MRN-CtIP, EXO1, and DNA2-WRN/BLM act bidirectionally to process DNA gaps in PARPi-treated cells without strand...

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• Single-stranded DNA (ssDNA) gaps are critical in maintaining genome stability.
• ssDNA gaps influence the sensitivity of BRCA1/2-deficient tumors to PARP inhibitors (PARPi).

Purpose of the Study:

• To elucidate the distinct mechanisms by which nucleases resect ssDNA gaps.
• To understand how ssDNA gap resection impacts DNA repair and PARPi sensitivity in BRCA-deficient cells.

Main Methods:

• Single-molecule DNA fiber analysis
• Electron microscopy
• Biochemical assays

Main Results:

• MRN, CtIP, EXO1, and DNA2-WRN/BLM enzymes resect ssDNA gaps via a novel mechanism distinct from DNA end resection.
• MRN utilizes its 3'-to-5' exonuclease activity, stimulated by CtIP, for ssDNA gap resection.
• EXO1 and DNA2-WRN/BLM independently resect the 5' end of ssDNA gaps.
• Excessive resection in BRCA1-deficient cells treated with PARPi leads to larger ssDNA gaps, impaired repair, and subsequent DNA breaks.

Conclusions:

• The study reveals specific nucleases and pathways involved in ssDNA gap processing.
• Altered ssDNA gap resection contributes to DNA breaks and PARPi sensitivity in BRCA-deficient tumors.
• Findings enhance understanding of DNA metabolism and PARPi therapeutic strategies.