TGF-β/Akt/Smad signaling regulates ionizing radiation-induced epithelial-mesenchymal transition in acquired radioresistant lung cancer cells

Objective:To define the properties of lung cancer cells that resisted conventionally fractionated radiation exposure.Methods:Acquired radioresistant lung cancer cell line A549 was constructed by X-ray irradiation with a clinical conventional fraction dose of 2 Gy daily during 30 fractions.Cell morphology,molecular markers,migration capacity and invasion potential were evaluated by the microscope,Western blot,immunofluorescence,wound healing test and transwell chamber assay,respectively.Results:Radioresistant A549 cells shifted from an epithelial to a mesenchymal morphology,termed as epithelial-mesenchymal transition(EMT),and was accompanied by decreased expressions of epithelial markers(F=4.568,P<0.05)and increased expression of mesenchymal markers(F=4.270,P<0.05),greater migratory and invasive capabilities(t=6.386,5.644,P<0.05).The expression of TGF-β,and phosphorylated levels of Akt and Smad3 were also enhanced(F=6.496,4.685,3.370,P<0.05).Furthermore,the EMT phenotype induced by radiation could be reversed through inhibition of TGF-β,Akt or Smad3,indicating a functional relationship be-tween them.Conclusions:EMT mediates acquired radioresistance of lung cancer cells induced by IR with clinical parameters,and the crosstalk mode of TGF-β/Akt/Smad signaling plays a critical regulatory role in this process.