Abstract
Organic Anion Transporter 4 (OAT4) is expressed in renal proximal brush border and mediates the transports of sulfate conjugates. The C-terminal domain of OAT4 is exposed to the cytoplasmic compartment and contains PDZ motif, one of the famous protein-protein interaction modules, suggesting that it may interact with PDZ proteins. In the present study, using the C-terminus of OAT4 as bait, we performed yeast two-hybrid assay against prey vectors containing PDZ domain containing proteins such as PDZK1, NHERF1, and IKEPP. We found that OAT4 C-terminus interacted with two PDZ proteins, PDZK1 and NHERF1. Such an interaction requires the PDZ motif of OAT4 in its extreme intracellular C-terminal region as identified by both yeast two-hybrid and in vitro binding assays. In addition, the first and fourth PDZ domains of PDZK1 and the first domain of NHERF1 associate with the OAT4 C-terminus. Immunohistochemical study revealed that OAT4 and two PDZ proteins are expressed at the apical membrane of renal proximal tubules. The association of OAT4 with PDZK1 or NHERF1 enhanced estrone sulfate transport activities in HEK293 cells (1.4 to 1.6-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 estrone sulfate transport via OAT4. The elucidation of these interactions will lead to the further understanding of the function and regulation of renal apical organic anion transports in the proximal tubules. [Jpn J Physiol 55 Suppl:S84 (2005)]
