Expression of the estrogen receptor-associated immunophilins, cyclophilin 40 and FKBP52, in breast cancer

NFAT activation by FKBP52 promotes cancer cell proliferation by suppressing p53

FK506-binding protein 52 (FKBP52) is a member of the FKBP family of proline isomerases. FKBP52 is up-regulated in various cancers and functions as a positive regulator of steroid hormone receptors. Depletion of FKBP52 is known to inhibit cell proliferation; however, the detailed mechanism remains poorly understood. In this study, we found that FKBP52 depletion decreased MDM2 transcription, leading to stabilization of p53, and suppressed cell proliferation. We identified NFATc1 and NFATc3 as transcription factors that regulate MDM2 We also found that FKBP52 associated with NFATc3 and facilitated its nuclear translocation. In addition, calcineurin, a well-known Ca2+ phosphatase essential for activation of NFAT, plays a role in MDM2 transcription. Supporting this notion, MDM2 expression was found to be regulated by intracellular Ca2+ Taken together, these findings reveal a new role of FKBP52 in promoting cell proliferation via the NFAT-MDM2-p53 axis, and indicate that inhibition of FKBP52 could be a new therapeutic tool to activate p53 and inhibit cell proliferation.

Sensory nerves directly promote osteoclastogenesis by secreting peptidyl-prolyl cis-trans isomerase D (Cyp40)

Given afferent functions, sensory nerves have recently been found to exert efferent effects and directly alter organ physiology. Additionally, several studies have highlighted the indirect but crucial role of sensory nerves in the regulation of the physiological function of osteoclasts. Nonetheless, evidence regarding the direct sensory nerve efferent influence on osteoclasts is lacking. In the current study, we found that high levels of efferent signals were transported directly from the sensory nerves into osteoclasts. Furthermore, sensory hypersensitivity significantly increased osteoclastic bone resorption, and sensory neurons (SNs) directly promoted osteoclastogenesis in an in vitro coculture system. Moreover, we screened a novel neuropeptide, Cyp40, using an isobaric tag for relative and absolute quantitation (iTRAQ). We observed that Cyp40 is the efferent signal from sensory nerves, and it plays a critical role in osteoclastogenesis via the aryl hydrocarbon receptor (AhR)-Ras/Raf-p-Erk-NFATc1 pathway. These findings revealed a novel mechanism regarding the influence of sensory nerves on bone regulation, i.e., a direct promoting effect on osteoclastogenesis by the secretion of Cyp40. Therefore, inhibiting Cyp40 could serve as a strategy to improve bone quality in osteoporosis and promote bone repair after bone injury.

FKBP25 regulates myoblast viability and migration and is differentially expressed in in vivo models of muscle adaptation

FKBP25 (FKBP3 gene) is a dual-domain PPIase protein that consists of a C-terminal PPIase domain and an N-terminal basic tilted helix bundle (BTHB). The PPIase domain of FKBP25 has been shown to bind to microtubules, which has impacts upon microtubule polymerisation and cell cycle progression. Using quantitative proteomics, it was recently found that FKBP25 was expressed in the top 10% of the mouse skeletal muscle proteome. However, to date there have been few studies investigating the role of FKBP25 in non-transformed systems. As such, this study aimed to investigate potential roles for FKBP25 in myoblast viability, migration and differentiation and in adaptation of mature skeletal muscle. Doxycycline-inducible FKBP25 knockdown in C2C12 myoblasts revealed an increase in cell accumulation/viability and migration in vitro that was independent of alterations in tubulin dynamics; however, FKBP25 knockdown had no discernible impact on myoblast differentiation into myotubes. Finally, a series of in vivo models of muscle adaptation were assessed, where it was observed that FKBP25 protein expression was increased in hypertrophy and regeneration conditions (chronic mechanical overload and the mdx model of Duchenne muscular dystrophy) but decreased in an atrophy model (denervation). Overall, the findings of this study establish FKBP25 as a regulator of myoblast viability and migration, with possible implications for satellite cell proliferation and migration and muscle regeneration, and as a potential regulator of in vivo skeletal muscle adaptation.

Sex Differences in the Neurobiology of Stress

This review highlights the existing knowledge and data that explain the physiologic impacts of stress, especially pertaining to neurobiology, and how these impacts differ by sex. Furthermore, this review explains the benefits of interventions aimed at preventing or mitigating the adverse effects of stress, because of both the significant toll of stress on the body and the disproportionate impact of these changes experienced by women.

The chaperone system in cancer therapies: Hsp90

The chaperone system (CS) of an organism is composed of molecular chaperones, chaperone co-factors, co-chaperones, and chaperone receptors and interactors. It is present throughout the body but with distinctive features for each cell and tissue type. Previous studies pertaining to the CS of the salivary glands have determined the quantitative and distribution patterns for several members, the chaperones, in normal and diseased glands, focusing on tumors. Chaperones are cytoprotective, but can also be etiopathogenic agents causing diseases, the chaperonopathies. Some chaperones such as Hsp90 potentiate tumor growth, proliferation, and metastasization. Quantitative data available on this chaperone in salivary gland tissue with inflammation, and benign and malignant tumors suggest that assessing tissue Hsp90 levels and distribution patterns is useful for differential diagnosis-prognostication, and patient follow up. This, in turn, will reveal clues for developing specific treatment centered on the chaperone, for instance by inhibiting its pro-carcinogenic functions (negative chaperonotherapy). Here, we review data on the carcinogenic mechanisms of Hsp90 and their inhibitors. Hsp90 is the master regulator of the PI3K-Akt-NF-kB axis that promotes tumor cell proliferation and metastasization. We discuss pathways and interactions involving these molecular complexes in tumorigenesis and review Hsp90 inhibitors that have been tested in search of an efficacious anti-cancer agent. This targeted therapy deserves extensive investigation in view of its theoretical potential and some positive practical results and considering the need of novel treatments for tumors of the salivary glands as well as other tissues.

Functions of the Hsp90-Binding FKBP Immunophilins

The Hsp90 chaperone is known to interact with a diverse array of client proteins. However, in every case examined, Hsp90 is also accompanied by a single or several co-chaperone proteins. One class of co-chaperone contains a tetratricopeptide repeat (TPR) domain that targets the co-chaperone to the C-terminal region of Hsp90. Within this class are Hsp90-binding peptidylprolyl isomerases, most of which belong to the FK506-binding protein (FKBP) family. Despite the common association of FKBP co-chaperones with Hsp90, it is abundantly clear that the client protein influences, and is often influenced by, the particular FKBP bound to Hsp90. Examples include Xap2 in aryl hydrocarbon receptor complexes and FKBP52 in steroid receptor complexes. In this chapter, we discuss the known functional roles played by FKBP co-chaperones and, where possible, relate distinctive functions to structural differences between FKBP members.

Central stress processing, T cell responsivity to stress hormones, and disease severity in multiple sclerosis

Epidemiological, clinical and neuroscientific studies support a link between psychobiological stress and multiple sclerosis. Neuroimaging suggests that blunted central stress processing goes along with higher multiple sclerosis severity, neuroendocrine studies suggest that blunted immune system sensitivity to stress hormones is linked to stronger neuroinflammation. Until now, however, no effort has been made to elucidate whether central stress processing and immune system sensitivity to stress hormones are related in a disease-specific fashion, and if so, whether this relation is clinically meaningful. Consequently, we conducted two functional MRI analyses based on a total of 39 persons with multiple sclerosis and 25 healthy persons. Motivated by findings of an altered interplay between neuroendocrine stress processing and T-cell glucocorticoid sensitivity in multiple sclerosis, we searched for neural networks whose stress task-evoked activity is differentially linked to peripheral T-cell glucocorticoid signalling in patients versus healthy persons as a potential indicator of disease-specific CNS–immune crosstalk. Subsequently, we tested whether this activity is simultaneously related to disease severity. We found that activity of a network comprising right anterior insula, right fusiform gyrus, left midcingulate and lingual gyrus was differentially coupled to T-cell glucocorticoid signalling across groups. This network’s activity was simultaneously linked to patients’ lesion volume, clinical disability and information-processing speed. Complementary analyses revealed that T-cell glucocorticoid signalling was not directly linked to disease severity. Our findings show that alterations in the coupling between central stress processing and T-cell stress hormone sensitivity are related to key severity measures of multiple sclerosis.

With or without You: Co-Chaperones Mediate Health and Disease by Modifying Chaperone Function and Protein Triage

Heat shock proteins (HSPs) are a family of molecular chaperones that regulate essential protein refolding and triage decisions to maintain protein homeostasis. Numerous co-chaperone proteins directly interact and modify the function of HSPs, and these interactions impact the outcome of protein triage, impacting everything from structural proteins to cell signaling mediators. The chaperone/co-chaperone machinery protects against various stressors to ensure cellular function in the face of stress. However, coding mutations, expression changes, and post-translational modifications of the chaperone/co-chaperone machinery can alter the cellular stress response. Importantly, these dysfunctions appear to contribute to numerous human diseases. Therapeutic targeting of chaperones is an attractive but challenging approach due to the vast functions of HSPs, likely contributing to the off-target effects of these therapies. Current efforts focus on targeting co-chaperones to develop precise treatments for numerous diseases caused by defects in protein quality control. This review focuses on the recent developments regarding selected HSP70/HSP90 co-chaperones, with a concentration on cardioprotection, neuroprotection, cancer, and autoimmune diseases. We also discuss therapeutic approaches that highlight both the utility and challenges of targeting co-chaperones.

FKBP4 integrates FKBP4/Hsp90/IKK with FKBP4/Hsp70/RelA complex to promote lung adenocarcinoma progression via IKK/NF-κB signaling

FKBP4 belongs to the family of immunophilins, which serve as a regulator for steroid receptor activity. Thus, FKBP4 has been recognized to play a critical role in several hormone-dependent cancers, including breast and prostate cancer. However, there is still no research to address the role of FKBP4 on lung adenocarcinoma (LUAD) progression. We found that FKBP4 expression was elevated in LUAD samples and predicted significantly shorter overall survival based on TCGA and our cohort of LUAD patients. Furthermore, FKBP4 robustly increased the proliferation, metastasis, and invasion of LUAD in vitro and vivo. Mechanistic studies revealed the interaction between FKBP4 and IKK kinase complex. We found that FKBP4 potentiated IKK kinase activity by interacting with Hsp90 and IKK subunits and promoting Hsp90/IKK association. Also, FKBP4 promotes the binding of IKKγ to IKKβ, which supported the facilitation role in IKK complex assembly. We further identified that FKBP4 TPR domains are essential for FKBP4/IKK interaction since its association with Hsp90 is required. In addition, FKBP4 PPIase domains are involved in FKBP4/IKKγ interaction. Interestingly, the association between FKBP4 and Hsp70/RelA favors the transport of RelA toward the nucleus. Collectively, FKBP4 integrates FKBP4/Hsp90/IKK with FKBP4/Hsp70/RelA complex to potentiate the transcriptional activity and nuclear translocation of NF-κB, thereby promoting LUAD progression. Our findings suggest that FKBP4 may function as a prognostic biomarker of LUAD and provide a newly mechanistic insight into modulating IKK/NF-κB signaling.

FKBP4 Accelerates Malignant Progression of Non-Small-Cell Lung Cancer by Activating the Akt/mTOR Signaling Pathway

Objective

To study the expression, biological function, and mechanism of FKBP4 in non-small-cell lung cancer (NSCLC).

Methods

First of all, the expression of FKBP4 in NSCLC tissues and cell lines was detected by qRT-PCR; then, the effects of FKBP4 on proliferation, apoptosis, migration, and invasion of NSCLC were studied by CCK-8 assays, flow cytometry assays, wound-healing assays, and Transwell assays. After that, tumor xenografts were used to explore the effect of FKBP4 on NSCLC tumor growth in vivo, and the phosphorylation of Akt and mTOR was measured by western blot.

Results

FKBP4 was highly expressed in NSCLC tissues and cells, and its expression was closely related to NSCLC tumor size, lymph node metastasis, and patient prognosis. In vitro, FKBP4 can promote NSCLC cell proliferation, migration, and invasion and inhibit NSCLC cell apoptosis. In vivo, FKBP4 can promote NSCLC tumor growth. Furthermore, FKBP4 can promote Akt and mTOR phosphorylation and activate the Akt/mTOR signaling pathway and an mTOR inhibitor can neutralize the functions of FKBP4 in NSCLC cells.

Conclusion

FKBP4 serves as an oncogene to promote malignant processes in NSCLC, and it has the potential to be used as a biological marker and therapeutic target for NSCLC.

Transcriptome network of the papillary thyroid carcinoma radiation marker CLIP2

Background

We present a functional gene association network of the CLIP2 gene, generated by de-novo reconstruction from transcriptomic microarray data. CLIP2 was previously identified as a potential marker for radiation induced papillary thyroid carcinoma (PTC) of young patients in the aftermath of the Chernobyl reactor accident. Considering the rising thyroid cancer incidence rates in western societies, potentially related to medical radiation exposure, the functional characterization of CLIP2 is of relevance and contributes to the knowledge about radiation-induced thyroid malignancies.

Methods

We generated a transcriptomic mRNA expression data set from a CLIP2-perturbed thyroid cancer cell line (TPC-1) with induced CLIP2 mRNA overexpression and siRNA knockdown, respectively, followed by gene-association network reconstruction using the partial correlation-based approach GeneNet. Furthermore, we investigated different approaches for prioritizing differentially expressed genes for network reconstruction and compared the resulting networks with existing functional interaction networks from the Reactome, Biogrid and STRING databases. The derived CLIP2 interaction partners were validated on transcript and protein level.

Results

The best reconstructed network with regard to selection parameters contained a set of 20 genes in the 1st neighborhood of CLIP2 and suggests involvement of CLIP2 in the biological processes DNA repair/maintenance, chromosomal instability, promotion of proliferation and metastasis. Peptidylprolyl Isomerase Like 3 (PPIL3), previously identified as a potential direct interaction partner of CLIP2, was confirmed in this study by co-expression at the transcript and protein level.

Conclusion

In our study we present an optimized preselection approach for genes subjected to gene-association network reconstruction, which was applied to CLIP2 perturbation transcriptome data of a thyroid cancer cell culture model. Our data support the potential carcinogenic role of CLIP2 overexpression in radiation-induced PTC and further suggest potential interaction partners of the gene.

Cancer and risk of Alzheimer's disease: Small association in a nationwide cohort study

INTRODUCTION

Small observational studies with short-term follow-up suggest that cancer patients are at reduced risk of Alzheimer's disease (AD) compared to the general population.

METHODS

A nationwide cohort study using Danish population-based health registries (1980-2013) with cancer patients (n = 949,309) to identify incident diagnoses of AD. We computed absolute reductions in risk attributed to cancer and standardized incidence rate ratios (SIRs) accounting for survival time, comparing the observed to expected number of AD cases.

RESULTS

During up to 34 years of follow-up of cancer survivors, the attributable risk reduction was 1.3 per 10,000 person-years, SIR = 0.94 (95% confidence interval 0.92-0.96). SIRs were similar after stratification by sex, age, and cancer stage, and approached that of the general population for those surviving >10 years.

DISCUSSION

Inverse associations between cancer and AD were small and diminished over time. Incidence rates in cancer survivors approached those of the general population, suggesting limited association between cancer and AD risk.

FKBP4 connects mTORC2 and PI3K to activate the PDK1/Akt-dependent cell proliferation signaling in breast cancer

Purpose: Among the FKBP family members, FKBP4 has been described to have a potential role in tumorigenesis, and as a putative tissue marker. We previously showed that FKBP4, an HSP90-associated co-chaperone, can elicit immune response as a tumor-specific antigen, and are overexpressed in breast cancer. Experimental design: In this study, we examined how loss of FKBP4 affect breast cancer progression and exploited protein interactomics to gain mechanistic insight into this process. Results: We found that FKBP4 expression is associated with breast cancer progression and prognosis, especially of ER-negative breast cancer. Furthermore, FKBP4 depletion specifically reduces cell growth and proliferation of triple negative breast cancer cell model and xenograft tumor model. Using specific protein interactome strategy by BirA proximity-dependent biotin identification, we demonstrated that FKBP4 is a novel PI3K-Akt-mTOR proximal interacting protein. Conclusion: Our results suggest that FKBP4 interacts with PI3K and can enhance Akt activation through PDK1 and mTORC2.

Biological Actions of the Hsp90-binding Immunophilins FKBP51 and FKBP52

Immunophilins are a family of proteins whose signature domain is the peptidylprolyl-isomerase domain. High molecular weight immunophilins are characterized by the additional presence of tetratricopeptide-repeats (TPR) through which they bind to the 90-kDa heat-shock protein (Hsp90), and via this chaperone, immunophilins contribute to the regulation of the biological functions of several client-proteins. Among these Hsp90-binding immunophilins, there are two highly homologous members named FKBP51 and FKBP52 (FK506-binding protein of 51-kDa and 52-kDa, respectively) that were first characterized as components of the Hsp90-based heterocomplex associated to steroid receptors. Afterwards, they emerged as likely contributors to a variety of other hormone-dependent diseases, stress-related pathologies, psychiatric disorders, cancer, and other syndromes characterized by misfolded proteins. The differential biological actions of these immunophilins have been assigned to the structurally similar, but functionally divergent enzymatic domain. Nonetheless, they also require the complementary input of the TPR domain, most likely due to their dependence with the association to Hsp90 as a functional unit. FKBP51 and FKBP52 regulate a variety of biological processes such as steroid receptor action, transcriptional activity, protein conformation, protein trafficking, cell differentiation, apoptosis, cancer progression, telomerase activity, cytoskeleton architecture, etc. In this article we discuss the biology of these events and some mechanistic aspects.

Everolimus induces Met inactivation by disrupting the FKBP12/Met complex

Inhibition of the mechanistic target of rapamycin (mTOR) is a promising treatment strategy for several cancer types. Rapamycin derivatives such as everolimus are allosteric mTOR inhibitors acting through interaction with the intracellular immunophilin FKBP12, a prolyl isomerase with different cellular functions. Although mTOR inhibitors have significantly improved survival of different cancer patients, resistance and lack of predictive factors of response remain unsolved issues. To elucidate the mechanisms of resistance to everolimus, we evaluated Met activation in everolimus-sensitive/resistant human cancer cells, in vitro and in vivo. Biochemical and computational analyses were performed. Everolimus-resistant cells were xenografted into mice (10/group) and studied for their response to everolimus and Met inhibitors. The statistical significance of the in vitro results was evaluated by Student's t test.

Everolimus reduced Met phosphorylation in everolimus-sensitive cells. This event was mediated by the formation of a Met-FKBP12 complex, which in turn is disrupted by everolimus. Aberrant Met activation in everolimus-resistant cells and overexpression of wild-type/mutant Met caused everolimus resistance. Pharmacological inhibition and RNA silencing of Met are effective in condition of everolimus resistance (P<0.01). In mice xenografted with everolimus-resistant cells, the combination of everolimus with the Met inhibitor PHA665752 reduced tumor growth and induced a statistically significant survival advantage (combination vs control P=0.0005).

FKBP12 binding is required for full Met activation and everolimus can inhibit Met. Persistent Met activation might sustain everolimus resistance. These results identify a novel everolimus mechanism of action and suggest the development of clinical strategies based on Met inhibitors in everolimus-resistant cancers.

Elevated FKBP52 expression indicates a poor outcome in patients with breast cancer

The 52-kDa FK506-binding protein (FKBP52), a regulator of steroid hormone receptor signaling, is potentially involved in a variety of hormone-dependent cancer types. The present study investigated the expression and clinical implications of FKBP52 in breast cancer. Immunohistochemistry was performed on samples from 145 breast cancer patients and on 66 unmatched breast non-cancerous tissues (as controls) to determine the expression level of FKBP52. Publicly available microarray and RNA-seq datasets used in the present study were downloaded from the European Bioinformatics Institute ArrayExpress. Kaplan-Meier survival analysis was also performed. FKBP52 expression was moderately higher in the tumors than that in the non-cancerous tissues, but this difference was not statistically significant (P=0.176). However, available microarray datasets exhibited a significant difference in FKBP52 mRNA levels between breast tumors and controls. In the 145 breast cancer patients, elevated FKBP52 expression was significantly associated with advanced Tumor-Node-Metastasis (TNM) stage (P=0.015), lymph node metastasis (P=0.015) and tumors with poor histological differentiation (P=0.047). FKBP52 expression was negatively associated with estrogen receptor expression (P=0.033), but positively associated with human epidermal growth factor receptor 2 expression (P=0.033). However, there was no association between FKBP52 and progesterone receptor expression. Survival analyses demonstrated that FKBP52 was indicative of a poor overall survival rate (P=0.026), which was consistent with the result of Kaplan-Meier analysis, exhibiting a negative association between the mRNA of FKBP52 and overall survival (OS) (P=0.044). Other than for FKBP52 [hazard ratio (HR), 2.315; 95% confidence interval (CI), 1.077-4.975; P=0.032], univariate analysis revealed that clinical stage exhibited a significant influence on the prognosis of the breast cancer patients (HR, 2.148; 95% CI, 1.011-4.566; P=0.047). However, multivariate analysis revealed that only clinical stage, not FKBP52, was an independent prognostic factor (HR, 2.721; 95% CI, 1.169-6.335; P=0.020). Patients were further classified according to their OS. Compared with the controls (3.94±2.992), FKBP52 expression in breast cancer patients with OS of ≤3 years (5.39±3.409; P=0.042) or OS of ≤5 years (5.88±3.473; P=0.005) was significantly increased, respectively. However, no significant difference in FKBP52 expression was observed between controls and individuals with an OS time of >3 years (4.84±3.769; P=0.109) or >5 years (5.32±3.372; P=0.090). Elevated FKBP52 expression may be involved in tumor progression and invasion, given its positive association with TNM stage and lymph node metastasis. Although it is not an independent predictor, FKBP52 has promise as a biological marker for estimating the progression of breast cancer.

FKBP3 Promotes Proliferation of Non-Small Cell Lung Cancer Cells through Regulating Sp1/HDAC2/p27

FKBP3 is a member of FK506-binding proteins (FKBPs). Little is known about the expression and functional role(s) of FKBP3 in non-small cell lung cancer (NSCLC). In the present study, we demonstrated up-regulation of FKBP3 expression, both at mRNA and protein levels, in NSCLC samples which closely correlated with poor survival in NSCLC patients. In vitro and in vivo experiments revealed that FKBP3 could promote NSCLC cell proliferation. Furthermore, knockdown of FKBP3 significantly decreased histone deacetylase 2 (HDAC2) expression and increased p27 (a cell cycle inhibitor) expression. HDAC2 modulated the acetylation of histone H3K4 by directly binding to the p27 promoter. The proliferation-promoting effect of FKBP3 was dependent on HDAC2 and inhibited by p27. Also, FKBP3 induced HDAC2 promoter activity via inhibiting the ubiquitination of transcription factor Sp1. Additionally, we identified miR-145-5p as a regulator of FKBP3. miR-145-5p overexpression suppressed cell proliferation of NSCLC cells which was abrogated by FKBP3 overexpression. Taken together, our data clearly show that FKBP3/Sp1/HDAC2/p27 control cell proliferation during NSCLC development.

Peptidyl-Proline Isomerases (PPIases): Targets for Natural Products and Natural Product-Inspired Compounds

Peptidyl-proline isomerases (PPIases) are a chaperone superfamily comprising the FK506-binding proteins (FKBPs), cyclophilins, and parvulins. PPIases catalyze the cis/trans isomerization of proline, acting as a regulatory switch during folding, activation, and/or degradation of many proteins. These "clients" include proteins with key roles in cancer, neurodegeneration, and psychiatric disorders, suggesting that PPIase inhibitors could be important therapeutics. However, the active site of PPIases is shallow, solvent-exposed, and well conserved between family members, making selective inhibitor design challenging. Despite these hurdles, macrocyclic natural products, including FK506, rapamycin, and cyclosporin, bind PPIases with nanomolar or better affinity. De novo attempts to derive new classes of inhibitors have been somewhat less successful, often showcasing the "undruggable" features of PPIases. Interestingly, the most potent of these next-generation molecules tend to integrate features of the natural products, including macrocyclization or proline mimicry strategies. Here, we review recent developments and ongoing challenges in the inhibition of PPIases, with a focus on how natural products might inform the creation of potent and selective inhibitors.

Biological relevance of Hsp90-binding immunophilins in cancer development and treatment

Immunophilins are a family of intracellular receptors for immunosuppressive drugs. Those immunophilins that are related to immunosuppression are the smallest proteins of the family, i.e., FKBP12 and CyPA, whereas the other members of the family have higher molecular weight because the show additional domains to the drug-binding site. Among these extra domains, the TPR-domain is perhaps the most relevant because it permits the interaction of high molecular weight immunophilins with the 90-kDa heat-shock protein, Hsp90. This essential molecular chaperone regulates the biological function of several protein-kinases, oncogenes, protein phosphatases, transcription factors and cofactors . Hsp90-binding immunophilins where first characterized due to their association with steroid receptors. They regulate the cytoplasmic transport and the subcellular localization of these and other Hsp90 client proteins, as well as transcriptional activity, cell proliferation, cell differentiation and apoptosis. Hsp90-binding immunophilins are frequently overexpressed in several types of cancers and play a key role in cell survival. In this article we analyze the most important biological actions of the best characterized Hsp90-binding immunophilins in both steroid receptor function and cancer development and discuss the potential use of these immunophilins for therapeutic purposes as potential targets of specific small molecules.

Pleiotropic roles in cancer biology for multifaceted proteins FKBPs

BACKGROUND

FK506 binding proteins (FKBP) are multifunctional proteins highly conserved across the species and abundantly expressed in the cell. In addition to a well-established role in immunosuppression, FKBPs modulate several signal transduction pathways in the cell, due to their isomerase activity and the capability to interact with other proteins, inducing changes in conformation and function of protein partners. Increasing literature data support the concept that FKBPs control cancer related pathways.

SCOPE OF THE REVIEW

The aim of the present article is to review current knowledge on FKBPs roles in regulation of key signaling pathways associated with cancer.

MAJOR CONCLUSIONS

Some family members appear to promote disease while others are protective against tumorigenesis.

GENERAL SIGNIFICANCE

FKBPs family proteins are expected to provide new biomarkers and small molecular targets, in the near future, increasing diagnostic and therapeutic opportunities in the cancer field. This article is part of a Special Issue entitled Proline-Directed Foldases: Cell Signaling Catalysts and Drug Targets.

Differential promoter methylation of kinesin family member 1a in plasma is associated with breast cancer and DNA repair capacity

Methylation alterations of CpG islands, CpG island shores and first exons are key events in the formation and progression of human cancer, and an increasing number of differentially methylated regions and genes have been identified in breast cancer. Recent studies of the breast cancer methylome using deep sequencing and microarray platforms are providing a novel insight on the different roles aberrant methylation plays in molecular subtypes of breast cancer. Accumulating evidence from a subset of studies suggests that promoter methylation of tumor-suppressor genes associated with breast cancer can be quantified in circulating DNA. However, there is a paucity of studies that examine the combined presence of genetic and epigenetic alterations associated with breast cancer using blood-based assays. Dysregulation of DNA repair capacity (DRC) is a genetic risk factor for breast cancer that has been measured in lymphocytes. We isolated plasma DNA from 340 participants in a breast cancer case control project to study promoter methylation levels of five genes previously shown to be associated with breast cancer in frozen tissue and in cell line DNA: MAL, KIF1A, FKBP4, VGF and OGDHL. Methylation of at least one gene was found in 49% of the cases compared to 20% of the controls. Three of the four genes had receiver characteristic operator curve values of ≥0.50: MAL (0.64), KIF1A (0.51) and OGDHL (0.53). KIF1A promoter methylation was associated with breast cancer and inversely associated with DRC. This is the first evidence of a significant association between genetic and epigenetic alterations in breast cancer using blood-based tests. The potential diagnostic utility of these biomarkers and their relevance for breast cancer risk prediction should be examined in larger cohorts.

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.

Stress-induced sex differences: adaptations mediated by the glucocorticoid receptor

Clinical evidence has indicated that women are more susceptible to stress-related and autoimmune disorders than men. Although females may be more susceptible to some disease states, males do not escape unscathed and are more susceptible to metabolic dysfunction. The hypothalamic-pituitary-axis plays a pivotal role in the sexually dimorphic effects of chronic stress through alterations in negative feedback. Recent evidence has implicated the glucocorticoid receptor and its co-chaperones in the etiology of psychiatric and somatic diseases. Gonadal hormones heavily interact with both glucocorticoid receptor expression and glucocorticoid receptor action either through direct or indirect effects on proteins in the chaperone and co-chaperone complex. Diverse systems including the hypothalamic-pituitary-axis, the immune system, and metabolism are affected differently in males and females, possibly through the glucocorticoid receptor system. New considerations of glucocorticoid regulation through the co-chaperone complex in the brain will be vital to the development of treatment strategies for men and women afflicted by neuropsychiatric and somatic disorders.

The Hsp90 chaperone machinery: conformational dynamics and regulation by co-chaperones

Hsp90 is a dimeric molecular chaperone required for the activation and stabilization of numerous client proteins many of which are involved in essential cellular processes like signal transduction pathways. This activation process is regulated by ATP-induced large conformational changes, co-chaperones and posttranslational modifications. For some co-chaperones, a detailed picture on their structures and functions exists, for others their contributions to the Hsp90 system is still unclear. Recent progress on the conformational dynamics of Hsp90 and how co-chaperones affect the Hsp90 chaperone cycle significantly increased our understanding of the gearings of this complex molecular machinery. This article is part of a Special Issue entitled: Heat Shock Protein 90 (Hsp90).

Regulation of steroid hormone receptor function by the 52-kDa FK506-binding protein (FKBP52)

The large FK506-binding protein FKBP52 has been characterized as an important positive regulator of androgen, glucocorticoid and progesterone receptor signaling pathways. FKBP52 associates with receptor-Hsp90 complexes and is proposed to have roles in both receptor hormone binding and receptor subcellular localization. Data from biochemical and cellular studies have been corroborated in whole animal models as fkbp52-deficient male and female mice display characteristics of androgen, glucocorticoid and/or progesterone insensitivity. FKBP52 receptor specificity and the specific phenotypes displayed by the fkbp52-deficient mice have firmly established FKBP52 as a promising target for the treatment of a variety of hormone-dependent diseases. Recent studies demonstrated that the FKBP52 FK1 domain and the proline-rich loop within this domain are functionally important for FKBP52 regulation of receptor function. Based on these data, efforts are currently underway to target the FKBP52 FK1 domain and the proline-rich loop with small molecule inhibitors.

The emerging role of FK506-binding proteins as cancer biomarkers: a focus on FKBPL

FKBPs (FK506-binding proteins) have long been recognized as key regulators of the response to immunosuppressant drugs and as co-chaperones of steroid receptor complexes. More recently, evidence has emerged suggesting that this diverse protein family may also represent cancer biomarkers owing to their roles in cancer progression and response to treatment. FKBPL (FKBP-like) is a novel FKBP with roles in GR (glucocorticoid receptor), AR (androgen receptor) and ER (oestrogen receptor) signalling. FKBPL binds Hsp90 (heat-shock protein 90) and modulates translocation, transcriptional activation and phosphorylation of these steroid receptors. It has been proposed as a novel prognostic and predictive biomarker, where high levels predict for increased recurrence-free survival in breast cancer patients and enhanced sensitivity to endocrine therapy. Since this protein family has roles in a plethora of signalling pathways, its members represent novel prognostic markers and therapeutic targets for cancer diagnosis and treatment.

FKBP family proteins as promising new biomarkers for cancer

FK506-binding proteins (FKBPs) belong to the immunophilin family and bind immunosuppressive drugs, such as FK506 and rapamycin. These proteins, through interactions with steroid hormone receptors, kinases, or other cellular factors, play important roles in various physiological processes and, more interestingly, in pathological processes in mammals. Accumulating evidence has implicated some FKBP members in a variety of processes, such as the cell cycle and survival and apoptotic signaling pathways, particularly in cancers. After the deregulation of their expression was observed in cancer tissues, it became increasingly clear that FKBP members played an important role in tumorigenesis and the response to chemotherapies and radiotherapies and that FKBP members could act as oncogenes or tumor suppressors depending on the tissue type. A wealth of data from in vitro and clinical studies is paving the way for novel, promising roles of FKBPs as diagnostic, prognostic or therapy-monitoring cancer biomarkers.

Probing the topological tolerance of multimeric protein interactions: evaluation of an estrogen/synthetic ligand for FK506 binding protein conjugate

Bivalent small molecules composed of a targeting element and an element that recruits endogenous proteins have been shown to block protein-protein interactions in some systems. We have attempted to apply such an approach to disrupt the interaction of the estrogen receptor α with either its associated coactivators or its dimerization partner (i.e., another estrogen receptor). We show here that a conjugate capable of simultaneously binding both the estrogen receptor and a recruited protein (FK506 Binding Protein 12 kDa) is, however, incapable of disrupting the multimeric estrogen receptor dimer/coactivator complex both in vitro and in cell-based reporter gene assays. We postulate why it may not be possible to disrupt this particular protein-protein complex-as well as other systems having high topological tolerance-with such bivalent inhibitors.

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.

FKBPL regulates estrogen receptor signaling and determines response to endocrine therapy

The HSP90 chaperone and immunophilin FKBPL is an estrogen-responsive gene that interacts with estogen receptor alpha (ERalpha) and regulates its levels. In this study, we explored the effects of FKBPL on breast cancer proliferation. Breast cancer cells stably overexpressing FKBPL became dependent on estrogen for their growth and were dramatically more sensitive to the antiestrogens tamoxifen and fulvestrant, whereas FKBPL knockdown reverses this phenotype. FKBPL knockdown also decreased the levels of the cell cycle inhibitor p21WAF1 and increased ERalpha phosphorylation on Ser(118) in response to 17beta-estradiol and tamoxifen. In support of the likelihood that these effects explained FKBPL-mediated cell growth inhibition and sensitivity to endocrine therapies, FKBPL expression was correlated with increased overall survival and distant metastasis-free survival in breast cancer patients. Our findings suggest that FKBPL may have prognostic value based on its impact on tumor proliferative capacity and sensitivity to endocrine therapies, which improve outcome.

Modulated T-complex protein 1 ζ and peptidyl-prolyl cis-trans isomerase B are two novel indicators for evaluating lymph node metastasis in colorectal cancer: Evidence from proteomics and bioinformatics

Lymph node metastasis (LNM) is an important indicator for systematic therapy, which could increase the survival of colorectal cancer (CRC) patients. However, effective clinical evaluation for LNM is still absent to date. In this study, protein expression profiles of CRC tissues were compared between patients with and without LNM. Based on average expression level, 12 proteins were found to be differentially expressed in the CRC tissues with LNM, whose discrimination reliability was confirmed by PCA. With stepwise linear discriminant analysis, T-complex protein 1 ζ subunit and peptidyl-prolyl cis-trans isomerase B (PPIB) were identified as two main contributors for separating CRC tissues with positive LNM from those negative ones in both original-grouped and cross-validated-grouped cases, which was also supported in subsequent linear support vector machine analysis. In addition, the expression alterations of the two proteins were verified by Western blot and immunohistochemistry. Functional studies also confirmed the role of PPIB in migration and invasion of cancer cells. Taken together, the down-regulated T-complex protein 1 ζ subunit and up-regulated PPIB were identified as two promising indicators for the clinical evaluation of LNM in CRC patients.

Multi-faceted role of HSP40 in cancer

HSP40 (DNAJ) is an understudied family of co-chaperones. The human genome codes for over 41 members of HSP40 family that reside at distinct intracellular locations. Despite their large numbers, little is known about their physiologic roles. Recent research has revealed involvement of some of the DNAJ family members in various types of cancers. In this article we summarize the information about the involvement of human DNAJ family members in various aspects of cancer biology. Furthermore we discuss the potential role of the J domain of DNAJ proteins in cancer biology.

Pharmacologic unmasking of epigenetically silenced genes in breast cancer

PURPOSE

Aberrant promoter hypermethylation of several known or putative tumor suppressor genes occurs frequently during the pathogenesis of various cancers including breast cancer. Many epigenetically inactivated genes involved in breast cancer development remain to be identified. Therefore, in this study we used a pharmacologic unmasking approach in breast cancer cell lines with 5-aza-2'-deoxycytidine (5-aza-dC) followed by microarray expression analysis to identify epigenetically inactivated genes in breast cancer.

EXPERIMENTAL DESIGN

Breast cancer cell lines were treated with 5-aza-dC followed by microarray analysis to identify epigenetically inactivated genes in breast cancer. We then used bisulfite DNA sequencing, conventional methylation-specific PCR, and quantitative fluorogenic real-time methylation-specific PCR to confirm cancer-specific methylation in novel genes.

RESULTS

Forty-nine genes were up-regulated in breast cancer cells lines after 5-aza-dC treatment, as determined by microarray analysis. Five genes (MAL, FKBP4, VGF, OGDHL, and KIF1A) showed cancer-specific methylation in breast tissues. Methylation of at least two was found at high frequency only in breast cancers (40 of 40) as compared with normal breast tissue (0 of 10; P<0.0001, Fisher's exact test).

CONCLUSIONS

This study identified new cancer-specific methylated genes to help elucidate the biology of breast cancer and as candidate diagnostic markers for the disease.

Deficiency of immunophilin FKBP52 promotes endometriosis

Endometriosis is a common gynecological disease that affects approximately 10% of women of childbearing age. It is characterized by endometrial growth outside the uterus and often results in inflamed lesions, pain, and reduced fertility. Although heightened estrogenic activity and/or reduced progesterone responsiveness are considered to be involved in the etiology of endometriosis, neither the extent of their participation nor the underlying mechanisms are clearly understood. Heterogeneous uterine cell types differentially respond to estrogen and progesterone (P(4)). P(4), primarily acting via its nuclear receptor (PR), activates gene transcription and impacts many reproductive processes. Deletion of Fkbp52, an immunophilin cochaperone for PR, results in uterine-specific P(4) resistance in mice, creating an opportunity to study the unique aspects of P(4) signaling in endometriosis. Here we explored the roles of FKBP52 in this disease using Fkbp52(-/-) mice. We found that the loss of FKBP52 encourages the growth of endometriotic lesions with increased inflammation, cell proliferation, and angiogenesis. We also found remarkable down-regulation of FKBP52 in cases of human endometriosis. Our results provide the first evidence corroborated by genetic studies in mice for a potential role of an immunophilin cochaperone in the etiology of human endometriosis. This investigation is highly relevant for clinical application, particularly because P(4) resistance is favorably indicated in endometriosis and other gynecological diseases.

Identification of estrogen-responsive proteins in MCF-7 human breast cancer cells using label-free quantitative proteomics

17beta-Estradiol (E(2)) is a key regulatory steroid hormone that is involved in the control of a number of developmental and other functions. The aim of the present work was to identify estrogen-dependent proteomic changes by determining the levels of expressed proteins in MCF-7 human breast cancer cells following treatment with E(2). A number of methods exist for differential analysis of complex proteomic mixtures. Here, a label-free mass spectrometric approach comparing the ion intensities of tryptic peptides was adopted, which was combined with prefractionation of whole cell lysate proteins by 1-D SDS-PAGE. Using this approach, 60 proteins were found to be affected by E(2). These comprised 55 up-regulated and five down-regulated proteins. These proteins varied widely in their physiochemical properties with pIs of 4-12 and molecular weights of 9-500 kDa. Pathway analysis revealed that the majority of changes were related and together describe an up-regulated pathway consistent with the events of cell proliferation. The quantitative approach used here is relatively straightforward, avoids the use of costly labelling reagents, was reproducible within acceptable limits and has a linear response over a useful concentration range.

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.

Pharmacological targeting of catalyzed protein folding: the example of peptide bond cis/trans isomerases

Peptide bond isomerases are involved in important physiological processes that can be targeted in order to treat neurodegenerative disease, cancer, diseases of the immune system, allergies, and many others. The folding helper enzyme class of Peptidyl-Prolyl-cis/trans Isomerases (PPIases) contains the three enzyme families of cyclophilins (Cyps), FK506 binding proteins (FKBPs), and parvulins (Pars). Although they are structurally unrelated, all PPIases catalyze the cis/trans isomerization of the peptide bond preceding the proline in a polypeptide chain. This process not only plays an important role in de novo protein folding, but also in isomerization of native proteins. The native state isomerization plays a role in physiological processes by influencing receptor ligand recognition or isomer-specific enzyme reaction or by regulating protein function by catalyzing the switch between native isomers differing in their activity, e.g., ion channel regulation. Therefore elucidating PPIase involvement in physiological processes and development of specific inhibitors will be a suitable attempt to design therapies for fatal and deadly diseases.

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.

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.

mRNA expression levels of (co)chaperone molecules of the glucocorticoid receptor are not involved in glucocorticoid resistance in pediatric ALL

Resistance to glucocorticoids (GC) is an important adverse risk factor in the treatment of acute lymphoblastic leukemia (ALL). To induce apoptosis, GC bind to the GC receptor (GR), which is regulated by various (co)chaperone proteins such as heat-shock protein 70 (HSP-70), HSP-40, HIP (HSP-70-interacting protein), BAG-1 (BCL-2-associated gene product-1), HOP (HSP-70/HSP-90-Organizing protein), HSP-90, P-23, FKBP-51, FKBP-52 and CYP-40. In this study, we tested the hypothesis that mRNA expression levels of these molecules are determinants of GC resistance in childhood ALL. In all, 20 children with ALL cells in vitro sensitive to prednisolone (LC(50) < 0.1 microg/ml) were compared each with a resistant patient (LC(50) >150 mug/ml), matched for immunophenotype, age and white blood cell count. mRNA expression levels of the (co)chaperone molecules were measured by quantitative real-time RT-PCR and normalized to GAPDH and RNaseP levels. In vitro resistance to prednisolone was measured by MTT assay. HSP-90 mRNA expression levels were 2000-fold higher as compared to HSP-70. Using matched pair analysis, mRNA expression levels of the various (co)chaperone molecules were not significantly different between in vitro-sensitive and -resistant patients. GC resistance in childhood ALL cannot be attributed to different mRNA expression levels of the investigated (co)chaperone molecules involved in GC binding and transport to the nucleus.

Estrogen receptor alpha and beta subtype expression and transactivation capacity are differentially affected by receptor-, hsp90- and immunophilin-ligands in human breast cancer cells

In MCF-7 (estrogen receptor (ER)+) and in MDA-MB-231 (ER-) cells stably transfected with either estrogen receptor alpha (ERalpha) or beta (ERbeta) subtype (MDA-MB-231 stably transfected with the mouse ERalpha cDNA (MERA) and MDA-MB-231 stably transfected with the human ERbeta cDNA (HERB), respectively) N-term heat shock protein of 90kDa (hsp90) ligands (geldanamycin and radicicol) and C-term hsp90 ligands (novobiocin) decrease the basal and estradiol (E(2))-induced transcription activity of ER on an estrogen responsive element (ERE)-LUC reporter construct concomitantly with or 1h after E(2) treatment. All hsp90 ligands induced an E(2)- and MG132-inhibited decrease of both ER cell content. However, the kinetics of these degradations are slower than those induced by the selective estrogen receptor down-regulator RU 58668 (RU). This suggests that inhibition of the hsp90 ATPase activity targets both ERs to the 26S proteasome and that hsp90 interacts with both ER subtypes. Rapamycin (Rapa) and cyclosporin A (CsA), ligands of immunophilins FK506 binding protein (FKBP52) and cyclophilin of 40kDa (CYP40) interacting in separate ER-hsp90 complexes, both induced a proteasomal-mediated degradation of ERs but not of their cognate immunophilin. Moreover, they also decrease the E(2)-induced luciferase transcription but weaker than RU and hsp90 ligands. Fluorescence activated cell sorter (FACS) analysis revealed a blockade of cell progression by RU and 4-hydroxy-tamoxifen at the G(1) phase of the cell cycle and an induction of apoptosis in MCF-7 cells. Rapa and mainly CsA (but not FK506) and hsp90 ligands promote by their own apoptosis in MCF-7, in MERA, and in HERB cells and in MDA-MB-231 ER-null cells. These data suggest that (1) hsp90, as for all steroid receptors, acts as a molecular chaperone for ERbeta; (2) ER-ligands (except tamoxifen), hsp90- and immunophilin-ligands (except FK506) target the two ER subtypes to a proteasome-mediated proteolysis via different signalling pathways; (3) hsp90- and immunophilin-ligands Rapa and CsA, alone or in association with anti-estrogens such as RU, may constitute a potential therapeutic strategy for breast cancer treatment.

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.

Effect of geldanamycin on androgen receptor function and stability

In the ligand-binding inactive state, the steroid receptor heterocomplex contains Hsp90, Hsp70, high-molecular weight immunophilins, and other proteins. Hsp90 acts in association with co-chaperones to maintain the native state of the receptor within the cells. It was reported earlier that Hsp90 might not be as important for the androgen receptor (AR) activity as for the glucocorticoid receptor (GR) and the progesterone receptor (PR) activities. We used the Hsp90 inhibitor geldanamycin (GA) to explore the role of Hsp90 in the function of the AR heterocomplex. GA selectively binds to Hsp90 and inhibits its activity, leading to the loss of steroid receptor activity, and frequently, its degradation. In our study, LNCaP prostate cancer cells were treated with GA for 30 minutes or 24 hours, in the presence of mibolerone, a synthetic androgen. GA reduced the androgen-induced AR protein levels to 15% after 24 hours of treatment. Several androgen up-regulated genes, including immunophilin FKBP51 and prostate specific antigen (PSA), were reduced by GA treatment. In cells treated with GA after transfection with a PSA promoter or an androgen response element-driven reporter gene, AR-mediated transactivation of reporter gene expression was reversibly inhibited by GA. Loss of androgen-binding ability and AR levels was attributed to reduced transcription of AR-regulated gene expression. Degradation rate of 35S-labeled AR was significantly increased by GA in the presence or absence of mibolerone. GA induced the degradation of AR through the proteasomal pathway. AR in cells treated with proteasomal inhibitor lactacystin, was insoluble in Nonidet P-40 (NP40)-based buffer and could not restore the androgen-binding ability. We report here that GA treatment disrupted both hormone-binding activity and receptor protein stability, resulting in a dramatic loss of androgen-induced gene activation. These results show that Hsp90 activity is important for both the chaperone-mediated folding of the AR into a high-affinity ligand-binding conformation and the functional activity of the AR.

Estradiol-regulated expression of the immunophilins cyclophilin 40 and FKBP52 in MCF-7 breast cancer cells

The immunophilins, cyclophilin 40 (CyP40) and FKBP52, are associated with the unactivated estrogen receptor in mutually exclusive heterocomplexes and may differentially modulate receptor activity. We have recently shown that CyP40 and FKBP52 mRNA's are differentially elevated in breast carcinomas compared with normal breast tissue. Other studies suggest that such alterations in the ratio of immunophilins might potentially influence steroid receptor function. Studies were therefore initiated to investigate the influence of estradiol on CyP40 and FKBP52 expression in MCF-7 breast cancer cells. Over a 24-h-treatment period with estradiol, CyP40 and FKBP52 mRNA expression was increased approximately five- and 14-fold, respectively. The corresponding protein levels were also elevated in comparison to controls. The antiestrogen, ICI 182,780, was an antagonist for CyP40 and FKBP52 mRNA induction. Cycloheximide treatment did not inhibit this increased immunophilin expression, suggesting that estradiol-mediated activation is independent of de novo protein synthesis. Treatment of MCF-7 cells with estradiol resulted in an increased half-life of both CyP40 and FKBP52 mRNA, as determined by actinomycin D studies. These results suggest that estradiol regulates CyP40 and FKBP52 mRNA expression through both transcriptional and posttranscriptional mechanisms.

Lupus: why women?

Estrogens are believed to play a role in the etiology of both human and murine systemic lupus erythematosus (lupus, SLE), presumably through the agency of their cellular receptor proteins. There is now considerable interest in the molecular mechanism of action of estrogens in immune tissues, particularly with regard to autoimmune disorders, which are generally more prevalent in women. In this laboratory, an attempt is being made to characterize estrogen receptors in murine models of SLE, namely NZB/W and MRL/MP-lpr/lpr mice, and to try to relate this to estrogen receptor function in vivo. It is hypothesized that estradiol (E(2)), through its receptors, mediates the progression of murine SLE and that in autoimmune disease, the estrogen receptor is functionally or structurally changed, or both. Initial studies suggest there are differences in estrogen receptors between BALB/c mice, which do not get autoimmune disease, and two strains that do, MRL/MP-lpr/lpr and NZB/W mice. There is evidence that in at least one model of SLE, the normal regulation of estrogen action by progesterone may be impaired. In several laboratories, attempts are being made to relate estrogen action to immune function and to autoimmune diseases. The study of estrogen action on the immune system may lead to the development of treatments that attenuate the immunostimulant effects of E(2) in autoimmune diseases such as SLE.