A TOCA/CDC-42/PAR/WAVE functional module required for retrograde endocytic recycling.

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Endosome-to-Golgi transport is essential for cellular functions, involving proteins like signaling receptors and transporters.
• The retromer complex is known for cargo sorting from early endosomes to the trans-Golgi network (TGN).
• Transport from recycling endosomes to the TGN is less understood, with few identified mediating molecules.

Purpose of the Study:

• To identify and characterize the molecular machinery mediating transport from recycling endosomes to the TGN in Caenorhabditis elegans.
• To elucidate the roles of F-BAR proteins TOCA-1/TOCA-2, CDC-42, PAR-6, PKC-3, and the WAVE complex in this trafficking pathway.
• To investigate the relationship between this pathway and the known retromer-mediated transport.

Main Methods:

• Utilized Caenorhabditis elegans as a model organism.
• Employed genetic depletion strategies (e.g., targeting SNX-3 and CDC-42).
• Performed protein localization studies using immunofluorescence on recycling endosomes (RME-1 positive) and early endosomes.

Main Results:

• Identified TOCA-1/TOCA-2, CDC-42, PAR-6, PKC-3, and the WAVE complex as mediators of recycling endosome-to-TGN transport.
• Showed CDC-42, TOCA proteins, and WVE-1 are enriched on recycling endosomes, distinct from early endosome-acting retromer components.
• Demonstrated that TGN-38 cargo is trapped in recycling endosomes upon CDC-42 depletion, indicating a post-retromer function.

Conclusions:

• A novel protein complex involving CDC-42 and TOCA proteins mediates retrograde transport from recycling endosomes to the TGN.
• This pathway is distinct from and acts downstream of retromer-mediated transport.
• The identified pathway is physiologically important, particularly for WNT signaling.