Fernandes D J, Qiu J, Catapano C V
Department of Experimental Oncology, Hollings Cancer Center, Medical University of South Carolina, Charleston 29425, USA.
Adv Enzyme Regul. 1995;35:265-81. doi: 10.1016/0065-2571(94)00009-r.
DNA topoisomerase II is a major protein of the nuclear matrix. The enzyme appears to have a central role in both DNA organization and replication. The importance of nuclear matrix topoisomerase II alpha as a target for certain anticancer agents was evaluated in CEM human leukemia cells. Studies were done to determine the extent to which the alpha (170 kDa) and beta (180 kDa) isozymes of topoisomerase II form covalent enzyme-DNA complexes in whole cells and in the nuclear matrix and nonmatrix fractions of CEM cells that are either sensitive or resistant to topoisomerase II-active anticancer agents. Topoisomerase II alpha was detected in both the high salt-soluble (nonmatrix) and matrix fractions of nuclei from parental CEM cells. Most of the matrix topoisomerase II alpha was tightly bound to DNA in cells incubated with VM-26. In contrast, topoisomerase II beta was detected only in the high salt-soluble (nonmatrix) fraction of the nucleus. The subnuclear distribution of the alpha and beta topoisomerase II isozymes in CEM/VM-1 cells resistant to topoisomerase-active drugs was similar to that in drug-sensitive CEM cells. However, the amount and activity of topoisomerase II alpha in nuclear matrices of CEM/VM-1 cells were decreased 3- to 6-fold relative to that of CEM cells. The differences observed in the subnuclear distribution and DNA binding pattern of the topoisomerase II isozymes support the hypotheses that each isozyme has a distinct cellular function. Furthermore, these results provide evidence that topoisomerase II alpha is the nuclear matrix target for VM-26, and that depletion of the nuclear matrix isozyme contributes to cellular resistance to this anticancer agent.
DNA拓扑异构酶II是核基质的一种主要蛋白质。该酶似乎在DNA组织和复制中都起着核心作用。在CEM人白血病细胞中评估了核基质拓扑异构酶IIα作为某些抗癌药物靶点的重要性。进行了相关研究，以确定拓扑异构酶II的α（170 kDa）和β（180 kDa）同工酶在全细胞、CEM细胞的核基质及非基质部分中形成共价酶-DNA复合物的程度，这些CEM细胞对拓扑异构酶II活性抗癌药物敏感或耐药。在亲本CEM细胞核的高盐可溶性（非基质）部分和基质部分均检测到拓扑异构酶IIα。在用VM-26处理的细胞中，大部分基质拓扑异构酶IIα与DNA紧密结合。相比之下，拓扑异构酶IIβ仅在细胞核的高盐可溶性（非基质）部分被检测到。对拓扑异构酶活性药物耐药的CEM/VM-1细胞中，α和β拓扑异构酶II同工酶的亚核分布与药物敏感的CEM细胞相似。然而，相对于CEM细胞，CEM/VM-1细胞核基质中拓扑异构酶IIα的量和活性降低了3至6倍。拓扑异构酶II同工酶在亚核分布和DNA结合模式上的差异支持了这样的假设，即每种同工酶都具有独特的细胞功能。此外，这些结果提供了证据，表明拓扑异构酶IIα是VM-26的核基质靶点，并且核基质同工酶的减少导致细胞对这种抗癌药物产生耐药性。
