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Malignant progression in cancer requires populations of tumor-initiating cells (TICs) endowed with unlimited self renewal, survival under stress, and establishment of distant metastases. Additionally, the acquisition of invasive properties driven by epithelial-mesenchymal transition (EMT) is critical for the evolution of neoplastic cells into fully metastatic populations. Here, we characterize 2 human cellular models derived from prostate and bladder cancer cell lines to better understand the relationship between TIC and EMT programs in local invasiveness and distant metastasis. The model tumor subpopulations that expressed a strong epithelial gene program were enriched in highly metastatic TICs, while a second subpopulation with stable mesenchymal traits was impoverished in TICs. Constitutive overexpression of the transcription factor Snai1 in the epithelial/TIC-enriched populations engaged a mesenchymal gene program and suppressed their self renewal and metastatic phenotypes. Conversely, knockdown of EMT factors in the mesenchymal-like prostate cancer cell subpopulation caused a gain in epithelial features and properties of TICs. Both tumor cell subpopulations cooperated so that the nonmetastatic mesenchymal-like prostate cancer subpopulation enhanced the in vitro invasiveness of the metastatic epithelial subpopulation and, in vivo, promoted the escape of the latter from primary implantation sites and accelerated their metastatic colonization. Our models provide new insights into how dynamic interactions among epithelial, self-renewal, and mesenchymal gene programs determine the plasticity of epithelial TICs., Introduction There is a wealth of evidence that the acquisition of aggressive traits of cancer, or malignant progression, can be determined both by the occurrence of genetic mutations and by [...]

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.

Author(s): Hector G Palmer [1, 8]; Maria Jesus Larriba [1, 8]; Jose Miguel Garcia [2]; Paloma Ordonez-Moran [1]; Cristina Pena [2]; Sandra Peiro [3]; Isabel Puig [3]; Rufo Rodriguez [4]; [...]

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.