Ritchie J W, Taylor P M
Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Biochem J. 2001 Jun 15;356(Pt 3):719-25. doi: 10.1042/0264-6021:3560719.
The feto-placental unit relies on a maternal supply of indispensable amino acids and iodothyronines for early development and normal growth. We examined the role of the System L transporter in placental uptake of these substances, using the human placental choriocarcinoma cell line BeWo as a model experimental system. BeWo cells express both heavy (4F2hc) and light (LAT1, LAT2) chains of the System L holotransporter. Saturable transport of both L-[(3)H]tryptophan and [(125)I]tri-iodo-L-thyronine in BeWo cells includes components sensitive to inhibition by the System-L-specific substrate 2-endoamino-bicycloheptane-2-carboxylic acid; kinetic properties of these components indicate that the 4F2hc-LAT1 transporter isoform is likely to predominate for the carriage of both substances at physiologically relevant concentrations. Both 4F2hc and LAT1 proteins are also expressed in human placental membranes and LAT1 at least is localized largely to the syncytiotrophoblast layer of the term human placenta. The 4F2hc-LAT1 transporter might therefore serve a vital role in supplying the developing fetus and the placenta with both thyroid hormones and indispensable amino acids from the maternal circulation.
胎儿 - 胎盘单位依赖母体提供必需氨基酸和碘甲状腺原氨酸以实现早期发育和正常生长。我们使用人胎盘绒毛膜癌细胞系BeWo作为模型实验系统，研究了L系统转运蛋白在胎盘摄取这些物质中的作用。BeWo细胞表达L系统全转运蛋白的重链（4F2hc）和轻链（LAT1、LAT2）。BeWo细胞中L - [（3）H]色氨酸和[（125）I]三碘 - L - 甲状腺原氨酸的可饱和转运包括对L系统特异性底物2 - 内氨基 - 双环庚烷 - 2 - 羧酸抑制敏感的成分；这些成分的动力学特性表明，在生理相关浓度下，对于这两种物质的转运，4F2hc - LAT1转运异构体可能占主导地位。4F2hc和LAT1蛋白也在人胎盘膜中表达，并且至少LAT1主要定位于足月人胎盘的合体滋养层。因此，4F2hc - LAT1转运蛋白可能在从母体循环为发育中的胎儿和胎盘提供甲状腺激素和必需氨基酸方面发挥重要作用。
