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ToxSci Advance Access published online on December 7, 2005
Toxicological Sciences, doi:10.1093/toxsci/kfj070
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© The Author 2005. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received September 29, 2005
Accepted November 30, 2005

Carcinogenicity

Depletion of Securin Increases Arsenite-Induced Chromosome Instability and Apoptosis via a p53-independent Pathway

Jui-I Chao 1 *, Shih-Hsin Hsu 1, and Tsui-Chun Tsou 2

1 Molecular Anticancer Laboratory, Institute of Pharmacology and Toxicology, College of Life Sciences, Tzu Chi University, Hualien, Taiwan
2 Division of Environmental Health and Occupational Medicine, National Health Research Institutes, Kaohsiung, Taiwan

* To whom correspondence should be addressed.
Jui-I Chao, E-mail: chaoji{at}mail.tcu.edu.tw


  Abstract

Arsenic is a pathologic factor of cardiovascular diseases and cancers; nevertheless, it also acts as an anticancer agent effective on acute promyelocytic leukemia and multiple myeloma. Securin, a proposed proto-oncogene, regulates cell proliferation and tumorigenesis. However, roles of securin on the arsenic-induced cell cycle arrest and apoptosis remain unknown. In this study, the effects of sodium arsenite on the expression of securin in two tissue types of cell lines, the vascular endothelial and colorectal epithelial cells, were investigated. Arsenite (8-16 µM, 24 h) increased the cytotoxicity, apoptosis, and growth inhibition in both endothelial and epithelial cells. The levels of phospho-CDC2 (threonine-161), CDC2, and cyclin B1 proteins were decreased and the G2/M fractions were increased by arsenite. Concomitantly, arsenite markedly diminished the securin protein expression and induced the abnormal sister chromatid separation. The depletion of securin proteins increased the induction of mitotic arrest, aberrant chromosome segregation, and apoptosis after arsenite treatment. p53, a tumor suppressor protein, balances the cell survival and apoptosis. Arsenite raised the levels of phospho-p53 (serine-15) and p53 (DO-1) proteins in both the securin-wild type and -null cells. The p53-functional cells were more susceptible than the p53-mutational cells to arsenite on the cytotoxicity and apoptosis. Besides, arsenite decreased the levels of securin proteins to a similar degree in both the p53-functional and -mutational cells. Together, it is the first time to demonstrate that the inhibition of securin expression induced by arsenite increases the chromosomal instability and apoptosis via a p53-independent pathway.

Keywords: arsenite; apoptosis; securin; separase; mitosis; p53.
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