Epithelial-mesenchymal transition in oral squamous cell carcinoma triggered by transforming growth factor-β1 is Snail family-dependent and correlates with matrix metalloproteinase-2 and -9 expressions

Snail and Slug play important roles in cancer progression by promoting epithelial-mesenchymal transition (EMT). Although Snail is well studied, its role in oral squamous cell carcinoma (OSCC) and its regulatory relationship with Slug remain unclear. We aimed to determine whether Snail and Slug interplay occurs in transforming growth factor-β1 (TGF-β1)-initiated EMT of OSCC cells, and to assess the expression of matrix metalloproteinases (MMPs) in this process. Three OSCC cell lines, SCC9, SCC15 and SCC25 were treated with recombinant TGF-β1 for 0-6 days. Activities of the EMT regulators, Snail and Slug, and of extracellular hallmarks, MMP2 and 9, were detected using real-time PCR and Western blots. An in vitro wound healing assay then assessed short-term EMT, whilst phenotypic changes associated with the above gene expressions were evaluated by immunocytochemistry. Results showed that Slug and MMP9 were up-regulated at both mRNA and protein levels, while Snail expression rose and fell, in concert with expression of MMP2. In the wound healing assay, Snail was seen alone at the invasive front in SCC9 and SCC15 cultures, while both Snail and Slug appeared at wound margins in SCC25. Both MMP2 and MMP9 were detected at wound edges in all cell lines, with MMP2 localised in cell nuclei, MMP9 was restricted to the cytoplasm. The study suggests that both Snail and Slug act as regulators of TGF-β1-trigged EMT in OSCC cells. Snail may up-regulate MMP2 or MMP9 initiating EMT, while Slug may share a role with Snail in maintaining longer-term EMT, by stimulating MMP9 expression.