Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA.
Mol Cell. 2011 Jul 22;43(2):192-202. doi: 10.1016/j.molcel.2011.06.019.
The ataxia telangiectasia-mutated and Rad3-related (ATR) kinase is a master checkpoint regulator safeguarding the genome. Upon DNA damage, the ATR-ATRIP complex is recruited to sites of DNA damage by RPA-coated single-stranded DNA and activated by an elusive process. Here, we show that ATR is transformed into a hyperphosphorylated state after DNA damage, and that a single autophosphorylation event at Thr 1989 is crucial for ATR activation. Phosphorylation of Thr 1989 relies on RPA, ATRIP, and ATR kinase activity, but unexpectedly not on the ATR stimulator TopBP1. Recruitment of ATR-ATRIP to RPA-ssDNA leads to congregation of ATR-ATRIP complexes and promotes Thr 1989 phosphorylation in trans. Phosphorylated Thr 1989 is directly recognized by TopBP1 via the BRCT domains 7 and 8, enabling TopBP1 to engage ATR-ATRIP, to stimulate the ATR kinase, and to facilitate ATR substrate recognition. Thus, ATR autophosphorylation on RPA-ssDNA is a molecular switch to launch robust checkpoint response.
共济失调毛细血管扩张突变和 Rad3 相关（ATR）激酶是基因组的主要检查点调节剂。在 DNA 损伤时，ATR-ATRIP 复合物通过 RPA 包裹的单链 DNA 招募到 DNA 损伤部位，并通过一个难以捉摸的过程被激活。在这里，我们表明，ATR 在 DNA 损伤后被转化为高度磷酸化状态，并且 Thr1989 处的单个自身磷酸化事件对于 ATR 的激活至关重要。Thr1989 的磷酸化依赖于 RPA、ATRIP 和 ATR 激酶活性，但出乎意料的是不依赖于 ATR 刺激因子 TopBP1。ATR-ATRIP 向 RPA-ssDNA 的募集导致 ATR-ATRIP 复合物的聚集，并促进 Thr1989 的磷酸化。磷酸化的 Thr1989 通过 BRCT 结构域 7 和 8 被 TopBP1 直接识别，从而使 TopBP1 能够与 ATR-ATRIP 结合，刺激 ATR 激酶，并促进 ATR 底物的识别。因此，ATR 在 RPA-ssDNA 上的自身磷酸化是启动强大的检查点反应的分子开关。
