Objective: Irradiation may enhance migration and/or invasiveness of cancer cells in vitro and in vivo, the mechanism of which may be associated with epithelial-mesenchymal transition (EMT). The present study explored the mechanisms of EMT induced by irradiation in esophageal cancer cells. Methods: Human esophageal cancer cell line EC109 was treated with increased doses of irradiation (0 Gy, 20 Gy, 40 Gy and 60 Gy). Cell morphology was observed. Expressions of E-cadherin and vimentin were determined by immunofluorescence assay or western blot. Secretion of transforming growth factor-β1 (TGF-β1) by cells was determined by enzyme-linked immunosorbent assay (ELISA), and the expressions of Smad2/3 and phosphorated Smad2 (p-Smad2) were also examined by Western blot. The mRNA expressions of BMP-4, a bone morphogenetic protein (BMP) ligand, and two secreted BMP antagonists (Chordin and Gremlin), were detected with reverse transcription-polymerase chain reaction (RT-PCR). Cell migratory capacity was evaluated. Results: Irradiation induced EMT in EC109 cells in a dose-dependent manner as evidenced by morphological changes, decreased expression of E-cadherin and increased expression of vimentin, and increased cell motility. The secretion of TGF-β1 and expression of p-Smad2 were gradually increased in an irradiation dose-dependent manner, but the Smad2/3 protein levels remained stable. The mRNA expression of BMP-4 was gradually down-regulated, but the expressions of Chordin and Gremlin were gradually up-regulated in cells treated with increased doses of irradiation. Conclusion: Irradiation can induce EMT in esophageal cancer cells in a dose-dependent manner, and the mechanism may be associated with activation of TGF-β and restriction of BMP signaling.
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