Abstract 229: A cross-species approach to identifying genetic modifiers of BRCA1-associated breast cancer risk

Abstract

Abstract Background: Although carriers of germline mutations of BRCA1 have a high risk of developing breast and ovarian cancers, penetrance is not complete, and it is likely that unidentified genes modify the risk for individual mutation carriers. We hypothesize that genes that modify the penetrance of cancer in BRCA1 carriers interact with BRCA1 mutations to confer increased sensitivity to DNA damage at the cellular level, and that cellular sensitivity to DNA damage can be used as an intermediate phenotype to predict breast cancer susceptibility in humans. Objective: Our goal is to test a cross-species systems biology approach to predict gene-gene interactions underlying breast cancer susceptibility, using sensitivity to DNA damage as an intermediate phenotype. Experiment Procedure: The yeast RAD9 gene is one putative homolog of the human breast tumor suppressor gene BRCA1. We conducted a genome-wide screen to identify genes that interact with a rad9 mutation to confer enhanced sensitivity to DNA damage. The yeast screen identified 25 interactions, from which we selected 10 candidate gene-gene interactions to be tested in human breast epithelial cells. To determine if the gene-gene interactions discovered in yeast are conserved in human mammary epithelial cells, we built stable human mammary epithelial cells (MCF10A) capable of single- or double-gene knockdown via lentivirus-mediated RNA interference. Cells confirmed for intended gene knockdown were subject to a clonogenic assay to determine if increased sensitivity to DNA damage can be observed in double gene vs. single gene knockdowns. Results: Among the 10 pairs of interactions tested in MCF10A cells, two genes, HLTF and MGMT, were found to interact with BRCA1 to confer enhanced DNA damage sensitivity, based on a clonogenic assay. Cells with combined knockdown of BRCA1 and HLTF show increased sensitivity to a chronic low dose of MMS treatment compared with those with only single knockdown of BRCA1 or HLTF. In addition, distinct morphological features were observed in double knockdown cells with MMS treatment. Cells became enlarged and showed a flat, senescence-like morphology. Even a low concentration of 0.001% MMS induced a strong and irreversible growth arrest in cells with combined knockdown of BRCA1 and HLTF, but not in the single knockdown cells. Conclusion: Our results suggest that it is feasible to use a cross-species (yeast-to-human) comparative systems genetics strategy to identify gene-gene and pathway-pathway interactions. Ongoing studies are aimed at determining whether any of the observed gene-gene interactions contribute to breast cancer penetrance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 229. doi:10.1158/1538-7445.AM2011-229