DNA nicks induce mutational signatures associated with BRCA1 deficiency

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• BRCA1-deficient tumors exhibit distinct mutational signatures.
• The mechanisms driving these signatures are not fully understood.

Purpose of the Study:

• To investigate the role of DNA nicks versus double-strand breaks (DSBs) in generating mutational signatures in BRCA1-deficient cells.
• To elucidate the mechanisms by which BRCA1 deficiency contributes to cancer mutations.

Main Methods:

• Utilized CRISPR/Cas9 to induce nicks in DNA.
• Compared DNA repair pathways and resulting mutations in Brca1-deficient and wild-type cells.
• Analyzed chromosomal aberrations, micronuclei, gene conversion, and tandem duplications.

Main Results:

• One-ended DNA double strand breaks (DSBs) converted from nicks, rather than two-ended DSBs, caused more aberrations in Brca1-deficient cells.
• BRCA1 is crucial for homologous recombination of nick-converted DSBs and prevents biased gene conversion and tandem duplication.
• Aberrant repair of nick-converted one-ended DSBs in Brca1-deficient cells generated cancer-like mutational signatures (indels, translocations, tandem duplications).

Conclusions:

• DNA nicks converted during replication are a significant source of mutations in BRCA1-deficient cancers.
• Aberrant repair of these nick-converted DSBs underlies characteristic mutational signatures observed in BRCA1-deficient tumors.