Abstract GMM-027: DYNLL1 INHIBITS DNA END RESECTION IN BRCA1-DEFICIENT CELLS AND REGULATES PARP INHIBITOR SENSITIVITY
Authors: He Yizhou Joseph , Meghani Khyati , Caron Marie-Christine , Yang Chunyu , Ronato Daryl A. , Bian Jie , Sharma Anchal , Miller Jessica , Joshi Niraj , Detappe Alexandre , Doench John G. , Legube Gaelle , Root David E. , D'Andrea Alan D. , Drané Pascal , De Subhojyoti , Konstantinopoulos Panagiotis , Masson Jean-Yves , Chowdhury Dipanjan 
Published: June 2021

Abstract
High-grade serous ovarian carcinoma (HGSOC) patients with germline mutations in BRCA1/2 exhibit high sensitivity and improved outcome to double strand DNA break (DSB)-inducing agents [i.e. platinum and Poly(ADP-ribose) polymerase inhibitors (PARPi)] due to underlying defects in DNA repair via homologous recombination (HR). Due to their effectiveness, three PARP inhibitors (olaparib, rucaparib, niraparib) have recently gained FDA approval for the treatment of HGSOCs. However, de novo and acquired resistance to these agents is common even in the BRCA mutation carriers, and pose a significant, and unsolved, clinical challenge. Therefore, we adopted a systematic approach to comprehensibly identify unexplored factors/pathways that could be responsible for PARPi/platinum resistance in BRCA-defective HGSOC patients.
Here we identify DYNLL1 as a negative regulator of DNA end resection through a loss-of-function CRISPR screen in BRCA1-mutant ovarian carcinoma cells. DNA end resection is a vital process that initiates homologous recombination (HR)-mediated repair of double-stranded DNA breaks (DSBs), and consequently influences genome stability. In BRCA-defective HGSOC patients, DNA end resection is greatly compromised and contribute to the loss of HR and PARP inhibitor sensitivity. Loss of DYNLL1 allows DNA end resection and restores HR in BRCA1-mutant cells, thereby inducing resistance to platinum drugs and PARP inhibitors. In primary ovarian carcinomas low BRCA1 expression correlates with increased chromosomal aberrations, and the junction sequences of somatic structural variants indicate the loss of HR. Concurrent decrease in DYNLL1 expression in BRCA1 low ovarian cancers ‘rescued' this phenotype with reduced genomic alterations and increased homology at putative lesions. DYNLL1 limits nucleolytic degradation of DNA ends by interacting with the DNA end resection machinery (MRN complex, BLM helicase and DNA2) in cells. The impact of DYNLL1 on end resection can be re-capitulated in vitro and this is dependent on direct interaction with MRE11. In the absence of exogenous stress, depletion of DYNLL1 slows DNA replication fork progression due to ectopic activity of MRE11. Therefore, we infer that DYNLL1 is an important anti-resection factor that significantly influences genomic stability and response to DNA damaging chemotherapy.
Citation Format: Yizhou Joseph He, Khyati Meghani, Marie-Christine Caron, Chunyu Yang, Daryl A. Ronato, Jie Bian, Anchal Sharma, Jessica Miller, Niraj Joshi, Alexandre Detappe, John G. Doench, Gaelle Legube, David E. Root, Alan D. D'Andrea, Pascal Drané, Subhojyoti De, Panagiotis Konstantinopoulos, Jean-Yves Masson, and Dipanjan Chowdhury. DYNLL1 INHIBITS DNA END RESECTION IN BRCA1-DEFICIENT CELLS AND REGULATES PARP INHIBITOR SENSITIVITY [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-027.