Retromer is involved in epithelial Na⁺ channel trafficking

Area of Science:

• Cell biology
• Membrane protein trafficking
• Renal physiology

Background:

• Epithelial sodium channel (ENaC) regulates sodium reabsorption, and its plasma membrane levels are tightly controlled.
• Dysregulation of ENaC can lead to hypertension or hypotension.
• ENaC is trafficked via early endosomes, with pathways leading to either lysosomal degradation or plasma membrane recycling.

Purpose of the Study:

• To investigate the role of the retromer complex in the recycling of ENaC.
• To identify proteins involved in the retromer-mediated trafficking of ENaC.

Main Methods:

• Manipulating retromer function using a stabilizing chaperone (R55).
• Knockdown and overexpression of retromer components and associated proteins.
• Co-immunoprecipitation assays to identify protein interactions.
• Measurement of ENaC current and cell surface ENaC levels.

Main Results:

• Stabilizing retromer function increased ENaC current.
• Altering retromer or associated protein levels affected ENaC current and cell surface expression.
• KIBRA was identified as an ENaC-binding protein linking it to sorting nexin 4.
• CCDC22, a CCC-complex protein, co-immunoprecipitated with ENaC, and its knockdown reduced ENaC current and surface levels.

Conclusions:

• The retromer complex is essential for the recycling of ENaC to the plasma membrane.
• The CCC complex, including CCDC22, also plays a significant role in ENaC trafficking.
• These findings elucidate a novel pathway regulating ENaC surface abundance and function.