Protein Binding and Functional Characterization of Plakophilin 2
EVIDENCE FOR ITS DIVERSE ROLES IN DESMOSOMES AND β-CATENIN SIGNALING*
- From the ‡Departments of Pathology and Dermatology and the Robert H. Lurie Cancer Center, Northwestern University Medical School, Chicago, Illinois 60611, the§Molecular Cell Biology Unit, Department of Molecular Biology, VIB-University of Ghent, Ledeganckstraat 35, B-9000 Ghent, Belgium, and the ¶Molecular Biology Group of the Medical Faculty, University of Halle, 06097 Halle/Saale, Germany
Abstract
Plakophilins are a subfamily of p120-related arm-repeat proteins that can be found in both desmosomes and the nucleus. Among the three known plakophilin members, plakophilin 1 has been linked to a genetic skin disorder and shown to play important roles in desmosome assembly and organization. However, little is known about the binding partners and functions of the most widely expressed member, plakophilin 2. To better understand the cellular functions of plakophilin 2, we have examined its protein interactions with other junctional molecules using co-immunoprecipitation and yeast two-hybrid assays. Here we show that plakophilin 2 can interact directly with several desmosomal components, including desmoplakin, plakoglobin, desmoglein 1 and 2, and desmocollin 1a and 2a. The head domain of plakophilin 2 is critical for most of these interactions and is sufficient to direct plakophilin 2 to cell borders. In addition, plakophilin 2 is less efficient than plakophilin 1 in localizing to the nucleus and enhancing the recruitment of excess desmoplakin to cell borders in transiently transfected COS cells. Furthermore, plakophilin 2 is able to associate with β-catenin through its head domain, and the expression of plakophilin 2 in SW480 cells up-regulates the endogenous β-catenin/T cell factor-signaling activity. This up-regulation by plakophilin 2 is abolished by ectopic expression of E-cadherin, suggesting that these proteins compete for the same pool of signaling active β-catenin. Our results demonstrate that plakophilin 2 interacts with a broader repertoire of desmosomal components than plakophilin 1 and provide new insight into the possible roles of plakophilin 2 in regulating the signaling activity of β-catenin.
Footnotes
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↵* This work is supported by a R. H. Lurie Baseball Charities Cancer Fellowship (to X. C.), an Institute for the Promotion of Innovation by Science and Technology-Flanders Fellowship (to S. B), Deutsche Forschungsgemeinschaft Grant Hal791/3-4 (to M. H.), a Fund for Scientific Research-Flanders grant (to F. v.-R.), and National Institutes of Health Grants RO1 AR43380, PO1 DE12328 (project 4), and AR41836 (to K. G.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‖ To whom correspondence should be addressed: Dept. of Pathology, Northwestern University Medical School, 303 East Chicago Ave., Chicago, IL 60611. Tel.: 312-503-5300; Fax: 312-503-8240; E-mail: kgreen@northwestern.edu.
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Published, JBC Papers in Press, January 14, 2002, DOI 10.1074/jbc.M108765200
- Abbreviations:
- PKP
-
plakophilin
- IF
-
intermediate filament
- Pg
-
plakoglobin
- Dsg
-
desmoglein
- Dsc
-
desmocollin
- DP
-
desmoplakin
- DPNTP
-
desmoplakin N-terminal polypeptide
- IP
-
immunoprecipitation
- nt
-
nucleotide(s)
- kb
-
kilobase
- PBS
-
phosphate-buffered saline
- X-α-gal
-
5-bromo-4-chloro-3-indolyl α-d-galactopyranoside
- TCF
-
T cell factor
-
- Received September 11, 2001.
- Revision received December 18, 2001.
- The American Society for Biochemistry and Molecular Biology, Inc.
