INHIBITION OF T-CELL ACTIVATION BY PHARMACOLOGICAL DISRUPTION OF THE MEK1 ERK MAP KINASE OR CALCINEURIN SIGNALING PATHWAYS RESULTS IN DIFFERENTIAL MODULATION OF CYTOKINE PRODUCTION/

Productive T cell activation leading to cytokine secretion requires th e cooperation of multiple signaling pathways coupled to the TCR and to costimulatory molecules such as CD28. Here, we utilized two pharmacop hores, PD98059 and FK506, that inhibit, respectively, mitogen-activate d protein (MAP) kinase kinase 1 (MEK 1) and calcineurin, to determine the relative role of the signaling pathways controlled by these enzyme s in T cell activation. Although the two compounds had distinctive eff ects on CD69 induction, they both suppressed T cell proliferation indu ced by anti-CD3 mAb, in a manner reversible by exogenous IL-2, suggest ing that PD98059, like FK506, affects the production of, rather than t he responsiveness to growth-promoting cytokines. Accordingly, IL-2 pro duction by T cells stimulated with anti-CD3 mAb in conjunction with PM A or with anti-CD28 mAb was inhibited by both compounds. However, thes e compounds differentially affected the production of other cytokines, depending on the mode of activation. PD98059 inhibited TNF-alpha, IL- 3, granulocyte-macrophage (GM)-CSF, IFN-gamma, and to a lesser extent IL-6 and IL-10 production but enhanced IL-4, IL-5, and IL-13 productio n induced by CD3/PMA or CD3/CD28. FK506 suppressed CD3/PMA-induced pro duction of all cytokines examined here but to a lesser extent IL-13. F K506 also reduced CD3/CD28-induced production of IL-3, IL-4, IL-10, TN F-alpha, and IL-6 but augmented that of GM-CSF, IL-5, IFN-gamma, and I L-13. Therefore, the biochemical targets of PD98059 and FK506 contribu te differently to the production of various cytokines by T cells, whic h may have implications for the therapeutic manipulation of this produ ction.