Iijima Kenta, Muranaka Chizuko, Kobayashi Junya, Sakamoto Shuichi, Komatsu Kenshi, Matsuura Shinya, Kubota Nobuo, Tauchi Hiroshi
Department of Environmental Sciences, Faculty of Science, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki, Japan.
DNA Repair (Amst). 2008 Oct 1;7(10):1705-16. doi: 10.1016/j.dnarep.2008.06.013. Epub 2008 Jul 31.
DNA damage induced apoptosis, along with precise DNA damage repair, is a critical cellular function, and both of these functions are necessary for cancer prevention. The NBS1 protein is known to be a key regulator of DNA damage repair. It acts by forming a complex with Rad50/Mre11 and by activating ATM. We show here that NBS1 regulates a novel p53 independent apoptotic pathway in response to DNA damage. DNA damage induced apoptosis was significantly reduced in NBS1 deficient cells regardless of their p53 status. Experiments using a series of cell lines expressing mutant NBS1 proteins revealed that NBS1 is able to regulate the activation of Bax and Caspase-3 without the FHA, Mre11-binding, or the ATM-interacting domains, whereas the phosphorylation sites of NBS1 were essential for Bax activation. Expression of apoptosis-related transcription factors such as E2F1 and their downstream pro-apoptotic factors were not related to this apoptosis induction. Interestingly, NBS1 regulates a novel Bax activation pathway by disrupting the Ku70-Bax complex which is required for activation of the mitochondrial apoptotic pathway. This dissociation of the Ku70-Bax complex can be mediated by acetylation of Ku70, and NBS1 can function in this process through a protein-protein interaction with Ku70. Thus, NBS1 is a key protein involved in the prevention of carcinogenesis, not only through the precise repair of damaged DNA by homologous recombination (HR) but also by its role in the elimination of inappropriately repaired cells.
DNA损伤诱导的细胞凋亡，连同精确的DNA损伤修复，是一种关键的细胞功能，而这两种功能对于预防癌症都是必需的。已知NBS1蛋白是DNA损伤修复的关键调节因子。它通过与Rad50/Mre11形成复合物并激活ATM来发挥作用。我们在此表明，NBS1在响应DNA损伤时调节一种新的p53非依赖性凋亡途径。无论p53状态如何，NBS1缺陷细胞中DNA损伤诱导的细胞凋亡均显著减少。使用一系列表达突变NBS1蛋白的细胞系进行的实验表明，NBS1能够在没有FHA、Mre11结合或ATM相互作用结构域的情况下调节Bax和Caspase-3的激活，而NBS1的磷酸化位点对于Bax激活至关重要。凋亡相关转录因子如E2F1及其下游促凋亡因子的表达与这种凋亡诱导无关。有趣的是，NBS1通过破坏线粒体凋亡途径激活所需的Ku70-Bax复合物来调节一种新的Bax激活途径。Ku70-Bax复合物的这种解离可由Ku70的乙酰化介导，并且NBS1可通过与Ku70的蛋白质-蛋白质相互作用在这一过程中发挥作用。因此，NBS1不仅通过同源重组（HR）精确修复受损DNA，还通过其在消除修复不当的细胞中的作用，成为参与预防癌症发生的关键蛋白。
