Department of Stem Cell Biology and Regenerative Medicine, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.
EMBO J. 2011 Mar 2;30(5):800-13. doi: 10.1038/emboj.2011.10. Epub 2011 Feb 4.
Glioblastomas (GBMs) are highly lethal brain tumours with current therapies limited to palliation due to therapeutic resistance. We previously demonstrated that GBM stem cells (GSCs) display a preferential activation of DNA damage checkpoint and are relatively resistant to radiation. However, the molecular mechanisms underlying the preferential checkpoint response in GSCs remain undefined. Here, we show that L1CAM (CD171) regulates DNA damage checkpoint responses and radiosensitivity of GSCs through nuclear translocation of L1CAM intracellular domain (L1-ICD). Targeting L1CAM by RNA interference attenuated DNA damage checkpoint activation and repair, and sensitized GSCs to radiation. L1CAM regulates expression of NBS1, a critical component of the MRE11-RAD50-NBS1 (MRN) complex that activates ataxia telangiectasia mutated (ATM) kinase and early checkpoint response. Ectopic expression of NBS1 in GSCs rescued the decreased checkpoint activation and radioresistance caused by L1CAM knockdown, demonstrating that L1CAM signals through NBS1 to regulate DNA damage checkpoint responses. Mechanistically, nuclear translocation of L1-ICD mediates NBS1 upregulation via c-Myc. These data demonstrate that L1CAM augments DNA damage checkpoint activation and radioresistance of GSCs through L1-ICD-mediated NBS1 upregulation and the enhanced MRN-ATM-Chk2 signalling.
胶质母细胞瘤（GBM）是一种高度致命的脑肿瘤，目前的治疗方法仅限于缓解症状，因为存在治疗抵抗。我们之前的研究表明，GBM 干细胞（GSCs）表现出对 DNA 损伤检查点的优先激活，并且对辐射相对耐受。然而，GSCs 中优先检查点反应的分子机制仍未确定。在这里，我们表明 L1CAM（CD171）通过 L1CAM 细胞内结构域（L1-ICD）的核易位调节 GSCs 的 DNA 损伤检查点反应和放射敏感性。通过 RNA 干扰靶向 L1CAM 减弱了 DNA 损伤检查点的激活和修复，并使 GSCs 对辐射敏感。L1CAM 调节 NBS1 的表达，NBS1 是 MRE11-RAD50-NBS1（MRN）复合物的关键组成部分，该复合物激活共济失调毛细血管扩张突变（ATM）激酶和早期检查点反应。在 GSCs 中外源表达 NBS1 挽救了 L1CAM 敲低导致的检查点激活降低和放射抵抗，表明 L1CAM 通过 NBS1 信号转导来调节 DNA 损伤检查点反应。从机制上讲，L1-ICD 的核易位通过 c-Myc 介导 NBS1 的上调。这些数据表明，L1CAM 通过 L1-ICD 介导的 NBS1 上调和增强的 MRN-ATM-Chk2 信号转导，增强 GSCs 的 DNA 损伤检查点激活和放射抵抗。
