CTLA-4 and PD-1 Receptors Inhibit T-Cell Activation by Distinct Mechanisms

Abstract

CTLA-4 and PD-1 are receptors that negatively regulate T-cell activation. Ligation of both CTLA-4 and PD-1 blocked CD3/CD28-mediated upregulation of glucose metabolism and Akt activity, but each accomplished this regulation using separate mechanisms. CTLA-4-mediated inhibition of Akt phosphorylation is sensitive to okadaic acid, providing direct evidence that PP2A plays a prominent role in mediating CTLA-4 suppression of T-cell activation. In contrast, PD-1 signaling inhibits Akt phosphorylation by preventing CD28-mediated activation of phosphatidylinositol 3-kinase (PI3K). The ability of PD-1 to suppress PI3K/AKT activation was dependent upon the immunoreceptor tyrosine-based switch motif located in its cytoplasmic tail, adding further importance to this domain in mediating PD-1 signal transduction. Lastly, PD-1 ligation is more effective in suppressing CD3/CD28-induced changes in the T-cell transcriptional profile, suggesting that differential regulation of PI3K activation by PD-1 and CTLA-4 ligation results in distinct cellular phenotypes. Together, these data suggest that CTLA-4 and PD-1 inhibit T-cell activation through distinct and potentially synergistic mechanisms.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/.

ACKNOWLEDGMENTS

We thank Carl June, Richard Carroll, Bob Vonderheide, Kim Nichols, and Bruce Levine for insightful discussions; Stephen Ward for assistance with kinase assays; Beatriz Carreno for the kind gift of PD-1 and CTLA-4 antibodies; Coral Haas for administrative support; Faraz Samadi for proofreading; Gwen Scott for graphing; the Rosetta Gene Expression Laboratory for performing the hybridizations; Hongyue Di for assistance with the gene expression analysis; and Bob Rutherford and Goro Osawa for isolation of T lymphocytes.

J.M.C. is supported by a grant from the Mildred Scheel Stiftung der Deutschen Krebshilfe. This work was supported by Public Health Service grant AI057838 from the National Institute of Allergy and Infectious Diseases.