The adhesion protein E-cadherin plays a central part in the process of epithelial morphogenesis. Expression of this protein is downregulated during the acquisition of metastatic potential at late stages of epithelial tumour progression. There is evidence for a transcriptional blockage of E-cadherin gene expression in this process. Here we show that the transcription factor Snail, which is expressed by fibroblasts and some E-cadherin-negative epithelial tumour cell lines, binds to three E-boxes present in the human E-cadherin promoter and represses transcription of E-cadherin. Inhibition of Snail function in epithelial cancer cell lines lacking E-cadherin protein restores the expression of the E-cadherin gene.

Epithelial-mesenchymal transition (EMT) is a cellular process during which epithelial cells acquire mesen chymal phenotypes and behaviour following the down regulation of epithelial features. EMT is triggered in response to signals that cells receive from their micro environment. The epithelial state of the cells in which EMT is initiated is characterized by stable epithelial cell-cell junctions, apical-basal polarity and interac tions with basement membrane. During EMT, changes in gene expression and posttranslational regulation mechanisms lead to the repression of these epithelial characteristics and the acquisition of mesenchymal char acteristics. Cells then display fibroblastlike morphol ogy and cytoarchitecture, as well as increased migratory capacity. Furthermore, these now migratory cells often acquire invasive properties (Fig. 1). EMT was first described by researchers studying early embryogenesis as a programme with welldefined cellular features 1,2. It is now widely accepted that EMT occurs normally during early embryonic development, to enable a variety of morphogenetic events, as well as later in development and during wound healing in adults.

The β-catenin signaling pathway is deregulated in nearly all colon cancers. Nonhypercalcemic vitamin D3 (1α,25-dehydroxyvitamin D3) analogues are candidate drugs to treat this neoplasia. We show that these compounds promote the differentiation of human colon carcinoma SW480 cells expressing vitamin D receptors (VDRs) (SW480-ADH) but not that of a malignant subline (SW480-R) or metastasic derivative (SW620) cells lacking VDR. 1α,25(OH)2D3 induced the expression of E-cadherin and other adhesion proteins (occludin, Zonula occludens [ZO]-1, ZO-2, vinculin) and promoted the translocation of β-catenin, plakoglobin, and ZO-1 from the nucleus to the plasma membrane. Ligand-activated VDR competed with T cell transcription factor (TCF)-4 for β-catenin binding. Accordingly, 1α,25(OH)2D3 repressed β-catenin–TCF-4 transcriptional activity. Moreover, VDR activity was enhanced by ectopic β-catenin and reduced by TCF-4. Also, 1α,25(OH)2D3 inhibited expression of β-catenin–TCF-4-responsive genes, c-myc, peroxisome proliferator-activated receptor δ, Tcf-1, and CD44, whereas it induced expression of ZO-1. Our results show that 1α,25(OH)2D3 induces E-cadherin and modulates β-catenin–TCF-4 target genes in a manner opposite to that of β-catenin, promoting the differentiation of colon carcinoma cells.

Epithelial-mesenchymal transitions (EMT) are essential for organogenesis and triggered in carcinoma progression into an invasive state1. Transforming growth factor-β (TGF-β) cooperates with signalling pathways, such as Ras and Wnt, to induce EMT2-5, but the molecular mechanisms are not clear. Here, we report that SMAD3 and SMAD4 interact and form a complex with SNAIL1, a transcriptional repressor and promoter of EMT6, 7. The SNAIL1-SMAD3/4 complex was targeted to the gene promoters of CAR, a tight junction protein, and E-cadherin during TGF-β-driven EMT in breast epithelial cells. SNAIL1 and SMAD3/4 acted as co-repressors of CAR, occludin, claudin-3 and E-cadherin promoters in transfected cells. Conversely, co-silencing of SNAIL1 and SMAD4 by siRNA inhibited the repression of CAR and occludin during EMT. Moreover, loss of CAR and E-cadherin correlated with nuclear co-expression of SNAIL1 and SMAD3/4 in a mouse model of breast carcinoma and at the invasive fronts of human breast cancer. We propose that activation of a SNAIL1-SMAD3/4 transcriptional complex represents a novel mechanism of gene repression during EMT.