M-Ras/R-Ras3, a transforming Ras protein regulated by Sos1, GRF1, and p120 Ras GTPase-activating protein, interacts with the putative Ras effector AF6

Lawrence A. Quilliam, Ariel F. Castro, Kelley S. Rogers-Graham, Carol B. Martin, Channing J. Der, Chen Bi

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M-Ras is a Ras-related protein that shares ~55% identity with K-Ras and TC21. The M-Ras message was widely expressed but was most predominant in ovary and brain. Similarly to Ha-Ras, expression of mutationally activated M- Ras in NIH 3T3 mouse fibroblasts or C2 myoblasts resulted in cellular transformation or inhibition of differentiation, respectively. M-Ras only weakly activated extracellular signal-regulated kinase 2 (ERK2), but it cooperated with Raf, Rac, and Rho to induce transforming foci in NIH 3T3 cells, suggesting that M-Ras signaled via alternate pathways to these effectors. Although the mitogen-activated protein kinase/ERK kinase inhibitor, PD98059, blocked M-Ras-induced transformation, M-Ras was more effective than an activated mitogen-activated protein kinase/ERK kinase mutant at inducing focus formation. These data indicate that multiple pathways must contribute to M-Ras-induced transformation. M-Ras interacted poorly in a yeast two-hybrid assay with multiple Ras effectors, including c- Raf-1, A-Raf, B-Raf, phosphoinositol-3 kinase δ, RalGDS, and Rin1. Although M-Ras coimmunoprecipitated with AF6, a putative regulator of cell junction formation, overexpression of AF6 did not contribute to fibroblast transformation, suggesting the possibility of novel effector proteins. The M- Ras GTP/GDP cycle was sensitive to the Ras GEFs, Sos1, and GRF1 and to p120 Ras GAP. Together, these findings suggest that while M-Ras is regulated by similar upstream stimuli to Ha-Ras, novel targets may be responsible for its effects on cellular transformation and differentiation.

Original languageEnglish (US)
Pages (from-to)23850-23857
Number of pages8
JournalJournal of Biological Chemistry
Issue number34
StatePublished - Aug 20 1999


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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