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The Wnt Transcriptional Switch: TLE Removal or Inactivation?
Aravinda-Bharathi Ramakrishnan1, Abhishek Sinha1, Vinson B Fan1
1Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109-1048.
Abstract:
Many targets of the Wnt/β-catenin signaling pathway are regulated by TCF transcription factors, which play important roles in animal development, stem cell biology, and oncogenesis. TCFs can regulate Wnt targets through a "transcriptional switch," repressing gene expression in unstimulated cells and promoting transcription upon Wnt signaling. However, it is not clear whether this switch mechanism is a general feature of Wnt gene regulation or limited to a subset of Wnt targets. Co-repressors of the TLE family are known to contribute to the repression of Wnt targets in the absence of signaling, but how they are inactivated or displaced by Wnt signaling is poorly understood. In this mini-review, we discuss several recent reports that address the prevalence and molecular mechanisms of the Wnt transcription switch, including the finding of Wnt-dependent ubiquitination/inactivation of TLEs. Together, these findings highlight the growing complexity of the regulation of gene expression by the Wnt pathway.
Insights
The Wnt/β-catenin pathway uses a transcriptional switch regulated by TCF transcription factors. Recent studies reveal Wnt-dependent TLE inactivation, adding complexity to gene regulation in development and cancer.
Area of Science:
- Molecular Biology
- Developmental Biology
- Cancer Biology
Background:
- The Wnt/β-catenin signaling pathway is crucial in development, stem cell biology, and cancer.
- TCF transcription factors mediate Wnt target gene regulation via a transcriptional switch mechanism.
- TLE co-repressors are involved in Wnt target repression but their inactivation is unclear.
Purpose of the Study:
- To investigate the prevalence of the Wnt transcriptional switch mechanism.
- To elucidate the molecular mechanisms underlying TLE co-repressor inactivation in Wnt signaling.
- To highlight the regulatory complexity of Wnt-mediated gene expression.
Main Methods:
- Mini-review of recent research reports.
- Analysis of findings on Wnt target gene regulation.
- Examination of molecular mechanisms of TLE inactivation.
Main Results:
- The Wnt transcriptional switch is a significant feature of Wnt gene regulation.
- Wnt signaling can lead to the ubiquitination and inactivation of TLE co-repressors.
- Recent findings reveal novel layers of Wnt pathway regulation.
Conclusions:
- The Wnt transcriptional switch is a widespread mechanism.
- Wnt-dependent TLE inactivation is a key regulatory event.
- Wnt pathway regulation is more complex than previously understood.
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