Yuan Xi, Srividhya Jeyaraman, De Luca Thomas, Lee Ju-Hyong E, Pomerening Joseph R
Department of Biology, Indiana University, Bloomington, IN 47405-7003 Biocomplexity Institute, Department of Physics, Indiana University, Bloomington, IN 47405-7003 Department of Environmental Health, School of Public Health, Indiana University, Bloomington, IN 47408-2671 Department of Statistics, Indiana University, Bloomington, IN 47408-3825.
Mol Biol Cell. 2014 Feb;25(4):441-56. doi: 10.1091/mbc.E13-08-0480. Epub 2013 Dec 19.
Cdh1, a coactivator of the anaphase-promoting complex (APC), is a potential tumor suppressor. Cdh1 ablation promotes precocious S-phase entry, but it was unclear how this affects DNA replication dynamics while contributing to genomic instability and tumorigenesis. We find that Cdh1 depletion causes early S-phase onset in conjunction with increase in Rb/E2F1-mediated cyclin E1 expression, but reduced levels of cyclin E1 protein promote this transition. We hypothesize that this is due to a weakened cyclin-dependent kinase inhibitor (CKI)-cyclin-dependent kinase 2 positive-feedback loop, normally generated by APC-Cdh1-mediated proteolysis of Skp2. Indeed, Cdh1 depletion increases Skp2 abundance while diminishing levels of the CKI p27. This lowers the level of cyclin E1 needed for S-phase entry and delays cyclin E1 proteolysis during S-phase progression while corresponding to slowed replication fork movement and reduced frequency of termination events. In summary, using both experimental and computational approaches, we show that APC-Cdh1 establishes a stimulus-response relationship that promotes S phase by ensuring that proper levels of p27 accumulate during G1 phase, and defects in its activation accelerate the timing of S-phase onset while prolonging its progression.
Cdh1是后期促进复合物（APC）的一种共激活因子，是一种潜在的肿瘤抑制因子。Cdh1缺失会促进细胞过早进入S期，但尚不清楚这如何影响DNA复制动力学，同时导致基因组不稳定和肿瘤发生。我们发现，Cdh1缺失会导致S期提前开始，同时Rb/E2F1介导的细胞周期蛋白E1表达增加，但细胞周期蛋白E1蛋白水平的降低促进了这种转变。我们推测这是由于细胞周期蛋白依赖性激酶抑制剂（CKI）-细胞周期蛋白依赖性激酶2正反馈环减弱，该正反馈环通常由APC-Cdh1介导的Skp2蛋白水解产生。事实上，Cdh1缺失会增加Skp2的丰度，同时降低CKI p27的水平。这降低了进入S期所需的细胞周期蛋白E1水平，并在S期进程中延迟了细胞周期蛋白E1的蛋白水解，同时对应于复制叉移动减慢和终止事件频率降低。总之，通过实验和计算方法，我们表明APC-Cdh1建立了一种刺激-反应关系，通过确保在G1期积累适当水平的p27来促进S期，其激活缺陷会加速S期开始的时间，同时延长其进程。
