Phosphorylation of SDT repeats in the MDC1 N terminus triggers retention of NBS1 at the DNA damage-modified chromatin.
DNA double-strand breaks (DSBs) trigger accumulation of the MRE11-RAD50-Nijmegen breakage syndrome 1 (NBS1 [MRN]) complex, whose retention on the DSB-flanking chromatin facilitates survival. Chromatin retention of MRN requires the MDC1 adaptor protein, but the mechanism behind the MRN-MDC1 interaction is unknown. We show that the NBS1 subunit of MRN interacts with the MDC1 N terminus enriched in Ser-Asp-Thr (SDT) repeats. This interaction was constitutive and mediated by binding between the phosphorylated SDT repeats of MDC1 and the phosphate-binding forkhead-associated domain of NBS1. Phosphorylation of the SDT repeats by casein kinase 2 (CK2) was sufficient to trigger MDC1-NBS1 interaction in vitro, and MDC1 associated with CK2 activity in cells. Inhibition of CK2 reduced SDT phosphorylation in vivo, and disruption of the SDT-associated phosphoacceptor sites prevented the retention of NBS1 at DSBs. Together, these data suggest that phosphorylation of the SDT repeats in the MDC1 N terminus functions to recruit NBS1 and, thereby, increases the local concentration of MRN at the sites of chromosomal breakage.
Melander
Fredrik
F
Institute of Cancer Biology and 2Centre for Genotoxic Stress Research, Danish Cancer Society, DK-2100 Copenhagen, Denmark.
Bekker-Jensen
Simon
S
Falck
Jacob
J
Bartek
Jiri
J
Mailand
Niels
N
Lukas
Jiri
J
D048868:Adaptor Proteins, Signal Transducing; D001859:Bone Neoplasms; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D000076228:MRE11 Homologue Protein; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D012516:Osteosarcoma; D010446:Peptide Fragments / Q000378:metabolism; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C413163:MDC1 protein, human; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; D009842:Oligopeptides; D010446:Peptide Fragments; D011994:Recombinant Proteins; D015534:Trans-Activators; D000076228:MRE11 Homologue Protein