Defective coupling of apical PTH receptors to phospholipase C prevents internalization of the Na+-phosphate cotransporter NaPi-IIa in Nherf1-deficient mice

Phosphate reabsorption in the renal proximal tubule occurs mostly via the type IIa Na+- phosphate cotransporter ( NaPi- IIa) in the brush border membrane ( BBM). The activity and localization of NaPi- IIa are regulated, among other factors, by parathyroid hormone ( PTH). NaPi- IIa interacts in vitro via its last three COOH- terminal amino acids with the PDZ protein Na+/ H+- exchanger isoform 3 regulatory factor ( NHERF)-1 ( NHERF1). Renal phosphate reabsorption in Nherf1-deficient mice is altered, and NaPi- IIa expression in the BBM is reduced. In addition, it has been proposed that NHERF1 and NHERF2 are important for the coupling of PTH receptors ( PTHRs) to phospholipase C ( PLC) and the activation of the protein kinase C pathway. We tested the role of NHERF1 in the regulation of NaPi- IIa by PTH in Nherf1-deficient mice. Immunohistochemistry and Western blotting demonstrated that stimulation of apical and basolateral receptors with PTH-(1- 34) led to internalization of NaPi- IIa in wild- type and Nherf1-deficient mice. Stimulation of only apical receptors with PTH-(3-34) failed to induce internalization in Nherf1- deficient mice. Expression and localization of apical PTHRs were similar in wild- type and Nherf1- deficient mice. Activation of the protein kinase C- and A- dependent pathways with 1,2- dioctanoyl- sn- glycerol or 8- bromo- cAMP induced normal internalization of NaPi-IIa in wild- type, as well as Nherf1- deficient, mice. Stimulation of PLC activity due to apical PTHRs was impaired in Nherf1- deficient mice. These data suggest that NHERF1 in the proximal tubule is important for PTH- induced internalization of NaPi- IIa and, specifically, couples the apical PTHR to PLC.