Abstract 339: Heterozygous germline mutation in ABRAXAS causes BRCA1 mislocalization and DNA damage response defects

Abstract

Abstract Whilst heterozygous germline mutations in the ABRAXAS gene have been associated with hereditary breast cancer predisposition, their initial effect on promoting tumorigenesis at the cellular level has not been explored. Here, we demonstrate in patient-derived cells that the Finnish ABRAXAS founder mutation (c.1082G>A, Arg361Gln), even in the heterozygous state leads to decreased BRCA1 protein levels as well as reduced nuclear localization and foci formation of BRCA1 and CtIP. This causes disturbances in basal BRCA1-A complex localization, which is reflected by a restraint in error-prone DNA double-strand break (DSB) repair pathway usage, attenuated DNA damage response, deregulated G2-M checkpoint control and apoptosis. Most importantly, mutation carrier cells display a change in their transcriptional profile, which we attribute to the reduced nuclear levels of BRCA1. The current study clearly demonstrates how the Finnish ABRAXAS founder mutation acts in a dominant-negative manner on BRCA1 to promote genome destabilisation in heterozygous carrier cells. Citation Format: Robert Winqvist, Muthiah Bose, Juliane Sachsenweger, Niina Laurila, Ann Christin Parplys, Jonas Willmann, Leila Eshraghi, Thomas W. Dunlop, Marco Groth, Katrin Rapakko, Pentti Nieminen, Thomas W. Friedl, Lisa Heiserich, Felix Meyer, Hanna Tuppurainen, Ganapathy Raman Devarajan, Hellevi Peltoketo, Heli Nevanlinna, Katri Pylkäs, Kerstin Borgmann, Lisa Wiesmuller, Helmut Pospiech. Heterozygous germline mutation in ABRAXAS causes BRCA1 mislocalization and DNA damage response defects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 339.