Gotoh T, Hattori S, Nakamura S, Kitayama H, Noda M, Takai Y, Kaibuchi K, Matsui H, Hatase O, Takahashi H
Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan.
Mol Cell Biol. 1995 Dec;15(12):6746-53. doi: 10.1128/MCB.15.12.6746.
C3G, which was identified as a Crk SH3 domain-binding guanine nucleotide-releasing factor, shows sequence similarity to CDC25 and Sos family proteins (S. Tanaka, T. Morishita, Y. Hashimoto, S. Hattori, S. Nakamura, M. Shibuya, K. Matuoka, T. Takenawa, T. Kurata, K. Nagashima, and M. Matsuda, Proc. Natl. Acad. Sci. USA 91:3443-3447, 1994). The substrate specificity of C3G was examined by in vitro and in vivo experiments. C3G markedly stimulated dissociation of bound GDP from Rap1B but marginally affected the same reaction of other Ras family proteins (Ha-Ras, N-Ras, and RalA). C3G also stimulated binding of GTP-gamma S [guanosine 5'-3-O-(thio)triphosphate] to Rap1B. When C3G and Rap1A were expressed in COS7 cells, marked accumulation of the active GTP-bound form of Rap1A was observed, while Sos was not effective in the activation of Rap1A. These results clearly show that C3G is an activator for Rap1. Furthermore, expression of C3G with a membrane localization signal in a v-Ki-ras transformant, DT, induced a reversion of the cells to the flat form, possibly through the activation of endogenous Rap1.
C3G被鉴定为一种Crk SH3结构域结合鸟嘌呤核苷酸释放因子，与CDC25和Sos家族蛋白具有序列相似性（S. Tanaka、T. Morishita、Y. Hashimoto、S. Hattori、S. Nakamura、M. Shibuya、K. Matuoka、T. Takenawa、T. Kurata、K. Nagashima和M. Matsuda，《美国国家科学院院刊》91:3443 - 3447，1994年）。通过体外和体内实验研究了C3G的底物特异性。C3G显著刺激Rap1B结合的GDP解离，但对其他Ras家族蛋白（Ha - Ras、N - Ras和RalA）的相同反应影响较小。C3G还刺激GTP - γS[鸟苷5'-3 - O -（硫代）三磷酸]与Rap1B结合。当C3G和Rap1A在COS7细胞中表达时，观察到活性GTP结合形式的Rap1A显著积累，而Sos对Rap1A的激活无效。这些结果清楚地表明C3G是Rap1的激活剂。此外，在v - Ki - ras转化细胞DT中表达带有膜定位信号的C3G，可能通过激活内源性Rap1诱导细胞恢复为扁平形态。
