Characterization of ER Stress-Mediated Inhibition of Topoisomerase Inhibitor-Induced Apoptosis in HCC

• Main Authors: Jui-Ling Hsu, 徐瑞苓
• Other Authors: Jih-Hwa Guh
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/24787668767799192606

碩士 === 國立臺灣大學 === 藥學研究所 === 95 === Hepatocellular carcinoma is a very common malignancy and is chemoresistant to clinical chemotherapeutic agents. Camptothecin and etoposide are two well-known anticancer drugs, targeting topoisomerase I and II, respectively. Tunicamycin, an N-glycosylation inhibitor, can cause unfolded protein response (UPR) and be widely used as pharmacological inducer of endoplasmic reticulum (ER) stress. Our data demonstrated that the combined co-treatment with tunicamycin could prevent cell apoptosis induced by camptothecin or etoposide in hepatocellular carcinoma Hep3B other than HepG2 cells, and only inhibit the activation of caspase-3、-7 and bcl-2 family protein in Hep3B cell. The following assessments were conducted to characterize the varied responses to tunicamycin inhibition in these two cell lines. Several protein expressions and functions were examined in this study, including topoisomerases (I, IIα and IIβ), HBV-related protein, p-glycoprotein and the levels of reactive oxygen species (ROS).The data demonstrated that none of these proteins, enzymes or free radicals could explain tunicamycin-mediated resistance in Hep3B but not in HepG2 cells. Using siRNA to knockdown p53, the data also excluded the involvement of this tumor suppressor gene. During the co-treatment， the expression of several cell cycle regulator could be changed compare to alone treat TOP posions. Furthermore, in the design of post-treatment of tunicamycin after camptothecin/etoposide addition, the results showed that tunicamycin-reversed effect declined when the duration of post-treatment was increased in Hep3B cells, indicating the necessity of cell cycle regulation for the reduction of camptothecin/etoposide effect. GRP78 expression had a good correlation with survival percentage in Hep3B other than HepG2. By using siRNA approaches, the data demonstrated that the knockdown of GRP78 expression induced a moderate increase of tunicamycin-induced apoptosis, revealing the pro-survival properties of GRP78, and tunicamycin-mediated resistance to camptothecin/etoposide action in Hep3B could be declined, accompanying the change of cell cycle distribution. The data suggested that GRP78 played an important role in the resistant mechanism. Taken together, the data suggest that tunicamycin could cause resistance to TOP poisons through cell cycle regulation, and induce an increase of GRP78 expression contributing to resistance of TOP poisons in Hep3B other than HepG2.