The adaptor protein PDZK1/NHERF3 interacts with the glutamate transporter EAAC1 and controls its surface activity in epithelial cells

In epithelia, the glutamate transporter EAAC1/EAAT3 mediates the absorption of dicarboxylic amino acids and has been involved in dicarboxylic aminoaciduria, a rare disease in which glutamate and aspartate accumulate in urine. EAAC1 cell-surface distribution is regulated by interaction with accessory proteins, which remain to be identified. By means of yeast two hybrid system, we identified the PDZ domain containing protein 1 (PDZK1), an adaptor protein involved in the apical domain organization of epithelia. The interaction was confirmed by affinity chromatography and co-immunoprecipitation experiments. Immunostaining of pig jejunum with antisera against PDZK1 and EAAC1 revealed co-localization between the two proteins in the apical domain of enterocytes and in sub-apical vesicular compartments. PDZK1 not only co-localized but also functionally interacted with the transporter, because its presence increased the glutamate uptake in MDCK cells expressing wild type EAAC1, but not a mutant transporter lacking the PDZ interaction sequence. Taken together, these results demonstrate that PDZK1 functionally interacts with EAAC1 and modulates its cell-surface activity.