Transforming growth factor-β1 induces epithelial-mesenchymal transition and integrin α3β1-mediated cell migration of HSC-4 human squamous cell carcinoma cells through Slug

We investigated whether transforming growth factor (TGF)-beta 1 promoted epithelial-mesenchymal transition (EMT) and migration of human oral squamous cell carcinoma (hOSCC) cells. Among 6 hOSCC cell lines investigated, Smad2 phosphorylation and TGF-beta target genes expression were most clearly upregulated following TGF-beta 1 stimulation in HSC-4 cells, indicating that HSC-4 cells were the most responsive to TGF-beta 1. In addition, the expression levels of the mesenchymal markers N-cadherin and vimentin were most clearly induced in HSC-4 cells among the hOSCC cell lines by TGF-beta 1 stimulation. Interestingly, E-cadherin and beta-catenin at the cell surface were internalized in HSC-4 cells stimulated with TGF-beta 1. In addition, the expression levels of the EMT-related transcription factor Slug was significantly upregulated on TGF-beta 1 stimulation. Moreover, the downregulation of Slug by RNA interference clearly inhibited the TGF-beta 1-induced expression of mesenchymal marker and the migration of HSC-4 cells. Proteomics analysis also revealed that the expression levels of integrin alpha 3 beta 1-targeted proteins were upregulated in TGF-beta 1-stimulated HSC-4 cells. Neutral antibodies against integrin alpha 3 and beta 1, as well as a focal adhesion kinase (FAK) inhibitor, clearly suppressed TGF-beta 1-induced cell migration. These results suggest that the EMT and integrin alpha 3 beta 1/FAK pathway-mediated migration of TGF-beta 1-stimulated HSC-4 hOSCC cells is positively controlled by Slug.