Function of Rac1 in T cell development and activation

Rac 1是Rho家族小G蛋白酶之一，在多种信号转导途径中起着“分子开关”的作用。为了直接评价Rac 1在T细胞发育中的作用，我们将显性负性（dn）Rac 1基因导入Pax 5缺陷的小鼠pro-B细胞，使其在体内重建T细胞发育。GFP阳性的dnRac 1表达胸腺细胞分化为CD 4-和CD 8-单阳性（SP）细胞严重受损，表明Rac 1是胸腺细胞的阳性选择的关键。表达dnRac 1的胸腺细胞表现出对TCR刺激的凋亡增加。为了研究Rac 1在DP胸腺细胞TCR信号转导中的详细功能，我们利用了在体外经TCR刺激后可分化为CD 4-SP细胞的DP细胞系DPK。DPK表达dn-Rac 1在TCR刺激后发生大量凋亡，导致CD 4-SP细胞分化缺陷。在dnRac 1-DPK中TCR依赖的肌动蛋白聚合和Bcl-2转录的上调被抑制。总的来说，这些数据表明，Rac 1是关键的积极选择胸腺细胞不仅通过重组肌动蛋白细胞骨架，而且还防止TCR诱导的凋亡，通过Bcl-2上调。

Rac1, one of the Rho family small GTPases has been shown to work as a "molecular switch" in various signal transduction pathways. In order to directly assess the function of Rac1 in T cell development, we introduced dominant negative (dn) Rac1 gene into Pax5-deficient mouse pro-B cells, which can reconstitute T cell development in vivo. Differentiation of GFP positive dnRac1 expressing thymocytes into CD4- and CD8-single positive (SP) cells was severely impaired, indicating that Rac1 is critical in positive selection of thymocytes. Thymocytes expressing dnRac1 demonstrated increased apoptosis against TCR stimulation. In order to study detailed function of Rac1 in TCR signal transduction of DP thymocytes, we utilized DP cell line DPK, which can differentiate into CD4-SP cells upon TCR stimulation in vitro. DPK expressing dn-Rac1 underwent massive apoptosis upon TCR stimulation and resulted in defective differentiation of CD4-SP cells. TCR dependent actin polymerization and upregulation of Bcl-2 transcription were suppressed in dnRac1-DPK. Collectively, these data indicate that Rac1 is critical in positive selection of thymocyte through not only reorganizing actin cytoskeleton, but also preventing TCR-induced apoptosis via Bcl-2 upregulation.