Owen Ryan P, Lagpacan Leah L, Taylor Travis R, De La Cruz Melanie, Huang Conrad C, Kawamoto Michiko, Johns Susan J, Stryke Doug, Ferrin Thomas E, Giacomini Kathleen M
Department of Biopharmaceutical Sciences, University of California, San Francisco, California 94158, USA.
Drug Metab Dispos. 2006 Jan;34(1):12-5. doi: 10.1124/dmd.105.006270. Epub 2005 Oct 7.
The equilibrative nucleoside transporter 2 (ENT2; SLC29A2) is a bidirectional transporter that is involved in the disposition of naturally occurring nucleosides as well as a variety of anticancer and antiviral nucleoside analogs. The goal of the current study was to evaluate the function of genetic variants in ENT2 in cellular assays and to determine the haplotype structure of the coding and flanking intronic region of the gene. As part of a large study focused on genetic variation in membrane transporters (Leabman et al., 2003), DNA samples from ethnically diverse populations (100 African-Americans, 100 European-Americans, 30 Asians, 10 Mexicans, and 7 Pacific Islanders) were screened for variants in membrane transporters, including SLC29A2. Fourteen polymorphic sites in SLC29A2 were found, including 11 in the coding region. Five protein-altering variants were identified: three nonsynonymous variants, and two deletions. Each of the protein-altering variants was found at a very low frequency, occurring only once in the sample population. The nonsynonymous variants and the deletions were constructed via site-directed mutagenesis and were subsequently characterized in Xenopus laevis oocytes. All variants were able to take up inosine with the exception of ENT2-Delta845-846, which resulted in a frameshift mutation that prematurely truncated the protein. ENT2 showed very infrequent variation compared with most other transporter proteins studied, and it was found that five haplotypes were sufficient to describe the entire sample set. The low overall genetic diversity in SLC29A2 makes it unlikely that variation in the coding region contributes significantly to clinically observed differences in drug response.
平衡核苷转运体2（ENT2；SLC29A2）是一种双向转运体，参与天然核苷以及多种抗癌和抗病毒核苷类似物的处置。本研究的目的是在细胞试验中评估ENT2基因变异体的功能，并确定该基因编码区和侧翼内含子区域的单倍型结构。作为一项关注膜转运体基因变异的大型研究的一部分（Leabman等人，2003年），对来自不同种族人群（100名非裔美国人、100名欧裔美国人、30名亚洲人、10名墨西哥人和7名太平洋岛民）的DNA样本进行了膜转运体变异筛查，包括SLC29A2。在SLC29A2中发现了14个多态性位点，其中11个位于编码区。鉴定出5个蛋白质改变变异体：3个非同义变异体和2个缺失。每个蛋白质改变变异体的出现频率都非常低，在样本群体中仅出现一次。通过定点诱变构建了非同义变异体和缺失变异体，随后在非洲爪蟾卵母细胞中对其进行了表征。除了ENT2-Delta845-846导致移码突变并提前截断蛋白质外，所有变异体都能够摄取肌苷。与大多数其他研究的转运体蛋白相比，ENT2的变异非常罕见，并且发现5种单倍型足以描述整个样本集。SLC29A2总体遗传多样性较低，使得编码区的变异不太可能对临床上观察到的药物反应差异有显著贡献。
