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

Calcineurin inhibitor nephrotoxicity

The use of the calcineurin inhibitors cyclosporine and tacrolimus led to major advances in the field of transplantation, with excellent short-term outcome. However, the chronic nephrotoxicity of these drugs is the Achilles' heel of current immunosuppressive regimens. In this review, the authors summarize the clinical features and histologic appearance of both acute and chronic calcineurin inhibitor nephrotoxicity in renal and nonrenal transplantation, together with the pitfalls in its diagnosis. The authors also review the available literature on the physiologic and molecular mechanisms underlying acute and chronic calcineurin inhibitor nephrotoxicity, and demonstrate that its development is related to both reversible alterations and irreversible damage to all compartments of the kidneys, including glomeruli, arterioles, and tubulo-interstitium. The main question--whether nephrotoxicity is secondary to the actions of cyclosporine and tacrolimus on the calcineurin-NFAT pathway--remains largely unanswered. The authors critically review the current evidence relating systemic blood levels of cyclosporine and tacrolimus to calcineurin inhibitor nephrotoxicity, and summarize the data suggesting that local exposure to cyclosporine or tacrolimus could be more important than systemic exposure. Finally, other local susceptibility factors for calcineurin inhibitor nephrotoxicity are reviewed, including variability in P-glycoprotein and CYP3A4/5 expression or activity, older kidney age, salt depletion, the use of nonsteroidal anti-inflammatory drugs, and genetic polymorphisms in genes like TGF-beta and ACE. Better insight into the mechanisms underlying calcineurin inhibitor nephrotoxicity might pave the way toward more targeted therapy or prevention of calcineurin inhibitor nephrotoxicity.

Parvulin (Par14), a peptidyl-prolyl cis-trans isomerase, is a novel rRNA processing factor that evolved in the metazoan lineage

Although parvulin (Par14/eukaryotic parvulin homolog), a peptidyl-prolyl cis-trans isomerase, is found associated with the preribosomal ribonucleoprotein (pre-rRNP) complexes, its roles in ribosome biogenesis remain undetermined. In this study, we describe a comprehensive proteomics analysis of the Par14-associated pre-rRNP complexes using LC-MS/MS and a knockdown analysis of Par14. Together with our previous results, we finally identified 115 protein components of the complexes, including 39 ribosomal proteins and 54 potential trans-acting factors whose yeast homologs are found in the pre-rRNP complexes formed at various stages of ribosome biogenesis. We give evidence that, although Par14 exists in both the phosphorylated and unphosphorylated forms in the cell, only the latter form is associated with the pre-40 S and pre-60 S ribosomal complexes. We also show that Par14 co-localizes with the nucleolar protein B23 during the interphase and in the spindle apparatus during mitosis and that actinomycin D treatment results in the exclusion of Par14 from the nucleolus. Finally we demonstrate that knockdown of Par14 mRNA decelerates the processing of pre-rRNA to 18 and 28 S rRNAs. We propose that Par14 is a component of the pre-rRNA complexes and functions as an rRNA processing factor in ribosome biogenesis. As the amino acid sequence of Par14 including that in the amino-terminal pre-rRNP binding region is conserved only in metazoan homologs, we suggest that its roles in ribosome biogenesis have evolved in the metazoan lineage.

Accessory proteins are vital for the functional expression of certain G protein-coupled receptors

Certain G protein-coupled receptors (GPCRs) fail to be expressed in a functional form at the cell surface. This may be due to the improper folding and maturation of GPCRs which are highly intricate events that need to take place before these integral membrane proteins can be transported from the endoplasmic reticulum (ER), where they are synthesised, to the plasma membrane which is their site of action. Once at the plasma membrane they act as the recognition elements for a vast range of endogenous ligands including biogenic amines, peptides, glycoproteins, lipids, nucleotides, ions and proteases. The assistance of molecular chaperones has been widely implicated in the trafficking and function of these proteins. Characterisation of certain GPCRs has identified a novel group of membrane proteins collectively named 'accessory proteins' as being important for the expression and function of GPCRs. In this review we will summarise the importance of these accessory proteins for the function of their respective GPCRs. Understanding their roles in GPCR expression would not only give us an insight into these receptors from a cell biological point of view but may also potentially lead to the development of novel therapeutics.

Introduction: cell-based assays for high-throughput screening

Cell-based assays represent approximately half of all high-throughput screens (HTS) currently performed. Here we review the history and status of HTS, and summarize some of the challenges and benefits associated with the use of cell-based assays in HTS, drawing upon themes that will reemerge in subsequent chapters in this book. Approaches for successful experimental design and execution of cell-based HTS are introduced, including strategies for assay development, implementation of primary and secondary screens, and target identification. In doing so, we hope to provide a comprehensive review of the cell-based HTS process and an introduction to the methodologies and techniques described in this book.

Host factors involved in resistance to retroviral infection

Viral replication requires the help of host cell factors, whose species specificity may affect viral tropism. On the other hand, there exist host factors that restrict viral replication. The anti-viral system mediated by some of these restriction factors, which is termed intrinsic immunity and is distinguished from conventional innate and adaptive immunity, has been described as playing an important role in making species-specific barriers against viral infection. Here, we describe the current progress in understanding of such restriction factors against retroviral replication, focusing on TRIM5alpha and APOBEC, whose anti-retroviral effects have recently been recognized. Additionally, we mention cyclophilin A, which is essential for HIV-1 replication in human cells and may affect viral tropism. Understanding of these host factors would contribute to identification of the determinants for viral tropism.

A cyclophilin A inducible expressed in gonad of zhikong scallop Chlamys farreri

Cyclophilin A (CypA), a receptor for the immunosuppressive agent cyclosporin A (CsA), is a cis-trans peptidyl-prolyl isomerase (PPIase) which accelerates the cis-trans isomerization of prolyl-peptide bonds, interacts with a variety of proteins and therefore regulates their activities. One CypA (designated CfCypA) cDNA was cloned from Chlamys farreri by expressed sequence tag (EST) and rapid amplification of cDNA ends (RACE) techniques. The full-length cDNA of CfCypA consisted of 1,248 nucleotides with a canonical polyadenylation signal sequence AATAAA, a poly (A) tail, and an open reading frame (ORF) of 495 nucleotides encoding a polypeptide of 164 amino acids. The deduced amino acid sequence shared high similarity with CypA from the other species, indicating that CfCypA should be a new member of the CypA family. Quantitative real-time (RT) PCR was employed to assess the mRNA expression of CfCypA in various tissues and its temporal expression in haemocytes and gonad of scallops challenged with Vibrio anguillarum. The mRNA transcripts of CfCypA could be detected in all the examined tissues with highest expression level in gonad. After bacterial challenge, the expression level of CfCypA was almost unchanged in haemocytes, but up-regulated in gonad and increased to the peak (22.59-fold; P < 0.05) at 4 h post-injection, and then dropped to the original level at 8 h post-injection. These results indicated that CfCypA was constitutive expressed in haemocytes, but could be induced in gonad, and perhaps played a critical role in response to the bacterial challenge in gonad.

Evidence for the role of calcineurin in morphogenesis and calcium homeostasis during mycelium-to-yeast dimorphism of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is a dimorphic fungus that causes paracoccidioidomycosis, the most prevalent human deep mycosis in Latin America. The dimorphic transition from mycelium to yeast (M-Y) is triggered by a temperature shift from 25 degrees C to 37 degrees C and is critical for pathogenicity. Intracellular Ca(2+) levels increased in hyphae immediately after temperature-induced dimorphism. The chelation of Ca(2+) with extracellular (EGTA) or intracellular (BAPTA) calcium chelators inhibited temperature-induced dimorphism, whereas the addition of extracellular Ca(2+) accelerated dimorphism. The calcineurin inhibitor cyclosporine A (CsA), but not tacrolimus (FK506), effectively decreased cell growth, halted the M-Y transition that is associated with virulence, and caused aberrant growth morphologies for all forms of P. brasiliensis. The difference between CsA and FK506 was ascribed by the higher levels of cyclophilins contrasted to FKBPs, the intracellular drug targets required for calcineurin suppression. Chronic exposure to CsA abolished intracellular Ca(2+) homeostasis and decreased mRNA transcription of the CCH1 gene for the plasma membrane Ca(2+) channel in yeast-form cells. CsA had no detectable effect on multidrug resistance efflux pumps, while the effect of FK506 on rhodamine excretion was not correlated with the transition to yeast form. In this study, we present evidence that Ca(2+)/calmodulin-dependent phosphatase calcineurin controls hyphal and yeast morphology, M-Y dimorphism, growth, and Ca(2+) homeostasis in P. brasiliensis and that CsA is an effective chemical block for thermodimorphism in this organism. The effects of calcineurin inhibitors on P. brasiliensis reinforce the therapeutic potential of these drugs in a combinatory approach with antifungal drugs to treat endemic paracoccidioidomycosis.

Ricinus communis cyclophilin: functional characterisation of a sieve tube protein involved in protein folding

The phloem translocation stream of the angiosperms contains a special population of proteins and RNA molecules which appear to be produced in the companion cells prior to being transported into the sieve tube system through the interconnecting plasmodesmata. During this process, these non-cell-autonomous proteins are thought to undergo partial unfolding. Recent mass spectroscopy studies identified peptidyl-prolyl cis-trans isomerase (PPIases) as potential molecular chaperones functioning in the phloem translocation stream (Giavalisco et al. 2006). In the present study, we describe the cloning and characterisation of a castor bean phloem cyclophilin, RcCYP1 that has high peptidyl-prolyl cis-trans isomerase activity. Equivalent enzymatic activity was detected with phloem sap or purified recombinant (His)(6)-tagged RcCYP1. Mass spectrometry analysis of proteolytic peptides, derived from a 22 kDa band in HPLC-fractionated phloem sap, immunolocalisation studies and Western analysis of proteins extracted from castor bean tissues/organs indicated that RcCYP1 is an abundant protein in the companion cell-sieve element complex. Microinjection experiments established that purified recombinant (His)(6)-RcCYP1 can interact with plasmodesmata to both induce an increase in size exclusion limit and mediate its own cell-to-cell trafficking. Collectively, these findings support the hypothesis that RcCYP1 plays a role in the refolding of non-cell-autonomous proteins after their entry into the phloem translocation stream.

Cyclophilin and the regulation of symbiosis in Aiptasia pallida

The sea anemone Aiptasia pallida, symbiotic with intracellular dinoflagellates, expresses a peptydyl-prolyl cis-trans isomerase (PPIase) belonging to the conserved family of cytosolic cyclophilins (ApCypA). Protein extracts from A. pallida exhibited PPIase activity. Given the high degree of conservation of ApCypA and its known function in the cellular stress response, we hypothesized that it plays a similar role in the cnidarian-dinoflagellate symbiosis. To explore its role, we inhibited the activity of cyclophilin with cyclosporin A (CsA). CsA effectively inhibited the PPIase activity of protein extracts from symbiotic A. pallida. CsA also induced the dose-dependent release of symbiotic algae from host tissues (bleaching). Laser scanning confocal microscopy using superoxide and nitric oxide-sensitive fluorescent dyes on live specimens of A. pallida revealed that CsA strongly induced the production of these known mediators of bleaching. We tested whether the CsA-sensitive isomerase activity is important for maintaining the activity of the antioxidant enzyme superoxide dismutase (SOD). SOD activity of protein extracts was not affected by pre-incubation with CsA in vitro.

Effects of FK506 on ca release channels (review)

Tacrolimus (FK506), which was isolated from the fermentation broth of Streptomyces tsukubaensis No. 9993, has an immunosuppressive effect. In T-lymphocytes, FK506 binds to the intracellular receptor, a 12-kDa FK506-binding protein (FKBP12). The FK506-FKBP12 complex binds to the phosphatase calcineurin (CN) and inhibits the activity of CN. By inhibition of the activity of CN, dephosphorylation of a nuclear factor of activated T-cells (NFAT) is inhibited, and translocation of the NFAT to the nucleus is suppressed. Thereby, the production of T-cell-derived mediators such as interleukin 2 (IL-2) is inhibited, and the proliferation of cytotoxic T-cells is suppressed. In muscle cells, FKBP12 and FKBP12.6 are associated with ryanodine-sensitive Ca²⁺ release channels (ryanodine receptors: RyRs) on the skeletal and cardiac muscle sarcoplasmic reticulum (SR), respectively. FK506 modulates the RyR by dissociating FKBP12 or FKBP12.6 from the RyR complex. FKBP12 is also associated with inositol 1,4,5-trisphosphate (IP₃)-sensitive Ca²⁺ release channels (IP₃ receptors: IP₃Rs) on the endoplasmic reticulum (ER) of non-muscle cells. The IP₃R-FKBP12 complex binds to CN, which dephosphorylates the protein kinase C (PKC) phosphorylation site on the receptor. When FKBP12 is dissociated from the IP₃R complex by FK506, CN is also dissociated from the IP₃R. Thereby, the IP₃R is phosphorylated by PKC, and the receptor is modulated. Recently, it was found that FK506 itself induces Ca²⁺ release through RyRs in some tissues.

Thioredoxins and glutaredoxins as facilitators of protein folding

Thiol-disulfide oxidoreductase systems of bacterial cytoplasm and eukaryotic cytosol favor reducing conditions and protein thiol groups, while bacterial periplasm and eukaryotic endoplasmatic reticulum provide oxidizing conditions and a machinery for disulfide bond formation in the secretory pathway. Oxidoreductases of the thioredoxin fold superfamily catalyze steps in oxidative protein folding via protein-protein interactions and covalent catalysis to act as chaperones and isomerases of disulfides to generate a native fold. The active site dithiol/disulfide of thioredoxin fold proteins is CXXC where variations of the residues inside the disulfide ring are known to increase the redox potential like in protein disulfide isomerases. In the catalytic mechanism thioredoxin fold proteins bind to target proteins through conserved backbone-backbone hydrogen bonds and induce conformational changes of the target disulfide followed by nucleophilic attack by the N-terminally located low pK(a) Cys residue. This generates a mixed disulfide covalent bond which subsequently is resolved by attack from the C-terminally located Cys residue. This review will focus on two members of the thioredoxin superfamily of proteins known to be crucial for maintaining a reduced intracellular redox state, thioredoxin and glutaredoxin, and their potential functions as facilitators and regulators of protein folding and chaperone activity.

Genetic transformation of the dermatophyte, Trichophyton mentagrophytes, based on the use of G418 resistance as a dominant selectable marker

BACKGROUND

Dermatophytes are closely related keratinophilic fungal pathogens and are the causative agents of a superficial cutaneous infection called dermatophytosis (ringworm). A lack of gene manipulation techniques has prevented detailed analyses of the mechanisms of host invasion by dermatophytes. We have introduced the tetracycline-regulatable (TR) gene expression system into dermatophytes to facilitate functional analyses of genes essential for growth and virulence. As the TR gene expression system consists of two plasmid vector components, two dominant selectable markers are required for genetic transformation. In dermatophytes, only the hygromycin B phosphotransferase gene (hph) is available as a selectable marker.

OBJECTIVE

We investigated the possibility of G418 resistance as a secondary selectable marker for genetic transformation in dermatophytes.

METHODS

A series of plasmid vectors carrying the neomycin phosphotransferase gene (nptII) were introduced into the protoplasts of Trichophyton mentagrophytes, one of the most clinically important dermatophyte species, by polyethylene glycol (PEG)-mediated transformation. Transformants were selected on selective medium containing G418 at 300-500 microg/ml.

RESULTS

Molecular biological analyses indicated that colonies appearing on the selective medium harbored nptII in their chromosomes. Colonies produced from protoplasts transformed with the enhanced green fluorescent protein (eGFP) gene-T. mentagrophytes cyclophilin cDNA (TmcypB) fusion vector also exhibited GFP fluorescence throughout their mycelia, but accumulation of the GFP-TmCYPB fusion protein in specific intracellular compartments was not observed.

CONCLUSIONS

This study has provided a new selectable marker for genetic transformation in dermatophytes.

Prolyl cis-trans isomerization as a molecular timer

Proline is unique in the realm of amino acids in its ability to adopt completely distinct cis and trans conformations, which allows it to act as a backbone switch that is controlled by prolyl cis-trans isomerization. This intrinsically slow interconversion can be catalyzed by the evolutionarily conserved group of peptidyl prolyl cis-trans isomerase enzymes. These enzymes include cyclophilins and FK506-binding proteins, which are well known for their isomerization-independent role as cellular targets for immunosuppressive drugs. The significance of enzyme-catalyzed prolyl cis-trans isomerization as an important regulatory mechanism in human physiology and pathology was not recognized until the discovery of the phosphorylation-specific prolyl isomerase Pin1. Recent studies indicate that both phosphorylation-dependent and phosphorylation-independent prolyl cis-trans isomerization can act as a novel molecular timer to help control the amplitude and duration of a cellular process, and prolyl cis-trans isomerization might be a new target for therapeutic interventions.

Anti-Trypanosoma cruzi effects of cyclosporin A derivatives: possible role of a P-glycoprotein and parasite cyclophilins

Cyclophilins are target molecules for cyclosporin A (CsA), an immunosuppressive antimicrobial drug. We have previously reported the in vitro anti-Trypanosoma cruzi activity of H-7-94 and F-7-62 non-immunosuppressive CsA analogues. In this work, we continue the study of the parasiticidal effect of H-7-94 and F-7-62 CsA analogues in vitro and in vivo and we analyse 3 new CsA derivatives: MeIle-4-CsA (NIM 811), MeVal-4-CsA (MeVal-4) and D-MeAla-3-EtVal-4-CsA, (EtVal-4). The most efficient anti-T. cruzi effect was observed with H-7-94, F-7-62 and MeVal-4 CsA analogues evidenced as inhibition of epimastigote proliferation, trypomastigote penetration, intracellular amastigote development and in vivo T. cruzi infection. This trypanocidal activity could be due to inhibition of the peptidyl prolyl cis-trans isomerase activity on the T. cruzi recombinant cyclophilins tested. Furthermore, CsA and F-7-62 derivative inhibited the efflux of rhodamine 123 from T. cruzi epimastigotes, suggesting an interference with a P-glycoprotein activity. Moreover, H-7-94 and F-7-62 CsA analogues were not toxic as shown by cell viability and by aminopyrine-N-demethylase activity on mammalian cells. Our results show that H-7-94, F-7-62 and MeVal-4 CsA analogues expressed the highest inhibiting effects on T. cruzi, being promissory parasiticidal drugs worthy of further studies.

Sensitivity of hepatitis C virus to cyclosporine A depends on nonstructural proteins NS5A and NS5B

HCV re-occurs after liver transplantation and increases mortality. Cyclosporine, but not tacrolimus, has potent antiviral effects against HCV replication in cell culture. To determine the conditions, if any, under which HCV is susceptible to cyclosporine in vivo, we selected for cyclosporine-resistant mutant HCV in vitro. The resulting mutations were mapped to x-ray crystallographic structures and sequence databases. Mutations selected by cyclosporine were clustered in the nonstructural (NS) proteins NS5A and NS5B. Different sets of mutations in NS5A, paired with the same 2 NS5B mutations, conferred different levels of cyclosporine resistance when engineered back into the HCV replicon. Mutations in NS5B are structurally consistent with a proposed model of regulation of RNA binding by cyclophilin B (CyPB). These mutations also highlight a natural polymorphism between different HCV genotypes that correlates with the variation in response to cyclosporine A (CsA) noted in some clinical trials. Replicons engineered to have mutations in only NS5A (P < or = 0.0001) or only NS5B (P = 0.002) suggest that while both NS5A or NS5B variants alter cyclosporine susceptibility, NS5A has the largest effect.

CONCLUSION

Preexisting sequence variation could alter the effect of cyclosporine on HCV in vivo.

Inhibition of endogenous MHC class II-restricted antigen presentation by tacrolimus (FK506) via FKBP51

The effect of tacrolimus (FK506) on down-regulation of IL-2 production by T cells is considered to be mainly responsible for its strong suppression of immunological events. In this study, we show that FK506 also has an affect on antigen presentation by antigen-presenting cells in vitro. FK506 was able to inhibit the presentation of endogenous MHC class II-restricted minor histocompatibility antigens in primary dendritic cells (DC) in vitro, but cyclosporine A (CsA) and rapamycin (RAP) were not. RNA interference (RNAi)-mediated reduction of endogenous FK506-binding protein (FKBP)51 expression resulted in a marked decrease in antigen presentation, suggesting that FKBP51 plays a role in endogenous MHC class II-restricted antigen presentation. Since our model used naturally expressed cytosolic antigens in primary DC, these effects might have been due to novel properties of the immunosuppressive drugs and may allow us to elucidate a new paradigm for the immunosuppressive mechanism of FK506.

Immunoglobulin-E-mediated reactivity to self antigens: a controversial issue

Immunoglobulin E (IgE) reactivity to self antigens is well established in vitro by ELISA, inhibition ELISA, Western blot analyses and T cell proliferation experiments. In vivo, IgE-binding self antigens are able to elicit strong type I reactions in sensitized individuals and, in the case of human manganese superoxide dismutase, to elicit eczematous reactions on healthy skin areas of patients suffering from atopic eczema. The reactions against self antigens sharing structural homology with environmental allergens can be plausibly explained by molecular mimicry between common B cell epitopes. For the second class of IgE-binding self antigens without sequence homology to known allergens, it is still unclear if the structures are able to induce a B cell switch to IgE production, or if the reactivity is due to sequence similarity shared with not yet detected environmental allergens. However, in all cases, cross-reactivity is never complete, indicating either a lower affinity of IgE antibodies to self allergens than to the homologous environmental allergens or the presence of additional B cell epitopes on the surface of the environmental allergens, or both. Increasing evidence shows that self allergens could play a decisive role in the exacerbation of long-lasting atopic diseases. However, the only observation supporting a clinical role of IgE-mediated autoreactivity is confined to the fact that IgE levels against self antigens correlate with disease severity.

Analysis of human cell heterokaryons demonstrates that target cell restriction of cyclosporine-resistant human immunodeficiency virus type 1 mutants is genetically dominant

The host cell protein cyclophilin A (CypA) binds to CA of human immunodeficiency virus type 1 (HIV-1) and promotes HIV-1 infection of target cells. Disruption of the CypA-CA interaction, either by mutation of the CA residue at G89 or P90 or with the immunosuppressive drug cyclosporine (CsA), reduces HIV-1 infection. Two CA mutants, A92E and G94D, previously were identified by selection for growth of wild-type HIV-1 in cultures of CD4(+) HeLa cell cultures containing CsA. Interestingly, infection of some cell lines by these mutants is enhanced in the presence of CsA, while in other cell lines these mutants are minimally affected by the drug. Little is known about this cell-dependent phenotype of the A92E and G94D mutants, except that it is not dependent on expression of the host factor TRIM5alpha. Here, we show that infection by the A92E and G94D mutants is restricted at an early post-entry stage of the HIV-1 life cycle. Analysis of heterokaryons between CsA-dependent HeLa-P4 cells and CsA-independent 293T cells indicated that the CsA-dependent infection by A92E and G94D mutants is due to a dominant cellular restriction. We also show that addition of CsA to target cells inhibits infection by wild-type HIV-1 prior to reverse transcription. Collectively, these results support the existence of a cell-specific human cellular factor capable of restricting HIV-1 at an early post-entry step by a CypA-dependent mechanism.

Cyclosporine A in the treatment of psoriasis: a clinical and mechanistic perspective

Cyclosporine A, a unique immunomodulatory agent, has been used increasingly over the last 5 years in the management of severe psoriasis. The remarkable efficacy of this drug coupled with its known immunosuppressive properties have enabled a further appreciation of the role of the immune system in the induction and maintenance of psoriatic plaques. Although acting primarily on T lymphocytes, there is also evidence for an effect of cyclosporine A on other constitutive cell types within the skin. The future use of systemically administered cyclosporine A in the treatment of psoriasis and other cutaneous diseases is dependent on the successful balance of efficacy and side-effect profile; namely, the dose-related problems of hypertension and nephrotoxicity. As a result of the toxicity encountered with systemically administered cyclosporine A, attempts to formulate a successful topical preparation for use in cutaneous disease are being made. The advent of cyclosporine A provides the dermatologist with a new therapeutic strategem in the management of psoriasis, although the long-term safety of such interventional therapy remains to be discerned.

Hypothetical protein AF2241 from Archaeoglobus fulgidus adopts a cyclophilin-like fold

AF2241 is a hypothetical protein from Archaeoglobus fulgidus and it belongs to the PFam domain of unknown function 369 (DUF369). NMR structural determination reveals that AF2241 adopts a cyclophilin-like fold, with a beta-barrel core composed of eight beta-strands, one alpha-helix, and one 3(10) helix located at each end of the barrel. The protein displays a high structural similarity to TM1367, another member of DUF369 whose structure has been determined recently by X-ray crystallography. Structural similarity search shows that AF2241 also has a high similarity to human cyclophilin A, however, sequence alignment and electrostatic potential analysis reveal that the residues in the PPIase catalytic site of human cyclophilin A are not conserved in AF2241 or TM1367. Instead, a putative active site of AF2241 maps to a negatively charged pocket composed of 9 conserved residues. Our results suggest that although AF2241 adopts the same fold as the human cyclophilin A, it may have distinct biological function.

Structure-based identification of small molecule compounds targeting cell cyclophilin A with anti-HIV-1 activity

Cyclophilin A acts as protein folding chaperones and intracellular transports in many cellular processes. Previous studies have shown that cyclophilin A can interact with HIV-1 (human immunodeficiency virus type 1) gag protein and enhance viral infectivity. Many cyclophilin A inhibitors such as cyclosporin A can inhibit HIV-1 replication in vitro. Here, we report a structure-based identification of novel non-peptidic cyclophilin A inhibitors as anti-HIV lead compounds. Following a computer-aided virtual screening and subsequent surface plasmon resonance (SPR) analysis, 12 low molecular weight cyclophilin A ligands were selected for further evaluation of their in vitro inhibition of peptidyl-prolyl cis-trans isomerase (PPIase) activity of cyclophilin A and HIV-1 replication. Five of these compounds (FD5, FD8, FD9, FD10 and FD12) exhibited inhibition against both PPIase activity and HIV-1 infection. These active compounds will be used as leads for structure and activity relationship (SAR) and optimization studies in order to design more effective anti-HIV-1 therapeutics, and as probes for investigating the effect of cyclophilins on HIV-1 replication.

Cyclosporine inhibits mouse cytomegalovirus infection via a cyclophilin-dependent pathway specifically in neural stem/progenitor cells

The potential of neural stem and progenitor cell (NSPC) transplantation in neurodegenerative disease raises a concern about immunosuppressive agents and opportunistic neurotropic pathogens that may interfere with engraftment. Cytomegalovirus (CMV) is an important opportunistic pathogen infecting the central nervous system, where it may remain latent for life, following transplacental transmission. Cyclosporine (Cs), an immunosuppressive drug used in organ transplantation, where its use is associated with CMV reactivation, suppressed murine CMV (MCMV) infection in cultured NSPCs but not in fibroblasts. This activity of Cs appears to be mediated via cyclophilin (CyP) rather than via calcineurin. First, the calcineurin-specific inhibitor FK506 failed to suppress replication. Second, the CyP-specific inhibitor NIM811 strongly suppressed replication in NSPC. NSPCs maintained in the presence of NIM811 retained viral genomes for several weeks without detectable viral gene expression or obvious deleterious effects. The withdrawal of NIM811 reactivated viral replication, suggesting that the inhibitory mechanism was reversible. Finally, inhibition of endogenous CyP A (CyPA) by small interfering RNA also inhibited replication in NSPCs. These results show that MCMV replication depends upon cellular CyPA pathways in NSPCs (in a specific cell type-dependent fashion), that CyPA plays an important role in viral infection in this cell type, and that inhibition of viral replication via CyP leads to persistence of the viral genome without cell damage. Further, the calcineurin-signaling pathway conferring immunosuppression in T cells does not influence viral replication in a detectable fashion.

cDNA microarray analysis of cyclosporin A (CsA)-treated human peripheral blood mononuclear cells reveal modulation of genes associated with apoptosis, cell-cycle regulation and DNA repair

Cyclosporin A (CsA) is a potent immunosuppressant that has been extensively used to attenuate patient immune response following organ transplantation. The molecular biological mechanism of CsA has been extensively investigated in human T cells, and it has been shown to involve modulation of the intracellular calcineurin pathway. However, it is plausible that this chemical immunosuppressant certainly up- or down-regulate many other biochemical pathways of immune cells. In the present study, we used the cDNA microarray method to characterize the gene expression profile of human peripheral blood mononuclear cells (PBMC) treated in vitro with CsA and controls. The CsA treated PBMC displayed statistically significant induction of genes involved in the control of cell-cycle regulation (TRRAP), apoptosis/DNA repair (PRKDC, MAEA, TIA1), DNA metabolism/response to DNA damage stimulus (PRKDC, FEN1), transcription (NR4A2, THRA) and cell proliferation (FEN1, BIN1), whose data have permitted identification of target genes involved in CsA immunosuppression.

Structural basis for high-affinity peptide inhibition of human Pin1

Human Pin1 is a key regulator of cell-cycle progression and plays growth-promoting roles in human cancers. High-affinity inhibitors of Pin1 may provide a unique opportunity for disrupting oncogenic pathways. Here we report two high-resolution X-ray crystal structures of human Pin1 bound to non-natural peptide inhibitors. The structures of the bound high-affinity peptides identify a type-I beta-turn conformation for Pin1 prolyl peptide isomerase domain-peptide binding and an extensive molecular interface for high-affinity recognition. Moreover, these structures suggest chemical elements that may further improve the affinity and pharmacological properties of future peptide-based Pin inhibitors. Finally, an intramolecular hydrogen bond observed in both peptide complexes mimics the cyclic conformation of FK506 and rapamycin. Both FK506 and rapamycin are clinically important inhibitors of other peptidyl-prolyl cis-trans isomerases. This comparative discovery suggests that a cyclic peptide polyketide bridge, like that found in FK506 and rapamycin or a similar linkage, may significantly improve the binding affinity of structure-based Pin1 inhibitors.

Screening of immunophilin ligands by quantitative analysis of neurofilament expression and neurite outgrowth in cultured neurons and cells

Immunophilins are protein receptors for the immunosuppressant drugs FK506, cyclosporin A (CsA), and rapamycin. Two categories of immunophilins are the FK506-binding proteins (FKBPs), which bind to FK506, rapamycin, and CCI-779 and the cyclophilins, which bind to CsA. Reports have shown that immunophilins are expressed in the brain and spinal cord, are 10-100-fold higher in CNS tissue than immune tissue, and their expression is increased following nerve injury, suggesting that their chemical ligands may have therapeutic utility in the treatment of neurodegenerative diseases. In this study, we report the development and utility of a rapid neurofilament (NF) enzyme-linked immunosorbent assay (ELISA) to quantify neuronal survival and the Cellomics ArrayScan platform to quantify neurite outgrowth following treatment with immunophilin ligands. Cultured neurons or F-11 cells were treated with various immunophilin ligands for 72 or 96h and their promotion of neuronal survival and neurite outgrowth were determined. The results showed that all immunophilin ligands, in a concentration-dependent manner, significantly increased neuronal survival and neurite outgrowth, when compared to control cultures. Taken together, these results demonstrate the potential utility of the neurofilament ELISA and Cellomics ArrayScan platform to efficiently quantify neurotrophic effects of immunophilin ligands on cultured neurons and cell lines.

The peptidyl prolyl cis/trans isomerase FKBP38 determines hypoxia-inducible transcription factor prolyl-4-hydroxylase PHD2 protein stability

The heterodimeric hypoxia-inducible transcription factors (HIFs) are central regulators of the response to low oxygenation. HIF-alpha subunits are constitutively expressed but rapidly degraded under normoxic conditions. Oxygen-dependent hydroxylation of two conserved prolyl residues by prolyl-4-hydroxylase domain-containing enzymes (PHDs) targets HIF-alpha for proteasomal destruction. We identified the peptidyl prolyl cis/trans isomerase FK506-binding protein 38 (FKBP38) as a novel interactor of PHD2. Yeast two-hybrid, glutathione S-transferase pull-down, coimmunoprecipitation, colocalization, and mammalian two-hybrid studies confirmed specific FKBP38 interaction with PHD2, but not with PHD1 or PHD3. PHD2 and FKBP38 associated with their N-terminal regions, which contain no known interaction motifs. Neither FKBP38 mRNA nor protein levels were regulated under hypoxic conditions or after PHD inhibition, suggesting that FKBP38 is not a HIF/PHD target. Stable RNA interference-mediated depletion of FKBP38 resulted in increased PHD hydroxylation activity and decreased HIF protein levels and transcriptional activity. Reconstitution of FKBP38 expression abolished these effects, which were independent of the peptidyl prolyl cis/trans isomerase activity. Downregulation of FKBP38 did not affect PHD2 mRNA levels but prolonged PHD2 protein stability, suggesting that FKBP38 is involved in PHD2 protein regulation.

Catalytic mechanism of cyclophilin as observed in molecular dynamics simulations: pathway prediction and reconciliation of X-ray crystallographic and NMR solution data

Cyclophilins are proteins that catalyze X-proline cis-trans interconversion, where X represents any amino acid. Its mechanism of action has been investigated over the past years but still generates discussion, especially because until recently structures of the ligand in the cis and trans conformations for the same system were lacking. X-ray crystallographic structures for the complex cyclophilin A and HIV-1 capsid mutants with ligands in the cis and trans conformations suggest a mechanism where the N-terminal portion of the ligand rotates during the cis-trans isomerization. However, a few years before, a C-terminal rotating ligand was proposed to explain NMR solution data. In the present study we use molecular dynamics (MD) simulations to generate a trans structure starting from the cis structure. From simulations starting from the cis and trans structures obtained through the rotational pathways, the seeming contradiction between the two sets of experimental data could be resolved. The simulated N-terminal rotated trans structure shows good agreement with the equivalent crystal structure and, moreover, is consistent with the NMR data. These results illustrate the use of MD simulation at atomic resolution to model structural transitions and to interpret experimental data.

Syndecan-1/CD147 association is essential for cyclophilin B-induced activation of p44/42 mitogen-activated protein kinases and promotion of cell adhesion and chemotaxis

Many of the biological functions attributed to cell surface proteoglycans are dependent on the interaction with extracellular mediators through their heparan sulphate (HS) moieties and the participation of their core proteins in signaling events. A class of recently identified inflammatory mediators is secreted cyclophilins, which are mostly known as cyclosporin A-binding proteins. We previously demonstrated that cyclophilin B (CyPB) triggers chemotaxis and integrin-mediated adhesion of T lymphocytes mainly of the CD4+/CD45RO+ phenotype. These activities are related to interactions with two types of binding sites, CD147 and cell surface HS. Here, we demonstrate that CyPB-mediated adhesion of CD4+/CD45RO+ T cells is related to p44/42 mitogen-activated protein kinase (MAPK) activation by a mechanism involving CD147 and HS proteoglycans (HSPG). Although HSPG core proteins are represented by syndecan-1, -2, -4, CD44v3 and betaglycan in CD4+/CD45RO+ T cells, we found that only syndecan-1 is physically associated with CD147. The intensity of the heterocomplex increased in response to CyPB, suggesting a transient enhancement and/or stabilization in the association of CD147 to syndecan-1. Pretreatment with anti-syndecan-1 antibodies or knockdown of syndecan-1 expression by RNA interference dramatically reduced CyPB-induced p44/p42 MAPK activation and consequent migration and adhesion, supporting the model in which syndecan-1 serves as a binding subunit to form the fully active receptor of CyPB. Altogether, our findings provide a novel example of a soluble mediator in which a member of the syndecan family plays a critical role in efficient interaction with signaling receptors and initiation of cellular responses.

A molecular dynamics study of Cyclophilin A free and in complex with the Ala-Pro dipeptide

Six different molecular dynamics simulations of Cyclophilin A, three with the protein free in water and three with the Ala-Pro dipeptide bound to the protein, have been performed, and analysed with respect to structure and hydration of the active site. The water structure in the binding pocket of the free Cyclophilin A was found to mimic the experimentally obtained binding cis conformation of the dipeptide. Cyclophilin A is a peptidyl-prolyl cis-trans isomerase (PPIase), but the mechanism of the cis/trans isomerization is not exactly clear. This study was performed to understand better the binding between dipeptide and Cyclophilin A, but also two previously proposed isomerization mechanisms are discussed.

The peptidyl-prolyl isomerase Pin1 regulates granulocyte-macrophage colony-stimulating factor mRNA stability in T lymphocytes

Cytokine production is associated with both the normal and pathologic inflammatory response to injury. Previous studies have shown that the immunosuppressants cyclosporin A or FK506, which interact with the peptidyl-propyl isomerases cyclophilin A and FK506-binding protein (FKBP12), respectively, block cytokine expression. A third member of the peptidyl-propyl isomerase family, Pin1 is expressed by immune and other cells. Pin1 has been implicated in cell cycle progression, is overexpressed in human tumors, and may rescue neurons from tau-associated degeneration. However, the role of Pin1 in the immune system remains largely unknown. In this study, we analyze the role of Pin1 in GM-CSF expression by human PBMC and CD4+ lymphocytes. We show that Pin1 isomerase activity is necessary for activation-dependent, GM-CSF mRNA stabilization, accumulation, and protein secretion, but not non-AU-rich elements containing cytokine mRNAs, including TGF-beta and IL-4. Mechanistically, Pin1 mediated the association of the AU-rich element-binding protein, AUF1, with GM-CSF mRNA, which determined the rate of decay by the exosome.

Molecular and functional characterization of a cyclophilin with antifungal activity from Chinese cabbage

An antifungal protein that inhibits the growth of filamentous fungal pathogens was isolated from Chinese cabbage (Brassica campestris L. ssp. pekinensis) by affinity chromatography on Affi-gel blue gel and ion exchange chromatography on CM-Sepharose. The N-terminal amino acid sequence of the protein was highly homologous to that of plant cyclophilins and consequently the protein was denoted as C-CyP. To understand the antifungal activity of C-CyP, we isolated a cDNA encoding its gene from a Chinese cabbage leaf cDNA library. The Chinese cabbage genome bears more than one C-CyP gene copy and C-CyP mRNA is highly expressed in all tissues except the seeds. Recombinant C-CyP catalyzed the cis-trans inter-conversion of the Ala-Pro bond of the substrate, which indicates this protein has peptidyl-prolyl cis-trans isomerase activity. It also inhibited the growth of several fungal pathogens.

Cyclosporin A binding toMycobacterium tuberculosispeptidyl-prolylcis-transisomerase A - Investigation by CD, FTIR and fluorescence spectroscopy

Circular dichroism and resolution-enhanced Fourier transform infrared reveal induction of secondary structural elements on peptidyl-prolyl cis-trans isomerase A (PpiA) from Mycobacterium tuberculosis upon binding cyclosporin A (CsA). Thermal denaturation shows aggregation of PpiA at higher temperatures (>70 degrees C) and CsA fails to impart stabilization in protein structure. However, CsA stabilizes PpiA structure in urea denaturation. In presence/absence of CsA, urea-induced reversible unfolding of secondary and tertiary structures follows two-state and three-state transition, respectively. The chemical unfolding results also demonstrate that loss in the tertiary structure precedes the loss in secondary structure both in presence and absence of CsA at the initial stages. Fluorescence quenching suggests presence of a positive barrier around tryptophan microenvironment of PpiA.

Modelling and study of cyclosporin A and related compounds in complexes with a Trypanosoma cruzi cyclophilin

Cyclophilins (CyPs) are enzymes involved in protein folding, catalyzing the isomerisation of peptidyl prolyl bonds in proteins and peptides between the cis- and trans-conformations. They are also the major cellular target for the immunosuppressive drug Cyclosporin A (CsA). In Trypanosoma cruzi, the most abundantly expressed CyP is an isoform of 19 kDa, TcCyP19, in which the enzymatic activity is inhibited by CsA. Among a reported set of CsA analogues, two non-immunosuppressive compounds, H-7-94 and F-7-62, proved to be the best inhibitors of TcCyP19 enzymatic activity as well as the most efficient trypanocidal drugs. With the objective of analysing, at the molecular level, how the structural differences between the three above-mentioned inhibitors justify their different inhibitory activity on TcCyP19, three-dimensional molecular modelling structures were generated to computationally simulate behaviours and interactions. An energy-minimized model of each binary complex in water with ions was obtained. These models were then used as starting point for molecular dynamic simulations, performed with GROMOS96 program. With the resulting set of co-ordinates and energies, a comparison of the interaction between CsA and both CsA analogues in T. cruzi and human cyclophilins were performed. Within the different magnitudes analysed, the total potential complex energy exhibited the best correlation with the experimental data. The results obtained in this study support the use of this methodology when designing new lead inhibitor compounds.

α-Tocopherol induces calnexin in renal tubular cells: Another protective mechanism against free radical-induced cellular damage

Pre-administration of alpha-tocopherol is protective against oxidative renal tubular damage and subsequent carcinogenesis by ferric nitrilotriacetate (Fe-NTA) in rats. We searched for mechanisms other than the scavenging effect of alpha-tocopherol with microarray analyses, which implicated calnexin, a chaperone for glycoproteins. Renal mRNA levels of calnexin significantly increased 3h after an injection of Fe-NTA in rats fed a standard diet whereas those fed an alpha-tocopherol-supplemented diet showed an increase prior to injection, but after injection showed a decrease in renal calnexin mRNA levels, with unaltered protein levels. In experiments using LLC-PK1 cells, addition of alpha-tocopherol was protective against oxidative stress by H2O2, concomitant with calnexin induction. Knockdown of calnexin by siRNA significantly reduced this protection. Furthermore, COS-7 cells transfected with the calnexin gene were more resistant to H2O2. Together with the fact that alpha-tocopherol induced N-acetylglucosaminyltransferase 3, our data suggest that alpha-tocopherol modifies glycoprotein metabolism partially by conferring mild ER stress. This adds another molecular mechanism of alpha-tocopherol toward cancer prevention.

Analysis of the Trypanosoma cruzi cyclophilin gene family and identification of Cyclosporin A binding proteins

The Trypanosoma cruzi cyclophilin gene family comprises 15 paralogues whose nominal masses vary from 19 to 110 kDa, namely TcCyP19, TcCyP20, TcCyP21, TcCyP22, TcCyP24, TcCyP25, TcCyP26, TcCyP28, TcCyP29, TcCyP30, TcCyP34, TcCyP35, TcCyP40, TcCyP42 and TcCyP110. Under the conditions used, only some of the T. cruzi cyclophilin paralogue products could be isolated by affinity chromatography. The 15 paralogues were aligned with 495 cyclophilins from diverse organisms. Analyses of clusters formed by the T. cruzi cyclophilins with others encoded in various genomes revealed that 8 of them (TcCyP19, TcCyP21, TcCyP22, TcCyP24, TcCyP35, TcCyP40, TcCyP42 and TcCyP110) have orthologues in many different genomes whereas the other 7 display less-defined patterns of their sequence attributes and their classification to a specific group of cyclophilin's orthologues remains uncertain. Seven epimastigote cDNA clones encoding cyclophilin isoforms were further studied. These genes were found dispersed throughout the genome of the parasite. Amastigote and trypomastigote mRNAs encoding these 7 genes were also detected. We isolated 4 cyclosporin A-binding proteins in T. cruzi epimastigote extracts, which were identified by mass spectrometry as TcCyP19, TcCyP22, TcCyP28 and TcCyP40. Cyclosporin A-binding to these cyclophilins might be of importance to the mechanism of action of Cyclosporin A and its non-immunosuppressive analogues, whose trypanocidal effects were previously reported, and therefore, of potential interest in the chemotherapy of Chagas' disease.

FK506-Binding Protein Ligands: Structure-Based Design, Synthesis, and Neurotrophic/Neuroprotective Properties of Substituted 5,5-Dimethyl-2-(4-thiazolidine)carboxylates

Structure-based design and discovery of novel neuroimmunophilin FK506-binding protein (FKBP) ligands were pursued in the present study. The binding mode of the known FKBP ligand 1 (3-(3-pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate) in complex with FKBP12 was investigated using LUDI simulation and upon which a novel scaffold structure predicted to possess improved binding affinity was designed. A virtual combinatorial library composed of diverse combinations of two substituted groups was constructed using Project Library, followed by an automated screening of the library against the ligand binding site on FKBP52 using DOCK. Forty-three candidate compounds that displayed favorable binding with the receptor were identified and synthesized. The neurotrophic activity of the candidate compounds was evaluated on chick dorsal root ganglion cultures in vitro. As a result, 15 compounds exhibited positive effects on ganglion neurite outgrowth in the presence of 0.15 ng/mL NGF, among which 7 compounds at testing concentrations of 1 pM and 100 pM showed greater efficacy than 1 at 100 pM. Compound 18 (3-(3-pyridyl)-1-propyl (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxobutyl)-2-(4-thiazolidine)carboxylate) afforded the most potent effect in promoting the processes of neurite outgrowth and which was in a concentration-dependent manner from 1 pM to 100 pM. Half-maximal effect occurred at about 10 pM. Moreover, 18 at a dosage of 10 mg/kg was found to be significantly neuroprotective in a mouse peripheral sympathetic nerve injury model induced by 8 mg/kg 6-hydroxydopamine. This study further suggests the clinical potential of novel FKBP ligands as a new therapeutic approach in the treatment of neurodegenerative disorders, such as Parkinson's disease.

The diageotropica gene of tomato encodes a cyclophilin: a novel player in auxin signaling

The single gene, auxin-resistant diageotropica (dgt) mutant of tomato displays a pleiotropic auxin-related phenotype that includes a slow gravitropic response, lack of lateral roots, reduced apical dominance, altered vascular development, and reduced fruit growth. Some auxin responses are unaltered in dgt plants, however, and the levels, metabolism, and transport of auxin appear normal, indicating that the Dgt gene encodes a component of a specific auxin signaling pathway. By combining map-based cloning with comparative microsynteny, we determined that the Dgt gene encodes a cyclophilin (CYP) (LeCYP1; gi:170439) that has not previously been identified as a component of auxin signaling and plant development. Each of the three known dgt alleles contains a unique mutation in the coding sequence of LeCyp1. Alleles dgt(1-1)and dgt(1-2) contain single nucleotide point mutations that generate an amino acid change (G137R) and a stop codon (W128stop), respectively, while dgt(dp) has an amino acid change (W128CDelta129-133) preceding a 15 bp deletion. Complementation of dgt plants with the wild-type LeCyp1 gene restored the wild-type phenotype. Each dgt mutation reduced or nullified the peptidyl-prolyl isomerase activity of the GST-LeCYP1 fusion proteins in vitro. RT-PCR and immunoblot analyses indicated that the dgt mutations do not affect the expression of LeCyp1 mRNA, but the accumulation of LeCYP1 protein is greatly reduced for all three mutant alleles. The CYP inhibitor, cyclosporin A, partially mimics the effects of the dgt mutation in inhibiting auxin-induced adventitious root initiation in tomato hypocotyl sections and reducing the auxin-induced expression of the early auxin response genes, LeIAA10 and 11. These observations confirm that the PPIase activity of the tomato CYP, LeCYP1, encoded by the Dgt gene is important for specific aspects of auxin regulation of plant growth, development, and environmental responses.

Analysis of the cross-reactivity and of the 1.5 A crystal structure of the Malassezia sympodialis Mala s 6 allergen, a member of the cyclophilin pan-allergen family

Cyclophilins constitute a family of proteins involved in many essential cellular functions. They have also been identified as a panallergen family able to elicit IgE-mediated hypersensitivity reactions. Moreover, it has been shown that human cyclophilins are recognized by serum IgE from patients sensitized to environmental cyclophilins. IgE-mediated autoreactivity to self-antigens that have similarity to environmental allergens is often observed in atopic disorders. Therefore comparison of the crystal structure of human proteins with similarity to allergens should allow the identification of structural similarities to rationally explain autoreactivity. A new cyclophilin from Aspergillus fumigatus (Asp f 27) has been cloned, expressed and showed to exhibit cross-reactivity in vitro and in vivo. The three-dimensional structure of cyclophilin from the yeast Malassezia sympodialis (Mala s 6) has been determined at 1.5 A (1 A=0.1 nm) by X-ray diffraction. Crystals belong to space group P4(1)2(1)2 with unit cell dimensions of a=b=71.99 A and c=106.18 A. The structure was solved by molecular replacement using the structure of human cyclophilin A as the search model. The refined structure includes all 162 amino acids of Mala s 6, an active-site-bound Ala-Pro dipeptide and 173 water molecules, with a crystallographic R- and free R-factor of 14.3% and 14.9% respectively. The overall structure consists of an eight-stranded antiparallel beta-barrel and two alpha-helices covering the top and bottom of the barrel, typical for cyclophilins. We identified conserved solvent-exposed residues in the fungal and human structures that are potentially involved in the IgE-mediated cross-reactivity.

RpoH mediates the expression of some, but not all, genes induced in Neisseria gonorrhoeae adherent to epithelial cells

Neisseria gonorrhoeae (gonococcus [GC]), is highly adapted to the human host, the only known reservoir for gonococcal infection. However, since it is sexually transmitted, infection of a new host likely requires a regulatory response on the part of the gonococcus to respond to this significant change in environment. We previously showed that adherence of gonococci to epithelial cells results in changes of gene expression in the bacteria that presumably prepare them for subsequent steps in the infection process. Expression of the heat shock sigma factor gene, rpoH, was shown to be important for the invasion step, as gonococci depleted for rpoH were reduced in their ability to invade epithelial cells. Here, we show that of the genes induced in adherent gonococci, two are part of the gonococcal RpoH regulon. When RpoH is depleted, expression of these genes is no longer induced by host cell contact, indicating that RpoH is mediating the host cell induction response of these genes. One RpoH-dependent gene, NGO0376, is shown to be important for invasion of epithelial cells, consistent with earlier observations that RpoH is necessary for this step of infection. Two genes, NGO1684 and NGO0340, while greatly induced by host cell contact, were found to be RpoH independent, indicating that more than one regulator is involved in the response to host cell contact. Furthermore, NGO0340, but not NGO1684, was shown to be important for both adherence and invasion of epithelial cells, suggesting a complex regulatory network in the response of gonococci to contact with host cells.

One novel quinoxaline derivative as a potent human cyclophilin A inhibitor shows highly inhibitory activity against mouse spleen cell proliferation

Cyclophilin A (CypA) is a ubiquitous cellular enzyme playing critical roles in many biological processes, and its inhibitor has been reported to have potential immunosuppressive activity. In this work, we reported a novel quinoxaline derivative, 2,3-di(furan-2-yl)-6-(3-N,N-diethylcarbamoyl-piperidino)carbonylamino quinoxaline (DC838, 3), which was confirmed to be a potent inhibitor against human CypA. By using the surface plasmon resonance (SPR) and fluorescence titration techniques, the kinetic analysis of CypA/DC838 interaction was quantitatively performed. CypA peptidyl prolyl cis–trans isomerase (PPIase) activity inhibition assay showed that DC838 demonstrated highly CypA PPIase inhibitory activity. In vivo assay results showed that DC838 could inhibit mouse spleen cell proliferation induced by concanavalin A (Con A). Molecular docking simulation further elucidated the specific DC838 binding to CypA at the atomic level. The current work should provide useful information in the discovery of immunosuppressor based on CypA inhibitor.