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Genomic expression programs and the integration of the CD28 costimulatory signal in T cell activation
Maximilian Diehn1, Ash A Alizadeh, Oliver J Rando
1Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
Abstract:
Optimal activation of T cells requires effective occupancy of both the antigen-specific T cell receptor and a second coreceptor such as CD28. We used cDNA microarrays to characterize the genomic expression program in human peripheral T cells responding to stimulation of these receptors. We found that CD28 agonists alone elicited few, but reproducible, changes in gene expression, whereas CD3 agonists elicited a multifaceted temporally choreographed gene expression program. The principal effect of simultaneous engagement of CD28 was to increase the amplitude of the CD3 transcriptional response. The induced genes whose expression was most enhanced by costimulation were significantly enriched for known targets of nuclear factor of activated T cells (NFAT) transcription factors. This enhancement was nearly abolished by blocking the nuclear translocation of NFATc by using the calcineurin inhibitor FK506. CD28 signaling promoted phosphorylation, and thus inactivation, of the NFAT nuclear export kinase glycogen synthase kinase-3 (GSK3), coincident with enhanced dephosphorylation of NFATc proteins. These results provide a detailed picture of the transcriptional program of T cell activation and suggest that enhancement of transcriptional activation by NFAT, through inhibition of its nuclear export, plays a key role in mediating the CD28 costimulatory signal.
Insights
CD28 costimulation enhances T cell activation by amplifying CD3 signaling. It increases the expression of nuclear factor of activated T cells (NFAT) targets by inhibiting NFAT nuclear export, crucial for T cell responses.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- T cell activation requires T cell receptor (TCR) and coreceptor signaling.
- CD28 is a key coreceptor that provides costimulatory signals for T cells.
Purpose of the Study:
- To characterize the genomic expression program of human peripheral T cells upon TCR and CD28 stimulation.
- To elucidate the role of CD28 costimulation in T cell activation pathways.
Main Methods:
- cDNA microarrays were used to analyze gene expression.
- Stimulation of T cells with CD3 and CD28 agonists.
- Inhibition of nuclear factor of activated T cells (NFAT) nuclear translocation using FK506.
Main Results:
- CD3 agonists induced a complex gene expression program, while CD28 agonists alone had minimal effects.
- CD28 costimulation amplified the CD3-induced transcriptional response.
- Enhanced genes were enriched for NFAT targets, and this enhancement was blocked by FK506.
- CD28 signaling inhibited glycogen synthase kinase-3 (GSK3), promoting NFAT dephosphorylation and nuclear retention.
Conclusions:
- CD28 costimulation significantly enhances T cell activation by amplifying the TCR-mediated transcriptional program.
- CD28 costimulation primarily acts by promoting NFAT-mediated transcription through inhibition of NFAT nuclear export.
- This mechanism highlights the critical role of NFAT regulation in CD28-mediated T cell costimulation.