title: Regulation of epithelial sodium channels in urokinase plasminogen activator deficiency.
abstract: Epithelial sodium channels (ENaC) govern transepithelial salt and fluid homeostasis. ENaC contributes to polarization, apoptosis, epithelial-mesenchymal transformation, etc. Fibrinolytic proteases play a crucial role in virtually all of these processes and are elaborated by the airway epithelium. We hypothesized that urokinase-like plasminogen activator (uPA) regulates ENaC function in airway epithelial cells and tested that possibility in primary murine tracheal epithelial cells (MTE). Both basal and cAMP-activated Na(+) flow through ENaC were significantly reduced in monolayers of uPA-deficient cells. The reduction in ENaC activity was further confirmed in basolateral membrane-permeabilized cells. A decrease in the Na(+)-K(+)-ATPase activity in the basolateral membrane could contribute to the attenuation of ENaC function in intact monolayer cells. Dysfunctional fluid resolution was seen in uPA-disrupted cells. Administration of uPA and plasmin partially restores ENaC activity and fluid reabsorption by MTEs. ERK1/2, but not Akt, phosphorylation was observed in the cells and lungs of uPA-deficient mice. On the other hand, cleavage of γ ENaC is significantly depressed in the lungs of uPA knockout mice vs. those of wild-type controls. Expression of caspase 8, however, did not differ between wild-type and uPA(-/-) mice. In addition, uPA deficiency did not alter transepithelial resistance. Taken together, the mechanisms for the regulation of ENaC by uPA in MTEs include augmentation of Na(+)-K(+)-ATPase, proteolysis, and restriction of ERK1/2 phosphorylation. We demonstrate for the first time that ENaC may serve as a downstream signaling target by which uPA controls the biophysical profiles of airway fluid and epithelial function.
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China.
authors.forename: Zaixing
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas;
authors.forename: Runzhen
authors.initials: R
authors.lastname: Zhao
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China.
authors.forename: Meimi
authors.initials: M
authors.lastname: Zhao
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas;
authors.forename: Xinrong
authors.initials: X
authors.lastname: Liang
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas;
authors.forename: Deepa
authors.initials: D
authors.lastname: Bhattarai
authors.affiliation: Department of Pulmonary Immunology, The University of Texas Health Science Center at Tyler, Tyler, Texas;
authors.forename: Rohan
authors.initials: R
authors.lastname: Dhiman
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas;
authors.forename: Sreerama
authors.initials: S
authors.lastname: Shetty
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and Department of Medicine, The University of Texas Health Science Center at Tyler, Tyler, Texas;
authors.forename: Steven
authors.initials: S
authors.lastname: Idell
authors.affiliation: Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and james.ji@uthct.edu.
authors.forename: Hong-Long
authors.initials: HL
authors.lastname: Ji
mesh_terms: D000818:Animals; D017209:Apoptosis; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D017136:Ion Transport; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D059748:Proteolysis; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014132:Trachea / Q000166:cytology / Q000378:metabolism*; D014568:Urokinase-Type Plasminogen Activator / Q000502:physiology*; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D053503:Epithelial Sodium Channels; D034741:RNA, Small Interfering; D014568:Urokinase-Type Plasminogen Activator; D000254:Sodium-Potassium-Exchanging ATPase
keywords: airway surface fluid; epithelial sodium channel; knockout; mouse tracheal epithelial cells; proteolysis; short-circuit current; urokinase