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Mus81-Mms4 endonuclease is an Esc2-STUbL-Cullin8 mitotic substrate impacting on genome integrity

Anja Waizenegger1, Madhusoodanan Urulangodi1,2, Carl P Lehmann3

  • 1IFOM, the FIRC Institute of Molecular Oncology, Via Adamello 16, 20139, Milan, Italy.

Nature Communications
|November 13, 2020
PubMed

Insights

Phosphorylated Mms4 is degraded by the proteasome after its role in resolving DNA recombination structures. Failure to degrade Mms4 causes genome instability and delays DNA damage checkpoints.

Area of Science:

  • Molecular Biology
  • Cell Cycle Regulation
  • DNA Repair

Background:

  • The Mus81-Mms4 nuclease resolves DNA recombination structures during the G2/M phase, a process requiring Mms4 phosphorylation.
  • The fate of phosphorylated Mms4 after its activation and function remains unclear.

Purpose of the Study:

  • To investigate the post-activation fate of phosphorylated Mms4.
  • To understand the regulatory mechanisms controlling Mms4 levels and its impact on genome stability.

Main Methods:

  • SUMOylation and ubiquitylation assays to detect Mms4 modification.
  • Proteasome degradation assays.
  • Chromatin immunoprecipitation to assess Mms4 localization.
  • Analysis of DNA damage checkpoint activation and genome integrity in wild-type and mutant strains.

Main Results:

  • Phosphorylated Mms4 undergoes (poly)SUMOylation and ubiquitylation, targeting it for proteasome degradation.
  • Mms4 is a substrate for the Esc2-STUbL-Cul8 ubiquitin ligase complex.
  • Loss of Esc2-STUbL-Cul8 activity leads to Mms4 accumulation on chromatin, causing aberrant processing of recombination intermediates and delayed DNA damage checkpoint activation.
  • Mutants stabilizing phosphorylated Mms4 compromise genome integrity.

Conclusions:

  • Mms4 is regulated by proteasomal degradation, a process crucial for resetting its activity between cell cycles.
  • The Esc2-STUbL-Cul8 complex plays a key role in replication protection by ensuring timely Mms4 turnover.
  • Proper regulation of phosphorylated Mms4 is essential for maintaining genome stability.

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