Abstract
E12/E47 proteins (encoded by E2A gene) are members of the class I basic helix-loop-helix (bHLH) transcription factors (also known as E proteins). E47 has been described as repressor of E-cadherin and inducer of epithelial-mesenchymal transition (EMT). We reported previously that EMT mediated by E47 in MDCK cells occurs with a concomitant overexpression of Id1 and Id3 proteins. Id proteins belong to class V of HLH factors that lack the basic domain; they dimerise with E proteins and prevent their DNA interaction, thus, acting as dominant negative of E proteins. Here, we show that E47 interacts with Id1 in E47 overexpressing MDCK cells that underwent a full EMT as well as in mesenchymal breast carcinoma and melanoma cell lines. By conducting chromatin immunoprecipitation assays we demonstrate that E47 binds directly to the endogenous E-cadherin promoter of mesenchymal MDCK-E47 cells in a complex devoid of Id1. Importantly, our data suggest that both E47 and Id1 are required to maintain the mesenchymal phenotype of MDCK-E47 cells. These data support the collaboration between E47 and Id1 in the maintenance of EMT by mechanisms independent of the dominant negative action of Id1 on E47 binding to E-cadherin promoter. Finally, the analysis of several N0 breast tumour series indicates that the expression of E47 and ID1 is significantly associated with the basal-like phenotype supporting the biological significance of the present findings.
Highlights
Epithelial-mesenchymal transition (EMT) is presently recognised as a key process for tumour invasion and metastasis [1,2,3]
Extensive characterization of MDCKEGFP-E47 cells was performed in three independent clones that showed almost complete repression of E-cadherin and the same mesenchymal phenotype and properties than previously described for MDCK-E47 cells including a full EMT conversion and overexpression of Id1 and Id3 factors (Figure 1A; Figure S1)
Confocal analysis in MDCK-EGFP-E47 cells showed that Id1 protein was localized mainly in the nuclei; Id1 colocalized with EGFP-E47 in the majority of cells (Figure1C, panels f, h)
Summary
Epithelial-mesenchymal transition (EMT) is presently recognised as a key process for tumour invasion and metastasis [1,2,3]. The hallmarks defining the EMT process are the loss of Ecadherin mediated cell-cell adhesion and epithelial cell polarity concomitant to the acquisition of mesenchymal markers and increased motility and invasiveness [2,3,4]. The molecular mechanisms underlying the action of the various EMT-TFs are unequally known for Snail1 [6,7,8,9,10,11], Snail and ZEB1 factors [12,13]. Much less is known on the mechanism of bHLH factors participating in EMT [14]
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