Phospho-dependent interactions between NBS1 and MDC1 mediate chromatin retention of the MRN complex at sites of DNA damage

EMBO Rep. 2008 Aug;9(8):795-801. doi: 10.1038/embor.2008.103. Epub 2008 Jun 27.


Mammalian cells respond to DNA double-strand breaks (DSBs) by recruiting DNA repair and cell-cycle checkpoint proteins to such sites. Central to these DNA damage response (DDR) events is the DNA damage mediator protein MDC1. MDC1 interacts with several DDR proteins, including the MRE11-RAD50-NBS1 (MRN) complex. Here, we show that MDC1 is phosphorylated on a cluster of conserved repeat motifs by casein kinase 2 (CK2). Moreover, we establish that this phosphorylation of MDC1 promotes direct, phosphorylation-dependent interactions with NBS1 in a manner that requires the closely apposed FHA and twin BRCT domains in the amino terminus of NBS1. Finally, we show that these CK2-targeted motifs in MDC1 are required to mediate NBS1 association with chromatin-flanking sites of unrepaired DSBs. These findings provide a molecular explanation for the MDC1-MRN interaction and yield insights into how MDC1 coordinates the focal assembly and activation of several DDR factors in response to DNA damage.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Casein Kinase II / genetics
  • Casein Kinase II / metabolism
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Line, Tumor
  • Chromatin / metabolism*
  • DNA Damage*
  • DNA Repair Enzymes / genetics
  • DNA Repair Enzymes / metabolism
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Flow Cytometry
  • HeLa Cells
  • Humans
  • Immunoblotting
  • Immunoprecipitation
  • MRE11 Homologue Protein
  • Mass Spectrometry
  • Mice
  • Microscopy, Fluorescence
  • Molecular Sequence Data
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Protein Binding
  • Sequence Homology, Amino Acid
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*


  • Cell Cycle Proteins
  • Chromatin
  • DNA-Binding Proteins
  • MDC1 protein, human
  • MRE11 protein, human
  • NBN protein, human
  • Nuclear Proteins
  • Trans-Activators
  • Casein Kinase II
  • MRE11 Homologue Protein
  • Rad50 protein, human
  • DNA Repair Enzymes