Rev7 and 53BP1/Crb2 prevent RecQ helicase-dependent hyper-resection of DNA double-strand breaks

Area of Science:

• Molecular Biology
• Cancer Research
• Genetics

Background:

• Poly(ADP ribose) polymerase inhibitors (PARPi) are effective against cancers with defective homology-directed repair (HDR) of DNA double-strand breaks (DSBs).
• PARPi resistance in preclinical models is associated with altered nucleolytic processing (resection) at DSB 5' ends.
• Loss of 53BP1 or Rev7/MAD2L2/FANCV leads to derepressed resection and PARPi resistance, but the underlying mechanisms remain unclear.

Purpose of the Study:

• To investigate the mechanisms by which 53BP1 and Rev7 regulate DNA resection and PARPi resistance.
• To differentiate the roles of distinct resection machineries in response to DNA damage.

Main Methods:

• Development of a novel single-cell microscopy assay in *S. pombe* to simultaneously observe different phases and machineries of DNA resection.
• Interrogation of resection pathways in the context of 53BP1 and Rev7 function.

Main Results:

• The 53BP1 orthologue and Rev7 were found to specifically inhibit long-range resection via the RecQ helicase-dependent pathway.
• This repression by 53BP1 and Rev7 prevents hyper-resection.
• The findings implicate the 'rewiring' of BRCA1-deficient cells to an Exo1-independent hyper-resection pathway as a driver of PARPi resistance.

Conclusions:

• 53BP1 and Rev7 act as critical repressors of the RecQ helicase-Dna2 resection pathway, thereby preventing excessive DNA end resection.
• Understanding these regulatory mechanisms is crucial for overcoming PARPi resistance in cancer therapy.