Replication fork reversal triggers fork degradation in BRCA2-defective cells.

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• BRCA2 is a tumor suppressor crucial for homologous recombination (HR) and replication fork stability.
• Defects in BRCA2 lead to genomic instability and increased sensitivity to chemotherapy.
• Mechanisms linking BRCA2 deficiency to fork instability and breakage remain unclear.

Purpose of the Study:

• To investigate the role of BRCA2 in protecting stalled replication forks from degradation.
• To identify factors involved in fork degradation in BRCA2-defective cells.
• To elucidate the interplay between fork remodeling, stability, and chromosomal integrity.

Main Methods:

• DNA fiber spreading assays to visualize replication intermediates.
• Direct visualization of replication fork structures.
• Analysis of gene inactivation effects on fork stability and chromosome integrity.

Main Results:

• Reversed replication forks serve as entry points for degradation in BRCA2-defective cells.
• RAD52, MRE11, and PTIP promote stalled fork degradation and chromosomal breakage.
• Inactivating these factors restores fork frequency and chromosome integrity.
• Impairing fork reversal prevents degradation but increases breakage, uncoupling fork protection and chromosome stability.
• BRCA2 facilitates RAD51 nucleofilament assembly on regressed fork arms for protection.

Conclusions:

• BRCA2 is essential for protecting reversed replication forks from degradation by assembling stable RAD51 nucleofilaments.
• RAD52 plays a significant role in promoting fork degradation and chromosomal breakage in BRCA2-deficient cells.
• These findings illuminate the complex roles of HR factors in maintaining genome stability and have implications for cancer therapy.