Functional cooperation of epithelial heteromeric amino acid transporters expressed in madin-darby canine kidney cells
Functional cooperation of epithelial heteromeric amino acid transporters expressed in madin-darby canine kidney cells
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DOI：
10.1074/jbc.m210449200
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发表时间：
2003-01-10
影响因子：
4.8
通讯作者：
Verrey, F
中科院分区：
文献类型：
--
作者：
Bauch, C;Forster, N;Verrey, F
异构体氨基酸转运体b(0，+)AT-rBAT(心尖)，y(+)LAT1-4F2hc，可能还有LAT2-4F2hc(碱侧)参与了阳离子和中性氨基酸在小肠和肾脏近端小管的(再)吸收。我们现在通过免疫荧光显示，它们的表达水平沿着肾脏近端小管(S1和GT；S2远大于S3)遵循相同的轴向梯度。我们重组了它们在I MDCK细胞上的共表达，并通过免疫荧光验证了它们的极化定位。B(0，+)AT-rBAT的单独表达导致L-Arg(与L-Leu一起给药)的净重吸收。共表达基侧y(+)LAT1-4F2hc可增加L-精氨酸的重吸收，逆转L-亮氨酸从(重)吸收到分泌的转运。同样，当b(0，+)AT-rBAT单独表达时，L-胱氨酸被(重新)吸收。由于LAT2(外源和/或内源)被动员到基侧膜上，4F2hc的共表达进一步增加了这种净转运。综上所述，顶端b(0，+)AT-rBAT分别与y(+)LAT1-4F2hc或LAT2-4F2hc协同完成阳离子氨基酸和胱氨酸的跨上皮重吸收。L-精氨酸的重吸收导致L-亮氨酸的分泌，这一事实表明，所涉及的异构型氨基酸转运体在上皮细胞中作为串联的交换器发挥作用，并支持单向中性氨基酸转运体的平行活性是驱动氨基酸净重吸收所必需的。
The heteromeric amino acid transporters b(0,+)AT-rBAT (apical), y(+)LAT1-4F2hc, and possibly LAT2-4F2hc (basolateral) participate to the (re)absorption of cationic and neutral amino acids in the small intestine and kidney proximal tubule. We show now by immunofluorescence that their expression levels follow the same axial gradient along the kidney proximal tubule (S1 > S2 much greater than S3). We reconstituted their co-expression in I MDCK cell epithelia and verified their polarized localization by immunofluorescence. Expression of b(0,+)AT-rBAT alone led to a net reabsorption Of L-Arg (given together with L-Leu). Coexpression of basolateral y(+)LAT1-4F2hc increased L-Arg reabsorption and reversed L-Leu transport from (re)absorption to secretion. Similarly, L-cystine was (re)absorbed when b(0,+)AT-rBAT was expressed alone. This net transport was further increased by the coexpression of 4F2hc, due to the mobilization of LAT2 (exogenous and/or endogenous) to the basolateral membrane. In summary, apical b(0,+)AT-rBAT cooperates with y(+)LAT1-4F2hc or LAT2-4F2hc for the transepithelial reabsorption of cationic amino acids and cystine, respectively. The fact that the reabsorption of L-Arg led to the secretion Of L-Leu demonstrates that the implicated heteromeric amino acid transporters function in epithelia as exchangers coupled in series and supports the notion that the parallel activity of unidirectional neutral amino acid transporters is required to drive net amino acid reabsorption.