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T cell activation induced by novel gain-of-function mutants of Syk and ZAP-70
L Zeitlmann1, T Knorr, M Knoll
1Laboratorium für Molekulare Biologie, Genzentrum der Universität München, Feodor Lynen Strasse 25, D-81377 München, Germany.
Abstract:
The Syk family tyrosine kinases play a crucial role in antigen receptor-mediated signal transduction, but their regulation and cellular targets remain incompletely defined. Following receptor engagement, phosphorylation of tyrosine residues within ZAP-70 and Syk is thought to control both kinase activity and recruitment of modulatory factors. We report here the characterization of novel mutants of ZAP-70 and Syk, in which conserved C-terminal tyrosine residues have been replaced by phenylalanines (ZAP YF-C, Syk YF-C). Both mutant kinases display a prominent gain-of-function phenotype in Jurkat T cells, as demonstrated by lymphokine promoter activation, tyrosine phosphorylation of potential targets in vivo, and elevated intracellular calcium mobilization. While the presence of p56-Lck was required for ZAP YF-C-induced signaling, Syk YF-C showed enhanced functional activity in Lck-deficient JCaM1 Jurkat cells. Our results implicate the C terminus of Syk family kinases as an important regulatory region modulating T cell activation.
Insights
Novel mutants of ZAP-70 and Syk kinases show enhanced activity, implicating their C-termini in regulating T cell activation. These findings advance understanding of antigen receptor signaling pathways.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Syk family tyrosine kinases (ZAP-70 and Syk) are critical for T cell receptor signaling.
- Regulation and specific cellular targets of these kinases are not fully understood.
- Phosphorylation of tyrosine residues is believed to control kinase activity and protein interactions.
Purpose of the Study:
- To investigate the role of conserved C-terminal tyrosine residues in ZAP-70 and Syk kinase function.
- To characterize novel ZAP-70 and Syk mutants with C-terminal tyrosine residues replaced by phenylalanines (ZAP YF-C, Syk YF-C).
Main Methods:
- Generation and characterization of ZAP YF-C and Syk YF-C mutants.
- Assessment of kinase gain-of-function phenotypes in Jurkat T cells.
- Analysis of lymphokine promoter activation, in vivo tyrosine phosphorylation, and intracellular calcium mobilization.
- Evaluation of signaling in Lck-dependent and Lck-deficient T cell lines.
Main Results:
- Both ZAP YF-C and Syk YF-C mutants exhibited a gain-of-function phenotype.
- Mutant kinases induced lymphokine promoter activation, increased tyrosine phosphorylation, and elevated intracellular calcium.
- ZAP YF-C signaling required p56-Lck, whereas Syk YF-C showed enhanced activity in Lck-deficient cells.
Conclusions:
- The C terminus of Syk family kinases is a crucial regulatory region.
- Modulation of C-terminal tyrosines significantly impacts T cell activation signaling.
- These findings provide new insights into the regulation of T cell receptor signaling.