title: cAMP has distinct acute and chronic effects on aquaporin-5 in lung epithelial cells.
abstract: Aquaporin-5 (AQP5) is present on the apical membrane of epithelial cells in various secretory glands as well as on the apical membrane of the airway epithelium, airway submucosal glands, and type 1 pneumocytes, where it can participate in respiratory tract water homeostasis. We examined the effects of cAMP on AQP5 distribution and abundance. When AQP5-expressing mouse lung epithelial cells were treated with cAMP or the beta-adrenergic agonist terbutaline, a biphasic AQP5 response was observed. Short term (minutes) exposure to cAMP produced internalization of AQP5 off of the membrane and a decrease in protein abundance. Both of these responses were blocked by inhibition of protein kinase A and the decrease in abundance was blocked by chloroquine, indicating lysosome-mediated degradation. Sustained cAMP exposure (hours) produced an increase in membrane localization and increased abundance; these effects were also blocked by protein kinase A inhibition. The beta-adrenergic agonist terbutaline produced changes in AQP5 abundance in mouse trachea and lung, consistent with our findings in cultured epithelial cells. Purified AQP5 protein was phosphorylated by protein kinase A but not protein kinase C or casein kinase II, and aquaporin-5 was phosphorylated in cultured cells after long term (but not short term) exposure to cAMP. These studies indicate that cAMP and beta-adrenergic agonists produce distinct short and long term effects on AQP5 distribution and abundance that may contribute to regulation of lung water homeostasis.
authors.affiliation: Department of Medicine, Division of Pulmonary and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224, USA.
authors.forename: Venkataramana
authors.initials: V
authors.lastname: Sidhaye
authors.forename: Jason D
authors.initials: JD
authors.lastname: Hoffert
authors.forename: Landon S
authors.initials: LS
authors.lastname: King
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D051402:Aquaporin 5; D020346:Aquaporins / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D008168:Lung / Q000166:cytology*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D013726:Terbutaline / Q000494:pharmacology; D014132:Trachea / Q000166:cytology*; D014867:Water / Q000378:metabolism
chemical_list: D000318:Adrenergic beta-Agonists; C496038:Aqp5 protein, mouse; D051402:Aquaporin 5; D020346:Aquaporins; D008565:Membrane Proteins; D014867:Water; D000242:Cyclic AMP; D013726:Terbutaline