Induction of heat shock 70 mRNA by cadmium is mediated by glutathione suppressive and non-suppressive triggers

The stability and function of human cochaperone Hsp40/DNAJA1 are affected by zinc removal and partially restored by copper

The imbalance in metal homeostasis can be associated with several human diseases, and exposure to increasing concentrations of metals promotes cell stress and toxicity. Therefore, understanding the cytotoxic effect of metal imbalance is important to unravel the biochemical mechanism of homeostasis and the action of potential protective proteins against metal toxicity. Several studies, including gene deletion in yeast, provide evidence indicating the possible indirect involvement of cochaperones from the Hsp40/DNAJA family in metal homeostasis, possibly through modulating the activity of Hsp 70.This work first investigated the effect of zinc and copper on the conformation and function of the human Hsp40 cochaperone DNAJA1, a zinc-binding protein. DNAJA1 was capable to complement the phenotype of a yeast strain deleted of the ydj1 gene, which was more sensitive to the presence of zinc and copper than the wild-type strain. To gain further insight about the role of the DNAJA family in metal binding, the recombinant human DNAJA1 protein was studied. Zinc removal from DNAJA1 affected both its stability and ability to act as a chaperone, i.e., to protect other proteins from aggregation. The reintroduction of zinc restored the native properties of DNAJA1 and, surprisingly, the addition of copper partially restored the native properties.

Bio-indicators in cadmium toxicity: Role of HSP27 and HSP70

Heat shock proteins (HSPs) are a family of proteins that are expressed by cells in reply to stressors. The changes in concentration of HSPs could be utilized as a bio-indicator of oxidative stress caused by heavy metal. Exposure to the different heavy metals may induce or reduce the expression of different HSPs. The exposure to cadmium ion (Cd²⁺) could increase HSP70 and HSP27 over 2- to 10-fold or even more. The in vitro and in vivo models indicate that the HSP70 family is more sensitive to Cd intoxication than other HSPs. The analyses of other HSPs along with HSP70, especially HSP27, could also be useful to obtain more accurate results. In this regard, this review focuses on examining the literature to bold the futuristic uses of HSPs as bio-indicators in the initial assessment of Cd exposure risks in defined environments.

Characterization of cadmium chloride-induced BiP accumulation in Xenopus laevis A6 kidney epithelial cells

Endoplasmic reticulum (ER) stress can result in the accumulation of unfolded/misfolded protein in the ER lumen, which can trigger the unfolded protein response (UPR) resulting in the activation of various genes including immunoglobulin-binding protein (BiP; also known as glucose-regulated protein 78 or HSPA5). BiP, an ER heat shock protein 70 (HSP70) family member, binds to unfolded protein, inhibits their aggregation and re-folds them in an ATP-dependent manner. While cadmium, an environmental contaminant, was shown to induce the accumulation of HSP70 in vertebrate cells, less information is available regarding the effect of this metal on BiP accumulation or function. In this study, cadmium chloride treatment of Xenopus laevis A6 kidney epithelial cells induced a dose- and time-dependent increase in BiP, HSP70 and heme oxygenase-1 (HO-1) accumulation. Exposure of cells to a relatively low cadmium concentration at a mild heat shock temperature of 30°C greatly enhanced BiP and HSP70 accumulation compared to cadmium at 22°C. Treatment of cells with the glutathione synthesis inhibitor, buthionine sulfoximine, enhanced cadmium-induced BiP and HSP70 accumulation. Immunocytochemistry revealed that cadmium-induced BiP accumulation occurred in a punctate pattern in the perinuclear region. In some cells treated with cadmium chloride or the proteasomal inhibitor, MG132, large BiP complexes were observed that co-localized with aggregated protein or aggresome-like structures. These BiP/aggresome-like structures were also observed in cells treated simultaneously with cadmium at 30°C or in the presence of buthionine sulfoximine. In amphibians, the association of BiP with unfolded protein and its possible role in aggresome function may be vital in the maintenance of cellular proteostasis.

Synergistic effects of toxic elements on heat shock proteins

Heat shock proteins show remarkable variations in their expression levels under a variety of toxic conditions. A research span expanded over five decades has revealed their molecular characterization, gene regulation, expression patterns, vast similarity in diverse groups, and broad range of functional capabilities. Their functions include protection and tolerance against cytotoxic conditions through their molecular chaperoning activity, maintaining cytoskeleton stability, and assisting in cell signaling. However, their role as biomarkers for monitoring the environmental risk assessment is controversial due to a number of conflicting, validating, and nonvalidating reports. The current knowledge regarding the interpretation of HSPs expression levels has been discussed in the present review. The candidature of heat shock proteins as biomarkers of toxicity is thus far unreliable due to synergistic effects of toxicants and other environmental factors. The adoption of heat shock proteins as "suit of biomarkers in a set of organisms" requires further investigation.

Changes of heavy metal, metallothionein and heat shock proteins in Sertoli cells induced by cadmium exposure

In this study, we examined the levels of Cadmium (Cd), iron (Fe) and zinc (Zn), which were considered to be involved in Sertoli cell damage caused by Cd exposure. We also examined metallothionein (MT), heat shock protein 70 (Hsp70) and heme oxygenase-1 (HO-1) expressions in Sertoli cells induced by Cd exposure. Evaluation by the in-air micro-particle induced X-ray emission (PIXE) method revealed that Cd and Fe distribution was increased in the cytoplasm of Sertoli cells after Cd exposure. By contrast, Zn was decreased in the cytoplasm of Sertoli cells after Cd exposure. It was suggested that the target of Cd toxicity was the cytoplasm of Sertoli cells, Fe was considered to enhance damage to Sertoli cells caused by Cd exposure. The DNA fragmentation rate was determined by ELISA after Cd exposure to Sertoli cells. It remained essentially unchanged with 2.5 microM Cd exposure of Sertoli cells; however, MT, Hsp70 and HO-1 were significantly increased by Cd exposure. As a result, Cd-induced MT was protected Sertoli cells against apoptosis, and Cd-induced HO-1 was involved in protection against oxidative stress. Incidentally, MT, Hsp70 and HO-1 showed similar responses to Cd exposure.

The changes of heavy metal and metallothionein distribution in testis induced by cadmium exposure

Cadmium (Cd) is known to cause various disorders in the testis, and metallothionein (MT) is known as a protein, which has a detoxification function for heavy metals. However, the changes of Fe, Cu, and Zn distribution in the testis induced by Cd exposure have not been well examined. Moreover, only a few studies have been reported on the localization of MT after Cd exposure. In this study, we have investigated the changes of Fe, Cu, and Zn distribution in Cd-exposed testis by a newly developed in air micro-Particle Induced X-ray Emission (PIXE) method. Also, we examined the distribution of MT expression in testis. In the testis of Cd-treated rats with significant increases of lipid peroxidation, the sertoli cell tight junction was damaged by Cd exposure, resulting from disintegration of the blood testis barrier (BTB). Evaluation by in air micro-PIXE method revealed that Cd and Fe distribution were increased in the interstitial tissues and seminiferous tubules. The histological findings indicated that the testicular tissue damage was advanced, which may have been caused by Fe flowing into seminiferous tubules followed by disintegration of the BTB. As a result, Fe was considered to enhance the tissue damage caused by Cd exposure. MT was detected in spermatogonia, spermatocytes, and Sertoli's cells in the testis of Cd-treated rats, but was not detected in interstitial tissues. These results suggested that MT was induced by Cd in spermatogonia, spermatocytes, and Sertoli's cells, and was involved in the resistance to tissue damage induced by Cd.

Differential Induction of Proteins in Anopheles gambiae sensu stricto (Diptera: Cullicidae) Larvae in Response to Heavy Metal Selection

Investigations were conducted to establish the magnitude and pattern of differential expression of proteins due to generational selection of third instar An. gambiae s.s. larvae by cadmium, copper and lead heavy metals, three possible common urban pollutants.A susceptible strain of An. gambiae s.s. third instar larvae was separately placed under selection pressure with cadmium, copper and lead at LC(30) and controls through five generations. First, third and fifth generation selection survivors were screened for differentially expressed proteins relative to non-exposed control by two-dimensional gel electrophoresis. Distribution patterns of the spots were analysed by Chi Square or Fishers exact test and variations in expressions between and within generation by ANOVA. Most differentially expressed spots were acidic and of low molecular weight among all metals and generations. Type of heavy metals and generation were main indicators of variations in differential expressions. Variation between generations was most significant among cadmium-selected populations of which most number of spots were induced in the fifth generation. Most spots were induced in the copper-selected population in the third generation. The induced protein spots may be products from respective genes that respond to heavy metals and counter their toxicity, thus building An. gambiae s.s. tolerance to these pollutants. The differential pattern and magnitude of expressed spots has potential application as molecular markers for assessment of anopheline adaptation status to heavy metals, and provide insight into the extent of environmental pollution.

cDNA cloning and expression analysis of the catalytic subunit of glutamate cysteine ligase gene in an annelid polychaete after cadmium exposure: a potential tool for pollution biomonitoring

The enzyme glutamate cysteine ligase (GCL) is the rate-limiting enzyme in glutathione (GSH) synthesis and is formed by a catalytic (GCLC) and a modulatory subunit (GCLM). Some studies have demonstrated that environmental pollutants can regulate the expression of these subunits. Despite the importance of these genes in toxicological responses, no sequences are available for the GCL subunits in annelids. The present study reports, for the first time, the cDNA sequence for the GCLC in an annelid species, the polychaete Laeonereis acuta (Nereididae). The deduced amino acid sequence of L. acuta GCLC showed homology with other animal species, and was used to infer a phylogenetic tree with GCLC amino acid sequences from other taxonomic groups. Exposure to cadmium (100 and 1000 microg Cd/L) during 14 days augmented the level of L. acuta GCLC transcripts in a dose-dependent manner. These gene expression results can be related to the known cadmium effect on GSH depletion. Since a number of contaminants can also exert their toxicity through this mechanism, GCLC gene expression might be applied not only for cadmium biomonitoring, but also for a wide range of contaminants that directly or indirectly promote the same effect in the cellular GSH content.

Lipid peroxidation and HSP72/73 expression in rat following cadmium chloride administration: Interactions of magnesium supplementation

OBJECTIVE

to determine whether magnesium (Mg) supplementation could have a protective effect against the cadmium (Cd)-induced oxidative stress in liver, kidneys and testes of adult male rats. Stress was evaluated by measuring lipid peroxidation by thiobarbituric acid reactive substances (TBARS) and the heat shock protein (HSP) 72/73 expression. CdCl2 injections (2.5mg/day/kg body weight) for 10 days resulted in a time dependent increase of Cd accumulation in liver, kidney and testes, the highest levels being found in liver (400 microg/g dried tissue). At the same time, an increase of lipid peroxidation was observed. The effect was maximal at day 1 of Cd treatment in liver and testes, and later (day 5) in kidney. Then, Cd-induced lipid peroxidation decreased, suggesting the activation of antioxidant defense mechanisms. Injections of Mg SO4 (300-600 mg/day/kg body weight) reduced in a dose-dependent manner Cd-induced lipid peroxidation in liver and kidney as well as the accumulation of Cd in liver, kidney and testes. In testes, a protective effect of Mg was found only during the early phase of Cd-poisoning. On days 5 and 10, lipid peroxidation was even increased as compared to controls. In liver and testes only the constitutive HSP73 was detected whereas in kidney both HSP73 and the inducible HSP72 were expressed. HSP72/73 expression was not significantly increased by Cd and HSP73 was even lowered in kidney, probably due to the strong dose used. These results were not modified by Mg injections.

CONCLUSION

Mg supplementation can reduce Cd accumulation in organs and lipid peroxidation related to Cd administration.

Influence of selenium on heat shock protein 70 expression in heat stressed turkey embryos (Meleagris gallopavo)

Heat shock protein 70 (hsp70) family of proteins, which functions as molecular chaperones, has been associated with tolerance to stressors in avian species. Selenium (Se) is an essential trace mineral incorporated into the seleno-enzymes such as glutathione peroxidase (GSHpx). GSHpx reduces oxidized glutathione (GSSG) to reduced glutathione (GSH) in the GSH/GSSG antioxidant system and protects cells from oxidative damage. This study was conducted to examine if the relationship between dietary supplementation of selenium to turkey (Meleagris gallopavo) hens and the embryonic expression of hsp70 and GSHpx activity in heat stressed embryos. Livers of embryos developing in eggs from turkey hens fed diets with or without supplemental Se were analyzed for hsp70 concentration and GSHpx activity before and after recovery from a heating episode. Before heat stress, hsp70 concentrations were equivalent in each treatment, but GSHpx activity was maximized in the SE treatment group. After recovery from the heating episode, hsp70 concentrations were significantly higher (P<0.05) in the non-Se-supplemented groups, but in the Se-supplemented groups the hsp70 concentrations were not different from pre-stress concentrations. In the pre-stress Se-supplemented group, liver GSHpx activity was significantly higher than GSHpx activity in the non-Se-supplemented embryo livers, and in the livers from embryos recovering from heat stress, GSHpx activity in the non-Se-supplemented group was lower than the pre-stress activity and significantly lower than the GSHpx activity in liver from Se-supplemented embryos recovering from heat distress. Se supplementation to the dams resulted in a significant increase in their embryos and that condition would facilitate a decreased incidence of oxidative damage to cells. A more reduced redox status in embryos from Se-supplemented dams decreased the need for cellular protection attributed to stress induced hsp70 and presumably allows heat distressed embryos to resume normal growth and development than embryos from dams with inadequate selenium nutrition.

Integrating time-course microarray gene expression profiles with cytotoxicity for identification of biomarkers in primary rat hepatocytes exposed to cadmium

MOTIVATION

DNA microarrays can provide information about the expression levels of thousands of genes simultaneously at the transcriptomic level, while conventional cell viability and cytotoxicity measurement methods provide information about the biological functions at the cellular level. Integrating these data at different levels provides a promising approach for evaluating or predicting how cells respond to chemical exposure. It is important to investigate the multi-scale biological system in a systematic way to better understand the gene regulation networks and signal transduction pathways involved in the cellular responses to environmental factors.

RESULTS

Primary rat hepatocytes were exposed to cadmium acetate at 0, 1.25 and 2 microM. mRNA expression profiles at 0, 3, 6, 12 and 24 h were measured using the Affymetrix RatTox U34 GeneChip arrays. Simultaneously, cytotoxicity was assessed by lactase dehydrogenase leakage assay. Gene expression profiles at different time points were used to evaluate cytotoxicity at subsequent time points using partial least squares, and it was found that gene expression profiles at 0 h had the best prediction accuracy for the cytotoxicity observed at 12 h. Some biomarkers whose expression profiles showed strong relationship with cytotoxicity were identified and the underlying pathways were reconstructed to illustrate how hepatocytes respond to cadmium exposure. Permutation studies were also applied to assess the reliability of the predictive models.

AVAILABILITY

Matlab source code is available upon request and DNA microarray data are available at GEO (http://www.ncbi.nlm.nih.gov/geo).

Regulation of heat shock genes in isolated hepatocytes from an Antarctic fish, Trematomus bernacchii

The Antarctic fishes, isolated over evolutionary history in the sub-zero waters of the Southern Ocean, are an ideal group for studying the processes of cold adaptation. One species of Antarctic notothenioid fish, Trematomus bernacchii, has lost the ability to induce heat shock proteins (Hsps) in response to exposure to acute thermal stress or to the toxic heavy metal cadmium, an important part of the cellular defense response to such stressors. To elucidate the mechanism responsible for the lack of Hsp induction, we examined several stages of the hsp gene expression pathway, including transcription factor activity, Hsp70 mRNA production and protein synthesis patterns, in hepatocytes from T. bernacchii. Hsp70 mRNA was detected, as was heat shock factor 1 (HSF1) with DNA-binding activity. However, exposure to elevated temperature and to chemical inducers of the heat shock response failed to increase Hsp70 mRNA levels, HSF1 activity or the concentration of any size class of Hsps. These results suggest that Hsps, inducible in nearly every other species, are expressed constitutively in the cold-adapted T. bernacchii.

Endurance exercise training inhibits activity of plasma GOT and liver caspase-3 of rats exposed to stress by induction of heat shock protein 70

A single bout of exercise increases production of heat shock protein 70 (HSP70), which protects cells against various stresses. In this study, we investigated whether endurance exercise training enhances liver level of HSP70 and, if so, whether HSP70 contributes to hepatic protection against stress in vivo. Mice of an exercise-training group performed 60 min of treadmill running 5 days/wk for 4 wk. The resting level of liver HSP70 was 4.5 times higher in the trained than in sedentary mice. After 4 wk of exercise training, both groups of mice were exposed to the following stresses: 1) heat stress, 2) cold stress, 3) oxidative stress, 4) ethanol stress, and 5) exercise stress by compelling the mice to run on a treadmill until exhausted. After exposure to the stresses, the liver was immediately isolated. Elevation of liver HSP70 in the trained mice was evident, whereas no elevation was found in the sedentary mice. On exposure to heat, diethyldithiocarbamate and ethanol, activities of glutanic oxalacetic transaminase in plasma, and liver caspase-3, a key enzyme of apoptotic processing, were elevated in the sedentary mice but not in the trained mice. These results suggest that exercise training enhanced the resting level of liver HSP70 and hepatic protection against various stresses, at least partly attributing to the suppression of caspase-3 activity by the increase in HSP70.

Modulation of the stress response during apoptosis and necrosis induction in cadmium-treated U-937 human promonocytic cells

Treatment for 2 h with 200 microM cadmium chloride, followed by recovery, caused apoptosis and induced heat-shock protein 70 (HSP70) expression in U-937 promonocytic cells. However, pre-incubation with the GSH depleting agent L-buthionine-[S,R]-sulfoximine (BSO, 1 mM for 24 h) caused necrosis instead of apoptosis and failed to induce HSP70 expression. This failure was a consequence of necrosis instead of GSH depletion, since BSO allowed or even potentiated HSP70 induction when used in combination with heat shock (2 h at 42.5 degrees C) or with 50 microM cadmium, which caused apoptosis. The administration of N-acetyl-L-cysteine (NAC) at the beginning of recovery after BSO/200 microM cadmium treatment prevented the execution of necrosis and restored the execution of apoptosis, but did not restore HSP70 induction, indicating that the inhibition by BSO of HSP70 expression is an early regulated event. This contrasted with the capacity of NAC to prevent the alterations caused by BSO/200 microM cadmium in other proteins, namely the suppression of Bax expression and the increase in Bcl-2 and HSP-60 expression. Finally, it was observed that treatment with 200 microM cadmium rapidly increased the HSP70 mRNA level and stimulated heat-shock factor 1 (HSF1) trimerization and binding, and that these effects were prevented by pre-incubation with BSO. Taken together, these results indicate that the stress response is compatible with apoptosis but not with necrosis in cadmium-treated promonocytic cells. The suppression of the stress response is specifically due to the early inhibition of HSF1 activation.

Exposure of developing oligodendrocytes to cadmium causes HSP72 induction, free radical generation, reduction in glutathione levels, and cell death

Primary cultures of oligodendrocytes were used to study the toxic effects of cadmium chloride. Cell viability was evaluated by the mitochondrial dehydrogenase activity and confirmed by propidium iodide (PI) fluorescence staining. The expression of the 72 kDa stress protein, HSP72, was assayed by Western blot analysis. The results showed that Cd(2+)-induced toxicity was dependent on the time and dose of exposure, as well as on the developmental stage of the cultures. Oligodendrocyte progenitors were more vulnerable to Cd(2+) toxicity than were mature oligodendrocytes. Mature oligodendrocytes accumulated relatively higher levels of Cd(2+) than did progenitors, as determined by (109)CdCl(2) uptake; treatment with the metal ion caused a more pronounced reduction in intracellular glutathione levels and significantly higher free radical accumulation in progenitors. The latter could explain the observed differences in Cd(2+) susceptibility. HSP72 protein expression was increased both in progenitors and in mature cells exposed to Cd(2+). Pretreatment with N-acetylcysteine, a thiocompound with antioxidant activity and a precursor of glutathione, prevented Cd(2+)-induced (i) reduction in glutathione levels and (ii) induction of HSP72 and diminished (i) Cd(2+) uptake and (ii) Cd(2+)-evoked cell death. In contrast, buthionine sulfoximine, an inhibitor of gamma-glutamyl-cysteine synthetase, depleted glutathione, and potentiated the toxic effect of Cd(2+). These results strongly suggest that Cd(2+)-induced cytotoxicity in oligodendrocytes is mediated by reactive oxygen species and is modulated by glutathione levels.

Reduced glutathione oxidation ratio and 8 ohdG accumulation by mild ischemic pretreatment

A critical role of oxidative stress has been implicated in ischemic brain damage. Mild ischemic pretreatment and/or synthesis of heat shock proteins (HSPs) has been suggested to protect against oxidative brain damage. However, experimental support of this suggestion have proven to be difficult partly because sensitive indices to assess oxidative consequences of ischemic brain damage were few. In this study, we have attempted to establish biochemical assay systems to quantitate oxidative brain damage following ischemia. We produced experimental brain ischemia in the Mongolian gerbil (Meriones unguiculatus) and examined the hippocampus for ischemic brain damage. The results obtained from ischemic gerbil hippocampus demonstrated that oxidative brain damage can be quantitated by determining glutathione oxidation ratio together with the accumulation of the oxidative DNA damage product, 8-hydroxy-2'-deoxyguanosine (8 ohdG). Our results also demonstrated a role for mild ischemic pretreatment and synthesis of HSPs against oxidative brain damage. We showed that mild 2-min ischemic pretreatment reduced the degree of both glutathione oxidation ratio and 8 ohdG accumulation in gerbil hippocampus subsequent to 10 min ischemic challenge. We also showed that the accumulation of HSP70 was closely associated with the reduction of oxidative brain damage. To our knowledge, this is the first report to investigate glutathione redox states and oxidative DNA damage levels to evaluate a protective role of mild ischemic pretreatment and HSP synthesis following brain ischemia. Our data validate the previous suggestions and provide new additional data that argue for the protective role of mild ischemic pretreatment and HSP70 synthesis against oxidative brain damage.

Attenuation by glutathione of hsp72 gene expression induced by cadmium in cisplatin-resistant human ovarian cancer cells

Intracellular GSH has some effects on protecting cells against cadmium and is involved in the development of resistance to cisplatin (CDDP). To determine the effects of intracellular GSH on expression of the heat shock genes (hsp) induced by cadmium in CDDP-resistant cancer cells, we used two human ovarian cancer cell lines: CDDP-sensitive A2780 and its CDDP-resistant derivative A2780CP. The concentration of intracellular GSH was significantly higher in A2780CP than in A2780 cells. A2780CP cells were more resistant to CdCl2 exposure than A2780 cells. The treatment of the two cell lines with 50 microM CdCl2 induced hsp72, hsp32 and metallothionein (MT-II) mRNAs, and the induction level of each mRNA did not differ in the two cell lines. However, the treatment with 20 microM CdCl2 induced the hsp72 and hsp32 mRNAs in A2780CP cells less than in A2780 cells, while the MT-II mRNA was induced to similar levels in the two cell lines. The DNA binding activity of the heat shock factor (HSF) in response to 20 microM CdCl2 exposure was also significantly lower in A2780CP cells. The treatment of A2780 cells with N-acetyl-L-cysteine increased the intracellular GSH concentration, and profoundly suppressed hsp72 mRNA induction and HSF activation by CdCl2. These results indicate that the regulation of the hsp72 gene expression induced by CdCl2 was more suppressive in A2780CP than in A2780 cells. Our findings suggest that increased GSH biosynthesis in CDDP-resistant cancer cells may be involved in the attenuation of HSF activation by CdCl2.

Higher induction of heat shock protein 72 by heat stress in cisplatin-resistant than in cisplatin-sensitive cancer cells

Induction of the heat shock proteins (HSPs) is involved in the increased resistance to cancer therapies such as chemotherapy and hyperthermia. We used two human ovarian cancer cell lines; a cisplatin (CDDP)-sensitive line A2780 and its CDDP-resistant derivative, A2780CP. The concentration of intracellular glutathione (GSH) is higher (2.7-fold increase) in A2780CP cells than in A2780 cells. A mild treatment with a heat stress (42 degrees C for 30 min) induced synthesis of both the heat shock protein 72 (Hsp72) mRNA and the HSP72 protein in A2780CP cells, but not in A2780 cells. In contrast, a severe heat stress (45 degrees C for 30 min) increased synthesis of the HSP72 protein in the two cell lines. The induced level of the HSP72 protein by the severe treatment was higher in A2780CP than in A2780 cells. The gel mobility shift assay showed that DNA binding activities of the heat shock factor (HSF) in the two cell lines were induced similarly and significantly by the mild heat stress. Immunocytochemistry using an anti HSF1 antibody also indicated that mild heat stress activated the HSF1 translocation from the cytosol to the nucleus similarly in the both cell lines. Pretreatment of CDDP-sensitive A2780 cells with N-acetyl-L-cysteine, a precursor of GSH, effectively enhanced induction of the Hsp72 mRNA by the mild heat stress. The present findings demonstrate that induction of the Hsp72 mRNA by the mild heat stress was more extensive in CDDP-resistant A2780CP cells. It is likely that the higher GSH concentration in A2780CP cells plays an important role in promoting Hsp72 gene expression induced by the mild heat stress probably through processes downstream of activation of HSF-DNA binding.

Cadmium uptake and defense mechanism in insect cells

The uptake of cadmium and the defense mechanism against this heavy metal were studied in the Aedes albopictus C6/36 cell line. The internalization of cadmium was a very quick process and exhibited saturation kinetics over the metal concentration gradient (1.37 to 131 micromol/L). Cd toxicity and influx were both shown to be temperature dependent. The uptake was not influenced by a 2, 4-dinitrophenol pretreatment but was significantly decreased by the Ca2+ antagonist verapamil. These data suggest that cadmium is readily taken up through mediated transport, not requiring metabolic energy. A considerable amount of the metal passes through the Ca2+ channels, but probably (an)other transporting molecule(s) also play(s) an important role in the uptake process. The remarkable, nonsigmoid viability pattern of Cd-treated cultures suggests that CdCl2 concentrations above 33 micromol/L induce a cellular defense system. This phenomenon went together with increased protein synthesis. We found a major induction of a group consisting of 71-, 75-, and 78-kDa proteins, probably belonging to the HSP70 family, as similar proteins were induced by heat shock. A slight induction of a 120-kDa protein also occurred. At the highest Cd concentrations 98-, 108-, and 110-kDa proteins were induced. These data suggest that heat shock proteins may play an important role in the Aedes cell protection against Cd insult.

Metal chelator NNNNN-tetrakis-(2-pyridymethyl)ethylene diamine inhibits the induction of heat shock protein 70 synthesis by heat in cultured keratinocytes

Heat shock protein (HSP) synthesis results from various types of injury, including heat shock (HS) and some oxidants. The intracellular signals leading to HSP synthesis are not yet fully elucidated. We have studied the influence of NNN'N'-tetrakis(2-pyridylmethyl)ethylene diamine (TPEN), a metal chelator known to induce cellular zinc and copper deprivation, on resistance to heat and on hsp70 synthesis in HaCaT keratinocytes. TPEN was shown to sensitize HaCaT cells to heat shock. The effect of TPEN was neutralized by equimolar Zn2+. By the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and Western blotting characterization of hsp70, it was shown that cultured HaCaT cells constitutively express the inducible form of hsp70. The application of TPEN alone slightly increases the level of hsp70 but inhibits its induction by HS. This inhibitory effect is related to metal deprivation, because it is eliminated when Cu2+ or Zn2+ ions are supplied together with TPEN. These results suggest that these metals are involved in the expression by keratinocytes of a stress protein which has a protective action against environmental stress.

Cadmium-regulated genes from the nematode Caenorhabditis elegans. Identification and cloning of new cadmium-responsive genes by differential display

The transition metal cadmium is a pervasive and persistent environmental contaminant that has been shown to be both a human toxicant and carcinogen. To inhibit cadmium-induced damage, cells respond by increasing the expression of genes encoding stress-response proteins. In most cases, the mechanism by which cadmium affects the expression of these genes remains unknown. It has been demonstrated in several instances that cadmium activates gene transcription through signal transduction pathways, mediated by protein kinase C, cAMP-dependent protein kinase, or calmodulin. A codicil is that cadmium should influence the expression of numerous genes. To investigate the ability of cadmium to affect gene transcription, the differential display technique was used to analyze gene expression in the nematode Caenorhabditis elegans. Forty-nine cDNAs whose steady-state levels of expression change 2-6-fold in response to cadmium exposure were identified. The nucleotide sequences of the majority of the differentially expressed cDNAs are identical to those of C. elegans cosmids, yeast artificial chromosomes, expressed sequence tags, or predicted genes. The translated amino acid sequences of several clones are identical to C. elegans metallothionein-1, HSP70, collagens, and rRNAs. In addition, C. elegans homologues of pyruvate carboxylase, DNA gyrase, beta-adrenergic receptor kinase, and human hypothetical protein KIAA0174 were identified. The translated amino acid sequences of the remaining differentially expressed cDNAs encode novel proteins.

Tobacco smoke induces coordinate activation of HSF and inhibition of NFkappaB in human monocytes: effects on TNFalpha release

Tobacco smoke (TS) exposure is a major risk factor for human disease, and macrophages of healthy smokers have a depressed capacity to release cytokines, including tumor necrosis factor (TNF)alpha. TS induces the synthesis of heat shock (HS)/stress proteins (HSP), and, in particular, of Hsp70. We determined whether Hsp70 induction by TS was mediated by the activation of the HS transcription factor, HSF. HSF activation has been shown to inhibit NFkappaB. Thus, we also determined the effects of TS on NFkappaB. U937 cells and human peripheral blood monocytes were exposed to TS, binding activities of the respective transcription factors were analyzed, and Hsp70 expression and TNFalpha release were determined in parallel. TS activated HSF, which was associated with Hsp70 overexpression and inhibition of NFkappaB binding activity and TNFalpha release. The altered cytokine profile observed in smokers may relate to an HSF/Hsp70-mediated inhibition of NFkappaB activity.

Concentration-dependent differential effects of N-acetyl-L-cysteine on the expression of HSP70 and metallothionein genes induced by cadmium in human amniotic cells

Cadmium induces the expression of the 70 kDa heat shock protein (HSP70) and metallothionein (MT), both of which are considered to be associated with intracellular glutathione (GSH) metabolism in the cellular protection mechanism against cadmium-induced cellular injury. We determined the effects of N-acetyl-L-cysteine (NAC), which increases the intracellular GSH levels, on the induction of HSP70 and MT gene expression in a cultured cell line of human amniotic cells (WISH) exposed to CdCl2. The mRNA level of MT-II, a major isoform of MT genes, was more prominently increased than that of HSP70 when WISH cells were exposed to CdCl2 (5-15 microM, for 6 h). The treatment of WISH cells with 1.5 and 30 mM NAC for 2 h increased the intracellular GSH levels by 1.4- and 3.1-fold, respectively. Pretreatment of cells with 30 mM NAC significantly reduced both HSP70 and MT-II mRNA levels in the cells exposed to 50 microM CdCl2. This concentration of NAC also efficiently suppressed the cadmium-induced lethality. On the contrary, pretreatment with 1.5 mM NAC suppressed only the induction of HSP70 gene expression in the 50 microM CdCl2-treated cells, and did not inhibit the metal toxicity. However, this low concentration of NAC efficiently suppressed lipid peroxidation which was increased by 50 microM CdCl2. Furthermore, this low concentration of NAC also decreased the CdCl2-induced gene expression of HSP32 which represents a general response to oxidative stress. Taken together, NAC seems to have at least two concentration-dependent functions in WISH cells exposed to CdCl2; the low concentration of NAC can suppress the induction of HSP70 gene expression as well as the increase of lipid peroxidation via an antioxidant pathway, while the high concentration of NAC can suppress the induction of MT-II mRNA as well as cadmium-induced cell death. Our present data suggest that changes in intracellular redox status, as reflected by GSH concentration, have more important effects on the induction of HSP70 mRNA rather than that of MT-II mRNA in human amniotic cells exposed to cadmium.

GRP78, HSP72/73, and cJun stress protein levels in lung epithelial cells exposed to asbestos, cadmium, or H2O2

Occupational exposure to crocidolite asbestos is associated with the development of nonmalignant and malignant pulmonary disease. Considerable evidence indicates that the mechanisms of asbestos-induced toxicity involve the production of active oxygen species (AOS). Production of AOS in excess of cellular defenses creates an environment of oxidative stress and stimulates the expression of a number of different genes whose products may be involved in mediating responses from oxidant injury. To further investigate the mechanisms of asbestos-induced pathogenicity, we have examined by Western blot analyses the induction of the stress response proteins GRP78 and HSP72/73 in rat lung epithelial cells (RLE) exposed to crocidolite asbestos. In comparative studies, we also examined GRP78, HSP72/73, and cJun expression in RLE cells exposed to equitoxic concentrations of cadmium chloride (CdCl2) and hydrogen peroxide (H2O2). Our results demonstrate that asbestos and H2O2 do not alter GRP78 or HSP72/73 protein levels in RLE cells, but do increase levels of cJun protein. Increases by asbestos and H2O2 were not accompanied by alterations in cellular glutathione levels in this cell type, but asbestos caused elevations in protein levels of manganese-containing superoxide dismutase (MnSOD), an indirect indicator of oxidant stress. In contrast, exposure of cells to CdCl2 led to no changes in MnSOD protein levels, but increases in GRP78, HSP72/73, and cJun proteins as well as significant increases in oxidized and reduced thiol pools. Results suggest that environmental agents causing oxidative injury to lung epithelium elicit different patterns of stress responses.

Inhibition of nucleolar function and morphological change by adriamycin associated with heat shock protein 70 accumulation

Adriamycin (ADR) has been considered to target mainly DNA metabolism in the nucleus. Recently, we observed the nuclear translocation of heat shock protein 70 (HSP70) after ADR treatment. We examined which intranuclear changes might be related to this alteration of HSP70 localization. We found considerable alternations in the nucleolar morphology and function in ADR-treated tumor cells, i.e., a ring-shaped segregation of granular components of almost all nucleoli and a dramatic reduction of nucleolar 45S ribosomal precursor RNA biosynthesis in HeLa cells exposed to 100 microM ADR for 2 h. Concomitantly with these changes, HSP70 was concentrated into the nucleoli, as in the case of heat shock treatment. These results indicate a novel anticancer effect of ADR via the suppression of cellular protein biosynthesis, in addition to its effect on DNA.

Expression of heat shock proteins, glutathione peroxidase and catalase in childhood acute lymphoblastic leukemia and nephroblastoma

In this study we analyzed the mRNA expression of the heat shock proteins 27 and 70, and the expression of the radical scavenging enzymes catalase and glutathione peroxidase (GPX) in childhood acute lymphoblastic leukemia (ALL, n = 54) and in nephroblastoma (n = 34). We found a significant positive correlation between both heat shock proteins and also between glutathione peroxidase and both heat shock proteins in ALL and nephroblastoma. There was also a significant correlation between catalase and glutathione peroxidase detectable. Furthermore, we investigated whether the expression of the heat shock proteins and the antioxidant enzymes glutathione peroxidase and catalase have implications in the clinical outcome in ALL. However, we found no significant correlation between the expression of these proteins and relapse rate, the relapse free intervals or the overall survival.