Sustained induction of epithelial to mesenchymal transition activates DNA methylation of genes silenced in basal-like breast cancers

Department of Pathology and Comprehensive Cancer Center, University of California, San Francisco, CA 94143-0511, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 10/2008; 105(39):14867-72. DOI: 10.1073/pnas.0807146105
Source: PubMed


The active acquisition of epigenetic changes is a poorly understood but important process in development, differentiation, and disease. Our work has shown that repression of the p16/pRb pathway in human epithelial cells, a condition common to stem cells and many tumor cells, induces dynamic epigenetic remodeling resulting in the targeted methylation of a selected group of CpG islands. We hypothesized that cells in this epigenetically plastic state could be programmed by the microenvironment to acquire epigenetic changes associated with tumorigenesis. Here, we describe an in vitro model system where epigenetically plastic cells were placed in an environment that induced epithelial to mesenchymal transition (EMT) and led to a program of acquired de novo DNA methylation at targeted sites. In this model, we found that repression of E-cadherin transcription preceded the subsequent acquisition of methylated CpG sites. Furthermore, the induction of EMT was accompanied by de novo methylation of several other gene promoters, including those of the estrogen receptor and Twist. These data demonstrate that signals from the microenvironment can induce phenotypic and gene expression changes associated with targeted de novo epigenetic alterations important in tumor progression, and that these alterations occur through a deterministic, rather than stochastic, mechanism. Given the dynamic epigenetic reprogramming that occurs in these cells, DNA methylation profiles observed in human tumors may reflect the history of environmental exposures during the genesis of a tumor.

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    • "In cancer cells, the genome is globally hypomethylated whereas CpG islands are frequently hypermethylated, resulting in reduced expression of tumor suppressor genes [29]. For example, the CDH1 gene encoding E-cadherin is frequently hypermethylated in breast cancer cell lines exhibiting an EMT-like phenotype [30] and is also shown to be methylated along with several other genes silenced in basal-like breast cancers [31]. In addition to methylation of cytosine, subsequent hydroxylation of 5mC to 5-hydroxymethyl-cytosine (5hmC) and further oxidation to non-methylated cytosine by the Ten-Eleven Translocation (TET) family of methylcytosine dioxygenases plays a tumor suppressor function in many types of cancers [32,33,34]. "
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    ABSTRACT: Tumor metastasis is the major cause of mortality and morbidity in most solid cancers. A growing body of evidence suggests that the epithelial-to-mesenchymal transition (EMT) plays a central role during tumor metastasis and frequently imparts a stem cell-like phenotype and therapeutic resistance to tumor cells. The induction of EMT is accompanied by a dynamic reprogramming of the epigenome involving changes in DNA methylation and several post-translational histone modifications. These changes in turn promote the expression of mesenchymal genes or repress those associated with an epithelial phenotype. Importantly, in order for metastatic colonization and the formation of macrometastases to occur, tumor cells frequently undergo a reversal of EMT referred to as the mesenchymal-to-epithelial transition (MET). Thus, a high degree of epigenetic plasticity is required in order to induce and reverse EMT during tumor progression. In this review, we describe various epigenetic regulatory mechanisms employed by tumor cells during EMT and elaborate on the importance of the histone code in controlling both the expression and activity of EMT-associated transcription factors. We propose that a more thorough understanding of the epigenetic mechanisms controlling EMT may provide new opportunities which may be harnessed for improved and individualized cancer therapy based on defined molecular mechanisms.
    Full-text · Article · Apr 2014 · Oncotarget
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    • "Moreover, certain human basal-type breast cancer cell lines have undergone EMT but have not lost E-cadherin expression, showing that Ecadherin deficiency is not an absolute necessity for EMT of carcinoma cells (Hollestelle et al. 2013). E-cadherin silencing might, therefore, be a consequence, rather than the cause, of EMT induction (Dumont et al. 2008). "
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    ABSTRACT: Cadherins are cell adhesion receptors that play important roles in embryogenesis and tissue homoeostasis. Endothelial cells express various members of the cadherin superfamily, in particular vascular endothelial (VE-) cadherin, which is the main adhesion receptor of endothelial adherens junctions and neural (N-) cadherin, which is normally localized outside the junctions and may mediate adhesion between endothelial cells and non-endothelial cells. Dysregulation of cadherin expression has been implicated in tumor progression, in particular the loss of epithelial (E-) cadherin expression or function and the gain of N-cadherin. Moreover, more recently, aberrant expression of VE-cadherin was observed in certain cancer types. In breast carcinoma, VE-cadherin was shown to promote tumor cell proliferation and invasion through enhancing TGF-β signaling. Thus, in breast cancer, the cadherin switch involves another player, vascular endothelial cadherin, which is part of an intricate interplay of classical cadherins in breast cancer progression.
    Full-text · Article · Mar 2014 · Cell and Tissue Research
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    • "This finding links EMT to more aggressive clinical behavior [16]. In breast cancer, a similar link has been established between EMT markers in primary and disseminated bone marrow tumor cells and aggressive clinical behavior [17]. Furthermore, in liver cancer cell lines, CD133+ cells showed upregulated N-cadherin expression and downregulated E-cadherin expression compared with CD133-negative cells, which suggest that EMT more commonly occurs in CD133-positive cells than in CD133-negative cells [18]. "
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    ABSTRACT: Pancreatic cancer is a lethal disease due to the high incidence of metastasis at the time of detection. CD133 expression in clinical pancreatic cancer correlates with poor prognosis and metastasis. However, the molecular mechanism of CD133-regulated metastasis remains unclear. In recent years, epithelial-mesenchymal transition (EMT) has been linked to cancer invasion and metastasis. In the present study we investigated the role of CD133 in pancreatic cancer metastasis and its potential regulatory network. A highly migratory pancreatic cancer cell line, Capan1M9, was established previously. After shRNA was stable transducted to knock down CD133 in Capan1M9 cells, gene expression was profiled by DNA microarray. Orthotopic, splenic and intravenous transplantation mouse models were set up to examine the tumorigenesis and metastatic capabilities of these cells. In further experiments, real-time RT-PCR, Western blot and co-immunoprecipitate were conducted to evaluate the interactions of CD133, Slug, N-cadherin, ERK1/2 and SRC. We found that CD133+ human pancreatic cancer cells were prone to generating metastatic nodules in in vivo models using immunodeficient mice. In contrast, CD133 knockdown suppressed cancer invasion and metastasis in vivo. Gene profiling analysis suggested that CD133 modulated mesenchymal characteristics including the expression of EMT-related genes, such as Slug and N-cadherin. These genes were down-regulated following CD133 knockdown. Moreover, CD133 expression could be modulated by the extracellular signal-regulated kinase (ERK)1/2 and SRC signaling pathways. The binding of CD133 to ERK1/2 and SRC acts as an indispensable mediator of N-cadherin expression. These results demonstrate that CD133 plays a critical role in facilitating the EMT regulatory loop, specifically by upregulated N-cadherin expression, leading to the invasion and metastasis of pancreatic cancer cells. Our study provides a novel insight into the function of CD133 in the EMT program and a better understanding of the mechanism underlying the involvement of CD133 in pancreatic cancer metastasis.
    Full-text · Article · Jan 2014 · Molecular Cancer
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