Verschuren Emmy W, Ban Kenneth H, Masek Marilyn A, Lehman Norman L, Jackson Peter K
Department of Tumor Biology and Angiogenesis, Genentech Inc., 1 DNA way, South San Francisco, California 94080, USA.
Mol Cell Biol. 2007 Nov;27(22):7955-65. doi: 10.1128/MCB.00908-07. Epub 2007 Sep 17.
Expression of the anaphase-promoting complex/cyclosome (APC/C) inhibitor Emi1 is required for the accumulation of APC/C substrates crucial for DNA synthesis and mitotic entry. We show that in vivo Emi1 expression correlates with the proliferative status of the cellular compartment and that cells lacking Emi1 undergo cellular senescence. Emi1 depletion leads to strong decreases in E2F target mRNA and APC/C substrate protein abundances. However, cyclin E mRNA and cyclin E protein levels and associated kinase activities are increased. Cells lacking Emi1 undergo DNA damage, likely explained by replication stress upon deregulated cyclin E- and A-associated kinase activities. Inhibition of ATM kinase prevents induction of senescence, implying that senescence is a consequence of DNA damage. Surprisingly, no senescence or no extensive amount of senescence is evident upon depletion of the Emi1-stabilizing factor Evi5 or Pin1, respectively. Our data suggest that maintenance of a protein stabilization/mRNA expression positive-feedback circuit fueled by Emi1 is required for accurate cell cycle progression, maintenance of DNA integrity, and prevention of cellular senescence.
后期促进复合物/细胞周期体（APC/C）抑制剂Emi1的表达对于DNA合成和有丝分裂进入至关重要的APC/C底物的积累是必需的。我们发现，在体内Emi1的表达与细胞区室的增殖状态相关，并且缺乏Emi1的细胞会发生细胞衰老。Emi1的缺失导致E2F靶标mRNA和APC/C底物蛋白丰度大幅下降。然而，细胞周期蛋白E mRNA和细胞周期蛋白E蛋白水平以及相关激酶活性却增加了。缺乏Emi1的细胞会发生DNA损伤，这可能是由于细胞周期蛋白E和A相关激酶活性失调导致的复制应激所致。抑制ATM激酶可防止衰老的诱导，这意味着衰老是DNA损伤的结果。令人惊讶的是，分别缺失Emi1稳定因子Evi5或Pin1时，未观察到衰老或未出现大量衰老现象。我们的数据表明，由Emi1驱动的蛋白质稳定/mRNA表达正反馈回路的维持对于准确的细胞周期进程、DNA完整性的维持以及细胞衰老的预防是必需的。
