title: Cathepsin B contributes to Na+ hyperabsorption in cystic fibrosis airway epithelial cultures.
abstract: In cystic fibrosis (CF) lung disease, the absence of functional CF transmembrane conductance regulator results in Cl(-)/HCO3 (-) hyposecretion and triggers Na(+) hyperabsorption through the epithelial Na(+) channel (ENaC), which contribute to reduced airway surface liquid (ASL) pH and volume. Prostasin, a membrane-anchored serine protease with trypsin-like substrate specificity has previously been shown to activate ENaC in CF airways. However, prostasin is typically inactive below pH 7.0, suggesting that it may be less relevant in acidic CF airways. Cathepsin B (CTSB) is present in both normal and CF epithelia and is secreted into ASL, but little is known about its function in the airways. We hypothesized that the acidic ASL seen in CF airways may stimulate CTSB to activate ENaC, contributing to Na(+) hyperabsorption and depletion of CF ASL volume. In Xenopus laevis oocytes, CTSB triggered α- and γENaC cleavage and induced an increase in ENaC activity. In bronchial epithelia from both normal and CF donor lungs, CTSB localized to the apical membrane. In normal and CF human bronchial epithelial cultures, CTSB was detected at the apical plasma membrane and in the ASL. CTSB activity was significantly elevated in acidic ASL, which correlated with increased abundance of ENaC in the plasma membrane and a reduction in ASL volume. This acid/CTSB-dependent activation of ENaC was ameliorated with the cell impermeable, CTSB-selective inhibitor CA074, suggesting that CTSB inhibition may have therapeutic relevance. Taken together, our data suggest that CTSB is a pathophysiologically relevant protease that activates ENaC in CF airways.
authors.affiliation: Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Chong Da
authors.initials: CD
authors.lastname: Tan
authors.affiliation: Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Carey
authors.initials: C
authors.lastname: Hobbs
authors.affiliation: Department of Pharmacology, Wayne State University, School of Medicine, Detroit, MI, USA.
authors.forename: Mansoureh
authors.initials: M
authors.lastname: Sameni
authors.affiliation: Department of Pharmacology, Wayne State University, School of Medicine, Detroit, MI, USA.
authors.forename: Bonnie F
authors.initials: BF
authors.lastname: Sloane
authors.affiliation: Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: M Jackson
authors.initials: MJ
authors.lastname: Stutts
authors.affiliation: Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC, USA robert_tarran@med.unc.edu.
authors.forename: Robert
authors.initials: R
authors.lastname: Tarran
mesh_terms: D000818:Animals; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002918:Chymotrypsin / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003550:Cystic Fibrosis / Q000188:drug therapy / Q000378:metabolism*; D004151:Dipeptides / Q000494:pharmacology; D053503:Epithelial Sodium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009865:Oocytes / Q000378:metabolism; D021122:Protein Subunits; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D011994:Recombinant Proteins; C068250:N-(3-propylcarbamoyloxirane-2-carbonyl)-isoleucyl-proline; D012964:Sodium; D002918:Chymotrypsin; C533912:CTSB protein, human; D002401:Cathepsin B