Inhibition of TLR9 expression by siRNA influences radiosensitivity of lung cancer A549 cells

Objective: To study the influence of TLR9 on the radiosensitivity of radiation-resistance lung cancer A549 cells (R-A549). Methods: TLR9 siRNA was transfected to R-A549 cells with liposome and TLR9 expression level was examined by Western blot. After X-ray irradiation with doses from 0 to 8 Gy, colony formation assay was performed and cell survival curve was fitted with the multi-target single-hitting model and D₀, D_q, and N value of the survival of A549, R-A549, control siRNA transfected and TLR9 siRNA transfected cells was calculated. Cell proliferation ability and cell cycle distributions of these four groups were also determined. Results: TLR9 siRNA successfully suppressed TLR9 expression in R-A549 cells and reduced the colony formation after irradiation with a sensitization enhancement ratio (SER_D0) of 1.37 to R-A549. SER_D0 of A549 to R-A549 was 1.09. After irradiation, compared to R-A549, cells in G₂/M phase of TLR9 siRNA transfected population increased significantly (t = 4.323, P < 0.05) but G₁/G₀ phase decreased significantly (t = 7.616, P < 0.05). Conclusions: TLR9 siRNA increased the radiosensitivity of R-A549. Radiation induced G₂/M phase arrest and G₁/G₀ phase decrease could suppress potential lethal damage repair and results in the enhancement of radiation sensitivity. (authors)