A Dominant Mutation in Human RAD51 Reveals Its Function in DNA Interstrand Crosslink Repair Independent of Homologous...

Area of Science:

• Genetics and Molecular Biology
• DNA Repair Mechanisms
• Genomic Instability

Background:

• DNA interstrand crosslinks (ICLs) are severe DNA lesions requiring multiple repair pathways, including homologous recombination (HR).
• RAD51 (also known as FANCR) is a key recombinase protein crucial for HR-mediated repair.
• Fanconi anemia (FA) is a genetic disorder characterized by genomic instability and sensitivity to DNA crosslinking agents, often linked to defects in HR pathways.

Observation:

• A patient presented with a Fanconi anemia-like phenotype and a de novo heterozygous T131P mutation in RAD51/FANCR.
• In vitro studies showed the RAD51-T131P mutant had DNA-independent ATPase activity and impaired DNA pairing, exhibiting a dominant-negative effect.
• Despite the mutant, patient cells maintained homologous recombination proficiency due to a low mutant-to-wild-type RAD51 ratio.

Findings:

• Patient cells exhibited sensitivity to crosslinking agents, indicating a defect in ICL repair.
• Hyperphosphorylation of Replication Protein A (RPA) was observed, suggesting increased activity of DNA2 and Werner syndrome (WRN) helicase at ICL sites.
• This points to a crucial role for RAD51 function in ICL repair pathways that operate independently of homologous recombination.

Implications:

• Proper RAD51 function is essential for DNA interstrand crosslink repair, even in homologous recombination-independent pathways.
• The study elucidates a molecular mechanism for RAD51 and associated factors in maintaining genomic integrity outside of canonical HR.
• This provides insights into the pathogenesis of Fanconi anemia-like disorders and potential therapeutic targets.