DNA double-strand breaks (DSBs) can cause genomic instability and cancer through point mutations and genomic translocations if they are not properly repaired. DSBs are repaired by two major pathways: homologous recombination (HR) or nonhomologous end joining (NHEJ). The cellular choice between these two pathways is critical to cell survival and is altered in cancers. 53BP1, which promotes NHEJ by blocking CtIP-dependent DNA resection, is a key protein mediating repair pathway choice. Here, we present a new negative regulation mechanism of 53BP1 that relies on the structural nuclear protein NuMA. Apart from its role in mitotic spindle assembly, NuMA influences chromatin organization during the interphase and modulates the chromatin response to DNA damage. We identified an interaction between NuMA and 53BP1 by proteomics analysis of a 53BP1 pull-down and confirmed this interaction by NuMA immunoprecipitation. We measured greater than 50% decreased 53BP1-NuMA binding in response to DSB, which suggest that, in the absence of DNA damage, NuMA may restrain 53BP1 diffusion. This hypothesis is supported by fluorescence correlation spectroscopy (FCS) measurements in cells expressing GFP-tagged 53BP1, as well as by microirradiation experiments in which NuMA overexpression or silencing inhibited or promoted 53BP1 recruitment at DNA damage sites, respectively. 53BP1 has an essential role in B cell class switch recombination (CSR) and mediates PARPi sensitivity in BRCA1-null cells. We will present how modulating NuMA expression affects both aspects of 53BP1 function. The results from our work will help to understand how 53BP1 is controlled, and shed light on the mechanisms regulating this modulator of PARPi sensitivity in the presence or absence of DNA damage.

Citation Format: Naike Salvador Moreno. Regulation of 53BP1 by the structural nuclear protein NuMA. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2755.