LncRNA MIR4435-2HG confers radioresistance in NSCLC by sponging miR-1-3p to upregulate DNA-PKcs and selectively promote NHEJ repair.

Emerging evidence indicates that long non-coding RNAs (lncRNAs) are critical regulators of tumor radiosensitivity and hold promise as novel targets for radiosensitization. However, the underlying mechanisms by which most lncRNAs modulate radiosensitivity remain elusive. This study aimed to elucidate the functional significance and mechanistic basis of lncRNA MIR4435-2HG in regulating non-small cell lung cancer (NSCLC) radiosensitivity. Our findings demonstrated that ionizing radiation induced upregulation of lncRNA MIR4435-2HG. High expression of MIR4435-2HG was significantly associated with poor prognosis in patients with lung adenocarcinoma. Inhibition of MIR4435-2HG increased the radiosensitivity of NSCLC cells. Mechanistically, MIR4435-2HG acted as a competing endogenous RNA (ceRNA) to sponge miR-1-3p, thereby derepressing DNA-PKcs at both mRNA and protein levels. Knockdown of MIR4435-2HG impaired non-homologous end joining (NHEJ) repair, as evidenced by increased 53BP1 and γH2AX foci, reduced interaction of DNA-PKcs with Ku70 and XRCC4, and decreased NHEJ repair efficiency. Conversely, overexpression of MIR4435-2HG induced a radioresistant phenotype. Dual-luciferase reporter assays confirmed the interaction between miR-1-3p and both MIR4435-2HG and DNA-PKcs. Rescue experiments confirmed that miR-1-3p overexpression reversed MIR4435-2HG-mediated DNA-PKcs upregulation, proliferation enhancement, and radioresistance. Notably, MIR4435-2HG selectively promoted error-prone NHEJ without affecting homologous recombination. In summary, our study delineates a novel and functionally specific ceRNA axis wherein MIR4435-2HG sequesters miR-1-3p to upregulate DNA-PKcs and selectively activate NHEJ-mediated DSB repair. These findings not only introduce a critical regulatory node into the DNA repair network but also position the MIR4435-2HG/miR-1-3p/DNA-PKcs axis as a promising predictive biomarker and therapeutic target for overcoming radioresistance in NSCLC.