Rad51 in regulating the radiosensitivity of non‐small cell lung cancer with different epidermal growth factor receptor mutation status

BACKGROUND: Non‐small cell lung cancer (NSCLC) harboring kinase‐domain mutations in epidermal growth factor receptors (EGFR) has been observed to be sensitive to ionizing radiation (IR). We explore Rad51‐dependent homologous recombination (HR) DNA repair in regulating radiosensitivity in two NSCLC cell lines with different EGFR mutation status. METHODS: NSCLC cell lines, wild‐type EGFR A549 and mutant EGFR H820 with an in‐frame deletion in exon 19 of EGFR (ΔE746–E750), were cultured. Radiosensitivity was estimated by colony forming assay. Rad51 expression was evaluated by quantitative real time‐polymerase chain reaction and Western‐blot. Lentiviral small hairpin ribonucleic acid‐Rad51 and ΔE746–E750 deletion mutant EGFR were constructed and transfected into cells. Flowcytometry assay was used to analyze DNA double strand breaks, cell cycle alterations, and apoptosis. RESULTS: A549 had a higher survival factor (SF)2 (0.66 vs. 0.44) and lower α/β value (4.07 vs. 9.01). Compared with the A549 cell, the H820 cell exhibited defective arrest in the S‐phase, a higher rate of G2/M accumulation, early apoptosis, and residual γ‐H2AX. Downregulated Rad51 expression decreased SF2 (0.42 vs. 0.31) and increased the α/β ratio (7.51 vs. 10.5), G2/M accumulation, early apoptosis, and γ‐H2AX in two cell lines. H820 had a low IR‐induced Rad51 expression and nuclear translocation. Exogenous expression of the ΔE746–E750 deletion mutant EGFR caused the A549 cell to become more radiosensitive. CONCLUSIONS: An EGFR mutated NSCLC cell line is sensitive to IR , which is correlated with reduced IR‐induced Rad51 expression and nuclear translocation. The signaling pathway of EGFR maintaining Rad51 protein levels maybe a novel lung cancer therapeutic target to overcome radioresistance.