title: Regulation of pendrin by pH: dependence on glycosylation.
abstract: Mutations in the anion exchanger pendrin are responsible for Pendred syndrome, an autosomal recessive disease characterized by deafness and goitre. Pendrin is highly expressed in kidney collecting ducts, where it acts as a chloride/bicarbonate exchanger and thereby contributes to the regulation of acid-base homoeostasis and blood pressure. The present study aimed to characterize the intrinsic properties of pendrin. Mouse pendrin was transfected in HEK (human embryonic kidney) 293 and OKP (opossum kidney proximal tubule) cells and its activity was determined by monitoring changes in the intracellular pH induced by variations of transmembrane anion gradients. Combining measurements of pendrin activity with mathematical modelling we found that its affinity for Cl-, HCO3- and OH- varies with intracellular pH, with increased activity at low intracellular pH. Maximal pendrin activity was also stimulated at low extracellular pH, suggesting the presence of both intracellular and extracellular proton regulatory sites. We identified five putative pendrin glycosylation sites, only two of which are used. Mutagenesis-induced disruption of pendrin glycosylation did not alter its cell-surface expression or polarized targeting to the apical membrane and basal activity, but fully abrogated its sensitivity to extracellular pH. The hither to unknown regulation of pendrin by external pH may constitute a key mechanism in controlling ionic exchanges across the collecting duct and inner ear.
authors.affiliation: Université Pierre et Marie Curie, Université Paris Descartes, INSERM/UMRS 812, Centre National de la Recherche Scientifique ERL 7226, Laboratoire de génomique, physiologie et physiopathologie ŕenales, Center de Recherche des Cordeliers, 15 rue de I'Ecole de Medecine, Paris, France.
authors.forename: Anie
authors.initials: A
authors.lastname: Azroyan
authors.forename: Kamel
authors.initials: K
authors.lastname: Laghmani
authors.forename: Gilles
authors.initials: G
authors.lastname: Crambert
authors.forename: David
authors.initials: D
authors.lastname: Mordasini
authors.forename: Alain
authors.initials: A
authors.lastname: Doucet
authors.forename: Aurélie
authors.initials: A
authors.lastname: Edwards
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D003001:Cloning, Molecular; D006031:Glycosylation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009893:Opossums; D000076988:Sulfate Transporters
chemical_list: D027321:Anion Transport Proteins; D002712:Chlorides; C494849:Slc26a4 protein, mouse; D000076988:Sulfate Transporters; D017665:Hydroxyl Radical