p56lck-independent activation and tyrosine phosphorylation of p72syk by T-cell antigen receptor/CD3 stimulation

Proc Natl Acad Sci U S A. 1994 Jun 7;91(12):5301-5. doi: 10.1073/pnas.91.12.5301.


Activation of resting T lymphocytes by ligands to the T-cell antigen receptor (TCR)/CD3 complex is initiated by rapid tyrosine phosphorylation of cellular proteins. Protein-tyrosine kinases (PTKs) of the src family are known to be important, but the mechanism of their recruitment and their interactions with PTKs of other families are incompletely understood. We show that a member of another family of PTKs, the p72syk kinase, is constitutively bound to the TCR/CD3 complex and becomes tyrosine phosphorylated and activated within 1 min after TCR/CD3 stimulation. This activation did not depend on the presence of p56lck in T cells and in transfected COS cells. In both cases, however, the phosphorylation of cellular substrates was augmented by src family PTKs. We propose that p72syk may act as an immediate receptor-activated kinase upstream of the related p70zap PTK and the src family PTKs p56lck and p59fyn in T cells and that these src family PTKs act as signal amplifiers.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • CD3 Complex / physiology*
  • Enzyme Precursors / metabolism*
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Lymphocyte Specific Protein Tyrosine Kinase p56(lck)
  • Macromolecular Substances
  • Molecular Sequence Data
  • Phosphorylation
  • Phosphotyrosine
  • Protein Binding
  • Protein-Tyrosine Kinases / metabolism*
  • Receptors, Antigen, T-Cell / physiology*
  • Signal Transduction
  • Syk Kinase
  • T-Lymphocytes / physiology*
  • Tyrosine / analogs & derivatives
  • Tyrosine / metabolism


  • CD3 Complex
  • Enzyme Precursors
  • Intracellular Signaling Peptides and Proteins
  • Macromolecular Substances
  • Receptors, Antigen, T-Cell
  • Phosphotyrosine
  • Tyrosine
  • Protein-Tyrosine Kinases
  • Lymphocyte Specific Protein Tyrosine Kinase p56(lck)
  • SYK protein, human
  • Syk Kinase