| Summary: | 碩士 === 國立臺灣大學 === 微生物學研究所 === 105 === Hepatitis C virus (HCV) infection is associated with the development of hepatocellular carcinoma. Increase of DNA damage and/or decrease of DNA repair caused by viral infection are associated with an increased risk of tumor formation. The HCV nonstructural protein 3 (NS3) was shown to be responsible for the increase of DNA damage and inhibition of DNA repair, mediated by NO and ROS. The effect of NS3 on DNA damage and repair resulted in a decrease in the survival rate of cells response to genotoxic agents. NS4A is a cofactor of NS3 protease. In addition, NS4A facilitates the transforming activity of NS3. In this study, NS3-4A stable cell line was used to investigate whether the expression of NS3-4A would affect cell viability in response to genotoxic agents that generate DNA double strand breaks. The data showed that NS3-4A decreased cell viability in response to bleomycin. To investigate the effect of NS3-4A on DNA damage and repair in response to bleomycin, γ-H2AX level that represents DNA double strand breaks was analyzed by western blotting. The results showed that NS3-4A increased the γ-H2AX level in response to bleomycin in a dose dependent manner. To examine whether the effect of NS3-4A on γ-H2AX level is associated with NS4A or NS3 protease activity, NS3 and NS3 protease activity deficiency NS3pd-4A stable cell lines were used. The data showed that both expressing NS3 and NS3pd-4A increased the γ-H2AX level in response to bleomycin. The results indicated that the effect of NS3-4A on γ-H2AX level is independent of NS4A and NS3 protease activity. Further study is required for the detailed mechanism of NS3-4A-mediated decrease of cell viability and increase of γ-H2AX level in response to bleomycin.
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