The Ubiquitin-Proteasome Pathway and Serine Kinase Activity Modulate Adenomatous Polyposis Coli Protein-mediated Regulation of β-Catenin-Lymphocyte Enhancer-binding Factor Signaling*
- From the ‡Department of Cell Biology, Georgetown University School of Medicine and Lombardi Cancer Research Center, Washington, D. C. 20007 and §Onyx Pharmaceuticals, Richmond, California 94806
Abstract
The tumor suppressor function of the adenomatous polyposis coli protein (APC) depends, in part, on its ability to bind and regulate the multifunctional protein, β-catenin. β-Catenin binds the high mobility group box transcription factors, lymphocyte enhancer-binding factor (LEF) and T-cell factor, to directly regulate gene transcription. Using LEF reporter assays we find that APC-mediated down-regulation of β-catenin-LEF signaling is reversed by proteasomal inhibitors in a dose-dependent manner. APC down-regulates signaling induced by wild type β-catenin but not by the non-ubiquitinatable S37A mutant, β-catenin. Bisindoylmaleimide-type protein kinase C inhibitors, which prevent β-catenin ubiquitination, decrease the ability of APC to down-regulate β-catenin-LEF signaling. All these effects on LEF signaling are paralleled by changes in β-catenin protein levels. Lithium, an inhibitor of glycogen synthase kinase-3β, does not alter the ability of APC to down-regulate β-catenin protein and β-catenin-LEF signaling in the colon cancer cells that were tested. These results point to a role for β-catenin ubiquitination, proteasomal degradation, and potentially a serine kinase other than glycogen synthase kinase-3β in the tumor-suppressive actions of APC.
Footnotes
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↵* This work was supported by Grants DAMD1794J-4171 (to V. E.) and DAMD17-98-1-8089 (to S. B.) from the Department of Defense.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: E415 The Research Building, GUMC, 3970 Reservoir Rd., NW, Washington, D. C. 20007. Tel.: 202-687-1813; Fax: 202-687-7505; E-mail:byerss{at}gunet.georgetown.edu.
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↵2 V. Easwaran and S. Byers, unpublished observations.
- Abbreviations:
- APC
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adenomatous polyposis coli
- GSK-3β
-
glycogen synthase kinase-3β
- LEF
-
lymphocyte enhancer-binding factor
- ALLN
-
N-acetyl-Leu-Leu-norleucinal
- ALLM
-
N-acetyl-Leu-Leu-methional
- WT
-
wild type
- PKC
-
protein kinase C
- TPA
-
12-O-tetradecanoylphorbol 13-acetate
- DAG
-
diacylglycerol
- NKκB
-
nuclear factor κB
- IκB
-
inhibitor of NFκB
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- Received January 21, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
