title: NaPO(4) cotransport type III (PiT1) expression in human embryonic kidney cells and regulation by PTH.
abstract: The aim of the present study was to characterize the type(s) of NaPO(4) cotransporter expressed in the human renal cell line HEK-293 and its regulation by parathyroid hormone (PTH) in wild-type cells and in cells transfected by the PTH/PTH-related protein (PTHrP) receptor. The results showed that human embryonic kidney HEK-293 cells expressed NaPO(4) cotransporter type III (PiT1) mRNA and protein. In contrast, type I (NPT1) or II (NPT2) cotransporter mRNA were not expressed. Na(+)-dependent phosphate uptake followed a Michaelis-Menten model (apparent maximal transport rate and affinity constant: 23.32 +/- 0.69 nmol PO(4). mg protein(-1). 10 min(-1) and 0.147 +/- 0.014 mM KH(2)PO(4), respectively), was stimulated by phosphate deprivation (maximal increase 24.5 +/- 0.8%, P < 0.001, after 15 h of phosphate deprivation), and was inhibited by increasing pH (3.6 +/- 0.2-fold decrease at pH 8.5, P < 0.0001). It was inhibited in a time- and concentration-dependent fashion by PTH in HEK-293 cells stably transfected by PTH/PTHrP receptors but not in parental HEK-293 cells. Maximal inhibition of Na(+)-dependent phosphate transport was observed at 30 min after the addition of 72 nM PTH-(1-34) (31.5 +/- 2.4% inhibition, P < 0.01). PTH inhibition of phosphate transport was maintained in phosphate-deprived cells and reversed by both GF109203X (10(-6) M) or staurosporine (5.5 nM), two protein kinase C inhibitors. Na(+)-dependent phosphate uptake was also significantly inhibited by phorbol 12-myristate 13-acetate (20.9 +/- 3.9% inhibition, P < 0.001) but not by dibutyril-cAMP (10(-4) M) or forskolin (50 microM). The physiological role played by type III NaPO(4) cotransport expression in the overall renal regulation of phosphate homeostasis remains to be established.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine Xavier Bichat, 75018 Paris, France.
authors.forename: I
authors.initials: I
authors.lastname: Fernandes
authors.forename: R
authors.initials: R
authors.lastname: Béliveau
authors.forename: G
authors.initials: G
authors.lastname: Friedlander
authors.forename: C
authors.initials: C
authors.lastname: Silve
mesh_terms: D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000196:embryology*; D007700:Kinetics; D010281:Parathyroid Hormone / Q000502:physiology*; D010710:Phosphates / Q000493:pharmacokinetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D027981:Symporters; D013997:Time Factors
chemical_list: D002352:Carrier Proteins; D010281:Parathyroid Hormone; D010710:Phosphates; C493546:SLC17A1 protein, human; C493548:SLC17A2 protein, human; C493586:SLC20A1 protein, human; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D027981:Symporters