Department of Radiation Oncology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
EMBO Rep. 2010 Nov;11(11):876-82. doi: 10.1038/embor.2010.153. Epub 2010 Oct 8.
Cyclin-dependent kinase 9 (CDK9) is a well-characterized subunit of the positive transcription elongation factor b complex in which it regulates transcription elongation in cooperation with cyclin T. However, CDK9 also forms a complex with cyclin K, the function of which is less clear. Using a synthetic lethal RNA interference screen in human cells, we identified CDK9 as a component of the replication stress response. Loss of CDK9 activity causes an increase in spontaneous levels of DNA damage signalling in replicating cells and a decreased ability to recover from a transient replication arrest. This activity is restricted to CDK9-cyclin K complexes and is independent of CDK9-cyclin T complex. CDK9 accumulates on chromatin in response to replication stress and limits the amount of single-stranded DNA in cells under stress. Furthermore, we show that CDK9 and cyclin K interact with ataxia telangiectasia and Rad3-related protein and other checkpoint signalling proteins. These results reveal an unexpectedly direct role for CDK9-cyclin K in checkpoint pathways that maintain genome integrity in response to replication stress.
细胞周期蛋白依赖性激酶 9（CDK9）是正转录延伸因子 b 复合物中一个特征明确的亚基，它与细胞周期蛋白 T 协同调节转录延伸。然而，CDK9 也与细胞周期蛋白 K 形成复合物，其功能不太清楚。我们使用人类细胞的合成致死 RNA 干扰筛选，鉴定 CDK9 为复制应激反应的一个组成部分。CDK9 活性丧失导致复制细胞中自发 DNA 损伤信号增加，并且从短暂的复制停滞中恢复的能力降低。这种活性仅限于 CDK9-细胞周期蛋白 K 复合物，并且独立于 CDK9-细胞周期蛋白 T 复合物。CDK9 响应复制应激而在染色质上积累，并限制应激下细胞中单链 DNA 的含量。此外，我们表明 CDK9 和细胞周期蛋白 K 与共济失调毛细血管扩张症和 Rad3 相关蛋白和其他检查点信号蛋白相互作用。这些结果揭示了 CDK9-细胞周期蛋白 K 在检查点途径中的一个出人意料的直接作用，该途径响应复制应激来维持基因组完整性。
