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Distinct tyrosine phosphorylation sites in ZAP-70 mediate activation and negative regulation of antigen receptor

G Kong1, M Dalton, J Bubeck Wardenburg

  • 1Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110, USA.

Molecular and Cellular Biology
|September 1, 1996
PubMed

Insights

Phosphorylation of ZAP-70 protein tyrosine kinase (PTK) is crucial for T- and B-cell receptor signaling. Specific phosphorylation sites on ZAP-70 mediate both signal activation and inactivation.

Area of Science:

  • Immunology
  • Cell signaling
  • Molecular biology

Background:

  • Protein tyrosine kinases (PTKs), including Src- and Syk-PTKs, are vital for T- and B-cell antigen receptor signaling.
  • ZAP-70, a Syk-PTK, binds to the T-cell receptor and is tyrosine phosphorylated upon activation.
  • Three key tyrosine residues (Tyr-292, -492, -493) on ZAP-70 are phosphorylated after T-cell receptor engagement.

Purpose of the Study:

  • To investigate the functional role of specific ZAP-70 tyrosine phosphorylation sites in T- and B-cell antigen receptor signaling.
  • To elucidate the mechanisms by which ZAP-70 phosphorylation regulates calcium and ras pathway activation.
  • To determine how different phosphorylation sites contribute to either signal activation or inactivation.

Main Methods:

  • Utilized ZAP-70- and Syk-deficient lymphocytes (Syk-DT40 cells) for biochemical and functional analyses.
  • Employed site-directed mutagenesis to study the effects of specific tyrosine residue mutations (Tyr-292, -492, -493).
  • Assessed T- and B-cell antigen receptor signaling pathways, including calcium and ras activation.

Main Results:

  • Heterologous trans-phosphorylation of Tyr-493 by a Src-PTK is essential for antigen receptor-mediated activation of calcium and ras pathways.
  • Mutations at Tyr-292 or Tyr-492 resulted in hyperactive T- and B-cell antigen receptor signaling phenotypes.
  • Demonstrated that ZAP-70 phosphorylation differentially regulates signaling pathways.

Conclusions:

  • ZAP-70 phosphorylation plays a dual role in antigen receptor signaling, mediating both activation and inactivation.
  • Tyr-493 phosphorylation is critical for initiating downstream signaling cascades.
  • Dysregulation of ZAP-70 phosphorylation at Tyr-292 or Tyr-492 leads to aberrant receptor signaling.

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