Equilibrative nucleoside transporter 1
basolateral plasma membrane
Localization of human equilibrative nucleoside transporters, hENT1 and hENT2, in renal epithelial cells.
Nucleoside transporters are important in the disposition of nucleosides and nucleoside analogs in the kidney. Two human equilibrative nucleoside transporters have been cloned and characterized, hENT1 and hENT2. The primary goal of this study was to localize these transporters in polarized renal epithelia. hENT1 and hENT2 were tagged with green fluorescence protein, stably expressed in renal epithelial cells, and localized by immunofluorescence and functional analysis. Our data demonstrated that both transporters are expressed on the basolateral membrane. hENT1 is also present on the apical membrane. Additionally, we examined the importance to basolateral targeting of two COOH-terminal targeting motifs: a RXXV motif for hENT1 and a dileucine repeat for hENT2. Neither motif appeared to affect targeting, but the dileucine repeat was implicated in surface expression of hENT2. In addition, a splice variant of hENT2 was identified that is predicted to result in a 156-residue COOH-terminal truncation. This variant had a tissue distribution similar to wild-type hENT2 but was retained intracellularly. These data suggest that hENT1 and hENT2 on the basolateral membrane function with concentrative nucleoside transporters on the apical membrane to mediate active reabsorption of nucleosides within the kidney.