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

Activity-Regulated Cytoskeleton-Associated Protein (Arc/Arg3.1) is Transiently Expressed after Heat Shock Stress and Suppresses Heat Shock Factor 1

Heat shock proteins are induced by activation of heat shock factor 1 (HSF1) in response to heat shock and protect against heat stress. However, the molecular mechanisms underlying the downstream signal of heat shock have not been fully elucidated. We found that similarly to canonical Hsps, Arc/Arg3.1 is also markedly induced by heat shock and by other cellular stress inducers, including diamide, sodium arsenite and H₂O₂ in various cells. We noted that heat stress–induced Arc/Arg3.1 protein is short lived, with a half-life of <30 min, and is readily degraded by the ubiquitin–proteasome system. Arc/Arg3.1 overexpression inhibited the up-regulation of heat shock–induced Hsp70 and Hsp27, suggesting that Arc/Arg3.1 is a negative regulator of heat shock response (HSR). Studying the effect of Arc/Arg3.1 on HSF1, a major transcription factor in HSR, we found that Arc/Arg3.1 binds to HSF1 and inhibits its binding to the heat shock element in gene promoters, resulting in reduced induction of Hsp27 and Hsp70 mRNAs, without affecting HSF1′s phosphorylation-dependent activation, or nuclear localization. Arc/Arg3.1 overexpression decreased cell survival in response to heat shock. We conclude that Arc/Arg3.1 is transiently expressed after heat shock and negatively regulates HSF1 in the feedback loop of HSR.

Visualizing cellular stress: A hypothesis-driven confocal laboratory exercise to identify compounds that activate heat shock factor binding at Hsp70 loci

Exposure of organisms to high temperatures and various chemical and physical stressors can cause protein misfolding and aggregation. In turn, this can disrupt the functions of proteins, threatening both development and homeostasis. To overcome this, cells can initiate the highly conserved heat shock (HS) stress response pathway. In eukaryotes, this is a coordinated cellular response, in which the master HS activator, heat shock factor (HSF), is rapidly recruited to the HS protein genes, and triggers the recruitment of additional coactivator proteins that facilitate gene expression. This results in the production of HS proteins that function as nuclear and cytosolic molecular chaperones, to promote refolding of proteins and prevent aggregation and increase protein degradation pathways. Here, we describe a laboratory exercise in which students visualize and quantify Green Fluorescent Protein (GFP)-tagged HSF binding to the HS protein genes in living Drosophila salivary gland nuclei as an output of chemically induced protein misfolding. Students are assigned an array of chemicals, and using the scientific literature, predict impacts of these chemicals on protein folding. Students then test the effects of their chemicals by measuring GFP-tagged HSF binding to the HS genes in salivary glands using confocal microscopy. Designed for junior and senior level students in a cell/molecular biology course, this is a two-part lab, in which student work closely with an instructor to help familiarize them with developing hypotheses supported by scientific literature and testing these hypotheses by quantitating the levels of GFP-HSF binding, using confocal microscopy of living Drosophila cells. © 2018 International Union of Biochemistry and Molecular Biology, 46(5):445-452, 2018.

Silver nanoparticles cause osmoregulatory impairment and oxidative stress in Caspian kutum (Rutilus kutum, Kamensky 1901)

Silver nanoparticles (AgNPs) are increasingly used in several industrial and household products because of their antibacterial and antifungal properties. Hence, there is an inevitable risk that these chemicals may end up in aquatic biotopes and have adverse effects on the fauna. In order to assess potential health effects on aquatic organisms, this study evaluated the effects of waterborne AgNP exposure for 7 days on a set of critical stress parameters in juvenile Caspian kutum (Rutilus kutum), an economically important fish in the Caspian Sea. The applied level 11 μg/l of AgNP is high compared to reported water concentrations and corresponds to 40% of the 96 h LC₅₀ value, initially determined to be 28 μg/l. Gill heat shock protein 70 (hsp70) mRNA expression, Na⁺/K⁺-ATPase activity and enzymatic activities of liver superoxide dismutase (SOD), glutathione peroxidase (Gpx), lactate dehyrogenase (LDH) and alkaline phosphatase (ALP), and whole-body cortisol and thyroid hormones (T3 and T4) were measured as endpoints. Gill hsp70 mRNA expression increased and gill Na⁺/K⁺-ATPase activity decreased in AgNP-exposed fish compared to controls. The specific activities of all liver enzymes decreased significantly compared to controls. Whole-body cortisol and thyroid hormones decreased compared to controls. In conclusion, the study demonstrates that AgNPs cause oxidative stress and gill osmoregulatory disruption in Caspian kutum juveniles.

Heterogeneous nuclear ribonucleoprotein K inhibits heat shock-induced transcriptional activity of heat shock factor 1

When cells are exposed to heat shock and various other stresses, heat shock factor 1 (HSF1) is activated, and the heat shock response (HSR) is elicited. To better understand the molecular regulation of the HSR, we used 2D-PAGE-based proteome analysis to screen for heat shock-induced post-translationally modified cellular proteins. Our analysis revealed that two protein spots typically present on 2D-PAGE gels and containing heterogeneous nuclear ribonucleoprotein K (hnRNP K) with trioxidized Cys¹³² disappeared after the heat shock treatment and reappeared during recovery, but the total amount of hnRNP K protein remained unchanged. We next tested whether hnRNP K plays a role in HSR by regulating HSF1 and found that hnRNP K inhibits HSF1 activity, resulting in reduced expression of hsp70 and hsp27 mRNAs. hnRNP K also reduced binding affinity of HSF1 to the heat shock element by directly interacting with HSF1 but did not affect HSF1 phosphorylation-dependent activation or nuclear localization. hnRNP K lost its ability to induce these effects when its Cys¹³² was substituted with Ser, Asp, or Glu. These findings suggest that hnRNP K inhibits transcriptional activity of HSF1 by inhibiting its binding to heat shock element and that the oxidation status of Cys¹³² in hnRNP K is critical for this inhibition.

HSP70 colocalizes with PLK1 at the centrosome and disturbs spindle dynamics in cells arrested in mitosis by arsenic trioxide

Heat shock protein 70 (HSP70) has been shown to be a substrate of Polo-like kinase 1 (PLK1), and it prevents cells arrested in mitosis by arsenic trioxide (ATO) from dying. Here, we report that HSP70 participates in ATO-induced spindle elongation, which interferes with mitosis progression. Our results demonstrate that HSP70 and PLK1 colocalize at the centrosome in ATO-arrested mitotic cells. HSP70 located at the centrosome was found to be phosphorylated by PLK1 at Ser⁶³¹ and Ser⁶³³. Moreover, unlike wild-type HSP70 (HSP70(wt)) and its phosphomimetic mutant (HSP70(SS631,633DD)), a phosphorylation-resistant mutant of HSP70 (HSP70(SS631,633AA)) failed to localize at the centrosome. ATO-induced spindle elongation was abolished in cells overexpressing HSP70(SS631,633AA). Conversely, mitotic spindles in cells ectopically expressing HSP70(SS631,633DD) were more resistant to nocodazole-induced depolymerization than in those expressing HSP70(wt) or HSP70(SS631,633AA). In addition, inhibition of PLK1 significantly reduced HSP70 phosphorylation and induced early onset of apoptosis in ATO-arrested mitotic cells. Taken together, our results indicate that PLK1-mediated phosphorylation and centrosomal localization of HSP70 may interfere with spindle dynamics and prevent apoptosis of ATO-arrested mitotic cells.

Systemic analysis of heat shock response induced by heat shock and a proteasome inhibitor MG132

The molecular basis of heat shock response (HSR), a cellular defense mechanism against various stresses, is not well understood. In this, the first comprehensive analysis of gene expression changes in response to heat shock and MG132 (a proteasome inhibitor), both of which are known to induce heat shock proteins (Hsps), we compared the responses of normal mouse fibrosarcoma cell line, RIF- 1, and its thermotolerant variant cell line, TR-RIF-1 (TR), to the two stresses. The cellular responses we examined included Hsp expressions, cell viability, total protein synthesis patterns, and accumulation of poly-ubiquitinated proteins. We also compared the mRNA expression profiles and kinetics, in the two cell lines exposed to the two stresses, using microarray analysis. In contrast to RIF-1 cells, TR cells resist heat shock caused changes in cell viability and whole-cell protein synthesis. The patterns of total cellular protein synthesis and accumulation of poly-ubiquitinated proteins in the two cell lines were distinct, depending on the stress and the cell line. Microarray analysis revealed that the gene expression pattern of TR cells was faster and more transient than that of RIF-1 cells, in response to heat shock, while both RIF-1 and TR cells showed similar kinetics of mRNA expression in response to MG132. We also found that 2,208 genes were up-regulated more than 2 fold and could sort them into three groups: 1) genes regulated by both heat shock and MG132, (e.g. chaperones); 2) those regulated only by heat shock (e.g. DNA binding proteins including histones); and 3) those regulated only by MG132 (e.g. innate immunity and defense related molecules). This study shows that heat shock and MG132 share some aspects of HSR signaling pathway, at the same time, inducing distinct stress response signaling pathways, triggered by distinct abnormal proteins.

The effects of gabapentin pretreatment on brain injury induced by focal cerebral ischemia/reperfusion in the rat

Background

Experimental studies have shown that gabapentin can reduce neuronal injury in the setting of cerebral ischemia, but the mechanisms have not yet been clearly determined. This study was conducted to determine whether gabapentin pretreatment altered expression levels of heat shock protein 70 and reduced acute phase neuronal injury in rats subjected to transient focal cerebral ischemia/reperfusion.

Methods

Forty male Sprague-Dawley rats (260-300 g) were randomly assigned to one of four groups (saline-treated, or 0.1, 0.5, or 5 mg/kg gabapentin group). In all animals, focal cerebral ischemia was induced by intraluminal middle cerebral artery occlusion for 1 hour. The animals of the gabapentin groups were pretreated with a single intravenous administration of gabapentin 20 minutes before ischemic insults. The infarct volume, brain edema and motor behavior deficits were analyzed 24 hours after ischemic insult. Caspase-3-reactive cells and cells showing Hsp70 activity were counted in the caudoputamen and fronto-parietal cortex.

Results

The infarction ratio was significantly decreased in the 5 mg/kg gabapentin group (P < 0.05) and brain edema ratios were significantly reduced in the 0.1 mg/kg, 0.5 mg/kg, and 5 mg/kg gabapentin groups 24 hours after ischemia/reperfusion injury (P < 0.05). There were more Hsp70-reactive cells in the 5 mg/kg gabapentin group than in the saline group in both the caudoputamen and fronto-parietal cortex (P < 0.05).

Conclusions

These results indicate that gabapentin may have a neuroprotective effect and can reduce early neuronal injury caused by focal cerebral ischemia/reperfusion; this may be mediated by expression of Hsp70. However, gabapentin pretreatment did not prevent caspase-dependent apoptosis.

Induction of Thermotolerance by Chemical Agents in Enucleate Erythrocytes

Erythrocytes treated with various chemical agents for 1 h at 37 degrees C showed resistance to a subsequent 1 h heat treatment at 53 degrees C. Maximal thermotolerance was observed 6 h after 3 mM DNP and 0.03 mM disulfiram treatment and 4 h after diamide exposure at 0.3 mM. Our results suggest that chemically induced thermotolerance to heat treatment in erythrocytes was similar to heat-induced thermotolerance.

Role of Membrane Components in Thermal Injury of Cells and Development of Thermotolerance

Exposure of cells to hyperthermia induces a transient resistance to subsequent heat treatment. The specific mechanisms responsible for hyperthermic cell killing and thermotolerance development are not well understood. It seems that heat may induce at least two different states of thermotolerance, of which one is dependent on protein synthesis. The expression of thermotolerance may include multiple cytoplasmic and membrane components. A number of studies have indicated that membranes play an important role in governing the thermal injury of cells. It seems, therefore, that heat denatured plasma membrane proteins may be a potential target for thermal stress and a trigger for the induction of thermotolerance. The localization of heat shock proteins in the plasma membrane and the suggestion of thermal resistance in enucleate erythrocytes support this suggestion. However, a direct relationship between the plasma membrane and hyperthermic killing or development of thermotolerance has not been found.

Sodium arsenite reduces severity of dextran sulfate sodium-induced ulcerative colitis in rats

The histopathological features and the associated clinical findings of ulcerative colitis (UC) are due to persistent inflammatory response in the colon mucosa. Interventions that suppress this response benefit UC patients. We tested whether sodium arsenite (SA) benefits rats with dextran sulfate sodium (DSS)-colitis. The DSS-colitis was induced by 5% DSS in drinking water. SA (10 mg/kg; intraperitoneally) was given 8 h before DSS treatment and then every 48 h for 3 cycles of 7, 14 or 21 d. At the end of each cycle rats were sacrificed and colon sections processed for histological examination. DSS induced diarrhea, loose stools, hemoccult positive stools, gross bleeding, loss of body weight, loss of epithelium, crypt damage, depletion of goblet cells and infiltration of inflammatory cells. The severity of these changes increased in the order of Cycles 1, 2 and 3. Treatment of rats with SA significantly reduced this severity and improved the weight gain.

Cerebral neurons and glial cell types inducing heat shock protein Hsp70 following heat stress in the rat

In this chapter, the distribution of Hsp70 in brain cell types following whole body hyperthermia is reviewed. The prevalence of Hsp70 expression in oligodendrocytes, microglia, and vascular cells in this type of stress contrasts with scarcity of Hsp70 induction in astrocytes and most neurons of the hyperthermic brain. However, a similarity between hyperthermic- and arsenite-induced brain patterns of Hsp70 expression supports the view that denaturation of specific proteins plays a major role in the selectivity of glial/vascular expression also during hyperthermia in vivo. The mechanism of neuronal Hsp70 non-responsiveness in heat stress despite their ability to use Hsc70 in a partial heat stress response remains to be elucidated.

Benzo(a)pyrene inhibits expression of inducible heat shock protein 70 in vascular endothelial cells

Benzo(a)pyrene (BaP), a ubiquitous environmental pollutant known to cause many diseases including atherosclerosis, induces a dose-dependent reduction in the levels of the inducible Hsp70. To explore the mechanism underlying the reduction of Hsp70, we measured the levels of Hsp70, cytoplasmic and nuclear heat shock factor 1 (HSF1) in porcine aortic endothelial cells using Western blot, and then further characterized the binding ability of HSF1 and heat shock element (HSE) by electrophoretic mobility shift assay. We found that when porcine aortic endothelial cells were treated by 0.1-10 microM of BaP for 24 h, there was a significant reduction of Hsp70, cytoplasmic and nuclear HSF1 and the binding rate of HSF1 and HSE at 5, 10 microM of BaP but less effective at lower concentrations. The effect of BaP on the Hsp70 expression level was markedly attenuated by co-treatment with phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC). Staurosporine (STP), an inhibitor of PKC, blocked the effect of PMA treatment in combination with BaP. These results suggest that BaP might inhibit Hsp70 levels by reducing the expression of HSF1 and decreasing binding of HSF1 and HSE via PKC-dependent signaling pathways that might be involved in the regulation of Hsp70 gene expression under BaP.

Cross‐Tolerance in the Tidepool Sculpin: The Role of Heat Shock Proteins

Cross-tolerance, or the ability of one stressor to transiently increase tolerance to a second heterologous stressor, is thought to involve the induction of heat shock proteins (Hsp). We thus investigated the boundaries of cross-tolerance in tidepool sculpins (Oligocottus maculosus) and their relationship to Hsp70 levels. Survival of sculpins exposed to severe osmotic (90 ppt, 2 h) and hypoxic (0.33 mg O(2)/L, 2 h) stressors increased from 68% to 96%, and from 47% to 76%, respectively, following a +12 degrees C heat shock. The magnitude of this heat shock was critical for protection. A +10 degrees C heat shock did not confer cross-tolerance, while a +15 degrees C heat shock was deleterious. Sculpins required between 8 and 48 h of recovery following the +12 degrees C heat shock to develop cross-tolerance. There was no association between Hsp70 levels before the onset of the secondary stressor and cross-tolerance. However, branchial Hsp70 levels following osmotic shock were highly correlated with the time frame of cross-tolerance. Thus, Hsp70 induction by the priming stressor may be less important than the ability of the cell to mount an Hsp response to subsequent stressors. The time frame of cross-tolerance is similar to the interval between low tides, suggesting the possible relevance of this response in nature.

Mild hypothermia reduces expression of heat shock protein 60 in leukocytes from severely head-injured patients

BACKGROUND

Infectious complications are among the most serious problems that occur in severely head-injured patients treated with mild hypothermia. The mechanism underlying the susceptibility to infection has not been clarified. Heat shock protein (HSP) 60 has been reported to play an essential role in innate immunity. Thus, we conducted a study to clarify the impact of mild hypothermia on the expression of HSPs in polymorphonuclear leukocytes (PMNLs) in severely head-injured patients.

METHODS

Between September 1997 and November 1999, 17 severely head-injured patients with a Glasgow Coma Scale score of 8 or less at admission in whom intracranial pressure could be maintained below 20 mm Hg by conventional therapy were randomly assigned to two treatment groups: a mild hypothermia group (HT group, nine patients) and a normothermia group (NT group, eight patients). The HT group was subjected to mild hypothermia (intracranial temperature, 34 degrees C) for 48 hours followed by rewarming at a rate of 1 degrees C per day for 3 days, whereas the NT group was subjected to normothermia (intracranial temperature, 37 degrees C) for 5 days. Blood samples were serially obtained at three time points; days 0 to 1, days 2 to 5, and days 6 to 14 after head injury. We measured the expression of HSP27, HSP60, HSP70, and HSP90 by flow cytometry.

RESULTS

The two groups were similar with respect to prognostic factors, and there was no difference in clinical outcome. The expression of PMNL HSP60 in the HT group was significantly lower in all three time periods compared with that in the NT group (p < 0.05), whereas expression of the other HSPs did not differ significantly between the groups. The incidence of infectious complications was significantly increased in the HT group over that in the NT group (p < 0.05). In in vitro studies, PMNLs from 10 healthy volunteers were incubated at 37 degrees C, 34 degrees C, or 26 degrees C for 1 hour with sodium arsenite (100 micromol/L), an HSP inducer. The expression of HSP60 at 26 degrees C and 34 degrees C was significantly lower than that at 37 degrees C (p < 0.05), whereas expression of the other HSPs did not differ significantly at 26 degrees C, 34 degrees C, or 37 degrees C.

CONCLUSION

Mild hypothermia reduces the expression of HSP60 in PMNLs from severely head-injured patients. Thus, mild hypothermia may suppress innate immunity.

Many Mechanisms for Hsp70 Protection From Cerebral Ischemia

Overexpression of inducible Hsp70 has been shown to provide protection from cerebral ischemia both in animal models of stroke and in cell culture models. New work suggests that there are multiple routes of cell death, including apoptotic and necrotic cell death. Hsp70 is known to protect from both necrotic and apoptotic cell death. In addition to the well-studied role of Hsp70 as a molecular chaperone assisting in correct protein folding, several new mechanisms by which Hsp70 can prevent cell death have been described. Hsp70 is now known to regulate apoptotic cell death both directly by interfering with the function of several proteins that induce apoptotic cell death as well as indirectly by increasing levels of the anti-death protein bcl-2. Despite these new insights into the ways in which Hsp70 functions as an anti-death protein, further surprises are likely as we continue to gain insight into the functioning of this multifaceted protein.

Antistress effects of bacosides of Bacopa monnieri: modulation of Hsp70 expression, superoxide dismutase and cytochrome P450 activity in rat brain

The antistress effect of bacosides of Brahmi (Bacopa monnieri, BBM), dissolved in distilled water, was -studied in adult male Sprague Dawley rats by administering oral doses of 20 and 40 mg/kg for 7 consecutive days. In half of the animals treated with 20 or 40 mg/kg of BBM, stress was given 2 h after the last dose. Stress was also administered to the animals treated with distilled water alone. BBM, at both doses, did not induce a significant change in the expression of Hsp70 in any brain region studied while stress alone produced a significant increase in the Hsp70 expression in all the brain regions. A significant decrease in the activity of superoxide dismutase (SOD) was evident in the hippocampus with the lower dose of BBM and in animals given stress alone, while an increase in the activity of SOD was observed in the brain regions with the higher dose of BBM. An increase in the activity of cytochrome P450 (P450) dependent 7-pentoxyresorufin-o-dealkylase (PROD) and 7-ethoxyresorufin-o-deethylase (EROD) was observed in all the brain regions after exposure to stress alone and with both doses of BBM although the magnitude of induction of P450 expression was less with a higher dose of BBM. Interestingly, stress when given to the animals pretreated with BBM for 7 days resulted in a decrease in Hsp70 expression in all the brain regions with a significant decrease occurring only in the hippocampus. Likewise the activity of SOD was found to be further reduced in all the brain regions in the animals treated with the lower dose of BBM followed by stress. However, when stress was given to the animals pretreated with the higher dose of BBM, a significant increase in the enzyme activity was observed in the cerebral cortex and in the rest of the brain while the activity of SOD was reduced to a much greater extent in the cerebellum and in the hippocampus. Likewise, the activity of P450 enzymes was found to be restored to almost control levels in the animals given stress and pretreated with the higher dose of BBM, while a lesser degree of induction, compared with animals treated with BBM or stress alone, was observed in the animals pretreated with the lower dose of BBM and given stress. The data indicate that BBM has potential to modulate the activities of Hsp70, P450 and SOD thereby possibly allowing the brain to be prepared to act under adverse conditions such as stress.

Stress protection by a fluorescent Hsp27 chimera that is independent of nuclear translocation or multimeric dissociation

A chimeric protein consisting of enhanced green fluorescent protein (EGFP) fused to the N-terminus of human Hsp27 conferred stress protection in human A549 lung carcinoma and murine L929 cells that were stably transfected to express the chimera constitutively. The resultant protection was comparable with that in the same cell lines when they were transfected to express corresponding levels of Hsp27. Unlike L929 cells, A549 cells exhibit endogenous Hsp27 expression, whose expression was inhibited in proportion to the amount of fluorescent chimera expressed, suggesting that the A549 cells recognized the latter as Hsp27. Upregulation of Hsp27 or chimeric Hsp27 in all transfected cell lines (stable or transient transfection) caused no measurable change in cellular glutathione levels, indicating that glutathione played no role in the stress protection associated with either protein. Chimeric Hsp27 had a monomeric molecular weight of 55 kDa (that of Hsp27 plus EGFP) in both cell types and formed a 16-mer complex twice as massive as that formed by Hsp27. Heat shock or sodium arsenite induced phosphorylation of both chimeric Hsp27 and Hsp27, which resulted in the disaggregation of Hsp27 multimers in both cell types and disaggregation of 20% of the chimeric multimers in L929 cells. But chimeric Hsp27 multimers did not disaggregate after stress in A549 cells. Epifluorescence and confocal microscopy demonstrated that chimeric Hsp27 was restricted to the cytoplasm under normal growth conditions and after heat shock in all cells. This study supports the conclusions that Hsp27 stress protection requires neither its translocation into the nucleus nor the dissociation of its multimeric complex. Furthermore, it demonstrates that fluorescent chimeras of heat shock proteins can be functional and used to observe the protein's distribution within living cells.

Arsenite pretreatment attenuates benzo[a]pyrene cytotoxicity in a human lung adenocarcinoma cell line by decreasing cyclooxygenase-2 levels

Both simultaneous and sequential exposure to arsenite and benzo[a]pyrene (BaP) potentially occur in human populations drinking arsenic-contaminated water or burning arsenic-contaminated coal. Although arsenite and BaP are both well-documented hazardous substances and human carcinogens, interactions between these two agents have not been well defined. In this study, we demonstrated that posttreatment with arsenite synergistically enhanced the cytotoxicity of BaP for a human lung adenocarcinoma cell line, CL3. In contrast, pretreatment of CL3 cells with arsenite attenuated BaP cytotoxicity. Involvement of heat-shock protein 70 and heme oxygenase-1 in this arsenite-mediated attenuation of BaP cytotoxicity was ruled out. Our data also indicated that arsenite pretreatment did not affect the BaP-mediated induction of CYP1A1, the initial enzyme involved in its metabolic activation, but did result in a significant decrease in mRNA and protein levels of cyclooxygenase-2 (COX-2), which is required to convert the BaP metabolite BaP 7,8-dihydrodiol to the ultimate epoxide. In contrast to the high susceptibility of CL3 cells to BaP, the human lung carcinoma cells, H460, and CL3R15 cells (arsenic-resistant CL3 cells) showed normal CYP1A1 inducibility by BaP, had negligible amounts of COX-2, and were highly resistant to BaP. The involvement of COX-2 in BaP activation was confirmed by transfection of H460 cells with a recombinant adenovirus, Ad-pgk-Cox2, coding for COX-2, which resulted in a significant increase in the levels of the COX-2 product prostaglandin E2 in the medium and in the susceptibility of H460 cells to BaP. The present study confirms the importance of COX-2 in BaP activation and demonstrates that the arsenite-mediated attenuation of BaP cytotoxicity is mediated by a reduction in COX-2 levels.

Heat shock and ceramide have different apoptotic pathways in radiation induced fibrosarcoma (RIF) cells

Heat shock induces various cellular responses including inhibition of protein synthesis, production of heat shock proteins (HSPs) and induction of thermotolerance. The molecular mechanisms of the processes have not been well understood. It has been proposed that ceramide formation during heat shock mediates heat shock induced apoptosis. We examined whether C2-ceramide mimicked the cellular response to heat shock in RIF-1 cells and their thermotolerant derivative TR-RIF-1 cells. Discernible effects between heat shock and C2-ceramide treatments were observed in cellular changes such as total protein synthesis, HSP synthesis, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) activity and PARP cleavage. Heat shock immediately inhibited cellular protein synthesis, which was recovered by synthesizing HSPs first and then whole proteins later. Heat shock also activated SAPK/JNK and increased PARP cleavage in dose-dependent manner. Thermotolerant TR-RIF-1 cells responded to heat shock more insensitively than RIF-1 cells. On the other hand, C2-ceramide treatment did not accompany any changes induced by heat shock. No discernible differences between RIF-1 and TR-RIF-1 cells were observed by C2-ceramide treatment. We tried to figure out how C2-ceramide interacts with cellular membrane and found that exogenous C2-ceramide was incorporated into the outer monolayer and flipped into the inner monolayer of human erythrocytes in ATP-dependent manner. However, the rate of C2-ceramide incorporation was similar in control and thermotolerant cells. In summary, thermotolerant cells are resistant to heat shock induced apoptotic signaling but not resistant, rather sensitive to membrane disturbing C2-ceramide mediated apoptosis. These results suggest that heat shock and ceramide have different signal transduction pathways.

Enhanced expression of heat shock proteins in activated polymorphonuclear leukocytes in patients with sepsis

BACKGROUND

Heat shock proteins (HSPs) in cells, as molecular chaperons, have been reported to regulate cell functions. The objective of this study was to investigate the HSP expression in polymorphonuclear leukocytes (PMNLs) from severe septic patients and the relation between the expression of HSPs and PMNL function.

METHODS

In blood samples from 21 patients with sepsis and serum C-reactive protein levels more than 10 mg/dL, we used flow cytometry to measure expressions of HSP27, HSP60, HSP70, and HSP90; oxidative activity; and levels of apoptosis in PMNLs during sepsis. In in vitro studies, we used cells from 14 healthy volunteers to examine the relation between the expression of HSP70 and PMNL function. Quercetin (30 microM), a suppressor of HSP, and sodium arsenite (100 microM), an inducer of HSP, were used to regulate the expression of HSP70 in PMNLs, and oxidative activity and apoptosis in these cells were measured.

RESULTS

In patients with sepsis, the expressions of HSP27, HSP60, HSP70, and HSP90 and oxidative activity in PMNLs were significantly increased. Apoptosis of these PMNLs was markedly inhibited. In the in vitro studies, administration of sodium arsenite enhanced the expression of HSP70, significantly increased oxidative activity, and inhibited apoptosis. Administration of quercetin before sodium arsenite prevented the expression of HSP70, the increase in oxidative activity, and the inhibition of apoptosis.

CONCLUSION

Sepsis causes the enhanced expression of HSPs in activated PMNLs. In PMNLs with enhanced expression of HSP70, oxidative activity is increased and apoptosis is inhibited. The enhanced expression of HSPs may play a role in regulating PMNL function in patients with sepsis.

Resolution, detection, and characterization of redox conformers of human HSF1

We describe here an experimental protocol for the resolution, detection, and quantitation of the reduced and oxidized conformers of human heat shock factor 1 (hHSF1) and report on the effects in vitro and in vivo of redox-active agents on the redox status, structure, and function of hHSF1. We showed that diamide, a reagent that promotes disulfide bond formation, caused a loss of immunorecognition of the monomeric hHSF1 protein in a standard Western blot detection procedure. Modification of the Western blot procedure to include dithiothreitol in the equilibration and transfer buffers after gel electrophoresis allowed for the detection of a compact, intramolecularly disulfide cross-linked oxidized hHSF1 (ox-hHSF1) in the diamide-treated sample. The effect of diamide was blocked by pretreatment with N-ethylmaleimide and was reversed by dithiothreitol added to the sample prior to gel electrophoresis. Incubation with nitrosoglutathione at 42 degrees C also promoted the conversion of HSF1 to ox-HSF1; at 25 degrees C, however, nitrosoglutathione was by itself without effect but blocked the formation of ox-hHSF1 in the presence of diamide. The disulfide cross-linked ox-hHSF1 was monomeric and resistant to the in vitro heat-induced trimerization and activation. The possibility that ox-HSF1 may occur in oxidatively stressed cells was evaluated. Treatment of HeLa cells with 2 mm l-buthionine sulfoximine promoted the formation of ox-HSF1 and blocked the heat-induced activation of HSF DNA binding activity. Our result suggests that hHSF1 may have integrated redox chemistry of cysteine sulfhydryl into its functional responses.

Stress factors acting at the level of the plasma membrane induce transcription via the stress response element (STRE) of the yeast Saccharomyces cerevisiae

A variety of stress factors induces transcription via the stress response element (STRE) present in control regions of a number of genes of the yeast Saccharomyces cerevisiae. Induction of transcription involves nuclear translocation of the STRE-binding transcription activators Msn2p and Msn4p. The primary cellular events triggering this translocation are presently not well understood. In this investigation, we have observed that a number of factors acting at the level of the yeast plasma membrane, including the antifungal agent nystatin, the steroidal alkaloid tomatine, benzyl alcohol, a number of detergents and the plasma membrane H+-ATPase inhibitor diethylstilbestrol or mutations in the PMA1 gene encoding the plasma membrane ATPase, induce Msn2p nuclear accumulation and STRE-dependent transcription. At least some of the stress factors acting via STREs cause an increase in plasma membrane permeability, leading to a decrease in membrane potential, which might be a primary cellular stress signal. A decrease in internal pH triggered by permeabilization of the plasma membrane or a change in cAMP levels are at least not obligatory factors in intracellular stress signal transduction. The signal transduction pathway transmitting the signal generated at the plasma membrane to Msn2p is still unknown.

On the path to the heat shock response: destabilization and formation of partially folded protein intermediates, a consequence of protein thiol modification

This review discusses the initial events that occur during oxidative stress that induce the synthesis of heat shock proteins. The focus is on non-native oxidation or modification of protein thiols and the destablization that can result. Proteins that contain non-native modified thiols can become destablized such that they unfold into molten globule-like intermediates at or below 37 degrees C, relieving Hsf-1 negative regulation, and inducing Hsp transcription.

Thermotolerance inhibits various stress-induced apoptosis in NIH3T3 cells

When NIH3T3 cells were exposed to mild heat and recovered at 37 degrees C for various time intervals, they were thermotolerant and resistant to subsequent stresses including heat, oxidative stresses, and antitumor drug methotrexate which are apoptotic inducers. The induction kinetics of apoptosis by stresses were determined by DNA fragmentation and protein synthesis using [35S]methionine pulse labeling. We investigated the hypothesis that thermotolerant cells were resistant to apoptotic cell death compared to control cells when both cells were exposed to various stresses inducing apoptosis. The cellular changes in thermotolerant cells were examined to determine which components are involved in this resistance. At first, the degree of resistance correlates with the extent of heat shock protein synthesis which were varied depending on the heating times at 45 degrees C and recovery times at 37 degrees C after heat shock. Secondly, membrane permeability change was observed in thermotolerant cells. When cells prelabeled with [3H]thymidine were exposed to various amounts of heat and recovered at 37 degrees C for 1/2 to 24 h, the permeability of cytosolic [3H]thymidine in thermotolerant cells was 4 fold higher than that in control cells. Thirdly, the protein synthesis rates in thermotolerant and control cells were measured after exposing the cells to the same extent of stress. It turned out that thermotolerant cells were less damaged to same amount of stress than control cells, although the recovery rates are very similar to each other. These results demonstrate that an increase of heat shock proteins and membrane changes in thermotolerant cells may protect the cells from the stresses and increase the resistance to apoptotic cell death, even though the exact mechanism should be further studied.

Transcriptional modulation of viral reporter gene constructs following induction of the cellular stress response

In this study, we report that commonly used methods of transient transfection induce the cellular stress response and a recovery period is required following transfection when analyzing cellular stress responsive genes. Four transfection methods were examined for their ability to induce the stress response by measuring the expression of heat shock protein (hsp) 72. We demonstrate that electroporation increases expression of hsp 72 in HUT 78 cells. Additionally, DEAE-dextran and liposome-mediated transfection resulted in increased hsp 72 expression in an adherent cell line (HeLa). Liposome-mediated transfection differentially induced cell stress, dependent on the transfection time in serum-free culture conditions. The stress responsiveness of two viral promoters, the HTLV-1 long terminal repeat and CMV immediate early transcriptional unit were examined. We found the maximal stress-mediated enhancement of transcription with both promoters did not occur until the cells recovered for 24 h following transfection.

Thermotolerance expression in mitotic CHO cells without increased translation of heat shock proteins

The objective of this study was to unequivocally demonstrate thermotolerance expression in mammalian cells in the absence of stress-induced synthesis of heat shock proteins (HSPs). Mitotic cells were selected as an experimental system since their genome was in the form of condensed chromosomes and ostensibly incapable of being transcribed; thus, obviating stress-induced HSP gene expression. Asynchronous Chinese hamster ovary (CHO) cells were treated with 0.2 microgram/ml nocodazole to accumulate cells in mitosis for harvest by mitotic shakeoff. Cells were maintained in mitosis with nocodazole during thermotolerance induction, thermotolerance development, and all challenge hyperthermia exposures. Although the heat shock transcription factor was activated by the thermotolerance inducing heat shock, as indicated by gel mobility shift assay, no increase in steady-state HSP mRNA levels was detected, as expected. Preferential synthesis of HSPs from extant mRNA was not detected during thermotolerance development and cellular levels of the 27 kDa, 70 kDa, and 90 kDa heat shock proteins remained constant, as determined by Western Blot analyses. The magnitude and induction threshold of expressed thermotolerance was not diminished when cells were incubated with 10.0 micrograms/ml cycloheximide during thermotolerance development confirming that new protein synthesis was not requisite. Parallel experiments were performed using nonmitotic cells in which protein synthesis was inhibited during thermotolerance development with 10.0 micrograms/ml cycloheximide. As with mitotic cells, high levels of thermotolerance were attained without detectable increases in the cellular content of the 27 kDa, 70 kDa, and 90 kDa heat shock proteins. The results of this study demonstrated that high levels of thermotolerance could be expressed in mitotic cells without stress-induced, preferential synthesis of HSPs, and support the contention that a substantial fraction of thermotolerance expressed in nonmitotic cells also occurs independently of induced HSP synthesis.

The outcome of poliovirus infections in K562 cells is cytolytic rather than persistent after hemin-induced differentiation

K562-Mu erythroleukemia cells readily establish a long-term persistent poliovirus infection characterized by continuous virus production in the absence of complete p220 cleavage and host translation shutoff (R. E. Lloyd and M. Bovee, Virology 194:200-209, 1993). The mechanism of resistance appears to be modulated at the intracellular level and to be related to decreased virus-mediated cytopathic effects (P. A. Benton, J. W. Murphy, and R. E. Lloyd Virology 213:7-18, 1995). It is well documented that hemin induces the differentiation of K562 cells and alters the expression of several host proteins. We report here that growth of K562 cells in hemin prior to poliovirus infection results in a dose-dependent increase in virus-induced cell lysis and thereby alters the normally persistent outcome of infection to a more lytic phenotype. K562 cells infected after hemin treatment displayed increased host translation shutoff, p220 cleavage, viral protein synthesis, and viral RNA accumulation compared with nontreated cells. Since hemin treatment of K562 cells also induced the increased expression of several heat shock proteins (Hsp70, Hsc70, Hsp90, and cohort p60), we tested the hypothesis that their increased expression may play a role in altering poliovirus infection in hemin-treated K562 cells. However, neither heat stress nor oxidative stress, inducers of heat shock protein synthesis, altered the outcome (of virus infections. In addition, we report the novel finding that subunits of two translation initiation factors, p220 (eIF-4G) and eIF-2alpha, are cleaved as a result of hemin treatment of K562 cells. It is proposed that hemin alters the expression of specific host proteins in K562 cells, probably other than heat shock proteins, which changes the initial response to poliovirus infections from persistent to lytic.

Thermotolerance and nuclear protein aggregation: protection against initial damage or better recovery?

Heat-induced nuclear protein aggregation and subsequent disaggregation were measured in nonpreheated and preheated (thermotolerant) HeLa S3 cells. The effect of thermotolerance on the formation of and recovery from heat-induced nuclear protein aggregates was related to the cellular levels of hsp27, hsp60, hsp70, hsc70, and hsp90. Cells heated at different time points after the thermotolerance trigger showed various levels of protection against heat-induced nuclear protein aggregation. This protection, however, did not parallel the development and decay of thermotolerance on cell survival. The protection was maximal when the thermotolerance level already had started to decay. The level of protection against nuclear protein aggregation did however parallel the cellular level of hsp70 indicating that hsp70 may be involved in this process. At all stages during the development and decay, thermotolerant cells showed a more rapid recovery (disaggregation) from the heat-induced nuclear protein aggregates than non-thermotolerant cells. The rates of disaggregation during development and decay of thermotolerance paralleled the cellular levels of hsp27 suggesting that hsp27 is somehow involved in this recovery process from heat-induced nuclear protein aggregates. The total cellular levels of none of the individual hsp's completely correlate with development and decay of thermotolerance, indicating that overexpression of any of these hsp's alone does not determine the level of thermotolerance. Clonogenic cell survival paralleled the rates of disaggregation, leading to the notion that recovery processes are the most important determinant for the thermotolerant state of HeLa S3 cells. The best correlation with clonogenic survival was found when both initial aggregation and subsequent disaggregation were taken into account, suggesting that the combined action of various hsp's in these two processes have to be included in thermotolerance development and decay.

Characterization of a signal generated by oxidation of protein thiols that activates the heat shock transcription factor

The diazenecarbonyl derivative, diamide, was used to produce nonnative protein disulfides in Chinese hamster ovary cells in order to characterize the events that occur during thiol oxidation-induced denaturation that trigger induction of Hsp 70. We limit the term protein denaturation to a process involving a conformational rearrangement by which the ordered native structure of a protein changes to a more disordered structure. Protein thiol oxidation resulted in immediate destabilization of proteins, as assessed by differential scanning calorimetry (DSC). The DSC profile indicated both a decrease in the onset temperature for detection of denaturation and destabilization of a class of proteins with an average transition temperature (Tm) of 60 degrees C. Concomitant with destabilization was an increase in proteins associated with isolated nuclei. Thiol oxidation also induced heat shock transcription factor (HSF) binding activity, however, this was nearly undetectable immediately following diamide treatment: maximum activation occurred 3 hr following exposure. In contrast, heat shock denatured thermolabile proteins which exhibited a Tm of < or = 48 degrees C. Heat shock also resulted in a rapid increase in proteins associated with isolated nuclei and produced immediate and maximum activation of HSF binding. The accumulation of Hsp and Hsc 70 mRNA following thiol oxidation reflected the delay in HSF binding. Acquisition of HSF binding activity occurred immediately if diamide-treated cells were subsequently exposed to a heat shock, indicating that HSF was not inactivated by the diamide treatment. Ostensibly, the cellular system for detecting denatured/abnormal proteins failed to immediately recognize the signal generated by thiol oxidation. These results suggest that at least two processes are involved in the induction of Hsp 70 by nonnative disulfide bond formation: destabilization of protein structure resulting in denaturation and recognition of denatured protein.

Induction of heat-shock protein 72 protects against ischemia/reperfusion in rat small intestine

BACKGROUND & AIMS

Induction of heat-shock protein 72 is associated with enhanced tolerance to subsequent nonthermal stresses. This study evaluated whether induction of heat-shock protein 72 protects against intestinal ischemia/reperfusion injury.

METHODS

Groups of nonheated and heated rats underwent sham operation, 30 minutes of ischemia by occlusion of the superior mesenteric artery, or ischemia followed by 60 minutes of reperfusion. Whole-body hyperthermia to a core temperature of 41.5-42 degrees C for 15-20 minutes was followed by passive cooling 2-3 hours before the experiment. Samples of small intestine were obtained for determination of heat-shock protein 72 production and ex vivo generation of prostaglandin E2 and leukotriene B4 and for histological assessment of mucosal injury and number of neutrophils.

RESULTS

Hyperthermia significantly increased heat-shock protein 72 production and significantly reduced ischemia/reperfusion-induced mucosal injury, neutrophilic infiltration, and leukotriene B4 production. Levels of leukotriene B4 and numbers of neutrophils were well correlated in nonheated (r = 0.72) but not in heated groups (r = -0.16). The elevation of prostaglandin E2 levels in response to ischemia and reperfusion was unaltered by hyperthermia.

CONCLUSIONS

The mechanism of heat stress-induced protection against intestinal ischemia/reperfusion injury involves inhibition of leukotriene B4 production and subsequent prevention of neutrophil activation and chemotaxis.

Protocol for freezing thermotolerant cells and maintaining thermotolerance following thawing

Two independent laboratories have demonstrated that suspension-grown, Chinese hamster ovary (CHO) cells can be made thermotolerant, frozen and subsequently thawed such that they still express thermotolerance. Thermotolerance was determined as the ability to protect cells against hyperthermic cell killing (colony formation assay) and the ability to reduce protein aggregation within the nuclei of heated cells. Cells were frozen either following development of full or partial thermotolerance. In the former case frozen cells maintained thermotolerance upon thawing and in the latter case cells subsequently developed full thermotolerance following thawing and incubation at 37.0 degrees C. After thawing, frozen cells displayed a temporal course of thermotolerance development and decay that was similar to that for never-frozen cells. Success was obtained using either asynchronous or synchronous cell populations, and the heat sensitivity of the cells was not altered by the freezing procedure. The experimental results demonstrate the plausibility of utilizing a frozen stock of thermotolerant cells to make thermotolerance experiments more convenient.

Potential involvement of a constitutive heat shock element binding factor in the regulation of chemical stress-induced hsp70 gene expression

It was reported that chemical stresses such as arsenite, cadmium or salicylate fail to induce synthesis of the inducible form of HSP70 (HSP70i). We report here that exposure of cells to higher doses of these chemical treatments induced significant synthesis of HSP70i in CHO cells as well as other cell lines. The synthesis of HSP70i is primarily regulated at the transcriptional level. Although all tested chemical treatments induced heat shock factor (HSF) binding to the heat shock element (HSE), HSP70i synthesis appears to be regulated by an alternative factor (CHBF) which constitutively binds to the HSE at 37 degrees C. The treatments, which dissociate the HSE-CHBF complex, induced significant HSP70i synthesis. The treatments, which failed to induce HSP70i synthesis, still activated HSF binding to HSE but the HSE-CHBF complex remained as that of untreated control cells.

Integrity of intermediate filaments is associated with the development of acquired thermotolerance in 9L rat brain tumor cells

Withangulatin A (WA), a newly discovered withanolide isolated from an antitumor Chinese herb, has been shown to be a vimentin intermediate filament-targeting drug by using immunofluorescence microscopy. Together with cytochalasin D and colchicine, these drugs were employed to investigate the importance of vimentin intermediate filaments, actin filaments, and microtubules in the development of acquired thermotolerance in 9L rat brain tumor cells treated at 45 degrees C for 15 min (priming heat-shock). Acquired thermotolerance was abrogated in cells incubated with WA before the priming heat-shock but it could be detected in cells treated with WA after the priming heat-shock. In contrast, cytochalasin D and colchicine do not interfere with the development of thermotolerance at all. The intracellular localizations of vimentin and the constitutive heat-shock protein70 (HSC70) in treated cells were examined by using immunofluorescence microscopy and detergent-extractability studies. In cells treated with WA before the priming heat-shock, vimentin IFs were tightly aggregated around the nucleus and unable to return to their normal organization after a recovery under normal growing conditions. In contrast, the IF network in cells treated with WA after the priming heat-shock was able to reorganize into filamentous form after a recovery period, a behavior similar to that of the cells treated with heat-shock only. HSC70 was found to be co-localized with vimentin during these changes. It is suggested that the integrity of intermediate filaments is important for the development of thermotolerance and that HSC70 may be involved in this process by stabilizing the intermediate filaments through direct or indirect binding.

HSP-72 synthesis is promoted by increase in [Ca2+]i or activation of G proteins but not pHi or cAMP

The family of 70-kDa heat-shock proteins (HSP-70) is evolutionarily highly conserved and has been shown to enhance cell survival from thermal injury. This study characterized HSP-72 induction in human epidermoid A-431 cells exposed to 45 degrees C for 10 min and determined the relationship between HSP-72, intracellular pH (pHi), adenosine 3',5'-cyclic monophosphate (cAMP), G proteins, and intracellular cytosolic free Ca2+ concentration ([Ca2+]i). Heat shock induced HSP-72 production, which was dependent on both temperature and the duration of heating. This HSP-72 induction was confirmed by Western blot analysis. HSP-72 levels in cells that had been heated then returned to 37 degrees C were elevated at 2 h (1.5 +/- 0.1 x control), reached a maximum at 8 h (2.7 +/- 0.1 x control), and remained above baseline for up to 4 days. Levels of HSP-72 mRNA, determined by dot-blot analysis, reached a maximum at 2 h and returned to baseline within 8 h. Both actinomycin D and cycloheximide blocked HSP-72 induction. Because heating causes intracellular acidification and increases in cAMP and [Ca2+]i, we studied the effect of pHi, cellular cAMP, and [Ca2+]i on HSP-72 induction. The reduction of pHi to 6.9 by acid loading did not affect the basal level of HSP-72 in unheated cells. Treatment with pertussis toxin, cholera toxin, or forskolin, but not 8-bromo-cAMP, 3-isobutyl-1-methylxanthine, or N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide potentiated heat-induced HSP-72 production. Inhibition of the heat-induced increase in [Ca2+]i attenuated, but failed to completely block, heat-induced HSP-72 production, mRNA synthesis, and the heat-shock transcriptional factor-heat-shock element binding complex formation, which suggests there are Ca(2+)-dependent and -independent processes involved in HSP-72 synthesis. Our results show that an increase in [Ca2+]i or activation of G proteins, but not pHi and cAMP, enhances HSP-72 induction.

Synthesis of heat shock proteins following oxidative challenge: role of glutathione

The relationship between glutathione metabolism, menadione sodium bisulphite oxidation of protein thiols, and the synthesis of hsc70 was investigated using CHO cells. A 30-min/37 degrees C exposure to menadione, a compound which redox cycles to produce superoxide anion radicals and hydrogen peroxide, resulted in rapid accumulation of hsc70 mRNA. PAGE and Western blot analysis indicated increased synthesis such that accumulation of hsc70 occurred. These changes were preceded by rapid oxidation of GSH to GSSG, followed by GSH depletion, and subsequent protein thiol oxidation. As a test of whether a correlation existed between GSH oxidation and depletion, protein thiol oxidation and hsp synthesis, cells were exposed to menadione in the absence and presence of glucose. Synthesis of hsc70 was increased in cells exposed to menadione in the absence of glucose compared with its presence. As a further test, cells were exposed to BSO/DEM in order to deplete GSH and then exposed to menadione. The synthesis of hsc70 following exposure to menadione was greatly increased in GSH-depleted cells compared with GSH-replete cells. Experiments were conducted to determine if electroporation of cells in GSSG containing buffer affected hsp synthesis. Electroporation in glucose-free buffer containing 3 mM GSSG did not affect hsp synthesis. We interpret these results to indicate that the inability to maintain glutathione in a reduced form during menadione redox cycling resulted in protein thiol oxidation. This, in turn, resulted in accumulation of hsc70 mRNA with a subsequent increase in the synthesis of hsc70.

Protein aggregation as primary and characteristic cell reaction to various stresses

Ehrlich carcinoma and EL-4 thymoma ascites cells were subjected in vitro to heat shock, ATP depletion, oxidative stress, Ca2+ overloading and iodoacetamide treatment. After the transient stresses, Triton (X-100)insoluble (TIS) fractions were isolated from the cells and analysed by electrophoresis and immunoblotting. All stresses used caused rapid aggregation of cell proteins. This was manifested in a significant rise in protein content in the TIS fractions. The protein increase was mostly due to an increase in the insolubility of actin, 57 kDa protein of intermediate filaments, 70 kDa heat shock protein (HSP 70), and some specific proteins whose insolubilization was a characteristic sign for each type of cell injury. Different survival rates in the cell lines after either stress correlated well with differences in their TIS protein accretion. Possible mechanisms for stress-induced protein aggregation and its relationship with cell viability are suggested.

Induction of tolerance to hypothermia and hyperthermia by a common mechanism in mammalian cells

Pretreatment by hypothermic (25 degrees C) cycling (PHC) of attached exponential-phase V79 Chinese hamster cells by Method 4 (24 hr at 25 degrees C + 1.5 hr at 37 degrees C + 24 hr at 25 degrees C + trypsin + 3 hr at 37 degrees C) or by Method 3 (48 hr at 25 degrees C + trypsin + 3 hr at 37 degrees C) make mammalian V79 cells significantly more resistant to 43 degrees C hyperthermia. There is no significant difference in the 43 degrees C curves whether Method 3 or 4 is used for pre-exposure. If pre-exposure at 15 or 10 degrees C, the resistance to hyperthermia is significantly reduced. PHC by Method 4 significantly increases survival of cells exposed to 5 degrees C and, to a lesser extent, to 10 degrees C. The increase in hyper- and hypothermic survival after PHC cannot be accounted for by changes in cell cycle distribution. Heat-shock protein synthesis is not induced by PHC; hence, protection does not result from newly synthesized proteins. When cells are made tolerant to hyperthermia by a pretreatment in 2% DMSO for 24 hr at 37 degrees C (Method 8), the cells are not more resistant to subsequent exposures to hypothermia, either at 5 or 10 degrees C. The results imply that there may be two mechanisms of inducing resistance to hyperthermia, only one of which also confers resistance to hypothermia.

Induction of vimentin modification and vimentin-HSP72 association by withangulatin A in 9L rat brain tumor cells

Withangulatin A induced cell rounding up and the morphological alteration resulted from the reorganization of all of the major cytoskeletal components, i.e., vimentin, tubulin, and actin, as revealed by immunofluorescence techniques. When the withangulatin A-treated cells changed to a round-up morphology, vimentin intermediate filaments were found to be collapsed and clustered around the nucleus. The alteration was accompanied by characteristic changes of vimentin molecules, including augmentation of phosphorylation, retardation of electrophoretic mobility, and decrease in detergent extractability. The levels of vimentin phosphorylation were augmented by 2.5- and 1.8-fold in cells incubated with 50 microM withangulatin A for 1 and 3 h, respectively. The electrophoretic mobility of vimentin was partially retarded in cells treated with withangulatin A for 1 h at 10 microM and a completely upshift mobility was observed after 5 h treatment at 50 microM. In addition, vimentin molecules became less extractable by nonident P-40 after the cells were treated with withangulatin A and this effect was dose dependent. The decrease in solubility of vimentin was accompanied by the redistribution of HSP72 into the detergent nonextractable fraction and these two events were well correlated. Our results suggest that withangulatin A induced the modification of vimentin, which resulted in the alteration of cell morphology and redistribution of intracellular HSP72, an event that may play an important role in the induction of heat-shock response.

Synthesis of heat shock/stress proteins during cellular injury

Several conclusions can be drawn from available data on the expression of stress proteins in brain with respect to their utility as markers of cellular injury. First, it is evident that all cell types in brain are capable of expressing stress proteins, although there is striking specificity in the population responding to a given insult. The apparent hierarchy of responsiveness indicated by hsp72 expression correlates well with the relative vulnerability of specific cell populations in a given model. With increasing severity of injury there can be an attenuation of the translational component of the stress response, in that hsp72 immunoreactivity fails to accumulate even though its mRNA is abundantly expressed. For this reason, hsp72 immunoreactivity provides an index of cell populations that have responded to an insult with a functional stress response. Such a response is not sufficient to guarantee survival, since many CA1 neurons that show significant hsp72 staining are eventually lost after global ischemia in the rat. However, brief insults that result in expression of hsp72 and other proteins encoded by induced mRNAs do result in tolerance to subsequent insults. Future studies may be expected to reveal the contributions of specific gene products to the tolerant state. Meanwhile, complementary evaluations of hsp72 mRNA and protein expression provide practical means of identifying cell populations responding to diverse injuries.

Enhanced phosphorylation of a 65 kDa protein is associated with rapid induction of stress proteins in 9L rat brain tumor cells

Induction of heat-shock proteins and glucose-regulated proteins in 9L rat brain tumor cells can be differentially elicited by sodium arsenite, cadmium chloride, zinc chloride, copper sulfate, sodium fluoride, and L-azetidine-2-carboxylic acid. The kinds of stress protein induced by the above chemicals varied considerably, mainly determined by the nature and the concentration of the chemicals, as well as the treatment protocols. In addition, at the concentrations where stress proteins can be induced, the above chemicals were able to suppress general protein synthesis and were cytotoxic. Enhanced phosphorylation of a protein with an apparent molecular weight of 65 kDa was detected during the induction of stress proteins except in azetidine treatments during which uptake of phosphate by the cells was impaired after prolonged incubation. The phosphate moiety on the 65 kDa phosphoprotein appeared to be alkaline-stable and two-dimensional gel electrophoresis revealed that the phosphoprotein resolved into four isoforms with isoelectric points ranging from 5.1 to 5.6. Enhanced phosphorylation of the same protein was also detected in heat-shocked and withangulatin A-treated 9L cells in which stress proteins were induced. It is suggested that this phosphoprotein may be a common target for heat stress response-stimulated phosphorylation and important in the further metabolic responses of the cell to stress.

Changes in heat shock protein 70 and ubiquitin mRNA levels in C1300 N2A mouse neuroblastoma cells following treatment with iron

We have shown that following heat shock (42.5 degree C for 30 min), mouse-derived C1300 N2A neuroblastoma cells contain increased levels of mRNA coding for the inducible form of heat shock protein 70 and for ubiquitin. Incubation of C1300 cells with iron also induces an elevation in content of mRNAs coding for the same two proteins that can be blocked by alpha-tocopherol and desferrioxamine. Iron was shown to increase mitochondrial and lysosomal activities in differentiated C1300 N2A cultures, as shown by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and neutral red cytotoxicity assays. These responses were not initially associated with any loss of viability, as assessed by the lactate dehydrogenase release assay. These results suggest that there is production of cytoprotective heat shock proteins in response to iron-mediated cell damage, probably involving free radical generation, in neural cells. The apparent stress response of vulnerable neurones in human neurodegenerative diseases, particularly Parkinson's disease, may be induced by iron-mediated free radical production in degenerating neurones, making investigation of the mechanism of free radical-induced responses in neuronal cells of special interest.

Arsenite induced sensitization and self-tolerance of Reuber H35 hepatoma cells

Our data show that a short incubation with arsenite (30-300 microM) induces a biphasic change in cellular sensitivity towards a second exposure to arsenite. A transient sensitization was followed by the development of self-tolerance. Sensitization was measured using the step-down protocol; i.e., application of a high dose of arsenite pretreatment (100 or 300 microM) followed immediately by incubation in a low dose of arsenite (1-30 microM), with extensive rinsing in between. Whereas no effect of 1 and 3 microM on cellular survival is observed without pretreatment, a large decrease in cell survival can be established when these low doses of arsenite are applied immediately after a 1 hr pretreatment with 100 or 300 microM arsenite. According to the step-down protocol, a high dose of toxic compounds is applied and is followed by prolonged incubation in a lower concentration of the initial toxic compound. This might be a more accurate model for studying the effects of toxic insults on cells and organisms in the manner in which they occur in their natural environment. The level of tolerance was determined by a 1 hr test treatment with 300 microM arsenite applied at different times after pretreatment. Using this fractionated treatment protocol, it was established that tolerance increases with the increasing time intervals between the sodium arsenite treatments, during the 6 hr studied. These observations suggest that sensitization gradually decreases, whereas tolerance develops. Furthermore, our data indicate that the condition of pretreatment determines the extent to which the early sensitivity increases, as well as the development of tolerance later on. A relatively high arsenite concentration leads to more sensitized cells, which are transformed into more tolerant cells in comparison with the effect of a lower arsenite concentration.

Possible role of localized protein denaturation in the mechanism of induction of thermotolerance by heat, sodium-arsenite and ethanol

Heat, sodium-arsenite, and ethanol-induced thermotolerance are compared, especially with regard to the induced resistance of proteins of the particulate fraction (PF) against heat-induced denaturation. While all three agents induce thermotolerance as expressed as an enhanced survival after hyperthermic treatment, it is found that while heat and sodium-arsenite also induce resistance in the PF, this is not the case for ethanol. To explain these differences a hypothesis is postulated in which resistance is induced in those subcellular fractions/structures that are damaged by the agent used for the induction of thermotolerance. Furthermore, the effect of inhibition of protein synthesis by cycloheximide during the development of thermotolerance is investigated. It is found that while heat- and ethanol-induced thermotolerance (survival) are partly protein synthesis-independent, sodium-arsenite-induced thermotolerance (survival) is completely protein synthesis-dependent. Protein-synthesis-independent thermotolerance induced heat resistance in the proteins of the PF to the same extent as protein-synthesis-independent thermotolerance. To explain the differences in the ability of the agents to induce protein-synthesis-independent thermotolerance a hypothesis is postulated in which this ability depends on the mechanism by which this agent inhibits protein synthesis during the thermotolerance-inducing treatment. In this hypothesis the involvement of hsp in protein synthesis-independent thermotolerance is assumed.