title: A new human NHERF1 mutation decreases renal phosphate transporter NPT2a expression by a PTH-independent mechanism.
abstract: BACKGROUND
  The sodium-hydrogen exchanger regulatory factor 1 (NHERF1) binds to the main renal phosphate transporter NPT2a and to the parathyroid hormone (PTH) receptor. We have recently identified mutations in NHERF1 that decrease renal phosphate reabsorption by increasing PTH-induced cAMP production in the renal proximal tubule.
  
  
  METHODS
  We compared relevant parameters of phosphate homeostasis in a patient with a previously undescribed mutation in NHERF1 and in control subjects. We expressed the mutant NHERF1 protein in Xenopus Oocytes and in cultured cells to study its effects on phosphate transport and PTH-induced cAMP production.
  
  
  RESULTS
  We identified in a patient with inappropriate renal phosphate reabsorption a previously unidentified mutation (E68A) located in the PDZ1 domain of NHERF1.We report the consequences of this mutation on NHERF1 function. E68A mutation did not modify cAMP production in the patient. PTH-induced cAMP synthesis and PKC activity were not altered by E68A mutation in renal cells in culture. In contrast to wild-type NHERF1, expression of the E68A mutant in Xenopus oocytes and in human cells failed to increase phosphate transport. Pull down experiments showed that E68A mutant did not interact with NPT2a, which robustly interacted with wild type NHERF1 and previously identified mutants. Biotinylation studies revealed that E68A mutant was unable to increase cell surface expression of NPT2a.
  
  
  CONCLUSIONS
  Our results indicate that the PDZ1 domain is critical for NHERF1-NPT2a interaction in humans and for the control of NPT2a expression at the plasma membrane. Thus we have identified a new mechanism of renal phosphate loss and shown that different mutations in NHERF1 can alter renal phosphate reabsorption via distinct mechanisms.
authors.affiliation: Faculté de Médecine, Université Paris Descartes, Paris, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Courbebaisse
authors.forename: Christine
authors.initials: C
authors.lastname: Leroy
authors.forename: Naziha
authors.initials: N
authors.lastname: Bakouh
authors.forename: Christine
authors.initials: C
authors.lastname: Salaün
authors.forename: Laurent
authors.initials: L
authors.lastname: Beck
authors.forename: Bernard
authors.initials: B
authors.lastname: Grandchamp
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Planelles
authors.forename: Randy A
authors.initials: RA
authors.lastname: Hall
authors.forename: Gérard
authors.initials: G
authors.lastname: Friedlander
authors.forename: Dominique
authors.initials: D
authors.lastname: Prié
mesh_terms: D000368:Aged; D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D009893:Opossums; D010281:Parathyroid Hormone / Q000378:metabolism*; D028061:Phosphate Transport Proteins / Q000096:biosynthesis / Q000235:genetics*; D010710:Phosphates / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa / Q000235:genetics* / Q000378:metabolism; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism
chemical_list: D010281:Parathyroid Hormone; D028061:Phosphate Transport Proteins; D010710:Phosphates; D010750:Phosphoproteins; C493554:SLC34A1 protein, human; D017923:Sodium-Hydrogen Exchangers; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; C093376:sodium-hydrogen exchanger regulatory factor; D000242:Cyclic AMP; D011493:Protein Kinase C