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Interaction between G proteins and tyrosine kinases upon T cell receptor.CD3-mediated signaling
J Stanners1, P S Kabouridis, K L McGuire
1Department of Biology and Molecular Biology Institute, San Diego State University, California 92182, USA.
Abstract:
Engagement of the T cell receptor (TCR).CD3 complex results in the induction of multiple intracellular events, with protein tyrosine kinases playing a pivotal role in their initiation. Biochemical studies also exist suggesting the involvement of heterotrimeric GTP-binding proteins (G proteins); however, the functional consequence of this participation in TCR.CD3-mediated signaling is unresolved. Here, we report TCR.CD3-mediated guanine nucleotide exchange among the 42-kDa G protein alpha subunits of the G alpha q/11 family, their physical association with CD3 epsilon, and the G alpha 11-dependent activation of phospholipase C beta. Protein tyrosine kinase inhibitors, however, abrogate TCR.CD3-mediated G protein activation. Quite interesting is the observation that cells transfected with a function-deficient mutant of G alpha 11 display diminished tyrosine phosphorylation of TCR.CD3 zeta and epsilon chains, as well as ZAP-70, upon anti-CD3 antibody triggering. These data indicate the involvement of the G alpha q/11 family in TCR.CD3 signaling at a step proximal to the receptor and suggest a reciprocal regulation between tyrosine kinases and G proteins in T cells.
Insights
T cell receptor (TCR) signaling involves G proteins and tyrosine kinases. This study reveals G alpha q/11 proteins associate with CD3 epsilon, activating phospholipase C beta and showing reciprocal regulation with kinases in T cells.
Area of Science:
- Immunology
- Cell Signaling
- Molecular Biology
Background:
- T cell receptor (TCR)/CD3 complex engagement initiates intracellular signaling cascades.
- Protein tyrosine kinases are critical for initiating TCR/CD3 signaling.
- The role of heterotrimeric GTP-binding proteins (G proteins) in TCR/CD3 signaling remains unclear.
Purpose of the Study:
- To investigate the functional involvement of G proteins in TCR/CD3-mediated signaling.
- To elucidate the relationship between G proteins and tyrosine kinases in T cell activation.
Main Methods:
- Biochemical assays to detect guanine nucleotide exchange and protein association.
- Enzyme activity assays for phospholipase C beta.
- T cell transfection with function-deficient G protein mutants.
- Western blotting to assess protein phosphorylation.
Main Results:
- TCR/CD3 engagement induced guanine nucleotide exchange in G alpha q/11 family proteins.
- G alpha 11 physically associated with CD3 epsilon, leading to phospholipase C beta activation.
- Tyrosine kinase inhibitors blocked TCR/CD3-mediated G protein activation.
- Impaired G alpha 11 function reduced tyrosine phosphorylation of TCR/CD3 zeta/epsilon and ZAP-70.
Conclusions:
- The G alpha q/11 family is involved in TCR/CD3 signaling proximal to the receptor.
- A reciprocal regulatory relationship exists between tyrosine kinases and G proteins in T cell signaling.