Golgi-associated retrograde protein (GARP) complex-dependent endosomes to trans Golgi network retrograde trafficking...

Area of Science:

• Cell Biology
• Molecular Biology
• Organelle Trafficking

Background:

• Endosome to trans-Golgi network (TGN) cargo transport involves sequential steps: sorting, tethering, and fusion.
• The Golgi-associated retrograde protein (GARP) complex is essential for tethering, with its localization regulated by Arl and Rab GTPases.
• The mechanism by which GARP recognizes specific endosome-derived carriers for TGN fusion remains unclear.

Purpose of the Study:

• To investigate the role of Rab4b in the retrograde trafficking of cargo from endosomes to the TGN.
• To elucidate how the Golgi-associated retrograde protein (GARP) complex recognizes endosome-derived carriers for TGN fusion.

Main Methods:

• Utilized fluorescent cargoes in cells with manipulated Rab4b levels (overexpression or knockdown).
• Employed small interfering RNA (siRNA) to downregulate GARP complex subunits.
• Applied immunofluorescence, Super Resolution Radial Fluctuation, and 3D reconstruction imaging, alongside biochemical assays.

Main Results:

• Identified VPS52, a GARP complex subunit, as a Rab4b effector.
• Rab4b overexpression enhanced retrograde trafficking of cation-independent mannose-6-phosphate receptor (CI-MPR) to the TGN in a GARP-dependent manner.
• Rab4b depletion or inactivation blocked CI-MPR in early endosomes, preventing its access to VPS52-labeled carriers and the TGN.

Conclusions:

• Rab4b mediates directional specificity in cargo carrier transport to the TGN by sorting CI-MPR to VPS52 microdomains.
• Disruption of the Rab4b/GARP pathway may have significant implications in diseases related to impaired endocytic recycling.