Identification of the mitogen-activated protein kinase phosphorylation sites on human Sos1 that regulate interaction with Grb2

Mol Cell Biol. 1996 Oct;16(10):5674-82. doi: 10.1128/MCB.16.10.5674.


The Son of sevenless proteins (Sos) are guanine nucleotide exchange factors involved in the activation of Ras by cytoplasmic and receptor tyrosine kinases. Growth factor stimulation rapidly induces the phosphorylation of Sos on multiple serine and threonine sites. Previous studies have demonstrated that growth factor-induced Sos phosphorylation occurs at the C-terminal region of the protein and is mediated, in part, by mitogen-activated protein (MAP) kinase. In this report, we describe the identification of five MAP kinase sites (S-1137, S-1167, S-1178, S-1193, and S-1197) on hSos1. We demonstrate that four of these sites, S-1132, S-1167, S-1178, and S-1193, become phosphorylated following growth factor stimulation. The MAP kinase phosphorylation sites are clustered within a region encompassing three proline-rich SH3-binding sites in the C-terminal domain of hSos1. Replacing the MAP kinase phosphorylation sites with alanine residues results in an increase in the binding affinity of Grb2 to hSos1. Interestingly, hSos2 contains only one MAP kinase phosphorylation site and, as demonstrated previously, has an increased affinity toward Grb2 compared with hSos1. These results suggest a role for MAP kinase in the regulation of Grb2-Sos interactions. Since the binding of Grb2 is important for Sos function, the phosphorylation-dependent modulation of Grb2-Sos association may provide a means of controlling Ras activation.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • COS Cells
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism*
  • DNA Primers
  • ErbB Receptors / metabolism
  • GRB2 Adaptor Protein
  • Guanine Nucleotide Exchange Factors
  • Humans
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Peptide Fragments / chemistry
  • Peptide Fragments / isolation & purification
  • Phosphopeptides / chemistry
  • Phosphopeptides / isolation & purification
  • Phosphorylation
  • Point Mutation
  • Proteins / chemistry*
  • Proteins / metabolism*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Sequence Tagged Sites
  • Serine
  • Threonine
  • Transfection
  • ras Guanine Nucleotide Exchange Factors


  • Adaptor Proteins, Signal Transducing
  • DNA Primers
  • GRB2 Adaptor Protein
  • GRB2 protein, human
  • Guanine Nucleotide Exchange Factors
  • Peptide Fragments
  • Phosphopeptides
  • Proteins
  • Recombinant Proteins
  • ras Guanine Nucleotide Exchange Factors
  • Threonine
  • Serine
  • ErbB Receptors
  • Calcium-Calmodulin-Dependent Protein Kinases