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T-Cell Antigen CD28 Interacts with the Lipid Kinase Phosphatidylinositol 3-Kinase by a Cytoplasmic Tyr(P)-Met-Xaa-Met Motif
The T-cell antigen CD28 provides a costimulatory signal that is required for T-cell proliferation. T-cell receptor ζ/CD3 engagement without CD28 ligation leads to a state of nonresponsiveness/anergy, thereby implicating CD28 in the control of peripheral tolerance to foreign antigens or tumors. A key...
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Published in: | Proceedings of the National Academy of Sciences - PNAS 1994-03, Vol.91 (7), p.2834-2838 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that cite this one |
Online Access: | Get full text |
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Summary: | The T-cell antigen CD28 provides a costimulatory signal that is required for T-cell proliferation. T-cell receptor ζ/CD3 engagement without CD28 ligation leads to a state of nonresponsiveness/anergy, thereby implicating CD28 in the control of peripheral tolerance to foreign antigens or tumors. A key unresolved question has concerned the mechanism by which CD28 generates intracellular signals. Phosphatidylinositol 3-kinase (PI 3-kinase) is a lipid kinase with Src-homology 2 (SH2) domain(s) that binds to the platelet-derived growth factor receptor (PDGF-R), an interaction that is essential for signaling by growth factor. In this study, we demonstrate that CD28 binds to PI 3-kinase by means of a Y(P)MXM motif within its cytoplasmic tail. CD28-associated PI 3-kinase was detected by lipid kinase and HPLC analysis as well as by reconstitution experiments with baculoviral-expressed p85 subunit of PI 3-kinase. CD28 bound directly to the p85 subunit without the need for the associated p110 subunit. Site-directed mutagenesis and peptide competition analysis using Y(P)-MXM-containing peptides showed that PI 3-kinase bound to a Y(P)MXM motif within the CD28 cytoplasmic tail (residues 191-194). Mutation of the Y191 within the motif resulted in a complete loss of binding, while mutation of M194 caused partial loss of binding. Binding analysis showed that the CD28 Y(P)-MXM motif bound to the p85 C- and N-terminal SH2 domains with an affinity comparable to that observed for PDGF-R and insulin receptor substrate 1. In terms of signaling, CD28 ligation induced a dramatic increase in the recruitment and association of PI 3-kinase with the receptor. CD28 is likely to use PI 3-kinase as the second signal leading to T-cell proliferation, an event with implications for anergy and peripheral T-cell tolerance. |
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ISSN: | 0027-8424 1091-6490 |
DOI: | 10.1073/pnas.91.7.2834 |