BRCA1’s Phosphorylation Dependent Interaction with Abraxas, BACH1, and CtIP: Elucidation of the BRCA1 Mediated DNA Damage Response
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Date
2014-05
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The Ohio State University
Abstract
Women carrying germline mutations of the BRCA1 gene show an increased risk of breast and ovarian cancer, implying that the BRCA1 protein acts as a tumor suppressor in mammary and ovarian epithelial cells. The rationale of this thesis is to elucidate how BRCA1 suppresses tumor development..
To investigate BRCA1’s tumor suppression activity, our lab has recently developed a mouse model of the basal-like breast tumors that arise in women who carry BRCA1 mutations. Furthermore, this model was used successfully to define specific functions of BRCA1 that are and are not required for tumor suppression. Our lab has shown that deletion of Brca1 results in embryonic lethality, implying that the Brca1 protein is essential in embryonic development. Inactivation of Brca1 in mammary epithelial cells resulted in development of mammary tumors similar to the basal-like tumors observed in patients carrying BRCA1 mutations. These studies indicate that BRCA1 is essential for tumor suppression.
Many tumor-associated BRCA1 alleles have frameshift or nonsense mutations that delete one or both of the BRCT motifs (Fig. 1), suggesting that these motifs may operate either directly or through interaction with other proteins to suppress tumor development1. Our lab has shown that these BRCT repeats are essential for tumor suppression in part by playing a key role in homology directed DNA repair (HDR) of double-stranded breaks (DSBs), and repair of DNA interstrand cross-linking (ICL) damage. Specifically, the phosphoserine interaction of BRCA1 to other partners is essential in mediating error-proof DNA repair1. In addition, mice carrying Brca1 BRCT mutations are susceptible to spontaneous tumor development 1; 2. These results indicate that the BRCT motifs in BRCA1 facilitate DNA repair and tumor suppression either directly and/or via interactions with other DNA repair proteins. In particular, we are interested in the interaction with three phosphorylated isoforms of repair proteins: Abraxas, BACH1, and CtIP. The goal of this thesis is to elucidate the BRCT interacting partners of BRCA1 and their particular functions in maintaining genomic stability and facilitating DNA repair.
To accomplish this, our lab will cross mice to generate primary embryonic fibroblasts (pMEFs) containing mutations that ablate the phosphoserine interaction capability of the three phosphorylated isoforms of repair proteins,individually or in combination with the intact Brca1 protein. Further, a combination of mutations in the three repair proteins will be generated in cells with a deleted 53BP1 gene to study their specific role in ICL repair or HDR. Cells expressing these mutant alleles will be tested for sensitivity to DNA damaging agents, proliferation in culture, and HDR.
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DNA Repair and Tumor Suppression