Reversibility of the Snail-induced epithelial-mesenchymal transition revealed by the Cre-loxP system

The epithelial-mesenchymal transition (EMT), a key process in the tumor metastatic cascade, is characterized by the loss of cell-cell junctions and cell polarity, as well as the acquisition of migratory and invasive properties. Snail is an EMT-inducer whose expression in several different epithelial cells, e.g., Madin-Darby canine kidney (MDCK), leads to EMT. To further understand EMT induced by Snail expression, the Cre-loxP site-specific recombination system was used to investigate its reversibility. Transfection of MDCK cells with loxP-flanked Snail (Snail-loxP) resulted in EMT induction, which included the acquisition of a spindle-shaped fibroblastic morphology, the downregulation of epithelial markers, and the upregulation of mesenchymal markers. DNA methylation of the E-cadherin promoter, which often occurs during E-cadherin downregulation, was not observed in Snail+ cells. After Cre-mediated excision of Snail-loxP, the cells reacquired an epithelial morphology, upregulated epithelial markers, and downregulated mesenchymal markers. Thus, EMT induced by Snail expression was reversible.