sq-23377 and Chromosome-Deletion

Antigen recognition by the T-cell receptor (TCR) initiates events including lymphokine gene transcription, particularly interleukin-2, that lead to T-cell activation. The immunosuppressive drugs, cyclosporin A (CsA) and FK-506, prevent T-cell proliferation by inhibiting a Ca(2+)-dependent event required for induction of interleukin-2 transcription. Complexes of FK-506 or CsA and their respective intracellular binding proteins inhibit the calmodulin-dependent protein phosphatase, calcineurin, in vitro. The pharmacological relevance of this observation to immunosuppression or drug toxicity is undetermined. Calcineurin, although present in lymphocytes, has not been implicated in TCR-mediated activation of lymphokine genes or in transcriptional regulation in general. Here we report that transfection of a calcineurin catalytic subunit increases the 50% inhibitory concentration (IC50) of the immunosuppressants FK-506 and CsA, and that a mutant subunit acts in synergy with phorbol ester alone to activate the interleukin-2 promoter in a drug-sensitive manner. These results implicate calcineurin as a component of the TCR signal transduction pathway by demonstrating its role in the drug-sensitive activation of the interleukin-2 promoter.

Topics: Animals; Calcineurin; Calmodulin-Binding Proteins; Cell Line; Chloramphenicol O-Acetyltransferase; Chromosome Deletion; Cyclosporine; Gene Expression Regulation; Humans; Interleukin-2; Ionomycin; Kinetics; Macromolecular Substances; Mice; Phosphoprotein Phosphatases; Polymerase Chain Reaction; Promoter Regions, Genetic; Recombinant Proteins; Tacrolimus; Tetradecanoylphorbol Acetate; Transcription, Genetic; Transfection

T-cell tolerance to the minor lymphocyte-stimulating antigen Mls-1a in a T-cell receptor (TcR) V beta 8.1 transgenic line of mice is maintained by both clonal deletion and clonal anergy. Approximately 20-50% of peripheral CD4+ (but not CD8+) T cells isolated from these mice are anergic and fail to proliferate following TcR ligation. We have examined key events in T-cell signaling in peripheral T cells isolated from these mice. In this report, we show that the anergic CD4+ T cells did not mobilize calcium or express receptors for interleukin 2 (IL-2) following TcR ligation. However, the cells retained viability and functional potential because stimulation with phorbol 12-myristate 13-acetate and ionomycin bypassed the block in receptor-mediated signaling and induced IL-2 receptor expression and proliferation of the anergic cells.

Topics: Animals; Antigens, Surface; Calcium; CD4 Antigens; Chromosome Deletion; Crosses, Genetic; Gene Expression; H-2 Antigens; Immune Tolerance; Ionomycin; Macromolecular Substances; Mice; Mice, Inbred Strains; Mice, Transgenic; Minor Lymphocyte Stimulatory Antigens; Receptors, Antigen, T-Cell; Receptors, Interleukin-2; Signal Transduction; T-Lymphocyte Subsets; T-Lymphocytes; Tetradecanoylphorbol Acetate