Presenter(s)
R. Xu, J. Zhai, X. Chen, X. Xu, and M. Deng; State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
Purpose/Objective(s):
Radiotherapy is a cornerstone therapy, and tumor DNA repair capacity determines therapeutic efficacy and radiosensitivity. This study aims to elucidate the transcriptional and non-transcriptional regulatory mechanisms of the RNA-binding protein LUC7L3 in DNA damage repair induced by radiotherapy and to evaluate its potential as a novel target for radiosensitization.Materials/Methods:
LUC7L3 post-translational modifications and subcellular localization are assessed by mass spectrometry, immunoblotting, immunofluorescence, and site-directed mutagenesis. Protein interactions were examined by co-immunoprecipitation. Chromatin accessibility and transcription factor binding at HR and base excision repair (BER) gene promoters were evaluated by ATAC-seq and ChIP-qPCR. CRISPR/Cas9-mediated LUC7L3 knockout cell lines were generated. HR and NHEJ efficiencies were quantified using reporter assays. Radiosensitivity was assessed by clonogenic survival and CCK-8 assays. In vivo therapeutic response was evaluated using CDX and PDX tumor models. A cell-penetrating peptide (CPP) designed to disrupt the LUC7L3–MDC1 interaction was synthesized to test translational targeting strategies.Results:
Our findings demonstrate that upon radiation-induced DNA damage, LUC7L3 is phosphorylated at the T429 site by ATM and subsequently recruited to DNA damage sites through interaction with the FHA domain of MDC1, where it contributes to the formation of DNA repair foci. At the transcriptional level, LUC7L3 maintains chromatin accessibility at the promoter regions of key genes involved in homologous recombination (HR) and base excision repair (BER), thereby preserving their open chromatin state following DNA damage. In addition, LUC7L3 enhances the binding and transcriptional activation activity of the transcription factor E2F1 at these promoters, promoting the inducible expression of DNA repair genes after radiotherapy. Loss of LUC7L3 significantly impairs HR efficiency and attenuates the transcriptional response of repair-related genes, sensitizing cells and tumor models to radiotherapy. Notably, a cell-penetrating peptide(CPP) that specifically disrupts the interaction between LUC7L3 and MDC1 effectively blocks LUC7L3 recruitment, and markedly increases tumor cell sensitivity to radiotherapy.
Conclusion:
This study uncovers the transcriptional and non-transcriptional roles of LUC7L3 in the response to radiotherapy. Upon radiation-induced DNA damage, LUC7L3 is phosphorylated and recruited to DNA damage sites. It regulates DNA repair gene expression by maintaining promoter chromatin accessibility and enhancing E2F1 transcriptional activity. Both depletion of LUC7L3 and pharmacological disruption of its recruitment using a cell-penetrating peptide significantly increase radiosensitivity. Collectively, our findings identify LUC7L3 as a key regulator of DNA damage repair and a promising translational target for radiosensitization.