Autophagy links β-catenin and Smad signaling to promote epithelial-mesenchymal transition via upregulation of integrin linked kinase

TGF-beta 1 induces epithelial-mesenchymal transition (EMT) and autophagy in a variety of cells. However, the role of autophagy in TGF-beta 1-induced EMT has not been clearly elucidated and the underlying mechanisms are unclear. In the present study, we found that TGF-beta 1 induced both autophagy and EMT in mouse tubular epithelial C1.1 cells. Inhibition of autophagy by 3-methyladenine or siRNA knockdown of Beclin 1 reduced TGF-beta 1-induced increase of vimentin and decreased E-cadherin expression. In contrast, rapamycin-associated enhancement of TGF-beta 1-induced autophagy increased EMT of C1.1 cells. Serum rescue inhibited autophagy followed by reversal of EMT. Blocking of autophagosome-lysosomal but not proteosomal degradation reduced the decrease of E-cadherin, demonstrating a role for autophagy in degradation of E-cadherin during EMT. Autophagy promoted the activation of Src and Src-associated phosphorylation of beta-catenin at Y-654 leading to pY654-beta-cateninip-Smad2 complex formation. Chromatin immunoprecipitation assay demonstrated binding by the pY654-beta-cateninip-Smad2 complex to ILK promoter thus increasing ILK expression. Taken together, our results demonstrate that TGF-beta 1-induced autophagy links beta-catenin and Smad signaling to promote EMT in C1.1 cells through a novel pY654-13-catenin/p-Smad2/ILK pathway. The pathway delineated links disruption of E-cadherin/beta-catenin-mediated cell-cell contact to induction of EMT via upregulation of ILK. (C) 2016 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).