Defective coupling of apical PTH receptors to phospholipase C prevents internalization of the [Na.sup.+]-phosphate cotransporter [NaP.sub.i]-IIa in Nherf1-deficient mice

Phosphate reabsorption in the renal proximal tubule occurs mostly via the type IIa [Na.sup.+]-phosphate cotransporter ([NaP.sub.i]-IIa) in the brush border membrane (BBM). The activity and localization of [NaP.sub.i]-IIa are regulated, among other factors, by parathyroid hormone (PTH). [NaP.sub.i]-IIa interacts in vitro via its last three COOH-terminal amino acids with the PDZ protein [Na.sup.+]/[H.sup.+]-exchanger isoform 3 regulatory factor (NHERF)-1 (NHERF1). Renal phosphate reabsorption in Nherf1-deficient mice is altered, and [NaP.sup.i]-IIa expression in the BBM is reduced. In addition, it has been proposed that NHERF1 and NHERF-2 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 [NaP.sub.i]-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 [NaP.sub.i]-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 [NaP.sub.i]-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 [NaP.sub.i]-IIa and, specifically, couples the apical PTHR to PLC. phosphate cotransporter; PDZ protein; parathyroid hormone; proximal tubule