Identification of Murr1 as a Regulator of the Human δ Epithelial Sodium Channel

Abstract

The human δ epithelial sodium channel (δENaC) subunit is related to the α, β, and γENaC subunits that control salt homeostasis. δENaC forms an amiloride-sensitive Na+ channel with the β and γ subunits. However, the in vivo function of δENaC is not known. To gain insight into the function of δENaC, a yeast two-hybrid screen of a human brain cDNA library was carried out using the C- and N-terminal domains of δENaC. A novel δENaC-interacting protein called Murr1 (mouse U2af1-rs1 region) was isolated in the C-terminal domain screen. Murr1 is a 21-kDa protein mutated in Bedlington terriers suffering from copper toxicosis. The interaction of Murr1 and δENaC was confirmed by glutathione S-transferase pulldown assay and coimmunoprecipitation. To test the functional significance of the interaction, Murr1 was coexpressed with δβγNaC in Xenopus oocytes. Murr1 inhibited amiloride-sensitive sodium current in a dose-dependent manner. In addition, deletion of the last 59 amino acids of δENaC abolished the inhibition. Murr1 also bound to the β- and γENaC subunits and inhibited αβγENaC sodium current. Therefore, these results suggest that Murr1 is a novel regulator of ENaC.