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Interaction of axin and Dvl-2 proteins regulates Dvl-2-stimulated TCF-dependent transcription
M J Smalley1, E Sara, H Paterson
1Developmental Biology, Section of Cell Biology and Experimental Pathology, Toby Robins Breakthrough Breast Cancer Research Centre, London, UK.
Abstract:
Axin promotes the phosphorylation of beta-catenin by GSK-3beta, leading to beta-catenin degradation. Wnt signals interfere with beta-catenin turnover, resulting in enhanced transcription of target genes through the increased formation of beta-catenin complexes containing TCF transcription factors. Little is known about how GSK-3beta-mediated beta-catenin turnover is regulated in response to Wnt signals. We have explored the relationship between Axin and Dvl-2, a member of the Dishevelled family of proteins that function upstream of GSK-3beta. Expression of Dvl-2 activated TCF-dependent transcription. This was blocked by co-expression of GSK-3beta or Axin. Expression of a 59 amino acid GSK-3beta-binding region from Axin strongly activated transcription in the absence of an upstream signal. Introduction of a point mutation into full-length Axin that prevented GSK-3beta binding also generated a transcriptional activator. When co-expressed, Axin and Dvl-2 co-localized within expressing cells. When Dvl-2 localization was altered using a C-terminal CAAX motif, Axin was also redistributed, suggesting a close association between the two proteins, a conclusion supported by co-immunoprecipitation data. Deletion analysis suggested that Dvl-association determinants within Axin were contained between residues 603 and 810. The association of Axin with Dvl-2 may be important in the transmission of Wnt signals from Dvl-2 to GSK-3beta.
Insights
Axin and Dishevelled-2 (Dvl-2) proteins interact, influencing beta-catenin turnover and TCF-dependent transcription in Wnt signaling pathways. This interaction is crucial for transmitting Wnt signals.
Area of Science:
- Cellular biology
- Molecular signaling pathways
- Wnt signaling pathway
Background:
- Axin facilitates beta-catenin phosphorylation by GSK-3beta, promoting degradation.
- Wnt signals inhibit beta-catenin turnover, enhancing TCF transcription factor activity.
- Regulation of GSK-3beta-mediated beta-catenin turnover by Wnt signals remains unclear.
Purpose of the Study:
- To investigate the relationship between Axin and Dishevelled-2 (Dvl-2) in Wnt signaling.
- To elucidate the role of Axin-Dvl-2 interaction in regulating beta-catenin turnover and transcription.
Main Methods:
- Co-expression of Dvl-2, GSK-3beta, and Axin constructs in cells.
- Analysis of TCF-dependent transcription.
- Site-directed mutagenesis to disrupt GSK-3beta binding to Axin.
- Co-localization studies using fluorescent tags.
- Co-immunoprecipitation assays.
- Deletion analysis to map Axin domains interacting with Dvl-2.
Main Results:
- Dvl-2 expression activated TCF-dependent transcription, which was inhibited by GSK-3beta or Axin.
- A GSK-3beta-binding region of Axin, or a mutated full-length Axin lacking GSK-3beta binding, acted as a transcriptional activator.
- Axin and Dvl-2 co-localized in cells, and Dvl-2 altered Axin localization, indicating a close association.
- The Dvl-2 association domain in Axin is located between residues 603 and 810.
Conclusions:
- Axin and Dvl-2 interact physically and functionally.
- This interaction is critical for Wnt signal transmission from Dvl-2 to GSK-3beta.
- The Axin-Dvl-2 association influences beta-catenin turnover and TCF-mediated transcription.