The study of relationship between STAT3 activation and anti-cancer agents

• Main Authors: I-Hwi Tu, 杜怡蕙
• Other Authors: Hisao-Sheng Liu
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/09952169122342516573

碩士 === 國立成功大學 === 分子醫學研究所 === 91 === Activation of STAT3 has been shown to induce expression of a group of genes regulating cell cycle progression, cellular proliferation and survival, such as cyclin D1, p21/Waf1, c-Myc and Bcl-xl. Therefore, STAT3 activation may not only provide a growth advantage to tumor cells but also resistance to chemotherapeutic drugs. We tried to find out the relationship between the activation of STAT3 and anti-cancer agents. We have established a NIH-3T3 cell line (NIH3T3-S3C) that expressed constitutively activated STAT3. Besides, a human lung adenocarcinoma cell line — PC14PE6/AS2 with constitutively activated STAT3- was transfected with dominant-negative STAT3 (AS2-S3F-C20). With these two systems, various categories of anti-cancer agents including alkylating agents, antimetabolites, topoisomerase inhibitors, mitosis inhibitors, natural products (chemopreventive agents), and other categories have been added to cells for evaluating cytotoxic effects. Cell viability was measured by the MTT assay, the degree of cellular apoptosis and progression of cell cycle were analyzed by flow cytometry. We found cells with activated STAT3 were more resistant to cytotoxic agent — cisplatin and paclitaxel — but not others. After treatment with most of anti-cancer agents, the activation of STAT3 in PC14PE6/AS2 cells was further enhanced at earlier period (around 3 hours), and then declined gradually to different levels. The early response after exposure to drugs suggests activation of STAT3 may provide a protective mechanism for cells to stress. We suspect that oxidative stress due to the drug treatment might up-regulate STAT3 activation at earlier period, and the degradation of STAT3 activation at later period may be caused by caspases or other factors generated during drug-induced apoptosis. In addition, the level of STAT3 activation at 24 hours correlated well with cytotoxic activity of chemotherapeutic drugs, but not chemopreventive agents. To confirm the relationship between STAT3 phosphorylation and drug resistance, AG490 — a JAK2 inhibitor and EGCG — a component of green tea extracts were used to inhibit activation of STAT3. The pretreatment of AG490 or EGCG sensitize cancer cells with activated STAT3 to cisplatin and paclitaxel, but induce opposite effect in cells in which activation of STAT3 was blocked. Therefore treating cancer with inhibitors of JAK2 or STAT3 should be careful. To uncover more underlying mechanisms for the drug resistance induced by activated STAT3, cDNA microarray studies were performed. A preliminary analysis found Bfl-1, instead of Bcl-2, Bcl-x or Mcl-1, has the highest expression in AS2-TLH-G5 cells, and several IAP family genes (eg. IAP-1 and Survivin) are also up-regulated in the cells, suggesting the anti-apoptotic signals from STAT3 in AS2 cells may not follow the conventional concepts. The expressions of genes about JAK/STAT pathway, cellular proliferation, cell cycle progression, apoptosis and drug resistance have also been analyzed. These results from the current study provide valuable information for targeting activated STAT3 in the treatment of neoplastic diseases.