Abstract 1471: Roles of the KU70 C-terminus SAP domain in resilience to ionizing radiation

Abstract Ionizing radiation (IR) is a critical modality in cancer therapy but also carries carcinogenic risks, necessitating precise optimization. The KU70 protein is integral to DNA repair, primarily known for its N-terminal domain's role in dimerizing with KU80 to repair DNA double-strand breaks (DSBs). Our study aims to elucidate the function of the less-explored C-terminal SAP domain of KU70. We engineered a variant, KU70-∆SAP, lacking this domain, to assess its role in cellular responses to radiation. KU70-∆SAP mice exhibited increased sensitivity to an 8 Gy dose of whole-body irradiation (TBI), significantly affecting hematopoietic stem cells, with marked reductions in long-term and short-term stem cells, as well as in common myeloid and granulocyte-monocyte progenitors post-irradiation. These findings suggest that the SAP domain is crucial for the survival of hematopoietic stem and progenitor populations following IR-induced damage, as well as for the subsequent hematopoiesis necessary to replenish bone marrow and blood. Further analysis using mouse embryonic fibroblast (MEF) clones from our mouse model indicated that deletion of the SAP domain impaired KU70's early recruitment to UV-laser-induced DSB sites, coinciding with decreased Ligase IV levels, an essential enzyme for DNA repair, and increased γH2AX signals, which indicate DNA damage and repair inefficiency. These results highlight the SAP domain's essential role in orchestrating effective DNA repair mechanisms post-IR and enhance our understanding of KU70’s function in improving radiation therapy outcomes and bolstering cellular resilience against radiation-induced damage. Citation Format: Yuan Wang, Michael S. Czap, Hailey Kim, Huimei Lu, Jingmei Liu, Zhiyuan Shen. Roles of the KU70 C-terminus SAP domain in resilience to ionizing radiation [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 1471.