Human cyclophilin 40 is a heat shock protein that exhibits altered intracellular localization following heat shock

Mycobacterium tuberculosis Peptidyl-Prolyl Isomerases Are Immunogenic, Alter Cytokine Profile and Aid in Intracellular Survival

Mycobacterium tuberculosis (M. tb) has two peptidyl-prolyl isomerases (Ppiases) PpiA and PpiB, popularly known as cyclophilin A and cyclophilin B. The role of cyclophilins in processes such as signaling, cell surface recognition, chaperoning, and heat shock response has been well-documented. We present evidence that M. tb Ppiases modulate the host immune response. ELISA results revealed significant presence of antibodies to M. tb Ppiases in patient sera as compared to sera from healthy individuals. Treatment of THP-1 cells with increasing concentrations of rPpiA, induced secretion of pro-inflammatory cytokines TNF-α and IL-6. Alternatively, treatment with rPpiB inhibited secretion of TNF-α and induced secretion of IL-10. Furthermore, heterologous expression of M. tb PpiA and PpiB in Mycobacterium smegmatis increased bacterial survival in THP-1 cells as compared to those transformed with the vector control. Our results demonstrate that M. tb Ppiases are immunogenic proteins that can possibly modulate host immune response and enhance persistence of the pathogen within the host by subverting host cell generated stresses.

Mycobacterium tuberculosis Peptidyl-Prolyl Isomerases Also Exhibit Chaperone like Activity In-Vitro and In-Vivo

Peptidyl-prolyl cis-trans isomerases (Ppiases), also known as cyclophilins, are ubiquitously expressed enzymes that assist in protein folding by isomerization of peptide bonds preceding prolyl residues. Mycobacterium tuberculosis (M.tb) is known to possess two Ppiases, PpiA and PpiB. However, our understanding about the biological significance of mycobacterial Ppiases with respect to their pleiotropic roles in responding to stress conditions inside the macrophages is restricted. This study describes chaperone-like activity of mycobacterial Ppiases. We show that recombinant rPpiA and rPpiB can bind to non-native proteins in vitro and can prevent their aggregation. Purified rPpiA and rPpiB exist in oligomeric form as evident from gel filtration chromatography.E. coli cells overexpressing PpiA and PpiB of M.tb could survive thermal stress as compared to plasmid vector control. HEK293T cells transiently expressing M.tb PpiA and PpiB proteins show increased survival as compared to control cells in response to oxidative stress and hypoxic conditions generated after treatment with H₂O₂ and CoCl₂ thereby pointing to their likely role in adaption under host generated oxidative stress and conditions of hypoxia. The chaperone-like function of these M.tuberculosis cyclophilins may possibly function as a stress responder and consequently contribute to virulence.

Activation of the Mitochondrial Apoptotic Signaling Platform during Rubella Virus Infection

Mitochondria- as well as p53-based signaling pathways are central for the execution of the intrinsic apoptotic cascade. Their contribution to rubella virus (RV)-induced apoptosis was addressed through time-specific evaluation of characteristic parameters such as permeabilization of the mitochondrial membrane and subsequent release of the pro-apoptotic proteins apoptosis-inducing factor (AIF) and cytochrome c from mitochondria. Additionally, expression and localization pattern of p53 and selected members of the multifunctional and stress-inducible cyclophilin family were examined. The application of pifithrin μ as an inhibitor of p53 shuttling to mitochondria reduced RV-induced cell death to an extent similar to that of the broad spectrum caspase inhibitor z-VAD-fmk (benzyloxycarbonyl-V-A-D-(OMe)-fmk). However, RV progeny generation was not altered. This indicates that, despite an increased survival rate of its cellular host, induction of apoptosis neither supports nor restricts RV replication. Moreover, some of the examined apoptotic markers were affected in a strain-specific manner and differed between the cell culture-adapted strains: Therien and the HPV77 vaccine on the one hand, and a clinical isolate on the other. In summary, the results presented indicate that the transcription-independent mitochondrial p53 program contributes to RV-induced apoptosis.

Adipogenesis is under surveillance of Hsp90 and the high molecular weight Immunophilin FKBP51

Adipose tissue plays a central role in the control of energy balance as well as in the maintenance of metabolic homeostasis. It was not until recently that the first evidences of the role of heat shock protein (Hsp) 90 and high molecular weight immunophilin FKBP51 have been described in the process of adipocyte differentiation. Recent reports describe their role in the regulation of PPARγ, a key transcription factor in the control of adipogenesis and the maintenance of the adipocyte phenotype. In addition, novel roles have been uncovered for FKBP51 in the organization of the architecture of the nucleus through its participation in the reorganization of the nuclear lamina. Therefore, the aim of this review is to integrate and discuss the recent advances in the field, with special emphasis on the roles of Hsp90 and FKBP51 in the process of adipocyte differentiation.

Cyclophilin40 isomerase activity is regulated by a temperature-dependent allosteric interaction with Hsp90

Cyclophilin 40 (Cyp40) comprises an N-terminal cyclophilin domain with peptidyl-prolyl isomerase (PPIase) activity and a C-terminal tetratricopeptide repeat (TPR) domain that binds to the C-terminal-EEVD sequence common to both heat shock protein 70 (Hsp70) and Hsp90. We show in the present study that binding of peptides containing the MEEVD motif reduces the PPIase activity by ∼30%. CD and fluorescence assays show that the TPR domain is less stable than the cyclophilin domain and is stabilized by peptide binding. Isothermal titration calorimetry (ITC) shows that the affinity for the-MEEVD peptide is temperature sensitive in the physiological temperature range. Results from these biophysical studies fit with the MD simulations of the apo and holo (peptide-bound) structures which show a significant reduction in root mean square (RMS) fluctuation in both TPR and cyclophilin domains when-MEEVD is bound. The MD simulations of the apo-protein also highlight strong anti-correlated motions between residues around the PPIase-active site and a band of residues running across four of the seven helices in the TPR domain. Peptide binding leads to a distortion in the shape of the active site and a significant reduction in these strongly anti-correlated motions, providing an explanation for the allosteric effect of ligand binding and loss of PPIase activity. Together the experimental and MD results suggest that on heat shock, dissociation of Cyp40 from complexes mediated by the TPR domain leads to an increased pool of free Cyp40 capable of acting as an isomerase/chaperone in conditions of cellular stress.

Cyclophilin 40 alters UVA-induced apoptosis and mitochondrial ROS generation in keratinocytes

The CyP40 protein encoded by PPID gene is a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family. PPIases catalyze the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and accelerate the folding of proteins. The CyP40 protein has been shown to possess PPIase activity and, similar to other family members, can bind to the immunosuppressant drug cyclosporin A (CsA). In this study, we created keratinocyte cell lines with CyP40 being stably knocked down using viral particles containing shRNA for CyP40 which knocked down the expression level of CyP40 transcripts by 90-99%. The proliferation rates of the cell lines with silenced CyP40 were decreased compared to the control cells. After UVA irradiation, the rate of apoptosis was found to be significantly lower in CyP40 silenced cell lines than it was in control cells. Moreover, mitochondrial membrane potential (MMP) was found to be less dissipated and mitochondrial permeability transition pore (MPTP) less active in cells with knocked down CyP40 than in control cells after UVA irradiation. Also, less mitochondrial superoxide was detected in the cells with silenced CyP40 compared to control cells after UVA exposure. Moreover, silencing of CyP40 partially modulates expression of key genes involved in mitochondrial pore formation including CyPD, ANTs and VDAC family members. The ability of CyP40 to regulate UV induced apoptosis implicates this protein as a potential target for therapy in cancer cells.

Nucleoplasmic/nucleolar translocation and identification of a nuclear localization signal (NLS) in Dictyostelium BAF60a/SMARCD1 homologue Snf12

Dictyostelium is a model eukaryote for the study of several cellular processes; however, comparatively little is known about its nucleolus. Identification of nucleolar proteins is key to understanding this nuclear subcompartment, but only four have been identified in Dictyostelium. As discussed in this article, a potential relationship between nucleolar NumA1 and BAF60a/SMARCD1 suggested BAF60a may also reside in the nucleolus. Here, we identify BAF60a homologue Snf12 as the fifth nucleolar protein in Dictyostelium. Immunolocalization experiments demonstrate that Snf12 is nucleoplasmic, but translocates to nucleoli upon actinomycin-D-induced transcription inhibition (0.05 mg/mL, 4 h). Translocation was accompanied by a microtubule-independent protrusion of nucleolar Snf12 regions from the nucleus followed by detection of Snf12 in cytoplasmic circles for at least 48 h. Residues (372)KRKR(375) are both necessary and sufficient for nucleoplasmic localization of Snf12 and represent a functional nuclear localization signal (NLS), similar to recently identified NLSs in other Dictyostelium proteins. Since nucleolar and nucleoplasmic proteins redistribute during mitosis, we investigated Snf12 dynamics during this time. Dictyostelium undergoes closed mitosis, meaning its nuclear envelope remains intact. Despite this, during metaphase and anaphase Snf12 redistributed throughout the cytoplasm before reaccumulating in the nucleus during telophase, unlike the previously reported nucleoplasmic redistribution of nucleolar NumA1. The nuclear exit of Snf12 was independent of its putative nuclear export signal and not inhibited by exportin inhibition, suggesting that the redistribution of nuclear proteins during mitosis in Dictyostelium is mediated by other mechanisms. Snf12 is the second Dictyostelium nucleolar protein for which its dynamics during mitosis have been investigated.

Identification of cyclophilin-40-interacting proteins reveals potential cellular function of cyclophilin-40

Cyclophilin-40 (CyP40) is part of the immunophilin family and is found in Hsp90-containing protein complexes. We were interested in identifying proteins that interact with CyP40. CyP40-interacting proteins in HeLa cells were identified using the tandem affinity purification approach. Adenovirus expressing human CyP40 protein (Ad-CyP40), fused with streptavidin and calmodulin binding peptides at the N terminus, was generated. Proteins were separated on a sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel after tandem affinity purification. Here 10 silver-stained protein bands that were enriched in the Ad-CyP40-infected lysate and the corresponding regions in the control lysate were excised, digested by trypsin, and identified by tandem mass spectrometric analysis. Of 11 interacting proteins that were identified, 4 (RACK1, Ku70, RPS3, and NF45) were expressed in rabbit reticulocyte lysate, bacteria, and MCF-7 cells. We confirmed that these proteins interact with CyP40. We observed that RACK1 suppressed the cobalt chloride-induced, hypoxia response element-dependent luciferase activity in MCF-7 cells but not in MCF-7 stable cells expressing approximately 10% of the cellular CyP40 content. In addition, RACK1 reduced the HIF-1α protein accumulation after cobalt chloride treatment, which was not observed when the CyP40 content was down-regulated. Collectively, we conclude that reduction of the HIF-1 α protein by RACK1 is CyP40-mediated.

An Overview of Cyclophilins in Human Cancers

Cyclophilins (Cyps) belong to a group of proteins that have peptidyl-prolyl cis–trans isomerase (PPIase) and molecular chaperone activities. Originally, Cyps were identified as the intracellular receptors for the immunosuppressive drug cyclosporin A. Cyps are found in all prokaryotes and eukaryotes, and have been structurally conserved throughout evolution, implying their importance in cellular function. There are seven major Cyp isoforms in humans. CypA is up-regulated in many human cancers, and there is a strong correlation between over-expression of the CYPA gene and malignant transformation in some cancers. Moreover, CypA is directly under the transcriptional control of two critical transcription factors for cancer development: p53 and hypoxia inducible factor-1α. This review discusses the general biological functions of Cyps under a variety of stress conditions, and the importance and diverse roles of over-expression of CYP genes in human cancers, with a particular emphasis on CYPA. These oncogenic properties suggest that CypA is a promising target for cancer therapy.

Identification and comparative analysis of the peptidyl-prolyl cis/trans isomerase repertoires of H. sapiens, D. melanogaster, C. elegans, S. cerevisiae and Sz. pombe

The peptidyl-prolyl cis/trans isomerase (PPIase) class of proteins comprises three member families that are found throughout nature and are present in all the major compartments of the cell. Their numbers appear to be linked to the number of genes in their respective genomes, although we have found the human repertoire to be smaller than expected due to a reduced cyclophilin repertoire. We show here that whilst the members of the cyclophilin family (which are predominantly found in the nucleus and cytoplasm) and the parvulin family (which are predominantly nuclear) are largely conserved between different repertoires, the FKBPs (which are predominantly found in the cytoplasm and endoplasmic reticulum) are not. It therefore appears that the cyclophilins and parvulins have evolved to perform conserved functions, while the FKBPs have evolved to fill ever-changing niches within the constantly evolving organisms. Many orthologous subgroups within the different PPIase families appear to have evolved from a distinct common ancestor, whereas others, such as the mitochondrial cyclophilins, appear to have evolved independently of one another. We have also identified a novel parvulin within Drosophila melanogaster that is unique to the fruit fly, indicating a recent evolutionary emergence. Interestingly, the fission yeast repertoire, which contains no unique cyclophilins and parvulins, shares no PPIases solely with the budding yeast but it does share a majority with the higher eukaryotes in this study, unlike the budding yeast. It therefore appears that, in comparison with Schizosaccharomyces pombe, Saccharomyces cerevisiae is a poor representation of the higher eukaryotes for the study of PPIases.

Role of cyclophilin a during oncogenesis

Cyclophilins (Cyps) are ubiquitously expressed proteins that are evolutionarily conserved. CypA is the most abundant among the Cyps and is expressed in the cytosol. With its chaperone and PPIase activities, CypA contributes to the maintenance of correct conformation of nascent or denatured proteins and also provides protection against environmental insults. Also, its expression is induced in response to a wide variety of stressors including cancer. Upregulation of CypA in small cell lung cancer, pancreatic cancer, breast cancer, colorectal cancer, squamous cell carcinoma and melanoma has been reported. In some cancers a correlation between CypA overexpression and malignant transformation has been established. While molecular partners of CypA that promote cancer development are yet to be discovered, various mechanisms have been proposed to account for the cytoprotective functions of CypA during cancer development. CypA may promote the survival of cells under the stressful condition of cancer. CypA may well be essential for maintaining the conformation of oncogenic proteins, signalling proteins for cell proliferation, antiapoptotic components, transcription factors, or cell motility regulatory proteins. Antioxidant effects of CypA, which have been suggested by some researchers, may also become critical to reactive oxygen species (ROS) creating an oncogenetic environment. Developing new CypA inhibitors for therapeutics has been surmised from the cytoprotective functions of CypA and its overexpression in many cancer types. Therefore, CypA can be further investigated as a useful tool for early diagnosis, treatment and prevention of human cancers.

Cyclophilin 40: an Hsp90-cochaperone associated with apo-steroid receptors

Cyclophilin 40, a divergent loop cyclophilin first identified in association with the estrogen receptor alpha, contains a C-terminal tetratricopeptide repeat domain through which it shares structural identity with FK506-binding protein 52 (FKBP52) and other partner cochaperones in steroid receptor-heat shock protein 90 (Hsp90) complexes. By dynamically competing for Hsp90 interaction, the cochaperones allow the receptors to establish distinct Hsp90-chaperone complexes, with the potential to exert tissue-specific control over receptor activity. Cyclophilin 40 regulates Hsp90 ATPase activity during receptor-Hsp90 assembly. Functional deletion of the cyclophilin 40 yeast homologue, Cpr7, adversely affected estrogen receptor alpha and glucocorticoid receptor activity that could be fully restored, either with wild type Cpr7 or Cpr7 with a cyclophilin domain lacking isomerase activity. We draw parallels with the mechanism already established for FKBP52 and propose that the cyclophilin 40 divergent loop interfaces with a contact surface on the steroid receptor ligand-binding domain to achieve an optimal orientation for receptor activity.

Characterization of cyclophilin-encoding genes in Phytophthora

Recent research has shown that cyclophilins, proteins that catalyze the isomerization of peptidyl-prolyl bonds, play a variety of important roles in infection, including facilitating host penetration and colonization and activating pathogen effector proteins within the host cytoplasm. In the current study, bioinformatic analysis of the genomes of three species of plant pathogens in the genus Phytophthora has revealed extensive synteny between the 20 or 21 members of the cyclophilin gene family. In P. infestans, extensive EST studies give evidence of the expression of 14 of the 21 genes. Sequences homologous to 12 of the 14 expressed P. infestans cyclophilins were isolated using PCR and gene-specific primers in the broad host range pathogen, P. nicotianae. Quantitative real-time PCR measurements of transcript levels in P. nicotianae at four stages of asexual development and during infection of resistant and susceptible tobacco plants gave evidence of expression of seven of the P. nicotianae homologs. The most abundantly expressed gene, PnCyPA, has a lower mRNA level in zoospores compared to other stages of asexual development and its expression increases during infection of susceptible plants. Immunocytochemical studies indicate that PnCyPA occurs in the nucleus and cytoplasm of P. nicotianae cells and is secreted from germinated cysts.

Cyclophilin-40 has a cellular role in the aryl hydrocarbon receptor signaling

Cyclophilin-40 (CyP40) promotes the formation of the gel shift complex that contains the aryl hydrocarbon receptor (AhR), AhR nuclear translocator (Arnt) and dioxin response element (DRE) using baculovirus expressed proteins. Here we reported that CyP40 plays a role in the AhR signaling. When the CyP40 content in MCF-7 cells is reduced, up-regulation of cyp1a1 and cyp1b1 by 3-methylchloranthrene (3MC) is also reduced, suggesting that CyP40 is essential for maximal AhR function. The CyP40 region containing amino acids 186-215, but not the peptidyl-prolyl cis-trans isomerase and tetratricopeptide repeat domains, is essential for forming the AhR/Arnt/DRE complex. CyP40 is found in the cell nucleus after 3MC treatment and appears to promote the DRE binding form of the AhR/Arnt heterodimer.

The cyclophilin repertoire of the fission yeast Schizosaccharomyces pombe

The cyclophilin repertoire of the fission yeast Schizosaccharomyces pombe is comprised of nine members that are distributed over all three of its chromosomes and range from small single-domain to large multi-domain proteins. Each cyclophilin possesses only a single prolyl-isomerase domain, and these vary in their degree of consensus, including at positions that are likely to affect their drug-binding ability and catalytic activity. The additional identified motifs are involved in putative protein or RNA interactions, while a novel domain that is specific to SpCyp7 and its orthologues may have functions that include an interaction with hnRNPs. The Sz. pombe cyclophilins are found throughout the cell but appear to be absent from the mitochondria, which is unique among the characterized eukaryotic repertoires. SpCyp5, SpCyp6 and SpCyp8 have exhibited significant upregulation of their expression during the meiotic cycle and SpCyp5 has exhibited significant upregulation of its expression during heat stress. All nine have identified members in the repertoires of H. sapiens, D. melanogaster and A. thaliana. However, only three identified members in the cyclophilin repertoire of S. cerevisiae with SpCyp7 identifying a fourth protein that is not a member of the recognized repertoire due to its possession of a degenerate prolyl-isomerase domain. The cyclophilin repertoire of Sz. pombe therefore represents a better model group for the study of cyclophilin function in the higher eukaryotes.

Glucocorticoid receptor and heat shock factor 1: novel mechanism of reciprocal regulation

Glucocorticoids control a host of bodily responses, ranging from carbohydrate metabolism in the liver to immunity and inflammation in the lymph system. In response to stress, glucocorticoid levels are known to rise-a response thought to provide a protective function against the stress event. It is now understood that the major function of glucocorticoids under stress is to protect not against the stress event itself but against overstimulation by host defenses (e.g., inflammation). Control of these responses is achieved by the glucocorticoid receptor, a member of the steroid receptor transcription factor family. The oldest, most conserved, and most ubiquitous of the stress responses is induced expression of heat shock proteins that act as chaperones against stress-induced denaturation of protein. Expression of heat shock protein genes is controlled by heat shock transcription factor 1. In this work, we review our observations and those of other laboratories demonstrating a relationship between the glucocorticoid and heat shock responses. We show that complex but reciprocal mechanisms of regulation occur between glucocorticoid receptor and heat shock transcription factor 1 and present a model of coordinated action that likely serves to fully reestablish homeostasis following stress.

Roles of cyclophilins in cancers and other organ systems

Cyclophilins are originally identified as cellular binding proteins for the immunosuppressive drug cyclosporin A. Many cyclophilins, including CypA, CypB, CypC, CypD, and Cyp40, have been discovered and shown to be ubiquitously distributed in many types of cells and organ systems. Recent investigations have uncovered many important properties and functions for cyclophilins including peptidyle-prolyl-isomerase activity and protein folding/repair; maintaining mitochondrial functions and involvement in apoptosis; roles in regulation of T-cell function and inflammation; interaction with CD147; and pathogenesis of vascular disease, human immunodeficiency virus infection, and rheumatoid arthritis. Furthermore, the expression and functions of cyclophilins may be correlated with tumor biology of several types of cancers including pancreatic carcinoma. Molecular mechanisms of cyclophilin-mediated biologic events and future directions of research are discussed in this review. Understanding the roles of cyclophilins in cancers and other organ systems will be crucial in determining clinical applications for the treatment or diagnosis of human diseases.

Intronic hormone response elements mediate regulation of FKBP5 by progestins and glucocorticoids

Expression of FKBP51, a large molecular weight immunophilin, is strongly enhanced by glucocorticoids, progestins, and androgens. However, the activity of a 3.4-kb fragment of the FKBP51 gene (FKBP5) promoter was only weakly increased by progestin and we show here that it is unresponsive to glucocorticoids and androgens. The entire FKBP5 was scanned for consensus hormone response elements (HREs) using MatInspector. We found that 2 regions of intron E, which are conserved in rat and mouse FKBP5, contain HRE-like sequences with high match scores. Deoxyribonucleic acid fragments (approximately 1 kb in length) containing these regions were amplified and tested in reporter gene assays for steroid responsiveness. One region of intron E of FKBP5 (pIE2) conferred both glucocorticoid and progestin responsiveness to 2 heterologous reporter genes, whereas the other, less-conserved region of intron E (pIE1) was responsive only to progestins. The inclusion of pIE1 upstream of pIE2 (pIE1IE2) enhanced progestin but not glucocorticoid responsiveness. None of the constructs containing intronic sequences was responsive to androgens. Mutation of the putative HREs within pIE1 and pIE2 eliminated hormone responsiveness. Electrophoretic mobility shift assays demonstrated that progesterone receptors (PR) bound to the HRE in pIE1, whereas both PR and glucocorticoid receptors interacted with the HRE in pIE2. These data suggest that distal intronic elements significantly contribute to transcriptional regulation of FKBP5 by glucocorticoids and progestins.

Tetratricopeptide repeat cochaperones in steroid receptor complexes

The molecular chaperone machinery contains multiple protein components that have 1 or more structural domains composed of tetratricopeptide repeat (TPR) motifs. Many other proteins of separate or unknown function also have TPR domains, so this motif is not exclusive to molecular chaperones. A general function of TPR domains is to bind other polypeptides, but this otherwise prosaic function has been exploited in an assortment of ways that link chaperones and other protein systems into cooperative networks. Among the best-characterized TPR proteins are several cochaperones that participate in assembly and regulation of steroid receptor complexes. Steroid receptors, members of the nuclear receptor subfamily, are hormone-dependent transcription factors that regulate many vertebrate pathways of homeostasis, growth, differentiation, reproduction, and pathology and, as such, have been of great interest to biologists and clinicians. Moreover, the steroid receptors are among the first recognized native clients for chaperones and have been widely studied models for complex chaperone interactions. To provide a coherent, representative minireview of TPR protein function, the scope of this article has been narrowed down primarily to functions of steroid receptor-associated TPR cochaperones.

CyP40, but not Hsp70, in rabbit reticulocyte lysate causes the aryl hydrocarbon receptor-DNA complex formation

Upon ligand binding, the aryl hydrocarbon receptor (AhR) translocates into the nucleus and dimerizes with its partner aryl hydrocarbon receptor nuclear translocator (Arnt). The AhR-Arnt heterodimer binds to the dioxin response element (DRE) to regulate target gene expression. Using baculovirus expressed human AhR and Arnt, we showed that the formation of the ligand-dependent AhR-Arnt-DRE complex requires protein factors in vitro. Recently, we provided evidence that p23, an Hsp90-associated protein, is involved in the complex formation. The aim of this study was to determine whether two other Hsp90-associated proteins present in rabbit reticulocyte lysate (RRL), namely CyP40 and Hsp70, play any role in forming the AhR-Arnt-DRE complex. Fractionation and immunodepletion experiments revealed that Hsp70 is not necessary for the formation of this complex. In contrast, CyP40 is involved in forming the complex since (1) immunodepletion of CyP40 from a RRL fraction reduces the intensity of the AhR-Arnt-DRE complex by 48% and (2) recombinant human CyP40 alone causes the formation of this complex. In addition, CyP40-interacting proteins appear to be essential for the full CyP40 effect on the AhR gel shift complex.

Interaction of the Hsp90 cochaperone cyclophilin 40 with Hsc70

The high-affinity ligand-binding form of unactivated steroid receptors exists as a multicomponent complex that includes heat shock protein (Hsp)90; one of the immunophilins cyclophilin 40 (CyP40), FKBP51, or FKBP52; and an additional p23 protein component. Assembly of this heterocomplex is mediated by Hsp70 in association with accessory chaperones Hsp40, Hip, and Hop. A conserved structural element incorporating a tetratricopeptide repeat (TPR) domain mediates the interaction of the immunophilins with Hsp90 by accommodating the C-terminal EEVD peptide of the chaperone through a network of electrostatic and hydrophobic interactions. TPR cochaperones recognize the EEVD structural motif common to both Hsp90 and Hsp70 through a highly conserved clamp domain. In the present study, we investigated in vitro the molecular interactions between CyP40 and FKBP52 and other stress-related components involved in steroid receptor assembly, namely Hsp70 and Hop. Using a binding protein-retention assay with CyP40 fused to glutathione S-transferase immobilized on glutathione-agarose, we have identified the constitutively expressed form of Hsp70, heat shock cognate (Hsc)70, as an additional target for CyP40. Deletion mapping studies showed the binding determinants to be similar to those for CyP40-Hsp90 interaction. Furthermore, a mutational analysis of CyP40 clamp domain residues confirmed the importance of this motif in CyP40-Hsc70 interaction. Additional residues thought to mediate binding specificity through hydrophobic interactions were also important for Hsc70 recognition. CyP40 was shown to have a preference for Hsp90 over Hsc70. Surprisingly, FKBP52 was unable to compete with CyP40 for Hsc70 binding, suggesting that FKBP52 discriminates between the TPR cochaperone-binding sites in Hsp90 and Hsp70. Hop, which contains multiple units of the TPR motif, was shown to be a direct competitor with CyP40 for Hsc70 binding. Similar to Hop, CyP40 was shown not to influence the adenosine triphosphatase activity of Hsc70. Our results suggest that CyP40 may have a modulating role in Hsc70 as well as Hsp90 cellular function.

A novel binding protein for a member of CyP40-type Cyclophilins: N.crassa CyPBP37, a growth and thiamine regulated protein homolog to yeast Thi4p

Cyclophilins belong to the family of peptidyl-prolyl cis/trans isomerases (PPIases), which are ubiquitous and highly conserved enzymes capable of cis/trans isomerizing Xaa-Pro peptide bonds. Members of the CyP40-type cyclophilins have originally been described as components of hormone receptor complexes. Here, we describe NcCyP41, a CyP40 ortholog from Neurospora crassa, its expression in Escherichia coli and subsequent purification. Characterization of NcCyP41 reveals that it is a heat shock protein, which is active as a cyclosporin A-sensitive PPIase. Affinity chromatography using immobilized recombinant NcCyP41 yielded two major NcCyP41-binding proteins: Hsp80 (a Hsp90 ortholog from N.crassa) and CyPBP37. CyPBP37 has not been described. In addition, this is the first record describing an interaction between a member of Cyp40-type cyclophilins and of CyPBP37-type proteins, respectively. CyPBP37 expression is repressed by thiamine and in the stationary phase in N.crassa. CyPBP37 is present in different isoforms. The expression of a CyPBP37 ortholog in yeast, Thi4p, is diminished in a mutant lacking one of the two CyP40 orthologs (Cpr7p). In addition, the DeltaCpr7p deletion mutant shows a thiamine-dependent growth defect. We conclude that, in yeast, Cpr7p and Thi4p interact functionally.

Organization of the human FK506-binding immunophilin FKBP52 protein gene (FKBP4)

FKBP52 is a widely expressed FK506-binding immunophilin that possesses peptidylprolyl isomerase activity and a tetratricopeptide repeat involved in protein-protein interaction. FKBP52 plays an important role in steroid receptor function and is implicated in other diverse processes, including regulation of transcription, cation channel activity, and gene transfer efficiency. Reported here is the genomic organization of the human FKBP52 gene (FKBP4), which shares all but one of the same exon-intron boundaries as the structurally related immunophilin FKBP51 gene (FKBP5). Approximately 3.5 kb of 5'-flanking DNA of FKBP4 was subcloned into a luciferase reporter vector and was found to exhibit robust activity in T-47D, MCF7, and COS-7 cells. Promoter constructs with only 143 bp of upstream sequence maintained high activity. This region contains a CAAT motif sequence and consensus binding sites for Sp1, heat-shock factor, and MYC-MAX, which are conserved in the rabbit FKBP4 promoter and, when deleted, dramatically reduced promoter activity in T-47D cells.

Alteration of C-MYB DNA binding to cognate responsive elements in HL-60 variant cells

AIMS

To establish whether the MYB protein expressed in HL-60 variant cells, which are cells resistant to 12-O-tetradecanoylphorbol-13-acetate (TPA) induced differentiation, is able to bind MYB recognition elements (MREs) involved in the transcriptional regulation of myb target genes. In addition, to determine whether alterations in the binding of the MYB protein to MREs affects HL-60 cell proliferation and differentiation.

METHODS

Nuclear extracts of HL-60 variant cells exhibiting different degrees of resistance to TPA induced monocytic differentiation were used in electrophoretic mobility shift experiments (EMSAs), bandshift experiments performed with labelled oliogonucleotides containing the MYB consensus binding sequences.

RESULTS

The MYB protein contained in nuclear extracts from HL-60 variant cells did not bind efficiently to the MYB recognition elements identified in the mim-1 and PR264 promoters. Molecular cloning of the myb gene and analysis of the MYB protein expressed in the HL-60 variant cells established that the lack of binding did not result from a structural alteration of MYB in these cells. The lack of MRE binding did not abrogate the ability of variant HL-60s to proliferate and to undergo differentiation. Furthermore, the expression of the PR264/SC35 splicing factor was not affected as a result of the altered MYB DNA binding activity.

CONCLUSIONS

Because the MYB protein expressed in HL-60 variant cells did not appear to be structurally different from the MYB protein expressed in parental HL-60 cells, it is possible that the HL-60 variant cells contain a MYB binding inhibitory factor (MBIF) that interferes with MYB binding on MREs. The increased proliferation rate of HL-60 variant cells and their reduced serum requirement argues against the need for direct MYB binding in the regulation of cell growth.

Regulation of heat shock proteins, Hsp70 and Hsp64, in heat-shocked Malpighian tubules of Drosophila melanogaster larvae

It is known from earlier studies that the heat shock (HS) response in Malpighian tubules (MTs) of Drosophila larvae is different from that in other tissues because instead of the Hsp70 and other common heat shock proteins, Hsp64 and certain other new proteins are induced immediately after HS. In the present study, we examined the kinetics of the synthesis of Hsp70 and Hsp64 immediately after HS and during recovery from HS by 35S-methionine labeling and Western blotting. In addition, we also examined the transcriptional activity of hsp70 genes in larval MT cells at different times after HS by in situ hybridization and Northern blotting. The HS-induced synthesis of Hsp64 ceased by 1 hour of recovery from the HS when synthesis of the Hsp70 commenced. Our results revealed that the induced synthesis of Hsp64 immediately after HS was dependent on new transcription. Although the levels of Hsp70 in MT cells rapidly increased after its synthesis began during recovery, the levels of Hsp64 remained unaltered irrespective of its new synthesis occurring during or after HS. Inhibition of new Hsp64 synthesis by transcriptional or translational inhibitors also did not affect the total amount of this protein in MTs. The Hsp64 polypeptides synthesized in response to HS are degraded rapidly. Apparently, the cells in MTs maintain a balance between new synthesis of Hsp64 and its turnover so that under all conditions a more or less constant level of this protein is maintained. Although the Hsp70 synthesis started only after 1 hour of recovery, the hsp70 genes were transcriptionally activated immediately after HS and they continued to transcribe till at least 4 hours after the HS. The hsp70 transcripts in MT cells that recovered for 2 hours or longer did not contain the 3' untranslated regions (UTRs), which may allow their longer stability and translatability at normal temperature. Synthesis of Hsp70 during recovery period was dependent on continuing transcription. Assessment of the beta-galactosidase activity in 2 transgenic lines carrying the LacZ reporter gene under hsp70 promoter and different lengths of the 5'UTR suggested that the delayed translation of hsp70 transcripts in MTs is probably regulated by some elements in the 5'UTR.

Regulation of the Hsp90-binding immunophilin, cyclophilin 40, is mediated by multiple sites for GA-binding protein (GABP)

Within steroid receptor heterocomplexes the large tetratricopeptide repeat-containing immunophilins, cyclophilin 40 (CyP40), FKBP51, and FKBP52, target a common interaction site in heat shock protein 90 (Hsp90) and act coordinately with Hsp90 to modulate receptor activity. The reversible nature of the interaction between the immunophilins and Hsp90 suggests that relative cellular abundance might be a key determinant of the immunophilin component within steroid receptor complexes. To investigate CyP40 gene regulation, we have isolated a 5-kilobase (kb) 5'-flanking region of the human gene and demonstrated that a approximately 50 base pair (bp) sequence adjacent to the transcription start site is essential for CyP40 basal expression. Three tandemly arranged Ets sites within this critical region were identified as binding elements for the multimeric Ets-related transcription factor, GA binding protein (GABP). Functional studies of this proximal promoter sequence, in combination with mutational analysis, confirmed these sites to be crucial for basal promoter function. Furthermore, overexpression of both GABP alpha and GABP beta subunits in Cos1 cells resulted in increased endogenous CyP40 mRNA levels. Significantly, a parallel increase in FKBP52 mRNA expression was not observed, highlighting an important difference in the mode of regulation of the CyP40 and FKBP52 genes. Our results identify GABP as a key regulator of CyP40 expression. GABP is a common target of mitogen and stress-activated pathways and may integrate these diverse extracellular signals to regulate CyP40 gene expression.