Syk and ZAP-70 mediate recruitment of p56lck/CD4 to the activated T cell receptor/CD3/zeta complex

J Exp Med. 1995 Jun 1;181(6):1997-2006. doi: 10.1084/jem.181.6.1997.


During antigen recognition by T cells, CD4 and the T-cell receptor (TCR)/CD3/zeta complex are thought to interact with the same major histocompatibility complex II molecule in a stable ternary complex. Evidence has suggested that the association of CD4 with TCR/CD3/zeta requires the interaction of the protein tyrosine kinase p56lck with CD4. We have taken a biochemical approach to understand the mechanism by which p56lck and, in particular, its src homology (SH) 2 domain contributes to the association of CD4 with TCR/CD3/zeta during activation. We have previously shown that the p56lck SH2 domain binds directly to tyrosine-phosphorylated ZAP-70. Here we formally demonstrate the in vivo association of p56lck with the homologous protein tyrosine kinases Syk and ZAP-70 after CD3 stimulation of Jurkat cells. A tyrosine-phosphorylated peptide containing the sequence predicted to be optimal for binding to the SH2 domain of src family kinases specifically competes for this association, indicating that tyrosine-phosphorylated ZAP-70 and Syk bind to p56lck by an SH2-mediated interaction. We also show that the same peptide is able to compete for the activation-dependent TCR/CD4 association in Jurkat cells. Moreover, ZAP-70 and CD4 cocap only after CD3 stimulation in human T lymphoblasts. We propose that the interaction of the p56lck SH2 domain with zeta-associated tyrosine-phosphorylated ZAP-70 and/or Syk enables CD4 to associate with antigen-stimulated TCR/CD3/zeta complexes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigens, CD / immunology*
  • CD4 Antigens / immunology*
  • Cell Line
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme Precursors / isolation & purification
  • Enzyme Precursors / metabolism*
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Kinetics
  • Lymphocyte Activation
  • Lymphocyte Specific Protein Tyrosine Kinase p56(lck)
  • Membrane Proteins / immunology*
  • Phosphorylation
  • Phosphotyrosine
  • Protein Binding
  • Protein-Tyrosine Kinases / isolation & purification
  • Protein-Tyrosine Kinases / metabolism*
  • Receptor-CD3 Complex, Antigen, T-Cell / immunology*
  • Receptors, Antigen, T-Cell / immunology*
  • Syk Kinase
  • T-Lymphocytes / immunology*
  • Tumor Cells, Cultured
  • Tyrosine / analogs & derivatives
  • Tyrosine / analysis
  • ZAP-70 Protein-Tyrosine Kinase


  • Antigens, CD
  • CD4 Antigens
  • Enzyme Precursors
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Receptor-CD3 Complex, Antigen, T-Cell
  • Receptors, Antigen, T-Cell
  • antigen T cell receptor, zeta chain
  • Phosphotyrosine
  • Tyrosine
  • Protein-Tyrosine Kinases
  • Lymphocyte Specific Protein Tyrosine Kinase p56(lck)
  • SYK protein, human
  • Syk Kinase
  • ZAP-70 Protein-Tyrosine Kinase
  • ZAP70 protein, human