Induction of heat shock proteins and thermotolerance by ethanol in Saccharomyces cerevisiae

Heat Shock Factor 1 forms condensates and restructures the yeast genome before activating target genes

In insects and mammals, 3D genome topology has been linked to transcriptional states yet whether this link holds for other eukaryotes is unclear. Using both ligation proximity and fluorescence microscopy assays, we show that in Saccharomyces cerevisiae, Heat Shock Response (HSR) genes dispersed across multiple chromosomes and under the control of Heat Shock Factor (Hsf1) rapidly reposition in cells exposed to acute ethanol stress and engage in concerted, Hsf1-dependent intergenic interactions. Accompanying 3D genome reconfiguration is equally rapid formation of Hsf1-containing condensates. However, in contrast to the transience of Hsf1-driven intergenic interactions that peak within 10-20 min and dissipate within 1 h in the presence of 8.5% (v/v) ethanol, transcriptional condensates are stably maintained for hours. Moreover, under the same conditions, Pol II occupancy of HSR genes and RNA expression are detectable only later in the response and peak much later (>1 h). This contrasts with the coordinate response of HSR genes to thermal stress (39 C) where Pol II occupancy, transcription, intergenic interactions, and formation of Hsf1 condensates are all rapid yet transient (peak within 2.5-10 min and dissipate within 1 h). Therefore, Hsf1 forms condensates, restructures the genome and transcriptionally activates HSR genes in response to both forms of proteotoxic stress but does so with strikingly different kinetics. In cells subjected to ethanol stress, Hsf1 forms condensates and repositions target genes before transcriptionally activating them.

Deletion of the transcription factors Hsf1, Msn2 and Msn4 in yeast uncovers transcriptional reprogramming in response to proteotoxic stress

The response to proteotoxic stresses such as heat shock allows organisms to maintain protein homeostasis under changing environmental conditions. We asked what happens if an organism can no longer react to cytosolic proteotoxic stress. To test this, we deleted or depleted, either individually or in combination, the stress-responsive transcription factors Msn2, Msn4, and Hsf1 in Saccharomyces cerevisiae. Our study reveals a combination of survival strategies, which together protect essential proteins. Msn2 and 4 broadly reprogram transcription, triggering the response to oxidative stress, as well as biosynthesis of the protective sugar trehalose and glycolytic enzymes, while Hsf1 mainly induces the synthesis of molecular chaperones and reverses the transcriptional response upon prolonged mild heat stress (adaptation).

Quantitative Comparison of HSF1 Activators

The heat shock response (HSR) pathway is a highly conserved rescue mechanism, which protects the cells from harmful insults disturbing the cellular protein homeostasis via expression of chaperones. Furthermore, it was demonstrated to play crucial roles in various diseases like neurodegeneration and cancer. For neurodegenerative diseases, an overexpression of chaperones is a potential therapeutic approach to clear the cells from non-functional protein aggregates. Therefore, activators of the HSR pathway and its master regulator HSF1 are under close observation. There are numerous HSR activators published in the literature using different model systems, experimental designs, and readout assays. The aim of this work was to provide a quantitative comparison of a broad range of published activators using a newly developed HSF responsive dual-luciferase cell line. Contrary to natural target genes, which are regulated by multiple input pathways, the artificial reporter exclusively reacts to HSF activity. In addition, the results were compared to endogenous heat shock protein expression. As a result, great differences in the intensity of pathway activation were observed. In addition, a parallel viability assessment revealed high variability in the specificity of the drugs. Furthermore, the differences seen compared to published data indicate that some activators exhibit tissue-specific differences leading to interesting assumptions about the regulation of HSF1.

Production of Bioethanol—A Review of Factors Affecting Ethanol Yield

Fossil fuels are a major contributor to climate change, and as the demand for energy production increases, alternative sources (e.g., renewables) are becoming more attractive. Biofuels such as bioethanol reduce reliance on fossil fuels and can be compatible with the existing fleet of internal combustion engines. Incorporation of biofuels can reduce internal combustion engine (ICE) fleet carbon dioxide emissions. Bioethanol is typically produced via microbial fermentation of fermentable sugars, such as glucose, to ethanol. Traditional feedstocks (e.g., first-generation feedstock) include cereal grains, sugar cane, and sugar beets. However, due to concerns regarding food sustainability, lignocellulosic (second-generation) and algal biomass (third-generation) feedstocks have been investigated. Ethanol yield from fermentation is dependent on a multitude of factors. This review compares bioethanol production from a range of feedstocks, and elaborates on available technologies, including fermentation practices. The importance of maintaining nutrient homeostasis of yeast is also examined. The purpose of this review is to provide industrial producers and policy makers insight into available technologies, yields of bioethanol achieved by current manufacturing practices, and goals for future innovation.

Anesthetic pretreatment confers thermotolerance on Saccharomyces cerevisiae yeast

Saccharomyces cerevisiae yeast, when pretreated with elevated temperatures, undergo adaptive changes that promote survival after an otherwise lethal heat stress. The heat shock response, a cellular stress response variant, mediates these adaptive changes. Ethanol, a low-potency anesthetic, promotes thermotolerance possibly through heat shock response activation. Therefore, we hypothesized other anesthetic compounds, like ethanol, may invoke the heat shock response to promote thermotolerance. To test this hypothesis, we pretreated yeast with a series of non-volatile anesthetic and anesthetic-related compounds and quantified survival following lethal heat shock (52 °C for 5 min). Most compounds invoked thermoprotection and promoted survival with a potency proportional to hydrophobicity: tribromoethanol (5.6 mM, peak survival response), trichloroethanol (17.8 mM), dichloroethanol (100 mM), monochloroethanol (316 mM), trifluoroethanol (177.8 mM), ethanol (1 M), isopropanol (1 M), propofol (316 μM), and carbon tetrabromide (32 μM). Thermoprotection conferred by pretreatment with elevated temperatures was "left shifted" by anesthetic co-treatment from (in °C) 35.3 ± 0.1 to 32.2 ± 0.1 with trifluoroethanol (177.8 mM), to 31.2 ± 0.1 with trichloroethanol (17.8 mM), and to 29.1 ± 0.3 with tribromoethanol (5.6 mM). Yeast in postdiauxic shift growth phase, relative to mid-log, responded with greater heat shock survival; and media supplementation with tryptophan and leucine blocked thermoprotection, perhaps by reversing the amino acid starvation response. Our results suggest S. cerevisase may serve as a model organism for understanding anesthetic toxicity and anesthetic preconditioning, a process by which anesthetics promote tissue survival after hypoxic insult.

Improved fermentation efficiency of S. cerevisiae by changing glycolytic metabolic pathways with plasma agitation

Production of ethanol by the yeast Saccharomyces cerevisiae is a process of global importance. In these processes, productivities and yields are pushed to their maximum possible values leading to cellular stress. Transient and lasting enhancements in tolerance and performance have been obtained by genetic engineering, forced evolution, and exposure to moderate levels of chemical and/or physical stimuli, yet the drawbacks of these methods include cost, and multi-step, complex and lengthy treatment protocols. Here, plasma agitation is shown to rapidly induce desirable phenotypic changes in S. cerevisiae after a single treatment, resulting in improved conversion of glucose to ethanol. With a complex environment rich in energetic electrons, highly-reactive chemical species, photons, and gas flow effects, plasma treatment simultaneously mimics exposure to multiple environmental stressors. A single treatment of up to 10 minutes performed using an atmospheric pressure plasma jet was sufficient to induce changes in cell membrane structure, and increased hexokinase 2 activity and secondary metabolite production. These results suggest that plasma treatment is a promising strategy that can contribute to improving metabolic activity in industrial microbial strains, and thus the practicality and economics of industrial fermentations.

Induction of Stress Proteins in Murine and Human Melanoma Cell Cultures

The induction of stress proteins was studied in two human and two murine melanoma cell lines. Exposure for 1 h to heat (42 °C), to ethanol (6%), to arsenate (100 μM) and to disulfiram (50 μM) induced the expression of SPs with apparent molecular weights of 100, 86, 70-72 and 24-26 Kd. Quantitation of the single SPs indicated that the basal level as well as the enhanced synthesis following the various stressors were different in each cell line. The induction of the 100 Kd species occurred in only one murine melanoma and not in the others. The 86 and in particular the 70-72 Kd species were the most prominent groups, whereas the 24-26 SPs were induced only following arsenate and disulfiram exposure in the three melanoma cell lines. In one of the murine melanomas, the expression of SPs was markedly reduced compared to the other cell lines. No definite specific patterns of SP expression could be identified in tumors of the same histologic type.

Physiology of Saccharomyces cerevisiae strains isolated from Brazilian biomes: new insights into biodiversity and industrial applications

Fourteen indigenous Saccharomyces cerevisiae strains isolated from the barks of three tree species located in the Atlantic Rain Forest and Cerrado biomes in Brazil were genetically and physiologically compared to laboratory strains and to strains from the Brazilian fuel ethanol industry. Although no clear correlation could be found either between phenotype and isolation spot or between phenotype and genomic lineage, a set of indigenous strains with superior industrially relevant traits over commonly known industrial and laboratory strains was identified: strain UFMG-CM-Y257 has a very high specific growth rate on sucrose (0.57 ± 0.02 h^-1), high ethanol yield (1.65 ± 0.02 mol ethanol mol hexose equivalent^-1), high ethanol productivity (0.19 ± 0.00 mol L^-1 h^-1), high tolerance to acetic acid (10 g L^-1) and to high temperature (40°C). Strain UFMG-CM-Y260 displayed high ethanol yield (1.67 ± 0.13 mol ethanol mol hexose equivalent^-1), high tolerance to ethanol and to low pH, a trait which is important for non-aseptic industrial processes. Strain UFMG-CM-Y267 showed high tolerance to acetic acid and to high temperature (40°C), which is of particular interest to second generation industrial processes.

Heat shock proteins in the retina: Focus on HSP70 and alpha crystallins in ganglion cell survival

Heat shock proteins (HSPs) belong to a superfamily of stress proteins that are critical constituents of a complex defense mechanism that enhances cell survival under adverse environmental conditions. Cell protective roles of HSPs are related to their chaperone functions, antiapoptotic and antinecrotic effects. HSPs' anti-apoptotic and cytoprotective characteristics, their ability to protect cells from a variety of stressful stimuli, and the possibility of their pharmacological induction in cells under pathological stress make these proteins an attractive therapeutic target for various neurodegenerative diseases; these include Alzheimer's, Parkinson's, Huntington's, prion disease, and others. This review discusses the possible roles of HSPs, particularly HSP70 and small HSPs (alpha A and alpha B crystallins) in enhancing the survival of retinal ganglion cells (RGCs) in optic neuropathies such as glaucoma, which is characterized by progressive loss of vision caused by degeneration of RGCs and their axons in the optic nerve. Studies in animal models of RGC degeneration induced by ocular hypertension, optic nerve crush and axotomy show that upregulation of HSP70 expression by hyperthermia, zinc, geranyl-geranyl acetone, 17-AAG (a HSP90 inhibitor), or through transfection of retinal cells with AAV2-HSP70 effectively supports the survival of injured RGCs. RGCs survival was also stimulated by overexpression of alpha A and alpha B crystallins. These findings provide support for translating the HSP70- and alpha crystallin-based cell survival strategy into therapy to protect and rescue injured RGCs from degeneration associated with glaucomatous and other optic neuropathies.

Cross-stress resistance in Saccharomyces cerevisiae yeast--new insight into an old phenomenon

Acquired stress resistance is the result of mild stress causing the acquisition of resistance to severe stress of the same or a different type. The mechanism of "same-stress" resistance (resistance to a second, strong stress after mild primary stress of the same type) probably depends on the activation of defense and repair mechanisms specific for a particular type of stress, while cross-stress resistance (i.e., resistance to a second, strong stress after a different type of mild primary stress) is the effect of activation of both a specific and general stress response program, which in Saccharomyces cerevisiae yeast is known as the environmental stress response (ESR). Advancements in research techniques have made it possible to study the mechanism of cross-stress resistance at various levels of cellular organization: stress signal transduction pathways, regulation of gene expression, and transcription or translation processes. As a result of this type of research, views on the cross-stress protection mechanism have been reconsidered. It was originally thought that cross-stress resistance, irrespective of the nature of the two stresses, was determined by universal mechanisms, i.e., the same mechanisms within the general stress response. They are now believed to be more specific and strictly dependent on the features of the first stress.

AAV-mediated and pharmacological induction of Hsp70 expression stimulates survival of retinal ganglion cells following axonal injury

We evaluated the effect of AAV2- and 17-AAG (17-N -allylamino-17-demethoxygeldanamycin)-mediated upregulation of Hsp70 expression on the survival of retinal ganglion cells (RGCs) injured by optic nerve crush (ONC). AAV2-Hsp70 expression in the retina was primarily observed in the ganglion cell layer. Approximately 75% of all transfected cells were RGCs. RGC survival in AAV2-Hsp70 injected animals was increased by an average of 110% 2 weeks after the axonal injury compared to the control. The increase in cell numbers was not even across the retinas with a maximum effect of approximately 306% observed in the inferior quadrant. 17-AAG-mediated expression of Hsp70 has been associated with cell protection in various models of neurodegenerative diseases. We show here that a single intravitreal injection of 17-AAG (0.2 ug/ul) results in an increased survival of ONC injured RGCs by approximately 49% compared to the vehicle-treated animals. Expression of Hsp70 in retinas of 17-AAG-treated animals was upregulated approximately by 2-fold compared to control animals. Our data support the idea that the upregulation of Hsp70 has a beneficial effect on the survival of injured RGCs, and the induction of this protein could be viewed as a potential neuroprotective strategy for optic neuropathies.

Mechanisms of heat shock response in mammals

Heat shock (HS) is one of the best-studied exogenous cellular stresses. The cellular response to HS utilizes ancient molecular networks that are based primarily on the action of stress-induced heat shock proteins and HS factors. However, in one way or another, all cellular compartments and metabolic processes are involved in such a response. In this review, we aimed to summarize the experimental data concerning all aspects of the HS response in mammalian cells, such as HS-induced structural and functional alterations of cell membranes, the cytoskeleton and cellular organelles; the associated pathways that result in different modes of cell death and cell cycle arrest; and the effects of HS on transcription, splicing, translation, DNA repair, and replication.

Changes in heat shock protein 70, blood parameters, and fear-related behavior in broiler chickens as affected by pleasant and unpleasant human contact

An experiment was conducted to determine the effects of combining both pleasant and unpleasant contacts with human beings on physiology and behavior of broiler chickens. Birds were subjected to the following treatments: (i) received no physical or visual contact with humans (control); (ii) from d 1 to 28, chicks were individually stroked gently for 30 s once daily (PL); (iii) from d 1 to 28, chicks were picked up individually, suspended by both legs, exposed to recorded noise, and swung gently for 15 s once daily (UNPL); (iv) from d 1 to 14 and from d 15 to 28, chicks were subjected to PL and UNPL, respectively (PL-UNPL); and (v) from d 1 to 14 and from d 15 to 28, chicks were subjected to UNPL and PL, respectively (UNPL-PL). On d 42, birds from each treatment group were road-transported for 3 h. Heat shock protein (hsp) 70 expression, plasma levels of corticosterone, serum creatine kinase concentration, heterophil/lymphocyte ratios (HLR), and tonic immobility duration were determined pre- and posttransit. There were significant (P < 0.05) duration of transportation × human contact treatment interactions for HLR and hsp 70 density. Following transit, the PL chicks had significantly (P < 0.05) lower HLR and greater hsp 70 density than the other groups. The corticosterone of PL and UNPL chicks were lower than their control, PL-UNPL, and UNPL-PL counterparts. The PL and PL-UNPL treatments were effective in shortening tonic immobility duration significantly (P < 0.05). Except for UNPL-PL, the serum creatine kinase activity of PL was significantly lower than the other groups. In conclusion, subjecting birds to pleasant human contact reduced stress and fear reactions to transportation by enhancing the ability to express hsp 70 in the brain. Unpleasant human contact had adverse effect on the birds' response to transportation. Early age pleasant experience with humans failed to negate the adverse effects of subsequent unpleasant contact.

Protein changes during ethanol induced seed germination in Aconitum heterophyllum

Aconitum heterophyllum is a high altitude medicinal plant that has become endangered due to overexploitation for their aconitins. The most effective, conventional propagation method for any plant species is by seed. However, in Aconitum seed germination is erratic, and seedling survival is low. In the present study results have been discussed on the possible implication of ethanol treatment on removal of barriers on radical emergence in terms of protein changes. Eighty seven percent of seed germination was achieved in Aconitum with ethanol treatment. Comparative 2-DE analysis of ethanol treated and untreated seed protein profiles in Phase II of germination revealed 40 differentially expressed proteins. Twenty-seven out of 40 proteins were induced, 5 were increased and 8 were repressed. Mass spectrometry and subsequent identification confirmed that these proteins were involved in metabolism, DNA regulation, stress tolerance and plasmamembrane/cell wall biosynthesis/extension processes. These protein changes might be responsible for physiological and physical changes, respectively, resulted in increase in germination percentage. Further, characterization of these proteins will be of great help in understanding the molecular mechanism lying behind enhanced germination in response to ethanol treatment.

Understanding resistant germplasm-induced virulence variation through analysis of proteomics and suppression subtractive hybridization in a maize pathogen Curvularia lunata

Curvularia lunata is an important pathogen causing Curvularia leaf spot in maize. Significant pathogenic variation has been found in C. lunata. To better understand the mechanism of this phenomenon, we consecutively put the selective pressures of resistant maize population on C. lunata strain WS18 (low virulence) artificially. As a result, the virulence of this strain was significantly enhanced. Using 2DE, 12 up-regulated and four down-regulated proteins were identified in virulence-increased strain compared to WS18. Our analysis revealed that melanin synthesis-related proteins (Brn1, Brn2, and scytalone dehydratase) and stress tolerance-related proteins (HSP 70) directly involved in the potential virulence growth as crucial markers or factors in C. lunata. To validate 2DE results and screen differential genes at mRNA level, we constructed a subtracted cDNA library (tester: virulence-increased strain; driver: WS18). A total of 188 unigenes were obtained this way, of which 14 were indicators for the evolution of pathogen virulence. Brn1 and hsp genes exhibited similar expression patterns corresponding to proteins detected by 2DE. Overall, our results indicated that differential proteins or genes, being involved with melanin synthesis or tolerance response to stress, could be considered as hallmarks of virulence increase in C. lunata.

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.

Microbial alcohol-conferred hemolysis is a late response to alcohol stress

We have reported previously that growth on alcohol vapors confers hemolytic properties on certain yeast species and strains ['microbial alcohol-conferred hemolysis' (MACH)]. In a recent study, we analyzed the genetic basis of MACH in Saccharomyces cerevisiae using the EUROSCARF mutant collection. The data suggested that intact mitochondrial and respiratory chain functions are critical for the observed alcohol-mediated hemolysis. We proposed that the uncontrolled cellular uptake of alcohol results in yeast 'hyper-respiration', leading to elaboration of hemolytic molecules such as hydrogen peroxide and lytic lipids. In the current study, we have further analyzed the molecular mechanisms involved in the MACH phenomenon in S. cerevisiae, using DNA microarrays. The patterns of regulation were confirmed by quantitative reverse transcriptase PCR. The results presented here lend further support to this hypothesis, based on upregulation of the genes responsible for coping with vast amounts of hydrogen peroxide produced as a byproduct of excessive oxidation of alcohol. These results, taken together, show that alcohol-mediated hemolysis in yeast appears to be related to the overproduction of hemolytic byproducts, particularly hydrogen peroxide, which accumulates during long-term exposure of S. cerevisiae to both ethanol and n-butanol.

Glutathione depletion and recovery after acute ethanol administration in the aging mouse

Glutathione (GSH) plays an important role in the detoxification of ethanol (EtOH) and acute EtOH administration leads to GSH depletion in the liver and other tissues. Aging is also associated with a progressive decline in GSH levels and impairment in GSH biosynthesis in many tissues. Thus, the present study was designed to examine the effects of aging on EtOH-induced depletion and recovery of GSH in different tissues of the C57Bl/6NNIA mouse. EtOH (2-5 g/kg) or saline was administered i.p. to mice of ages 6 months (young), 12 months (mature), and 24 months (old); and GSH and cyst(e)ine concentrations were measured 0-24h thereafter. EtOH administration (5 g/kg) depleted hepatic GSH levels >50% by 6h in all animals. By 24h, levels remained low in both young and old mice, but recovered to baseline levels in mature mice. At 6h, the decrease in hepatic GSH was dose-dependent up to 3g/kg EtOH, but not at higher doses. The extent of depletion at the 3g/kg dose was dependent upon age, with old mice demonstrating significantly lower GSH levels than mature mice (P<0.001). Altogether these results indicate that aging was associated with a greater degree of EtOH and fasting-induced GSH depletion and subsequent impaired recovery in liver. An impaired ability to recover was also observed in young animals. Further studies are required to determine if an inability to recover from GSH depletion by EtOH is associated with enhanced toxicity.

STRESS PROTEIN EXPRESSION KINETICS

In all organisms there is an elevated synthesis of a select family of "stress proteins" in response to a broad array of environmentally driven stress vectors including elevated or depressed temperature, changes in pH, treatment with many classes of chemicals, ischemia, desiccation, and UV irradiation. The presence of stress proteins, often termed heat shock proteins (HSPs), has been recognized for more than four decades, and there is an extensive literature that addresses the structure and properties of HSPs, their function in normal and injured cells and tissues, and the molecular mechanisms of HSP expression in response to stress. Owing to this substantial aggregate of research, there is a growing appreciation of the potential for manipulating the magnitude and timing of elevated HSP expression to achieve targeted therapeutic objectives. The successful realization of this potential requires an understanding of the kinetics of the HSP expression process in response to sublethal stress regimens along with the ability to model the governing events in the process to design practical protocols that could be applied in therapeutic settings. Significant progress has been made in recent years in defining and developing capabilities in these two areas.

Comprehensive gene expression analysis of the response to straight-chain alcohols in Saccharomyces cerevisiae using cDNA microarray

AIMS

The purpose of this study was to examine the gene expression profiles of yeast Saccharomyces cerevisiae subjected to straight-chain alcohols.

METHODS AND RESULTS

Lipophilic alcohols with high log Pow values were more toxic to yeast than those with low log Pow values. Morphological changes after exposure to ethanol, 1-pentanol, 1-octanol were observed, whereas n-pentane as a model hydrocarbon affected the surface of the outer membrane, with little change in organelles. Using cDNA microarrays, quite a few up-regulated gene categories were classified into the category 'cell rescue, defence and virulence' by ethanol, and the category 'energy' and 'metabolism' by 1-pentanol. Meanwhile, the characteristic genes up-regulated by n-pentane were not observed, and the expression profile was distantly related to ethanol, 1-pentanol and 1-octanol.

CONCLUSIONS

This study suggests that gene expression profiles at the whole genome level were intimately associated with the cell growth inhibition and morphological changes by straight-chain alcohols with differing log Pow values.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study of comprehensive gene expression profiles by cDNA microarrays elucidates the straight-chain alcohol adaptation mechanisms.

Microbial synergy via an ethanol-triggered pathway

We have discovered a microbial interaction between yeast, bacteria, and nematodes. Upon coculturing, Saccharomyces cerevisiae stimulated the growth of several species of Acinetobacter, including, A. baumannii, A. haemolyticus, A. johnsonii, and A. radioresistens, as well as several natural isolates of Acinetobacter. This enhanced growth was due to a diffusible factor that was shown to be ethanol by chemical assays and evaluation of strains lacking ADH1, ADH3, and ADH5, as all three genes are involved in ethanol production by yeast. This effect is specific to ethanol: methanol, butanol, and dimethyl sulfoxide were unable to stimulate growth to any appreciable level. Low doses of ethanol not only stimulated growth to a higher cell density but also served as a signaling molecule: in the presence of ethanol, Acinetobacter species were able to withstand the toxic effects of salt, indicating that ethanol alters cell physiology. Furthermore, ethanol-fed A. baumannii displayed increased pathogenicity when confronted with a predator, Caenorhabditis elegans. Our results are consistent with the concept that ethanol can serve as a signaling molecule which can affect bacterial physiology and survival.

An etiologic model proposing that non-insulin-dependent diabetes mellitus is chronic hypoxic stress hyperglycemia

This etiologic model equates non-insulin-dependent diabetes mellitus (NIDDM) to chronic hypoxic stress hyperglycemia produced by increased stimulation of the sympathetic nervous system and hypothalamic-pituitary-adrenal axis. In the initial stages of the disease, hypoxia is believed to result from hemodilutional anemia precipitated by a reduction in vascular smooth muscle tone. The reduction increases lumen diameter necessitating an increased blood volume to maintain pressure. Increased lumen diameter may also trigger atherosclerotic changes that characterize the later stages of NIDDM. The increased diameter decreases the shear stress experienced by endothelial cells and they respond by releasing endothelin, a smooth muscle constrictor and mitogen. The constricting action is hypothesized to be relatively ineffective in NIDDM leading to long-term endothelin release and activation of its mitogenic properties. The resulting increase in the number of smooth muscle cells may explain the intimal thickening of atherosclerosis. Restoration of vascular muscle tone is proposed as a treatment strategy for mild NIDDM.

Phenotypic analysis of gene deletant strains for sensitivity to oxidative stress

Ascertaining the impact of inhibitors on the growth phenotype of yeast mutants can be useful in elucidating the function of genes within the cell. Microtitre plates and robotics have been used to screen over 600 deletions from EUROSCARF, constructed in an FY1679 strain background, for sensitivity to various oxidants. These included the inorganic hydroperoxide, H(2)O(2), an organic peroxide (cumene hydroperoxide) and a lipid hydroperoxide (linoleic acid hydroperoxide). These produce within the cell several different reactive oxygen species that can cause damage to DNA, proteins and lipids. Approximately 14% of deletants displayed sensitivity to at least one of the oxidants and there was also a distribution of deletants that showed sensitivity to all or different combinations of the oxidants. Deletants included genes encoding proteins involved in stress responses, heavy metal homeostasis and putative cell wall proteins. Although global mechanisms have been identified that provide general stress responses, these results imply that there are also distinct mechanisms involved in the protection of the cell against specific damage caused by different oxidants. Further analysis of these genes may reveal unknown mechanisms protecting the cell against reactive oxygen species.

Influence of magnesium ions on heat shock and ethanol stress responses of Saccharomyces cerevisiae

This study has highlighted the role of magnesium ions in the amelioration of the detrimental effects of ethanol toxicity and temperature shock in a winemaking strain of Saccharomyces cerevisiae. Specifically, results based on measurements of cellular viability and heat shock protein synthesis together with scanning electron microscopy have shown that, by increasing the bioavailability of magnesium ions, physiological protection is conferred on yeast cells. Elevating magnesium levels in the growth medium from 2 to 20 mM results in repression of certain heat shock proteins following a typical heat shock regime (30-42 degrees C shift). Seed inocula cultures prepropagated in elevated levels of magnesium (i.e. 'preconditioned') also conferred thermotolerance on cells and repressed the biosynthesis of heat shock proteins. Similar results were observed in response to ethanol stress. Extra- and intracellular magnesium may both act in the physiological stress protection of yeast cells and this approach offers potential benefits in alcoholic fermentation processes. The working hypothesis based on our findings is that magnesium protects yeast cells by preventing increases in cell membrane permeability elicited by ethanol and temperature-induced stress.

Guanidine hydrochloride blocks a critical step in the propagation of the prion-like determinant [PSI(+)] of Saccharomyces cerevisiae

The cytoplasmic heritable determinant [PSI(+)] of the yeast Saccharomyces cerevisiae reflects the prion-like properties of the chromosome-encoded protein Sup35p. This protein is known to be an essential eukaryote polypeptide release factor, namely eRF3. In a [PSI(+)] background, the prion conformer of Sup35p forms large oligomers, which results in the intracellular depletion of functional release factor and hence inefficient translation termination. We have investigated the process by which the [PSI(+)] determinant can be efficiently eliminated from strains, by growth in the presence of the protein denaturant guanidine hydrochloride (GuHCl). Strains are "cured" of [PSI(+)] by millimolar concentrations of GuHCl, well below that normally required for protein denaturation. Here we provide evidence indicating that the elimination of the [PSI(+)] determinant is not derived from the direct dissolution of self-replicating [PSI(+)] seeds by GuHCl. Although GuHCl does elicit a moderate stress response, the elimination of [PSI(+)] is not enhanced by stress, and furthermore, exhibits an absolute requirement for continued cell division. We propose that GuHCl inhibits a critical event in the propagation of the prion conformer and demonstrate that the kinetics of curing by GuHCl fit a random segregation model whereby the heritable [PSI(+)] element is diluted from a culture, after the total inhibition of prion replication by GuHCl.

Stress tolerance in a yeast lipid mutant: membrane lipids influence tolerance to heat and ethanol independently of heat shock proteins and trehalose

The response of a yeast unsaturated fatty acid auxotroph, defective in delta 9-desaturase activity, to heat and ethanol stresses was examined. The most heat- and ethanol-tolerant cells had membranes enriched with oleic acid (C18:1), followed in order by cells enriched with linoleic (C18:2) and linolenic (C18:3) acids. Cells subjected to a heat shock (25-37 degrees C for 30 min) accumulated trehalose and synthesized typical heat shock proteins. Although there were no obvious differences in protein profiles attributable to lipid supplementation of the mutant, relative protein synthesis as determined by densitometric analysis of autoradiograms suggested that hsp expression was different. However, there was no consistent relationship between the synthesis of heat shock proteins and the acquisition of thermotolerance in the lipid supplemented auxotroph or related wild type. Furthermore, trehalose accumulation was also not closely related to stress tolerance. On the other hand, the data presented indicated a more consistent role for membrane lipid composition in stress tolerance than trehalose, heat shock proteins, or ergosterol. We suggest that the sensitivity of C18:3-enriched cells to heat and ethanol may be attributable to membrane damage associated with increases in membrane fluidity and oxygen-derived free radical attack of membrane lipids.

Stress tolerance in a yeast sterol auxotroph: role of ergosterol, heat shock proteins and trehalose

The role of ergosterol in yeast stress tolerance, together with heat shock proteins (hsps) and trehalose, was examined in a sterol auxotrophic mutant of Saccharomyces cerevisiae. Ergosterol levels paralleled viability data, with cells containing higher levels of the sterol exhibiting greater tolerances to heat and ethanol. Although the mutant synthesised hsps and accumulated trehalose upon heat shock to the same levels as the wild-type cells, these parameters did not relate to stress tolerance. These results indicate that the role of ergosterol in stress tolerance is independent of hsps or trehalose.

Polyamine metabolism in Saccharomyces cerevisiae exposed to ethanol

Growth of the yeast Saccharomyces cerevisiae was unaffected by up to 24 h exposure to ethanol concentrations ranging from 1% to 9%, but was reduced following exposure to 12% ethanol. Concentrations of the polyamines putrescine, cadaverine and spermidine were not affected by a 24 h exposure to 12% ethanol, although there was a significant increase in spermine level. These changes were accompanied by significant increases in the activities of the polyamine biosynthetic enzymes ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) and in the flux of label from ornithine into the polyamines. Formation of the cadaverine derivatives aminopropylcadaverine and N,N-bis(3-aminopropyl)cadaverine was greatly increased in yeast exposed to 12% ethanol for 24 h, probably via the action of ODC, AdoMetDC and the aminopropyltransferases. Exposure to 12% ethanol also led to substantial reductions in the uptake of putrescine and spermidine and the amino acid methionine.

Proteome research: complementarity and limitations with respect to the RNA and DNA worlds

A methodological overview of proteome analysis is provided along with details of efforts to achieve high-throughput screening (HTS) of protein samples derived from two-dimensional electrophoresis gels. For both previously sequenced organisms and those lacking significant DNA sequence information, mass spectrometry has a key role to play in achieving HTS. Prototype robotics designed to conduct appropriate chemistries and deliver 700-1000 protein (genes) per day to batteries of mass spectrometers or liquid chromatography (LC)-based analyses are well advanced, as are efforts to produce high density gridded arrays containing > 1000 proteins on a single matrix assisted laser desorption ionisation/time-of-flight (MALDI-TOF) sample stage. High sensitivity HTS of proteins is proposed by employing principally mass spectrometry in an hierarchical manner: (i) MALDI-TOF-mass spectrometry (MS) on at least 1000 proteins per day; (ii) electrospray ionisation (ESI)/MS/MS for analysis of peptides with respect to predicted fragmentation patterns or by sequence tagging; and (iii) ESI/MS/MS for peptide sequencing. Genomic sequences when complemented with information derived from hybridisation assays and proteome analysis may herald in a new era of holistic cellular biology. The current preoccupation with the absolute quantity of gene-product (RNA and/or protein) should move backstage with respect to more molecularly relevant parameters, such as: molecular half-life; synthesis rate; functional competence (presence or absence of mutations); reaction kinetics; the influence of individual gene-products on biochemical flux; the influence of the environment, cell-cycle, stress and disease on gene-products; and the collective roles of multigenic and epigenetic phenomena governing cellular processes. Proteome analysis is demonstrated as being capable of proceeding independently of DNA sequence information and aiding in genomic annotation. Its ability to confirm the existence of gene-products predicted from DNA sequence is a major contribution to genomic science. The workings of software engines necessary to achieve large-scale proteome analysis are outlined, along with trends towards miniaturisation, analyte concentration and protein detection independent of staining technologies. A challenge for proteome analysis into the future will be to reduce its dependence on two-dimensional (2-D) gel electrophoresis as the preferred method of separating complex mixtures of cellular proteins. Nonetheless, proteome analysis already represents a means of efficiently complementing differential display, high density expression arrays, expressed sequence tags, direct or subtractive hybridisation, chromosomal linkage studies and nucleic acid sequencing as a problem solving tool in molecular biology.

Mitochondrial superoxide dismutase is essential for ethanol tolerance of Saccharomyces cerevisiae in the post-diauxic phase

This work reports the role of both superoxide dismutases-CuZnSOD (encoded by SOD1) and MnSOD (encoded by SOD2)-in the build-up of tolerance to ethanol during growth of Saccharomyces cerevisiae from exponential to post-diauxic phase. Both enzyme activities increase from the exponential phase to the diauxic shift and from the diauxic shift to the post-diauxic phase. The levels of mRNA-SOD1 and mRNA-SOD2 increase from the exponential phase to the diauxic shift; however, during the post-diauxic phase mRNA-SOD1 levels decrease while mRNA-SOD2 levels remain unchanged. These data indicate the existence of two regulatory mechanisms involved in the induction of SOD activity during growth: synthesis de novo of the proteins (until the diauxic shift), and post-transcriptional or post-translational regulation (during the post-diauxic phase). Ethanol does not alter the activities of either enzyme in cells from the diauxic shift or post-diauxic-phases, although the respective mRNA levels decrease in post-diauxic-phase cells treated with ethanol (14% or 20%). Results of experiments with sod1 and sod2 mutants show that MnSOD, but not CuZnSOD, is essential for ethanol tolerance of diauxic-shift and post-diauxic-phase cells. Evidence that ethanol toxicity is correlated with the production of reactive oxygen species in the mitochondria is obtained from results with respiration-deficient mutants. In these cells, the induction of superoxide dismutase activity by ethanol is low; also, the respiratory deficiency restores the capacity of sod2 cells to acquire ethanol tolerance.

Adaptive larval thermotolerance and induced cross-tolerance to propoxur insecticide in mosquitoes Anopheles stephensi and Aedes aegypti

Fourth-instar larvae of mosquitoes Anopheles stephensi and Aedes aegypti normally died within 90 min at 43 degrees C. Pre-exposure to high but sublethal temperatures conferred adaptive thermotolerance, dependent on the temperature and the duration of pre-exposure. Adaptive cross-tolerance to propoxur (a carbamate insecticide) was also induced in larvae by pre-exposing them to sublethal temperatures. Pre-exposure to sublethal concentrations of propoxur was found to confer cross-thermotolerance to a lower extent. These results suggest that the shock proteins (e.g. heat shock proteins) induced by unrelated stress factors play an important role in the development of adaptive cross-protection (stress response) to other stress conditions.

Cellular stress inhibits transposition of the yeast retrovirus-like element Ty3 by a ubiquitin-dependent block of virus-like particle formation

Many stress proteins and their cognates function as molecular chaperones or as components of proteolytic systems. Viral infection can stimulate synthesis of stress proteins and particular associations of viral and stress proteins have been documented. However, demonstrations of functions for stress proteins in viral life cycles are few. We have initiated an investigation of the roles of stress proteins in eukaryotic viral life cycles using as a model the Ty3 retrovirus-like element of Saccharomyces cerevisiae. During stress, Ty3 transposition is inhibited; Ty3 DNA is not synthesized and, although precursor proteins are detected, mature Ty3 proteins and virus-like particles (VLPs) do not accumulate. The same phenotype is observed in the constitutively stressed ssa1 ssa2 mutant, which lacks two cytoplasmic members of the hsp70 family of chaperones. Ty3 VLPs preformed under nonstress conditions are degraded more rapidly if cells are shifted from 30 degrees C to 37 degrees C. These results suggest that Ty3 VLPs are destroyed by cellular stress proteins. Elevated expression of the yeast UBP3 gene, which encodes a protease that removes ubiquitin from proteins, allows mature Ty3 proteins and VLPs to accumulate in the ssa1 ssa2 mutant, suggesting that, at least under stress conditions, ubiquitination plays a role in regulating Ty3 transposition.

The heat shock and ethanol stress responses of yeast exhibit extensive similarity and functional overlap

Sublethal heat and ethanol exposure induce essentially identical stress responses in yeast. These responses are characterized by the induction of heat shock proteins, proteins requiring a temperature above about 35 degrees C or ethanol levels above a threshold level of 4-6% (v/v) for strong induction. One induced protein, Hsp104, contributes to both thermotolerance and ethanol tolerance, while others are anti-oxidant enzymes. Heat and ethanol stress cause similar changes to plasma membrane protein composition, reducing the levels of plasma membrane H(+)-ATPase protein and inducing the plasma membrane-associated Hsp30. Both stresses also stimulate the activity of the fraction of H(+)-ATPase remaining in the plasma membrane. The resulting enhancement to catalysed proton efflux from the cell represents a considerable energy demand, yet may help to counteract the adverse effects for homeostasis of the increased membrane permeability that results from stress.