NFBD1/MDC1 regulates ionizing radiation‐induced focus formation by DNA checkpoint signaling and repair factors

• Published in: The FASEB journal 2003-10, Vol.17 (13), p.1842-1848
• Main Authors: Xu, Xingzhi, Stern, David F.
• Format: Article
• Language: English
• Subjects: 53BP1; Apoptosis; assembly of ionizing radiation-induced foci; ATM/ ATR substrates; Cell Line; Cell Nucleus - metabolism; Cell Nucleus - radiation effects; DNA Damage; DNA Repair; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - physiology; HeLa Cells; Humans; Macromolecular Substances; MRE11 complex; Nuclear Proteins - chemistry; Nuclear Proteins - metabolism; Nuclear Proteins - physiology; Protein Structure, Tertiary; Radiation, Ionizing; Signal Transduction; Trans-Activators - chemistry; Trans-Activators - physiology; γ‐H2AX
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fj.03-0310com

NFBD1/MDC1 (mediator of DNA damage checkpoint 1) is a nuclear factor with an aminoterminal 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 γ‐H2AX. An overexpressed FHA domain‐containing fragment of NFBD1 binds to endogenous NFBD1 and components of the MRN complex, but not to γ‐H2AX. This fragment interferes with IRIF formation by endogenous NFBD1, MRE11, or NBS1. A BRCT domain‐containing fragment of NFBD1 binds to γ‐H2AX and 53BP1, but not to components of the MRN complex, and abolishes IRIF formation by NFBD1, MRE11, NBS1, 53BP1, CHK2 phospho‐T68, γ‐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.—Xu, X., Stern, D. F. NFBD1/MDC1 regulates ionizing radiation‐induced focus formation of DNA checkpoint signaling and repair factors. FASEB J. 17, 1842–1848 (2003)