Function of Rac1 in T cell development and activation

Rho家族中的一种小分子GTP酶rac1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rac1在T细胞发育中的作用，我们将显性负性(DN)rac1基因导入到Pax5基因缺陷的小鼠Pro-B细胞中，可以在体内重建T细胞的发育。GFP阳性的dnrac1表达的胸腺细胞向CD4和CD8单一阳性(SP)细胞的分化受到严重损害，表明rac1在胸腺细胞的阳性选择中起关键作用。在TCR刺激下，表达dnrac1的胸腺细胞的凋亡率增加。为了研究Rac1在胸腺细胞TCR信号转导中的详细功能，我们选用了DPK细胞系，DPK细胞在TCR刺激下可在体外分化为CD4-SP细胞。表达dN-rac1的DPK在TCR刺激下发生大量凋亡，导致CD4-SP细胞分化障碍。Dnrac1-DPK抑制TCR依赖的肌动蛋白聚合和Bcl2转录上调。综上所述，这些数据表明，rac1不仅通过重组肌动蛋白细胞骨架在胸腺细胞的正向选择中起关键作用，而且还通过上调Bcl-2来阻止TCR诱导的细胞凋亡。

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.