NA-DEPENDENT PURINE NUCLEOSIDE TRANSPORTER FROM HUMAN KIDNEY - CLONING AND FUNCTIONAL-CHARACTERIZATION()

Many purine nucleosides and their analogs are actively transported in the kidney. Using homology cloning strategies and reverse transcriptas e-polymerase chain reactions, we isolated a cDNA encoding a Na+-depend ent nucleoside transporter, hSPNT1, from human kidney. Functional expr ession in Xenopus laevis oocytes identified hSPNT1 as a Na+-dependent nucleoside transporter that selectively transports purine nucleosides but also transports uridine. The Michaelis constant (K-m) of uridine ( 80 mu M) in interacting with hSPNT1 was substantially higher than that of inosine (4.5 mu M). hSPNT1 (653 amino acids) is 81% identical to t he previously cloned rat Na+-nucleoside transporter, SPNT, but differs markedly from SPNT in terms of its primary structure in the NH2 termi nus. In addition, an Alu repetitive element (similar to 282 bp) is pre sent in the 3'-untranslated region of the hSPNT1 cDNA. Northern analys is revealed that multiple transcripts of hSPNT1 are widely distributed in human tissues including human kidney. In contrast, rat SPNT transc ripts are absent in kidney and highly localized to liver and intestine . The hSPNT1 gene was localized to chromosome 15. This is the first de monstration of a purine nucleoside transporter in human kidney.