Abstract
Replication stress (RS) is a major source of genomic instability and is intrinsic to cancer cells. RS is also the consequence of chemotherapeutic drugs for treating cancer. However, adaptation to RS is also a mechanism of resistance to chemotherapy. BRCA2 deficiency results in replication stress in human cells. BRCA2 protein's main functions include DNA repair by homologous recombination (HR) both at induced DNA double-strand breaks (DSB) and spontaneous replicative lesions. At stalled replication forks, BRCA2 protects the DNA from aberrant nucleolytic degradation and is thought to limit the appearance of ssDNA gaps by arresting replication and via post-replicative HR. However, whether and how BRCA2 acts to limit the formation of ssDNA gaps or mediate their repair, remains ill-defined. Here, we use breast cancer variants affecting different domains of BRCA2 to shed light on this function. We demonstrate that the N-terminal DNA binding domain (NTD), and specifically, its dsDNA binding activity, is required to prevent and repair/fill-in ssDNA gaps upon nucleotide depletion but not to limit PARPi-induced ssDNA gaps. Thus, these findings suggest that nucleotide depletion and PARPi trigger gaps via distinct mechanisms and that the NTD of BRCA2 prevents nucleotide depletion-induced ssDNA gaps.