| Summary: | 碩士 === 國立陽明大學 === 藥理學研究所 === 99 === Most chemotherapeutic drugs can cause genotoxic stress, and how tumor cells react in order to facilitate survival has been the focus of many studies. It has been reported that the expression level of KLF4 increased in a p53-dependent manner after DNA damage in colon cancer. It is well known that doxorubicin can cause DNA damage, and cells treated by different concentrations of doxorubicin eventually came to cell cycle arrest or apoptosis. In addition, hypoxia is also an important factor that modulates tumor growth and survival. This study investigated the expression level of KLF4 and its regulation mechanism in HepG2 cells treated by doxorubicin under normoxic and hypoxic conditions. Firstly, MTT assay was used to assess cell sensitivity to doxorubicin, and cytostatic (0.1 μM) and cytotoxic (10 μM) concentration was determined. Secondly, flow cytometry analyses showed that doxorubicin-induced DNA damage was dose-dependent. Cell cycle arrested at G2/M phase after treatment of cytostatic dose of doxorubicin; sub G0/G1 peak was found after treatment with cytotoxic dose. Furthermore, under both normoxic and hypoxic conditions, the expression of KLF4 in HepG2 cells was up-regulated after cells treated by cytotoxic concentration of doxorubicin while p53 and p21 decreased. Treatment of HepG2 cells with cytostatic concentration of doxorubicin resulted in cell cycle arrest, while cytotoxic dose of doxorubicin treatment resulted in cell apoptosis under both normoxic and hypoxic conditions. After KLF4 knockdown by siRNA, MTT results showed that cell proliferation of HepG2 became slower. After treatment with cytostatic dose of doxorubicin, cell cycle did not arrest at G2/M phase, and an increase of sub G0/G1 peak was observed (> 12%). In contrast, a subG0/G1 peak (> 16%) was detected at cytotoxic dose. Knockdown of KLF4 in HepG2 cells resulted in cell growth inhibition. These results suggested that abolishment of KLF4 plays an important role in suppression of tumor cell survival in HepG2 cells.
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