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

Abstract

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 between 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.

Keywords

• Ionizing radiation
• Acquired radioresistance
• Epithelial-mesenchymal transition
• Lung cancer cell line A549
• Transforming growth factor-beta/Smad/Akt