title: R-Ras is regulated by activators and effectors distinct from those that control Ras function.
abstract: 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.
authors.affiliation: University of North Carolina at Chapel Hill, Department of Microbiology and Immunology, 27599, USA.
authors.forename: S Y
authors.initials: SY
authors.lastname: Huff
authors.forename: L A
authors.initials: LA
authors.lastname: Quilliam
authors.forename: A D
authors.initials: AD
authors.lastname: Cox
authors.forename: C J
authors.initials: CJ
authors.lastname: Der
mesh_terms: D016475:3T3 Cells / Q000378:metabolism / Q000473:pathology; D000818:Animals; D002455:Cell Division / Q000235:genetics; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D051379:Mice; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D020668:rap GTP-Binding Proteins; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D011518:Proto-Oncogene Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; C513254:Rras protein, mouse; D020668:rap GTP-Binding Proteins; D018631:ras Proteins