Institute of Molecular Oncology and Göttingen Centre of Molecular Biosciences, Faculty of Medicine, University of Göttingen, 37077 Göttingen, Germany.
Proc Natl Acad Sci U S A. 2013 Oct 15;110(42):16856-61. doi: 10.1073/pnas.1304355110. Epub 2013 Sep 30.
DNA damage can obstruct replication forks, resulting in replicative stress. By siRNA screening, we identified kinases involved in the accumulation of phosphohistone 2AX (γH2AX) upon UV irradiation-induced replication stress. Surprisingly, the strongest reduction of phosphohistone 2AX followed knockdown of the MAP kinase-activated protein kinase 2 (MK2), a kinase currently implicated in p38 stress signaling and G2 arrest. Depletion or inhibition of MK2 also protected cells from DNA damage-induced cell death, and mice deficient for MK2 displayed decreased apoptosis in the skin upon UV irradiation. Moreover, MK2 activity was required for damage response, accumulation of ssDNA, and decreased survival when cells were treated with the nucleoside analogue gemcitabine or when the checkpoint kinase Chk1 was antagonized. By using DNA fiber assays, we found that MK2 inhibition or knockdown rescued DNA replication impaired by gemcitabine or by Chk1 inhibition. This rescue strictly depended on translesion DNA polymerases. In conclusion, instead of being an unavoidable consequence of DNA damage, alterations of replication speed and origin firing depend on MK2-mediated signaling.
DNA 损伤可阻碍复制叉的前进，导致复制应激。通过 siRNA 筛选，我们鉴定出在紫外线照射诱导的复制应激下磷酸组蛋白 H2AX（γH2AX）积累所涉及的激酶。令人惊讶的是，在紫外线照射诱导的复制应激下，MK2（一种目前被认为与 p38 应激信号和 G2 阻滞有关的激酶）的敲低导致磷酸组蛋白 H2AX 的减少最为显著。MK2 的耗竭或抑制也能保护细胞免受 DNA 损伤诱导的细胞死亡，MK2 缺失的小鼠在紫外线照射后皮肤中的细胞凋亡减少。此外，MK2 活性对于损伤反应、ssDNA 的积累以及在用核苷类似物吉西他滨处理或抑制检查点激酶 Chk1 时细胞存活率的降低都是必需的。通过使用 DNA 纤维分析，我们发现 MK2 抑制或敲低可挽救吉西他滨或 Chk1 抑制引起的 DNA 复制受损。这种挽救严格依赖于跨损伤 DNA 聚合酶。总之，复制速度和起始原点的改变并不是 DNA 损伤的必然结果，而是依赖于 MK2 介导的信号。
