Kantidze Omar L, Iarovaia Olga V, Razin Sergey V
Laboratory of Structural and Functional Organization of Chromosomes, Institute of Gene Biology RAS, Moscow, Russia.
J Cell Physiol. 2006 Jun;207(3):660-7. doi: 10.1002/jcp.20597.
Topoisomerases maintain the DNA structure by relieving the torsional stress and alleviating other topological problems occurring in DNA during transcription and replication. Topoisomerase II appears to have a close association with the family of proteins involved in the organization of chromatin in a series of loops on the proteinaceous chromosomal matrix. Beyond its physiological functions, topoisomerase II is the target for some of the most active anticancer drugs. Inhibition of the topoisomerase II function can result in DNA double-strand breaks (DSBs) and, thus, lead to chromosomal translocations. The earliest event during DSB repair is phosphorylation of histone H2AX at S139 (so-called gammaH2AX) which is believed to serve as a focal point for the assembly of repair proteins at the DSB. In this work, we have demonstrated the formation of gammaH2AX foci in two human cell lines--K562 and HeLa--after suppression of topoisomerase II activity with etoposide. Furthermore, these foci remained visible at nuclear matrices and colocalized with the major components of non-homologous end joining (NHEJ) system of DSBs repair. Thus, inhibition of topoisomerase II activity triggers assembly of NHEJ complexes at the nuclear matrix.
拓扑异构酶通过缓解转录和复制过程中DNA产生的扭转应力并减轻其他拓扑问题来维持DNA结构。拓扑异构酶II似乎与一系列参与蛋白质染色体基质上染色质环化组织的蛋白质家族密切相关。除了其生理功能外，拓扑异构酶II还是一些最有效的抗癌药物的作用靶点。抑制拓扑异构酶II的功能可导致DNA双链断裂（DSB），进而导致染色体易位。DSB修复过程中最早的事件是组蛋白H2AX在S139位点的磷酸化（即所谓的γH2AX），据信它是DSB处修复蛋白组装的焦点。在这项工作中，我们已经证明在用依托泊苷抑制拓扑异构酶II活性后，在两种人类细胞系——K562和HeLa——中形成了γH2AX焦点。此外，这些焦点在核基质中仍然可见，并与DSB修复的非同源末端连接（NHEJ）系统的主要成分共定位。因此，抑制拓扑异构酶II的活性会触发NHEJ复合物在核基质处的组装。
