A yeast recombination assay to characterize human BRCA1 missense variants of unknown pathological significance

The BRCA1 tumor suppressor gene is found mutated in familial breast cancer. Although many of the mutations are clearly pathological because they give rise to truncated proteins, several missense variants of uncertain pathological consequences have been identified. A novel functional assay to screen for BRCA1 missense variants in a simple genetic system could be very useful for the identification of potentially deleterious mutations. By using two prediction computer programs, Sorting Intolerant from Tolerant (SIFT) and Polymorphism Phenotyping (PolyPhen), seven nonsynonymous missense BRCA1 variants likely disrupting the gene function were selected as potentially deleterious. The budding yeast Saccharomyces cerevisiae (S. cerevisiae) was used to test these cancer-related missense mutations for their ability to affect cell growth and homologous recombination (HR) at the HIS3 and ADE2 loci. The variants localized in the BRCA1 C-Terminus (BRCT) domain did not show any growth inhibition when overexpressed in agreement with previous results. Overexpression of either wild-type BRCA1 or two neutral missense variants did not increase yeast HR but when cancer-related variants were overexpressed a significant increase in recombination was observed. Results clearly showed that this genetic system can be useful to discriminate between neutral and deleterious BRCA1 missense variants.