BRCT-domain protein BRIT1 influences class switch recombination.

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• DNA double-strand breaks (DSBs) are essential intermediates in immunoglobulin heavy chain (Igh) class switch recombination (CSR).
• Mechanisms for resolving DSBs during CSR to ensure proper DNA end-joining and prevent genomic instability are not fully understood.

Purpose of the Study:

• To identify novel factors involved in CSR by screening for proteins that regulate DSB resolution.
• To investigate the role of the BRCT-domain protein BRIT1 in CSR and DNA repair.

Main Methods:

• Utilized a targeted short-hairpin RNA screen in a B-cell lymphoma line.
• Generated mice with conditional genetic deletion of BRIT1.
• Assessed CSR efficiency and DNA break repair in ex vivo activated splenic B cells.
• Investigated protein interactions using immunoprecipitation and analyzed protein recruitment to the Igh locus.

Main Results:

• Identified BRIT1 as a critical effector of CSR.
• BRIT1 deletion in mice resulted in increased unrepaired Igh breaks and reduced CSR.
• BRIT1 interacts with phosphorylated H2AX via its BRCT domains and is recruited to the Igh locus in an AID- and H2AX-dependent manner.
• Depletion of MDC1 in BRIT1-deleted cells exacerbated the CSR defect, indicating a collaborative role.

Conclusions:

• BRIT1 is a novel factor essential for efficient CSR.
• Multiple BRCT-domain proteins, including BRIT1 and MDC1, cooperate in the optimal resolution of activation-induced cytidine deaminase (AID)-induced DSBs.
• These findings contribute to understanding the molecular mechanisms maintaining genomic integrity during B cell development and antibody diversification.