Abstract
BackgroundEpithelial-to-mesenchymal transition (EMT) has been associated with the acquisition of metastatic potential and the resistance of cancer cells to therapeutic treatments. MCF-7 breast cancer cells engineered to constitutively express the zinc-finger transcriptional repressor gene Snail (MCF-7-Snail cells) have been previously shown to display morphological and molecular changes characteristic of EMT. We report here the results of a comprehensive systems level molecular analysis of changes in global patterns of gene expression and levels of glutathione and reactive oxygen species (ROS) in MCF-7-Snail cells and the consequence of these changes on the sensitivity of cells to radiation treatment and therapeutic drugs.MethodsSnail-induced changes in global patterns of gene expression were identified by microarray profiling using the Affymetrix platform (U133 Plus 2.0). The resulting data were processed and analyzed by a variety of system level analytical methods. Levels of ROS and glutathione (GSH) were determined by fluorescent and luminescence assays, and nuclear levels of NF-κB protein were determined by an ELISA based method. The sensitivity of cells to ionizing radiation and anticancer drugs was determined using a resazurin-based cell cytotoxicity assay.ResultsConstitutive ectopic expression of Snail in epithelial-like, luminal A-type MCF-7 cells induced significant changes in the expression of >7600 genes including gene and miRNA regulators of EMT. Mesenchymal-like MCF-7-Snail cells acquired molecular profiles characteristic of triple-negative, claudin-low breast cancer cells, and displayed increased sensitivity to radiation treatment, and increased, decreased or no change in sensitivity to a variety of anticancer drugs. Elevated ROS levels in MCF-7-Snail cells were unexpectedly not positively correlated with NF-κB activity.ConclusionsEctopic expression of Snail in MCF-7 cells resulted in morphological and molecular changes previously associated with EMT. The results underscore the complexity and cell-type dependent nature of the EMT process and indicate that EMT is not necessarily predictive of decreased resistance to radiation and drug-based therapies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2274-5) contains supplementary material, which is available to authorized users.
Highlights
Epithelial-to-mesenchymal transition (EMT) has been associated with the acquisition of metastatic potential and the resistance of cancer cells to therapeutic treatments
Among 38,226 probe sets included in the differential expression analysis, over 12,000 probe sets corresponding to 7602 genes were found to display statistically significant differences in expression (4242 up-regulated; 3291 downregulated; 69 discordant) between MCF-7-Snail and MCF7-Control cells (FDR = 2.12 % and |fold change (FC)| ≥1.5 (Additional file 2: Figure S3, Additional files 3 and 4)
The overexpression of SNAI1 (Snail) and SNAI2 (Slug) genes in MCF-7-Snail relative to MCF-7-Control cells was confirmed by qPCR
Summary
Epithelial-to-mesenchymal transition (EMT) has been associated with the acquisition of metastatic potential and the resistance of cancer cells to therapeutic treatments. Metastatic breast cancer (MBC) is present in ~6 % of patients at the time of initial diagnosis and eventually develops in 20–50 % of all breast cancer patients [2]. Epithelial-to-mesenchymal transition (EMT) is an essential process in normal embryonic development [4, 5] and has been associated with the acquisition of metastatic potential [6, 7] and the resistance of breast and other types of cancers to ionizing radiation [8] and anticancer drugs (reviewed in [9]). One of the genes frequently associated with EMT is the zinc-finger transcriptional repressor Snail (SNAI1) [10]. Previous studies indicate that both Snail and Slug may contribute to the progression of breast and other types of cancer by the down regulation of E-cadherin (CDH1) and other genes associated with the epithelial phenotype and the up regulation of genes associated with the mesenchymal phenotype (reviewed in [10, 12])
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