Laboratory of Cancer Cell Biology, Institute of Molecular Genetics, Czech Academy of Sciences, Prague, Czech Republic.
Department of Medical Oncology, University Medical Center Groningen, University of Groningen, The Netherlands.
Mol Oncol. 2024 Jan;18(1):6-20. doi: 10.1002/1878-0261.13433. Epub 2023 Oct 16.
Oncogene-induced replication stress has been recognized as a major cause of genome instability in cancer cells. Increased expression of cyclin E1 caused by amplification of the CCNE1 gene is a common cause of replication stress in various cancers. Protein phosphatase magnesium-dependent 1 delta (PPM1D) is a negative regulator of p53 and has been implicated in termination of the cell cycle checkpoint. Amplification of the PPM1D gene or frameshift mutations in its final exon promote tumorigenesis. Here, we show that PPM1D activity further increases the replication stress caused by overexpression of cyclin E1. In particular, we demonstrate that cells expressing a truncated mutant of PPM1D progress faster from G1 to S phase and fail to complete licensing of the replication origins. In addition, we show that transcription-replication collisions and replication fork slowing caused by CCNE1 overexpression are exaggerated in cells expressing the truncated PPM1D. Finally, replication speed and accumulation of focal DNA copy number alterations caused by induction of CCNE1 expression was rescued by pharmacological inhibition of PPM1D. We propose that increased activity of PPM1D suppresses the checkpoint function of p53 and thus promotes genome instability in cells expressing the CCNE1 oncogene.
癌基因诱导的复制应激已被认为是癌细胞基因组不稳定的主要原因。CCNE1 基因扩增导致的细胞周期蛋白 E1 的过度表达是各种癌症中复制应激的常见原因。蛋白磷酸酶镁依赖性 1 德尔塔（PPM1D）是 p53 的负调节剂，与细胞周期检查点的终止有关。PPM1D 基因的扩增或其最后外显子的移码突变促进了肿瘤的发生。在这里，我们表明 PPM1D 的活性进一步增加了 cyclin E1 过表达引起的复制应激。特别是，我们证明表达 PPM1D 截断突变体的细胞从 G1 期更快地进入 S 期，并且无法完成复制起点的许可。此外，我们还表明，CCNE1 过表达引起的转录-复制碰撞和复制叉减缓在表达截断 PPM1D 的细胞中被夸大。最后，通过药理学抑制 PPM1D，诱导 CCNE1 表达引起的复制速度和焦点 DNA 拷贝数改变的积累得到了挽救。我们提出，PPM1D 活性的增加抑制了 p53 的检查点功能，从而促进了表达 CCNE1 癌基因的细胞的基因组不稳定性。
