title: The PDZ protein tax-interacting protein-1 inhibits beta-catenin transcriptional activity and growth of colorectal cancer cells.
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.
authors.affiliation: Laboratory for Genome Exploration Research Group, RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan.
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Kanamori
authors.forename: Peter
authors.initials: P
authors.lastname: Sandy
authors.forename: Stefania
authors.initials: S
authors.lastname: Marzinotto
authors.forename: Roberta
authors.initials: R
authors.lastname: Benetti
authors.forename: Chikatoshi
authors.initials: C
authors.lastname: Kai
authors.forename: Yoshihide
authors.initials: Y
authors.lastname: Hayashizaki
authors.forename: Claudio
authors.initials: C
authors.lastname: Schneider
authors.forename: Harukazu
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D000362:Agar / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002352:Carrier Proteins; D002455:Cell Division; D002460:Cell Line; D015179:Colorectal Neoplasms / Q000378:metabolism*; D006224:Cricetinae; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D017930:Genes, Reporter; D005972:Glutaminase; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000502:physiology*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D020798:Two-Hybrid System Techniques; D051176:beta Catenin
chemical_list: C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D034741:RNA, Small Interfering; C421249:TAX1BP3 protein, human; D015534:Trans-Activators; D051176:beta Catenin; D000362:Agar; D008156:Luciferases; D005982:Glutathione Transferase; D005972:Glutaminase