Hsp90 modulates CAG repeat instability in human cells

The Hsp90 molecular chaperone has been implicated as a contributor to evolution in several organisms by revealing cryptic variation that can yield dramatic phenotypes when the chaperone is diverted from its normal functions by environmental stress. In addition, as a cancer drug target, Hsp90 inhibition has been documented to sensitize cells to DNA-damaging agents, suggesting a function for Hsp90 in DNA repair. Here we explore the potential role of Hsp90 in modulating the stability of nucleotide repeats, which in a number of species, including humans, exert subtle and quantitative consequences for protein function, morphological and behavioral traits, and disease. We report that impairment of Hsp90 in human cells induces contractions of CAG repeat tracks by tenfold. Inhibition of the recombinase Rad51, a downstream target of Hsp90, induces a comparable increase in repeat instability, suggesting that Hsp90-enabled homologous recombination normally functions to stabilize CAG repeat tracts. By contrast, Hsp90 inhibition does not increase the rate of gene-inactivating point mutations. The capacity of Hsp90 to modulate repeat-tract lengths suggests that the chaperone, in addition to exposing cryptic variation, might facilitate the expression of new phenotypes through induction of novel genetic variation.

Antibody responses to galectin-8, TARP and TRAP1 in prostate cancer patients treated with a GM-CSF-secreting cellular immunotherapy

A critical factor in clinical development of cancer immunotherapies is the identification of tumor-associated antigens that may be related to immunotherapy potency. In this study, protein microarrays containing >8,000 human proteins were screened with serum from prostate cancer patients (N = 13) before and after treatment with a granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting whole cell immunotherapy. Thirty-three proteins were identified that displayed significantly elevated (P Collapse

Key Words

• immunotherapy
• tumor antigen
• autoantibody
• protein microarray
• prostate cancer
• biomarker

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MESH Headings

• Antibodies/blood
• Antibodies/immunology
• Biomarkers, Pharmacological
• Biomarkers, Tumor/immunology
• Clinical Trials as Topic
• Disease Progression
• Galectins/immunology
• Granulocyte-Macrophage Colony-Stimulating Factor/therapeutic use
• HSP90 Heat-Shock Proteins/biosynthesis
• HSP90 Heat-Shock Proteins/genetics
• HSP90 Heat-Shock Proteins/immunology
• High-Throughput Screening Assays
• Humans
• Immunotherapy, Adoptive
• Male
• Neoplasm Metastasis
• Nuclear Proteins/biosynthesis
• Nuclear Proteins/genetics
• Nuclear Proteins/immunology
• Prognosis
• Prostatic Neoplasms/diagnosis
• Prostatic Neoplasms/immunology
• Prostatic Neoplasms/mortality
• Prostatic Neoplasms/pathology
• Prostatic Neoplasms/therapy
• Protein Array Analysis
• Retrospective Studies
• Survival Analysis
• Treatment Outcome

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Regulation of glucocorticoid receptor transcription and nuclear translocation during single and repeated immobilization stress

We have previously reported reduced glucocorticoid receptor (GR) mRNA levels in the hippocampus and hypothalamic paraventricular nucleus (PVN) during repeated immobilization, which is potentially associated with persistent activation of the hypothalamic-pituitary-adrenocortical axis. We used in situ hybridization and Western blot to examine the transcriptional regulation of the GR gene, GR nuclear translocation, and expression of cytosolic heat shock protein 90 (hsp90), a chaperone protein essential for GR nuclear translocation, in the hippocampus, PVN, and anterior pituitary (AP) during single immobilization (sIMO) and the final immobilization on d 7 after daily IMO for 6 days (rIMO). As with GR mRNA, GR heteronuclear RNA levels decreased in the hippocampus and PVN and increased in the AP during sIMO and rIMO, indicating that the GR mRNA levels in these regions were regulated at the transcriptional level. In both sIMO and rIMO, nuclear GR levels were significantly increased in the hippocampus, medial basal hypothalamus (MBH), and AP. However, GR nuclear translocation was reduced in the hippocampus, unchanged in the MBH, and enhanced in the AP during rIMO, as compared with sIMO. Cytosolic hsp90 expression was unchanged in the hippocampus and MBH, whereas it significantly increased in the AP at 30 min during rIMO but not during sIMO. These results suggest that the site-specific changes in GR nuclear translocation during sIMO vs. rIMO are partially linked to hsp90 responses to immobilization. The reduced nuclear translocation of GR in the hippocampus during rIMO may reflect decreased glucocorticoid-mediated negative feedback on the hypothalamic-pituitary-adrenocortical axis.

Geldanamycin selectively targets the nascent form of ERBB3 for degradation

Heat shock protein 90 (HSP90) targets a broad spectrum of client proteins with divergent modes of interaction and consequences. The homologous epidermal growth factor receptor (EGFR) and ERBB2 receptors as well as kinase-deficient mutants thereof differ in their requirement for HSP90 in the nascent versus mature state of the receptor. Specific features of the kinase domain have been implicated for the selective association of HSP90 with mature ERBB2. We evaluated the role of HSP90 for the homologous ERBB3 receptor. ERBB3 is naturally kinase deficient, a central mediator in cell survival and stress response and the primary dimerization partner for ERBB2 in signaling. Cellular studies indicate that, similar to EGFR, the geldanamycin (GA) sensitivity of ERBB3 and HSP90 binding resides in the nascent state and is dependent on the presence of the kinase domain of ERBB3. Furthermore, despite its intrinsic lack of kinase activity and in contrast to the reported GA sensitivity of mature and kinase-deficient EGFR, the GA sensitivity of the nascent state of ERBB3 appears to be exclusive. Geldanamycin disrupts the interaction of ERBB3 and HSP90 and inhibits ERBB3 maturation at an early stage of synthesis, prior to export from the ER. Studies with a photo-convertible fusion protein of ERBB3 suggest geldanamycin sensitivity at a later stage in maturation, possibly through the putative role of HSP90 in structural proofreading.

Characterization of plant p23-like proteins for their co-chaperone activities

The small acidic protein p23 is best described as a co-chaperone of Hsp90, an essential molecular chaperone in eukaryotes. p23 binds to the ATP-bound form of Hsp90 and stabilizes the Hsp90-client protein complex by slowing down ATP turnover. The stabilizing activity of p23 was first characterized in studies of steroid receptor-Hsp90 complexes. Earlier studies of the Hsp90 chaperone complex in plants suggested that a p23-like stabilizing activity was absent in plant cell lysates. Here, we show that p23-like proteins are present in plants and are capable of binding Hsp90, but unlike human p23 and yeast ortholog Sba1, the plant p23-like proteins do not stabilize the steroid receptor-Hsp90 complexes formed in wheat germ lysate. Furthermore, these proteins do not inhibit the ATPase activity of plant Hsp90. While transcripts of Arabidopsis thaliana p23-1 and Atp23-2 were detected under normal growing conditions, those of the closely related Brassica napus p23-1 were present only after moderate heat stress. These observations suggest that p23-like proteins in plants are conserved in their binding to Hsp90 but have evolved mechanisms of action different from their yeast and animal counterparts.

Stress, genomes, and evolution

Evolutionary change, whether in populations of organisms or malignant tumor cells, is contingent on the availability of inherited variation for natural selection to act upon. It is becoming clear that the Hsp90 chaperone, which normally functions to buffer client proteins against the effects of genetic variation, plays a central role in this process. Severe environmental stress can overwhelm the chaperone's buffering capacity, causing previously cryptic genetic variation to be expressed. Recent studies now indicate that in addition to exposing existing variation, Hsp90 can induce novel epigenetic and genetic changes. We discuss key findings that suggest a rich set of pathways by which Hsp90 can mediate the influences of the environment on the genome.

PKC signaling regulates drug resistance of the fungal pathogen Candida albicans via circuitry comprised of Mkc1, calcineurin, and Hsp90

Fungal pathogens exploit diverse mechanisms to survive exposure to antifungal drugs. This poses concern given the limited number of clinically useful antifungals and the growing population of immunocompromised individuals vulnerable to life-threatening fungal infection. To identify molecules that abrogate resistance to the most widely deployed class of antifungals, the azoles, we conducted a screen of 1,280 pharmacologically active compounds. Three out of seven hits that abolished azole resistance of a resistant mutant of the model yeast Saccharomyces cerevisiae and a clinical isolate of the leading human fungal pathogen Candida albicans were inhibitors of protein kinase C (PKC), which regulates cell wall integrity during growth, morphogenesis, and response to cell wall stress. Pharmacological or genetic impairment of Pkc1 conferred hypersensitivity to multiple drugs that target synthesis of the key cell membrane sterol ergosterol, including azoles, allylamines, and morpholines. Pkc1 enabled survival of cell membrane stress at least in part via the mitogen activated protein kinase (MAPK) cascade in both species, though through distinct downstream effectors. Strikingly, inhibition of Pkc1 phenocopied inhibition of the molecular chaperone Hsp90 or its client protein calcineurin. PKC signaling was required for calcineurin activation in response to drug exposure in S. cerevisiae. In contrast, Pkc1 and calcineurin independently regulate drug resistance via a common target in C. albicans. We identified an additional level of regulatory control in the C. albicans circuitry linking PKC signaling, Hsp90, and calcineurin as genetic reduction of Hsp90 led to depletion of the terminal MAPK, Mkc1. Deletion of C. albicans PKC1 rendered fungistatic ergosterol biosynthesis inhibitors fungicidal and attenuated virulence in a murine model of systemic candidiasis. This work establishes a new role for PKC signaling in drug resistance, novel circuitry through which Hsp90 regulates drug resistance, and that targeting stress response signaling provides a promising strategy for treating life-threatening fungal infections.

Treating fungal infections is challenging due to the emergence of drug resistance and the limited number of clinically useful antifungal drugs. We screened a library of 1,280 pharmacologically active compounds to identify those that reverse resistance of the leading human fungal pathogen, Candida albicans, to the most widely used antifungals, the azoles. This revealed a new role for protein kinase C (PKC) signaling in resistance to drugs targeting the cell membrane, including azoles, allylamines, and morpholines. We dissected mechanisms through which PKC regulates resistance in C. albicans and the model yeast Saccharomyces cerevisiae. PKC enabled survival of cell membrane stress at least in part through the mitogen-activated protein kinase (MAPK) cascade in both species. In S. cerevisiae, inhibition of PKC signaling blocked activation of a key regulator of membrane stress responses, calcineurin. In C. albicans, Pkc1 and calcineurin independently regulate resistance via a common target. Deletion of C. albicans PKC1 rendered fungistatic drugs fungicidal and reduced virulence in a mouse model. The molecular chaperone Hsp90, which stabilizes client proteins including calcineurin, also stabilized the terminal C. albicans MAPK, Mkc1. We establish new circuitry connecting PKC with Hsp90 and calcineurin and suggest a promising strategy for treating life-threatening fungal infections.

Apis mellifera has two isoforms of cytoplasmic HSP90

Unlike most other insects, annotated genomic data suggest that Apis mellifera has two homologous copies of the cytoplasmic gene HSP90. In this study, we did a phylogenetic analysis on these two copies with some other insects HSP90 genes, and we also manipulated a reverse transcript (RT)-PCR to find all the putative transcripts for both copies. Phylogenetic analysis indicates that A. mellifera possesses two isoforms of cytoplasmic HSP90: The 'traditional' isoform clusters with cytoplasmic HSP90 of other insects. The other isoform, which occurs phylogenetically as the sister group of all insects, may be a new gene and specific to A. mellifera. The results of RT-PCR indicate that this new isoform contains at least eight transcripts derived from the same genomic locus by complicated alternative splicing (GenBank accession numbers: FJ713701, FJ713702, FJ713703, FJ713704, FJ713705, FJ713706, FJ713707 and FJ713708, respectively). The existence of this specific HSP90 might be related to the caste differentiation of bees.

Identification of genes for normalization of quantitative real-time PCR data in ovarian tissues

Increased attention has been paid to the determination of the potential biomarker and therapeutic target for ovarian cancer in recent years. However, the normalization of quantitative real-time PCR is important to obtain accurate gene expression data. We investigated the stability of 20 reference genes in ovarian tissues under different conditions to determine the most adequate for this application. The study characterized the expression of 20 possible reference genes among 52 ovarian tissue samples involving the normal, non-malignant, and primary ovarian carcinomas. One-way analysis of variance (ANOVA) method was used to compare the candidate gene changes brought about by the disease progression. The stability and suitability of the genes with no statistic difference were further validated employing geNorm and NormFinder softwares. Results showed that the expression levels of the 20 reference genes varied, while the RPL4, RPLP0, HSPCB, TPT1, RPL13A, 18S rRNA, PPIA, TBP, and GUSB kept statistic stability despite different ovarian tissue conditions. RPL4, RPLP0, and HSPCB were demonstrated as the most stable reference genes and the combination of the RPLP0 and RPL4 should be recommended as a much more reliable normalization strategy.

The small heat shock protein 20 RSI2 interacts with and is required for stability and function of tomato resistance protein I-2

Race-specific disease resistance in plants depends on the presence of resistance (R) genes. Most R genes encode NB-ARC-LRR proteins that carry a C-terminal leucine-rich repeat (LRR). Of the few proteins found to interact with the LRR domain, most have proposed (co)chaperone activity. Here, we report the identification of RSI2 (Required for Stability of I-2) as a protein that interacts with the LRR domain of the tomato R protein I-2. RSI2 belongs to the family of small heat shock proteins (sHSPs or HSP20s). HSP20s are ATP-independent chaperones that form oligomeric complexes with client proteins to prevent unfolding and subsequent aggregation. Silencing of RSI2-related HSP20s in Nicotiana benthamiana compromised the hypersensitive response that is normally induced by auto-active variants of I-2 and Mi-1, a second tomato R protein. As many HSP20s have chaperone properties, the involvement of RSI2 and other R protein (co)chaperones in I-2 and Mi-1 protein stability was examined. RSI2 silencing compromised the accumulation of full-length I-2 in planta, but did not affect Mi-1 levels. Silencing of heat shock protein 90 (HSP90) and SGT1 led to an almost complete loss of full-length I-2 accumulation and a reduction in Mi-1 protein levels. In contrast to SGT1 and HSP90, RSI2 silencing led to accumulation of I-2 breakdown products. This difference suggests that RSI2 and HSP90/SGT1 chaperone the I-2 protein using different molecular mechanisms. We conclude that I-2 protein function requires RSI2, either through direct interaction with, and stabilization of I-2 protein or by affecting signalling components involved in initiation of the hypersensitive response.

Structural basis for assembly of Hsp90-Sgt1-CHORD protein complexes: implications for chaperoning of NLR innate immunity receptors

Hsp90-mediated function of NLR receptors in plant and animal innate immunity depends on the cochaperone Sgt1 and, at least in plants, on a cysteine- and histidine-rich domains (CHORD)-containing protein Rar1. Functionally, CHORD domains are associated with CS domains, either within the same protein, as in the mammalian melusin and Chp1, or in separate but interacting proteins, as in the plant Rar1 and Sgt1. Both CHORD and CS domains are independently capable of interacting with the molecular chaperone Hsp90 and can coexist in complexes with Hsp90. We have now determined the structure of an Hsp90-CS-CHORD ternary complex, providing a framework for understanding the dynamic nature of Hsp90-Rar1-Sgt1 complexes. Mutational and biochemical analyses define the architecture of the ternary complex that recruits nucleotide-binding leucine-rich repeat receptors (NLRs) by manipulating the structural elements to control the ATPase-dependent conformational cycle of the chaperone.

In vitro assembly of plant RNA-induced silencing complexes facilitated by molecular chaperone HSP90

RNA-induced silencing complexes (RISCs) play central roles in posttranscriptional gene silencing. In plants, the mechanism of RISC assembly has remained elusive due to the lack of cell-free systems that recapitulate the process. In this report, we demonstrate that plant AGO1 protein synthesized by in vitro translation using an extract of evacuolated tobacco protoplasts incorporates synthetic small interfering RNA (siRNA) and microRNA (miRNA) duplexes to form RISCs that sequester the single-stranded siRNA guide strand and miRNA strand, respectively. The formed RISCs were able to recognize and cleave the complementary target RNAs. In this system, the siRNA duplex was incorporated into HSP90-bound AGO1, and subsequent removal of the passenger strand was triggered by ATP hydrolysis by HSP90. Removal of the siRNA passenger strand required the ribonuclease activity of AGO1, while that of the miRNA star strand did not. Based on these results, the mechanism of plant RISC formation is discussed.

Degradation of HER2/neu by ANT2 shRNA suppresses migration and invasiveness of breast cancer cells

BACKGROUND

In breast cancer, the HER2/neu oncoprotein, which belongs to the epidermal growth factor receptor family, may trigger activation of the phosphoinositide-3 kinase (PI3K)/Akt pathway, which controls cell proliferation, survival, migration, and invasion. In this study, we examined the question of whether or not adenine nucleotide translocase 2 (ANT2) short hairpin RNA (shRNA)-mediated down-regulation of HER2/neu and inhibitory effects on the PI3K/Akt signaling pathway suppressed migration and invasiveness of breast cancer cells.

METHODS

We utilized an ANT2 vector-based RNA interference approach to inhibition of ANT2 expression, and the HER2/neu-overexpressing human breast cancer cell line, SK-BR3, was used throughout the study.

RESULTS

In this study, ANT2 shRNA decreased HER2/neu protein levels by promoting degradation of HER2/neu protein through dissociation from heat shock protein 90 (HSP90). As a result, ANT2 shRNA induced inhibitory effects on the PI3K/Akt signaling pathway. Inhibition of PI3K/Akt signaling by ANT2 shRNA caused down-regulation of membrane-type 1 matrix metalloproteinase (MT1-MMP) and vascular endothelial growth factor (VEGF) expression, decreased matrix metalloproteinase 2 (MMP2) and MMP9 activity, and suppressed migration and invasion of breast cancer cells.

CONCLUSIONS

These results indicate that knock-down of ANT2 by shRNA down-regulates HER2/neu through suppression of HSP90's function and inhibits the PI3K/Akt signaling pathway, resulting ultimately in suppressed migration and invasion of breast cancer cells.

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.

Promoter complexity and tissue-specific expression of stress response components in Mytilus galloprovincialis, a sessile marine invertebrate species

The mechanisms of stress tolerance in sessile animals, such as molluscs, can offer fundamental insights into the adaptation of organisms for a wide range of environmental challenges. One of the best studied processes at the molecular level relevant to stress tolerance is the heat shock response in the genus Mytilus. We focus on the upstream region of Mytilus galloprovincialis Hsp90 genes and their structural and functional associations, using comparative genomics and network inference. Sequence comparison of this region provides novel evidence that the transcription of Hsp90 is regulated via a dense region of transcription factor binding sites, also containing a region with similarity to the Gamera family of LINE-like repetitive sequences and a genus-specific element of unknown function. Furthermore, we infer a set of gene networks from tissue-specific expression data, and specifically extract an Hsp class-associated network, with 174 genes and 2,226 associations, exhibiting a complex pattern of expression across multiple tissue types. Our results (i) suggest that the heat shock response in the genus Mytilus is regulated by an unexpectedly complex upstream region, and (ii) provide new directions for the use of the heat shock process as a biosensor system for environmental monitoring.

A naturally occurring variant of Hsp90 that is associated with decanalization

The heat shock protein Hsp90 has been the focus of many studies since it was suggested that it acts to mediate the buffering of phenotypic variation. Hsp90-mediated buffering may result in the accumulation of cryptic genetic variation that, when released either as a consequence of environmental or genetic stress, increases the evolvability of a population. Recent studies using laboratory-induced mutations of Hsp90 and/or chemical inhibition to disrupt Hsp90 function confirm that Hsp90 can buffer cryptic genetic variation. We have previously identified a naturally occurring variant in the charged linker region of the Hsp90 gene, and now examine whether this variant is associated with altered levels of trait variability. The variant is associated with the release of cryptic genetic variation for canalized morphological (bristle) traits, but not for uncanalized morphological (wing and bristle) traits, and the effect on canalized traits depends on culture temperature. This suggests that natural genetic variation in Hsp90 may mediate the evolution of canalized morphological traits even if it does not influence the expression of variation for uncanalized traits.

Expression of mutant protein p53 and Hsp70 and Hsp90 chaperones in cockles Cerastoderma edule affected by neoplasia

High prevalence of disseminated neoplasia has been found in cockles Cerastoderma edule of Galicia (NW Spain). Disseminated neoplasia has been associated with high mortalities of various bivalve species. In vertebrates, proteins such as p53 and heat shock proteins (HSPs) play important roles in carcinogenesis. The protein p53 has been detected in neoplastic cells of bivalve molluscs such as Mytilus edulis, Mytilus trossulus, Mya arenaria, Spisula solidissima, Crassostrea rhizophorae and Crassostrea gigas. In this study, western blotting analyses were used to test the expression of Hsp70, Hsp90 and mutant p53 proteins in the cells and plasma of the haemolymph of cockles showing various intensities of neoplasia. Disseminated neoplasia was previously diagnosed by examination of stained haemolymph monolayers with light microscopy. In the present study, mutant p53 was detected in haemolymph cells of cockles diagnosed as affected by moderate and heavy neoplasia intensity, whereas it was not detected in cockles with either no or light neoplasia. The higher the neoplasia intensity, the higher the levels of Hsp70 and Hsp90. These proteins were not found in plasma. The results reveal the possible association between p53 and HSPs in neoplastic cells of cockles, which could prevent p53 from carrying out its functions, as occurs in human cancers.

Polymorphisms in the HSP90AA1 5' flanking region are associated with scrapie incubation period in sheep

Susceptibility to scrapie is mainly controlled by point mutations at the PRNP locus. However, additional quantitative trait loci (QTL) have been identified across the genome including a region in OAR18. The gene which encodes the inducible form of the cytoplasmic Hsp90 chaperone (HSP90AA1) maps within this region and seems to be associated with the resistance/susceptibility to scrapie in sheep. Here, we have analyzed several polymorphisms which were previously described in the ovine HSP90AA1 5' flanking region and in intron 10 in two naturally scrapie infected Romanov sheep populations. First, we have studied 58 ARQ/VRQ animals pertaining to the sire family where the QTL influencing scrapie incubation period in OAR18 was detected. We have found a significant association between polymorphisms localized at -660 and -528 in the HSP90AA1 5' flanking region and the scrapie incubation period. These two polymorphisms have also been studied in a second sample constituted by 62 VRQ/VRQ sheep showing an extreme incubation period. Results are concordant with the first dataset. Finally, we have studied the HSP90AA1 expression in scrapie and control animals (N = 41) with different HSP90AA1 genotypes by real time PCR on blood samples. The HSP90AA1 expression rate was equivalent in CC(-600)AA(-528) and CG(-600)AG(-528) scrapie resistant animals (ARR/ARR) and was higher in their CC(-600)AA(-528) than in their CG(-600)AG(-528) scrapie susceptible counterparts (VRQ/VRQ). Our results support the hypothesis that the ovine HSP90AA1 gene acts as a modulator of scrapie susceptibility, contributing to the observed differences in the incubation period of scrapie infected animals with the same PRNP genotype.

RET is a heat shock protein 90 (HSP90) client protein and is knocked down upon HSP90 pharmacological block

CONTEXT

Mutations of the RET receptor tyrosine kinase are associated to multiple endocrine neoplasia type 2 (MEN2) and sporadic medullary thyroid carcinoma (MTC). The heat shock protein (HSP) 90 chaperone is required for folding and stability of several kinases. HSP90 is specifically inhibited by 17-allyl-amino-17-demethoxygeldanamycin (17-AAG).

OBJECTIVE

Our aim was to investigate whether RET protein half-life depends on HSP90 and to dissect the molecular pathway responsible for the degradation of RET upon HSP90 inhibition by 17-AAG.

DESIGN

17-AAG effects were studied in RAT1 fibroblasts exogenously expressing MEN2-associated RET mutants and human MTC-derived cell lines.

RESULTS

17-AAG induced a 26S proteasome-dependent degradation of wild-type RET and MEN2-associated RET mutants. The compound hampered HSP90/RET interaction and stabilized RET binding to HSP70, leading to the recruitment of the HSP70-associated E3 ligase C-terminus of Hsc70-interacting protein. In turn, C-terminus of Hsc70-interacting protein polyubiquitinated RET, promoting its proteasomal degradation. 17-AAG blocked RET downstream effectors and RET-dependent transcriptional activation of gene promoters. In human MTC cells carrying oncogenic RET mutants, HSP90 inhibition induced receptor degradation and signaling hindrance leading to cell cycle arrest.

CONCLUSION

RET and MEN2-associated RET mutants rely on HSP90 for protein stability, and HSP90 blockade by 17-AAG promotes RET degradation.

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.

Hsp90 directly modulates the spatial distribution of AF9/MLLT3 and affects target gene expression

AF9/MLLT3 contributes to the regulation of the gene encoding the epithelial sodium channel alpha, ENaCalpha, in renal tubular cells. Specifically, increases in AF9 protein lead to a reduction in ENaCalpha expression and changes in AF9 activity appear to be an important component of aldosterone signaling in the kidney. Whereas AF9 is found in the nucleus where it interacts with the histone H3 lysine 79 methyltransferase, Dot1, AF9 is also present in the cytoplasm. Data presented in this report indicate that the heat shock protein Hsp90 directly and specifically interacts with AF9 as part of an Hsp90-Hsp70-p60/Hop chaperone complex. Experimental manipulation of Hsp90 function by the inhibitor novobiocin, but not 17-AAG, results in redistribution of AF9 from a primarily nuclear to cytoplasmic location. Knockdown of Hsp90 with siRNA mimics the effect elicited by novobiocin. As expected, a shift in AF9 from the nucleus to the cytoplasm in response to Hsp90 interference leads to increased ENaCalpha expression. This is accompanied by a decrease in AF9 occupancy at the ENaCalpha promoter. Our data suggest that the interaction of Hsp90, Hsp70, and p60/Hop with AF9 is necessary for the proper subnuclear localization and activity of AF9. AF9 is among a growing number of nuclear proteins recognized to rely on the Hsp90 complex for nuclear targeting.

[Correlation of HSP90 mRNA expression with migration ability of human multiple myeloma cells]

This study was aimed to investigate the correlation of heat shock protein 90 (HSP90) expression with migration ability of human multiple myeloma cells. The HSP90 mRNA expression and migration change of human multiple myeloma cell line (U266) were detected by RT-PCR and Transwell chamber respectively after treatment of U266 cells with final concentration 50, 100, 150, 200 nmol/L of bortezomib (proteosome inhibitor) for 4 hours. The results indicated that along with the increasing of bortezomib concentration, the expression level of HSP90alpha mRNA in U266 cells was enhanced, while no obvious increase of HSP90beta mRNA expression was observed in spite of statistical difference as a whole (p<0.05), but with the increasing of drug concentration in cells, their migration ability gradually decreased (p<0.05). It is concluded that the correlation of HSP90 expression with migration ability of human multiple myeloma cells exists.

Hsp70/Hsp90 co-chaperones are required for efficient Hsp104-mediated elimination of the yeast [PSI(+)] prion but not for prion propagation

The continued propagation of the yeast [PSI(+)] prion requires the molecular chaperone Hsp104 yet in cells engineered to overexpress Hsp104; prion propagation is impaired leading to the rapid appearance of prion-free [psi(-)] cells. The underlying mechanism of prion loss in such cells is unknown but is assumed to be due to the complete dissolution of the prion aggregates by the ATP-dependent disaggregase activity of this chaperone. To further explore the mechanism, we have sought to identify cellular factors required for prion loss in such cells. Sti1p and Cpr7p are co-chaperones that modulate the activity of Hsp70/Ssa and Hsp90 chaperones and bind to the C-terminus of Hsp104. Neither Sti1p nor Cpr7p is necessary for prion propagation but we show that deletion of the STI1 and CPR7 genes leads to a significant reduction in the generation of [psi(-)] cells by Hsp104 overexpression. Deletion of the STI1 and CPR7 genes does not modify the elimination of [PSI(+)] by guanidine hydrochloride, which inhibits the ATPase activity of Hsp104 but does block elimination of [PSI(+)] by overexpression of either an ATPase-defective mutant of Hsp104 (hsp104(K218T/K620T)) or a 'trap' mutant Hsp104 (hsp104(E285Q/E687Q)) that can bind its substrate but can not release it. These results provide support for the hypothesis that [PSI(+)] elimination by Hsp104 overexpression is not simply a consequence of complete dissolution of the prion aggregates but rather is through a mechanism distinct from the remodelling activity of Hsp104.

KLF4 is a novel regulator of the constitutively expressed HSP90

Krüppel-like factor 4 (KLF4) is a zinc finger-containing transcription factor with diverse regulatory functions in cell growth, proliferation, and differentiation. But little is known about the regulation of KLF4 on the expression of HSP90 (HSP84 and HSP86). In the current study, overexpression of KLF4 was firstly identified to promote the basal expression of HSP90 (HSP84 and HSP86) but not the inducible expression in the C2C12 cells and RAW264.7 cells. Conversely, KLF4 inhibition by antisense oligonucleotides markedly decreased the constitutive expression of HSP90 (HSP84 and HSP86). Here, we also presented data that overexpression of KLF4 resulted in enhanced promoter activities of HSP84. Consistently, KLF4 bind to the KLF4 binding sites in the promoter regions of HSP84 directly. Together, these findings support a role for KLF4 as a novel regulator of the constitutive expression of HSP90.

Human GTSE-1 regulates p21(CIP1/WAF1) stability conferring resistance to paclitaxel treatment

p21(CIP1/WAF1) belongs to the CIP/KIP family of Cdk inhibitors, and its expression is tightly controlled during the cell cycle, mainly by transcriptional and post-translational mechanisms. Fine regulation of p21(CIP1/WAF1) levels is critical for cell cycle control and for cellular response to stress. In the present work, we describe a novel mechanism to modulate p21(CIP1/WAF1) levels mediated by the human GTSE-1 (G(2) and S phase-expressed-1) protein. Our results provide evidence that hGTSE-1 protects p21(CIP1/WAF1) from proteasome-dependent degradation as part of a functional complex containing the Hsp90-binding TPR protein WISp39. We further show that the hGTSE-1 N-terminal portion is sufficient for p21(CIP1/WAF1) binding and stabilization. Finally, we demonstrate that hGTSE-1 mediated-p21(CIP1/WAF1) stabilization is clearly involved in the ability of cells to counteract cytotoxicity induced by the microtubule poison paclitaxel.