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The p300/CBP acetyltransferases function as transcriptional coactivators of beta-catenin in vertebrates
A Hecht1, K Vleminckx, M P Stemmler
1Max-Planck-Institute of Immunobiology, Stuebeweg 51, D-79108 Freiburg, Germany. hecht@immunbio.mpg.de
Abstract:
Wnt growth factors regulate a variety of developmental processes by altering specific gene expression patterns. In vertebrates beta-catenin acts as transcriptional activator, which is needed to overcome target gene repression by Groucho/TLE proteins, and to permit promoter activation as the final consequence of Wnt signaling. However, the molecular mechanisms of transcriptional activation by beta-catenin are only poorly understood. Here we demonstrate that the closely related acetyltransferases p300 and CBP potentiate beta-catenin-mediated activation of the siamois promoter, a known Wnt target. beta-catenin and p300 also synergize to stimulate a synthetic reporter gene construct, whereas activation of the cyclin D1 promoter by beta-catenin is refractory to p300 stimulation. Axis formation and activation of the beta-catenin target genes siamois and Xnr-3 in Xenopus embryos are sensitive to the E1A oncoprotein, a known inhibitor of p300/CBP. The C-terminus of beta-catenin interacts directly with a region overlapping the CH-3 domain of p300. p300 could participate in alleviating promoter repression imposed by chromatin structure and in recruiting the basal transcription machinery to promoters of particular Wnt target genes.
Insights
Wnt signaling involves beta-catenin (a transcriptional activator) and its interaction with p300/CBP acetyltransferases. This study shows p300/CBP potentiate Wnt target gene activation, crucial for developmental processes.
Area of Science:
- Molecular Biology
- Developmental Biology
- Gene Regulation
Background:
- Wnt growth factors are key regulators of gene expression during development.
- Beta-catenin functions as a transcriptional activator in Wnt signaling, overcoming Groucho/TLE repression.
- The precise mechanisms of beta-catenin-mediated transcriptional activation remain incompletely understood.
Purpose of the Study:
- To investigate the role of p300 and CBP acetyltransferases in beta-catenin-mediated transcriptional activation.
- To elucidate the molecular interactions between beta-catenin and p300/CBP.
- To determine the functional significance of these interactions in embryonic development.
Main Methods:
- Assays to measure beta-catenin-mediated activation of the siamois promoter and synthetic reporter constructs.
- Co-immunoprecipitation to assess protein-protein interactions.
- Xenopus embryo experiments to evaluate the effects of E1A oncoprotein on Wnt target gene activation and axis formation.
Main Results:
- p300 and CBP were shown to potentiate beta-catenin-mediated activation of the siamois promoter.
- Beta-catenin and p300 synergistically activated a synthetic reporter gene.
- Activation of the cyclin D1 promoter by beta-catenin was not enhanced by p300.
- Axis formation and Wnt target gene activation in Xenopus embryos were sensitive to E1A, an inhibitor of p300/CBP.
- Direct interaction was observed between the C-terminus of beta-catenin and a region of p300.
Conclusions:
- p300 and CBP are important co-activators of beta-catenin-mediated transcription for specific Wnt target genes.
- These acetyltransferases may facilitate Wnt signaling by alleviating chromatin-mediated repression and recruiting the basal transcription machinery.
- The interaction between beta-catenin and p300 is critical for Wnt pathway function in embryonic development.