Effects of altered sialic acid biosynthesis on N-linked glycan branching and cell surface interactions.
Effects of altered sialic acid biosynthesis on N-linked glycan branching and cell surface interactions.
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DOI：
10.1074/jbc.m116.764597
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发表时间：
2017-06-09
期刊：
影响因子：
--
通讯作者：
Kohler JJ
中科院分区：
文献类型：
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作者：
Pham ND;Pang PC;Krishnamurthy S;Wands AM;Grassi P;Dell A;Haslam SM;Kohler JJ
GNE（UDP-GlcNAc 2-差向异构酶/ManNAc激酶）肌病是一种罕见的与衰老相关的肌肉疾病，与散发性包涵体肌炎（最常见的衰老获得性肌肉疾病）有关。虽然散发性包涵体肌炎的原因尚不清楚，但GNE肌病与GNE突变有关。GNE具有哺乳动物细胞中唾液酸生物合成所需的两种酶活性。两个GNE结构域的突变与GNE肌病有关。然而，突变相关的唾液酸产生减少和疾病严重程度之间的相关性是不完善的。为了研究GNE突变的其他潜在影响，我们比较了表达野生型或突变型GNE的细胞系中唾液酸的产生。虽然我们没有检测到任何差异归因于疾病相关的突变，凝集素结合和质谱分析表明，GNE缺乏与细胞表面聚糖的结构上的意外影响。除了表现出低水平的唾液酸化，GNE缺陷细胞产生不同的N-连接的聚糖结构，增加分支和延长聚-N-乙酰乳糖胺。GNE缺乏可能影响UDP-GlcNAc的水平，UDP-GlcNAc是营养敏感己糖胺生物合成途径中的关键代谢物，但这种适度的影响并不能完全解释N-连接聚糖结构的变化。此外，GNE缺乏和葡萄糖补充剂独立地和相加地增加N-连接聚糖分支。值得注意的是，由GNE缺陷细胞产生的N-连接聚糖显示出与半乳糖凝集素-1的结合增强，表明GNE活性的变化可以改变细胞表面糖蛋白对半乳糖凝集素晶格的亲和力。这些发现表明GNE活性可能通过细胞表面受体影响信号传导的一种意想不到的机制。
GNE (UDP-GlcNAc 2-epimerase/ManNAc kinase) myopathy is a rare muscle disorder associated with aging and is related to sporadic inclusion body myositis, the most common acquired muscle disease of aging. Although the cause of sporadic inclusion body myositis is unknown, GNE myopathy is associated with mutations in GNE. GNE harbors two enzymatic activities required for biosynthesis of sialic acid in mammalian cells. Mutations to both GNE domains are linked to GNE myopathy. However, correlation between mutation-associated reductions in sialic acid production and disease severity is imperfect. To investigate other potential effects of GNE mutations, we compared sialic acid production in cell lines expressing wild type or mutant forms of GNE. Although we did not detect any differences attributable to disease-associated mutations, lectin binding and mass spectrometry analysis revealed that GNE deficiency is associated with unanticipated effects on the structure of cell-surface glycans. In addition to exhibiting low levels of sialylation, GNE-deficient cells produced distinct N-linked glycan structures with increased branching and extended poly-N-acetyllactosamine. GNE deficiency may affect levels of UDP-GlcNAc, a key metabolite in the nutrient-sensing hexosamine biosynthetic pathway, but this modest effect did not fully account for the change in N-linked glycan structure. Furthermore, GNE deficiency and glucose supplementation acted independently and additively to increase N-linked glycan branching. Notably, N-linked glycans produced by GNE-deficient cells displayed enhanced binding to galectin-1, indicating that changes in GNE activity can alter affinity of cell-surface glycoproteins for the galectin lattice. These findings suggest an unanticipated mechanism by which GNE activity might affect signaling through cell-surface receptors.