Accumulation Of Heat Shock Proteins Research Articles

Activation of the mitogen-activated protein kinase pathways by heat shock.

In addition to inducing new transcriptional activities that lead within a few hours to the accumulation of heat shock proteins (Hsps), heat shock activates within minutes the major signaling transduction pathways involving mitogen-activated protein kinases, extracellular signal-regulated kinase, stress-activated protein kinase 1 (SAPK1)-c-Jun N-terminal kinase, and SAPK2-p38. These kinases are involved in both survival and death pathways in response to other stresses and may, therefore, contribute significantly to the heat shock response. In the case of p38, the activation leads to the phosphorylation and activation of one of the Hsps, Hsp27. Phosphorylation occurs very early during stress, is tightly regulated, and results from the triggering of a highly specific heat shock-sensing pathway.

Pallido-nigral spheroids in nonhuman primates: accumulation of heat shock proteins in astroglial processes.

Alpha-B crystallin, ubiquitin and heat shock protein 27 (hsp27) belong to a class of proteins that are overexpressed in response to pathological conditions associated with increased cellular stress. In the present study, brain sections of old rhesus monkeys ( Macaca mulatta; n=10; mean age, 29.4 years) and baboons ( Papio anubis; n=8; mean age, 18.3 years) were examined for ubiquitin, alpha-B crystallin and hsp27-immunopositive structures. In both species, immunoreactive spheroid-like bodies were found in the globus pallidus and in the substantia nigra, pars reticulata. These structures frequently were associated with abnormally swollen cellular processes. To further clarify the origin of the pallido-nigral spheroids, single- and double-immunostaining was performed for hsp27, alpha-B crystallin and the astroglial marker glial fibrillary acidic protein (GFAP) as well as for neuronal markers against neurofilament and dendritic microtubule-associated protein 2. Confocal microscopic analysis demonstrated that spheroids were localized in swollen astroglial processes, whereas they were not seen in neuronal structures. Thus, pallido-nigral spheroids can be classified as astroglial accumulations of heat shock proteins. Further investigations of these structures may provide information pertinent to our understanding of astroglial heat shock protein inclusions developing in degenerative human brain diseases.

Cell death and survival alterations in Malpighian tubules of Triatoma infestans following heat shock.

In this study, we examined cell survival and cell death in response to heat shock in an insect organ composed of highly polyploid cells no longer capable of cell division. For this, the frequency of nuclear phenotypes in Feulgen-stained Malpighian tubules of the blood-sucking insect, Triatoma infestans, was analyzed at various times after a short heat shock with or without subsequent moderate fasting. Cell death DNA fragmentation was studied immunocytochemically. Normal phenotypes and phenotypes indicative of cell survival (heterochromatin decondensation, nuclear fusion) and death (apoptosis, necrosis) were observed, especially in heat-shocked specimens. While the number of total and normal nuclei decreased following heat shock, the frequency of apoptosis increased during a short period (7 days) after heat shock. During a 30-day period following heat shock, the frequency of necrosis in fasted but not in fully nourished nymphs increased simultaneously with a decrease in the frequency of apoptosis. This finding suggests that the stress promoted by heat shock, but not that associated with heat shock plus fasting, can be dealt with by the apoptosis program. When considering the forms of cell survival, heterochromatin decondensation was more relevant in fully nourished nymphs, whereas nuclear and cell fusions were more important in fasted specimens. The forms of cell survival and cell death reported here may have protected the organ from damage by the stressing agents. In cells with no induction or accumulation of heat-shock proteins, cell death and the forms of cell survival observed here were the probable consequence.

Reduction of chilling injury and transcript accumulation of heat shock proteins in tomato fruit by methyl jasmonate and methyl salicylate

Changes in heat shock protein (HSP) gene expression induced by vapor application of methyl jasmonate (MeJA) and methyl salicylate (MeSA) in tomato fruit were investigated and compared to the well-described heat shock response. Northern hybridization experiments involving six cDNAs, encoding class I and II tomato small HSPs (sHSPs) and three members of HSP 70 family, showed that accumulation of class I and II sHSP mRNAs was increased significantly by MeJA and MeSA. When the treated fruits were transferred to low temperature, class I and II mRNA levels initially decreased, but then subsequently increased. Accumulation of HSP transcripts was also observed in non-treated fruit between 7 and 14 days at low-temperature storage, but all decreased to undetectable levels after 21 days. Following MeJA and MeSA treatments, the transcripts of HSP 70 family accumulated to higher levels than following the heat treatment. MeJA- and MeSA-treatments were clearly shown to alleviate chilling injury (CI), whereas tomato fruit stored at 5 °C without pretreatment developed typical symptoms and severe decay. These results demonstrated that MeJA and MeSA induced the accumulation of sHSP transcripts in tomato. The increased transcript abundance of HSPs, especially class II sHSPs, was correlated with protection against CI.

Hyperthermia induces gene expression of heat shock protein 70 and phosphorylation of mitogen activated protein kinases in the rat cerebellum

In-vivo heat-shock induced heat shock factor (HSF) DNA-binding activity and accumulation of heat shock protein (hsp)70 mRNA in newborn and adult rat cerebellum was studied. We identified a high basal level of c-Jun N-terminal kinase (JNK) and p38 MAP kinase phosphorylation in the cerebellum, independently of age. Hyperthermia increased JNK1, decreased JNK2 but did not modify JNK3 phosphorylation in the newborn cerebellum, whereas decreased the phosphorylation of both JNK1 and JNK3 in adult rats. During recovery from hyperthermia, JNK2 phosphorylation returned to control level in the newborn, JNK1 appeared hyperphosphorylated only in the newborn, and JNK3 in all animals. JNK2 never appeared phosphorylated in the adult cerebellum. Hyperthermia increased p38 MAP kinase phosphorylation in the cerebellum, with different trends in newborn and adult rats during recovery. Heat shock increased extracellular signal-regulated kinase phosphorylation concomitant to tyrosine kinase receptor activation (epidermal growth factor-receptor in the newborn and insulin-like growth factor-receptor in the adult cerebellum). The behavior of stress kinases may underlie a different age-related vulnerability to heat stress of the cerebellum.

Protection of phenylpropanoid metabolism by prior heat treatment in Lycopersicon esculentum exposed to Ralstonia solanacearum

Heat shock inhibits pathogen-induced resistance mechanisms in incompatible plant hosts, leaving them vulnerable to pathogen attack. Prior exposure of organisms to non-lethal heat induces heat shock proteins and acquired thermotolerance to otherwise lethal high temperatures. The phenylpropanoid pathway is a target of heat-related inhibition but it is unknown whether thermotolerance protects this pathway or its key regulator, phenylalanine ammonia-lyase (EC 4.3.1.5, PAL). It was hypothesised that prior exposure to a heat shock pulse to induce the accumulation of heat shock proteins, specifically the 70-kDa heat shock protein (Hsp70 – inducible/Hsc70 – constitutive), would protect phenylpropanoid metabolism from heat-induced inhibition. The tomato, Lycopersicon esculentum L. cv. UC82B, transformed with PAL2-GUS, and Ralstonia solanacearum, biovar II, were used as incompatible host-pathogen model. A prior heat shock pulse induced significant accumulation of Hsp70/Hsc70 and enhanced cell viability. This protected the pathogen-activated phenylpropanoid pathway (PAL2-GUS activity, PAL enzyme activity, lignin deposition) from heat-induced inhibition and promoted cell survival after a subsequent prolonged heat shock. This study suggests phenylpropanoid metabolism as a target of Hsp70/Hsc70-related protection of the resistance response activated in tomato against avirulent strains of Ralstonia solanacearum from heat-induced inhibition during a concomitant heat shock.

Heat-shock responses in two leguminous plants: a comparative study

Relative growth rates, basal and acclimated thermotolerance, membrane damage, fluorescence emission, and relative levels of free and conjugated ubiquitin and HSP70 were compared after 2 h of treatment at different temperatures between Prosopis chilensis and Glycine max (soybean), cv. McCall, to evaluate if the thermotolerance of these two plants was related to levels of accumulation of heat shock proteins. Seedlings of P. chilensis germinated at 25 degrees C and at 35 degrees C and grown at temperatures above germination temperature showed higher relative growth than soybean seedlings treated under the same conditions. The lethal temperature of both species was 50 degrees C after germination at 25 degrees C. However, they were able to grow at 50 degrees C after germination at 35 degrees C. Membrane damage determinations in leaves showed that P. chilensis has an LT(50) 6 degrees C higher than that of soybean. There were no differences in the quantum yield of photosynthesis (F(v)/F(m)), between both plants when the temperatures were raised. P. chilensis showed higher relative levels of free ubiquitin, conjugated ubiquitin and HSP70 than soybean seedlings when the temperatures were raised. Time-course studies of accumulation of these proteins performed at 40 degrees C showed that the relative accumulation rates of ubiquitin, conjugated ubiquitin and HSP70 were higher in P. chilensis than in soybean. In both plants, free ubiquitin decreased during the first 5 min and increased after 30 min of heat shock, conjugated ubiquitin increased after 30 min and HSP70 began to increase dramatically after 20 min of heat shock. From these data it is concluded that P. chilensis is more tolerant to acute heat stress than soybean.

Heat shock protein accumulation is upregulated in a long-lived mutant of Caenorhabditis elegans.

We present evidence for elevated levels of heat shock protein 16 (HSP16) in an intrinsically thermotolerant, long-lived strain of Caenorhabditis elegans during and after heat stress. Mutation of the age-1 gene, encoding a phosphatidylinositol 3-kinase catalytic subunit, results in both extended life span (Age) and increased intrinsic thermotolerance (Itt) in adult hermaphrodites. We subjected age-synchronous cohorts of worms to lethal and nonlethal thermal stress and observed the accumulation of a small (16-18 kd) heat-shock-specific polypeptide detected by an antibody raised against C. elegans HSP16. Strains carrying the mutation hx546 consistently accumulated HSP16 to higher levels than a wild-type strain. Significantly, overaccumulation of HSP16 in the age-1(hx546) strain following heat was observed throughout the adult life span. A chimeric transgene containing the Escherichia coli beta-galactosidase gene fused to a C. elegans HSP16-41 transcriptional promoter was introduced into wild-type and age-1(hx546) backgrounds. Heat-inducible expression of the transgene was elevated in the age-1(hx546) strain compared with the wild-type strain under a wide variety of heat shock and recovery conditions. These observations are consistent with a model in which Age mutations exhibit thermotolerance and extended life span as a result of elevated levels of molecular chaperones.

Effect of heat stress on LPS-induced febrile response in D-galactosamine-sensitized rats.

We have previously reported that heat conditioning augments lipopolysaccharide (LPS)-induced fever in rats, which is accompanied by an accumulation of heat shock protein (HSP) in the liver and the reduction of the plasma level of tumor necrosis factor (TNF-alpha) (Kluger MJ, Rudolph K, Soszynski D, Conn CA, Leon LR, Kozak W, Wallen ES, and Moseley PL. Am J Physiol Regulatory Integrative Comp Physiol 273: R858-R863, 1997). In the present study we have tested whether inhibition of protein synthesis in the liver can reduce the effect of this heat conditioning on the LPS-induced febrile response in the rat. D-galactosamine (D-gal) was used to selectively inhibit liver protein synthesis. D-gal (500 mg/kg) or PBS as control was administered intraperitoneally 1 h before heat stress. LPS (50 microg/kg ip) was injected 24 h post-heat exposure. Treatment with D-gal blunted the febrile response to LPS. Moreover, heat-conditioned rats treated first with D-gal and subsequently with LPS demonstrated a profound fall in core temperature 10--18 h post-LPS. A significant increase of serum TNF-alpha accompanied this effect of D-gal on fever. Heat-conditioned animals receiving D-gal showed an inhibition in inducible HSP-70 in the liver. These data support the role of hepatic function in modulating the febrile response to LPS.

Cytoprotective Mechanism of Heat Shock Protein 70 against Hypoxia/Reoxygenation Injury

The role of heat shock protein 70 (HSP70) in the cytoprotection against hypoxia/reoxygenation injury was examined. Adult rat cardiomyocytes were isolated, subjected to hyperthermia at 42°C for 15 min (heat shock treatment), and then incubated at 37°C for 3 to 24 h (HSP production process). Heat shock treatment increased HSP70 production (80–260% increase); the peak increase was seen after 9 h of HSP production process. Thereafter, the cells were subjected to 120-min hypoxia and 15-min reoxygenation. Heat shock treatment increased the survival of the cells subjected to hypoxia/reoxygenation (1.5–2.5-fold); the maximal cytoprotection was observed after 12 h of HSP production process. Heat shock treatment increased HSP70 content in the nucleus when cells were subjected to 12 h of HSP production process. To examine the role of HSP70 accumulation in the nuclear fraction, the activity of poly(ADP-ribose) synthetase (PARS), which functions in the nucleus and consumes high-energy phosphates excessively in the reoxygenated state, were measured in the cells with heat shock and 12 h of HSP production process. Heat shock treatment attenuated the hypoxia/reoxygenation-induced increase in the PARS activity (50% decrease). Treatment of the cells with 3-aminobenzamide, an inhibitor of PARS, exerted the effects similar to those of heat shock treatment. These results suggest that attenuation of the PARS activity in the nucleus may play an important role in the cytoprotective effect of HSP70 on hypoxia/reoxygenation injury.

Phenylarsine oxide inhibits heat shock protein 70 induction in cultured guinea pig gastric mucosal cells.

Phenylarsine oxide (PAO) forms a stable ring complex with vicinal dithiols that can be reversed with 2,3-dimercaptopropanol (DMP) but not by dithiothreitol (DTT) or 2-mercaptoethanol (2-ME). PAO at 2 microM or higher inhibited heat shock protein 70 (HSP70) induction within minutes in cultured guinea pig gastric mucosal cells exposed to heat (43 degrees C) for 30 min. PAO did not affect the nuclear translocation and phosphorylation of heat shock factor 1 (HSF1) induced by heat stress, but it completely blocked the binding activity of HSF1 to the heat shock element (HSE), leading to the block of expression of HSP70 mRNA and accumulation of HSP70 in the cells. These inhibitions were completely reversed with 2 microM DMP but not with 0.1 mM DTT or 1 mM 2-ME, suggesting specific interactions between PAO and vicinal dithiol-containing molecules. Thioredoxin (Trx) reversed the inhibition of the binding activity of HSF1 in whole cell extracts prepared from PAO-treated, heat-stressed cells. Our results suggest that PAO may react with vicinal-containing molecules including Trx and specifically block the interaction between HSF1 and HSE.

Enhancement of heat-induced heat shock protein (hsp)72 accumulation by doxorubicin (Dox) in vitro

Previous studies have shown that cellular thermotolerance develops in response to exposure to doxorubicin (Dox) and treatment with hyperthermia. In the present study, we evaluated the induction of thermotolerance and the accumulation of heat shock protein (hsp)72 after treatment with Dox and/or hyperthermia at 44°C in Chinese hamster V-79 cells. Thermotolerance developed after exposure to Dox at 37°C for 2 h in a dose-dependent manner. Western blot analysis showed no accumulation of hsp72 after exposure to Dox (0.2 μg/ml) for 2 h (lethal dose (LD) 15). Hsp72 accumulated 12 h after hyperthermia at 44°C for 35 min (LD 15). However, when the cells were exposed to Dox (0.1 μg/ml) followed by heating at 44°C for 25 min (LD 15), accumulation of hsp72 was observed after 6 h. These results suggest that enhancement of induction of hsp72 accumulation by Dox may be involved in the development of thermotolerance induced by sequential treatment with Dox and hyperthermia.

A ditelosomic line of ‘Chinese Spring’ wheat with augmented acquired thermotolerance

A study of the ditelosomic series of ‘Chinese Spring’ wheat has yielded a number of lines displaying either an increased or decreased ability to acquire thermotolerance. One such ditelosomic (DT) is termed DT1BS which refers to the missing short arm of chromosome 1 in the B genome. The DT1BS line has the ability to acquire thermotolerance at lower induction temperatures and provide greater protection to the plant against otherwise lethal elevated temperatures. Using a chlorophyll accumulation assay to measure plant health, we show that DT1BS accumulates chlorophyll optimally at the same temperature, and to similar levels as ‘Chinese Spring’. We also show that maximum acquired thermotolerance against a 48°C challenge is induced at 40°C, but significant levels of protection can be obtained at temperatures as low as 34°C in DT1BS or 36°C in ‘Chinese Spring’. Heat-shock protein accumulation is observed in DT1BS at temperatures 4°C lower than the ‘Chinese Spring’ and is correlated with the induction of acquired thermotolerance.

Phosphorylation at tyrosine-524 influences nuclear accumulation of HSP72 with heat stress.

Nuclear accumulation of heat shock protein (HSP) 72 occurs after cardiac ischemia. This nuclear accumulation of HSP72 with stress occurs in other tissues and species. We postulated that nuclear accumulation of HSP72 was important for the protective effect of HSP72 and that phosphorylation of a single tyrosine (Y(524)) regulated nuclear accumulation of HSP72. Western blots of immunoprecipitated HSP72 from Cos-1 cells demonstrated that tyrosine becomes phosphorylated after heat shock. Treatment with the tyrosine kinase inhibitor geldanamycin blocked nuclear accumulation of HSP72 with heat shock. Two epitope-tagged constructs were made: M17 converting Y(524) to aspartic acid (pseudophosphorylation) and M18 converting Y(524) to phenylalanine. When transfected into Cos-1 cells, M17 accumulates more rapidly and M18 less rapidly than wild-type (WT) HSP72 in the nucleus following heat shock. Cells expressing M18 had less viability after heat shock at 43.5 degrees C than other constructs. After heat shock at 45 degrees C, cells expressing M17 had superior survival compared with WT and M18. These data suggest that phosphorylation at Y(524) facilitates nuclear accumulation of HSP72 following heat stress, and substitution of aspartic acid at Y(524) enhances resistance to heat-shock injury.

Stress-protein response in tributyltin-exposed clams.

The heat-shock proteins (HSPs) or stress proteins are a family of diverse proteins containing both constitutive and stress-induced members (Hightower, 1991). Under normal conditions, these proteins are involved in the transport, folding and assembly of newly synthesised proteins; under adverse environmental situations, their synthesis increases and they act to repair and protect cellular proteins and to minimise protein aggregation (Cheng et al. 1989; Chiang et al. 1989; Martin et al. 1992; Kim et al. 1993). The most abundant and best studied groups are the 70 kDa (HSP70) stress protein family and the 60 kDa (HSP60) family. Both of them are known to be induced in response to a wide variety of physical and chemical stressors, including UV light, salinity, temperature, anoxia, but also oxidizing agents, heavy metals, and organic xenobiotics (Sanders, 1990). Thus, over the past decade, an increasing number of studies have explored the possibility of using HSPs as biomarkers of adverse effects at the cellular level and some authors have proposed that the induction and subsequent accumulation of HSPs may be useful in environmental monitoring (Sanders, 1990; Sanders and Martin, 1993). The use of HSPs as biomarkers has been assessed in laboratory and field experiments, and their induction by metals and other environmental contaminants or physical parameters has been demonstrated in molluscs (Hightower, 1993; Roberts et al. 1997).

Enhanced expression of heat-shock proteins in thermo-tolerant lines of sunflower and their progenies selected on the basis of temperature-induction response

The major lacuna in developing stress-tolerant lines through breeding is the lack of suitable techniques for screening the segregating population. We report here the development of an efficient technique for identifying high-temperature-tolerant lines in sunflower. The rationale behind this technique is that the stress-responsive genes are expressed during sub-lethal (induction) stress, and its products impart tolerance at subsequent lethal stresses. The genetic variability in gene expression upon induction stress is responsible for the differential survival and recovery following exposure to severe lethal stress in a heterogeneous population. Optimization of induction and subsequent lethal temperature levels is a pre-requisite for developing a standardized screening protocol. The optimum induction temperature in sunflower was identified by subjecting the germinated seedlings to various sub-lethal temperatures followed by exposure to a specific lethal temperature for a fixed duration. Gradual temperature induction was found to be optimum in bringing about a maximum response in terms of the recovery growth of seedlings after exposure to a lethal temperature. Following the optimum induction treatment, seedlings were subjected to a specific high temperature for different periods to arrive at a high-stringency lethal temperature treatment. By adopting this approach an open-pollinated population of Helianthus annuus L. (morden) was screened for high-temperature tolerance. The seedlings which survived at the high-stringency lethal temperature following the optimum induction treatment were identified as thermo-tolerant lines. At the plant level too these identified lines showed higher tolerance as reflected by a higher membrane integrity and recovery leaf-area. The progeny population of these identified lines also exhibited higher tolerance to temperature compared to the original population, indicating the persistence of the selected trait. This tolerance was associated with a higher accumulation of heat-shock proteins (HSPs). We propose that this technique can be used as a potential tool to identify and select temperature-tolerant lines from a heterogeneous/segregating population.

Heat-shock protein 72/73 and impaired wound healing in diabetic and hypercortisolemic states

Background: Impaired wound healing is a well-documented phenomenon in experimental and clinical diabetes. Emerging evidence favors the involvement of glucocorticoids (GCs) in the pathogenesis of this diabetic complication. Recent data indicated that a heat-shock protein (HSP) with a molecular weight of about 70 kd is expressed in wound healing and it is under the control of the hypothalamic-pituitary-adrenal axis. In view of these findings, the current study was designed to examine the influence of diabetes and the hypercortisolemic state on the expression of HSP 72/73 during wound healing. Methods: Induction of diabetes was achieved by the intravenous injection of streptozotocin at a dose of 55 mg/kg. Subcutaneously implanted polyvinyl alcohol (PVA) sponges were used as a wound healing model. Control and diabetic animals received, respectively, subcutaneous 30-day timed-release pellets of GC (200 mg) and RU 486 (25 mg). Corresponding animals received placebo pellets. Expression of HSP 72/73 within the PVA sponges was assayed with use of Western blotting and immunohistochemical techniques. Results: GCs caused a Cushing-like syndrome with weight loss and adrenal atrophy. A pronounced accumulation of constitutive HSP 72/73 was observed in the cytoplasm of various cell types including fibroblasts, macrophages, and endothelium of nondiabetic controls. The PVA sponge contents of HSP 72/73 were decreased as a function of diabetes. A similar phenomenon was seen in control animals receiving high doses of GCs. Partial normalization of the associated hyperglycemic and hypercortisolemic states of diabetes with insulin (hyperglycemia) and the GC receptor block RU 486 (hypercortisolemia) ameliorated the diabetes-related decrease in PVA sponge contents of HSP 72/73. Conclusions: The current study provides evidence that both diabetes and the hypercortisolemic state are associated with a reduction in PVA sponge content of HSP 72/73. An amelioration of these changes was achieved by the institution of RU 486 therapy. Although our data may point to the possibility that the diabetes-related decrease in HSP 72/73 is mediated at least in part by GCs, a confirmation regarding this premise awaits further investigation. (Surgery 1999;125:594-601.)

Treatment with 24-epibrassinolide, a brassinosteroid, increases the basic thermotolerance of Brassica napus and tomato seedlings.

Brassinosteroids are plant growth-promoting compounds that exhibit structural similarities to animal steroid hormones. Recent studies have indicated that brassinosteroids are essential for proper plant development. In addition to a role in development, several lines of evidence suggest that brassinosteroids exert anti-stress effects on plants. However, the mechanism by which they modulate plant stress responses is not understood. We show here that Brassica napus and tomato seedlings grown in the presence of 24-epibrassinolide (EBR) are significantly more tolerant to a lethal heat treatment than are control seedlings grown in the absence of the compound. Since a preconditioning treatment of seedlings was not required to observe this effect, we conclude that EBR treatment increases the basic thermotolerance of seedlings. An analysis of heat shock proteins (HSPs) in B. napus seedlings by western blot analysis indicated that the HSPs did not preferentially accumulate in EBR-treated seedlings at the control temperature. However, after heat stress, HSP accumulation was higher in EBR-treated than in untreated seedlings. The results of the present study provide the first direct evidence for EBR-induced expression of HSPs. The higher accumulation of HSPs in EBR-treated seedlings raises the possibility that HSPs contribute, at least in part, to thermotolerance in EBR-treated seedlings. A search for factors other than HSPs, which may directly or indirectly contribute to brassinosteroid-mediated increase in thermotolerance, is underway.

Heat shock proteins and the inflammatory response.

The heat shock proteins (HSPs) are important in the cellular response to stress and in cellular homeostatic functions such as protein synthesis and protein transport across membranes. An emerging body of data supports a role for HSPs in the inflammatory response, suggesting that HSPs participate in cytokine signal transduction and in the control of cytokine gene expression, that HSPs enhance antigen presentation to T lymphocytes, and that HSPs displayed on the surface of cells are important in targeting cytotoxic cells. Because changes in HSP accumulation occur in the whole organism under physiologic conditions, understanding the role of HSPs in the immune/inflammatory response may aid in understanding the organism's response to danger.

Volume of ground motion and seismic hazard

Heat shock proteins (HSPs) are molecular chaperones that aid in protein folding, translocation and in preventing stress-induced protein aggregation. The present study examined the effect of simultaneous sodium arsenite and cadmium chloride treatment on the pattern of HSP30 and HSP70 accumulation in A6 kidney epithelial cells of the frog, Xenopus laevis. Immunoblot analysis revealed that HSP30 and HSP70 accumulation in concurrent stressor treatments were significantly higher than the sum of HSP30 or HSP70 accumulation in individual treatments. This finding suggested a synergistic action between sodium arsenite and cadmium chloride. KNK437 inhibitor studies indicated that the combined stressor-induced accumulation of HSPs may be regulated, at least in part, at the level of transcription. Immunocytochemistry revealed that simultaneous treatment of cells with the two stressors induced HSP30 accumulation primarily in the cytoplasm in a punctate pattern with some dysregulation of F-actin structure. Increased ubiquitinated protein accumulation was observed with combined sodium arsenite and cadmium chloride treatment compared to individual stressors suggesting an impairment of the ubiquitin proteasome degradation system. The addition of a mild heat shock further enhanced the accumulation of HSP30 and HSP70 in response to relatively low concentrations of sodium arsenite plus cadmium chloride.