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Mol. Cell. Biol., Sep 1996, 5026-5035, Vol 16, No. 9
G Kong, M Dalton, JB Wardenburg, D Straus, T Kurosaki and AC Chan
Biochemical and genetic evidence has implicated two families of protein
tyrosine kinases (PTKs), the Src- and Syk-PTKs, in T- and B-cell antigen
receptor signaling. ZAP-70 is a member of the Syk-PTKs that associates with
the T-cell antigen receptor and undergoes tyrosine phosphorylation
following receptor activation. Three tyrosine residues, Tyr-292, -492, and
-493, have been identified as sites of phosphorylation following T-cell
antigen receptor engagement. Utilizing ZAP-70- and Syk-deficient
lymphocytes (Syk-DT40 cells), we provide biochemical and functional
evidence that heterologous trans- phosphorylation of Tyr-493 by a Src-PTK
is required for antigen receptor-mediated activation of both the calcium
and ras pathways. In contrast, cells expressing mutations at Tyr-292 or
-492 demonstrate hyperactive T- and B-cell antigen receptor phenotypes.
Thus, phosphorylation of ZAP-70 mediates both activation and inactivation
of antigen receptor signaling.
Copyright © 1996, American Society for Microbiology
Distinct tyrosine phosphorylation sites in ZAP-70 mediate activation and negative regulation of antigen receptor function
Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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