ATM orchestrates the DNA-damage response to counter toxic non-homologous end-joining at broken replication forks

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Mutations in the ATM tumor suppressor gene lead to hypersensitivity to DNA-damaging chemotherapy.
• Understanding resistance mechanisms is crucial for optimizing cancer treatment strategies.

Purpose of the Study:

• To identify genetic factors conferring resistance to topotecan in ATM-deficient cells.
• To elucidate the role of DNA repair pathways in topotecan sensitivity and resistance.

Main Methods:

• Genome-wide CRISPR-Cas9 screening was employed in cells treated with the topoisomerase I inhibitor, topotecan.
• Analysis of DNA repair pathway engagement, including homologous recombination and non-homologous end-joining (NHEJ).

Main Results:

• Inactivating terminal components of the NHEJ machinery or the BRCA1-A complex specifically conferred topotecan resistance to ATM-deficient cells.
• ATM-mutant cells exhibit delayed homologous recombination and increased susceptibility to toxic NHEJ at single-ended double-strand breaks (DSBs).
• Disrupting NHEJ or the BRCA1-A complex suppressed topotecan toxicity in ATM-deficient cells.

Conclusions:

• ATM plays a critical role in preventing toxic LIG4-mediated chromosome fusions by ensuring timely homologous recombination.
• Suppressor mutations in ATM-mutant backgrounds differ from those in BRCA1-mutant scenarios, indicating potential for patient stratification.
• These findings suggest new therapeutic vulnerabilities and opportunities for clinical exploitation in ATM-mutant cancers.