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© The Rockefeller University Press, 0021-9525/1997//693 $5.00
The Journal of Cell Biology, Volume 136, Number 3, , 1997 693-706

Article

NH2-terminal Deletion of β-Catenin Results in Stable Colocalization of Mutant β-Catenin with Adenomatous Polyposis Coli Protein and Altered MDCK Cell Adhesion



Angela I.M. Barth*, Anne L. Pollack{ddagger}, Yoram Altschuler{ddagger}, Keith E. Mostov{ddagger}, and W. James Nelson*

* Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305-5426; and {ddagger} Department of Anatomy, Department of Biochemistry and Cardiovascular Research Institute, University of California at San Francisco, San Francisco, California 94143-0452

β-Catenin is essential for the function of cadherins, a family of Ca2+-dependent cell–cell adhesion molecules, by linking them to {alpha}-catenin and the actin cytoskeleton. β-Catenin also binds to adenomatous polyposis coli (APC) protein, a cytosolic protein that is the product of a tumor suppressor gene mutated in colorectal adenomas. We have expressed mutant β-catenins in MDCK epithelial cells to gain insights into the regulation of β-catenin distribution between cadherin and APC protein complexes and the functions of these complexes. Full-length β-catenin, β-catenin mutant proteins with NH2-terminal deletions before ({Delta}N90) or after ({Delta}N131, {Delta}N151) the {alpha}-catenin binding site, or a mutant β-catenin with a COOH-terminal deletion ({Delta}C) were expressed in MDCK cells under the control of the tetracycline-repressible transactivator. All β-catenin mutant proteins form complexes and colocalize with E-cadherin at cell–cell contacts; {Delta}N90, but neither {Delta}N131 nor {Delta}N151, bind {alpha}-catenin. However, β-catenin mutant proteins containing NH2-terminal deletions also colocalize prominently with APC protein in clusters at the tips of plasma membrane protrusions; in contrast, full-length and COOH-terminal– deleted β-catenin poorly colocalize with APC protein. NH2-terminal deletions result in increased stability of β-catenin bound to APC protein and E-cadherin, compared with full-length β-catenin. At low density, MDCK cells expressing NH2-terminal–deleted β-catenin mutants are dispersed, more fibroblastic in morphology, and less efficient in forming colonies than parental MDCK cells. These results show that the NH2 terminus, but not the COOH terminus of β-catenin, regulates the dynamics of β-catenin binding to APC protein and E-cadherin. Changes in β-catenin binding to cadherin or APC protein, and the ensuing effects on cell morphology and adhesion, are independent of β-catenin binding to {alpha}-catenin. These results demonstrate that regulation of β-catenin binding to E-cadherin and APC protein is important in controlling epithelial cell adhesion.

Abbreviations used in this paper: APC, adenomatous polyposis coli; Dox, doxycycline; GSK3β, glycogen synthase kinase 3β; RT, room temperature; Tet, tetracycline.

We are very thankful to Drs. Inke Näthke and Paul Polakis for providing APC protein antisera and for helpful discussions. We also thank Dr. Rolf Kemler for providing the β-catenin cDNA; Dr. Hermann Bujard for providing the plasmids for the tetracycline-repressible expression system; Dr. Gernot Walter for providing the mAb KT3; and Drs. Helen McNeill and Eugenio de Hostos for their advice during preparation of the manuscript.

A.I.M. Barth and A.L. Pollack contributed equally to this work.


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