Institute for Cancer Genetics, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY 10032, USA; Herbert Irving Comprehensive Cancer Center, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY 10032, USA.
New York University School of Medicine, New York, NY 10016, USA.
Mol Cell. 2024 Oct 17;84(20):3916-3931.e7. doi: 10.1016/j.molcel.2024.09.020. Epub 2024 Oct 8.
Poly (ADP-ribose) polymerase (PARP) 1 and 2 enzymatic inhibitors (PARPi) are promising cancer treatments. But recently, their use has been hindered by unexplained severe anemia and treatment-related leukemia. In addition to enzymatic inhibition, PARPi also trap PARP1 and 2 at DNA lesions. Here we report that, unlike Parp2 mice, which develop normally, mice expressing catalytically inactive Parp2 (E534A and Parp2) succumb to Tp53- and Chk2-dependent erythropoietic failure in utero, mirroring Lig1 mice. While DNA damage mainly activates PARP1, we demonstrate that DNA replication activates PARP2 robustly. PARP2 is selectively recruited and activated by 5'-phosphorylated nicks (5'p-nicks), including those between Okazaki fragments, resolved by ligase 1 (Lig1) and Lig3. Inactive PARP2, but not its active form or absence, impedes Lig1- and Lig3-mediated ligation, causing dose-dependent replication fork collapse, which is detrimental to erythroblasts with ultra-fast forks. This PARylation-dependent structural function of PARP2 at 5'p-nicks explains the detrimental effects of PARP2 inactivation on erythropoiesis, shedding light on PARPi-induced anemia and the selection for TP53/CHK2 loss.
聚（ADP-核糖）聚合酶（PARP）1 和 2 酶抑制剂（PARPi）是很有前途的癌症治疗方法。但最近，由于不明原因的严重贫血和治疗相关的白血病，它们的应用受到了阻碍。除了酶抑制作用外，PARPi 还能将 PARP1 和 2 捕获到 DNA 损伤处。在这里，我们报告说，与正常发育的 Parp2 小鼠不同，表达无催化活性 Parp2（E534A 和 Parp2）的小鼠在子宫内会因 Tp53 和 Chk2 依赖性红细胞生成失败而死亡，这与 Lig1 小鼠相似。虽然 DNA 损伤主要激活 PARP1，但我们证明 DNA 复制能强烈激活 PARP2。PARP2 被 5'-磷酸化的缺口（5'p-nicks）选择性募集和激活，包括由 Lig1 和 Lig3 解决的那些缺口。无活性的 PARP2，但不是其活性形式或不存在，会阻碍 Lig1 和 Lig3 介导的连接，导致复制叉的剂量依赖性崩溃，这对具有超快叉的红细胞不利。PARP2 在 5'p-nicks 处的这种依赖 PARylation 的结构功能解释了 PARP2 失活对红细胞生成的有害影响，为 PARPi 诱导的贫血和 TP53/CHK2 缺失的选择提供了线索。
