title: The post-translational modification of ras p21 is important for Raf-1 activation.
abstract: Raf-1, a serine/threonine kinase, is required for the mitogenic action of ras p21. It has been recently demonstrated that ras p21 directly associates with Raf-1. The C-terminal region of ras p21 is modified by farnesylation and carboxyl methylation. This modification is necessary for ras p21 function. To elucidate the role of post-translational modification of ras p21 in Raf-1 activation, we examined ras p21-dependent Raf-1 activity in baculovirus/Sf9 cells overexpressing Raf-1 and ras p21. Coexpression of Raf-1 with v-ras p21 in Sf9 cells stimulated the autophosphorylating activity of Raf-1. The activity of Raf-1, as assessed by its ability to activate extracellular signal-regulated kinase kinase (MEK) in vitro, was also increased when Raf-1 was coexpressed with v-ras p21. However, neither the autophosphorylating activity of Raf-1 nor its ability to activate MEK was stimulated by v-ras p21 mutants which are not post-translationally modified. Raf-1 formed a complex with v-ras p21 and the v-ras p21 mutants in Sf9 cells. These results indicate that the post-translational modification of ras p21 is necessary for Raf-1 activation but that the association of Raf-1 with ras p21 is not sufficient to activate Raf-1.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco 94143-0130.
authors.forename: A
authors.initials: A
authors.lastname: Kikuchi
authors.forename: L T
authors.initials: LT
authors.lastname: Williams
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D002460:Cell Line; D003001:Cloning, Molecular; D004789:Enzyme Activation; D005982:Glutathione Transferase / Q000378:metabolism; D009036:Moths; D015689:Oncogene Protein p21(ras) / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D015689:Oncogene Protein p21(ras)