Peptidyl-prolyl cis-trans isomerase is the cyclosporin A-binding protein cyclophilin

Is cyclophilin involved in the immunosuppressive and nephrotoxic mechanism of action of cyclosporin A?

In this report we have approached two questions relating to the mechanism of action of cyclosporin A (CsA). First, we address whether the major cytosolic protein for CsA, cyclophilin, is directly involved in mediating the immunosuppressive activity of this drug, and, in particular, whether inhibition of this protein's peptidyl-prolyl cis-trans isomerase (PPIase) activity results in inhibition of murine T cell activation. Second, we ask whether the nephrotoxicity observed with CsA is related to inhibition of PPIase-dependent pathways in cells other than lymphocytes. Using a series of 61 cyclosporin analogues, we generally found a good correlation between cyclophilin binding and immunosuppressive activity for the majority of analogues analyzed. However, a number of compounds of distinct structural classes were found that could interact with cyclophilin but were much less immunosuppressive than expected. The inability of these analogues to inhibit lymphocyte activation could not be explained by their failure to enter the cell and bind to cyclophilin under the conditions used in the cellular assays. Surprisingly, a nonimmunosuppressive analogue, MeAla-6, which bound well to cyclophilin and was active as a PPIase inhibitor, did not induce renal pathology in vivo. Furthermore, another analogue, MeBm2t, which was immunosuppressive in vitro, possessed little or no activity as a PPIase inhibitor. These findings pose serious questions concerning a direct role of cyclosporin in mediating CsA's immunosuppressive and nephrotoxic activities. In addition, they raise doubts about whether PPIase has a direct function in lymphocyte signal transduction.

FK 506-binding protein proline rotamase is a target for the immunosuppressive agent FK 506 in Saccharomyces cerevisiae

FK 506 and cyclosporin A are potent immunosuppressive compounds that inhibit T-cell activation by interfering with signal transduction. In vitro, FK 506 binds and inhibits the activity of FK 506-binding protein (FKBP), a peptidylprolyl rotamase (cis-trans isomerase). Cyclosporin A acts similarly on a different proline rotamase, cyclophilin. Experiments described here demonstrate genetically that FKBP is a target for FK 506 in vivo. We have isolated the gene encoding the FKBP proline rotamase (FPR1) from Saccharomyces cerevisiae. The encoded yeast protein is highly homologous with bovine and human FKBP and shares no homology with cyclophilin. Disruption of FPR1 and CPR1 (encoding cyclophilin) individually or in combination is not lethal; thus, either enzymatic proline rotamerization is not essential for life or an unknown proline rotamase can substitute for the missing enzymes. Overexpression or disruption of FPR1 confers resistance to growth inhibition by FK 506, suggesting that FKBP is a target for FK 506 in yeast. However, FKBP is only one of at least two targets because strains lacking FKBP are only partially resistant to FK 506.

Human cyclophilin B: a second cyclophilin gene encodes a peptidyl-prolyl isomerase with a signal sequence

We report the cloning and characterization of a cDNA encoding a second human cyclosporin A-binding protein (hCyPB). Homology analyses reveal that hCyPB is a member of the cyclophilin B (CyPB) family, which includes yeast CyPB, Drosophila nina A, and rat cyclophilin-like protein. This family is distinguished from the cyclophilin A (CyPA) family by the presence of endoplasmic reticulum (ER)-directed signal sequences. hCyPB has a hydrophobic leader sequence not found in hCyPA, and its first 25 amino acids are removed upon expression in Escherichia coli. Moreover, we show that hCyPB is a peptidyl-prolyl cis-trans isomerase which can be inhibited by cyclosporin A. These observations suggest that other members of the CyPB family will have similar enzymatic properties. Sequence comparisons of the CyPB proteins show a central, 165-amino acid peptidyl-prolyl isomerase and cyclosporin A-binding domain, flanked by variable N-terminal and C-terminal domains. These two variable regions may impart compartmental specificity and regulation to this family of cyclophilin proteins containing the conserved core domain. Northern blot analyses show that hCyPB mRNA is expressed in the Jurkat T-cell line, consistent with its possible target role in cyclosporin A-mediated immunosuppression.

Further evidence that cyclosporin A protects mitochondria from calcium overload by inhibiting a matrix peptidyl-prolyl cis-trans isomerase. Implications for the immunosuppressive and toxic effects of cyclosporin

The Ki values of cyclosporins A, G and H for the peptidyl-prolyl cis-trans isomerase (PPIase) of liver and heart mitochondria are about 2, 20 and 500 nM respectively. This parallels their profile as inhibitors of non-specific pore opening of mitochondria induced by supraphysiological Ca2+ concentrations. The novel immunosuppressant FK-506 gave little inhibition of either process at 5 microM. These data support our previous hypothesis [Halestrap & Davidson (1990) Biochem. J. 268, 153-160] that pore opening involves an interaction between matrix PPIase and the adenine nucleotide translocase. It is suggested that this model may help to clarify the mechanism of action of cyclosporin as an immunosuppressant and its toxic effects on the liver and kidney following prolonged therapy.

Rapamycin sensitivity in Saccharomyces cerevisiae is mediated by a peptidyl-prolyl cis-trans isomerase related to human FK506-binding protein

Rapamycin is a macrolide antifungal agent with structural similarity to FK506. It exhibits potent immunosuppressive properties analogous to those of both FK506 and cyclosporin A (CsA). Unlike FK506 and CsA, however, rapamycin does not inhibit the transcription of early T-cell activation genes, including interleukin-2, but instead appears to block downstream events leading to T-cell activation. FK506 and CsA receptor proteins (FKBP and cyclophilin, respectively) have been identified and shown to be distinct members of a class of enzymes that possess peptidyl-prolyl cis-trans isomerase (PPIase) activity. Despite the apparent differences in their mode of action, rapamycin and FK506 act as reciprocal antagonists in vivo and compete for binding to FKBP. As a means of rapidly identifying a target protein for rapamycin in vivo, we selected and genetically characterized rapamycin-resistant mutants of Saccharomyces cerevisiae and isolated a yeast genomic fragment that confers drug sensitivity. We demonstrate that the resonse to rapamycin in yeast cells is mediated by a gene encoding a 114-amino-acid, approximately 13-kDa protein which has a high degree of sequence homology with human FKBP; we designated this gene RBP1 (for rapamycin-binding protein). The RBP1 protein (RBP) was expressed in Escherichia coli, purified to homogeneity, and shown to catalyze peptidyl-prolyl isomerization of a synthetic peptide substrate. PPIase activity was completely inhibited by rapamycin and FK506 but not by CsA, indicating that both macrolides bind to the recombinant protein. Expression of human FKBP in rapamycin-resistant mutants restored rapamycin sensitivity, indicating a functional equivalence between the yeast and human enzymes.

T cell activation in the absence of interleukin 2 (IL 2) results in the induction of high-affinity IL 2 receptor unable to transmit a proliferative signal

Although interleukin 2 (IL 2) clearly up-regulates the expression of the p55 chain of the IL 2 receptor (IL 2R) little is known about its role in the induction of the high-affinity IL 2R. Resting T lymphocytes were induced to express IL 2R under experimental conditions in which IL 2 production was not induced or was prevented. Under these conditions high- and low-affinity IL 2R were easily demonstrated by Scatchard analysis. Northern blot analysis confirmed the accumulation of p55 specific mRNA and the absence of the IL 2 transcript. High-affinity IL 2R induced in the complete absence of IL 2 were unable to transmit a proliferative response unless exposed to extremely high concentrations of IL 2. The addition of picomolar amounts of recombinant IL 2 or the initiation of endogenous IL 2 production during the induction period restored the functionality of high-affinity IL 2R. Also, T cells induced to generate IL 2 displayed functional high-affinity IL 2R even in the presence of monoclonal antibodies blocking extracellular IL 2 and IL 2R. These results indicate that the presence of IL 2 during the early phase of T cell activation is an absolute requirement for the induction of fully operational high-affinity IL 2R and that low amounts of intracellular IL 2 are sufficient to confer functional properties to these receptors. The data also suggest that an intracellular as well as an extracellular high-affinity structure, expressed as a consequence of cell activation, is responsible for conferring competence to the high-affinity IL 2R involved in IL 2-dependent proliferation.

The larvicidal activity of cyclosporin A against Schistosoma mansoni in mice

Treatment of BALB/c or MF1 mice with cyclosporin A (CsA) around the time of infection with Schistosoma mansoni conferred almost complete protection. The migration kinetics of L-[75Se]selenomethionine-labelled infective cercariae were investigated by compressed tissue autoradiography. Similar levels of skin penetration were achieved by cercariae in control and drug-treated individuals. CsA arrested 87-94% of the worms in the skin and ultimately all of these died in this site. Few worms (7-14%) migrated from the skin to the lungs and none completed migration to the liver. Nevertheless, the autoradiograms revealed a limited degree of lateral cutaneous migration by the worms present in the skins of CsA-treated mice. Results of perfusion recovery experiments carried out during the course of infection reinforced the tracking data.

Purification and characterization of cyclosporine and FK-506 binding proteins from a human T-helper cell line

Cytosolic proteins that specifically bind cyclosporine A and FK-506 were isolated and purified from the JURKAT human T-helper cell line. These binding proteins were purified by affinity, molecular weight exclusion and weak cation exchange column chromatography. Radiolabeled cyclosporine A specifically bound to a approximately 17 kDa molecule which is cyclophilin and also bound to a approximately 50 kDa protein(s). Radiolabeled FK-506 did not bind to the approximately 17 kDa molecular weight protein, but specifically bound to soluble approximately 10 kDa and approximately 50 kDa proteins.

Correlation of cyclosporine and metabolite binding to cyclophilin and a 50 kDa binding protein with in vitro immunosuppression: a preliminary report

Seven purified cyclosporine (CsA) metabolites were analyzed for binding to cyclophilin and to a 50 kDa protein purified from a JURKAT cell line. In addition, the potency of the seven metabolites, relative to CsA, was obtained using a primary mixed lymphocyte culture (MLC) suppression assay. CsA, M1, 17, and 21 were found to be immunosuppressive in the concentration range used (0-500 ng/mL). These results were then compared to protein binding. CsA and metabolite 17 (M17) bound to both proteins. Conversely, M1, 13, 21, and 26 bound only to cyclophilin, while M8 and M18 bound only to the 50 kDa protein.

Functional analysis of the fic gene involved in regulation of cell division

We have shown that cAMP may be a regulation factor in cell division of Escherichia coli (Utsumi et al., 1982, 1989). The fic (filamentation induced by cAMP) gene of this system found previously (Utsumi, et al., 1982) was analysed in this study. The open reading frame of the fic gene coded for 200 amino acids. The pabA (p-aminobenzoate synthase) gene was found downstream from the fic gene. The distance between the end of fic and the start of pabA was 31 base pairs. To deduce the function of Fic protein, the fic gene was destroyed by the kanamycin-resistant (Kmr) gene and the fic gene was shown to be essential for growth of E. coli. Such mutants required PAB (p-aminobenzoate) or folate for growth. These data suggested that the Fic protein is involved in the synthesis of PAB or folate and the fic gene could be part of a pab operon. In cells starved of them, cell division was inhibited. Addition of folate also repressed the filamentation induced by cAMP at 43 degrees C in the fic-1 mutant. These results would indicate that Fic protein and cAMP are involved in a new regulatory mechanism of cell division via folate metabolism. Furthermore, it is also shown that cell division could be controlled by coordination of cAMP, Fic and Fts proteins.

Pharmacology and pharmacokinetics of cyclosporine

Cyclosporine (CsA) is a lipophilic, immunosuppressive peptide which selectively inhibits T-lymphocyte activation in response to antigen stimulation. Although it is the drug of choice in organ transplantation, its clinical use is hampered by toxicity and unpredictable pharmacokinetics. CsA absorption from the small intestine is normally incomplete and is further reduced by intestinal dysfunction and low bile flow. That which enters the systemic blood is metabolized almost entirely by the liver and excreted in the bile. Blood CsA levels are altered to a clinically relevant degree by abnormal liver function and by drugs that induce or inhibit hepatic metabolism. Intestinal absorption may also play a role in some drug interactions. The narrow therapeutic range of CsA and the various factors that alter its kinetics underlie the continuing need to monitor this drug in blood.

The mechanism of action of cyclosporine: a perspective for the 90's

The introduction of cyclosporine (CyA) as a pharmacological agent has resulted not only in a dramatic improvement in the clinical management of transplant recipients but also in a better understanding of the molecular basis of the immune response, especially T cell function. Knowledge of the mechanism of action of CyA has led to exciting areas of study. Among these are the sequence of regulatory events leading to T cell activation, the potential relevance of isomerases in signal transduction pathways (as the receptor for CyA, cyclophilin has been shown to be an isomerase), the blocking effect of CyA on the development of multidrug resistance, and the striking parallelism between CyA and the newer immunosuppressive agent FK-506. These fields promise to be relevant in solving some of the crucial questions in transplantation immunology, and developing better strategies for immunosuppression.

FKB1 encodes a nonessential FK 506-binding protein in Saccharomyces cerevisiae and contains regions suggesting homology to the cyclophilins

FK 506, a powerful immunosuppressant that blocks allograft rejection by preventing T-cell activation, binds to an 11-kDa protein called the FK 506-binding protein (FKBP). Like cyclophilin, a cytosolic protein that binds another immunosuppressant, cyclosporin A, FKBP possesses peptidylprolyl cis-trans isomerase activity. We have isolated a genomic clone encoding the yeast FKBP (FKB1). The gene encodes a protein of 114 amino acids having a calculated Mr of 12,158. Disruption of the gene shows that FKB1 is not essential for growth. A search of translated nucleic acid data bases revealed bacterial FKBP homologs in Neisseria meningiditis and Pseudomonas aeruginosa. Comparison of the conserved amino acids in FKBP homologs with the conserved amino acids in the cyclophilins has revealed a region of similarity that we speculate to be a homologous domain related to the functional similarities of the two proteins.

The effect of the immunosuppressant FK-506 on alternate pathways of T cell activation

Structurally unrelated, FK-506 and cyclosporin (CsA) bind to and inhibit the action of distinct cytoplasmic receptors, FK-506-binding protein (FKBP) and cyclophilin (CyP), respectively. These receptors, termed immunophilins, share no sequence similarity, and yet both have been demonstrated to be capable of catalyzing the cis-trans isomerization of peptidyl-prolyl bonds (rotamase activity). Because FK-506 and CsA bind to different intracellular target structures, we investigated the spectrum of action of FK-506, in comparison to CsA, on T cell activation. We have shown that FK-506, like CsA, is able to inhibit T cell activation mediated not only by the T cell receptor-CD3 complex, but also via another surface molecule, CD2. T cell proliferation, stimulation of interleukin 2 production, and induction of apoptosis were all sensitive to inhibition by both FK-506 and CsA. With each parameter of activation, FK-506 is approximately 10-100-fold more effective than CsA. In contrast, FK-506 did not affect T cell proliferation induced by anti-CD28 monoclonal antibody in the presence of phorbol 12-myristate 13-acetate. This CD28 pathway, however, was inhibited by a structural homology of FK-506, rapamycin, demonstrating that the mechanism of action of FK-506 has specificity. These data suggest that immunophilins or the complex of drug coupled to immunophilin (i.e. FK-506/FKBP, CsA/CyP) are involved in and regulate selective pathways of T cell stimulation.

Molecular cloning and regional distribution of rat brain cyclophilin

Cyclosporine A (CsA) is a potent immunosuppressive drug that has widespread clinical uses in organ transplantation and the treatment of autoimmune disorders. However, the drug's clinical applications are on an empiric basis with a poor understanding of the basic mechanism(s) of action. CsA may exert some of its effects by binding to a cellular receptor protein--the cyclosporine receptor (also called cyclophilin). Cyclophilin (CyP) is an ubiquitous, soluble, cytoplasmic 17 kDa protein which has recently been shown to be a peptide-prolyl isomerase. CsA specifically binds to this protein and inhibits its isomerase activity. A rat cyclophilin cDNA clone was isolated from a rat brain lambda gt11 cDNA library. Northern blot analysis shows a single 1 kb messenger RNA in rat brain. In order to determine the regional distribution of the Cyp mRNA in situ hybridization was performed. The Cyp mRNA appeared to be expressed throughout the brain but there were particularly high levels in the cerebral cortex and hippocampus compared to the relatively low levels in white matter areas and tracts. At the cellular level, the Cyp mRNA is expressed at much higher levels in neurons than in glia. The high levels of Cyp in cortical (neuronal) areas may, in part, explain the global encephalopathic symptoms clinically observed in CsA neurotoxicity.

Chemistry and biology of the immunophilins and their immunosuppressive ligands

Cyclosporin A, FK506, and rapamycin are inhibitors of specific signal transduction pathways that lead to T lymphocyte activation. These immunosuppressive agents bind with high affinity to cytoplasmic receptors termed immunophilins (immunosuppressant binding proteins). Studies in this area have focused on the structural basis for the molecular recognition of immunosuppressants by immunophilins and the biological consequences of their interactions. Defining the biological roles of this emerging family of receptors and their ligands may illuminate the process of protein trafficking in cells and the mechanisms of signal transmission through the cytoplasm.

The immunosuppressives FK 506 and cyclosporin A inhibit the generation of protein factors binding to the two purine boxes of the interleukin 2 enhancer

Like Cyclosporin A (CsA), the macrolide FK 506 is a potent immunosuppressive that inhibits early steps of T cell activation, including the synthesis of Interleukin 2 (II-2) and numerous other lymphokines. The block of II-2 synthesis occurs at the transcriptional level. At concentrations that block T cell activation, FK 506 and CsA inhibit the proto-enhancer activity of Purine boxes of the II-2 promoter and the generation of lymphocyte-specific factors binding to the Purine boxes. Under the same conditions, the DNA binding of other II-2 enhancer factors remains unaffected by both compounds. These results support the view that FK 506 and CsA, which both inhibit the activity of peptidylprolyl cis/trans isomerases, suppress T cell activation by a similar, if not identical mechanism.

Cyclosporin A and its metabolites, distribution in blood and tissues

Cyclosporin A (CsA), a non-myelotoxic immunosuppressant, and its metabolites are widely distributed in the body. Highest concentrations of CsA have been detected in the pancreas, adipose tissue and liver, lowest concentrations in brain, muscle, blood and other body fluids. Metabolites are distributed differently to CsA. In addition to lipid partition, intracellular binding to cyclophilin, a peptidyl-prolyl cis-trans isomerase, appears to play a role in its tissue distribution. The temperature dependence of such binding in erythrocytes poses difficulty in serum or plasma measurements. Tissue specific processes may also influence action and toxicity of CsA and its metabolites; thus, a better understanding of the complex distribution pattern of CsA and its metabolites would be important for establishing improved strategies and selection of appropriate specific methodologies for drug monitoring.

cDNA sequence of cyclophilin from Dictyostelium discoideum

A cDNA encoding a protein homologous to cyclophilins from other species has been isolated from a Dictyostelium discoideum cDNA library. From the deduced amino acid sequence a protein with a molecular mass of 19 kD and 64% identity with human cyclophilin is predicted. Southern blot analysis indicates that there is one cyclophilin gene in the D. discoideum genome. The mRNA is present in all developmental stages.

Treatment of pyoderma gangrenosum with cyclosporine: results in seven patients

The mainstay of therapy for pyoderma gangrenosum has been corticosteroids, but many patients respond poorly. During the past 2 years we have treated seven patients who had pyoderma gangrenosum with cyclosporine after their condition proved resistant to conventional therapy. No evidence of permanent toxicity from cyclosporine was detected and treatment with other immunosuppressive agents was discontinued in five of seven cases. Tuberculosis was reactivated in one patient. Three patients had a remission, three had an intermediate response, and one did not respond. These results indicate that cyclosporine is useful in the treatment of patients with refractory pyoderma gangrenosum and suggest an immune mechanism in the pathogenesis of this disorder.

Dipyridamole in vitro suppresses the generation of T-cell cytotoxic functions: synergistic activity with cyclosporine

The pharmacological activity of dipyridamole has been related to its ability to increase intracellular cAMP. Elevated cAMP concentrations can tone down T-cell effector functions. The aim of this study was to evaluate the dipyridamole effect in vitro on the generation of alloreactive cytotoxic and lymphokine-activated killer cells in normal T-cell subpopulations. Dipyridamole suppressed T-cell cytotoxic functions in a dose-dependent way. The kinetics of suppression showed that dipyridamole prevented the first step of cytotoxicity, i.e. activation of the lytic program following allogeneic or interleukin-2 stimulation. The ability of dipyridamole to interact with the immunosuppressive activity of cyclosporine was also investigated. By itself, cyclosporine suppressed the generation of alloreactive cytotoxicity, but not the generation of lymphokine-activated killer cells. A synergistic immunosuppressive activity between dipyridamole and cyclosporine was observed on the generation of alloreactive cytotoxic T lymphocytes.

Cyclosporine A inhibits induction of DNA synthesis by PDGF and other peptide mitogens in cultured rat aortic smooth muscle cells and dermal fibroblasts

The immunosuppressive drug cyclosporine A was recently shown to inhibit smooth muscle proliferation in the vascular response to injury. To examine if this may be due to a direct effect of the drug on the smooth muscle cells (SMCs), we have studied its influence on the phenotypic modulation of rat aortic SMCs in primary cultures and on the induction of DNA synthesis by peptide mitogens in serum-starved subcultures. The results demonstrate that cyclosporine A does not interfere with the transition of the SMCs from a contractile to a synthetic phenotype, an early step in the preparation for cell division. On the other hand, it inhibits induction of DNA synthesis by recombinant platelet-derived growth factor-BB (PDGF-BB), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), and insulin-like growth factor-I (IGF-I). Maximum effect was obtained at a concentration of 1-3 micrograms/ml and the drug could be added 4-6 h after the growth factors with full inhibitory effect. No distinct effect on the stimulation of overall RNA and protein synthesis by PDGF-BB was observed, indicating that the drug was not of general cytotoxicity at the concentrations used. Throughout this part of the investigation, similar results were obtained with rat dermal fibroblasts. The findings indicate that cyclosporine A inhibits induction of DNA synthesis by peptide mitogens, and suggest that the inhibitory effect of cyclosporine A on smooth muscle proliferation in vivo at least in part may be due to a direct action on these cells.

Immunomodulator, LZ-8, prevents antibody production in mice

LZ-8, a new and recently discovered immunomodulator from Ganoderma lucidum, has been shown to have immunosuppressive activity in vivo and to be a member of the immunoglobulin superfamily. In this paper we examined the in vivo effect of LZ-8 on antibody production using the hepatitis B surface antigen (HBs Ag) in mice. LZ-8 had mitogenic activity in vitro towards spleen cells of C57BL/10 (B10) and C57BL/10BR (B10BR) as previously shown towards those of DBA/2 mice. B10 and B10BR mice produced anti-HBs Ag antibody by the twice sensitization of the antigen while intraperitoneal administration of LZ-8 twice weekly into the mice (8 and 12 mg/kg) greatly prevented the production of antibody to HBs Ag (83.3-96.8% inhibition). We further examined the effect of LZ-8 administration on mitogen responsibility of spleen cells and on the T-cell subset population in both the spleen and lymph node but no significant differences were observed between the LZ-8 treated and untreated mice. These results suggest that the immunosuppressive activities of LZ-8, previously shown, such as the prevention of systemic anaphylaxis and the Arthus reactions, were caused by the blocking of antigen-specific antibody production.

Hepatotrophic effects of FK506 in dogs

Portacaval shunt (Eck fistula) in dogs causes hepatocyte atrophy and organelle disruption, as well as tripling of hepatocyte mitoses. After submitting dogs to this procedure, FK506 was infused into the tied-off left portal vein. The size, anatomic quality, and replication of hepatocytes were enhanced in the portion of liver infused with FK506, with a significant spillover effect in the noninfused portion. These hepatotrophic qualities of FK506 may explain part of FK506's efficacy for the treatment of chronic liver rejection. Also, the observations support a trial with this drug for the treatment of autoimmune liver diseases because, in addition to turning off the immunologic genesis of such disorders, repair and regeneration of the damaged liver may be augmented. Finally, these hepatrophic qualities are part of an emerging spectrum of biologic effects caused by drugs that may modulate the enzyme cis-trans peptidyl-prolyl isomerase (PPIase), the principal constituent of the cytosolic binding sites of FK506, repatomycin, cyclosporine, and presumably other immunosuppressive drugs as yet undiscovered.

Comparison of the in vitro and biophysical effects of cyclosporine A, FK-506, and mycophenolic acid on human peripheral blood lymphocytes

The immunosuppressive drugs FK-506 and mycophenolic acid (MPA) have recently been described, but their mode(s) of action are not well understood. We have compared them to cyclosporine A (CsA) in several assays. We have shown that CsA (1 microgram/ml), MPA (0.1 microgram/ml), and FK-506 (0.5 microgram/ml) all induce a state of unresponsiveness to anti-CD3 stimulation as measured by [3H]-thymidine uptake. This suggests that the target of these drugs may be present only after mitogenic stimulation. These drugs also cause a hyperpolarization of the plasma membrane of lymphocytes. This effect is blocked by quinine or verapamil. All three immunosuppressors only slightly modulate the increase in intracellular Ca++ caused by Con-A or by anti-CD3 stimulation but do not affect Ca++ levels alone. They also decrease expression of IL-2 receptors on alpha CD3-stimulated lymphocytes. Similarities in their modes of action, as measured by these biophysical and cell biological tests, indicate the possibility that these three drugs will show similarities in their clinical performance.

Systemic administration of kainic acid differentially regulates the levels of prodynorphin and proenkephalin mRNA and peptides in the rat hippocampus

The effects of systemic kainic acid (KA) administration on hippocampal levels of prodynorphin and proenkephalin mRNA, as well as opioid peptides derived from these precursors, were evaluated. A single subcutaneous injection of KA induced a range of seizure states, from mild wet dog shakes to generalized motor seizures. Northern blot analysis of hippocampal mRNA revealed an increase in both prodynorphin and proenkephalin mRNA levels which corresponded to the intensity of the convulsions. Conversely, hippocampal levels of immunoreactive dynorphin A (1-8) and [Met]5-enkephalin were decreased as a function of seizure frequency and intensity. The time course of KA-induced alterations in prodynorphin and proenkephalin mRNA and peptide levels was also investigated. Hippocampal prodynorphin mRNA levels rose at a dramatic rate. At 3 h following KA administration, mRNA levels were maximally elevated approximately 13-fold. The levels decreased over a 48 h period, eventually reaching control values. In contrast, proenkephalin mRNA levels increased more slowly. At 24 h, a maximal 24-fold increase was observed. At 72 h after injection, proenkephalin mRNA levels were still slightly elevated. In the same experiment, immunoreactive enkephalin peptide levels, although somewhat decreased at 3-12 h, began to increase between 12 and 24 h after injection, and were still rising at 72 h. In marked contrast, immunoreactive dynorphin peptide levels ranged from 40% to 80% of control values at all times tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective alteration of cytokeratin intermediate filament by cyclosporine A is a lethal toxicity in PTK2 cell cultures

The cytoplasm of eukaryotic cells contain a series of three filamentous structures, microtubules, microfilaments, and intermediate filaments that are termed the cytoskeleton. Cytokeratin, one type of intermediate filament, has no known physiological function, yet, can comprise up to 30% of the total cytoplasmic protein content. As there are no selective toxins to cytokeratins, it is not known if alterations to these hydrophobic filaments is a lethal event. Cyclosporine A, a novel hydrophobic immunosuppressant compound used to prevent allograft rejection, may show a selective toxicity to the cytokeratin filaments. This effect is seen in PtK2 cell cultures as a single large perinuclear aggregate of collapsed cytokeratin filaments (5 mM, 72 hr). Microtubules and microfilaments are not affected in PtK2 cell cultures (5 mM, 72 hr). Increased LDH levels into cell culturing media occur soon after cyclosporine exposure to PtK2 cell cultures (5 mM, 2 hr). Cytokeratin filaments show no changes at 12 hr exposure but show thickening, decreased plasma membrane attachments and some peri-nuclear ring formations at 24 hr (5 mM, 24 hr). Cyclosporine G, an analog of cyclosporine A, does not exhibit the cytokeratin filament collapse (5 mM, 72 hr). The effect of cyclosporine A on DNA binding protein (Mr 64 kd), believed to be a nuclear scaffolding protein related to intermediate filaments, exhibited an early invagination and folding of the nuclear membrane (5 mM, 4 hr). Due to a hydrophobic bonding potential between cyclosporine A and cytokeratin and cytokeratin-like intermediate filaments, cyclosporin A may be a selective cytokeratin toxin. Alteration of the cytokeratin filaments in PtK2 cell cultures may be a lethal event.

Prediction of prolyl residues in cis-conformation in protein structures on the basis of the amino acid sequence

In proteins most peptide bonds are in trans-conformation: the torsion angle omega = 180 degrees. Only few show cis-conformation in known protein structures (omega = 0 degrees). Most of them are prolyl residues. About 6% of about 4000 prolyl residues are in cis-conformation. Between trans- and cis-prolyl residues significant differences are observed in the surrounding sequences. E.g. there are large amounts of aromatic residues N-terminally in case of cis-prolyl residues, but in the case of trans-prolyl residues more aromatic amino acids occur C-terminally. But in all cases there are only complex patterns which are indicative of cis- and trans-conformation, respectively. Considering the neighbours (+/- 6 residues) of prolyl residues and their physicochemical properties we find 6 different patterns which allow one to assign correctly about 75% of known cis-structured prolyl residues, whereby no false positive one is predicted.

A Candida albicans homolog of a human cyclophilin gene encodes a peptidyl-prolyl cis-trans isomerase

A Candida albicans cDNA and its genomic counterpart were isolated from lambda phage libraries using a human T-cell cyclophilin (Cyp) cDNA as a hybridization probe. The clones contain a 486-bp open reading frame predicting a 162-amino acid, approx. 18 kDa protein which is similar in size to, and which shares 68 and 81% homology with, human T-cell Cyp and cytosolic Saccharomyces cerevisiae Cyp, respectively. Northern blots show the presence of a single mRNA species of about 800 bp. However, genomic Southern blots suggest the presence of at least one other Cyp-related gene in C. albicans. The cDNA was engineered for expression in Escherichia coli, and the resulting recombinant protein, like mammalian Cyps, exhibited a peptidyl-prolyl cis-trans isomerase (PPIase) activity which was sensitive to inhibition by cyclosporin A in vitro. These results indicate that the gene which we have cloned encodes a C. albicans Cyp. We designate this gene CYP1 (cyclophilin). Interestingly, the predicted C. albicans protein contains only two cysteine residues which do not align with any of the four cysteines conserved among mammalian Cyps. This suggests that the PPIase catalytic mechanism may not involve an enzyme-bound hemithioorthoamide, as previously reported for porcine Cyp.

The presence of two classes of high-affinity cyclosporin A binding sites in mitochondria. Evidence that the minor component is involved in the opening of an inner-membrane Ca(2+)-dependent pore

The inner membrane of rat liver mitochondria contains a reversible Ca(2+)-dependent pore, opening of which is largely blocked by cyclosporin A. Analyses of [3H]cyclosporin binding to rat liver mitochondria demonstrate two classes of high-affinity binding site with capacities of less than 5 pmol and approximately 60 pmol cyclosporin.mg mitochondrial protein-1 in addition to partitioning into membrane phospholipids (0.03 pmol.mg mitochondrial protein.nM-1). Direct measurement [14C]sucrose entry into the matrix space indicates that cyclosporin A inhibits pore opening by interacting with the low-capacity sites. The same low-capacity sites (Kd cyclosporin, 8 nM) are possibly attributable to peptidylprolyl cis-trans-isomerase, although investigation of pore state interconversion from the rapid kinetics of [14C]sucrose entrapment in the matrix space does not indicate that cyclosporin-sensitive prolyl isomerization occurs at the actual step of pore opening/closure. It is suggested that the low-capacity cyclosporin-binding component may stabilize the open pore state; this is supported by the observations that Ca2+ decreases cyclosporin binding to this component and that cyclosporin brings about closure of the pre-opened pore. The implications for the possible number of functional pores in mitochondria are discussed.

Crystallisation and preliminary X-ray diffraction studies of cyclophilin-tetrapeptide and cyclophilin-cyclosporin complexes

Recombinant human cyclophilin has been co-crystallised with a number of peptides to give crystals suitable for X-ray analysis. The crystal complexes for which heavy-atom derivatives have been prepared and X-ray data collected are: cyclophilin with N-acetyl-Ala-Ala-Pro-Ala-amidomethyl-coumarin (I) which crystallises in space group P2(1)2(1)2(1) with a = 108.2, b = 123.0, c = 35.8 A, and cyclophilin with cyclosporin (II) which crystallises as tetragonal plates in space group P4(1)2(1)2 or P4(3)2(1)2 with a = b = 94.98, c = 278.55 A.

Isotope-edited NMR of cyclosporin A bound to cyclophilin: evidence for a trans 9,10 amide bond

The binding of a 13C-labeled cyclosporin A (CsA) analog to cyclophilin (peptidyl prolyl isomerase) was examined by means of isotope-edited nuclear magnetic resonance (NMR) techniques. A trans 9,10 peptide bond was adopted when CsA was bound to cyclophilin, in contrast to the cis 9,10 peptide bond found in the crystalline and solution conformations of CsA. Furthermore, nuclear Overhauser effects (NOEs) were observed between the zeta 3 and epsilon 3 protons of the methylleucine (MeLeu) residue at position 9 of CsA and tryptophan121 (Trp121) and phenylalanine (Phe) protons of cyclophilin, suggesting that the MeLeu9 residue of CsA interacts with cyclophilin. These results illustrate the power of isotope-edited NMR techniques for rapidly providing useful information about the conformations and active site environment of inhibitors bound to their target enzymes.

Two distinct signal transmission pathways in T lymphocytes are inhibited by complexes formed between an immunophilin and either FK506 or rapamycin

Proliferation and immunologic function of T lymphocytes are initiated by signals from the antigen receptor that are inhibited by the immunosuppressant FK506 but not by its structural analog, rapamycin. On the other hand, interleukin 2 (IL-2)-induced signals are blocked by rapamycin but not by FK506. Remarkably, these two drugs inhibit each other's actions, raising the possibility that both act by means of a common immunophilin (immunosuppressant binding protein). We find that the dissociation constant of rapamycin to the FK506 binding protein FKBP (Kd = 0.2 nM) is close to the dissociation constant of FK506 to FKBP (Kd = 0.4 nM) and to their effective biologic inhibitory concentrations. However, an excess of rapamycin is needed to revert FK506-mediated inhibition of IL-2 production, apoptosis, and transcriptional activation of NF-AT, a T-cell-specific transcription factor necessary for IL-2 gene activation. Similarly, an excess of FK506 is needed to revert rapamycin-mediated inhibition of IL-2-induced proliferation. The drug concentrations required for antagonism may be explained by the relative affinity of the drugs to, and by the abundance of, the immunophilin FKBP. FKBP has been shown to catalyze the interconversion of the cis- and trans-rotamers of the peptidyl-prolyl amide bond of peptide substrates; here we show that rapamycin, like FK506, is a potent inhibitor of the rotamase activity of FKBP (Ki = 0.2 nM). Neither FKBP binding nor inhibition of rotamase activity of FKBP alone is sufficient to explain the biologic actions of these drugs. Rather, these findings suggest that immunophilin bound to FK506 interferes with antigen receptor-induced signals, while rapamycin bound to the immunophilin interferes with IL-2-induced signals.

Effects of cyclosporine on immunologic mechanisms in psoriasis

A major impetus for further investigation of cellular immunologic mechanisms in psoriasis has been the discovery that cyclosporine, a potent immunosuppressive, is highly effective in the treatment of psoriasis. Cyclosporine has significant inhibitory effects on the ability of T cells to become activated. However, a direct activity of this drug on human keratinocyte signal transduction or growth has been difficult to demonstrate at relevant concentrations. Nevertheless, treatment of psoriasis or of 12-O-tetradecanoyl phorbol-13-acetate-treated murine skin with cyclosporine does reverse many epidermal abnormalities that are common to these two systems. This suggests that the compound exerts an indirect effect on epidermal keratinocytes in vivo, perhaps through immunocyte inhibition. During treatment of psoriasis patients, cyclosporine therapy resulted in selective changes in the numbers and functions of certain antigen-presenting cell subsets (which were distinct from Langerhans cells) and T-cell subsets. These changes were accompanied by indirect evidence of decreased T-cell lymphokine release. Lesional activity of cyclosporine-treated psoriasis patients was closely correlated with the degree of T-cell activation caused by antigen-presenting cells. Cyclosporine inhibition of lymphokine or cytokine release may result in decreased recruitment of non-Langerhans antigen-presenting cells into the epidermis and thus decreased immunoreactivity in the lesion.

Structure and expression of cytosolic cyclophilin/peptidyl-prolyl cis-trans isomerase of higher plants and production of active tomato cyclophilin in Escherichia coli

cDNA clones encoding proteins of approximately 18 kDa in which 83% of the amino acids are conserved relative to the published sequences of mammalian cyclophilin/rotamase (CyP) have been isolated from tomato, maize, and Brassica napus. In correspondence with the mammalian genes, but in contrast with the Neurospora gene and one yeast CyP gene, the plant CyP genes encode only mature proteins lacking transit peptides. RNA blot analyses demonstrate that CyP genes are expressed in all plant organs tested. Southern blots of genomic DNA indicate that there are small families (two to eight members) of CyP-related genes in maize and B. napus. A vector was constructed for expression of the tomato cDNA in E. coli. SDS/polyacrylamide gels show that extracts of appropriately induced cells harboring this vector contain nearly 40% of the protein as a single approximately 18-kDa band. While the majority of this protein is sequestered in insoluble inclusion bodies, the soluble extracts have higher levels of peptidyl-prolyl cis-trans isomerase (rotamase) activity than extracts of wild-type cells. This additional activity is sensitive to inhibition by the cyclic undecapeptide cyclosporin A.

Intracellular targets of cyclosporine

Since cyclosporine was first reported to improve psoriasis, investigators have been trying to determine its mechanism of action. In addition to the well-documented effects on cytokine production by T lymphocytes, a direct effect on keratinocytes has been proposed. Cyclophilin and calmodulin, two proteins that are present in both lymphocytes and keratinocytes, have been considered as possible intracellular targets for cyclosporine. Cyclophilin binds cyclosporine with high affinity and the ability to bind cyclophilin correlates with the immunosuppressive effects of cyclosporine analogs. Cyclophilin is identical to peptidyl-prolyl cis-trans isomerase, an enzyme that catalyzes refolding of proteins. The process of protein folding may be important in DNA-protein and protein-protein interactions. Calmodulin is an intracellular calcium-binding protein that is important in the regulation of cell proliferation. Cyclosporine binds to calmodulin with low affinity, and such binding of cyclosporine isomers does not reflect their immunosuppressive activity. The physiologic importance of calmodulin-to-cyclosporine binding is controversial.