title: RAS signalling is abnormal in a c-raf1 MEK1 double mutant.
abstract: A mutant rat cell clone that suppresses the transformation defects of RAS effector loop substitutions is heterozygous for mutations in c-raf1 and MEK1. The mutant cells can be transformed by many otherwise defective RAS effector mutants, including RAS genes with the effector regions of distantly related GTPases, even though the encoded RAS proteins do not interact with either the mutant or wild-type RAF in Saccharomyces cerevisiae. While the significance of the c-raf1 mutation is unclear, the MEK1 mutation increases MEK1 activity and leads to activation of mitogen-activated protein kinase. The mutant MEK1 is coupled to the epidermal growth factor pathway but exhibits decreased physical interaction with RAF. When overexpressed, the MEK1 mutation is transforming and causes hyperphosphorylation of RAF. Signalling from RAS to MEK1 may be mediated by something other than RAF alone, but signalling through MEK1 is probably sufficient for RAS transformation.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Bottorff
authors.forename: S
authors.initials: S
authors.lastname: Stang
authors.forename: S
authors.initials: S
authors.lastname: Agellon
authors.forename: J C
authors.initials: JC
authors.lastname: Stone
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D002999:Clone Cells; D005786:Gene Expression Regulation; D006579:Heterozygote; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D008969:Molecular Sequence Data; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D013489:Suppression, Genetic; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D011518:Proto-Oncogene Proteins; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins