Cargo-selective endosomal sorting for retrieval to the Golgi requires retromer

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Trafficking

Background:

• Endosome-to-Golgi retrieval of mannose 6-phosphate receptors (MPR) is vital for lysosome biogenesis.
• The underlying molecular mechanisms of this pathway remain largely uncharacterized.
• Yeast studies identified the retromer complex as essential for cargo retrieval, but its role in mammalian cells is less understood.

Purpose of the Study:

• To investigate the role of the retromer complex in mammalian endosome-to-Golgi transport.
• To determine if retromer mediates the retrieval of the cation-independent MPR (CI-MPR).
• To elucidate the function of mammalian VPS26 in membrane protein trafficking.

Main Methods:

• Electron microscopy was used to localize mVPS26.
• CD8 reporter protein constructs were employed to track membrane protein trafficking.
• Functional assays were performed on cells lacking VPS26.

Main Results:

• Mammalian retromer, specifically VPS26, is required for efficient CI-MPR retrieval.
• Loss of VPS26 leads to CI-MPR degradation or mislocalization to the plasma membrane.
• mVPS26 localizes to multivesicular body endosomes.
• Retromer mediates selective retrieval, as furin trafficking was unaffected.

Conclusions:

• The retromer complex plays a selective role in endosome-to-Golgi transport of the CI-MPR.
• VPS26 is essential for maintaining proper CI-MPR localization and function.
• This study provides insights into the molecular machinery governing lysosome biogenesis and receptor recycling.