Teixeira Leonardo K, Wang Xianlong, Li Yongjiang, Ekholm-Reed Susanna, Wu Xiaohua, Wang Pei, Reed Steven I
Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
Curr Biol. 2015 May 18;25(10):1327-33. doi: 10.1016/j.cub.2015.03.022. Epub 2015 May 7.
Cell-cycle progression is regulated by the cyclin-dependent kinase (Cdk) family of protein kinases, so named because their activation depends on association with regulatory subunits known as cyclins. Cyclin E normally accumulates at the G1/S boundary, where it promotes S phase entry and progression by activating Cdk2. In normal cells, cyclin E/Cdk2 activity is associated with DNA replication-related functions. However, deregulation of cyclin E leads to inefficient assembly of pre-replication complexes, replication stress, and chromosome instability. In malignant cells, cyclin E is frequently overexpressed, correlating with decreased survival in breast cancer patients. Transgenic mice deregulated for cyclin E in the mammary epithelia develop carcinoma, confirming that cyclin E is an oncoprotein. However, it remains unknown how cyclin E-mediated replication stress promotes genomic instability during carcinogenesis. Here, we show that deregulation of cyclin E causes human mammary epithelial cells to enter into mitosis with short unreplicated genomic segments at a small number of specific loci, leading to anaphase anomalies and ultimately deletions. Incompletely replicated regions are preferentially located at late-replicating domains, fragile sites, and breakpoints, including the mixed-lineage leukemia breakpoint cluster region (MLL BCR). Furthermore, these regions are characterized by a paucity of replication origins or unusual DNA structures. Analysis of a large set of breast tumors shows a significant correlation between cyclin E amplification and deletions at a number of the genomic loci identified in our study. Our results demonstrate how oncogene-induced replication stress contributes to genomic instability in human cancer.
细胞周期进程受细胞周期蛋白依赖性激酶（Cdk）家族蛋白激酶的调控，因其激活依赖于与称为细胞周期蛋白的调节亚基结合而得名。细胞周期蛋白E通常在G1/S边界积累，通过激活Cdk2促进进入S期并推动其进程。在正常细胞中，细胞周期蛋白E/Cdk2活性与DNA复制相关功能有关。然而，细胞周期蛋白E的失调会导致复制前复合物组装效率低下、复制应激和染色体不稳定。在恶性细胞中，细胞周期蛋白E经常过度表达，这与乳腺癌患者生存率降低相关。乳腺上皮细胞中细胞周期蛋白E失调的转基因小鼠会发生癌变，证实细胞周期蛋白E是一种癌蛋白。然而，细胞周期蛋白E介导的复制应激在致癌过程中如何促进基因组不稳定仍不清楚。在此，我们表明细胞周期蛋白E的失调会导致人类乳腺上皮细胞在少数特定基因座带有短的未复制基因组片段进入有丝分裂，导致后期异常并最终缺失。未完全复制的区域优先位于晚期复制结构域、脆性位点和断点处，包括混合谱系白血病断点簇区域（MLL BCR）。此外，这些区域的特征是复制起点稀少或存在异常DNA结构。对大量乳腺肿瘤的分析表明，细胞周期蛋白E扩增与我们研究中确定的多个基因组位点的缺失之间存在显著相关性。我们的结果证明了癌基因诱导的复制应激如何导致人类癌症中的基因组不稳定。
