Cyclophilin-A Is Bound through Its Peptidylprolyl Isomerase Domain to the Cytoplasmic Dynein Motor Protein Complex

Inhibitors of Cyclophilin A: Current and Anticipated Pharmaceutical Agents for Inflammatory Diseases and Cancers

Cyclophilin A, a widely prevalent cellular protein, exhibits peptidyl-prolyl cis-trans isomerase activity. This protein is predominantly located in the cytosol; additionally, it can be secreted by the cells in response to inflammatory stimuli. Cyclophilin A has been identified to be a key player in many of the biological events and is therefore involved in several diseases, including vascular and inflammatory diseases, immune disorders, aging, and cancers. It represents an attractive target for therapeutic intervention with small molecule inhibitors such as cyclosporin A. Recently, a number of novel inhibitors of cyclophilin A have emerged. However, it remains elusive whether and how many cyclophilin A inhibitors function in the inflammatory diseases and cancers. In this review, we discuss current available data about cyclophilin A inhibitors, including cyclosporin A and its derivatives, quinoxaline derivatives, and peptide analogues, and outline the most recent advances in clinical trials of these agents. Inhibitors of cyclophilin A are poised to enhance our comprehension of the molecular mechanisms that underpin inflammatory diseases and cancers associated with cyclophilin A. This advancement will aid in the development of innovative pharmaceutical treatments in the future.

Corticosteroid receptors as a model for the Hsp90•immunophilin-based transport machinery

Steroid receptors form soluble heterocomplexes with the 90-kDa heat-shock protein (Hsp90) and other chaperones and co-chaperones. The assembly and composition of the oligomer is influenced by the presence and nature of the bound steroid. Although these receptors shuttle dynamically in and out of the nucleus, their primary localization in the absence of steroid can be mainly cytoplasmic, mainly nuclear, or partitioned into both cellular compartments. Upon steroid binding, receptors become localized to the nucleus via the transportosome, a retrotransport molecular machinery that comprises Hsp90, a high-molecular-weight immunophilin, and dynein motors. This molecular machinery, first evidenced in steroid receptors, can also be used by other soluble proteins. In this review, we dissect the complete model of this transport machinery system.

Cyclophilin A is a mitochondrial factor that forms complexes with p23 - correlative evidence for an anti-apoptotic action

Cyclophilin A (CyPA, also known as PPIA) is an abundant and ubiquitously expressed protein belonging to the immunophilin family, which has intrinsic peptidyl-prolyl-(cis/trans)-isomerase enzymatic activity. CyPA mediates immunosuppressive action of the cyclic undecapeptide cyclosporine A and is also involved in multiple cellular processes, such as protein folding, intracellular trafficking, signal transduction and transcriptional regulation. CyPA is abundantly expressed in cancer cells, and, owing to its chaperone nature, its expression is induced upon the onset of stress. In this study, we demonstrated that a significant pool of this immunophilin is primarily an intramitochondrial factor that migrates to the nucleus when cells are stimulated with stressors. CyPA shows anti-apoptotic action per se and the capability of forming ternary complexes with cytochrome c and the small acidic co-chaperone p23, the latter interaction being independent of the usual association of p23 with the heat-shock protein of 90 kDa, Hsp90. These CyPA•p23 complexes enhance the anti-apoptotic response of the cell, suggesting that both proteins form a functional unit, the high level of expression of which plays a significant role in cell survival.

Cyclophilin 19 secreted in the host cell cytosol by Trypanosoma cruzi promotes ROS production required for parasite growth

Infection by Trypanosoma cruzi, the protozoan parasite that causes Chagas disease, depends on reactive oxygen species (ROS), which has been described to induce parasite proliferation in mammalian host cells. It is unknown how the parasite manages to increase host ROS levels. Here, we found that intracellular T. cruzi forms release in the host cytosol its major cyclophilin of 19 kDa (TcCyp19). Parasites depleted of TcCyp19 by using CRISPR/Cas9 gene replacement proliferate inefficiently and fail to increase ROS, compared to wild type parasites or parasites with restored TcCyp19 gene expression. Expression of TcCyp19 in L6 rat myoblast increased ROS levels and restored the proliferation of TcCyp19 depleted parasites. These events could also be inhibited by cyclosporin A, (a cyclophilin inhibitor), and by polyethylene glycol-linked to antioxidant enzymes. TcCyp19 was found more concentrated in the membrane leading edges of the host cells in regions that also accumulate phosphorylated p47^phox , as observed to the endogenous cyclophilin A, suggesting some mechanisms involved with the translocation process of the regulatory subunit p47^phox in the activation of the NADPH oxidase enzymatic complex. We concluded that cyclophilin released in the host cell cytosol by T. cruzi mediates the increase of ROS, required to boost parasite proliferation in mammalian hosts.

Regulation of FKBP51 and FKBP52 functions by post-translational modifications

FKBP51 and FKBP52 are two iconic members of the family of peptidyl-prolyl-(cis/trans)-isomerases (EC: 5.2.1.8), which comprises proteins that catalyze the cis/trans isomerization of peptidyl-prolyl peptide bonds in unfolded and partially folded polypeptide chains and native state proteins. Originally, both proteins have been studied as molecular chaperones belonging to the steroid receptor heterocomplex, where they were first discovered. In addition to their expected role in receptor folding and chaperoning, FKBP51 and FKBP52 are also involved in many biological processes, such as signal transduction, transcriptional regulation, protein transport, cancer development, and cell differentiation, just to mention a few examples. Recent studies have revealed that both proteins are subject of post-translational modifications such as phosphorylation, SUMOlyation, and acetylation. In this work, we summarize recent advances in the study of these immunophilins portraying them as scaffolding proteins capable to organize protein heterocomplexes, describing some of their antagonistic properties in the physiology of the cell, and the putative regulation of their properties by those post-translational modifications.

The prolyl isomerase FKBP25 regulates microtubule polymerization impacting cell cycle progression and genomic stability

FK506 binding proteins (FKBPs) catalyze the interconversion of cis-trans proline conformers in proteins. Importantly, FK506 drugs have anti-cancer and neuroprotective properties, but the effectors and mechanisms underpinning these properties are not well understood because the cellular function(s) of most FKBP proteins are unclear. FKBP25 is a nuclear prolyl isomerase that interacts directly with nucleic acids and is associated with several DNA/RNA binding proteins. Here, we show the catalytic FKBP domain binds microtubules (MTs) directly to promote their polymerization and stabilize the MT network. Furthermore, FKBP25 associates with the mitotic spindle and regulates entry into mitosis. This interaction is important for mitotic spindle dynamics, as we observe increased chromosome instability in FKBP25 knockdown cells. Finally, we provide evidence that FKBP25 association with chromatin is cell-cycle regulated by Protein Kinase C phosphorylation. This disrupts FKBP25-DNA contacts during mitosis while maintaining its interaction with the spindle apparatus. Collectively, these data support a model where FKBP25 association with chromatin and MTs is carefully choreographed to ensure faithful genome duplication. Additionally, they highlight that FKBP25 is a MT-associated FK506 receptor and potential therapeutic target in MT-associated diseases.

Extracellular Matrix Metalloproteinase Inducer EMMPRIN (CD147) in Cardiovascular Disease

The receptor EMMPRIN is involved in the development and progression of cardiovascular diseases and in the pathogenesis of myocardial infarction. There are several binding partners of EMMPRIN mediating the effects of EMMPRIN in cardiovascular diseases. EMMPRIN interaction with most binding partners leads to disease progression by mediating cytokine or chemokine release, the activation of platelets and monocytes, as well as the formation of monocyte-platelet aggregates (MPAs). EMMPRIN is also involved in atherosclerosis by mediating the infiltration of pro-inflammatory cells. There is also evidence that EMMPRIN controls energy metabolism of cells and that EMMPRIN binding partners modulate intracellular glycosylation and trafficking of EMMPRIN towards the cell membrane. In this review, we systematically discuss these multifaceted roles of EMMPRIN and its interaction partners, such as Cyclophilins, in cardiovascular disease.

Cyclophilin A as a target in the treatment of cytomegalovirus infections

BACKGROUND

Viruses are obligate parasites that depend on the cellular machinery of the host to regenerate and manufacture their proteins. Most antiviral drugs on the market today target viral proteins. However, the more recent strategies involve targeting the host cell proteins or pathways that mediate viral replication. This new approach would be effective for most viruses while minimizing drug resistance and toxicity.

METHODS

Cytomegalovirus replication, latency, and immune response are mediated by the intermediate early protein 2, the main protein that determines the effectiveness of drugs in cytomegalovirus inhibition. This review explains how intermediate early protein 2 can modify the action of cyclosporin A, an immunosuppressive, and antiviral drug. It also links all the pathways mediated by cyclosporin A, cytomegalovirus replication, and its encoded proteins.

RESULTS

Intermediate early protein 2 can influence the cellular cyclophilin A pathway, affecting cyclosporin A as a mediator of viral replication or anti-cytomegalovirus drug.

CONCLUSION

Cyclosporin A has a dual function in cytomegalovirus pathogenesis. It has the immunosuppressive effect that establishes virus replication through the inhibition of T-cell function. It also has an anti-cytomegalovirus effect mediated by intermediate early protein 2. Both of these functions involve cyclophilin A pathway.

Extracellular Cyclophilin A Augments Platelet-Dependent Thrombosis and Thromboinflammation

Cyclophilin A (CyPA) is involved in the pathophysiology of several inflammatory and cardiovascular diseases. To our knowledge, there is no specific inhibitor targeting extracellular CyPA without affecting other extracellular cyclophilins or intracellular CyPA functions. In this study, we developed an antibody-based inhibitor of extracellular CyPA and analysed its effects in vitro and in vivo. To generate a specific antibody, mice and rats were immunized with a peptide containing the extracellular matrix metalloproteinase inducer binding site and various antibody clones were selected and purified. At first, antibodies were tested for their binding capacity to recombinant CyPA and their functional activity. The clone 8H7-mAb was chosen for further experiments. 8H7-mAb reduced the CyPA-induced migration of inflammatory cells in vitro and in vivo. Furthermore, 8H7-mAb revealed strong antithrombotic effects by inhibiting CyPA-dependent activation of platelets and thrombus formation in vitro and in vivo. Surprisingly, 8H7-mAb did not influence in vivo tail bleeding time or in vitro whole blood coagulation parameters. Our study provides first evidence that antibody-based inhibition of extracellular CyPA inhibits thrombosis and thromboinflammation without affecting blood homeostasis. Thus, 8H7-mAb may be a promising compound for thrombi modulation in inflammatory diseases to prevent organ dysfunction.

Cyclophilin A Maintains Glioma-Initiating Cell Stemness by Regulating Wnt/β-Catenin Signaling

Purpose: Glioma-initiating cells (GIC) are glioma stem-like cells that contribute to glioblastoma (GBM) development, recurrence, and resistance to chemotherapy and radiotherapy. They have recently become the focus of novel treatment strategies. Cyclophilin A (CypA) is a cytosolic protein that belongs to the peptidyl-prolyl isomerase (PPIase) family and the major intracellular target of the immunosuppressive drug cyclosporin A (CsA). In this study, we investigate the functions of CypA and its mechanism of action in GICs' development.Experimental Design: We analyzed differences in CypA expression between primary tumors and neurospheres from the GDS database, both before and after GIC differentiation. A series of experiments was conducted to investigate the role of CypA in GIC stemness, self-renewal, proliferation, radiotherapy resistance, and mechanism. We then designed glutathione S-transferase (GST) pulldown and coimmunoprecipitation assays to detect signaling activity.Results: In this study, we demonstrated that CypA promotes GIC stemness, self-renewal, proliferation, and radiotherapy resistance. Mechanistically, we found that CypA binds β-catenin and is recruited to Wnt target gene promoters. By increasing the interaction between β-catenin and TCF4, CypA enhances transcriptional activity.Conclusions: Our results demonstrate that CypA enhances GIC stemness, self-renewal, and radioresistance through Wnt/β-catenin signaling. Due to its promotive effects on GICs, CypA is a potential target for future glioma therapy. Clin Cancer Res; 23(21); 6640-9. ©2017 AACR.

Downregulation of Peptidylprolyl isomerase A promotes cell death and enhances doxorubicin-induced apoptosis in hepatocellular carcinoma

Peptidylprolyl isomerase A (PPIA) is a peptidyl-prolyl cis-trans isomerase that is known to play a critical role in the development of many human cancers. However, the precise biological function of PPIA in hepatocellular carcinoma (HCC) remains largely unclear. In this study, lentiviral overexpression vectors and small interfering RNA knockdown methods were employed to investigate the biological effects of PPIA in HCC. PPIA levels in HCC tissues and peritumoral tissues were detected by real-time Polymerase Chain Reaction (RT-PCR), Western blotting, and immunohistochemistry. Our results indicate that PPIA levels were significantly higher in the HCC tissues compared to the matched peritumoral tissues. Moreover, PPIA expression was significantly associated with tumor size in these tissues. Interestingly, serum PPIA (sPPIA) levels were significantly higher in healthy controls compared to the HCC patients. Knockdown or overexpression of PPIA was shown to downregulate and upregulate cell growth, respectively. Moreover, PPIA siRNA knockdown appears to promote doxorubicin-induced apoptosis in HCC cells, altering the expression of downstream apoptotic factors. In summary, our results indicate that PPIA may play a pivotal role in HCC by regulating cell growth and could serve as a novel marker and therapeutic molecular target for HCC patients.

Cyclophilin A Enhances Cell Proliferation and Xenografted Tumor Growth of Early Gastric Cancer

BACKGROUND

Recently Cyclophilin A (CypA) was identified as a candidate target protein in gastric carcinoma. However, the role of CypA in gastric cancer (GC) has not been investigated extensively so far.

AIM

The purpose of this study was to determine the expression pattern of CypA in human GC, and to explore the effects of suppressed CypA expression on cell proliferation and xenografted tumor growth of gastric cancer.

METHODS

In the present study, we detected the expression pattern of CypA in human GC by immunohistochemistry analysis. Further, the RNAi method was used to silence CypA, and colony formation assay, growth curves, cell cycle and mouse xenograft were analysed.

RESULTS

An elevated expression of CypA in GC tissues compared with normal gastric mucosa was observed, especially in TNM stage-I and intestinal type of tumor. CypA was overexpressed in most GC cell lines and endogenous expression of CypA correlated with cell growth phenotypes. Transient suppression of CypA reduced the proliferation of BGC-823 and SGC-7901 GC cell lines. Exogenous CypA promoted the proliferation of NCI-N87 GC cells in a concentration dependent manner. Further study revealed that stable CypA silencing inhibited the proliferation, prevented cell cycle and reduced autophagy of BGC-823 GC cells in vitro through suppressing the ERK1/2 signal pathway. Stable CypA silencing also inhibited the growth of xenografted tumor of BGC-823 GC cell in nude mice.

CONCLUSIONS

These results indicate a special function mode for CypA of playing more important roles in the early stage of gastric tumorigenesis and suggest CypA as a new molecular target of diagnosis and treatment for GC patients.

Prolyl isomerization and its catalysis in protein folding and protein function

Prolyl isomerizations are intrinsically slow processes. They determine the rates of many protein folding reactions and control regulatory events in folded proteins. Prolyl isomerases are able to catalyze these isomerizations, and thus, they have the potential to assist protein folding and to modulate protein function. Here, we provide examples for how prolyl isomerizations limit protein folding and are accelerated by prolyl isomerases and how native-state prolyl isomerizations regulate protein functions. The roles of prolines in protein folding and protein function are closely interrelated because both of them depend on the coupling between cis/trans isomerization and conformational changes that can involve extended regions of a protein.

The cyclophilin A DIAGEOTROPICA gene affects auxin transport in both root and shoot to control lateral root formation

Cyclophilin A is a conserved peptidyl-prolyl cis-trans isomerase (PPIase) best known as the cellular receptor of the immunosuppressant cyclosporine A. Despite significant effort, evidence of developmental functions of cyclophilin A in non-plant systems has remained obscure. Mutations in a tomato (Solanum lycopersicum) cyclophilin A ortholog, DIAGEOTROPICA (DGT), have been shown to abolish the organogenesis of lateral roots; however, a mechanistic explanation of the phenotype is lacking. Here, we show that the dgt mutant lacks auxin maxima relevant to priming and specification of lateral root founder cells. DGT is expressed in shoot and root, and localizes to both the nucleus and cytoplasm during lateral root organogenesis. Mutation of ENTIRE/IAA9, a member of the auxin-responsive Aux/IAA protein family of transcriptional repressors, partially restores the inability of dgt to initiate lateral root primordia but not the primordia outgrowth. By comparison, grafting of a wild-type scion restores the process of lateral root formation, consistent with participation of a mobile signal. Antibodies do not detect movement of the DGT protein into the dgt rootstock; however, experiments with radiolabeled auxin and an auxin-specific microelectrode demonstrate abnormal auxin fluxes. Functional studies of DGT in heterologous yeast and tobacco-leaf auxin-transport systems demonstrate that DGT negatively regulates PIN-FORMED (PIN) auxin efflux transporters by affecting their plasma membrane localization. Studies in tomato support complex effects of the dgt mutation on PIN expression level, expression domain and plasma membrane localization. Our data demonstrate that DGT regulates auxin transport in lateral root formation.

Prolyl isomerases in gene transcription

BACKGROUND

Peptidyl-prolyl isomerases (PPIases) are enzymes that assist in the folding of newly-synthesized proteins and regulate the stability, localization, and activity of mature proteins. They do so by catalyzing reversible (cis-trans) rotation about the peptide bond that precedes proline, inducing conformational changes in target proteins.

SCOPE OF REVIEW

This review will discuss how PPIases regulate gene transcription by controlling the activity of (1) DNA-binding transcription regulatory proteins, (2) RNA polymerase II, and (3) chromatin and histone modifying enzymes.

MAJOR CONCLUSIONS

Members of each family of PPIase (cyclophilins, FKBPs, and parvulins) regulate gene transcription at multiple levels. In all but a few cases, the exact mechanisms remain elusive. Structure studies, development of specific inhibitors, and new methodologies for studying cis/trans isomerization in vivo represent some of the challenges in this new frontier that merges two important fields.

GENERAL SIGNIFICANCE

Prolyl isomerases have been found to play key regulatory roles in all phases of the transcription process. Moreover, PPIases control upstream signaling pathways that regulate gene-specific transcription during development, hormone response and environmental stress. Although transcription is often rate-limiting in the production of enzymes and structural proteins, post-transcriptional modifications are also critical, and PPIases play key roles here as well (see other reviews in this issue). This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.

The Leishmania donovani chaperone cyclophilin 40 is essential for intracellular infection independent of its stage-specific phosphorylation status

During its life cycle, the protozoan pathogen Leishmania donovani is exposed to contrasting environments inside insect vector and vertebrate host, to which the parasite must adapt for extra- and intracellular survival. Combining null mutant analysis with phosphorylation site-specific mutagenesis and functional complementation we genetically tested the requirement of the L. donovani chaperone cyclophilin 40 (LdCyP40) for infection. Targeted replacement of LdCyP40 had no effect on parasite viability, axenic amastigote differentiation, and resistance to various forms of environmental stress in culture, suggesting important functional redundancy to other parasite chaperones. However, ultrastructural analyses and video microscopy of cyp40-/- promastigotes uncovered important defects in cell shape, organization of the subpellicular tubulin network and motility at stationary growth phase. More importantly, cyp40-/- parasites were unable to establish intracellular infection in murine macrophages and were eliminated during the first 24 h post infection. Surprisingly, cyp40-/- infectivity was restored in complemented parasites expressing a CyP40 mutant of the unique S274 phosphorylation site. Together our data reveal non-redundant CyP40 functions in parasite cytoskeletal remodelling relevant for the development of infectious parasites in vitro independent of its phosphorylation status, and provide a framework for the genetic analysis of Leishmania-specific phosphorylation sites and their role in regulating parasite protein function.

Prenatal alcohol exposure modifies glucocorticoid receptor subcellular distribution in the medial prefrontal cortex and impairs frontal cortex-dependent learning

Prenatal alcohol exposure (PAE) has been shown to impair learning, memory and executive functioning in children. Perseveration, or the failure to respond adaptively to changing contingencies, is a hallmark on neurobehavioral assessment tasks for human fetal alcohol spectrum disorder (FASD). Adaptive responding is predominantly a product of the medial prefrontal cortex (mPFC) and is regulated by corticosteroids. In our mouse model of PAE we recently reported deficits in hippocampal formation-dependent learning and memory and a dysregulation of hippocampal formation glucocorticoid receptor (GR) subcellular distribution. Here, we examined the effect of PAE on frontal cortical-dependent behavior, as well as mPFC GR subcellular distribution and the levels of regulators of intracellular GR transport. PAE mice displayed significantly reduced response flexibility in a Y-maze reversal learning task. While the levels of total nuclear GR were reduced in PAE mPFC, levels of GR phosphorylated at serines 203, 211 and 226 were not significantly changed. Cytosolic, but not nuclear, MR levels were elevated in the PAE mPFC. The levels of critical GR trafficking proteins, FKBP51, Hsp90, cyclophilin 40, dynamitin and dynein intermediate chain, were altered in PAE mice, in favor of the exclusion of GR from the nucleus, indicating dysregulation of GR trafficking. Our findings suggest that there may be a link between a deficit in GR nuclear localization and frontal cortical learning deficits in prenatal alcohol-exposed mice.

Hsp90-binding immunophilins as a potential new platform for drug treatment

Immunophilins are proteins that contain a PPIase domain as a family signature. Low-molecular-weight immunophilins were first described associated to immunosuppressive action and protein folding. Recent studies of other members of the family have led to the identification of their participation in basic processes such as protein-protein interactions, signal transduction cascades, cell differentiation, cell cycle progression, metabolic activity, apoptosis mechanisms, microorganisms infection, cancer, neurotrophism and neuroprotection, among several other physiological and pathophysiological processes. Due to all these emerging features, the development of specific ligands for immunophilins appears to have promising perspectives, in particular in the fields of cancer biology and neuroregeneration fields. We review the emerging role of immunophilins in protein transport, transcription regulation, malignancies development and neurotrophic action, in addition to a number of biological properties that transform these proteins in potential targets for novel therapeutic strategies.

Cyclophilin A is required for angiotensin II-induced p47phox translocation to caveolae in vascular smooth muscle cells

OBJECTIVE

Angiotensin II (AngII) signal transduction in vascular smooth muscle cells (VSMC) is mediated by reactive oxygen species (ROS). Cyclophilin A (CyPA) is a ubiquitously expressed cytosolic protein that possesses peptidyl-prolyl cis-trans isomerase activity, scaffold function, and significantly enhances AngII-induced ROS production in VSMC. We hypothesized that CyPA regulates AngII-induced ROS generation by promoting translocation of NADPH oxidase cytosolic subunit p47phox to caveolae of the plasma membrane.

APPROACH AND RESULTS

Overexpression of CyPA in CyPA-deficient VSMC (CyPA(-/-)VSMC) significantly increased AngII-stimulated ROS production. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors (VAS2870 or diphenylene iodonium) significantly attenuated AngII-induced ROS production in CyPA and p47phox-overexpressing CyPA(-/-)VSMC. Cell fractionation and sucrose gradient analyses showed that AngII-induced p47phox plasma membrane translocation, specifically to the caveolae, was reduced in CyPA(-/-)VSMC compared with wild-type-VSMC. Immunofluorescence studies demonstrated that AngII increased p47phox and CyPA colocalization and translocation to the plasma membrane. In addition, immunoprecipitation of CyPA followed by immunoblotting of p47phox and actin showed that AngII increased CyPA and p47phox interaction. AngII-induced p47phox and actin cell cytoskeleton association was attenuated in CyPA(-/-)VSMC. Mechanistically, inhibition of p47phox phosphorylation and phox homology domain deletion attenuated CyPA and p47phox interaction. Finally, cyclosporine A and CyPA-peptidyl-prolyl cis-trans isomerase mutant, R55A, inhibited AngII-stimulated CyPA and p47phox association in VSMC, suggesting that peptidyl-prolyl cis-trans isomerase activity was required for their interaction.

CONCLUSIONS

These findings provide the mechanism by which CyPA is an important regulator for AngII-induced ROS generation in VSMC through interaction with p47phox and cell cytoskeleton, which enhances the translocation of p47phox to caveolae.

HCV NS5A and IRF9 compete for CypA binding

BACKGROUND & AIMS

Cyclophilin A (CypA) is vital for HCV replication. Cyp inhibitors successfully decrease viral loads in HCV-infected patients. However, their mechanisms of action remain unknown. Since interferon (IFN) can also suppress HCV replication, we asked whether a link between CypA and the IFN response exists.

METHODS

We used cellular and recombinant pulldown approaches to investigate the possibility of a specific association of CypA with host ligands.

RESULTS

We found for the first time that CypA binds to a major component of the IFN response - the IFN regulatory factor 9 (IRF9). IRF9 is the DNA-binding component of the transcriptional IFN-stimulated gene factor 3 (ISGF3). CypA binds directly to IRF9 via its peptidyl-prolyl isomerase (PPIase) pocket. Cyp inhibitors such as cyclosporine A (CsA) or non-immunosuppressive derivates such as alisporivir and SCY-635, prevent IRF9-CypA complex formation. CypA binds to the C-terminal IRF-association-domain (IAD), but not to the DNA-binding or linker domains of IRF9. Remarkably, CypA associates with the multimeric ISGF3 complex. We also obtained evidence that CypA neutralization enhances IFN-induced transcription. Interestingly, the hepatitis C virus (HCV) non-structural 5A (NS5A) protein, which is known to modulate the IFN response, competes with IRF9 for CypA binding and can prevent the formation of IRF9-CypA complexes.

CONCLUSIONS

This study demonstrates for the first time that CypA binds specifically to a component of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, IRF9. This study also reveals a novel opportunity of HCV to modulate the IFN response via NS5A.

Uncaria rhynchophylla Upregulates the Expression of MIF and Cyclophilin A in Kainic Acid-Induced Epilepsy Rats: A Proteomic Analysis

Uncaria rhynchophylla (Miq) Jack (UR) is a traditional Chinese herb and is used for the treatment of convulsive disorders, including epilepsy. Our previous study has shown that UR, as well as its major component rhynchophylline (RH), has an anticonvulsive effect and this effect is closely related to its scavenging activities of oxygen free radicals. The purpose of the present study was to investigate the effect of (UR) on the expression of proteins using a proteomics analysis in Sprague-Dawley (SD) rats with kainic acid (KA)-induced epileptic seizures. We profiled the differentially expressed proteins on two-dimensional electrophoresis (2-DE) maps derived from the frontal cortex and hippocampus of rat brain tissue 24 hours after KA-induced epileptic seizures. The results indicated that macrophage migration inhibitory factor (MIF) and cyclophilin A were under expressed in frontal cortex by an average of 0.19- and 0.23-fold, respectively. In the frontal cortex, MIF and cyclophilin A were significantly decreased in the KA group and these decreases were confirmed by the Western blots. However, in the hippocampus, only cyclophilin A was significantly decreased in the KA group. In addition, in real-time quantitative PCR (Q-PCR), MIF and cyclophilin A gene expressions were also significantly under expressed in the frontal cortex, and only the cyclophilin A gene was also significantly under expressed in the hippocampus in the KA group. These under expressions of MIF and cyclophilin A could be overcome by the treatment of UR and RH. In conclusion, the under expressions of MIF and cyclophilin A in the frontal cortex and hippocampus in KA-treated rats, which were overcome by both UR and UH treatment, suggesting that both MIF and cyclophilin A at least partly participate in the anticonvulsive effect of UR.

Cyclophilin A enhances cell proliferation and tumor growth of liver fluke-associated cholangiocarcinoma

Background

Cyclophilin A (CypA) expression is associated with malignant phenotypes in many cancers. However, the role and mechanisms of CypA in liver fluke-associated cholangiocarcinoma (CCA) are not presently known. In this study, we investigated the expression of CypA in CCA tumor tissues and CCA cell lines as well as regulation mechanisms of CypA in tumor growth using CCA cell lines.

Methods

CypA expression was determined by real time RT-PCR, Western blot or immunohistochemistry. CypA silence or overexpression in CCA cells was achieved using gene delivery techniques. Cell proliferation was assessed using MTS assay or Ki-67 staining. The effect of silencing CypA on CCA tumor growth was determined in nude mice. The effect of CypA knockdown on ERK1/2 activation was assessed by Western blot.

Results

CypA was upregulated in 68% of CCA tumor tissues. Silencing CypA significantly suppressed cell proliferation in several CCA cell lines. Likewise, inhibition of CypA peptidyl-prolyl cis-trans isomerase (PPIase) activity using cyclosporin A (CsA) decreased cell proliferation. In contrast, overexpression of CypA resulted in 30% to 35% increases in proliferation of CCA cell lines. Interestingly, neither silence nor overexpression of CypA affected cell proliferation of a non-tumor human cholangiocyte cell line, MMNK1. Suppression of CypA expression attenuated ERK1/2 activity in CCA M139 cells by using both transient and stable knockdown methods. In the in vivo study, there was a 43% reduction in weight of tumors derived from CypA-silenced CCA cell lines compared with control vector CCA tumors in mice; these tumors with stable CypA silencing showed a reduced cell proliferation.

Conclusions

CypA is upregulated in majority of CCA patients' tissues and confers a significant growth advantage in CCA cells. Suppression of CypA expression decreases proliferation of CCA cell lines in vitro and reduces tumor growth in the nude mouse model. Inhibition of CypA activity also reduces CCA cell proliferation. The ERK1/2 pathway may be involved in the CypA-mediated CCA cell proliferation. Thus, CypA may represent an important new therapeutic target for liver fluke-associated CCA.

Management of cytoskeleton architecture by molecular chaperones and immunophilins

Cytoskeletal structure is continually remodeled to accommodate normal cell growth and to respond to pathophysiological cues. As a consequence, several cytoskeleton-interacting proteins become involved in a variety of cellular processes such as cell growth and division, cell movement, vesicle transportation, cellular organelle location and function, localization and distribution of membrane receptors, and cell-cell communication. Molecular chaperones and immunophilins are counted among the most important proteins that interact closely with the cytoskeleton network, in particular with microtubules and microtubule-associated factors. In several situations, heat-shock proteins and immunophilins work together as a functionally active heterocomplex, although both types of proteins also show independent actions. In circumstances where homeostasis is affected by environmental stresses or due to genetic alterations, chaperone proteins help to stabilize the system. Molecular chaperones facilitate the assembly, disassembly and/or folding/refolding of cytoskeletal proteins, so they prevent aberrant protein aggregation. Nonetheless, the roles of heat-shock proteins and immunophilins are not only limited to solve abnormal situations, but they also have an active participation during the normal differentiation process of the cell and are key factors for many structural and functional rearrangements during this course of action. Cytoskeleton modifications leading to altered localization of nuclear factors may result in loss- or gain-of-function of such factors, which affects the cell cycle and cell development. Therefore, cytoskeletal components are attractive therapeutic targets, particularly microtubules, to prevent pathological situations such as rapidly dividing tumor cells or to favor the process of cell differentiation in other cases. In this review we will address some classical and novel aspects of key regulatory functions of heat-shock proteins and immunophilins as housekeeping factors of the cytoskeletal network.

The 90-kDa heat-shock protein (Hsp90)-binding immunophilin FKBP51 is a mitochondrial protein that translocates to the nucleus to protect cells against oxidative stress

Confocal microscopy images revealed that the tetratricopeptide repeat motif (TPR) domain immunophilin FKBP51 shows colocalization with the specific mitochondrial marker MitoTracker. Signal specificity was tested with different antibodies and by FKBP51 knockdown. This unexpected subcellular localization of FKBP51 was confirmed by colocalization studies with other mitochondrial proteins, biochemical fractionation, and electron microscopy imaging. Interestingly, FKBP51 forms complexes in mitochondria with the glucocorticoid receptor and the Hsp90/Hsp70-based chaperone heterocomplex. Although Hsp90 inhibitors favor FKBP51 translocation from mitochondria to the nucleus in a reversible manner, TPR domain-deficient mutants of FKBP51 are constitutively nuclear and fully excluded from mitochondria, suggesting that a functional TPR domain is required for its mitochondrial localization. FKBP51 overexpression protects cells against oxidative stress, whereas FKBP51 knockdown makes them more sensitive to injury. In summary, this is the first demonstration that FKBP51 is a major mitochondrial factor that undergoes nuclear-mitochondrial shuttling, an observation that may be related to antiapoptotic mechanisms triggered during the stress response.

Bending tau into shape: the emerging role of peptidyl-prolyl isomerases in tauopathies

The Hsp90-associated cis-trans peptidyl-prolyl isomerase--FK506 binding protein 51 (FKBP51)--was recently found to co-localize with the microtubule (MT)-associated protein tau in neurons and physically interact with tau in brain tissues from humans who died from Alzheimer's disease (AD). Tau pathologically aggregates in neurons, a process that is closely linked with cognitive deficits in AD. Tau typically functions to stabilize and bundle MTs. Cellular events like calcium influx destabilize MTs, disengaging tau. This excess tau should be degraded, but sometimes it is stabilized and forms higher-order aggregates, a pathogenic hallmark of tauopathies. FKBP51 was also found to increase in forebrain neurons with age, further supporting a novel role for FKBP51 in tau processing. This, combined with compelling evidence that the prolyl isomerase Pin1 regulates tau stability and phosphorylation dynamics, suggests an emerging role for isomerization in tau pathogenesis.

Involvement of cyclophilin B in the replication of Japanese encephalitis virus

Japanese encephalitis virus (JEV) is a mosquito-borne RNA virus that belongs to the Flaviviridae family. In this study, we have examined the effect of cyclosporin A (CsA) on the propagation of JEV. CsA exhibited potent anti-JEV activity in various mammalian cell lines through the inhibition of CypB. The propagation of JEV was impaired in the CypB-knockdown cells and this reduction was cancelled by the expression of wild-type but not of peptidylprolyl cis-trans isomerase (PPIase)-deficient CypB, indicating that PPIase activity of CypB is critical for JEV propagation. Infection of pseudotype viruses bearing JEV envelope proteins was not impaired by the knockdown of CypB, suggesting that CypB participates in the replication but not in the entry of JEV. CypB was colocalized and immunoprecipitated with JEV NS4A in infected cells. These results suggest that CypB plays a crucial role in the replication of JEV through an interaction with NS4A.

Inhibition of Drp1-dependent mitochondrial fragmentation and apoptosis by a polypeptide antagonist of calcineurin

During apoptosis, mitochondria lose their membrane potential and undergo fragmentation around the time of release of cytochrome c. Apoptotic fission is at least in part sustained by the translocation of dynamin-related protein 1 (Drp1), normally located in the cytosol, to mitochondria. This process depends on dephosphorylation of Drp1 by the phosphatase calcineurin. Here, we report the identification of a novel inhibitor of this process. A polypeptide (PPD1) from the immunophilin FKBP52 inhibits calcineurin activation triggered by mitochondrial dysfunction. PPD1 blocks Drp1 translocation to mitochondria and fragmentation of the organelle. PPD1 delays apoptosis by intrinsic stimuli by preventing fragmentation and release of cytochrome c. Cells expressing PPD1 display enhanced clonogenic ability after exposure to staurosporine. A genetic analysis revealed that the activity of PPD1 is independent of the BH3-only protein BAD, another target of calcineurin during apoptosis, and is not additive to inhibition of Drp1. Thus, PPD1 is a novel inhibitor of apoptosis that elucidates the function of calcineurin-dependent mitochondrial fragmentation in the amplification of cell death.

Nuclear import of the glucocorticoid receptor-hsp90 complex through the nuclear pore complex is mediated by its interaction with Nup62 and importin beta

Glucocorticoid receptor (GR) is cytoplasmic in the absence of ligand and localizes to the nucleus after steroid binding. Previous evidence demonstrated that the hsp90-based heterocomplex bound to GR is required for the efficient retrotransport of the receptor to the nuclear compartment. We examined the putative association of GR and its associated chaperone heterocomplex with structures of the nuclear pore. We found that importin beta and the integral nuclear pore glycoprotein Nup62 interact with hsp90, hsp70, p23, and the TPR domain proteins FKBP52 and PP5. Nup62 and GR were able to interact in a more efficient manner when chaperoned by the hsp90-based heterocomplex. Interestingly, the binding of hsp70 and p23 to Nup62 does not require the presence of hsp90, whereas the association of FKBP52 and PP5 is hsp90 dependent, as indicated by the results of experiments where the hsp90 function was disrupted with radicicol. The ability of both FKBP52 and PP5 to interact with Nup62 was abrogated in cells overexpressing the TPR peptide. Importantly, GR cross-linked to the hsp90 heterocomplex was able to translocate to the nucleus in digitonin-permeabilized cells treated with steroid, suggesting that GR could pass through the pore in its untransformed state.

Suppression of GATA-3 nuclear import and phosphorylation: a novel mechanism of corticosteroid action in allergic disease

BACKGROUND

GATA-3 plays a critical role in regulating the expression of the cytokines interleukin (IL)-4, IL-5, and IL-13 from T helper-2 (Th2) cells and therefore is a key mediator of allergic diseases. Corticosteroids are highly effective in suppressing allergic inflammation, but their effects on GATA-3 are unknown. We investigated the effect of the corticosteroid fluticasone propionate on GATA-3 regulation in human T-lymphocytes in vitro and in vivo.

METHODS AND FINDINGS

In a T lymphocyte cell line (HuT-78) and peripheral blood mononuclear cells stimulated by anti-CD3 and anti-CD28 in vitro we demonstrated that fluticasone inhibits nuclear translocation of GATA-3 and expression of Th2 cytokines via a mechanism independent of nuclear factor-kappaB and is due, in part, to competition between GATA-3 and the ligand-activated glucocorticoid receptor for nuclear transport through the nuclear importer importin-alpha. In addition, fluticasone induces the expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1), the endogenous inhibitor of p38 MAPK, which is necessary for GATA-3 nuclear translocation. These inhibitory effects of fluticasone are rapid, potent, and prolonged. We also demonstrated that inhaled fluticasone inhibits GATA-3 nuclear translocation in peripheral blood lymphocytes of patients with asthma in vivo.

CONCLUSIONS

Corticosteroids have a potent inhibitory effect on GATA-3 via two interacting mechanisms that potently suppress Th2 cytokine expression. This novel mechanism of action of corticosteroids may account for the striking clinical efficacy of corticosteroids in the treatment of allergic diseases.

Multidimensional degradomics identifies systemic autoantigens and intracellular matrix proteins as novel gelatinase B/MMP-9 substrates

The action radius of matrix metalloproteinases or MMPs is not restricted to massive extracellular matrix (ECM) degradation, it extends to the proteolysis of numerous secreted and membrane-bound proteins. Although many instances exist in which cells disintegrate, often in conjunction with induction of MMPs, the intracellular MMP substrate repertoire or degradome remains relatively unexplored. We started an unbiased exploration of the proteolytic modification of intracellular proteins by MMPs, using gelatinase B/MMP-9 as a model enzyme. To this end, multidimensional degradomics technology was developed by the integration of broadly available biotechniques. In this way, 100-200 MMP-9 candidate substrates were isolated, of which 69 were identified. Integration of these results with the known biological functions of the substrates revealed many novel MMP-9 substrates from the intracellular matrix (ICM), such as actin, tubulin, gelsolin, moesin, ezrin, Arp2/3 complex subunits, filamin B and stathmin. About 2/3 of the identified candidates were autoantigens described in multiple autoimmune conditions and in cancer (e.g. annexin I, nucleolin, citrate synthase, HMGB1, alpha-enolase, histidyl-tRNA synthetase, HSP27, HSC70, HSP90, snRNP D3). These findings led to the insight that MMPs and other proteases may have novel (immuno)regulatory properties by the clearance of toxic and immunogenic burdens of abundant ICM proteins released after extensive necrosis. In line with the extracellular processing of organ-specific autoantigens, proteolysis might also assist in the generation of immunodominant 'neo-epitopes' from systemic autoantigens. The study of proteolysis of ICM molecules, autoantigens, alarmins and other crucial intracellular molecules may result in the discovery of novel roles for proteolytic modification.

Cyclophilin A interacts with influenza A virus M1 protein and impairs the early stage of the viral replication

Influenza A virus matrix protein (M1) is the most abundant conservative protein that regulates the replication, assembly and budding of the viral particles upon infection. Several host cell factors have been determined to interact with M1 possibly in regulating influenza virus replication. By yeast two-hybrid screening, the isomerase cyclophilin A (CypA) was identified to interact with the M1 protein. CypA specifically interacted with M1 both in vitro and in vivo. The mutagenesis results showed CypA bound to the functional middle (M) domain of M1. The depletion of endogenous CypA by RNA interference resulted in the increase of influenza virus infectivity while overexpression of CypA caused decreasing the infectivity in affected cells. The immunofluorescence assays indicated that overexpressed CypA deduced the infectivity and inhibited the translocation of M1 protein into the nucleus while did not affect nucleoprotein entering the nucleus. Further studies indicated that overexpression of CypA significantly increased M1 self-association. Western blot with purified virions confirmed that CypA was encapsidated within the virus particle. These results together indicated that CypA interacted with the M1 protein and affected the early stage of the viral replication.

Targeted ablation reveals a novel role of FKBP52 in gene-specific regulation of glucocorticoid receptor transcriptional activity

FKBP52 is a tetratricopeptide repeat (TPR) protein with peptidyl-prolyl isomerase activity and is found in steroid receptor complexes, including glucocorticoid receptor (GR). It is generally accepted that FKBP52 has a stimulatory effect on GR transcriptional activity. However, the mechanism by which FKBP52 controls GR is not yet clear, with reports showing effects on GR hormone-binding affinity and/or hormone-induced nuclear translocation. To address this issue, we have generated mice with targeted ablation of the FKBP52 gene. To date, no overt defects of GR-regulated physiology have been found in these animals, demonstrating that FKBP52 is not an essential regulator of global GR activity. To better assess the impact of FKBP52 on GR, mouse embryonic fibroblasts (MEFs) were generated from wild-type (WT) and FKBP52-deficient (KO) animals. Analysis of GR activity at reporter genes showed an approximate 70% reduction of activity in 52KO MEF cells, with no effect of FKBP52 loss on thyroid receptor. Interestingly, GR activity at endogenous genes was not globally affected in 52KO cells, with reduced activity at GILZ and FKBP51, but not at SGK and p21. Thus, FKBP52 appears to be a gene-specific modulator of GR. To investigate the mechanism of this action, analyses of GR heterocomplex composition, hormone-binding affinity, and ability to undergo hormone-induced nuclear translocation and DNA-binding were performed. Interestingly, no effect of FKBP52 loss was found for any of these GR properties, suggesting that the main function of FKBP52 is a heretofore-unknown ability to control GR activity at target genes. Lastly, loss of FKBP52 did not affect the ability of GR to undergo hormone-induced autologous down-regulation, showing that FKBP52 does not contribute to all branches of GR signaling. The implications of these results to the potential actions of FKBP52 on GR activity in vivo are discussed.

Coupling genetics and proteomics to identify aphid proteins associated with vector-specific transmission of polerovirus (luteoviridae)

Cereal yellow dwarf virus-RPV (CYDV-RPV) is transmitted specifically by the aphids Rhopalosiphum padi and Schizaphis graminum in a circulative nonpropagative manner. The high level of vector specificity results from the vector aphids having the functional components of the receptor-mediated endocytotic pathways to allow virus to transverse the gut and salivary tissues. Studies of F(2) progeny from crosses of vector and nonvector genotypes of S. graminum showed that virus transmission efficiency is a heritable trait regulated by multiple genes acting in an additive fashion and that gut- and salivary gland-associated factors are not genetically linked. Utilizing two-dimensional difference gel electrophoresis to compare the proteomes of vector and nonvector parental and F(2) genotypes, four aphid proteins (S4, S8, S29, and S405) were specifically associated with the ability of S. graminum to transmit CYDV-RPV. The four proteins were coimmunoprecipitated with purified RPV, indicating that the aphid proteins are capable of binding to virus. Analysis by mass spectrometry identified S4 as a luciferase and S29 as a cyclophilin, both of which have been implicated in macromolecular transport. Proteins S8 and S405 were not identified from available databases. Study of this unique genetic system coupled with proteomic analysis indicated that these four virus-binding aphid proteins were specifically inherited and conserved in different generations of vector genotypes and suggests that they play a major role in regulating polerovirus transmission.

The immunophilin ligands cyclosporin A and FK506 suppress prostate cancer cell growth by androgen receptor-dependent and -independent mechanisms

The androgen receptor (AR) contributes to growth of prostate cancer even under conditions of androgen ablation. Thus, new strategies to target AR activity are needed. The AR interacts with the immunophilin FK506-binding protein 52 (FKBP52), and studies in the FKBP52 knockout mouse have shown that this protein is essential to AR activity in the prostate. Therefore, we tested whether the immunophilin ligand FK506 affected AR activity in prostate cancer cell lines. We also tested the hypothesis that the AR interacts with another immunophilin, cyclophilin 40 (Cyp40), and is regulated by its cognate ligand cyclosporin A (CsA). We show that levels of FKBP52, FKBP51, Cyp40, and a related co-chaperone PP5 were much higher in prostate cancer cells lines [(LNCaP), PC-3, and DU145] compared with primary prostate cells, and that the AR of LNCaP cells can interact with Cyp40. In the absence of androgen, CsA caused inhibition of cell growth in the AR-positive LNCaP and AR-negative PC-3 and DU145 cell lines. Interestingly, FK506 only inhibited LNCaP cells, suggesting a dependence on the AR for this effect. Both CsA and FK506 inhibited growth without inducing apoptosis. In LNCaP cells, CsA completely blocked androgen-stimulated growth, whereas FK506 was partially effective. Further studies in LNCaP cells revealed that CsA and FK506 were able to block or attenuate several stages of AR signaling, including hormone binding, nuclear translocation, and activity at several AR-responsive reporter and endogenous genes. These findings provide the first evidence that CsA and FK506 can negatively modulate proliferation of prostate cells in vitro. Immunophilins may now serve as new targets to disrupt AR-mediated prostate cancer growth.

Cyclophilin A participates in the nuclear translocation of apoptosis-inducing factor in neurons after cerebral hypoxia-ischemia

Upon cerebral hypoxia-ischemia (HI), apoptosis-inducing factor (AIF) can move from mitochondria to nuclei, participate in chromatinolysis, and contribute to the execution of cell death. Previous work (Cande, C., N. Vahsen, I. Kouranti, E. Schmitt, E. Daugas, C. Spahr, J. Luban, R.T. Kroemer, F. Giordanetto, C. Garrido, et al. 2004. Oncogene. 23:1514–1521) performed in vitro suggests that AIF must interact with cyclophilin A (CypA) to form a proapoptotic DNA degradation complex. We addressed the question as to whether elimination of CypA may afford neuroprotection in vivo. 9-d-old wild-type (WT), CypA^+/−, or CypA^−/− mice were subjected to unilateral cerebral HI. The infarct volume after HI was reduced by 47% (P = 0.0089) in CypA^−/− mice compared with their WT littermates. Importantly, CypA^−/− neurons failed to manifest the HI-induced nuclear translocation of AIF that was observed in WT neurons. Conversely, CypA accumulated within the nuclei of damaged neurons after HI, and this nuclear translocation of CypA was suppressed in AIF-deficient harlequin mice. Immunoprecipitation of AIF revealed coprecipitation of CypA, but only in injured, ischemic tissue. Surface plasmon resonance revealed direct molecular interactions between recombinant AIF and CypA. These data indicate that the lethal translocation of AIF to the nucleus requires interaction with CypA, suggesting a model in which two proteins that normally reside in separate cytoplasmic compartments acquire novel properties when moving together to the nucleus.

Evidence that intracellular cyclophilin A and cyclophilin A/CD147 receptor-mediated ERK1/2 signalling can protect neurons against in vitro oxidative and ischemic injury

We previously reported that cyclophilin A protein is up-regulated in cortical neuronal cultures following several preconditioning treatments. In the present study, we have demonstrated that adenoviral-mediated over-expression of cyclophilin A in rat cortical neuronal cultures can protect neurons from oxidative stress (induced by cumene hydroperoxide) and in vitro ischemia (induced by oxygen glucose deprivation). We subsequently demonstrated that cultured neurons, but not astrocytes, express the recently identified putative cyclophilin A receptor, CD147 (also called neurothelin, basigin and EMMPRIN), and that administration of purified cyclophilin A protein to neuronal cultures induces a rapid but transient phosphorylation of the extracellular signal-regulated kinase (ERK) 1/2. Furthermore, administration of purified cyclophilin A protein to neuronal cultures protects neurons from oxidative stress and in vitro ischemia. Interestingly, we detected up-regulation of cyclophilin A mRNA, but not protein in the hippocampus following a 3-min period of sublethal global cerebral ischemia in the rat. Despite our in vivo findings, our in vitro data show that cyclophilin A has both intracellular- and extracellular-mediated neuroprotective mechanisms. To this end, we propose cyclophilin A's extracellular-mediated neuroprotection occurs via CD147 receptor signalling, possibly by activation of ERK1/2 pro-survival pathways. Further characterization of cyclophilin A's neuroprotective mechanisms may aid the development of a neuroprotective therapy.

cis-Regulatory control of cyclophilin, a member of the ETS-DRI skeletogenic gene battery in the sea urchin embryo

The Strongylocentrotus purpuratus cyclophilin1 gene (Sp-cyp1) is expressed exclusively in skeletogenic mesenchyme cells of the embryo, beginning in the micromere lineage of the early blastula stage and continuing after gastrulation during the syncytial deposition of the skeleton. This gene encodes a protein which is a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family. Sp-cyp1 is among the differentiation genes activated in the skeletogenic territory as a terminal function of the endomesodermal gene regulatory network. Network perturbation analysis had predicted the skeletogenic regulators Ets1 and Deadringer (Dri) to be its driver inputs. Here, we show that a 218-bp cis-regulatory DNA fragment recapitulates skeletogenic Sp-cyp1 expression; that elimination of either Ets1 or Dri inputs severely depresses the activity of expression constructs containing this DNA fragment; and that Ets1 and Dri target sites within the 218 bp fragment are required for normal expression. This indicates that the predicted inputs are direct. Other studies indicate that the same inputs are evidently necessary for expression of several other skeletogenic differentiation genes, and these genes probably constitute a skeletogenic gene battery, defined by its Ets plus Dri regulatory inputs.

Chaperoning of glucocorticoid receptors

A multiprotein hsp90/hsp70-based chaperone machinery functions as a 'cradle-to-grave' system for regulating the steroid binding, trafficking and turnover of the glucocorticoid receptor (GR). In an ATP-dependent process where hsp70 and hsp90 act as essential chaperones and Hop, hsp40, and p23 act as nonessential co-chaperones, the machinery assembles complexes between the ligand binding domain of the GR and hsp90. During GR-hsp90 heterocomplex assembly, the hydrophobic ligand-binding cleft is opened to access by steroid, and subsequent binding of steroid within the cleft triggers a transformation of the receptor such that it engages in more dynamic cycles of assembly/disassembly with hsp90 that are required for rapid dynein-dependent translocation to the nucleus. Within the nucleus, the hsp90 chaperone machinery plays a critical role both in GR movement to transcription regulatory sites and in the disassembly of regulatory complexes as the hormone level declines. The chaperone machinery also plays a critical role in stabilization of the GR to ubiquitylation and proteasomal degradation. The initial GR interaction with hsp70 appears to be critical for the triage between hsp90 heterocomplex assembly and preservation of receptor function vs CHIP-dependent ubiquitylation and proteasomal degradation. The hsp90 chaperone machinery is ubiquitous and functionally conserved among eukaryotes, and it is possible that all physiologically significant actions of hsp90 require the hsp70-dependent assembly of client protein-hsp90 heterocomplexes.