R-Ras Is Regulated by Activators and Effectors Distinct From Those That Control Ras Function

Oncogene. 1997 Jan 16;14(2):133-43. doi: 10.1038/sj.onc.1200815.


Like Ras, constitutively activated mutants of the Ras-related protein R-Ras cause tumorigenic transformation of NIH3T3 cells. However, since R-Ras causes a transformed phenotype distinct from that induced by Ras, it is likely that R-Ras controls signaling pathways and cellular processes distinct from those regulated by Ras. To address this possibility, we determined if R-Ras is regulated by activators and effectors distinct from those that regulate Ras function. We observed that Ras guanine nucleotide exchange factors failed to activate R-Ras in vivo, indicating that R-Ras is activated by distinct GEFs. Consistent with this, mutants of R-Ras with mutations analogous to the Ras(15A)/(17N) dominant negative proteins did not antagonize Ras GEF function and lacked the growth inhibitory activity seen with these mutant Ras proteins. Thus, R-Ras, but not Ras, is dispensable for the viability of NIH3T3 cells. Finally, whereas constitutively activated Ras can overcome the growth inhibitory action of the Ras(17N) dominant negative protein via Raf-dependent and -independent activities, transforming mutants of R-Ras failed to do so. This inability was consistent with our observation that Ras-, but not R-Ras-transformed, NIH3T3 cells possessed constitutively upregulated Raf kinase activities. Thus, R-Ras and Ras are regulators of distinct signaling pathways and cellular processes.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells / metabolism
  • 3T3 Cells / pathology
  • Animals
  • Cell Division / genetics
  • Cell Transformation, Neoplastic / genetics
  • Cell Transformation, Neoplastic / metabolism*
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism*
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / metabolism*
  • Guanosine Diphosphate / metabolism
  • Guanosine Triphosphate / metabolism
  • Mice
  • Mutation
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-raf
  • rap GTP-Binding Proteins
  • ras Proteins / genetics
  • ras Proteins / metabolism*


  • Proto-Oncogene Proteins
  • Guanosine Diphosphate
  • Guanosine Triphosphate
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-raf
  • GTP Phosphohydrolases
  • GTP-Binding Proteins
  • Rras protein, mouse
  • rap GTP-Binding Proteins
  • ras Proteins