Identification of a desmocollin 3–β-catenin complex modulated by Vwde–calpain signaling in ameloblast differentiation

Desmocollin 3 (Dsc3), a desmosomal cadherin, mediates cell-cell adhesion, but its role in dental epithelial cell differentiation remains largely unknown. Using in situ hybridization and immunostaining of mouse incisors, Dsc3 is expressed in the outer enamel epithelium, inner enamel epithelium (IEE) containing transit-amplifying (TA) cells, stratum intermedium, and stellate reticulum, but absent in differentiated ameloblasts. Knockdown of endogenous Dsc3 by siRNA in the odontogenic dental epithelial cell line M3H1 inhibited the expression of the ameloblast makers ameloblastin (Ambn) and amelogenin, indicating the involvement of Dsc3 in ameloblast differentiation. Immunostaining and immunoprecipitation analyses revealed that DSC3 directly co-localized with β-catenin at the cell membrane; this association was disrupted by calpain activity during ameloblast differentiation. von Willebrand factor D and epidermal growth factor domains (Vwde), which was highly expressed in the IEE and particularly in TA cells, upregulated calpain 2 expression in M3H1 cells. VWDE-overexpressing M3H1 cells exhibited enhanced Ambn expression, whereas this induction was suppressed by the calpain inhibitor calpeptin. Western blotting further revealed that VWDE-overexpressing cells induced a 75-kDa β-catenin fragment in the nucleus. These findings suggest that Vwde-calpain signaling regulates DSC3-β-catenin complex, acting as a molecular switch that links cell adhesion to β-catenin-dependent ameloblast differentiation.