Mre11 ATLD17/18 mutation retains Tel1/ATM activity but blocks DNA double-strand break repair

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• The Mre11 complex (MRN) is crucial for maintaining genome stability by repairing DNA double-strand breaks.
• MRN interacts with CtIP/Ctp1/Sae2 and ATM/Tel1 to regulate DNA repair, checkpoint signaling, and telomere maintenance.

Purpose of the Study:

• To investigate the functional consequences of the Mre11-W243R mutation identified in pediatric cancer patients with ataxia telangiectasia-like disorder.
• To elucidate the molecular mechanisms underlying the mutation's impact on genome stability.

Main Methods:

• Biochemical assays to assess Mre11 nuclease and DNA binding activities.
• X-ray crystallography to determine the structural impact of analogous mutations.
• In vivo functional studies in fission yeast to evaluate MRN complex function, DNA damage response, and cell viability.

Main Results:

• The Mre11-W243R mutation retains in vitro nuclease and DNA binding activities.
• Structural analysis shows the mutation disorders surface loops regulating DNA and Rad50 interactions without altering active sites.
• In vivo, the analogous mutation supports MRN complex formation, DNA break binding, and Tel1/ATM activation but impairs DNA end processing, leading to genomic instability.

Conclusions:

• The Mre11-W243R mutation acts as a separation-of-function mutation, specifically disrupting MRN subunit and Ctp1 interactions required for DNA end processing.
• Despite impaired DNA repair, the mutation maintains MRN interactions sufficient for Tel1/ATM checkpoint activation and telomere maintenance.
• This study provides insights into the complex regulation of DNA double-strand break repair and its implications for cancer development.