title: Activation of brain B-Raf protein kinase by Rap1B small GTP-binding protein.
abstract: Rap1 small GTP-binding protein has the same amino acid sequence at its effector domain as that of Ras. Rap1 has been shown to antagonize the Ras functions, such as the Ras-induced transformation of NIH 3T3 cells and the Ras-induced activation of the c-Raf-1 protein kinase-dependent mitogen-activated protein (MAP) kinase cascade in Rat-1 cells, whereas we have shown that Rap1 as well as Ras stimulates DNA synthesis in Swiss 3T3 cells. We have established a cell-free assay system in which Ras activates bovine brain B-Raf protein kinase. Here we have used this assay system and examined the effect of Rap1 on the B-Raf activity to phosphorylate recombinant MAP kinase kinase (MEK). Recombinant Rap1B stimulated the activity of B-Raf, which was partially purified from bovine brain and immunoprecipitated by an anti-B-Raf antibody. The GTP-bound form was active, but the GDP-bound form was inactive. The fully post-translationally lipid-modified form was active, but the unmodified form was nearly inactive. The maximum B-Raf activity stimulated by Rap1B was nearly the same as that stimulated by Ki-Ras. Rap1B enhanced the Ki-Ras-stimulated B-Raf activity in an additive manner. These results indicate that not only Ras but also Rap1 is involved in the activation of the B-Raf-dependent MAP kinase cascade.
authors.affiliation: Department of Molecular Biology and Biochemistry, Osaka University Medical School, Suita, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ohtsuka
authors.forename: K
authors.initials: K
authors.lastname: Shimizu
authors.forename: B
authors.initials: B
authors.lastname: Yamamori
authors.forename: S
authors.initials: S
authors.lastname: Kuroda
authors.forename: Y
authors.initials: Y
authors.lastname: Takai
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001921:Brain / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002417:Cattle; D002461:Cell Line, Transformed; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000302:isolation & purification / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020668:rap GTP-Binding Proteins
chemical_list: D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D006160:Guanosine Triphosphate; D005982:Glutathione Transferase; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins