title: Dietary isothiocyanate-induced apoptosis via thiol modification of DNA topoisomerase IIα.
abstract: 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 IκB kinase and nuclear factor κB 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 Top2α 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 Top2α cleavage complexes in vitro. 3) ITC-induced Top2α cleavage complexes were abolished by co-incubation with excess glutathione. In addition, proteomic analysis revealed that several cysteine residues on human Top2α were covalently modified by benzyl-ITC, suggesting that ITC-induced Top2α cleavage complexes may involve cysteine modification. Interestingly, consistent with the thiol modification mechanism for Top2α cleavage complex induction, the thiol-reactive selenocysteine, but not the non-thiol-reactive selenomethionine, was shown to induce Top2α cleavage complexes. In the aggregate, our results suggest that thiol modification of Top2α may contribute to apoptosis induction in transformed cells by ITCs.
authors.affiliation: Department of Pharmacology and the Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Jersey 08854, USA.
authors.forename: Ren-Kuo
authors.initials: RK
authors.lastname: Lin
authors.forename: Nai
authors.initials: N
authors.lastname: Zhou
authors.forename: Yi Lisa
authors.initials: YL
authors.lastname: Lyu
authors.forename: Yuan-Chin
authors.initials: YC
authors.lastname: Tsai
authors.forename: Chang-Hsien
authors.initials: CH
authors.lastname: Lu
authors.forename: John
authors.initials: J
authors.lastname: Kerrigan
authors.forename: Yu-tsung
authors.initials: YT
authors.lastname: Chen
authors.forename: Ziqiang
authors.initials: Z
authors.lastname: Guan
authors.forename: Tao-Shih
authors.initials: TS
authors.lastname: Hsieh
authors.forename: Leroy F
authors.initials: LF
authors.lastname: Liu
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects*; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003545:Cysteine / Q000378:metabolism; D004249:DNA Damage; D053938:DNA Fragmentation / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000172:deficiency / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000378:metabolism*; D004032:Diet; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D055785:Gene Knockdown Techniques; D020868:Gene Silencing / Q000187:drug effects; D006657:Histones / Q000378:metabolism; D006801:Humans; D017879:Isothiocyanates / Q000494:pharmacology*; D051379:Mice; D009707:Nucleosomes / Q000187:drug effects / Q000378:metabolism; D000075223:Poly-ADP-Ribose Binding Proteins; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D017879:Isothiocyanates; D009707:Nucleosomes; D000075223:Poly-ADP-Ribose Binding Proteins; D034741:RNA, Small Interfering; D013438:Sulfhydryl Compounds; C037152:isothiocyanic acid; C058305:phenethyl isothiocyanate; C031403:benzyl isothiocyanate; D018631:ras Proteins; D004250:DNA Topoisomerases, Type II; C000618811:TOP2A protein, human; C000618812:Top2a protein, mouse; D003545:Cysteine