Abstract
Epithelial-mesenchymal transition (EMT) plays an important role in development and also in initiation of metastasis during cancer. Disruption of cell-cell contacts during EMT allowing cells to detach from and migrate away from their neighbors remains poorly understood. Using immunofluorescent staining and live-cell imaging, we analyzed early events during EMT induced by epidermal growth factor (EGF) in IAR-20 normal epithelial cells. Control cells demonstrated stable adherens junctions (AJs) and robust contact paralysis, whereas addition of EGF caused rapid dynamic changes at the cell-cell boundaries: fragmentation of the circumferential actin bundle, assembly of actin network in lamellipodia, and retrograde flow. Simultaneously, an actin-binding protein EPLIN was phosphorylated, which may have decreased the stability of the circumferential actin bundle. Addition of EGF caused gradual replacement of linear E-cadherin–based AJs with dynamic and unstable punctate AJs, which, unlike linear AJs, colocalized with the mechanosensitive protein zyxin, confirming generation of centripetal force at the sites of cell-cell contacts during EMT. Our data show that early EMT promotes heightened dynamics at the cell-cell boundaries—replacement of stable AJs and actin structures with dynamic ones—which results in overall weakening of cell-cell adhesion, thus priming the cells for front-rear polarization and eventual migration.
Highlights
Epithelial-mesenchymal transition (EMT) plays an important role in development and wound healing
Our observations show that treatment with epidermal growth factor (EGF) of immortalized IAR-20 epithelial cells immediately triggers a series of events at the cell-cell boundaries that actively lead to increased dynamics of the actin cytoskeleton and adherens junctions (AJs)
As revealed by immunofluorescent staining, individual cells and cells joined into islands had a marginal actin bundle at the free edges and circumferential bundles which colocalized with linear AJs. (Figure 1a–c)
Summary
Epithelial-mesenchymal transition (EMT) plays an important role in development and wound healing. The EMT program is regarded as the driver of invasion and metastatic dissemination of carcinoma cells [3,4]. It has long been thought that in cancer, EMT is a transcriptionally regulated program where tumor cells repress epithelial gene transcription and upregulate mesenchymal genes. It has been shown that E-cadherin, the main mediator of stable cell-cell adhesion in epithelial tissues, is transcriptionally repressed by EMT transcription factors (e.g., Snail, Twist, and Zeb). EMT transcription factors can induce expression of mesenchymal markers such as N-cadherin, vimentin, and fibronectin [2,3,5]
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