Activation of Raf as a Result of Recruitment to the Plasma Membrane

• Published in: Science (American Association for the Advancement of Science) Vol. 264; no. 5164; pp. 1463 - 1467
• Main Authors: Stokoe, David, Macdonald, Susan G., Cadwallader, Karen, Symons, Marc, Hancock, John F.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for the Advancement of Science 03-06-1994; American Association for the Advancement of Science
• Subjects: Amino Acid Sequence; Amino acids; Animals; Biological and medical sciences; Cell Line; Cell lines; Cell Membrane - enzymology; Cell membranes; Cell physiology; Cellular signal transduction; COS cells; Cytosol; Cytosol - enzymology; Enzyme Activation; Fundamental and applied biological sciences. Psychology; GTP-Binding Proteins - metabolism; Immunoblotting; MAP Kinase Kinase 1; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase Kinases; Models, Biological; Molecular and cellular biology; Molecular Sequence Data; P branes; Plasma membranes; Plasmids; Protein kinases; Protein-Serine-Threonine Kinases - chemistry; Protein-Serine-Threonine Kinases - metabolism; Protein-Tyrosine Kinases - metabolism; Proto-Oncogene Proteins - chemistry; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-raf; Recombinant Fusion Proteins - metabolism; Signal transduction; String theory; Binding protein; Signal transduction; GTP; Enzyme; Protein kinase; Transferases; C-Onc gene; Models; Microtubule associated protein; Membrane translocation; Biological activity; G protein
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.7811320

The small guanine nucleotide binding protein Ras participates in a growth promoting signal transduction pathway. The mechanism by which interaction of Ras with the protein kinase Raf leads to activation of Raf was studied. Raf was targeted to the plasma membrane by addition of the COOH-terminal localization signals of K-ras. This modified form of Raf (RafCAAX) was activated to the same extent as Raf coexpressed with oncogenic mutant Ras. Plasma membrane localization rather than farnesylation or the presence of the additional COOH-terminal sequence accounted for the activation of RafCAAX. The activation of RafCAAX was completely independent of Ras; it was neither potentiated by oncogenic mutant Ras nor abrogated by dominant negative Ras. Raf, once recruited to the plasma membrane, was not anchored there by Ras; most activated Raf in cells was associated with plasma membrane cytoskeletal elements, not the lipid bilayer. Thus, Ras functions in the activation of Raf by recruiting Raf to the plasma membrane where a separate, Ras-independent, activation of Raf occurs.