MicroRNAs as regulators of epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) describes the molecular reprogramming and phenotypic changes involved in the conversion of polarised immotile epithelial cells to motile mesenchymal cells. This process allows the remodelling of tissues during embryonic development and is implicated in the promotion of tumor invasion and metastasis. Several recent studies have identified the miR-200 family and miR-205 as key regulators of EMT and enforcers of the epithelial phenotype. The miR-200 family participates in a signalling network with the E-cadherin transcriptional repressors ZEB1/delta EF1 and ZEB2/SIP1, and TGF beta 2 that is postulated to facilitate maintenance of stable epithelial or mesenchymal states but also allow reversible switching between these states in response to EMT effectors (such as TGF beta). This review summarises these recent findings and their implications in both developmental EMT and tumor progression.