Xu Xingzhi, Stern David F
Department of Pathology, School of Medicine, Yale University, 310 Cedar St., BML342, New Haven, Connecticut 06510, USA.
FASEB J. 2003 Oct;17(13):1842-8. doi: 10.1096/fj.03-0310com.
NFBD1/MDC1 (mediator of DNA damage checkpoint 1) is a nuclear factor with an amino-terminal FHA (forkhead-associated) domain and a tandem repeat of BRCT (breast cancer susceptibility gene-1 carboxyl terminus) domains. We have previously shown that NFBD1 is an early participant in DNA damage signaling pathways and that ionizing radiation-induced nuclear foci (IRIF) of NFBD1 colocalize with several DNA checkpoint signaling and repair factors. We report here that NFBD1 physically associates with ATM, p53, components of the MRE11-RAD50-NBS1 (MRN) complex, and gamma-H2AX. An overexpressed FHA domain-containing fragment of NFBD1 binds to endogenous NFBD1 and components of the MRN complex, but not to gamma-H2AX. This fragment interferes with IRIF formation by endogenous NFBD1, MRE11, or NBS1. A BRCT domain-containing fragment of NFBD1 binds to gamma-H2AX and 53BP1, but not to components of the MRN complex, and abolishes IRIF formation by NFBD1, MRE11, NBS1, 53BP1, CHK2 phospho-T68, gamma-H2AX, and possible ATM/ATR substrates recognized by anti-phospho-SQ/TQ antibody. These results suggest that NFBD1 is an ATM/ATR-dependent organizer that recruits DNA checkpoint signaling and repair proteins to the sites of DNA damage.
NFBD1/MDC1（DNA损伤检查点1介导因子）是一种核因子，具有一个氨基末端FHA（叉头相关）结构域和BRCT（乳腺癌易感基因-1羧基末端）结构域的串联重复序列。我们之前已经表明，NFBD1是DNA损伤信号通路的早期参与者，并且电离辐射诱导的NFBD1核灶（IRIF）与几种DNA检查点信号和修复因子共定位。我们在此报告，NFBD1与ATM、p53、MRE11-RAD50-NBS1（MRN）复合物的组分以及γ-H2AX存在物理关联。过表达的含NFBD1 FHA结构域的片段与内源性NFBD1和MRN复合物的组分结合，但不与γ-H2AX结合。该片段干扰内源性NFBD1、MRE11或NBS1的IRIF形成。含NFBD1 BRCT结构域的片段与γ-H2AX和53BP1结合，但不与MRN复合物的组分结合，并消除NFBD1、MRE11、NBS1、53BP1、CHK2磷酸化-T68、γ-H2AX以及抗磷酸化-SQ/TQ抗体识别的可能的ATM/ATR底物的IRIF形成。这些结果表明，NFBD1是一种依赖ATM/ATR的组织者，可将DNA检查点信号和修复蛋白募集到DNA损伤位点。
