Murai H, Ikeda M, Kishida S, Ishida O, Okazaki-Kishida M, Matsuura Y, Kikuchi A
Department of Biochemistry, Hiroshima University School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima 734, Japan.
J Biol Chem. 1997 Apr 18;272(16):10483-90. doi: 10.1074/jbc.272.16.10483.
Ral GDP dissociation stimulator-like (RGL) has been identified to be a possible effector protein of Ras. RGL shares 50% amino acid identity with Ral GDP dissociation stimulator and contains the CDC25-like domain in the central region and the Ras-interacting domain in the C-terminal region. Since the modes of activation and action of RGL have not yet been clarified, in this paper we have analyzed the functions of RGL. In COS cells, RGL interacted with RasG12V/E37G (a Ras mutant in which Gly-12 and Glu-37 were changed to Val and Gly, respectively) which failed to bind to Raf, but not with RasG12V/T35S which bound to Raf. Raf did not inhibit the binding of RGL to RasG12V/E37G under the condition that Raf inhibited that of RGL to RasG12V. Expression of either RGL or Raf into NIH3T3 cells slightly activated c-fos promoter, while coexpression of both proteins greatly stimulated the c-fos promoter activity. RGL stimulated the GDP/GTP exchange of Ral and this action was enhanced by the post-translational modification of Ral. However, RGL was not active on Ras, Rac, CDC42, Rap, or Rho. Furthermore, this action of RGL to stimulate the GDP/GTP exchange of Ral was dependent on Ras in COS cells. These results suggest that RGL constitutes another Ras-signaling pathway which is distinct from the Raf pathway and indicate that the RGL pathway regulates the c-fos promoter activity and the GDP/GTP exchange of Ral.
类Ral GDP解离刺激因子（RGL）已被确定为Ras可能的效应蛋白。RGL与Ral GDP解离刺激因子有50%的氨基酸同一性，在中央区域含有类CDC25结构域，在C端区域含有Ras相互作用结构域。由于RGL的激活和作用模式尚未阐明，本文我们分析了RGL的功能。在COS细胞中，RGL与RasG12V/E37G（一种Ras突变体，其中Gly-12和Glu-37分别被替换为Val和Gly）相互作用，该突变体无法与Raf结合，但不与能与Raf结合的RasG12V/T35S相互作用。在Raf抑制RGL与RasG12V结合的条件下，Raf并不抑制RGL与RasG12V/E37G的结合。将RGL或Raf导入NIH3T3细胞中均可轻微激活c-fos启动子，而两种蛋白共表达则极大地刺激了c-fos启动子活性。RGL刺激Ral的GDP/GTP交换，并且这种作用通过Ral的翻译后修饰而增强。然而，RGL对Ras、Rac、CDC42、Rap或Rho无活性。此外，RGL刺激Ral的GDP/GTP交换的这种作用在COS细胞中依赖于Ras。这些结果表明，RGL构成了另一条与Raf途径不同的Ras信号通路，并表明RGL途径调节c-fos启动子活性和Ral的GDP/GTP交换。
