title: Regulation of the epithelial sodium channel by serine proteases in human airways.
abstract: The epithelial sodium channel (ENaC) constitutes the rate-limiting step for sodium absorption across airway epithelia, which in turn regulates airway surface liquid (ASL) volume and the efficiency of mucociliary clearance. This role in ASL volume regulation suggests that ENaC activity is influenced by local factors rather than systemic signals indicative of total body volume homeostasis. Based on reports that ENaC may be regulated by extracellular serine protease activity in Xenopus and mouse renal epithelia, we sought to identify proteases that serve similar functions in human airway epithelia. Homology screening of a human airway epithelial cDNA library identified two trypsin-like serine proteases (prostasin and TMPRSS2) that, as revealed by in situ hybridization, are expressed in airway epithelia. Functional studies in the Xenopus oocyte expression system demonstrated that prostasin increased ENaC currents 60--80%, whereas TMPRSS2 markedly decreased ENaC currents and protein levels. Studies of primary nasal epithelial cultures in Ussing chambers revealed that inhibition of endogenous serine protease activity with aprotinin markedly decreased ENaC-mediated currents and sensitized the epithelia to subsequent channel activation by exogenous trypsin. These data, therefore, suggest that protease-mediated regulation of sodium absorption is a function of human airway epithelia, and prostasin is a likely candidate for this activity.
authors.affiliation: Cystic Fibrosis Research and Treatment Center, Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. Scott_Donaldson@med.unc.edu
authors.forename: Scott H
authors.initials: SH
authors.lastname: Donaldson
authors.forename: Andrew
authors.initials: A
authors.lastname: Hirsh
authors.forename: Dong Chen
authors.initials: DC
authors.lastname: Li
authors.forename: Ginger
authors.initials: G
authors.lastname: Holloway
authors.forename: Julie
authors.initials: J
authors.lastname: Chao
authors.forename: Richard C
authors.initials: RC
authors.lastname: Boucher
authors.forename: Sherif E
authors.initials: SE
authors.lastname: Gabriel
mesh_terms: D000328:Adult; D000367:Age Factors; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004594:Electrophysiology; D053503:Epithelial Sodium Channels; D005786:Gene Expression Regulation; D015723:Gene Library; D006801:Humans; D017403:In Situ Hybridization; D008168:Lung / Q000378:metabolism; D051379:Mice; D008875:Middle Aged; D008969:Molecular Sequence Data; D009297:Nasal Mucosa / Q000166:cytology / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D015222:Sodium Channels / Q000378:metabolism*; D014357:Trypsin; D014981:Xenopus; D000099271:Prostasin
chemical_list: D000596:Amino Acids; D018076:DNA, Complementary; D053503:Epithelial Sodium Channels; D012697:Serine Endopeptidases; D015222:Sodium Channels; D014357:Trypsin; D000099271:Prostasin