Impact of CHK2-small interfering RNA on CpG ODN7909-enhanced radiosensitivity in lung cancer A549 cells

OBJECTIVE To investigate the impact of checkpoint kinase 2 (CHK2)-small interfering RNA (CHK2-siRNA) on the enhancement of radiosensitivity by CpG oligodeoxynucleotide (ODN) 7909 in lung cancer A549 cells. METHODS The A549 cells were randomly divided into five groups: control, CpG, X-ray, CpG + X-ray, and CHK2-siRNA + CpG + X-ray. Cell colonization was observed using inverted microscopy. Cell cycle and apoptosis were analyzed by flow cytometry. CHK2 expression was detected by Western blot. CHK2-siRNA was adopted to silence the expression of CHK2. RESULTS The level of CHK2 phosphorylation was higher in the CpG + X-ray group than in the X-ray group. Increases in G(2)/mitotic (M) phase arrest and apoptosis and a decrease of cell survival rate in the CpG + X-ray group were statistically significant (P < 0.05) when compared with the CHK2-siRNA + CpG + X-ray group in which the expression of CHK2 was obviously inhibited. The combination of CpG ODN7909 and X-ray irradiation was found to enhance the mitotic death of A549 cells. The sensitization enhancement ratio of mean death dose (D(0)) was 1.42 in the CpG + X-ray group, which was higher than that of the CHK2-siRNA + CpG + X-ray group, in which D(0) was 1.05. CONCLUSION To a certain extent, the impact of a combination of CpG ODN7909 and X-ray on G(2)/M phase arrest, apoptosis, and rate of cell survival was attenuated by CHK2-siRNA in human lung adenocarcinoma A549 cells, indicating that increased phosphorylation of CHK2 might be a radiosensitive pathway.