Abstract 1187 A novel activity of the RAD52 protein that is essential for the viability of BRCA-deficient breast and ovarian cancer cells

RAD52 functions in homologous recombination (HR): a major pathway for repair of DNA double-strand breaks (DSBs), the most lethal DNA lesion type. HR is also essential for faithful segregation of homologous chromosomes during gametogenesis. Disfunctions in HR lead to genome instability causing cancer or infertility. Mutations in HR genes BRCA1 and BRCA2 are responsible for nearly half of all hereditary breast and ovarian cancers. While mutations in RAD52 cause no discernible HR phenotype in normal human cells; in BRCA1/2-deficient cancer cells, RAD52 inactivation becomes lethal. This synthetically lethal BRCA/RAD52 relationship renders RAD52 a promising therapeutic target. However, the mechanism underlying RAD52-BRCA synthetic lethality is poorly understood. The human recombinase RAD51 plays a central role in HR. RAD51 binds to ssDNA and promotes a search for homologous undamaged dsDNA to generate joint molecules (D-loops) that provide a template for DSB repair. However, in BRCA-deficient cancer cells the activity of RAD51 is suppressed. We found previously that the RAD52 protein also catalyzes DNA pairing. However, it does so in an inverse way, by forming a complex with dsDNA and promoting strand exchange with ssDNA. The RAD52-dsDNA complex can also interact with RNA resulting in formation of DNA-RNA hybrids. Here, using biochemical, biophysical, and structural methods we investigated the mechanism of this novel RAD52 activity. We found that this RAD52 activity is responsible for the generation of highly stable recombinational intermediates: double-D-loops and RNA-D-loops (R/D-loops). We suggest that this non-canonical DNA pairing activity of RAD52 contributes to the viability of BRCA-deficient cancer cells. These findings will facilitate our ongoing work of developing RAD52 inhibitors targeting BRCA-deficient cancer cells. Funding: R01 GM136717, R01 CA23728 (A.V.M.). Congressionally Directed Medical Research Programs BC191160 (AV.M.) A.V.M. is the holder of the Joe R. and Teresa Lozano Long Chair in Cancer Research and is recipient of a CPRIT REI Award (RR210023) and UT System Faculty STARs Award.