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Grb2 forms an inducible protein complex with CD28 through a Src homology 3 domain-proline interaction
1Department of Immunology, University of Toronto, Toronto, Ontario M5S 1A2, Canada.
The Journal of Biological Chemistry
|August 8, 1998
Summary
CD28 costimulation involves Grb2 binding to CD28 via SH3 domains, independent of tyrosine phosphorylation. This interaction recruits signaling proteins, potentially mediating phosphatidylinositol 3-kinase (PI3K)-independent T cell activation.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- CD28 is crucial for optimal T cell activation, providing a costimulatory signal.
- The precise signal transduction pathways for CD28-mediated costimulation are not fully understood.
- While CD28 tyrosine phosphorylation and PI3K binding are known, their role in costimulation is debated.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying CD28-mediated costimulation.
- To investigate the role of Src homology 3 (SH3) domain-containing proteins in CD28 signaling.
- To determine the relationship between CD28 ligation, tyrosine phosphorylation, and protein interactions.
Main Methods:
- Investigated the interaction between CD28 and Grb2 using biochemical assays.
- Mapped the binding sites for Grb2 on the cytoplasmic domain of CD28.
- Assessed the role of CD28 ligation versus tyrosine phosphorylation in Grb2 binding.
Main Results:
- CD28 binds to the SH3 domains of proteins like Grb2 through a C-terminal diproline motif.
- Optimal Grb2 binding requires both SH3 domains of Grb2 and is induced by CD28 ligation, not tyrosine phosphorylation.
- This interaction facilitates the recruitment of tyrosine-phosphorylated proteins, such as p52(shc), to CD28.
Conclusions:
- A novel, inducible SH3-mediated interaction between Grb2 and CD28 is identified.
- This Grb2-CD28 association may mediate phosphatidylinositol 3-kinase (PI3K)-independent signaling pathways.
- The findings provide new insights into the complex signaling network of T cell costimulation.
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