Abstract
Recent studies have emphasized the role of the dioxin receptor (AhR) in maintaining cell morphology, adhesion, and migration. These novel AhR functions depend on the cell phenotype, and although AhR expression maintains mesenchymal fibroblasts migration, it inhibits keratinocytes motility. These observations prompted us to investigate whether AhR modulates the epithelial-to-mesenchymal transition (EMT). For this, we have used primary AhR(+/+) and AhR(-/-) keratinocytes and NMuMG cells engineered to knock down AhR levels (sh-AhR) or to express a constitutively active receptor (CA-AhR). Both AhR(-/-) keratinocytes and sh-AhR NMuMG cells had increased migration, reduced levels of epithelial markers E-cadherin and β-catenin, and increased expression of mesenchymal markers Snail, Slug/Snai2, vimentin, fibronectin, and α-smooth muscle actin. Consistently, AhR(+/+) and CA-AhR NMuMG cells had reduced migration and enhanced expression of epithelial markers. AhR activation by the agonist FICZ (6-formylindolo[3,2-b]carbazole) inhibited NMuMG migration, whereas the antagonist α-naphthoflavone induced migration as did AhR knockdown. Exogenous TGFβ exacerbated the promigratory mesenchymal phenotype in both AhR-expressing and AhR-depleted cells, although the effects on the latter were more pronounced. Rescuing AhR expression in sh-AhR cells reduced Snail and Slug/Snai2 levels and cell migration and restored E-cadherin levels. Interference of AhR in human HaCaT cells further supported its role in EMT. Interestingly, co-immunoprecipitation and immunofluorescence assays showed that AhR associates in common protein complexes with E-cadherin and β-catenin, suggesting the implication of AhR in cell-cell adhesion. Thus, basal or TGFβ-induced AhR down-modulation could be relevant in the acquisition of a motile EMT phenotype in both normal and transformed epithelial cells.
Highlights
The dioxin receptor (AhR) regulates cell migration and has a role in TGF activation
In this study we have investigated the role of aryl hydrocarbon receptor (AhR) in epithelial-to-mesenchymal transition (EMT) under both basal and TGF-induced conditions with the aim to determine whether or not AhR expression restrains the acquisition of a migratory EMT phenotype in epithelial cells
AhR Knockdown Induces EMT under Basal Cell Conditions— To analyze the role of AhR in EMT under normal cellular conditions, we have used primary keratinocytes from AhRϩ/ϩ and AhRϪ/Ϫ mouse pups and NMuMG epithelial cells engineered by retroviral transduction to encode a small hairpin RNA for AhR or a constitutively active AhR receptor (CAAhR)
Summary
The dioxin receptor (AhR) regulates cell migration and has a role in TGF activation. Results: AhR expression inhibits basal and TGF-induced epithelial-to-mesenchymal transition (EMT). Recent studies have emphasized the role of the dioxin receptor (AhR) in maintaining cell morphology, adhesion, and migration. These novel AhR functions depend on the cell phenotype, and AhR expression maintains mesenchymal fibroblasts migration, it inhibits keratinocytes motility. These observations prompted us to investigate whether AhR modulates the epithelial-to-mesenchymal transition (EMT). Basal or TGF-induced AhR down-modulation could be relevant in the acquisition of a motile EMT phenotype in both normal and transformed epithelial cells. Among the EMT features that are conserved in most epithelial cell types are the repression of the
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