Mechanisms Underlying Replication Stress And Genome Instability Upon BRCA2 Deficiency

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PROJECT SUMMARY BRCA2 mutation carriers are highly predisposed to breast and ovarian cancer (60% risk for breast cancer and 30-40% for ovarian cancer), and also have increased risk for other cancers like prostate and pancreatic. However, the mechanisms underlying these phenomena are still poorly understood. The molecular pathogenic steps, especially the earliest ones that drive the transition of normal cells (BRCA2mut/+) in a BRCA2 mutation carrier to tumor cells are largely unknown. Experiments detailed in this proposal will provide valuable clues to what those early steps could be. The knowledge and understanding of the way a normal, presumably healthy cell in BRCA2 mutation carrying individual starts becoming a tumor cell, will give us a much-needed early advantage to help design preventive strategies and contribute towards decreasing B2 mutant cancer incidence. The experimental strategy described in this proposal is based on our recently published work that shows increased single stranded DNA (ssDNA) accumulation in BRCA2 deficient cells, and on our preliminary data that shows high abasic site and uracil accumulation in BRCA2 deficient cells. Our preliminary data also shows defective nucleotide excision repair (NER) pathway in BRCA2 deficient cells. Based on our strong preliminary data, we propose to study the role of APOBEC/AID family of cytosine deaminases in generating abasic sites in BRCA2 deficient cells. We will also use BRCA2 patient derived tissue to design new ways to classify variants of unknown significance and also learn how increased abasic site and uracil in B2 heterozygous cells could contribute to genomic instability and tumorigenesis. Finally, we will also study whether BRCA2 deficient cells are defective in NER when undergoing replication stress, and if this weakness in BRCA2 mutant tumors could be targeted by combination drug therapy. This study provides an opportunity to address the question of early DNA damaging events that drive BRCA2 mutant tumorigenesis, and has the potential to provide the much needed, critical information that will help with the design of effective cancer prevention and therapeutic strategies for BRCA2 mutation bearing women.