PolyI:C Suppresses TGF-β1-Induced Akt Phosphorylation and Reduces the Motility of A549 Lung Carcinoma Cells

Abstract Backgrounds: Transforming growth factor (TGF)-β is shown to play a critical role in cancer progression by inducing epithelial mesenchymal transition (EMT). Polyinosinic-polycytidylic acid (polyI:C), a synthetic agonist for toll-like receptor (TLR) 3, has been successfully used to treat some cancer patients as a vaccine adjuvant, but its direct action on the proliferation or migration of cancer cells, such as lung cancer cells, undergoing EMT remains unknown. Methods and results: By an in vitro cell proliferation assay, polyI:C showed no effect on the growth of TGF-β1-treated A549 human lung cancer cells at the concentration range up to 10 mg/ml; however, it markedly suppressed the motility in a cell scratch and a cell invasion assay. By Western blotting, polyI:C dramatically decreased TGF-β1-induced Ak strain transforming (Akt) phosphorylation and increased phosphatase and tensin homologue (PTEN) expression without affecting the Son of mothers against decapentaplegic (Smad) 3 phosphorylation or the expression level of E-cadherin, N-cadherin or Snail, indicating that polyI:C suppressed cell motility independently of the ‘cadherin switching’. The Akt inhibitor perifosine inhibited TGF-β1-induced cell invasion, and the PTEN-specific inhibitor VO-OHpic appeared to reverse the inhibitory effect of polyI:C. Conclusion: Our results indicate that polyI:C has the capacity to suppress the motility of TGF-β1-treated A549 cells by targeting the phosphatidylinositol 3-kinase /Akt pathway partly via PTEN and suggest that polyI:C may be used to prevent or reduce the metastasis of lung cancer cells.