R-spondin-1 induces Axin degradation via the LRP6-CK1ε axis

Area of Science:

• Cellular signaling
• Molecular biology
• Developmental biology

Background:

• R-spondins (RSPOs) are secreted proteins that enhance Wnt/β-catenin signaling.
• RSPO1 plays a vital role in tissue development and homeostasis.
• The precise molecular mechanism of RSPO-mediated Wnt/β-catenin activation is not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanism by which R-spondins (RSPOs) activate the Wnt/β-catenin pathway.
• To investigate the role of Axin degradation in RSPO signaling.
• To identify key protein interactions involved in RSPO-induced Wnt pathway activation.

Main Methods:

• Co-immunoprecipitation (Co-IP) assays to study protein interactions.
• Gene knockout and inhibitor treatments to assess protein degradation pathways.
• Western blotting to analyze protein levels.
• Reporter gene assays (SuperTOPFlash) to measure Wnt/β-catenin transcriptional activity.

Main Results:

• RSPOs mediate Axin degradation through the ubiquitin-proteasome pathway.
• RSPO1 promotes the interaction between Axin1 and CK1ε, facilitating Axin1 degradation.
• CK1ε knockout or inhibition increases Axin1 levels and blocks RSPO1-induced Axin1 degradation.
• RSPO1 stimulation increases LRP6 association with CK1ε and Axin1.
• RSPO1 and Wnt3A synergistically decrease Axin1 protein levels and enhance SuperTOPFlash activity.

Conclusions:

• RSPOs activate Wnt/β-catenin signaling via a novel mechanism involving LRP6/CK1ε-mediated degradation of Axin.
• This pathway is crucial for regulating Wnt/β-catenin signaling in biological processes.
• Understanding this mechanism provides insights into tissue development and homeostasis.