Dietary isothiocyanate-induced apoptosis via thiol modification of DNA topoisomerase IIa.

The Journal of biological chemistry

PubMedID: 21828038

Lin RK, Zhou N, Lyu YL, Tsai YC, Lu CH, Kerrigan J, Chen YT, Guan Z, Hsieh TS, Liu LF. Dietary isothiocyanate-induced apoptosis via thiol modification of DNA topoisomerase IIa. J Biol Chem. 2011;286(38):33591-600.
Studies in animal models have indicated that dietary isothiocyanates (ITCs) exhibit cancer preventive activities through carcinogen detoxification-dependent and -independent mechanisms. The carcinogen detoxification-independent mechanism of cancer prevention by ITCs has been attributed at least in part to their ability to induce apoptosis of transformed (initiated) cells (e.g. through suppression of I?B kinase and nuclear factor ?B as well as other proposed mechanisms). In the current studies we show that ITC-induced apoptosis of oncogene-transformed cells involves thiol modification of DNA topoisomerase II (Top2) based on the following observations. 1) siRNA-mediated knockdown of Top2a in both SV40-transformed MEFs and Ras-transformed human mammary epithelial MCF-10A cells resulted in reduced ITC sensitivity. 2) ITCs, like some anticancer drugs and cancer-preventive dietary components, were shown to induce reversible Top2a cleavage complexes in vitro. 3) ITC-induced Top2a cleavage complexes were abolished by co-incubation with excess glutathione. In addition, proteomic analysis revealed that several cysteine residues on human Top2a were covalently modified by benzyl-ITC, suggesting that ITC-induced Top2a cleavage complexes may involve cysteine modification. Interestingly, consistent with the thiol modification mechanism for Top2a cleavage complex induction, the thiol-reactive selenocysteine, but not the non-thiol-reactive selenomethionine, was shown to induce Top2a cleavage complexes. In the aggregate, our results suggest that thiol modification of Top2a may contribute to apoptosis induction in transformed cells by ITCs.