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)

The immunosuppressant FK506 (tacrolimus) is an antifungal natural product macrolide that suppresses the immune system by blocking T-cell activation. In complex with the intracellular protein FKBP12, FK506 inhibits calcineurin, a Ca(2+)-calmodulin-dependent serine-threonine protein phosphatase. We recently reported that growth of the opportunistic fungal pathogen Cryptococcus neoformans is resistant to FK506 at 24 degrees C but sensitive at 37 degrees C and that calcineurin, the target of FKBP12-FK506, is required for growth at 37 degrees C in vitro and pathogenicity in vivo. These findings identify calcineurin as a potential antifungal drug target. In previous studies the calcineurin inhibitor cyclosporin A (CsA) was effective against murine pulmonary infections but exacerbated cryptococcal meningitis in rabbits and mice, likely because CsA does not cross the blood-brain barrier. Although we find that FK506 penetrates the CNS, FK506 also exacerbates cryptococcal meningitis in rabbits. Thus, FK506 immunosuppression outweighs antifungal action in vivo. Like FK506, the nonimmunosuppressive FK506 analog L-685,818 is toxic to C. neoformans in vitro at 37 degrees C but not at 24 degrees C, and FK506-resistant mutants are resistant to L-685,818, indicating a similar mechanism of action. Fluconazole-resistant C. neoformans clinical isolates were also found to be susceptible to both FK506 and L-685,818. Our findings identify calcineurin as a novel antifungal drug target and suggest the nonimmunosuppressive FK506 analog L-685,818 or other congeners warrant further consideration as antifungal drugs for C. neoformans.
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PMID:The immunosuppressant FK506 and its nonimmunosuppressive analog L-685,818 are toxic to Cryptococcus neoformans by inhibition of a common target protein. 898 Jul 72

Cyclosporin A (CsA) and FK506 are antimicrobial, immunosuppressive natural products that inhibit signal transduction. In T cells and Saccharomyces cerevisiae, CsA and FK506 bind to the immunophilins cyclophilin A and FKBP12 and the resulting complexes inhibit the Ca2+-regulated protein phosphatase calcineurin. We find that growth of the opportunistic fungal pathogen Cryptococcus neoformans is sensitive to CsA and FK506 at 37 degrees C but not at 24 degrees C, suggesting that CsA and FK506 inhibit a protein required for C. neoformans growth at elevated temperature. Genetic evidence supports a model in which immunophilin-drug complexes inhibit calcineurin to prevent growth at 37 degrees C. The gene encoding the C. neoformans calcineurin A catalytic subunit was cloned and disrupted by homologous recombination. Calcineurin mutant strains are viable but do not survive in vitro conditions that mimic the host environment (elevated temperature, 5% CO2 or alkaline pH) and are no longer pathogenic in an animal model of cryptococcal meningitis. Introduction of the wild-type calcineurin A gene complemented these growth defects and restored virulence. Our findings demonstrate that calcineurin is required for C. neoformans virulence and may define signal transduction elements required for fungal pathogenesis that could be targets for therapeutic intervention.
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PMID:Calcineurin is required for virulence of Cryptococcus neoformans. 918 5

The basidiomycetous yeast Cryptococcus neoformans is a human pathogen. Several phenotypes of this organism are defined as virulence traits including the polysaccharide capsule, melanin, and the ability to grow at 37 degreesC. The signaling pathways regulating the expression of these phenotypes and other important cellular processes are being defined on a molecular level. For example, the highly conserved signaling molecule calcineurin regulates high temperature growth in C. neoformans. A cryptococcal homolog of Saccharomyces cerevisiae STE12, the gene for a transcriptional regulator activated by the MAP kinase cascade, has also been identified. Additionally, the C. neoformans Galpha protein GPA1 and cAMP regulate mating, melanin production, encapsulation, and pathogenicity. This fungus is an excellent model to further dissect virulence-associated signaling pathways. The conserved role of Galpha proteins and cAMP-associated signaling pathways in fungal differentiation and pathogenicity is also reviewed.
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PMID:Signal transduction pathways regulating differentiation and pathogenicity of Cryptococcus neoformans. 980 1

FK506 and rapamycin are immunosuppressants that inhibit signalling cascades required for T-cell activation, yet both are natural products of Streptomyces that live in the soil. FK506 and rapamycin also have potent antimicrobial activity against yeast and pathogenic fungi, suggesting a natural role in inhibiting growth of competing micro-organisms. The immunosuppressive and antimicrobial activities of FK506 and rapamycin are mediated by binding to the FKBP12 prolyl isomerase and the resulting FKBP12/FK506 and FKBP12/rapamycin complexes inhibit conserved protein targets, either the phosphatase calcineurin or the TOR (target of rapamycin) kinases, respectively. Streptomyces sp., 'Streptomyces hygroscopicus subsp. ascomyceticus' and Streptomyces hygroscopicus, which produce FK506, FK520 (also known as ascomycin, a C21 ethyl derivative of FK506) and rapamycin, respectively, produced toxins that inhibited the growth of competing cells of the yeast Saccharomyces cerevisiae and the pathogenic fungus Cryptococcus neoformans. Yeast and fungal mutants lacking FKBP12 or expressing dominant drug-resistant calcineurin or TOR mutants were resistant to FK506 and rapamycin, and to the toxins produced by Streptomyces. Streptomyces strains with mutations in the FK506 or rapamycin biosynthetic enzymes were impaired in toxin production. Finally, the toxins secreted by 'S. hygroscopicus subsp. ascomyceticus' and S. hygroscopicus promoted formation of FKBP12/calcineurin and FKBP12/TOR complexes in a two-hybrid assay and mutations that rendered calcineurin or TOR drug-resistant prevented interaction. These observations support the hypothesis that Streptomyces evolved to secrete FK506, FK520 and rapamycin as toxins to inhibit the growth of competing yeast and fungi.
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PMID:Secretion of FK506/FK520 and rapamycin by Streptomyces inhibits the growth of competing Saccharomyces cerevisiae and Cryptococcus neoformans. 1046 65

Cyclosporine (CsA) is an immunosuppressive and antimicrobial drug which, in complex with cyclophilin A, inhibits the protein phosphatase calcineurin. We recently found that Cryptococcus neoformans growth is resistant to CsA at 24 degrees C but sensitive at 37 degrees C and that calcineurin is required for growth at 37 degrees C and pathogenicity. Here CsA analogs were screened for toxicity against C. neoformans in vitro. In most cases, antifungal activity was correlated with cyclophilin A binding in vitro and inhibition of the mixed-lymphocyte reaction and interleukin 2 production in cell culture. Two unusual nonimmunosuppressive CsA derivatives, (gamma-OH) MeLeu(4)-Cs (211-810) and D-Sar (alpha-SMe)(3) Val(2)-DH-Cs (209-825), which are also toxic to C. neoformans were identified. These CsA analogs inhibit C. neoformans via fungal cyclophilin A and calcineurin homologs. Our findings identify calcineurin as a novel antifungal drug target and suggest nonimmunosuppressive CsA analogs warrant investigation as antifungal agents.
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PMID:Immunosuppressive and nonimmunosuppressive cyclosporine analogs are toxic to the opportunistic fungal pathogen Cryptococcus neoformans via cyclophilin-dependent inhibition of calcineurin. 1060 36

The calcineurin gene was cloned and disrupted in serotype D strains of Cryptococcus neoformans. Serotype A and serotype D calcineurin mutants were inviable at 37 degrees C and avirulent in mice, whereas only serotype A mutants were cation stress sensitive. Thus, calcineurin plays conserved and divergent roles in serotype A and serotype D strains.
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PMID:Comparison of the roles of calcineurin in physiology and virulence in serotype D and serotype A strains of Cryptococcus neoformans. 1063 77

Cryptococcus neoformans is an opportunistic fungal pathogen that causes life-threatening infections of the central nervous system. Existing therapies include amphotericin B, fluconazole, and flucytosine, which are limited by toxic side effects and the emergence of drug resistance. We recently demonstrated that the protein phosphatase calcineurin is required for growth at 37 degrees C and virulence of C. neoformans. Because calcineurin is the target of potent inhibitors in widespread clinical use, cyclosporine and FK506 (tacrolimus), it is an attractive drug target for novel antifungal agents. Here we have explored the synergistic potential of combining the calcineurin inhibitor FK506 or its nonimmunosuppressive analog, L-685,818, with other antifungal agents and examined the molecular basis of FK506 action by using genetically engineered fungal strains that lack the FK506 target proteins FKBP12 and calcineurin. We demonstrate that FK506 exhibits marked synergistic activity with the H(+)ATPase inhibitor bafilomycin A(1) via a novel action distinct from calcineurin loss of function. FK506 also exhibits synergistic activity with the pneumocandin MK-0991/caspofungin acetate (formerly L-743,873), which targets the essential beta-1,3 glucan synthase, and in this case, FK506 action is mediated via FKBP12-dependent inhibition of calcineurin. Finally, we demonstrate that FK506 and fluconazole have synergistic activity that is independent of both FKBP12 and calcineurin and may involve the known ability of FK506 to inhibit multidrug resistance pumps, which are known to export azoles from fungal cells. In summary, our studies illustrate the potential for synergistic activity of a variety of different drug combinations and the power of molecular genetics to define the mechanisms of drug action, as well as identify a novel action of FK506 that could have profound implications for therapeutic or toxic effects in other organisms, including humans.
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PMID:Synergistic antifungal activities of bafilomycin A(1), fluconazole, and the pneumocandin MK-0991/caspofungin acetate (L-743,873) with calcineurin inhibitors FK506 and L-685,818 against Cryptococcus neoformans. 1068 48

Calcineurin is the conserved target of the immunosuppressants cyclosporin A and FK506. Using the yeast two-hybrid system, we identified a novel calcineurin binding protein, CBP1, from the pathogenic fungus Cryptococcus neoformans. We show that CBP1 binds to calcineurin in vitro and in vivo, and FKBP12-FK506 inhibits CBP1 binding to calcineurin. Cryptococcus neoformans cbp1 mutant strains exhibit modest defects in growth under stress conditions and virulence, similar to but less severe than the phenotypes of calcineurin mutants. Saccharomyces cerevisiae mutants lacking the CBP1 homolog RCN1 are, like calcineurin mutants, sensitive to lithium cation stress. CBP1 shares a central peptide sequence motif, SPPxSPP, with related proteins in S.CEREVISIAE:, Schizosaccharomyces pombe, Drosophila melanogaster, Caenorhabditis elegans and humans, and peptides containing this motif altered calcineurin activity in vitro. Interestingly, the human CBP1 homolog DSCR1 is encoded by the Down's syndrome candidate region interval on chromosome 21, is highly expressed in the heart and central nervous system, and may play a role in calcineurin functions in heart development, neurite extension and memory.
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PMID:Identification and characterization of a highly conserved calcineurin binding protein, CBP1/calcipressin, in Cryptococcus neoformans. 1089 16

Cryptococcus neoformans is a fungal pathogen that causes meningitis in immunocompromised patients. Its growth is sensitive to the immunosuppressants FK506 and cyclosporin, which inhibit the Ca2+- calmodulin-activated protein phosphatase calcineurin. Calcineurin is required for growth at 37 degrees C and virulence of C.neoformans. We found that calcineurin is also required for mating. FK506 blocks mating of C.neoformans via FKBP12-dependent inhibition of calcineurin, and mutants lacking calcineurin are bilaterally sterile. Calcineurin is not essential for the initial fusion event, but is required for hyphal elongation and survival of the heterokaryon produced by cell fusion. It is also required for hyphal elongation in diploid strains and during asexual haploid fruiting of MATalpha cells in response to nitrogen limitation. Because mating and haploid fruiting produce infectious basidiospores, our studies suggest a second link between calcineurin and virulence of C.neoformans. Calcine urin regulates filamentation and 37 degrees C growth via distinct pathways. Together with studies revealing that calcineurin mediates neurite extension and neutrophil migration in mammals, our findings indicate that calcineurin plays a conserved role in the control of cell morphology.
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PMID:Calcineurin is required for hyphal elongation during mating and haploid fruiting in Cryptococcus neoformans. 1123 Jan 26

Calcineurin is a Ca2+-calmodulin-regulated protein phosphatase that is the target of the immunosuppressive drugs cyclosporin A and FK506. Calcineurin is a heterodimer composed of a catalytic A and a regulatory B subunit. In previous studies, the calcineurin A homologue was identified and shown to be required for growth at 37 degrees C and hence for virulence of the pathogenic fungus Cryptococcus neoformans. Here, we identify the gene encoding the calcineurin B regulatory subunit and demonstrate that calcineurin B is also required for growth at elevated temperature and virulence. We show that the FKR1-1 mutation, which confers dominant FK506 resistance, results from a 6 bp duplication generating a two-amino-acid insertion in the latch region of calcineurin B. This mutation was found to reduce FKBP12-FK506 binding to calcineurin both in vivo and in vitro. Molecular modelling based on the FKBP12-FK506-calcineurin crystal structure illustrates how this mutation perturbs drug interactions with the phosphatase target. In summary, our studies reveal a central role for calcineurin B in virulence and antifungal drug action in the human fungal pathogen C. neoformans.
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PMID:Calcineurin regulatory subunit is essential for virulence and mediates interactions with FKBP12-FK506 in Cryptococcus neoformans. 1125 6


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