Morino Masayuki, Nukina Kohei, Sakaguchi Hiroki, Maeda Takeshi, Takahara Michiyo, Shiomi Yasushi, Nishitani Hideo
Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan.
PLoS One. 2015 Mar 23;10(3):e0120553. doi: 10.1371/journal.pone.0120553. eCollection 2015.
Cdt1 begins to accumulate in M phase and has a key role in establishing replication licensing at the end of mitosis or in early G1 phase. Treatments that damage the DNA of cells, such as UV irradiation, induce Cdt1 degradation through PCNA-dependent CRL4-Cdt2 ubiquitin ligase. How Cdt1 degradation is linked to cell cycle progression, however, remains unclear. In G1 phase, when licensing is established, UV irradiation leads to Cdt1 degradation, but has little effect on the licensing state. In M phase, however, UV irradiation does not induce Cdt1 degradation. When mitotic UV-irradiated cells were released into G1 phase, Cdt1 was degraded before licensing was established. Thus, these cells exhibited both defective licensing and G1 cell cycle arrest. The frequency of G1 arrest increased in cells expressing extra copies of Cdt2, and thus in cells in which Cdt1 degradation was enhanced, whereas the frequency of G1 arrest was reduced in cell expressing an extra copy of Cdt1. The G1 arrest response of cells irradiated in mitosis was important for cell survival by preventing the induction of apoptosis. Based on these observations, we propose that mammalian cells have a DNA replication-licensing checkpoint response to DNA damage induced during mitosis.
Cdt1在M期开始积累，并在有丝分裂末期或G1期早期建立复制许可过程中发挥关键作用。诸如紫外线照射等破坏细胞DNA的处理，会通过依赖增殖细胞核抗原（PCNA）的CRL4 - Cdt2泛素连接酶诱导Cdt1降解。然而，Cdt1降解如何与细胞周期进程相关联仍不清楚。在G1期，当建立许可时，紫外线照射会导致Cdt1降解，但对许可状态影响不大。然而，在M期，紫外线照射不会诱导Cdt1降解。当有丝分裂期经紫外线照射的细胞进入G1期时，Cdt1在许可建立之前就被降解了。因此，这些细胞表现出许可缺陷和G1期细胞周期停滞。在表达额外拷贝Cdt2的细胞中，也就是Cdt1降解增强的细胞中，G1期停滞的频率增加，而在表达额外拷贝Cdt1的细胞中，G1期停滞的频率降低。有丝分裂期受照射细胞的G1期停滞反应通过防止细胞凋亡诱导，对细胞存活至关重要。基于这些观察结果，我们提出哺乳动物细胞对有丝分裂期间诱导的DNA损伤具有DNA复制许可检查点反应。
