Badagnani I, Chan W, Castro R A, Brett C M, Huang C C, Stryke D, Kawamoto M, Johns S J, Ferrin T E, Carlson E J, Burchard E G, Giacomini K M
Department of Biopharmaceutical Sciences, University of California, San Francisco, CA 94143-0446, USA.
Pharmacogenomics J. 2005;5(3):157-65. doi: 10.1038/sj.tpj.6500303.
The human concentrative nucleoside transporter, CNT3 (SLC28A3), plays an important role in mediating the cellular entry of a broad array of physiological nucleosides and synthetic anticancer nucleoside analog drugs. As a first step toward understanding the genetic basis for interindividual differences in the disposition and response to antileukemic nucleoside analogs, we examined the genetic and functional diversity of CNT3. In all, 56 variable sites in the exons and flanking intronic region of SLC28A3 were identified in a collection of 270 DNA samples from US populations (80 African-Americans, 80 European-Americans, 60 Asian-Americans, and 50 Mexican-Americans). Of the 16 coding region variants, 12 had not been previously reported. Also, 10 resulted in amino-acid changes and three of these had total allele frequencies of >/=1%. Nucleotide diversity (pi) at nonsynonymous and synonymous sites was estimated to be 1.81 x 10(4) and 18.13 x 10(4), respectively, suggesting that SLC28A3 is under negative selection. All nonsynonymous variants, constructed by site-directed mutagenesis and expressed in Xenopus laevis oocytes, transported purine and pyrimidine model substrates, except for c. 1099G>A (p. Gly367Arg). This rare variant alters an evolutionarily conserved site in the putative substrate recognition domain of CNT3. The presence of three additional evolutionarily conserved glycine residues in the vicinity of p. Gly367Arg that are also conserved in human paralogs suggest that these glycine residues are critical in the function of the concentrative nucleoside transporter family. The genetic analysis and functional characterization of CNT3 variants suggest that this transporter does not tolerate nonsynonymous changes and is important for human fitness.
人类浓缩核苷转运体CNT3（SLC28A3）在介导多种生理核苷和合成抗癌核苷类似物药物进入细胞过程中发挥重要作用。作为了解抗白血病核苷类似物处置和反应个体差异遗传基础的第一步，我们研究了CNT3的遗传和功能多样性。在美国人群的270份DNA样本（80名非裔美国人、80名欧洲裔美国人、60名亚裔美国人及50名墨西哥裔美国人）中，共鉴定出SLC28A3外显子及侧翼内含子区域的56个可变位点。在16个编码区变体中，有12个此前未被报道。此外，10个导致氨基酸改变，其中3个的总等位基因频率≥1%。非同义位点和同义位点的核苷酸多样性（pi）分别估计为1.81×10⁻⁴和18.13×10⁻⁴，表明SLC28A3处于负选择之下。通过定点诱变构建并在非洲爪蟾卵母细胞中表达的所有非同义变体，除了c.1099G>A（p.Gly367Arg）外，均能转运嘌呤和嘧啶模型底物。这种罕见变体改变了CNT3推定底物识别域中一个进化保守位点。在p.Gly367Arg附近还有另外三个进化保守的甘氨酸残基，它们在人类旁系同源物中也保守，这表明这些甘氨酸残基对浓缩核苷转运体家族的功能至关重要。CNT3变体的遗传分析和功能表征表明，该转运体不容忍非同义变化，对人类健康很重要。
