Ting A T, Karnitz L M, Schoon R A, Abraham R T, Leibson P J
Department of Immunology, Mayo Clinic and Foundation, Rochester, Minnesota 55905.
J Exp Med. 1992 Dec 1;176(6):1751-5. doi: 10.1084/jem.176.6.1751.
Crosslinking of the low affinity immunoglobulin G (IgG) Fc receptor (Fc gamma R type III) on natural killer (NK) cells initiates antibody-dependent cellular cytotoxicity. During this process, Fc gamma R stimulation results in the rapid activation of phospholipase C (PLC), which hydrolyzes membrane phosphoinositides, generating inositol-1,4,5-trisphosphate and sn-1,2-diacylglycerol as second messengers. We have recently reported that PLC activation after Fc gamma R stimulation can be inhibited by a protein tyrosine kinase (PTK) inhibitor. Based on the paradigm provided by the receptor tyrosine kinases, we investigated whether PLC-gamma 1 and/or PLC-gamma 2 are expressed in NK cells, and whether the PLC-gamma isoforms are tyrosine phosphorylated in response to Fc gamma R stimulation. Immunoblotting analyses with PLC-gamma 1- and PLC-gamma 2-specific antisera demonstrate that both isoforms are expressed in human NK cells. Furthermore, Fc gamma R crosslinking triggers the tyrosine phosphorylation of both PLC-gamma 1 and PLC-gamma 2 in these cells. Phosphorylation of both isoforms is detectable within 1 min, and returns to basal level within 30 min. Pretreatment with herbimycin A, a PTK inhibitor, blocked the Fc gamma R-induced tyrosine phosphorylation of PLC-gamma 1 and PLC-gamma 2, and the subsequent release of inositol phosphates. These results suggest that Fc gamma R-initiated phosphoinositide turnover in human NK cells is regulated by the tyrosine phosphorylation of PLC-gamma. More broadly, these observations demonstrate that nonreceptor PTK(s) activated by crosslinkage of a multisubunit receptor can phosphorylate both PLC-gamma isoforms.
自然杀伤（NK）细胞上低亲和力免疫球蛋白G（IgG）Fc受体（FcγRⅢ型）的交联引发抗体依赖性细胞毒性。在此过程中，FcγR刺激导致磷脂酶C（PLC）迅速激活，后者水解膜磷酸肌醇，生成肌醇-1,4,5-三磷酸和sn-1,2-二酰基甘油作为第二信使。我们最近报道，FcγR刺激后的PLC激活可被蛋白酪氨酸激酶（PTK）抑制剂抑制。基于受体酪氨酸激酶提供的模式，我们研究了PLC-γ1和/或PLC-γ2是否在NK细胞中表达，以及PLC-γ同工型是否会因FcγR刺激而发生酪氨酸磷酸化。用PLC-γ1和PLC-γ2特异性抗血清进行的免疫印迹分析表明，这两种同工型均在人NK细胞中表达。此外，FcγR交联触发了这些细胞中PLC-γ1和PLC-γ2的酪氨酸磷酸化。两种同工型的磷酸化在1分钟内即可检测到，并在30分钟内恢复到基础水平。用PTK抑制剂赫伯霉素A预处理可阻断FcγR诱导的PLC-γ1和PLC-γ2的酪氨酸磷酸化以及随后肌醇磷酸的释放。这些结果表明，人NK细胞中FcγR启动的磷酸肌醇转换受PLC-γ酪氨酸磷酸化的调节。更广泛地说，这些观察结果表明，由多亚基受体交联激活的非受体PTK可使两种PLC-γ同工型磷酸化。
