Retraction

Abstract

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.

Structural Features Essential to the Antimicrobial Functions of Human SPLUNC1

“…It has been established previously that the N-terminal S18 region of SPLUNC1 inhibits the epithelium sodium channel (ENaC), reducing the influx of sodium and water into pulmonary epithelial cells and maintaining the height of the airway surface liquid. 5,6 We found that the Δα4, LA x 4 and M3+LA x 4 forms of human SPLUNC1 were not significantly different from SPLUNC1 in ASL height (Fig. 4A).…”

“…In the context of cystic fibrosis (CF) inactivating mutations of the CFTR channel, ENaC’s actions exacerbate the dehydration of CF pulmonary tissues. 5 Eighteen amino acids in the N-terminal region of SPLUNC1 (S18) were found to be necessary and sufficient for regulating ENaC in normal conditions in vitro ; however, in the low pH of CF tissues, both S18 and the body of SPLUNC1 were required to control ENaC. 6 SPLUNC1 has also been shown to act as a surfactant to spread fluids at the air-water interface, and an innate antibacterial factor against Gram-negative bacterial pathogens.…”

Human Neutrophil Elastase Degrades SPLUNC1 and Impairs Airway Epithelial Defense against Bacteria

“…In the current study, we focused on the effects of HNE on the function of a recently described host defense protein short palate, lung, and nasal epithelium clone 1 (SPLUNC1). A previous study suggests that HNE is involved in SPLUNC1 degradation [11]. However, the role of HNE-mediated SPLUNC1 degradation in host defense against bacterial infection has not been investigated.…”