title: Regulation of epidermal growth factor receptor signaling by phosphorylation of the ras exchange factor hSOS1.
abstract: In response to stimulation with epidermal growth factor (EGF), the guanine nucleotide exchange factor human SOS1 (hSOS1) promotes the activation of Ras by forming a complex with Grb2 and the human EGF receptor (hEGFR). hSOS1 was phosphorylated in cells stimulated with EGF or phorbol 12-myristate 13-acetate or following co-transfection with activated Ras or Raf. Co-transfection with dominant negative Ras resulted in a decrease of EGF-induced hSOS1 phosphorylation. The mitogen-activated protein kinase (MAPK) phosphorylated hSOS1 in vitro within the carboxyl-terminal proline-rich domain. The same region of hSOS1 was phosphorylated in vivo, in cells stimulated with EGF. Tryptic phosphopeptide mapping showed that MAPK phosphorylated hSOS1 in vitro on sites which were also phosphorylated in vivo. Phosphorylation by MAPK did not affect hSOS1 binding to Grb2 in vitro. However, reconstitution of the hSOS1-Grb2-hEGFR complex showed that phosphorylation by MAPK markedly reduced the ability of hSOS1 to associate with the hEGFR through Grb2. Similarly, phosphorylated hSOS1 was unable to form a complex with Shc through Grb2. Thus phosphorylation of hSOS1, by affecting its interaction with the hEGFR or Shc, down-regulates signal transduction from the hEGFR to the Ras pathway.
authors.affiliation: ONYX Pharmaceuticals, Richmond, California 94806, USA.
authors.forename: E
authors.initials: E
authors.lastname: Porfiri
authors.forename: F
authors.initials: F
authors.lastname: McCormick
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000096:biosynthesis / Q000502:physiology*; D051380:GRB2 Adaptor Protein; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000502:physiology*; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D007700:Kinetics; D051379:Mice; D016296:Mutagenesis; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000737:chemistry / Q000302:isolation & purification; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D010769:Phosphothreonine / Q000032:analysis; D014176:Protein Biosynthesis; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D016324:Sequence Tagged Sites; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D020663:ras Guanine Nucleotide Exchange Factors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D010748:Phosphopeptides; D011506:Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D010769:Phosphothreonine; D010768:Phosphoserine; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate