DNA Lesions as Endogenous Topoisomerase Poisons

描述（由申请方提供）：拓扑异构酶II是一种必需酶，通过使完整的双螺旋通过其在单独的DNA片段中产生的瞬时双链断裂，使DNA松弛并从遗传物质中去除结和缠结。然而，由于拓扑异构酶II必须产生双链DNA断裂以执行其催化功能，因此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，拓扑异构酶II是目前临床使用的一些最活跃的抗癌药物的主要靶标。这些药物通过增加共价拓扑异构酶II切割的DNA复合物的水平起作用，所述复合物是酶的催化循环中的正常但短暂的中间体。当所产生的酶相关DNA断裂以高浓度存在时，它们会产生突变、染色体易位并触发细胞死亡途径。靶向II型酶的抗癌药物被称为拓扑异构酶II毒药，因为它们将这种必需的酶转化为使基因组片段化的强效生理毒素。虽然拓扑异构酶II是癌症治疗的最重要靶点之一，但有令人信服的证据表明，这种酶产生的DNA断裂也会引发特定类型的白血病。这表明拓扑异构酶II靶向药物可能代表诱导DNA重组、诱变或细胞死亡途径的细胞组分的外源对应物。先前的研究（许多来自申请人的实验室）表明，碱性位点（DNA中最常见的损伤）和其他生理DNA损伤刺激拓扑异构酶II介导的DNA切割，其效力显著高于广泛处方的抗癌药物依托泊苷的效力。因此，本提案的最终目标是进一步定义拓扑异构酶II和DNA损伤之间的相互作用，并确定DNA损伤是否在细胞中作为内源性拓扑异构酶II毒物发挥作用。本研究的模型将是人拓扑异构酶II α和β以及培养的哺乳动物细胞系。相关性：拓扑异构酶II是临床使用的一些最重要的抗癌药物的靶点。然而，也有证据表明，这种酶会引发染色体断裂，从而引发白血病。目前的建议测试的假设，DNA病变作为内源性对应的抗癌药物，并可能参与启动拓扑异构酶II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.