title: Identification of the SPLUNC1 ENaC-inhibitory domain yields novel strategies to treat sodium hyperabsorption in cystic fibrosis airway epithelial cultures.
abstract: The epithelial sodium channel (ENaC) is responsible for Na(+) and fluid absorption across colon, kidney, and airway epithelia. Short palate lung and nasal epithelial clone 1 (SPLUNC1) is a secreted, innate defense protein and an autocrine inhibitor of ENaC that is highly expressed in airway epithelia. While SPLUNC1 has a bactericidal permeability-increasing protein (BPI)-type structure, its NH2-terminal region lacks structure. Here we found that an 18 amino acid peptide, S18, which corresponded to residues G22-A39 of the SPLUNC1 NH2 terminus inhibited ENaC activity to a similar degree as full-length SPLUNC1 (∼2.5 fold), while SPLUNC1 protein lacking this region was without effect. S18 did not inhibit the structurally related acid-sensing ion channels, indicating specificity for ENaC. However, S18 preferentially bound to the βENaC subunit in a glycosylation-dependent manner. ENaC hyperactivity is contributory to cystic fibrosis (CF) lung disease. Unlike control, CF human bronchial epithelial cultures (HBECs) where airway surface liquid (ASL) height was abnormally low (4.2 ± 0.6 μm), addition of S18 prevented ENaC-led ASL hyperabsorption and maintained CF ASL height at 7.9 ± 0.6 μm, even in the presence of neutrophil elastase, which is comparable to heights seen in normal HBECs. Our data also indicate that the ENaC inhibitory domain of SPLUNC1 may be cleaved away from the main molecule by neutrophil elastase, suggesting that it may still be active during inflammation or neutrophilia. Furthermore, the robust inhibition of ENaC by the S18 peptide suggests that this peptide may be suitable for treating CF lung disease.
authors.affiliation: Cystic Fibrosis/Pulmonary Research and Treatment Center, 7125 Thurston Bowles Bldg., UNC, Chapel Hill, NC 27599-7248. robert_tarran@med.unc.edu.
authors.forename: Carey A
authors.initials: CA
authors.lastname: Hobbs
authors.forename: Maxime G
authors.initials: MG
authors.lastname: Blanchard
authors.forename: Omar
authors.initials: O
authors.lastname: Alijevic
authors.forename: Chong Da
authors.initials: CD
authors.lastname: Tan
authors.forename: Stephan
authors.initials: S
authors.lastname: Kellenberger
authors.forename: Sompop
authors.initials: S
authors.lastname: Bencharit
authors.forename: Rui
authors.initials: R
authors.lastname: Cao
authors.forename: Mehmet
authors.initials: M
authors.lastname: Kesimer
authors.forename: William G
authors.initials: WG
authors.lastname: Walton
authors.forename: Ashley G
authors.initials: AG
authors.lastname: Henderson
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Redinbo
authors.forename: M Jackson
authors.initials: MJ
authors.lastname: Stutts
authors.forename: Robert
authors.initials: R
authors.lastname: Tarran
mesh_terms: D000042:Absorption / Q000502:physiology*; D002478:Cells, Cultured; D003550:Cystic Fibrosis / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000378:metabolism; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport / Q000502:physiology; D019272:Leukocyte Elastase / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
chemical_list: C485599:BPIFA1 protein, human; D053503:Epithelial Sodium Channels; D006023:Glycoproteins; D010750:Phosphoproteins; D012964:Sodium; D019272:Leukocyte Elastase
keywords: BPIFA1; COPD; SPLUNC; glycosylation; neutrophil elastase