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Phosphorylated CtIP Functions as a Co-factor of the MRE11-RAD50-NBS1 Endonuclease in DNA End Resection

Roopesh Anand1, Lepakshi Ranjha1, Elda Cannavo1

  • 1Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.

Molecular Cell
|November 28, 2016
PubMed

Insights

DNA double-strand break (DSB) repair via homologous recombination (HR) requires DNA end resection. This study reveals CtIP phosphorylation is essential for the MRE11-RAD50-NBS1 complex to initiate DSB resection, a key step in HR.

Area of Science:

  • Molecular Biology
  • DNA Repair Mechanisms
  • Cellular Biology

Background:

  • Homologous recombination (HR) is a critical DNA repair pathway.
  • DNA end resection is the initial step in HR, processing double-strand breaks (DSBs).
  • The MRE11-RAD50-NBS1 (MRN) complex and CtIP protein are implicated in initiating DNA resection.

Purpose of the Study:

  • To elucidate the mechanism by which the MRN complex and CtIP initiate DNA end resection.
  • To define the role of CtIP phosphorylation in the MRE11 endonuclease activity.
  • To clarify the necessity of NBS1 in human DNA resection compared to yeast.

Main Methods:

  • In vitro biochemical assays to assess endonuclease activity.
  • Analysis of protein-cofactor interactions within the MRN complex.
  • Site-directed mutagenesis to investigate the role of CtIP phosphorylation.

Main Results:

  • CtIP acts as a co-factor for the MRE11 endonuclease activity within the MRN complex.
  • CtIP phosphorylation, particularly at Thr-847, is essential for its co-factor function.
  • NBS1 is indispensable for the human MRN complex's resection activity in vitro.
  • The phosphorylated MRN-CtIP complex preferentially cleaves 5'-terminated DNA strands near DSBs.

Conclusions:

  • The study defines the molecular mechanism for the initiation of DNA end resection by the human MRN-CtIP complex.
  • Phosphorylated CtIP is a critical regulator of MRE11 endonuclease activity during DSB repair.
  • This finding is particularly relevant for understanding the repair of DSBs with protein blocks, impacting HR efficiency.
Keywords:
DNA end resectiondouble-strand DNA breakhelicasehomologous recombinationnuclease

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