Lum P Y, Ngo L Y, Bakken A H, Unadkat J D
Department of Pharmaceutics, University of Washington, Seattle 98195, USA.
Cancer Chemother Pharmacol. 2000;45(4):273-8. doi: 10.1007/s002800050040.
To clone and sequence the equilibrative nitrobenzylthioinosine (NBMPR)-sensitive nucleoside transporter (es) from the human small intestine and to examine the capacities of nucleosides and nucleoside analogs to inhibit the uptake of uridine by this transporter.
Using PCR, es was cloned from a cDNA library of the human small intestine. The uptake of 3H-uridine (10 microM) by the recombinant es, expressed in Xenopus oocytes, was measured in the presence (2 mM) and absence of nucleosides and nucleoside analogs.
The amino acid sequence of this es transporter was identical to that of the human placental es transporter. Uptake of 3H-uridine by this es transporter was inhibitable by 1 microM NBMPR. Removal of the oxygen from the 3' position or from both the 2' and 3' positions, but not from 2' or 5' position, resulted in a partial or total loss of the capacity of the nucleosides to inhibit 3H-uridine uptake. No modifications of the adenosine base or of the uridine base (except for 3 and 6 positions on uracil) affected nucleoside inhibitory capacity.
The es transporters of the human intestine and placenta are identical in their amino acid sequences. Moreover, the inhibitory profiles of various nucleoside analogs in inhibiting the uptake of uridine by the intestinal es transporter are similar to those obtained with the as-yet-uncloned human erythrocyte es transporter. Collectively, these findings suggest that the es transporter does not appear to be functionally variant in the human placenta, small intestine or erythrocytes.
克隆并测序人小肠中对平衡型硝基苄硫基肌苷（NBMPR）敏感的核苷转运体（es），并检测核苷及核苷类似物抑制该转运体摄取尿苷的能力。
利用聚合酶链反应（PCR）从人小肠cDNA文库中克隆es。在非洲爪蟾卵母细胞中表达重组es，在存在（2 mM）和不存在核苷及核苷类似物的情况下，测定其对3H-尿苷（10 microM）的摄取。
该es转运体的氨基酸序列与人胎盘es转运体相同。1 microM NBMPR可抑制该es转运体对3H-尿苷的摄取。3'位或2'和3'位同时去除氧原子，但2'位或5'位去除氧原子则不会导致核苷抑制3H-尿苷摄取的能力部分或完全丧失。腺苷碱基或尿苷碱基（尿嘧啶的3位和6位除外）的修饰均不影响核苷的抑制能力。
人小肠和胎盘的es转运体氨基酸序列相同。此外, 各种核苷类似物抑制小肠es转运体摄取尿苷的抑制谱与尚未克隆的人红细胞es转运体相似。总体而言，这些发现表明es转运体在人胎盘、小肠或红细胞中似乎没有功能差异。
