TIRR regulates 53BP1 by masking its histone methyl-lysine binding function

Area of Science:

• DNA repair mechanisms
• Epigenetics
• Cellular signaling

Background:

• P53-binding protein 1 (53BP1) is crucial for DNA double-strand break repair and cancer therapy.
• 53BP1's function relies on its tandem Tudor domain binding to histone H4K20me2.
• Understanding 53BP1 regulation is key for targeted cancer treatments.

Purpose of the Study:

• Identify novel regulators of 53BP1 function in DNA repair.
• Elucidate the mechanism by which TIRR influences 53BP1 activity.
• Investigate the role of TIRR in DNA damage response pathways.

Main Methods:

• Protein interaction studies to characterize TIRR and 53BP1 binding.
• Cellular assays to assess 53BP1 localization and function upon DNA damage.
• Genetic manipulation (overexpression and depletion) to study TIRR's impact on DNA repair.

Main Results:

• Tudor interacting repair regulator (TIRR) directly binds 53BP1's Tudor domain, masking H4K20me2 binding.
• ATM-mediated phosphorylation of 53BP1 and RIF1 recruitment disrupt the 53BP1-TIRR complex upon DNA damage.
• TIRR overexpression inhibits 53BP1 recruitment to double-strand breaks, while TIRR depletion destabilizes 53BP1.

Conclusions:

• TIRR acts as a novel inhibitor of 53BP1 by masking its histone binding site.
• The 53BP1-TIRR interaction is dynamically regulated by ATM signaling during DNA repair.
• TIRR represents a new therapeutic target for modulating DNA repair in cancer.