Abstract 1404: Regulation of 53BP1 by the structural nuclear protein NuMA

Abstract

Abstract Cells repair DNA double-strand breaks (DSB) through two major pathways: homologous recombination (HR) and non-homologous end joining (NHEJ). The choice between these two pathways is critical to cell survival and is altered in cancers. 53BP1 is a protein with an important role in this choice: it promotes NHEJ by blocking CtIP-dependent DNA resection. Here, we present a new negative regulation mechanism of 53BP1 that relies on the structural protein NuMA. This protein participates in mitotic spindle assembly, influences chromatin organization during the interphase and modulates the chromatin response to DNA damage. We identified NuMA in a proteomics analysis of a 53BP1-interacting proteins. The interaction was confirmed by reciprocal immunoprecipitation and with a FRET assay. In response to DSB, we measured greater than 50% decreased 53BP1-NuMA binding, which suggests that NuMA may restrain 53BP1 diffusion in the absence of DNA damage. Fluorescence correlation spectroscopy (FCS) measurements in cells expressing GFP-tagged 53BP1 support this hypothesis. Moreover, NuMA overexpression inhibited 53BP1 recruitment at DNA damage sites in laser microirradiation assays, whereas NuMA silencing had the opposite effect. 53BP1 plays an essential role in B cell class switch recombination and mediates PARP inhibitor sensitivity in BRCA1-null cells. NuMA overexpression prevented immunoglobulin switching, and overwrote cancer cell sensitivity to PARP inhibitors to the same extent as 53BP1 loss of function. Our results help understand how 53BP1 is controlled, and shed light on the mechanisms regulating PARPi sensitivity. Citation Format: Naike Salvador Moreno. Regulation of 53BP1 by the structural nuclear protein NuMA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1404. doi:10.1158/1538-7445.AM2017-1404