Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63104, USA.
Mol Cell. 2019 Jun 20;74(6):1123-1137.e6. doi: 10.1016/j.molcel.2019.04.003. Epub 2019 Apr 30.
Abnormal processing of stressed replication forks by nucleases can cause fork collapse, genomic instability, and cell death. Despite its importance, it is poorly understood how the cell properly controls nucleases to prevent detrimental fork processing. Here, we report a signaling pathway that controls the activity of exonuclease Exo1 to prevent aberrant fork resection during replication stress. Our results indicate that replication stress elevates intracellular Ca concentration ([Ca]), leading to activation of CaMKK2 and the downstream kinase 5' AMP-activated protein kinase (AMPK). Following activation, AMPK directly phosphorylates Exo1 at serine 746 to promote 14-3-3 binding and inhibit Exo1 recruitment to stressed replication forks, thereby avoiding unscheduled fork resection. Disruption of this signaling pathway results in excessive ssDNA, chromosomal instability, and hypersensitivity to replication stress inducers. These findings reveal a link between [Ca] and the replication stress response as well as a function of the Ca-CaMKK2-AMPK signaling axis in safeguarding fork structure to maintain genome stability.
核酸内切酶异常处理有压力的复制叉会导致叉崩溃、基因组不稳定和细胞死亡。尽管它很重要，但细胞如何正确控制核酸内切酶以防止有害的叉处理还知之甚少。在这里，我们报告了一个信号通路，该通路控制外切核酸酶 Exo1 的活性，以防止复制应激期间异常的叉切除。我们的结果表明，复制应激会升高细胞内 Ca 浓度 ([Ca])，导致钙调蛋白激酶 2 (CaMKK2) 和下游激酶 5' 腺苷单磷酸激活蛋白激酶 (AMPK) 的激活。激活后，AMPK 直接将 Exo1 丝氨酸 746 磷酸化，促进与 14-3-3 的结合，并抑制 Exo1 招募到有压力的复制叉，从而避免非计划的叉切除。该信号通路的破坏会导致过多的单链 DNA、染色体不稳定以及对复制应激诱导剂的过度敏感。这些发现揭示了 [Ca] 与复制应激反应之间的联系，以及 Ca-CaMKK2-AMPK 信号轴在保护叉结构以维持基因组稳定性方面的功能。
