Chromatin-specific regulation of LEF-1-beta-catenin transcription activation and inhibition in vitro.
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.
Pubmed ID: 11751639 RIS Download
Amino Acid Sequence | Animals | Anti-Inflammatory Agents, Non-Steroidal | Binding Sites | Cell Nucleus | Chromatin | Cytoskeletal Proteins | DNA-Binding Proteins | Drosophila | Humans | Lymphoid Enhancer-Binding Factor 1 | Molecular Sequence Data | Mutation | Nuclear Proteins | Proto-Oncogene Proteins | Sequence Homology, Amino Acid | Signal Transduction | Sulindac | TCF Transcription Factors | Trans-Activators | Transcription Factor 7-Like 2 Protein | Transcription Factors | Transcription, Genetic | Transcriptional Activation | Wnt Proteins | Zebrafish Proteins | beta Catenin