The function of steroid hormone receptors is inhibited by the hsp90-specific compound geldanamycin

Environmentally relevant concentrations of Triclosan cause transcriptomic and biomolecular alterations in the hatchlings of Labeo rohita

Suppression (p ≤ 0.05) of antioxidative/detoxification (except GPx and CYP3a) and cytoskeletal (except DHPR) genes but induction of metabolic (except for AST and TRY) and heat shock (except HSP60) genes of Labeo rohita hatchlings after 14 days of exposure to environmentally relevant concentrations of Triclosan (0.0063, 0.0126, 0.0252 and 0.06 mg/L) was followed by an increase (p ≤ 0.05) for most of the genes after 10 days recovery period. After recovery, LDH, ALT, CK, CHY, PA, HSP47 and DHPR declined, while SOD, CAT, GST, GR, GPx, CYP1a, CYP3a, AST, AChE, TRY, HSP60, HSP70, HSc71, HSP90 MLP-3, α-tropomyosin, desmin b and lamin b1 increased over exposure. Peak area of biomolecules (except 3290-3296, 2924-2925 and 2852-2855 cm^-1) declined (p ≤ 0.01) more after recovery [except for an increase (p ≤ 0.01) at 1398-1401 cm^-1]. CYP3a, CK, HSP90, MLP-3 and secondary structure of amide A are the most sensitive markers for the environmentally relevant concentrations of Triclosan.

Androgen receptor polyglutamine expansion drives age-dependent quality control defects and muscle dysfunction

Skeletal muscle has emerged as a critical, disease-relevant target tissue in spinal and bulbar muscular atrophy, a degenerative disorder of the neuromuscular system caused by a CAG/polyglutamine (polyQ) expansion in the androgen receptor (AR) gene. Here, we used RNA-sequencing (RNA-Seq) to identify pathways that are disrupted in diseased muscle using AR113Q knockin mice. This analysis unexpectedly identified substantially diminished expression of numerous ubiquitin/proteasome pathway genes in AR113Q muscle, encoding approximately 30% of proteasome subunits and 20% of E2 ubiquitin conjugases. These changes were age, hormone, and glutamine length dependent and arose due to a toxic gain of function conferred by the mutation. Moreover, altered gene expression was associated with decreased levels of the proteasome transcription factor NRF1 and its activator DDI2 and resulted in diminished proteasome activity. Ubiquitinated ADRM1 was detected in AR113Q muscle, indicating the occurrence of stalled proteasomes in mutant mice. Finally, diminished expression of Drosophila orthologues of NRF1 or ADRM1 promoted the accumulation of polyQ AR protein and increased toxicity. Collectively, these data indicate that AR113Q muscle develops progressive proteasome dysfunction that leads to the impairment of quality control and the accumulation of polyQ AR protein, key features that contribute to the age-dependent onset and progression of this disorder.

The andean anticancer herbal product BIRM causes destabilization of androgen receptor and induces caspase-8 mediated-apoptosis in prostate cancer

BIRM is an anticancer herbal formulation from Ecuador. Previous study established its antitumor and antimetastatic activity against prostate cancer models. The activity of BIRM against human prostate cancer (PCa) cells was investigated to uncover its mechanism of antitumor activity. In androgen receptor (AR)-expressing PCa cells BIRM was 2.5-fold (250%) more cytotoxic in presence of androgen (DHT) compared to cells grown in the absence of DHT. In AR-positive cells (LAPC-4 and LNCaP) BIRM caused a dose and time-dependent down-regulation of AR and increased apoptosis. Exposing cells to BIRM did not affect the synthesis of AR and AR promoter activity but increased degradation of AR via proteasome-pathway. BIRM caused destabilization of HSP90-AR association in LAPC-4 cells. It induced apoptosis in PCa cells by activation of caspase-8 via death receptor and FADD-mediated pathways. A synthetic inhibitor of Caspase-8 cleavage (IETD-CHO) aborted BIRM-induced apoptosis. The effect of BIRM on AKT-mediated survival pathway in both AR+ and AR- negative (PC-3 and DU145) showed decreased levels of p-AKTser 473 in all PCa cell lines. BIRM dosed by oral gavage in mice bearing PC-3ML tumors showed selective efficacy on tumor growth; before tumors are established but limited efficacy when treated on existing tumors. Moreover, BIRM inhibited the LNCaP tumor generated by orthotropic implantation into dorsal prostate of nude mice. Partial purification of BIRM by liquid-liquid extraction and further fractionation by HPLC showed 4-fold increased specific activity on PCa cells. These results demonstrate a mechanistic basis of anti-tumor activity of the herbal extract BIRM.

Fibronectin is a stress responsive gene regulated by HSF1 in response to geldanamycin

Fibronectin is an extracellular matrix glycoprotein with key roles in cell adhesion and migration. Hsp90 binds directly to fibronectin and Hsp90 depletion regulates fibronectin matrix stability. Where inhibition of Hsp90 with a C-terminal inhibitor, novobiocin, reduced the fibronectin matrix, treatment with an N-terminal inhibitor, geldanamycin, increased fibronectin levels. Geldanamycin treatment induced a stress response and a strong dose and time dependent increase in fibronectin mRNA via activation of the fibronectin promoter. Three putative heat shock elements (HSEs) were identified in the fibronectin promoter. Loss of two of these HSEs reduced both basal and geldanamycin-induced promoter activity, as did inhibition of the stress-responsive transcription factor HSF1. Binding of HSF1 to one of the putative HSE was confirmed by ChIP under basal conditions, and occupancy shown to increase with geldanamycin treatment. These data support the hypothesis that fibronectin is stress-responsive and a functional HSF1 target gene. COLA42 and LAMB3 mRNA levels were also increased with geldanamycin indicating that regulation of extracellular matrix (ECM) genes by HSF1 may be a wider phenomenon. Taken together, these data have implications for our understanding of ECM dynamics in stress-related diseases in which HSF1 is activated, and where the clinical application of N-terminal Hsp90 inhibitors is intended.

Novel galeterone analogs act independently of AR and AR-V7 for the activation of the unfolded protein response and induction of apoptosis in the CWR22Rv1 prostate cancer cell model

The androgen receptor (AR) has long been the primary target for the treatment of prostate cancer (PC). Despite continuous efforts to block AR activity through ligand depletion, AR antagonism, AR depletion and combinations thereof, advanced PC tumors remain resilient. Herein, we evaluate two galeterone analogs, VNPT-178 and VNLG-74A, in PC cell models of diverse androgen and AR dependence attempting to delineate their mechanisms of action and potential clinical utility. Employing basic biochemical techniques, we determined that both analogs have improved antiproliferative and anti-AR activities compared to FDA-approved abiraterone and enzalutamide. However, induction of apoptosis in these models is independent of the AR and its truncated variant, AR-V7, and instead likely results from sustained endoplasmic reticulum stress and deregulated calcium homeostasis. Using in silico molecular docking, we predict VNPT-178 and VNLG-74A bind the ATPase domain of BiP/Grp78 and Hsp70-1A with greater affinity than the AR. Disruption of 70 kDa heat shock protein function may be the underlying mechanism of action for these galeterone analogs. Therefore, despite simultaneously antagonizing AR activity, AR and/or AR-V7 expression alone may inadequately predict a patient's response to treatment with VNPT-178 or VNLG-74A. Future studies evaluating the context-specific limitations of these compounds may provide clarity for their clinical application.

Effects of thermal stress on the expression of glucocorticoid receptor complex linked genes in Senegalese sole (Solea senegalensis): Acute and adaptive stress responses

The present study examined the short and mid-term effects of a rise in temperature from 18°C to 24°C on the expression of genes related to the stress response regulation in juveniles of Senegalese sole, Solea senegalensis. The animals were exposed to a temperature increase of 6°C, after 1month of acclimation at 18°C. After this process, samples of different tissues were collected from a total of 96 fish at four sampling points: 1h, 24h, 3days and 1week. The transcript levels of a set of genes involved in the stress response such as glucocorticoid receptors 1 and 2, corticotrophin-releasing factor, corticotrophin-releasing factor binding proteins, proopiomelanocortin A and B, and cellular stress defense (heat shock protein 70, 90AA and 90AB) were quantified at these sampling points. Additionally, blood samples were also taken to measure the circulating plasma cortisol concentration. Thermal stress induced by increasing temperature prompted an elevation of plasma cortisol levels in juvenile Senegalese sole after 1h as a short-term response, and a consecutive increase after one week, as a mid-term response. Senegalese sole seemed to respond positively in terms of adaptive mechanisms, with a rapid over-expression of grs and hsps in liver and brain, significantly higher after one hour post stress, denoting the fast and acute response of those tissues to a rapid change on temperature. The ratio hsp90/gr also increased 24h after thermal shock, ratio proposed to be an adaptive mechanism to prevent proteosomal degradation of GR. As a mid-term response, the elevation of brain crfbp gene expression one week after thermal shock could be an adaptive mechanism of negative feedback on HPI axis. Taken together, these data suggested an initial up-regulation of the glucocorticoid receptor complex linked genes in response to a temperature increase in Senegalese sole, with heat shock protein 90 potentially being a regulatory factor for the glucocorticoid receptor in the presence of cortisol.

Hsp90 as a "Chaperone" of the Epigenome: Insights and Opportunities for Cancer Therapy

The cellular functions of Hsp90 have historically been attributed to its ability to chaperone client proteins involved in signal transduction. Although numerous stimuli and the signaling cascades they activate contribute to cancer progression, many of these pathways ultimately require transcriptional effectors to elicit tumor-promoting effects. Despite this obvious connection, the majority of studies evaluating Hsp90 function in malignancy have focused upon its regulation of cytosolic client proteins, and particularly members of receptor and/or kinase families. However, in recent years, Hsp90 has emerged as a pivotal orchestrator of nuclear events. Discovery of an expanding repertoire of Hsp90 clients has illuminated a vital role for Hsp90 in overseeing nuclear events and influencing gene transcription. Hence, this chapter will cast a spotlight upon several regulatory themes involving Hsp90-dependent nuclear functions. Highlighted topics include a summary of chaperone-dependent regulation of key transcription factors (TFs) and epigenetic effectors in malignancy, as well as a discussion of how the complex interplay among a subset of these TFs and epigenetic regulators may generate feed-forward loops that further support cancer progression. This chapter will also highlight less recognized indirect mechanisms whereby Hsp90-supported signaling may impinge upon epigenetic regulation. Finally, the relevance of these nuclear events is discussed within the framework of Hsp90's capacity to enable phenotypic variation and drug resistance. These newly acquired insights expanding our understanding of Hsp90 function support the collective notion that nuclear clients are major beneficiaries of Hsp90 action, and their impairment is likely responsible for many of the anticancer effects elicited by Hsp90-targeted approaches.

Hsp90: A New Player in DNA Repair?

Heat shock protein 90 (Hsp90) is an evolutionary conserved molecular chaperone that, together with Hsp70 and co-chaperones makes up the Hsp90 chaperone machinery, stabilizing and activating more than 200 proteins, involved in protein homeostasis (i.e., proteostasis), transcriptional regulation, chromatin remodeling, and DNA repair. Cells respond to DNA damage by activating complex DNA damage response (DDR) pathways that include: (i) cell cycle arrest; (ii) transcriptional and post-translational activation of a subset of genes, including those associated with DNA repair; and (iii) triggering of programmed cell death. The efficacy of the DDR pathways is influenced by the nuclear levels of DNA repair proteins, which are regulated by balancing between protein synthesis and degradation as well as by nuclear import and export. The inability to respond properly to either DNA damage or to DNA repair leads to genetic instability, which in turn may enhance the rate of cancer development. Multiple components of the DNA double strand breaks repair machinery, including BRCA1, BRCA2, CHK1, DNA-PKcs, FANCA, and the MRE11/RAD50/NBN complex, have been described to be client proteins of Hsp90, which acts as a regulator of the diverse DDR pathways. Inhibition of Hsp90 actions leads to the altered localization and stabilization of DDR proteins after DNA damage and may represent a cell-specific and tumor-selective radiosensibilizer. Here, the role of Hsp90-dependent molecular mechanisms involved in cancer onset and in the maintenance of the genome integrity is discussed and highlighted.

Traditional Chinese medicine's intervention in endothelial nitric oxide synthase activation and nitric oxide synthesis in cardiovascular system

Cardiovascular disease (CVD) is one of the most dangerous diseases which has become a major cause of human death. Many researches evidenced that nitric oxide (NO)/endothelial nitric oxide synthase (eNOS) system plays a significant role in the occurrence and development of CVD. NO, an important signaling molecule, closely associated with the regulation of vasodilatation, blood rheology, blood clotting and other physiological and pathological processes. The synthesis of NO in the endothelial cells primarily depends on the eNOS activity, thus the exploration of the mechanisms and effects of the eNOS activation on NO production is of great significance. Recently, studies on the effects of traditional Chinese medicine (TCM) and its extracts on eNOS activation and NO synthesis have gradually attracted more and more attentions. In this paper, we reviewed the mechanisms of NO synthesis and eNOS activation in the vascular endothelial cells (VECs) and intervention of TCM, so as to provide reference and train of thought to the intensive study of NO/eNOS system and the research and development of new drug for the treatment of CVD.

A C-terminal HSP90 inhibitor restores glucocorticoid sensitivity and relieves a mouse allograft model of Cushing disease

One function of the glucocorticoid receptor (GR) in corticotroph cells is to suppress the transcription of the gene encoding proopiomelanocortin (POMC), the precursor of the stress hormone adrenocorticotropin (ACTH). Cushing disease is a neuroendocrine condition caused by partially glucocorticoid-resistant corticotroph adenomas that excessively secrete ACTH, which leads to hypercortisolism. Mutations that impair GR function explain glucocorticoid resistance only in sporadic cases. However, the proper folding of GR depends on direct interactions with the chaperone heat shock protein 90 (HSP90, refs. 7,8). We show here that corticotroph adenomas overexpress HSP90 compared to the normal pituitary. N- and C-terminal HSP90 inhibitors act at different steps of the HSP90 catalytic cycle to regulate corticotroph cell proliferation and GR transcriptional activity. C-terminal inhibitors cause the release of mature GR from HSP90, which promotes its exit from the chaperone cycle and potentiates its transcriptional activity in a corticotroph cell line and in primary cultures of human corticotroph adenomas. In an allograft mouse model, the C-terminal HSP90 inhibitor silibinin showed anti-tumorigenic effects, partially reverted hormonal alterations, and alleviated symptoms of Cushing disease. These results suggest that the pathogenesis of Cushing disease caused by overexpression of heat shock proteins and consequently misregulated GR sensitivity may be overcome pharmacologically with an appropriate HSP90 inhibitor.

Protein folding, misfolding and quality control: the role of molecular chaperones

Cells have to cope with stressful conditions and adapt to changing environments. Heat stress, heavy metal ions or UV stress induce damage to cellular proteins and disturb the balanced status of the proteome. The adjusted balance between folded and folding proteins, called protein homoeostasis, is required for every aspect of cellular functionality. Protective proteins called chaperones are expressed under extreme conditions in order to prevent aggregation of cellular proteins and safeguard protein quality. These chaperones co-operate during de novo folding, refolding and disaggregation of damaged proteins and in many cases refold them to their functional state. Even under physiological conditions these machines support protein homoeostasis and maintain the balance between de novo folding and degradation. Mutations generating unstable proteins, which are observed in numerous human diseases such as Alzheimer's disease, Huntington's disease, amyotrophic lateral sclerosis and cystic fibrosis, also challenge the protein quality control system. A better knowledge of how the protein homoeostasis system is regulated will lead to an improved understanding of these diseases and provide potential targets for therapy.

Hsp90 modulates PPARγ activity in a mouse model of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a highly prevalent complication of obesity, yet cellular mechanisms that lead to its development are not well defined. Previously, we have documented hepatic steatosis in mice carrying a mutation in the Sec61a1 gene. Here we examined the mechanism behind NAFLD in Sec61a1 mutant mice. Livers of mutant mice exhibited upregulation of Pparg and its target genes Cd36, Cidec, and Lpl, correlating with increased uptake of fatty acid. Interestingly, these mice also displayed activation of the heat shock response (HSR), with elevated levels of heat shock protein (Hsp) 70, Hsp90, and heat shock factor 1. In cell lines, inhibition of Hsp90 function reduced Pparγ signaling and protein levels. Conversely, overexpression of Hsp90 increased Pparγ signaling and protein levels by reducing degradation. This may occur via a physical interaction as Hsp90 and Pparγ coimmunoprecipitated in vivo. Furthermore, inhibition of Hsp90 in Sec61a1 mutant hepatocytes also reduced Pparγ protein levels and signaling. Finally, overexpression of Hsp90 in liver cell lines increased neutral lipid accumulation, and this accumulation was blocked by Hsp90 inhibition. Our results show that the HSR and Hsp90 play an important role in the development of NAFLD, opening new avenues for the prevention and treatment of this highly prevalent disease.

Methylmercury alters the activities of Hsp90 client proteins, prostaglandin E synthase/p23 (PGES/23) and nNOS

Methylmercury (MeHg) is a persistent pollutant with known neurotoxic effects. We have previously shown that astrocytes accumulate MeHg and play a prominent role in mediating MeHg toxicity in the central nervous system (CNS) by altering glutamate signaling, generating oxidative stress, depleting glutathione (GSH) and initiating lipid peroxidation. Interestingly, all of these pathways can be regulated by the constitutively expressed, 90-kDa heat shock protein, Hsp90. As Hsp90 function is regulated by oxidative stress, we hypothesized that MeHg disrupts Hsp90-client protein functions. Astrocytes were treated with MeHg and expression of Hsp90, as well as the abundance of complexes of Hsp90-neuronal nitric oxide synthase (nNOS) and Hsp90-prostaglandin E synthase/p23 (PGES/p23) were assessed. MeHg exposure decreased Hsp90 protein expression following 12 h of treatment while shorter exposures had no effect on Hsp90 protein expression. Interestingly, following 1 or 6 h of MeHg exposure, Hsp90 binding to PGES/p23 or nNOS was significantly increased, resulting in increased prostaglandin E₂ (PGE₂) synthesis from MeHg-treated astrocytes. These effects were attenuated by the Hsp90 antagonist, geldanmycin. NOS activity was increased following MeHg treatment while cGMP formation was decreased. This was accompanied by an increase in •O₂⁻ and H₂O₂ levels, suggesting that MeHg uncouples NO formation from NO-dependent signaling and increases oxidative stress. Altogether, our data demonstrates that Hsp90 interactions with client proteins are increased following MeHg exposure, but over time Hsp90 levels decline, contributing to oxidative stress and MeHg-dependent excitotoxicity.

A Novel Mechanism for Cross-Adaptation between Heat and Altitude Acclimation: The Role of Heat Shock Protein 90

Heat shock protein 90 (HSP90) is a member of a family of molecular chaperone proteins which can be upregulated by various stressors including heat stress leading to increases in HSP90 protein expression. Its primary functions include (1) renaturing and denaturing of damaged proteins caused by heat stress and (2) interacting with client proteins to induce cell signaling for gene expression. The latter function is of interest because, in cancer cells, HSP90 has been reported to interact with the transcription hypoxic-inducible factor 1α (HIF1α). In a normoxic environment, HIF1α is degraded and therefore has limited physiological function. In contrast, in a hypoxic environment, stabilized HIF1α acts to promote erythropoiesis and angiogenesis. Since HSP90 interacts with HIF1α, and HSP90 can be upregulated from heat acclimation in humans, we present a proposal that heat acclimation can mimic molecular adaptations to those of altitude exposure. Specifically, we propose that heat acclimation increases HSP90 which then stabilizes HIF1α in a normoxic environment. This has many implications since HIF1α regulates red blood cell and vasculature formation. In this paper we will discuss (1) the functional roles of HSP90 and HIF1α, (2) the interaction between HSP90 and other client proteins including HIF1α, and (3) results from in vitro studies that may suggest how the relationship between HSP90 and HIF1α might be applied to individuals preparing to make altitude sojourns.

Hsp90 prevents interaction between CHIP and HERG proteins to facilitate maturation of wild-type and mutant HERG proteins

AIMS

We examined the role of Hsp90 in expression and maturation of wild-type (WT) and mutant ether-a-go-go related gene (HERG) proteins by using Hsp90 inhibitors, geldanamycin (GA) and radicicol, and Hsp90 overexpression.

METHODS AND RESULTS

The proteins were expressed in HEK293 cells or collected from HL-1 mouse cardiomyocytes, and analysed by western blotting, immunoprecipitation, immunofluorescence, and whole-cell patch-clamp techniques. GA and radicicol suppressed maturation of HERG-FLAG proteins and increased their immature forms. Co-expression of Hsp90 counteracted the effects of Hsp90 inhibitors and suppressed ubiquitination of HERG proteins. Overexpressed Hsp90 also inhibited the binding of endogenous C-terminus of Hsp70-interacting protein (CHIP) to HERG-FLAG proteins. Hsp90-induced increase of functional HERG proteins was verified by their increased expression on the cell surface and enhanced HERG channel currents. CHIP overexpression decreased both mature and immature forms of HERG-FLAG proteins in cells treated with GA. Hsp90 facilitated maturation of endogenous ERG proteins, whereas CHIP decreased both forms of ERG proteins in HL-1 cells. Mutant HERG proteins harbouring disease-causing missense mutations were mainly in the immature form and had a higher binding capacity to CHIP than the WT; Hsp90 overexpression suppressed this association. Overexpressed Hsp90 increased the mature form of HERG(1122fs/147) proteins, reduced its ubiquitinated form, increased its immunoreactivity in the endoplasmic reticulum and on the plasma membrane, and increased the mutant-mediated membrane current. CHIP overexpression decreased the immature form of HERG(1122fs/147) proteins.

CONCLUSION

Enhancement of HERG protein expression through Hsp90 inhibition of CHIP binding might be a novel therapeutic strategy for long QT syndrome 2 caused by trafficking abnormalities of HERG proteins.

A ligand-specific kinetic switch regulates glucocorticoid receptor trafficking and function

The ubiquitously expressed glucocorticoid receptor (GR) is a major drug target for inflammatory disease, but issues of specificity and target tissue sensitivity remain. We now identify high potency, non-steroidal GR ligands, GSK47867A and GSK47869A, which induce a novel conformation of the GR ligand-binding domain (LBD) and augment the efficacy of cellular action. Despite their high potency, GSK47867A and GSK47869A both induce surprisingly slow GR nuclear translocation, followed by prolonged nuclear GR retention, and transcriptional activity following washout. We reveal that GSK47867A and GSK47869A specifically alter the GR LBD structure at the HSP90-binding site. The alteration in the HSP90-binding site was accompanied by resistance to HSP90 antagonism, with persisting transactivation seen after geldanamycin treatment. Taken together, our studies reveal a new mechanism governing GR intracellular trafficking regulated by ligand binding that relies on a specific surface charge patch within the LBD. This conformational change permits extended GR action, probably because of altered GR-HSP90 interaction. This chemical series may offer anti-inflammatory drugs with prolonged duration of action due to altered pharmacodynamics rather than altered pharmacokinetics.

Fluorescent ligand for human progesterone receptor imaging in live cells

We employed molecular modeling to design and then synthesize fluorescent ligands for the human progesterone receptor. Boron dipyrromethene (BODIPY) or tetramethylrhodamine were conjugated to the progesterone receptor antagonist RU486 (Mifepristone) through an extended hydrophilic linker. The fluorescent ligands demonstrated comparable bioactivity to the parent antagonist in live cells and triggered nuclear translocation of the receptor in a specific manner. The BODIPY labeled ligand was applied to investigate the dependency of progesterone receptor nuclear translocation on partner proteins and to show that functional heat shock protein 90 but not immunophilin FKBP52 activity is essential. A tissue distribution study indicated that the fluorescent ligand preferentially accumulates in tissues that express high levels of the receptor in vivo. The design and properties of the BODIPY-labeled RU486 make it a potential candidate for in vivo imaging of PR by positron emission tomography through incorporation of (18)F into the BODIPY core.

Heat shock protein 90 functions to stabilize and activate the testis-specific serine/threonine kinases, a family of kinases essential for male fertility

Spermiogenesis is characterized by a profound morphological differentiation of the haploid spermatid into spermatozoa. The testis-specific serine/threonine kinases (TSSKs) comprise a family of post-meiotic kinases expressed in spermatids, are critical to spermiogenesis, and are required for male fertility in mammals. To explore the role of heat shock protein 90 (HSP90) in regulation of TSSKs, the stability and catalytic activity of epitope-tagged murine TSSKs were assessed in 293T and COS-7 cells. TSSK1, -2, -4, and -6 (small serine/threonine kinase) were all found to associate with HSP90, and pharmacological inhibition of HSP90 function using the highly specific drugs 17-AAG, SNX-5422, or NVP-AUY922 reduced TSSK protein levels in cells. The attenuation of HSP90 function abolished the catalytic activities of TSSK4 and -6 but did not significantly alter the specific activities of TSSK1 and -2. Inhibition of HSP90 resulted in increased TSSK ubiquitination and proteasomal degradation, indicating that HSP90 acts to control ubiquitin-mediated catabolism of the TSSKs. To study HSP90 and TSSKs in germ cells, a mouse primary spermatid culture model was developed and characterized. Using specific antibodies against murine TSSK2 and -6, it was demonstrated that HSP90 inhibition resulted in a marked decrease of the endogenous kinases in spermatids. Together, our findings demonstrate that HSP90 plays a broad and critical role in stabilization and activation of the TSSK family of protein kinases.

Estradiol receptors in breast cancer cells: associated co-factors as targets for new therapeutic approaches

Estrogen receptors α (ERα) and β (ERβ) are nuclear receptors which transduce estradiol (E2) response in many tissues including the mammary gland and breast cancers (BC). They activate or inhibit specific genes involved in cell cycle progression and cell survival through multiple enzyme activities leading to malignant transformation. Hormone therapy (antiestrogens (AEs) and aromatase inhibitors (AIs) have been widely used to block the mitogenic action of E2 in patients with ER-positive BC. ERs act in concert with numerous other proteins outside and inside the nucleus where co-activators such as histone modifying enzymes help reaching optimum gene activation. Moreover, E2-mediated gene regulation can occur through ERs located at the plasma membrane or G protein-coupled estrogen receptor (GPER), triggering protein kinase signaling cascades. Classical AEs as well as AIs are inefficient to block the cascades of events emanating from the membrane and from E2 binding to GPER, leading patients to escape anti-hormone treatments and hormone therapy resistance. Many pathways are involved in resistance, mostly resulting from over-expression of growth factor membrane receptors, in particular the HER2/ErbB2 which can be inhibited by specific antibodies or tyrosine kinases inhibitors. Together with the Hsp90 molecular chaperone machinery, a complex interplay between ERs, co-activators, co-repressors and growth factor-activated membrane pathways represents potent targets which warrant to be manipulated alone and in combination to designing novel therapies. The discovery of new potential targets arising from micro array studies gives the opportunity to activate or inhibit different new ER-modulating effectors for innovative therapeutic interventions.

Role of the HSP90-associated cochaperone p23 in enhancing activity of the androgen receptor and significance for prostate cancer

Prostate tumor growth initially depends on androgens, which act via the androgen receptor (AR). Despite androgen ablation therapy, tumors eventually progress to a castrate-resistant stage in which the AR remains active. The mechanisms are poorly understood but it may be that changes in levels or activity of AR coregulators affect trafficking and activation of the receptor. A key stage in AR signaling occurs in the cytoplasm, where unliganded receptor is associated with the heat shock protein (HSP)90 foldosome complex. p23, a key component of this complex, is best characterized as a cochaperone for HSP90 but also has HSP90-independent activity and has been reported as having differential effects on the activity of different steroid receptors. Here we report that p23 increases activity of the AR, and this appears to involve steps both in the cytoplasm (increasing ligand-binding capacity, possibly via direct interaction with AR) and the nucleus (enhancing AR occupancy at target promoters). We show, for the first time, that AR and p23 can interact, perhaps directly, when HSP90 is not present in the same complex. The effects of p23 on AR activity are at least partly HSP90 independent because a mutant form of p23, unable to bind HSP90, nevertheless increases AR activity. In human prostate tumors, nuclear p23 was higher in malignant prostate cells compared with benign/normal cells, supporting the utility of p23 as a therapeutic target in prostate cancer.

Withanolides-induced breast cancer cell death is correlated with their ability to inhibit heat protein 90

Withanolides are a large group of steroidal lactones found in Solanaceae plants that exhibit potential anticancer activities. We have previously demonstrated that a withanolide, tubocapsenolide A, induced cycle arrest and apoptosis in human breast cancer cells, which was associated with the inhibition of heat shock protein 90 (Hsp90). To investigate whether other withanolides are also capable of inhibiting Hsp90 and to analyze the structure-activity relationships, nine withanolides with different structural properties were tested in human breast cancer cells MDA-MB-231 and MCF-7 in the present study. Our data show that the 2,3-unsaturated double bond-containing withanolides inhibited Hsp90 function, as evidenced by selective depletion of Hsp90 client proteins and induction of Hsp70. The inhibitory effect of the withanolides on Hsp90 chaperone activity was further confirmed using in vivo heat shock luciferase activity recovery assays. Importantly, Hsp90 inhibition by the withanolides was correlated with their ability to induce cancer cell death. In addition, the withanolides reduced constitutive NF-κB activation by depleting IκB kinase complex (IKK) through inhibition of Hsp90. In estrogen receptor (ER)-positive MCF-7 cells, the withanolides also reduced the expression of ER, and this may be partly due to Hsp90 inhibition. Taken together, our results suggest that Hsp90 inhibition is a general feature of cytotoxic withanolides and plays an important role in their anticancer activity.

Hsp90 regulates O-linked β-N-acetylglucosamine transferase: a novel mechanism of modulation of protein O-linked β-N-acetylglucosamine modification in endothelial cells

O-linked β-N-acetylglucosamine (O-GlcNAc) modification of proteins is involved in many important cellular processes. Increased O-GlcNAc has been implicated in major diseases, such as diabetes and its complications and cardiovascular and neurodegenerative diseases. Recently, we reported that O-GlcNAc modification occurs in the proteasome and serves to inhibit proteasome function by blocking the ATPase activity in the 19S regulatory cap, explaining, at least in part, the adverse effects of O-GlcNAc modification and suggesting that downregulating O-GlcNAc might be important in the treatment of human diseases. In this study, we report on a novel mechanism to modulate cellular O-GlcNAc modification, namely through heat shock protein 90 (Hsp90) inhibition. We observed that O-linked β-N-acetylglucosamine transferase (OGT) interacts with the tetratricopeptide repeat binding site of Hsp90. Inhibition of Hsp90 by its specific inhibitors, radicicol or 17-N-allylamino-17-demethoxygeldanamycin, destabilized OGT in primary endothelial cell cultures and enhanced its degradation by the proteasome. Furthermore, Hsp90 inhibition downregulated O-GlcNAc protein modifications and attenuated the high glucose-induced increase in O-GlcNAc protein modification, including high glucose-induced increase in endothelial or type 3 isoform of nitric oxide synthase (eNOS) O-GlcNAcylation. These results suggest that Hsp90 is involved in the regulation of OGT and O-GlcNAc modification and that Hsp90 inhibitors might be used to modulate O-GlcNAc modification and reverse its adverse effects in human diseases.

Lysine 419 targets human glucocorticoid receptor for proteasomal degradation

Glucocorticoid receptors (GRs) are members of a highly conserved family of ligand dependent transcription factors which following hormone binding undergo homologous down-regulation reducing the levels of receptor protein. This decline in human GR (hGR) is due in part to a decrease in protein receptor stability that may limit cellular responsiveness to ligand. To examine the role of the proteasome protein degradation pathway in steroid-dependent hGR responsiveness, we utilized the proteasomal inhibitors MG-132, beta-lactone, and epoxomicin. HeLa cells and COS cells were treated with proteasome inhibitors in the presence of the GR agonist dexamethasone (Dex), or were pretreated with proteasomal inhibitor and then Dex. Dexamethasone induced glucocorticoid responsive reporter activity significantly over untreated controls, whereas cells treated with proteasomal inhibitors and Dex together showed 2-3-fold increase in activity. Protein sequence analysis of the hGR protein identified several candidate protein degradation motifs including a PEST element. Mutagenesis of this element at lysine 419 was done and mutant K419A hGR failed to undergo ligand dependent down-regulation. Mutant K419A hGR displayed 2-3-fold greater glucocorticoid responsive reporter activity in the presence of Dex than wild type hGR. These differences in transcriptional activity were not due to altered subcellular localization, since when the mutant K419A hGR was fused with the green fluorescent protein (GFP) it was found to move in and out of the nucleus similarly to wild type hGR. Together these results suggest that the proteasome and the identified PEST degradation motif limit steroid-dependent human glucocorticoid receptor signaling.

Differential impact of tetratricopeptide repeat proteins on the steroid hormone receptors

BACKGROUND

Tetratricopeptide repeat (TPR) motif containing co-chaperones of the chaperone Hsp90 are considered control modules that govern activity and specificity of this central folding platform. Steroid receptors are paradigm clients of Hsp90. The influence of some TPR proteins on selected receptors has been described, but a comprehensive analysis of the effects of TPR proteins on all steroid receptors has not been accomplished yet.

METHODOLOGY AND PRINCIPAL FINDINGS

We compared the influence of the TPR proteins FK506 binding proteins 51 and 52, protein phosphatase-5, C-terminus of Hsp70 interacting protein, cyclophillin 40, hepatitis-virus-B X-associated protein-2, and tetratricopeptide repeat protein-2 on all six steroid hormone receptors in a homogeneous mammalian cell system. To be able to assess each cofactor's effect on the transcriptional activity of on each steroid receptor we employed transient transfection in a reporter gene assay. In addition, we evaluated the interactions of the TPR proteins with the receptors and components of the Hsp90 chaperone heterocomplex by coimmunoprecipitation. In the functional assays, corticosteroid and progesterone receptors displayed the most sensitive and distinct reaction to the TPR proteins. Androgen receptor's activity was moderately impaired by most cofactors, whereas the Estrogen receptors' activity was impaired by most cofactors only to a minor degree. Second, interaction studies revealed that the strongly receptor-interacting co-chaperones were all among the inhibitory proteins. Intriguingly, the TPR-proteins also differentially co-precipitated the heterochaperone complex components Hsp90, Hsp70, and p23, pointing to differences in their modes of action.

CONCLUSION AND SIGNIFICANCE

The results of this comprehensive study provide important insight into chaperoning of diverse client proteins via the combinatorial action of (co)-chaperones. The differential effects of the TPR proteins on steroid receptors bear on all physiological processes related to steroid hormone activity.

Alterations in mRNA expression of steroid receptors and heat shock proteins in the liver of rare minnow (Grobiocypris rarus) exposed to atrazine and p,p'-DDE

The chaperon role of heat shock proteins (HSPs) throughout the life cycle of steroid receptors have been demonstrated in vitro. However, the actions of HSPs in steroid pathways in animals especially in fish were unclear. In this study, sexually mature rare minnows (Gobiocypris rarus) were exposed to typical endocrine disruptors (atrazine and p,p'-DDE). Hypertrophy of hepatocytes at the 333 microg/l atrazine treatment and atrophy of hepatocytes in all p,p'-DDE treatments were observed. The expression of liver hsp70 and hsp90 in atrazine treatments were significantly up-regulated. Moreover, remarkable increases in the expression of androgen receptor (ar) and estrogen receptor (er) were observed, while alterations of the glucoticorcoid receptor (gr) expression was not significant in atrazine exposed fish. The expression of ar, er, gr, hsp70 and hsp90 were significantly suppressed following p,p'-DDE exposure. These results demonstrate that the expression of hsp70 and hsp90 is altered along with changes of steroid receptors in vivo. Therefore, the results are consistent with the possibility that in fish heat shock proteins (HSPs) play chaperon roles for the steroid receptors in vivo, which also concurs with previous in vitro mammalian studies.

Atrazine affects kidney and adrenal hormones (AHs) related genes expressions of rare minnow (Gobiocypris rarus)

Atrazine, one of the most widely used herbicides, has been proved to interfere with sexual hormones. However few studies have considered the effects of atrazine on adrenal hormones (AH). In this study, rare minnow (Gobiocypris rarus) was exposed to 0, 3, 10, 33, 100 and 333microg/l atrazine for 28 days. The histopathology of kidney and gill was examined and the expressions of AHs-related genes including Na(+),K(+)-ATPase, glucocorticoid receptor (gr), heat shock protein 70 (hsp70), and heat shock protein 90 (hsp90) in kidney and gill were quantitatively determined. Histopathological observation revealed obvious lesions in gill including hyperplasia, necrosis in epithelium region, aneurysm and lamellar fusion at concentrations as low as 10microg/l. The observed lesions in kidney included extensive expansion in the lumen, degenerative and necrotic changes of the tubular epithelia, shrinkage of the glomerulus as well as increase of the Bowman's space at concentrations as low as 10microg/l. The expressions of Na(+),K(+)-ATPase, gr, hsp70 and hsp90 in the kidney of females were significantly decreased at all concentrations. For males, the expressions of hsp90 in the kidney of all treated groups were significantly down-regulated, while gr at all concentrations and hsp70 at 10, 33, 100microg/l were significantly up-regulated. However in the gill, the expressions of these genes were not significantly different from the control. These results indicated that exposure to atrazine caused impairments of kidney and gill of fish at environmental related concentrations. Histopathological lesions could partly attribute to the changes of the expressions of AHs-related genes in kidney. We concluded also that atrazine is a potential AHs-disruptor and AHs-related genes in kidney of fish could be used as sensitive molecular biomarkers.

Small molecule screening reveals a transcription-independent pro-survival function of androgen receptor in castration-resistant prostate cancer

In prostate cancer (PCa) patients, initial responsiveness to androgen deprivation therapy is frequently followed by relapse due to development of treatment-resistant androgen-independent PCa. This is typically associated with acquisition of mutations in AR that allow activity as a transcription factor in the absence of ligand, indicating that androgen-independent PCa remains dependent on AR function. Our strategy to effectively target AR in androgen-independent PCa involved using a cell-based readout to isolate small molecules that inhibit AR transactivation function through mechanisms other than modulation of ligand binding. A number of the identified inhibitors were toxic to AR-expressing PCa cells regardless of their androgen dependence. Among these, some only suppressed PCa cell growth (ARTIS), while others induced cell death (ARTIK). ARTIK, but not ARTIS, compounds caused disappearance of AR protein from treated cells. siRNA against AR behaved like ARTIK compounds, while a dominant negative AR mutant that prevents AR-mediated transactivation but does not eliminate the protein showed only a growth suppressive effect. These observations reveal a transcription-independent function of AR that is essential for PCa cell viability and, therefore, is an ideal target for anti-PCa treatment. Indeed, several of the identified AR inhibitors demonstrated in vivo efficacy in mouse models of PCa and are candidates for pharmacologic optimization.

Estrogen, NFkappaB, and the heat shock response

Estrogen has pleiotropic actions, among which are its anti-apoptotic, anti-inflammatory, and vasodilatory effects. Recently, an interaction between 17beta-estradiol (E2) and the transcription factor nuclear factor kappaB (NFkappaB) has been identified. NFkappaB has a central role in the control of genes involved in inflammation, proliferation, and apoptosis. Prolonged activation of NFkappaB is associated with numerous inflammatory pathological conditions. An important facet of E2 is its ability to modulate activity of NFkappaB via both genomic and nongenomic actions. E2 can activate NFkappaB rapidly via nongenomic pathways, increase cellular resistance to injury, and induce expression of the protective class of proteins, heat shock proteins (HSPs). HSPs can bind to many of the pro-apoptotic and pro-inflammatory targets of NFkappaB and, thus, indirectly inhibit many of its deleterious effects. In addition, HSPs can block NFkappaB activation and binding directly. Similarly, genomic E2 signaling can inhibit NFkappaB, but does so through alternative mechanisms. This review focuses on the molecular mechanisms of cross-talk between E2, NFkappaB, and HSPs, and the biological relevance of this cross-talk.

Glucocorticoid receptor phosphorylation differentially affects target gene expression

The glucocorticoid receptor (GR) is phosphorylated at multiple sites within its N terminus (S203, S211, S226), yet the role of phosphorylation in receptor function is not understood. Using a range of agonists and GR phosphorylation site-specific antibodies, we demonstrated that GR transcriptional activation is greatest when the relative phosphorylation of S211 exceeds that of S226. Consistent with this finding, a replacement of S226 with an alanine enhances GR transcriptional response. Using a battery of compounds that perturb different signaling pathways, we found that BAPTA-AM, a chelator of intracellular divalent cations, and curcumin, a natural product with antiinflammatory properties, reduced hormone-dependent phosphorylation at S211. This change in GR phosphorylation was associated with its decreased nuclear retention and transcriptional activation. Molecular modeling suggests that GR S211 phosphorylation promotes a conformational change, which exposes a novel surface potentially facilitating cofactor interaction. Indeed, S211 phosphorylation enhances GR interaction with MED14 (vitamin D receptor interacting protein 150). Interestingly, in U2OS cells expressing a nonphosphorylated GR mutant S211A, the expression of IGF-binding protein 1 and interferon regulatory factor 8, both MED14-dependent GR target genes, was reduced relative to cells expressing wild-type receptor across a broad range of hormone concentrations. In contrast, the induction of glucocorticoid-induced leucine zipper, a MED14-independent GR target, was similar in S211A- and wild-type GR-expressing cells at high hormone levels, but was reduced in S211A cells at low hormone concentrations, suggesting a link between GR phosphorylation, MED14 involvement, and receptor occupancy. Phosphorylation also affected the magnitude of repression by GR in a gene-selective manner. Thus, GR phosphorylation at S211 and S226 determines GR transcriptional response by modifying cofactor interaction. Furthermore, the effect of GR S211 phosphorylation is gene specific and, in some cases, dependent upon the amount of activated receptor.

Regulation of ER alpha signaling pathway in neuronal HN10 cells: role of protein acetylation and Hsp90

Estrogen has a variety of neuroprotective effects but the molecular basis of its function is still mainly unclear. Estrogen receptor (ER) signaling is highly dependent on posttranslational modifications and the assembly of coactivator and corepressor complexes. Several proteins involved in ER alpha signaling have recently been found to be acetylated, including ER alpha itself and Hsp90, a key chaperone in the functional regulation of ER alpha. ER alpha complexes also contain histone deacetylases (HDAC) which repress transactivation. Our purpose was to clarify the role of protein acetylation and Hsp90 function in the ERE-mediated ER alpha signaling in neuronal HN10 cells. We observed that increasing protein/histone acetylation status with trichostatin A, a potent HDAC inhibitor, increased the 17beta-estradiol (E2)-induced transactivation of ERE-driven luciferase in non-transfected cells, and even more extensively in pER alpha-transfected cells. E2-induced ERE-driven transactivation was blocked by ICI 182.780. Several ER antagonists, such as raloxifene and tamoxifen, were unresponsive. Valproate, an antiepileptic drug which is recently characterized as a HDAC inhibitor, was also able to potentiate the E2-induced ERE-transactivation. Inhibition of the function of Hsp90 chaperone with geldanamycin strongly inhibited the E2-induced ERE-transactivation. Overexpression of SIRT2 protein deacetylase did not inhibit the acetylation-potentiated ERE-driven transactivation indicating that SIRT2 deacetylase is not involved in ER alpha signaling. Our results reveal that ER alpha signaling is dependent on protein acetylation and epigenetic regulation.

Phase I pharmacokinetic and pharmacodynamic study of 17-N-allylamino-17-demethoxygeldanamycin in pediatric patients with recurrent or refractory solid tumors: a pediatric oncology experimental therapeutics investigators consortium study

PURPOSE

Heat shock protein 90 (Hsp90) is essential for the posttranslational control of many regulators of cell growth, differentiation, and apoptosis. 17-N-Allylamino-17-demethoxygeldanamycin (17-AAG) binds to Hsp90 and alters levels of proteins regulated by Hsp90. We conducted a phase I trial of 17-AAG in pediatric patients with recurrent or refractory neuroblastoma, Ewing's sarcoma, osteosarcoma, and desmoplastic small round cell tumor to determine the maximum tolerated dose, define toxicity and pharmacokinetic profiles, and generate data about molecular target modulation.

EXPERIMENTAL DESIGN

Escalating doses of 17-AAG were administered i.v. over 1 to 2 h twice weekly for 2 weeks every 21 days until patients experienced disease progression or toxicity. harmacokinetic and pharmacodynamic studies were done during cycle 1.

RESULTS

Fifteen patients were enrolled onto dose levels between 150 and 360 mg/m(2); 13 patients were evaluable for toxicity. The maximum tolerated dose was 270 mg/m(2). DLTs were grade 3 transaminitis and hypoxia. Two patients with osteosarcoma and bulky pulmonary metastases died during cycle 1 and were not evaluable for toxicity. No objective responses were observed. 17-AAG pharmacokinetics in pediatric patients were linear; clearance and half-life were 21.6 +/- 6.21 (mean +/- SD) L/h/m(2) and 2.6 +/- 0.95 h, respectively. Posttherapy increases in levels of the inducible isoform of Hsp70, a marker of target modulation, were detected in peripheral blood mononuclear cells at all dose levels.

CONCLUSION

17-AAG was well tolerated at a dose of 270 mg/m(2) administered twice weekly for 2 of 3 weeks. Caution should be used in treatment of patients with bulky pulmonary disease.

The Hsp90 inhibitor, 17-AAG, prevents the ligand-independent nuclear localization of androgen receptor in refractory prostate cancer cells

BACKGROUND

Androgen receptor (AR) is the key molecule in androgen-refractory prostate cancer. Despite androgen ablative conditions, AR remains active and is necessary for the growth of androgen-refractory prostate cancer cells. Nuclear localization of AR is a prerequisite for its transcriptional activation. We examined AR localization in androgen-dependent and androgen-refractory prostate cancer cells.

METHODS AND RESULTS

We demonstrate increased nuclear localization of a GFP-tagged AR in the absence of hormone in androgen-refractory C4-2 cells compared to parental androgen-sensitive human prostate cancer LNCaP cells. Analysis of AR mutants impaired in ligand-binding indicates that the nuclear localization of AR in C4-2 cells is truly androgen-independent. The hsp90 inhibitor, 17-allylamino-17-demethoxygeldanamycin (17-AAG), inhibits basal PSA expression and disrupts the ligand-independent nuclear localization of AR at doses much lower than required to inhibit androgen-induced nuclear import.

CONCLUSIONS

Hsp90 is a key regulator of ligand-independent nuclear localization and activation of AR in androgen-refractory prostate cancer cells.

Total synthesis of herbimycin A

[structure: see text] Hsp90 has recently emerged as a promising biological target for treatment of cancer. Herbimycin A and other members of the benzoquinoid ansamycin class of natural products are known to inhibit Hsp90 activity. The total synthesis of herbimycin A was achieved from the commercially available Roche ester 1 by using allylmetals to control the stereogenic centers at C6, C7, C10, C11, and C12 and a ring-closing metathesis to control the (Z)-double bond of the (E,Z)-dienic moiety.

Adamantyl-substituted retinoid-related molecules bind small heterodimer partner and modulate the Sin3A repressor

6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalenecarboxylic acid (CD437/AHPN) and 4-[3-(1-adamantyl)-4-hydroxyphenyl]-3-chlorocinnamic acid (3-Cl-AHPC/MM002) are inducers of apoptosis of malignant cells both in vitro and in vivo. Numerous mechanisms have been proposed for how these compounds exert this effect. This report shows that AHPN/3-Cl-AHPC binds specifically to the orphan nuclear receptor small heterodimer partner (SHP; NR0B2), and this binding promotes interaction of the receptor with a corepressor complex that minimally contains Sin3A, N-CoR, histone deacetylase 4, and HSP90. Formation of the SHP-Sin3A complex is essential for the ability of AHPN and 3-Cl-AHPC to induce apoptosis, as both knockout SHP and knockdown of Sin3A compromise the proapoptotic activity of these compounds but not other apoptosis inducers. These results suggest that AHPN/3-Cl-AHPC and their analogues are SHP ligands and their induction of apoptosis is mediated by their binding to the SHP receptor.

Geldanamycin, an inhibitor of Hsp90, blocks cytoplasmic retention of progesterone receptors and glucocorticoid receptors via their respective ligand binding domains

Steroid hormone receptors (SHRs), such as glucocorticoid receptors (GR) and progesterone receptors (PR), are shuttling proteins that undergo continuous nuclear import and export. Various mechanisms have been proposed to explain the localization of SHRs. It has been suggested that the ligand-binding domain (LBD) of SHRs is important in determining the subcellular localization. We have studied the localization of GR-LBD and PR-LBD alone, as well as of full-length GR and PR in the presence of geldanamycin (GA), a benzoquinoid ansamycin that specifically inhibits heat shock protection (Hsp90), using transient transfections and fluorescent microscopy. Our studies have indicated that GR-LBD and PR-LBD are retained in the cytoplasm via interaction with Hsp90. It was observed that in the unliganded state, treatment with GA translocates these LBDs to the nucleus. Similar results were obtained for full-length PR and GR. Additionally, it was found that after ligand induction, GA accelerated reexport of SHRs after ligand washout, implicating Hsp90 in nuclear retention of SHRs in the washout state. We also propose that a recently found "export" signal present in the LBD of SHRs is involved in interactions with Hsp90 and hence cytoplasmic retention of these receptors. After ligand induction, Hsp90 also may play a role in nuclear retention of SHRs following hormone washout.

Induction of multiple heat shock proteins and neuroprotection in a primary culture model of familial amyotrophic lateral sclerosis

High threshold for stress-induced activation of the heat shock transcription factor, Hsf1, may contribute to vulnerability of motor neurons to disease and limit efficacy of agents promoting expression of neuroprotective heat shock proteins (Hsps) through this transcription factor. Plasmid encoding a constitutively active form of Hsf1, Hsf1act, and chemicals shown to activate Hsf1 in other cells were investigated in a primary culture model of familial amyotrophic lateral sclerosis. Hsf1act and the Hsp90 inhibitor, geldanamycin, induced high expression of multiple Hsps in cultured motor neurons and conferred dramatic neuroprotection against SOD1G93A in comparison to Hsp70 or Hsp25 alone. Two other Hsp90 inhibitors, 17-allylamino-17-demethoxygeldanamycin (17-AAG) and radicicol, and pyrrolidine dithiocarbamate induced robust expression of Hsp70 and Hsp40 in motor neurons, but at cytotoxic concentrations. 17-AAG, which penetrates the blood-brain barrier, has exhibited a higher therapeutic index than geldanamycin, but this may not be the case when activation of Hsf1 in neurons is targeted.

Differential expression of genes in eutopic and ectopic endometrium from patients with ovarian endometriosis

OBJECTIVE

To investigate whether genes that had been found to be differentially expressed in deep-infiltrating endometriosis and matched eutopic endometrium in our previous complementary DNA microarray study also are differentially expressed in ovarian endometriosis and matched eutopic endometrium.

DESIGN

Prospective study.

SETTING

University hospital in France.

PATIENT(S)

Patients with ovarian endometriosis.

INTERVENTION(S)

During surgery, paired samples of tissue representing ovarian endometriosis and eutopic endometrium were obtained from 12 patients.

MAIN OUTCOME MEASURE(S)

Expression levels of messenger RNA for heat shock protein 90 alpha (HSP90A), chicken ovalbumin upstream promoter transcription factor 2 (COUP-TF2), prostaglandin E(2) receptor subtype EP3 (PGE(2)EP3), tyrosine kinase receptor B (TrKB), and 17beta-hydroxysteroid dehydrogenase type 2 (17betaHSD2; epithelial cells) and of platelet-derived growth factor receptor alpha (PDGFRA), protein kinase C beta 1 (PKCbeta1), Janus kinase 1 (JAK1), mitogen-activated protein kinase kinase (MKK7), Sprouty2, mu-opioid receptor (MOR), and 5HTT (stromal cells) from ovarian endometriosis and matched eutopic endometrium were determined by using laser capture microdissection and real-time reverse-transcription polymerase chain reaction (RT-PCR) techniques.

RESULT(S)

Expression of PDGFRA, PKCbeta1, JAK1, HSP90A, COUP-TF2, MOR, and 17betaHSD2 was significantly higher in ovarian endometriosis than in eutopic endometrium, whereas that of Sprouty2 and PGE(2)EP3 was significantly lower. There was no significant difference in mitochondrial RNA expression of MKK 7, TrKB, and 5HTT.

CONCLUSION(S)

Ovarian endometriosis might share several common molecules with deep-infiltrating endometriosis that act to sustain endometriotic lesions, whereas molecules involved in local endocrine control might be different between these two types of endometriosis.

Chaperoning steroid hormone action

Those that efface themselves in the action tend to be forgotten. But molecular chaperones are always there, often serving as equal partners. Because of their intrinsic functional frailty, a large number of signaling molecules have come to depend on molecular chaperones, notably the Hsp90 chaperone machine. This applies to the subset of nuclear receptors that converts steroid hormone signals to transcriptional outputs. Steroid receptors appear to rely on the Hsp90 machine for folding, regulation of the allosteric switch and recycling. This review discusses the complexities of the chaperone machinery and the diversity of regulatory options afforded by this assistance for hormone action.

Chaperoning of glucocorticoid receptors

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

Geldanamycin-induced degradation of Chk1 is mediated by proteasome

Checkpoint kinase 1 (Chk1) is a cell cycle regulator and a heat shock protein 90 (Hsp90) client. It is essential for cell proliferation and survival. In this report, we analyzed the mechanisms of Chk1 regulation in U87MG glioblastoma cells using Geldanamycin (GA), which interferes with the function of Hsp90. GA reduced Chk1 protein level but not its mRNA level in glioblastoma cells. Co-treatment with GA and cycloheximide (CHX), a protein synthesis inhibitor, induced a decrease of half-life of the Chk1 protein to 3h and resulted in Chk1 down-regulation. CHX alone induced only 32% reduction of Chk1 protein even after 24h. These findings indicated that reduction of Chk1 by GA was due to destabilization and degradation of the protein. In addition, GA-induced down-regulation of Chk1 was reversed by MG132, a specific proteasome inhibitor. And it was revealed that Chk1 was ubiquitinated by GA. These results have indicated that degradation of Chk1 by GA was mediated by the ubiquitin-proteasome pathway in U87MG glioblastoma cells.

Emodin down-regulates androgen receptor and inhibits prostate cancer cell growth

Hormone-refractory relapse is an inevitable and lethal event for advanced prostate cancer patients after hormone deprivation. A growing body of evidence indicates that hormone deprivation may promote this aggressive prostate cancer phenotype. Notably, androgen receptor (AR) not only mediates the effect of androgen on the tumor initiation but also plays the major role in the relapse transition. This provides a strong rationale for searching new effective agents targeting the down-regulation of AR to treat or prevent advanced prostate cancer progression. Here, we show that emodin, a natural compound, can directly target AR to suppress prostate cancer cell growth in vitro and prolong the survival of C3(1)/SV40 transgenic mice in vivo. Emodin treatment resulted in repressing androgen-dependent transactivation of AR by inhibiting AR nuclear translocation. Emodin decreased the association of AR and heat shock protein 90 and increased the association of AR and MDM2, which in turn induces AR degradation through proteasome-mediated pathway in a ligand-independent manner. Our work indicates a new mechanism for the emodin-mediated anticancer effect and justifies further investigation of emodin as a therapeutic and preventive agent for prostate cancer.

Heat-shock protein 90 inhibitors as novel cancer chemotherapeutic agents

Heat-shock protein 90 (Hsp90) is a molecular chaperone whose association is required for the stability and function of multiple mutated, chimeric and overexpressed signalling proteins that promote cancer cell growth and/or survival. Hsp90 client proteins include mutated p53, Bcr-Abl, Raf-1, Akt, HER2/Neu (ErbB2) and hypoxia inducible factor-1alpha (HIF-1alpha). Through specific interaction with a single molecular target, Hsp90 inhibitors cause the destabilisation and eventual degradation of Hsp90 client proteins, and they have shown promising antitumour activity in preclinical model systems. One Hsp90 inhibitor, 17-allylamino-geldanamycin (17-AAG), is currently in Phase I clinical trials. Hsp90 inhibitors are unique in that, although they are directed towards a specific molecular target, they simultaneously inhibit multiple signalling pathways on which cancer cells depend for growth and survival. Further, because of the unique effect that Hsp90 inhibition has on cancer cells, combination of an Hsp90 inhibitor with standard chemotherapeutic agents may dramatically increase the in vivo efficacy of the standard agent.

DNA microarray analysis of gene expression profiles in deep endometriosis using laser capture microdissection

Endometriosis, a common gynecological disorder that causes infertility and pelvic pain, is defined as the presence of endometrial glands and stroma within extra-uterine sites. However, despite extensive studies its etiology and pathogenesis are not completely understood. Differentially expressed genes were investigated in epithelial and stromal cells from deep endometriosis and matched eutopic endometrium using cDNA microarrays and laser capture microdissection. Validation of results of several up- and down-regulated genes was performed by quantitative real-time RT-PCR. Our data showed that platelet-derived growth factor receptor alpha (PDGFRA), protein kinase C beta1 (PKC beta1) and janus kinase 1 (JAK1) were upregulated, and Sprouty2 and mitogen-activated protein kinase kinase 7 (MKK7) were downregulated in endometriosis stromal cells, suggesting the involvement of the RAS/RAF/MAPK signaling pathway through PDGFRA in endometriosis pathophysiology. In addition, two potential negative regulators of aromatase expression, chicken ovalbumin upstream promoter transcription factor 2 (COUP-TF2) and prostaglandin E2 receptor subtype EP3 (PGE2EP3), were downregulated in endometriosis epithelial cells, which might result in increased local production of estrogen in endometriosis epithelial cells. Furthermore, three potential candidate genes that might be involved in endometriosis related pain were identified: tyrosine kinase receptor B (TRkB) in endometriosis epithelial cells, and serotonin transporter (5HTT) and mu opioid receptor (MOR) in endometriosis stromal cells were all upregulated. One of the candidate genes, MOR, may be involved in a defective immune system in endometriosis. This study has provided new insights into endometriosis pathophysiology.

Role of the ubiquitin-proteasome pathway in the diagnosis of human diseases

The ubiquitin-proteasome pathway constitutes the major system for nuclear and extralysosomal cytosolic protein degradation in eukaryotic cells. A plethora of cell proteins implicated in the maintenance and regulation of essential cellular processes undergoes processing and functional modification by proteolytic degradation via the ubiquitin-proteasome pathway. Deregulations of the pathway have been shown to contribute to the pathogenesis of several human diseases, such as cancer, neurodegenerative, autoimmune, genetic and metabolic disorders, most of them exhibiting abnormal accumulation and altered composition of components of the pathway that is suitable for diagnostic proceedings. While the ubiquitin-proteasome pathway is currently exploited to develop novel therapeutic strategies, it is less regarded as a diagnostic area. Future research should lead to an improved understanding of the pathophysiology of the ubiquitin-proteasome pathway with the aim of allowing the development of subtle diagnostic strategies.

Partial agonist/antagonist properties of androstenedione and 4-androsten-3beta,17beta-diol

Androgens play important endocrine roles in development and physiology. Here, we characterize activities of two "Andro" prohormones, androstenedione (A-dione) and 4-androsten-3beta,17beta-diol (A-diol) in MDA-MB-453 (MDA) and LNCaP cells. A-dione and A-diol, like cyproterone acetate, were partial agonists of transfected mouse mammary tumor virus (MMTV) and endogenous prostate-specific antigen (PSA) promoters. Different from bicalutamide but similar to CPA, both are inducers of LNCaP cell proliferation with only mild suppression of 5alpha-dihydrotestosterone (DHT)-enhanced cell growth. Like bicalutamide and cyproterone acetate, A-dione and A-diol significantly antagonized DHT/R1881-induced PSA expression by up to 30% in LNCaP cells. Meanwhile, in MDA cells, EC(50)s for the MMTV promoter were between 10 and 100nM. Co-factor studies showed GRIP1 as most active for endogenous androgen receptor (AR), increasing MMTV transcription by up to five-fold, without substantially altering EC(50)s of DHT, A-dione or A-diol. Consistent with their transcriptional activities, A-dione and A-diol bound full-length endogenous AR from MDA or LNCaP cells with affinities of 30-70nM, although binding to expressed ligand-binding domain (LBD) was >20-fold weaker. In contrast, DHT, R1881, and bicalutamide bound similarly to LBD or aporeceptor. Together, these data suggest that A-dione and A-diol are ligands for AR with partial agonist/antagonist activities in cell-based transcription assays. Binding affinities for both are most accurately assessed by AR aporeceptor complex. In addition to being testosterone precursors in vivo, either may impart its own transcriptional regulation of AR.

An Androgen Receptor NH2-terminal Conserved Motif Interacts with the COOH Terminus of the Hsp70-interacting Protein (CHIP)

The NH2-terminal sequence of steroid receptors is highly variable between different receptors and in the same receptor from different species. In this study, a primary sequence homology comparison identified a 14-amino acid NH2-terminal motif of the human androgen receptor (AR) that is common to AR from all species reported, including the lower vertebrates. The evolutionarily conserved motif is unique to AR, with the exception of a partial sequence in the glucocorticoid receptor of higher species. The presence of the conserved motif in AR and the glucocorticoid receptor and its absence in other steroid receptors suggests convergent evolution. The function of the AR NH2-terminal conserved motif was suggested from a yeast two-hybrid screen that identified the COOH terminus of the Hsp70-interacting protein (CHIP) as a binding partner. We found that CHIP functions as a negative regulator of AR transcriptional activity by promoting AR degradation. In support of this, two mutations in the AR NH2-terminal conserved motif previously identified in the transgenic adenocarcinoma of mouse prostate model reduced the interaction between CHIP and AR. Our results suggest that the AR NH2-terminal domain contains an evolutionarily conserved motif that functions to limit AR transcriptional activity. Moreover, we demonstrate that the combination of comparative sequence alignment and yeast two-hybrid screening using short conserved peptides as bait provides an effective strategy to probe the structure-function relationships of steroid receptor NH2-terminal domains and other intrinsically unstructured transcriptional regulatory proteins.

Drug resistance reversal--are we getting closer?

Clinical drug resistance is a major barrier to overcome before chemotherapy can become curative for most patients presenting with metastatic cancer. Rational attempts to tackle clinical drug resistance need to be based on an understanding of the mechanisms involved; these are likely to be complex and multifactorial, and may be due to inadequate drug exposure or alterations in the cancer cell itself. This article reviews a number of strategies used to tackle drug resistance, focussing on work in our institution related to the treatment of ovarian cancer and resistance to platinum and taxane-based chemotherapy. Further progress towards drug resistance reversal will require a three-pronged approach, namely: the development of novel cytotoxics which exploit selectively expressed targets; modulation of resistance to conventional agents and, most importantly, a serious attempt to understand resistance mechanisms in tumour samples taken both pre- and post-chemotherapy.

Cytosolic HSP90 associates with and modulates the Arabidopsis RPM1 disease resistance protein

The Arabidopsis protein RPM1 activates disease resistance in response to Pseudomonas syringae proteins targeted to the inside of the host cell via the bacterial type III delivery system. We demonstrate that specific mutations in the ATP-binding domain of a single Arabidopsis cytosolic HSP90 isoform compromise RPM1 function. These mutations do not affect the function of related disease resistance proteins. RPM1 associates with HSP90 in plant cells. The Arabidopsis proteins RAR1 and SGT1 are required for the action of many R proteins, and display some structural similarity to HSP90 co-chaperones. Each associates with HSP90 in plant cells. Our data suggest that (i) RPM1 is an HSP90 client protein; and (ii) RAR1 and SGT1 may function independently as HSP90 cofactors. Dynamic interactions among these proteins can regulate RPM1 stability and function, perhaps similarly to the formation and regulation of animal steroid receptor complexes.