Division of Cell Signalling and Immunology, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom.
J Biol Chem. 2011 Oct 7;286(40):34522-32. doi: 10.1074/jbc.M111.243410. Epub 2011 Aug 11.
It is well established that murine T-lymphocyte activation is accompanied by major changes in cell-surface sialylation, potentially influencing interactions with sialic acid-binding immunoglobulin-like lectins (siglecs). In the present study, we analyzed early activation of murine CD4+ and CD8+ T-lymphocytes at 24 h. We observed a striking and selective up-regulation in the binding of a recombinant soluble form of siglec-E, an inhibitory siglec, which is expressed on several myeloid cell types including antigen-presenting dendritic cells. In contrast, much lower levels of T cell binding were observed with other siglecs, including sialoadhesin, CD22, and siglec-F and the plant lectins Maackia amurensis leukoagglutinin and Sambucus nigra agglutinin. By mass spectrometry, the sialic acid content of 24-h-activated CD4+ and CD8+ T-lymphocytes exhibited an increased proportion of N-acetyl-neuraminic acid (NeuAc) to N-glycolyl-neuraminic acid (NeuGc) in N-glycans. Reduced levels of NeuGc on the surface of activated T cells were demonstrated using an antibody specific for NeuGc and the expression levels of the gene encoding NeuAc- to NeuGc-converting enzyme, CMP-NeuAc hydroxylase, were also reduced. Siglec-E bound a wide range of sialylated structures in glycan arrays, had a preference for NeuAc versus NeuGc-terminated sequences and could recognize a set of sialoglycoproteins that included CD45, in lysates from activated T-lymphocytes. Collectively, these results show that early in T cell activation, glycan remodelling involves a switch from NeuGc- to NeuAc-terminating oligosaccharides on cell surface glycoproteins. This is associated with a strong up-regulation of siglec-E ligands, which may be important in promoting cellular interactions between early activated T-lymphocytes and myeloid cells expressing this inhibitory receptor.
已证实，鼠 T 淋巴细胞的激活伴随着细胞表面唾液酸化的重大变化，这可能影响与唾液酸结合免疫球蛋白样凝集素（Siglec）的相互作用。在本研究中，我们分析了 24 小时时鼠 CD4+和 CD8+T 淋巴细胞的早期激活。我们观察到一种显著且选择性的上调，即一种表达在包括抗原呈递树突状细胞在内的几种髓样细胞上的抑制性 Siglec-E 的重组可溶性形式的结合。相比之下，观察到其他 Siglec 的 T 细胞结合水平要低得多，包括唾液酸结合蛋白、CD22 和 Siglec-F 以及植物凝集素 Maackia amurensis 白细胞凝集素和 Sambucus nigra 凝集素。通过质谱分析，24 小时激活的 CD4+和 CD8+T 淋巴细胞的 N-乙酰神经氨酸（NeuAc）与 N-羟乙酰神经氨酸（NeuGc）在 N-糖链中的比例增加。使用针对 NeuGc 的抗体和编码 NeuAc 向 NeuGc 转化酶 CMP-NeuAc 羟化酶的基因表达水平降低，证明了激活 T 细胞表面 NeuGc 水平降低。Siglec-E 结合糖链阵列中的广泛的唾液酸化结构，对 NeuAc 与 NeuGc 末端序列具有偏好性，并能识别一组包括 CD45 的糖蛋白，这些糖蛋白来自激活的 T 淋巴细胞的裂解物。总的来说，这些结果表明，在 T 细胞激活的早期，糖基化修饰涉及到细胞表面糖蛋白上从 NeuGc 到 NeuAc 末端寡糖的转换。这与 Siglec-E 配体的强烈上调有关，这可能在促进早期激活的 T 淋巴细胞与表达这种抑制性受体的髓样细胞之间的细胞相互作用中很重要。
