Heat shock proteins and thermal resistance in yeast

Bioinformatics Analysis, Expression Profiling, and Functional Characterization of Heat Shock Proteins in Wolfi-poria cocos

Heat shock proteins (HSPs) play critical roles in regulating different mechanisms under high-temperature conditions. HSPs have been identified and well-studied in different plants. However, there is a lack of information about their genomic organization and roles in medicinal plants and fungi, especially in Wolfi-poria cocos (W. cocos). We identified sixteen heat shock proteins (HSPs) in W. cocos and analyzed in terms of phylogenetic analysis, gene structure, motif distribution patterns, physiochemical properties, and expression comparison in different strains. Based on phylogenetic analysis, HSPs were divided into five subgroups (WcHSP100, WcHSP90, WcHSP70, WcHSP60, and WcsHSP). Subgroups WcHSP100s, WcHSP90s, WcHSP70s, WcHSP60, and WcsHSPs were further divided into 3, 2, 3, 1, and 6 subfamilies, respectively. Moreover, the expression profiling of all HSP genes in five strains of W. cocos under different temperature extremes revealed that expression of most HSPs were induced by high temperature. However, every subfamily showed different expression suggesting distinctive role in heat stress tolerance. WcHSP70-4, WcHSP90-1, and WcHSP100-1 showed the highest response to high temperature stress. Heterologous expression of WcHSP70-4, WcHSP90-1, and WcHSP100-1 genes in Escherichia coli enhanced survival rate of E. coli during heat stress. These findings suggest the role of W. cocos heat shock genes in the high temperature stress tolerance.

Heat stress regulates the expression of TPK1 gene at transcriptional and post-transcriptional levels in Saccharomyces cerevisiae

In Saccharomyces cerevisiae cAMP regulates different cellular processes through PKA. The specificity of the response of the cAMP-PKA pathway is highly regulated. Here we address the mechanism through which the cAMP-PKA pathway mediates its response to heat shock and thermal adaptation in yeast. PKA holoenzyme is composed of a regulatory subunit dimer (Bcy1) and two catalytic subunits (Tpk1, Tpk2, or Tpk3). PKA subunits are differentially expressed under certain growth conditions. Here we demonstrate the increased abundance and half-life of TPK1 mRNA and the assembly of this mRNA in cytoplasmic foci during heat shock at 37 °C. The resistance of the foci to cycloheximide-induced disassembly along with the polysome profiling analysis suggest that TPK1 mRNA is impaired for entry into translation. TPK1 expression was also evaluated during a recurrent heat shock and thermal adaptation. Tpk1 protein level is significantly increased during the recovery periods. The crosstalk of cAMP-PKA pathway and CWI signalling was also studied. Wsc3 sensor and some components of the CWI pathway are necessary for the TPK1 expression upon heat shock. The assembly in foci upon thermal stress depends on Wsc3. Tpk1 expression is lower in a wsc3∆ mutant than in WT strain during thermal adaptation and thus the PKA levels are also lower. An increase in Tpk1 abundance in the PKA holoenzyme in response to heat shock is presented, suggesting that a recurrent stress enhanced the fitness for the coming favourable conditions. Therefore, the regulation of TPK1 expression by thermal stress contributes to the specificity of cAMP-PKA signalling.

A peptide derived from GAPDH enhances resistance to DNA damage in budding yeast

Social behaviors do not only exist in higher organisms but are also present in microbes that interact for the common good. Here, we report that budding yeast cells interact with their neighboring cells after exposure to DNA damage. Yeast cells irradiated with DNA-damaging ultraviolet light secrete signal peptides that can increase the survival of yeast cells exposed to DNA-damaging stress. The secreted peptide is derived from glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and it induced cell death of a fraction of yeast cells in the group. The data suggest that the GAPDH-derived peptide serves in budding yeast's social interaction in response to DNA-damaging stress. Importance Many studies have shown that microorganisms, including bacteria and yeast, display increased tolerance to stress after exposure to the same stressor. However, the mechanism remains unknown. In this manuscript, we report a striking finding that S. cerevisiae cells respond to DNA damage by secreting a peptide that facilitates resistance to DNA-damaging stress. Although it has been shown that GAPDH possesses many key functions in cells aside from its well-established role in glycolysis, this study demonstrated that GAPDH is also involved in the social behaviors response to DNA-damaging stress. The study opens the gate to an interesting research field about microbial social activity for adaptation to a harsh environment.

The role and therapeutic potential of Hsp90, Hsp70, and smaller heat shock proteins in peripheral and central neuropathies

Heat shock proteins (Hsps) are molecular chaperones that also play important roles in the activation of the heat shock response (HSR). The HSR is an evolutionary conserved and protective mechanism that is used to counter abnormal physiological conditions, stressors, and disease states, such as those exemplified in cancer and/or neurodegeneration. In normal cells, heat shock factor-1 (HSF-1), the transcription factor that regulates the HSR, remains in a dormant multiprotein complex that is formed upon association with chaperones (Hsp90, Hsp70, etc.), co-chaperones, and client proteins. However, under cellular stress, HSF-1 dissociates from Hsp90 and induces the transcriptional upregulation of Hsp70 to afford protection against the encountered cellular stress. As a consequence of both peripheral and central neuropathies, cellular stress occurs and results in the accumulation of unfolded and/or misfolded proteins, which can be counterbalanced by activation of the HSR. Since Hsp90 is the primary regulator of the HSR, modulation of Hsp90 by small molecules represents an attractive therapeutic approach against both peripheral and central neuropathies.

Heat shock protein 70 (HmHsp70) from Hypsizygus marmoreus confers thermotolerance to tobacco

The 70-kD heat shock proteins (Hsp70s) have been proved to be important for stress tolerance and protein folding and unfolding in almost all organisms. However, the functions of Hsp70s in mushroom are not well understood. In the present study, a hsp70 gene from Hypsizygus marmoreus, hmhsp70, was cloned and transferred to tobacco (Nicotiana tabacum) to evaluate its function in thermotolerance. Sequence alignments and phylogenetic analysis revealed that HmHsp70 may be located in the mitochondria region. qPCR analysis revealed that the transcription level of hmhsp70 in H. marmoreus mycelia increased after heat shock treatment in high temperature (42 °C) compared with untreated mycelia (at 25 °C). Transgenic tobaccos expressing hmhsp70 gene showed enhanced resistance to lethal temperature compared with the wild type (WT) plants. Nearly 30% of the transgenic tobaccos survived after treated at a high temperature (50 °C and 52 °C for 4 h); however, almost all the WT tobaccos died after treated at 50 °C and no WT tobacco survived after heat shock at 52 °C. This study firstly showed the function of a hsp70 gene from H. marmoreus.

Heat Shock Proteins: Dynamic Biomolecules to Counter Plant Biotic and Abiotic Stresses

Due to the present scenario of climate change, plants have to evolve strategies to survive and perform under a plethora of biotic and abiotic stresses, which restrict plant productivity. Maintenance of plant protein functional conformation and preventing non-native proteins from aggregation, which leads to metabolic disruption, are of prime importance. Plant heat shock proteins (HSPs), as chaperones, play a pivotal role in conferring biotic and abiotic stress tolerance. Moreover, HSP also enhances membrane stability and detoxifies the reactive oxygen species (ROS) by positively regulating the antioxidant enzymes system. Additionally, it uses ROS as a signal to molecules to induce HSP production. HSP also enhances plant immunity by the accumulation and stability of pathogenesis-related (PR) proteins under various biotic stresses. Thus, to unravel the entire plant defense system, the role of HSPs are discussed with a special focus on plant response to biotic and abiotic stresses, which will be helpful in the development of stress tolerance in plant crops.

Improvement of thermotolerance in Lachancea thermotolerans using a bacterial selection pressure

The use of thermotolerant yeast strains is an important attribute for a cost-effective high temperature biofermentation processes. However, the availability of thermotolerant yeast strains remains a major challenge. Isolation of temperature resistant strains from extreme environments or the improvements of current strains are two major strategies known to date. We hypothesised that bacteria are potential “hurdles” in the life cycle of yeasts, which could influence the evolution of extreme phenotypes, such as thermotolerance. We subjected a wild-type yeast, Lachancea thermotolerans to six species of bacteria sequentially for several generations. After coevolution, we observed that three replicate lines of yeasts grown in the presence of bacteria grew up to 37 °C whereas the controls run in parallel without bacteria could only grow poorly at 35 °C retaining the ancestral mesophilic trait. In addition to improvement of thermotolerance, our results show that the fermentative ability was also elevated, making the strains more ideal for the alcoholic fermentation process because the overall productivity and ethanol titers per unit volume of substrate consumed during the fermentation process was increased. Our unique method is attractive for the development of thermotolerant strains or to augment the available strain development approaches for high temperature industrial biofermentation.

Heat shock modulates the subcellular localization, stability, and activity of HIPK2

The homeodomain-interacting protein kinase-2 (HIPK2) is a highly conserved serine/threonine kinase and is involved in transcriptional regulation. HIPK2 is a highly unstable protein, and is kept at a low level under normal physiological conditions. However, exposure of cells to physiological stress - such as hypoxia, oxidative stress, or UV damage - is known to stabilize HIPK2, leading to the HIPK2-dependent activation of p53 and the cell death pathway. Therefore HIPK2 is also known as a stress kinase and as a stress-activated pro-apoptotic factor. We demonstrate here that exposure of cells to heat shock results in the stabilization of HIPK2 and the stabilization is mediated via K63-linked ubiquitination. Intriguingly, a sub-lethal heat shock (42 °C, 1 h) results in the cytoplasmic localization of HIPK2, while a lethal heat shock (45 °C, 1 h) results in its nuclear localization. Cells exposed to the lethal heat shock showed significantly higher levels of the p53 activity than those exposed to the sub-lethal thermal stress, suggesting that both the level and the nuclear localization are essential for the pro-apoptotic activity of HIPK2 and that the lethal heat shock could retain the HIPK2 in the nucleus to promote the cell death. Taken together our study underscores the importance of HIPK2 in stress mediated cell death, and that the HIPK2 is a generic stress kinase that gets activated by diverse set of physiological stressors.

Anthocyanin-rich tea Sunrouge upregulates expressions of heat shock proteins in the gastrointestinal tract of ICR mice: A comparison with the conventional tea cultivar Yabukita

Sunrouge is an anthocyanin-rich, new tea cultivar that contains similar levels of catechins as Yabukita, the most popular tea cultivar consumed in Japan. Interestingly, Sunrouge preparations have previously been shown to have more pronounced acetylcholinesterase inhibitory and anticolitis activities than those of Yabukita. In this study, we examined their effects on expressions of self-defensive molecules, including heat shock proteins (HSPs), which are molecular chaperones involved in homeostasis and longevity. Hot water extract from freeze-dried Sunrouge significantly upregulated messenger RNA (mRNA) expressions of HSP40, HSP70, and HSP32 (heme oxygenase-1), with grades greater than those shown by Yabukita. Oral administration of freeze-dried preparation of Sunrouge to male ICR mice at a dose of 1% in the basal diet for 1 month resulted in marked upregulations of several HSP mRNA expressions in mucosa from the gastrointestinal tract, especially the upper small intestine. Again, its efficacy was remarkably higher than that of Yabukita. Moreover, exposure of Caenorhabditis elegans to Sunrouge conferred thermoresistant phenotype, and also resulted in a significant life-span elongation. Taken together, our results suggest that Sunrouge is a unique and promising tea cultivar for regulating self-defense systems.

Mechanism of Saccharomyces cerevisiae yeast cell death induced by heat shock. Effect of cycloheximide on thermotolerance

The mechanism of yeast cell death induced by heat shock was found to be dependent on the intensity of heat exposure. Moderate (45°C) heat shock strongly increased the generation of reactive oxygen species (ROS) and cell death. Pretreatment with cycloheximide (at 30°C) suppressed cell death, but produced no effect on ROS production. The protective effect was absent if cycloheximide was added immediately before heat exposure and the cells were incubated with the drug during the heat treatment and recovery period. The rate of ROS production and protective effect of cycloheximide on viability were significantly decreased in the case of severe (50°C) heat shock. Treatment with cycloheximide at 39°C inhibited the induction of Hsp104 synthesis and suppressed the development of induced thermotolerance to severe shock (50°C), but it had no effect on induced thermotolerance to moderate (45°C) heat shock. At the same time, Hsp104 effectively protected cells from death independently of the intensity of heat exposure. These data indicate that moderate heat shock induced programmed cell death in the yeast cells, and cycloheximide suppressed this process by inhibiting general synthesis of proteins.

Adaptive response in stress granule formation and bulk translational repression upon a combined stress of mild heat shock and mild ethanol stress in yeast

The formation of cytoplasmic mRNA-protein complex granules termed 'processing bodies and stress granules' is often induced in the stress responses of eukaryotic cells. Most previous studies on stress granules have focused on the response to a single type of stress, and little information is available about the response to combined stress. Additionally, the effects of adaptation on stress granule formation and bulk translation activity are poorly understood. We investigated the formation of stress granules upon combined exposure to mild heat shock (37 °C) and mild ethanol stress (5% v/v) in Saccharomyces cerevisiae. Although neither stress alone induced stress granule formation, their combination caused a pronounced repression of translation activity and the formation of stress granules. Pretreatment with each mild stress significantly attenuated the formation of stress granules and caused changes in the composition of stress granules upon the subsequent combined stress and facilitated stress granule disassembly accompanied by smooth translational resurrection during the recovery process, indicating that yeast cells can induce adaptations in stress granule formation. However, the pretreated cells still exhibited a severe repression of translation activity. These findings provide novel and fundamental insight into the regulation of yeast stress granules.

The NADPH metabolic network regulates human αB-crystallin cardiomyopathy and reductive stress in Drosophila melanogaster

Dominant mutations in the alpha-B crystallin (CryAB) gene are responsible for a number of inherited human disorders, including cardiomyopathy, skeletal muscle myopathy, and cataracts. The cellular mechanisms of disease pathology for these disorders are not well understood. Among recent advances is that the disease state can be linked to a disturbance in the oxidation/reduction environment of the cell. In a mouse model, cardiomyopathy caused by the dominant CryAB(R120G) missense mutation was suppressed by mutation of the gene that encodes glucose 6-phosphate dehydrogenase (G6PD), one of the cell's primary sources of reducing equivalents in the form of NADPH. Here, we report the development of a Drosophila model for cellular dysfunction caused by this CryAB mutation. With this model, we confirmed the link between G6PD and mutant CryAB pathology by finding that reduction of G6PD expression suppressed the phenotype while overexpression enhanced it. Moreover, we find that expression of mutant CryAB in the Drosophila heart impaired cardiac function and increased heart tube dimensions, similar to the effects produced in mice and humans, and that reduction of G6PD ameliorated these effects. Finally, to determine whether CryAB pathology responds generally to NADPH levels we tested mutants or RNAi-mediated knockdowns of phosphogluconate dehydrogenase (PGD), isocitrate dehydrogenase (IDH), and malic enzyme (MEN), the other major enzymatic sources of NADPH, and we found that all are capable of suppressing CryAB(R120G) pathology, confirming the link between NADP/H metabolism and CryAB.

Osmo-, Thermo- and Ethanol- Tolerances of Saccharomyces cerevisiae S1

Saccharomyces cerevisiae S₁, which is a locally isolated and improved strain showed viability at 40, 45 and 50°C and produced ethanol at 40, 43 and 45°C. When the cells were given heat shock at 45°C for 30min and grown at 40°C, 100% viability was observed for 60h, and addition of 200gL⁻¹ ethanol has led to complete cell death at 30h. Heat shock given at 45°C (for 30min) has improved the tolerance to temperature induced ethanol shock leading to 37% viability at 30h. When the cells were subjected to ethanol (200gL⁻¹ for 30 min) and osmotic shock (sorbitol 300gL⁻¹), trehalose contents in the cells were increased. The heat shocked cells showed better viability in presence of added ethanol. Soy flour supplementation has improved the viability of S. cerevisiae S₁ to 80% in presence of 100gL⁻¹ added ethanol and to 60% in presence of 300gL⁻¹sorbitol. In presence of sorbitol (200gL⁻¹) and ethanol (50gL⁻¹) at 40°C, 46% viability was retained by S. cerevisiae S₁ at 48h and it was improved to 80% by soy flour supplementation.

Modelling the regulation of thermal adaptation in Candida albicans, a major fungal pathogen of humans

Eukaryotic cells have evolved mechanisms to sense and adapt to dynamic environmental changes. Adaptation to thermal insults, in particular, is essential for their survival. The major fungal pathogen of humans, Candida albicans, is obligately associated with warm-blooded animals and hence occupies thermally buffered niches. Yet during its evolution in the host it has retained a bona fide heat shock response whilst other stress responses have diverged significantly. Furthermore the heat shock response is essential for the virulence of C. albicans. With a view to understanding the relevance of this response to infection we have explored the dynamic regulation of thermal adaptation using an integrative systems biology approach. Our mathematical model of thermal regulation, which has been validated experimentally in C. albicans, describes the dynamic autoregulation of the heat shock transcription factor Hsf1 and the essential chaperone protein Hsp90. We have used this model to show that the thermal adaptation system displays perfect adaptation, that it retains a transient molecular memory, and that Hsf1 is activated during thermal transitions that mimic fever. In addition to providing explanations for the evolutionary conservation of the heat shock response in this pathogen and the relevant of this response to infection, our model provides a platform for the analysis of thermal adaptation in other eukaryotic cells.

Hormesis: why it is important to biogerontologists

This paper offers a broad assessment of the hormetic dose response and its relevance to biogerontology. The paper provides detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how the hormesis concept could be further applied in the development of new therapeutic advances in the treatment of age-related diseases. The concept of hormesis has direct application to biogerontology not only affecting the quality of the aging process but also experimental attempts to extend longevity.

Genome-wide analysis of yeast stress survival and tolerance acquisition to analyze the central trade-off between growth rate and cellular robustness

A genome-wide analysis of the acquisition of stress cross-tolerance shows that reduction of growth rate is an important determinant of severe stress survival. Cellular functions important for the coupling of growth rate to stress resistance are identified, as are those required for cross-tolerance acquisition independent of growth rate reduction.

All organisms have evolved to cope with changes in environmental conditions, ensuring the optimal combination of proliferation and survival. In yeast, exposure to a mild stress leads to an increased tolerance for other stresses. This suggests that yeast uses information from the environment to prepare for future threats. We used the yeast knockout collection to systematically investigate the genes and functions involved in severe stress survival and in the acquisition of stress (cross-) tolerance. Besides genes and functions relevant for survival of heat, acid, and oxidative stress, we found an inverse correlation between mutant growth rate and stress survival. Using chemostat cultures, we confirmed that growth rate governs stress tolerance, with higher growth efficiency at low growth rates liberating the energy for these investments. Cellular functions required for stress tolerance acquisition, independent of the reduction in growth rate, were involved in vesicular transport, the Rpd3 histone deacetylase complex, and the mitotic cell cycle. Stress resistance and acquired stress tolerance in Saccharomyces cerevisiae are governed by a combination of stress-specific and general processes. The reduction of growth rate, irrespective of the cause of this reduction, leads to redistribution of resources toward stress tolerance functions, thus preparing the cells for impending change.

Extension of lifespan in C. elegans by naphthoquinones that act through stress hormesis mechanisms

Hormesis occurs when a low level stress elicits adaptive beneficial responses that protect against subsequent exposure to severe stress. Recent findings suggest that mild oxidative and thermal stress can extend lifespan by hormetic mechanisms. Here we show that the botanical pesticide plumbagin, while toxic to C. elegans nematodes at high doses, extends lifespan at low doses. Because plumbagin is a naphthoquinone that can generate free radicals in vivo, we investigated whether it extends lifespan by activating an adaptive cellular stress response pathway. The C. elegans cap‘n’collar (CNC) transcription factor, SKN-1, mediates protective responses to oxidative stress. Genetic analysis showed that skn-1 activity is required for lifespan extension by low-dose plumbagin in C. elegans. Further screening of a series of plumbagin analogs identified three additional naphthoquinones that could induce SKN-1 targets in C. elegans. Naphthazarin showed skn-1dependent lifespan extension, over an extended dose range compared to plumbagin, while the other naphthoquinones, oxoline and menadione, had differing effects on C. elegans survival and failed to activate ARE reporter expression in cultured mammalian cells. Our findings reveal the potential for low doses of naturally occurring naphthoquinones to extend lifespan by engaging a specific adaptive cellular stress response pathway.

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.

Adult heat tolerance variation in Drosophila melanogaster is not related to Hsp70 expression

Expression of heat-inducible Hsp70 is considered closely linked to thermotolerance in Drosophila melanogaster and other ectotherms. However, intra-specific variation of Hsp70 expression levels and its relationship to heat resistance has only been investigated in a few studies. Although in Drosophila larvae Hsp70 expression may be a key determinant of heat tolerance, the evidence for this in adults is equivocal. We therefore examined heat-induced Hsp70 expression and several measurements of adult heat tolerance in three independent collections of D. melanogaster, measured in three laboratories and using slightly different protocols. Expression levels of Hsp70 were quantified using ELISA or Western blots on extracts from adult females. Both Hsp70 and heat tolerance exhibited substantial within-population variation as previously reported. However, in all experiments there were no significant correlation between Hsp70 expression and laboratory assays of adult heat tolerance commonly used in Drosophila. When combining data across three studies we had high power to detect associations but the results showed that variation in Hsp70 expression is only likely to explain a small proportion of variation in adult heat tolerance. Therefore, although Hsp70 expression is a major component of the cellular heat stress response, its influence on intra-specific heat tolerance variation may be life-stage specific.

Hsp104 and prion propagation

High-ordered aggregates (amyloids) may disrupt cell functions, cause toxicity at certain conditions and provide a basis for self-perpetuated, protein-based infectious heritable agents (prions). Heat shock proteins acting as molecular chaperones counteract protein aggregation and influence amyloid propagation. The yeast Hsp104/Hsp70/Hsp40 chaperone complex plays a crucial role in interactions with both ordered and unordered aggregates. The main focus of this review will be on the Hsp104 chaperone, a molecular "disaggregase".

Chaperone effects on prion and nonprion aggregates

Exposure to high temperature or other stresses induces a synthesis of heat shock proteins. Many of these proteins are molecular chaperones, and some of them help cells to cope with heat-induced denaturation and aggregation of other proteins. In the last decade, chaperones have received increased attention in connection with their role in maintenance and propagation of the Saccharomyces cerevisiae prions, infectious or heritable agents transmitted at the protein level. Recent data suggest that functioning of the chaperones in reactivation of heat-damaged proteins and in propagation of prions is based on the same molecular mechanisms but may lead to different consequences depending on the type of aggregate. In both cases the concerted and balanced action of "chaperones' team," including Hsp104, Hsp70, Hsp40 and possibly other proteins, determines whether a misfolded protein is to be incorporated into an aggregate, rescued to the native state or targeted for degradation.

Activation of PI3-K/Akt pathway for thermal preconditioning to protect cultured cerebellar granule neurons against low potassium-induced apoptosis

AIM

This study was designed to investigate whether the activation of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway is required for thermal preconditioning to protect rat cerebellar granule neurons (CGN) against apoptosis induced by low potassium, and to explore the possibility of a link between the upregulated heat shock protein (HSP)70 expression and Akt activation in the acquisition of neuroprotection induced by thermal preconditioning.

METHODS

CGN cultured for 8 d in vitro were switched to 5K medium for 24 h after thermal preconditioning (TP; 43.5 degree for 90 min, then 37 degree for 1 h). To study the role of the PI3-K/Akt pathway, a PI3-K inhibitor, LY294002 (20 micromol/L) was added into the cultures 1 h before TP. 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay and fluorescein diacetate staining were used to determine cell viability. Hoechst 33258 staining and agar gel electrophoresis were used to test the morphological and biological characters of CGN. Western blot analysis was employed to detect the levels of phospho-Akt, phospho-glycogen synthase kinase 3beta (GSK3beta) Akt, GSK3beta, and HSP70.

RESULTS

TP protected CGN against apoptosis induced by low potassium. LY294002 inhibited the neuroprotective effect on CGN induced by TP. TP induced a robust activation of Akt and the inactivation of GSK3beta via PI3-K. Furthermore, the activation of the PI3-K/Akt pathway by TP persisted for 24 h in the 5K cultures. LY294002 (20 micromol/L) failed to inhibit the upregulated HSP70 expression induced by TP.

CONCLUSION

The activation of the PI3-K/Akt pathway is required for TP to protect CGN against apoptosis induced by low potassium, but the neuroprotective effect by Akt activation is not mediated through the downstream induction of HSP70 expression.

Loss of Hsp70 in Drosophila is pleiotropic, with effects on thermotolerance, recovery from heat shock and neurodegeneration

The heat-shock response is a programmed change in gene expression carried out by cells in response to environmental stress, such as heat. This response is universal and is characterized by the synthesis of a small group of conserved protein chaperones. In Drosophila melanogaster the Hsp70 chaperone dominates the profile of protein synthesis during the heat-shock response. We recently generated precise deletion alleles of the Hsp70 genes of D. melanogaster and have used those alleles to characterize the phenotypes of Hsp70-deficient flies. Flies with Hsp70 deletions have reduced thermotolerance. We find that Hsp70 is essential to survive a severe heat shock, but is not required to survive a milder heat shock, indicating that a significant degree of thermotolerance remains in the absence of Hsp70. However, flies without Hsp70 have a lengthened heat-shock response and an extended developmental delay after a non-lethal heat shock, indicating Hsp70 has an important role in recovery from stress, even at lower temperatures. Lack of Hsp70 also confers enhanced sensitivity to a temperature-sensitive lethal mutation and to the neurodegenerative effects produced by expression of a human polyglutamine disease protein.

Biological stress responses to radio frequency electromagnetic radiation: are mobile phones really so (heat) shocking?

Cells phenotypically adapt to alterations in their intra- and extracellular environment via organised alterations to gene and protein expression. Many chemical and physical stimuli are known to drive such responses, including the induction of oxidative stress and heat shock. Increasing use of mobile telephones in our society, has brought focus on the potential for radio frequency (microwave) electromagnetic radiation to elicit biological stress responses, in association with potentially detrimental effects of this to human health. Here we review evidence suggesting altered gene and protein expression in response to such emissions, with particular focus on heat shock proteins. Non-thermal induction of heat shock proteins has been claimed by a number of investigations in in vitro cellular systems, and appears pleiotropic for many other regulatory events. However, many of these studies are flawed by inconsistencies in exposure models, cell types used and the independent reproducibility of the findings. Further, the paucity of evidence from in vivo experimentation is largely contradictory. Therefore, the validity of these effects in human health risk assessment remain unsubstantiated. Where possible, suggestions for further experimental clarification have been provided.

Anticancer drugs as inducers of thermotolerance in yeast

Yeast cell viability was evaluated microscopically following exposure to heat shock for 30 min at 53 degrees C. The cells were previously grown in the presence of potential stressors (anticancer drugs; e.g., 5-fluorouracil, methotrexate, cisplatin, bleomycin, mitomycin-C and camptothecin-11). The induction of thermotolerance was documented by significantly increased viability after heat shock. This effect, which was reversed by cycloheximide, was comparable to that observed following exposure to a mild heat stress. These data demonstrate that pretreatment with sub-toxic concentrations of some of the clinically used antineoplastic agents conferres thermotolerance to yeast, possibly through the synthesis of protein components.

Cloning, sequencing, and functional expression in Escherichia coli of chaperonin (groESL) genes from Vibrio cholerae

Using a series of oligonucleotides synthesized on the basis of conserved nucleotide motifs in heat-shock genes, the groESL heat-shock operon from a Vibrio cholerae TSI-4 strain has been cloned and sequenced, revealing that the presence of two open reading frames (ORFs) of 291 nucleotides and 1,632 nucleotides separated by 54 nucleotides. The first ORF encoded a polypeptide of 97 amino acids, GroES homologue, and the second ORF encoded a polypeptide of 544 amino acids, GroEL homologue. A comparison of the deduced amino acid sequences revealed that the primary structures of the V. cholerae GroES and GroEL proteins showed significant homology with those of the GroES and GroEL proteins of other bacteria. Complementation experiments were performed using Escherichia coli groE mutants which have the temperature-sensitive growth phenotype. The results showed that the groES and groEL from V. cholerae were expressed in E. coli, and groE mutants harboring V. cholerae groESL genes regained growth ability at high temperature. The evolutionary analysis indicates a closer relationship between V. cholerae chaperonins and those of the Haemophilus and Yersinia species.

Molybdate induces thermotolerance in yeast

Application of a mild heat pretreatment, performed by shifting cells from 27 degrees C to 37 degrees C led to the protection of yeast cells from death due to a subsequent extreme heat shock at 53 degrees C. The presence of cycloheximide inhibited this induction of thermotolerance, indicating the involvement of de novo protein. The phosphatase inhibitor sodium molybdate induced thermotolerance to the non-pretreated yeast cells. This induction of thermotolerance did not seem to depend upon de novo protein synthesis. Thus, acquisition of thermotolerance in yeast may involve a number of cellular mechanisms depending on the conditions the organism encounters at any particular time.

Expression of heat shock protein 72 by alveolar macrophages in hypersensitivity pneumonitis

The current study was done to look at a possible role of heat shock proteins (HSPs) in hypersensitivity pneumonitis (HP). The specific aims were to determine whether there was a difference in the expression of HSP72 in alveolar macrophages (AMs) between mice challenged with HP antigen and saline-treated control mice and between AMs obtained by bronchoalveolar lavage from 18 patients with HP and 11 normal subjects. The expression of HSP72 was studied under basal conditions and under a mild heat shock. HSP72 expression by AMs in response to in vitro stimulation with Saccharopolyspora rectivirgula was lower in AMs of control mice than in those of HP animals. HSP72 was constitutively expressed in AMs of both normal and HP subjects. Densitometric ratios showed that AMs from normal subjects responded to heat shock with a 39 degrees C-to-37 degrees C ratio of 1.72 +/- 0.18 (mean +/- SE), and AMs from HP patients responded with a ratio of 1.16 +/- 0.16 (P = 0.0377). This decreased induction by additional stress of AMs could lead to an altered immunoregulatory activity and account for the inflammation seen in HP.

Oxidants differentially regulate the heat shock response

Cells, animals, and humans respond to hyperthermia through the synthesis of a family of proteins termed heat shock proteins (HSPs). Because hyperthermic stress may also result in mitochondrial uncoupling and the generation of reactive oxygen species, we wondered whether oxidant stress was sufficient to increase cellular levels of HSP70. HSP70 was detected in cells heated or treated with menadione but not in those treated with hydrogen peroxide or xanthine/xanthine oxidase. We speculate that oxidant stress from menadione exposure is qualitatively different from exposure from hydrogen peroxide or xanthine/xanthine oxidase.

Heat-shock response of the entomopathogenic fungus Beauveria brongniartii

The heat-shock response of five strains of the entomopathogenic fungus Beauveria brongniartii was studied using two-dimensional (2D) gel electrophoresis. The fungal cells were heat shocked at 45 °C for 1 h and the total cellular protein was subjected to 2D gel electrophoresis. Proteins were separated in the first dimension using isoelectric focusing (pH range of 3.0–10) and in the second dimension by sodium dodecyl sulphate – polyacrylamide gel electrophoresis. More than 150 polypeptides for each strain were visualized by silver staining and have been assigned individual numbers as polypeptide coordinates. Analysis of the polypeptide map obtained by 2D gels indicated three patterns; several unique heat-shock proteins (HSPs) were (i) induced, (ii) enhanced, or (iii) repressed. Some of the HSPs induced by 45 °C were unique for each of the strains tested. Identification of heat-inducible protein synthesis or repression has ramifications for field survival and performance of entomopathogenic fungi. As well, the HSPs can be used as "signature proteins" for identification pruposes and this raises the possibility of using HSPs as a diagnostic tool applicable to other pest control fungi.Key words: heat-shock proteins, heat-shock response, two-dimensional electrophoresis, entomopathogenic fungi, Beauveria brongniartii.

Submerged batch culture of the psychrophile Monographella nivalis in a defined medium; growth, carbohydrate utilization and responses to temperature

An asporogenous strain of the pink snow mould fungus, Monographella nivalis (Schaffnit) E. Müller, anamorph Gerlachia nivalis (Ces. ex Sac.) W. Gams & E. Müller (Syn. Fusarium nivale Ces. ex Sacc.), grew at 5 °C on a denned salts medium plus vitamins and utilized a variety of simple and polymeric carbohydrates as the sole carbon and energy source. Mycelium was grown at temperatures between 3 and 15 °C in aerated submerged fermentation culture in chemically defined medium plus sucrose. Optimum growth rates of 0·035-0·033 h^-1 occurred between 9 and 12 °C. Growth in a simple medium showed that all biochemical and physiological processes necessary for growth were functional at 3 °C. The growth performance of the organism at low temperatures was no better than would be expected from extrapolation of mesophilic growth responses to temperature. The optimum growth temperature of 9-12°C showed that some biochemical or physiological process was impaired above 12 °C. Uptake and incorporation of ³⁵ S-methionine by mycelium at different temperatures showed that general protein synthesis increased up to 25 °C, and hence was not responsible per se for the sensitivity to temperatures above 12 °C. Heat shock proteins were synthesized at the relatively low temperature of 25 °C, consistent with the low temperature optimum for growth. When grown with sucrose as the sole carbon source, the mycelium catalyzed the extracellular hydrolysis of sucrose, releasing glucose and fructose together with a small amount of fructan trisaccharides and a trace of tetra- and penta-saccharides. Fructan accumulation was transient, corresponding with maximal rates of sucrose hydrolysis. Most biomass formation occurred in the absence of fructan in the culture, hence fructan was not necessary for growth at low temperature and did not appear to function as a cryoprotectant. Invertase activity was mostly (60-70%) bound to mycelium; the remainder was free in the culture supernatant. The regulation of invertase expression appeared to be by sucrose-induction, rather than by end-product repression. Rates of sucrose hydrolysis in culture were temperature-sensitive and were markedly depressed above 12 °C, indicating inhibition of invertase formation.

Heat shock response and heat shock protein antigens of Vibrio cholerae

Sixteen heat shock proteins (Hsps) have been identified in the hypertoxinogenic strain 569B of Vibrio cholerae which are synthesized in response to small and large elevations of temperature. The induction of the Hsps is necessary for the cells to survive the deleterious effects of heat. There is no difference in the pattern of induction of the Hsps in V. cholerae strains varying in levels of toxinogenicity. One of the major low-molecular-mass Hsps, a 16-kDa protein, is preferentially degraded following shift down of temperature. This protein is induced at a much lower level at high temperatures in cells maintained in the laboratory for a prolonged period. The only Hsp located in the outer membrane of V. cholerae cells is a 23-kDa protein. Western immunoblot analysis with human immune sera collected from convalescent cholera patients revealed that this protein is markedly immunogenic. The human immune serum also reacted with the 69- and 16-kDa major Hsps and the 88-, 66-, and 46-kDa Hsps but not with the 61-kDa major Hsp identified as the groEL gene product. All major Hsps reacted with rabbit anti-V. cholerae sera. Ethanol stress leads to the induction of four of the major Hsps and three additional proteins.

The yeast and mammalian Ras pathways control transcription of heat shock genes independently of heat shock transcription factor

Yeast strains in which the Ras-cyclic AMP (cAMP) pathway is constitutively active are sensitive to heat shock, whereas mutants in which the activity of this pathway is low are hyperresistant to heat shock. To determine the molecular basis for these differences, we examined the transcriptional induction of heat shock genes in various yeast strains. Activation of heat shock genes was attenuated in the strains in which the Ras-cAMP pathway is constitutively active. In contrast, in a strain deficient in cAMP production, several heat shock genes were induced by removal of cAMP from the medium. These results indicate that the Ras-cAMP pathway affects the induction of heat shock genes. In all of the mutants, heat shock transcription factor expression and activity were identical to those in wild-type cells. The response to heat shock in Ha-ras-transformed rat fibroblasts was also studied. While no induction of Hsp68 was observed in Ha-ras-transformed cells, proper regulation of heat shock transcription factor was found. Therefore, in mammals, as in Saccharomyces cerevisiae, the Ras pathway controls the transcription of heat shock genes via a mechanism not involving the heat shock transcription factor.

The yeast and mammalian Ras pathways control transcription of heat shock genes independently of heat shock transcription factor

Yeast strains in which the Ras-cyclic AMP (cAMP) pathway is constitutively active are sensitive to heat shock, whereas mutants in which the activity of this pathway is low are hyperresistant to heat shock. To determine the molecular basis for these differences, we examined the transcriptional induction of heat shock genes in various yeast strains. Activation of heat shock genes was attenuated in the strains in which the Ras-cAMP pathway is constitutively active. In contrast, in a strain deficient in cAMP production, several heat shock genes were induced by removal of cAMP from the medium. These results indicate that the Ras-cAMP pathway affects the induction of heat shock genes. In all of the mutants, heat shock transcription factor expression and activity were identical to those in wild-type cells. The response to heat shock in Ha-ras-transformed rat fibroblasts was also studied. While no induction of Hsp68 was observed in Ha-ras-transformed cells, proper regulation of heat shock transcription factor was found. Therefore, in mammals, as in Saccharomyces cerevisiae, the Ras pathway controls the transcription of heat shock genes via a mechanism not involving the heat shock transcription factor.

Effect of heat shock on intracellular calcium mobilization in neuroblastoma x glioma hybrid cells

The effect of heat shock on agonist-stimulated intracellular Ca2+ mobilization and the expression of heat shock protein 72 (hsp72) in neuroblastoma x glioma hybrid cells (NG 108-15 cells) were examined. Hsp72 was expressed at 6 h after heat shock (42.5 degrees C, 2 h), reached a maximum at 12 h, and decreased thereafter. Bradykinin-induced [Ca2+]i rise was attenuated to 28% of control by heat shock at 2 h after heat shock, and reversion to the control level was seen 12 h later. When the cells were treated with quercetin or antisense oligodeoxyribonucleotide against hsp72 cDNA, the synthesis of hsp72 was not induced by heat shock, whereas bradykinin-induced [Ca2+]i rise was abolished and the [Ca2+]i rise was not restored. Recovery from this stressed condition was evident when cells were stimulated by the Ca(2+)-ATPase inhibitor thapsigargin, even in the presence of either quercetin or antisense oligodeoxyribonucleotide. Inositol 1,4,5-trisphosphate (IP3) production was not altered by heat shock at 12 h after heat shock, whereas IP3 receptor binding activity was reduced to 45.3%. In the presence of quercetin or antisense oligodeoxyribonucleotide, IP3 receptor binding activity decreased and reached 27.2% of the control 12 h after heat shock. Our working thesis is that heat shock transiently suppresses the IP3-mediated intracellular Ca2+ signal transduction system and that hsp72 is involved in the recovery of bradykinin-induced [Ca2+]i rise.

Gene expression under temperature stress

In this review, changes in plant gene expression in response to environmental stresses are discussed using the examples of high and low temperature treatments. While some changes may contribute to acclimatory processes which improve plant survival or performance under stress, others may be 'shock' responses indicative of sensitivity. The heat-shock response, which is almost ubiquitous among eukaryotic organisms, is characterized by repression of normal cellular protein synthesis mediated at both the transcriptional and the translational level, and induction of heat-shock protein (HSP) synthesis. There is a correlation between HSP synthesis and induced thermotolerance in plants, but the evidence for a causal relationship is not conclusive. The possible biochemical functions of some of the HSPs are now becoming apparent; they are believed to play an important role in preventing accumulation of damaged proteins in the cell during heat shock. Although no other environmental stress elicits the full heat-shock response, certain treatments do induce synthesis of subsets of the HSPs, and the reasons for this are considered. Alterations in gene expression in response to low temperatures are more diverse and usually less dramatic than the heat-shock response, with which they share little, if any, homology. Biochemical adjustments during cold treatment are discussed, with particular reference to those which contribute to acclimation. Several genes whose expression is induced by cold have been cloned and characterized, and in some cases it is possible to attribute in vivo functions to them; they include enzymes of lipid, carbohydrate and protein metabolism, structural proteins and putative cryoprotectants. The use of transgenic plants is further facilitating an investigation of the biochemical factors which are important in cold acclimation. Drought, osmotic stress and abscisic acid induce expression of many of the same genes as does cold treatment; it seems likely that some of the products of these genes contribute to increased freezing tolerance by protecting against intracellular dehydration. Contents Summary 1 I. Introduction 1 II. High temperature stress 3 III. Low temperature stress 10 IV. Concluding remarks 20 Acknowledgements 21 References 21.

Heat shock-mediated cell cycle blockage and G1 cyclin expression in the yeast Saccharomyces cerevisiae

For cells of the yeast Saccharomyces cerevisiae, heat shock causes a transient inhibition of the cell cycle-regulatory step START. We have determined that this heat-induced START inhibition is accompanied by decreased CLN1 and CLN2 transcript abundance and by possible posttranscriptional changes to CLN3 (WHI1/DAF1) cyclin activity. Persistent CLN2 expression from a heterologous promoter or the CLN2-1 or CLN3-1 alleles that are thought to encode cyclin proteins with increased stability eliminated heat-induced START inhibition but did not affect other aspects of the heat shock response. Heat-induced START inhibition was shown to be independent of functions that regulate cyclin activity under other conditions and of transcriptional regulation of SWI4, an activator of cyclin transcription. Cells lacking Bcy1 function and thus without cyclic AMP control of A kinase activity were inhibited for START by heat shock as long as A kinase activity was attenuated by mutation. We suggest that heat shock mediates START blockage through effects on the G1 cyclins.

Stress response of yeast

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Heat shock-mediated cell cycle blockage and G1 cyclin expression in the yeast Saccharomyces cerevisiae

For cells of the yeast Saccharomyces cerevisiae, heat shock causes a transient inhibition of the cell cycle-regulatory step START. We have determined that this heat-induced START inhibition is accompanied by decreased CLN1 and CLN2 transcript abundance and by possible posttranscriptional changes to CLN3 (WHI1/DAF1) cyclin activity. Persistent CLN2 expression from a heterologous promoter or the CLN2-1 or CLN3-1 alleles that are thought to encode cyclin proteins with increased stability eliminated heat-induced START inhibition but did not affect other aspects of the heat shock response. Heat-induced START inhibition was shown to be independent of functions that regulate cyclin activity under other conditions and of transcriptional regulation of SWI4, an activator of cyclin transcription. Cells lacking Bcy1 function and thus without cyclic AMP control of A kinase activity were inhibited for START by heat shock as long as A kinase activity was attenuated by mutation. We suggest that heat shock mediates START blockage through effects on the G1 cyclins.