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Molecular and Cellular Biology, June 2000, p. 4238-4252, Vol. 20, No. 12
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Differential Mechanisms of LEF/TCF Family-Dependent Transcriptional Activation by beta -Catenin and Plakoglobin

Jacob Zhurinsky, Michael Shtutman, and Avri Ben-Ze'ev*

Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot, 76100, Israel

Received 5 October 1999/Returned for modification 15 November 1999/Accepted 27 March 2000

beta -Catenin and plakoglobin are highly homologous components of cell-cell adherens junctions linking cadherin receptors to the actin cytoskeleton. beta -Catenin, in addition, activates transcription by forming a complex with LEF/TCF family transcription factors in the nucleus. Plakoglobin can also bind to LEF-1 and, when overexpressed in mammalian cells, enhances LEF-1-directed transcription. Plakoglobin overexpression, however, results in the elevation and nuclear translocation of endogenous beta -catenin. We show here, by DNA mobility shift analysis, that the formation of a plakoglobin-LEF/TCF-DNA complex in vitro is very inefficient compared to a complex containing beta -catenin-LEF-DNA. Moreover, in plakoglobin-transfected cells plakoglobin-LEF/TCF-DNA complexes were not formed; rather, the endogenous beta -catenin, whose level is elevated by plakoglobin transfection, formed a beta -catenin-LEF-DNA complex. Removal of the N- and C-terminal domains of both beta -catenin and plakoglobin (leaving the armadillo repeat domain intact) induced plakoglobin-LEF-DNA complex formation and also enhanced beta -catenin-LEF-DNA complexing, both with in vitro-translated components and in transfected cells. Transfection with these truncated catenins increased endogenous beta -catenin levels, but the truncated catenins acted as dominant-negative inhibitors of beta -catenin-driven transcription by forming transcriptionally inactive complexes with LEF-1. When these catenin mutants were prevented from entering the nucleus, by their fusion to the connexin transmembrane domain, they indirectly activated transcription by increasing endogenous beta -catenin levels. These results suggest that overexpression of plakoglobin does not directly activate transcription and that formation of catenin-LEF-DNA complexes is negatively regulated by the catenin N- and C-terminal domains.

* Corresponding author. Mailing address: Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot, 76100, Israel. Phone: (972)-8-934-2422. Fax: (972)-8-946-5261. E-mail: avri.ben-zeev{at}weizmann.ac.il.

Molecular and Cellular Biology, June 2000, p. 4238-4252, Vol. 20, No. 12
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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