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Diminished tyrosine protein kinase activity in T cells unresponsive to TCR stimulation
A Y Tsygankov1, H W Kim, J C Pratt
1Department of Molecular Biology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, NJ 08543-4000.
Abstract:
Tyrosine phosphorylation is thought to be one of the earliest steps in antigenic activation of T cells. Three nonreceptor tyrosine kinases, p56lck, p60fyn, and ZAP-70, are known to be involved in T cell receptor (TCR) signaling, albeit their functional roles appear to be different. Whereas p60fyn and ZAP-70 are functionally associated with the T cell antigen receptor, p56lck is essential for TCR signaling without being directly coupled to the TCR. We have studied a mutant variant of the Jurkat T cell line (J32-3.2), in which basal activities of p56lck and p60fyn are 2- to 2.5-fold reduced relative to those in its parental line (J32) while basal activity of ZAP-70 remains unchanged, and compared responses of J32-3.2 and J32 to TCR stimulation. We have demonstrated that tyrosine phosphorylation following CD3 cross-linking in J32-3.2 cells was extremely short-lived and thus insufficient for the induction of subsequent physiological responses. This was at least partially due to the diminished tyrosine kinase activity in these cells. A decrease in the activity of src-related kinases was caused primarily by their lower expression, whereas expression of ZAP-70 was unchanged but its response to CD3 cross-linking was diminished, correlating with the deficient tyrosine phosphorylation of the CD3 zeta-chain, recently observed in J32-3.2. These data are consistent with the idea that src-related kinases phosphorylate the zeta-chain, which in turn recruits ZAP-70 required to sustain the signal.
Insights
Reduced activity of src-related kinases impairs T cell receptor signaling by diminishing tyrosine phosphorylation of the CD3 zeta-chain, which is crucial for ZAP-70 recruitment and sustained signaling. This impacts T cell activation.
Area of Science:
- Immunology
- Cell Signaling
- Molecular Biology
Background:
- Tyrosine phosphorylation is a critical early event in T cell activation via the T cell receptor (TCR).
- p56lck, p60fyn, and ZAP-70 are key nonreceptor tyrosine kinases involved in TCR signaling, with distinct roles.
- p56lck is essential for TCR signaling, though not directly coupled to the TCR, unlike p60fyn and ZAP-70.
Purpose of the Study:
- To investigate the role of reduced src-related kinase activity in TCR signaling using a mutant Jurkat T cell line (J32-3.2).
- To compare the TCR signaling responses of J32-3.2 cells with reduced p56lck and p60fyn activity to their parental J32 cells.
Main Methods:
- Utilized a mutant Jurkat T cell line (J32-3.2) with decreased basal activity of p56lck and p60fyn.
- Stimulated J32-3.2 and J32 cells via CD3 cross-linking to assess TCR signaling.
- Analyzed tyrosine phosphorylation levels, kinase activities, and protein expression.
Main Results:
- TCR stimulation in J32-3.2 cells resulted in transient tyrosine phosphorylation, insufficient for physiological responses, due to diminished kinase activity.
- Reduced src-related kinase activity in J32-3.2 cells was primarily due to lower expression levels.
- While ZAP-70 expression was unchanged, its response to CD3 cross-linking was diminished, correlating with deficient CD3 zeta-chain phosphorylation.
Conclusions:
- Src-related kinases phosphorylate the CD3 zeta-chain, a necessary step for recruiting ZAP-70 to sustain TCR signaling.
- The data support the model where src-related kinases initiate TCR signal transduction by phosphorylating the zeta-chain, enabling subsequent ZAP-70-mediated signaling events.