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