Long non-coding RNA LOC401312 induces radiosensitivity through upregulation of CPS1 in non-small cell lung cancer

Long noncoding RNAs (lncRNAs), non-protein-coding transcripts exceeding 200 nu-cleotides, are critical regulators of gene expression through chromatin remodeling, transcriptional modulation, and post-transcriptional modifications. While ionizing radiation (IR) induces cellular damage through direct DNA breaks, reactive oxygen species (ROS)-mediated oxidative stress, and bystander effects, the functional in-volvement of lncRNAs in radiation response remains incompletely characterized. Here, through genome-wide CRISPR activation (CRISPRa) screening in non-small cell lung cancer (NSCLC) cells, we identified LOC401312 as a novel radiosensitizing lncRNA, the stable overexpression of which significantly enhanced IR sensitivity. Tran-scriptomic profiling revealed that LOC401312 transcriptionally upregulates car-bamoyl-phosphate synthase 1 (CPS1), a mitochondrial enzyme involved in pyrimidine biosynthesis. Notably, CPS1 overexpression recapitulated the radiosensitization phe-notype observed with LOC401312 activation. Mechanistic investigations revealed that CPS1 suppresses the phosphorylation of ATM kinase (Ser1981) and XRCC1 protein levels, which are key mediators of DNA damage checkpoint activation and base exci-sion repair, respectively. This study establishes the LOC401312-CPS1-ATM/XRCC1 axis as a previously unrecognized regulatory network governing radiation sensitivity, highlighting the potential of lncRNA-directed metabolic rewiring to impair DNA re-pair fidelity. Our findings not only expand the functional landscape of lncRNAs in DNA damage response but also provide a therapeutic rationale for targeting the LOC401312-CPS1 axis to improve radiotherapy efficacy in NSCLC.