Immunophilin ligands demonstrate common features of signal transduction leading to exocytosis or transcription.

Abstract

Investigations of the actions and interactions of the immunophilin ligands FK506, cyclosporin A (CsA), rapamycin, and 506BD suggest that complexes of FK506 with an FK506-binding protein or of CsA with a cyclophilin (CsAbinding protein) inhibit the T-cell receptor-mediated signal transduction that results in the transcription of interleukin 2. Now we report an identical spectrum of activities of FK506, CsA, rapamycin, and 506BD on IgE receptor-mediated signal transduction that results in exocytosis of secretory granules from the rat basophilic leukemia cell line RBL-2113, a mast cell model. Both FK506 and CsA inhibit receptor-mediated exocytosis (CsA IC50 = 200 nM; FK506 IC5s = 2 nM) without affecting early receptor-associated events (hydrolysis of phosphatidylinositol, synthesis and release of eicosanoids, uptake of Ca21). In contrast, rapamycin and 506BD, which share common structural elements with FK506, by themselves have no effect on IgE receptor-mediated exocytosis. Both compounds, however, prevent inhibition by FK506 but not by CsA. Affinity chromatography with FKS06, CsA, and rapamycin matrices indicates that the same set of immunophilins present in RBL-2113 cells have been found in Jurkat T cells and calf thymus; however, the relative amounts ofthese proteins differ in the two cell types. These results suggest the existence of a common step in cytoplasmic signaling in T cells and mast cells that may be part of a general signaling mechanism. Despite significant progress in our understanding of the events at the plasma membrane involved in receptormediated activation, little is known of the mechanisms of signal transduction through the cytoplasm. The immunosuppressive agents FK506, cyclosporin A (CsA), and rapamycin inhibit cytoplasmic signaling events in T cells (1-5), probably through the formation of complexes with cytoplasmic receptors termed immunophilins (1,2,4). The rat basophilic leukemia cell line RBL-2H3, a tumor analog of a mucosal mast cell that has been used to study the biochemical events of mast cell activation (6-8), was used to investigate the effects of FK506, rapamycin, and 506BD on IgE receptormediated exocytosis. These cells contain both CsA-sensitive (9) and FK506-sensitive (T.H. and R.J.H., unpublished results) rotamases. To date, every known immunophilin is a rotamase (i.e., a peptidyl-prolyl cis-trans isomerase).Here we show that the same interactions of these immunosuppressive agents that take place in the human T-cell line Jurkat are operative in a rat mast cell line. IgE receptormediated exocytosis from these cells is inhibited by concentrations of CsA (10) (1, 2, 4, 11, 12), inhibit the actions of FK506, but not CsA, in both mast cell and T-cell lines. However, rapamycin and 506BD by themselves have no effect on the TCR-mediated pathway or IgE receptor-mediated pathway. A preliminary characterization ofthe immunophilins in this mast cell line by affinity chromatography indicates that all of the proteins observed from Jurkat cells are present in RBL-2H3 cells, although ...

Partial inhibition of human neutrophil activation by FK-506 at supratherapeutic concentrations

“…These data suggest that the FK-506-FKBP complex mediates the immunosuppressive effects of the drug in these cells. In addition, FK-506 inhibits activation of mast cells and basophils with ICs0 values of 1-5 nM (De Paulis et al 1991a, b;Hultsch et al 1991). By comparison, FK-506 at these concentrations was without effect on fMet-Leu-Phe-induced O~-production, and FK-506 (1 gM) showed no or only relatively small inhibitory effects on various neutrophil activation parameters (see Figs.…”

“…Thus, FK-506 apparently does not act via inhibition of gene transcription or protein synthesis. Interestingly, inhibitory effects of FK-506 on basophil and mast cell activation are also evident after short-term preincubation (De Paulis et al 1991 a,b;Hultsch et al 1991).…”

“…Interestingly, FK-506 has recently been reported to be a very potent and effective inhibitor of A 23187-induced exocytosis in human neutrophils (Forrest et al 1991). Additionally, FK-506 partially inhibits interleukin-la release from human macrophages (Keicho et al 1991) and potently inhibits mediator release from basophils and mast cells (De Paulis et al 1991a, b;Hultsch et al 1991). All these findings prompted us to study in detail the effects of FK-506 on human neutrophil activation.…”

The immunosuppressant FK506 inhibits amino acid import in Saccharomyces cerevisiae.

“…NF-AT nuclear import by dephosphorylation. CsA and FK506 are also known to block mast cell degranulation (8,46).Although the cytoplasmic proline isomerases cyclophilin A and FKBP12 are thought to be the relevant targets for immunosuppressant action, interactions with other cyclophilins and FKBPs may be involved in either immunosuppressive or toxic drug effects (6,43,80). Multiple additional cyclophilins and FKBPs have been identified.…”

“…The role of calcineurin in T-cell activation may be to drive NF-AT nuclear import by dephosphorylation. CsA and FK506 are also known to block mast cell degranulation (8,46).…”