RAD52 influences the effect of BRCA1/2 missense variants on homologous recombination and gene reversion in Saccharomyces cerevisiae

The breast and ovarian cancer susceptibility genes, BRCA1 and BRCA2, are key players in the homologous recombination (HR) repair pathway and act as tumor suppressors by maintaining genome stability. The yeast Saccharomyces cerevisiae has no BRCA1/2 homolog; however, a number of HR genes are evolutionary conserved between human and yeast. Among them, RAD52 is involved in DNA double strand break (DSB) repair by HR, and promotes genome stability. We previously reported that the heterologous expression of cancer-associated BRCA1/2 missense variants in growing yeast cultures affects both spontaneous HR and gene reversion (GR) suggesting that yeast could be a reliable system to assess the functional impact of variants. Because inhibition of Rad52p is lethal in BRCA1/2 mutated tumors, and Rad52p is conserved between humans and yeast, we asked if the effect of BRCA1/2 variants on HR and GR could be affected by loss of RAD52. We found that the rad52 increment mutation predominantly suppressed the stimulation of HR in yeast by pathogenic BRCA1 variants but also facilitated increased GR by pathogenic variants. Conversely, the rad52 increment mutation stimulated HR by a pathogenic BRCA2 variant in yeast but had no effect on GR. These results demonstrate a functional interplay between the pathogenic BRCA1/2 variants and Rad52p in budding yeast, supporting the use of budding yeast as a suitable system for evaluating potential chemotherapeutic strategies. Yeast is a good model to investigate the complex genetic interaction in cancer.