Fig. 3.

Progression of molecular and cellular events in EMT. A) Under homeostatic conditions, epithelial cells form coherent epithelial sheets and express molecules uniquely associated with the epithelial-phenotype, such as E-cadherin, β-catenin, occludins, and α6β4 integrins. B) Exposure of epithelial cells to EMT-inducer(s), e.g., cytokines or Gram-negative bacterial components, triggers the EMT process. Early events include loss of apico-basal polarity followed by downregulation of attachment proteins concomitant with up-regulation of mesenchymal proteins, such as vimentin. At this stage, both epithelial and mesenchymal biomarkers are co-expressed in the same cell and this is defined as partial EMT. C) Prolonged exposure to EMT-inducers results in a complete loss of the epithelial phenotype and acquisition of a mesenchymal phenotype. Transitioned cells exhibit increased motility together with increased expression of matrix metalloproteinases that degrade the basement membrane, thereby, facilitating migration of these mesenchymal cells to the underlying connective tissue.