Soluble (Pro)Renin Receptor Regulation of ENaC Involved in Aldosterone Signaling in Cultured Collecting Duct Cells.

We have previously shown that activation of (pro)renin receptor (PRR) induces ENaC activity in cultured collecting duct (CD) cells. Here we examined the role of soluble PRR (sPRR), the cleavage product of PRR in ENaC regulation and further tested its relevance to aldosterone (Aldo) signaling. In cultured mpkCCD cells, administration of a recombinant histidine-tagged sPRR, sPRR-His at 10 nM within minutes induced a significant and transient increase in the amiloride-sensitive short circuit current (Isc) as assessed by using Ussing chamber technique. The acute ENaC activation was blocked by a Nox1/4 inhibitor GKT137892 and siRNA against Nox4 but not a β-catenin inhibitor ICG-001. In primary rat IMCD cells, administration of sPRR-His at 10 nM for 24 h induced protein expression of α- but not β- or γ-subunit of ENaC, in parallel with upregulation of mRNA expression as well as promoter activity of the α-subunit. The transcriptional activation of α-ENaC was dependent on β-catenin signaling. Consistent results obtained by epithelial volt-ohmmeter measurement of equivalent current (Ieq) and Ussing chamber determination of Isc showed that Aldo-induced transepithelial Na+ transport was inhibited by a PRR decoy inhibitor PRO20 and PF-429242 (PF), an inhibitor of sPRR-generating enzyme site-1 protease (S1P) and the response was restored by addition of sPRR-His. Medium sPRR was elevated by Aldo and inhibited by PF. Taken together, these results demonstrate that sPRR induces two phases of ENaC activation via distinct mechanisms and functions as a mediator of the natriferic action of Aldo.