Bender Ryan P, Lehmler Hans J, Robertson Larry W, Ludewig Gabriele, Osheroff Neil
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
Biochemistry. 2006 Aug 22;45(33):10140-52. doi: 10.1021/bi0524666.
Polychlorinated biphenyls (PCBs) are associated with a broad spectrum of human health problems and cause cancer in rodents. In addition, these compounds cause chromosomal aberrations in humans and treated human cells. Although the underlying basis for the chromosomal damage induced by PCBs is not understood, it is believed that these compounds act through a series of phenolic and quinone-based metabolites. Recent studies indicate that several quinones that promote chromosomal damage also act as topoisomerase II poisons. Therefore, the effects of PCB quinone metabolites (including mono and dichlorinated compounds and p- and o-quinones) on the activity of human topoisomerase IIalpha were examined. Results indicate that these compounds are potent topoisomerase IIalpha poisons in vitro and act by adducting the enzyme. They also increase DNA cleavage by topoisomerase IIalpha in cultured human cells. In contrast, incubation of topoisomerase IIalpha with PCB metabolites in the absence of DNA leads to a rapid loss of enzyme activity. On the basis of (1) the differential ability of quinone-treated enzyme to bind circular and linear DNA molecules and (2) the generation of salt-stable noncovalent complexes between topoisomerase IIalpha and circular plasmids in the presence of PCB quinones, it appears that these compounds alter enzyme function (at least in part) by blocking the N-terminal gate of the protein. Finally, exposure to quinones generates a protein species with a molecular mass approximately twice that of a monomeric topoisomerase IIalpha protomer. This finding suggests that PCB quinones block the N-terminal gate by cross-linking the protomer subunits of topoisomerase IIalpha.
多氯联苯（PCBs）与一系列人类健康问题相关，并可在啮齿动物中引发癌症。此外，这些化合物会导致人类及经处理的人类细胞出现染色体畸变。尽管多氯联苯诱导染色体损伤的潜在机制尚不清楚，但据信这些化合物是通过一系列基于酚类和醌类的代谢产物发挥作用的。最近的研究表明，几种促进染色体损伤的醌类也可作为拓扑异构酶II的毒物。因此，研究了多氯联苯醌类代谢产物（包括单氯和二氯化合物以及对醌和邻醌）对人类拓扑异构酶IIα活性的影响。结果表明，这些化合物在体外是有效的拓扑异构酶IIα毒物，通过与该酶结合发挥作用。它们还会增加培养的人类细胞中拓扑异构酶IIα对DNA的切割。相反，在无DNA的情况下，拓扑异构酶IIα与多氯联苯代谢产物一起孵育会导致酶活性迅速丧失。基于（1）醌处理的酶结合环状和线性DNA分子的能力差异，以及（2）在多氯联苯醌存在的情况下，拓扑异构酶IIα与环状质粒之间生成盐稳定的非共价复合物，这些化合物似乎通过阻断蛋白质的N端门控来改变酶的功能（至少部分如此）。最后，暴露于醌类会产生一种分子量约为单体拓扑异构酶IIα原体两倍的蛋白质物种。这一发现表明，多氯联苯醌通过使拓扑异构酶IIα的原体亚基交联来阻断N端门控。
