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

Abstract

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 γ-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 β-catenin, which stabilizes and redistributes both proteins to the cytosol and nucleus, leading to up-regulation of β-catenin, CyclinD1, Snail2, and Snail2 promoter-based GFP expression in vivo. A CTF2 β-catenin–binding mutant, however, fails to alter gene expression, indicating that CTF2 modulates β-catenin–responsive EMT effector genes. Notably, CTF2 association with the endogenous Snail2 promoter in the neural crest is β-catenin 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.

Should I stay or should I go? Cadherin function and regulation in the neural crest

“…Building on their prior findings, Schiffmacher et al (2016) discovered that, like Cadherin-6B NTFs, Cadherin-6B CTFs are generated both prior to and during EMT. As cadherin CTF2s in cultured cells have been shown to interact with catenin proteins (Ferber et al, 2008; Marambaud et al, 2002; Sadot, Simcha, Shtutman, Ben-Ze’ev, & Geiger, 1998; Uemura et al, 2006), this possibility was also tested for Cadherin-6B CTF2.…”

“…Altogether, these data suggest that continual proteolysis of Cadherin-6B, both prior to and during EMT, is key to allow sufficient levels of a Cadherin-6B CTF2/β-catenin complex to accumulate, translocate to the nucleus, and activate genes important for cranial neural crest EMT (Schiffmacher et al, 2016). Arguably one important function for CTF2 is to protect β-catenin from degradation, allowing it to accumulate in the cytosol, followed by co-import of both proteins to the nucleus, wherein β-catenin can then modulate transcription through interactions with TCF/LEF or other proteins.…”

“…The authors propose a model in which binding of Snail2 to E-boxes in the Cadherin-6B promoter, coupled with PHD12 binding to the Cadherin-6B transcriptional start site and the formation of a Sin3A/HDAC-repressive complex, results in the de-acetylation of the Cadherin-6B promoter and the repression of Cadherin-6B transcription during cranial neural crest EMT. A recent study has now shown that Snail2-mediated repression of Cadherin-6B during neural crest cell EMT is in part regulated through proteolysis of Cadherin-6B itself (Schiffmacher, Xie, & Taneyhill, 2016). The intracellular Cadherin-6B C-terminal fragment (CTF2) that arises after Cadherin-6B proteolysis associates with the endogenous Snail2 promoter in cranial neural crest cells and upregulates the expression of Snail2 and other EMT effector genes (see below for additional details).…”

“…The molecular mechanism behind this pro-EMT function for Cadherin-6B has recently been elucidated (Schiffmacher et al, 2016). Building on their prior findings, Schiffmacher et al (2016) discovered that, like Cadherin-6B NTFs, Cadherin-6B CTFs are generated both prior to and during EMT.…”

Cadherins function during the collective cell migration of Xenopus Cranial Neural Crest cells: revisiting the role of E-cadherin

“…If it were shown to happen for E-cadherin in the context of CNC, it would provide an elegant way to remove any lingering negative impact of E-Cadherin cytoplasmic domain on CNC migration and possibly protect β-catenin from degradation during the transit toward the nucleus. Recently, the cleaved CTF of cadherin-6B was shown to associate with β-catenin, translocate into the nucleus and regulate the expression of multiple genes associated with EMT in Chick neural crest (Schiffmacher et al, 2016). …”