Figure 1.

Scheme of the epithelial–mesenchymal transition (EMT)/mesenchymal–epithelial transition (MET) program. Epithelial cells are defined primarily by their cell–cell contacts consisting of tight junctions, adherens junctions, and desmosomes. The contact to the underlying basement membrane is mediated by hemidesmosomes. Proteins associated mainly with the epithelial state modulate cell polarity and cell–cell contact (green box). Induction of EMT by various stimuli results in expression of the EMT transcription factors (TFs) (Zinc finger E-box-binding homeobox (ZEB), Snail, T Twist), red box), which inhibit the expression of “epithelial genes” (green box) and activate the expression of “mesenchymal genes” (red box). The subsequent cellular changes like disassembly of epithelial cell–cell contacts, loss of apical-basal cell polarity, and degradation of the underlying basement membrane are achieved via repression of crumbs, Protein associated with LIN-7 (PALS1)-associated tight junction protein (PATJ), and lethal giant larvae (LGL), which regulate tight junction formation and apical-basal polarity (orange box). During EMT, cells acquire motility and invasive capabilities. MET can reverse EMT and cells revert to an epithelial state. The whole process is neither black and white nor always complete, but it can show intermediate states (orange box). Modified from Dongre and Weinberg [46].