Endocytosis and micropinocytosis internalise cadherin-6B in EMT

Epithelial-to-mesenchymal transition (EMT) is an integral developmental and physiological process, but can also be utilised by cancer cells at the initiation of metastasis. A requirement for EMT is the post-translational removal of adhesion proteins from the plasma membrane. Here (p. 1773), Lisa Taneyhill and Rangarajan Padmanabhan study cadherin-6B (Cad6B) internalisation to elucidate the mechanisms of EMT in chick cranial neural crest cells. The authors found that in neural crest cells that are initiating EMT, Cad6B was detected in cytosolic puncta that were endocytic, rather than exocytic, in nature. They then identified two intracellular motifs that were potentially important for regulating Cad6B internalisation. Mutating the p120-catenin-binding (EED) motif, but not the dileucine (LI) motif, significantly increased Cad6B internalisation, supporting the idea that Cad6B is removed from the plasma membrane through endocytosis. However, although Cad6B colocalised with clathrin, the colocalisation was not exhaustive, suggesting that an additional mechanism is involved in Cad6B internalisation. Therefore, the authors used an array of pharmacological treatments to show that Cad6B was removed from the plasma membrane through both endocytosis and macropinocytosis, and that both of these processes depended on dynamin. This study demonstrates that EMT and neural crest migration require Cad6B internalisation through endocytosis and macropinocytosis.