Sodium-Hydrogen Exchanger Regulatory Factor-1 Interacts with Mouse Urate Transporter 1 to Regulate Renal Proximal Tubule Uric Acid Transport

Abstract

T he sodium-hydrogen exchanger regulatory factor (NHERF) proteins represent a family of proteins that are abundantly expressed in the apical membranes of transporting epithelia, such as the renal proximal convoluted tubule and small intestine. These adaptor proteins have multiple PSD-95/Dlg/ZO-1 (PDZ) protein interactive domains and, in the case of NHERF-1 and NHERF-2, a C-terminal domain that binds to ezrin, radixin, moesin, and merlin (1-4). In mice, inactivation of the NHERF-1 gene, the founding member of this family, results in increased urinary excretion of phosphate as a result of decreased membrane abundance of the sodium-dependent phosphate co-transporter 2a (Npt2a), hypercalciuria as a result of the reciprocating changes in the plasma concentrations of 1,25 (OH) 2 vitamin D, and the interstitial deposition of calcium primarily in the papilla of the kidney (5,6). We also observed that both male and female NHERF-1 Ϫ/Ϫ mice have an increase in the urinary excretion of uric acid, the mechanism of which is unknown (6). Accordingly, these experiments were designed to study the relation between NHERF-1 and the renal transport of uric acid. In cultured proximal tubule cells, we demonstrate a decrease in the uptake of uric acid NHERF-1 null cells. This was associated with a decrease in the brush border membrane (BBM) abundance of mURAT1 (7,8). Although mouse URAT1 (mURAT1) does not transport para-aminohippurate (PAH), our studies indicate that uric acid transport was inhibited by PAH in cultured wild-type proximal tubule cells but not in NHERF-1 null cells. Rescue of NHERF-1 null cells using adenovirus-mediated gene transfer significantly increased uric acid transport and restored the inhibitory effect of PAH. When considered together, these findings indicate an important role for NHERF-1 in regulating uric acid transport in renal proximal tubule cells and provide evidence that NHERF-1 interacts with mURAT1 as well as other uric acid transporters. Materials and MethodsMale NHERF-1 Ϫ/Ϫ mice (F.129-Slc9a3r1 tmSsl /Ssl) that were bred into a C57BL/6 background for six generations and parental wild-type

Parathyroid hormone inhibits renal phosphate transport by phosphorylation of serine 77 of sodium-hydrogen exchanger regulatory factor–1

“…Immunoprecipitation studies were performed as previously described using wild-type mouse renal proximal tubule cells under control conditions and after treatment with DOG (10 -4 M) or 8-bromo-cAMP (10 -4 M) for 45 minutes (22). The precipitated proteins were separated using SDS-PAGE, transferred to nitrocellulose, and blotted for Npt2a and NHERF-1.…”

The Molecular Physiology of Uric Acid Homeostasis

“…URAT1 interacts with PDZK1 (143, 144) and NHERF1 (144), well-characterized PDZ domain proteins that regulate trafficking and activity of multiple transport proteins in the proximal tubule. PDZK1 is a genetic determinant of serum urate levels (145), and targeted deletion of NHERF1 reduces renal urate reabsorption in mice (146). URAT1 proteins are thus retained in intracellular vesicles in NHERF1 knockout mice, indicating a critical role for NHERF1 in brush-border membrane targeting of the protein (146).…”

“…PDZK1 is a genetic determinant of serum urate levels (145), and targeted deletion of NHERF1 reduces renal urate reabsorption in mice (146). URAT1 proteins are thus retained in intracellular vesicles in NHERF1 knockout mice, indicating a critical role for NHERF1 in brush-border membrane targeting of the protein (146). MRP4 also interacts with NHERF1 (147,148), but NHERF1 appears to have the opposite effect as that on URAT1, stimulating MRP4 internalization (148).…”

Control of renal uric acid excretion and gout

“…These three molecules, together with URAT1, have been reported to interact with scaffolding proteins PDZK1 and Na/H exchange regulatory factor-1 (NHERF1), and may form a urate-transporting multimolecular complex [7 ,12]. Mice lacking NHERF1 showed a 56% decrease in the expression of URAT1 in the brush border membrane compared with the wildtype kidneys, suggesting that the scaffolding protein may exert a significant effect on the renal tubular reabsorption of uric acid by modulating the expression of urate transporters [13].…”