Selective inhibition of bleomycin-induced G2 cell cycle checkpoint by simaomicin α

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Abstract

Human T-cell leukemia-derived Jurkat cells are known to be defective in the G1 checkpoint. DNA-damaging agent bleomycin arrests the cell cycle at G2 phase of Jurkat cells, and microtubule-acting colchicine arrests it at the M phase. Simaomicin α, an actinomycete metabolite, itself showed no effect on the cell cycle status of Jurkat cells at least up to 6.0 nM. However, the compound (0.6–6.0 nM) was found to abrogate the bleomycin-induced G2 arrest, yielding a drastic decrease in cells at the G2 phase and increase in cells at the subG1 and G1 phases. On the other hand, the compound did not show any effect on the colchicine-induced M phase arrest in Jurkat cells. Furthermore, the compound showed almost no effect on the cell cycle status of the bleomycin-treated or -untreated normal cell line HUVEC. These data suggested that simaomicin α disrupts the cell cycle G2 checkpoint of cancer cells selectively, leading to sensitization of cancer cells to anti-cancer reagents.

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Materials and methods

Materials. Simaomicin α was isolated from the culture broth of Actinomadura sp. KA-6744. Xanthoquinodins and cervinomycins (Fig. 1) were isolated from culture broths of Humicola sp. FO-888 [24] and Streptomyces cervinus AM-5344 [25], respectively. Jurkat cells were kindly provided by the Cell Resource Center for Biomedical Research, Tohoku University, Japan. Human umbilical vein endothelial cells (HUVEC) were purchased from Dainippon Pharmaceutical (Osaka, Japan). Fetal calf serum (FCS) was

Inhibition of bleomycin-induced G2 arrest in Jurkat cells by simaomicin α

Jurkat cells were cultured for 20 h and the cell cycle status was analyzed. The distribution ratios in subG1, G1, S, and G2/M phases were 4.5%, 51.9%, 21.9%, and 21.2%, respectively (Fig. 2C). When Jurkat cells were incubated in the presence of simaomicin α (0.6–6.0 nM), the distribution ratios in subG1, G1, S, and G2/M phases were almost fundamentally unchanged; 4.7–10.1%, 47.2–49.7%, 21.5–23.2%, and 15.2–20.2% (Fig. 2C), respectively. These data indicated that simaomicin α alone shows no effect

Acknowledgements

This study was supported in part by a grant from the 21st Century COE Program, Ministry of Education, Culture, Sports, Science and Technology, Japan.

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