Widespread chromatin context-dependencies of DNA double-strand break repair proteins

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• DNA double-strand breaks are critical lesions repaired by distinct pathways.
• Non-homologous end-joining (NHEJ) and microhomology-mediated end-joining (MMEJ) are major repair pathways.
• The regulation of NHEJ and MMEJ balance by chromatin context is poorly understood.

Purpose of the Study:

• To identify proteins that modulate the balance between NHEJ and MMEJ repair pathways.
• To investigate the role of chromatin context in DNA repair pathway choice.
• To understand how these regulatory mechanisms function in human cancer.

Main Methods:

• Utilized a dual MMEJ:NHEJ reporter system inserted into 19 distinct chromatin environments.
• Performed knockout screening to identify DNA repair proteins influencing pathway balance.
• Analyzed mutation distributions in human cancer types to assess the in vivo relevance of identified proteins.

Main Results:

• Identified numerous DNA repair proteins that alter the MMEJ:NHEJ balance in a chromatin-dependent manner.
• Proteins favoring NHEJ generally synergize with euchromatin (e.g., BRCA2, POLL).
• Proteins favoring MMEJ typically synergize with specific types of heterochromatin (e.g., FANC complex, ATM).
• Loss of several identified proteins affects the distribution of pathway-specific mutations between heterochromatin and euchromatin in human cancers.

Conclusions:

• Uncovered a complex network of proteins regulating MMEJ:NHEJ balance.
• Demonstrated that chromatin context is a critical determinant of DNA repair pathway choice.
• Provided insights into the chromatin-dependent regulation of DNA repair relevant to cancer biology.