Geldanamycin, an hsp90/GRP94-binding drug, induces increased transcription of endoplasmic reticulum (ER) chaperones via the ER stress pathway

Selective delivery of imaging probes and therapeutics to the endoplasmic reticulum or Golgi apparatus: Current strategies and beyond

To maximize therapeutic effects and minimize unwanted effects, the interest in drug targeting to the endoplasmic reticulum (ER) or Golgi apparatus (GA) has been recently growing because two organelles are distributing hubs of cellular building/signaling components (e.g., proteins, lipids, Ca2+) to other organelles and the plasma membrane. Their structural or functional damages induce organelle stress (i.e., ER or GA stress), and their aggravation is strongly related to diseases (e.g., cancers, liver diseases, brain diseases). Many efforts have been developed to image (patho)physiological functions (e.g., oxidative stress, protein/lipid-related processing) and characteristics (e.g., pH, temperature, biothiols, reactive oxygen species) in the target organelles and to deliver drugs for organelle disruption using organelle-targeting moieties. Therefore, this review will overview the structure, (patho)physiological functions/characteristics, and related diseases of the organelles of interest. Future direction on ER or GA targeting will be discussed by understanding current strategies and investigations on targeting, imaging/sensing, and therapeutic systems.

General Structural and Functional Features of Molecular Chaperones

Molecular chaperones are a group of structurally diverse and highly conserved ubiquitous proteins. They play crucial roles in facilitating the correct folding of proteins in vivo by preventing protein aggregation or facilitating the appropriate folding and assembly of proteins. Heat shock proteins form the major class of molecular chaperones that are responsible for protein folding events in the cell. This is achieved by ATP-dependent (folding machines) or ATP-independent mechanisms (holders). Heat shock proteins are induced by a variety of stresses, besides heat shock. The large and varied heat shock protein class is categorised into several subfamilies based on their sizes in kDa namely, small Hsps (HSPB), J domain proteins (Hsp40/DNAJ), Hsp60 (HSPD/E; Chaperonins), Hsp70 (HSPA), Hsp90 (HSPC), and Hsp100. Heat shock proteins are localised to different compartments in the cell to carry out tasks specific to their environment. Most heat shock proteins form large oligomeric structures, and their functions are usually regulated by a variety of cochaperones and cofactors. Heat shock proteins do not function in isolation but are rather part of the chaperone network in the cell. The general structural and functional features of the major heat shock protein families are discussed, including their roles in human disease. Their function is particularly important in disease due to increased stress in the cell. Vector-borne parasites affecting human health encounter stress during transmission between invertebrate vectors and mammalian hosts. Members of the main classes of heat shock proteins are all represented in Plasmodium falciparum, the causative agent of cerebral malaria, and they play specific functions in differentiation, cytoprotection, signal transduction, and virulence.

Proteostasis In The Endoplasmic Reticulum: Road to Cure

The endoplasmic reticulum (ER) is an interconnected organelle that is responsible for the biosynthesis, folding, maturation, stabilization, and trafficking of transmembrane and secretory proteins. Therefore, cells evolve protein quality-control equipment of the ER to ensure protein homeostasis, also termed proteostasis. However, disruption in the folding capacity of the ER caused by a large variety of pathophysiological insults leads to the accumulation of unfolded or misfolded proteins in this organelle, known as ER stress. Upon ER stress, unfolded protein response (UPR) of the ER is activated, integrates ER stress signals, and transduces the integrated signals to relive ER stress, thereby leading to the re-establishment of proteostasis. Intriguingly, severe and persistent ER stress and the subsequently sustained unfolded protein response (UPR) are closely associated with tumor development, angiogenesis, aggressiveness, immunosuppression, and therapeutic response of cancer. Additionally, the UPR interconnects various processes in and around the tumor microenvironment. Therefore, it has begun to be delineated that pharmacologically and genetically manipulating strategies directed to target the UPR of the ER might exhibit positive clinical outcome in cancer. In the present review, we summarize recent advances in our understanding of the UPR of the ER and the UPR of the ER-mitochondria interconnection. We also highlight new insights into how the UPR of the ER in response to pathophysiological perturbations is implicated in the pathogenesis of cancer. We provide the concept to target the UPR of the ER, eventually discussing the potential of therapeutic interventions for targeting the UPR of the ER for cancer treatment.

Deep insights into the response of human cervical carcinoma cells to a new cyano enone-bearing triterpenoid soloxolone methyl: a transcriptome analysis

Semisynthetic triterpenoids, bearing cyano enone functionality in ring A, are considered now as novel promising anti-tumor agents. However, despite the large-scale studies, their effects on cervical carcinoma cells and, moreover, mechanisms underlying cell death activation by such compounds in this cell type have not been fully elucidated. In this work, we attempted to reconstitute the key pathways and master regulators involved in the response of human cervical carcinoma KB-3-1 cells to the novel glycyrrhetinic acid derivative soloxolone methyl (SM) by a transcriptomic approach. Functional annotation of differentially expressed genes, analysis of their cis^- regulatory sequences and protein-protein interaction network clearly indicated that stress of endoplasmic reticulum (ER) is the central event triggered by SM in the cells. A range of key ER stress sensors and transcription factor AP-1 were identified as upstream transcriptional regulators, controlling the response of the cells to SM. Additionally, by using Gene Expression Omnibus data, we showed the ability of SM to modulate the expression of key genes involved in regulation of the high proliferative rate of cervical carcinoma cells. Further Connectivity Map analysis revealed similarity of SM's effects with known ER stress inducers thapsigargin and geldanamycin, targeting SERCA and Grp94, respectively. According to the molecular docking study, SM could snugly fit into the active sites of these proteins in the positions very close to that of both inhibitors. Taken together, our findings provide a basis for the better understanding of the intracellular processes in tumor cells switched on in response to cyano enone-bearing triterpenoids.

HSP90 Inhibitor Geldanamycin as a Radiation Response Modificator in Human Blood Cells

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone, involved in the folding, assembly, stabilization and activation of numerous proteins with unrelated amino acid sequences and functions. Geldanamycin (GA), a natural benzoquinone, can inhibit the chaperone activity of Hsp90. It has been shown that GA can produce superoxide anions and increase the intracellular oxidative stress, which, in addition to the direct inhibition of Hsp90, might also contribute to the modifying effects of the inhibitor on the early response in human mononuclear cells exposed to ionizing radiation. The present study shows that GA antagonizes the radiation-induced suppression on MnSOD and catalase, key enzymes of the radical scavenging systems. By significantly up-regulating catalase levels over the entire range of doses from 0.5 to 4 Gy, the inhibitor of Hsp90 exerted adaptive protection and modified the early radiation response of the human blood cells.

Hsp90 and hepatobiliary transformation during sea lamprey metamorphosis

BACKGROUND

Biliary atresia (BA) is a human infant disease with inflammatory fibrous obstructions in the bile ducts and is the most common cause for pediatric liver transplantation. In contrast, the sea lamprey undergoes developmental BA with transient cholestasis and fibrosis during metamorphosis, but emerges as a fecund adult. Therefore, sea lamprey liver metamorphosis may serve as an etiological model for human BA and provide pivotal information for hepatobiliary transformation and possible therapeutics.

RESULTS

We hypothesized that liver metamorphosis in sea lamprey is due to transcriptional reprogramming that dictates cellular remodeling during metamorphosis. We determined global gene expressions in liver at several metamorphic landmark stages by integrating mRNA-Seq and gene ontology analyses, and validated the results with real-time quantitative PCR, histological and immunohistochemical staining. These analyses revealed that gene expressions of protein folding chaperones, membrane transporters and extracellular matrices were altered and shifted during liver metamorphosis. HSP90, important in protein folding and invertebrate metamorphosis, was identified as a candidate key factor during liver metamorphosis in sea lamprey. Blocking HSP90 with geldanamycin facilitated liver metamorphosis and decreased the gene expressions of the rate limiting enzyme for cholesterol biosynthesis, HMGCoA reductase (hmgcr), and bile acid biosynthesis, cyp7a1. Injection of hsp90 siRNA for 4 days altered gene expressions of met, hmgcr, cyp27a1, and slc10a1. Bile acid concentrations were increased while bile duct and gall bladder degeneration was facilitated and synchronized after hsp90 siRNA injection.

CONCLUSIONS

HSP90 appears to play crucial roles in hepatobiliary transformation during sea lamprey metamorphosis. Sea lamprey is a useful animal model to study postembryonic development and mechanisms for hsp90-induced hepatobiliary transformation.

SB225002 Induces Cell Death and Cell Cycle Arrest in Acute Lymphoblastic Leukemia Cells through the Activation of GLIPR1

Acute Lymphoblastic Leukemia (ALL) is the most frequent childhood malignancy. In the effort to find new anti-leukemic agents, we evaluated the small drug SB225002 (N-(2-hydroxy-4-nitrophenyl)-N’-(2-bromophenyl)urea). Although initially described as a selective antagonist of CXCR2, later studies have identified other cellular targets for SB225002, with potential medicinal use in cancer. We found that SB225002 has a significant pro-apoptotic effect against both B- and T-ALL cell lines. Cell cycle analysis demonstrated that treatment with SB225002 induces G2-M cell cycle arrest. Transcriptional profiling revealed that SB225002-mediated apoptosis triggered a transcriptional program typical of tubulin binding agents. Network analysis revealed the activation of genes linked to the JUN and p53 pathways and inhibition of genes linked to the TNF pathway. Early cellular effects activated by SB225002 included the up-regulation of GLIPR1, a p53-target gene shown to have pro-apoptotic activities in prostate and bladder cancer. Silencing of GLIPR1 in B- and T-ALL cell lines resulted in increased resistance to SB225002. Although SB225002 promoted ROS increase in ALL cells, antioxidant N-Acetyl Cysteine pre-treatment only modestly attenuated cell death, implying that the pro-apoptotic effects of SB225002 are not exclusively mediated by ROS. Moreover, GLIPR1 silencing resulted in increased ROS levels both in untreated and SB225002-treated cells. In conclusion, SB225002 induces cell cycle arrest and apoptosis in different B- and T-ALL cell lines. Inhibition of tubulin function with concurrent activation of the p53 pathway, in particular, its downstream target GLIPR1, seems to underlie the anti-leukemic effect of SB225002.

Novel therapeutic strategies for multiple myeloma

Multiple myeloma (MM) is a plasma-cell malignancy which remains incurable despite the recent emergence of multiple novel agents. Importantly, recent genetic and molecular analyses have revealed the complexity and heterogeneity of this disease, highlighting the need for therapeutic strategies to eliminate all clones. Moreover, the bone marrow microenvironment, including stromal cells and immune cells, plays a central role in MM pathogenesis, promoting tumor cell growth, survival, and drug resistance. New classes of agents including proteasome inhibitors, immunomodulatory drugs, monoclonal antibodies, and histone deacetylase inhibitors have shown remarkable efficacy; however, novel therapeutic approaches are still urgently needed to further improve patient outcomes. In this review, we discuss the recent advances and future strategies to ultimately develop MM therapies with curative potential.

Hsp90 inhibition induces both protein-specific and global changes in the ubiquitinome

Inhibition of the essential chaperone Hsp90 with drugs causes a global perturbation of protein folding and the depletion of direct substrates of Hsp90, also called clients. Ubiquitination and proteasomal degradation play a key role in cellular stress responses, but the impact of Hsp90 inhibition on the ubiquitinome has not been characterized on a global scale. We used stable isotope labeling and antibody-based peptide enrichment to quantify more than 1500 protein sites modified with a Gly-Gly motif, the remnant of ubiquitination, in human T-cells treated with an Hsp90 inhibitor. We observed rapid changes in GlyGly-modification sites, with strong increases for some Hsp90 clients but also decreases for a majority of cellular proteins. A comparison with changes in total protein levels and protein synthesis and decay rates from a previous study revealed a complex picture with different regulatory patterns observed for different protein families. Overall the data support the notion that for Hsp90 clients GlyGly-modification correlates with targeting by the ubiquitin-proteasome system and decay, while for other proteins levels of GlyGly-modification appear to be mainly influenced by their synthesis rates. Therefore a correct interpretation of changes in ubiquitination requires knowledge of multiple parameters. Data are available via ProteomeXchange with identifier PXD001549.

BIOLOGICAL SIGNIFICANCE

Proteostasis, i.e. the capacity of the cell to maintain proper synthesis and maturation of proteins, is a fundamental biological process and its perturbations have far-reaching medical implications e.g. in cancer or neurodegenerative diseases. Hsp90 is an essential chaperone responsible for the correct maturation and stability of a number of key proteins. Inhibition of Hsp90 triggers a global stress response caused by accumulation of misfolded chains, which have to be either refolded or eliminated by protein degradation pathways such as the Ubiquitin-Proteasome System (UPS). We present the first global assessment of the changes in the ubiquitinome, the subset of ubiquitin-modified proteins, following Hsp90 inhibition in human T-cells. The results provide clues on how cells respond to a specific proteostasis challenge. Furthermore, our data also suggest that basal ubiquitination levels for most proteins are influenced by synthesis rates. This has broad significance as it implies that a proper interpretation of data on ubiquitination levels necessitates simultaneous knowledge of other parameters.

Sil1, a nucleotide exchange factor for BiP, is not required for antibody assembly or secretion

Sil1 is a nucleotide exchange factor for the ER chaperone BiP, and mutations in this gene lead to Marinesco–Sjögren syndrome, a multisystem disorder. Effects of loss of Sil1 on biosynthesis and secretion of antibodies, a well-characterized BiP client, are determined in a mouse model for this disease and patient-derived lymphoblastoid cell lines.

Sil1 is a nucleotide exchange factor for the endoplasmic reticulum chaperone BiP, and mutations in this gene lead to Marinesco–Sjögren syndrome (MSS), a debilitating autosomal recessive disease characterized by multisystem defects. A mouse model for MSS was previously produced by disrupting Sil1 using gene-trap methodology. The resulting Sil1^Gt mouse phenocopies several pathologies associated with MSS, although its ability to assemble and secrete antibodies, the best-characterized substrate of BiP, has not been investigated. In vivo antigen-specific immunizations and ex vivo LPS stimulation of splenic B cells revealed that the Sil1^Gt mouse was indistinguishable from wild-type age-matched controls in terms of both the kinetics and magnitude of antigen-specific antibody responses. There was no significant accumulation of BiP-associated Ig assembly intermediates or evidence that another molecular chaperone system was used for antibody production in the LPS-stimulated splenic B cells from Sil1^Gt mice. ER chaperones were expressed at the same level in Sil1^WT and Sil1^Gt mice, indicating that there was no evident compensation for the disruption of Sil1. Finally, these results were confirmed and extended in three human EBV-transformed lymphoblastoid cell lines from individuals with MSS, leading us to conclude that the BiP cofactor Sil1 is dispensable for antibody production.

Worming our way to novel drug discovery with the Caenorhabditis elegans proteostasis network, stress response and insulin-signaling pathways

INTRODUCTION

Many human diseases result from a failure of a single protein to achieve the correct folding and tertiary conformation. These so-called 'conformational diseases' involve diverse proteins and distinctive cellular pathologies. They all engage the proteostasis network (PN), to varying degrees in an attempt to mange cellular stress and restore protein homeostasis. The insulin/insulin-like growth factor signaling (IIS) pathway is a master regulator of cellular stress response, which is implicated in regulating components of the PN.

AREAS COVERED

This review focuses on novel approaches to target conformational diseases. The authors discuss the evidence supporting the involvement of the IIS pathway in modulating the PN and regulating proteostasis in Caenorhabditis elegans. Furthermore, they review previous PN and IIS drug screens and explore the possibility of using C. elegans for whole organism-based drug discovery for modulators of IIS-proteostasis pathways.

EXPERT OPINION

An alternative approach to develop individualized therapy for each conformational disease is to modulate the global PN. The involvement of the IIS pathway in regulating longevity and response to a variety of stresses is well documented. Increasing data now provide evidence for the close association between the IIS and the PN pathways. The authors believe that high-throughput screening campaigns, which target the C. elegans IIS pathway, may identify drugs that are efficacious in treating numerous conformational diseases.

Involvement of calcium-mediated reactive oxygen species in inductive GRP78 expression by geldanamycin in 9L rat brain tumor cells

Treatment with geldanamycin (GA) leads to an increase in [Ca2+]c and the production of reactive oxygen species (ROS) in rat brain tumor 9L RBT cells. GA-exerted calcium signaling was blocked by BAPTA/AM and EGTA. The effect of GA on [Ca2+]c was significantly reduced in the presence of thapsigargin (TG) and ruthenium red (RR). GA-induced GRP78 expression is significantly decreased in the presence of BAPTA/AM, EGTA and RR, suggesting that the calcium influx from the extracellular space and intracellular calcium store oscillations are contributed to by the calcium mobilization and GRP78 expression induced by GA. The induced GRP78 expression is sensitive to added U73122 and Ro-31-8425, pinpointing the involvement of phospholipase C (PLC) and protein kinase C (PKC) in GA-induced endoplasmic reticulum (ER) stress. The antioxidants N-acetylcysteine (NAC), BAPTA/AM, EGTA and H7 also have significant inhibitory effects on ROS generation. Finally, neither H7 nor NAC was able to affect the calcium response elicited by GA. Our results suggest that the causal signaling cascade during GA-inducted GRP78 expression occurs via a pathway that connects PLC to cytoplasmic calcium increase, PKC activation and, then, finally, ROS generation. Our data provides new insights into the influence of GA on ER stress response in 9L RBT cells.

The anticancer drug AUY922 generates a proteomics fingerprint that is highly conserved among structurally diverse Hsp90 inhibitors

AUY922 is a potent synthetic Hsp90 antagonist that is moving steadily through clinical trials against a small range of cancers. To identify protein markers that might measure the drug's effects, and to gain understanding of mechanisms by which AUY922 might inhibit the proliferation of leukemia cells, we characterized AUY922's impacts on the proteomes of cultured Jurkat cells. We describe a robust and readily assayed proteomics fingerprint that AUY922 shares with the flagship Hsp90 inhibitors 17-DMAG and radicicol. We also extend our proteomics findings, demonstrating that an unrelated antagonist of protein folding potentiates the antiproliferative effects of AUY922. Results provide a set of candidate biomarkers for responses to AUY922 in leukemia cells and suggest new modalities for enhancing AUY922's anticancer activities.

Hsp90 inhibition by PU-H71 induces apoptosis through endoplasmic reticulum stress and mitochondrial pathway in cancer cells and overcomes the resistance conferred by Bcl-2

Heat shock protein 90 (Hsp90) has recently emerged as an attractive therapeutic target in cancer treatment because of its role in stabilizing the active form of a wide range of client oncoproteins. This study investigated the mechanism of apoptosis induced by the purine-scaffold Hsp90 inhibitor PU-H71 in different human cancer cell lines and examined the role of Bcl-2 and Bax in this process. We demonstrated that Hsp90 inhibition by PU-H71 generated endoplasmic reticulum (ER) stress and activated the Unfolded Protein Response (UPR) as evidenced by XBP1 mRNA splicing and up-regulation of Grp94, Grp78, ATF4 and CHOP. In response to PU-H71-induced ER stress, apoptosis was triggered in melanoma, cervix, colon, liver and lung cancer cells, but not in normal human fibroblasts. Apoptosis was executed through the mitochondrial pathway as shown by down-regulation of Bcl-2, up-regulation and activation of Bax, permeabilization of mitochondrial membranes, release of cytochrome c and activation of caspases. We also found that, in contrast to the ER stressor thapsigargin, PU-H71 induced apoptosis in cells overexpressing Bcl-2 and thus overcame the resistance conferred by this anti-apoptotic protein. In addition, although Bax deficiency rendered cells resistant to PU-H71, combined treatment with the anticancer drugs cisplatin or melphalan greatly sensitized these cells to PU-H71. Taken together, these data suggest that inhibition of Hsp90 by PU-H71 is a promising strategy for cancer treatment, particularly in the case of tumors resistant to conventional chemotherapy.

Endoplasmic reticulum stress: its role in disease and novel prospects for therapy

The endoplasmic reticulum (ER) is a multifunctional organelle required for lipid biosynthesis, calcium storage, and protein folding and processing. A number of physiological and pathological conditions, as well as a variety of pharmacological agents, are able to disturb proper ER function and thereby cause ER stress, which severely impairs protein folding and therefore poses the risk of proteotoxicity. Specific triggers for ER stress include, for example, particular intracellular alterations (e.g., calcium or redox imbalances), certain microenvironmental conditions (e.g., hypoglycemia, hypoxia, and acidosis), high-fat and high-sugar diet, a variety of natural compounds (e.g., thapsigargin, tunicamycin, and geldanamycin), and several prescription drugs (e.g., bortezomib/Velcade, celecoxib/Celebrex, and nelfinavir/Viracept). The cell reacts to ER stress by initiating a defensive process, called the unfolded protein response (UPR), which is comprised of cellular mechanisms aimed at adaptation and safeguarding cellular survival or, in cases of excessively severe stress, at initiation of apoptosis and elimination of the faulty cell. In recent years, this dichotomic stress response system has been linked to several human diseases, and efforts are underway to develop approaches to exploit ER stress mechanisms for therapy. For example, obesity and type 2 diabetes have been linked to ER stress-induced failure of insulin-producing pancreatic beta cells, and current research efforts are aimed at developing drugs that ameliorate cellular stress and thereby protect beta cell function. Other studies seek to pharmacologically aggravate chronic ER stress in cancer cells in order to enhance apoptosis and achieve tumor cell death. In the following, these principles will be presented and discussed.

Biology of the heat shock response and protein chaperones: budding yeast (Saccharomyces cerevisiae) as a model system

The eukaryotic heat shock response is an ancient and highly conserved transcriptional program that results in the immediate synthesis of a battery of cytoprotective genes in the presence of thermal and other environmental stresses. Many of these genes encode molecular chaperones, powerful protein remodelers with the capacity to shield, fold, or unfold substrates in a context-dependent manner. The budding yeast Saccharomyces cerevisiae continues to be an invaluable model for driving the discovery of regulatory features of this fundamental stress response. In addition, budding yeast has been an outstanding model system to elucidate the cell biology of protein chaperones and their organization into functional networks. In this review, we evaluate our understanding of the multifaceted response to heat shock. In addition, the chaperone complement of the cytosol is compared to those of mitochondria and the endoplasmic reticulum, organelles with their own unique protein homeostasis milieus. Finally, we examine recent advances in the understanding of the roles of protein chaperones and the heat shock response in pathogenic fungi, which is being accelerated by the wealth of information gained for budding yeast.

Small molecule activators of the heat shock response: chemical properties, molecular targets, and therapeutic promise

All cells have developed various mechanisms to respond and adapt to a variety of environmental challenges, including stresses that damage cellular proteins. One such response, the heat shock response (HSR), leads to the transcriptional activation of a family of molecular chaperone proteins that promote proper folding or clearance of damaged proteins within the cytosol. In addition to its role in protection against acute insults, the HSR also regulates lifespan and protects against protein misfolding that is associated with degenerative diseases of aging. As a result, identifying pharmacological regulators of the HSR has become an active area of research in recent years. Here, we review progress made in identifying small molecule activators of the HSR, what cellular targets these compounds interact with to drive response activation, and how such molecules may ultimately be employed to delay or reverse protein misfolding events that contribute to a number of diseases.

Blockade of XBP1 splicing by inhibition of IRE1α is a promising therapeutic option in multiple myeloma

Multiple myeloma (MM) cells are characterized by high protein synthesis resulting in chronic endoplasmic reticulum (ER) stress, which is adaptively managed by the unfolded protein response. Inositol-requiring enzyme 1α (IRE1α) is activated to splice X-box binding protein 1 (XBP1) mRNA, thereby increasing XBP1s protein, which in turn regulates genes responsible for protein folding and degradation during the unfolded protein response. In this study, we examined whether IRE1α-XBP1 pathway is a potential therapeutic target in MM using a small-molecule IRE1α endoribonuclease domain inhibitor MKC-3946. MKC-3946 triggered modest growth inhibition in MM cell lines, without toxicity in normal mononuclear cells. Importantly, it significantly enhanced cytotoxicity induced by bortezomib or 17-AAG, even in the presence of bone marrow stromal cells or exogenous IL-6. Both bortezomib and 17-AAG induced ER stress, evidenced by induction of XBP1s, which was blocked by MKC-3946. Apoptosis induced by these agents was enhanced by MKC-3946, associated with increased CHOP. Finally, MKC-3946 inhibited XBP1 splicing in a model of ER stress in vivo, associated with significant growth inhibition of MM cells. Taken together, our results demonstrate that blockade of XBP1 splicing by inhibition of IRE1α endoribonuclease domain is a potential therapeutic option in MM.

Quantitative proteomics reveals that Hsp90 inhibition preferentially targets kinases and the DNA damage response

Despite the increasing importance of heat shock protein 90 (Hsp90) inhibitors as chemotherapeutic agents in diseases such as cancer, their global effects on the proteome remain largely unknown. Here we use high resolution, quantitative mass spectrometry to map protein expression changes associated with the application of the Hsp90 inhibitor, 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG). In depth data obtained from five replicate SILAC experiments enabled accurate quantification of about 6,000 proteins in HeLa cells. As expected, we observed activation of a heat shock response with induced expression of molecular chaperones, which refold misfolded proteins, and proteases, which degrade irreparably damaged polypeptides. Despite the broad range of known Hsp90 substrates, bioinformatics analysis revealed that particular protein classes were preferentially affected. These prominently included proteins involved in the DNA damage response, as well as protein kinases and especially tyrosine kinases. We followed up on this observation with a quantitative phosphoproteomic analysis of about 4,000 sites, which revealed that Hsp90 inhibition leads to much more down- than up-regulation of the phosphoproteome (34% down versus 6% up). This study defines the cellular response to Hsp90 inhibition at the proteome level and sheds light on the mechanisms by which it can be used to target cancer cells.

A novel epidermal growth factor receptor variant lacking multiple domains directly activates transcription and is overexpressed in tumors

The epidermal growth factor receptor (EGFR) is essential to multiple physiological and neoplastic processes via signaling by its tyrosine kinase domain and subsequent activation of transcription factors. EGFR overexpression and alteration, including point mutations and structural variants, contribute to oncogenesis in many tumor types. In this study, we identified an in-frame splice variant of the EGFR called mini-LEEK (mLEEK) that is more broadly expressed than the EGFR and is overexpressed in several cancers. Unlike previously characterized EGFR variants, mLEEK lacks the extracytoplasmic, transmembrane and tyrosine kinase domains. mLEEK localizes in the nucleus and functions as a transcription factor to regulate target genes involved in the cellular response to endoplasmic reticulum (ER) stress, including the master regulator of the unfolded protein response (UPR) pathways, molecular chaperone GRP78/Bip. We demonstrated that mLEEK regulates GRP78 transcription through direct interaction with a cis-regulatory element within the gene promoter. Several UPR pathways were interrogated and mLEEK expression was found to attenuate the induction of all pathways upon ER stress. Conversely, knockdown of mLEEK resulted in caspase-mediated cell death and sensitization to ER stress. These findings indicate that mLEEK levels determine cellular responses to unfavorable conditions that cause ER stress. This information, along with the overexpression of mLEEK in tumors, suggests unique strategies for therapeutic intervention. Furthermore, the identification of mLEEK expands the known mechanisms by which the EGFR gene contributes to oncogenesis and represents the first link between two previously disparate areas in cancer cell biology: EGFR signaling and the UPR.

Endoplasmic reticulum stress in disease: mechanisms and therapeutic opportunities

Various stresses, which impair ER (endoplasmic reticulum) function, lead to an accumulation of unfolded or misfolded proteins. ER stress triggers many rescuer responses, including a UPR (unfolded protein response). Increasing evidence has suggested that ER stress is involved in neurodegenerative diseases (Alzheimer's disease, Parkinson's disease and cerebral ischaemic insults), cancer, obesity and diabetes. In the present review, we consider the importance of ER stress under pathological conditions in mammals. Furthermore, we discuss the therapeutic potential for treatment targeting ER stress.

Reduced expression of alpha-1,2-mannosidase I extends lifespan in Drosophila melanogaster and Caenorhabditis elegans

Exposure to sub-lethal levels of stress, or hormesis, was a means to induce longevity. By screening for mutations that enhance resistance to multiple stresses, we identified multiple alleles of alpha-1,2-mannosidase I (mas1) which, in addition to promoting stress resistance, also extended longevity. Longevity enhancement is also observed when mas1 expression is reduced via RNA interference in both Drosophila melanogaster and Caenorhabditis elegans. The screen also identified Edem1 (Edm1), a gene downstream of mas1, as a modulator of lifespan. As double mutants for both mas1 and Edm1 showed no additional longevity enhancement, it appeared that both mutations function within a common pathway to extend lifespan. Molecular analysis of these mutants revealed that the expression of BiP, a putative biomarker of dietary restriction (DR), is down-regulated in response to reductions in mas1 expression. These findings suggested that mutations in mas1 may extend longevity by modulating DR.

Different poses for ligand and chaperone in inhibitor-bound Hsp90 and GRP94: implications for paralog-specific drug design

Hsp90 chaperones contain an N-terminal ATP binding site that has been effectively targeted by competitive inhibitors. Despite the myriad of inhibitors, none to date have been designed to bind specifically to just one of the four mammalian Hsp90 paralogs, which are cytoplasmic Hsp90alpha and beta, endoplasmic reticulum GRP94, and mitochondrial Trap-1. Given that each of the Hsp90 paralogs is responsible for chaperoning a distinct set of client proteins, specific targeting of one Hsp90 paralog may result in higher efficacy and therapeutic control. Specific inhibitors may also help elucidate the biochemical roles of each Hsp90 paralog. Here, we present side-by-side comparisons of the structures of yeast Hsp90 and mammalian GRP94, bound to the pan-Hsp90 inhibitors geldanamycin (Gdm) and radamide. These structures reveal paralog-specific differences in the Hsp90 and GRP94 conformations in response to Gdm binding. We also report significant variation in the pose and disparate binding affinities for the Gdm-radicicol chimera radamide when bound to the two paralogs, which may be exploited in the design of paralog-specific inhibitors.

Valproate, a mood stabilizer, induces WFS1 expression and modulates its interaction with ER stress protein GRP94

BACKGROUND

Valproate is a standard treatment for bipolar disorder and a first-line mood stabilizer. The molecular mechanisms underlying its actions in bipolar disorder are unclear. It has been suggested that the action of valproate is linked to changes in gene expression and induction of endoplasmic reticulum (ER) stress-response proteins.

PRINCIPAL FINDINGS

Here we show that valproate modulates the ER stress response through the regulation of WFS1, an important component for mitigating ER stress. Therapeutic concentrations of valproate induce expression of WFS1 mRNA and activate the WFS1 promoter. In addition, WFS1 forms a complex with GRP94, an ER stress-response protein, in which valproate dose-dependently enhances its dissociation from GRP94.

CONCLUSIONS

These results suggest that the therapeutic effects of valproate in bipolar disorder may be mediated by WFS1 expression and its dissociation from GRP94.

Tosylcyclonovobiocic acids promote cleavage of the hsp90-associated cochaperone p23

The cochaperone p23 is required for the chaperoning cycle of hsp90 and to enhance the maturation of several client proteins. Tosylcyclonovobiocic acids (4TCNA and 7TCNA) are potent analogs of novobiocin and induce cell cycle arrest, apoptosis and degradation of hsp90 client proteins in a panel of cancer cells. In this study, Western blotting shows that 4TCNA and 7TCNA triggered processing of the hsp90 cochaperone p23 in a dose-dependent manner. Small interfering RNA (siRNA)-mediated reduction of p23 expression in MCF-7 breast cancer cells did not block 4TCNA-induced caspase activation as assessed by the cleavage of PARP. This result indicates that 4TCNA-mediated cell death is a p23-independent process. In HT29 colon cancer cells, 4TCNA and 7TCNA up-regulated GRP78 and GRP94 supporting involvement of ER stress in apoptosis.

Proteomic and transcriptomic study on the action of a cytotoxic saponin (Polyphyllin D): induction of endoplasmic reticulum stress and mitochondria-mediated apoptotic pathways

Polyphyllin D (PD) is a potent cytotoxic saponin found in Paris polyphylla. In the present study, bioinformatic, proteomic and transcriptomic analyses were performed to study the mechanisms of action of PD on human nonsmall cell lung cancer (NSCLC) cell line (NCI-H460). Using a gene expression-based bioinformatic tool (connectivity map), PD was identified as a potential ER stress inducer. Our proteomic and transcriptomic analyses revealed that PD treatment led to upregulation of typical ER stress-related proteins/genes including glucose-regulated protein 78 (BiP/GRP78) and protein disulfide isomerase (PDI). In particular, elevated expression of C/EBP homologous transcription factor (chop) and activation of caspase-4 occurred at early time point (8 h) of PD treatment, signifying an initial ER stress-mediated apoptosis. Induction of tumor suppressor p53, disruption of mitochondrial membrane, activation of caspase-9 and caspase-3 were detected upon prolonged PD treatment. Collectively, these data revealed that PD induced the cytotoxic effect through a mechanism initiated by ER stress followed by mitochondrial apoptotic pathway. The ability of activating two major pathways of apoptosis makes PD an attractive drug lead for anticancer therapeutics.

Cytosolic chaperones influence the fate of a toxin dislocated from the endoplasmic reticulum

The plant cytotoxin ricin enters target mammalian cells by receptor-mediated endocytosis and undergoes retrograde transport to the endoplasmic reticulum (ER). Here, its catalytic A chain (RTA) is reductively separated from the cell-binding B chain, and free RTA enters the cytosol where it inactivates ribosomes. Cytosolic entry requires unfolding of RTA and dislocation across the ER membrane such that it arrives in the cytosol in a vulnerable, nonnative conformation. Clearly, for such a dislocated toxin to become active, it must avoid degradation and fold to a catalytic conformation. Here, we show that, in vitro, Hsc70 prevents aggregation of heat-treated RTA, and that RTA catalytic activity is recovered after chaperone treatment. A combination of pharmacological inhibition and cochaperone expression reveals that, in vivo, cytosolic RTA is scrutinized sequentially by the Hsc70 and Hsp90 cytosolic chaperone machineries, and that its eventual fate is determined by the balance of activities of cochaperones that regulate Hsc70 and Hsp90 functions. Cytotoxic activity follows Hsc70-mediated escape of RTA from an otherwise destructive pathway facilitated by Hsp90. We demonstrate a role for cytosolic chaperones, proteins typically associated with folding nascent proteins, assembling multimolecular protein complexes and degrading cytosolic and stalled, cotranslocational clients, in a toxin triage, in which both toxin folding and degradation are initiated from chaperone-bound states.

Interleukin-18 prevents apoptosis via PI3K/Akt pathway in normal human keratinocytes

Interleukin-18 (IL-18) is a pleiotropic cytokine expressed in both immune and non-immune cells. In the present study, we demonstrate an anti-apoptotic role of IL-18 in normal human neonatal foreskin epidermal keratinocytes (NHEK-F). Cultured NHEK-F spontaneously produced the active form of IL-18. Treatment of NHEK-F cells with anti-IL-18 receptor alpha-chain neutralizing antibody increased apoptosis and caspase-3 activity. Exogenous IL-18 augmented phosphorylation of Akt and activation of NF-kappaB. The promotion of Akt phosphorylation by IL-18 was abolished by LY294002, a PI3K inhibitor, but not SN50, an NF-kappaB inhibitor, indicating that IL-18 functions via the PI3K/Akt pathway and independently of NF-kappaB. In addition, IL-18 was found to augment expression of anti-apoptotic proteins, Bcl-2, XIAP and glucose regulated protein78/BiP, while anti-IL-18 receptor alpha-chain neutralizing antibody suppressed expression of Bcl-2, XIAP, glucose regulated protein94 and protein disulfide isomerase. Taken together, these results indicate that IL-18 plays an important role in keratinocyte survival.

The effects of long-duration, low-temperature ground transportation on physiological and biochemical indicators of stress in mice

Transportation can cause stress to laboratory animals and alter physiological characteristics that may confound experimental results. The authors investigated stress-related effects of 3-4 h of transportation by truck in two strains of mice (C57BL/6, which are known to be aggressive, and ICR, which are less aggressive). Transported mice had sufficient space and access to water, though temperature in the truck was lower than what is usually recommended. Transportation affected the following parameters in both strains of mice: (i) serum corticosterone concentrations, (ii) expression of the chaperone proteins Hsp70 and Grp78 in various tissues and (iii) concentrations of serological enzymes that are associated with liver disease. These parameters also differed substantially between the two strains of mice.

The 90-kDa heat shock protein stabilizes the polysomal ribonuclease 1 mRNA endonuclease to degradation by the 26S proteasome

The polysomal ribonuclease 1 (PMR1) mRNA endonuclease forms a selective complex with its translating substrate mRNAs where it is activated to initiate mRNA decay. Previous work showed tyrosine phosphorylation is required for PMR1 targeting to this polysome-bound complex, and it identified c-Src as the responsible kinase. c-Src phosphorylation occurs in a distinct complex, and the current study shows that 90-kDa heat shock protein (Hsp90) is also recovered with PMR1 and c-Src. Hsp90 binding to PMR1 is inhibited by geldanamycin, and geldanamycin stabilizes substrate mRNA to PMR1-mediated decay. PMR1 is inherently unstable and geldanamycin causes PMR1 to rapidly disappear in a process that is catalyzed by the 26S proteasome. We present a model where Hsp90 interacts transiently to stabilize PMR1 in a manner similar to its interaction with c-Src, thus facilitating the tyrosine phosphorylation and targeting of PMR1 to polysomes.

17-Allylamino-17-demethoxygeldanamycin enhances the lethality of deoxycholic acid in primary rodent hepatocytes and established cell lines

Ansamycin antibiotics that target heat shock protein 90 function are being developed as anticancer agents but are also known to be dose limiting in patients due to hepatotoxicity. Herein, to better understand how the normal tissue toxicity of geldanamycins could be ameliorated to improve the therapeutic index of these agents, we examined the interactions of 17-allylamino-17-demethoxygeldanamycin (17AAG) and the secondary bile acid deoxycholic acid (DCA) in hepatocytes and fibroblasts. DCA and 17AAG interacted in a greater than additive fashion to cause hepatocyte cell death within 2 to 6 h of coadministration. As single agents DCA, but not 17AAG, enhanced the activity of extracellular signal-regulated kinase 1/2, AKT, c-Jun NH(2)-terminal kinase 1/2 (JNK1/2), and p38 mitogen-activated protein kinase (MAPK). Combined exposure of cells to DCA and 17AAG further enhanced JNK1/2 and p38 MAPK activity. Inhibition of JNK1/2 or p38 MAPK, but not activator protein-1, suppressed the lethality of 17AAG and of 17AAG and DCA. Constitutive activation of AKT, but not MAPK/extracellular signal-regulated kinase kinase 1/2, suppressed 17AAG- and DCA-induced cell killing and reduced activation of JNK1/2. DCA and 17AAG exposure promoted association of BAX with mitochondria, and functional inhibition of BAX or caspase-9, but not of BID and caspase-8, suppressed 17AAG and DCA lethality. DCA and 17AAG interacted in a greater than additive fashion to promote and prolong the generation of reactive oxygen species (ROS). ROS-quenching agents, inhibition of mitochondrial function, expression of dominant-negative thioredoxin reductase, or expression of dominant-negative apoptosis signaling kinase 1 suppressed JNK1/2 and p38 MAPK activation and reduced cell killing after 17AAG and DCA exposure. The potentiation of DCA-induced ROS production by 17AAG was abolished by Ca(2+) chelation and ROS generation, and cell killing following 17AAG and DCA treatment was abolished in cells lacking expression of PKR-like endoplasmic reticulum kinase. Thus, DCA and 17AAG interact to stimulate Ca(2+)-dependent and PKR-like endoplasmic reticulum kinase-dependent ROS production; high levels of ROS promote intense activation of the p38 MAPK and JNK1/2 pathways that signal to activate the intrinsic apoptosis pathway.

IPI-504, a novel and soluble HSP-90 inhibitor, blocks the unfolded protein response in multiple myeloma cells

BACKGROUND

Inhibitors of heat shock protein (Hsp) 90 induce apoptosis in multiple myeloma (MM) cells, but the molecular mechanisms underlying this cytotoxic outcome are not clear. Here, we investigate the effect of IPI-504, a novel and highly soluble inhibitor of the Hsp90 ATPase activity, on the unfolded protein response (UPR) in MM cells. The UPR is a stress response pathway triggered by sensors located at the endoplasmic reticulum (ER) membrane whose function is to reduce an excessive accumulation of misfolded protein in the ER. During normal development of B-lymphocytes to antibody-producing plasma cells, a partial UPR has been described, where IREalpha and ATF-6 are stimulated, whereas the third sensor, PERK, is not induced.

METHODS

Levels of the activated forms of the three main UPR sensors ATF-6, XBP-1 and PERK/eIF-2 were monitored in two different MM cells lines and one non-MM cell lines under various experimental conditions including incubation with increasing concentration of IPI-504. Also, MM cells were incubated with IPI-504 and several apoptosis markers were monitored.

RESULTS

We show here that a partial UPR is constitutively activated in plasma cell-derived MM cells and that IPI-504 can potently inhibit this pathway. IPI-504 achieves this by inactivating the transcription factors XBP1 and ATF6. In addition, IPI-504 also blocks the tunicamycin-induced phosphorylation of eIF2 by PERK. Dose-response and time course experiments reveal that IPI-504's inhibitory effect on the UPR parallels its cytotoxic and pro-apoptotic effects on MM cells.

CONCLUSION

The results presented here suggest that the IPI-504-induced apoptosis might be, in part, mediated by the inhibition of the partial UPR. Other malignancies that rely on intact and efficient UPR to survive could be considered as new indications for Hsp90 inhibitors.

Inhibition of Hsp90 attenuates inflammation in endotoxin-induced uveitis

Heat shock protein (Hsp) 90 inhibitors, such as 17-allylamino-17-demethoxy-geldanamycin (17-AAG), constitute promising novel therapeutic agents. We investigated the anti-inflammatory activity of 17-AAG in endotoxin-induced uveitis (EIU) in rats. After the induction of EIU with a footpad injection of lipopolysaccharide (LPS), female Lewis rats received a single intraperitoneal. (i.p.) injection of 17-AAG or vehicle. Twenty-four hours later, the retinas were extracted and assayed for leukocyte adhesion; blood-retinal barrier breakdown; VEGF, TNF-alpha, IL-1beta, and CD14 protein levels; NF-kappaB and HIF-1alpha activity; hsp90 and 70 levels and expression and phosphorylation of the tight junction proteins ZO-1 and occludin. 17-AAG treatment significantly suppressed the LPS-induced increase in retinal leukocyte adhesion; vascular leakage; NF-kappaB, HIF-1alpha, p38, and PI-3K activity; and VEGF, TNF-alpha, and IL-1beta levels. 17-AAG also suppressed phosphorylation of ZO-1 and occludin by inhibiting their association with p38 and PI-3K. Although 17-AAG treatment did not reduce the LPS-induced increase in total CD14 levels in leukocytes, it significantly decreased membrane CD14 levels. These data suggest that Hsp90 inhibition suppresses several cardinal manifestations of endotoxin-induced uveitis in the rat. 17-AAG has demonstrated a favorable safety profile in clinical trials in cancer patients and represents a promising therapeutic agent for the treatment of inflammatory eye diseases.

Endoplasmic Reticulum Vacuolization and Valosin-Containing Protein Relocalization Result from Simultaneous Hsp90 Inhibition by Geldanamycin and Proteasome Inhibition by Velcade

Geldanamycin and Velcade, new anticancer drugs with novel mechanisms of action, are currently undergoing extensive clinical trials. Geldanamycin interrupts Hsp90 chaperone activity and causes down-regulation of its many client proteins by the ubiquitin-proteasome pathway; Velcade is a specific proteasome inhibitor. Misfolded Hsp90 clients within the endoplasmic reticulum (ER) lumen are cleared by ER--associated protein degradation, a sequential process requiring valosin-containing protein (VCP)-dependent retrotranslocation followed by ubiquitination and proteasomal proteolysis. Cotreatment of cells with geldanamycin and Velcade prevents destruction of destabilized, ubiquitinated Hsp90 client proteins, causing them to accumulate. Here, we report that misfolded protein accumulation within the ER resulting from geldanamycin and Velcade exposure overwhelms the ability of the VCP--centered machine to maintain the ER secretory pathway, causing the ER to distend into conspicuous vacuoles. Overexpression of dominant-negative VCP or the "small VCP--interacting protein" exactly recapitulated the vacuolated phenotype provoked by the drugs, associating loss of VCP function with ER vacuolization. In cells transfected with a VCP--enhanced yellow fluorescent protein fluorescent construct, geldanamycin plus Velcade treatment redistributed VCP--enhanced yellow fluorescent protein from the cytoplasm and ER into perinuclear aggresomes. In further support of the view that compromise of VCP function is responsible for ER vacuolization, small interfering RNA interference of VCP expression induced ER vacuolization that was markedly increased by Velcade. VCP knockdown by small interfering RNA eventually deconstructed both the ER and Golgi and interdicted protein trafficking through the secretory pathway to the plasma membrane. Thus, simultaneous geldanamycin and Velcade treatment has far-reaching secondary cytotoxic consequences that likely contribute to the cytotoxic activity of this anticancer drug combination.

Bortezomib sensitizes pancreatic cancer cells to endoplasmic reticulum stress-mediated apoptosis

Bortezomib (PS-341, Velcade) is a potent and selective inhibitor of the proteasome that is currently under investigation for the treatment of solid malignancies. We have shown previously that bortezomib has activity in pancreatic cancer models and that the drug induces endoplasmic reticulum (ER) stress but also suppresses the unfolded protein response (UPR). Because the UPR is an important cytoprotective mechanism, we hypothesized that bortezomib would sensitize pancreatic cancer cells to ER stress-mediated apoptosis. Here, we show that bortezomib promotes apoptosis triggered by classic ER stress inducers (tunicamycin and thapsigargin) via a c-Jun NH(2)-terminal kinase (JNK)-dependent mechanism. We also show that cisplatin stimulates ER stress and interacts with bortezomib to increase ER dilation, intracellular Ca(2+) levels, and cell death. Importantly, combined therapy with bortezomib plus cisplatin induced JNK activation and apoptosis in orthotopic pancreatic tumors resulting in a reduction in tumor burden. Taken together, our data establish that bortezomib sensitizes pancreatic cancer cells to ER stress-induced apoptosis and show that bortezomib strongly enhances the anticancer activity of cisplatin.

Pharmacological modulation of the heat shock response

Life presents a continuous series of stresses. Increasing the adaptation capacity of the organism is a long-term survival factor of various organisms and has become an attractive field of intensive therapeutic research. Induction of the heat shock response promotes survival after a wide variety of environmental stresses. Preclinical studies have proven that physiological and pharmacological chaperone inducers and co-inducers are an efficient therapeutic approach in different acute and chronic diseases. In this chapter, we summarize current knowledge of the current state of chaperone modulation and give a comprehensive list of the main drug candidates.

Interaction of Hsp90 with ribosomal proteins protects from ubiquitination and proteasome-dependent degradation

Heat-shock protein 90 (Hsp90) is a molecular chaperone that plays a key role in the conformational maturation of various transcription factors and protein kinases in signal transduction. Multifunctional ribosomal protein S3 (rpS3), a component of the ribosomal small subunit, is involved in DNA repair and apoptosis. Our data show that Hsp90 binds directly to rpS3 and the functional consequence of Hsp90-rpS3 interaction results in the prevention of the ubiquitination and the proteasome-dependent degradation of rpS3, subsequently retaining the function and the biogenesis of the ribosome. Interference of Hsp90 activity by Hsp90 inhibitors appears to dissociate rpS3 from Hsp90, associate the protein with Hsp70, and induce the degradation of free forms of rpS3. Furthermore, ribosomal protein S6 (rpS6) also interacted with Hsp90 and exhibited a similar effect upon treatment with Hsp90 inhibitors. Therefore, we conclude that Hsp90 regulates the function of ribosomes by maintaining the stability of 40S ribosomal proteins such as rpS3 and rpS6.

Phase I trial of 17-allylamino-17-demethoxygeldanamycin in patients with advanced cancer

PURPOSE

We determined the maximum-tolerated dose (MTD) and the dose-limiting toxicities (DLT) of 17-allylamino-17-demethoxygeldanamycin (17-AAG) when infused on days 1, 8, and 15 of a 28-day cycle in advanced solid tumor patients. We also characterized the pharmacokinetics of 17-AAG, its effect on chaperone and client proteins, and whether cytochrome P450 (CYP) 3A5 and NAD(P)H:quinone oxidoreductase 1 (NQO1) polymorphisms affected 17-AAG disposition or toxicity.

PATIENTS AND METHODS

An accelerated titration design was used. Biomarkers were measured in peripheral-blood mononuclear cells (PBMCs) at baseline and on days 1 and 15, and pharmacokinetic analysis was performed on day 1 of cycle 1. CYP3A5*3 and NQO1*2 genotypes were determined and correlated with pharmacokinetics and toxicity.

RESULTS

Twenty-one patients received 52 courses at 11 dose levels. DLTs at 431 mg/m(2) were grade 3 bilirubin (n = 1), AST (n = 1), anemia (n = 1), nausea (n = 1), vomiting (n = 1), and myalgias (n = 1). No tumor responses were seen. 17-AAG consistently increased heat shock protein (Hsp) 70 levels in PBMCs. At the MTD, the clearance and half-life (t(1/2)) of 17-AAG were 11.6 L/h/m(2) and 4.15 hours, respectively; whereas the active metabolite 17-aminogeldanamycin had a t(1/2) of 7.63 hours. The CYP3A5*3 and NQO1*2 polymorphisms were not associated with 17-AAG toxicity. The CYP3A5*3 polymorphism was associated with higher 17-AAG clearance.

CONCLUSION

The MTD of weekly 17-AAG is 308 mg/m(2). 17-AAG induced Hsp70 in PBMCs, indicating that Hsp90 has been affected. Further evaluation of 17-AAG is ongoing using a twice-weekly regimen, and this schedule of 17-AAG is being tested in combination with chemotherapy.

Distinct but overlapping functions of Hsp70, Hsp90, and an Hsp70 nucleotide exchange factor during protein biogenesis in yeast

Hsp70 and Hsp90 molecular chaperones play essential roles in protein expression and maturation, and while catalyzing protein folding they can "decide" to target mis-folded substrates for degradation. In this report, we show for the first time distinct but partially overlapping requirements for Hsp90, Hsp70, and an Hsp70 nucleotide exchange factor (NEF) at different steps during the biogenesis of a model substrate, firefly luciferase (FFLux), in yeast. By examining the inducible expression of FFLux in wild type cells and in specific yeast mutants, we find that the Fes1p NEF is required for efficient FFLux folding, whereas the Hsp70, Ssa1p, is required for both protein folding and stability, and to maintain maximal FFLux mRNA levels. In contrast, Hsp90 function was primarily necessary to express the FFLux-encoding gene from an inducible promoter. Together, these data indicate previously unknown roles for these proteins and point to the complexity with which chaperones and cochaperones function in the cell.

ERdj3, a stress-inducible endoplasmic reticulum DnaJ homologue, serves as a cofactor for BiP's interactions with unfolded substrates

We recently identified ERdj3 as a component of unassembled immunoglobulin (Ig) heavy chain:BiP complexes. ERdj3 also associates with a number of other protein substrates, including unfolded light chains, a nonsecreted Ig light chain mutant, and the VSV-G ts045 mutant at the nonpermissive temperature. We produced an ERdj3 mutant that was unable to stimulate BiP's ATPase activity in vitro or to bind BiP in vivo. This mutant retained the ability to interact with unfolded protein substrates, suggesting that ERdj3 binds directly to proteins instead of via interactions with BiP. BiP remained bound to unfolded light chains longer than ERdj3, which interacted with unfolded light chains initially, but quickly disassociated before protein folding was completed. This suggests that ERdj3 may bind first to substrates and serve to inhibit protein aggregation until BiP joins the complex, whereas BiP remains bound until folding is complete. Moreover, our findings support a model where interactions with BiP help trigger the release of ERdj3 from the substrate:BiP complex.

Characterization of a novel interaction between the secretory Na+-K+-Cl- cotransporter and the chaperone hsp90

The first isoform of the Na(+)-K(+)-Cl(-) cotransporter (NKCC1) is of central importance for the control of cellular ion concentration and epithelium-mediated salt secretion. Several studies have established that a change in intracellular [Cl(-)] (Cl(-)(i)) represents a key signaling mechanism by which NKCC1-induced Cl(-) movement is autoregulated and by which Cl(-) entry and exit on opposite sides of polarized cells are coordinated. Although this signaling mechanism is coupled to a pathway that leads to post-translational modification of the carrier, no unifying model currently accounts for the ion dependence of NKCC1 regulation. In this paper, evidence is presented for the first time that hsp90 associates with the cytosolic C terminus of NKCC1, probably when the carrier is predominantly in its unfolded form during early biogenesis. Evidence is also presented that the Cl(-)(i)-dependent regulatory pathway can be activated by a thermal stress but that it is no longer operational if NKCC1-expressing cells are pretreated with geldanamycin, an antibiotic that inhibits hsp90, albeit nonspecifically. Taken together, our data indicate that binding of hsp90 to NKCC1 may be required for Na(+)-K(+)-Cl(-) cotransport to occur at the cell surface and that it could play an important role in ion-dependent signaling mechanisms, insofar as the maneuvers that were used to alter the expression or activity of the chaperone do not exert their main effect by inducing other cellular events such as the unfolded protein response. Further studies will be required to elucidate the functional relevance of this novel interaction.

Distinct roles for the Hsp40 and Hsp90 molecular chaperones during cystic fibrosis transmembrane conductance regulator degradation in yeast

Aberrant secreted proteins can be destroyed by ER-associated protein degradation (ERAD), and a prominent, medically relevant ERAD substrate is the cystic fibrosis transmembrane conductance regulator (CFTR). To better define the chaperone requirements during CFTR maturation, the protein was expressed in yeast. Because Hsp70 function impacts CFTR biogenesis in yeast and mammals, we first sought ER-associated Hsp40 cochaperones involved in CFTR maturation. Ydj1p and Hlj1p enhanced Hsp70 ATP hydrolysis but CFTR degradation was slowed only in yeast mutated for both YDJ1 and HLJ1, suggesting functional redundancy. In contrast, CFTR degradation was accelerated in an Hsp90 mutant strain, suggesting that Hsp90 preserves CFTR in a folded state, and consistent with this hypothesis, Hsp90 maintained the solubility of an aggregation-prone domain (NBD1) in CFTR. Soluble ERAD substrate degradation was unaffected in the Hsp90 or the Ydj1p/Hlj1p mutants, and surprisingly CFTR degradation was unaffected in yeast mutated for Hsp90 cochaperones. These results indicate that Hsp90, but not the Hsp90 complex, maintains CFTR structural integrity, whereas Ydj1p/Hlj1p catalyze CFTR degradation.