Sandri M I, Isaacs R J, Ongkeko W M, Harris A L, Hickson I D, Broggini M, Vikhanskaya F
Imperial Cancer Research Fund, University of Oxford, John Radcliffe Hospital, UK.
Nucleic Acids Res. 1996 Nov 15;24(22):4464-70. doi: 10.1093/nar/24.22.4464.
DNA topoisomerase IIalpha is an essential enzyme for chromosome segregation during mitosis. Consistent with a cell division-specific role, the expression of the topoisomerase IIalpha gene is strongly influenced by the proliferation status of cells. The p53 protein is one of the most important regulators of cell cycle progression in mammals, with an apparent dual role in the induction of cell cycle arrest following cytotoxic insults and in the regulation of the apoptotic cell death pathway. We have analysed whether p53 plays a role in regulating expression of the human topoisomerase IIalpha gene. We show that wild-type, but not mutant, p53 is able to decrease substantially the activity of the full length topoisomerase IIalpha gene promoter. Using a series of constructs comprising various deleted or mutated versions of the promoter lacking critical cis-acting elements, we show that this p53-specific regulation of the topoisomerase IIalpha promoter is independent of all characterised transcription factor binding sites and is directed at the minimal gene promoter. We conclude that expression of wild-type p53 induces downregulation of the human topoisomerase IIalpha promoter by acting on the basal transcription machinery. These findings implicate topoisomerase II as one of the downstream targets for p53-dependent regulation of cell cycle progression in human cells.
DNA拓扑异构酶IIα是有丝分裂期间染色体分离所必需的酶。与细胞分裂特异性作用一致，拓扑异构酶IIα基因的表达受到细胞增殖状态的强烈影响。p53蛋白是哺乳动物细胞周期进程最重要的调节因子之一，在细胞毒性损伤后诱导细胞周期停滞以及调节凋亡性细胞死亡途径中具有明显的双重作用。我们分析了p53是否在调节人类拓扑异构酶IIα基因的表达中发挥作用。我们发现野生型而非突变型p53能够大幅降低全长拓扑异构酶IIα基因启动子的活性。使用一系列包含缺乏关键顺式作用元件的启动子的各种缺失或突变版本的构建体，我们表明拓扑异构酶IIα启动子的这种p53特异性调节独立于所有已鉴定的转录因子结合位点，并且针对最小基因启动子。我们得出结论，野生型p53的表达通过作用于基础转录机制诱导人类拓扑异构酶IIα启动子的下调。这些发现表明拓扑异构酶II是人类细胞中p53依赖性细胞周期进程调节的下游靶点之一。
