Acquired thermotolerance following heat shock protein synthesis prevents impairment of mitochondrial ATPase activity at elevated temperatures in Saccharomyces cerevisiae

Genetic inactivation of essential HSF1 reveals an isolated transcriptional stress response selectively induced by protein misfolding

Heat Shock Factor 1 (Hsf1) in yeast drives the basal transcription of key proteostasis factors and its activity is induced as part of the core heat shock response. Exploring Hsf1 specific functions has been challenging due to the essential nature of the HSF1 gene and the extensive overlap of target promoters with environmental stress response (ESR) transcription factors Msn2 and Msn4 (Msn2/4). In this study, we constructed a viable hsf1∆ strain by replacing the HSF1 open reading frame with genes that constitutively express Hsp40, Hsp70, and Hsp90 from Hsf1-independent promoters. Phenotypic analysis showed that the hsf1∆ strain grows slowly, is sensitive to heat as well as protein misfolding and accumulates protein aggregates. Transcriptome analysis revealed that the transcriptional response to protein misfolding induced by azetidine-2-carboxylic acid is fully dependent on Hsf1. In contrast, the hsf1∆ strain responded to heat shock through the ESR. Following HS, Hsf1 and Msn2/4 showed functional compensatory induction with stronger activation of the remaining stress pathway when the other branch was inactivated. Thus, we provide a long-overdue genetic test of the function of Hsf1 in yeast using the novel hsf1∆ construct. Our data highlight that the accumulation of misfolded proteins is uniquely sensed by Hsf1-Hsp70 chaperone titration inducing a highly selective transcriptional stress response.

Mitochondrial HSP70 Chaperone System-The Influence of Post-Translational Modifications and Involvement in Human Diseases

Since their discovery, heat shock proteins (HSPs) have been identified in all domains of life, which demonstrates their importance and conserved functional role in maintaining protein homeostasis. Mitochondria possess several members of the major HSP sub-families that perform essential tasks for keeping the organelle in a fully functional and healthy state. In humans, the mitochondrial HSP70 chaperone system comprises a central molecular chaperone, mtHSP70 or mortalin (HSPA9), which is actively involved in stabilizing and importing nuclear gene products and in refolding mitochondrial precursor proteins, and three co-chaperones (HSP70-escort protein 1-HEP1, tumorous imaginal disc protein 1-TID-1, and Gro-P like protein E-GRPE), which regulate and accelerate its protein folding functions. In this review, we summarize the roles of mitochondrial molecular chaperones with particular focus on the human mtHsp70 and its co-chaperones, whose deregulated expression, mutations, and post-translational modifications are often considered to be the main cause of neurological disorders, genetic diseases, and malignant growth.

Modulating the Heat Stress Response to Improve Hyperthermia-Based Anticancer Treatments

Simple Summary

Hyperthermia is a method to expose a tumor to elevated temperatures. Heating of the tumor promotes the effects of various treatment regimens that are based on chemo and radiotherapy. Several aspects, however, limit the efficacy of hyperthermia-based treatments. This review provides an overview of the effects and limitations of hyperthermia and discusses how current drawbacks of the therapy can potentially be counteracted by inhibiting the heat stress response—a mechanism that cells activate to defend themselves against hyperthermia.

Abstract

Cancer treatments based on mild hyperthermia (39–43 °C, HT) are applied to a widening range of cancer types, but several factors limit their efficacy and slow down more widespread adoption. These factors include difficulties in adequate heat delivery, a short therapeutic window and the acquisition of thermotolerance by cancer cells. Here, we explore the biological effects of HT, the cellular responses to these effects and their clinically-relevant consequences. We then identify the heat stress response—the cellular defense mechanism that detects and counteracts the effects of heat—as one of the major forces limiting the efficacy of HT-based therapies and propose targeting this mechanism as a potentially universal strategy for improving their efficacy.

Fungal survival under temperature stress: a proteomic perspective

BACKGROUND

Increases in knowledge of climate change generally, and its impact on agricultural industries specifically, have led to a greater research effort aimed at improving understanding of the role of fungi in various fields. Fungi play a key role in soil ecosystems as the primary agent of decomposition, recycling of organic nutrients. Fungi also include important pathogens of plants, insects, bacteria, domestic animals and humans, thus highlighting their importance in many contexts. Temperature directly affects fungal growth and protein dynamics, which ultimately will cascade through to affect crop performance. To study changes in the global protein complement of fungi, proteomic approaches have been used to examine links between temperature stress and fungal proteomic profiles.

SURVEY METHODOLOGY AND OBJECTIVES

A traditional rather than a systematic review approach was taken to focus on fungal responses to temperature stress elucidated using proteomic approaches. The effects of temperature stress on fungal metabolic pathways and, in particular, heat shock proteins (HSPs) are discussed. The objective of this review is to provide an overview of the effects of temperature stress on fungal proteomes.

CONCLUDING REMARKS

Elucidating fungal proteomic response under temperature stress is useful in the context of increasing understanding of fungal sensitivity and resilience to the challenges posed by contemporary climate change processes. Although useful, a more thorough work is needed such as combining data from multiple -omics platforms in order to develop deeper understanding of the factor influencing and controlling cell physiology. This information can be beneficial to identify potential biomarkers for monitoring environmental changes in soil, including the agricultural ecosystems vital to human society and economy.

Cellular Control of Viscosity Counters Changes in Temperature and Energy Availability

Cellular functioning requires the orchestration of thousands of molecular interactions in time and space. Yet most molecules in a cell move by diffusion, which is sensitive to external factors like temperature. How cells sustain complex, diffusion-based systems across wide temperature ranges is unknown. Here, we uncover a mechanism by which budding yeast modulate viscosity in response to temperature and energy availability. This "viscoadaptation" uses regulated synthesis of glycogen and trehalose to vary the viscosity of the cytosol. Viscoadaptation functions as a stress response and a homeostatic mechanism, allowing cells to maintain invariant diffusion across a 20°C temperature range. Perturbations to viscoadaptation affect solubility and phase separation, suggesting that viscoadaptation may have implications for multiple biophysical processes in the cell. Conditions that lower ATP trigger viscoadaptation, linking energy availability to rate regulation of diffusion-controlled processes. Viscoadaptation reveals viscosity to be a tunable property for regulating diffusion-controlled processes in a changing environment.

Heat Shock Proteins Are Essential Components in Transformation and Tumor Progression: Cancer Cell Intrinsic Pathways and Beyond

Heat shock protein (HSP) synthesis is switched on in a remarkably wide range of tumor cells, in both experimental animal systems and in human cancer, in which these proteins accumulate in high levels. In each case, elevated HSP concentrations bode ill for the patient, and are associated with a poor outlook in terms of survival in most cancer types. The significance of elevated HSPs is underpinned by their essential roles in mediating tumor cell intrinsic traits such as unscheduled cell division, escape from programmed cell death and senescence, de novo angiogenesis, and increased invasion and metastasis. An increased HSP expression thus seems essential for tumorigenesis. Perhaps of equal significance is the pronounced interplay between cancer cells and the tumor milieu, with essential roles for intracellular HSPs in the properties of the stromal cells, and their roles in programming malignant cells and in the release of HSPs from cancer cells to influence the behavior of the adjacent tumor and infiltrating the normal cells. These findings of a triple role for elevated HSP expression in tumorigenesis strongly support the targeting of HSPs in cancer, especially given the role of such stress proteins in resistance to conventional therapies.

Heat shock-induced mitotic arrest requires heat shock protein 105 for the activation of spindle assembly checkpoint

Heat shock causes proteotoxic stress that induces various cellular responses, including delayed mitotic progression and the generation of an aberrant number of chromosomes. In this study, heat shock delayed the onset of anaphase by increasing the number of misoriented cells, accompanied by the kinetochore localization of budding uninhibited by benzimidazole-related (BubR)1 in a monopolar spindle (Mps)1-dependent manner. The mitotic delay was canceled by knockdown of mitotic arrest defect (Mad)2. Knockdown of heat shock protein (Hsp)105 partially abrogated the mitotic delay with the loss of the kinetochore localization of BubR1 under heat shock conditions and accelerated mitotic progression under nonstressed conditions. Consistent with this result, Hsp105 knockdown increased the number of anaphase cells with lagging chromosomes, through mitotic slippage, and decreased taxol sensitivity more than Mad2 knockdown. Hsp105 was coprecipitated with cell division cycle (Cdc)20 in an Mps1-dependent manner; however, its knockdown did not affect coprecipitation of Mad2 and BubR1 with Cdc20. We propose that heat shock delays the onset of anaphase via the activation of the spindle assembly checkpoint (SAC). Hsp105 prevents abnormal cell division by contributing to SAC activation under heat shock and nonstressed conditions by interacting with Cdc20 but not affecting formation of the mitotic checkpoint complex.-Kakihana, A., Oto, Y., Saito, Y., Nakayama, Y. Heat shock-induced mitotic arrest requires heat shock protein 105 for the activation of spindle assembly checkpoint.

A Novel Differential Ion Mobility Device Expands the Depth of Proteome Coverage and the Sensitivity of Multiplex Proteomic Measurements

The depth of proteomic analyses is often limited by the overwhelming proportion of confounding background ions that compromise the identification and quantification of low abundance peptides. To alleviate these limitations, we present a new high field asymmetric waveform ion mobility spectrometry (FAIMS) interface that can be coupled to the Orbitrap Tribrid mass spectrometers. The interface provides several advantages over previous generations of FAIMS devices, including ease of operation, robustness, and high ion transmission. Replicate LC-FAIMS-MS/MS analyses (n = 100) of HEK293 protein digests showed stable ion current over extended time periods with uniform peptide identification on more than 10,000 distinct peptides. For complex tryptic digest analyses, the coupling of FAIMS to LC-MS/MS enabled a 30% gain in unique peptide identification compared with non-FAIMS experiments. Improvement in sensitivity facilitated the identification of low abundance peptides, and extended the limit of detection by almost an order of magnitude. The reduction in chimeric MS/MS spectra using FAIMS also improved the precision and the number of quantifiable peptides when using isobaric labeling with tandem mass tag (TMT) 10-plex reagent. We compared quantitative proteomic measurements for LC-MS/MS analyses performed using synchronous precursor selection (SPS) and LC-FAIMS-MS/MS to profile the temporal changes in protein abundance of HEK293 cells following heat shock for periods up to 9 h. FAIMS provided 2.5-fold increase in the number of quantifiable peptides compared with non-FAIMS experiments (30,848 peptides from 2,646 proteins for FAIMS versus 12,400 peptides from 1,229 proteins with SPS). Altogether, the enhancement in ion transmission and duty cycle of the new FAIMS interface extended the depth and comprehensiveness of proteomic analyses and improved the precision of quantitative measurements.

Upregulation of heat-shock proteins in larvae, but not adults, of the flesh fly during hot summer days

Heat-shock proteins (HSPs) are highly expressed when organisms are exposed to thermal stresses. The HSPs are considered to play significant roles in thermal adaptation because they function as molecular chaperones facilitating proper protein synthesis. The expression of HSPs under field conditions, however, has not been evaluated much, and their importance, based on the ecological contexts in nature, is still unclear. We investigated this aspect in the larvae and adults of the flesh fly, Sarcophaga similis. These larvae spend their larval life in the carrion or faeces of vertebrates; therefore, they are less mobile and are occasionally exposed to high temperature. In contrast, the adults of this species can fly and, therefore, they are highly mobile. Massive transcription of Hsps was detected both in the larvae and adults in a laboratory heat-shock experiment. The larvae in the field showed no or less Hsp production on thermally mild days, whereas considerable upregulation of Hsp expression was detected on days with high temperature. The adults can also be exposed to thermal stress as high as 40 °C or higher in the field. However, most of the flies showed no or less Hsp expression. The observations in the experimental cage under field conditions revealed behavioural thermoregulation of adults through microhabitat selection. The present study demonstrates ontogenetic alteration of the strategy to overcome thermal stress in an insect; in the field, less mobile larvae use physiological protection against heat (HSP production), whereas highly mobile adults avoid the stress behaviourally (through microhabitat selection).

A Model of Exposure to Extreme Environmental Heat Uncovers the Human Transcriptome to Heat Stress

The molecular mechanisms by which individuals subjected to environmental heat stress either recover or develop heat-related complications are not well understood. We analysed the changes in blood mononuclear gene expression patterns in human volunteers exposed to extreme heat in a sauna (temperature of 75.7 ± 0.86 °C). Our analysis reveals that expression changes occur rapidly with no significant increase in core temperature and continue to amplify one hour after the end of heat stress. The reprogramed transcriptome was predominantly inhibitory, as more than two-thirds of the expressed genes were suppressed. The differentially expressed genes encoded proteins that function in stress-associated pathways; including proteostasis, energy metabolism, cell growth and proliferation, and cell death, and survival. The transcriptome also included mitochondrial dysfunction, altered protein synthesis, and reduced expression of genes -related to immune function. The findings reveal the human transcriptomic response to heat and highlight changes that might underlie the health outcomes observed during heat waves.

Saccharomyces cerevisiae genes involved in survival of heat shock

The heat-shock response in cells, involving increased transcription of a specific set of genes in response to a sudden increase in temperature, is a highly conserved biological response occurring in all organisms. Despite considerable attention to the processes activated during heat shock, less is known about the role of genes in survival of a sudden temperature increase. Saccharomyces cerevisiae genes involved in the maintenance of heat-shock resistance in exponential and stationary phase were identified by screening the homozygous diploid deletants in nonessential genes and the heterozygous diploid mutants in essential genes for survival after a sudden shift in temperature from 30 to 50°. More than a thousand genes were identified that led to altered sensitivity to heat shock, with little overlap between them and those previously identified to affect thermotolerance. There was also little overlap with genes that are activated or repressed during heat-shock, with only 5% of them regulated by the heat-shock transcription factor. The target of rapamycin and protein kinase A pathways, lipid metabolism, vacuolar H⁺-ATPase, vacuolar protein sorting, and mitochondrial genome maintenance/translation were critical to maintenance of resistance. Mutants affected in l-tryptophan metabolism were heat-shock resistant in both growth phases; those affected in cytoplasmic ribosome biogenesis and DNA double-strand break repair were resistant in stationary phase, and in mRNA catabolic processes in exponential phase. Mutations affecting mitochondrial genome maintenance were highly represented in sensitive mutants. The cell division transcription factor Swi6p and Hac1p involved in the unfolded protein response also play roles in maintenance of heat-shock resistance.

Heat shock pretreatment reduces intestinal injury in a neonatal rat model of early necrotizing enterocolitis

BACKGROUND

Increased pro-inflammatory cytokines are suggested in the pathogenesis of necrotizing enterocolitis (NEC). The transcription factor, nuclear factor-ĸB (NF-ĸB), is a central regulator of inflammatory and immune responses, and recent rodent NEC models have shown that NF-ĸB may have a critical role in the disease processes that underlie NEC. Heat shock proteins have important functions in response to stress-related events in a variety of systems, including digestive organs.

OBJECTIVES

We investigated whether heat shock pretreatment protects intestinal epithelial damage in the early NEC rat model.

METHODS

We generated human NEC-like lesions in neonatal rat ileum by administering oral endotoxin (10 mg/kg), intermittent 8% hypoxia, and hypertonic formula. Heat shock was administered by raising the chamber temperature to 42°C for 20 min, 3 h prior to endotoxin ingestion.

RESULTS

Heat shock pretreatment increased the expression of HSP70 in the ileal tissue and attenuated histological severity of early experimental NEC. NF-ĸB was activated in the ileal tissue of the NEC group and this activation was attenuated by heat shock pretreatment, which was determined by electrophoretic mobility shift assay and Western blot analysis of p50 in subcellular fractionated samples.

CONCLUSIONS

Heat shock pretreatment reduced the incidence and severity of early experimental NEC in rats. A possible mechanism underlying this protective effect includes inhibition of NF-ĸB activation through increased HSP70 expression.

Membrane proteomic analysis comparing squamous cell lung cancer tissue and tumour-adjacent normal tissue

Lung cancer is the leading cause of cancer-related deaths worldwide. Squamous cell carcinoma is one of the predominant histological subtypes of lung cancer. Detecting lung cancer at an early stage is essential for successful therapy and increasing survival. There are still no satisfactory biomarkers for the early detection of lung cancer. In this study, tumour tissue paired with tumour-adjacent normal bronchial epithelial tissue was obtained from patients with squamous cell lung carcinoma without metastasis. The proteins extracted from the cell membrane were separated by two-dimensional polyacrylamide gel electrophoresis (2-DE) and were analysed with the Image Master two-dimensional platinum software. Twenty-five significantly different protein spots were selected and identified with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). A total of 19 proteins were successfully identified. Twelve proteins were up-regulated, and seven proteins were down-regulated in the cancerous tissue compared with the tumour-adjacent normal tissue. One up-regulated protein and one down-regulated protein in squamous cell lung carcinoma were verified by Western blot analysis and RT-PCR; the results were consistent with the 2-DE analysis. In conclusion, membrane proteomics identified a number of candidate biomarker proteins that were differentially expressed between squamous cell lung cancer tissue and adjacent normal tissue. These biomarker candidates have the potential to elucidate the underlying pathogenesis of squamous cell lung cancer.

Hsp90 and mitochondrial proteases Yme1 and Yta10/12 participate in ATP synthase assembly in Saccharomyces cerevisiae

Hsc82 and Hsp82, the Hsp90 family proteins of yeast, are both required for fermentative growth at 37°C. Inactivation of either of the mitochondrial AAA proteases, Yme1 or Yta10/12, allows fermentative growth of hsc82∆ or hsp82∆ strains at 37°C. Genetic evidence indicates interaction of Hsc82/Hsp82 with the Yme1 and Yta10/Yta12 complexes in promoting F(1)F(o)-ATPase activity, with Hsc82 specifically required for F(1)-ATPase assembly. A previously reported mutation in Rpt3, one of the six ATPases of the proteasome, suppresses yme1∆ phenotypes and increases transcription of HSC82 but not HSP82. These genetic interactions describe a functional role for Hsp90 proteins in mitochondrial biogenesis.

The heat shock response: life on the verge of death

Organisms must survive a variety of stressful conditions, including sudden temperature increases that damage important cellular structures and interfere with essential functions. In response to heat stress, cells activate an ancient signaling pathway leading to the transient expression of heat shock or heat stress proteins (Hsps). Hsps exhibit sophisticated protection mechanisms, and the most conserved Hsps are molecular chaperones that prevent the formation of nonspecific protein aggregates and assist proteins in the acquisition of their native structures. In this Review, we summarize the concepts of the protective Hsp network.

Changes in membrane fluid state and heat shock response cause attenuation of virulence

So far attenuation of pathogens has been mainly obtained by chemical or heat treatment of microbial pathogens. Recently, live attenuated strains have been produced by genetic modification. We have previously demonstrated that in several prokaryotes as well as in yeasts and mammalian cells the heat shock response is controlled by the membrane physical state (MPS). We have also shown that in Salmonella enterica serovar Typhimurium LT2 (Salmonella Typhimurium) overexpression of a Delta(12)-desaturase gene alters the MPS, inducing a sharp impairment of transcription of major heat shock genes and failure of the pathogen to grow inside macrophage (MPhi) (A. Porta et al., J. Bacteriol. 192:1988-1998, 2010). Here, we show that overexpression of a homologous Delta(9)-desaturase sequence in the highly virulent G217B strain of the human fungal pathogen Histoplasma capsulatum causes loss of its ability to survive and persist within murine MPhi along with the impairment of the heat shock response. When the attenuated strain of H. capsulatum was injected in a mouse model of infection, it did not cause disease. Further, treated mice were protected when challenged with the virulent fungal parental strain. Attenuation of virulence in MPhi of two evolutionarily distant pathogens was obtained by genetic modification of the MPS, suggesting that this is a new method that may be used to produce attenuation or loss of virulence in both other intracellular prokaryotic and eukaryotic pathogens. This new procedure to generate attenuated forms of pathogens may be used eventually to produce a novel class of vaccines based on the genetic manipulation of a pathogen's membrane fluid state and stress response.

HSP 70 and atherosclerosis--protector or activator?

BACKGROUND

Atherosclerosis and its complications represent the leading cause of morbidity and mortality. Heat shock protein 70 (HSP70) protects cellular elements from injury by reducing oxidation, inflammation and apoptosis and by refolding damaged proteins. HSP70 improves viability of stressed vascular smooth muscle cells, possibly via its chaperone functions. It has been proposed that the response mounted against bacterial HSPs results in an autoimmune reaction, which has the potential to cause complement-mediated endothelial injury, and hence accelerate atherogenesis.

OBJECTIVE

to examine the roles of HSPs in atherosclerosis.

METHODS

A literature review.

RESULTS/CONCLUSIONS

The role of HSPs in atherosclerosis is controversial. HSP60 probably acts as an autoantigen, and may trigger both cell- and antibody-mediated immune responses, while HSP70 is likely to be involved in cytoprotection. The significance of this inverse relation between HSP70 and atherosclerosis has not yet been elucidated. Whether HSPs will become therapeutic targets remains to be established.

Mechanisms of Activation and Regulation of the Heat Shock-Sensitive Signaling Pathways

Heat shock (HS), like many other stresses, induces specific and highly regulated signaling cascades that promote cellular homeostasis. The three major mitogen-activated protein kinases (MAPK) and protein kinase B (PKB/Akt) are the most notable of these HS-stimulated pathways. Their activation occurs rapidly and sooner than the transcriptional upregulation of heat shock proteins (Hsp), which generate a transient state of extreme resistance against subsequent thermal stress. The direct connection of these signaling pathways to cellular death or survival mechanisms suggests that they contribute importantly to the HS response. Some of them may counteract early noxious effects of heat, while others may bolster key apoptosis events. The triggering events responsible for activating these pathways are unclear. Protein denaturation, specific and nonspecific receptor activation, membrane alteration and chromatin structure perturbation are potential initiating factors.

Genomic analysis of heat-shock factor targets in Drosophila

We have used a chromatin immunoprecipitation-microarray (ChIP-array) approach to investigate the in vivo targets of heat-shock factor (Hsf) in Drosophila embryos. We show that this method identifies Hsf target sites with high fidelity and resolution. Using cDNA arrays in a genomic search for Hsf targets, we identified 141 genes with highly significant ChIP enrichment. This study firmly establishes the potential of ChIP-array for whole-genome transcription factor target mapping in vivo using intact whole organisms.

Preconditioned somatothermal stimulation on median nerve territory increases myocardial heat shock protein 70 and protects rat hearts against ischemia-reperfusion injury

OBJECTIVE

This study was designed to test the hypotheses that local somatothermal stimulation on the left median nerve territory increases myocardial heat shock protein 70 and that preconditioning of rats with local somatothermal stimulation protects the hearts against subsequent ischemia-reperfusion injury.

METHODS

Local somatothermal stimulation was brought about by means of application of a heating rod over and above the left median nerve territory (1.5 cm proximal to the palm crease) in male Sprague-Dawley rats. After rats were treated with local somatothermal stimulation, the gene expression of heat shock protein 70 in regional muscle, heart, and liver was assessed by means of Western blotting and reverse transcription-polymerase chain reaction. In addition, durations of arrhythmia, mortality rates, and mitochondrial functions were compared between groups preconditioned with or without local somatothermal stimulation followed by subsequent myocardial ischemia-reperfusion injury.

RESULTS

The results showed that the gene expression of heat shock protein 70 was upregulated in the muscle beneath the area of local somatothermal stimulation, as well as in the heart, although not in the liver. When animals were preconditioned with local somatothermal stimulation on the left median nerve territory followed by subsequent ischemia-reperfusion injury of the heart, there were significant decreases of creatine kinase level from the heart, duration of arrhythmia, mortality rate, and improved mitochondrial respiratory function compared with that seen in those without local somatothermal stimulation preconditioning.

CONCLUSION

We conclude that local heat stress preconditioning on the left median nerve territory has a potential cardioprotective effect against subsequent ischemia-reperfusion injury.

HSP90 as a new therapeutic target for cancer therapy: the story unfolds

Current anticancer drug development strategies involve identifying novel molecular targets which are crucial for tumourigenesis. The molecular chaperone heat shock protein (HSP) 90 is of interest as an anticancer drug target because of its importance in maintaining the conformation, stability and function of key oncogenic client proteins involved in signal transduction pathways leading to proliferation, cell cycle progression and apoptosis, as well as other features of the malignant phenotype such as invasion, angiogenesis and metastasis. The natural product HSP90 inhibitors geldanamycin and radicicol exert their antitumour effect by inhibiting the intrinsic ATPase activity of HSP90, resulting in degradation of HSP90 client proteins via the ubiquitin proteosome pathway. Anticancer selectivity may derive from the simultaneous combinatorial effects of HSP90 inhibitors on multiple cancer targets and pathways. 17-allylamino, 17-demethoxygeldanamycin (17AAG), a geldanamycin derivative, showed good activity and cancer selectivity in preclinical models and has now progressed to Phase I clinical trial in cancer patients with encouraging initial results. Phase II trials including combination studies with cytotoxic agents are now being planned and these should allow the therapeutic activity of 17AAG to be determined. Second generation HSP90 inhibitors may be designed to overcome some of the drawbacks of 17AAG, including limited oral bioavailability and solubility. They could also be engineered to target specific functions of HSP90, which may not only provide greater molecular selectivity and clinical benefit but may also increase understanding of the complex functions of this molecular chaperone. HSP90 inhibitors provide proof of concept for drugs directed at HSP90 and protein folding and this principle may be applicable to other medical conditions involving protein aggregation and stability.

Attenuation of sepsis-induced apoptosis by heat shock pretreatment in rats

Apoptosis is a process by which cells undergo a form of non-necrotic cellular suicide. Although it is a programmed process, apoptosis can be induced by various stressors. During sepsis, apoptosis has been regarded as an important cause of cell death in the immune system, leading to unresponsiveness to treatment. This study was designed to investigate how prior heat shock induction can influence the rate of apoptosis in animals that have experienced sepsis. Sprague-Dawley rats were used, and experimental sepsis was induced by cecal ligation and puncture (CLP). Animals in the heated group were anesthetized and received heat shock by whole-body hyperthermia. They were sacrificed 9 h and 18 h after CLP as early and late sepsis, respectively. Apoptosis was evaluated by "DNA ladder" detection in agarose electrophoresis and Tdt-mediated dUTP nick end-labeling (TUNEL) assay. Hsp72 was detected by Western blot analysis. The results showed that the DNA ladder was detected most clearly in the thymus at the late phase of sepsis with time course dependence, while it showed less clearly in heat shock treated animals. Histopathological study by TUNEL assay obtained similar results in the thymus, where the cortex was more susceptible to apoptosis than the medulla. The Western blot analysis showed that the heat shock induced Hsp72 concomitant with an increase in Bcl-2:Bax ratio. In conclusion, heat shock pretreatment prevents rats from sepsis-induced apoptosis that may account for the better outcome of experimental sepsis. An increase in the Bcl-2:Bax ratio may in part explain the molecular mechanism of the effect of heat shock pretreatment.

Potential protective effect of NF-kappaB activity on the polymicrobial sepsis of rats preconditioning heat shock treatment

The present study was designed to investigate the role of NF-kappaB in influencing the outcome of sepsis modulated by previous heat shock treatment. Sepsis was induced in rats by cecum ligation and puncture (CLP) method, which manifests two distinct clinical phases: an initial hyperdynamic phase (9 h after CLP, early sepsis) followed by a hypodynamic phase (18 h after CLP, late sepsis). Rats of heated group were treated by whole body hyperthermia 24 h prior to the CLP operation. Lymphocytes were collected during the early and late sepsis phases. The expressions of Hsp72, p65 and I-kappa B were evaluated by Western blot and immunochemical analysis. NF-kappaB activity was detected by EMSA. The results showed that NF-kappaB activation was initiated during early sepsis and apparently suppressed during late stage of sepsis. Previously treated by heat shock, late-sepsis rats emerged with high preservation of p65 expression and NF-kappaB activity, while Hsp72 was over-expressed. In conclusion, down-regulation of NF-kappaB activity during late sepsis could be attenuated by pretreatment of heat shock through the preservation of p65 expression. The results may provide a mechanistic explanation for the improved outcome to polymicrobial sepsis of rats that are preconditioned with heat shock, as well as a novel highlight for therapeutic intervention of severe infection.

Heat-shock protein 70 inhibits apoptosis by preventing recruitment of procaspase-9 to the Apaf-1 apoptosome

The cellular-stress response can mediate cellular protection through expression of heat-shock protein (Hsp) 70, which can interfere with the process of apoptotic cell death. Stress-induced apoptosis proceeds through a defined biochemical process that involves cytochrome c, Apaf-1 and caspase proteases. Here we show, using a cell-free system, that Hsp70 prevents cytochrome c/dATP-mediated caspase activation, but allows the formation of Apaf-1 oligomers. Hsp70 binds to Apaf-1 but not to procaspase-9, and prevents recruitment of caspases to the apoptosome complex. Hsp70 therefore suppresses apoptosis by directly associating with Apaf-1 and blocking the assembly of a functional apoptosome.

Attenuation of sepsis-induced apoptosis by heat shock pretreatment in rats

Apoptosis is a process by which cells undergo a form of non-necrotic cellular suicide. Although it is a programmed process, apoptosis can be induced by various stressors. During sepsis, apoptosis has been regarded as an important cause of cell death in the immune system, leading to unresponsiveness to treatment. This study was designed to investigate how prior heat shock induction can influence the rate of apoptosis in animals that have experienced sepsis. Sprague-Dawley rats were used, and experimental sepsis was induced by cecal ligation and puncture (CLP). Animals in the heated group were anesthetized and received heat shock by whole-body hyperthermia. They were sacrificed 9 h and 18 h after CLP as early and late sepsis, respectively. Apoptosis was evaluated by "DNA ladder" detection in agarose electrophoresis and Tdt-mediated dUTP nick end-labeling (TUNEL) assay. Hsp72 was detected by Western blot analysis. The results showed that the DNA ladder was detected most clearly in the thymus at the late phase of sepsis with time course dependence, while it showed less clearly in heat shock treated animals. Histopathological study by TUNEL assay obtained similar results in the thymus, where the cortex was more susceptible to apoptosis than the medulla. The Western blot analysis showed that the heat shock induced Hsp72 concomitant with an increase in Bcl-2:Bax ratio. In conclusion, heat shock pretreatment prevents rats from sepsis-induced apoptosis that may account for the better outcome of experimental sepsis. An increase in the Bcl-2:Bax ratio may in part explain the molecular mechanism of the effect of heat shock pretreatment.

Mitochondrial impairment and recovery after heat shock treatment in a human microglial cell line

The application of a heat shock on the human microglial cell line (CHME 5) has been shown to cause cytoskeleton modifications and alterations in phosphorylated metabolite content (Macouillard-Poulletier de Gannes et al., 1998a Metabolic and cellular characterization of immortalized human microglial cells under heat stress. Neurochem. Int. 33, 61-73). In this study, we focused on the possible involvement of mitochondria in this heat stress response. The cell respiratory properties were followed during the recovering period and the possible relationships between mitochondria and the cytoskeleton were studied. We observed that the heat shock induced changes in mitochondrial activity due to protein denaturation, rather than mitochondrial loss. Furthermore, these alterations were correlated with cytoskeleton disorganization since vimentine, tubuline and mitochondria shift, simultaneously, to a perinuclear location. The perturbations of the mitochondrial distribution persisted until cytoskeleton networks had recovered. Nevertheless, the respiratory properties recovered rapidly suggesting a renaturation of mitochondrial proteins in connection with mitochondrial cytoplasmic redistribution.

Cyclophilins and their possible role in the stress response

Cyclophilins are proteins which are remarkably conserved through evolution; moreover they have been found in every possible existing organism, which indicates their fundamental importance. Due to their enzymatic properties, multiplicity, cellular localization and role in protein folding they belong to the group of proteins termed molecular chaperones. All the proteins of the cyclophilin family possess enzymatic peptidyl-prolyl isomerase activity (PPI-ase), which is essential to protein folding in vivo. Recently PPI-ase activity was suggested as playing a role in regulation of transcription and differentiation. However, not all cyclophilin functions are explained by PPI-ase activity. For instance, one of the cyclophilins plays a regulatory role in the heat shock response and the mitochondrial cyclophilin (Cyclophilin D) is an integral part of the mitochondrial permeability transition complex, which is regarded as having a crucial role in mechanisms of cell death. In support of a role in the stress response, the expression of certain cyclophilins has recently been shown to be up-regulated under various stressful conditions. Current evidence of functional involvement of cyclophilins in various intracellular pathways is reviewed along with the indications that cyclophilin D (Cyp D) represents a crucial part of the mitochondrial permeability transition pore, which is detrimental in apoptotic and necrotic cell death. This review does not attempt to cover all the existing information related to cyclophilin family of proteins, but focus on the existing evidence of the involvement of these proteins in the intracellular stress response.

Does the membrane's physical state control the expression of heat shock and other genes?

Membranes provide the structural framework that divides cells from their environment and that, in eukaryotic cells, permits compartmentation. They are not simply passive barriers that are liable to be damaged during environmental challenge or pathological states, but are involved in cellular responses and in modulating intracellular signalling. Recent data show that the expression of several genes, particularly those that respond to changes in temperature, ageing or disease, is influenced and/or controlled by the membrane's physical state.

Stress (heat shock) proteins: molecular chaperones in cardiovascular biology and disease

How a cell responds to stress is a central problem in cardiovascular biology. Diverse physiological stresses (eg, heat, hemodynamics, mutant proteins, and oxidative injury) produce multiple changes in a cell that ultimately affect protein structures and function. Cells from different phyla initiate a cascade of events that engage essential proteins, the molecular chaperones, in decisions to repair or degrade damaged proteins as a defense strategy to ensure survival. Accumulative evidence indicates that molecular chaperones such as the heat shock family of stress proteins (HSPs) actively participate in an array of cellular processes, including cytoprotection. The versatility of the ubiquitous HSP family is further enhanced by stress-inducible regulatory networks, both at the transcriptional and posttranscriptional levels. In the present review, we discuss the regulation and function of HSP chaperones and their clinical significance in conditions such as cardiac hypertrophy, vascular wall injury, cardiac surgery, ischemic preconditioning, aging, and, conceivably, mutations in genes encoding contractile proteins and ion channels.

In vivo heat shock protects rat myocardial mitochondria

Heat shock (HS)/stress proteins (HSP) provide protection from a variety of stresses other than HS, including oxidative stress and mitochondria have been implicated as the target of HS-related protection in stressed cultured cells. Here we investigated whether mitochondria also are targets for the HS-mediated protection in vivo. Sprague Dawley rats were exposed, or not, to HS (41 degrees C, 15 min). After a 21 h recovery period, hearts were excised and perfused with or without H2O2 (0.15 mM). Myocardial mitochondria were then isolated, and their oxygen consumption was analyzed. HS prevented H2O2-induced alterations in state 3 respiration while increasing the expression of Hsp70 and heme oxygenase (HO). Thus, in vivo HS protects rat myocardial mitochondrial respiration against the deleterious effects of oxidative injury, a protection relating to Hsp70 and/or HO and targeting state 3 respiration.

Modulation of lipid unsaturation and membrane fluid state in mammalian cells by stable transformation with the delta9-desaturase gene of Saccharomyces cerevisiae

The composition and physical state of membrane lipids determine the dynamic nature of membranes, which in turn, could directly be linked to the activity of various membrane-associated cellular functions. To better understand the molecular basis of different membrane-related phenomena we established a novel strategy to alter unsaturation of mammalian cell membranes with an identical genetic background. We transfected L929 mouse fibroblastoid cells with DNA constructs containing the Delta9-fatty acid desaturase gene (Ole1) of S. cerevisiae under the control of desaturase promoters derived either from wild type or mutant strains of the dimorphic fungus H. capsulatum.

Binding of non-native protein to Hsp25 during heat shock creates a reservoir of folding intermediates for reactivation

Small heat shock proteins (sHsps) are a conserved and ubiquitous protein family. Their ability to convey thermoresistance suggests their participation in protecting the native conformation of proteins. However, the underlying functional principles of their protective properties and their role in concert with other chaperone families remain enigmatic. Here, we analysed the influence of Hsp25 on the inactivation and subsequent aggregation of a model protein, citrate synthase (CS), under heat shock conditions in vitro. We show that stable binding of several non-native CS molecules to one Hsp25 oligomer leads to an accumulation of CS unfolding intermediates, which are protected from irreversible aggregation. Furthermore, a number of different proteins which bind to Hsp25 can be isolated from heat-shocked extracts of cells. Under permissive folding conditions, CS can be released from Hsp25 and, in cooperation with Hsp70, an ATP-dependent chaperone, the native state can be restored. Taken together, our findings allow us to integrate sHsps functionally in the cellular chaperone system operating under heat shock conditions. The task of sHsps in this context is to efficiently trap a large number of unfolding proteins in a folding-competent state and thus create a reservoir of non-native proteins for an extended period of time, allowing refolding after restoration of physiological conditions in cooperation with other chaperones.

Mitochondria are selective targets for the protective effects of heat shock against oxidative injury

Heat shock (HS) proteins (HSPs) induce protection against a number of stresses distinct from HS, including reactive oxygen species. In the human premonocytic line U937, we investigated in whole cells the effects of preexposure to HS and exposure to hydrogen peroxide (H2O2) on mitochondrial membrane potential, mass, and ultrastructure. HS prevented H2O2-induced alterations in mitochondrial membrane potential and cristae formation while increasing expression of HSPs and the protein product of bcl-2. Protection correlated best with the expression of the 70-kDa HSP, hsp70. We propose that mitochondria represent a selective target for HS-mediated protection against oxidative injury.

Membrane lipid perturbation modifies the set point of the temperature of heat shock response in yeast

Addition of a saturated fatty acid (SFA) induced a strong increase in heat shock (HS) mRNA transcription when cells were heat-shocked at 37 degrees C, whereas treatment with an unsaturated fatty acid (UFA) reduced or eliminated the level of HS gene transcription at 37 degrees C. Transcription of the delta 9-desaturase gene (Ole1) of Histoplasma capsulatum, whose gene product is responsible for the synthesis of UFA, is up-regulated in a temperature-sensitive strain. We show that when the L8-14C mutant of Saccharomyces cerevisiae, which has a disrupted Ole1 gene, is complemented with its own Ole1 coding region under control of its own promoter or Ole1 promoters of H. capsulatum, the level of HS gene transcription depends on the activity of the promoters. Fluorescence anisotropy of mitochondrial membranes of completed strains corresponded to the different activity of the Ole1 promoter used. We propose that the SFA/UFA ratio and perturbation of membrane lipoprotein complexes are involved in the perception of rapid temperature changes and under HS conditions disturbance of the preexisting membrane physical state causes transduction of a signal that induces transcription of HS genes.

Previous heat shock treatment attenuates bicuculline-induced convulsions in rats

Exposure to elevated temperature provokes a sequence of events (heat shock response) in all living organisms. Through this response, heat shock proteins (HSPs) are induced and protect the cells against subsequent injury. We investigated the effect of heat treatment on bicuculline-induced convulsions, and analyzed a possible role of HSPs. Screw electrodes were implanted in the brain of mature male Wistar rats for electroencephalogram (EEG) recording. Experimental rats were subjected to whole-body hyperthermia at 41-42 degrees C for 15 min. Fifteen hours later, bicuculline was injected intraperitoneally to induce convulsions in both experimental and control groups. The heated rats showed a significant attenuation of the convulsive response, in terms of both spike discharges in EEG and clinical seizures. Further-more, induction of HSP72 was detected in the brain of heat-treated rats by immunoblotting, appearing at 4 h and reaching a maximal level 16-24 h after the heat shock. We conclude that the previous heat treatment stabilized neuronal excitability, most probably through the induction of HSP72.

Stress proteins in inflammation

Inflammation provides those searching in the field with a number of "models" allowing them to study, in vivo, in humans and in animals, the regulation and the functions of HSP, which are being considered as a new and promising marker for the severity and the prognosis of inflammatory diseases. HSP are differentially regulated according to the type of inflammation, whether acute or chronic, whether self-limiting (inflammatory cell elimination by apoptosis) or self-perpetuating (inflammatory cell death by necrosis). We propose that mitochondria are a key organelle in determining the outcome of inflammation, because they are both the cellular "switchboard" for apoptosis and a selective target for the protective effects of HSP against the cytotoxic effects of TNF alpha and ROS. On the other hand, HSP exert multiple protective effects in inflammation, including self/non-self discrimination, enhancement of immune responses, immune protection, thermotolerance and protection against the cytotoxicity of inflammatory mediators. The latter protective effects against the deleterious effects of the mediators of inflammation, including ROS and cytokines, open new avenues for the development of original anti-inflammatory therapies, such as non-toxic inducers of a complete HS response. It may well be that the "beneficial effects of fever" already described by Hippocrates actually relate to increased HSP expression during fever, and to their protective effects....

Expression of heat-shock/stress proteins in Duchenne muscular dystrophy

Heat-shock/stress proteins (HSPs) are induced in response to stressful conditions and are essential for survival during and after cellular stress. We investigated whether dystrophin deficiency in muscle from Duchenne muscular dystrophy (DMD) patients induces HSPs. Immunohistochemical studies were performed on cryosections from normal muscle, heat-shocked muscle, and muscle from patients with DMD, dermatomyositis, and mitochondrial myopathy using antibodies against HSP 72/73, HSP 72, HSP 90, groEL (HSP 65 homologue), and ubiquitin. Computer-assisted image processing revealed a significant (P < 0.05) induction of HSP 72/73, 72, 65, and ubiquitin in hypercontracted fibers; HSP 90 and ubiquitin in regenerating fibers; and ubiquitin in macrophage invaded necrotic fibers of DMD muscle. No significant induction of HSPs was observed in dermatomyositis or mitochondrial myopathies. The stress response induced in DMD may relate to the metabolic stress characteristic of the disease and could represent an autoprotective mechanism. Manipulation of this protective response may reduce injury and have potential therapeutic application.

Hsp70 in parasites: as an inducible protective protein and as an antigen

The heat shock (HS) response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stresses. It has been demonstrated that heat shock proteins (HSP) play major roles in many cellular processes, and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology, from cancer research to interaction between host and parasites. This review deals with the hsp70 gene family and with its protein product, hsp70, as an antigen when pathogens infect humans. Members of HSP have been shown to be major antigens of many pathogenic organisms when they experience a major temperature shift upwards at the onset of infection and become targets for host B and T cells.

The effect of hyperthermic treatment on electroencephalographic recovery after interruption of respiration in rats

Electroencephalography (EEG) was utilized for investigating the effect of hyperthermia followed by apneic hypoxia in rats. They were heated whole-bodily to 41 degrees C for 15 min under the control of an artificial rodent ventilator, after drug-induced generalized paralysis. A transcutaneous oxygen saturation monitor was applied to detect the hypoxic condition. EEG was monitored with bipolar needle electrodes. The 72-kDa heat-shock protein (HSP72) in brain was analyzed by sodium dodecyl sulfate-polyacrylamide electrophoresis, followed by immunostaining with an anti-HSP72 antibody. There was no difference in the time interval from onset of apneic hypoxia to flat EEG between the hyperthermic and control groups, but cortical electrical activity appeared earlier in the hyperthermia group than the control group, after 90 s of ventilation interruption. The cardiac function did not change in the two groups. The HSP72 synthesis significantly increased in the brain of the rats with hyperthermic treatment.

Heat shock in human neutrophils: superoxide generation is inhibited by a mechanism distinct from heat-denaturation of NADPH oxidase and is protected by heat shock proteins in thermotolerant cells

Independently of the stimulating agent used, generation of O2- by human neutrophils is transiently inhibited when the cells have been exposed to elevated temperatures. This phenomenon is concomitant with the synthesis of heat shock proteins (HSPs). We have investigated a possible relationship between HSPs and modulation of NADPH oxidase activity in human neutrophils exposed to heat. HSPs were not involved in the inhibition of O2- generation since 1) in enucleated cytoplasts, which are unable to synthesize proteins, the generation of O2- was inhibited after exposure to 43 degrees C, 2) using actinomycin D (Act D) in intact cells, it was possible selectively to inhibit the synthesis of HSPs without modifying the inhibition of NADPH oxidase activity that followed HS. Furthermore, the recovery of NADPH oxidase activity was not under the control of HSPs because the enzyme recovered as well in Act D-treated neutrophils. The NADPH oxidase activity was reconstituted in a cell-free assay by combining the cytosol with the plasma membrane-enriched fraction in the presence of arachidonic acid (AA) and NADPH. Subcellular fractions obtained from control or heated neutrophils exhibited similar oxidase activities suggesting that heat exposure did not induce denaturation of the oxidase components but rather altered the mechanisms of translocation and/or assembly of these components with the plasma membrane. This hypothesis was supported by the inhibition of the granule release in heated cells, a process which also requires translocation and association fusion with the plasma membrane. On the other hand, preexposure of neutrophils to HS prevented the inhibition of O2- generation during a second challenging HS. This acquired thermotolerance was abolished when the synthesis of HSPs was inhibited during the first HS with Act D, indicating a direct relationship between protection of O2- generation and synthesis of HSP. Here we demonstrate that synthesis of HSPs and inhibition or recovery of NADPH oxidase activity are concomitant but unrelated phenomena. In contrast, accumulation of HSPs in thermotolerant neutrophils appeared to play an important role in the prevention of NADPH oxidase inhibition. These results provide further insights into the behavior of human neutrophils and NADPH oxidase upon heat injury.

Stress response of yeast

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The biology of the heat shock response in parasites

The heat shock response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stress. It has been shown that heat shock proteins play major roles in many cellular processes and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology and from cancer research to interactions between host and parasite. In this review, Bruno Maresca and Luisella Carratu deal with some of the unique characteristics of the heat shock response in parasitic organisms.