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© The Rockefeller University Press, 0021-9525/1999//687 $5.00
The Journal of Cell Biology, Volume 144, Number 4, , 1999 687-699

Regular Articles

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



Yih-Tai Chen, Daniel B. Stewart, and W. James Nelson

Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305-5435

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.

Key Words: polarity • epithelia • adhesion • protein targeting • membrane domains

Abbreviations used in this paper: aa, amino acids; arm, armadillo; CYT, cytoplasmic; endo H, endoglycosidase H; GFP, green fluorescent protein; GPI, glycosylphosphotidylinositol; LDL, low density lipoprotein; TER, transepithelial electrical resistance; TM, transmembrane.

Address correspondence to W. James Nelson, Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5435. Tel.: (650) 725-7596. Fax: (650) 498-5286. E-mail: wjnelson{at}leland.stanford.edu

Yih-Tai Chen's current address is Cellomics, Inc., 635 William Pitt Way, Pittsburgh, PA 15238.


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