Abstract
The urate/anion exchanger URAT1 regulates blood urate level and is expressed only in the kidney, where it is thought to participate in tubular urate reabsorption. We found that the multivalent PDZ domain-containing protein, PDZK1 interacts with URAT1 in a yeast two-hybrid screen. Such an interaction requires the PDZ motif of URAT1 in its extreme intracellular C-terminal region as identified by both yeast two-hybrid and in vitro binding assays. In addition, the first, second, and fourth PDZ domains within PDZK1 associate with the URAT1 C-terminal. Co-immunoprecipitation studies revealed that the wild-type URAT1, but not its mutant lacking the PDZ-motif, directly interacts with PDZK1. When transfected into HEK293 cells with pDsRed2-C1/PDZK1 and pEGFP-C2/ wild-type URAT1, PDZK1 colocalized with URAT1 on the surface membrane. The association of URAT1 with PDZK1 enhanced urate transport activities in HEK293 cells (1.4-folds), and the deletion of the URAT1 C-terminal PDZ motif abolished this effect. The augmentation of the transport activity was accompanied by a significant increase in the Vmax of urate transport via URAT1, although it was not associated with the high URAT1 protein level in crude membrane fractions from URAT1-expressing HEK293 cells prepared with or without PDZK1 transfection. Taken together, the present study indicates the novel role of PDZK1 in regulating the functional activity of URAT1-mediated urate transport in the membrane of renal proximal tubules. [Jpn J Physiol 54 Suppl:S87 (2004)]
