Repair of G1 induced DNA double-strand breaks in S-G2/M by alternative NHEJ

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• The non-homologous end-joining (NHEJ) pathway is crucial for repairing DNA double-strand breaks (DSBs).
• Alternative NHEJ pathways are thought to operate throughout the cell cycle, especially when canonical pathways are compromised.

Purpose of the Study:

• To investigate the cell cycle-dependent repair of DSBs in G1-arrested cells.
• To elucidate the mechanisms and consequences of alternative NHEJ in the absence of canonical repair factors.

Main Methods:

• Induction of DNA breaks in G1-arrested XRCC4-deficient cells.
• Tracking DNA repair upon cell cycle progression into S-G2/M phases.
• Analysis of repair products for DNA end resection, micro-homologies, and chromosomal translocations.

Main Results:

• DSB joining is non-functional in G1-arrested XRCC4-deficient cells.
• Cell cycle entry into S-G2/M restores DSB repair via Pol θ-dependent, PARP1-independent alternative NHEJ.
• Repair products exhibit extensive DNA end resection, micro-homologies, and lead to chromosome translocations.
• A synthetic lethal interaction between XRCC4 and Pol θ was identified for G1 DSBs.

Conclusions:

• Alternative NHEJ of G1 DSBs during S-G2/M progression is a significant source of genomic instability.
• This pathway represents a potential therapeutic target for DNA repair-based cancer treatments.