Identification of SPLUNC1's ENaC-inhibitory domain yields novel strategies to treat sodium hyperabsorption in cystic fibrosis airways.
The epithelial sodium channel (ENaC) is responsible for Na+ and fluid absorption across colon, kidney, and airway epithelia. We have previously identified SPLUNC1 as an autocrine inhibitor of ENaC. We have now located the ENaC inhibitory domain of SPLUNC1 to SPLUNC1's N terminus, and a peptide corresponding to this domain, G22-A39, inhibited ENaC activity to a similar degree as full-length SPLUNC1 (∼2.5 fold). However, G22-A39 had no effect on the structurally related acid-sensing ion channels, indicating specificity for ENaC. G22-A39 preferentially bound to the β-ENaC subunit in a glycosylation-dependent manner. ENaC hyperactivity is contributory to cystic fibrosis (CF) lung disease. Addition of G22-A39 to CF human bronchial epithelial cultures (HBECs) resulted in an increase in airway surface liquid height from 4.2±0.6 to 7.9±0.6 μm, comparable to heights seen in normal HBECs, even in the presence of neutrophil elastase. Our data also indicate that the ENaC inhibitory domain of SPLUNC1 may be cleaved away from the main molecule by neutrophil elastase, which suggests that it may still be active during inflammation or neutrophilia. Furthermore, the robust inhibition of ENaC by the G22-A39 peptide suggests that this peptide may be suitable for treating CF lung disease.
Cystic Fibrosis/Pulmonary Research and Treatment Center, Department of Prosthodontics, University of North Carolina, Chapel Hill, 7125 Thurston Bowles Bldg., Chapel Hill, NC 27599-7248, USA.
Carey A
CA
Hobbs
Maxime G
MG
Blanchard
Stephan
S
Kellenberger
Sompop
S
Bencharit
Rui
R
Cao
Mehmet
M
Kesimer
William G
WG
Walton
Matthew R
MR
Redinbo
M Jackson
MJ
Stutts
Robert
R
Tarran
D000042:Absorption / Q000187:drug effects; D062565:Acid Sensing Ion Channels / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002942:Circular Dichroism; D003550:Cystic Fibrosis / Q000378:metabolism*; D004594:Electrophysiology; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D009865:Oocytes; D010455:Peptides / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000378:metabolism*; D014981:Xenopus
D062565:Acid Sensing Ion Channels; C485599:BPIFA1 protein, human; D053503:Epithelial Sodium Channels; D006023:Glycoproteins; D010455:Peptides; D010750:Phosphoproteins; D012964:Sodium