Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Genes (Basel). 2020 Nov 27;11(12):1423. doi: 10.3390/genes11121423.
The novel high-affinity tryptophan (Trp)-selective transport system is present at elevated levels in human interferon-γ (IFN-γ)-treated and indoleamine 2,3-dioxygenase 1 (IDO1)-expressing cells. High-affinity Trp uptake into cells results in extracellular Trp depletion and immune suppression. We have previously shown that both IDO1 and tryptophanyl-tRNA synthetase (TrpRS), whose expression levels are increased by IFN-γ, have a crucial function in high-affinity Trp uptake into human cells. Here, we aimed to elucidate the relationship between TrpRS and IDO1 in high-affinity Trp uptake. We demonstrated that overexpression of IDO1 in HeLa cells drastically enhances high-affinity Trp uptake upon addition of purified TrpRS protein to uptake assay buffer. We also clarified that high-affinity Trp uptake by Trp-starved cells is significantly enhanced by the addition of TrpRS protein to the assay buffer. Moreover, we showed that high-affinity Trp uptake is also markedly elevated by the addition of TrpRS protein to the assay buffer of cells overexpressing another Trp-metabolizing enzyme, tryptophan 2,3-dioxygenase (TDO2). Taken together, we conclude that Trp deficiency is crucial for high-affinity Trp uptake mediated by extracellular TrpRS.
新型高亲和力色氨酸（Trp）选择性转运系统在人干扰素-γ（IFN-γ）处理和吲哚胺 2,3-双加氧酶 1（IDO1）表达的细胞中高水平表达。细胞内高亲和力色氨酸摄取会导致细胞外色氨酸耗竭和免疫抑制。我们之前已经表明，IDO1 和色氨酰-tRNA 合成酶（TrpRS）都具有高亲和力色氨酸摄取到人类细胞中的关键功能，其表达水平可被 IFN-γ 上调。在这里，我们旨在阐明 TrpRS 和 IDO1 在高亲和力色氨酸摄取中的关系。我们证明，在加入纯化的 TrpRS 蛋白到摄取测定缓冲液中后，HeLa 细胞中 IDO1 的过表达可极大地增强高亲和力色氨酸摄取。我们还阐明了在测定缓冲液中加入 TrpRS 蛋白可显著增强色氨酸饥饿细胞的高亲和力色氨酸摄取。此外，我们表明，在测定缓冲液中加入 TrpRS 蛋白也可显著提高过表达另一种色氨酸代谢酶色氨酸 2,3-双加氧酶（TDO2）的细胞的高亲和力色氨酸摄取。综上所述，我们得出结论，细胞外 TrpRS 介导的高亲和力色氨酸摄取需要色氨酸缺乏。
