Competitive inhibition of hsp70 gene expression causes thermosensitivity

Induction of HSP70 is associated with vincristine resistance in heat-shocked 9L rat brain tumour cells

The most prominent cellular changes in heat-shock response are induction of HSPs synthesis and reorganisation of cytoskeleton. Vincristine was used as a tool to evaluate the integrity of microtubules in 9L rat brain tumour cells recovering from heat-shock treatment. Cells treated at 45 degrees C for 15 min and recovered under normal growing condition became resistant to vincristine-inflicted cytotoxicity and microtubule destruction. Among all HSPs, the level of HSP70 and the degree of vincristine resistance are best correlated. HSP70 and tubulin were found to be associated with each other as they were co-immunoprecipitated by either anti-HSP70 or anti-beta-tubulin monoclonal antibody. The current studies establish for the first time that HSP70 can complex with tubulin in cells and this association may stabilise the organisation of microtubules thus protect the heat-treated cells from vincristine damage. These findings are noteworthy in combining hyperthermia and chemotherapy in the management of malignant diseases.

Accumulation of heat shock protein 72 (hsp 72) in postimplantation rat embryos after exposure to various periods of hyperthermia (40 degrees -43 degrees C) in vitro: evidence that heat shock protein 72 is a biomarker of heat-induced embryotoxicity

A monoclonal antibody to the 72 kDa heat shock protein and Western blot analysis were used to determine the induction, accumulation and turnover of hsp 72 after day 10 rat embryos were exposed to elevated temperatures (40 degrees-43 degrees C) for various lengths of time (2.5 minutes to 18 hours). Embryos exposed to temperatures that exceed the normal culture temperature (37 degrees C) by 4 degrees C or more for as little as 2.5 minutes (43 degrees C) or 15 minutes (41, 42 degrees C) synthesized and accumulated detectable amounts of heat-inducible hsp 72. Hsp 72 could not be detected by Western blot analysis of proteins from embryos cultured at 40 degrees C or below. Once induced, hsp 72 can be detected in embryos for 24-48 hours after they are removed from the hyperthermic conditions and returned to normothermic conditions. Our results also indicate that hsp 72 is induced by all hyperthermic exposures that induce alterations in rat embryo growth and development; therefore, hsp 72 is a potential biomarker for heat-induced embryotoxicity.

Reduction in heat shock gene expression correlates with increased thermosensitivity in senescent human fibroblasts

The expression of three major classes of heat shock genes was examined in human diploid cells at differing in vitro ages. Metabolic labeling of cellular proteins following a brief heat shock showed that the synthesis of heat shock proteins was significantly reduced in late-passage cells. Northern blot analyses revealed that the reduced expression of heat shock proteins in old cells correlated with a reduced accumulation of heat shock-specific transcripts. The attenuation of heat shock gene activity in senescent cells was not unique to thermal stress since exposure of cells to sodium arsenite (10-50 microM) elicited a similar response. The reduced expression of heat shock gene products correlated with an increased thermal lability in late-passage cells following acute hyperthermic (49 degrees C) exposure. The preinduction of heat shock genes protected cells against the lethal effects of acute hyperthermia and abolished the increased thermal lability observed in senescent cells. The reduced expression of the heat shock response demonstrates that old cells possess a diminished ability to withstand adverse environmental conditions and maintain homeostasis.

Genetic differences in heat-induced tolerance to cadmium in cultured mouse embryos are not correlated with changes in a 68-kD heat shock protein

Heat-induced cross-tolerance to cadmium was investigated in two inbred strains of mice, BALB/c and SWV, using a whole embryo culture system. Embryos were exposed to a pretreatment of 5 min at 43 degrees C and subsequently to an embryotoxic concentration of cadmium, 1.75 microM. The two types of embryos responded differently to the heat pretreatment, as cross-tolerance was induced in SWV but not in BALB/c mice. In SWV embryos, prior exposure to 43 degrees C for 5 min essentially eliminated the negative effects of cadmium on embryonic development and growth. However, in BALB/c embryos, no protection was observed. The variation in development of cross-tolerance in embryos from the two strains of mice was not correlated with differences in the induction of a 68-kD heat-shock protein (hsp68). There was a rapid increase in this protein in both strains after the initial heat exposure but not excess induction in the SWV strain that developed tolerance. The induction of hsp68 is therefore not sufficient to elicit cross-tolerance, and other mechanisms are likely to be important in the protective response of the embryo.

The consequences of expressing hsp70 in Drosophila cells at normal temperatures

In Drosophila cells, regulatory mechanisms not only act to provide rapid induction of hsp70 during heat shock but also to prevent expression at normal temperatures. To determine whether expression of hsp70 is detrimental to cells growing at normal temperatures, we used heterologous promoters to force expression of the protein in tissue culture cells and in larval salivary glands. Initially, constitutive expression of hsp70 substantially reduces the rate of cell growth. With continued expression, however, growth rates recover. At the same time, the intracellular distribution of hsp70 changes. Immediately after induction, the protein is diffusely distributed throughout the cell, but as growth resumes it coalesces into discrete points of high concentration, which we term hsp70 granules. hsp70 granules are also observed both in wild-type Drosophila tissue culture cells and in salivary glands after extended periods of recovery from heat shock. The protein in these granules appears to be irreversibly inactivated. It cannot be dispersed with a second heat shock, and cells containing these granules do not show thermotolerance. Only partial overlap between hsp70 granules and lysosomes indicates that the granules form independently of lysosomes. We conclude that expression of hsp70 is detrimental to growth at normal temperatures. We suggest that the change in hsp70 distribution, from diffuse to granular, represents a mechanism for controlling the protein's activity by sequestration.

Emerging role of heat shock proteins in biology and medicine

All cells, procaryotic and eucaryotic, respond to an elevation in temperature by increasing the synthesis of a family of proteins collectively known as heat shock proteins (HSPs). HSPs are among the most highly conserved and abundant proteins in nature. Studies on the regulation of the synthesis of HSPs have for several years shed light on the mechanisms regulating gene expression. The results from recent years, showing that HSPs play crucial roles in a wide variety of normal cellular processes, has made them an object of even broader interest, first to molecular and cellular biologists and later to specialists in various fields of medicine including oncology, immunology, infectious disease, autoimmunity, embryology, neurology and endocrinology. The aim of this review is to briefly summarize our present knowledge of the regulation of the heat shock response and the structure of the relevant gene products, HSPs. Moreover, some of the exciting associations between HSPs and various fields of medicine will be discussed.

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

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

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.

Effects of culture temperature on the expression of heat-shock proteins in murine ts85 cells

The murine temperature-sensitive cell-cycle mutant, ts85, shows an abnormal induction of heat-shock proteins which is different from the wild type FM3A cells. This paper explores the effect of culture temperature on the expression of heat shock proteins in ts85 cells. When ts85 cells were maintained at 33 or 37 degrees C, these cells synthesized heat-shock protein (hsp) 70 following continuous heating at 39 degrees C or subsequent incubation after heating at 42 degrees C for 15 min. In contrast, these conditions are not conducive for hsp70 synthesis by FM3A cells. Moreover, ts85 cells which were maintained at 37 degrees C synthesized hsp70 following continuous heating at 42 degrees C or subsequent incubation after heating at 45 degrees C for 15 min. The synthesis of hsp70 in these cells corresponded to an increased level of hsp70 mRNA. Furthermore, the constitutive hsp105 level of cells maintained at 33 degrees C was only half of that of cells which were maintained at 37 degrees C, and cells maintained at 33 degrees C were more sensitive to subsequent heat treatment than those maintained at 37 degrees C. These results indicate that culture temperature not only affects the induction of hsp70 mRNA, but also cellular levels of hsp105 and the resulting thermal sensitivity of ts85 cells. These findings suggest that the other phenotypic characteristic of the mutant ts85 cells is also affected by culture temperature.

Evidence for heterophilic adhesion of embryonic retinal cells and neuroblastoma cells to substratum-adsorbed NCAM

The adhesion of embryonic chicken retinal cells and mouse N2A neuroblastoma cells to purified embryonic chicken retinal NCAM adsorbed on a solid substratum was examined using a quantitative centrifugal adhesion assay. Both cell types adhered to NCAM and the adhesion was specifically inhibited by monovalent anti-NCAM antibody fragments. N2A cell adhesion depended on the amount of NCAM applied to the substratum, was cation independent, and was insensitive to treatment with the cytoskeletal perturbing drugs colchicine and cytochalasin D. These results indicated that the tubulin and actin cytoskeletons were not critically required for adhesion to NCAM and make it unlikely that the cell surface ligand for NCAM is an integrin. Adhesion was however temperature dependent, strengthening greatly after a brief incubation at 37 degrees C. CHO cells transfected with NCAM cDNAs did not adhere specifically to substratum-bound NCAM and pretreatment of N2A cells and retinal cells with anti-NCAM antibodies did not inhibit adhesion to substratum-bound NCAM. These results suggest that a heterophilic interaction between substratum-adsorbed NCAM and a non-NCAM ligand on the surface of the probe cells affects adhesion in this system and support the possibility that heterophilic adhesion may be a function of NCAM in vivo.

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.

Distribution of constitutive- and hyperthermia-inducible heat shock mRNA species (hsp70) in the Purkinje layer of the rabbit cerebellum

In previous studies we have analyzed the effect of hyperthermia on the expression of hsp70 genes in the rabbit cerebellum using an hsp70 riboprobe which hydridized to both constitutively expressed and stress-inducible transcripts. These studies have now been extended utilizing riboprobes which are able to discriminate hyperthermia-inducible hsp70 mRNA of size 2.7 kb and constitutively expressed mRNA of size 2.5 kb. In situ hybridization with the inducible specific riboprobe revealed a prominent induction of the 2.7 kb species 1 hr after a 2-3 degrees C increase in body temperature in the following cerebellar cell types: i) Bergmann glial cells in the Purkinje layer, ii) glial cells in deep white matter fiber tracts and iii) granule neurons. The inducible transcript was not detected in the cerebellum of control animals. The constitutive specific riboprobe detected the 2.5 kb transcript in several neuronal cell types of the cerebellum such as Purkinje and granule neurons with little increase in signal in hyperthermic animals compared to controls.

High constitutive expression of heat shock protein 90 alpha in human acute leukemia cells

The constitutive expression of the genes for four heat shock proteins (hsps) was studied in leukemia cell lines, cells obtained from patients with acute leukemia, and normal blood cells by means of Northern-blot analysis. Western-blot analysis with hsp90 antibody showed that the leukemia cells contained larger amounts of hsp90 than the normal peripheral mononuclear cells. The expression of the hsp90 alpha gene was enhanced in the leukemia cell lines and the acute leukemia cells from patients as compared with the normal blood cells. In contrast, the expression of the hsp90 beta gene could hardly be recognized in either the acute leukemia cells or the normal blood cells. An increased expression of hsp70 gene was observed in only one patient. The expression of the hsp27 gene was enhanced in one-half the patients with common acute lymphoblastic leukemia. Thus, exclusively the hsp90 alpha gene was expressed highly in the leukemia cells, indicating its association with cellular proliferation.

Induction of the 72-kD heat shock protein in organ-cultured normal human skin

To study the induction of heat shock protein (HSP) of normal human skin, the indirect immunofluorescence method, using monoclonal antibody directed against 72-kD HSP, was applied in organ-cultured normal human skin that was treated with heat, UV, or chemicals. The present study provided new evidence that HSP 72 was induced not only by heat and chemical agents, such as L-azetidine 2-carboxylic acid, and sodium arsenite, but also by ultraviolet (UV B and C). The result suggests that normal human skin has an induced protective function against numerous environmental stresses.

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.

Expression of heat shock genes (hsp70) in the rabbit spinal cord: localization of constitutive and hyperthermia-inducible mRNA species

We have previously reported that hyperthermia induces the expression of a heat shock gene in the rabbit brain (Sprang and Brown, Mol Brain Res 3:89-93, 1987). Striking regional and cell type differences in the pattern of induction of the hsp70 mRNA were noted. Tissue injury also induces the rapid induction of hsp70 mRNA in the mammalian brain (Brown et al., Neuron 2:1559-1564, 1989). In the present study, in situ hybridization with 35S-labelled riboprobes specific for constitutive and inducible hsp70 mRNA species was employed to investigate the effect of fever-like temperatures on hsp70 gene expression in the rabbit spinal cord. Expression of constitutive hsp70 mRNA was detected in large motor neurons of both control and hyperthermic animals. Within 1 hr after hyperthermia, a massive induction of inducible hsp70 mRNA was noted in fibre tracts of the spinal cord, a pattern consistent with a strong glial response to heat shock. Induction was not observed in the large motor neurons.

Induction of constitutive heat shock protein 73 mRNA in the dentate gyrus by seizures

We examined the effects of generalized seizures on heat shock protein (hsp) mRNA induction in the rat brain using in situ hybridization. Seizures induced by electroconvulsive shock, electrical or cocaine kindling caused a selective induction of the constitutive hsp 73 gene in the dentate gyrus. In these seizure paradigms, not thought to induce widespread tissue damage, neither the heat-inducible hsp 72 gene nor a member of the hsp 90 family (hsp 84) were induced. Hsp 73 may play a role in the adaptation and/or in the maintenance of dentate granule cell integrity following seizures.

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.

Immunocytochemical detection of the 72-kDa heat shock protein in halothane--induced hepatotoxicity in rats

Liver sections removed from phenobarbital induced rats 24 to 48 hours after a 2 hour exposure to 1.0% halothane with 10% oxygen and subjected to immunocytochemical treatment showed evidence of centrilobular damage as well as evidence of the production of a protein which has immunoreactivity with anti HSP 72 antibodies. The cells showing evidence of immunoreactivity were within the area of the centrilobular lesion. The level of immunoreactive protein varied directly with the intensity of the lesion. Liver sections from animals treated with phenobarbital alone, phenobarbital plus 10% oxygen, or phenobarbital plus 20% oxygen and 1.0% halothane all were without lesions as well as the immunoreactive protein.

Characterization of the major 68 kDa heat shock protein in a rat transformed astroglial cell line

The heat shock response in a transformed astrocyte line was compared with nontransformed astrocytes. The synthesis of HSP 68, the major inducible heat shock protein (HSP 68) was induced by a non-lethal 45 degrees C, 10 min heat shock. Although the incorporation of [35S]methionine into HSP 68 suggested that similar amounts of protein were being synthesized after heat shock, Western immunoblotting demonstrated striking differences in the HSP immunostaining between the two cell types. By one- and 'two-dimensional gel electrophoresis the major 68 kDa heat shock protein (HSP 68) was similar in both cell types. However, HSP 68 from heat shocked, transformed astrocytes did not immunostain with the monoclonal antibody, C-92, which is specific for the major inducible heat shock protein of HeLa cells. In contrast HSP 68 from heat shocked, nontransformed astrocytes immunostained quite well. A polyclonal antibody raised against the inducible 72 kDa heat shock protein of HeLa cells immunostained the HSP 68 from both astrocytes and transformed astrocytes. Analysis of the mRNA from the two cell types after heat shock revealed two bands of approximately 2.5 and 2.8 kb in astrocytes but only a single 2.5 kb band in the heat shocked transformed astroglia. These results suggest that structural differences in the HSP 68 may be present in the transformed astrocytes compared to the normal astrocytes.

Axon-glia exchange of macromolecules

The periaxonal and perineurial glia of crayfish and squid are strategically situated to regulate the neuronal microenvironment. Diverse molecules rapidly traverse the periaxonal sheath and a fraction of them enters the axons from glia or the glia from axons. The significance of these intercellular exchanges has not been tested directly. However, recent reports suggest that stress proteins, which probably are synthesized by both types of glia and transferred to axons, may be essential components by which the glia directly and indirectly assist neurons in tolerating ambient stress.

Heat shock protects cultured neurons from glutamate toxicity

Expression of heat shock proteins (HSPs) occurs in brain after ischemia and status epilepticus. We report that induction of the heat shock response in cortical cultures protects neurons from glutamate-induced excitotoxicity. Cultures heated to 42.2 degrees C for 20 min showed an overall decrease in protein synthesis but an increase in the synthesis of approximately 72 and approximately 85 kd proteins and in the levels of HSP70 mRNA. Heat shock inhibited excitotoxicity in cells exposed to glutamate at 3 or 24 hr following heat exposure, but not when the interval between heat and glutamate exposure was shortened to 15 min or lengthened to 48 hr. Protection due to heat shock required new protein synthesis, since it did not occur when protein or RNA synthesis inhibitors were added. By ameliorating excitotoxic processes, HSPs may attenuate brain injury in certain pathologic conditions.

Competitive inhibition of a set of endoplasmic reticulum protein genes (GRP78, GRP94, and ERp72) retards cell growth and lowers viability after ionophore treatment

GRP78, a 78-kDa protein localized in the endoplasmic reticulum (ER), has been implicated in protein processing and stress protection. Its promoter contains a 36-bp region which is conserved among GRP genes across species and has the ability to compete for trans-acting factors mediating GRP gene expression. Integration of about 800 tandem copies of this sequence into the genome of a Chinese hamster ovary cell line (DG44) results in transfectants with the following phenotypes: (i) the induction level of GRP78 by the calcium ionophore A23187 and tunicamycin is reduced 4- and 2-fold, respectively, (ii) the induction levels of two other ER luminal protein genes, GRP94 and ERp72, are simultaneously down-regulated, (iii) the growth rate of these cells is half that of transfectants without the amplified sequence, and (iv) cell viability is decreased by 25-fold after A23187 treatment. These results provide new evidence that ERp72 shares common trans-acting regulatory factors with the GRP genes and that a reduction of this set of ER proteins correlates with lower viability after ionophore treatment.

Competitive inhibition of a set of endoplasmic reticulum protein genes (GRP78, GRP94, and ERp72) retards cell growth and lowers viability after ionophore treatment

GRP78, a 78-kDa protein localized in the endoplasmic reticulum (ER), has been implicated in protein processing and stress protection. Its promoter contains a 36-bp region which is conserved among GRP genes across species and has the ability to compete for trans-acting factors mediating GRP gene expression. Integration of about 800 tandem copies of this sequence into the genome of a Chinese hamster ovary cell line (DG44) results in transfectants with the following phenotypes: (i) the induction level of GRP78 by the calcium ionophore A23187 and tunicamycin is reduced 4- and 2-fold, respectively, (ii) the induction levels of two other ER luminal protein genes, GRP94 and ERp72, are simultaneously down-regulated, (iii) the growth rate of these cells is half that of transfectants without the amplified sequence, and (iv) cell viability is decreased by 25-fold after A23187 treatment. These results provide new evidence that ERp72 shares common trans-acting regulatory factors with the GRP genes and that a reduction of this set of ER proteins correlates with lower viability after ionophore treatment.

Constitutive expression of heat-shock protein 70 in mammalian cells confers thermoresistance

A 70-kDa heat-shock-protein (hsp 70) expression vector which contains the human hsp 70 gene linked to the human beta-actin promoter, was constructed and used to transfect CV1 monkey cells. Stably transfected CV1 clones were isolated which constitutively synthesized increased amounts of hsp70 at normal temperature. It is shown that these clones are resistant to elevated temperature. This finding indicates that hsp70 is involved in the protection of the cells against a lethal heat treatment and maybe responsible for the phenomenon of thermotolerance.

Heat shock protein hsp72 induction in cortical and striatal astrocytes and neurons following infarction

Transient global and transient focal ischemia induced the 72 kDa heat shock protein (hsp72) in neurons in cortex, striatum, and other regions known to be injured during transient ischemia. A novel finding was the induction of hsp72 in islands (cylinders in three dimensions) of cells composed of astrocytes around the perimeter and neurons in the interior. Since histology showed pale staining in these regions, it is proposed that these islands represent areas of focal infarction in the distribution of small cortical and lenticulostriate arteries. Although the factors responsible for hsp72 induction during ischemia and infarction are unknown, these results suggest differences in mechanisms of hsp72 induction in astrocytes compared to neurons.

Expression of heat shock protein 70 and heat shock cognate 70 messenger RNAs in rat cortex and cerebellum after heat shock or amphetamine treatment

The expression of strictly inducible hsp70 mRNAs and constitutively expressed hsc70 mRNAs was compared in cerebellum and cerebral cortex of control rats, heat-shocked rats, and rats made hyperthermic with amphetamine. An hsc70-specific oligonucleotide probe identified a 2.55-kb mRNA in cerebellum and cerebral cortex of all rats. An hsp70-specific oligonucleotide probe identified a 3.05-kb mRNA and a 3.53-kb mRNA in cerebellum and cerebral cortex of heat-shocked and amphetamine-treated rats, but not in control rats. Quantitation demonstrated that both hsp70 and hsc70 mRNA levels, relative to 18S rRNA levels, were increased following each treatment. The relative levels of both mRNAs were higher in cerebellum than in cerebral cortex. In amphetamine-treated rats, hsc70 mRNA relative levels increased at body temperatures greater than 39 degrees C, whereas hsp70 mRNA synthesis was induced at temperatures greater than 40 degrees C. Total thermal response values and relative levels of both mRNAs were compared. The results suggested that both the transcription and turnover of hsp70 mRNAs differed between cerebellum and cerebral cortex. At equivalent total thermal response values, amphetamine-treated rats had higher relative levels of hsp70 mRNAs than heat-shocked rats, suggesting that amphetamine enhanced the induction of hsp70 mRNAs.

Characterization of the Heat Shock Response in Lactococcus lactis subsp. lactis

The heat shock response in Lactococcus lactis subsp. lactis was characterized with respect to synthesis of a unique set of proteins induced by thermal stress. A shift in temperature from 30 to 42°C was sufficient to arrest the growth of L. lactis subsp. lactis , but growth resumed after a shift back to 30°C. Heat shock at 50°C reduced the viable cell population by 10 3 ; however, pretreatment of the cells at 42°C made them more thermoresistant to exposure at 50°C. The enhanced synthesis of approximately 13 proteins was observed in cells labeled with 35 S upon heat shock at 42°C. Of these heat shock-induced proteins, two appeared to be homologs of GroEL and DnaK, based on their molecular weights and reactivity with antiserum against the corresponding Escherichia coli proteins. Therefore, we conclude that L. lactis subsp. lactis displays a heat shock response similar to that observed in other mesophilic bacteria.

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.

Phosphorylation of HSP27 during development and decay of thermotolerance in Chinese hamster cells

The small molecular weight heat shock protein HSP27 was recently shown to confer a stable thermoresistant phenotype when expressed constitutively in mammalian cells after structural gene transfection. These results suggested that HSP27 may also play an important role in the development of thermotolerance, the transient ability to survive otherwise lethal heat exposure after a mild heat shock. In Chinese hamster O23 cells increased thermoresistance is first detected at 2 h after a triggering treatment of 20 min at 44 degrees C, attains a maximum at 5 hours, and decays thereafter with a half-life of 10 h. We found that the development and decay of transient thermotolerance cannot be solely explained on the basis of changes in the cellular concentration of HSP27. The cellular HSP27 concentration is not increased appreciably at 2 h after heat shock and attains a maximum at 14 h. Similar results were obtained in the case of another heat shock protein, HSP70. HSP70 follows slightly faster kinetics of accumulation (peaks at 10 h) and decays much more rapidly (ti/2 = 4h) than HSP27 (t1/2 = 13h). HSP27 has 3 isoelectric variants A, B, and C of which B and C are phosphorylated. In cells maintained at normal temperature, HSP27A represents more than 90% of all HSP27. Shifting the cell culture temperature from 37 to 44 degrees C induces the incorporation of 32P into the more acidic B and C forms, a process that occurs very rapidly since the reduction in the concentration of the A form and a corresponding increase in the level of B and C is detectable by immunoblot analysis within 2.5 min at 44 degrees C. Analyses performed at various times during development and decay of transient thermotolerance revealed a close relationship between the effect of heat shock on HSP27 phosphorylation and cell ability to survive. For example, fully thermotolerant cells (5 h post-induction) are refractory to induction of HSP27 phosphorylation by a 20-min heat shock. The induction of HSP27 phosphorylation was also studied in a family of clonal cell lines of O23 cells that are thermoresistant as a result of the constitutive expression of a transfected human HSP27 gene. In these thermoresistant cells, phosphorylation of the endogenous hamster HSP27 is induced to a level comparable to that found in the thermosensitive parental cells. However, phosphorylation of the exogenous human protein, which represents more than 80% of total HSP27 in these cells, was much less induced.(ABSTRACT TRUNCATED AT 250 WORDS)

Heat shock in cultured neurons and astrocytes: correlation of ultrastructure and heat shock protein synthesis

Cultured cerebral cortical neurons and astrocytes were compared after a brief shock. Morphological findings were correlated with the synthesis of the 68 kD heat shock protein (HSP68). Heat shocked neurons demonstrated many severe morphological changes after exposure to temperatures of 43 degrees C for 15 min and 45 degrees C for 10 min. Nuclear membrane 'blebbing' with lysis of the membrane, chromatin clumping, and disappearance of the nucleolus were prominent after both conditions. Lysis of the cell membrane was noted in severely injured neurons; this was more prominent at the higher temperature. In addition, alterations to polyribosomes, Golgi apparatus, rough endoplasmic reticulum and mitochondria were noted in the cytoplasm of neurons after heat shock. In contrast, no significant changes were noted in either the nucleus or cytoplasm of heat shocked astrocytes. The severity of morphological changes in neurons directly correlated with the low level of induction of HSP68 in neurons. Neurons synthesized much less 68 kD heat shock protein than similarly heat shocked astrocytes. We conclude that cultured cerebral cortical neurons are more susceptible to injury after heat shock than heat resistant astrocytes and that one possible mechanism of injury is failure to synthesize adequate amounts of HSP68 after injury.

Role of glutathione and hsp 70 in the acquisition of thermotolerance in postimplantation rat embryos

Studies were initiated to determine the extent to which reduced glutathione (GSH) may be involved in the capacity of cultured rat embryos to develop heat-induced tolerance to the deleterious effects of exposure to high temperatures (heat shock). Investigations of the modulation of dysmorphogenic responses of embryos to heat shock (43 degrees C, 30 min) as well as to the expression of the hsp70 gene and subsequent formation of hsps indicated that the acquisition of thermotolerance by rat embryos could be significantly influenced by the inhibition of GSH synthesis. Treatment of conceptuses with L-buthionine-S,R-sulfoximine (BSO) reduced intracellular GSH concentrations and compromised the capacity of embryos to mount a thermotolerance response as assessed by alterations in indices of growth and development. Embryonic thermotolerance elicited by preexposure to 42 degrees C for 30 min was accompanied by increases in GSH to levels greater than those measured in control embryos at 37 degrees C just prior to the subsequent 43 degrees C heat exposure. Expression of hsp70 mRNA was detectable soon after elevation of the temperature to 42 degrees C and reached its highest level of accumulation 1.5 hr after the 43 degrees C heat shock. BSO treatment had little if any effect on hsp70 message levels or on the synthesis of hsp70. The fact that BSO-treatment attenuated the thermotolerance response but did not produce a decrease in hsp70 RNA or the synthesis of hsp70 suggests that hsp70 alone is not sufficient to confer thermotolerance upon cultured rat embryos.

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.

Thermal response of rat fibroblasts stably transfected with the human 70-kDa heat shock protein-encoding gene

The major heat shock protein hsp70 is synthesized by cells of a wide variety of organisms in response to heat shock or other environmental stresses and is assumed to play an important role in protecting cells from thermal stress. We have tested this hypothesis directly by transfecting a constitutively expressed recombinant human hsp70-encoding gene into rat fibroblasts and examining the relationship between the levels of human hsp70 expressed and thermal resistance of the stably transfected rat cells. Successful transfection and expression of the gene for human hsp70 were characterized by RNA hybridization analysis, two-dimensional gel electrophoresis, and immunoblot analysis. When individual cloned cell lines were exposed to 45 degrees C and their thermal survivals were determined by colony-formation assay, we found that the expression of human hsp70 conferred heat resistance to the rat cells. These results reinforce the hypothesis that hsp70 has a protective function against thermal stress.

Regulation of heat shock protein synthesis in rat astrocytes

Rat forebrain astrocytes synthesize heat shock proteins with molecular weights 97, 89, 70, 68, and 30-34 kilodaltons. The stress inducible 68-kDa heat shock protein (HSP-68) was vigorously expressed by astrocytes in culture after a 45 degrees C, 20 min heat shock. HSP-68 synthesis was poorly inducible by a second heat shock given 16 hr after the initial heat shock. Decreased [35S]methionine incorporation into HSP-68 correlated with low levels of HSP-68 mRNA present after the second heat shock. The data suggest that control of HSP-68 mRNA levels by transcriptional/posttranscriptional mechanisms is a major site for regulation of HSP-68 synthesis.

Thermolability of mouse oocytes is due to the lack of expression and/or inducibility of Hsp70

Eukaryotic and prokaryotic cells have been shown to respond to physical and chemical stress by the induction of proteins called heat shock proteins. Heat shock protein 70 (Hsp70), is the most ubiquitous of these proteins. Although heat shock proteins are generally thought to protect cells from physiologically stressful stimuli, it cannot be assumed that this is so, because several cases exist in which thermotolerance is acquired without the production of heat shock proteins, and in several other cases the hyperproduction of these heat shock proteins does not produce thermotolerance. In this study we show that unfertilized mouse oocytes are sensitive to elevated temperatures, and that the synthesis of Hsp70 cannot be induced in these oocytes. Furthermore, our data demonstrate that the expression of Hsp70 in mouse oocytes is sufficient for the acquisition of thermotolerance. Mouse oocytes were injected with mRNA for Hsp70, and the viability of these oocytes was determined after heating. The number of viable oocytes was significantly higher in the group injected with Hsp70 mRNA and then heated compared with oocytes injected with Hsp70 antisense mRNA and sham-injected controls treated in an identical manner. No significant differences in the number of viable oocytes were found between the group that had been injected with Hsp70 mRNA, heated, and then allowed to recover for 3 hr and the group maintained at 37 degrees C throughout.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

Comparison of the heat shock response in cultured cortical neurons and astrocytes

Cultured cortical neurons and astrocytes were compared for synthesis of the major inducible 68 kDa heat shock protein. By one- and two-dimensional electrophoresis the inducible 68 kDa protein appeared similar, but astrocytes produced greater amounts of the protein by 3 h than did neurons. Antibodies raised against HeLa cell inducible 72 and constitutive 73 kDa heat shock proteins were used to characterizes the inducible heat shock proteins in neurons and astrocytes. Unlike the gels, major differences were noted of the major inducible heat shock protein in astrocytes compared with neurons when analyzed by Western immunoblots. Heat shock protein 68 kDa mRNA induction in neurons was less than astrocytes suggesting an attenuated inducible 68 kDa heat shock protein response in neurons. The neuronal protein may be a different isoform of the 70 kDa family of heat shock proteins.