Activation of R-Ras by Ras-Guanine Nucleotide-releasing Factor

doi:10.1074/jbc.272.30.18602

Activation of R-Ras by Ras-Guanine Nucleotide-releasing Factor*

From the ^‡Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187, Japan, the ^§Department of Physiology, First Division, Faculty of Medicine, Kagawa Medical University, Miki, Kagawa, 761-07, Japan, and the ^¶Department of Pathology, Research Institute, International Medical Center of Japan, 1-21-1 Toyama, Shinjuku-ku, Tokyo 162, Japan

Abstract

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.

Footnotes

↵* This work was supported in part by Grants-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science and Culture of Japan.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‖ To whom correspondence should be addressed: Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187, Japan. Tel.: 81-423-46-1722; Fax: 81-423-46-1752; E-mail: hattori{at}ncnaxp.ncnp.go.jp.
↵1 The abbreviations used are: GRF, guanine nucleotide-releasing factor; GAP, GTPase-activating protein; GST, glutathione-S-transferase; PCR, polymerase chain reaction.
↵2 S. Li, S. Nakamura, and S. Hattori, unpublished results.
- Received January 23, 1997.
- Revision received May 8, 1997.