Fig. 5

ATRA exposure increases the sensitivities of MCF7/C6 cells to radiation treatment. a Clonogenic survival of MCF7/C6 cells exposed to ATRA treatment. Cells were plated and treated with indicated doses of ATRA for 24 h, and cells were then cultured for colony formation. b ATRA exposure reduces NHEJ activity in MCF 7 FIR cells, and increases radiosensitivity. Cells were co-transfected with control pDsRed and linearized EJ5-GFP plasmid, and were then treated with 1.0 μM of ATRA for 72 h. in vivo EJ5 activity was measured as described in Materials. Left: in vivo EJ5 assay; Right: diagram showing the inhibition of EJ5 reunion ability in ATRA-treated cells; c Clonogenic survival assay was performed to determine the changes of sensitivity in cells treated with 2Gy ionizing radiation. Cells were pretreated with 1.0 μM of ATRA, or DMSO as control, for 72 h, and 500 cells were then plated and irradiated with 2 Gy of IR. Left: ATRA treatment reduced clonogenic survival of irradiated cells. Right: demonstrative images for colony survival of irradiated cells. Data represent the average from at least three independent experiments. *Indicates statistical significance (p < 0.05)