Carcinogenesis Advance Access originally published online on May 19, 2005
Carcinogenesis 2005 26(10):1716-1730; doi:10.1093/carcin/bgi133
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Carcinogenesis vol.26 no.10 © Oxford University Press 2005; all rights reserved.
Justicidin A decreases the level of cytosolic Ku70 leading to apoptosis in human colorectal cancer cells


Department of Surgery and 1 Department of Microbiology, College of Medicine, National Cheng Kung University, Tainan, Taiwan, 2 Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN, USA, 3 Department of Nursing, Chang Jung Christian University, Tainan, Taiwan and 4 School of Pharmacy, Kaohsiung Medical University, Kaohsiung, Taiwan
* To whom correspondence should be addressed. Tel: +886 6 2744435; Fax: +886 6 2082705; Email: a725{at}mail.ncku.edu.tw
The natural product justicidin A, an arylnaphthalide lignan isolated from Justicia procumbens, significantly inhibited the growth of human colorectal cancer cells HT-29 and HCT 116 at day 6 post-treatment. Further study revealed that justicidin A-treated HT-29 and HCT 116 colorectal cancer cells died of apoptosis. Justicidin A treatment caused DNA fragmentation and an increase in phosphatidylserine exposure of the cells. The number of cells in the sub-G1 phase was also increased upon justicidin A treatment. Caspase-9 but not caspase-8 was activated, suggesting that justicidin A treatment damaged mitochondria. The mitochondrial membrane potential was altered and cytochrome c and Smac were released from mitochondria to the cytoplasm upon justicidin A treatment. The level of Ku70 in the cytoplasm was decreased, but that of Bax in mitochondria was increased by justicidin A. Since Ku70 normally binds and sequesters Bax, these results suggest that justicidin A decreases the level of Ku70 leading to translocation of Bax from the cytosol to mitochondria to induce apoptosis. Oral administration of justicidin A was shown to suppress the growth of HT-29 cells transplanted into NOD-SCID mice, suggesting chemotherapeutic potential of justicidin A on colorectal cancer cells.