Abstract
Epithelial tumour cells can gain invasive and metastatic capabilities by undergoing an epithelial–mesenchymal transition. Transcriptional regulators and post-transcriptional effectors like microRNAs orchestrate this process of high cellular plasticity and its malignant consequences. Here, using microRNA sequencing in a time-resolved manner and functional validation, we have identified microRNAs that are critical for the regulation of an epithelial–mesenchymal transition and of mesenchymal tumour cell migration. We report that miR-1199-5p is downregulated in its expression during an epithelial–mesenchymal transition, while its forced expression prevents an epithelial–mesenchymal transition, tumour cell migration and invasion in vitro, and lung metastasis in vivo. Mechanistically, miR-1199-5p acts in a reciprocal double-negative feedback loop with the epithelial–mesenchymal transition transcription factor Zeb1. This function resembles the activities of miR-200 family members, guardians of an epithelial cell phenotype. However, miR-1199-5p and miR-200 family members share only six target genes, indicating that, besides regulating Zeb1 expression, they exert distinct functions during an epithelial–mesenchymal transition.
Highlights
Epithelial tumour cells can gain invasive and metastatic capabilities by undergoing an epithelial–mesenchymal transition
To identify regulatory miRNAs involved in the gradual process of an epithelial-to-mesenchymal transition (EMT), we performed miRNA sequencing on a detailed time course of a transforming growth factor β (TGFβ)-induced EMT in normal murine mammary gland cells (NMuMG subclone E9; NMuMG/E9)
In order to identify the miRNAs functionally impacting on a TGFβ-induced EMT, we performed a microscopy-based screen in which NMuMG/E9 cells were transfected with miRNA mimics and cultured in the absence or presence of TGFβ for 4 days (Fig. 1b)
Summary
Epithelial tumour cells can gain invasive and metastatic capabilities by undergoing an epithelial–mesenchymal transition. MiR-1199-5p acts in a reciprocal double-negative feedback loop with the epithelial–mesenchymal transition transcription factor Zeb[1] This function resembles the activities of miR-200 family members, guardians of an epithelial cell phenotype. Among many growth factors and environmental cues, such as tissue hypoxia, transforming growth factor β (TGFβ) strongly activates the dedifferentiation process in epithelial tumour cells and, induces global changes in a cell’s transcriptional and post-transcriptional networks[2,3,4]. Zeb[1] and Zeb[2] directly suppress the transcription of miR-200 family members[14,15,16,17] Such a double-negative feedback loop is a major example for a reciprocal TF-miRNA regulation during an EMT. MiR-200 family members and miR-1199-5p seem to exert distinct functions; they share only six of their many target mRNAs, among them Zeb[1]
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