Besides an ITIM/SHP-1-dependent pathway, CD22 collaborates with Grb2 and plasma membrane calcium-ATPase in an ITIM/SHP-1-independent pathway of attenuation of Ca2+i signal in B cells.
Besides an ITIM/SHP-1-dependent pathway, CD22 collaborates with Grb2 and plasma membrane calcium-ATPase in an ITIM/SHP-1-independent pathway of attenuation of Ca2+i signal in B cells.
复制标题
除了 ITIM/SHP-1 依赖性途径外，CD22 还与 Grb2 和质膜钙 ATP 酶合作，以 ITIM/SHP-1 依赖性途径减弱 B 细胞中的 Ca-i(2 ) 信号
DOI：
10.18632/oncotarget.9794
复制
发表时间：
2016-08-30
期刊：
影响因子：
--
通讯作者：
Wang YP
中科院分区：
文献类型：
--
作者：
Chen J;Wang H;Xu WP;Wei SS;Li HJ;Mei YQ;Li YG;Wang YP
CD22是一种表面免疫球蛋白，参与B细胞受体(BCR)信号的负调控，尤其是抑制细胞内钙信号。其胞质尾部含有6个酪氨酸残基(Y773/Y783/Y817/Y828/Y843/Y863，分别命名为Y1~Y6)，其中3个(Y2/5/6)位于免疫受体酪氨酸抑制基序(ITIMs)中，这些基序在BCR激活诱导的磷酸化后募集蛋白酪氨酸磷酸酶SHP-1。CD22抑制Ca~(2+)i的机制一直知之甚少。先前的研究表明，CD22与质膜钙-ATPase(PMCA)结合并增强其活性(Chen，J.等人)。NAT免疫2004年；5：651-7)。这种关联依赖于BCR激活诱导的胞浆酪氨酸磷酸化，因为CD22无论是所有六种酪氨酸突变为苯丙氨酸还是胞浆尾巴被截断都失去了与PMCA关联的能力。然而，哪个个体或一组酪氨酸残基决定了这种联系以及CD22和PMCA是如何相互作用的，仍然不清楚。在本研究中，利用一系列CD22酪氨酸突变体，我们发现ITIM Y2/5/6对钙离子的抑制作用为34.3~37.1%，但与CD22/PMCA的结合无关。Non-ITIM Y4及其YEND基序贡献了剩余的69.4~71.7%的钙离子抑制，是PMCA相关Grb2的结合部位。在鸡和人B细胞中，Grb2独立于BCR交联，与PMCA构成相关并直接结合。CRISPR/Cas9对Grb2的敲除完全破坏了CD22/PMCA的结合。因此，我们的结果首次证明，除了先前发现的依赖于ITIM/SHP-1的途径外，CD22还具有一条主要的钙信号负调控途径，该途径不依赖于ITIM/SHP-1，而依赖于Y4/Grb2/PMCA。
CD22 is a surface immunoglobulin implicated in negative regulation of B cell receptor (BCR) signaling; particularly inhibiting intracellular Ca2+ (Ca2+i)signals. Its cytoplasmic tail contains six tyrosine residues (Y773/Y783/Y817/Y828/Y843/Y863, designated Y1~Y6 respectively), including three (Y2/5/6) lying within immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that serve to recruit the protein tyrosine phosphatase SHP-1 after BCR activation-induced phosphorylation. The mechanism of inhibiting Ca2+i by CD22 has been poorly understood. Previous study demonstrated that CD22 associated with plasma membrane calcium-ATPase (PMCA) and enhanced its activity (Chen, J. et al. Nat Immunol 2004;5:651-7). The association is dependent on BCR activation-induced cytoplasmic tyrosine phosphorylation, because CD22 with either all six tyrosines mutated to phenylalanines or cytoplasmic tail truncated loses its ability to associate with PMCA. However, which individual or a group of tyrosine residues determine the association and how CD22 and PMCA interacts, are still unclear. In this study, by using a series of CD22 tyrosine mutants, we found that ITIM Y2/5/6 accounts for 34.3~37.1% Ca2+i inhibition but is irrelevant for CD22/PMCA association. Non-ITIM Y4 and its YEND motif contribute to the remaining 69.4~71.7% Ca2+i inhibition and is the binding site for PMCA-associated Grb2. Grb2, independently of BCR cross-linking, is constitutively associated with and directly binds to PMCA in both chicken and human B cells. Knockout of Grb2 by CRISPR/Cas9 completely disrupted the CD22/PMCA association. Thus, our results demonstrate for the first time that in addition to previously-identified ITIM/SHP-1-dependent pathway, CD22 holds a major pathway of negative regulation of Ca2+i signal, which is ITIM/SHP-1-independent, but Y4/Grb2/PMCA-dependent.