Background:Radiotherapy is one of the most important treatments for esophageal squamous cell carcinoma (ESCC). Previously, we found that EphA5 expression was increased in ESCC cells and tumor tissues. Studies from other groups reported that EphA5 is abnormally expressed in numerous malignant tumors and may be involved in the radiosensitivity of lung cancer. However, the role of EphA5 in radiotherapy for ESCC remains unclear. Methods:The siRNA sequences against human EPHA5 were transfected to the ESCC cells (KYSE150 and KYSE450). After ionizing radiation (IR), cell viability and colony formation assays were used to test the changes of cell proliferation in EphA5-silenced cells. Flow cytometry analysis was performed to investigate the cell apoptosis and cycle in the irradiated cells interfered by siRNA. The key molecules involved in cell cycle checkpoints and DNA damage repair were evaluated by Western blot and immunofluorescence. Results:CCK8 assay and clonogenic assay showed that the proliferation of EphA5-silenced ESCC cells was inhibited after IR. At 24 h post-IR treatment, we found that the G1/S checkpoint triggered by DNA damage in EphA5-silenced cells was defective. γ-H2AX foci in the irradiated EphA5-silenced cells were impaired at 0.5 h post-IR treatment as well as ATM activation. The defective activation of ATM resulted in a decrease of p-Chk2, p-p53 and p21 expression. Conclusion:In conclusion, these results indicate that EphA5 silencing increases radiosensitivity in ESCC cells through ATM-dependent pathway, which provides a potential target for the radiotherapy in ESCC.