Cyclophilin B trafficking through the secretory pathway is altered by binding of cyclosporin A

The mechanism of extracellular CypB promotes glioblastoma adaptation to glutamine deprivation microenvironment

Glioblastoma, previously known as glioblastoma multiform (GBM), is a type of glioma with a high degree of malignancy and rapid growth rate. It is highly dependent on glutamine (Gln) metabolism during proliferation and lags in neoangiogenesis, leading to extensive Gln depletion in the core region of GBM. Gln-derived glutamate is used to synthesize the antioxidant Glutathione (GSH). We demonstrated that GSH levels are also reduced in Gln deficiency, leading to increased reactive oxygen species (ROS) levels. The ROS production induces endoplasmic reticulum (ER) stress, and the proteins in the ER are secreted into the extracellular medium. We collected GBM cell supernatants cultured with or without Gln medium; the core and peripheral regions of human GBM tumor tissues. Proteomic analysis was used to screen out the target-secreted protein CypB. We demonstrated that the extracellular CypB expression is associated with Gln deprivation. Then, we verified that GBM can promote the glycolytic pathway by activating HIF-1α to upregulate the expression of GLUT1 and LDHA. Meanwhile, the DRP1 was activated, increasing mitochondrial fission, thus inhibiting mitochondrial function. To explore the specific mechanism of its regulation, we constructed a si-CD147 knockout model and added human recombinant CypB protein to verify that extracellular CypB influenced the expression of downstream p-AKT through its cell membrane receptor CD147 binding. Moreover, we confirmed that p-AKT could upregulate HIF-1α and DRP1. Finally, we observed that extracellular CypB can bind to the CD147 receptor, activate p-AKT, upregulate HIF-1α and DRP1 in order to promote glycolysis while inhibiting mitochondrial function to adapt to the Gln-deprived microenvironment.

Veneer Is a Webtool for Rapid, Standardized, and Transparent Interpretation, Annotation, and Reporting of Mammalian Cell Surface N-Glycocapture Data

Currently, no consensus exists regarding criteria required to designate a protein within a proteomic data set as a cell surface protein. Most published proteomic studies rely on varied ontology annotations or computational predictions instead of experimental evidence when attributing protein localization. Consequently, standardized approaches for analyzing and reporting cell surface proteome data sets would increase confidence in localization claims and promote data use by other researchers. Recently, we developed Veneer, a web-based bioinformatic tool that analyzes results from cell surface N-glycocapture workflows─the most popular cell surface proteomics method used to date that generates experimental evidence of subcellular location. Veneer assigns protein localization based on defined experimental and bioinformatic evidence. In this study, we updated the criteria and process for assigning protein localization and added new functionality to Veneer. Results of Veneer analysis of 587 cell surface N-glycocapture data sets from 32 published studies demonstrate the importance of applying defined criteria when analyzing cell surface proteomics data sets and exemplify how Veneer can be used to assess experimental quality and facilitate data extraction for informing future biological studies and annotating public repositories.

Sanglifehrin A mitigates multiorgan fibrosis by targeting the collagen chaperone cyclophilin B

Pathological deposition and crosslinking of collagen type I by activated myofibroblasts drives progressive tissue fibrosis. Therapies that inhibit collagen synthesis have potential as antifibrotic agents. We identify the collagen chaperone cyclophilin B as a major cellular target of the natural product sanglifehrin A (SfA) using photoaffinity labeling and chemical proteomics. Mechanistically, SfA inhibits and induces the secretion of cyclophilin B from the endoplasmic reticulum (ER) and prevents TGF-β1-activated myofibroblasts from synthesizing and secreting collagen type I in vitro, without inducing ER stress or affecting collagen type I mRNA transcription, myofibroblast migration, contractility, or TGF-β1 signaling. In vivo, SfA induced cyclophilin B secretion in preclinical models of fibrosis, thereby inhibiting collagen synthesis from fibrotic fibroblasts and mitigating the development of lung and skin fibrosis in mice. Ex vivo, SfA induces cyclophilin B secretion and inhibits collagen type I secretion from fibrotic human lung fibroblasts and samples from patients with idiopathic pulmonary fibrosis (IPF). Taken together, we provide chemical, molecular, functional, and translational evidence for demonstrating direct antifibrotic activities of SfA in preclinical and human ex vivo fibrotic models. Our results identify the cellular target of SfA, the collagen chaperone cyclophilin B, as a mechanistic target for the treatment of organ fibrosis.

Cyclophilin D knockout significantly prevents HCC development in a streptozotocin-induced mouse model of diabetes-linked NASH

A family of Peptidyl-prolyl isomerases (PPIases), called Cyclophilins, localize to numerous intracellular and extracellular locations where they contribute to a variety of essential functions. We previously reported that non-immunosuppressive pan-cyclophilin inhibitor drugs like reconfilstat (CRV431) or NV556 decreased multiple aspects of non-alcoholic fatty liver disease (NAFLD) in mice under two different non-alcoholic steatohepatitis (NASH) mouse models. Both CRV431 and NV556 inhibit several cyclophilin isoforms, among which cyclophilin D (CypD) has not been previously investigated in this context. It is unknown whether it is necessary to simultaneously inhibit multiple cyclophilin family members to achieve therapeutic benefits or if loss-of-function of one is sufficient. Furthermore, narrowing down the isoform most responsible for a particular aspect of NAFLD/NASH, such as hepatocellular carcinoma (HCC), would allow for more precise future therapies. Features of human diabetes-linked NAFLD/NASH can be reliably replicated in mice by administering a single high dose of streptozotocin to disrupt pancreatic beta cells, in conjunction with a high sugar, high fat, high cholesterol western diet over the course of 30 weeks. Here we show that while both wild-type (WT) and Ppif-/- CypD KO mice develop multipe severe NASH disease features under this model, the formation of HCC nodules was significantly blunted only in the CypD KO mice. Furthermore, of differentially expressed transcripts in a qPCR panel of select HCC-related genes, nearly all were downregulated in the CypD KO background. Cyclophilin inhibition is a promising and novel avenue of treatment for diet-induced NAFLD/NASH. This study highlights the impact of CypD loss-of-function on the development of HCC, one of the most severe disease outcomes.

Mice lacking cyclophilin B, but not cyclophilin A, are protected from the development of NASH in a diet and chemical-induced model

Cyclophilins are a diverse family of peptidyl-prolyl isomerases (PPIases) of importance in a variety of essential cellular functions. We previously reported that the pan-cyclophilin inhibitor drug reconfilstat (CRV431) decreased disease in mice under the western-diet and carbon tetrachloride (CCl4) non-alcoholic steatohepatitis (NASH) model. CRV431 inhibits several cyclophilin isoforms, among which cyclophilin A (CypA) and B (CypB) are the most abundant. It is not known whether simultaneous inhibition of multiple cyclophilin family members is necessary for the observed therapeutic effects or if loss-of-function of one is sufficient. Identifying the responsible isoform(s) would enable future fine-tuning of drug treatments. Features of human liver fibrosis and complete NASH can be reliably replicated in mice by administration of intraperitoneal CCl4 alone or CCl4 in conjunction with high sugar, high cholesterol western diet, respectively. Here we show that while wild-type (WT) and Ppia-/- CypA KO mice develop severe NASH disease features under these models, Ppib-/- CypB KO mice do not, as measured by analysis of picrosirius red and hematoxylin & eosin-stained liver sections and TNFα immuno-stained liver sections. Cyclophilin inhibition is a promising and novel avenue of treatment for diet-induced NASH. In this study, mice without CypB, but not mice without CypA, were significantly protected from the development of the characteristic features of NASH. These data suggest that CypB is necessary for NASH disease progression. Further investigation is necessary to determine whether the specific role of CypB in the endoplasmic reticulum secretory pathway is of significance to its effect on NASH development.

p53 restoration in small cell lung cancer identifies a latent cyclophilin-dependent necrosis mechanism

The p53 tumor suppressor regulates multiple context-dependent tumor suppressive programs. Although p53 is mutated in ~90% of small cell lung cancer (SCLC) tumors, how p53 mediates tumor suppression in this context is unknown. Here, using a mouse model of SCLC in which endogenous p53 expression can be conditionally and temporally regulated, we show that SCLC tumors maintain a requirement for p53 inactivation. However, we identify tumor subtype heterogeneity between SCLC tumors such that p53 reactivation induces senescence in a subset of tumors, while in others, p53 induces necrosis. We pinpoint cyclophilins as critical determinants of a p53-induced transcriptional program that is specific to SCLC tumors and cell lines poised to undergo p53-mediated necrosis. Importantly, inhibition of cyclophilin isomerase activity, or genetic ablation of specific cyclophilin genes, suppresses p53-mediated necrosis by limiting p53 transcriptional output without impacting p53 chromatin binding. Our study demonstrates that intertumoral heterogeneity in SCLC influences the biological response to p53 restoration, describes a cyclophilin-dependent mechanism of p53-regulated cell death, and uncovers putative mechanisms for the treatment of this most-recalcitrant tumor type.

Sanglifehrin A mitigates multi-organ fibrosis in vivo by inducing secretion of the collagen chaperone cyclophilin B

Pathological deposition and crosslinking of collagen type I by activated myofibroblasts drives progressive tissue fibrosis. Therapies that inhibit collagen synthesis by myofibroblasts have clinical potential as anti-fibrotic agents. Lysine hydroxylation by the prolyl-3-hydroxylase complex, comprised of cartilage associated protein, prolyl 3-hydroxylase 1, and cyclophilin B, is essential for collagen type I crosslinking and formation of stable fibers. Here, we identify the collagen chaperone cyclophilin B as a major cellular target of the macrocyclic natural product sanglifehrin A (SfA) using photo-affinity labeling and chemical proteomics. Our studies reveal a unique mechanism of action in which SfA binding to cyclophilin B in the endoplasmic reticulum (ER) induces the secretion of cyclophilin B to the extracellular space, preventing TGF-β1-activated myofibroblasts from synthesizing collagen type I in vitro without inhibiting collagen type I mRNA transcription or inducing ER stress. In addition, SfA prevents collagen type I secretion without affecting myofibroblast contractility or TGF-β1 signaling. In vivo, we provide chemical, molecular, functional, and translational evidence that SfA mitigates the development of lung and skin fibrosis in mouse models by inducing cyclophilin B secretion, thereby inhibiting collagen synthesis from fibrotic fibroblasts in vivo . Consistent with these findings in preclinical models, SfA reduces collagen type I secretion from fibrotic human lung fibroblasts and precision cut lung slices from patients with idiopathic pulmonary fibrosis, a fatal fibrotic lung disease with limited therapeutic options. Our results identify the primary liganded target of SfA in cells, the collagen chaperone cyclophilin B, as a new mechanistic target for the treatment of organ fibrosis.

Human Cyclophilin B Nuclease Activity Revealed via Nucleic Acid-Based Electrochemical Sensors

Human cyclophilin B (CypB) is oversecreted by pancreatic cancer cells, making it a potential biomarker for early-stage disease diagnosis. Our group is motivated to develop aptamer-based assays to measure CypB levels in biofluids. However, human cyclophilins have been postulated to have collateral nuclease activity, which could impede the use of aptamers for CypB detection. To establish if CypB can hydrolyze electrode-bound nucleic acids, we used ultrasensitive electrochemical sensors to measure CypB's hydrolytic activity. Our sensors use ssDNA and dsDNA in the biologically predominant d-DNA form, and in the nuclease resistant l-DNA form. Challenging such sensors with CypB and control proteins, we unequivocally demonstrate that CypB can cleave nucleic acids. To our knowledge, this is the first study to use electrochemical biosensors to reveal the hydrolytic activity of a protein that is not known to be a nuclease. Future development of CypB bioassays will require the use of nuclease-resistant aptamer sequences.

Non-Immunosuppressive Cyclophilin Inhibitors

Cyclophilins, enzymes with peptidyl-prolyl cis/trans isomerase activity, are relevant to a large variety of biological processes. The most abundant member of this enzyme family, cyclophilin A, is the cellular receptor of the immunosuppressive drug cyclosporine A (CsA). As a consequence of the pathophysiological role of cyclophilins, particularly in viral infections, there is a broad interest in cyclophilin inhibition devoid of immunosuppressive activity. This Review first gives an introduction into the physiological and pathophysiological roles of cyclophilins. The presentation of non-immunosuppressive cyclophilin inhibitors will commence with drugs based on chemical modifications of CsA. The naturally occurring macrocyclic sanglifehrins have become other lead structures for cyclophilin-inhibiting drugs. Finally, de novo designed compounds, whose structures are not derived from or inspired by natural products, will be presented. Relevant synthetic concepts will be discussed, but the focus will also be on biochemical studies, structure-activity relationships, and clinical studies.

Cyclophilins A and B oppositely regulate renal tubular epithelial cell phenotype

Restoration of kidney tubular epithelium following sublethal injury sequentially involves partial epithelial–mesenchymal transition (pEMT), proliferation, and further redifferentiation into specialized tubule epithelial cells (TECs). Because the immunosuppressant cyclosporine-A produces pEMT in TECs and inhibits the peptidyl-prolyl isomerase (PPIase) activity of cyclophilin (Cyp) proteins, we hypothesized that cyclophilins could regulate TEC phenotype. Here we demonstrate that in cultured TECs, CypA silencing triggers loss of epithelial features and enhances transforming growth factor β (TGFβ)-induced EMT in association with upregulation of epithelial repressors Slug and Snail. This pro-epithelial action of CypA relies on its PPIase activity. By contrast, CypB emerges as an epithelial repressor, because CypB silencing promotes epithelial differentiation, prevents TGFβ-induced EMT, and induces tubular structures in 3D cultures. In addition, in the kidneys of CypB knockout mice subjected to unilateral ureteral obstruction, inflammatory and pro-fibrotic events were attenuated. CypB silencing/knockout leads to Slug, but not Snail, downregulation. CypB support of Slug expression depends on its endoplasmic reticulum location, where it interacts with calreticulin, a calcium-buffering chaperone related to Slug expression. As CypB silencing reduces ionomycin-induced calcium release and Slug upregulation, we suggest that Slug expression may rely on CypB modulation of calreticulin-dependent calcium signaling. In conclusion, this work uncovers new roles for CypA and CypB in modulating TEC plasticity and identifies CypB as a druggable target potentially relevant in promoting kidney repair.

Host factor cyclophilin B affects Orf virus replication by interacting with viral ORF058 protein

Poxviruses have evolved multiple strategies to modulate host-derived factors to create an optimal environment for viral efficient replication. Our previous study indicated that cyclophilin B (CypB) is a critical factor for ORFV replication in MDBK cells. However, the precise molecular mechanism by which CypB facilitates ORFV replication remains less understood. In the present study, the function of CypB in ORFV replication is further evaluated. The overexpression of CypB was observed to facilitate ORFV replication in OFTu cells and HeLa cells, however, RNA interference (RNAi)-mediated reduction of endogenous CypB decreased the levels of ORFV replication. Coimmunoprecipitation experiments revealed that the CypB interacted with ORFV ORF058 protein, a late protein involved in virus entry. The interaction of host factor CypB and ORF058 protein was further confirmed by confocal microscopy analysis and GST-pull down. In addition, the 52-55 aa was identified as the critical binding sites for CypB on ORF058 protein by GST-pull down with OFTu cells overexpressing CypB and purified GST-tagged truncated ORF058. In conclusion, we demonstrate that CypB is a critical host factor for ORFV replication in vitro by interacting with ORF058 protein, providing new insights into ORFV pathogenesis.

Cross-Platform Comparison of Computer-assisted Image Analysis Quantification of In Situ mRNA Hybridization in Investigative Pathology

Although availability of automated platforms has proliferated, there is no standard practice for computer-assisted generation of scores for mRNA in situ hybridization (ISH) visualized by brightfield microscopic imaging on tissue sections. To address this systematically, an ISH for peptidylprolyl isomerase B (PPIB) (cyclophilin B) mRNA was optimized and applied to a tissue microarray of archival non-small cell lung carcinoma cases, and then automated image analysis for PPIB was refined across 4 commercially available software platforms. Operator experience and scoring results from ImageScope, HALO, CellMap, and Developer XD were systematically compared with each other and to manual pathologist scoring. Markup images were compared and contrasted for accuracy, the ability of the platform to identify cells, and the ease of visual assessment to determine appropriate interpretation. Comparing weighted scoring approaches using H-scores (Developer XD, ImageScope, and manual scoring) a correlation was observed (R value=0.7955), and association between the remaining 2 approaches (HALO and CellMap) was of similar value. ImageScope showed the highest R value in comparison with manual scoring (0.7377). Mean-difference plots showed that HALO produced the highest relative normalized values, suggesting higher relative sensitivity. ImageScope overestimated PPIB ISH signal at the high end of the range scores; however, this tendency was not observed in other platforms. HALO emerged with the highest number of favorable observations, no apparent systematic bias in score generation compared with the other methods, and potentially higher sensitivity to detect ISH. HALO may serve as a tool to empower teams of investigative pathology laboratory scientists to assist pathologists readily with quantitative scoring of ISH.

Inorganic polyphosphate controls cyclophilin B-mediated collagen folding in osteoblast-like cells

Evidence is emerging that inorganic polyphosphate (polyP) is a fundamental molecule involved in a wide range of biological processes. In higher eukaryotes, polyP is abundant in osteoblasts but questions remain as to its functions. Here, we find that polyP is particularly enriched in endoplasmic reticulum (ER) where it colocalizes with cyclophilin B (CypB) using osteoblastic SaOS-2 model cell line. PolyP binds directly and specifically to CypB, inhibiting its peptidyl-prolyl cis-trans isomerase activity which is critical for collagen folding. PolyP sequestration by spermine and ER-specific polyP reduction by polyphosphatase expression in cells reduced collagen misfolding and confirmed that endogenous polyP acts as a molecular control of CypB-mediated collagen folding. We propose that polyP is a previously unrecognized critical regulator of protein homeostasis in ER.

Influences of cyclosporin A and non-immunosuppressive derivatives on cellular cyclophilins and viral nucleocapsid protein during human coronavirus 229E replication

The well-known immunosuppressive drug cyclosporin A inhibits replication of various viruses including coronaviruses by binding to cellular cyclophilins thus inactivating their cis-trans peptidyl-prolyl isomerase function. Viral nucleocapsid proteins are inevitable for genome encapsidation and replication. Here we demonstrate the interaction between the N protein of HCoV-229E and cyclophilin A, not cyclophilin B. Cyclophilin inhibitors abolish this interaction. Upon infection, cyclophilin A stays evenly distributed throughout the cell, whereas cyclophilin B concentrates at ER-bleb-like structures. We further show the inhibitory potential of non-immunosuppressive CsA derivatives Alisporivir, NIM811, compound 3 on HCoV-229E-GFP and -Luciferase replication in human Huh-7.5 hepatoma cells at 18 and 48 h time points post infection with EC₅₀ s at low micromolar ranges. Thus, non-immunosuppressive CsA derivatives effectively inhibit HCoV-229E replication suggesting them as possible candidates for the treatment of HCoV infection. The interruption of interaction between CypA and N protein by CsA and its derivatives suggest a mechanism how CypA inhibitors suppress viral replication.

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HCoV-229E replication is inhibited by Alisporivir, NIM811 and other non-immunosuppressive Cyclosporin A derivatives.

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HCoV-229E N protein interacts with cyclophilin A.

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Cyclophilin A is required for coronavirus replication.

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Cyclophilin B concentrates in bleb-like structures of the ER in HCoV-infected Huh7 cells.

Pharmacological Targeting of the ER-Resident Chaperones GRP94 or Cyclophilin B Induces Secretion of IL-22 Binding Protein Isoform-1 (IL-22BPi1)

Of the three interleukin-22 binding protein (IL-22BP) isoforms produced by the human IL22RA2 gene, IL-22BPi2 and IL-22BPi3 are capable of neutralizing IL-22. The longest isoform, IL-22BPi1, does not bind IL-22, is poorly secreted, and its retention within the endoplasmic reticulum (ER) is associated with induction of an unfolded protein response (UPR). Therapeutic modulation of IL-22BPi2 and IL-22BPi3 production may be beneficial in IL-22-dependent disorders. Recently, we identified the ER chaperones GRP94 and cyclophilin B in the interactomes of both IL-22BPi1 and IL-22BPi2. In this study, we investigated whether secretion of the IL-22BP isoforms could be modulated by pharmacological targeting of GRP94 and cyclophilin B, either by means of geldanamycin, that binds to the ADP/ATP pocket shared by HSP90 paralogs, or by cyclosporin A, which causes depletion of ER cyclophilin B levels through secretion. We found that geldanamycin and its analogs did not influence secretion of IL-22BPi2 or IL-22BPi3, but significantly enhanced intracellular and secreted levels of IL-22BPi1. The secreted protein was heterogeneously glycosylated, with both high-mannose and complex-type glycoforms present. In addition, cyclosporine A augmented the secretion of IL-22BPi1 and reduced that of IL-22BPi2 and IL-22BPi3. Our data indicate that the ATPase activity of GRP94 and cyclophilin B are instrumental in ER sequestration and degradation of IL-22BPi1, and that blocking these factors mobilizes IL-22BPi1 toward the secretory route.

Cyclophilins and cyclophilin inhibitors in nidovirus replication

Cyclophilins (Cyps) belong to the family of peptidyl-prolyl isomerases (PPIases). The PPIase activity of most Cyps is inhibited by the immunosuppressive drug cyclosporin A and several of its non-immunosuppressive analogs, which can also block the replication of nidoviruses (arteriviruses and coronaviruses). Cyclophilins have been reported to play an essential role in the replication of several other RNA viruses, including human immunodeficiency virus-1, hepatitis C virus, and influenza A virus. Likewise, the replication of various nidoviruses was reported to depend on Cyps or other PPIases. This review summarizes our current understanding of this class of nidovirus-host interactions, including the potential function of in particular CypA and the inhibitory effect of Cyp inhibitors. Also the involvement of the FK-506-binding proteins and parvulins is discussed. The nidovirus data are placed in a broader perspective by summarizing the most relevant data on Cyp interactions and Cyp inhibitors for other RNA viruses.

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Nidovirus replication is inhibited by cyclophilin inhibitors.

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Arterivirus replication depends on cyclophilin A.

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Cyclosporin A blocks arterivirus RNA synthesis.

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Using cyclophilin inhibitors against nidoviruses in vivo needs more investigation.

A potential role of the unfolded protein response in post-transplant cancer

Cancer is one of the major causes of mortality in organ transplant patients receiving immunosuppressive regimen based on Cyclosporin A (CsA). Organ transplantation and chronic immunosuppression are typically associated with skin cancers (both squamous cell carcinoma and melanoma) and renal cell carcinoma (RCC). Recent studies have shown that in addition to its immunosuppressive effects, accounted for by the inhibition of calcineurin and the modulation of the transcriptional programme of lymphocytes, CsA also directly stimulates the growth and aggressive behaviour of various cancer cells. Using renal carcinogenesis as an example, we discuss the current evidence for a role of cellular proteostasis, i.e. the regulation of the production, maturation and turnover of proteins in eukaryotic cells, in tumorigenesis arising under conditions of chronic immunosuppression. We present the recent studies showing that CsA induces the unfolded protein response (UPR) in normal and transformed kidney cells. We examine how the UPR might be important, considering in particular the genomic analyses showing the existence of a correlation between the levels of expression of the actors of the UPR, the chaperones of the endoplasmic reticulum (ER) and the aggressiveness of renal carcinoma. The UPR may offer a possible explanation for how immunosuppressive regimens based on CsA promote renal carcinogenesis. We discuss the opportunities offered by this biological knowledge in terms of screening, diagnosis and treatment of post-transplant cancers, and propose possible future translational studies examining the role of tumour proteostasis and the UPR in this context.

Cyclophilin B facilitates the replication of Orf virus

BACKGROUND

Viruses interact with host cellular factors to construct a more favourable environment for their efficient replication. Expression of cyclophilin B (CypB), a cellular peptidyl-prolyl cis-trans isomerase (PPIase), was found to be significantly up-regulated. Recently, a number of studies have shown that CypB is important in the replication of several viruses, including Japanese encephalitis virus (JEV), hepatitis C virus (HCV) and human papillomavirus type 16 (HPV 16). However, the function of cellular CypB in ORFV replication has not yet been explored.

METHODS

Suppression subtractive hybridization (SSH) technique was applied to identify genes differentially expressed in the ORFV-infected MDBK cells at an early phase of infection. Cellular CypB was confirmed to be significantly up-regulated by quantitative reverse transcription-PCR (qRT-PCR) analysis and Western blotting. The role of CypB in ORFV infection was further determined using Cyclosporin A (CsA) and RNA interference (RNAi). Effect of CypB gene silencing on ORFV replication by 50% tissue culture infectious dose (TCID₅₀) assay and qRT-PCR detection.

RESULTS

In the present study, CypB was found to be significantly up-regulated in the ORFV-infected MDBK cells at an early phase of infection. Cyclosporin A (CsA) exhibited suppressive effects on ORFV replication through the inhibition of CypB. Silencing of CypB gene inhibited the replication of ORFV in MDBK cells. In conclusion, these data suggest that CypB is critical for the efficient replication of the ORFV genome.

CONCLUSIONS

Cellular CypB was confirmed to be significantly up-regulated in the ORFV-infected MDBK cells at an early phase of infection, which could effectively facilitate the replication of ORFV.

Cyclophilin PpiB is involved in motility and biofilm formation via its functional association with certain proteins

PpiB belongs to the superfamily of peptidyl-prolyl cis/trans isomerases (PPIases, EC: 5.2.1.8), which catalyze the rate-limiting protein folding step at peptidyl-prolyl bonds and control several biological processes. In this study, we show that PpiB acts as a negative effector of motility and biofilm formation ability of Escherichia coli. We identify multicopy suppressors of each ΔppiB phenotype among putative PpiB prey proteins which upon deletion are often characterized by analogous phenotypes. Many putative preys show similar gene expression in wild-type and ΔppiB genetic backgrounds implying possible post-translational modifications by PpiB. We further conducted in vivo and in vitro interaction screens to determine which of them represent true preys. For DnaK, acetyl-CoA carboxylase, biotin carboxylase subunit (AccC) and phosphate acetyltransferase (Pta) we also showed a direct role of PpiB in the functional control of these proteins because it increased the measured enzyme activity of each protein and further interfered with DnaK localization and the correct folding of AccC. Taken together, these results indicate that PpiB is involved in diverse regulatory mechanisms to negatively modulate motility and biofilm formation via its functional association with certain protein substrates.

Cyclophilin B enhances HIV-1 infection

Cyclophilin B (CypB) is a member of the immunophilin family and intracellular chaperone. It predominantly localizes to the ER, but also contains a nuclear localization signal and is secreted from cells. CypB has been shown to interact with the Gag protein of human immunodeficiency type 1 (HIV-1). Several proteomic and genetic studies identified it as a potential factor involved in HIV replication. Herein, we show that over-expression of CypB enhances HIV infection by increasing nuclear import of viral DNA. This enhancement was unaffected by cyclosporine treatment and requires the N-terminus of the protein. The N-terminus contains an ER leader sequence, putative nuclear localization signal, and is required for secretion. Deletion of the N-terminus resulted in mislocalization from the ER and suppression of HIV infection. Passive transfer experiments showed that secreted CypB did not impact HIV infection. Combined, these experiments show that intracellular CypB modulates a pathway of HIV nuclear import.

Identification of Proteins Modulated in the Date Palm Stem Infested with Red Palm Weevil (Rhynchophorus ferrugineus Oliv.) Using Two Dimensional Differential Gel Electrophoresis and Mass Spectrometry

A state of the art proteomic methodology using Matrix Assisted Laser Desorption/Ionization-Time of Flight (MALDI TOF) has been employed to characterize peptides modulated in the date palm stem subsequent to infestation with red palm weevil (RPW). Our analyses revealed 32 differentially expressed peptides associated with RPW infestation in date palm stem. To identify RPW infestation associated peptides (I), artificially wounded plants (W) were used as additional control beside uninfested plants, a conventional control (C). A constant unique pattern of differential expression in infested (I), wounded (W) stem samples compared to control (C) was observed. The upregulated proteins showed relative fold intensity in order of I > W and downregulated spots trend as W > I, a quite interesting pattern. This study also reveals that artificially wounding of date palm stem affects almost the same proteins as infestation; however, relative intensity is quite lower than in infested samples both in up and downregulated spots. All 32 differentially expressed spots were subjected to MALDI-TOF analysis for their identification and we were able to match 21 proteins in the already existing databases. Relatively significant modulated expression pattern of a number of peptides in infested plants predicts the possibility of developing a quick and reliable molecular methodology for detecting plants infested with date palm.

Pea lectin receptor-like kinase functions in salinity adaptation without yield penalty, by alleviating osmotic and ionic stresses and upregulating stress-responsive genes

Lectin receptor-like kinases (LecRLKs) are members of RLK family composed of lectin-like extracellular recognition domain, transmembrane domain and cytoplasmic kinase domain. LecRLKs are plasma membrane proteins believed to be involved in signal transduction. However, most of the members of the protein family even in plants have not been functionally well characterized. Herein, we show that Pisum sativum LecRLK (PsLecRLK) localized in plasma membrane systems and/or other regions of the cell and its transcript upregulated under salinity stress. Overexpression of PsLecRLK in transgenic tobacco plants confers salinity stress tolerance by alleviating both the ionic as well the osmotic component of salinity stress. The transgenic plants show better tissue compartmentalization of Na(+) and higher ROS scavenging activity which probably results in lower membrane damage, improved growth and yield maintenance even under salinity stress. Also, expression of several genes involved in cellular homeostasis is perturbed by PsLecRLK overexpression. Alleviation of osmotic and ionic components of salinity stress along with reduced oxidative damage and upregulation of stress-responsive genes in transgenic plants under salinity stress conditions could be possible mechanism facilitating enhanced stress tolerance. This study presents PsLecRLK as a promising candidate for crop improvement and also opens up new avenue to investigate its signalling pathway.

Functional aspects of extracellular cyclophilins

The cyclophilin family of peptidyl prolyl cis/trans isomerases includes several isoforms found to be secreted in response to different stimuli, thus existing both in the interior and the exterior of cells. The extracellular fractions of the cyclophilins CypA and CypB are involved in the control of cell-cell communication. By binding to the cell membrane receptor CD147 and cell surface heparans they elicit a variety of intracellular signaling cascades involved in inflammatory processes. Increased levels of cyclophilins in inflammatory tissues and body fluids are considered as an inflammatory response to injury. Thus, the extracellular portion of cyclophilins probably plays an important role in human diseases associated with acute or chronic inflammation like rheumatoid arthritis, sepsis, asthma and cardiovascular diseases. Specific inhibition of the cyclophilins in the extracellular space may open an effective therapeutic approach for treating inflammatory diseases.

Hypoxia induces cyclophilin B through the activation of transcription factor 6 in gastric adenocarcinoma cells

Hypoxia is an important form of physiological stress that induces cell death, due to the resulting endoplasmic reticulum (ER) stress, particularly in solid tumors. Although previous studies have indicated that cyclophilin B (CypB) plays a role in ER stress, there is currently no direct information supporting the mechanism of CypB involvement under hypoxic conditions. However, it has previously been demonstrated that ER stress positively regulates the expression of CypB. In the present study, it was demonstrated that CypB is transcriptionally regulated by hypoxia-mediated activation of transcription factor 6 (ATF6), an ER stress transcription factor. Subsequently, the effects of ATF6 on CypB promoter activity were investigated and an ATF6-responsive region in the promoter was identified. Hypoxia and ATF6 expression each increased CypB promoter activity. Collectively, these results demonstrate that ATF6 positively regulates the expression of CypB by binding to an ATF6-responsive region in the promoter, which may play an important role in the attenuation of apoptosis in the adaption to hypoxia. These results suggest that CypB may be a key molecule in the adaptation of cells to hypoxic conditions.

Biomarkers of calcineurin inhibitor nephrotoxicity in transplantation

Over 35 years of use has demonstrated the revolutionary therapeutic benefits of calcineurin inhibitors (CNI) in not only preventing transplant rejection, but also the renal and nonrenal toxicity of CNI. Acute reversible and insidious irreversible forms of CNI nephrotoxicity have been identified, with ischemia from an imbalance between vasoconstrictors and vasodilators playing an important role. The ongoing search to define toxicity pathways has been enriched by ‘Omics’ studies. Changes in proteins including those involved in activation of pro-inflammatory responses, oxidative stress, ER stress and the unfolded protein response have been identified, and these may serve as biomarkers of toxicity. However, the current standard of CNI toxicity, histology, lacks specificity, which creates challenges for biomarker validation. This review focuses on progress in nephrotoxic pathway identification of CNI and biomarker validation.

Cyclophilin inhibition as potential therapy for liver diseases

The cyclophilins are a group of proteins with peptidyl-prolyl isomerase enzymatic activity, localised in different cellular compartments and involved in a variety of functions related to cell metabolism and energy homeostasis, having enhanced expression in inflammation or malignancy. Cyclophilin A (CypA), the most abundantly expressed cyclophilin, is present mainly in the cytoplasm and is a host factor involved in the life cycle of multiple viruses. The extracellular fractions of CypA and CypB are potent pro-inflammatory mediators. CypD, located in mitochondria, is a key regulator of mitochondrial permeability transition pores, and is critical for necrotic cell death. Cyclosporines are the prototype cyclophilin inhibitors. Cyclic peptides, which bind and inhibit cyclophilins without having immunosuppressive properties, have been generated by chemical modifications of cyclosporin A. In addition, cyclophilin inhibitors that are structurally different from cyclosporines have been synthesized. The involvement of cyclophilins in the pathogenesis of different liver diseases has been established using both in vitro and in vivo investigations, thus indicating that cyclophilin inhibition may be of therapeutic benefit. This review summarises the evidence for potential therapeutic applications of non-immunosuppressive cyclophilin inhibitors, alone or in combination with other agents, in virus-induced liver diseases like hepatitis C, B or Delta, liver inflammation and fibrosis, acetaminophen-induced liver toxicity and hepatocellular carcinoma.

Depletion of cyclophilins B and C leads to dysregulation of endoplasmic reticulum redox homeostasis

Protein folding within the endoplasmic reticulum is assisted by molecular chaperones and folding catalysts that include members of the protein-disulfide isomerase and peptidyl-prolyl isomerase families. In this report, we examined the contributions of the cyclophilin subset of peptidyl-prolyl isomerases to protein folding and identified cyclophilin C as an endoplasmic reticulum (ER) cyclophilin in addition to cyclophilin B. Using albumin and transferrin as models of cis-proline-containing proteins in human hepatoma cells, we found that combined knockdown of cyclophilins B and C delayed transferrin secretion but surprisingly resulted in more efficient oxidative folding and secretion of albumin. Examination of the oxidation status of ER protein-disulfide isomerase family members revealed a shift to a more oxidized state. This was accompanied by a >5-fold elevation in the ratio of oxidized to total glutathione. This "hyperoxidation" phenotype could be duplicated by incubating cells with the cyclophilin inhibitor cyclosporine A, a treatment that triggered efficient ER depletion of cyclophilins B and C by inducing their secretion to the medium. To identify the pathway responsible for ER hyperoxidation, we individually depleted several enzymes that are known or suspected to deliver oxidizing equivalents to the ER: Ero1αβ, VKOR, PRDX4, or QSOX1. Remarkably, none of these enzymes contributed to the elevated oxidized to total glutathione ratio induced by cyclosporine A treatment. These findings establish cyclophilin C as an ER cyclophilin, demonstrate the novel involvement of cyclophilins B and C in ER redox homeostasis, and suggest the existence of an additional ER oxidative pathway that is modulated by ER cyclophilins.

The nuclear retention signal of HPV16 L2 protein is essential for incoming viral genome to transverse the trans-Golgi network

The Human papillomavirus (HPV) capsid is composed of the major and minor capsid proteins, L1 and L2, respectively. Infectious entry requires a complex series of conformational changes in both proteins that lead to uptake and allow uncoating to occur. During entry, the capsid is disassembled and host cyclophilins dissociate L1 protein from the L2/DNA complex. Herein, we describe a mutant HPV16 L2 protein (HPV16 L2-R302/5A) that traffics pseudogenome to the trans-Golgi network (TGN) but fails to egress. Our data provide further evidence that HPV16 traffics through the TGN and demonstrates that L2 is essential for TGN egress. Furthermore, we show that cyclophilin activity is required for the L2/DNA complex to be transported to the TGN which is accompanied by a reduced L1 protein levels.

Secretion of VEGF-165 has unique characteristics, including shedding from the plasma membrane

VEGF secretion is studied using VEGF165-GFP chimera. Efficient secretion requires Sar1- and Arf1-dependent steps and glycosylation in the Golgi. VEGF is retained in the outer surface of the plasma membrane, and shedding with other membrane components is an important step in the secretion process.

Vascular endothelial growth factor (VEGF) is a critical regulator of endothelial cell differentiation and vasculogenesis during both development and tumor vascularization. VEGF-165 is a major form that is secreted from the cells via a poorly characterized pathway. Here we use green fluorescent protein– and epitope-tagged VEGF-165 and find that its early trafficking between the endoplasmic reticulum and the Golgi requires the small GTP-binding proteins Sar1 and Arf1 and that its glycosylation in the Golgi compartment is necessary for efficient post-Golgi transport and secretion from the cells. The relative temperature insensitivity of VEGF secretion and its Sar1 and Arf1 inhibitory profiles distinguish it from other cargoes using the “constitutive” secretory pathway. Prominent features of VEGF secretion are the retention of the protein on the outer surface of the plasma membrane and the stimulation of its secretion by Ca²⁺ and protein kinase C. Of importance, shedding of VEGF-165 from the cell surface together with other membrane components appears to be a unique feature by which some VEGF is delivered to the surroundings to exert its known biological actions. Understanding VEGF trafficking can reveal additional means by which tumor vascularization can be inhibited by pharmacological interventions.

Molecular characterization of cyclophilin A-like protein from Piriformospora indica for its potential role to abiotic stress tolerance in E. coli

Background

Cyclophilins (CyP), conserved in all genera, are known to have regulatory responses of various cellular processes including stress tolerance. Interestingly, CyP has a crucial role as peptidyl-prolyl cis–trans isomerases (PPIases). Our earlier in silico based approach resulted into the identification of cyclophilin family from rice, Arabidopsis and yeast. In our recent report, we discovered a new OsCYP-25 from rice. Here, we identified a novel cyclophylin A-like protein (PiCyP) from Piriformospora indica which is responsible for abiotic stress tolerance in E. coli.

Results

Cyclophylin A-like protein (CyPA) (accession number GQ214003) was selected from cDNA library. The genomic organization CyPA revealed a 1304 bp of CyPA in P. indica genome, showing 10 exons and 9 introns. Further, CyPA was evident in PCR with gDNA and cDNA and Southern blot analysis. The phylogenetic examination of CyPA of P. indica showed that it is closed to human cyclophilin. The uniqueness of PiCyPA protein was apparent in western blot study. Kinetics of purified PiCyPA protein for its PPIas activity was determined via first order rate constant (0.104 s^-1) in the presence of 1 μg of PiCyPA, with increasing PiCyPA concentration, in the presence of cyclosporin A (CsA) and the inhibition constant (4.435 nM) of CsA for inhibition of PiCyPA. The differential response of E. coli harbouring pET28a-PiCypA was observed for their different degree of tolerance to different abiotic stresses as compared to empty pET28a vector.

Conclusions

Overexpression of PiCyPA protein E. coli cells confer enhanced tolerance to wide range of abiotic stresses. Thus, this study provides the significance of PiCypA as a molecular chaperone which advanced cellular stress responses of E. coli cells under adverse conditions, and it, furthermore, confirms the mounting the sustainability of E. coli for exploitation in recombinant proteins production. Additionally, the PiCyPA gene cooperates substantial functions in cellular network of stress tolerance mechanism, essentially required for various developmental stages, and might be a potential paramount candidate for crop improvement and its sustainable production under adverse conditions.

A critical review on fungi mediated plant responses with special emphasis to Piriformospora indica on improved production and protection of crops

The beneficial fungi are potentially useful in agriculture sector to avail several services to crop plants such as water status, nutrient enrichment, stress tolerance, protection, weed control and bio-control. Natural agro-ecosystem relies on fungi because of it takes part in soil organic matter decomposition, nutrient acquisition, organic matter recycling, nutrient recycling, antagonism against plant pests, and crop management. The crucial role of fungi in normalizing the toxic effects of phenols, HCN and ROS by β-CAS, ACC demainase and antioxidant enzymes in plants is well documented. Fungi also play a part in various physiological processes such as water uptake, stomatal movement, mineral uptake, photosynthesis and biosynthesis of lignan, auxins and ethylene to improve growth and enhance plant fitness to cope heat, cold, salinity, drought and heavy metal stress. Here, we highlighted the ethylene- and cyclophilin A (CypA)-mediated response of Piriformospora indica for sustainable crop production under adverse environmental conditions.

Genomic and proteomic analysis of Schizaphis graminum reveals cyclophilin proteins are involved in the transmission of cereal yellow dwarf virus

Yellow dwarf viruses cause the most economically important virus diseases of cereal crops worldwide and are transmitted by aphid vectors. The identification of aphid genes and proteins mediating virus transmission is critical to develop agriculturally sustainable virus management practices and to understand viral strategies for circulative movement in all insect vectors. Two cyclophilin B proteins, S28 and S29, were identified previously in populations of Schizaphisgraminum that differed in their ability to transmit the RPV strain of Cereal yellow dwarf virus (CYDV-RPV). The presence of S29 was correlated with F2 genotypes that were efficient virus transmitters. The present study revealed the two proteins were isoforms, and a single amino acid change distinguished S28 and S29. The distribution of the two alleles was determined in 12 F2 genotypes segregating for CYDV-RPV transmission capacity and in 11 genetically independent, field-collected S. graminum biotypes. Transmission efficiency for CYDV-RPV was determined in all genotypes and biotypes. The S29 isoform was present in all genotypes or biotypes that efficiently transmit CYDV-RPV and more specifically in genotypes that efficiently transport virus across the hindgut. We confirmed a direct interaction between CYDV-RPV and both S28 and S29 using purified virus and bacterially expressed, his-tagged S28 and S29 proteins. Importantly, S29 failed to interact with a closely related virus that is transported across the aphid midgut. We tested for in vivo interactions using an aphid-virus co-immunoprecipitation strategy coupled with a bottom-up LC-MS/MS analysis using a Q Exactive mass spectrometer. This analysis enabled us to identify a third cyclophilin protein, cyclophilin A, interacting directly or in complex with purified CYDV-RPV. Taken together, these data provide evidence that both cyclophilin A and B interact with CYDV-RPV, and these interactions may be important but not sufficient to mediate virus transport from the hindgut lumen into the hemocoel.

Arrest Functions of the MIF Ligand/Receptor Axes in Atherogenesis

Macrophage migration inhibitory factor (MIF) has been defined as an important chemokine-like function (CLF) chemokine with an essential role in monocyte recruitment and arrest. Adhesion of monocytes to the vessel wall and their transendothelial migration are critical in atherogenesis and many other inflammatory diseases. Chemokines carefully control all steps of the monocyte recruitment process. Those chemokines specialized in controlling arrest are typically immobilized on the endothelial surface, mediating the arrest of rolling monocytes by chemokine receptor-triggered pathways. The chemokine receptor CXCR2 functions as an important arrest receptor on monocytes. An arrest function has been revealed for the bona fide CXCR2 ligands CXCL1 and CXCL8, but genetic studies also suggested that additional arrest chemokines are likely to be involved in atherogenic leukocyte recruitment. While CXCR2 is known to interact with numerous CXC chemokine ligands, the CLF chemokine MIF, which structurally does not belong to the CXC chemokine sub-family, was surprisingly identified as a non-cognate ligand of CXCR2, responsible for critical arrest functions during the atherogenic process. MIF was originally identified as macrophage migration inhibitory factor (this function being eponymous), but is now known as a potent inflammatory cytokine with CLFs including chemotaxis and leukocyte arrest. This review will cover the mechanisms underlying these functions, including MIF’s effects on LFA1 integrin activity and signal transduction, and will discuss the structural similarities between MIF and the bona fide CXCR2 ligand CXCL8 while emphasizing the structural differences. As MIF also interacts with CXCR4, a chemokine receptor implicated in CXCL12-elicited lymphocyte arrest, the arrest potential of the MIF/CXCR4 axis will also be scrutinized as well as the recently identified role of pericyte MIF in attracting leukocytes exiting through venules as part of the pericyte “motility instruction program.”

Screening for drug-induced hepatotoxicity in primary mouse hepatocytes using acetaminophen, amiodarone, and cyclosporin a as model compounds: an omics-guided approach

Drug-induced hepatotoxicity is a leading cause of attrition for candidate pharmaceuticals in development. New preclinical screening methods are crucial to predict drug toxicity prior to human studies. Of all in vitro hepatotoxicity models, primary human hepatocytes are considered as 'the gold standard.' However, their use is hindered by limited availability and inter-individual variation. These barriers may be overcome by using primary mouse hepatocytes. We used differential in gel electrophoresis (DIGE) to study large-scale protein expression of primary mouse hepatocytes. These hepatocytes were exposed to three well-defined hepatotoxicants: acetaminophen, amiodarone, and cyclosporin A. Each hepatotoxicant induces a different hepatotoxic phenotype. Based on the DIGE results, the mRNA expression levels of deregulated proteins from cyclosporin A-treated cells were also analyzed. We were able to distinguish cyclosporin A from controls, as well as acetaminophen and amiodarone-treated samples. Cyclosporin A induced endoplasmic reticulum (ER) stress and altered the ER-Golgi transport. Moreover, liver carboxylesterase and bile salt sulfotransferase were differentially expressed. These proteins were associated with a protective adaptive response against cyclosporin A-induced cholestasis. The results of this study are comparable with effects in HepG2 cells. Therefore, we suggest both models can be used to analyze the cholestatic properties of cyclosporin A. Furthermore, this study showed a conserved response between primary mouse hepatocytes and HepG2 cells. These findings collectively lend support for use of omics strategies in preclinical toxicology, and might inform future efforts to better link preclinical and clinical research in rational drug development.

Genome wide analysis of Cyclophilin gene family from rice and Arabidopsis and its comparison with yeast

Cyclophilin proteins are the members of immunophillin group of proteins, known for their property of binding to the immune-suppressant drug cyclosporin A, hence named as cyclophilins. These proteins are characterized by the presence of peptidyl prolyl isomerase (PPIase) domain which catalyzes the cis-trans isomerisation process of proline residues. In the present study, an in-silico based approach was followed to identify and characterize the cyclophilin family from rice, Arabidopsis and yeast. We were able to identify 28 rice, 35 Arabidopsis and 8 yeast cyclophilin genes from their respective genomes on the basis of their annotation as well as the presence of highly conserved PPIase domain. The evolutionary relationship of the cyclophilin genes from the three genomes was analyzed using the phylogenetic tree. We have also classified the rice cyclophilin genes on the basis of localization of the protein in cell. The structural similarity of the cyclophilins was also analyzed on the basis of their homology model. The expression analysis performed using Genevestigator revealed a very strong stress responsive behavior of the gene family which was more prominent in later stages of stress. The study indicates the importance of the gene family in stress response as well as several developmental stages thus opening up many avenues for future study on the cyclophilin proteins.

Development of a flow cytometry live cell assay for the screening of inhibitors of hepatitis C virus (HCV) replication

In this study, we established a flow cytometry live cell-based assay that permits the screening of hepatitis C virus (HCV) inhibitors. Specifically, we created a stable cell line, which harbors a subgenomic replicon encoding an NS5A-YFP fusion protein. This system allows direct measurement of YFP fluorescence in live hepatoma cells in which the HCV replicon replicates. We demonstrated that this stable fluorescent system permits the rapid and sensitive quantification of HCV replication inhibition by direct-acting antiviral agents (DAA) including protease and NS5A inhibitors and host-targeting antiviral agents (HTA) including cyclophilin inhibitors. This flow cytometry-based live cell assay is well suited for multiple applications such as the evaluation of HCV replication as well as antiviral drug screening.

Cyclosporin A impairs the secretion and activity of ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeat)

The protease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeat) cleaves multimers of von Willebrand factor, thus regulating platelet aggregation. ADAMTS13 deficiency leads to the fatal disorder thrombotic thrombocytopenic purpura (TTP). It has been observed that cyclosporin A (CsA) treatment, particularly in transplant patients, may sometimes be linked to the development of TTP. Until now, the reason for such a link was unclear. Here we provide evidence demonstrating that cyclophilin B (CypB) activity plays an important role in the secretion of active ADAMTS13. We found that CsA, an inhibitor of CypB, reduces the secretion of ADAMTS13 and leads to conformational changes in the protein resulting in diminished ADAMTS13 proteolytic activity. A direct, functional interaction between CypB (which possesses peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone functions) and ADAMTS13 is demonstrated using immunoprecipitation and siRNA knockdown of CypB. Finally, CypB knock-out mice were found to have reduced ADAMTS13 levels. Taken together, our findings indicate that cyclophilin-mediated activity is an important factor affecting secretion and activity of ADAMTS13. The large number of proline residues in ADAMTS13 is consistent with the important role of cis-trans isomerization in the proper folding of this protein. These results altogether provide a novel mechanistic explanation for CsA-induced TTP in transplant patients.

Different mechanisms of hepatitis C virus RNA polymerase activation by cyclophilin A and B in vitro

BACKGROUND

Cyclophilins (CyPs) are cellular proteins that are essential to hepatitis C virus (HCV) replication. Since cyclosporine A was discovered to inhibit HCV infection, the CyP pathway contributing to HCV replication is a potential attractive stratagem for controlling HCV infection. Among them, CyPA is accepted to interact with HCV nonstructural protein (NS) 5A, although interaction of CyPB and NS5B, an RNA-dependent RNA polymerase (RdRp), was proposed first.

METHODS

CyPA, CyPB, and HCV RdRp were expressed in bacteria and purified using combination column chromatography. HCV RdRp activity was analyzed in vitro with purified CyPA and CyPB.

RESULTS

CyPA at a high concentration (50× higher than that of RdRp) but not at low concentration activated HCV RdRp. CyPB had an allosteric effect on genotype 1b RdRp activation. CyPB showed genotype specificity and activated genotype 1b and J6CF (2a) RdRps but not genotype 1a or JFH1 (2a) RdRps. CyPA activated RdRps of genotypes 1a, 1b, and 2a. CyPB may also support HCV genotype 1b replication within the infected cells, although its knockdown effect on HCV 1b replicon activity was controversial in earlier reports.

CONCLUSIONS

CyPA activated HCV RdRp at the early stages of transcription, including template RNA binding. CyPB also activated genotype 1b RdRp. However, their activation mechanisms are different.

GENERAL SIGNIFICANCE

These data suggest that both CyPA and CyPB are excellent targets for the treatment of HCV 1b, which shows the greatest resistance to interferon and ribavirin combination therapy.

Cloning, purification, crystallization and preliminary X-ray crystallographic analysis of a cyclophilin A-like protein from Piriformospora indica

Cyclophilins are widely distributed both in eukaryotes and prokaryotes and have a primary role as peptidyl-prolyl cis-trans isomerases (PPIases). This study focuses on the cloning, expression, purification and crystallization of a salinity-stress-induced cyclophilin A (CypA) homologue from the symbiotic fungus Piriformospora indica. Crystallization experiments in the presence of 56 mM sodium phosphate monobasic monohydrate, 1.34 M potassium phosphate dibasic pH 8.2 yielded crystals that were suitable for X-ray diffraction analysis. The crystals belonged to the orthorhombic space group C222(1), with unit-cell parameters a = 121.15, b = 144.12, c = 110.63 Å. The crystals diffracted to a resolution limit of 2.0 Å. Analysis of the diffraction data indicated the presence of three molecules of the protein per asymmetric unit (V(M) = 4.48 Å(3) Da(-1), 72.6% solvent content).

A major prolactin-binding complex on human milk fat globule membranes contains cyclophilins A and B: the complex is not the prolactin receptor

Prolactin (PRL) in milk influences maturation of gastrointestinal epithelium and development of both the hypothalamo-pituitary and immune systems of offspring. Here, we demonstrate that most PRL in human milk is part of a novel, high-affinity, multicomponent binding complex found on the milk fat globule membrane and not in whey. To examine properties of the complex, a sensitive ELISA was developed such that human PRL (hPRL) binding to the complex was measured by loss of hPRL detectability; thus, as much as 50 ng of hPRL was undetectable in the presence of 10 μl of human milk. Using the same methodology, no comparable complex formation was observed with human serum or amniotic fluid. hPRL complexation in milk was rapid, time dependent, and cooperative. Antibodies to or competitors of the hPRL receptor (placental lactogen and growth hormone) showed the hPRL receptor was not involved in the complex. However, hPRL complexation was antagonized by cyclosporine A and anti-cyclophilins. The complex was very stable, resisting dissociation in SDS, urea, and dithiothreitol. Western analysis revealed an ∼75-kDa complex that included hPRL, cyclophilins A and B, and a 16-kDa cyclophilin A. Compared with noncomplexed hPRL, complexed hPRL in whole milk showed similar activation of STAT5 but markedly delayed activation of ERK. Alteration of signaling suggests that complex formation may alter hPRL biological activity. This is the first report of a unique, multicomponent, high-capacity milk fat reservoir of hPRL; all other analyses of milk PRL have utilized defatted milk.

From Drosophila to humans: reflections on the roles of the prolyl isomerases and chaperones, cyclophilins, in cell function and disease

Despite remarkable advances in human genetics and other genetic model systems, the fruit fly, Drosophila melanogaster, remains a powerful experimental tool to probe with ease the inner workings of a myriad of biological and pathological processes, even when evolutionary forces impart apparent divergences to some of such processes. The understanding of such evolutionary differences provides mechanistic insights into genotype-phenotype correlations underpinning biological processes across metazoans. The pioneering work developed by the William Pak laboratory for the past four decades, and the work of others, epitomize the notion of how the Drosophila system breaks new fertile ground or complements research fields of high scientific and medical relevance. Among the three major genetic complementation groups produced by the Pak's laboratory and impairing distinct facets of photoreceptor neuronal function, the nina group (ninaA, …., ninaJ) selectively affects the biogenesis of G protein-coupled receptors (GPCRs), mediating the photoconversion and transduction of light stimuli. Among the nina genes identified, ninaA arguably assumes heightened significance for several reasons. First, it presents unique physiological selectivity toward the biogenesis of a subset of GPCRs, a standalone biological manifestation yet to be discerned for most mammalian homologues of NinaA. Second, NinaA belongs to a family of proteins, immunophilins, which are the primary targets for immunosuppressive drugs at the therapeutic forefront of a multitude of medical conditions. Third, NinaA closest homologue, cyclophilin B (CyPB/PPIB), is an immunophilin whose loss-of-function was found recently to cause osteogenesis imperfecta in the human. This report highlights advances made by studies on some members of immunophilins, the cyclophilins. Finally, it reexamines critically data and dogmas derived from past and recent genetic, structural, biological, and pathological studies on NinaA and few other cyclophilins that support some of such paradigms to be less than definite and advance our understanding of the roles of cyclophilins in cell function, disease, and therapeutic interventions.

Cyclosporine A suppresses immunoglobulin G biosynthesis via inhibition of cyclophilin B in murine hybridomas and B cells

Immunoglubulin G (IgG) is a major isotype of antibody, which is predominantly involved in immune response. The complete tetramer is needed to fold and assemble in endoplasmic reticulum (ER) prior to secretion from cells. Protein quality control guided by ER chaperons is most essential for full biological activity. Cyclophilin B (CypB) was initially identified as a high-affinity binding protein for the immunosuppressive drug Cyclosporine A (CsA). CsA suppresses organ rejection by halting productions of pro-inflammatory molecules in T cell and abolishes the enzymatic property of CypB that accelerates the folding of proteins by catalysing the isomerization of peptidyl-proline bonds in ER. Here, we reported that CsA significantly inhibited IgG biosynthesis at posttranslational level in antibody secreting cells. Moreover, CsA stimulated the extracellular secretion of CypB and induced ROS generation, leading to expressions of ER stress markers. In addition, the absence of intracellular CypB impaired the formation of ER multiprotein complex, which is most important for resisting ER stress. Interestingly, CsA interrupted IgG folding via occupying the PPIase domain of CypB in ER. Eventually, unfolded IgG is degraded via Herp-dependent ERAD pathway. Furthermore, IgG biosynthesis was really abrogated by inhibition of CypB in primary B cells. We established for the first time the immunosuppressive effect of CsA on B cells. Conclusively, the combined results of the current study suggest that CypB is a pivotal molecule for IgG biosynthesis in ER quality control.