Lanni J S, Jacks T
Center for Cancer Research, and Department of Biology, Massachussets Institute of Technology, Cambridge 02139, USA.
Mol Cell Biol. 1998 Feb;18(2):1055-64. doi: 10.1128/MCB.18.2.1055.
The p53 tumor suppressor gene product is known to act as part of a cell cycle checkpoint in G1 following DNA damage. In order to investigate a proposed novel role for p53 as a checkpoint at mitosis following disruption of the mitotic spindle, we have used time-lapse videomicroscopy to show that both p53+/+ and p53-/- murine fibroblasts treated with the spindle drug nocodazole undergo transient arrest at mitosis for the same length of time. Thus, p53 does not participate in checkpoint function at mitosis. However, p53 does play a critical role in nocodazole-treated cells which have exited mitotic arrest without undergoing cytokinesis and have thereby adapted. We have determined that in nocodazole-treated, adapted cells, p53 is required during a specific time window to prevent cells from reentering the cell cycle and initiating another round of DNA synthesis. Despite having 4N DNA content, adapted cells are similar to G1 cells in that they have upregulated cyclin E expression and hypophosphorylated Rb protein. The mechanism of the p53-dependent arrest in nocodazole-treated adapted cells requires the cyclin-dependent kinase inhibitor p21, as p21-/- fibroblasts fail to arrest in response to nocodazole treatment and become polyploid. Moreover, p21 is required to a similar extent to maintain cell cycle arrest after either nocodazole treatment or irradiation. Thus, the p53-dependent checkpoint following spindle disruption functionally overlaps with the p53-dependent checkpoint following DNA damage.
已知p53肿瘤抑制基因产物在DNA损伤后的G1期作为细胞周期检查点的一部分发挥作用。为了研究p53在有丝分裂纺锤体破坏后作为有丝分裂检查点的一种新提出的作用，我们使用延时视频显微镜观察到，用纺锤体药物诺考达唑处理的p53+/+和p53-/-小鼠成纤维细胞在有丝分裂期都会经历相同时长的短暂停滞。因此，p53不参与有丝分裂期的检查点功能。然而，p53在未经历胞质分裂而退出有丝分裂停滞并因此适应的诺考达唑处理细胞中确实发挥着关键作用。我们已经确定，在诺考达唑处理的适应细胞中，在特定的时间窗口内需要p53来防止细胞重新进入细胞周期并启动另一轮DNA合成。尽管适应细胞的DNA含量为4N，但它们与G1期细胞相似，因为它们上调了细胞周期蛋白E的表达且Rb蛋白处于低磷酸化状态。在诺考达唑处理的适应细胞中，p53依赖性停滞的机制需要细胞周期蛋白依赖性激酶抑制剂p21，因为p21-/-成纤维细胞在诺考达唑处理后无法停滞并变成多倍体。此外，在诺考达唑处理或照射后，维持细胞周期停滞在相似程度上都需要p21。因此，纺锤体破坏后p53依赖性检查点在功能上与DNA损伤后p53依赖性检查点重叠。
