Cellular Mechanisms Controlling Surfacing of AICL Glycoproteins, Cognate Ligands of the Activating NK Receptor NKp80
Cellular Mechanisms Controlling Surfacing of AICL Glycoproteins, Cognate Ligands of the Activating NK Receptor NKp80
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DOI：
10.4049/jimmunol.1800059
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发表时间：
2018-08-15
影响因子：
4.4
通讯作者：
Steinle, Alexander
中科院分区：
文献类型：
--
作者：
Neuss, Sebastian;Bartel, Yvonne;Steinle, Alexander
AICL糖蛋白是C型凝集素样受体NKp80的同源激活诱导配体，几乎在所有成熟的人类NK细胞上都有表达，NKp80与AICL相互作用刺激NK细胞的效应功能，如细胞毒作用和细胞因子的分泌。值得注意的是，AICL和NKp80由NK基因复合体中相邻的基因编码，并由人类NK细胞共同表达。虽然AICL保留在静息的NK细胞内，但NK细胞暴露于促炎细胞因子会导致AICL表面出现，并对NKp80介导的NK杀伤药物易感。在这项研究中，我们描述了导致细胞内滞留的AICL糖蛋白的分子决定因素，从而控制AICL表面的表达。C型凝集素样结构域中的Cys(87)不仅通过二硫键确保AICL糖蛋白稳定的同源二聚，而且Cys(87)也是AICL同源二聚体在细胞表面高效表达所必需的，也是AICL-NKp80相互作用所必需的。相反，细胞质赖氨酸作为针对蛋白酶体降解的AICL的负调节因子。AICL C型凝集素样域中的一个非典型糖基化位点和三个常规N-连接糖基化位点对AICL的成熟和表型有重要影响，AICL的成熟和表型严格依赖于至少一个常规糖基化位点的糖基化。然而，尽管传统的N-连接糖基化程度与AICL表面表达呈正相关，但非典型糖基化位点损害了AICL表面表达。糖基化对AICL表面表达的严格控制反映在AICL与Calnexin的显著相互作用以及Calnexin缺陷细胞中AICL的表达受损。总而言之，我们的数据表明，AICL的表达和表面处理受到几个独立的细胞翻译后机制的严格控制。
AICL glycoproteins are cognate activation-induced ligands of the C-type lectin-like receptor NKp80, which is expressed on virtually all mature human NK cells, and NKp80-AICL interaction stimulates NK cell effector functions such as cytotoxicity and cytokine secretion. Notably, AICL and NKp80 are encoded by adjacent genes in the NK gene complex and are coexpressed by human NK cells. Whereas AICL is intracellularly retained in resting NK cells, exposure of NK cells to proinflammatory cytokines results in AICL surfacing and susceptibility to NKp80-mediated NK fratricide. In this study, we characterize molecular determinants of AICL glycoproteins that cause intracellular retention, thereby controlling AICL surface expression. Cys(87) residing within the C-type lectin-like domain not only ensures stable homodimerization of AICL glycoproteins by disulfide bonding, but Cys(87) is also required for efficient cell surface expression of AICL homodimers and essential for AICL-NKp80 interaction. In contrast, cytoplasmic lysines act as negative regulators targeting AICL for proteasomal degradation. One atypical and three conventional N-linked glycosylation sites in the AICL C-type lectin-like domain critically impact maturation and surfacing of AICL, which is strictly dependent on glycosylation of at least one conventional glycosylation site. However, although the extent of conventional N-linked glycosylation positively correlates with AICL surface expression, the atypical glycosylation site impairs AICL surfacing. Stringent control of AICL surface expression by glycosylation is reflected by the pronounced interaction of AICL with calnexin and the impaired AICL expression in calnexin-deficient cells. Collectively, our data demonstrate that AICL expression and surfacing are tightly controlled by several independent cellular posttranslational mechanisms.