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Tupaia CD81, SR-BI, Claudin-1, and Occludin Support Hepatitis C Virus Infection

ABSTRACT Hepatitis C virus (HCV)-related research has been hampered by the lack of appropriate small-animal models. It has been reported that tree shrews, or tupaias (Tupaia belangeri), can be infected with serum-derived HCV. However, these reports do not firmly establish the tupaia as a reliable model of HCV infection. Human CD81, scavenger receptor class B type I (SR-BI), claudin 1 (CLDN1), and occludin (OCLN) are considered essential receptors or coreceptors for HCV cell entry. In the present study, the roles of these tupaia orthologs in HCV infection were assessed. Both CD81 and SR-BI of tupaia were found to be able to bind with HCV envelope protein 2 (E2). In comparison with human CD81, tupaia CD81 exhibited stronger binding activity with E2 and increased HCV pseudoparticle (HCVpp) cell entry 2-fold. The 293T cells transfected with tupaia CLDN1 became susceptible to HCVpp infection. Moreover, simultaneous transfection of the four tupaia factors into mouse NIH 3T3 cells made the cells susceptible to HCVpp infection. HCVpp of diverse genotypes were able to infect primary tupaia hepatocytes (PTHs), and this infection could be blocked by either anti-CD81 or anti-SR-BI. PTHs could be infected by cell culture-produced HCV (HCVcc) and did produce infectious progeny virus in culture supernatant. These findings indicate that PTHs possess all of the essential factors required for HCV entry and support the complete HCV infection cycle. This highlights both the mechanisms of susceptibility of tupaia to HCV infection and the possibility of using tupaia as a promising small-animal model in HCV study.

DNA Vaccine of SARS-Cov S Gene Induces Antibody Response in Mice

Abstract The spike (S) protein, a main surface antigen of SARS-coronavirus (SARS-CoV), is one of the most important antigen candidates for vaccine design. In the present study, three fragments of the truncated S protein were expressed in E. coli, and analyzed with pooled sera of convalescence phase of SARS patients. The full length S gene DNA vaccine was constructed and used to immunize BALB/c mice. The mouse serum IgG antibody against SARS-CoV was measured by ELISA with E. coli expressed truncated S protein or SARS-CoV lysate as diagnostic antigen. The results showed that all the three fragments of S protein expressed by E. coli was able to react with sera of SARS patients and the S gene DNA candidate vaccine could induce the production of specific IgG antibody against SARS-CoV efficiently in mice with seroconversion ratio of 75% after 3 times of immunization. These findings lay some foundations for further understanding the immunology of SARS-CoV and developing SARS vaccines.

Inhibition of hepatitis C virus replication and expression by small interfering RNA targeting host cellular genes

Summary.Small interfering RNA (siRNA) is a powerful tool for functional genomics and gene therapy. Viral replication and gene expression are strongly inhibited by siRNA treatment of infected mammalian cells. However, the high sequence specificity of siRNAs, combined with prolonged treatment, promote the emergence of siRNA-resistant virus variants, especially among viruses that encode a polymerase lacking proofreading capabilities, indicating that the antiviral properties of specific siRNAs are not as effective as expected. To investigate the silencing effect of siRNAs against selected host cellular proteins that promote replication of hepatitis C virus (HCV), several siRNAs against human VAMP-associated protein (hVAP-A), La antigen and polypyrimidine-tract-binding protein (PTB) were evaluated. The data show that several siRNAs markedly decreased the expression levels of corresponding cellular genes that inhibited HCV replication in Huh-7 cells. These treatments were also shown to have no impact upon cell viability. These findings provide an alternative approach for blocking HCV replication. Hence, combination therapies with siRNAs against both the virus and host genes that support virus replication are likely to be a potent approach in the treatment of chronic hepatitis C.

Mitogen-activated protein kinase signalling pathways triggered by the hepatitis C virus envelope protein E2: implications for the prevention of infection.

Abstract.  Objective: Hepatitis C virus (HCV) is a major pathogenic factor of liver diseases. During HCV infection, interaction of the envelope protein E2 of the virion, with target cells, is a crucial process for viral penetration into the cell and its propagation. We speculate that such interaction may trigger early signalling events required for HCV infection. Materials and methods: Human liver cell line L‐02 was treated with HCV E2. The kinase phosphorylation levels of mitogen‐activated protein kinase (MAPK) signalling pathways in the treated cells were analyzed by Western blotting. The proliferation of the E2‐treated cells was evaluated by MTT assay. Results: HCV E2 was shown to be an efficient activator for MAPK pathways. Levels of phosphorylation of upstream kinases Raf‐1 and MEK1/2 were seen to be elevated following E2 treatment and similarly, phosphorylation levels of downstream kinases MAPK/ERK and p38 MAPK also increased in response to E2 treatment, and specificity of kinase activation by E2 was confirmed. E2‐induced MAPK/ERK activation was inhibited by the MEK1/2 inhibitor U0126 in a concentration‐dependent manner. Blockage of relevant cellular receptors reduced activation of Raf‐1, MEK1/2, MAPK/ERK and p38 MAPK by E2, indicating efflux of the E2 signal from extracellular to the intracellular spaces. Thus, kinase cascades of MAPK pathways were continuously affected by E2 presence. Moreover, enhancement of cell proliferation by E2 appeared to be associated with the dynamic phosphorylation of MAPK/ERK and p38 MAPK. Conclusion: These results suggest that MAPK signalling pathways triggered by E2 may be a potential target for prevention of HCV infection.

Application of HBx-induced anti-URGs as early warning biomarker of cirrhosis and HCC

BACKGROUND Hepatitis B virus (HBV) carriers are at high risk for the development of hepatocellular carcinoma (HCC), but there are no reliable markers that will identify such high-risk patients. HBV up-regulates the expression of selected genes (URGs) in the liver during chronic infection. These aberrantly expressed proteins trigger corresponding antibodies (anti-URGs) that appear prior to the detection of HCC. This study was undertaken to see if the anti-URGs could be used as early warning biomarker of HBV-induced liver cirrhosis and HCC. METHODS A cross sectional study using a total of 625 serum samples from HBV infected and uninfected controls were tested for the anti-URGs using specific ELISAs. RESULTS The number and specificity of anti-URGs correlated with the severity of liver disease Anti-URGs were predominantly present among patients with HBV-associated HCC (55.2%) and cirrhosis (60.7%), and at a lower frequency among patients with chronic hepatitis (35.8%), and at still lower frequencies in most asymptomatic carriers (12.3%) with normal ALT, among patients with chronic hepatitis C (38.5%) and blood donors (0.9%). These anti-URGs were rarely detected in sera from those with tumors other than HCC, except among HBV infected patients with cholangioicarcinoma and in some patients with drug induced hepatitis. 3 or more anti-URGs could precede the diagnosis of cirrhosis or HCC 11.8 months on average, and HBV hepatitis patients with 3 or more anti-URGs have much higher risk (5/20 vs 0/30) to develop cirrhosis and HCC than those patients with less anti-URGs. As the early warning biomarker, 3 or more anti-URGs were served as the threshold to separate the cirrhosis and HCC from others with a moderate sensitivity (58.3%) and specificity (80.0%), which was better than other biomarkers (AFP, AFP-L3, GPC3 and GP73) and would improve up to 70.3% when combined with another biomarker. CONCLUSIONS The results of this clinical validation study suggest that the anti-URGs might have diagnostic/prognostic utility among patients at high risk for the development of cirrhosis and HCC.

Identification and expression of human CD81 gene on murine NIH/3T3 cell membrane

The human CD81 (hCD81) molecule has been identified as a putative receptor for hepatitis C virus (HCV). In this study, eukaryotic expression vector pCDM8-hCD81 containing hCD81 cDNA and pSV2neo helper plasmid was used to cotransfect with lipofectamine into murine fibroblast cell line NIH/3T3 to establish an hCD81-expressing cell line. Resistant cell clones were obtained 20 days after the selection with neomycin (600 micro/ml) and then cultured as monoclones. The expression of the transfected hCD81 gene in the cells was verified by RT-PCR and flow cytometry analyses. One of the selected cell clones showed obvious expression of hCD81 and was named NIH/3T3-hCD81. Competitive inhibition tests indicated that the binding of monoclonal anti-hCD81 (JS-81) to NIH/3T3-hCD81 cells was inhibited by recombinant HCV E2 protein, suggesting that the expressed hCD81 molecules on NIH/3T3-hCD81 cells maintain natural conformation of binding to HCV E2. The transfected NIH/3T3-hCD81 cells should be of great potential value in studies on HCV attachment and onset of infection.