Department of Medicine, Microbiology, and Immunology, Rosalind Russell Medical Research Center, University of California at San Francisco (UCSF), USA.
Genes Dev. 2011 Oct 15;25(20):2158-72. doi: 10.1101/gad.16962311.
Various cyclin-dependent kinase (Cdk) complexes have been implicated in the regulation of transcription. In this study, we identified a 70-kDa Cyclin K (CycK) that binds Cdk12 and Cdk13 to form two different complexes (CycK/Cdk12 or CycK/Cdk13) in human cells. The CycK/Cdk12 complex regulates phosphorylation of Ser2 in the C-terminal domain of RNA polymerase II and expression of a small subset of human genes, as revealed in expression microarrays. Depletion of CycK/Cdk12 results in decreased expression of predominantly long genes with high numbers of exons. The most prominent group of down-regulated genes are the DNA damage response genes, including the critical regulators of genomic stability: BRCA1 (breast and ovarian cancer type 1 susceptibility protein 1), ATR (ataxia telangiectasia and Rad3-related), FANCI, and FANCD2. We show that CycK/Cdk12, rather than CycK/Cdk13, is necessary for their expression. Nuclear run-on assays and chromatin immunoprecipitations with RNA polymerase II on the BRCA1 and FANCI genes suggest a transcriptional defect in the absence of CycK/Cdk12. Consistent with these findings, cells without CycK/Cdk12 induce spontaneous DNA damage and are sensitive to a variety of DNA damage agents. We conclude that through regulation of expression of DNA damage response genes, CycK/Cdk12 protects cells from genomic instability. The essential role of CycK for organisms in vivo is further supported by the result that genetic inactivation of CycK in mice causes early embryonic lethality.
各种细胞周期蛋白依赖性激酶 (Cdk) 复合物被认为参与转录的调节。在这项研究中，我们鉴定出一种 70kDa 的细胞周期蛋白 K (CycK)，它与 Cdk12 和 Cdk13 结合形成两种不同的复合物 (CycK/Cdk12 或 CycK/Cdk13) 在人类细胞中。CycK/Cdk12 复合物调节 RNA 聚合酶 II C 末端结构域中丝氨酸 2 的磷酸化和一小部分人类基因的表达，这在表达微阵列中得到了揭示。CycK/Cdk12 的耗竭导致大多数具有高外显子数的长基因的表达减少。下调最显著的基因群是 DNA 损伤反应基因，包括基因组稳定性的关键调节剂：BRCA1（乳腺癌和卵巢癌 1 型易感性蛋白 1）、ATR（共济失调毛细血管扩张症和 Rad3 相关）、FANCI 和 FANCD2。我们表明，CycK/Cdk12 而不是 CycK/Cdk13 对于它们的表达是必需的。BRCA1 和 FANCI 基因的核跑实验和 RNA 聚合酶 II 的染色质免疫沉淀表明，在没有 CycK/Cdk12 的情况下存在转录缺陷。与这些发现一致，没有 CycK/Cdk12 的细胞会自发诱导 DNA 损伤，并对各种 DNA 损伤剂敏感。我们得出结论，通过调节 DNA 损伤反应基因的表达，CycK/Cdk12 保护细胞免受基因组不稳定性的影响。CycK 在体内对生物体的重要作用进一步得到了遗传失活 CycK 的小鼠会导致早期胚胎致死的结果的支持。
