Calcineurin is a phosphatase whose primary targets in T cells are NFAT transcription factors, and inhibition of calcineurin activity by treatment with cyclosporin A (CsA) or FK506 is a cornerstone of immunosuppressive therapies. Here we found that calcineurin was recruited to the T cell antigen receptor (TCR) signaling complex, where it reversed inhibitory phosphorylation of the tyrosine kinase Lck on Ser59 (LckS59). Loss of calcineurin activity impaired phosphorylation of Tyr493 of the tyrosine kinase ZAP-70 (ZAP-70Y493), as well as some downstream pathways in a manner consistent with signaling in cells expressing LckS59A (Lck that cannot be phosphorylated) or LckS59E (a phosphomimetic mutant). Notably, CsA inhibited integrin-LFA-1-dependent and NFAT-independent adhesion of T cells to the intercellular adhesion molecule ICAM-1, with little effect on cells expressing mutant Lck. These results provide new understanding of how widely used immunosuppressive drugs interfere with essential processes in the immune response.
Calcineurin/metabolism , Lymphocyte Specific Protein Tyrosine Kinase p56(lck)/metabolism , Receptors, Antigen, T-Cell/metabolism , T-Lymphocytes/immunology , ZAP-70 Protein-Tyrosine Kinase/metabolism , Animals , Cell Adhesion/drug effects , Cyclosporine/pharmacology , Humans , Immunosuppressive Agents/pharmacology , Intercellular Adhesion Molecule-1/metabolism , Jurkat Cells , Lymphocyte Activation/drug effects , Lymphocyte Function-Associated Antigen-1/metabolism , Lymphocyte Specific Protein Tyrosine Kinase p56(lck)/genetics , Mice , Mice, Transgenic , NFATC Transcription Factors/genetics , NFATC Transcription Factors/metabolism , Phosphorylation/drug effects , Phosphorylation/genetics , Protein Binding , Signal Transduction , T-Lymphocytes/drug effects , Tacrolimus/pharmacology
