Bhutia Yangzom D, Babu Ellappan, Ganapathy Vadivel
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430 USA.
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430 USA.
Biochim Biophys Acta. 2015 Feb;1848(2):453-62. doi: 10.1016/j.bbamem.2014.10.021. Epub 2014 Oct 23.
IDO1, which encodes the immunosuppressive and tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase-1 (IDO1), is a target for interferon-γ (IFN-γ). IDO1-mediated tryptophan catabolism in dendritic cells and macrophages arrests T cell proliferation, thereby providing a molecular basis for the immunosuppressive function of IDO1. Whether the entry of tryptophan into IDO1-expressing cells is also regulated by IFN-γ is not known. Here we used a human colonic epithelial cell line (CCD841) and a mouse dendritic cell line (DC2.4) to test the hypothesis that IFN-γ, which induces IDO1, also induces a tryptophan transporter to promote substrate availability to IDO1. Upon treatment with IFN-γ, there was a marked increase in IDO1 mRNA and a concomitant increase in tryptophan uptake in both cell lines. The induced uptake system was selective for tryptophan and saturable with a Michaelis constant of 36±3 μM in CCD841 cells and 0.5±0.1 μM in DC2.4 cells. The induction by IFN-γ and the tryptophan-selectivity of the induced transport system were demonstrable even in the presence of physiologic concentrations of all other amino acids. Since kynurenine, the catabolic end product of IDO1, is a signaling molecule as an agonist for the aryl hydrocarbon receptor (AhR), we examined if AhR signaling induces the tryptophan-selective transporter. Treatment of the cells with kynurenine and other AhR agonists increased tryptophan uptake. The present studies demonstrate that IFN-γ coordinately induces IDO1 and a tryptophan-selective transporter to maximize tryptophan depletion in IDO1-expressing cells and that the process involves a positive feedback mechanism via kynurenine-AhR signaling.
吲哚胺2,3-双加氧酶1（IDO1）由IDO1基因编码，该酶具有免疫抑制和色氨酸分解代谢功能，是γ干扰素（IFN-γ）的作用靶点。IDO1介导的树突状细胞和巨噬细胞中的色氨酸分解代谢会抑制T细胞增殖，从而为IDO1的免疫抑制功能提供分子基础。色氨酸进入表达IDO1的细胞是否也受IFN-γ调控尚不清楚。在此，我们使用人结肠上皮细胞系（CCD841）和小鼠树突状细胞系（DC2.4）来验证以下假说：诱导IDO1的IFN-γ也会诱导一种色氨酸转运体，以促进IDO1的底物供应。用IFN-γ处理后，两种细胞系中的IDO1 mRNA均显著增加，同时色氨酸摄取也随之增加。诱导的摄取系统对色氨酸具有选择性，在CCD841细胞中的米氏常数为36±3 μM，在DC2.4细胞中为0.5±0.1 μM，且具有饱和性。即使在存在所有其他氨基酸的生理浓度时，IFN-γ的诱导作用以及诱导转运系统对色氨酸的选择性仍然明显。由于IDO1的分解代谢终产物犬尿氨酸是一种作为芳烃受体（AhR）激动剂的信号分子，我们研究了AhR信号是否会诱导色氨酸选择性转运体。用犬尿氨酸和其他AhR激动剂处理细胞会增加色氨酸摄取。本研究表明，IFN-γ协同诱导IDO1和一种色氨酸选择性转运体，以使表达IDO1的细胞中的色氨酸消耗最大化，并且该过程涉及通过犬尿氨酸-AhR信号的正反馈机制。
