2475 - Investigating the SCARA5-NDUFS2 Axis in NAD?-Dependent DNA Repair and Radiosensitivity in Lung Adenocarcinoma
Presenter(s)
Y. He1, K. Wan2, W. Zhou1, T. Xiang3, and Y. Wu1; 1Department of Radiation Oncology, Chongqing University Cancer Hospital, Chongqing, China, 2Chongqing University Cancer Hospital, School of Medicine, Chongqing University, Chongqing, China, 3Chongqing Key Laboratory for the Mechanism and Intervention of Cancer Metastasis, Chongqing University Cancer Hospital, Chongqing University, Chongqing, China
Purpose/Objective(s): Lung adenocarcinoma (LUAD) is the dominant type of lung neoplasms, and radiotherapy is its mainstay treatment, yet poor prognosis caused by radioresistance remains problematic. Scavenger receptor class A member 5 (SCARA5) is a tumor suppressor implicated in iron metabolism and oxidative stress. However, the molecular mechanisms of SCARA5-mediated radioresponse in LUAD remain unclear.
Materials/Methods: Multi-omics integration of transcriptomic data, DNA methylome profiles, and radioresponse datasets was performed to identify candidate genes. Prognostic significance was evaluated using public survival databases. Radiosensitivity was assessed in vitro using clonogenic survival assays and in vivo using subcutaneous xenograft models. Radiation-induced DNA damage was quantified by comet assay and ?-H2AX immunofluorescence. Homologous recombination (HR; DR-GFP) and non-homologous end joining (NHEJ; EJ5-GFP) efficiencies were measured using plasmid-based GFP reporters. Mechanistic targets were identified through immunoprecipitation–mass spectrometry (IP-MS) integrated with transcriptomic analysis and validated by Western blotting. Intracellular NAD? levels, NAD?/NADH ratios, and PARP activity were measured, and rescue experiments were performed using NAD? precursors.
Results: Multi-omics integration identified SCARA5 as the sole overlapping candidate gene associated with radioresponse. SCARA5 was hypermethylated and downregulated in LUAD, with low expression correlating with poor prognosis. Immunohistochemistry and Western blot further confirmed that the expression of SCARA5 in tumor tissues was lower than that in normal tissues. SCARA5 overexpression significantly reduced clonogenic survival in vitro and tumor growth in vivo following irradiation and was associated with increased radiation-induced DNA damage and impaired HR and NHEJ repair efficiency. Mechanistically, NDUFS2, a mitochondrial complex I core subunit, was identified as a SCARA5-interacting protein. SCARA5 promoted ubiquitination-mediated degradation of NDUFS2, leading to reduced intracellular NAD? levels and NAD?/NADH ratio, decreased PARP activity and PARylation, and impaired DNA repair. Supplementation with NAD? precursors partially rescued DNA repair capacity and radiosensitivity.
Conclusion: SCARA5 enhances radiosensitivity in lung adenocarcinoma by promoting ubiquitination-mediated degradation of NDUFS2, leading to reduced NAD? availability, suppressed PARP activity, and impaired DNA damage repair. Targeting the SCARA5–NDUFS2–NAD? axis may represent a therapeutic strategy to overcome radioresistance.