuated vaccine for protection against both CDV and L. major infections in dogs.

Serum DHCR24 Auto-antibody as a new Biomarker for Progression of Hepatitis C

BACKGROUND

New biomarkers are needed to identify the stage of hepatitis C virus (HCV)-infected diseases in order to reduce the mortality rates. Herein, we investigated whether serum 3β-hydroxysterol Δ24-reductase antibody (DHCR24 Ab) may serve as a prognostic marker for hepatitis C infection progression to hepatocellular carcinoma (HCC).

METHODS

Serum DHCR24 Abs from 395 HCV-positive patients, including 133 chronic hepatitis (CHC), 85 liver cirrhosis (LCC), and 177 HCC (HCC-C) patients; 232 hepatitis B virus (HBV)-positive patients, including 103 chronic hepatitis (CHB), 56 liver cirrhosis (LCB), and 73 HCC (HCC-B) patients; and 24 healthy controls, were measured using enzyme-linked immunosorbent assay.

RESULTS

The serum DHCR24 Ab levels were significantly higher in patients with CHC than in healthy controls, in LCC than in CHC, and in LCC than in HCC-C (P < 0.0001 for all). The concentration of serum DHCR24 Ab in HCC-B patients showed no significant difference compared to CHB and LCB patients (P = 0.1247). The DHCR24 Ab levels were significantly higher in early HCC-C than CHC or LCC patients and in late HCC-C compared to early HCC-C patients. The sensitivity of the DHCR24 Ab for HCC-C detection (70.6%) was higher than that of alpha-fetoprotein (AFP; 54.8%) and protein induced by vitamin K absence or antagonist-II (PIVKA-II; 42 · 5%). Moreover, DHCR24 was up-regulated in HCV-positive, but not HBV-positive tissues or HBV-negative, HCV-negative HCC specimens.

CONCLUSIONS

DHCR24 auto-antibody represents a potential noninvasive biomarker for HCV-related liver disease and may facilitate the diagnosis of PIVKA-II and AFP-negative HCC.

3β-hydroxysterol δ24-reductase on the surface of hepatitis C virus-related hepatocellular carcinoma cells can be a target for molecular targeting therapy

In our previous study, we demonstrated that 3β-hydroxysterol Δ24-reductase (DHCR24) was overexpressed in hepatitis C virus (HCV)-related hepatocellular carcinoma (HCC), and that its expression was induced by HCV. Using a monoclonal antibody against DHCR24 (2-152a MAb), we found that DHCR24 was specifically expressed on the surface of HCC cell lines. Based on these findings, we aimed to establish a novel targeting strategy using 2-152a MAb to treat HCV-related HCC. In the present study, we examined the antitumor activity of 2-152a MAb. In the presence of complement, HCC-derived HuH-7 cells were killed by treatment with 2-152a MAb, which was mediated by complement-dependent cytotoxicity (CDC). In addition, the antigen recognition domain of 2-152a MAb was responsible for the unique anti-HCV activity. These findings demonstrate the feasibility of using 2-152a MAb for antibody therapy against HCV-related HCC. In addition, surface DHCR24 on HCC cells exhibited a functional property, agonist-induced internalization. We showed that 2-152a MAb-mediated binding of a cytotoxic agent (a saponin-conjugated secondary antibody) to surface DHCR24 led to significant cytotoxicity. This suggests that surface DHCR24 on HCC cells can function as a carrier for internalization. Therefore, surface DHCR24 could be a valuable target for HCV-related HCC therapy, and 2-152a MAb appears to be useful for this targeted therapy.

[Animal model for hepatitis C virus infection]

Hepatitis C virus (HCV) infects more than 170 million people in the world and chronic HCV infection develops into cirrhosis and hepatocellular carcinoma (HCC). Recently, the effective compounds have been approved for HCV treatment, the protease inhibitor and polymerase inhibitor (direct acting antivirals; DAA). DAA-based therapy enabled to cure from HCV infection. However, development of new drug and vaccine is still required because of the generation of HCV escape mutants from DAA, development of HCC after treatment of DAA, and the high cost of DAA. In order to develop new anti-HCV drug and vaccine, animal infection model of HCV is essential. In this manuscript, we would like to introduce the history and the current status of the development of HCV animal infection model.

Inhibitory effects of Pycnogenol® on hepatitis C virus replication

Chronic hepatitis C virus (HCV) infection increases the risk of liver cirrhosis and hepatocellular carcinoma. In the last decade, the current standard HCV treatment, pegylated interferon and ribavirin, have limited efficacy and significant side effects. Novel direct acting antivirals show promise, but escape mutants are expected, along with potential side effects. Pycnogenol®, a French maritime pine extract, has been reported to have antioxidant and antiviral effects. Here, we evaluated the effect of Pycnogenol® on HCV replication. Wild-type and protease inhibitor (VX-950; telaprevir)-resistant HCV replicon cells were treated with Pycnogenol®, Pycnogenol® and interferon-alpha, and ribavirin and telaprevir. Pycnogenol® effects on replication were also evaluated in HCV-infected chimeric mice. Pycnogenol® treatment showed antiviral effects without cytotoxicity at doses up to 50 μg/mL. Pycnogenol® in combination with interferon-alpha or ribavirin showed synergistic effects. Moreover, Pycnogenol® inhibited HCV replication in telaprevir-resistant replicon cells; telaprevir and Pycnogenol® acted additively to reduce HCV RNA levels in wild-type HCV replicon cells without significantly increasing cytotoxicity. Pycnogenol® antiviral activity was higher than its components procyanidin and taxifolin. Further, treatment of infected chimeric mice with Pycnogenol® suppressed HCV replication and showed a synergistic effect with interferon-alpha. In addition, Pycnogenol® treatment resulted in dose-dependent reduction of reactive oxygen species in HCV replicon cell lines. Pycnogenol® is a natural product that may be used to improve the efficacy of the current standard antiviral agents and even to eliminate resistant HCV mutants.

Tupaia belangeri as an experimental animal model for viral infection

Tupaias, or tree shrews, are small mammals that are similar in appearance to squirrels. The morphological and behavioral characteristics of the group have been extensively characterized, and despite previously being classified as primates, recent studies have placed the group in its own family, the Tupaiidae. Genomic analysis has revealed that the genus Tupaia is closer to humans than it is to rodents. In addition, tupaias are susceptible to hepatitis B virus and hepatitis C virus. The only other experimental animal that has been demonstrated to be sensitive to both of these viruses is the chimpanzee, but restrictions on animal testing have meant that experiments using chimpanzees have become almost impossible. Consequently, the development of the tupaia for use as an animal infection model could become a powerful tool for hepatitis virus research and in preclinical studies on drug development.

Toll-like receptor 4 and hepatitis B infection: molecular mechanisms and pathogenesis

Hepatitis B virus (HBV) infection mainly causes liver disease, including inflammation, cirrhosis, and hepatocellular carcinoma (HCC). It has been documented that prolonged hepatitis B-infected patients are unable to clear HBV from hepatocytes completely. Previous investigations have suggested that various genetic and immunologic parameters may be responsible for the induction of prolonged infection forms. Toll-like receptors (TLRs), as members of pathogen recognition receptors (PRRs), play critical roles in the recognition of viruses and the induction of appropriate immune responses. Thus, TLRs may be considered as essential sensors for the recognition of HBV and the induction of immune responses against this virus. It has been documented that TLR4 plays key roles in the detection of several microbial pathogen-associated molecular pattern molecules, including bacterial lipopolysaccharide (LPS), as well as endogenous ligands (damage-associated molecular pattern molecules) and subsequently activates pro-inflammatory transcription factors in either MYD88 or TRIF dependent pathways. Previous investigations have proposed that TLR4 might be involved in appropriate immune responses against HBV. Therefore, the aim of this review is to present the recent data regarding the important roles of TLR4 in HBV recognition and regulation of immune responses against this virus, and also its roles in the pathogenesis of cirrhosis and HCC as complications of prolonged hepatitis B infections.

Resistance to cyclosporin A derives from mutations in hepatitis C virus nonstructural proteins

Cyclosporine A (CsA) is an immunosuppressive drug that targets cyclophilins, cellular cofactors that regulate the immune system. Replication of hepatitis C virus (HCV) is suppressed by CsA, but the molecular basis of this suppression is still not fully understood. To investigate this suppression, we cultured HCV replicon cells (Con1, HCV genotype 1b, FLR-N cell) in the presence of CsA and obtained nine CsA-resistant FLR-N cell lines. We determined full-length HCV sequences for all nine clones, and chose two (clones #6 and #7) of the nine clones that have high replication activity in the presence of CsA for further analysis. Both clones showed two consensus mutations, one in NS3 (T1280V) and the other in NS5A (D2292E). Characterization of various mutants indicated that the D2292E mutation conferred resistance to high concentrations of CsA (up to 2 μM). In addition, the missense mutation T1280V contributed to the recovery of colony formation activity. The effects of these mutations are also evident in two established HCV replicon cell lines-HCV-RMT ([1], genotype 1a) and JFH1 (genotype 2a). Moreover, three other missense mutations in NS5A-D2303H, S2362G, and E2414K-enhanced the resistance to CsA conferred by D2292E; these double or all quadruple mutants could resist approximately 8- to 25-fold higher concentrations of CsA than could wild-type Con1. These four mutations, either as single or combinations, also made Con1 strain resistant to two other cyclophilin inhibitors, N-methyl-4-isoleucine-cyclosporin (NIM811) or Debio-025. Interestingly, the changes in IC50 values that resulted from each of these mutations were the lowest in the Debio-025-treated cells, indicating its highest resistant activity against the adaptive mutation.

B-cell-intrinsic hepatitis C virus expression leads to B-cell-lymphomagenesis and induction of NF-κB signalling

Hepatitis C virus (HCV) infection leads to the development of hepatic diseases, as well as extrahepatic disorders such as B-cell non-Hodgkin's lymphoma (B-NHL). To reveal the molecular signalling pathways responsible for HCV-associated B-NHL development, we utilised transgenic (Tg) mice that express the full-length HCV genome specifically in B cells and develop non-Hodgkin type B-cell lymphomas (BCLs). The gene expression profiles in B cells from BCL-developing HCV-Tg mice, from BCL-non-developing HCV-Tg mice, and from BCL-non-developing HCV-negative mice were analysed by genome-wide microarray. In BCLs from HCV-Tg mice, the expression of various genes was modified, and for some genes, expression was influenced by the gender of the animals. Markedly modified genes such as Fos, C3, LTβR, A20, NF-κB and miR-26b in BCLs were further characterised using specific assays. We propose that activation of both canonical and alternative NF-κB signalling pathways and down-regulation of miR-26b contribute to the development of HCV-associated B-NHL.

Recent insights into hepatitis B virus-host interactions

Hepatitis B virus (HBV) poses a threat to global public health mainly because of complications of HBV-related chronic liver disease. HBV exhibits a narrow host range, replicating primarily in hepatocytes by a still poorly understood mechanism. For the generation of progeny virions, HBV depends on interactions with specific host factors through its life cycle. Revealing and characterizing these interactions are keys to identifying novel antiviral targets, and to developing specific treatment strategies for HBV patients. In this review, recent insights into the HBV-host interactions, especially on virus entry, intracellular trafficking, genome transcription and replication, budding and release, and even cellular restriction factors were reviewed.

A serine palmitoyltransferase inhibitor blocks hepatitis C virus replication in human hepatocytes

BACKGROUND & AIMS

Host cell lipid rafts form a scaffold required for replication of hepatitis C virus (HCV). Serine palmitoyltransferases (SPTs) produce sphingolipids, which are essential components of the lipid rafts that associate with HCV nonstructural proteins. Prevention of the de novo synthesis of sphingolipids by an SPT inhibitor disrupts the HCV replication complex and thereby inhibits HCV replication. We investigated the ability of the SPT inhibitor NA808 to prevent HCV replication in cells and mice.

METHODS

We tested the ability of NA808 to inhibit SPT's enzymatic activity in FLR3-1 replicon cells. We used a replicon system to select for HCV variants that became resistant to NA808 at concentrations 4- to 6-fold the 50% inhibitory concentration, after 14 rounds of cell passage. We assessed the ability of NA808 or telaprevir to inhibit replication of HCV genotypes 1a, 1b, 2a, 3a, and 4a in mice with humanized livers (transplanted with human hepatocytes). NA808 was injected intravenously, with or without pegylated interferon alfa-2a and HCV polymerase and/or protease inhibitors.

RESULTS

NA808 prevented HCV replication via noncompetitive inhibition of SPT; no resistance mutations developed. NA808 prevented replication of all HCV genotypes tested in mice with humanized livers. Intravenous NA808 significantly reduced viral load in the mice and had synergistic effects with pegylated interferon alfa-2a and HCV polymerase and protease inhibitors.

CONCLUSIONS

The SPT inhibitor NA808 prevents replication of HCV genotypes 1a, 1b, 2a, 3a, and 4a in cultured hepatocytes and in mice with humanized livers. It might be developed for treatment of HCV infection or used in combination with pegylated interferon alfa-2a or HCV polymerase or protease inhibitors.