Intervention of a Communication Between PI3K/Akt and β-Catenin by (−)-Epigallocatechin-3-Gallate Suppresses TGF-β1-Promoted Epithelial-Mesenchymal Transition and Invasive Phenotype of NSCLC Cells

The epithelial-mesenchymal transition (EMT) assists in the acquisition of invasiveness, relapse, and resistance in non-small cell lung cancer (NSCLC) and can be caused by the signaling of transforming growth factor-β1 (TGF-β1) through Smad-mediated or Smad-independent pathways. (−)-Epigallocatechin-3-gallate (EGCG), a multifunctional cancer-preventing bioconstituent found in tea polyphenols, has been shown to repress TGF-β1-triggered EMT in the human NSCLC A549 cell line by inhibiting the activation of Smad2 and Erk1/2 or reducing the acetylation of Smad2 and Smad3. However, its impact on the Smad-independent pathway remains unclear. Here, we found that EGCG, similar to LY294002 (a specific inhibitor of phosphatidylinositol 3-kinase [PI3K]), downregulated Akt activation and restored the action of glycogen synthase kinase-3β (GSK-3β), accompanied by TGF-β1-caused changes in hallmarks of EMT such as N-cadherin, E-cadherin, vimentin, and Snail in A549 cells. EGCG inhibited β-catenin expression and its nuclear localization caused by TGF-β1, suggesting that EGCG blocks the crosstalk between the PI3K/Akt/GSK-3β route and β-catenin. Furthermore, it was shown that EGCG suppressed TGF-β1-elicited invasive phenotypes of A549 cells, including invading and migrating activities, matrix metalloproteinase-2 (MMP-2) secretion, cell adhesion, and wound healing. In summary, we suggest that EGCG inhibits the induction of EMT by TGF-β1 in NSCLC not only through a Smad-dependent pathway, but also through the regulation of the PI3K/Akt/β-catenin signaling axis.