title: M-Ras, a widely expressed 29-kD homologue of p21 Ras: expression of a constitutively active mutant results in factor-independent growth of an interleukin-3-dependent cell line.
abstract: M-Ras, a recently identified homologue of p21 Ras, is widely expressed, with levels of the 29-kD protein in spleen, thymus, and NIH 3T3 fibroblasts equaling or exceeding those of p21 Ras. A G22V mutant of M-Ras was constitutively active and its expression in an interleukin-3 (IL-3)-dependent mast cell/megakaryocyte cell line resulted in increased survival in the absence of IL-3, increased growth in IL-4, and, at high expression levels, in factor-independent growth. Expression of M-Ras G22V, however, had a negative effect on growth in the presence of IL-3, suggesting that M-Ras has both positive and negative effects on growth. Expression of M-Ras G22V in NIH-3T3 fibroblasts resulted in morphological transformation and growth to higher cell densities. M-Ras G22V induced activation of the c-fos promoter, and bound weakly to the Ras-binding domains of Raf-1 and RalGDS. Expression of a mutant of M-Ras G22V that was no longer membrane-bound partially inhibited (40%) activation of the c-fos promoter by N-Ras Q61K, suggesting that M-Ras shared some, but not all, of the effectors of N-Ras. An S27N mutant of M-Ras, like the analogous H-Ras S17N mutant, was a dominant inhibitor of activation of the c-fos promoter by constitutively active Src Y527F, suggesting that M-Ras and p21 Ras shared guanine nucleotide exchange factors and are likely to be activated in parallel. Moreover, M-Ras was recognized by the monoclonal anti-Ras antibody Y13-259, commonly used to study the function and activity of p21 Ras. Mammalian M-Ras and a Caenorhabditis elegans orthologue exhibit conserved structural features, and these are likely to mediate activation of distinctive signaling paths that function in parallel to those downstream of p21 Ras.
authors.affiliation: The Biomedical Research Centre, University of British Columbia, Vancouver, BC, Canada.
authors.forename: G R
authors.initials: GR
authors.lastname: Ehrhardt
authors.forename: K B
authors.initials: KB
authors.lastname: Leslie
authors.forename: F
authors.initials: F
authors.lastname: Lee
authors.forename: J S
authors.initials: JS
authors.lastname: Wieler
authors.forename: J W
authors.initials: JW
authors.lastname: Schrader
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D000906:Antibodies; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002461:Cell Line, Transformed; D017077:Culture Media, Conditioned; D000939:Epitopes / Q000032:analysis / Q000276:immunology; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology*; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D014407:Tumor Cells, Cultured; D018631:ras Proteins
chemical_list: D000906:Antibodies; D017077:Culture Media, Conditioned; D000939:Epitopes; D007377:Interleukin-3; D011994:Recombinant Proteins; C109418:Mras protein, mouse; C501009:HRAS protein, human; D020559:Monomeric GTP-Binding Proteins; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins