Labourier E, Riou J F, Prudhomme M, Carrasco C, Bailly C, Tazi J
Institut de Génétique Moléculaire, Université de Montpellier II, Montpellier, France.
Cancer Res. 1999 Jan 1;59(1):52-5.
We have investigated the mechanism of topoisomerase I inhibition by an indolocarbazole derivative, R-3. The compound is cytotoxic to P388 leukemia cells, but not to P388CPT5 camptothecin-resistant cells having a deficient topoisomerase I. R-3 can behave both as a specific topoisomerase I inhibitor trapping the cleavable complexes and as a nonspecific inhibitor of a DNA-processing enzyme acting via DNA binding. In addition, the drug is a potent inhibitor of the kinase activity of topoisomerase I. Unlike camptothecin, R-3 completely inhibits the phosphorylation of SF2/ASF, a member of the SR protein family, in the absence of DNA. The inhibitory effect is also observed using mutant enzyme Y723F that lacks DNA cleavage/religation activity but does not affect phosphotransferase activity, indicating, therefore, that R-3 acts independently at both DNA cleavage and protein kinase sites. R-3 is the only compound known thus far that interferes specifically with the kinase activity of topoisomerase I and not with other kinases, such as protein kinase C and the cdc2 kinase. The study reinforces the view that topoisomerase I is a dual enzyme with a DNA cleavage site juxtaposed to a functionally independent kinase site and shows for the first time that indolocarbazole drugs can inhibit both the DNA cleavage/religation and kinase activities of the enzyme.
我们研究了吲哚咔唑衍生物R-3抑制拓扑异构酶I的机制。该化合物对P388白血病细胞具有细胞毒性，但对拓扑异构酶I缺陷的P388CPT5喜树碱耐药细胞无毒性。R-3既可以作为捕获可裂解复合物的特异性拓扑异构酶I抑制剂，也可以作为通过DNA结合作用的DNA加工酶的非特异性抑制剂。此外，该药物是拓扑异构酶I激酶活性的有效抑制剂。与喜树碱不同，R-3在无DNA的情况下能完全抑制SR蛋白家族成员SF2/ASF的磷酸化。使用缺乏DNA切割/连接活性但不影响磷酸转移酶活性的突变酶Y723F也观察到了抑制作用，因此表明R-3在DNA切割和蛋白激酶位点均独立发挥作用。R-3是迄今为止已知的唯一一种特异性干扰拓扑异构酶I激酶活性而不影响其他激酶（如蛋白激酶C和cdc2激酶）的化合物。该研究强化了拓扑异构酶I是一种双功能酶的观点，其DNA切割位点与功能独立的激酶位点相邻，并首次表明吲哚咔唑类药物可以抑制该酶的DNA切割/连接和激酶活性。
