R-Ras is a small GTPase of the Ras family that regulates cell survival and integrin activity. Despite a number of in vitro studies, the in vivo function of R-Ras remains unclear. Here, we used R-Ras–null mice to explore the in vivo function of this small GTPase. Our results show a role for R-Ras as a regulator of vascular differentiation that primarily affects the remodeling of blood vessels. We show that R-Ras–null mice, although otherwise phenotypically normal, mount excessive vascular responses. We found that in vivo R-Ras expression is largely confined to fully differentiated smooth muscle cells, including those of blood vessels, and to endothelial cells. Challenging the R-Ras–null mice with arterial injury or tumor implantation showed exaggerated neointimal thickening in response to the injury and increased angiogenesis in the tumors. In wild-type mice, R-Ras expression was greatly reduced in hyperplastic neointimal smooth muscle cells and in angiogenic endothelial cells. Forced expression of activated R-Ras suppressed mitogenic and invasive activities of growth factor–stimulated vascular cells. These results establish an unexpected role for R-Ras in blood vessel homeostasis and suggest that R-Ras signaling may offer a target for therapeutic intervention in vascular diseases.
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We thank E. Engvall, D. Hanahan and Y. Yamaguchi for discussions and comments on the manuscript, S. Krajewski for help with immunohistology, M. Sata for providing a tutorial video on arterial wire injury, and R. Varghese for editing. This work was supported by US National Cancer Institute grants PO1 CA82713, RO1 CA79984 and RO1 CA098162 (to E.R.); T32 CA09579 (to M.K.); and P30 CA 30199 (Cancer Center Support Grant).
The authors declare no competing financial interests.
Disruption of Rras mRNA and the absence of protein expression in R-Ras–null mice. (PDF 244 kb)
Immunohistological detection of R-Ras expression in various mouse tissues. (PDF 409 kb)
Spatiotemporal pattern of R-Ras expression during mouse development. (PDF 321 kb)
Immunohistological characterization of neointimal lesions. (PDF 248 kb)
R-Ras expression is downregulated significantly in cultured vascular cells. (PDF 208 kb)
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Komatsu, M., Ruoslahti, E. R-Ras is a global regulator of vascular regeneration that suppresses intimal hyperplasia and tumor angiogenesis. Nat Med 11, 1346–1350 (2005) doi:10.1038/nm1324
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