Effects of cycloheximide on thermotolerance expression, heat shock protein synthesis, and heat shock protein mRNA accumulation in rat fibroblasts

LncRNA AIRN influences the proliferation and apoptosis of hepatocellular carcinoma cells by regulating STAT1 ubiquitination

Long non-coding RNAs (LncRNAs) have been implicated in the pathogenesis of various human diseases. In this study, we probed into the role and potential mechanisms of the antisense of IGF2R non-protein coding RNA (LncRNA AIRN) in the progression of hepatocellular carcinoma (HCC). Using a quantitative real-time polymerase chain reaction, we corroborated that LncRNA AIRN expression was raised in the HCC tissues and cells. The bioinformatic analysis revealed that a potential interaction between LncRNA AIRN and STAT1, which was verified by the RNA pull-down and RNA immunoprecipitation. In the cycloheximide-chase assay, the knockdown of LncRNA AIRN enhanced the stability of STAT1 protein. In the immunoprecipitation assay, the knockdown of LncRNA AIRN restrained the cullin 4A (CUL4A)-mediated ubiquitination of STAT1 protein. The cell transfection, MTT and flow cytometry assays expounded that the LncRNA AIRN/STAT1 axis was bound up with the regulation of the proliferation and apoptosis of HCC cells. The in vivo experiments corroborated that the knockdown of LncRNA AIRN restrained the tumor growth of HCC. Our data expounded that the knockdown of LncRNA AIRN restrained HCC cell proliferation and boosted cell apoptosis by restraining the CUL4A-mediated ubiquitination of STAT1 protein.

Heat shock proteins and resistance to desiccation in congeneric land snails

Land snails are subject to daily and seasonal variations in temperature and in water availability and depend on a range of behavioral and physiological adaptations for coping with problems of maintaining water, ionic, and thermal balance. Heat shock proteins (HSPs) are a multigene family of proteins whose expression is induced by a variety of stress agents. We used experimental desiccation to test whether adaptation to different habitats affects HSP expression in two closely related Sphincterochila snail species, a desiccation-resistant, desert species Sphincterochila zonata, and a Mediterranean-type, desiccation-sensitive species Sphincterochila cariosa. We examined the HSP response in the foot, hepatopancreas, and kidney tissues of snails exposed to normothermic desiccation. Our findings show variations in the HSP response in both timing and magnitude between the two species. The levels of endogenous Hsp72 in S. cariosa were higher in all the examined tissues, and the induction of Hsp72, Hsp74, and Hsp90 developed earlier than in S. zonata. In contrary, the induction of sHSPs (Hsp25 and Hsp30) was more pronounced in S. zonata compared to S. cariosa. Our results suggest that land snails use HSPs as part of their survival strategy during desiccation and as important components of the aestivation mechanism in the transition from activity to dormancy. Our study underscores the distinct strategy of HSP expression in response to desiccation, namely the delayed induction of Hsp70 and Hsp90 together with enhanced induction of sHSPs in the desert-dwelling species, and suggests that evolution in harsh environments will result in selection for reduced Hsp70 expression.

Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.

Protection of neuronal cells from apoptosis by Hsp27 delivered with a herpes simplex virus-based vector

Overexpression of the gene encoding the 70-kDa heat shock protein (hsp70) has previously been shown to protect neuronal cells against subsequent thermal or ischemic stress. It has no protective effect, however, against stimuli that induce apoptosis, although a mild heat shock (sufficient to induce hsp synthesis) does have a protective effect against apoptosis. We have prepared disabled herpes simplex virus-based vectors that are able to produce high level expression of individual hsps in infected neuronal cells without damaging effects. We have used these vectors to show that hsp27 and hsp56 (which have never previously been overexpressed in neuronal cells) as well as hsp70 can protect dorsal root ganglion neurons from thermal or ischemic stress. In contrast, only hsp27 can protect dorsal root ganglion neurons from apoptosis induced by nerve growth factor withdrawal, and hsp27 also protects the ND7 neuronal cell line from retinoic acid-induced apoptosis. However, hsp70 showed no protective effect against apoptosis in contrast to its anti-apoptotic effect in non-neuronal cell types. These results thus identify hsp27 as a novel neuroprotective factor and show that it can mediate this effect when delivered via a high efficiency viral vector.

Heat conditioning induces heat shock proteins in broiler chickens and turkey poults

Peripheral leukocyte heat shock proteins (HSP: HSP90, HSP70, and HSP23) from broiler chickens and turkey poults were induced by in vitro and in vivo high temperature exposure. Heat conditioning, via a daily 1 h exposure to 41 C, enhanced in vitro HSP expression in leukocytes from chickens heat-conditioned for 1 to 2 wk, and a similar response was found in turkey poults with 3 wk of heat conditioning causing the greatest HSP expression. In vivo heat exposure trials caused maximization of HSP expression after 1 wk of daily heat conditioning exposures in broilers, but no additional enhancement was seen in chickens heat conditioned for 2 wk. Enhancement in HSP expression was evident for periods up to 4 wk after termination of the daily heat conditioning episodes.

Multiple effects of trehalose on protein folding in vitro and in vivo

The disaccharide trehalose is produced in large quantities by diverse organisms during a variety of stresses. Trehalose prevents proteins from denaturing at high temperatures in vitro, but its function in stress tolerance in vivo is controversial. We report that trehalose stabilizes proteins in yeast cells during heat shock. Surprisingly, trehalose also suppresses the aggregation of denatured proteins, maintaining them in a partially-folded state from which they can be activated by molecular chaperones. The continued presence of trehalose, however, interferes with refolding, suggesting why it is rapidly hydrolyzed following heat shock. These findings reconcile conflicting reports on the role of trehalose in stress tolerance, provide a novel tool for accessing protein folding intermediates, and define new parameters for modulating stress tolerance and protein aggregation.

Trigeminal ganglion neurons are protected by the heat shock proteins hsp70 and hsp90 from thermal stress but not from programmed cell death following nerve growth factor withdrawal

A prior mild thermal stress (heat shock) can protect neuronal cells against a subsequent exposure to either severe thermal stress or the induction of programmed cell death (apoptosis). By micro-injecting trigeminal ganglion neurons with expression constructs we show that over-expression of the individual heat shock proteins hsp70 and hsp90 can protect these cells against severe thermal stress but not against apoptosis. However, the protective effect of prior heat shock against subsequent apoptosis is dependent upon its ability to induce heat shock protein (hsp) synthesis rather than, for example, the inhibition of other protein synthesis associated with heat shock. The significance of these effects is discussed in terms of the role of different hsps in protecting neuronal cells from distinct stresses.

Over-expression of heat shock protein 70 protects neuronal cells against both thermal and ischaemic stress but with different efficiencies

Primary cultures of dorsal root ganglia (DRG) sensory neurons can be protected against subsequent severe thermal or ischaemic stress by prior exposure to a mild thermal or ischaemic insult. The degree of protection correlates with the amount of 70 kDa heat shock protein (hsp70) induced by the mild stress. We show directly that over-expression of hsp70 alone is sufficient to protect DRG neurons against thermal or ischaemic stress with a given level of hsp70 over-expression providing greater protection against thermal stress. In contrast over-expression of the 90 kDa heat shock protein (hsp90) has little or no protective effect against either stress. These results are discussed in terms of the role of individual hsps in protecting neuronal cells against different stresses.

Heat-shock induced protein modifications and modulation of enzyme activities

Upon heat stress, the cell physiology is profoundly altered. The extent of the alterations depends on the severity of the stress and may lead to cell death. The heat shock response is an array of metabolic changes characterized by the impairment of major cellular functions and by an adaptative reprogramming of the cell metabolism. The enhanced synthesis of the HSPs is a spectacular manifestation of this reprogramming. Numerous post translational modifications of proteins occur in response to heat stress and can be related to altered cellular functions. Some proteins are heat-denatured and temporarily inactivated. Heat-denaturation is reversible, chaperones may contribute to the repair. The extent of heat-denaturation depends on the cell metabolism: (a) it is attenuated in thermotolerant cells or in cells overexpressing the appropriate chaperones (b) it is enhanced in energy-deprived cells. Covalent modifications may also rapidly alter protein function. Changes in protein glycosylation, methylation, acetylation, farnesylation, ubiquitination have been found to occur during stress. But protein phosphorylation is the most studied modification. Several protein kinase cascades are activated, among which the various mitogen activated protein kinase (MAP kinase) cascades which are also triggered by a wide range of stimuli. As a possible consequence, stress modifies the phosphorylation status and the activity of components from the transcriptional and translational apparatuses. The same kinases also target key enzymes of the cellular metabolism. Protein denaturation results in constitutive hsp titration, this titration is a signal to trigger the heat-shock gene transcription and to activate some of the protein kinase cascades.

The degree of protection provided to neuronal cells by a pre-conditioning stress correlates with the amount of heat shock protein 70 it induces and not with the similarity of the subsequent stress

A mild thermal stress protects primary cultures of dorsal root ganglion (DRG) neurons against a subsequent lethal heat stress as well as to a lesser extent against a subsequent lethal ischaemia. In contrast, a mild ischaemic stress protects DRG neurons only against a subsequent severe thermal stress and not against severe ischaemia. A greater induction of heat shock protein (hsp) synthesis was observed in these cells following mild temperature stress compared to mild ischaemia. This suggests that the protective effect observed is dependent on hsp synthesis resulting in the observed cross-protective effect and does not involve a particular pre-stress specifically protecting against a subsequent, more severe application of the same stress. Moreover, a particular level of hsp induction produces a better protective effect against lethal heat stress than against lethal ischaemia.

Transient acquired thermotolerance in Drosophila, correlated with rapid degradation of Hsp70 during recovery

Acquired thermotolerance, measured either as increased cell viability following a lethal heat shock or by translational thermotolerance, appears rapidly following a 'priming' heat treatment, but also decays rapidly. 4 hours after priming heating thermotolerance is reduced by > 50% and by 9 hours it is virtually undetectable. Heat-shock protein 70 (Hsp70) turns over with a half-life of approximately 2 hours, and the decline in its intracellular abundance parallels the loss of acquired thermotolerance. Continuous heat shock extends the half-life of Hsp70 to approximately 7 hours. When Hsp70 is expressed at normal temperature using a metallothionein promoter, only partial acquired translational thermotolerance results. The results suggest that acquired thermotolerance is tightly regulated in Drosophila and partly, but not wholly, determined by post-translational regulation of Hsp70 levels.

Heat shock proteins and molecular chaperones: implications for adaptive responses in the skin

Recent advances in the biology of heat-shock proteins (hsps) are reviewed. These abundant and evolutionarily highly conserved proteins (also called stress proteins) act as molecular escorts. Hsps bind to other cellular proteins, help them to fold into their correct secondary structures, and prevent misfolding and aggregation during stress. Cytoplasmic hsp70 and hsp60 participate in complicated protein-folding pathways during the synthesis of new polypeptides. Close relatives of hsp70 and hsp60 assist in the transport and assembly of proteins inside intracellular organelles. Hsp90 may have a unique role, binding to the glucocorticoid receptor in a manner essential for proper steroid hormone action. Hsps may also be essential for thermotolerance and for prevention and repair of damage caused by ultraviolet B light. A unique class of T lymphocytes, the gamma delta T cells, exhibits a restricted specificity against hsps. These T cells may constitute a general, nonspecific immune mechanism directed against the hsps within invading organisms or against very similar hsps within invading organisms or against very similar hsps expressed by infected (stressed) keratinocytes. Immunologic cross-reactivity between hsps of foreign organisms and of the host may play a role in some autoimmune diseases. Although hsps are expressed in the skin, many questions remain about their role during injury, infection, and other types of cutaneous pathophysiology.

Heat shock modulates UVB-induced cell death in human epidermal keratinocytes: evidence for a hyperthermia-inducible protective response

The ability of heat shock to induce functional protection against ultraviolet B (UVB) light was examined in keratinocytes cultured from human skin. Cell death, measured with fluorescent vital dyes, increased in a UVB dose-dependent manner (LD50 approximately 20-60 mJ/cm2). However, a 60-min heat shock at 40 degrees C or 42 degrees C, administered several hours before UVB irradiation, reduced cell death by 2.0-2.5 times. Inducible protection took time to develop, with an optimal interval of approximately 6 h between heat and UVB exposures. Heat-inducible protection was completely blocked if either cordycepin (3'-deoxyadenosine), to inhibit mRNA synthesis, or cycloheximide, to inhibit protein synthesis, were present during the heating period. To determine whether apoptosis might be involved in UVB-induced keratinocyte death in this system, evidence for endonuclease activity was sought via in situ enzymatic labeling with terminal deoxynucleotidyl transferase and biotinylated-dUTP. Labeled nuclei were detected in UVB-irradiated cultures, and heat pretreatment at 6 h prior to UVB exposure (< 60 mJ/cm2) resulted in a 50% reduction in labeled nuclei. Overall, the data show that UVB-induced cell death in human keratinocyte cultures is attenuated by a heat-inducible mechanism that requires ongoing synthesis of mRNA and protein.

The role of trehalose synthesis for the acquisition of thermotolerance in yeast. I. Genetic evidence that trehalose is a thermoprotectant

In the yeast Saccharomyces cerevisiae, accumulation of the non-reducing disaccharide trehalose is triggered by various stimuli that activate the heat-schock response. Several studies have shown a close correlation between trehalose levels and tolerance to heat stress, suggesting that trehalose may be a protectant which contributes to thermotolerance. In this study, we have examined mutants defective in genes coding for key enzymes involved in trehalose metabolism with respect to the heat-induced and stationary-phase-induced accumulation of trehalose and the acquisition of thermotolerance. Inactivation of either TPS1 or TPS2, encoding subunits of the trehalose-6-phosphate synthase/phosphatase complex, caused an inability to accumulate trehalose upon a mild heat-shock or upon initiation of the stationary phase and significantly reduced the levels of heat-induced and stationary-phase-induced thermotolerance. Deletion of NTH1, the gene coding for the neutral trehalase, resulted in a defect in trehalose mobilization during recovery from a heat shock which was paralleled by an abnormally slow decrease of thermotolerance. Our results provide strong genetic evidence that heat-induced synthesis of trehalose is an important factor for thermotolerance induction. In an accompanying study [Hottiger, T., De Virgilio, C., Hall, M. N., Boller, T. & Wiemken, A. (1993) Eur. J. Biochem. 219, 187-193], we present evidence that the function of heat-induced trehalose accumulation may be to increase the thermal stability of proteins.

Heat-shock-induced protein synthesis is responsible for the switch-off of hsp70 transcription in Tetrahymena

We had previously described that new RNA synthesis is required for expression of the heat shock protein HSP70. Here, we find that the HSP70 mRNA decreases its levels under stress conditions, heat shock (HS) or arsenite (As), and that its levels start to decline at the same time as maximal HSPs synthesis (including HSP70) occurs. This suggests that regulation of the hsp70 gene is mainly exerted at the transcriptional level. Accumulation of the HSP70 mRNA in cells stressed in presence of cycloheximide (CHX), indicates that (a) protein(s) non-existent before stress, possibly HSP70 itself (which is shown here to be relatively stable), is involved in negatively regulating hsp70 expression. Since degradation of the HSP70 mRNA is also shown to occur in cells heat-shocked under CHX, as seen from decay of its levels upon addition of actinomycin D (AMD), the protein(s) must repress hsp70 expression at the transcriptional level. Other conditions that affect normal protein synthesis, namely the translation inhibitor puromycin and the arginine-analog canavanine (shown here to be stress inducers in Tetrahymena pyriformis), also cause a delay in transcription-arrest of the HSP70 mRNA. Under severe stress conditions of HS (36 degrees C) or As (350 microM), the levels of HSP70 mRNA are higher than under mild stress conditions, however, no significant difference is seen in the pattern of HSP70 mRNA decay.

Effect of heat shock on susceptibility of normal lymphoblasts and of a heat shock protein 70-defective tumour cell line to cytotoxic T lymphocytes in vitro

The effect of heat shock pretreatment of target cells on their lysability by cytotoxic T lymphocytes was analysed. Killing of Concanavalin A-stimulated normal lymphocytes by minor or major histocompatibility antigen-specific cytotoxic T lymphocytes is unchanged or even slightly enhanced after heat shock, whereas cells of the myeloma line Y3, which is derived from one of the lymphocyte donor strains, become nearly resistant to killing after the same pretreatment. Cold target inhibition experiments show that heat-shocked cells are recognized specifically and that untreated and heat-shocked target cells possess similar inhibitory potential. Y3 cells are unable to express the strongly heat-inducible heat shock protein of 70 kDa (hsp70) after heat shock; the acquired resistance is thus independent of hsp70 induction. Possible mechanisms of the different lysability seen in lymphoblasts and tumour cells after heat shock are discussed.

Effect of amino acid analogs on the development of thermotolerance and on thermotolerant cells

Exposure of HA-1 Chinese hamster fibroblasts to amino acid analogs has been shown to have a heat-sensitizing effect as well as inducing the heat shock response (Li and Laszlo, 1985a). In this study, we have examined the effect of amino acid analogs on the development of thermotolerance after a brief heat shock or exposure to sodium arsenite and the effect of amino acid analogs on cells that are already thermotolerant. Exposure of HA-1 cells to amino acid analogs inhibited the development of thermotolerance following a mild heat shock or treatment with sodium arsenite. However, cells that were already thermotolerant were resistant to the sensitizing action of amino acid analogs. The refractoriness of thermotolerant cells to amino acid analog treatment developed in parallel with thermotolerance. The uptake of the arginine analog, canavanine, and its incorporation into proteins was not altered in the thermotolerant cells. Furthermore, another biological consequence of exposure to amino acid analogs, sensitization to ionizing radiation, also was not altered in the thermotolerant cells. The inhibition of the development of thermotolerance by amino acid analogs and the refractoriness of thermotolerant cells to the heat-sensitizing action of amino acid analogs lend further support the role of heat-shock proteins in the phenomenon of thermotolerance.

Stress protein and proto-oncogene expression as indicators of neuronal pathophysiology after ischemia

Induction of hsp70 mRNA and protein appear to provide useful markers for delineating stages in the progression of neuronal pathophysiology after ischemia. Detection of hsp70 encoded by the induced mRNA is dependent on complex interactions between the time course of mRNA expression and recovery of protein synthesis in a given neuron population, and perhaps other factors relating to specific aspects of hsp70 physiology, during recirculation intervals of hours to days. Transient mRNA expression and subsequent detection of immunoreactive hsp70 protein appear to identify neurons more likely to survive ischemia and other insults, while prolonged expression of hsp70 mRNA is associated with more severe neuronal injury. Fos and Jun immunoreactivities are also increased after ischemia, and provide indexes of functional gene expression during earlier recirculation periods. The accumulation of Fos immunoreactivity in particular designates neurons in which rapid recovery of protein synthesis during 1-3 h recirculation has allowed translation of the very transiently expressed c-fos mRNA. Jun-like immunoreactivity allows an evaluation of events at later recirculation intervals, and provides a clear demonstration of synthesis and accumulation of induced protein in CA1 neurons at 6 h following 2 min ischemia. Detailed understanding of the significance of such interactions between transcriptional and translational events will continue to evolve as information accumulates regarding the expression of additional mRNAs and proteins after ischemia. The present demonstration that Jun-like immunoreactivity accumulates in CA1 neurons after brief ischemia indicates that widespread changes in gene expression, expected as a consequence of such primary effects on transcription factor activity, are likely to contribute to the phenomenon of induced ischemic tolerance and to other persistent changes in the brain following diverse insults.

Heat-induced unresponsiveness of heat shock gene expression is regulated at the transcriptional level

The induction kinetics of the heat shock proteins hsp68, hsp70 and hsp84 were studied. Studies on hsp mRNA levels and protein synthetic rates, with or without the presence of actinomycin D, showed that regulation took place at the transcriptional level. Hsp mRNA induction was followed by a transient state of unresponsiveness. At the time point where the induced hsp mRNAs were decreasing again, hsp68, hsp70 and hsp84 mRNA could not be induced by a second, identical, heat shock. Hsp68 mRNA could be induced again 12-16 h after the first heat shock. Apparently, this state really seems to be a state of reduced sensitivity, since a higher heat dose could partially overcome this unresponsiveness.

Thermotolerance in mammalian cells. Protein denaturation and aggregation, and stress proteins

Cells that have been pre-exposed to thermal stress can acquire a transient resistance against the killing effect of a subsequent thermal stress. The cause for this phenomenon, called thermotolerance, seems to be an enhanced resistance of proteins against thermal denaturation and aggregation. This resistance can be expressed as an attenuation of damage formation (less initial damage) or as a better repair of the protein damage (facilitated recovery). Heat Shock (or better, Stress) Proteins (HSPs) may play a role in and even be required for thermal resistance. However, rather than stress-induced enhanced synthesis and elevated total levels of HSPs per se, the concentration of, both constitutive and inducible, HSPs at and/or (re)distributed to specific subcellular sites may be the most important factor for the acquisition of thermotolerance. Specific HSPs may be involved either in damage protection or in damage repair.

Quercetin, an inhibitor of heat shock protein synthesis, inhibits the acquisition of thermotolerance in a human colon carcinoma cell line

Here, we describe the effects of quercetin on the induction of thermotolerance as examined by colony forming assay in a cell line derived from human colon carcinoma (COLO320 DM). Cells became resistant to heat treatment at 45 degrees C when they were preheated at 42 degrees C for 1.5 h or at 45 degrees C for 10 min. This induction of thermotolerance was almost completely inhibited by continuous treatment with 100 microM quercetin during the first and second heating sessions, and the interval between. This effect of quercetin was demonstrated to be dose-dependent over a concentration range of 50-200 microM. Quercetin did not increase the thermosensitivity of non-tolerant cells. The presence of quercetin during the first conditioning heating was more effective in inhibiting thermotolerance than its presence during the second heating. Quercetin was also found to inhibit the acquisition of thermotolerance induced by sodium arsenite. Cycloheximide, a nonspecific inhibitor of protein synthesis, did not affect the acquisition of thermotolerance by the same cell line. Quercetin specifically inhibits the synthesis of all heat shock proteins so far reported previously, and this leads to inhibition of the induction of thermotolerance. Such inhibition of thermotolerance by quercetin may improve the efficacy of clinical fractionated hyperthermia.

Effects on the expression of heat shock proteins by step-down heating and hypothermia in rat hepatoma cells with a different degree of heat sensitivity

Thermosensitization induced by pretreatment at supra- and subnormal temperatures, rate of protein synthesis and expression of the major heat shock proteins under such conditions was investigated in relation to intrinsic heat sensitivity of rat hepatoma cells, i.e. Reuber H35 and HTC. The high degree of heat susceptibility of H35 cells was reflected by a high degree of thermosensitization after pretreatment by heat (step-down heating) at temperatures of 42-44 degrees C for 30 min or cold for 16 h at temperatures ranging from 0 to 25 degrees C. Sensitization under step-down heating conditions was found to be paralleled by a delayed recovery of protein synthesis. Despite an increased relative rate, enhancement of the absolute rate of synthesis of the major heat shock proteins, HSP28, HSP60, HSP68, HSP70, HSP84 and HSP100, was less pronounced during step-down exposure. Comparable results were obtained during recovery of sensitized H35 cells at 37 degrees C after exposure to heat following pretreatment at 0 degrees C. Furthermore, clear differences in the regulation of the specific HSP synthesis, depending on the particular treatment protocol, were observed.

Effect of pH on quercetin-induced suppression of heat shock gene expression and thermotolerance development in HT-29 cells

When cells were heated for 15 min at 45 degrees C, they became thermotolerant to a second heat exposure at 45 degrees C. Thermotolerance developed rapidly, reached its maximum 6 hr after heat shock, and then gradually decayed. The development of thermotolerance was partially suppressed by treatment with various concentrations of quercetin (0.05-0.2 mM) at pH 7.4 after the initial heat treatment. In contrast, the drug markedly inhibited thermotolerance development at pH 6.5. Furthermore, a combination of low pH and quercetin treatment distinctively altered the expression of HSP70 gene compared with that of HSP28 or HSP90 gene. These results demonstrate a good correlation between the amount of HSP70 gene expression and development of thermotolerance.

Inhibition of heat shock gene expression does not block the development of thermotolerance

After cells have been exposed to a nonlethal heat shock, they develop an enhanced resistance to subsequent prolonged heat shock. This process, termed thermotolerance, correlates with the expression of a group of proteins called the heat shock proteins. When cells are exposed to heat, protein synthesis is rapidly turned off and takes 5-6 hr to recover. In thermotolerant cells, protein synthesis is not blocked by heat. The heat shock proteins are thought to be responsible for the development of thermotolerance and the protection of the protein synthesis machinery from heat inactivation. To test the hypothesis that the heat shock proteins are involved in the heat shock response, we used two inhibitors to block their transcription and expression during heating and then monitored the effect on the development of thermotolerance and on protein synthesis. Camptothecin inhibits DNA topoisomerase I and blocks transcription of all actively transcribed genes, whereas dichloro-D-ribofuranosylbenzimidazole (DRB) inhibits only those genes transcribed by RNA polymerase II. Both DRB and camptothecin blocked the heat-induced expression of the heat shock proteins, but the absence of these proteins did not block either the development of thermotolerance or the protection of protein synthesis after heating. The data indicate that thermotolerance can develop in the absence of new protein synthesis.

Acquisition of thermotolerance induced by heat and arsenite in HeLa S3 cells: Multiple pathways to induce tolerance?

Recent data indicate that cells may acquire thermotolerance via more than one route. In this study, we observed differences in thermotolerance development in HeLa S3 cells induced by prior heating (15 minutes at 44 degrees C) or pretreatment with sodium-arsenite (1 hour at 37 degrees C, 100 microM). Inhibition of overall protein and heat shock protein (HSP) synthesis (greater than 95%) by cycloheximide (25 micrograms/ml) during tolerance development nearly completely abolished thermotolerance induced by arsenite, while significant levels of heat-induced thermotolerance were still apparent. The same dependence of protein synthesis was found for resistance against sodium-arsenite toxicity. Toxic heat, but not toxic arsenite treatments caused heat damage in the cell nucleus, measured as an increase in the protein mass of nuclei isolated from treated cells (intranuclear protein aggregation). Recovery from this intranuclear protein aggregation was observed during post-heat incubations of the cells at 37 degrees C. The rate of recovery was faster in heat-induced tolerant cells than in nontolerant cells. Arsenite-induced tolerant cells did not show an enhanced rate of recovery from the heat-induced intranuclear protein aggregation. In parallel, hyperthermic inhibition of RNA synthesis was the same in tolerant and nontolerant cells, whereas post-heat recovery was enhanced in heat-induced, but not arsenite-induced thermotolerant cells. The more rapid recovery from heat damage in the nucleus (protein aggregation and RNA synthesis) in cells made tolerant by a prior heat treatment seemed related to the ability of heat (but not arsenite) to induce HSP translocations to the nucleus.

Characteristic synthesis and redistribution of 70 kd heat shock protein in thermotolerant Chinese hamster V79 cells

Upon exposure to heat shock the increased rate of hsp70 synthesis decreased more rapidly in thermotolerant V79 cells than in the non-thermotolerant cells. However, the levels of hsp70 in the thermotolerant cells at 12 h after a heat shock were almost the same as those in the non-thermotolerant cells. On the other hand, the migration of hsp70 from cytoplasm to nucleoli after a heat shock was very rapid in both thermotolerant and non-thermotolerant cells, but hsp70 in the nucleoli disappeared faster in the thermotolerant cells than in the non-thermotolerant cells, and this coincided with the faster decline of hsp70 synthesis in the thermotolerant cells. For the characteristic distribution of hsp70, protein synthesis was not required. Furthermore, the induction and expression of thermotolerance by the cells were little affected by the inhibition of protein synthesis. Thus, the synthesis of hsp70 itself seemed not to be essential for the induction and expression of thermotolerance of the cells, although hsp70 may be essential for thermoresistance of cells. The rapid decrease of hsp70 synthesis and the rapid disappearance of hsp70 from the nucleoli after a heat shock may be essential for the expression of thermotolerance of the cells.

Effect of tunicamycin on glycosylation of a 50 kDa protein and thermotolerance development

We investigated whether or not a 50 kDa glycoprotein might play an important role in protein synthesis-independent thermotolerance development in CHO cells. When cells were heated for 10 min at 45.5 degrees C, they became thermotolerant to a heat treatment at 45.5 degrees C administered 12 hr later. The thermotolerance ratio at 10(-3) isosurvival was 4.4. The cellular heat shock response leads to enhanced glycosylation of a 50 kDa protein. The glycosylation of proteins including a 50 kDa glycoprotein was inhibited by treatment with various concentrations of tunicamycin (0.2-2 micrograms/ml). The development of thermotolerance was not affected by treatment with tunicamycin after the initial heat treatment, although 2 micrograms/ml tunicamycin inhibited glycosylation by 95%. However, inhibiting protein synthesis with cycloheximide (10 micrograms/ml) after the initial heat treatment partially inhibited the development of thermotolerance. Nevertheless, there was no further reduction of thermotolerance development by treatment with a combination of 2 micrograms/ml tunicamycin and 10 micrograms/ml cycloheximide. These data suggest that development of thermotolerance, especially protein synthesis-independent thermotolerance, is not correlated with increased glycosylation of the 50 kDa protein.

Differences in preferential synthesis and redistribution of HSP70 and HSP28 families by heat or sodium arsenite in Chinese hamster ovary cells

Since both heat and sodium arsenite induce thermotolerance, we investigated the differences in synthesis and redistribution of stress proteins induced by these agents in Chinese hamster ovary cells. Five major heat shock proteins (HSPs; Mr 110, 87, 70, 28, and 8.5 kDa) were preferentially synthesized after heat for 10 min at 45.5 degrees C, whereas four major HSPs (Mr 110, 87, 70, and 28 kDa) and one stress protein (33.3 kDa) were preferentially synthesized after treatment with 100 microM sodium arsenite (ARS) for 1 hr. Two HSP families (HSP70a,b,c, and HSP28a,b,c) preferentially relocalized in the nucleus after heat shock. In contrast, only HSP70b redistributed into the nucleus after ARS treatment. Furthermore, the kinetics of synthesis of each member of HSP70 and HSP28 families and their redistribution were different after these treatments. The maximum rates of synthesis of HSP70 and HSP28 families, except HSP28c, were 6-9 hr after heat shock, whereas those of HSP70b and HSP28b,c were 0-2 hr after ARS treatment. In addition, the maximum rates of redistribution of HSP70 and HSP28 families occurred 3-6 hr after heat shock, whereas that of HSP70b occurred immediately after ARS treatment. The degree of redistribution of HSP70b after ARS treatment was significantly less than that after heat treatment. These results suggest that heat treatment but not sodium arsenite treatment stimulates the entry of HSP70 and HSP28 families into the nucleus.

Thermotolerance in regional hyperthermia in vivo--an experimental study using the MH134 tumor

In the clinical application of hyperthermia, determining the thermotolerance that influences the anti-tumor effect is an important problem. The purpose of this study was to investigate the methods of induction and disappearance of thermotolerance in vivo. After transplanting MH134 cancer cells into the paws of C3H mice, local hyperthermia with warm water was administered, and the movement of thermotolerance in vivo studied in terms of the heating intervals and tumor growth times. When the first heating was applied on the 8th day after transplantation, thermotolerance appeared within 1 hour, increasing gradually to reach a maximum at 18 hours, after which it decreased gradually and disappeared after 48 hours. When the first heating was applied on the 13th day after transplantation, which fell during the rapid tumor proliferation period, the movement of thermotolerance presented a similar pattern of appearance and disappearance. The results of this study made it clear that there was no difference in the movement of thermotolerance between the two periods even though each had a different rate of tumor proliferation.

Role of heat-shock proteins in the induction of thermotolerance in Chinese hamster V79 cells by heat and chemical agents

To examine the involvement of heat shock proteins in the induction of thermotolerance in Chinese hamster V79 cells, thermotolerance was induced by heating of the cells at 42 degrees C for 4 h or at 44 degrees C for 20 min, or by treatment of the cells with 50 microM sodium arsenite for 3 h or 20 micrograms/ml puromycin for 4 h. Under unstressed conditions V79 cells synthesized constitutively three major heat-shock proteins, hsp70, hsp85 and hsp105. On exposure to conditions under which thermotolerance was induced, the synthesis of constitutive hsp70, hsp85 and hsp105 increased, but the inducible form of hsp70 was not synthesized, indicating that this inducible form was not necessary for the induction of thermotolerance. Although the amounts of heat-shock proteins synthesized in the cells that acquired thermotolerance were not always more than those synthesized constitutively in unstressed cells, the stressed cells synthesized heat-shock proteins (especially hsp70) preferentially over other proteins. As the level of hsp70 in the thermotolerant cells was almost the same as that in unstressed cells, the specific accumulation of hsp70 seemed not to be required for the acquisition of thermotolerance. From these findings it seemed likely that, for the induction of thermotolerance in V79 cells, hsp70 preferentially synthesized during or after the stress has an important function. Or the synthesis of heat shock proteins may not be important, and constitutively synthesized heat-shock proteins acquire a specific function during or after the stress.

Thermotolerance and the heat shock response in normal human keratinocytes in culture

Protective responses of normal human epidermal keratinocytes in culture, after exposure to elevated temperatures ("heat shock"), were examined. Cell viability, measured 24-48 h after a 20-min heat challenge at temperatures between 37 degrees C and 54 degrees C, declined sharply within a narrow 2 degrees-3 degrees C range. However, conditioning with a mild thermal pretreatment (40 degrees C or 42 degrees C for 1 h) protected the keratinocytes against a subsequent heat challenge. This induced thermotolerance was apparent when cells were challenged at 1, 3, and 6 h after the thermal pre-treatment, but disappeared by 24 h. Heating conditions that induce thermotolerance also stimulated the synthesis of heat-shock proteins (hsp) in these cells. Inductions of prominent 35S-methionine labeled bands at 70, 78, and 90 kDa were observed. However, the increases in synthesis of these heat-shock proteins did not correlate well with thermotolerance, because large increases were also observed at certain elevated temperatures that did not produce improved survival. Keratins observed in these cells (50 and 58 kDa classes) were not induced by heat shock. The development of thermotolerance, and the induction of hsp, were both completely blocked by 3'-deoxyadenosine (cordycepin), an inhibitor of newly synthesized messenger RNA, but not by adenosine, the normal analog. While heat-inducible mRNA apparently mediate some function important for the development of thermotolerance, the nature of that role remains speculative. Overall, our findings establish the existence of a functional thermal protective mechanism in human keratinocytes that appears to require the synthesis of new mRNA.

Correlation between redistribution of a 26 kDa protein and development of chronic thermotolerance in various mammalian cell lines

Previous studies suggested that a 26 kDa protein might play an important role in protein synthesis-independent thermotolerance development in CHO cells. To determine if this phenomenon was universal, four mammalian cell lines, viz., CHO, HA-1, murine Swiss 3T3, and human HeLa, were studied. Cells were heated at 42 degrees C, and the level of 26 kDa protein in the nucleus was measured, together with clonogenic survival and protein synthesis. The results demonstrated that 1) the 26-kDa protein was present in the four different cell lines, and 2) the level of the 26 kDa protein in their nuclei was decreased by 30-70% after heating at 42 degrees C for 1 hr. However, restoration of this protein occurred along with development of chronic thermotolerance. The protein synthesis inhibitor cycloheximide (10 micrograms/ml) neither inhibited the development of chronic thermotolerance nor affected the restoration of the 26 kDa protein in the nucleus. In fact, this drug protected cells from hyperthermic killing and heat-induced reduction of 26 kDa protein in the nucleus. Heat sensitizers, quercetin (0.1 mM), 3,3'-dipentyloxacarbocyanine iodide (DiOC5[3]: 5 micrograms/ml), and stepdown heating (45 degrees C-10 min----42 degrees C), potentiated hyperthermic killing and inhibited or delayed the restoration of the 26 kDa protein to the nucleus. These results support a correlated, perhaps causal relationship between the restoration of the 26 kDa protein and chronic thermotolerance development in four different mammalian cell lines.

Effects of heat and chemical stress on development

Similarities in the means by which developmental defects are induced in vertebrates and Drosophila suggest that some kinds of defects may be induced by similar mechanisms. The similarities include the fact that heat and a group of chemicals that induce synthesis of heat-shock proteins induce defects in mammals, chickens, and flies. Different kinds of defects are even produced in one type of animal, depending on the precise timing of the environmental insult. The effectiveness of the environmental treatment in inducing defects depends on the genetic background of the animal as well as on past exposure to chemicals and heat. Developmental defects induced by heat in mice, rats, and flies can all be prevented by thermotolerance-inducing treatments. The basis for these effects has been studied at the molecular level in Drosophila, and the evidence indicates that these teratogens and the thermotolerance-inducing treatments affect the level or timing of expression of specific genes during critical periods in the developmental program.

Possible involvement of ubiquitin function and ATP requirement in the development of thermotolerance in mammalian cells

Thermotolerance under chronic exposure to moderate hyperthermia at 41 degrees C was hardly induced in the mouse temperature-sensitive mutant ts85 cells, in contrast to the parental wild-type FM3A cells. Thermotolerance was induced at a reduced level in the mutant cells compared with the wild-type cells by incubation at 33 degrees C (permissive temperature), but not at 39 degrees C (non-permissive temperature), after a brief exposure at 44 degrees C. Under conditions where protein synthesis was inhibited by cycloheximide at 41 degrees C, significant amounts of thermotolerance developed in FM3A cells. FM3A cells depleted of cellular ATP by treatment with 2.4-dinitrophenol and 2-deoxyglucose were not sensitized to thermal cell killing at 44 degrees C, when drug-treated cells were washed and exposed to hyperthermia in drug-free growth medium, where cellular ATP rapidly recovered. However, the cells deprived of ATP under the treatment at 41 degrees C failed to develop thermotolerance, indicating a requirement of ATP for thermotolerance development. The decay of thermotolerance was not affected by ATP levels after it was developed. The degradation of abnormal cellular proteins which contained amino acid analogues was promoted at 33 degrees C relative to normal protein degradation in FM3A and ts85 cells. Both normal and abnormal proteins were degraded at a reduced rate at 43 degrees C. Pretreatment of cells at 41 degrees C decreased the rate of degradation of abnormal proteins at 33 degrees C by 20% in FM3A cells and by about 100% in ts85 cells. Pretreatment of cells at 41 degrees C increased significantly the conjugation of 125I-labeled ubiquitin to cellular endogenous proteins in extracts of FM3A cells, but decreased the conjugation in extracts of ts85 cells. The data presented here, in conjunction with the observations by others that the ts85 cell is a mutant defective in the ubiquitination of cellular proteins at nonpermissive temperatures, suggest that the ATP-dependent ubiquitination may be crucial for the development of thermotolerance.

Early response and induced tolerance to cycloheximide in Neurospora crassa

Incubation of Neurospora crassa mycelia with low doses of cycloheximide induces the expression of several genes. After 6 h in the presence of cycloheximide, mycelia become tolerant to further additions of the drug and the rate of protein synthesis exhibits a lower sensitivity to it. The polypeptide pattern is indicative of a stress situation.

Co-isolation of heat stress and cytoskeletal proteins with plasma membrane proteins

Previous reports have suggested the possible existence of a plasma-cell-membrane function associated with some heat stress proteins (HSPs). To investigate the effect of hyperthermia on plasma membrane proteins, rat mammary tumour clone C (MTC) cells were heated at 42 degrees C for 1 h. Their surface proteins were (1) labelled with [3H]leucine, (2) biotinylated, (3) affinity isolated with streptavidin-agarose beads under denaturing or non-denaturing conditions, and (4) analysed by one- and two-dimensional polyacrylamide-gel electrophoresis and protein blotting under denaturing conditions. Affinity isolation of biotinylated proteins enriched for a protein subfraction believed to be membrane-associated. Several proteins analogous to HSP or their heat-stress cognates (HSC) were present with these biotinylated protein subfractions in control or heated cells. The major and most consistent feature of affinity isolates from heated cells was the presence of a small fraction of the induced 68-kD HSP. The 112-, 90-, 70- and 22-kD HSC/HSP were also present in small amounts in affinity isolates of control cells, and the fraction increased in heated cells. Several structural proteins, including actin and the tubulins were present in the same affinity isolates. Protein blotting experiments indicated that none were exposed on the exterior of the plasma-cell membrane or biotinylated and thus none were exposed on the exterior of the plasma-cell membrane or biotinylated intracellularly through membrane damage. These results suggest that small fractions of several HSC are located at or near the cytoplasmic face of the plasma membrane along with cytoskeletal proteins, and that additional submembranous localization of HSP occurs after heat stress and may be part of the processes associated with membrane damage or cellular responses to heat. Further studies will be directed at establishing the relationships between these proteins and the role, if any, of the changes associated with heat stress.

Abnormal proteins as the trigger for the induction of stress responses: heat, diamide, and sodium arsenite

Thermotolerance and synthesis of heat shock proteins are induced in cells in response to a variety of environmental stresses. We examined the suggestion of Hightower (1980) that modifications of intracellular proteins may be the triggering event that induces heat shock protein synthesis and thermotolerance. We did so by modifying cellular proteins, using diamide, a sulfhydryl oxidizing agent, and dithio-bis (succinimidyl propionate), an agent that cross-links bifunctional amino groups. Both of these agents induced heat shock proteins and thermotolerance in CHO (HA-1) cells. Furthermore, we observed cross-resistance and self-tolerance with three seemingly unrelated stimuli (diamide, heat, and sodium arsenite). This observation suggests that the induction of protective responses to these stimuli is mediated by a common mechanism. The results support the hypothesis that production of abnormal proteins by various stresses induces the stress responses as well as tolerance.