PMID:12874278

Citation	Kanamori, M, Sandy, P, Marzinotto, S, Benetti, R, Kai, C, Hayashizaki, Y, Schneider, C and Suzuki, H (2003) The PDZ protein tax-interacting protein-1 inhibits beta-catenin transcriptional activity and growth of colorectal cancer cells. J. Biol. Chem. 278:38758-64
Abstract	Wnt signaling is essential during development while deregulation of this pathway frequently leads to the formation of various tumors including colorectal carcinomas. A key component of the pathway is beta-catenin that, in association with TCF-4, directly regulates the expression of Wnt-responsive genes. To identify novel binding partners of beta-catenin that may control its transcriptional activity, we performed a mammalian two-hybrid screen and isolated the Tax-interacting protein (TIP-1). The in vivo complex formation between beta-catenin and TIP-1 was verified by coimmunoprecipitation, and a direct physical association was revealed by glutathione S-transferase pull-down experiments in vitro. By using a panel of deletion mutants of both proteins, we demonstrate that the interaction is mediated by the PDZ (PSD-95/DLG/ZO-1 homology) domain of TIP-1 and requires primarily the last four amino acids of beta-catenin. TIP-1 overexpression resulted in a dose-dependent decrease in the transcriptional activity of beta-catenin when tested on the TOP/FOPFLASH reporter system. Conversely, siRNA-mediated knock-down of endogenous TIP-1 slightly increased endogenous beta-catenin transactivation function. Moreover, we show that overexpression of TIP-1 reduced the proliferation and anchorage-independent growth of colorectal cancer cells. These data suggest that TIP-1 may represent a novel regulatory element in the Wnt/beta-catenin signaling pathway.
Links	PubMed Online version:10.1074/jbc.M306324200
Keywords	Agar/pharmacology; Animals; Blotting, Western; CHO Cells; Carrier Proteins; Cell Division; Cell Line; Colorectal Neoplasms/metabolism; Cricetinae; Cytoskeletal Proteins/metabolism; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; Genes, Reporter; Glutaminase; Glutathione Transferase/metabolism; Humans; Intracellular Signaling Peptides and Proteins; Luciferases/metabolism; Mice; Microscopy, Fluorescence; Models, Genetic; Precipitin Tests; Protein Binding; Protein Structure, Tertiary; Proteins/physiology; RNA Interference; RNA, Small Interfering/metabolism; Signal Transduction; Trans-Activators/metabolism; Transcription, Genetic; Transcriptional Activation; Transfection; Two-Hybrid System Techniques; beta Catenin
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