IR up-regulates miR-300 expression in lung cancer cells. (A-D) Human lung cancer cells A549 (A), H446 (B), GLC82 (C) and H1299 (D) were exposed to 2 Gy of X-rays. The relative expression levels of miR-300 were evaluated by qRT-PCR at 0, 6, 24 h post-irradiation. * P < 0.05, ** P < 0.01, compared to control.