DNA Lesions as Endogenous Topoisomerase Poisons

描述(申请人提供)：拓扑异构酶II是一种重要的酶，它通过在一个单独的DNA片段中产生一个完整的双螺旋通过它产生的瞬时双链断裂来松弛DNA，并从遗传物质中去除打结和缠结。然而，由于拓扑异构酶II必须产生双链DNA断裂才能发挥其催化功能，该酶也对基因组完整性构成内在威胁。除了其关键的细胞功能外，拓扑异构酶II也是目前临床上使用的一些最活跃的抗癌药物的主要靶点。这些药物通过增加共价拓扑异构酶11裂解DNA复合体的水平来发挥作用，这些复合体是酶催化循环中正常但短暂的中间产物。当产生的酶相关DNA断裂浓度较高时，它们会产生突变、染色体易位，并触发细胞死亡途径。针对II型酶的抗癌药物被称为拓扑异构酶II型毒药，因为它们将这种重要的酶转化为一种有效的生理毒素，从而使基因组碎裂。尽管拓扑异构酶II是癌症治疗最重要的靶点之一，但有令人信服的证据表明，该酶产生的DNA断裂也会引发特定类型的白血病。这表明，以拓扑异构酶11为靶点的药物可能代表了诱导DNA重组、突变或细胞死亡途径的细胞成分的外源对应物。以前的研究(许多来自申请人的实验室)表明，DNA中最常见的形成损伤的碱性部位和其他生理性DNA损伤可以刺激拓扑异构酶11介导的DNA切割，其效力远远高于广泛使用的抗癌药物依托泊苷。因此，这项建议的最终目标是进一步确定拓扑异构酶II与DNA损伤之间的相互作用，并确定DNA损伤在细胞中是否作为内源性拓扑异构酶II毒物发挥作用。这项研究的模型将是人类拓扑异构酶11α和β，以及培养的哺乳动物细胞系。相关性：拓扑异构酶II是一些最重要的抗癌药物临床使用的靶点。然而，也有证据表明，这种酶会触发染色体断裂，从而引发白血病。目前的提议验证了这样的假设，即DNA损伤作为抗癌药物的内源性对应物，可能参与启动拓扑异构酶11介导的白血病染色体易位。

DESCRIPTION (provided by applicant): Topoisomerase II is an essential enzyme that relaxes DNA and removes knots and tangles from the genetic material by passing an intact double helix through a transient double-stranded break that it generates in a separate DNA segment. However, since topoisomerase II must create double-stranded DNA breaks in order to carry out its catalytic functions, the enzyme also poses an intrinsic threat to genomic integrity. Beyond its critical cellular functions, topoisomerase II is the primary target for some of the most active anticancer drugs currently in clinical use. These drugs act by increasing levels of covalent topoisomerase ll-cleaved DNA complexes that are normal, but fleeting, intermediates in the catalytic cycle of the enzyme. When the resulting enzyme-associated DNA breaks are present in high concentrations, they generate mutations, chromosomal translocations, and trigger cell death pathways. Anticancer drugs targeted to the type II enzyme are referred to as topoisomerase II poisons because they convert this essential enzyme to a potent physiological toxin that fragments the genome. Although topoisomerase II is one of the most important targets for cancer treatment, there is compelling evidence that DNA breaks created by the enzyme also trigger specific types of leukemia. This suggests that topoisomerase ll-targeted drugs may represent exogenous counterparts of cellular components that induce DNA recombination, mutagenesis, or cell death pathways. Previous studies (many from the applicant's lab) indicate that a basic sites, the most commonly formed lesion in DNA, and other physiological DNA lesions stimulate topoisomerase ll-mediated DNA cleavage with a potency that is considerably higher than that of the widely prescribed anticancer drug etoposide. Thus, the ultimate goals of this proposal are to further define interactions between topoisomerase II and DNA damage and to determine whether DNA lesions function in cells as endogenous topoisomerase II poisons. The models for this study will be human topoisomerase ll alpha and beta, and cultured mammalian cell lines. RELEVANCE: Topoisomerase II is the target for some of the most important anticancer drugs in clinical use. However, there is also evidence that the enzyme triggers chromosomal breaks that trigger leukemia. The current proposal tests the hypothesis that DNA lesions act as endogenous counterparts of anticancer drugs and may be involved in initiating topoisomerase ll-mediated leukemic chromosomal translocations.