Genomic organization and functional characterization of the human concentrative nucleoside transporter-3 isoform (hCNT3) expressed in mammalian cells

Shuy Vang Toan, Kenneth K.W. To, George P.H. Leung, Maria Olivia De Souza, Jeffrey L. Ward, Chung Ming Tse

Research output: Contribution to journalArticle

Abstract

Human CNT3 encodes the concentrative nucleoside transport N3 system. Previous expression studies in oocytes showed that the Kmvalues for nucleosides of the cloned hCNT3 were 7- to 25-fold lower than the endogenous N3 transporter in HL60 cells. Therefore, in the present study we re-examined the kinetic properties of the cloned hCNT3 using mammalian cell expression systems by transient expression in Cos7L cells and stably expression in nucleoside transporter deficient PK15NTD cells. We demonstrated that hCNT3 is a Na-dependent, broadly-selective nucleoside transporter with affinities (<11 μM) for nucleosides closely resembling the endogenous N3 transporter. Pharmacological studies showed that phloridzin is a mixed-type inhibitor of hCNT3 (Ki=15 μM), and the dideoxyuridine analogs are poor substrates. By epitope-tagging, we further demonstrated that hCNT3 is N-glycosylated as PNGase F and Endo H deglycosylated hCNT3 from 67 kDa to 58 kDa. Searching the human genome database, we identified the genomic organization of hCNT3. This gene contains 19 exons and its exon-intron boundaries within the coding sequence exactly match with those of hCNT1 and hCNT2 with one additional exon in the N-terminus. Our data suggest that hCNT3 gene is evolutionarily conserved with hCNT1 and hCNT2. Physiologically, hCNT3 is a glycoprotein, which transports purine and pyrimidine nucleosides in a Na-dependent manner with high affinities.

Original languageEnglish (US)
Pages (from-to)195-204
Number of pages10
JournalPflugers Archiv European Journal of Physiology
Volume447
Issue number2
DOIs
StatePublished - Nov 1 2003

Keywords

  • Adenosine
  • Cos7L cells
  • Genome
  • Nucleoside transport
  • PK15NTD cells
  • hCNT3

ASJC Scopus subject areas

  • Physiology
  • Clinical Biochemistry
  • Physiology (medical)

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