Peter MacCallum Cancer Centre, Melbourne 3000, VIC, Australia; The Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville 3010, VIC, Australia.
The Wistar Institute, Philadelphia, PA 19104, USA; Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Cell. 2021 Jun 10;184(12):3143-3162.e32. doi: 10.1016/j.cell.2021.04.022. Epub 2021 May 17.
Gene expression by RNA polymerase II (RNAPII) is tightly controlled by cyclin-dependent kinases (CDKs) at discrete checkpoints during the transcription cycle. The pausing checkpoint following transcription initiation is primarily controlled by CDK9. We discovered that CDK9-mediated, RNAPII-driven transcription is functionally opposed by a protein phosphatase 2A (PP2A) complex that is recruited to transcription sites by the Integrator complex subunit INTS6. PP2A dynamically antagonizes phosphorylation of key CDK9 substrates including DSIF and RNAPII-CTD. Loss of INTS6 results in resistance to tumor cell death mediated by CDK9 inhibition, decreased turnover of CDK9 phospho-substrates, and amplification of acute oncogenic transcriptional responses. Pharmacological PP2A activation synergizes with CDK9 inhibition to kill both leukemic and solid tumor cells, providing therapeutic benefit in vivo. These data demonstrate that fine control of gene expression relies on the balance between kinase and phosphatase activity throughout the transcription cycle, a process dysregulated in cancer that can be exploited therapeutically.
RNA 聚合酶 II（RNAPII）的基因表达受到细胞周期蛋白依赖性激酶（CDKs）在转录周期中的离散检查点的严格控制。转录起始后的暂停检查点主要由 CDK9 控制。我们发现，由 CDK9 介导的、由 RNAPII 驱动的转录受到一种蛋白磷酸酶 2A（PP2A）复合物的功能拮抗，该复合物通过整合体复合物亚基 INTS6 被募集到转录位点。PP2A 动态拮抗关键 CDK9 底物的磷酸化，包括 DSIF 和 RNAPII-CTD。INTS6 的缺失导致对 CDK9 抑制介导的肿瘤细胞死亡的抗性、CDK9 磷酸化底物的周转率降低以及急性致癌转录反应的放大。药理学上的 PP2A 激活与 CDK9 抑制协同作用，杀死白血病和实体瘤细胞，在体内提供治疗益处。这些数据表明，基因表达的精细控制依赖于激酶和磷酸酶活性在整个转录周期中的平衡，这一过程在癌症中失调，可以被治疗性地利用。
