The Absence of a Direct Relationship between the Ability of Yeasts to Grow at Elevated Temperatures and Their Survival after Lethal Heat Shock

The study of the growth of the yeasts Rhodotorula rubra, Saccharomyces cerevisiae, and Debaryomyces vanriji at elevated temperatures and their survival after transient lethal heat shock showed that the ability of these yeasts to grow at supraoptimal temperatures (i.e., their thermoresistance) and their ability to tolerate lethal heat shocks (i.e., their thermotolerance) are determined by different mechanisms. It is suggested that the thermotolerance of the yeasts is mainly determined by the division rate of cells before their exposure to heat shock.     

热休克诱导近江牡蛎对高温的耐受性

设计6个温度组成的梯度,即38℃、39℃、40℃、41℃、42℃、43℃,对近江牡蛎加热处理1.5h后放回室温海水中连续观察3d,发现致死温度为42℃,半致死温度是40℃,亚致死温度为36℃。经亚致死温度36℃热休克1.5h后,在正常环境温度下恢复6h,再经受致死温度42℃处理1.5h后,放回室温海水中连续观察3d,发现三次重复的平均存活率为96.7%,显著高于对照组的存活率(0),结果表明预先的热休克极显著地增强了近江牡蛎对致死温度(42℃)的耐受力。     

The effect of sodium malonate on yeast thermotolerance

The study of the effect of malonate (an inhibitor of the succinate dehydrogenase complex of the respiratory chain of mitochondria) on the thermotolerance of the fermentative Saccharomyces cerevisiae and nonfermentative Rhodotorula rubra yeasts showed that malonate augmented the damaging effect of heat shock on the yeasts utilizing glucose (or other sugars) by means of oxidative phosphorylation. At the same time, malonate did not influence and sometimes even improved the thermotolerance of the yeasts utilizing glucose through fermentation. The suggestion is made that cell tolerance to heat shock depends on the normal functioning of mitochondria. On the other hand, their increased activity at elevated temperatures may accelerate the formation of cytotoxic reactive oxygen species and, hence, is not beneficial to cells.     

Induced thermotolerance during early development of murine and bovine embryos

During early development, elevated temperatures have deleterious effects on embryonic viability and development. The primary objective of the current study was to determine the ontogeny of induced thermotolerance during early murine embryonic development. Embryos were either retrieved from superovulated ICR female mice at the 2 cell and 4 cell stages and cultured thereafter or were retrieved from oviducts or uterine horns at the desired stage of development. Induction of thermotolerance was detected by evaluating viability and further development after embryos were exposed to homeothermic temperature (37°C), mild heat shock (40°C for 1 h), severe heat shock (42°C for 1 h or 43°C for 2 h), or mild heat shock followed by severe heat shock (to induce thermotolerance). Induction of thermotolerance was observed beginning at the 8 cell stage when embryos were developed in culture from the 2 cell to 4 cell stage. When embryos were developed in vivo (i.e., were retrieved from the reproductive tract at the desired stage of development), thermotolerance was not induced until the blastocyst stage of development. The induction of thermotolerance was dependent on serum supplementation since induction of thermotolerance was not observed when embryos were placed in medium without serum. Induced thermotolerance could also be demonstrated in bovine blastocysts. In conclusion, embryos acquire the ability to undergo thermotolerance as they progress through development. The timing of processes leading to acquisition of thermotolerance can, however, be hastened by exposure of embryos to in vitro conditions.     

The Effect of Sodium Malonate on Yeast Thermotolerance

The study of the effect of malonate (an inhibitor of the succinate dehydrogenase complex of the respiratory chain of mitochondria) on the thermotolerance of the fermentative Saccharomyces cerevisiae and nonfermentative Rhodotorula rubra yeasts showed that malonate augmented the damaging effect of heat shock on the yeasts utilizing glucose (or other sugars) by means of oxidative phosphorylation. At the same time, malonate did not influence, and sometimes even improved, the thermotolerance of the yeasts utilizing glucose through fermentation. The suggestion is made that cell tolerance to heat shock depends on the normal functioning of mitochondria. On the other hand, their increased activity at elevated temperatures may accelerate the formation of cytotoxic reactive oxygen species and, hence, is not beneficial to cells.     

Acquisition of thermotolerance in bay scallops, Argopecten irradians irradians, via differential induction of heat shock proteins

Many cells and organisms are rendered transiently resistant to lethal heat shock by short exposure to sublethal temperatures. This induced thermotolerance is thought to be related to increased amounts of heat shock proteins (HSPs) which, as molecular chaperones, protect cells from stress-induced damage. As part of a study on bivalve stress and thermotolerance, work was undertaken to examine the effects of sublethal heat shock on stress tolerance of juveniles of the northern bay scallop, Argopecten irradians irradians, in association with changes in the levels of cytoplasmic HSP70 and 40. Juvenile bay scallops heat-shocked at a sublethal temperature of 32 °C survived an otherwise lethal heat treatment at 35 °C for at least 7 days. As determined by ELISA, acquisition of induced thermotolerance closely paralleled HSP70 accumulation, whereas HSP40 accrual appeared less closely associated with thermotolerance. Quantification of scallop HSPs following lethal heat treatment, with or without conditioning, suggested a causal role for HSP70 in stress tolerance, with HSP40 contributing to a lesser, but significant extent. Overall, this study demonstrated that sublethal heat shock promotes survival of A. irradians irradians juveniles upon thermal stress and the results support the hypothesis that HSPs have a role in this induced thermotolerance. Exploitation of the induced thermotolerance response shows promise as a means to improve survival of bay scallops in commercial culture.     

Stress proteins and cross-protection by heat shock and salt stress in Bacillus subtilis.

Bacillus subtilis induced a set of general stress proteins in response to a salt or heat stress. Cells subjected to a mild heat stress showed a protective response which enabled them to survive otherwise lethal temperatures (e.g. 52 degrees C). In a similar way bacteria were enabled to survive toxic concentrations of NaCl by pretreatment with lower salt concentrations. A mild heat shock induced a cross-protection against lethal salt stress. The pretreatment of cells with low salt, however, was less effective in the induction of thermotolerance than a preceding mild heat stress. Three stress proteins were identified on the basis of their N-terminal amino acid sequences as homologues of GroEL, DnaK and ClpP of Escherichia coli. The role of general and specific stress proteins in the induction of thermotolerance/salt tolerance and cross-protection is discussed.     

Identification of genetic diversity and mutations in higher plant acquired thermotolerance

Plants experience high air and soil temperatures during periods of drought and when fields receive limited irrigation. Elevated plant temperatures that occur under these conditions negatively impact plant health and productivity. Plants, like all organisms, respond to an elevation in temperature by the synthesis of heat shock proteins (HSP). The appearance of plant HSP is strongly correlated to the development of a condition termed 'acquired thermotolerance'. Acquired thermotolerance is induced by pre-exposure to elevated but non-lethal temperatures and leads to enhanced protection of plant cells from subsequent heat induced injury. Although the correlation between the development of acquired thermotolerance and the appearance of HSP is strong, a cause-and-effect relationship between the two has been difficult to demonstrate. To understand the relationship between HSP and acquired thermotolerance, mutations would be required that result in a coordinate change in the expressions of HSP. This paper describes research efforts leading to the development of a screening procedure for the isolation and characterization of acquired thermotolerance mutants. This method for identifying mutants is based on the inhibition of chlorophyll accumulation in etiolated tissue following challenges at lethal temperatures and the prevention of this inhibition by pre-incubation at a non-lethal elevated temperature; i.e. acquired thermotolerance. Arabidopsis thaliana mutants deficient in varying levels of acquired thermotolerance have been identified from both the RLD and Columbia ecotypes and these mutants are currently undergoing a detailed characterization at both the protein and molecular levels.     

Effects of heat shock,heat exposure pattern,and heat hardening on survival of the sycamore lace bug,Corythucha ciliata

The sycamore lace bug, Corythucha ciliata (Say) (Hemiptera: Tingidae), is an invasive exotic pest on Platanus trees in China. This study assessed the thermotolerance of C. ciliata in the laboratory. Detailed experiments were conducted on the effects of high temperature (35, 37, 39, 41, 43, and 45 °C), duration of exposure (0.5, 1, 2, 4, 6, and 8 h), and developmental stage (egg, nymph, and adult) on survival of the bug. Meanwhile, the effects of heat hardening on survival at lethal temperature (exposure to 33, 35, 37, 39, and 41 °C for 1 h prior to transfer to 43 °C for 2 h) were also assessed for nymphs and adults. Survival of eggs, nymphs, and adults was not affected by temperatures between 35 and 39 °C, but declined rapidly with increasing duration of exposure (from 0.5 to 8 h) at temperatures ≥41 °C. The lethal temperature that caused mortality of 50% (Ltemp₅₀) of all developmental stages decreased with increasing duration of exposure from 0.5 to 8 h. The Ltemp₅₀ for nymphs was 44.3, 42.0, and 39.0 °C after 0.5, 2, and 8 h exposure, respectively. Thermotolerance was the highest in eggs, followed by adults and then nymphs. Thermotolerance was slightly greater for adult males than for adult females. The ability of nymphs, females, and males to survive exposure to 43 °C for 2 h significantly increased by heat hardening, i.e., by exposure to a non‐lethal high temperature for 1 h; the optimal heat‐hardening temperature was 37 °C. The results indicate that survival of C. ciliata at heat‐shock temperatures depended on both the temperature and the duration of exposure, and the tolerance to heat shock was enhanced by heat hardening. The thermotolerance of C. ciliata may partially explain why C. ciliata has been rapidly spreading on Platanus trees in southern provinces of China.     

Effect of sodium azide on heat-shock resistance in Saccharomyces cerevisiae and Debaryomyces vanriji yeasts]

The pretreatment of Saccharomyces cerevisiae and Debaryomyces vanriji with sodium azide was found to induce thermotolerance in both yeasts, whereas sodium azide used in combination with heat shock enhanced the thermotolerance of S. cerevisiae and substantially decreased the thermotolerance of D. vanriji. It is suggested that the different responses of the yeasts to sodium azide during heat shock are due to the different functional organizations of their mitochondrial apparatus.     

Heat shock response of Saccharomyces cerevisiae mutants altered in cyclic AMP-dependent protein phosphorylation.

When Saccharomyces cerevisiae cells grown at 23 degrees C were transferred to 36 degrees C, they initiated synthesis of heat shock proteins, acquired thermotolerance to a lethal heat treatment given after the temperature shift, and arrested their growth transiently at the G1 phase of the cell division cycle. The bcy1 mutant which resulted in production of cyclic AMP (cAMP)-independent protein kinase did not synthesize the three heat shock proteins hsp72A, hsp72B, and hsp41 after the temperature shift. The bcy1 cells failed to acquire thermotolerance to the lethal heat treatment and were not arrested at the G1 phase after the temperature shift. In contrast, the cyr1-2 mutant, which produced a low level of cAMP, constitutively produced three heat shock proteins and four other proteins without the temperature shift and was resistant to the lethal heat treatment. The results suggest that a decrease in the level of cAMP-dependent protein phosphorylation results in the heat shock response, including elevated synthesis of three heat shock proteins, acquisition of thermotolerance, and transient arrest of the cell cycle.     

Heat shock and cold shock in Deinococcus radiodurans

On the basis of acquired thermotolerance and cryotolerance, the optimal heat shock and cold shock temperatures have been determined for Deinococcus radiodurans. A heat shock at 42°C maximized survival at the lethal temperature of 52°C and a cold shock at 20°C maximized survival after repeated freeze-thawing. Enhanced survival from heat shock was found to be strongly dependent on growth stage, with its greatest effect shortly after phase. Increased synthesis of a total of 67 proteins during heat shock and 42 proteins during cold shock were observed by two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and autoradiography. Eight of the most highly induced heat shock proteins shown by 2D PAGE were identified by MALDI-MS as Hsp20, GroEL, DnaK, SodA, Csp, Protease I and two proteins of unknown function.     

Acquisition of thermotolerance in sea urchin embryos correlates with the synthesis and age of the heat shock proteins

Preheating at 31 degrees C induces thermotolerance in Paracentrotus lividus embryos, which therefore become able to withstand 1-h treatment at the otherwise lethal temperature of 35 degrees C, and to develop normally. The acquisition of thermotolerance is positively correlated with the amount of heat shock proteins produced during the 31 degrees C treatment. Evidence is provided that the heat shock proteins, although present in the embryo for long periods after synthesis, lose their effect on thermotolerance within 3 h of the cessation of synthesis.     

Splicing thermotolerance maintains pre-mRNA transcripts in the splicing pathway during severe heat shock

Thermotolerance, the ability of cells and organisms to withstand severe elevated temperatures after brief exposure to mild elevated temperatures, has been studied in numerous laboratories. Survival thermotolerance is defined as the increase in cell or organism survival at severe elevated temperatures after a pretreatment at mild elevated temperatures. This study examines splicing thermotolerance in Drosophila melanogaster, the ability to splice pre-mRNAs made at the severe temperature (38 degrees C) after a brief pretreatment at a milder temperature (35 degrees C). It is probably one of a number of mechanisms by which cells adapt to heat shock. These experiments demonstrate that pre-mRNAs synthesized at the severe temperatures in splicing thermotolerant cells, although protected in splicing-competent complexes, are not actually processed to mature mRNAs until the cells are returned to their normal temperature. We have also studied the kinetics of acquisition and loss of splicing thermotolerance. As little as 10 min of pretreatment at 35 degrees C was sufficient to provide full splicing thermotolerance to a 30-min severe heat shock of 38 degrees C. Pretreatments of less than 10 min provide partial splicing thermotolerance for a 30-min severe heat shock. Full splicing thermotolerance activity begins to decay about 4 h after the cessation of the 35 degrees C incubation and is completely lost by 8 h after the pretreatment. The kinetics experiments of pre-mRNAs synthesized during the 38 degrees C treatment in splicing thermotolerant cells indicate that one or more splicing thermotolerance factors are synthesized during the 35 degrees C pretreatment which interact with pre-mRNA-containing complexes to keep them in a splicing-competent state. These kinetic experiments also indicate that in cells which are partially splicing thermotolerant, the pre-mRNAs synthesized early during the 38 degrees C incubation are protected, whereas those synthesized late are not. In the absence of splicing thermotolerant factors, the pre-mRNA-containing complexes leave the normal splicing pathway and are allowed to exit to the cytoplasm.     

Phenotypic plasticity of HSP70 and HSP70 gene expression in the Pacific oyster (Crassostrea gigas): implications for thermal limits and induction of thermal tolerance

Pacific oysters, Crassostrea gigas, living at a range of tidal heights, routinely encounter large seasonal fluctuations in temperature. We demonstrate that the thermal limits of oysters are relatively plastic, and that these limits are correlated with changes in the expression of one family of heat-shock proteins (HSP70). Oysters were cultured in the intertidal zone, at two tidal heights, and monitored for changes in expression of cognate (HSC) and inducible (HSP) heat-shock proteins during the progression from spring through winter. We found that the "control" levels (i.e., prior to laboratory heat shock) of HSC77 and HSC72 are positively correlated with increases in ambient temperature and were significantly higher in August than in January. The elevated level of HSCs during the summer was associated with moderate, 2-3 degrees C, increases in the upper thermal limits for survival. We measured concomitant increases in the threshold temperatures (T(on)) required for induction of HSP70. Total hsp70 mRNA expression reflected the seasonal changes in the expression of inducible but not cognate members of the HSP70 family of proteins. A potential cost of increased T(on) in the summer is that there was no extension of the upper thermal limits for survival (i.e., induction of thermotolerance) after sublethal heat shock at temperatures that were sufficient to induce thermotolerance during the winter months.     

Effect of Sodium Azide on the Thermotolerance of the Yeasts Saccharomyces cerevisiaeand Debaryomyces vanriji

The pretreatment of Saccharomyces cerevisiaeand Debaryomyces vanrijiwith sodium azide was found to induce thermotolerance in both yeasts, whereas sodium azide used in combination with heat shock enhanced the thermotolerance of S. cerevisiaeand substantially decreased the thermotolerance of D. vanriji.It is suggested that the different responses of the yeasts to sodium azide during heat shock are due to the different functional organizations of their mitochondrial apparatus.     

Molecular events associated with acquisition of heat tolerance by the yeast Saccharomyces cerevisiae

Abstract: The heat shock response is an inducible protective system of all living cells. It simultaneously induces both heat shock proteins and an increased capacity for the cell to wisthstand potentially lethal temperatures (an increased thermotolerance). This has lead to the suspicion that these two phenomena must be inexorably linked. However, analysis of heat shock protein function in Saccharomyces cerevisiae by molecular genetic techniques has revealed only a minority of the heat shock proteins of this organism having appreciable influences on thermotolerance. Instead, physiological perturbations and the accumulation of trehalose with heat stress may be more important in the development of thermotolerance during a preconditioning heat shock. Vegetative S. cerevisiae also acquires thermotolerance through osmotic dehydration, through treatment with certain chemical agents and when, due to nutrient limitation, it arrests growth in the GI phase of the cell cycle. There is evidence for the activities of the cAMP-dependent protein kinase and plasma membrane ATPase being very important in thermotolerance determination. Also, intracellular water activity and trehalose probably exert a strong influence over thermotolerance through their effects on stabilisation of membranes and intracellular assemblies. Future investigations should address the unresolved issue of whether the different routes to thermotolerance induction cause a common change to the physical state of the intracellular environment, a change that may result in an increased stabilisation of cellular structures through more stable hydrogen bonding and hydrophobic interactions.     

Trehalose synthesis is important for the acquisition of thermotolerance in Schizosaccharomyces pombe

Yeast cells show an adaptive response to a mild heat shock, resulting in thermotolerance acquisition. This is accompanied by induction of heat-shock protein (hsp) synthesis and rapid accumulation of trehalose. Genetic approaches to determine the specific role of trehalose in heat-induced thermotolerance in Saccharomyces cerevisiae have been hampered by the finding that deletion of TPS1 , the gene encoding trehalose-6-phosphate synthase, causes a variety of pleiotropic effects, including inability to grow on glucose-containing media. Here, we have studied a tps1 mutant of the yeast Schizosaccharomyces pombe that reportedly has no such growth defects. We show that tps1 mutants have a serious defect in heat shock-induced acquisition of thermotolerance if conditioned at highly elevated temperatures (40–42.5°C), which, in wild-type cells, prevent hsp but not trehalose synthesis. In contrast, hsp synthesis appears to become particularly important under conditions in which trehalose synthesis is either absent (in tps1 mutant strains) or not fully induced (conditioning at moderately elevated temperatures, i.e. 35°C). In addition, pka1 mutants deficient in cAMP-dependent protein kinase were examined. Unconditioned pka1 cells had low levels of trehalose but a high basal level of thermotolerance. It was found that pka1 mutant cells, contrary to wild-type cells, accumulated large amounts of trehalose, even during a 50°C treatment. pka1 tps1 double mutants lacked this ability and showed reduced intrinsic thermotolerance, indicating a particularly important role for trehalose synthesis, which takes place during the challenging heat shock.     

Interleukin-6 induces thermotolerance in cultured Caco-2 cells independent of the heat shock response

In recent studies, induction of the heat shock response increased IL-6 production in gut mucosa in vivo and in cultured Caco-2 cells in vitro. The heat shock response is associated with increased survival of cells exposed to otherwise lethal hyperthermia, so called thermotolerance, but the role of IL-6 in the induction of thermotolerance is not known. We tested the hypothesis that treatment of cultured Caco-2 cells with IL-6 results in the development of thermotolerance. Cells were treated with human recombinant IL-6 for 1h followed by 3 h recovery in cytokine-free medium whereafter cells were exposed to heat stress (48 degrees C for 2 h). In untreated cells, the heat stress resulted in an approximately 80% cell death. In cells treated with IL-6, cell viability after heat stress was significantly improved and was doubled at an IL-6 concentration of 20 ng/ml. Treatment of the cells with other cytokines (IL-4, IL-10, IL-1beta, or TNFalpha) did not induce thermotolerance, suggesting that the effect of IL-6 may be specific for this cytokine. The induction of thermotolerance by IL-6 was blocked by an IL-6 receptor antibody, suggesting that the development of thermotolerance was receptor-mediated. Treatment of cells with IL-6 did not induce an heat shock response as suggested by unaltered heat shock protein 70 and 90 levels and unaffected heat shock factor DNA binding activity. In addition, the IL-6-induced thermotolerance was not inhibited by quercetin. The present study provides the first evidence of IL-6-induced thermotolerance and suggests that this effect of IL-6 is independent of the heat shock response.