Verbrugge Annelies, Ruiter Td Talitha de, Clevers Hans, Meyaard Linde
Department of Immunology, University Medical Center Utrecht, Lundlaan 6, 3584 EA Utrecht, The Netherlands.
Int Immunol. 2003 Nov;15(11):1349-58. doi: 10.1093/intimm/dxg134.
Leukocyte-associated Ig-like receptor (LAIR)-1 is an inhibitory receptor expressed on most human leukocytes. It contains two immunoreceptor tyrosine-based inhibitory motifs (ITIM) in its cytoplasmic tail and recruits phosphatases upon phosphorylation. Here we show that both ITIM are required for full inhibition of cellular responses and optimal phosphatase recruitment. Mutation of the C-terminal ITIM still allows partial inhibition of the cytotoxic activity of the NK-like YT.2C2 cells, while mutation of the N-terminal ITIM completely abolishes this inhibitory activity. In contrast, in rat basophilic leukemia (RBL) cells, both mutants of LAIR-1 are partially effective. This is reflected in phosphorylation of these mutants in the different cell types upon pervanadate treatment. However, in both YT.2C2 cells and RBL cells, only the mutant containing the N-terminal ITIM recruits Src homology 2 domain-containing tyrosine phosphatase-2 (SHP-2), while the mutant containing the C-terminal ITIM does not. In RBL cells the mutant containing only the N-terminal ITIM also binds SHP-1, although to a lesser extent than wild-type LAIR-1. We find that in Jurkat T cells Lck is required for the association of SHP-1 with LAIR-1. Co-expression with Lck in 293T cells leads to phosphorylation of both wild-type LAIR-1 and the mutant containing only the N-terminal ITIM, while the mutant lacking this ITIM is not phosphorylated. These results indicate that Lck, or another Src family kinase, is essential for the consecutive phosphorylation of the N- and C-terminal ITIM. Our data imply that the N-terminal ITIM is dominant in LAIR-1 signaling, but that both ITIM contribute to an optimal inhibitory function.
白细胞相关免疫球蛋白样受体（LAIR）-1是一种在大多数人类白细胞上表达的抑制性受体。它在细胞质尾部含有两个基于免疫受体酪氨酸的抑制基序（ITIM），磷酸化后可募集磷酸酶。在此我们表明，两个ITIM对于细胞反应的完全抑制和最佳磷酸酶募集都是必需的。C末端ITIM的突变仍可部分抑制NK样YT.2C2细胞的细胞毒性活性，而N末端ITIM的突变则完全消除了这种抑制活性。相比之下，在大鼠嗜碱性粒细胞白血病（RBL）细胞中，LAIR-1的两种突变体都有部分效果。这在过钒酸盐处理后不同细胞类型中这些突变体的磷酸化情况中得到体现。然而，在YT.2C2细胞和RBL细胞中，只有含有N末端ITIM的突变体募集含Src同源2结构域的酪氨酸磷酸酶-2（SHP-2），而含有C末端ITIM的突变体则不募集。在RBL细胞中，仅含有N末端ITIM的突变体也结合SHP-1，尽管程度比野生型LAIR-1小。我们发现，在Jurkat T细胞中，Lck是SHP-1与LAIR-1结合所必需的。在293T细胞中与Lck共表达导致野生型LAIR-1和仅含有N末端ITIM的突变体都发生磷酸化，而缺乏该ITIM的突变体则不发生磷酸化。这些结果表明，Lck或另一种Src家族激酶对于N末端和C末端ITIM的连续磷酸化至关重要。我们的数据表明，N末端ITIM在LAIR-1信号传导中起主导作用，但两个ITIM都有助于实现最佳抑制功能。
