β-catenin-mediated Wnt signal transduction proceeds through an endocytosis-independent mechanism

Area of Science:

• Cell Biology
• Molecular Biology
• Developmental Biology

Background:

• The Wnt pathway is crucial for development, homeostasis, and regeneration.
• The precise molecular events linking Wnt ligand-receptor binding to target gene transcription are not fully understood.
• The role of receptor endocytosis in Wnt signal transduction remains controversial.

Purpose of the Study:

• To investigate whether receptor endocytosis is a necessary step for Wnt signal transduction.
• To resolve discrepancies in the literature regarding endocytosis's role in Wnt signaling.

Main Methods:

• Utilized a novel tool for quantitative, real-time, single-cell assessment of endogenous Wnt pathway activation.
• Employed knockdown or knockout of clathrin-mediated endocytosis components in mouse embryonic stem cells (mESCs).
• Assessed Wnt signal transduction, including β-catenin accumulation, nuclear translocation, and target gene transcription.

Main Results:

• Disruption of clathrin-mediated endocytosis did not impede β-catenin accumulation, nuclear translocation, or target gene transcription.
• Inhibition of caveolin-mediated endocytosis also showed no impact on Wnt pathway activation in mESCs.
• Findings were consistent across multiple cell lines, indicating endocytosis is not required for Wnt signaling.

Conclusions:

• Receptor endocytosis is not a prerequisite for Wnt signal transduction.
• Off-target effects of certain drugs may explain previous conflicting reports on endocytosis in Wnt signaling.
• This study provides a clearer understanding of the molecular mechanisms underlying Wnt pathway activation.