Coupling Assembly of the E-Cadherin/β-Catenin Complex to Efficient Endoplasmic Reticulum Exit and Basal-lateral Membrane Targeting of E-Cadherin in Polarized MDCK Cells

Abstract

The E-cadherin/catenin complex regulates Ca++-dependent cell–cell adhesion and is localized to the basal-lateral membrane of polarized epithelial cells. Little is known about mechanisms of complex assembly or intracellular trafficking, or how these processes might ultimately regulate adhesion functions of the complex at the cell surface. The cytoplasmic domain of E-cadherin contains two putative basal-lateral sorting motifs, which are homologous to sorting signals in the low density lipoprotein receptor, but an alanine scan across tyrosine residues in these motifs did not affect the fidelity of newly synthesized E-cadherin delivery to the basal-lateral membrane of MDCK cells. Nevertheless, sorting signals are located in the cytoplasmic domain since a chimeric protein (GP2CAD1), comprising the extracellular domain of GP2 (an apical membrane protein) and the transmembrane and cytoplasmic domains of E-cadherin, was efficiently and specifically delivered to the basal-lateral membrane. Systematic deletion and recombination of specific regions of the cytoplasmic domain of GP2CAD1 resulted in delivery of <10% of these newly synthesized proteins to both apical and basal-lateral membrane domains. Significantly, >90% of each mutant protein was retained in the ER. None of these mutants formed a strong interaction with β-catenin, which normally occurs shortly after E-cadherin synthesis. In addition, a simple deletion mutation of E-cadherin that lacks β-catenin binding is also localized intracellularly. Thus, β-catenin binding to the whole cytoplasmic domain of E-cadherin correlates with efficient and targeted delivery of E-cadherin to the lateral plasma membrane. In this capacity, we suggest that β-catenin acts as a chauffeur, to facilitate transport of E-cadherin out of the ER and the plasma membrane.

Scattering of Cell Clusters in Confinement

“…The cytoplasmic E-cadherin binds to b-catenin and translocates to the cell membrane to form new cell-cell bonds (29). Thus, in the model, the ruptured CC complexes are allowed to form new CC junctions as follows:…”

The importance of E-cadherin binding partners to evaluate the pathogenicity of E-cadherin missense mutations associated to HDGC

“…[23][24][25][26] The association of b-catenin and PIPKIg to E-cadherin cytoplasmic tail is necessary for newly synthesized E-cadherin delivery to basal-lateral membrane. 27,28 At the PM, E-cadherin molecules constitutively undergo endocytosis and can either be recycled back to the PM or be degraded. 23 The p120-catenin is the best known inhibitor of cadherin endocytosis, as its binding to the E-cadherin juxtamembrane domain is required for maintenance and stability of E-cadherin molecules at the PM and, simultaneously, it physically blocks the interaction with proteins from the endocytic machinery, such as clathrin adaptor proteins and Hakai.…”

“…Newly synthesized E-cadherin is transported from the Golgi apparatus to the plasma membrane (PM), after the association of b-catenin and Type Ig phosphatidylinositol phosphate kinase (PIPKIg) to the cytoplasmic tail of E-cadherin. 27,28 At the PM, p120-catenin binds to the cadherin juxtamembrane domain, stabilizing and preventing the entry of E-cadherin into degradative endocytic pathways. [29][30][31][32] E-cadherin deprived of p120 is prone to interact with other proteins, such as clathrin adapter proteins and Hakai, promoting E-cadherin internalization.…”

Formation of E-Cadherin/β-Catenin–based Adherens Junctions in Hepatocytes Requires Serine-10 in p27(Kip1)

“…The intracellular trafficking and mobilization of adherens junction components at the cell surface is important for growth and development and, possibly, cancer, and is subject to extensive research (Bryant and Stow, 2004). The exit of newly synthesized E-cadherin from the endoplasmic reticulum and its delivery to the lateral cell surface is facilitated by its interaction with ␤-catenin (Chen et al, 1999;Miranda et al, 2001). Once delivered, E-cadherin is subject to recycling via the endosomal system (Le et al, 1999), a process that is tightly regulated by various signaling molecules (reviewed in Bryant and Stow, 2004).…”