Abstract 4202: PD-L1 promotes DNA double-strand-break repair and radioresistance in cancer

Abstract Resistance to radiotherapy is a major barrier during cancer treatment. Using genome-scale CRISPR/Cas9 screening, we identified that the CD274 gene, which encodes PD-L1, confers lung cancer cell resistance to ionizing radiation (IR). Depletion of endogenous PD-L1 retarded the repair of IR-induced DNA double-strand breaks (DSBs). Treatment of lung cancer cells with IR or glycosylation inhibitor tunicamycin resulted in translocation of PD-L1 from the membrane into nucleus in a manner that is dependent on deglycosylation of PD-L1 at N219. CMTM6 transports PD-L1 from the cytoplasm into the nucleus via direct interaction. PD-L1 loss downregulated non-homologous end joining (NHEJ) while overexpression of PD-L1 upregulated NHEJ. Mechanistically, after IR exposure, PD-L1 was recruited to DSB sites to form foci, and to interact with Ku in the nucleus. PD-L1 not only enhanced Ku binding to DSB DNA but also facilitated binding of Ku to other NHEJ factors. PD-L1 deglycosylation and its interaction with Ku occurred in a cell cycle-dependent manner. Interaction between the IgC domain of PD-L1 and the core domain of Ku is required for PD-L1 to accelerate NHEJ-mediated DSB repair and produce radioresistance. Thus, PD-L1, in addition to its immune inhibitory activity, also acts as a mechanistic driver for NHEJ-mediated DSB repair in cancer. Specifically targeting this novel function of PD-L1 may represent an attractive strategy for cancer therapy. Citation Format: Zhen Shu, Bhakti Dwivedi, Jeffrey Switchenko, David Yu, Xingming Deng. PD-L1 promotes DNA double-strand-break repair and radioresistance in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4202.