Functional Characterization in Yeast of Genetic Variants in the Human Equilibrative Nucleoside Transporter, ENT1

The human equilibrative nucleoside transporter, ENT1, appears to play a critical role in the disposition of nucleosides and nucleoside analogs used clinically as anti-viral and anti-cancer drugs. Recently, we identified variants of ENT1 in an ethnically diverse DNA sample set from 247 individuals, focusing primarily on the coding region. The goal of the present study was to analyse the haplotype structure and functionally characterize the variants of ENT1. We observed that a single haplotype, ENT1*1, accounted for 91.3% of the 494 chromosomes. Functional analysis in Saccharomyces cerevisiae revealed no differences in the kinetics of uptake of nucleosides and nucleoside analogs by the two non-synonymous variant transporters, ENT1-I216T and ENT1-E391K, and the reference ENT1. These results, together with the observation that there are few haplotypes of ENT1, indicate that coding region variants of ENT1 do not contribute to inter-individual differences in response to nucleoside analog drugs.