The BRCA2 R2645G variant increases DNA binding and induces hyper-recombination

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• The BRCA2 tumor suppressor protein is vital for maintaining genome integrity through DNA repair via homologous recombination (HR).
• Its C-terminal DNA binding domain (BRCA2CTD) interacts with single-stranded DNA (ssDNA) and DSS1, crucial for HR.
• Pathogenic variants often reside in this conserved domain, impacting BRCA2 function.

Purpose of the Study:

• To investigate the functional impact of the BRCA2 R2645G variant, located at the DSS1 interface.
• To determine how this variant affects ssDNA binding, HR, and cellular response to DNA damage and therapies.

Main Methods:

• In vitro characterization of BRCA2CTD R2645G variant's ssDNA binding.
• Analysis of homologous recombination (HR) and chromosomal instability in human cells expressing the variant.
• Assessment of variant effects on viability and drug sensitivity in mouse embryonic stem cells (mES).

Main Results:

• The R2645G variant unexpectedly increased BRCA2CTD ssDNA binding in vitro.
• Human cells with the variant showed hyper-recombination, chromosomal instability (chromatid gaps), and heightened PARP inhibitor sensitivity.
• In mouse cells, the variant affected viability and increased sensitivity to cisplatin and Mitomycin C.

Conclusions:

• BRCA2 interaction with ssDNA requires tight regulation to prevent excessive HR and chromosomal instability.
• The protein DSS1 may play a role in controlling this regulatory mechanism.
• Findings suggest potential clinical implications for breast cancer patients carrying similar BRCA2 variants.