Howard Hughes Medical Institute and the Department of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, TX 78712, USA.
EMBO J. 2010 Feb 3;29(3):574-85. doi: 10.1038/emboj.2009.372. Epub 2009 Dec 10.
The Mre11/Rad50/Nbs1 (MRN) complex has a central function in facilitating activation of the ATM protein kinase at sites of DNA double-strand breaks (DSBs). However, several other factors are also required in human cells for efficient signalling through MRN and ATM, including the tumour suppressor proteins p53-binding protein 1 (53BP1) and BRCA1. In this study, we investigate the functions of these mediator proteins in ATM activation and find that the presence of 53BP1 and BRCA1 can amplify the effects of MRN when interactions between MRN and ATM are compromised. This effect is dependent on a direct interaction between MRN and the tandem breast cancer carboxy-terminal (BRCT) repeats in 53BP1, and is accompanied by hyper-phosphorylation of both Nbs1 and 53BP1. We also find that the BRCT domains of 53BP1 affect the overall structure of 53BP1 multimers and that this structure is important for promoting ATM phosphorylation of substrates as well as for the repair of DNA DSBs in mammalian cells.
Mre11/Rad50/Nbs1（MRN）复合物在促进 ATM 蛋白激酶在 DNA 双链断裂（DSBs）部位的激活方面具有核心功能。然而，在人类细胞中，还需要其他几种因子才能通过 MRN 和 ATM 进行有效的信号转导，包括肿瘤抑制蛋白 p53 结合蛋白 1（53BP1）和 BRCA1。在这项研究中，我们研究了这些中介蛋白在 ATM 激活中的功能，发现当 MRN 与 ATM 之间的相互作用受到损害时，53BP1 和 BRCA1 的存在可以放大 MRN 的作用。这种效应依赖于 MRN 与 53BP1 中的串联乳腺癌羧基末端（BRCT）重复序列之间的直接相互作用，并伴随着 Nbs1 和 53BP1 的过度磷酸化。我们还发现 53BP1 的 BRCT 结构域会影响 53BP1 多聚体的整体结构，并且这种结构对于促进 ATM 对底物的磷酸化以及在哺乳动物细胞中修复 DNA DSBs 很重要。
