Involvement of hepatitis C virus NS5A protein in replicative senescence
| Autor: | Hui-Chia Chen, 陳慧珈 |
|---|---|
| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 Globally, an estimated 71 million people have hepatitis C virus (HCV) infection, so it is a health issue in the world. HCV infection causes acute hepatitis, 85% of the cases become chronic, causing chronic hepatitis, cirrhosis (in 10~20% of cases after 10~20 years), and hepatocellular carcinoma (HCC). Previous studies in our laboratory found that HCV non-structural protein 5A (NS5A) caused a decreased hTERT mRNA level in a hepatoma cell line, so it was proposed that telomerase activity may also decrease in NS5A-expressing cells. It is known that a decreased telomerase activity may induce replicative senescence. Therefore, whether NS5A protein could induce cellular senescence by repressing hTERT expression was explored in this study. The effects of NS proteins on hTERT expression were first examined. RT-qPCR data showed that both HCVR cells, which express HCV NS proteins from NS3 to NS5B, and NS5A-expressing cells downregulated hTERT mRNA level. This result is consistent with our previous study. In addition, the phenomenon was not observed in NS3-expressing cells. Next, whether NS5A could induce replicative senescence was examined by using NS5A inducible-expressing cells cultured to different passage numbers. Results from senescence-associated β-galactosidase staining showed that NS5A induced replicative senescence in hepatoma cells earlier than the control group. In addition, the expression of p27 and p21, molecules to induce cellular senescence, were increased. The correlation between NS5A-induced replicative senescence and hTERT was further examined. The data showed that hTERT mRNA level decreased in every passage of the NS5A-expressing cells. The level of senescent cells induced by NS5A was repressed when hTERT was overexpressed, suggesting that NS5A induces cellular senescence by repressing hTERT expression. Replicative senescence was also observed in cells constitutively express NS5A. In conclusion, NS5A repressed hTERT and induced replicative senescence. In addition, NS5A induced p21 expression. Although p21 is known to induce replicative senescence, whether p21 is the predominant mediator in NS5A-induced senescence needs to be further confirmed. Moreover, NS5A also increased p27 expression. Whether NS5A is involved in stress-induced premature senescence needs to be further investigated. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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