Chromatin reader Brd4 functions in Ig class switching as a repair complex adaptor of nonhomologous end-joining

Area of Science:

• Immunology
• Molecular Biology
• Epigenetics

Background:

• Class switch recombination (CSR) is a critical B cell process involving DNA breaks and repair at the immunoglobulin heavy-chain locus.
• While factors promoting DNA break generation by activation-induced cytidine deaminase (AID) are known, the role of chromatin adaptors in DNA repair during CSR is unclear.

Purpose of the Study:

• To investigate the involvement of chromatin adaptors, specifically Brd4, in the DNA repair phase of class switch recombination.
• To elucidate the mechanism by which Brd4 influences nonhomologous end-joining (NHEJ) repair during CSR.

Main Methods:

• Depletion of Brd4 from chromatin in B cells.
• Analysis of DNA break generation and repair during CSR induced by AID and I-SceI.
• Assessment of repair factor recruitment (53BP1, uracil DNA glycosylase) to switch regions.
• Evaluation of switch junctional microhomology and Igh/c-myc translocation.

Main Results:

• Brd4 depletion impaired CSR without affecting DNA break formation.
• Brd4 was recruited to DNA break sites.
• Brd4 inhibition reduced the accumulation of 53BP1 and uracil DNA glycosylase at switch regions.
• Perturbation of switch junctional microhomology and reduced Igh/c-myc translocation were observed upon Brd4 inhibition.

Conclusions:

• Brd4 is a critical chromatin adaptor for the nonhomologous end-joining (NHEJ) repair pathway during class switch recombination.
• Brd4 functions as a chromatin platform, facilitating the recruitment of essential DNA repair components.
• These findings highlight Brd4's role in both CSR and general DNA damage repair mechanisms.