ERp29 regulates epithelial sodium channel functional expression by promoting channel cleavage

Area of Science:

• Cell Biology
• Molecular Physiology
• Ion Channel Regulation

Background:

• The epithelial sodium channel (ENaC) is crucial for blood pressure and airway fluid homeostasis.
• ERp29, an endoplasmic reticulum protein, is known to influence the biogenesis of other ion channels.
• Similarities in trafficking pathways between ENaC and CFTR suggested ERp29 might regulate ENaC.

Purpose of the Study:

• To investigate the role of ERp29 in the biogenesis and functional expression of ENaC in epithelial cells.

Main Methods:

• Overexpression and siRNA-mediated depletion of ERp29 in epithelial cells.
• Ussing chamber experiments to measure amiloride-sensitive short-circuit current (Isc) as a proxy for ENaC function.
• Western blot analysis to assess protein abundance, including cleaved γ-ENaC.
• Assessment of ENaC activation by trypsin and analysis of β-ENaC localization.
• Investigation of ERp29 interaction with the Sec24D component of the COPII machinery.

Main Results:

• Overexpression of wild-type ERp29 increased ENaC functional expression and γ-ENaC cleavage.
• ERp29 depletion or expression of a cysteine-mutant ERp29 (C157S) decreased ENaC functional expression.
• ERp29 facilitated the interaction of β-ENaC with Sec24D, a key component of ER export machinery.
• These effects were not linked to altered apical β-ENaC expression but to ERp29's role in trafficking.

Conclusions:

• ERp29 plays a significant role in promoting ENaC biogenesis and functional expression.
• ERp29 appears to direct ENaC to the Golgi for cleavage and trafficking to the apical membrane via interaction with Sec24D.
• These findings highlight ERp29 as a novel regulator of ENaC trafficking and function.