APC mutations disrupt β-catenin destruction complex condensates organized by Axin phase separation

Area of Science:

• Cell Biology
• Molecular Oncology
• Biochemistry

Background:

• The Wnt/β-catenin pathway regulates cell fate and is crucial in development.
• Aberrant Wnt signaling, particularly due to APC gene mutations, drives colorectal cancer (CRC) pathogenesis.
• Liquid-liquid phase separation (LLPS) is increasingly recognized as a mechanism organizing cellular processes.

Purpose of the Study:

• To elucidate the molecular mechanism of β-catenin destruction complex condensate formation via Axin phase separation.
• To investigate the impact of Adenomatous Polyposis Coli (APC) gene mutations on these condensates in colorectal cancer (CRC).
• To understand how Axin-driven phase separation influences β-catenin localization and Wnt pathway activity.

Main Methods:

• Cellular imaging and biochemical assays to observe condensate formation.
• Analysis of wild-type and mutant APC protein interactions within the destruction complex.
• Investigating the recruitment of key kinases (GSK 3β, CK1α) and β-catenin phosphorylation status.

Main Results:

• Axin facilitates the assembly of β-catenin destruction complex condensates through phase separation in CRC cells.
• Wild-type APC stabilizes these destruction complex condensates.
• Truncated APC, common in CRC, did not impede condensate formation but impaired the recruitment of GSK 3β and CK1α, preventing β-catenin phosphorylation.

Conclusions:

• Axin-driven phase separation is a key mechanism for organizing the β-catenin destruction complex.
• APC mutations disrupt the functional integrity of these condensates, leading to β-catenin accumulation and altered Wnt signaling in CRC.
• Axin's phase separation capability may also mediate nuclear translocation of β-catenin, impacting transcriptional activity.