The Role of BRCA1 Domains and Motifs in Tumor Suppression

The purpose of this research is to classify BRCA1 variants for which cancer association is not known called variants of uncertain significance or VUS. To approach this problem we hypothesized that poorly characterized but conserved domains in BRCA1 directly participate in its tumor suppression function. To test this hypothesis we set out to develop 1. A system of functional assays to test the functions of domains anywhere in coding region of BRCA1. Our results indicate that the intra S phase checkpoint function of BRCA1 can be used for further classification of BRCA1 unclassified variants for their cancer association as well as for analyzing BRCA1 function. 2. We also studied the function of under explored but conserved small motifs in BRCA1. Using as bait in yeast two hybrid screening one of these motifs we identified the cytoskeletal protein Filamin A as a specific BRCA1 binding partner. Their interaction is abrogated by a mutation found in breast cancer families. We systematically evaluated DNA damage signaling after treatment with ionizing radiation in cells that lack Filamin A. We found that these cells have an impaired BRCA1 and Rad51 foci formation and accumulate single stranded DNA. Our data showed that lack of Filamin A leads to an impairment in both HR and NHEJ repair pathways.