Once phosphorylated, tyrosines in carboxyl terminus of protein-tyrosine kinase Syk interact with signaling proteins, including TULA-2, a negative regulator of mast cell degranulation

J Biol Chem. 2012 Mar 9;287(11):8194-204. doi: 10.1074/jbc.M111.326850. Epub 2012 Jan 20.


Activation of the high affinity IgE-binding receptor (FcεRI) results in the tyrosine phosphorylation of two conserved tyrosines located close to the COOH terminus of the protein-tyrosine kinase Syk. Synthetic peptides representing the last 10 amino acids of the tail of Syk with these two tyrosines either nonphosphorylated or phosphorylated were used to precipitate proteins from mast cell lysates. Proteins specifically precipitated by the phosphorylated peptide were identified by mass spectrometry. These included the adaptor proteins SLP-76, Nck-1, Grb2, and Grb2-related adaptor downstream of Shc (GADS) and the protein phosphatases SHIP-1 and TULA-2 (also known as UBASH3B or STS-1). The presence of these in the precipitates was further confirmed by immunoblotting. Using the peptides as probes in far Western blots showed direct binding of the phosphorylated peptide to Nck-1 and SHIP-1. Immunoprecipitations suggested that there were complexes of these proteins associated with Syk especially after receptor activation; in these complexes are Nck, SHIP-1, SLP-76, Grb2, and TULA-2 (UBASH3B or STS-1). The decreased expression of TULA-2 by treatment of mast cells with siRNA increased the FcεRI-induced tyrosine phosphorylation of the activation loop tyrosines of Syk and the phosphorylation of phospholipase C-γ2. There was parallel enhancement of the receptor-induced degranulation and activation of nuclear factor for T cells or nuclear factor κB, indicating that TULA-2, like SHIP-1, functions as a negative regulator of FcεRI signaling in mast cells. Therefore, once phosphorylated, the terminal tyrosines of Syk bind complexes of proteins that are positive and negative regulators of signaling in mast cells.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Degranulation / drug effects
  • Cell Degranulation / physiology*
  • Cell Line
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / immunology
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Mast Cells / enzymology*
  • Mast Cells / immunology
  • Mice
  • NF-kappa B / genetics
  • NF-kappa B / immunology
  • NF-kappa B / metabolism
  • NFATC Transcription Factors / genetics
  • NFATC Transcription Factors / immunology
  • NFATC Transcription Factors / metabolism
  • Peptides / chemistry
  • Peptides / immunology
  • Peptides / metabolism
  • Peptides / pharmacology
  • Phosphorylation / drug effects
  • Phosphorylation / physiology
  • Protein Structure, Tertiary
  • Protein Tyrosine Phosphatases / genetics
  • Protein Tyrosine Phosphatases / immunology
  • Protein Tyrosine Phosphatases / metabolism*
  • Protein-Tyrosine Kinases / genetics
  • Protein-Tyrosine Kinases / immunology
  • Protein-Tyrosine Kinases / metabolism*
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / immunology
  • RNA, Small Interfering / pharmacology
  • Receptors, IgE / genetics
  • Receptors, IgE / immunology
  • Receptors, IgE / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*
  • Syk Kinase


  • Intracellular Signaling Peptides and Proteins
  • NF-kappa B
  • NFATC Transcription Factors
  • Peptides
  • RNA, Small Interfering
  • Receptors, IgE
  • Protein-Tyrosine Kinases
  • Syk Kinase
  • Syk protein, mouse
  • Protein Tyrosine Phosphatases
  • TULA-2 protein, mouse