Bjornsti M A, Knab A M, Benedetti P
Department of Biochemistry and Molecular Biology, Thomas Jefferson Univeristy, Philadelphia, PA 19107.
Cancer Chemother Pharmacol. 1994;34 Suppl:S1-5. doi: 10.1007/BF00684856.
Eukaryotic DNA topoisomerase I catalyzes the relaxation of positively and negatively supercoiled DNA and plays a critical role in processes involving DNA, such as DNA replication, transcription and recombination. The enzyme is encoded by the TOP1 gene and is highly conserved in its amino acid sequence and sensitivity to the anti-neoplatic agent camptothecin. This plant alkaloid specifically targets DNA topoisomerase I by reversibly stabilizing the covalent enzyme-DNA intermediate. Presumably, it is the interaction of these drug-stabilized adducts with other cellular components, such as replication forks, that actually produces the DNA lesions leading to cell death. A conservation of the mechanism(s) of camptothecin-induced cell killing is also implicit in studies of the yeast Saccharomyces cerevisiae, where the camptothecin sensitivity of delta TOP1 yeast cells can be restored by plasmids expressing either yeast or human TOP1 sequences. This genetically tractable system is currently being exploited to describe the specific molecular interactions required for the cytotoxic action of camptothecin. The results of mutational analyses of yeast and human DNA topoisomerase I are presented, as well as a genetic screen designed to identify genes, other than TOP1, that are required for the cytotoxic activity of camptothecin.
真核生物DNA拓扑异构酶I催化正超螺旋和负超螺旋DNA的松弛，并在涉及DNA的过程中发挥关键作用，如DNA复制、转录和重组。该酶由TOP1基因编码，其氨基酸序列和对抗肿瘤药物喜树碱的敏感性高度保守。这种植物生物碱通过可逆地稳定共价酶-DNA中间体来特异性靶向DNA拓扑异构酶I。据推测，正是这些药物稳定的加合物与其他细胞成分（如复制叉）的相互作用，实际产生了导致细胞死亡的DNA损伤。喜树碱诱导细胞杀伤机制的保守性在酿酒酵母的研究中也有体现，其中表达酵母或人类TOP1序列的质粒可恢复δTOP1酵母细胞对喜树碱的敏感性。目前正在利用这个易于进行基因操作的系统来描述喜树碱细胞毒性作用所需的特定分子相互作用。文中展示了酵母和人类DNA拓扑异构酶I的突变分析结果，以及一项旨在鉴定除TOP1外对喜树碱细胞毒性活性所需基因的遗传筛选。
