title: Intracellular Na+ regulates epithelial Na+ channel maturation.
abstract: Epithelial Na(+) channel (ENaC) function is regulated by the intracellular Na(+) concentration ([Na(+)]i) through a process known as Na(+) feedback inhibition. Although this process is known to decrease the expression of proteolytically processed active channels on the cell surface, it is unknown how [Na(+)]i alters ENaC cleavage. We show here that [Na(+)]i regulates the posttranslational processing of ENaC subunits during channel biogenesis. At times when [Na(+)]i is low, ENaC subunits develop mature N-glycans and are processed by proteases. Conversely, glycan maturation and sensitivity to proteolysis are reduced when [Na(+)]i is relatively high. Surface channels with immature N-glycans were not processed by endogenous channel activating proteases, nor were they sensitive to cleavage by exogenous trypsin. Biotin chase experiments revealed that the immature surface channels were not converted into mature cleaved channels following a reduction in [Na(+)]i. The hypothesis that [Na(+)]i regulates ENaC maturation within the biosynthetic pathways is further supported by the finding that Brefeldin A prevented the accumulation of processed surface channels following a reduction in [Na(+)]i. Therefore, increased [Na(+)]i interferes with ENaC N-glycan maturation and prevents the channel from entering a state that allows proteolytic processing.
authors.affiliation: From the Division of Pulmonary, Allergy, and Critical Care Medicine.
authors.forename: Elisa
authors.initials: E
authors.lastname: Heidrich
authors.affiliation: Renal-Electrolyte Division, and Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Marcelo D
authors.initials: MD
authors.lastname: Carattino
authors.affiliation: From the Division of Pulmonary, Allergy, and Critical Care Medicine, Renal-Electrolyte Division, and.
authors.forename: Rebecca P
authors.initials: RP
authors.lastname: Hughey
authors.affiliation: From the Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Pilewski
authors.affiliation: Renal-Electrolyte Division, and Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Kleyman
authors.affiliation: From the Division of Pulmonary, Allergy, and Critical Care Medicine, myerburgm@upmc.edu.
authors.forename: Mike M
authors.initials: MM
authors.lastname: Myerburg
mesh_terms: D053503:Epithelial Sodium Channels / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012964:Sodium / Q000378:metabolism*
chemical_list: D053503:Epithelial Sodium Channels; D011134:Polysaccharides; D012964:Sodium; D010447:Peptide Hydrolases
keywords: Epithelial Sodium Channel (ENaC); Posttranslational Modification (PTM); Protease; Proteoglycan; Sodium Transport