Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic.
Stem Cells. 2010 Jul;28(7):1143-52. doi: 10.1002/stem.451.
Embryonic stem cells progress very rapidly through the cell cycle, allowing limited time for cell cycle regulatory circuits that typically function in somatic cells. Mechanisms that inhibit cell cycle progression upon DNA damage are of particular importance, as their malfunction may contribute to the genetic instability observed in human embryonic stem cells (hESCs). In this study, we exposed undifferentiated hESCs to DNA-damaging ultraviolet radiation-C range (UVC) light and examined their progression through the G1/S transition. We show that hESCs irradiated in G1 phase undergo cell cycle arrest before DNA synthesis and exhibit decreased cyclin-dependent kinase two (CDK2) activity. We also show that the phosphatase Cdc25A, which directly activates CDK2, is downregulated in irradiated hESCs through the action of the checkpoint kinases Chk1 and/or Chk2. Importantly, the classical effector of the p53-mediated pathway, protein p21, is not a regulator of G1/S progression in hESCs. Taken together, our data demonstrate that cultured undifferentiated hESCs are capable of preventing entry into S-phase by activating the G1/S checkpoint upon damage to their genetic complement.
胚胎干细胞在细胞周期中快速前进，这使得通常在体细胞中起作用的细胞周期调控回路的作用时间有限。在 DNA 损伤时抑制细胞周期进程的机制尤为重要，因为它们的功能障碍可能导致在人类胚胎干细胞（hESC）中观察到的遗传不稳定性。在这项研究中，我们将未分化的 hESC 暴露于 DNA 损伤的紫外线 C 范围（UVC）光下，并检查它们在 G1/S 过渡中的进展。我们表明，在 G1 期受到照射的 hESC 在 DNA 合成之前经历细胞周期阻滞，并表现出降低的细胞周期蛋白依赖性激酶 2（CDK2）活性。我们还表明，磷酸酶 Cdc25A 通过检查点激酶 Chk1 和/或 Chk2 的作用在照射的 hESC 中下调，该磷酸酶直接激活 CDK2。重要的是，p53 介导途径的经典效应物蛋白 p21 不是 hESC 中 G1/S 进展的调节剂。总之，我们的数据表明，培养的未分化 hESC 能够通过在其遗传物质受到损伤时激活 G1/S 检查点来防止进入 S 期。
