Parathyroid hormone inhibits renal phosphate transport by phosphorylation of serine 77 of sodium-hydrogen exchanger regulatory factor-1.
Parathyroid hormone (PTH), via activation of PKC and/or protein kinase A, inhibits renal proximal tubular phosphate reabsorption by facilitating the internalization of the major sodium-dependent phosphate transporter, Npt2a. Herein, we explore the hypothesis that the effect of PTH is mediated by phosphorylation of serine 77 (S77) of the first PDZ domain of the Npt2a-binding protein sodium-hydrogen exchanger regulatory factor-1 (NHERF-1). Using recombinant polypeptides representing PDZ I, S77 of NHERF-1 is phosphorylated by PKC but not PKA. When expressed in primate kidney epithelial cells (BSC-1 cells), however, activation of either protein kinase phosphorylates S77, suggesting that the phosphorylation of PDZ I by PKC and PKA proceeds by different biochemical pathways. PTH and other activators of PKC and PKA dissociate NHERF-1/Npt2a complexes, as assayed using quantitative coimmunoprecipitation, confocal microscopy, and sucrose density gradient ultracentrifugation in mice. Murine NHERF-1-/- renal proximal tubule cells infected with adenovirus-GFP-NHERF-1 containing an S77A mutation showed significantly increased phosphate transport compared with a phosphomimetic S77D mutation and were resistant to the inhibitory effect of PTH compared with cells infected with wild-type NHERF-1. These results indicate that PTH-mediated inhibition of renal phosphate transport involves phosphorylation of S77 of the NHERF-1 PDZ I domain and the dissociation of NHERF-1/Npt2a complexes.
Weinman
Edward J
EJ
Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA. eweinman@medicine.umaryland.edu
Biswas
Rajat S
RS
Peng
Guihong
G
Peng
Quihong
Q
Shen
Lily
L
Turner
Christina L
CL
E
Xiaofei
X
Steplock
Deborah
D
Shenolikar
Shirish
S
Cunningham
Rochelle
R
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D054731:PDZ Domains; D010281:Parathyroid Hormone / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015290:Second Messenger Systems / Q000502:physiology; D012694:Serine / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
D004791:Enzyme Inhibitors; D010281:Parathyroid Hormone; D010710:Phosphates; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D017923:Sodium-Hydrogen Exchangers; C093376:sodium-hydrogen exchanger regulatory factor; D012694:Serine; D012964:Sodium; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C