Receptors and Signal Transduction Section, Oral Infection and Immunity Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 2010 May 21;285(21):15761-8. doi: 10.1074/jbc.M110.109413. Epub 2010 Mar 24.
Several studies with mast cells from knock-out mice have suggested that the tyrosine kinase Fyn and its downstream substrate Gab2 may play a role in high affinity IgE receptor (FcepsilonRI)-mediated mast cell activation. To better understand the role of these two molecules and of Syk, we transiently transfected mast cells with small interference RNA (siRNA) targeted to Fyn, Gab2, or Syk to specifically decrease their expression. The siRNA suppression of Gab2 but not Fyn reduced activation of the phosphoinositide-3-kinase (PI3K) pathway as demonstrated by the change in phosphorylation of Akt; this indicates that Gab2 but not Fyn regulates this pathway. The decreased expression of Gab2 and Fyn had minor effects on degranulation. There were also some minor changes in activation of the NFAT or NFkappaB transcription factors in cells with reduced expression of Fyn or Gab2. Decreased Gab2 but not Fyn reduced the FcepsilonRI-induced activation of the Erk, Jnk, and p38 MAP kinases and the release of TNF-alpha. In contrast, decreased expression of Syk dramatically reduced FcepsilonRI-induced degranulation, activation of NFAT and NFkappaB. Therefore, the reduction in expression of these proteins in mast cells indicates that Syk is the major regulator of FcepsilonRI-mediated reactions, whereas Fyn has minor if any effects and Gab2 regulates primarily late events including MAP kinase activation and release of cytokines.
几项针对基因敲除小鼠肥大细胞的研究表明，酪氨酸激酶 Fyn 及其下游底物 Gab2 可能在高亲和力 IgE 受体（FcepsilonRI）介导的肥大细胞活化中发挥作用。为了更好地理解这两个分子和 Syk 的作用，我们用针对 Fyn、Gab2 或 Syk 的小干扰 RNA（siRNA）瞬时转染肥大细胞，以特异性降低它们的表达。Gab2 的 siRNA 抑制而非 Fyn 的抑制降低了磷酸肌醇 3-激酶（PI3K）途径的激活，如 Akt 磷酸化的变化所表明的；这表明 Gab2 而不是 Fyn 调节此途径。Gab2 和 Fyn 的表达降低对脱颗粒的影响较小。在表达 Fyn 或 Gab2 减少的细胞中，NFAT 或 NFkappaB 转录因子的激活也有一些较小的变化。Gab2 的表达降低而非 Fyn 的表达降低了 FcepsilonRI 诱导的 Erk、Jnk 和 p38 MAP 激酶的激活和 TNF-alpha 的释放。相比之下，Syk 的表达降低显著降低了 FcepsilonRI 诱导的脱颗粒、NFAT 和 NFkappaB 的激活。因此，肥大细胞中这些蛋白表达的降低表明，Syk 是 FcepsilonRI 介导的反应的主要调节剂，而 Fyn 的作用较小或没有作用，Gab2 主要调节包括 MAP 激酶激活和细胞因子释放在内的晚期事件。
