Heparan Sulfate Modification of the Transmembrane Receptor CD47 Is Necessary for Inhibition of T Cell Receptor Signaling by Thrombospondin-1
Heparan Sulfate Modification of the Transmembrane Receptor CD47 Is Necessary for Inhibition of T Cell Receptor Signaling by Thrombospondin-1
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DOI：
10.1074/jbc.m110.179663
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发表时间：
2011-04-29
影响因子：
4.8
通讯作者：
Roberts, David D.
中科院分区：
文献类型：
--
作者：
Kaur, Sukhbir;Kuznetsova, Svetlana A.;Roberts, David D.
T细胞表面的蛋白多糖有助于逆转录病毒感染、趋化因子和其他蛋白质的结合，并且是某些T细胞对基质细胞糖蛋白血栓反应蛋白-1反应所必需的。由原代T细胞和Jurkat T细胞表达的主要细胞表面蛋白多糖具有明显的M-R和GT；200,000，并被硫酸软骨素和硫酸肝素链修饰。凝血酶敏感蛋白-1以肝素抑制的方式与这种蛋白多糖结合，并以可溶的形式释放到介质中。根据质谱学、基因敲除和免疫化学分析，该蛋白多糖包含两个主要的核心蛋白：淀粉样前体蛋白-2(APLP2，表观M-r 230,000)和CD47(表观M-r>；250,000)。CD47是一种已知的凝血酶敏感蛋白-1受体，但以前没有报道过它是一种蛋白多糖。CD47的这种蛋白多糖亚型广泛表达在血管细胞上。突变鉴定了CD47Ser()和Ser(79)的糖胺聚糖修饰。在表达APLP2蛋白多糖异构体的CD47缺陷T细胞中，凝血酶反应蛋白-1对T细胞受体信号的抑制作用消失，这表明与APLP2的结合是不够的。在CD47缺陷细胞中，通过重新表达CD47或S79A突变体可以恢复对CD69诱导的抑制，但S64A突变体不能。因此，凝血酶敏感蛋白-1对T细胞受体信号的抑制是由CD47介导的，需要在Ser()对其进行修饰。
Cell surface proteoglycans on T cells contribute to retroviral infection, binding of chemokines and other proteins, and are necessary for some T cell responses to the matricellular glycoprotein thrombospondin-1. The major cell surface proteoglycans expressed by primary T cells and Jurkat T cells have an apparent M-r > 200,000 and are modified with chondroitin sulfate and heparan sulfate chains. Thrombospondin-1 bound in a heparin-inhibitable manner to this proteoglycan and to a soluble form released into the medium. Based on mass spectrometry, knockdown, and immunochemical analyses, the proteoglycan contains two major core proteins as follows: amyloid precursor-like protein-2 (APLP2, apparent M-r 230,000) and CD47 (apparent M-r > 250,000). CD47 is a known thrombospondin-1 receptor but was not previously reported to be a proteoglycan. This proteoglycan isoform of CD47 is widely expressed on vascular cells. Mutagenesis identified glycosaminoglycan modification of CD47 at Ser(64) and Ser(79). Inhibition of T cell receptor signaling by thrombospondin-1 was lost in CD47-deficient T cells that express the proteoglycan isoform of APLP2, indicating that binding to APLP2 is not sufficient. Inhibition of CD69 induction was restored in CD47-deficient cells by re-expressing CD47 or an S79A mutant but not by the S64A mutant. Therefore, inhibition of T cell receptor signaling by thrombospondin-1 is mediated by CD47 and requires its modification at Ser(64).