COMPARISON OF FUNCTION OF RAS FAMILY MOLECULES

RAS家族是低分子量GTP结合蛋白的一个亚家族，由RAS、R-RAS、RAL和Rap组成。为了比较两种高度同源的蛋白RAS和R-RAS的生物学作用，我们使用了依赖IL-3的造血细胞BaF3细胞和C2C12成肌细胞。R-RAS和RAS均能抑制停用IL-3后BaF3细胞的凋亡。这两个分子的不同之处在于，仅激活RAS就足以抑制细胞凋亡，而R-RAS需要IGF-1。进一步的研究。揭示了观察到的差异是由于R-RAS中缺乏ERK激活活性所致。在C2C12细胞中，RAS和R-RAS的激活导致不同的表型。R-RAS促进C2C12细胞分化，而RAS则抑制其分化。另一方面，RAS参与了成纤维细胞生长因子、肝细胞生长因子和IGF-1对C2C12细胞的趋化作用，而R-RAS不是由这三种生长因子诱导的，因此不可能参与趋化作用。因此，本研究表明RAS和R-RAS在造血细胞存活中的作用相似，但在肌肉发生中的作用不同。由于Ralgef是RAS效应因子，已有迹象表明存在RAS&gt；Ralgef&ral途径。为了探讨ral在RAS诱导的细胞转化中的作用，以人纤维肉瘤HT1080细胞为模型，研究了ral突变体的表达对RAS依赖的锚定非依赖性生长的影响。结果提示，RAR参与了RAS诱导的HT1080细胞的贴壁非依赖性生长，RAL可能通过调节细胞周期抑制因子p27Kip1的量来调控HT1080细胞的贴壁非依赖性生长。

Ras family is a subfamily of low molecular weight GTP-binding protein and consists of Ras, R-Ras, Ral and Rap. To compare the biological roles of two highly homologous proteins, Ras and R-Ras, IL-3-dependent hematopoietic BaF3 cells and C2C12 myoblasts were utilized. R-Ras, as well as Ras, was found to suppress apoptosis of BaF3 cells upon IL-3 withdrawal. The difference between the two molecules was that activation of Ras alone was enough to inhibit apoptosis, while R-Ras required IGF-1. Further studies. revealed that the observed difference was due to the lack of ERK-activating activity in R-Ras. In the case of C2C12 cells, activation of Ras and R-Ras resulted in different phenotypes. R-Ras promoted differentiation of C2C12 cells, whereas Ras inhibited it. On the other hand, Ras was found to be involved in chemotaxis of C2C12 cells by FGF, HGF and IGF-1, while involvement of R-Ras in the chemotaxis was unlikely since activation of R-Ras was not induced by the three growth factors. Thus, the present study show that Ras and R-Ras play a similar role in survival of hematopoietic cells, but distinct roles in myogenesis.The relation between Ras and Ral was also examined. Since RalGEF is a Ras effector, existence of the Ras > RalGEF > Ral pathway has been indicated. To examine a role of Ral in Ras-induced cellular transformation, effect of expression of Ral mutants on Ras-dependent anchorage-independent growth was investigated using human fibrosarcoma HT1080 cells. As a result, it was suggested that Ral is involved in Ras-induced anchorage-independent growth of HT1080 cells and that Ral may modulate the anchorage-independent growth through regulation of the amount of a cell cycle inhibitor, p27Kip1.