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Evidence for phosphatidylinositol 3-kinase-dependent T cell antigen receptor (TCR) signal transduction
1Department of Hematology/Oncology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, U.S.A.
Abstract:
Recent evidence implicates PI 3-kinase in TCR signal transduction. The fungal metabolite wortmannin is a specific inhibitor of PI 3-kinase both in vitro and in vivo when used at nanomolar concentrations. Therefore, we examined the effect of wortmannin on stimulation of primary T cells and T cell lines. Wortmannin had a dose-dependent inhibitory effect on TCR-dependent primary T cell proliferation with IC50 in the nanomolar range. Furthermore, activation of T cell lines independently of antigen presenting cells and, therefore of any CD28 co-stimulatory signaling, was also sensitive to wortmannin. As expected, phorbol ester stimulation bypassed PI 3-kinase signal transduction. Importantly, the effect of wortmannin correlated with inhibition of activation of PI 3-kinase in stimulated T cells. The earliest step in T cell activation, tyrosine kinase activation, was not significantly affected by wortmannin. We conclude that a wortmannin-sensitive enzyme, probably PI 3-kinase, acting downstream of tyrosine kinases, but independently of the phorbol ester activated pathway, is necessary for stimulation of T cells via the TCR, and that this requirement is independent of any role of PI 3-kinase in co-stimulation via CD28 coreceptor. PI 3-kinase is most probably involved in generation of 3-phosphorylated lipid products, and is not merely an adaptor.
Insights
Wortmannin, a PI 3-kinase inhibitor, blocks T cell receptor (TCR) signaling and proliferation. This indicates that PI 3-kinase is crucial for T cell activation, independent of CD28 co-stimulation.
Area of Science:
- Immunology
- Cell Signaling
- Biochemistry
Background:
- Phosphoinositide 3-kinase (PI 3-kinase) is implicated in T cell receptor (TCR) signal transduction.
- Wortmannin, a fungal metabolite, is a specific inhibitor of PI 3-kinase at nanomolar concentrations.
Purpose of the Study:
- To investigate the effect of wortmannin on the stimulation of primary T cells and T cell lines.
- To determine the role of PI 3-kinase in TCR-mediated T cell activation.
Main Methods:
- Primary T cells and T cell lines were stimulated, and their proliferation was measured.
- The effect of wortmannin on TCR-dependent and independent T cell activation was assessed.
- PI 3-kinase activation and tyrosine kinase activation were monitored in stimulated T cells.
Main Results:
- Wortmannin exhibited a dose-dependent inhibition of TCR-dependent T cell proliferation (IC50 in nanomolar range).
- T cell activation, independent of CD28 co-stimulation, was sensitive to wortmannin.
- Phorbol ester stimulation bypassed PI 3-kinase inhibition, and wortmannin's effect correlated with inhibited PI 3-kinase activation.
- Early tyrosine kinase activation during T cell activation was not significantly affected by wortmannin.
Conclusions:
- A wortmannin-sensitive enzyme, likely PI 3-kinase, is essential for TCR-mediated T cell stimulation.
- This enzyme acts downstream of tyrosine kinases and independently of the phorbol ester pathway.
- PI 3-kinase's role in T cell activation is independent of its function in CD28 co-stimulation.