MOLECULAR-CLONING AND FUNCTIONAL EXPRESSION OF CDNAS ENCODING A HUMANNA-NUCLEOSIDE COTRANSPORTER (HCNT1)()

We report identification of a new human nucleoside transporter protein by molecular cloning and functional expression of its cDNA. Previousl y, we used expression selection in Xenopus oocytes to isolate a cDNA f rom rat jejunal epithelium encoding the pyrimidine-selective Na+-depen dent nucleoside transporter rCNT1 (Q.-Q. Huang, S. Y. M. Yao, M. W. L. Ritzel, A, R. P. Paterson, C. E. Cass, and J. D. Young. J. Biol. Chem . 269: 17757-17760, 1994). cDNAs for a human homologue of rCNT1, desig nated hCNT1, have been isolated from human kidney by hybridization clo ning and reverse transcriptase polymerase chain reaction amplification strategies. hCNT1 was 83% identical to rCNT1 in amino acid sequence a nd exhibited the transport characteristics of an Na+-dependent nucleos ide transporter with selectivity for pyrimidine nucleosides and adenos ine when expressed in Xenopus oocytes. Deoxyadenosine, which undergoes net renal secretion, and guanosine were poor permeants. hCNT1 did, ho wever, transport 3'-azido-3'-deoxythymidine. This is the first demonst ration that members of the CNT family exist in human cells and provide s evidence of their involvement in the renal transport of physiologica l nucleosides and nucleoside drugs. The hCNT1 gene was mapped to chrom osome 15q25-26.