Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia, USA.
J Pharm Sci. 2012 Jan;101(1):154-63. doi: 10.1002/jps.22733. Epub 2011 Sep 8.
The sodium-coupled oligopeptide transporters 1 and 2 (SOPT1 and SOPT2) transport peptides consisting of at least five amino acids and show potential for the delivery of therapeutically relevant peptides/peptidomimetics. Here, we examined the expression of these two transporters in the retinal neuronal cell line RGC-5. These cells showed robust uptake activity for the synthetic pentapeptide DADLE ([D-Ala(2),D-Leu(5)]-Enkephalin). The uptake was Na(+) dependent and saturable (K(t), 6.2 ± 0.6 μM). A variety of oligopeptides inhibited DADLE uptake. The uptake of the competing oligopeptides was directly demonstrated with fluorescein isothiocyanate-labeled Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys in RGC-5 cells and primary mouse retinal ganglion cells. The characteristics of DADLE uptake matched those of SOPT2. We then examined the expression of SOPT1 in these cells with deltorphin II (Tyr-D-Ala-Phe-Glu-Val-Val-Gly-NH(2)) as the substrate and found that RGC-5 cells also expressed SOPT1. As it is already known that SOPT1 is expressed in the neuronal cell line SK-N-SH, we investigated SOPT2 expression in these cells to determine whether the presence of both oligopeptide transporters is a common feature of neuronal cells. These studies showed that SK-N-SH cells also expressed SOPT2. This constitutes the first report on the functional characterization of SOPT1 and SOPT2 in retinal neuronal cells and on the expression of SOPT2 in nonretinal neuronal cells.
钠依赖性寡肽转运体 1 和 2（SOPT1 和 SOPT2）转运至少由五个氨基酸组成的肽，并显示出用于输送治疗相关肽/肽类似物的潜力。在这里，我们检查了这两种转运体在视网膜神经元细胞系 RGC-5 中的表达。这些细胞对合成五肽 DADLE（[D-Ala(2),D-Leu(5)]-脑啡肽）表现出强大的摄取活性。摄取是 Na(+) 依赖性和饱和的（K(t)，6.2 ± 0.6 μM）。各种寡肽抑制 DADLE 摄取。用荧光素异硫氰酸酯标记的 Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys 在 RGC-5 细胞和原代小鼠视网膜神经节细胞中直接证明了竞争寡肽的摄取。DADLE 摄取的特征与 SOPT2 相匹配。然后，我们用德尔塔啡 II（Tyr-D-Ala-Phe-Glu-Val-Val-Gly-NH(2)）作为底物检查这些细胞中 SOPT1 的表达，发现 RGC-5 细胞也表达 SOPT1。由于已知 SOPT1 在神经元细胞系 SK-N-SH 中表达，我们研究了这些细胞中 SOPT2 的表达，以确定两种寡肽转运体的存在是否是神经元细胞的共同特征。这些研究表明，SK-N-SH 细胞也表达 SOPT2。这是首次报道 SOPT1 和 SOPT2 在视网膜神经元细胞中的功能特征以及 SOPT2 在非视网膜神经元细胞中的表达。
