Characterization of the thermotolerant cell. I. Effects on protein synthesis activity and the regulation of heat-shock protein 70 expression

HSP72 induction by heat stress is not universal in mammalian neural cell lines

Heat-induced expression of 72-kDa heat shock protein (HSP72) was investigated in a panel of neuronal and non-neuronal cell lines by immunoblotting and immunocytochemistry using monoclonal antibodies directed to HSP72. By immunoblotting, HSP72 expression was observed in most cell lines of mouse (SN6.1b, CL8c4.7, NSC34.6, B2A, C2C12), rat (PC12, C-6, L3), and human (NB-1, GOTO, IMR-32, HeLa) origin under the heat-stressed condition. The mouse neuroblastoma cell line N18TG2, however, did not express HSP72 under the heat-stressed condition. By immunocytochemistry, HSP72 was undetectable in the heat-stressed N18TG2 cells, while it was identified in the heat-stressed SN6.1b cells, a clonal hybrid neuron between N18TG2 and mouse septal cholinergic neuron. By exposure to a priming sublethal heat shock, SN6.1b cells but not N18TG2 cells acquired a significant level of tolerance to a subsequent lethal heat shock. These results suggest that heat-induced expression of HSP72 may contribute to acquisition of the thermotolerant state in SN6.1b cells.

Endothelial cell hypoxia associated proteins are cell and stress specific

Vascular endothelial cells (EC) are one of the initial cells exposed to decreases in blood oxygen tension. Bovine EC respond not only by altering secretion of vasoactive, mitogenic, and thrombogenic substances, but also by developing adaptive mechanisms in order to survive acute and chronic hypoxic exposures. EC exposed to hypoxia in vitro upregulate a unique set of stress proteins of Mr 34, 36, 39, 47, and 56 kD. Previous studies have shown that these proteins are cell associated, upregulated in a time and oxygen-concentration dependent manner, and are distinct from heat shock (HSPs) and glucose-regulated proteins (GRPs). To further characterize these hypoxia-associated proteins (HAPs), we investigated their upregulation in human EC from various vascular beds and compared this to possible HAP upregulation in other cell types. Human aortic, pulmonary artery, and microvascular EC upregulated the same set of proteins in response to hypoxia. In comparison, neither lung fibroblasts, pulmonary artery smooth muscle cells, pulmonary alveolar type II cells, nor renal tubular epithelial cells upregulated proteins of these Mr. Instead, most of these cell types induced synthesis of proteins of Mrs corresponding to either HSPs, GRPs, or both. Further studies demonstrated that exposure of EC to related stresses such as cyanide, 2-deoxyglucose, hydrogen peroxide, dithiothreitol, and glucose deprivation did not cause upregulation of HAPs. Evaluation of cellular damage during hypoxia using phase-contrast microscopy, trypan blue exclusion, chromium release, and adherent cell counts showed that EC survived longer with less damage than any of the above cell types. The induction of HAPs, and the lack of induction of HSPs or GRPs, by EC in response to hypoxia may be related to their unique ability to tolerate hypoxia for prolonged periods.

Induction of translational thermotolerance in liver of thermally stressed rats

Heat-shock gene expression in cultures of single cell types has been well characterized but little is known about the heat-shock response of intact organs in vivo. In this study, the kinetics of hepatic heat-shock gene expression and the induction of thermotolerance were characterized in rats. Animals were subjected to a defined, reversible stress by increasing the core body temperature to 41 degrees C or 42 degrees C for 30 min. New synthesis of the inducible form of the heat shock-70 family of proteins (hsp-72) peaked simultaneously with the maximal level of hsp-72 transcripts at both temperatures. These data are consistent with previous observations in cultures of hepatoblastoma cells after thermal stress [De Maio, A., Beck, S. C. & Buchman, T. G. (1993) Circ. Shock 40, 177-186]. The incorporation of radioactive amino acids into polypeptides by the liver was blocked during the first hour of recovery after heat shock at 42 degrees C. This inhibition of protein synthesis by thermal stress could be prevented by prestressing rats at 42 degrees C for 30 min and allowing the rats to recover for 24 h at normal body temperature (37 degrees C). This phenomenon, previously defined as 'translational thermotolerance', correlates with the hepatic content of hsp-72; maximal protection occurs 24 h after a 42 degrees C thermal stress when hsp-72 (protein) is also maximum and decreases with the clearance of hsp-72 from the liver. These data suggest that the presence of hsp-72 within the liver may modulate the organ response to subsequent stresses and may be important to organ and animal survival after repeated insults.

Regulation of hsp70 induction in thermotolerant HeLa cells

Upon exposure to heat shock, non-thermotolerant (NT) HeLa cells transiently synthesize a large amount of 70-kDa heat-shock protein (hsp70), whereas thermotolerant (TT) cells synthesize a small amount of hsp70. When the hsp70 mRNA of HeLa cells was analyzed, it became apparent that hsp70 mRNA in TT cells did not increase following heat shock, whereas hsp70 mRNA in NT cells did increase dramatically. A further analysis of the activation of the heat-shock transcription factor (HSF) showed that significant activation of HSF was observed immediately after heat shock in both NT and TT cells. However, activated HSF was rapidly repressed in the TT cells, but not in the NT cells. Thus, the decreased induction of hsp70 synthesis observed in the TT HeLa cells may be due to the immediate repression of activated cellular HSF, which probably results in the reduced induction of hsp70 mRNA. The hsp70 content in the TT cells was usually higher than in the NT cells. However, after heat-shock treatment, the hsp70 content of the NT cells increased to nearly the level of the TT cells concomitant with the repression of hsp70 synthesis. The association of activated HSF with hsp70 was observed in both NT and TT cells, and the amount of HSF-hsp70 complex within the cell increased in proportion to the increase in hsp70 in the cells. These findings strongly suggest that the activity of HSF is negatively regulated by the intracellular content of hsp70 in these cells. Furthermore, in vitro experiments on the activation of HSF suggest that HSFs of NT and TT cells may have different properties, or an unknown factor may exist which regulates HSF activation in these cells.

The DNA-binding activity of the human heat shock transcription factor is regulated in vivo by hsp70

The human heat shock transcription factor (HSF) is maintained in an inactive non-DNA-binding form under nonstress conditions and acquires the ability to bind specifically to the heat shock promoter element in response to elevated temperatures or other conditions that disrupt protein structure. Here we show that constitutive overexpression of the major inducible heat shock protein, hsp70, in transfected human cells reduces the extent of HSF activation after a heat stress. HSF activation was inhibited more strongly in clones that express higher levels of hsp70. These results demonstrate that HSF activity is negatively regulated in vivo by hsp70 and suggest that the cell might sense elevated temperature as a decreased availability of hsp70. HSF activation in response to treatment with sodium arsenite or the proline analog azetidine was also depressed in hsp70-expressing cells relative to that in the nontransfected control cells. As well, the level of activated HSF decreased more rapidly in the hsp70-expressing clones when the cells were heat shocked and returned to 37 degrees C. These results suggest that hsp70 could play an active role in the conversion of HSF back to a conformation that does not bind the heat shock promoter element during the attenuation of the heat shock response.

Gene expression under temperature stress

In this review, changes in plant gene expression in response to environmental stresses are discussed using the examples of high and low temperature treatments. While some changes may contribute to acclimatory processes which improve plant survival or performance under stress, others may be 'shock' responses indicative of sensitivity. The heat-shock response, which is almost ubiquitous among eukaryotic organisms, is characterized by repression of normal cellular protein synthesis mediated at both the transcriptional and the translational level, and induction of heat-shock protein (HSP) synthesis. There is a correlation between HSP synthesis and induced thermotolerance in plants, but the evidence for a causal relationship is not conclusive. The possible biochemical functions of some of the HSPs are now becoming apparent; they are believed to play an important role in preventing accumulation of damaged proteins in the cell during heat shock. Although no other environmental stress elicits the full heat-shock response, certain treatments do induce synthesis of subsets of the HSPs, and the reasons for this are considered. Alterations in gene expression in response to low temperatures are more diverse and usually less dramatic than the heat-shock response, with which they share little, if any, homology. Biochemical adjustments during cold treatment are discussed, with particular reference to those which contribute to acclimation. Several genes whose expression is induced by cold have been cloned and characterized, and in some cases it is possible to attribute in vivo functions to them; they include enzymes of lipid, carbohydrate and protein metabolism, structural proteins and putative cryoprotectants. The use of transgenic plants is further facilitating an investigation of the biochemical factors which are important in cold acclimation. Drought, osmotic stress and abscisic acid induce expression of many of the same genes as does cold treatment; it seems likely that some of the products of these genes contribute to increased freezing tolerance by protecting against intracellular dehydration. Contents Summary 1 I. Introduction 1 II. High temperature stress 3 III. Low temperature stress 10 IV. Concluding remarks 20 Acknowledgements 21 References 21.

The DNA-binding activity of the human heat shock transcription factor is regulated in vivo by hsp70

The human heat shock transcription factor (HSF) is maintained in an inactive non-DNA-binding form under nonstress conditions and acquires the ability to bind specifically to the heat shock promoter element in response to elevated temperatures or other conditions that disrupt protein structure. Here we show that constitutive overexpression of the major inducible heat shock protein, hsp70, in transfected human cells reduces the extent of HSF activation after a heat stress. HSF activation was inhibited more strongly in clones that express higher levels of hsp70. These results demonstrate that HSF activity is negatively regulated in vivo by hsp70 and suggest that the cell might sense elevated temperature as a decreased availability of hsp70. HSF activation in response to treatment with sodium arsenite or the proline analog azetidine was also depressed in hsp70-expressing cells relative to that in the nontransfected control cells. As well, the level of activated HSF decreased more rapidly in the hsp70-expressing clones when the cells were heat shocked and returned to 37 degrees C. These results suggest that hsp70 could play an active role in the conversion of HSF back to a conformation that does not bind the heat shock promoter element during the attenuation of the heat shock response.

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

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

Denatured proteins inhibit translation in hemin-supplemented rabbit reticulocyte lysate by inducing the activation of the heme-regulated eIF-2 alpha kinase

The heme-regulated inhibitor (HRI) of protein synthesis becomes activated in rabbit reticulocyte lysates in response to a variety of conditions including heme-deficiency, addition of oxidants, and heat shock. Activated HRI inhibits translation by catalyzing the phosphorylation of the alpha-subunit of eukaryotic initiation factor eIF-2. The molecular nature of the "signal" that leads to the activation of HRI in response to heat shock has not been characterized. We have recently reported that HRI interacts with the 90- and 70-kDa heat shock proteins (hsp) and a 56-kDa protein in hemin-supplemented lysates [Matts, R.L., Xu, Z., Pal, J.K., & Chen, J.-J. (1992) J. Biol. Chem. 267m 18160-18167]. In this report, we demonstrate that addition of denatured proteins, bovine serum albumin (BSA), beta-lactoglobulin, or alpha-lactalbumin, but not the addition of the native proteins, inhibits protein synthesis in hemin-supplemented reticulocyte lysates. The inhibition was reversed upon the addition of 10 mM cAMP or purified eIF-2B, classical criteria for HRI-mediated translational inhibition. Denatured BSA, but not native BSA, stimulated the phosphorylation of the alpha-subunit of eIF-2. This stimulation of eIF-2 alpha phosphorylation was inhibited by a monoclonal antibody to HRI, confirming that denatured BSA was causing the activation of HRI. The concentration of denatured BSA required to inhibit protein synthesis by 50% correlated with the levels of hsp70 present in each lysate preparation. Lysate hsp70 co-immunoadsorbed with denatured BSA, but not with not with native BSA. Hsp70 was co-adsorbed with HRI from lysate in the presence of native BSA, but not in the presence of denatured BSA.(ABSTRACT TRUNCATED AT 250 WORDS)

Early recovery of protein synthesis following ischemia in hippocampal neurons with induced tolerance in the gerbil

Following brief cerebral ischemia, tolerance to subsequent ischemia is induced in the hippocampal neurons. In this experiment, recovery of protein synthesis was investigated autoradiographically in gerbils with induced tolerance. The animals were subjected to single forebrain ischemia for 5 min (5-min ischemia group) or 2 min (2-min ischemia group). To observe the effect of tolerance acquisition, double forebrain ischemia (double ischemia group), 2-min ischemia followed by 5-min ischemia was induced 2 days later. At various recirculation periods (90 min, 6 h, 1 day, and 4 days following ischemia), animals received a single dose of L-[2,3-3H]valine. In the 5-min ischemia group, protein synthesis in the CA1 sector was severely suppressed during the period from 90 min to 1 day of recirculation and never returned to the normal level even at 4 day of recirculation. In the 2-min ischemia group, protein synthesis recovered gradually and returned to near normal at 4 days of recirculation. On the other hand, in the double ischemia group, recovery of protein synthesis in the CA1 sector was rapid. At 1 day of recirculation, protein synthesis returned to near normal. Protein synthesis in the CA2 sector was inhibited during the 4 days of recirculation in this group. The present study revealed an early recovery of protein synthesis in the hippocampal CA1 neurons in the gerbil with induced tolerance. We suggest that recovery of protein synthesis is essential for the survival of neurons exposed to transient ischemia.

Putative determinants of the cellular response to hyperthermia

Recently, it has been demonstrated that two different thermal resistant states found in Chinese hamster cells, one transient, associated with thermotolerance, and the other permanent, associated with the increased expression of the cognate member of the hsp 70 family, are characterized by faster recovery from heat-induced perturbations in several cellular processes (Laszlo 1992b). These processes include total cellular protein and RNA synthesis, the localization of hsp70, the organization of vimentin, and the protein composition of the nucleus. In the present study, the recovery from heat-induced perturbations in cellular physiology was extended further to two more types of Chinese hamster cells: permanently heat resistant cells in which thermoresistance is associated with the overexpression of hsp27 and heat-sensitive cell lines. When the heat-resistant hsp27 transfected cell lines were compared with the control wild-type cell line, the recovery of protein synthesis from heat-induced inhibition was similar in the normal and hsp27 transfected cells, while the recovery from heat-induced inhibition of total RNA synthesis and the recovery from heat-induced increased association of hsp70 with nuclei were both more rapid in the hsp27 transfected cell lines. In the permanently heat-sensitive cell lines, the kinetics of recovery from heat-induced inhibition of protein synthesis did not correlate with the heat sensitive state. However, delays in the recovery from heat-induced alterations in total cellular RNA synthesis and from heat-induced excess nuclear association of hsp70 were associated with the heat-sensitive state. Overall, these results suggest that the kinetics of recovery from heat-induced alterations in total cellular RNA synthesis and the localization of hsp 70 are putative candidates for being determinants of the cellular response to hyperthermia, and thus have the potential to form the basis of predictive assays for use in conjunction with clinical hyperthermia.

Serum-stimulated cell cycle progression and stress protein synthesis in C3H10T1/2 fibroblasts treated with sodium arsenite

In this work, we demonstrated that a nonlethal dose of arsenite administered to quiescent C3H10T1/2 fibroblasts can enhance the mitogenic effect of suboptimal concentrations of serum. The mitogenic effect was dependent on the serum concentration and on the time interval between the administration of arsenite and that of serum. This suggests that mitogen sensitivity changes in time after arsenite treatment. It is shown that the concentrations of arsenite that enhance the mitogenic effect of serum also increase the mRNA levels of c-fos, HSP68, and HSP84 and induce the specific synthesis of Heat Shock Proteins (HSPs). The physiological significance of this phenomenon is most likely to counteract the long-term toxic effect of arsenite by early induction of compensation for cell loss.

Expression of constitutive heat shock protein-70 in normal (non-stressed) rabbit urinary bladder tissue

The expression of constitutive HSP-70 in the urinary bladder was determined by SDS-PAGE and western blotting using a mouse monoclonal antibody against HSP-70. The western blot analysis showed that the mouse anti-HSP-70 cross-reacted with a 70 kDa protein present in the extracts of the urinary bladder muscle and mucosa. Densitometric scanning of the western blots allowed us to specifically quantitate the relative amounts of the HSP-70. The quantitation of the HSP-70 by combining immunoblotting and densitometry using a laser scanner is reproducible and this technique requires only a small amount of tissue. The amounts of HSP-70 can be estimated from a standard curve of nanogram(ng) of HSP-70 vs absorption from the immunoblots. The amounts of HSP-70 in the muscular and mucosal layers in the body of the urinary bladder are more than those in the base of the bladder. The presence of HSP-70 in the muscle and mucosal epithelium of the bladder was demonstrated by immunohistochemical analysis of freshly removed tissue from the base and the body of bladder from normal animals.

The constitutive and stress inducible forms of hsp 70 exhibit functional similarities and interact with one another in an ATP-dependent fashion

Mammalian cells constitutively express a cytosolic and nuclear form of heat shock protein (hsp) 70, referred to here as hsp 73. In response to heat shock or other metabolic insults, increased expression of another cytosolic and nuclear form of hsp 70, hsp 72, is observed. The constitutively expressed hsp 73, and stress-inducible hsp 72, are highly related proteins. Still unclear, however, is exactly why most eukaryotic cells, in contrast to prokaryotic cells, express a novel form of hsp 70 (i.e., hsp 72) after experiencing stress. To address this question, we prepared antibodies specific to either hsp 72 or hsp 73 and have compared a number of biological properties of the two proteins, both in vivo and in vitro. Using metabolic pulse-chase labeling and immunoprecipitation analysis, both the hsp 72 and hsp 73 specific antibodies were found to coprecipitate a significant number of newly synthesized proteins. Such interactions appeared transient and sensitive to ATP. Consequently, we suspect that both hsp 72 and hsp 73 function as molecular chaperones, interacting transiently with nascent polypeptides. During the course of these studies, we routinely observed that antibodies specific to hsp 73 resulted in the coprecipitation of hsp 72. Similarly, antibodies specific to hsp 72 were capable of coprecipitating hsp 73. Using a number of different approaches, we show that the constitutively expressed, pre-existing hsp 73 rapidly forms a stable complex with the newly synthesized stress inducible hsp 72. As is demonstrated by double-label indirect immunofluorescence, both proteins exhibit a coincident locale within the cell. Moreover, injection of antibodies specific to hsp 73 into living cells effectively blocks the ability of both hsp 73 and hsp 72 to redistribute from the cytoplasm into the nucleus and nucleolus after heat shock. These results are discussed as they relate to the possible structure and function of the constitutive (hsp 73) and highly stress inducible (hsp 72) forms of hsp 70, both within the normal cell as well as in the cell experiencing stress.

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

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

Stress protein synthesis and accumulation after traumatic injury of crayfish CNS

By several days after a crush injury of crayfish CNS, the wound site heals. Changes in protein synthesis and accumulation occur at the lesion site and nearby. During the first few hours, synthesis of 35, 70, 90, and 150 kDa proteins is induced in the injured tissue. By one day, the relative amounts of 70-90 kDa proteins increase dramatically, particularly at the crush site and adjacent to it. The 70 kDa proteins, which are related to mammalian stress proteins (SPs), remain elevated for at least one month in the traumatized region or nearby. The crushed tissue contains an SP70 isoform not present in its uncrushed counterpart. These biochemical changes may reflect the cellular changes that accompany wound healing and/or a cellular stress response to compensate for the lesion. Since similar adaptations occur in the mammalian CNS, they may represent a phylogenetically conserved attempt to retard or repair CNS tissue deterioration.

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

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

Regulation of HSP60 mRNA expression in a human ovarian carcinoma cell line

The expression of the 60-kDa heat-shock protein (HSP60) varies markedly among patients with ovarian carcinoma, and high-level expression predicts poor survival in such patients treated with cisplatin (DDP)-containing chemotherapy programs. We investigated the expression of HSP60 in human ovarian carcinoma 2008 cells and an 11-fold DDP-resistant subline 2008/C13*5.25. Heating for 2 h at 44 degrees C produced a 2.7 +/- 0.16-fold increase (mean +/- SD) that was maximal at 4 h after the start of heat exposure. Exposure to an IC50 concentration of DDP for 1 h induced a 1.8 +/- 0.03-fold increase in hsp60 expression. The opposite was true for cadmium and zinc, both of which induced increases in metallothionein IIA but not in the hsp60 message. 2008/C13*5.25 cells constitutively over-expressed hsp60 mRNA by 1.7 +/- 0.16 orders of magnitude and contained a 3.8 +/- 0.45-fold higher level of HSP60 as detected by immunocytochemical staining. 2008/C13*5.25 cells showed 1.2-fold cross-resistance to thermal killing. Expression of hsp60 was markedly reduced in 2008 xenografts as compared with 2008 cells growing in vitro; however, neither serum starvation nor refeeding altered the message level. Exposure to a variety of growth factors and drug treatments known to alter the DDP sensitivity of 2008 cells, including epidermal growth factor, 12-O-tetradecanoylphorbol-13-acetate, buthionine sulfoximine, ouabain, and forskolin, did not alter hsp60 expression. These results suggest a role for HSP60 in mediating resistance to both DDP and hyperthermia but indicate that the hsp60 mRNA levels are not regulated by the factors listed above.

Cytoskeletal thermotolerance in NRK cells

We investigated the effect of heat shock on the cytoskeletons (actin stress fibres, intermediate filaments and microtubules) and the relation between thermotolerance of cytoskeletons and thermotolerance as defined by clonogenic survival in normal rat kidney (NRK) cells. Upon heating at 45 degrees C for 15 min, almost all actin stress fibres were disrupted. During the recovery period after heat shock the stress fibres were reorganized rapidly and returned to their preheated state by 16 h. When the cells were heated again at 45 degrees C for 15 min, the disruption of stress fibres was less severe, indicating thermotolerant state of stress fibres. However, the thermotolerant state of stress fibres induced by prior treatment with sodium arsenite or by heating at 42 degrees C for 2 h was less evident than that induced by prior heat shock at 45 degrees C. The intermediate filaments in NRK cells were very heat-resistant; no apparent changes were observed even after heat shock at 45 degrees C for 60 min, and prior conditioning treatments could not induce thermotolerance of microtubules. All prior conditioning treatments could induce heat shock proteins and thermotolerance as defined by clonogenic survival. From these results it is suggested that there is no correlation between cytoskeletal thermotolerance and either heat shock protein level or thermotolerance as defined by clonogenic survival in NRK cells.

Induction of heat stress proteins is associated with decreased mortality in an animal model of acute lung injury

This study examined the hypothesis that transient, whole-body hyperthermia would reduce lung damage and/or mortality in a previously described animal model of acute lung injury. Normal, adult Sprague-Dawley rats were randomly assigned either to a heated (n = 40) or to a sham-heated (n = 49) group. Heated animals were warmed to 41 to 42 degrees C 18 h before intratracheal instillation of phospholipase A2. Forty-eight hours after phospholipase A2 exposure, the two groups were compared in a blinded fashion for mortality rate, PaO2, AaPO2, lung wet/dry weight ratio, alveolar inflammatory cell number, and lung histopathology. Heated, injured animals exhibited a reduced mortality rate and less lung damage than did unheated animals: mortality (zero versus 27%, p < 0.001); AaPO2 (22 +/- 3 versus 36 +/- 15 mm Hg, p < 0.002); lung lavage cell counts (5.3 +/- 3 versus 16.9 +/- 7 x 10(6)/ml, p < 0.05); lung wet/dry weight ratio (4.1 +/- 0.6 versus 5.1 +/- 0.7, p < 0.025); parenchymal lung injury fraction (0.10 versus 0.51, p < 0.001). Transcription and translation of heat shock proteins (HSP70) were examined by Northern and Western analysis. Pulmonary tissue HSP70 mRNA was elevated 1 h after heating. HSP72 protein levels were increased over baseline levels between 12 and 72 h after whole-body hyperthermia, but they were unchanged in sham-heated animals. These data indicate that thermal pretreatment associated with the induction of HSP72 protein synthesis, attenuates tissue damage and mortality in experimental lung injury.

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

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

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

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

Induction of 70-kDa heat shock protein and hsp70 mRNA following transient focal cerebral ischemia in the rat

Induction of the 70-kDa heat shock protein (HSP70) was demonstrated immunocytochemically in adult rats 4 h to 7 days following temporary middle cerebral artery (MCA) occlusions lasting 30, 60, or 90 min. Maximal HSP70 induction occurred approximately 24 h following ischemia. Thirty minutes of ischemia induced HSP70 in neurons throughout the cortex in the MCA distribution, whereas 90 min of ischemia induced HSP70 in neurons in the penumbra. HSP70 protein was induced in endothelial cells in infarcted neocortex following 60-90 min of MCA occlusion, and HSP70 was induced in endothelial cells in infarcted regions of lateral striatum following 30-90 min of MCA occlusion. hsp70 mRNA was induced in the MCA distribution in cortex and to a lesser extent in striatum at 2 h to 3 days following 60 min of ischemia. It is proposed that brief ischemia induces hsp70 mRNA and HSP70 protein in the cells most vulnerable to ischemia--the neurons. HSP70 protein is not induced in most neurons and glia following 60-90 min of ischemia in areas destined to infarct, whereas it is induced in vascular endothelial cells.

Stress proteins in aquatic organisms: an environmental perspective

The cellular stress response protects organisms from damage resulting from exposure to a wide variety of stressors, including elevated temperatures, ultraviolet (UV) light, trace metals, and xenobiotics. The stress response entails the rapid synthesis of a suite of proteins referred to as stress proteins, or heat-shock proteins, upon exposure to adverse environmental conditions. These proteins are highly conserved and have been found in organisms as diverse as bacteria, molluscs, and humans. In this review, we discuss the stress response in aquatic organisms from an environmental perspective. Our current understanding of the cellular functions of stress proteins is examined within the context of their role in repair and protection from environmentally induced damage, acquired tolerance, and environmental adaptation. The tissue specificity of the response and its significance relative to target organ toxicity also are addressed. In addition, the usefulness of using the stress response as a diagnostic in environmental toxicology is evaluated. From the studies discussed in this review, it is apparent that stress proteins are involved in organismal adaptation to both natural and anthropogenic environmental stress, and that further research using this focus will make important contributions to both environmental physiology and ecotoxicology.

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

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

Heat-induced transcription from RNA polymerases II and III and HSF binding activity are co-ordinately regulated by the products of the heat shock genes

Heat shock leads to co-ordinate increases in transcription of a family of heat shock genes, including the mouse hsp70.1 and B2 genes. Activation of the heat shock transcription factor (HSF) by heat shock stimulates transcription of the murine hsp70.1 gene (by RNA polymerase II). B2 genes are short, repetitive sequences whose transcription (by RNA polymerase III) are also increased after heat shock. We have studied whether heat-induced transcription is auto-regulated by the products of the heat shock genes. The results indicate: (1) after an initial heat shock, transcription of the heat shock genes by RNA polymerases II and III becomes desensitized to further heat shock, and the heat-induced DNA binding activity of the HSF is lost, (2) if accumulation of heat shock gene products is inhibited, the desensitizing effect of a prior heat shock is removed, and (3) transcription of the hsp70.1 and B2 genes apparently involves different mechanisms, with hsp70.1 employing the HSF and the B2 gene using a separate, heat-activated transcriptional mechanism. However, the level of transcription from the hsp70.1 and B2 genes and the stability of their respective RNAs are co-ordinately regulated by the level of heat shock protein in the cell. The data indicate that auto-regulation of the level of mouse heat shock gene products is mediated by RNA polymerase II transcripts but that the regulatory mechanism can control transcription from RNA polymerase III genes as well.

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

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

The thermoresistant state: protection from initial damage or better repair?

The induction of and recovery from heat-induced perturbations in several cellular parameters were examined in normal, transiently thermotolerant, and permanently heat-resistant HA-1 Chinese hamster fibroblasts. The initial heat-induced perturbations in total cellular protein synthesis, RNA synthesis, vimentin-containing intermediate filaments, and nuclear protein mass were similar in the three different cell types which display various levels of thermal resistance as determined by clonogenic survival. The posthyperthermia recovery from the heat-induced perturbations in all of the cellular parameters was more rapid in both the permanently heat-resistant cells and in the transiently thermotolerant cells. This response was observed in cells in which transient thermotolerance was induced by either a mild heat shock or exposure to sodium arsenite. The development and decay of the capacity for more rapid recovery from the initial heat-induced perturbations in total cellular protein and RNA synthesis paralleled the development and decay of clonogenic thermotolerance. Overall, these results support the notion that more rapid recovery from similar levels of heat-induced perturbations in various cellular parameters are a salient feature of both the transiently and permanently heat-resistant state.

A human myocardial two-dimensional electrophoresis database: protein characterisation by microsequencing and immunoblotting

This communication briefly describes how a human heart two-dimensional electrophoresis (2-DE) protein database is being established in our laboratory. The database contains more than 1500 polypeptides and approximately fifty proteins from 2-DE gels of human myocardial tissue have been characterised. Information about the proteins has been compiled including molecular weight (M(r)), isoelectric point (pI), sample spot (SSP) number, protein name, partial sequence, and antibody reacting with the protein. The first stage of this project involves the investigation of protein with pIs in the range pH 4-7. Future studies will employ immobilised pH gradient (IPG) gels as the first dimension of the 2-DE to examine basic proteins. The ultimate goal of this project is to establish a global picture of human heart protein expression in both normal and disease conditions.

Reduction by delayed hypothermia of cerebral infarction following middle cerebral artery occlusion in the rat: a time-course study

The effect of hypothermia on neuronal injury following permanent middle cerebral artery (MCA) occlusion in the rat was examined. Moderate hypothermia (body temperature 24 degrees C) was induced before MCA occlusion (0-minute delay group) in six rats, at 30 minutes in eight rats, and at 1 (seven rats), 2 (seven rats), and 3 (nine rats) hours after occlusion. The rats were kept at a 24 degrees C body temperature for 1 hour, then allowed to rewarm over 90 minutes. The animals were sacrificed 24 hours after MCA occlusion, and infarction was visualized by staining of coronal sections with 2,3,5-triphenyltetrazolium chloride. Infarct volumes were compared to matched normothermic control rats (body temperature 36 degrees C). Additional groups of 0-minute delay hypothermic (10 rats) and control animals (nine rats) were sacrificed 72 hours after MCA occlusion to examine the effects of prolonged survival. A significant reduction in the percentage of infarcted right hemisphere was seen in the animals sacrificed after 24 hours with 0-minute, 30-minute, and 1-hour delays in inducing hypothermia (mean +/- standard error of the mean: 2.2% +/- 0.7%, 4.4% +/- 0.9%, and 3.6% +/- 1.1%, respectively) as compared to normothermic control rats (10.8% +/- 1.5%, p less than 0.01 by Student's t-test). In the 2- and 3-hour delay groups, the percentage of infarcted right hemisphere was 17.1% +/- 2.4% and 12.0% +/- 2.7%, respectively, and no decrease in infarct volume was observed. The 0-minute delay hypothermia group sacrificed after 72 hours also displayed a significant reduction in right hemisphere infarct compared to their respective controls (4.8% vs. 11.7%, p less than 0.05). These findings indicate that, in the setting of permanent MCA occlusion, hypothermia markedly decreases brain injury even when its induction is delayed for up to 1 hour after the onset of ischemia. Ischemic damage does not appear to be merely retarded but permanently averted.

hsp70 synthesis in Schwann cells in response to heat shock and infection with Mycobacterium leprae

Induction of heat shock protein synthesis was monitored in murine and monkey Schwann cells exposed to elevated temperatures. Synthesis of the stress-inducible 70-kDa heat shock protein (hsp70) was detected in both murine and primate Schwann cells by metabolic labelling and by immunoblotting with a specific monoclonal antibody. hsp70 synthesis was also induced in Schwann cells after infection with Mycobacterium leprae and was detected from 24 h to 1 week postinfection. These results are discussed with respect to the possible role of heat shock proteins in immunopathological events associated with the clinical manifestations of leprosy.

Experimental pneumococcal meningitis causes central nervous system pathology without inducing the 72-kd heat shock protein

We examined whether experimental pneumococcal meningitis induced the 72-kd heat shock protein (HSP72), a sensitive marker of neuronal stress in other models of central nervous system (CNS) injury. Brain injury was characterized by vasculitis, cerebritis, and abscess formation in the cortex of infected animals. The extent of these changes correlated with the size of the inoculum (P less than 0.003) and with pathophysiologic parameters of disease severity, i.e., cerebrospinal fluid (CSF) lactate (r = 0.61, P less than 0.0001) and CSF glucose concentrations (r = -0.55, P less than 0.0001). Despite the presence of numerous cortical regions having morphologic evidence of injury, HSP72 was not detected in most animals. When present, only rare neurons were HSP72 positive. Western blot analysis of brain samples confirmed the paucity of HSP72 induction. The lack of neuronal HSP72 expression in this model suggests that at least some of the events leading to neuronal injury in meningitis are unique, when compared with CNS diseases associated with HSP72 induction.

Heat Shock Proteins in Hypoxic-Ischemic Brain Injury: A Perspective

There is much to suggest that the induction of heat shock protein synthesis is an important response to injury and stress in the brain. The role of heat shock proteins in neurological disease has been approached from two points-of-view. First, the induction and synthesis of specific proteins after brain cell injury provide a window through which insight on the regulation of gene expression in pathological tissue can be obtained. These studies have broad implications for understanding pathophysiological mechanisms of disease. Second, putative cell protective effects of heat shock proteins in brain tissue provide insight into biochemical mechanisms of selective neuronal vulnerability. These studies have extremely important clinical implications since cell sensitivity to injury can seemingly be modified. The role of heat shock proteins in hypoxic-ischemic brain injury is discussed forthwith.

Examining the function and regulation of hsp 70 in cells subjected to metabolic stress

Members of the heat-shock protein (hsp) 70 family, distributed within various cellular compartments, have been implicated in facilitating protein maturation events. In particular, related hsp 70 family members appear to bind nascent polypeptides which are in the course of synthesis and/or translocation into organelles. We previously reported that in normal, unstressed cells, cytosolic hsp 70 (hsp 72/73) interacted transiently with nascent polypeptides. We suspect that such interactions function to prevent or slow down the folding of the nascent polypeptide chain. Once synthesis is complete, and now with all of the information for folding present, the newly synthesized protein appears to commence along its folding pathway, accompanied by the ATP-dependent release of hsp 72/73. Herein, we examined how these events occur in cells subjected to different types of metabolic stress. In cells exposed to either an amino acid analog or sodium arsenite, two potent inducers of the stress response, newly synthesized proteins bind to but are not released from hsp 70. Under these conditions of metabolic stress, we suspect that the newly synthesized proteins are unable to commence proper folding and consequently remain bound to their hsp 70 chaperone. In cells subjected to heat shock, a large number of both newly synthesized as well as mature proteins are rendered insoluble. Within this insoluble material are appreciable amounts of hsp 72/73. Finally, we show that in cells depleted of ATP, the release of hsp 70 from maturing proteins is inhibited. Thus, in cells experiencing metabolic stress, newly synthesized proteins unable to properly fold, as will as mature proteins which begin to unfold become stably bound to hsp 72/73. As a consequence and over time, the free or available levels of pre-existing hsp 72/73 are reduced. We propose that this reduction in the available levels of hsp 72/73 is the trigger by which the stress response is initiated.

Induced thermotolerance to apoptosis in a human T lymphocyte cell line

A brief exposure to elevated temperatures elicits, in all organisms, a transient state of increased heat resistance known as thermotolerance. The mechanism for this thermotolerant state is unknown primarily because it is not clear how mild hyperthermia leads to cell death. The realization that cell death can occur through an active process of self destruction, known as apoptosis, led us to consider whether thermotolerance provides protection against this mode of cell death. Apoptosis is a common and essential form of cell death that occurs under both physiological and pathological conditions. This mode of cell death requires the active participation of the dying cell and in this way differs mechanistically from the alternative mode of cell death, necrosis. Here we show that mild hyperthermia induces apoptosis in a human leukemic T cell line. This is evidenced by chromatin condensation, nuclear fragmentation and the cleavage of DNA into oligonucleosome size units. DNA fragmentation is a biochemical hallmark of apoptosis and requires the activation of an endogenous endonuclease. The extent of DNA fragmentation was proportional to the severity of heat stress for cells heated at 43 degrees C from 30 to 90 minutes. A brief conditioning heat treatment induced a resistance to apoptosis. This was evident as a resistance to DNA fragmentation and a reduction in the number of apoptotic cells after a heat challenge. Resistance to DNA fragmentation developed during a recovery period at 37 degrees C and was correlated with enhanced heat shock protein (hsp) synthesis. This heat-induced resistance to apoptosis suggests that thermotolerant cells have gained the capacity to prevent the onset of this pathway of self-destruction. An examination of this process in heated cells should provide new insights into the molecular basis of cellular thermotolerance.

Development of thermotolerance in hsp70 induction-defective mutant of NRK cells

We investigated the relation between the synthesis of inducible form of heat-shock protein 70 (hsp70) and the development of thermotolerance using NRK (normal rat kidney) cells and their mutant cell line (39-1 cells). In NRK cells, hsp70 was clearly induced by conditioning treatments (42 degrees C for 2 h, 45 degrees C for 15 min or 100 microM sodium arsenite for 1 h). On the other hand, the induction of hsp70 in 39-1 cells was very low or not detectable by these treatments. Other high molecular weight hsps, hsc70 (constitutive form), hsp90 and hsp110 were induced in both cell lines. However, thermotolerance as defined by clonogenic survival was induced in both cell lines to a similar extent by the conditioning treatments. When cells were made thermotolerant by conditioning heating at 45 degrees C for 15 min, the inhibition of protein synthesis after challenge (second) heating was less in NRK cells than in 39-1 cells. This indicated that the extent of 'translational thermotolerance' was much higher in NRK cells than in 39-1 cells. From these results, it is suggested that the synthesis of inducible hsp70 is involved in the translational thermotolerance rather than the development of thermotolerance as defined by clonogenic survival.

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

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

Heat shock protein induction in rat hearts. A role for improved myocardial salvage after ischemia and reperfusion?

BACKGROUND

To test the hypothesis that the heat shock response is associated with improved myocardial salvage after myocardial ischemia and reperfusion, rats treated with prior whole-body hyperthermia and 24 hours of recovery (n = 26) or 20 minutes of ischemic pretreatment and 8 hours of recovery (n = 24) and control rats (n = 27, n = 24, for hyperthermic and ischemic pretreatment, respectively) were subjected to 35 minutes of left coronary artery (LCA) occlusion and 120 minutes of reperfusion.

METHODS AND RESULTS

Although ventricular samples from rats subjected to either hyperthermia (n = 7) or ischemic pretreatment (n = 6) all showed induction of HSP72 (heat shock protein), Western blot analysis revealed significantly greater amounts of HSP72 in samples obtained from rats subjected to hyperthermia compared with those from rats subjected to ischemic pretreatment. Control rats (n = 7) showed no significant presence of myocardial HSP72. After 35 minutes of LCA occlusion and 2 hours of reperfusion, infarct size was significantly reduced in heat-shocked rats compared with controls (8.4 +/- 1.7%, n = 26 versus 15.5 +/- 1.9%, n = 27; p = 0.007; mean +/- SEM; infarct mass/left ventricular mass x 100). There were no significant differences in left ventricular (LV) systolic pressure, heart rate, LV dP/dt, or rate-pressure product between heat-shocked (n = 11) and control (n = 14) rats during the ischemic period. There were no differences in infarct size between ischemically pretreated and control rats subjected to 35 minutes of ischemia and reperfusion (9.7 +/- 2.1%, n = 23 versus 10.0 +/- 2.1, n = 24; p = NS).

CONCLUSIONS

In this model of ischemia and reperfusion, prior heat shock was associated with significantly improved myocardial salvage after 35 minutes of LCA occlusion and reperfusion. This improved salvage was correlated with marked HSP72 induction and was independent of the hemodynamic determinants of myocardial oxygen supply and myocardial oxygen demand during the ischemic period. In contrast, mild HSP72 induction by ischemic pretreatment was not associated with improved myocardial salvage after myocardial ischemia and reperfusion. Thus, the absolute levels of HSP72 may be important in conferring protection from ischemic injury in this animal model.

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

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

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

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

Hypothermia reduces 72-kDa heat-shock protein induction in rat brain after transient forebrain ischemia

BACKGROUND AND PURPOSE

We examined the influence of concurrent moderate hypothermia (30 degrees C) and transient forebrain ischemia on the induction of 72-kDa heat-shock protein and neuronal damage in male Wistar rats.

SUMMARY OF REPORT

Experimental groups included: normothermic with 8 minutes of transient forebrain ischemia (group 1, n = 7), hypothermic without ischemia (group 2, n = 9), and hypothermic (30 degrees C) with 8 minutes of transient forebrain ischemia (group 3, n = 5). Intense 72-kDa heat-shock protein immunoreactivity was demonstrated in rat forebrain 48 hours after induction of normothermic forebrain ischemia (group 1); it was not detected in the brain of animals subjected to hypothermia without ischemia (group 2), and hypothermia during ischemia (group 3) significantly inhibited its expression compared with that in normothermic ischemia animals (group 1).

CONCLUSIONS

These observations suggest that 72-kDa heat-shock protein induction is not the mechanism by which moderate hypothermia protects against ischemic cell damage.

The stress protein response in cultured neurons: characterization and evidence for a protective role in excitotoxicity

We used purified cultures of cerebellar granule cells to investigate the possible protective role of stress proteins in an in vitro model of excitotoxicity. Initial experiments used one- and two-dimensional polyacrylamide gel electrophoresis to confirm the induction of typical stress protein size classes by heat shock, sodium arsenite, and the calcium ionophore A23187. Immunoblot analysis and immunocytochemistry verified the expression of the highly inducible 72 kd heat shock protein (HSP72). Granule cell cultures exposed to glutamate showed evidence of cellular injury that was prevented by the noncompetitive NMDA antagonist MK-801, yet glutamate did not induce a detectable stress protein response. Nonetheless, preinduction of heat shock proteins was associated with protection from toxic concentrations of glutamate. These results imply that the HSP72 expression observed in in vivo models of excitotoxicity may not be directly related to the effects of excitatory amino acids. However, the ability of stress protein induction to protect against injury from glutamate may offer a novel approach toward ameliorating damage from excitotoxins.

The response of guinea pig airway epithelial cells and alveolar macrophages to environmental stress

Cells lining the respiratory tract form an interface between the organism and the external environment and are repeatedly exposed to physical, chemical, and metabolic stresses. We examined the response of cultured guinea pig tracheal epithelial cells and alveolar macrophages to various forms of stress, including clinically and environmentally relevant metabolic stresses such as ozone and acid exposure. Classic stress treatments such as heat shock and sodium arsenite treatment induced the synthesis of 28, 32, 72, 73, 90, and 110 kD stress proteins similar to those observed in other cell types. In contrast, no significant changes in the pattern of protein synthesis were detected after exposure to ambient concentrations of ozone, although ozone exposure caused significant cytotoxicity to both cell types. Another potent oxidant, hydrogen peroxide, similarly did not induce appreciable stress protein synthesis. However, surface acidification of tracheal epithelial cells and alveolar macrophages caused the induction of 72 and 78 kD stress proteins. While stress proteins may play a role in the response of respiratory cells to certain injuries such as hyperthermia and surface acidification, they may not be important in the defense against ozone or other forms of oxidative injury.

Axonal transport of two major components of the ubiquitin system: free ubiquitin and ubiquitin carboxyl-terminal hydrolase PGP 9.5

Ubiquitin (Ub), a stress protein thought to target abnormal proteins for degradation, is present in abnormal structures that occur in neuronal perikarya and axons of degenerative diseases including Alzheimer disease. To begin to assess the role of the Ub system in the axon, we studied expression and axonal transport of Ub and other stress proteins, as well as of Ub carboxyl-terminal hydrolase PGP 9.5, in the rat visual system in normal conditions and following heat-shock (HS). In the retina, both the constitutive and inducible forms of HSPs 70 were expressed under normal conditions, while in the superior colliculus the inducible form was detected only following HS. Ub, PGP 9.5 and HSPs 70 were transported in the axon exclusively with the slow component b (SCb), known to carry cytoskeletal and cytoplasmic proteins. The exceedingly long time needed for stress proteins to reach distant axonal locales at the rate of SCb (approximately 3 mm/day) makes it unlikely that they could contribute significantly to the stress response at those sites.

Stress protein synthesis by crayfish CNS tissue in vitro

Some crustacean axons remain functional for months after injury. This unusual property may require stress proteins synthesized by those neurons or provided to them by glial cells. To begin to explore this hypothesis, we examined the conditions that stimulated stress protein synthesis by crayfish CNS tissue in vitro. Incubation for 1-15 h with arsenite or at temperatures about 15 degrees C higher than the acclimation temperature of 20 degrees C induced transient expression of several stress proteins. The heat stress response was blocked by Actinomycin D, suggesting that synthesis of new mRNA was required. In addition, the major crayfish 66 kD stress protein and its mRNA had sequence identities with the 70 kD stress proteins of mammals. Since the crayfish stress response has much in common with that of other organisms, the unique advantages of the crayfish nervous system can be used to study the impact of stress proteins on glial and neuronal function.

Decreased heat- and tumor necrosis factor-mediated hsp28 phosphorylation in thermotolerant HeLa cells

Heat shock or tumor necrosis factor rapidly stimulated the phosphorylation of the mammalian low molecular weight stress protein hsp28. We have found that both phenomena are greatly decreased in cells which are made tolerant to heat. This observation correlated with a better survival of thermotolerant cells exposed to either heat or TNF treatment. The results suggest that the phosphorylation of hsp28 may be linked to the resistance of the cells to the deleterious effects induced by either heat or a mediator of inflammation such as TNF.

Induced tolerance to ischemia in gerbil hippocampal neurons

Brief ischemia induced tolerance to subsequent ischemia in the hippocampal neurons. Male Mongolian gerbils were subjected to 2 min of ischemia in an awake condition. This ischemic insult only rarely produced neuronal damage in the gerbil brain. One day (n = 9), 2 days (n = 9), or 4 days (n = 10) following the first brief ischemia, the animals (double-ischemia group) were subjected to the second ischemia for 5 min. The single-ischemia group received a sham procedure instead of the first ischemia and was identically subjected to the second ischemia 1 day (n = 9), 2 days (n = 10), and 4 days (n = 13) following the sham procedure. One week following the second ischemia, all gerbils were perfusion fixed and the neuronal density in the hippocampal CA1 sector was measured. In double-ischemia groups, the neuronal density per 1-mm length of the pyramidal cell layer was 103.4 +/- 93.1 (SD) in the 1-day subgroup, 125.6 +/- 64.2 in the 2-day subgroup, and 176.2 +/- 93.7 in the 4-day subgroup, while the density in normal gerbils was 254.7 +/- 18.6. The average neuronal density in the single-ischemia group was much lower than that in the double-ischemia group (whole control group: 10.9 +/- 27.4). Immunostaining using monoclonal antibody raised against 70-kDa heat-shock protein revealed an increase in 70-kDa heat-shock protein in the CA1 area following 2 min of ischemia. Very brief ischemia induces heat-shock proteins and, presumably, thereby renders neurons more tolerant to subsequent metabolic stress.

Effect of L-azetidine 2-carboxilic acid on the activity of the general amino-acid permease from Saccharomyces cerevisiae var. ellipsoideus

Addition of the L-proline analogue L-azetidine 2-carboxylic acid to growing cultures of Saccharomyces cerevisiae var. ellipsoideus promoted fast deactivation of the general aminoacid permease, measured as L-valine uptake, without an immediate decrease in the growth rate. Cells preincubated with the analogue for 3 h were unable to restore either growth ability or general aminoacid permease activity in analogue-free medium. Eadie-Hofstee plots of L-valine uptake in the presence of the analogue are consistent with a strong reduction in the number of active molecules of the general amino-acid permease located in the plasma membrane. Inhibitory effects on protein synthesis were seen after preincubations of the yeast with the analogue for 3 h although a 30 min preincubation had no effect.