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Epithelial-mesenchymal transition (EMT) is required for mesodermal differentiation during development. The zinc-finger transcription factor, Snail1, can trigger EMT and is sufficient to transcriptionally reprogram epithelial cells toward a mesenchymal phenotype during neoplasia and fibrosis. Whether Snail1 also regulates the behavior of terminally differentiated mesenchymal cells remains unexplored. Using a Snail conditional knockout model, we now identify Snail1 as a regulator of normal mesenchymal cell function. Snail1 expression in normal fibroblasts can be induced by agonists known to promote proliferation and invasion in vivo. When challenged within a tissue-like, three-dimensional extracellular matrix, Snail1-deficient fibroblasts exhibit global alterations in gene expression, which include defects in membrane type-1 matrix metalloproteinase (MT1-MMP)-dependent invasive activity. Snail1-deficient fibroblasts explanted atop the live chick chorioallantoic membrane lack tissue-invasive potential and fail to induce angiogenesis. These findings establish key functions for the EMT regulator Snail1 after terminal differentiation of mesenchymal cells.

The active vitamin D metabolite 1,25-dihydroxy-vitamin [D.sub.3] (1,25[(OH).sub.2][D.sub.3]) inhibits proliferation and promotes differentiation of colon cancer cells through the activation of vitamin D receptor (VDR), a transcription factor of the nuclear receptor superfamily. Additionally, 1,25[(OH).sub.2][D.sub.3] has several nongenomic effects of uncertain relevance. We show that 1,25[(OH).sub.2][D.sub.3] induces a transcription-independent [Ca.sup.2+] influx and activation of RhoA--Rho-associated coiled kinase (ROCK). This requires VDR and is followed by activation of the p38 mitogen-activated protein kinase (p38MAPK) and mitogen- and stress-activated kinase 1 (MSK1). As shown by the use of chemical inhibitors, dominant-negative mutants and small interfering RNA, RhoA--ROCK, and p38MAPK-MSK1 activation is necessary for the induction of CDH1/E-cadherin, CYP24, and other genes and of an adhesive phenotype by 1,25[(OH).sub.2][D.sub.3]. RhoA--ROCK and MSK1 are also required for the inhibition of Wnt--[beta]-catenin pathway and cell proliferation. Thus, the action of 1,25[(OH).sub.2][D.sub.3] on colon carcinoma cells depends on the dual action of VDR as a transcription factor and a nongenomic activator of RhoA--ROCK and p38MAPK-MSK1.

We report that the activity of glycogen synthase kinase-3 (GSK-3) is necessary for the maintenance of the epithelial architecture. Pharmacological inhibition of its activity or reducing its expression using small interfering RNAs in normal breast and skin epithelial cells results in a reduction of E-cadherin expression and a more mesenchymal morphology, both of which are features associated with an epithelial-mesenchymal transition (EMT). Importantly, GSK-3 inhibition also stimulates the transcription of Snail, a repressor of E-cadherin and an inducer of the EMT. We identify NFKB as a transcription factor inhibited by GSK-3 in epithelial cells that is relevant for Snail expression. These findings indicate that epithelial cells must sustain activation of a specific kinase to impede a mesenchymal transition.

The initiation and the regulation of the Zeb2 or Sip1 expression during the process of snail-1 induced epithelial-mesenchymal transition (EMT) are discussed. The activation of the Zeb2 expression is shown to be highly dependent on the presence of a natural antisense transcript (NAT) in the pathway.

The [Beta]-catenin signaling pathway is designated in nearly all colon cancers. Nonhypercalcemic vitamin D3 (1[Alpha], 25-dehydroxyvitamin [D.sub.3]) 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. 1[Alpha], 25[(OH).sub.2][D.sub.3] induced the expression of E-cadherin and other adhesion proteins (occludin, Zonula occludens [ZO]-1, ZO-2, vinculin) and promoted the translocation of [Beta]-catenin, plakoglobin, and ZO-1 from the nucleus to the plasma membrane. Ligand-activated VDR competed with T cell transcription factor (TCF)-4 for [Beta]-catenin binding. Accordingly, 1[Alpha], 25([OH.sub.2])[D.sub.3] repressed [Beta]-catenin-TCF-4 transcriptional activity. Moreover, VDR activity was enhanced by ectopic [Beta]-catenin and reduced by TCF-4. Also, 1[Alpha], 25[(OH).sub.2][D.sub.3] inhibited expression of [Beta]-catenin-TCF-4-responsive genes, c-myc, peroxisome proliferator-activated receptor [Delta], Tcf-1, and CD44, whereas it induced expression of ZO-1. Our results show that 1[Alpha], 25[(OH).sub.2][D.sub.3] induces E-cadherin and modulates [Beta]-catenin-TCF-4 target genes in a manner opposite to that of [Beta]-catenin, promoting the differentiation of colon carcinoma cells.