Competition between PARP-1 and Ku70 control the decision between high-fidelity and mutagenic DNA repair

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Antibody affinity maturation requires targeted gene mutation for immune response.
• DNA repair pathways can be mutagenic or high-fidelity, with location determining the outcome.
• PARP-1's BRCT domain is crucial for mutagenic repair in antibody gene diversification.

Purpose of the Study:

• To investigate the mechanism by which PARP-1 targets mutagenic repair in antibody genes.
• To identify proteins interacting with PARP-1's BRCT domain during this process.
• To elucidate the role of Ku70 and Lig4 in PARP-1-mediated DNA repair.

Main Methods:

• Immunoprecipitation of PARP-1's BRCT domain to identify interacting proteins.
• DNA-free pulldown assays to assess DNA-binding independence of interactions.
• Sequencing of IgL variable regions in PARP-1 deficient cells lacking Ku70 or Lig4.

Main Results:

• PARP-1's BRCT domain interacts with Ku70 and the DNA-PK complex in a DNA-independent manner.
• Ku70 or Lig4 deficiency restores GCV (gene conversion) to PARP-1 deficient cells.
• PARP-1 promotes mutagenic repair by inhibiting the high-fidelity repair mediated by Ku70/Lig4.

Conclusions:

• PARP-1 functions by suppressing high-fidelity repair, thereby favoring mutagenic repair for antibody diversification.
• The interaction between PARP-1, Ku70, and DNA-PK is key to regulating DNA repair pathway choice.
• This targeted repair mechanism ensures genomic stability while allowing essential antibody gene modifications.