Molecular Development of the Immune System Section, Laboratory of Immune System Biology, NIAID, National Institutes of Health, Bethesda, Maryland 20892.
Clinical Genomics Program, NIAID, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 2019 Sep 13;294(37):13638-13656. doi: 10.1074/jbc.RA119.008903. Epub 2019 Jul 23.
Magnesium transporter 1 (MAGT1) critically mediates magnesium homeostasis in eukaryotes and is highly-conserved across different evolutionary branches. In humans, loss-of-function mutations in the gene cause X-linked magnesium deficiency with Epstein-Barr virus (EBV) infection and neoplasia (XMEN), a disease that has a broad range of clinical and immunological consequences. We have previously shown that EBV susceptibility in XMEN is associated with defective expression of the antiviral natural-killer group 2 member D (NKG2D) protein and abnormal Mg transport. New evidence suggests that MAGT1 is the human homolog of the yeast OST3/OST6 proteins that form an integral part of the -linked glycosylation complex, although the exact contributions of these perturbations in the glycosylation pathway to disease pathogenesis are still unknown. Using MS-based glycoproteomics, along with CRISPR/Cas9-KO cell lines, natural killer cell-killing assays, and RNA-Seq experiments, we now demonstrate that humans lacking functional MAGT1 have a selective deficiency in both immune and nonimmune glycoproteins, and we identified several critical glycosylation defects in important immune-response proteins and in the expression of genes involved in immunity, particularly CD28. We show that MAGT1 function is partly interchangeable with that of the paralog protein tumor-suppressor candidate 3 (TUSC3) but that each protein has a different tissue distribution in humans. We observed that MAGT1-dependent glycosylation is sensitive to Mg levels and that reduced Mg impairs immune-cell function via the loss of specific glycoproteins. Our findings reveal that defects in protein glycosylation and gene expression underlie immune defects in an inherited disease due to MAGT1 deficiency.
镁转运蛋白 1（MAGT1）在真核生物中对镁稳态的调节至关重要，并且在不同进化分支中高度保守。在人类中， 基因中的功能丧失突变导致 X 连锁镁缺乏伴 EBV 感染和肿瘤（XMEN），这是一种具有广泛临床和免疫学后果的疾病。我们之前已经表明，XMEN 中的 EBV 易感性与抗病毒自然杀伤细胞组 2 成员 D（NKG2D）蛋白的表达缺陷和异常镁转运有关。新的证据表明，MAGT1 是酵母 OST3/OST6 蛋白的人类同源物，OST3/OST6 蛋白是 - 连接糖基化复合物的一个组成部分，尽管这些糖基化途径中的扰动对疾病发病机制的确切贡献仍不清楚。我们使用基于 MS 的糖蛋白质组学、CRISPR/Cas9-KO 细胞系、自然杀伤细胞杀伤测定和 RNA-Seq 实验，现在证明缺乏功能性 MAGT1 的人类在免疫和非免疫糖蛋白中都存在选择性缺乏，并且我们在重要免疫反应蛋白和参与免疫的基因的表达中鉴定出几个关键的糖基化缺陷，特别是 CD28。我们表明，MAGT1 的功能部分可与平行蛋白肿瘤抑制候选物 3（TUSC3）互换，但每种蛋白质在人类中具有不同的组织分布。我们观察到 MAGT1 依赖性糖基化对镁水平敏感，并且镁缺乏会通过丧失特定糖蛋白来损害免疫细胞功能。我们的研究结果表明，由于 MAGT1 缺乏导致的遗传性疾病中，蛋白质糖基化和基因表达的缺陷是免疫缺陷的基础。
