Wortmannin inhibits translation of tumor necrosis factor-α in superantigen-activated T cells

The superantigen toxic shock syndrome toxin (TSST)-1 can induce tumor necrosis factor (TNF)-α expression in T cells and monocytes, through different signaling pathways. We have stimulated peripheral blood mononuclear cells with TSST-1 and found that the major cell producers of TNF-α as detected by cytofluorimetry and immunocytochemistry were CD4+ T lymphocytes. The expression of TNF-α by CD4+ T cells can be inhibited by either, wortmannin (WN) or LY 294002, two phosphatidylinositol 3-kinase (PI 3-K) inhibitors. The inhibitory effect is not transcriptional as WN does not change the mRNA steady state of TNF-α at any of the concentrations tested and LY 294002 when preincubated with mononuclear cells at its median inhibitory concentration (IC50 = 1.4 μM) significantly inhibited the expression of TNF-α but not its mRNA. Immunoprecipitation of pulse-labeled intracellular TNF-α showed a specific decrease in the synthesis of this cytokine on cells treated with PI 3-K inhibitors. The p38 mitogen-activated protein kinase (MAPK) is involved in control of TNF-α translation in human macrophages. In T cells, we have found that the p38 MAPK inhibitor SB 203580 significantly decreased the secretion of TNF-α but not its mRNA. In addition, the combined use of WN and SB 203580 had an additive inhibitory effect on secretion of TNF-α. Therefore, both PI 3-K and p38 MAPK signaling pathways control TNF-α production in T cells.