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Carcinogenesis. 2006 May;27(5):936-44. Epub 2005 Dec 19.

Overexpression of thymosin beta-4 renders SW480 colon carcinoma cells more resistant to apoptosis triggered by FasL and two topoisomerase II inhibitors via downregulating Fas and upregulating Survivin expression, respectively.

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Institute of Pharmacology, College of Medicine, National Yang-Ming University, Shih-Pai, Taipei 11221, Taiwan, R.O. China.


The present work was conducted to further examine the effects of thymosin beta-4 (Tbeta4) upregulation on the apoptosis of SW480 colon cancer cells induced by T cells and various chemotherapeutic agents because reduced susceptibility to the cytotoxicity of an anti-Fas IgM (CH-11) in Tbeta4-overexpressing cells has previously been reported by us. As expected, Tbeta4 overexpressers were also more resistant to the killing effect of FasL-bearing Jurkat T cells. On the other hand, pretreating these cells with an MMP inhibitor restored not only their Fas levels but also their sensitivity to CH-11, suggesting a pivotal role of MMP in downregulating Fas in Tbeta4 overexpressers. Interestingly, while the susceptibilities of Tbeta4 overexpressers to 5-FU and irinotecan remained unchanged, they were more resistant to doxorubicin and etoposide which triggered apoptosis via a mitochondrial pathway. Concordantly, activation of both caspases 9 and 3 in Tbeta4 overexpressers by the two aforementioned topoisomerase II inhibitors was dramatically abrogated which could be accounted mainly by an increased expression of Survivin, a critical anti-apoptotic factor. Finally, poor survival was found in stage III colon cancer patients whose tumors were stained positively by the anti-Survivin antibody. Thus, advantages such as immune evasion and resistance to anticancer drug-induced apoptosis acquired by colon cancer cells through Tbeta4 overexpression might facilitate their survival during metastasis and chemotherapy.

[Indexed for MEDLINE]

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