Green J M, Schreiber A D, Brown E J
Division of Infectious Diseases, Washington University, School of Medicine, St. Louis, Missouri 63110, USA.
J Cell Biol. 1997 Dec 1;139(5):1209-17. doi: 10.1083/jcb.139.5.1209.
While many cell types express receptors for the Fc domain of IgG (Fc gamma R), only primate polymorphonuclear neutrophils (PMN) express an Fc gamma R linked to the membrane via a glycan phosphoinositol (GPI) anchor. Previous studies have demonstrated that this GPI-linked Fc gamma R (Fc gamma RIIIB) cooperates with the transmembrane Fc gamma R (Fc gamma RIIA) to mediate many of the functional effects of immune complex binding. To determine the role of the GPI anchor in Fc gamma receptor synergy, we have developed a model system in Jurkat T cells, which lack endogenously expressed Fc gamma receptors. Jurkat T cells were stably transfected with cDNA encoding Fc gamma RIIA and/or Fc gamma RIIIB. Cocrosslinking the two receptors produced a synergistic rise in intracytoplasmic calcium ([Ca2+]i) to levels not reached by stimulation of either Fc gamma RIIA or Fc gamma RIIIB alone. Synergy was achieved by prolonged entry of extracellular Ca2+. Cocrosslinking Fc gamma RIIA with CD59 or CD48, two other GPI-linked proteins on Jurkat T cells also led to a synergistic [Ca2+]i rise, as did crosslinking CD59 with Fc gamma RIIA on PMN, suggesting that interactions between the extracellular domains of the two Fc gamma receptors are not required for synergy. Replacement of the GPI anchor of Fc gamma RIIIB with a transmembrane anchor abolished synergy. In addition, tyrosine to phenylalanine substitutions in the immunoreceptor tyrosine-based activation motif (ITAM) of the Fc gamma RIIA cytoplasmic tail abolished synergy. While the ITAM of Fc gamma RIIA was required for the increase in [Ca2+]i, tyrosine phosphorylation of crosslinked Fc gamma RIIA was diminished when cocrosslinked with Fc gamma RIIIB. These data demonstrate that Fc gamma RIIA association with GPI-linked proteins facilitates Fc gamma R signal transduction and suggest that this may be a physiologically significant role for the unusual GPI-anchored Fc gamma R of human PMN.
虽然许多细胞类型都表达IgG Fc结构域的受体（FcγR），但只有灵长类多形核中性粒细胞（PMN）表达通过糖基磷脂酰肌醇（GPI）锚定与膜相连的FcγR。先前的研究表明，这种GPI连接的FcγR（FcγRIIIB）与跨膜FcγR（FcγRIIA）协同作用，介导免疫复合物结合的许多功能效应。为了确定GPI锚在Fcγ受体协同作用中的作用，我们在缺乏内源性表达的Fcγ受体的Jurkat T细胞中建立了一个模型系统。用编码FcγRIIA和/或FcγRIIIB的cDNA稳定转染Jurkat T细胞。两种受体的共交联导致细胞质内钙（[Ca2+]i）协同升高，达到单独刺激FcγRIIA或FcγRIIIB所未达到的水平。协同作用是通过细胞外Ca2+的长时间内流实现的。FcγRIIA与Jurkat T细胞上另外两种GPI连接蛋白CD59或CD48的共交联也导致[Ca2+]i协同升高，PMN上CD59与FcγRIIA的交联也是如此，这表明两种Fcγ受体的细胞外结构域之间的相互作用对于协同作用不是必需的。用跨膜锚替换FcγRIIIB的GPI锚消除了协同作用。此外，FcγRIIA细胞质尾部基于免疫受体酪氨酸的激活基序（ITAM）中的酪氨酸到苯丙氨酸的取代消除了协同作用。虽然FcγRIIA的ITAM是[Ca2+]i增加所必需的，但与FcγRIIIB共交联时，交联的FcγRIIA的酪氨酸磷酸化减少。这些数据表明，FcγRIIA与GPI连接蛋白的结合促进了FcγR信号转导，并表明这可能是人类PMN中异常的GPI锚定FcγR的生理重要作用。
