title: Chromatin-specific regulation of LEF-1-beta-catenin transcription activation and inhibition in vitro.
abstract: Transcriptional activation of Wnt/Wg-responsive genes requires the stabilization and nuclear accumulation of beta-catenin, a dedicated coactivator of LEF/TCF enhancer-binding proteins. Here we report that recombinant beta-catenin strongly enhances binding and transactivation by LEF-1 on chromatin templates in vitro. Interestingly, different LEF-1 isoforms vary in their ability to bind nucleosomal templates in the absence of beta-catenin, owing to N-terminal residues that repress binding to chromatin, but not nonchromatin, templates. Transcriptional activation in vitro requires both the armadillo (ARM) repeats and the C terminus of beta-catenin, whereas the phosphorylated N terminus is inhibitory to transcription. A fragment spanning the C terminus (CT) and ARM repeats 11 and 12 (CT-ARM), but not the CT alone, functions as a dominant negative inhibitor of LEF-1-beta-cat activity in vitro and can block ATP-dependent binding of the complex to chromatin. LEF-1-beta-cat transactivation in vitro was also repressed by inhibitor of beta-catenin and Tcf-4 (ICAT), a physiological inhibitor of Wnt/Wg signaling that interacts with ARM repeats 11 and 12, and by the nonsteroidal anti-inflammatory compound, sulindac. None of these transcription inhibitors (CT-ARM, ICAT, or sulindac) could disrupt the LEF-1-beta-cat complex after it was stably bound to chromatin. We conclude that the CT-ARM region of beta-catenin functions as a chromatin-specific activation domain, and that several inhibitors of the Wnt/Wg pathway directly modulate LEF-1-beta-cat activity on chromatin.
authors.affiliation: Regulatory Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
authors.forename: A V
authors.initials: AV
authors.lastname: Tutter
authors.forename: C J
authors.initials: CJ
authors.lastname: Fryer
authors.forename: K A
authors.initials: KA
authors.lastname: Jones
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000235:genetics / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila; D006801:Humans; D051821:Lymphoid Enhancer-Binding Factor 1; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013467:Sulindac / Q000494:pharmacology; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; C495270:CTNNB1 protein, human; D002843:Chromatin; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; C497573:LEF1 protein, human; D051821:Lymphoid Enhancer-Binding Factor 1; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D015534:Trans-Activators; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D013467:Sulindac