WLS retrograde transport to the endoplasmic reticulum during Wnt secretion

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Trafficking

Background:

• Wntless (WLS) is essential for Wnt secretion, typically moving from the Golgi to the plasma membrane (PM) and recycling back.
• Previous models focused on retromer-mediated recycling from the PM to the Golgi.

Purpose of the Study:

• To investigate the complete intracellular transport cycle of WLS.
• To identify the mechanisms and protein requirements for WLS retrograde trafficking.

Main Methods:

• Immunofluorescence microscopy
• Endogenous WLS detection
• Genetic manipulation of trafficking proteins (e.g., ARF, ERGIC2)
• Wnt secretion assays

Main Results:

• Endogenous WLS binds Wnts in the ER and cycles through the Golgi to the ER.
• An ER-targeting sequence at WLS's C-terminus mediates Golgi-to-ER retrograde transport.
• ERGIC2 and ARF are essential for WLS ER retrieval and Wnt secretion.

Conclusions:

• WLS undergoes a complete transport cycle involving ER retrieval, not just PM-Golgi recycling.
• ERGIC2-mediated retrograde transport from the Golgi to the ER is critical for Wnt secretion.
• ER retrieval is an integral and functionally important part of the WLS trafficking pathway.