Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.16 (calcineurin)
 17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Calcineurin, a Ca2+, calmodulin-dependent protein phosphatase, was recently found to bind with high affinity to two different immunosuppressant binding proteins (immunophilins) with absolute dependence on the presence of the immunosuppressants FK506 or cyclosporin A (CsA) [Liu et al. (1991) Cell 66, 807-815]. The binding affinities of the immunophilin-drug complexes toward calcineurin and the stoichiometry of the resultant multimeric complexes have now been determined, and structural elements of FK506, CsA, and calcineurin that are critical for mediating their interactions have been identified. Analogues of FK506 (FK520, FK523, 15-O-demethyl-FK520) and CsA (MeBm2t1-CsA and MeAla6-CsA) whose affinities for their cognate immunophilins do not correlate with their immunosuppressive activities have been prepared and evaluated in biochemical and cellular assays. We demonstrate a strong correlation between the ability of these analogues, when bound to their immunophilins, to inhibit the phosphatase activity of calcineurin and their ability to inhibit transcriptional activation by NF-AT, a T cell specific transcription factor that regulates IL-2 gene synthesis in human T cells. In addition, FKBP-FK506 and CyP-CsA do not inhibit members of the PP1, PP2A, and PP2C classes of serine/threonine phosphatases. These data suggest that calcineurin is the relevant cellular target of these immunosuppressive agents and is involved in Ca(2+)-dependent signal transduction pathways in, among others, T cells and mast cells.
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PMID:Inhibition of T cell signaling by immunophilin-ligand complexes correlates with loss of calcineurin phosphatase activity. 137 50

The immunosuppressive drugs cyclosporin A (CsA) and FK506 both interfere with a Ca(2+)-sensitive T-cell signal transduction pathway, thereby preventing the activation of specific transcription factors (such as NF-AT and NF-IL2A) involved in lymphokine gene expression. CsA and FK506 seem to act by interaction with their cognate intracellular receptors, cyclophilin and FKBP, respectively (see ref. 11 for review). The Ca2+/calmodulin-regulated phosphatase calcineurin is a major target of drug-isomerase complexes in vitro. We have therefore tested the hypothesis that this interaction is responsible for the in vivo effects of CsA/FK506. We report here that overexpression of calcineurin in Jurkat cells renders them more resistant to the effects of CsA and FK506 and augments both NFAT- and NFIL2A-dependent transcription. These results identify calcineurin as a key enzyme in the T-cell signal transduction cascade and provide biological evidence to support the notion that the interaction of drug-isomerase complexes with calcineurin underlies the molecular basis of CsA/FK506-mediated immunosuppression.
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PMID:Identification of calcineurin as a key signalling enzyme in T-lymphocyte activation. 137 62

The macrolide rapamycin blocks cell cycle progression in yeast and various animal cells by an unknown mechanism. We demonstrate that rapamycin blocks the phosphorylation and activation of the 70 kd S6 protein kinases (pp70S6K) in a variety of animal cells. The structurally related drug FK506 had no effect on pp70S6K activation but at high concentrations reversed the rapamycin-induced block, confirming the requirement for the rapamycin and FK506 receptor, FKBP. Rapamycin also interfered with signaling by these S6 kinases, blocking serum-stimulated S6 phosphorylation and delaying entry of Swiss 3T3 cells into S phase. Neither rapamycin nor FK506 blocked activation of a distinct family of S6 kinases (RSKs) or the MAP kinases. These studies identify a rapamycin-sensitive signaling pathway, argue for a ubiquitous role for FKBPs in signal transduction, indicate that FK506-FKBP-calcineurin complexes do not interfere with pp70S6K signaling, and show that in fibroblasts pp70S6K, not RSK, is the physiological S6 kinase.
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PMID:Rapamycin-FKBP specifically blocks growth-dependent activation of and signaling by the 70 kd S6 protein kinases. 137 6

The 3D structure of two unlabeled FK506 analogs, (R)- and (S)-[18-OH]ascomycin, when bound to [U-13C,15N]FKBP were determined by isotope-filtered 2D NMR experiments. The structures for the R and S isomers that bind tightly to FKBP but lack immunosuppressive activity are compared to each other and to the conformation of the potent immunosuppressant, ascomycin, when bound to FKBP. The results are interpreted in terms of calcineurin binding to the FKBP/ascomycin complex.
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PMID:Conformation of two non-immunosuppressive FK506 analogs when bound to FKBP by isotope-filtered NMR. 138 Apr 70

Migration of human polymorphonuclear neutrophils on vitronectin is dependent on repeated transient increases in the concentration of intracellular free calcium ([Ca2+]i). A specific peptide inhibitor of the Ca(2+)-calmodulin-dependent phosphatase calcineurin was introduced into the cytoplasm of neutrophils. The peptide inhibited neutrophil migration on vitronectin by interfering with the release of the cells from sites of attachment. A similar reduction in motility on vitronectin occurred when cells were treated with the immunosuppressant FK506, which also inhibits calcineurin when bound to its binding protein, FKBP. These results indicate that a rise in [Ca2+]i reduces integrin-mediated adhesion to vitronectin by a mechanism that requires calcineurin activity.
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PMID:Inhibition of neutrophil chemokinesis on vitronectin by inhibitors of calcineurin. 138 29

The immunosuppressants cyclosporin A (CsA), FK506, and rapamycin block T-cell activation by interfering with signal transduction. The institution of CsA therapy for prophylaxis against graft rejection revolutionized human organ transplants, and clinical trials with FK506 and rapamycin are in progress. The targets for these drugs, cyclophilin for CsA and FKBP for FK506 and rapamycin, are members of two unrelated families of ubiquitous, highly conserved, abundant proteins. Although unrelated, both cyclophilin and FKBP catalyze proline isomerization and may fold proteins. The structures of both cyclophilin and FKBP have been determined, in some cases in complex with drugs or substrates. The cyclophilin-CsA and FKBP-FK506 complexes prevent T-cell response to antigen, bind and modulate the activity of the protein phosphatase calcineurin, and prevent nuclear import of a subunit of NF-AT, a T-cell activation transcription factor. In contrast, rapamycin blocks T-cell responses to IL-2. Yeast genetic studies suggest that the FKBP-rapamycin target is a protein complex involved in cell cycle progression. Further studies should provide fundamental insights into T-cell activation, signal transduction, and protein folding, and hold the promise of more specific immunosuppressive therapies.
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PMID:Proline isomerases at the crossroads of protein folding, signal transduction, and immunosuppression. 151 10

Cyclosporin A, the major immunosuppressive drug in transplantation, and the more potent therapeutic drug candidate, FK506, have led to the discovery of two superfamilies of immunosuppressant binding proteins, the cyclophilins and the FK binding proteins. These proteins, enzymes with high kcat values for isomerization of X-Pro bonds in peptides and protein substrates, are distributed in all cell compartments where protein folding normally occurs. It is likely that they play major roles in the protein folding and protein trafficking in the cell. It is also likely that they have been suborned in T cells by the immunosuppressant drugs that are potent pseudosubstrate ligands that selectively block the signal transduction cascade. The discovery of the inhibition of protein phosphatase 2B (calcineurin) by the drug-immunophilin complex (CsA-CyP or FK506-FKBP) provides evidence for a specific downstream target of the drug-immunophilin complexes and may prompt a search for endogenous ligands of cyclophilin and FKBP that may effect signal transduction regulation. The molecular insights gained over a short time in this area have been remarkable; they promise to elucidate the steps in T cell activation and delineate new targets for immunosuppressive therapy.
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PMID:Cyclosporin A, the cyclophilin class of peptidylprolyl isomerases, and blockade of T cell signal transduction. 161 11

Although the immediate receptors (immunophilins) of the immunosuppressants cyclosporin A (CsA) and FK506 are distinct, their similar mechanisms of inhibition of cell signaling suggest that their associated immunophilin complexes interact with a common target. We report here that the complexes cyclophilin-CsA and FKBP-FK506 (but not cyclophilin, FKBP, FKBP-rapamycin, or FKBP-506BD) competitively bind to and inhibit the Ca(2+)- and calmodulin-dependent phosphatase calcineurin, although the binding and inhibition of calcineurin do not require calmodulin. These results suggest that calcineurin is involved in a common step associated with T cell receptor and IgE receptor signaling pathways and that cyclophilin and FKBP mediate the actions of CsA and FK506, respectively, by forming drug-dependent complexes with and altering the activity of calcineurin-calmodulin.
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PMID:Calcineurin is a common target of cyclophilin-cyclosporin A and FKBP-FK506 complexes. 171 44

Backbone dynamics of the ligand- (FK506-) bound protein FKBP-12 (107 amino acids) have been examined using 15N relaxation data derived from inverse-detected two-dimensional 1H-15N NMR spectra. A model free formalism [Lipari & Szabo (1982) J. Am. Chem. Soc. 104, 4546-4559] was used to derive the generalized order parameter (S2), the effective correlation time for internal motions (tau e), and the chemical-exchange line width (R(ex)) based on the measured 15N relaxation rate constants (R1, R2) and 1H-15N heteronuclear NOEs. The final optimized overall correlation time (tau m) was 9.0 ns. The average order parameter (S2) describing the amplitude of motions on the picosecond time scale was found to be 0.88 +/- 0.04, indicating that internal flexibility is restricted along the entire polypeptide chain. In contrast to results obtained for uncomplexed FKBP, the 80's loop (residues 82-87) surrounding the ligand binding site was found to be rigidly fixed, indicating that internal motions at this site are damped significantly due to stabilizing noncovalent interactions with the FK506 molecule. Structural implications of these differences in picosecond mobility as well as possible implications for calcineurin recognition are discussed.
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PMID:15N NMR relaxation studies of the FK506 binding protein: dynamic effects of ligand binding and implications for calcineurin recognition. 751 79

The specificity of cyclosporin A (CsA) binding to the major intracellular receptor proteins, cyclophilin A and B, as well as the interaction of CsA with the phosphatase calcineurin were investigated. Binding of photoaffinity-labeled CsA (PL-CS), a photoaffinity probe of CsA, to recombinant human cyclophilin A and B is saturable and specific. Non-specific PL-CS binding to calcineurin is observed in the absence of cyclophilin and calmodulin. In the presence of cyclophilin, cyclosporin-calcineurin binding becomes specific. Ternary complexes containing an equimolar ratio of cyclophilin A or B, PL-CS and calcineurin are resolved using the chemical-crosslinking technique. The formation of these complexes is specific, calcium- but not calmodulin-dependent, and is only inhibitable by cyclosporins, which bind cyclophilin. The drug-immunophilin complex binds to the calcineurin A subunit. The proteolytic 43 kDa product of calcineurin A retains binding properties, suggesting that the C-terminal domains are not necessary for complex formation. A trimeric complex of FKBP-calcineurin is also formed with FK506, but not with rapamycin. As expected, these complexes are only competed with by homologous derivatives. Chemical crosslinking of photolabeled Jurkat T-cells strongly suggests that drug-calcineurin complexes are of biological relevance.
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PMID:Demonstration of ternary immunophilin-calcineurin complexes with the immunosuppressants cyclosporin and macrolide FK506. 751 9


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