Activation of R-Ras by Ras-guanine nucleotide-releasing factor.
Ras-GRF/CDC25(Mm), mSos, and C3G have been identified as guanine nucleotide-releasing factors for Ras family proteins. We investigated in this study the guanine nucleotide-releasing activities of Ras-GRF, mSos, and C3G toward R-Ras, which shows high sequence similarity to Ras. Ras-GRF markedly stimulated the dissociation of GDP from R-Ras, and C3G also promoted the release of R-Ras-bound GDP. Under the same conditions, mSos little affected the reaction. When Ras-GRF and R-Ras were coexpressed in COS7 cells, the remarkable accumulation of the active GTP-bound form of R-Ras was observed. C3G also increased active R-Ras in COS7 cells, while mSos did not give any effect. These results indicated that Ras-GRF and C3G could activate R-Ras. Furthermore, the activation of R-Ras by Ras-GRF was enhanced when cells were treated with ionomycin, which is known to increase the intracellular calcium concentration. The examination of tissue distribution of R-Ras, Ras-GRF, and mSos by the reverse transcription-polymerase chain reaction revealed that Ras-GRF was expressed only in brain and testis, whereas R-Ras, C3G, and mSos were expressed rather ubiquitously. These findings raise the possibility that R-Ras is activated by Ras-GRF in brain and testis, and by C3G in other tissues, respectively.
Gotoh
T
T
Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187, Japan.
Niino
Y
Y
Tokuda
M
M
Hatase
O
O
Nakamura
S
S
Matsuda
M
M
Hattori
S
S
D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D004926:Escherichia coli; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D018411:Spodoptera; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins / Q000378:metabolism*; D020666:ras-GRF1
D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D020666:ras-GRF1; D006153:Guanosine Diphosphate; D020558:GTP Phosphohydrolases; D018631:ras Proteins; D002118:Calcium