Abstract 437: Novel function of the BAP1 nuclear deubiquitinase in the non-homologous end joining (NHEJ) pathway of double strand DNA repair

Abstract

Abstract Background- The deubiquitinating enzyme BAP1 is mutated in a hereditary cancer syndrome with increased risk of malignant pleural mesothelioma (MPM) and uveal melanoma and in subsets of sporadic cases of these cancers, as well as in clear cell renal carcinoma and intrahepatic cholangiocarcinoma. Methods and Results- We found that BAP1 knockdown is associated with increased DNA damage and that this effect of BAP1 knockdown is further enhanced by both X-irradiation and concomitant DNA-PKcs inhibitor II treatment in normal human mesenchymal stem cells and the MPM cell line H-Meso. A BAP1 mutant deficient in deubiquitinase activity is also associated with increased DNA damage in the H-Meso cells. Interactional total peptide (ITOP) analysis based on proteins identified by Liquid Chromatography coupled to tandem Mass Spectrometry (LC-MS/MS) of BAP1 protein complexes in H-Meso MPM cells and 293T cells identified known binding partners [HCF1, ASXL2, H2A] as well as possible novel interaction partners, notably PRKDC which encodes the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs) and functions with the Ku70/Ku80 heterodimer in the non-homologous end joining (NHEJ) pathway of DNA repair. Double stranded DNA damage resulted in prominent nuclear expression of BAP1 protein in H-Meso cells and phosphorylation of BAP1 at Serine 395. Overexpression of dominant negative BAP1 C91W mutant in MPM cells caused instability of DNA-PKcs. Although strong polyubiquitination of DNA-PKcs was observed upon DNA damage in MPM cells expressing BAP1 C91W, this polyubiquitination was not observed in the presence of wild type BAP1. A plasmid-based NHEJ assay also confirmed a significant effect of BAP1 on NHEJ activity. Conclusion- Functional complexes between BAP1 and the NHEJ family components point to a novel role in DNA repair and may shed light on BAP1's role as an important tumor suppressor Citation Format: Tatsuo Ito, Shigehisa Kitano, Hediye Erdjument-Bromage, Marc Ladanyi. Novel function of the BAP1 nuclear deubiquitinase in the non-homologous end joining (NHEJ) pathway of double strand DNA repair. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 437. doi:10.1158/1538-7445.AM2014-437