Suvorova I I, Kozhukharova I V, Nikol'skiĭ N N, Pospelov V A
Tsitologiia. 2013;55(12):841-51.
Embryonic stem cells (ESCs) are the progenitors of all adult cells so any disruption in their genome can have disastrous consequences for the developing organism. ESCs are characterized by a high proliferation activity and do not undergo checkpoints upon DNA-damage executing only G2/M delay after DNA damage. ATM and ATR kinase are key sensors of DNA double strands breaks and activate downstream signaling pathways involving checkpoints, DNA repair and apoptosis. We estimated ATM/ATR signaling pathway activation in human ESCs and have revealed that irradiation induced ATM, ATR Chk2 phosphorylation, γH2AX foci formation and their co-localization with 53BP1 and Rad51 proteins. Interestingly, human ESCs display non-induced yH2AX foci co-localized with Rad51 and marking DNA single-strand breaks. Next we have revealed the substantial contribution of ATM, Chk1 and Chk2 kinases to G2/M block after irradiation of human ESCs and ATM-dependent activation (phosphorylation) of p53. However p53 activation and subsequent induction of p21 gene expression after DNA damage do not result in p21 protein accumulation due to proteasomal degradation.
胚胎干细胞（ESC）是所有成体细胞的祖细胞，因此其基因组中的任何破坏都可能对发育中的生物体产生灾难性后果。胚胎干细胞的特征是具有高增殖活性，并且在DNA损伤时不会经历检查点，仅在DNA损伤后执行G2/M期延迟。ATM和ATR激酶是DNA双链断裂的关键传感器，并激活涉及检查点、DNA修复和细胞凋亡的下游信号通路。我们估计了人类胚胎干细胞中ATM/ATR信号通路的激活情况，并发现辐射诱导了ATM、ATR、Chk2磷酸化、γH2AX焦点形成以及它们与53BP1和Rad51蛋白的共定位。有趣的是，人类胚胎干细胞显示出与Rad51共定位且标记DNA单链断裂的非诱导性γH2AX焦点。接下来，我们揭示了ATM、Chk1和Chk2激酶在人类胚胎干细胞辐射后对G2/M期阻滞以及p53的ATM依赖性激活（磷酸化）的重大贡献。然而，DNA损伤后p53的激活以及随后p21基因表达的诱导并不会由于蛋白酶体降解而导致p21蛋白积累。
