Downstream caspases are novel targets for the antiapoptotic activity of the molecular chaperone hsp70

Induction of Chaperone Synthesis in Human Neuronal Cells Blocks Oxidative Stress-Induced Aging

Oxidative stress accompanies many pathologies that are characterized by neuronal degradation leading to a deterioration of the disease. The main causes are the disruption of protein homeostasis and activation of irreversible processes of cell cycle disruption and deterioration of cellular physiology, leading to senescence. In this paper, we propose a new approach to combating senescence caused by oxidative stress. This approach is based on the use of a low-molecular inducer of chaperone synthesis, one of the cell protective systems regulating proteostasis and apoptosis. We present data demonstrating the ability of the pyrrolylazine derivative PQ-29 to induce chaperone accumulation in human neuronal cells and prevent oxidative stress-induced aging.

Hsp70 Negatively Regulates Autophagy via Governing AMPK Activation, and Dual Hsp70-Autophagy Inhibition Induces Synergetic Cell Death in NSCLC Cells

Proteostasis mechanisms, such as proteotoxic-stress response and autophagy, are increasingly recognized for their roles in influencing various cancer hallmarks such as tumorigenesis, drug resistance, and recurrence. However, the precise mechanisms underlying their coordination remain not fully elucidated. The aim of this study is to investigate the molecular interplay between Hsp70 and autophagy in lung adenocarcinoma cells and elucidate its impact on the outcomes of anticancer therapies in vitro. For this purpose, we utilized the human lung adenocarcinoma A549 cell line and genetically modified it by knockdown of Hsp70 or HSF1, and the H1299 cell line with knockdown or overexpression of Hsp70. In addition, several treatments were employed, including treatment with Hsp70 inhibitors (VER-155008 and JG-98), HSF1 activator ML-346, or autophagy modulators (SAR405 and Rapamycin). Using immunoblotting, we found that Hsp70 negatively regulates autophagy by directly influencing AMPK activation, uncovering a novel regulatory mechanism of autophagy by Hsp70. Genetic or chemical Hsp70 overexpression was associated with the suppression of AMPK and autophagy. Conversely, the inhibition of Hsp70, genetically or chemically, resulted in the upregulation of AMPK-mediated autophagy. We further investigated whether Hsp70 suppression-mediated autophagy exhibits pro-survival- or pro-death-inducing effects via MTT test, colony formation, CellTiter-Glo 3D-Spheroid viability assay, and Annexin/PI apoptosis assay. Our results show that combined inhibition of Hsp70 and autophagy, along with cisplatin treatment, synergistically reduces tumor cell metabolic activity, growth, and viability in 2D and 3D tumor cell models. These cytotoxic effects were exerted by substantially potentiating apoptosis, while activating autophagy via rapamycin slightly rescued tumor cells from apoptosis. Therefore, our findings demonstrate that the combined inhibition of Hsp70 and autophagy represents a novel and promising therapeutic approach that may disrupt the capacity of refractory tumor cells to withstand conventional therapies in NSCLC.

Exogenous Hsp70 exerts neuroprotective effects in peripheral nerve rupture model

Hsp70 is the main molecular chaperone responsible for cellular proteostasis under normal conditions and for restoring the conformation or utilization of proteins damaged by stress. Increased expression of endogenous Hsp70 or administration of exogenous Hsp70 is known to exert neuroprotective effects in models of many neurodegenerative diseases. In this study, we have investigated the effect of exogenous Hsp70 on recovery from peripheral nerve injury in a model of sciatic nerve transection in rats. It was shown that recombinant Hsp70 after being added to the conduit connecting the ends of the nerve at the site of its extended severance, migrates along the nerve into the spinal ganglion and is retained there at least three days. In animals with the addition of recombinant Hsp70 to the conduit, a decrease in apoptosis in the spinal ganglion cells after nerve rupture, an increase in the level of PTEN-induced kinase 1 (PINK1), an increase in markers of nerve tissue regeneration and a decrease in functional deficit were observed compared to control animals. The obtained data indicate the possibility of using recombinant Hsp70 preparations to accelerate the recovery of patients after neurotrauma.

Autocrine regulation of tumor cell repopulation by Hsp70-HMGB1 alarmin complex

BACKGROUND

Cancer recurrence is regulated by a variety of factors, among which is the material of dying tumor cells; it is suggested that remaining after anti-cancer therapy tumor cells receive a signal from proteins called damage-associated molecular patterns (DAMPs), one of which is heat shock protein 70 (Hsp70).

METHODS

Two models of tumor repopulation were employed, based on minimal population of cancer cells and application of conditioned medium (CM). To deplete the CMs of Hsp70 affinity chromatography on ATP-agarose and immunoprecipitation were used. Cell proliferation and the dynamics of cell growth were measured using MTT assay and xCELLigence technology; cell growth markers were estimated using qPCR and with the aid of ELISA for prostaglandin E detection. Immunoprecipitation followed by mass-spectrometry was employed to identify Hsp70-binding proteins and protein-protein interaction assays were developed to reveal the above protein complexes.

RESULTS

It was found that CM of dying tumor cells contains tumor regrowth-initiating factors and the removal of one of them, Hsp70, caused a reduction in the relapse-activating capacity. The pull out of Hsp70 alone using ATP-agarose had no effect on repopulation, while the immunodepletion of Hsp70 dramatically reduced its repopulation activity. Using proteomic and immunochemical approaches, we showed that Hsp70 in conditioned medium binds and binds another abundant alarmin, the High Mobility Group B1 (HMGB1) protein; the complex is formed in tumor cells treated with anti-cancer drugs, persists in the cytosol and is further released from dying tumor cells. Recurrence-activating power of Hsp70-HMGB1 complex was proved by the enhanced expression of proliferation markers, Ki67, Aurka and MCM-10 as well as by increase of prostaglandin E production and autophagy activation. Accordingly, dissociating the complex with Hsp70 chaperone inhibitors significantly inhibited the pro-growth effects of the above complex, in both in vitro and in vivo tumor relapse models.

CONCLUSIONS

These data led us to suggest that the abundance of the Hsp70-HMGB1 complex in the extracellular matrix may serve as a novel marker of relapse state in cancer patients, while specific targeting of the complex may be promising in the treatment of cancers with a high risk of recurrence.

Anti-HSP70 alleviates cell migration and proliferation in colorectal cancer cells (CRC) by targeting CXCR4 (in vitro study)

Colorectal cancer (CRC), the third most common cancer in men and women, accounts for 8% of new cancer cases in the US and 8 to 9% of the nation's anticipated cancer mortality in 2014. In the pathophysiology of colon cancer, heat shock protein 70 (HSP70) and CXCR4 are essential. In this research, we concentrated on the connection between CXCR4 expression and HSP70 inhibitor activity in the development of colorectal cancer. The HSP70 inhibitor's effect on cell proliferation was also evaluated. Samples were obtained from patients with CRC; the surrounding marginal tissues were considered healthy. The One CRC cell lines (HCA-7) were divided into two groups based on untreated and treated with anti-HSP70. HSP70 and CXCR4 mRNA expression and migration (Wound healing assay) were measured in these groups. Also, we evaluated the expression levels of HSP70 and CXCR4 in thirty CRC and healthy non-cancerous samples (Using Real-time PCR and Western Blotting). Moreover, we examined the viability of CRC cells in untreated and treated groups with anti-HSP70. Higher expression levels of CXCR4 (p < 0.0001) and HSP70 (p = 0.002) mRNA were observed in patients who had CRC. In contrast, lower mRNA expressions of HSP70 (p < 0.0001) and CXCR4 (P < 0.0001) were detected in the CRC cell line (HCA-7) after being treated with anti-HSP70. Moreover, the viability and migration of cancer cells were remarkably reduced in CRC cells treated with anti-HSP70. Our study's innovation was the in vitro demonstration of inhibiting HSP70 in the CRC cancer cell line drastically reduced CXCR4 expression, viability, and cancer cell migration. These findings may pave the way for additional studies on CRC cancer treatment and be examined in vivo in studies, given that the primary goal of therapy is to decrease the viability and spread of cancer cells.

Investigation into the communication between unheated and heat-stressed Caenorhabditis elegans via volatile stress signals

Our research group has recently found that radiation-induced airborne stress signals can be used for communication among Caenorhabditis elegans (C. elegans). This paper addresses the question of whether heat stress can also induce the emission of airborne stress signals to alert neighboring C. elegans and elicit their subsequent stress response. Here, we report that heat-stressed C. elegans produces volatile stress signals that trigger an increase in radiation resistance in neighboring unheated C. elegans. When several loss-of-function mutations affecting thermosensory neuron (AFD), heat shock factor-1, HSP-4, and small heat-shock proteins were used to test heat-stressed C. elegans, we found that the production of volatile stress signals was blocked, demonstrating that the heat shock response and ER pathway are involved in controlling the production of volatile stress signals. Our data further indicated that mutations affecting the DNA damage response (DDR) also inhibited the increase in radiation resistance in neighboring unheated C. elegans that might have received volatile stress signals, indicating that the DDR might contribute to radioadaptive responses induction by volatile stress signals. In addition, the regulatory pattern of signal production and action was preliminarily clarified. Together, the results of this study demonstrated that heat-stressed nematodes communicate with unheated nematodes via volatile stress signals.

Ozone protects cardiomyocytes against ischemia/reperfusion injury: Regulating the heat shock protein 70 (HPS70) expression through activating the JAK2/STAT3 Pathway

Ischemia/reperfusion (I/R) injury causes complications in early coronary artery reperfusion for acute myocardial infarction (AMI). Ozone (O₃) has been reported to be applied for protecting I/R injury, but its detailed mechanism remains unclear. Our study focused on the protective effect of O₃ pretreatment on myocardial I/R injury and JAK2/STAT3 signaling and HSP70 regulation involving in the mediation. The rat hearts which were perfused and isolated as well as the cultured cardiomyocytes of neonatal rat were exposed to hypoxia/reoxygenation (H/R) and different concentrations of O₃ followed by heat shock protein 70 (HSP70) siRNA treatment. The results showed O₃ attenuated the suppression of cell viability induced by H/R and decreased the release of activity of creatine kinase (CK), lactate dehydrogenase (LDH) and apoptosis of cardiomyocytes in vitro. Moreover, O₃ also activated the JAK2/STAT3 signaling, upregulated the expression of HSP70 both in vitro and vivo, and decreased the index of apoptosis of cardiomyocytes caused by I/R as well as myocardial infarct area in vivo. In addition, HSP70 siRNA and JAK2 inhibitor AG490 inhibited the cardioprotective effect of O₃. And the expression of HSP70 increased by ozone was reduced by AG-490. In conclusion, our results demonstrated that ozone protects cardiomyocytes in I/R injury through regulation of the expression of HSP70 by activating the JAK2/STAT3 pathway.

Prevention of High Glucose-Mediated EMT by Inhibition of Hsp70 Chaperone

Hyperglycemia may contribute to the progression of carcinomas by triggering epithelial-to-mesenchymal transition (EMT). Some proteostasis systems are involved in metastasis; in this paper, we sought to explore the mechanism of Hsp70 chaperone in EMT. We showed that knockdown of Hsp70 reduced cell migration capacity concomitantly with levels of mRNA of the Slug, Snail, and Twist markers of EMT, in colon cancer cells incubated in high glucose medium. Conversely, treatment of cells with Hsp70 inducer U-133 were found to elevate cell motility, along with the other EMT markers. To prove that inhibiting Hsp70 may reduce EMT efficiency, we treated cells with a CL-43 inhibitor of the HSF1 transcription factor, which lowered Hsp70 and HSF1 content in the control and induced EMT in carcinoma cells. Importantly, CL-43 reduced migration capacity, EMT-linked transcription factors, and increased content of epithelial marker E-cadherin in colon cancer cells of three lines, including one derived from a clinical sample. To prove that Hsp70 chaperone should be targeted when inhibiting the EMT pathway, we treated cancer cells with 2-phenylethynesulfonamide (PES) and demonstrated that the compound inhibited substrate-binding capacity of Hsp70. Furthermore, PES suppressed EMT features, cell motility, and expression of specific transcription factors. In conclusion, the Hsp70 chaperone machine efficiently protects mechanisms of the EMT, and the safe inhibitors of the chaperone are needed to hamper metastasis at its initial stage.

Inhibition of the Human Hsc70 System by Small Ligands as a Potential Anticancer Approach

Simple Summary

High levels of Heat shock proteins (Hsps) in specific cancers are usually linked to a poor prognosis, tumor progression, invasiveness, and resistance to treatment. Chaperone inhibition could therefore be toxic for cancer cells due to their high dependence on chaperone activity to survive. This study shows the potential to repurpose the small chemical compound pinaverium bromide, currently used to treat functional gastrointestinal disorders, as a possible antitumor drug since it displays a marked toxicity against two melanoma cell lines without affecting the viability of fibroblast and primary melanocytes. This compound interacts with structural regions shared by representatives of the Hsp70 and Hsp110 families, inhibiting the substrate remodeling ability of the Hsp70 system in vitro and in a cellular context.

Abstract

Heat shock protein (Hsp) synthesis is upregulated in a wide range of cancers to provide the appropriate environment for tumor progression. The Hsp110 and Hsp70 families have been associated to cancer cell survival and resistance to chemotherapy. In this study, we explore the strategy of drug repurposing to find new Hsp70 and Hsp110 inhibitors that display toxicity against melanoma cancer cells. We found that the hits discovered using Apg2, a human representative of the Hsp110 family, as the initial target bind also to structural regions present in members of the Hsp70 family, and therefore inhibit the remodeling activity of the Hsp70 system. One of these compounds, the spasmolytic agent pinaverium bromide used for functional gastrointestinal disorders, inhibits the intracellular chaperone activity of the Hsp70 system and elicits its cytotoxic activity specifically in two melanoma cell lines by activating apoptosis. Docking and molecular dynamics simulations indicate that this compound interacts with regions located in the nucleotide-binding domain and the linker of the chaperones, modulating their ATPase activity. Thus, repurposing of pinaverium bromide for cancer treatment appears as a promising novel therapeutic approach.

Synthesis and approbation of new neuroprotective chemicals of pyrrolyl- and indolylazine classes in a cell model of Alzheimer's disease

One of the major causes of neurodegeneration in the pathogenesis of Alzheimer's disease is the accumulation of cytotoxic amyloid species within the intercellular compartments of the brain. The efficacy of the anti-proteotoxic mechanism based on the molecular chaperones Hsp70 and Hsp90 in numerous types of neurons is often low, while its pharmacological enhancement has been shown to ameliorate the physiological and cognitive functions of the brain. Suggesting that the chemicals able to induce heat shock protein synthesis and therefore rescue neural cells from cytotoxicity associated with amyloid, we have synthesized a group of pyrrolyl- and indolylazines that cause the accumulation of heat shock proteins, using a novel method of photocatalysis that is employed in green chemistry. The selected compounds were tested in a cell model of Alzheimer's disease and demonstrated a pronounced neuroprotective effect. These substances increased the survival of neurons, blocked the activation of β-galactosidase, and prevented apoptosis in neurons cultured in the presence of β-amyloid.

Ethanol Enhances Hyperthermia-Induced Cell Death in Human Leukemia Cells

Ethanol has been shown to exhibit therapeutic properties as an ablative agent alone and in combination with thermal ablation. Ethanol may also increase sensitivity of cancer cells to certain physical and chemical antitumoral agents. The aim of our study was to assess the potential influence of nontoxic concentrations of ethanol on hyperthermia therapy, an antitumoral modality that is continuously growing and that can be combined with classical chemotherapy and radiotherapy to improve their efficiency. Human leukemia cells were included as a model in the study. The results indicated that ethanol augments the cytotoxicity of hyperthermia against U937 and HL60 cells. The therapeutic benefit of the hyperthermia/ethanol combination was associated with an increase in the percentage of apoptotic cells and activation of caspases-3, -8 and -9. Apoptosis triggered either by hyperthermia or hyperthermia/ethanol was almost completely abolished by a caspase-8 specific inhibitor, indicating that this caspase plays a main role in both conditions. The role of caspase-9 in hyperthermia treated cells acquired significance whether ethanol was present during hyperthermia since the alcohol enhanced Bid cleavage, translocation of Bax from cytosol to mitochondria, release of mitochondrial apoptogenic factors, and decreased of the levels of the anti-apoptotic factor myeloid cell leukemia-1 (Mcl-1). The enhancement effect of ethanol on hyperthermia-activated cell death was associated with a reduction in the expression of HSP70, a protein known to interfere in the activation of apoptosis at different stages. Collectively, our findings suggest that ethanol could be useful as an adjuvant in hyperthermia therapy for cancer.

Bcl-2 Associated Athanogene 2 (BAG2) is Associated With Progression and Prognosis of Hepatocellular Carcinoma: A Bioinformatics-Based Analysis

Background: Bcl-2 associated athanogene2 (BAG2) is reported to act as an oncogene or a tumor-suppressor in tumors in a context-dependent way; however, its function in hepatocellular carcinoma (HCC) remains unclear.

Methods: Immunohistochemistry (IHC) staining, cell counting kit-8 (CCK-8) assay, apoptotic assay, cell invasion assay and a set of bioinformatics tools were integrated to analyze the role of BAG2 in hepatocellular carcinoma.

Results: BAG2 was significantly up-regulated in HCC. Prognostic analysis indicated that HCC patients with high expression of BAG2 had significantly shorter overall survival, progression free survival and disease specific survival. Besides, silencing BAG2 in HCC cells impaired cell proliferation, facilitated apoptosis and repressed invasion of the cells. Bioinformatics analysis showed that BAG2 might regulate ribosome biogenesis in HCC.

Conclusion: This study revealed that the up-regulated BAG2 in HCC was associated with a worse prognosis and might favor the progression of the disease.

Delivery of functional exogenous proteins by plant-derived vesicles to human cells in vitro

Plant-derived extracellular vesicles (EVs) gain more and more attention as promising carriers of exogenous bioactive molecules to the human cells. Derived from various edible sources, these EVs are remarkably biocompatible, biodegradable and highly abundant from plants. In this work, EVs from grapefruit juice were isolated by differential centrifugation followed by characterization of their size, quantity and morphology by nanoparticle tracking analysis, dynamic light scattering, atomic force microscopy and cryo-electron microscopy (Cryo-EM). In Cryo-EM experiments, we visualized grapefruit EVs with the average size of 41 ± 13 nm, confirmed their round-shaped morphology and estimated the thickness of their lipid bilayer as 5.3 ± 0.8 nm. Further, using cell culture models, we have successfully demonstrated that native grapefruit-derived extracellular vesicles (GF-EVs) are highly efficient carriers for the delivery of the exogenous Alexa Fluor 647 labeled bovine serum albumin (BSA) and heat shock protein 70 (HSP70) into both human peripheral blood mononuclear cells and colon cancer cells. Interestingly, loading to plant EVs significantly ameliorated the uptake of exogenous proteins by human cells compared to the same proteins without EVs. Most importantly, we have confirmed the functional activity of human recombinant HSP70 in the colon cancer cell culture upon delivery by GF-EVs. Analysis of the biodistribution of GF-EVs loaded with 125I-labeled BSA in mice demonstrated a significant uptake of the grapefruit-derived extracellular vesicles by the majority of organs. The results of our study indicate that native plant EVs might be safe and effective carriers of exogenous proteins into human cells.

Disruption of the Complex between GAPDH and Hsp70 Sensitizes C6 Glioblastoma Cells to Hypoxic Stress

Hypoxia, which commonly accompanies tumor growth, depending on its strength may cause the enhancement of tumorigenicity of cancer cells or their death. One of the proteins targeted by hypoxia is glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and we demonstrated here that hypoxia mimicked by treating C6 rat glioblastoma cells with cobalt chloride caused an up-regulation of the enzyme expression, while further elevation of hypoxic stress caused the enzyme aggregation concomitantly with cell death. Reduction or elevation of GAPDH performed with the aid of specific shRNAs resulted in the augmentation of the tumorigenicity of C6 cells or their sensitization to hypoxic stress. Another hypoxia-regulated protein, Hsp70 chaperone, was shown to prevent the aggregation of oxidized GAPDH and to reduce hypoxia-mediated cell death. In order to release the enzyme molecules from the chaperone, we employed its inhibitor, derivative of colchicine. The compound was found to substantially increase aggregation of GAPDH and to sensitize C6 cells to hypoxia both in vitro and in animals bearing tumors with distinct levels of the enzyme expression. In conclusion, blocking the chaperonic activity of Hsp70 and its interaction with GAPDH may become a promising strategy to overcome tumor resistance to multiple environmental stresses and enhance existing therapeutic tools.

Biopesticide emamectin benzoate in the liver of male mice: evaluation of oxidative toxicity with stress protein, DNA oxidation, and apoptosis biomarkers

Emamectin benzoate (EMB), which is used as a pesticide in agriculture, household, and veterinary medicine, can cause tissue damage with oxidative toxicity and can be considered as inducing apoptosis. In the present study, male mice were conducted by oral administration in EMB doses 25, 50, and 100 (mg/kg/day) for 14 days. Glutathione (GSH) and thiobarbituric acid reactive substance (TBARS) levels using spectrophotometric methods were measured. 8-hydroxy-2'-deoxyguanosine (8-OHdG) which is DNA oxidation biomarker and, stress protein (HSP70) levels, caspase 3 enzyme activities were measured by ELISA techniques. This study shows that in vivo administration of EMB caused a marked induction of oxidative damage in liver tissue as demonstrated by an increased level of TBARS and reduced GSH level. The increase in HSP70 level did not prevent the apoptosis caused by the increase of caspase 3 enzyme activity. Toxicity caused by EMB also showed the formation of genotoxicity with an increase in DNA oxidation biomarker 8-OHdG levels. As a result of the study, the effects of toxicity caused by EMB on lipid; protein; and DNA, structural macromolecules in cells, and the importance of enzymatic and non-enzymatic bonds of the cell's protective systems were determined. Consequently, under experimental conditions, EMB exposure caused toxicity in the liver of male mice, and significant adverse effects were determined with biomarkers.

Pyrrolylquinoxaline-2-One Derivative as a Potent Therapeutic Factor for Brain Trauma Rehabilitation

Traumatic brain injury (TBI) often causes massive brain cell death accompanied by the accumulation of toxic factors in interstitial and cerebrospinal fluids. The persistence of the damaged brain area is not transient and may occur within days and weeks. Chaperone Hsp70 is known for its cytoprotective and antiapoptotic activity, and thus, a therapeutic approach based on chemically induced Hsp70 expression may become a promising approach to lower post-traumatic complications. To simulate the processes of secondary damage, we used an animal model of TBI and a cell model based on the cultivation of target cells in the presence of cerebrospinal fluid (CSF) from injured rats. Here we present a novel low molecular weight substance, PQ-29, which induces the synthesis of Hsp70 and empowers the resistance of rat C6 glioma cells to the cytotoxic effect of rat cerebrospinal fluid taken from rats subjected to TBI. In an animal model of TBI, PQ-29 elevated the Hsp70 level in brain cells and significantly slowed the process of the apoptosis in acceptor cells in response to cerebrospinal fluid action. The compound was also shown to rescue the motor function of traumatized rats, thus proving its potential application in rehabilitation therapy after TBI.

A 12-mer Peptide of Tag7 (PGLYRP1) Forms a Cytotoxic Complex with Hsp70 and Inhibits TNF-Alpha Induced Cell Death

Investigation of interactions between a pro-inflammatory cytokine tumor necrosis factor (TNFα) and its receptor is required for the development of new treatments for autoimmune diseases associated with the adverse effects of TNFα. Earlier, we demonstrated that the innate immunity protein Tag7 (PGRP-S, PGLYRP1) can interact with the TNFα receptor, TNFR1, and block the transduction of apoptotic signals through this receptor. A complex formed between the Tag7 protein and the major heat shock protein Hsp70 can activate TNFR1 receptor and induce tumor cell death via either apoptotic or necroptotic pathway. In this study, we show that a 12-mer peptide, designated 17.1, which was derived from the Tag7 protein, can be regarded as a novel TNFα inhibitor, also is able to form a cytotoxic complex with the heat shock protein Hsp70. This finding demonstrates a new role for Hsp70 protein in the immune response. Also, this new inhibitory 17.1 peptide demonstrates an anti-inflammatory activity in the complete Freund's adjuvant (CFA)-induced autoimmune arthritis model in laboratory mice. It appears that the 17.1 peptide could potentially be used as an anti-inflammatory agent.

Combination of Anti-Cancer Drugs with Molecular Chaperone Inhibitors

Most molecular chaperones belonging to heat shock protein (HSP) families are known to protect cancer cells from pathologic, environmental and pharmacological stress factors and thereby can hamper anti-cancer therapies. In this review, we present data on inhibitors of the heat shock response (particularly mediated by the chaperones HSP90, HSP70, and HSP27) either as a single treatment or in combination with currently available anti-cancer therapeutic approaches. An overview of the current literature reveals that the co-administration of chaperone inhibitors and targeting drugs results in proteotoxic stress and violates the tumor cell physiology. An optimal drug combination should simultaneously target cytoprotective mechanisms and trigger the imbalance of the tumor cell physiology.

Therapeutic potency of heat-shock protein-70 in the pathogenesis of colorectal cancer: current status and perspectives

Heat-shock protein-70 (HSP70) is critical to the folding, stability, and activity of several client proteins including many responsible for cancer cell proliferation, apoptosis, drug toxicity, and metastasis. Up-regulation of HSP70 is positively associated with increased tumorigenicity as well as poor survival in colon cancer patients, supporting the diagnostic, prognostic, and therapeutic potencies of HSP70 in colorectal cancer. The administration of specific pharmacological inhibitors or gene knock-down for HSP70 suppresses tumor progression and enhances tumor cell chemosensitivity. This review summarizes the different tumorigenic properties of HSP70 and the potential therapeutic potency of HSP70 inhibitors in terms of a novel strategy for colorectal cancer therapy, for a better understanding, and hence better management of this disease.

Etoposide-Induced Apoptosis in Cancer Cells Can Be Reinforced by an Uncoupled Link between Hsp70 and Caspase-3

The Hsp70 chaperone binds and inhibits proteins implicated in apoptotic signaling including Caspase-3. Induction of apoptosis is an important mechanism of anti-cancer drugs, therefore Hsp70 can act as a protective system in tumor cells against therapeutic agents. In this study we present an assessment of candidate compounds that are able to dissociate the complex of Hsp70 with Caspase-3, and thus sensitize cells to drug-induced apoptosis. Using the PASS program for prediction of biological activity we selected a derivative of benzodioxol (BT44) that is known to affect molecular chaperones and caspases. Drug affinity responsive target stability and microscale thermophoresis assays indicated that BT44 bound to Hsp70 and reduced the chaperone activity. When etoposide was administered, heat shock accompanied with an accumulation of Hsp70 led to an inhibition of etoposide-induced apoptosis. The number of apoptotic cells increased following BT44 administration, and forced Caspase-3 processing. Competitive protein–protein interaction and immunoprecipitation assays showed that BT44 caused dissociation of the Hsp70–Caspase-3 complex, thus augmenting the anti-tumor activity of etoposide and highlighting the potential role of molecular separators in cancer therapy.

Molecular Chaperone Hsp70 and Its Constitutively Active Form Hsc70 Play an Indispensable Role During Eye Development of Drosophila melanogaster

In the present study, we demonstrate that molecular chaperone Hsp70 and Hsc70 is essential for normal organization and development of ommatidial cells in Drosophila melanogaster eye. An exogenously expressed dominant negative mutant of Hsp70 (K71E) and Hsc70.4 (K71S and D206S) in an eye-specific manner resulted in eye degeneration that includes loss of eye pigment, disorganized ommatidia, abnormality in bristle cell arrangement and reduction in the eye size. The developmental organization of ommatidial cells (cone, photoreceptor, pigment, and bristle cell complex) was disturbed in Hsp70 and Hsc70 mutants. Acridine orange (AO) and caspase 3 staining showed an increased cell death in Hsp70 and Hsc70 mutant eyes. Genetic interaction study of Hsp70 and Hsc70 mutants with candidate genes of JNK signaling pathway and immunocytochemistry study using phospho-JNK antibody suggested that mutation in Hsp70 and Hsc70 results in ectopic activation of JNK signaling in fly eye. Further, anti-PH3 staining in Hsp70 and Hsc70 mutant eyes revealed a reduced number of mitotic cells in second mitotic wave (SMW) of developing eye and anti-Rh1 staining showed reduced Rh1 expression, accumulation of Rh1 in the cytoplasm, and rhabdomere degeneration. Thus, on the basis of results, it was concluded that molecular chaperone Hsp70 and Hsc70 play an indispensable role during Drosophila eye development.

A comparison of cell survival and heat shock protein expression after radiation in normal dermal fibroblasts, microvascular endothelial cells, and different head and neck squamous carcinoma cell lines

OBJECTIVES

Head and neck squamous cell carcinoma (HNSCC) shows increased radioresistance due to the manipulation of homeostatic mechanisms like the heat shock response. This study intended to comparatively analyze effects of ionizing radiation on different HNSCC cell lines (PCI) and normal human dermal fibroblasts (NHFs) and human dermal microvascular endothelial cells (HDMECs) to uncover differences in radiation coping strategies.

MATERIALS AND METHODS

Proliferation (BrdU assay), apoptosis (caspase 3/7) and intracellular protein expression of heat shock protein (HSP)-70, and phosphorylated and total HSP27, determined by enzyme-linked immunosorbent assay (ELISA), were analyzed after exposure to increasing doses of ionizing radiation (2, 6, and 12 Gray, Gy).

RESULTS

Cell count decreased dose-dependently, but PCI cell lines consistently showed higher numbers compared to NHF and HDMEC. Likewise, high doses reduced cell proliferation, but low-dose radiation (2 Gy) instead increased proliferation in PCI 9 and 52. Apoptosis was not detectable in PCI cell lines. Basic HSP70 expression was high in PCI cells with little additional increase by irradiation. PCI cells yielded high basic total HSP27 concentrations but irradiation dose-dependently increased HSP27 in HDMEC, NHF, and PCI cells. Phosphorylated HSP27 concentrations were highest in NHF.

CONCLUSION

PCI cell lines showed higher resistance to dose-dependent reduction in cell number, proliferation, and protection from apoptosis compared to NHF and HDMEC. In parallel, we observed a high basic and radiation-induced expression of intracellular HSP70 leading to the assumption that the radioresistance of PCI cells is conferred by HSP70.

CLINICAL RELEVANCE

HNSCC use HSP to escape radiation-induced apoptosis and certain subtypes might increase proliferation after low-dose irradiation.

Attenuation of Oxidative Stress-Induced Cell Apoptosis in Schwann RSC96 Cells by Ocimum Gratissimum Aqueous Extract

Objectives: Cell transplantation therapy of Schwann cells (SCs) is a promising therapeutic strategy after spinal cord injury. However, challenges such as oxidative stress hinder satisfactory cell viability and intervention for enhancing SCs survival is critical throughout the transplantation procedures. Ocimum gratissimum, widely used as a folk medicine in many countries, has therapeutic and anti-oxidative properties and may protect SCs survival. Methods: We examined the protective effects of aqueous O. gratissimum extract (OGE) against cell damage caused by H₂O₂-induced oxidative stress in RSC96 Schwann cells. Results: Our results showed that the RSC96 cells, damaged by H₂O₂ oxidative stress, decreased their viability up to 32% after treatment with different concentrations of up to 300 μM H₂O₂, but OGE pretreatment (150 or 200 μg/mL) increased cell viability by approximately 62% or 66%, respectively. Cell cycle analysis indicated a high (43%) sub-G1 cell population in the H₂O₂-treated RSC96 cells compared with untreated cells (1%); whereas OGE pretreatment (150 and 200 μg/mL) of RSC96 cells significantly reduced the sub-G1 cells (7% and 8%, respectively). Furthermore, Western blot analysis revealed that OGE pretreatment inhibited H₂O₂-induced apoptotic protein caspase-3 activation and PARP cleavage, as well as it reversed Bax up-regulation and Bcl-2 down-regulation. The amelioration of OGE of cell stress and stress-induced apoptosis was proved by the HSP70 and HSP72 decrease. Conclusion: Our data suggest that OGE may minimize the cytotoxic effects of H₂O₂-induced SCs apoptosis by modulating the apoptotic pathway and could potentially supplement cell transplantation therapy.

Toxicogenomic analysis identifies the apoptotic pathway as the main cause of hepatotoxicity induced by tributyltin

Tributyltin (TBT) is one of the most widely used organotin biocides, which has severe endocrine-disrupting effects on marine species and mammals. Given that TBT accumulates at higher levels in the liver than in any other organ, and it acts mainly as a hepatotoxic agent, it is important to clearly delineate the hepatotoxicity of TBT. However, most of the available studies on TBT have focused on observations at the cellular level, while studies at the level of genes and proteins are limited; therefore, the molecular mechanisms of TBT-induced hepatotoxicity remains largely unclear. In the present study, we applied a toxicogenomic approach to investigate the effects of TBT on gene expression in the human normal liver cell line HL7702. Gene expression profiling identified the apoptotic pathway as the major cause of hepatotoxicity induced by TBT. Flow cytometry assays confirmed that medium- and high-dose TBT treatments significantly increased the number of apoptotic cells, and more cells underwent late apoptosis in the high-dose TBT group. The genes encoding heat shock proteins (HSPs), kinases and tumor necrosis factor receptors mediated TBT-induced apoptosis. These findings revealed novel molecular mechanisms of TBT-induced hepatotoxicity, and the current microarray data may also provide clues for future studies.

Osteoblasts activate the Nrf2 signalling pathway in response to arsenic trioxide treatment

Arsenic trioxide is used to treat a variety of leukaemia types and causes tumour cell death. However, it is not well known whether arsenic trioxide is toxic to bone osteoblast cells, the precursor cells from which leukaemia cells originate. The aim of this study was to examine the response of osteosarcoma cell line MG63 and primary cultured osteoblasts to arsenic trioxide treatment. After 24h of treatment, arsenic trioxide was more effective at inhibiting cell growth and increasing oxidative stress and DNA damage in MG63 cells than in osteoblasts. In addition, arsenic trioxide arrested cell cycle progression in the G2/M phase, and induced apoptosis in MG63 cells, but not in primary cultured osteoblasts. The results further showed that the expression of transcription factor Nrf2 and its downstream antioxidant effectors, including hemeoxygenase-1, glutathione, and superoxide dismutase, was increased in primary cultured osteoblasts. Additionally, expression of heat shock proteins was also increased. Experiments using inhibitors of antioxidant enzymes in the presence of arsenic trioxide-treated osteoblasts demonstrated that glutathione and superoxide dismutase were responsible for reducing oxidative stress, caspase-3 activity, and apoptosis and that heat shock proteins helped reduce caspase-3 activity. Unexpectedly, there was no apparent effect of the markedly increased hemeoxygenase-1, suggesting that other functions might exist for hemeoxygenase-1. These findings demonstrate that osteosarcoma cells are more sensitive to arsenic trioxide treatment than primary cultured osteoblasts and that primary cultured osteoblasts activate the Nrf2 signalling pathway in response to arsenic trioxide exposure to escape from oxidative damage and apoptosis.

The discovery of Hsp70 domain with cell-penetrating activity

Chaperone Hsp70 can cross the plasma membrane of living cells using mechanisms that so far have not received much research attention. Searching the part of the molecule that is responsible for transport ability of Hsp70, we found a cationic sequence composed of 20 amino acid residues on its surface, KST peptide, which was used in further experiments. We showed that KST peptide enters living cells of various origins with the same efficiency as the full-length chaperone. KST peptide is capable of carrying cargo with a molecular weight 30 times greater than its own into cells. When we compared the membrane-crossing activity of KST peptide in complex with Avidin (KST-Av complex) with that of similarly linked canonical TAT peptide, we found that TAT peptide penetrated SK-N-SH human neuroblastoma cells at a similar rate and efficiency as the KST peptide. Furthermore, KST peptide can carry protein complexes consisting of a specific antibody coupled to the peptide through the Avidin bridge. An antibody to Hsp70 delivered to SK-N-SH cells with high expression level of Hsp70 reduced the protective power of the chaperone and sensitized the cells to the pro-apoptotic effect of staurosporine. We studied the mechanisms of penetration of KST-Av and full-length Hsp70 inside human neuroblastoma SK-N-SH and human erythroleukemia K-562 cells and found that both used an active intracellular transport mechanism that included vesicular structures and negatively charged lipid membrane domains. Competition analysis of intracellular transport showed that the chaperone reduced intracellular penetration of KST peptide and conversely KST peptide prevented Hsp70 transport in a dose-dependent manner.

Design, synthesis and anticancer mechanistic studies of linked azoles

Herein we report the synthesis and biological activity evaluation of 2,4 linked azole-containing molecules.

Thermally induced apoptosis, necrosis, and heat shock protein expression in 3D culture

This study was conducted to compare the heat shock responses of cells grown in 2D and 3D culture environments as indicated by the level of heat shock protein 70 expression and the incidence of apoptosis and necrosis of prostate cancer cell lines in response to graded hyperthermia. PC3 cells were stably transduced with a dual reporter system composed of two tandem expression cassettes-a conditional heat shock protein promoter driving the expression of green fluorescent protein (HSPp-GFP) and a cytomegalovirus (CMV) promoter controlling the constitutive expression of a "beacon" red fluorescent protein (CMVp-RFP). Two-dimensional and three-dimensional cultures of PC3 prostate cancer cells were grown in 96-well plates for evaluation of their time-dependent response to supraphysiological temperature. To induce controlled hyperthermia, culture plates were placed on a flat copper surface of a circulating water manifold that maintained the specimens within ±0.1°C of a target temperature. Hyperthermia protocols included various combinations of temperature, ranging from 37°C to 57°C, and exposure times of up to 2 h. The majority of protocols were focused on temperature and time permutations, where the response gradient was greatest. Post-treatment analysis by flow cytometry analysis was used to measure the incidences of apoptosis (annexin V-FITC stain), necrosis (propidium iodide (PI) stain), and HSP70 transcription (GFP expression). Cells grown in 3D compared with 2D culture showed reduced incidence of apoptosis and necrosis and a higher level of HSP70 expression in response to heat shock at the temperatures tested. Cells responded differently to hyperthermia when grown in 2D and 3D cultures. Three-dimensional culture appears to enhance survival plausibly by activating protective processes related to enhanced-HSP70 expression. These differences highlight the importance of selecting physiologically relevant 3D models in assessing cellular responses to hyperthermia in experimental settings.

Regulation of apoptosis by heat shock proteins

Thermotolerance, the acquired resistance of cells to stress, is a well-established phenomenon. Studies of the key mediators of this response, the heat shock proteins (HSPs), have led to the discovery of the important roles played by these proteins in the regulation of apoptotic cell death. Apoptosis is critical for normal tissue homeostasis and is involved in diverse processes including development and immune clearance. Apoptosis is tightly regulated by both proapoptotic and antiapoptotic factors, and dysregulation of apoptosis plays a significant role in the pathophysiology of many diseases. In the recent years, HSPs have been identified as key determinants of cell survival, which can modulate apoptosis by directly interacting with components of the apoptotic machinery. Therefore, manipulation of the HSPs could represent a viable strategy for the treatment of diseases. Here, we review the current knowledge with regard to the mechanisms of HSP-mediated regulation of apoptosis.

Novel molecular mechanisms of antitumor action of dichloroacetate against T cell lymphoma: Implication of altered glucose metabolism, pH homeostasis and cell survival regulation

Pyruvate dehydrogenase kinase (PDK) inhibits pyruvate dehydrogenase (PDH) activity and thus promotes energetic switch from mitochondrial glucose oxidation to cytoplasmic glycolysis in cancerous cells (a phenomenon known as the 'Warburg effect') for their energy need, which facilitates the cancer progression by resisting induction of apoptosis and promoting tumor metastasis. Thus, in the present investigation, we explored the molecular mechanisms of the tumoricidal action of dichloroacetate (DCA), a pyruvate dehydrogenase kinase inhibitor, on cells of a murine T cell lymphoma, designated as Dalton's lymphoma (DL). In vitro treatment of tumor cells with DCA inhibited their survival accompanied by a modulation of the biophysical composition of tumor-conditioned medium with respect to pH, glucose and lactate. DCA treatment also altered expression of HIF1-α and pH regulators: VATPase and MCT1 and production of cytokines: IL-10, IL-6 and IFN-γ. Moreover, we also observed an alteration in the expression of other apoptosis and cell survival regulatory molecules: PUMA, GLUT1, Bcl2, p53, CAD, caspase-3 and HSP70. The study discusses the role of novel molecular mechanisms underlying DCA-dependent inhibition of tumor cell survival. This study shows for the first time that DCA-dependent alteration of tumor cell survival involves altered pH homeostasis and glucose metabolism. Thus, these findings will provide a new insight for therapeutic applications of DCA as a novel antineoplastic agent against T cell lymphoma.

Kinetics of chaperone activity of proteins Hsp70 and Hdj1 in human leukemia u-937 cells after preconditioning with thermal shock or compound u-133

Kinetics of the chaperone activity of proteins Hsp70 and Hdj1 were analyzed in human U-937 promonocytes during their response to heat shock or to treatment with the echinochrome triacetyl glucoside derivative U-133. To measure the chaperone activity of both proteins, a special test was developed for their recognition and binding of a denatured protein. Using this test, the chaperone activity could be concurrently estimated in large numbers of cellular or tissue extracts. We also estimated the contents of both chaperones in cells by immunoblotting. The values for contents of Hsp70 and Hdj1 obtained by two independent test systems coincided, and this suggested that the substrate-binding activity could change proportionally to the chaperone content in the protein mixture. Therefore, the test developed by us can be employed for high throughput screening of drugs activating cellular chaperones. The analysis of quantity and activity of two cellular chaperones during the cell response to heat stress or to the drug-like substance U-133 showed that both factors caused the accumulation of chaperones with similar kinetics. We conclude that the efficiency of drug preconditioning could be close to the efficiency of hyperthermia and that the high activity of chaperones could be retained in human cells for no less than 1.5 days.

Fas ligation and tumor necrosis factor α activation of murine astrocytes promote heat shock factor-1 activation and heat shock protein expression leading to chemokine induction and cell survival

Death-inducing ligands tumor necrosis factor alpha (TNFα) and Fas ligand (FasL) do not kill cultured astrocytes; instead they induce a variety of chemokines including macrophage-inflammatory protein-1α/CC chemokine ligand 3 (CCL3), monocyte chemoattractant protein-1 (CC CCL-2), macrophage-inflammatory protein-2/CXC chemokine ligand 2 (CXCL2, a murine homologue of interleukin 8), and interferon-induced protein of 10 kDa (CXCL10). Induction is enhanced by protein synthesis inhibition suggesting the existence of endogenous inhibitors. ERK, NF-κB, heat shock factor-1 (HSF-1) and heat shock proteins were examined for their possible roles in signal transduction. Inhibition of ERK activation by PD98059 partially inhibited expression of all but FasL-induced CXCL10. Although inhibition of NF-κB DNA binding inhibited chemokine induction, PD98059 did not inhibit TNFα-induced NF-κB DNA binding suggesting that ERK serves an NF-κB-independent pathway. Heat shock itself induced astrocytic chemokine expression; both TNFα and FasL induced HSF-1 DNA binding and Hsp72 production; and Hsp72-induced chemokine expression. Inhibition of either HSF-1 binding with quercetin or heat shock protein synthesis with KNK437 compromised chemokine induction without compromising cell survival. These data suggest that the induction of heat shock proteins via HSF-1 contribute to the TNFα- and FasL-induced expression of chemokines in astrocytes.

Inhibition of the JNK/Bim pathway by Hsp70 prevents Bax activation in UV-induced apoptosis

Here we studied the mechanism by which heat shock protein 70 (Hsp70) prevents Bax activation during ultraviolet (UV)-induced apoptosis. UV treatment led to c-Jun N-terminal kinase (JNK) phosphorylation, Bim redistribution and subsequent Bax activation. Bim depletion caused a smaller reduction in apoptosis than that by JNK inhibition, indicating that Bim activation is not entirely responsible for induction of apoptosis and other mechanisms are involved. Hsp70 knockdown resulted in high levels of activated JNK and Bax, while Hsp70 overexpression inhibited these processes. These findings demonstrate that Hsp70 prevented Bax activation via inhibiting the JNK/Bim pathway. Simultaneously, increased binding of Hsp70 to Bax was observed. Collectively, our results for the first time demonstrate that Hsp70 prevents Bax activation both by inhibiting the JNK/Bim pathway and by interacting with Bax in UV-induced apoptosis.

Heat shock proteins: cellular and molecular mechanisms in the central nervous system

Emerging evidence indicates that heat shock proteins (HSPs) are critical regulators in normal neural physiological function as well as in cell stress responses. The functions of HSPs represent an enormous and diverse range of cellular activities, far beyond the originally identified roles in protein folding and chaperoning. HSPs are now understood to be involved in processes such as synaptic transmission, autophagy, ER stress response, protein kinase and cell death signaling. In addition, manipulation of HSPs has robust effects on the fate of cells in neurological injury and disease states. The ongoing exploration of multiple HSP superfamilies has underscored the pluripotent nature of HSPs in the cellular context, and has demanded the recent revamping of the nomenclature referring to these families to reflect a re-organization based on structure and function. In keeping with this re-organization, we first discuss the HSP superfamilies in terms of protein structure, regulation, expression and distribution in the brain. We then explore major cellular functions of HSPs that are relevant to neural physiological states, and from there we discuss known and proposed HSP impacts on major neurological disease states. This review article presents a three-part discussion on the array of HSP families relevant to neuronal tissue, their cellular functions, and the exploration of therapeutic targets of these proteins in the context of neurological diseases.

Sodium 4-phenylbutyrate ameliorates the effects of cataract-causing mutant gammaD-crystallin in cultured cells

PURPOSE

gammaD-Crystallin (CRYGD) is a major structural lens crystallin and its mutations result in congenital cataract formation. In this study, we attempted to correct the altered protein features of G165fsX8 CRYGD protein with small chemical molecules.

METHODS

Recombinant FLAG-tagged mutants (R15C, R15S, P24T, R61C, and G165fsX8) of CRYGD were expressed in COS-7 cells and treated with small chemical molecules with reported protein chaperoning properties (sodium 4-phenylbutyrate [4-PBA], trimethylamine N-oxide [TMAO], and glycerol and DMSO [DMSO]). Protein solubility in 0.5% Triton X-100 and subcellular distribution was examined by western blotting and immunofluorescence, respectively. Apoptosis was assayed as the percentage of fragmented nuclei in transfected cells. Expression of heat-shock proteins (Hsp70 and Hsp90) was examined by reverse transcription-polymerase chain reaction analysis.

RESULTS

Unlike WT and most mutants (R15C, R15S, P24T, and R61C) of CRYGD, G165fsX8 CRYGD was significantly insoluble in 0.5% Triton X-100. This insolubility was alleviated by dose-dependent 4-PBA treatment. The treatment relieved the mislocalization of G165fsX8 CRYGD from the nuclear envelope. Also, 4-PBA treatment reduced cell apoptosis and caused an upregulation of Hsp70.

CONCLUSIONS

4-PBA treatment reduced the defective phenotype of mutant G165fsX8 CRYGD and rescued the affected cells from apoptosis. This could be a potential treatment for lens structural protein and prevent lens opacity in cataract formation.

Cellular stress responses: cell survival and cell death

Cells can respond to stress in various ways ranging from the activation of survival pathways to the initiation of cell death that eventually eliminates damaged cells. Whether cells mount a protective or destructive stress response depends to a large extent on the nature and duration of the stress as well as the cell type. Also, there is often the interplay between these responses that ultimately determines the fate of the stressed cell. The mechanism by which a cell dies (i.e., apoptosis, necrosis, pyroptosis, or autophagic cell death) depends on various exogenous factors as well as the cell's ability to handle the stress to which it is exposed. The implications of cellular stress responses to human physiology and diseases are manifold and will be discussed in this review in the context of some major world health issues such as diabetes, Parkinson's disease, myocardial infarction, and cancer.

Apoptosis and anti-apoptotic heat shock proteins in canine cutaneous infundibular keratinizing acanthomas and squamous cell carcinomas

Cell stress and death are linked in the neoplastic process, and heat shock proteins appear to play an important role by inhibiting apoptotic pathways. The apoptotic rates in 9 canine infundibular keratinizing acanthomas (IKAs) and 17 canine squamous cell carcinomas (SCCs) were correlated with the immunohistochemical expression of caspase-3 and the antiapoptotic heat shock proteins Hsp27, 72 and 73. Apoptosis was evaluated using the terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL) method. The absence of a correlation between the TUNEL index and active-caspase-3 expression, a paucity of active-caspase-3-positive cells and Hsp72 over-expression were considered to be indicative of inhibition of apoptosis, and suggestive that inhibition of cell death plays a key role in oncogenesis and tumour growth of some canine skin neoplasms.

Prostaglandin E2 stimulates expression of osmoprotective genes in MDCK cells and promotes survival under hypertonic conditions

The cells of the renal medulla produce large amounts of prostaglandin E2 (PGE2) via cyclooxygenases (COX)-1 and -2. PGE2 is well known to play a critical role in salt and water balance and maintenance of medullary blood flow. Since renal medullary PGE2 production increases in antidiuresis, and since COX inhibition is associated with damage to the renal medulla during water deprivation, PGE2 may promote the adaptation of renal papillary cells to high interstitial solute concentrations. To address this question, MDCK cells were exposed to a gradual tonicity increase in the presence or absence of 20 microM PGE2 prior to analysis of (i) cell survival, (ii) expression of osmoprotective genes (AR, BGT1, SMIT, HSP70 and COX-2), (iii) subcellular TonEBP/NFAT5 abundance, (iv) TonEBP/NFAT5 transcriptional activity and (v) aldose reductase promoter activity. Cell survival and apoptotic indices after raising the medium tonicity improved markedly in the presence of PGE2. PGE2 significantly increased tonicity-mediated up-regulation of AR, SMIT and HSP70 mRNAs. However, neither nuclear abundance nor TonEBP/NFAT5-driven reporter activity were elevated by PGE2, but aldose reductase promoter activity was significantly increased by PGE2. Interestingly, tonicity-induced COX-2 expression and activity was also stimulated by PGE2, suggesting the existence of a positive feedback loop. These results demonstrate that the major medullary prostanoid, PGE2, stimulates the expression of osmoprotective genes and favours the adaptation of medullary cells to increasing interstitial tonicities, an effect that is not explained directly by the presence of TonEs in the promoter region of the respective target genes. These findings may be relevant in the pathophysiology of medullary damage associated with analgesic drugs.

Drug-induced Myc-mediated apoptosis of cancer cells is inhibited by stress protein Hsp70

The Myc oncoprotein serves a dual function by stimulating cells both towards growth and apoptosis. The latter functions are often abrogated during tumor development. The Hsp70 stress protein is a potent anti-apoptotic molecule, but its potential role in protecting cells from Myc-mediated apoptosis has not been investigated. Our results show that activated Myc potentiated apoptosis induced by the cancer drugs etoposide (ETO) and camptothecin (CAMP) in v-Myc-expressing human U-937 monoblastic cells and in Rat1 cells containing a conditionally active Myc/estrogen receptor (MycER) fusion protein. However, both heat shock and ectopic Hsp70 expression protected the cells from Myc-mediated apoptosis after drug treatment in both systems. The increased susceptibility to the anti-tumor drugs by activated Myc was enhanced by siRNA-mediated knockdown of Hsp70 expression in U-937 cells. Addressing the mechanisms by which Myc and Hsp70 promotes and inhibits drug-induced apoptosis, respectively, we found that v-Myc stimulated cytochrome c release and activation of effector caspase-9, -3 and -7, but not of initiator caspase-8. Inhibition of caspase-9 specifically reduced v-Myc-stimulated apoptosis, whereas inhibition of caspase-8 and -3/7 reduced apoptosis both in v-myc-expressing and parental ETO-treated U-937 cells. Interestingly, Myc-stimulated activation of effector caspases was inhibited, but cytochrome c release was not affected by Hsp70 expression, suggesting that Hsp70 interferes with the proapoptotic function of Myc downstream of mitochondria, at the level of caspase-9 and downstream caspases. In conclusion, Hsp70 seems to have key function in inhibition of apoptosis mediated by Myc and may therefore play an important role in Myc-driven oncogenesis.

CpG-B oligodeoxynucleotide promotes cell survival via up-regulation of Hsp70 to increase Bcl-xL and to decrease apoptosis-inducing factor translocation

Unmethylated CpG oligodeoxynucleotides (ODNs) activate immune responses in a TLR9-dependent manner. In this study, stimulation of mouse macrophages with CpG-B ODN increased cellular Hsp70 expression and prevented apoptosis induced by serum starvation or staurosporine treatment. CpG-B ODN-induced Hsp70 expression depended on TLR9, MyD88, and phosphatidylinositol 3-kinase. Inhibition of Hsp70 synthesis by an inhibitor (quercetin) or antisense hsp70 attenuated not only Hsp70 expression but also the anti-apoptotic capacity of CpG-B ODN. Ectopic expression of Hsp70 rescued the inhibitory effect of quercetin on CpG-B ODN-induced anti-apoptosis. Additional experiments demonstrated that quercetin and anti-sense hsp70 modulated CpG-B ODN-induced anti-apoptosis via a caspase-3-independent pathway by down-regulating the survival gene bcl-x(L) and by increasing translocation of apoptosis-inducing factor. These findings suggest that CpG-B ODN may up-regulate Hsp70 via a TLR9/MyD88/phosphatidylinositol 3-kinase pathway to increase Bcl-x(L) and to decrease apoptosis-inducing factor nuclear translocation, resulting in anti-apoptosis.

Intracellular and extracellular functions of heat shock proteins: repercussions in cancer therapy

Stress or heat shock proteins (HSPs) are the most conserved proteins present in both prokaryotes and eukaryotes. Their expression is induced in response to a wide variety of physiological and environmental insults. These proteins play an essential role as molecular chaperones by assisting the correct folding of nascent and stress-accumulated misfolded proteins, and preventing their aggregation. HSPs have a dual function depending on their intracellular or extracellular location. Intracellular HSPs have a protective function. They allow the cells to survive lethal conditions. Various mechanisms have been proposed to account for the cytoprotective functions of HSPs. Several HSPs have also been demonstrated to directly interact with various components of the tightly regulated programmed cell death machinery, upstream and downstream of the mitochondrial events. On the other hand, extracellular located or membrane-bound HSPs mediate immunological functions. They can elicit an immune response modulated either by the adaptive or innate immune system. This review will focus on HSP27, HSP70, and HSP90. We will discuss the dual role of these HSPs, protective vs. immunogenic properties, making a special emphasis in their utility as targets in cancer therapy.

Induced and constitutive heat shock protein expression in the olfactory system—A review, new findings, and some perspectives

Heat shock, or stress, proteins (HSPs) are cellular proteins induced in response to conditions that cause protein denaturation, and their induction is essential for survival of such conditions. In the olfactory system we have found intense HSP expression occurs during normal processing of environmental odorants/inhalants as well as following hyperthermia and drug exposure. The HSPs involved include ubiquitin, HSP70, HSC70, and HSP25. Responses are both cell type- and stress-specific, occurring primarily in olfactory supporting cells and to some extent in Bowman's gland acinar cells. Responses to these stresses are not seen in olfactory sensory neurons. This article reviews those studies and the significance of their findings. It also discusses a distinct subpopulation of rat olfactory sensory neurons (OSNs), the 2A4(+)OSNs, found to be constitutively reactive with HSP70, the predominantly stress-inducible isoform of the 70 kD HSP family. Their high HSP70 expression appears to confer on the 2A4(+)OSNs an enhanced ability to survive damage-induced OSN turnover. New findings are also presented on HSP25-specific changes following olfactory bulbectomy. All data are discussed in the context of the overall olfactory and bioprotective functions of the olfactory mucosa.

Therapeutic aspects of chaperones/heat-shock proteins in neuro-oncology

Tumors of the CNS frequently have devastating consequences in terms of cognitive and motor function, personality and mortality. Despite decades of work, current therapies have done little to alter the course of these deadly diseases. The discovery that chaperones/heat-shock proteins play an important role in tumor biology and immunology have sparked much interest in utilizing these proteins as targets of therapeutics, or as therapeutics themselves, in the treatments of a variety of cancers. Neuro-oncology has only recently taken notice of these entities, and the purpose of this review is to provide a background, an update and a view to the future for the roles of chaperones/heat-shock proteins in the treatment of brain tumors.