EN1 knockdown increased intracellular ROS levels and elevated susceptibility to γ-ray irradiation. (A) EN1 knockdown elevated the intracellular ROS levels of glioma cells, assessed with H2DCFDA assays (● for shcon, ■ for shEN1-3898, ▲ for shEN1-3899, ◆ for shEN1-3901). (B) Colony forming assays demonstrating that EN1 knockdown elevated the susceptibility of glioma cells to γ-ray irradiation, assessed with plating efficiency (PE), where PE is the fraction of colonies counted divided by cells plated without radiation. Data are presented as the mean from three independent experiments. * p < 0.05, ** p < 0.01, *** p < 0.001 according to Student’s t-test.