ENaC trafficking via Rab‐dependent pathways

Abstract

The epithelial Na+ channel (ENaC) is an essential channel responsible for Na+ reabsorption, and it is regulated by different signaling pathways, including small G proteins. Rab proteins are well‐established as a participant in the regulation of trafficking. Co‐expression of Rab11a and Rab3a with ENaC results in a significant increase in channel activity. Biochemical and imaging methods demonstrate that Rab11a colocalized with ENaC and increased ENaC activity by affecting the plasma membrane levels of this channel. Rab11a increases ENaC activity in an additive manner with dominant‐negative dynamin, which is a GTPase responsible for endocytosis. Brefeldin A, an inhibitor of intracellular protein translocation, blocked the stimulatory action of Rab11a on ENaC activity. This is consistent with a mechanism of increased trafficking toward the plasma membrane. We further demonstrate that coexpression of ENaC with Rab11a and SGK1 together had no effect on Rab11a dependent increase of ENaC activity suggesting that SGK1 might be involved into Rab11a dependent vesicle exocytosis. These results demonstrate a novel role for Rab small GTPases in the control of epithelial ion transport. We conclude that ENaC channels, present on the apical plasma membrane, are being exchanged with channels from the intracellular (recycling) endosomes in a Rab11‐dependent manner.Supported by AHA and ASN.