Intracellular Ubiquitylation of the Epithelial Na+ Channel Controls Extracellular Proteolytic Channel Activation via Conformational Change

Abstract

The epithelial Na

Feedback inhibition of ENaC: Acute and chronic mechanisms

“…33, 34 However we observed similar effects on cleavage products with a Liddle's mutant b-subunit in which ubiquitination is at least partially disrupted. Other possible mechanisms include Na C -dependent changes in the activity of proteases, 14 or preferential retrieval of specific cleaved products of ENaC from the cell surface.…”

Mice carrying ubiquitin-specific protease 2 (Usp2) gene inactivation maintain normal sodium balance and blood pressure

“…Maintained diurnal rhythm of Na ϩ and K ϩ excretion in Usp2-KO mice. As it was previously proposed that USP2-45 is an aldosterone-induced protein in the kidney, able to stimulate ENaC expression and activity in heterologous expression systems, including Xenopus laevis oocytes, renal epithelial cells (mpkCCD cl4 cells) and Hek293 cells (14,44,45), we were interested to know whether Usp2-KO mice are defective in the regulation of Na ϩ homeostasis and other related renal parameters. Because USP2-45 protein is highly rhythmic, we housed mice in metabolic cages for 24 h and recorded water and food intake, urine volume, and creatinine excretion every 4 h around the clock (Fig.…”

“…Because we had previously shown that heterologous expression of USP2-45 regulates ENaC (14,44,45), we were wondering whether there is some compensation by proteins involved in ubiquitylation/deubiquitylation or in the control of Na ϩ homeostasis. We therefore carried out gene expression profiling of total kidneys of control or KO mice, using Affymetrix oligonucleotide arrays.…”

“…In Xenopus laevis oocytes, USP2-45 but not USP2-69 increased ENaC activity (14). Moreover, it was shown in vitro that USP2-45 was able to bind to ENaC to deubiquitylate the channel and increase ENaC activity, both by increasing its cell surface expression and by promoting proteolytic activation (14,36,44,45). Usp2 is also a bona fide circadian output gene (31, 37-39, 46, 51).…”

The N-terminal Domain Allosterically Regulates Cleavage and Activation of the Epithelial Sodium Channel

“…Recent studies indicate that the balance of ubiquitination/deubiquitination of ENaC N termini is coupled to the efficiency of proteolysis of the extracellular domain (11)(12)(13). It is hypothesized that ubiquitination of the cytosolic N termini controls the accessibility of cleavage sites in the extracellular domain to channel-activating proteases through conformational changes that propagate along the length of the channel.…”