Hsp90: chaperoning signal transduction

Heat shock protein families 70 and 90 in Duchenne muscular dystrophy and inflammatory myopathy: balancing muscle protection and destruction

Heat shock proteins are important factors in skeletal muscle physiology and stress response. We examined the effects of chronic inflammation on the distribution of heat shock protein families 70 and 90 using immunofluorescence and Western blotting, in muscle biopsies from 33 idiopathic inflammatory myopathy patients [aged 26-66 (dermatomyositis), 17-78 (polymyositis) and 57-80 (sporadic inclusion body myositis) years], and seven Duchenne muscular dystrophy patients (aged 3-19 years). Our results reveal the multifaceted role played by chaperones in inflammatory muscle tissue. On the one hand, regenerating, atrophic and vacuolated muscle fibers displayed upregulation of both protein families. Higher levels of chaperones in challenged fibers point to the myocyte's attempt to restore and regenerate. On the other hand, heat shock proteins of the 90 family were strongly upregulated in macrophages and cytotoxic T-cells actively invading nonnecrotic muscle fibers of sporadic inclusion body myositis and polymyositis, probably conferring enhanced myocytotoxic capacity. Our data provide positive arguments for exploring heat shock protein 90-based therapy in inflammatory muscle disease.

Identification of heat-shock protein 90 beta in Japanese encephalitis virus-induced secretion proteins

Five host cellular proteins were identified in the secretion medium from Japanese encephalitis virus (JEV)-infected baby hamster kidney-21 (BHK-21) cells, including three molecular chaperones: Hsp70, GRP78 and Hsp90. Hsp90 isoforms were characterized further. Hsp90α was observed to be retained inside the nuclei, whereas Hsp90β associated with virus particles during assembly and was released into the secretion medium upon JEV infection. The association of Hsp90β and viral E protein was demonstrated by using sucrose-density fractionation and Western blot analysis. Moreover, JEV viral RNA replication was not affected by treatment with geldanamycin, an Hsp90 inhibitor, but impaired virus infectivity that was determined by a plaque-forming assay. Our results show that Hsp90β, not Hsp90α, is present in the JEV-induced secretion medium and is required for JEV infectivity in BHK-21 cells.

Implications of the up-regulation of genes encoding protein degradation enzymes and heat shock protein 90 for intertidal green macroalga Ulva fasciata against hypersalinity-induced protein oxidation

The molecular acclimation of intertidal green macroalga Ulva fasciata Delile to high salinity stress were examined by the construction of a forward cDNA library via the suppressive subtractive hybridization between 30‰ and 90‰ (24 h) and by the time course dynamics of several abundantly expressed genes. Among the genes with known sequences, the expressed sequence tags are abundant in the function of protein synthesis (ribosomal protein) and destination. The cDNAs of ATP-dependent Clp protease (UfClpC), 20S proteasome β-subunit type 1 domain (UfPbf1), ubiquitin-conjugating enzyme E2 I (UfUbc9), and heat shock protein 90A (UfHsp90A) were cloned. UfClpC transcript increased 3 h after 90‰ treatment, followed by a decrease, while UfPbf1 and UfUbc9 transcripts increased after 12 h and decreased at 48 h. The transcripts of UfHsp90A increased 1 h after 90‰ treatment, followed by a drop and to the control level at 48 h. Protease activity increased 3 h after 90‰ treatment and decreased to the control level at 48 h. H₂O₂ contents increased 1 h after 90‰ treatment and then remained unchanged, but protein carbonyl group contents increased after 48 h. The treatments of reactive oxygen species scavengers partially alleviated 90‰ damage (partial growth rescue) and suppressed the increases in H₂O₂ content, protein carbonyl group content, protease activity, and UfClpC, UfPbf1, UfUbc9, and UfHsp90A transcripts by 90‰. The induction of specific chaperones and proteases at the molecular level for protein quality control can be considered as one of the molecular mechanisms of hypersalinity acclimation in U. fasciata.

The different roles of ER subtypes in cancer biology and therapy

By eliciting distinct transcriptional responses, the oestrogen receptors (ERs) ERα and ERβ exert opposite effects on cellular processes that include proliferation, apoptosis and migration and that differentially influence the development and the progression of cancer. Perturbation of ER subtype-specific expression has been detected in various types of cancer, and the differences in the expression of ERs are correlated with the clinical outcome. The changes in the bioavailability of ERs in tumours, together with their specific biological functions, promote the selective restoration of their activity as one of the major therapeutic approaches for hormone-dependent cancers.

Hsp90 can accommodate the simultaneous binding of the FKBP52 and HOP proteins

The regulation of steroidogenic hormone receptor-mediated activity plays an important role in the development of hormone-dependent cancers. For example, during prostate carcinogenesis, the regulatory function played by the androgen receptor is often converted from a growth suppressor to an oncogene thus promoting prostate cancer cell survival and eventual metastasis. Within the cytoplasm, steroid hormone receptor activity is regulated by the Hsp90 chaperone in conjunction with a series of co-chaperone proteins. Collectively, Hsp90 and its binding associates form a large heteromeric complex that scaffold the fully mature receptor for binding with the respective hormone. To date our understanding of the interactions between Hsp90 with the various TPR domain-containing co-chaperone proteins is limited due to a lack of available structural information. Here we present the stable formation of Hsp90₂-FKBP52₁- HOP₂ and Hsp90₂-FKBP52₁-p23₂-HOP₂ complexes as detected by immunoprecipitation, time course dynamic light scattering and electron microscopy. The simultaneous binding of FKBP52 and HOP to the Hsp90 dimer provide direct evidence of a novel chaperone sub-complex that likely plays a transient role in the regulation of the fully mature steroid hormone receptor.

To fold or not to fold: modulation and consequences of Hsp90 inhibition

BACKGROUND

The 90-kDa heat-shock proteins (Hsp90) have rapidly evolved into promising therapeutic targets for the treatment of several diseases, including cancer and neurodegenerative diseases. Hsp90 is a molecular chaperone that aids in the conformational maturation of nascent polypeptides, as well as the rematuration of denatured proteins.

DISCUSSION

Many of the Hsp90-dependent client proteins are associated with cellular growth and survival and, consequently, inhibition of Hsp90 represents a promising approach for the treatment of cancer. Conversely, stimulation of heat-shock protein levels has potential therapeutic applications for the treatment of neurodegenerative diseases that result from misfolded and aggregated proteins.

CONCLUSION

Hsp90 modulation exhibits the potential to treat unrelated disease states, from cancer to neurodegenerative diseases, and, thus, to fold or not to fold, becomes a question of great value.

Stimulation of CK2-dependent Grp94 phosphorylation by the nuclear localization signal peptide

The nuclear localization signal sequence (NLS) of SV40 Large T antigen is essential and sufficient for the nuclear translocation of the protein. Phosphorylation often modulates the intracellular distribution of signaling proteins. In this study, we investigated effects of the NLS-peptide of Large T antigen on protein phosphorylation. When crude cell lysates were incubated with [γ-(32)P]ATP, phosphorylation of several endogenous substrates with molecular masses of 100, 80, 50, and 45 kDa by an endogenous kinase was stimulated by the addition of the wild type NLS-peptide (CPKKKRKVEDP). The mutated NLS-peptide (CPKTKRKVEDP) and the reversed NLS-peptide (PDEVKRKKKPC) are weak in the nuclear localization activity, and they only weakly stimulated phosphorylation of these substrates. The mobility of the 100 kDa phosphoprotein was indistinguishable with that of an endoplasmic reticulum (ER)-resident molecular chaperone glucose-regulated protein 94 (Grp94) belonging to the Hsp90 family, and purified Grp94 was phosphorylated by a kinase in cell lysates in an NLS-dependent fashion. The 100 kDa protein was identified as Grp94 by immunoprecipitation and reconstitution experiments. Purification of the NLS-dependent Grp94 kinase by sequential biochemical column chromatography steps resulted in isolation of two polypeptides with molecular masses of 42 and 27 kDa, which were identified as α and β subunit of protein kinase CK2, respectively, by western blotting analysis and biochemical characterization. Moreover, effect of an excess amount of GTP and V8 peptide mapping showed that the NLS-dependent Grp94 kinase in the cell lysate is identical with CK2. Surprisingly purified CK2 did phosphorylate Grp94 even without the NLS-peptide, suggesting that an additional suppressive factor is required for NLS-dependent phosphorylation of Grp94 by CK2. We suggest a possible general role for CK2-catalyzed phosphorylation in the regulation of NLS-dependent protein nuclear translocation.

Cloning and expression of a heat shock protein (HSP) 90 gene in the haemocytes of Crassostrea hongkongensis under osmotic stress and bacterial challenge

Heat shock protein 90 (HSP90) is a highly conserved and multi-functional molecular chaperone that plays an essential role in both cellular metabolism and stress response. Here, we report the cloning of the HSP90 homologue in Crassostrea hongkongensis (ChHSP90) through SSH in combination with RACE from cDNA of haemocytes. The full-length cDNA of ChHSP90 is 2459 bp in length, consisting of a 3', 5'-untranslated region (UTR) and an open reading frame of 2169 bp encoding 722 amino acids. The identity analysis of the amino acid sequence of HSP90 revealed that ChHSP90 is highly conserved. Distribution of ChHSP90 mRNA in gonad, heart, adductor muscle, mantle, gill, digestive gland, and haemocytes suggested that ChHSP90 is ubiquitously expressed. The mRNA levels of ChHSP90 under salinity and bacterial challenges were analyzed by real-time PCR. Under hypo-osmotic treatment, ChHSP90 mRNA in gonad, heart and haemocytes were significantly up-regulated on day 2 and onwards; while in gill, digestive gland and adductor muscle it was significantly down-regulated; the expression in mantle was decreased significantly on day 2 and 3 (P < 0.01), and then up-regulated on day 4 (P < 0.05). Under hyper-osmotic treatment, the mRNA level in gonad, heart, adductor muscle was increased on day 2 and onwards; in gill, it was firstly increased, and then gradually decreased, reaching a minimum on day 3. On day 4, the expression level in gill recovered to pre-treatment level; in mantle and digestive gland, the expression levels were decreased, reaching to the minimum on day 3. During Vibrio alginolyticus challenge, the mRNA level of ChHSP90 increased 3-fold at 4 h post-infection, returned to its pre-challenge level at 6 h post-infection, then was further up-regulated from 8 to 36 h post-infection. These experiments demonstrate that ChHSP90 mRNA is constitutively expressed in various tissues and apparently inducible in haemocytes under salinity and bacterial challenges, suggesting its important role in response to both osmotic stress and bacterial invasion.

Dynamic Interaction of Hsp90 with Its Client Protein p53

Although the structure of the molecular chaperone Hsp90 has been extensively characterized by X-ray crystallography, the nature of the interactions between Hsp90 and its client proteins remains unclear. We present results from a series of spectroscopic studies that strongly suggest that these interactions are highly dynamic in solution. Extensive NMR assignments have been made for human Hsp90 through the use of specific isotopic labeling of one- and two-domain constructs. Sites of interaction of a client protein, the p53 DNA-binding domain, were then probed both by chemical shift mapping and by saturation transfer NMR spectroscopy. Specific spectroscopic changes were small and difficult to observe, but were reproducibly measured for residues over a wide area of the Hsp90 surface in the N-terminal, middle and C-terminal domains. A somewhat greater specificity, for the area close to the interface between the N-terminal and middle domains of Hsp90, was identified in saturation transfer experiments. These results are consistent with a highly dynamic and nonspecific interaction between Hsp90 and p53 DNA-binding domain in this chaperone-client system, which results in changes in the client protein structure that are detectable by spectroscopic and other methods.

HtpG is involved in the pathogenesis of Edwardsiella tarda

Hsp90 is a molecular chaperone that is involved in diverse cellular processes including protein folding/repairing and signal transduction. Edwardsiella tarda is a serious fish pathogen that affects fish aquaculture worldwide. The aim of this study was to investigate the potential importance of HtpG, the prokaryotic homologue of Hsp90, in the pathogenesis of E. tarda. E. tarda HtpG is 627-residue in length and contains domain structures that are conserved among Hsp90 family members. Quantitative real time RT-PCR analysis indicated that expression of htpG is induced by heat shock and oxidative stress. Recombinant HtpG (rHtpG) purified from Escherichia coli exhibits apparent ATPase activity, which is optimal at 40°C. Mutation of htpG (i) affects bacterial growth at elevated temperature and renders the cells more sensitive to stress induced by reactive oxygen species, (ii) causes dramatic reduction in blood dissemination and general bacterial virulence, (iii) weakens the ability of E. tarda to block head kidney macrophage activation and to resist against the bactericidal effect of macrophages, and (iv) upregulates the expression of pro-inflammatory cytokines in macrophages. Taken together, these results indicate that HtpG is a biologically active protein that is required for E. tarda to cope with various stress conditions especially that encountered in vivo the host system during infection.

The client protein p53 adopts a molten globule-like state in the presence of Hsp90

It is not currently known in what state (folded, unfolded or alternatively folded) client proteins interact with the chaperone Hsp90. We show that one client, the p53 DNA-binding domain, undergoes a structural change in the presence of Hsp90 to adopt a molten globule-like state. Addition of one- and two-domain constructs of Hsp90, as well as the full-length three-domain protein, to isotopically labeled p53 led to reduction in NMR signal intensity throughout p53, particularly in its central β-sheet. This reduction seems to be associated with a change of structure of p53 without formation of a distinct complex with Hsp90. Fluorescence and hydrogen-exchange measurements support a loosening of the structure of p53 in the presence of Hsp90 and its domains. We propose that Hsp90 interacts with p53 by multiple transient interactions, forming a dynamic heterogeneous manifold of conformational states that resembles a molten globule.

Conformational dynamics of the molecular chaperone Hsp90

The ubiquitous molecular chaperone Hsp90 makes up 1-2% of cytosolic proteins and is required for viability in eukaryotes. Hsp90 affects the folding and activation of a wide variety of substrate proteins including many involved in signaling and regulatory processes. Some of these substrates are implicated in cancer and other diseases, making Hsp90 an attractive drug target. Structural analyses have shown that Hsp90 is a highly dynamic and flexible molecule that can adopt a wide variety of structurally distinct states. One driving force for these rearrangements is the intrinsic ATPase activity of Hsp90, as seen with other chaperones. However, unlike other chaperones, studies have shown that the ATPase cycle of Hsp90 is not conformationally deterministic. That is, rather than dictating the conformational state, ATP binding and hydrolysis only shift the equilibria between a pre-existing set of conformational states. For bacterial, yeast and human Hsp90, there is a conserved three-state (apo-ATP-ADP) conformational cycle; however; the equilibria between states are species specific. In eukaryotes, cytosolic co-chaperones regulate the in vivo dynamic behavior of Hsp90 by shifting conformational equilibria and affecting the kinetics of structural changes and ATP hydrolysis. In this review, we discuss the structural and biochemical studies leading to our current understanding of the conformational dynamics of Hsp90, as well as the roles that nucleotide, co-chaperones, post-translational modification and substrates play. This view of Hsp90's conformational dynamics was enabled by the use of multiple complementary structural methods including, crystallography, small-angle X-ray scattering (SAXS), electron microscopy, Förster resonance energy transfer (FRET) and NMR. Finally, we discuss the effects of Hsp90 inhibitors on conformation and the potential for developing small molecules that inhibit Hsp90 by disrupting the conformational dynamics.

HDAC6 α-tubulin deacetylase: a potential therapeutic target in neurodegenerative diseases

Histone deacetylases (HDACs), or lysine deacetylases (KDAC), are epigenetic regulators that catalyze the removal of acetyl moieties from the tails of lysine residues of histones and other proteins. To date, eighteen HDAC family members (HDAC1-11 and SIRT1-7) have been identified and grouped into four classes according to their homology to yeast histone deacetylases. HDACs play an important role in regulating gene transcription as well as a variety of cellular functions. Recent studies have found that HDAC6 (α-tubulin deacetylase) has the novel ability to capture α-tubulin as a substrate and regulate the physiological level of its acetylated form. In addition, a growing body of evidence suggests that α-tubulin deacetylase plays a critical role in the cellular response to the accumulation of misfolded and aggregated proteins, which are a prominent pathological feature common to many age-related neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases. Therefore, the role of α-tubulin deacetylase and its potential as a therapeutic target for neurodegenerative diseases are areas of rapidly expanding investigation. Here we review the research of the role played by HDAC6 in the regulation of tubulin modification and aggresome formation. We also summarize the specific inhibitors of HDAC6 and address reports that implicate HDAC6 in various neurodegenerative disorders.

Hsp90/Cdc37 chaperone/co-chaperone complex, a novel junction anticancer target elucidated by the mode of action of herbal drug Withaferin A

BACKGROUND

HSPs (Heat shock proteins) are highly conserved ubiquitous proteins among species which are involved in maintaining appropriate folding and conformation of other proteins and are thus referred to as molecular chaperones. Hsp90 (Heat-shock protein 90 kDa) is one of a group of molecular chaperones responsible for managing protein folding and quality control in cell environment. However it is also involved in the maturation and stabilization of a wide range of oncogenic client proteins which are crucial for oncogenesis and malignant progression. Hsp90 requires a series of co-chaperones to assemble into a super-chaperone complex for its function. These co-chaperones bind and leave the complex at various stages to regulate the chaperoning process. Arresting the chaperone cycle at these stages by targeting different co-chaperone/Hsp90 interactions seems to be quite a viable alternative and is likely to achieve similar consequences as that of Hsp90 direct inhibition with added favors of high specificity and reduced side effect profile. The study conducted here is an attempt to explore the potential of Withania somnifera's major constituent WA (Withaferin A) in attenuating the Hsp90/Cdc37 chaperone/co-chaperone interactions for enhanced tumor arresting activity and to elucidate the underlying mode of action using computational approaches.

RESULTS

Formation of active Hsp90/Cdc37 complex is one of the essential steps for facilitation of chaperone client interaction, non-assembly of which can lead to prevention of the chaperone-client association resulting in apoptosis of tumor cells. From our flexible docking analysis of WA into active Hsp90/Cdc37 complex in which key interfacing residues of the complex were kept flexible, disruption of the active association complex can be discerned. While docking of WA into segregated Hsp90 leaves the interface residues untouched. Thus the molecular docking analysis of WA into Hsp90 and active Hsp90/Cdc37 complex conducted in this study provides significant evidence in support of the proposed mechanism of chaperone assembly suppression by inhibition or disruption of active Hsp90/Cdc37 complex formation being accounted by non-assembly of the catalytically active Hsp90/Cdc37 complex. Results from the molecular dynamics simulations in water show that the trajectories of the protein complexed with ligand WA are stable over a considerably long time period of 4 ns, with the energies of the complex being lowered in comparison to the un-docked association complex, suggesting the thermodynamic stability of WA complexed Hsp90/Cdc37.

CONCLUSIONS

The molecular chaperone Hsp90 has been a promising target for cancer therapy. Cancer is a disease marked by genetic instability. Thus specific inhibition of individual proteins or signalling pathways holds a great potential for subversion of this genetic plasticity of cancers. This study is a step forward in this direction. Our computational analysis provided a rationalization to the ability of naturally occurring WA to alter the chaperone signalling pathway. The large value of binding energy involved in binding of WA to the active Hsp90/Cdc37 complex consolidates the thermodynamic stability of the binding. Our docking results obtained substantiate the hypothesis that WA has the potential to inhibit the association of chaperone (Hsp90) to its co-chaperone (Cdc37) by disrupting the stability of attachment of Hsp90 to Cdc37. Conclusively our results strongly suggest that withaferin A is a potent anticancer agent as ascertained by its potent Hsp90-client modulating capability.

Function of cytosolic chaperones in Tom70-mediated mitochondrial import

The great majority of mitochondrial proteins are synthesized by cytosolic ribosomes and then imported into the organelle post-translationally. The translocase of the outer membrane (TOM) is a proteinaceous machinery that contains surface receptors for preprotein recognition and also serves as the main entry gateway into mitochondria. Mitochondrial targeting requires various cytosolic factors, in particular the molecular chaperones Hsc70/Hsp70 and Hsp90. The chaperone activity of Hsc70/Hsp70 and Hsp90 occurs in coordinated cycles of ATP hydrolysis and substrate binding, and is regulated by a number of co-chaperone proteins. The import receptor Tom70 is a member of the tetratricopeptide repeat (TPR) co-chaperone family and contains a conserved TPR clamp domain for interaction with Hsc70 and Hsp90. Such interaction is essential for the initiation of the import process. This review will discuss the roles of Hsc70 and Hsp90 in mitochondrial import and summarize recent progress in understanding these pathways.

Dealing with misfolded proteins: examining the neuroprotective role of molecular chaperones in neurodegeneration

Human neurodegenerative diseases arise from a wide array of genetic and environmental factors. Despite the diversity in etiology, many of these diseases are considered "conformational" in nature, characterized by the accumulation of pathological, misfolded proteins. These misfolded proteins can induce cellular stress by overloading the proteolytic machinery, ultimately resulting in the accumulation and deposition of aggregated protein species that are cytotoxic. Misfolded proteins may also form aberrant, non-physiological protein-protein interactions leading to the sequestration of other normal proteins essential for cellular functions. The progression of such disease may therefore be viewed as a failure of normal protein homeostasis, a process that involves a network of molecules regulating the synthesis, folding, translocation and clearance of proteins. Molecular chaperones are highly conserved proteins involved in the folding of nascent proteins, and the repair of proteins that have lost their typical conformations. These functions have therefore made molecular chaperones an active area of investigation within the field of conformational diseases. This review will discuss the role of molecular chaperones in neurodegenerative diseases, highlighting their functional classification, regulation, and therapeutic potential for such diseases.

Redox regulation of the stability of the SUMO protease SENP3 via interactions with CHIP and Hsp90

SENP3 was recently implicated as redox sensor affecting hypoxia-inducible factor-1-dependent transcription under conditions of mild oxidative stress. In a novel mechanism, the chaperone Hsp90 selectively stabilizes oxidized SENP3 by protecting it from ubiquitination mediated by the co-chaperone CHIP.

The molecular chaperone heat shock protein 90 (Hsp90) and the co-chaperone/ubiquitin ligase carboxyl terminus of Hsc70-interacting protein (CHIP) control the turnover of client proteins. How this system decides to stabilize or degrade the client proteins under particular physiological or pathological conditions is unclear. We report here a novel client protein, the SUMO2/3 protease SENP3, that is sophisticatedly regulated by CHIP and Hsp90. SENP3 is maintained at a low basal level under non-stress condition due to Hsp90-independent CHIP-mediated ubiquitination. Upon mild oxidative stress, SENP3 undergoes thiol modification, which recruits Hsp90. Hsp90/SENP3 association protects SENP3 from CHIP-mediated ubiquitination and subsequent degradation, but this effect of Hsp90 requires the presence of CHIP. Our data demonstrate for the first time that CHIP and Hsp90 interplay with a client alternately under non-stress and stress conditions, and the choice between stabilization and degradation is made by the redox state of the client. In addition, enhanced SENP3/Hsp90 association is found in cancer. These findings provide new mechanistic insight into how cells regulate the SUMO protease in response to oxidative stress.

Dynamics of heat shock protein 90 C-terminal dimerization is an important part of its conformational cycle

The molecular chaperone heat shock protein 90 (Hsp90) is an important and abundant protein in eukaryotic cells, essential for the activation of a large set of signal transduction and regulatory proteins. During the functional cycle, the Hsp90 dimer performs large conformational rearrangements. The transient N-terminal dimerization of Hsp90 has been extensively investigated, under the assumption that the C-terminal interface is stably dimerized. Using a fluorescence-based single molecule assay and Hsp90 dimers caged in lipid vesicles, we were able to separately observe and kinetically analyze N- and C-terminal dimerizations. Surprisingly, the C-terminal dimer opens and closes with fast kinetics. The occupancy of the unexpected C-terminal open conformation can be modulated by nucleotides bound to the N-terminal domain and by N-terminal deletion mutations, clearly showing a communication between the two terminal domains. Moreover our findings suggest that the C- and N-terminal dimerizations are anticorrelated. This changes our view on the conformational cycle of Hsp90 and shows the interaction of two dimerization domains.

Ribosomal protein L2 associates with E. coli HtpG and activates its ATPase activity

Although eukaryotic Hsp90 has been studied extensively, the function of its bacterial homologue HtpG remains elusive. Here we report that 50S ribosomal protein L2 was found as an associated protein with His-tagged HtpG from Escherichia coli cultured in minimum medium at 45 °C. L2 specifically activated ATPase activity of HtpG, but other denatured proteins did not. The analysis using domain derivatives of HtpG and L2 showed that C-terminal domain of L2 and the middle to C-terminal domain of HtpG are important for interaction. At physiological salt concentration, L2 was denatured state and was recognized by HtpG as well as other chaperones, DnaK/DnaJ/GrpE and GroEL/GroES. The ATPase of HtpG at increasing concentration of L2 indicated that an L2 molecule bound to a dimer HtpG with apparent K(D) of 0.3 μM at 100mM KCl and 3.3 μM at 200 mM KCl.

Polymer–drug conjugates for novel molecular targets

Polymer therapeutics can be already considered as a promising field in the human healthcare context. The discovery of the enhanced permeability and retention effect by Maeda, together with the modular model for the polymer–drug conjugate proposed by Ringsdorf, directed the early steps of polymer therapeutics towards cancer therapy. Orthodox anticancer drugs were preferentially chosen in the development of the first conjugates. The fast evolution of polymer chemistry and bioconjugation techniques, and a deeper understanding of cell biology has opened up exciting new challenges and opportunities. Four main directions have to be considered to develop this ‘platform technology’ further: the control of the synthetic process, the exhaustive characterization of the conjugate architectures, the conquest of combination therapy and the disclosure of new therapeutic targets. We illustrate in this article the exciting approaches offered by polymer–drug conjugates beyond classical cancer therapy, focusing on new, more effective and selective targets in cancer and in their use as treatments for other major human diseases.

Stress response in tardigrades: differential gene expression of molecular chaperones

Semi-terrestrial tardigrades exhibit a remarkable tolerance to desiccation by entering a state called anhydrobiosis. In this state, they show a strong resistance against several kinds of physical extremes. Because of the probable importance of stress proteins during the phases of dehydration and rehydration, the relative abundance of transcripts coding for two alpha-crystallin heat-shock proteins (Mt-sHsp17.2 and Mt-sHsp19.5), as well for the heat-shock proteins Mt-sHsp10, Mt-Hsp60, Mt-Hsp70 and Mt-Hsp90, were analysed in active and anhydrobiotic tardigrades of the species Milnesium tardigradum. They were also analysed in the transitional stage (I) of dehydration, the transitional stage (II) of rehydration and in heat-shocked specimens. A variable pattern of expression was detected, with most candidates being downregulated. Gene transcripts of one Mt-hsp70 isoform in the transitional stage I and Mt-hsp90 in the anhydrobiotic stage were significantly upregulated. A high gene expression (778.6-fold) was found for the small alpha-crystallin heat-shock protein gene Mt-sHsp17.2 after heat shock. We discuss the limited role of the stress-gene expression in the transitional stages between the active and anhydrobiotic tardigrades and other mechanisms which allow tardigrades to survive desiccation.

Novobiocin decreases SMYD3 expression and inhibits the migration of MDA-MB-231 human breast cancer cells

SET and MYND domain-containing protein 3 (SMYD3) is a histone methyltransferase that plays an important role in transcriptional regulation in human carcinogenesis, and heat-shock protein HSP90A has been shown to increase the activity of SMYD3. We previously reported that overexpression of SMYD3 stimulated the migration of cells. In this study, we further found that novobiocin, a HSP90 inhibitor, could decrease the expression of SMYD3 and dose dependently inhibit the proliferation and migration of MDA-MB-231 human breast cancer cells. As a control, the short hairpin RNA (shRNA) targeting SMYD3 gene also showed similar effects with novobicin. This study is the first to show that novobiocin can inhibit the migration of breast cancer cells and such event may involve the downregulation of SMYD3. These findings might throw light on the development of novel therapeutic approaches to human cancers, and lend further understanding to the potential role of SMYD3 in human carcinogenesis.

Screening for therapeutic targets of vorinostat by SILAC-based proteomic analysis in human breast cancer cells

Histone deacetylases (HDACs) play critical roles in silencing tumor suppressor genes. HDAC inhibitors reactivate tumor suppressor genes and inhibit tumor cell growth in vitro and in vivo, and several HDAC inhibitors are currently being evaluated in clinical trials for cancer therapy. A comprehensive analysis of proteins regulated by HDAC inhibitors would enhance our ability to define and characterize their essential therapeutic targets. Here, we employed stable isotope labeling with amino acids in cell culture-based quantitative proteomics to identify acetylated proteins in human breast cancer cells. Treatment with the clinically relevant HDAC inhibitor, suberoylanilide hydroxamic acid (vorinostat), induces lysine acetylation of 61 proteins in MDA-MB-231 human breast cancer cells. Suberoylanilide hydroxamic acid not only induces lysine acetylation in chromatin-associated proteins, but also acetylates previously unrecognized nonhistone proteins, including transcriptional factors and regulators, chaperones, cell structure proteins, and glycolytic enzymes in a time-dependent manner. Knowledge of the full repertoire of acetylated proteins will provide a foundation for further defining the functions of HDACs in cancer cells.

The Hop/Sti1-Hsp90 chaperone complex facilitates the maturation and transport of a PAMP receptor in rice innate immunity

Recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs) represents a critical first step of innate defense in plants and animals. However, maturation and transport of PRRs are not well understood. We find that the rice chitin receptor OsCERK1 interacts with Hsp90 and its cochaperone Hop/Sti1 in the endoplasmic reticulum (ER). Hop/Sti1 and Hsp90 are required for efficient transport of OsCERK1 from the ER to the plasma membrane (PM) via a pathway dependent on Sar1, a small GTPase which regulates ER-to-Golgi trafficking. Further, Hop/Sti1 and Hsp90 are present at the PM in a complex (designated the "defensome") with OsRac1, a plant-specific Rho-type GTPase. Finally, Hop/Sti1 was required for chitin-triggered immunity and resistance to rice blast fungus. Our results suggest that the Hop/Sti1-Hsp90 chaperone complex plays an important and likely conserved role in the maturation and transport of PRRs and may function to link PRRs and Rac/Rop GTPases.

Inhibition of heat-shock protein 90 reduces Ebola virus replication

Ebola virus (EBOV), a negative-sense RNA virus in the family Filoviridae, is known to cause severe hemorrhagic fever in humans and other primates. Infection with EBOV causes a high mortality rate and currently there is no FDA-licensed vaccine or therapeutic treatment available. Recently, heat-shock protein 90 (Hsp90), a molecular chaperone, was shown to be an important host factor for the replication of several negative-strand viruses. We tested the effect of several different Hsp90 inhibitors including geldanamycin, radicicol, and 17-allylamino-17-demethoxygeldanamycin (17-AAG; a geldanamycin analog) on the replication of Zaire EBOV. Our results showed that inhibition of Hsp90 significantly reduced the replication of EBOV. Classic Hsp90 inhibitors reduced viral replication with an effective concentration at 50% (EC(50)) in the high nanomolar to low micromolar range, while drugs from a new class of Hsp90 inhibitors showed markedly more potent inhibition. These compounds blocked EBOV replication with an EC(50) in the low nanomolar range and showed significant potency in blocking replication in primary human monocytes. These results validated that Hsp90 is an important host factor for the replication of filoviruses and suggest that Hsp90 inhibitors may be therapeutically effective in treating EBOV infection.

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.

The 90-kDa heat shock protein Hsp90 protects tubulin against thermal denaturation

Hsp90 and tubulin are among the most abundant proteins in the cytosol of eukaryotic cells. Although Hsp90 plays key roles in maintaining its client proteins in their active state, tubulin is essential for fundamental processes such as cell morphogenesis and division. Several studies have suggested a possible connection between Hsp90 and the microtubule cytoskeleton. Because tubulin is a labile protein in its soluble form, we investigated whether Hsp90 protects it against thermal denaturation. Both proteins were purified from porcine brain, and their interaction was characterized in vitro by using spectrophotometry, sedimentation assays, video-enhanced differential interference contrast light microscopy, and native polyacrylamide gel electrophoresis. Our results show that Hsp90 protects tubulin against thermal denaturation and keeps it in a state compatible with microtubule polymerization. We demonstrate that Hsp90 cannot resolve tubulin aggregates but that it likely binds early unfolding intermediates, preventing their aggregation. Protection was maximal at a stoichiometry of two molecules of Hsp90 for one of tubulin. This protection does not require ATP binding and hydrolysis by Hsp90, but it is counteracted by geldanamycin, a specific inhibitor of Hsp90.

Phase I study of 17-allylamino-17 demethoxygeldanamycin, gemcitabine and/or cisplatin in patients with refractory solid tumors

PURPOSE

To determine the maximum tolerated dose (MTD) and characterize the dose-limiting toxicities (DLT) of 17-AAG, gemcitabine and/or cisplatin. Levels of the proteins Hsp90, Hsp70 and ILK were measured in peripheral blood mononuclear cell (PMBC) lysates to assess the effects of 17-AAG.

EXPERIMENTAL DESIGN

Phase I dose-escalating trial using a "3 + 3" design performed in patients with advanced solid tumors. Once the MTD of gemcitabine + 17-AAG + cisplatin was determined, dose escalation of 17-AAG with constant doses of gemcitabine and cisplatin was attempted. After significant hematologic toxicity occurred, the protocol was amended to evaluate three cohorts: gemcitabine and 17-AAG; 17-AAG and cisplatin; and gemcitabine, 17-AAG and cisplatin with modified dosing.

RESULTS

The 39 patients enrolled were evaluable for toxicity and response. The MTD for cohort A was 154 mg/m(2) of 17-AAG, 750 mg/m(2) of gemcitabine, and 40 mg/m(2) of cisplatin. In cohort A, DLTs were observed at the higher dose level and included neutropenia, hyperbilirubinemia, dehydration, GGT elevation, hyponatremia, nausea, vomiting, and thrombocytopenia. The MTD for cohort C was 154 mg/m(2) of 17-AAG and 750 mg/m(2) of gemcitabine, with one DLT observed (alkaline phosphatase elevation) observed. In cohort C, DLTs of thrombocytopenia, fever and dyspnea were seen at the higher dose level. The remaining cohorts were closed to accrual due to toxicity. Six patients experienced partial responses. Mean Hsp90 levels were decreased and levels of Hsp70 were increased compared to baseline.

CONCLUSIONS

17-AAG in combination with gemcitabine and cisplatin demonstrated antitumor activity, but significant hematologic toxicities were encountered. 17-AAG combined with gemcitabine is tolerable and has demonstrated evidence of activity at the MTD. The recommended phase II dose is defined as 154 mg/m(2) of 17-AAG and 750 mg/m(2) of gemcitabine, and is currently being investigated in phase II studies in ovarian and pancreatic cancers. There is no recommended phase II dose for the cisplatin-containing combinations.

The synthesis and evaluation of flavone and isoflavone chimeras of novobiocin and derrubone

The natural products novobiocin and derrubone have both demonstrated Hsp90 inhibition and structure-activity relationships have been established for each scaffold. Given these compounds share several key structural features, we hypothesized that incorporation of elements from each could provide insight to structural features important for Hsp90 inhibition. Thus, chimeric analogues of novobiocin and derrubone were constructed and evaluated. These studies confirmed that the functionality present at the 3-position of the isoflavone plays a critical role in determining Hsp90 inhibition and suggests that the bicyclic ring system present in both novobiocin and derrubone do not share similar modes of binding.

Molecular modelling and docking studies on heat shock protein 90 (Hsp90) inhibitors

An adenosine tri-phosphate (ATP)-dependent molecular chaperone heat shock protein (Hsp90) is of current interest as a potential anticancer drug target. It has several oncogenic client proteins involved in signal transduction, cell cycle regulation and apoptosis. In order to identify essential chemical functional features for Hsp90 inhibition, a pharmacophore model consisting of one hydrogen bond donor, two hydrogen bond acceptor lipid and one hydrophobic feature has been developed using Hypogen (Catalyst 2.0 software) on a total set of 103 inhibitors consisting of 16 and 87 compounds in the training and the test set, respectively. The model shows good correlation for the training (r(2)= 0.887) and the test set ( [image omitted] = 0.692). In view of the X-ray data structure of Hsp90, GOLD 3.2 docking software was used to dock the 16 training set compounds. A good correlation (r(2)= 0.699) was observed between the experimental biological activity and the top-ranked Goldscore. The analysis of conserved patterns across the Hsp90 family, using the human Hsp90 X-ray structure as an alignment template, led to the identification of important amino acids involved in the ligand-binding interactions, which were found to be similar to those observed in docking studies. Hence, the best-generated pharmacophore model can be used for designing new Hsp90 inhibitors.

The regulatory mechanism of Hsp90alpha secretion and its function in tumor malignancy

Heat shock protein 90-alpha (Hsp90alpha) is an intracellular molecular chaperone. However, it can also be secreted with the underlying regulatory mechanism remaining far from clear. Here we show that the secreted Hsp90alpha is a C-terminal truncated form and its secretion is regulated by the C-terminal EEVD motif via interacting with proteins containing tetratricopeptide repeat domains. We also demonstrate that secretion of Hsp90alpha is determined by the phosphorylation status at residue Thr-90, regulated by protein kinase A and protein phosphatase 5. We further demonstrate that the secretion of Hsp90alpha is a prerequisite for its proinvasiveness function and blocking the secreted Hsp90alpha results in significant inhibition of tumor metastasis. Meanwhile, the level of plasma Hsp90alpha is positively correlated with tumor malignancy in clinical cancer patients. In sum, our results reveal the regulatory mechanism of Hsp90alpha secretion, and its function in tumor invasiveness, indicating it can be a promising diagnostic marker for tumor malignancy in clinical application.

Crystallographic structure of the tetratricopeptide repeat domain of Plasmodium falciparum FKBP35 and its molecular interaction with Hsp90 C-terminal pentapeptide

Plasmodium falciparum FK506-binding protein 35 (PfFKBP35) that binds to FK506 contains a conserved tetratricopeptide repeat (TPR) domain. Several known TPR domains such as Hop, PPP5, CHIP, and FKBP52 are structurally conserved and are able to interact with molecular chaperones such as Hsp70/Hsp90. Here, we present the crystal structure of PfFKBP35-TPR and demonstrate its interaction with Hsp90 C-terminal pentapeptide (MEEVD) by surface plasmon resonance and nuclear magnetic resonance spectroscopy-based binding studies. Our sequence and structural analyses reveal that PfFKBP35 is similar to Hop and PPP5 in possessing all the conserved residues which are important for carboxylate clamping with Hsp90. Mutational studies were carried out on positively charged clamp residues that are crucial for binding to carboxylate groups of aspartate, showing that all the mutated residues are important for Hsp90 binding. Molecular docking and electrostatic calculations demonstrated that the MEEVD peptide of Hsp90 can form aspartate clamp unlike FKBP52. Our results provide insightful information and structural basis about the molecular interaction between PfFKBP35-TPR and Hsp90.

Geldanamycin inhibits TGF-beta signaling through induction of Hsp70

Dysregulation of transforming growth factor-beta (TGF-beta) signaling has been implicated in the pathogenesis of a variety of diseases including cancer; therefore, pharmacological inhibitors that target the TGF-beta signaling pathway might be promising drugs for disease therapy. In this study, we investigated the mechanism of inhibition of TGF-beta signaling by the Hsp90 inhibitor geldanamycin (GA). Treatment with GA suppressed TGF-beta signaling, as evidenced by inhibition of TGF-beta-induced phosphorylation and transcriptional activity of Smad3 and decreased induction of target genes. Western blot analysis revealed that GA induced degradation of TGF-beta type I and type II receptors through a proteasome-dependent pathway. Notably, induction of Hsp70 by GA correlated with inhibition of TGF-beta signaling. Suppression of Hsp70 expression by Hsp70 siRNA or KNK437, an inhibitor of Hsp70 synthesis, blocked the inhibition of TGF-beta signaling by GA. Furthermore, Hsp70 interacted directly with TGF-beta receptors following GA treatment. Our results suggest that GA-mediated induction of Hsp70 and its subsequent interaction with TGF-beta receptors plays a crucial role in inhibition of TGF-beta signaling.

The regulatory mechanism of Hsp90alpha secretion and its function in tumor malignancy

Heat shock protein 90-alpha (Hsp90alpha) is an intracellular molecular chaperone. However, it can also be secreted with the underlying regulatory mechanism remaining far from clear. Here we show that the secreted Hsp90alpha is a C-terminal truncated form and its secretion is regulated by the C-terminal EEVD motif via interacting with proteins containing tetratricopeptide repeat domains. We also demonstrate that secretion of Hsp90alpha is determined by the phosphorylation status at residue Thr-90, regulated by protein kinase A and protein phosphatase 5. We further demonstrate that the secretion of Hsp90alpha is a prerequisite for its proinvasiveness function and blocking the secreted Hsp90alpha results in significant inhibition of tumor metastasis. Meanwhile, the level of plasma Hsp90alpha is positively correlated with tumor malignancy in clinical cancer patients. In sum, our results reveal the regulatory mechanism of Hsp90alpha secretion, and its function in tumor invasiveness, indicating it can be a promising diagnostic marker for tumor malignancy in clinical application.

Role of oxidative stress in geldanamycin-induced cytotoxicity and disruption of Hsp90 signaling complex

Heat shock protein 90 (Hsp90) is a chaperone protein regulating PC-12 cell survival by binding and stabilizing Akt, Raf-1, and Cdc37. Hsp90 inhibitor geldanamycin (GA) cytotoxicity has been attributed to the disruption of Hsp90 binding, and the contribution of oxidative stress generated by its quinone group has not been studied in this context. Reactive oxygen species (ROS) and cell survival were assessed in PC-12 cells exposed to GA or menadione (MEN), and Akt, Raf-1, and Cdc37 expression and binding to Hsp90 were determined. GA disrupted Hsp90 binding and increased ROS production starting at 1 h, and cell death occurred at 6 h, inhibited by N-acetylcysteine (NAC) without preventing dissociation of proteins. At 24 h, NAC prevented cytotoxicity and Hsp90 complex disruption. However, MnTBAP antioxidant treatment failed to inhibit GA cytotoxicity, suggesting that NAC acts by restoring glutathione. In contrast, 24 h MEN treatment induced cytotoxicity without disrupting Hsp90 binding. GA and MEN decreased Hsp90-binding protein expression, and proteasomal inhibition prevented MEN-, but not GA-induced degradation. In conclusion, whereas MEN cytotoxicity is mediated by ROS and proteasomal degradation, GA-induced cytotoxicity requires ROS but induces Hsp90 complex dissociation and proteasome-independent protein degradation. These differences between MEN- and GA-induced cytotoxicity may allow more specific targeting of cancer cells.

A truncated form of p23 down-regulates telomerase activity via disruption of Hsp90 function

The Hsp90-associated protein p23 modulates Hsp90 activity during the final stages of the chaperone pathway to facilitate maturation of client proteins. Previous reports indicate that p23 cleavage induced by caspases during cell death triggers destabilization of client proteins. However, the specific role of truncated p23 (Delta p23) in this process and the underlying mechanisms remain to be determined. One such client protein, hTERT, is a telomerase catalytic subunit regulated by several chaperone proteins, including Hsp90 and p23. In the present study, we examined the effects of p23 cleavage on hTERT stability and telomerase activity. Our data showed that overexpression of Delta p23 resulted in a decrease in hTERT levels, and a down-regulation in telomerase activity. Serine phosphorylation of Hsp90 was significantly reduced in cells expressing high levels of Delta p23 compared with those expressing full-length p23. Mutation analyses revealed that two serine residues (Ser-231 and Ser-263) in Hsp90 are important for activation of telomerase, and down-regulation of telomerase activity by Delta p23 was associated with inhibition of cell growth and sensitization of cells to cisplatin. Our data aid in determining the mechanism underlying the regulation of telomerase activity by the chaperone complex during caspase-dependent cell death.

Grp94, the endoplasmic reticulum Hsp90, has a similar solution conformation to cytosolic Hsp90 in the absence of nucleotide

The molecular chaperone, Hsp90, is an essential eukaryotic protein that assists in the maturation and activation of client proteins. Hsp90 function depends upon the binding and hydrolysis of ATP, which causes large conformational rearrangements in the chaperone. Hsp90 is highly conserved from bacteria to eukaryotes, and similar nucleotide-dependent conformations have been demonstrated for the bacterial, yeast, and human proteins. There are, however, important species-specific differences in the ability of nucleotide to shift the conformation from one state to another. Although the role of nucleotide in conformation has been well studied for the cytosolic yeast and human proteins, the conformations found in the absence of nucleotide are less well understood. In contrast to cytosolic Hsp90, crystal structures of the endoplasmic reticulum homolog, Grp94, show the same conformation in the presence of both ADP and AMPPNP. This conformation differs from the yeast AMPPNP-bound crystal state, suggesting that Grp94 may have a different conformational cycle. In this study, we use small angle X-ray scattering and rigid body modeling to study the nucleotide free states of cytosolic yeast and human Hsp90s, as well as mouse Grp94. We show that all three proteins adopt an extended, chair-like conformation distinct from the extended conformation observed for the bacterial Hsp90. For Grp94, we also show that nucleotide causes a small shift toward the crystal state, although the extended state persists as the major population. These results provide the first evidence that Grp94 shares a conformational state with other Hsp90 homologs.

Discovery of novel 2-aminobenzamide inhibitors of heat shock protein 90 as potent, selective and orally active antitumor agents

A novel class of heat shock protein 90 (Hsp90) inhibitors was developed from an unbiased screen to identify protein targets for a diverse compound library. These indol-4-one and indazol-4-one derived 2-aminobenzamides showed strong binding affinity to Hsp90, and optimized analogues exhibited nanomolar antiproliferative activity across multiple cancer cell lines. Heat shock protein 70 (Hsp70) induction and specific client protein degradation in cells on treatment with the inhibitors supported Hsp90 inhibition as the mechanism of action. Computational chemistry and X-ray crystallographic analysis of selected member compounds clearly defined the protein-inhibitor interaction and assisted the design of analogues. 4-[6,6-Dimethyl-4-oxo-3-(trifluoromethyl)-4,5,6,7-tetrahydro-1H-indazol-1-yl]-2-[(trans-4-hydroxycyclohexyl)amino]benzamide (SNX-2112, 9) was identified as highly selective and potent (IC(50) Her2 = 11 nM, HT-29 = 3 nM); its prodrug amino-acetic acid 4-[2-carbamoyl-5-(6,6-dimethyl-4-oxo-3-trifluoromethyl-4,5,6,7-tetrahydro-indazol-1-yl)-phenylamino]-cyclohexyl ester methanesulfonate (SNX-5422, 10) was orally bioavailable and efficacious in a broad range of xenograft tumor models (e.g. 67% growth delay in a HT-29 model) and is now in multiple phase I clinical trials.

Proteins participating to the post-transcriptional regulation of the mitochondrial cytochrome c oxidase subunit IV via elements located in the 3'UTR

In developing rat brain cytochrome c oxidase subunit IV (COXIV) expression is also regulated at post-transcriptional level and two 3'UTR-COXIV RNA-binding factors have been identified. Here, we report the enrichment and identification of the factors from just born rat brains by affinity chromatography of biotinylated 3'UTR-COXIV RNA-protein complexes on streptavidin-conjugated paramagnetic particles. We successfully isolated two main proteins of about 86 and 42kDa, whose sequences were highly attributable to Hsp90 and Actin. The purified proteins maintain RNA-binding ability and specificity for COXIV messenger and, interacting with the 3'UTR, then could negatively modulate mRNA translation. We also studied the content of Hsp90 and Actin during postnatal brain development and demonstrated that in just born rat brain, when the COXIV protein appears at low level, Hsp90 was not phosphorylated. Vice versa in the adult tissue, when COXIV accumulates, Hsp90 appeared phosphorylated in serine therefore it could be unable to bind COXIV messenger, suggesting that the phosphorylation event could provoke the loss of Hsp90 binding to mRNA. We hypothesize a new post-transcriptional mechanism regulating a messenger encoded by nuclear genome for a mitochondrial protein and that Hsp90 and Actin, could represent key players in COXIV translation.

Electrostatic interactions of Hsp-organizing protein tetratricopeptide domains with Hsp70 and Hsp90: computational analysis and protein engineering

The Hsp-organizing protein (HOP) binds to the C termini of the chaperones Hsp70 and Hsp90, thus bringing them together so that substrate proteins can be passed from Hsp70 to Hsp90. Because Hsp90 is essential for the correct folding and maturation of many oncogenic proteins, it has become a significant target for anti-cancer drug design. HOP binds to Hsp70 and Hsp90 via two independent tetratricopeptide (TPR) domains, TPR1 and TPR2A, respectively. We have analyzed ligand binding using Poisson-Boltzmann continuum electrostatic calculations, free energy perturbation, molecular dynamics simulations, and site-directed mutagenesis to delineate the contribution of different interactions to the affinity and specificity of the TPR-peptide interactions. We found that continuum electrostatic calculations could be used to guide protein design by removing unfavorable interactions to increase binding affinity, with an 80-fold increase in affinity for TPR2A. Contributions at buried charged residues, however, were better predicted by free energy perturbation calculations. We suggest using a combination of the two approaches for increasing the accuracy of results, with free energy perturbation calculations used only at selected buried residues of the ligand binding pocket. Finally we present the crystal structure of TPR2A in complex with its non-cognate Hsp70 ligand, which provides insight on the origins of specificity in TPR domain-peptide recognition.

Molecular characterization and induction of heat shock protein 90 in the Antarctic bivalve Laternula elliptica

Heat shock protein 90 (HSP90) is a highly conserved molecular chaperone that plays a key role in protein synthesis, folding, denaturation prevention, and signal transduction. We cloned the complete complementary DNA (cDNA) sequence of the Laternula elliptica HSP90. The full-length cDNA was 2,823 bp in size and contained an open reading frame of 2,190 bp that was translated into 729 amino acids with a calculated molecular weight of 83.4 kDa. The deduced amino acid sequence of HSP90 showed the highest homology to Haliotis tuberculata HSP90 (83%). Reverse-transcriptase polymerase chain reaction analysis revealed the presence of HSP90 transcripts in all of the tissues examined. We also studied the transcriptional expression pattern of HSP90 exposed to thermal stress with real-time polymerase chain reaction. The relative expression level of HSP90 messenger RNA was upregulated and peaked at 12 h in the digestive gland and at 24 h in the gills, then dropped progressively.

Partitioning the apical domain of the Arabidopsis embryo requires the BOBBER1 NudC domain protein

The apical domain of the embryo is partitioned into distinct regions that will give rise to the cotyledons and the shoot apical meristem. In this article, we describe a novel screen to identify Arabidopsis thaliana embryo arrest mutants that are defective in this partitioning, and we describe the phenotype of one such mutant, bobber1. bobber1 mutants arrest at the globular stage of development, they express the meristem-specific SHOOTMERISTEMLESS gene throughout the top half of the embryo, and they fail to express the AINTEGUMENTA transcript normally found in cotyledons. Thus, BOBBER1 is required to limit the extent of the meristem domain and/or to promote the development of the cotyledon domains. Based on expression of early markers for apical development, bobber1 mutants differentiate protodermis and undergo normal early apical development. Consistent with a role for auxin in cotyledon development, BOBBER1 mutants fail to express localized maxima of the DR5:green fluorescent protein reporter. BOBBER1 encodes a protein with homology to the Aspergillus nidulans protein NUDC that has similarity to protein chaperones, indicating a possible role for BOBBER1 in synthesis or transport of proteins involved in patterning the Arabidopsis embryo.

Targeted therapies for malignant glioma: progress and potential

Malignant gliomas represent one of the most aggressive forms of brain cancer. Recent advances in the understanding of the deregulated molecular pathways of gliomas have brought about targeted therapies that have the ability to increase therapeutic efficacy in tumors while decreasing toxicity. Multi-targeted kinase inhibitors, novel monoclonal antibodies, and new vaccines have been developed. Standard treatments and current development of new therapies for malignant gliomas are reviewed, focusing specifically on growth factors and their receptors (e.g. epidermal growth factor receptor, vascular endothelial growth factor receptor, and platelet-derived growth factor receptor), as well as the intracellular effector molecules that are downstream of these growth factors (e.g. Ras/Raf/mitogen-activated protein kinase, phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin, and protein kinase C). The efficacies of other novel targeted inhibitors such as deacetylase inhibitors and heat shock protein 90 inhibitors in the treatment of gliomas are also discussed, as well as new combination therapies. In order for new agents to increase treatment efficacy, new targets need to be developed, drug delivery efficiency needs to be improved, and new biomarkers need to be discovered. All of these goals can be accomplished with time through innovative experimental designs.