Xie Zhi-Hui, Ambudkar Indu, Siraganian Reuben P
Receptors and Signal Transduction Section, Oral Infection and Immunity Branch, Department of Health and Human Services, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.
J Immunol. 2002 May 1;168(9):4682-91. doi: 10.4049/jimmunol.168.9.4682.
The recently cloned scaffolding molecule Gab2 can assemble multiple molecules involved in signaling pathways. Bone marrow-derived mast cells isolated from Gab2(-/-) mice have defective signaling probably due to the lack of the activation of phosphatidylinositol-3 kinase (PI3-kinase). In this study, we investigated the role of Gab2 using the rat basophilic leukemia 2H3 cell line mast cells. Fc epsilon RI aggregation induced the tyrosine phosphorylation of Gab2 and translocation of a significant fraction of it from the cytosol to the plasma membrane. As in other cells, Gab2 was found to associate with several signaling molecules including Src homology 2-containing protein tyrosine phosphatase 2, Grb2, Lyn, and phospholipase C gamma (PLC gamma). The association of Gab2 with Lyn and PLC gamma were enhanced after receptor aggregation. Overexpression of Gab2 in rat basophilic leukemia 2H3 cell line cells inhibited the Fc epsilon RI-induced tyrosine phosphorylation of the subunits of the receptor, and the phosphorylation and/or activation of Syk and mitogen-activated protein kinase. Downstream events such as calcium mobilization, degranulation, and induction of TNF-alpha and IL-6 gene transcripts were decreased in Gab2 overexpressing cells, although Akt phosphorylation as a measure of PI3-kinase activation was unaffected. These results suggest that in addition to the positive effects mediated by PI3-kinase that are apparent in Gab2(-/-) mast cells, Gab2 by interacting with Lyn and PLC gamma may have negative regulatory effects on Fc epsilon RI-induced mast cell signaling and functions.
最近克隆出的支架分子Gab2能够组装多个参与信号通路的分子。从Gab2基因敲除小鼠中分离出的骨髓来源肥大细胞存在信号传导缺陷，这可能是由于磷脂酰肌醇-3激酶（PI3激酶）缺乏激活所致。在本研究中，我们利用大鼠嗜碱性白血病2H3细胞系肥大细胞研究了Gab2的作用。FcεRI聚集诱导Gab2的酪氨酸磷酸化，并使其很大一部分从胞质溶胶转位至质膜。与其他细胞一样，发现Gab2与几种信号分子相关联，包括含Src同源2结构域的蛋白酪氨酸磷酸酶2、Grb2、Lyn和磷脂酶Cγ（PLCγ）。受体聚集后，Gab2与Lyn和PLCγ的关联增强。在大鼠嗜碱性白血病2H3细胞系细胞中过表达Gab2可抑制FcεRI诱导的受体亚基酪氨酸磷酸化，以及Syk和丝裂原活化蛋白激酶的磷酸化和/或激活。在过表达Gab2的细胞中，诸如钙动员、脱颗粒以及TNF-α和IL-6基因转录物诱导等下游事件减少，尽管作为PI3激酶激活指标的Akt磷酸化未受影响。这些结果表明，除了在Gab2基因敲除肥大细胞中明显的由PI3激酶介导的积极作用外，Gab2通过与Lyn和PLCγ相互作用，可能对FcεRI诱导的肥大细胞信号传导和功能具有负调节作用。
