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Direct activation of the ATM protein kinase by the Mre11/Rad50/Nbs1 complex

Ji-Hoon Lee1, Tanya T Paull

  • 1Department of Molecular Genetics and Microbiology, Institute of Cellular and Molecular Biology, University of Texas at Austin, 1 University Station, A4800, Austin, TX 78712, USA.

Science (New York, N.Y.)
|April 6, 2004
PubMed

Insights

The Mre11-Rad50-Nbs1 (MRN) complex enhances DNA double-strand break repair by stimulating the ATM kinase. MRN facilitates substrate binding, with Nbs1 phosphorylation crucial for activating ATM toward Chk2.

Area of Science:

  • Molecular Biology
  • DNA Repair Mechanisms
  • Cell Signaling Pathways

Background:

  • The Mre11-Rad50-Nbs1 (MRN) complex is crucial for sensing and responding to DNA double-strand breaks.
  • Activation of the ATM (ataxia telangiectasia mutated) kinase is a key event in the DNA damage response.
  • MRN integrates DNA repair with checkpoint signaling activation via ATM.

Purpose of the Study:

  • To investigate the mechanism by which the MRN complex stimulates ATM kinase activity.
  • To identify the role of MRN-ATM interactions in substrate phosphorylation.
  • To determine the contribution of Nbs1 phosphorylation to MRN-mediated ATM activation.

Main Methods:

  • In vitro kinase assays using purified MRN complex and ATM.
  • Analysis of ATM substrate phosphorylation (p53, Chk2, H2AX).
  • Mutational analysis of Nbs1 phosphorylation sites.

Main Results:

  • MRN complex significantly stimulates ATM kinase activity towards p53, Chk2, and H2AX in vitro.
  • MRN interacts with ATM through multiple contact points, stabilizing substrate binding.
  • Nbs1 phosphorylation is essential for MRN-mediated ATM activation of Chk2, but not p53.
  • Kinase-deficient ATM exhibits a dominant-negative effect on wild-type ATM activity.

Conclusions:

  • The MRN complex acts as a potent stimulator of ATM kinase activity.
  • MRN enhances ATM function by promoting stable substrate interactions.
  • Specific phosphorylation events on Nbs1 are critical for regulating ATM's downstream signaling pathways.

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