Cadherin-6B proteolysis promotes the neural crest cell epithelial-to-mesenchymal transition through transcriptional regulation

During epithelial-to-mesenchymal transitions (EMTs), cells disassemble cadherin-based junctions to segregate from the epithelia. Chick premigratory cranial neural crest cells reduce Cadherin-6B (Cad6B) levels through several mechanisms, including proteolysis, to permit their EMT and migration. Serial processing of Cad6B by a disintegrin and metalloproteinase (ADAM) proteins and gamma-secretase generates intracellular C-terminal fragments (CTF2s) that could acquire additional functions. Here we report that Cad6B CTF2 possesses a novel pro-EMT role by up-regulating EMT effector genes in vivo. After proteolysis, CTF2 remains associated with beta-caten in, which stabilizes and redistributes both proteins to the cytosol and nucleus, leading to up-regulation of beta-catenin, CyclinD1, Snail2, and Snail2 promoter-based GFP expression in vivo. A CTF2 beta-catenin binding mutant, however, fails to alter gene expression, indicating that CTF2 modulates beta-catenin responsive EMT effector genes. Notably, CTF2 association with the endogenous Snail2 promoter in the neural crest is beta-caten in dependent. Collectively, our data reveal how Cad6B proteolysis orchestrates multiple pro-EMT regulatory inputs, including CTF2-mediated up-regulation of the Cad6B repressor Snail2, to ensure proper cranial neural crest EMT.