T cell antigen CD28 binds to the GRB-2/SOS complex, regulators of p21ras

Eur J Immunol. 1995 Apr;25(4):1044-50. doi: 10.1002/eji.1830250428.

Abstract

The T cell molecule CD28 provides a co-stimulatory signal that is required for T cell proliferation, and has been implicated in the control of T cell anergy. An important clue to the signaling mechanism of CD28 is the finding that CD28 can bind to phosphatidylinositol 3-kinase (PI 3-kinase) by means of a cytoplasmic phospho-YMNM (pYMNM) motif. A remaining issue concerns whether CD28 can recruit other intracellular signaling molecules. In this study, we show that CD28 uses the same pYMNM motif to recruit a second intracellular protein, GRB-2. CD28-associated GRB-2, as detected by anti-GRB-2 immunoblotting, was found in human peripheral T cells, HPB-ALL and Jurkat cells. As in the case of PI3-kinase, antibody-induced cross-linking of CD28 induces a time-dependent recruitment of GRB-2. Likewise, mutation of the pY-191 residue within the pYMNM motif reduces GRB-2 binding. Peptide binding studies show that the SH2 domain of GRB-2 binds to the pYMNM motif with an affinity comparable to GRB-2/SHC, but some 10- to 100-fold lower than the CD28/PI 3-kinase. Despite this, CD28/GRB-2 and CD28/PI 3-kinase complexes are found to co-exist in peripheral T cells. Finally, immunoblotting shows that CD28 also associates with the gene product of the human homolog of the Drosophila Son of sevenless gene (SOS), a GRB-2-complexed guanine nucleotide exchange factor responsible for converting p21ras to a GTP-bound active state. CD28-associated GRB2/SOS is likely to serve an important link in the regulation of p21ras and lymphokine expression mediated by CD28.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Amino Acid Sequence
  • Binding Sites / genetics
  • CD28 Antigens / genetics
  • CD28 Antigens / metabolism*
  • GRB2 Adaptor Protein
  • Humans
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Proteins / metabolism*
  • Proto-Oncogene Proteins p21(ras) / metabolism
  • Second Messenger Systems*
  • Sequence Analysis
  • Signal Transduction
  • Son of Sevenless Proteins
  • T-Lymphocytes / immunology
  • T-Lymphocytes / metabolism*
  • Tumor Cells, Cultured

Substances

  • Adaptor Proteins, Signal Transducing
  • CD28 Antigens
  • GRB2 Adaptor Protein
  • GRB2 protein, human
  • Membrane Proteins
  • Proteins
  • Son of Sevenless Proteins
  • HRAS protein, human
  • Proto-Oncogene Proteins p21(ras)