Regulation of development of type I allergy by the signal transducer specific for the high-affinity IgE receptor

MIST是SLP-76/BASH信号蛋白家族的第三个成员，作用于免疫受体的下游。这些接头蛋白在造血细胞中有不同的表达，非常独特的是，MIST只在肥大细胞系和细胞因子依赖型细胞系中表达。我们在这个项目中已经证明了MIST是在肥大细胞中高亲和力的IgE受体交联物上被酪氨酸磷酸化的，这主要是由Lyn激酶介导的。酪氨酸磷酸化的MIST可与PLCy、Vav和Grb2等其他信号蛋白相互作用。在RBL-2H3肥大细胞系中表达酪氨酸磷酸化缺陷的MIST突变体后，IgE受体介导的脱颗粒反应显著降低，提示MIST是IgE受体脱颗粒的重要支架蛋白。为了了解MIST在体内的功能，我们使用ES细胞系通过基因打靶产生了MIST缺陷小鼠。MIST纯合子小鼠在IL-3诱导的骨髓肥大细胞和IL-2诱导的脾NK细胞中不表达MIST蛋白。与野生型肥大细胞相比，雾缺陷肥大细胞的IgE受体介导的脱颗粒反应和细胞因子的产生显著减少。此外，体内IgE介导的被动和全身过敏反应在MIST缺陷小鼠中也有所减弱，表明MIST确实参与了IgE受体介导的体内肥大细胞功能。基于这些发现，我们相信雾剂将是抗过敏药物的极佳靶点。

MIST is the third member of SLP-76/BASH family signaling proteins, acting downstream of the immunoreceptors. These adaptor proteins are differentially expressed among hematopoietic cells, and very uniquely MIST is only expressed in mast cell lines and cytokine-dependent cell lines. We have demonstrated in this project that MIST is tyrosine phosphorylated upon high-affinity IgE receptor cross linking in mast cells, which is mainly mediated by Lyn kinase. Tyrosine-phosphorylated MIST can inter act with other signaling proteins including PLCy, Vav and Grb 2.The significant reduction of IgE recep-tor-mediated degranulation response was observed when the tyrosine phosphorylation-deficient MIST mutant was expressed in RBL-2H3 rat mast cell line, suggesting that MIST functions as an important scaffold protein for IgE receptor-degranulation. To understand MIST functions in vivo, we generated MIST-deficient mice by gene targeting using ES cell lines. MIST homozygous mice expressed no MIST protein in IL-3-induced bone marrow-derived mast cells and IL-2-induced spleen NK cells. IgE recep tor-mediated degranulation responses as well as cytokine production were profoundly reduced in MIST deficient mast cells, as compared with those in wild-type mast cells. Furthermore, IgE-mediated passive and systemic anaphylaxis in vivo were also attenuated in MIST-deficient mice, indicating that MIST is indeed involved in IgE receptor-mediated mast cell functions in vivo. Based on these findings, we be lieve that MIST would be an excellent target for anti-allergic drugs.