Expression and differential polarization of the reduced-folate transporter-1 and the folate receptor α in mammalian retinal pigment epitheliu
Expression and differential polarization of the reduced-folate transporter-1 and the folate receptor α in mammalian retinal pigment epitheliu
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DOI：
10.1074/jbc.m002328200
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发表时间：
2000-07-07
影响因子：
4.8
通讯作者：
Smith, SB
中科院分区：
文献类型：
--
作者：
Chancy, CD;Kekuda, R;Smith, SB
在正常小鼠视网膜色素上皮（RPE）和培养的人RPE细胞中，研究了叶酸转运蛋白（RFT-1）和叶酸受体α (FR α)的差异极化分布，这两种蛋白参与叶酸转运。RPE细胞介导脉络膜血液向神经视网膜的营养载体转移。虽然已知FR α存在于神经视网膜的许多细胞类型中，但本研究的原位杂交分析表明，RFT-1仅存在于RPE中，使用RFT-1特异性抗体的激光扫描共聚焦显微镜显示，在培养的人和完整的小鼠RPE中，该蛋白的顶端分布与FR α在这些细胞中的基底外侧分布形成对比。RFT-1在RPE细胞顶膜中的表达通过纯化牛RPE顶膜囊泡的功能研究得到证实，这些研究以n -5-甲基四氢叶酸（血液中主要的叶酸衍生物）和叶酸作为底物，表明RFT-1以Na+-和Cl-独立的方式起作用。转运蛋白是叶酸及其类似物的特异性转运蛋白，跨膜H+梯度显著影响该蛋白的转运功能；运输机制可能是叶酸/H+共运输或叶酸/OH-交换。基于FR α和RFT-1在RPE中的差异极化，我们认为这两种蛋白协同作用，使叶酸通过RPE细胞层从脉络膜血液到神经视网膜的载体转移。这构成了两种叶酸转运蛋白在任何极化上皮中的差异极化的第一个报告。
The differential polarized distribution of the reduced-folate transporter (RFT-1) and folate receptor alpha (FR alpha), the two proteins involved in the transport of folate, has been characterized in normal mouse retinal pigment epithelium (RPE) and in cultured human RPE cells. RPE cells mediate the vectorial transfer of nutrients from choroidal blood to neural retina. Whereas FR alpha is known to be present in many cell types of the neural retina, in situ hybridization analysis in the present study demonstrated that RFT-1 is present only in RPE, Laser-scanning confocal microscopy using antibodies specific for RFT-1 demonstrated an apical distribution of this protein in cultured human and intact mouse RPE, which contrasts with the basolateral distribution of FR alpha in these cells, The expression of RFT-1 in the RPE cell apical membrane was confirmed by functional studies with purified apical membrane vesicles from bovine RPE, These studies, done with N-5-methyltetrahydrofolate (the predominant folate derivative in blood) and folate as substrates, have shown that RFT-1 functions in a Na+- and Cl--independent manner. The transporter is specific for folate and its analogs, A transmembrane H+ gradient influences the transport function of this protein markedly; the transport mechanism is Likely to be either folate/H+ co-transport or folate/OH- exchange. Based on the differential polarization of FR alpha and RFT-1 in RPE, we suggest that these two proteins work in a concerted manner to bring about the vectorial transfer of folate across the RPE cell layer from the choroidal blood to the neural retina. This constitutes the first report of the differential polarization of the two folate transport proteins in any polarized epithelium.