Wang Feng, Stewart Jason, Price Carolyn M
a Department of Cancer Biology ; University of Cincinnati ; Cincinnati , OH USA.
Cell Cycle. 2014;13(22):3488-98. doi: 10.4161/15384101.2014.964100.
Mammalian CST (CTC1-STN1-TEN1) is a telomere-associated complex that functions in telomere duplex replication and fill-in synthesis of the telomeric C-strand following telomerase action. CST also facilitates genome-wide replication recovery after HU-induced fork stalling by increasing origin firing. CTC1 and STN1 were originally isolated as a DNA polymerase α stimulatory factor. Here we explore how CST abundance affects recovery from drugs that cause different types of DNA damage and replication stress. We show that recovery from HU and aphidicolin induced replication stress is increased by CST over-expression. Elevated CST increases dNTP incorporation and origin firing after HU release and decreases the incidence of anaphase bridges and micronuclei after aphidicolin removal. While the frequency of origin firing after HU release is proportional to CST abundance, the number of cells entering S-phase to initiate replication is unchanged by CST overexpression or STN1 depletion. Instead the CST-related changes in origin firing take place in cells that were already in S-phase at the time of HU addition, indicating that CST modulates firing of late or dormant origins. CST abundance also influences cell viability after treatment with HU, aphidicolin, MMS and camptothecin. Viability is increased by elevated CST and decreased by STN1 depletion, indicating that endogenous CST levels are limiting. However, CST abundance does not affect viability after MMC treatment. Thus, CST facilitates recovery from many, but not all, forms of exogenous DNA damage. Overall our results suggest that CST is needed in stoichiometric amounts to facilitate re-initiation of DNA replication at repaired forks and/or dormant origins.
哺乳动物的CST（CTC1-STN1-TEN1）是一种与端粒相关的复合体，在端粒双链复制以及端粒酶作用后端粒C链的填补合成过程中发挥作用。CST还通过增加起始点激发来促进HU诱导的叉状停滞之后全基因组范围的复制恢复。CTC1和STN1最初作为DNA聚合酶α刺激因子被分离出来。在这里，我们探究CST丰度如何影响从导致不同类型DNA损伤和复制应激的药物处理中恢复。我们发现，CST过表达可增强从HU和阿非迪霉素诱导的复制应激中恢复的能力。CST水平升高会增加HU释放后dNTP的掺入和起始点激发，并降低阿非迪霉素去除后后期桥和微核的发生率。虽然HU释放后起始点激发的频率与CST丰度成正比，但进入S期启动复制的细胞数量不受CST过表达或STN1缺失的影响。相反，与CST相关的起始点激发变化发生在HU添加时已经处于S期的细胞中，这表明CST调节晚期或休眠起始点的激发。CST丰度也会影响用HU、阿非迪霉素、MMS和喜树碱处理后的细胞活力。CST水平升高会提高细胞活力，而STN1缺失则会降低细胞活力，这表明内源性CST水平是有限的。然而，CST丰度不影响MMC处理后的细胞活力。因此，CST促进从多种但并非所有形式的外源性DNA损伤中恢复。总体而言，我们的结果表明，需要化学计量的CST来促进在修复的叉状结构和/或休眠起始点处重新启动DNA复制。
