Generation of Breast Cancer Stem Cells through Epithelial-Mesenchymal Transition

University of Helsinki, Finland
PLoS ONE (Impact Factor: 3.23). 02/2008; 3(8):e2888. DOI: 10.1371/journal.pone.0002888
Source: PubMed


Recently, two novel concepts have emerged in cancer biology: the role of so-called "cancer stem cells" in tumor initiation, and the involvement of an epithelial-mesenchymal transition (EMT) in the metastatic dissemination of epithelial cancer cells. Using a mammary tumor progression model, we show that cells possessing both stem and tumorigenic characteristics of "cancer stem cells" can be derived from human mammary epithelial cells following the activation of the Ras-MAPK pathway. The acquisition of these stem and tumorigenic characters is driven by EMT induction.

Download full-text


Available from: Clémence Thomas,
  • Source
    • "The PI3K pathway can also be activated independently of Ras activation and substantial crosstalk between the Raf and PI3K pathways has been established (Aksamitiene et al., 2012). Despite evidence that overexpression of oncogenic Ras can repress CD24 surface expression (Morel et al., 2008) the mechanism for this regulation of CD24 is not known. Here, we examined the regulation of CD24 mRNA, protein, and promoter levels in a model of oncogenic Ras activation. "
    [Show abstract] [Hide abstract]
    ABSTRACT: CD24 is a dynamically regulated cell surface protein. High expression of CD24 leads to progression of lung, prostrate, colon, and pancreatic cancers, among others. In contrast, low expression of CD24 leads to cell proliferation and metastasis of breast cancer stem cells (BCSCs). Activating mutations in Ras are found in 30% of all human cancers. Oncogenic Ras constitutively stimulates the Raf, PI3K, and Ral GDS signaling pathways, leading to cellular transformation. Previous studies have shown that expression of oncogenic Ras in breast cancer cells generates CD24(-) cells from CD24(+) cells. However, the molecular mechanisms involved in the generation of CD24(-) cells were not determined. Here, we demonstrate that oncogenic Ras (RasV12) expression suppresses CD24 mRNA, protein, and promoter levels when expressed in NIH/3T3 cells. Furthermore, activation of only the Raf pathway was sufficient to downregulate CD24 mRNA and protein expression to levels similar to those seen in with RasV12 expression. In contrast, activation of the PI3K pathway downregulated mRNA expression with a partial effect on protein expression whereas activation of the RalGDS pathway only partially affected protein expression. Surprisingly, inhibition of MEK with U0126 only partially restored CD24 mRNA expression but not surface protein expression. In contrast, inhibition of Raf with sorafenib did not restore CD24 mRNA expression but significantly increased the proportion of RasV12 cells expressing CD24. Therefore, the Raf pathway is the major repressor of CD24 mRNA and protein expression, with PI3K also able to substantially inhibit CD24 expression. Moreover, these data indicate that the levels of CD24 mRNA and surface protein are independently regulated. Although inhibition of Raf by sorafenib only partially restored CD24 expression, sorafenib should still be considered as a potential therapeutic strategy to alter CD24 expression in CD24(-) cells, such as BCSCs.
    Frontiers in Cell and Developmental Biology 08/2015; 3:47. DOI:10.3389/fcell.2015.00047
    • "In addition to being an argument in favor of the CSC(-like) phenotype of the pSP, the detection of EMT may also have implications for understanding of pituitary tumor behavior. In several cancers, EMT, or EMT-driven CSCs, are involved in expansion, invasion, resistance to hostile conditions (including therapy), and recurrence (Mani et al. 2008, Morel et al. 2008, Bertran et al. 2009, Kong et al. 2010, Pirozzi et al. 2011, De Craene & Berx 2013). The GO enrichment picture, which includes gene clusters associated with cell motility and migration as well as the expression of chemotactic receptors like CXCR4 in the adenoma pSP, further supports the migratory capacity. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Pituitary adenomas cause significant endocrine and mass-related morbidity. Only little is known about mechanisms underlying pituitary tumor pathogenesis. We searched for a side population (SP) in pituitary tumor, representing cells with high efflux capacity and potentially enriching for tumor stem cells (TSC). Human pituitary adenomas contain a SP irrespective of hormonal phenotype. This adenoma SP, as well as the purified SP (pSP) depleted from endothelial and immune cells, enriches for cells that express 'tumor stemness' markers and signaling pathways, including epithelial-mesenchymal transition (EMT)-linked factors. Pituitary adenomas were found to contain self-renewing sphere-forming cells, considered a property of TSC. These sphere-initiating cells were recovered in the pSP. Because benign pituitary adenomas do not grow in vitro and failed to expand in immunodeficient mice, the pituitary tumor cell line AtT20 was further used. We identified a SP in this cell line and found it more tumorigenic than the non-SP 'main population'. Of the two EMT-regulatory pathways tested, inhibition of C-X-C chemokine receptor type 4 (Cxcr4) signaling reduced EMT-associated cell motility in vitro as well as xenograft tumor growth, whereas activation of TGFβ had no effect. The adenoma pSP also showed upregulated expression of the pituitary stem cell marker SOX2. Pituitaries from dopamine receptor D2 knockout (Drd2-/-) mice bearing prolactinomas, contain more pSP, Sox2+ and colony-forming cells than wildtype glands. In conclusion, we detected a SP in pituitary tumor and identified TSC-associated characteristics. Our study adds new elements to the unravelment of pituitary tumor pathogenesis and may lead to new therapeutic targets.
    Endocrine Related Cancer 04/2015; 22(4). DOI:10.1530/ERC-14-0546 · 4.81 Impact Factor
  • Source
    • "Following the discovery that EMT generates CSCs (Mani et al., 2008; Morel et al., 2008), efforts have focused on targeting mesenchymal cells within breast cancer cell populations (Gupta et al., 2009; Tam et al., 2013). However, our data indicate that transient Twist1 activation enabled long-term invasive growth by promoting coexistence of epithelial and mesenchymal traits, whereas constitutive Twist1 activation switched cells to a migratory, nonproliferative state. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Master regulators of the epithelial-mesenchymal transition such as Twist1 and Snail1 have been implicated in invasiveness and the generation of cancer stem cells, but their persistent activity inhibits stem-cell-like properties and the outgrowth of disseminated cancer cells into macroscopic metastases. Here, we show that Twist1 activation primes a subset of mammary epithelial cells for stem-cell-like properties, which only emerge and stably persist following Twist1 deactivation. Consequently, when cells undergo a mesenchymal-epithelial transition (MET), they do not return to their original epithelial cell state, evidenced by acquisition of invasive growth behavior and a distinct gene expression profile. These data provide an explanation for how transient Twist1 activation may promote all steps of the metastatic cascade; i.e., invasion, dissemination, and metastatic outgrowth at distant sites.
    Cell Reports 01/2015; 338. DOI:10.1016/j.celrep.2014.12.032 · 8.36 Impact Factor
Show more