Heat shock is lethal to fibroblasts microinjected with antibodies against hsp70

Thermotolerance and the heat shock response in normal human keratinocytes in culture

Protective responses of normal human epidermal keratinocytes in culture, after exposure to elevated temperatures ("heat shock"), were examined. Cell viability, measured 24-48 h after a 20-min heat challenge at temperatures between 37 degrees C and 54 degrees C, declined sharply within a narrow 2 degrees-3 degrees C range. However, conditioning with a mild thermal pretreatment (40 degrees C or 42 degrees C for 1 h) protected the keratinocytes against a subsequent heat challenge. This induced thermotolerance was apparent when cells were challenged at 1, 3, and 6 h after the thermal pre-treatment, but disappeared by 24 h. Heating conditions that induce thermotolerance also stimulated the synthesis of heat-shock proteins (hsp) in these cells. Inductions of prominent 35S-methionine labeled bands at 70, 78, and 90 kDa were observed. However, the increases in synthesis of these heat-shock proteins did not correlate well with thermotolerance, because large increases were also observed at certain elevated temperatures that did not produce improved survival. Keratins observed in these cells (50 and 58 kDa classes) were not induced by heat shock. The development of thermotolerance, and the induction of hsp, were both completely blocked by 3'-deoxyadenosine (cordycepin), an inhibitor of newly synthesized messenger RNA, but not by adenosine, the normal analog. While heat-inducible mRNA apparently mediate some function important for the development of thermotolerance, the nature of that role remains speculative. Overall, our findings establish the existence of a functional thermal protective mechanism in human keratinocytes that appears to require the synthesis of new mRNA.

T lymphocyte stress response. II. Protection of translation and DNA replication against some forms of stress by prior hyperthermic stress

We have compared the effects of a mild heat shock and febrile temperatures on heat-shock protein (hsp) synthesis and development of stress tolerance in T lymphocytes. Our previous studies demonstrated that febrile temperatures (less than or equal to 41 degrees C) induced the synthesis of hsp110, hsp90, and the constitutive or cognate form of hsp70 (hscp70; a weak induction of the strongly stress-induced hsp70 was also observed. In the studies reported herein, we demonstrate that a mild heat shock (42.5 degrees C) reverses this ratio; that is, hsp70 and not hscp70 is the predominate member of this family synthesized at this temperature. Modest heat shock also enhanced the synthesis of hsp110 and hsp90. In order to assess the relationship between hsp synthesis and the acquisition of thermotolerance, purified T cells were first incubated at 42.5 degrees C (induction temperature) and then subsequently subjected to a severe heat-shock challenge (45 degrees C, 30 min). T cells first incubated at a mild heat-shock temperature were capable of total protein synthesis at a more rapid rate following a severe heat shock than control cells (induction temperature 37 degrees C). This phenomenon, which has been previously termed translational tolerance, did not develop in cells incubated at the febrile temperature (induction temperature 41 degrees C). Protection of translation also extended to immunologically relevant proteins such as interleukin-2 and the interleukin-2 receptor. Because clonal expansion is a critical event during an immune response, the effects of hyperthermic stress on DNA replication (mitogen-induced T cell proliferation) was also evaluated in thermotolerant T cells. DNA synthesis in control cells (induction temperature 37 degrees C) was severely inhibited following heat-shock challenge at 44 degrees C or 45 degrees C; in contrast, T cells preincubated at 42.5 degrees C rapidly recovered their DNA synthetic capacity. T cells preincubated at a febrile temperature were moderately protected against hyperthermic stress. The acquisition of thermotolerance was also associated with enhanced resistance to chemical (ethanol)-induced stress but not to heavy metal toxicity (cadmium) or dexamethasone-induced immunosuppression. These studies suggest that prior hsp synthesis may protect immune function against some forms of stress (e.g., febrile episode) but would be ineffective against others such as elevated glucocorticoid levels which normally occur during an immune response.

Induction of heat shock (stress) genes in the mammalian brain by hyperthermia and other traumatic events: a current perspective

Is the heat shock response physiologically relevant? For example, following hyperthermia or ischemia, what neural cell types show induction of heat shock genes and what is the time course of the effect? Initial experiments in this area demonstrated the prominent induction of a 70 kDa heat shock protein (hsp70) when labeled brain proteins isolated from hyperthermic animals were analyzed. Recently, in situ hybridization and immunocytochemistry have been utilized to map out the pattern of expression of both constitutively expressed and stress-inducible members of the hsp70 multigene family. Different types of neural trauma have been found to induce characteristic cellular responses in the mammalian brain with regard to the type of brain cell that responds by inducing hsp70 and the timing of the induction response. Fever-like temperature causes a dramatic induction of hsp70 mRNA within 1 hr in fiber tracts of the forebrain and cerebellum, a pattern consistent with a strong glial response to heat shock. Tissue injury, namely, a small surgical cut in the cerebral cortex, induces a rapid and highly localized induction of hsp70 mRNA in cells proximal to the injury site. Using an immunocytochemical approach, a neuronal pattern of induction of hsp70 has been demonstrated following ischemia or kainic acid-induced seizures. It is apparent that the pattern of induction of hsp70 may be a useful early marker of cellular injury and may identify previously unrecognized areas of vulnerability in the nervous system.

The pattern of 72-kDa heat shock protein-like immunoreactivity in the rat brain following flurothyl-induced status epilepticus

The inducible 72-kDa heat shock protein (HSP72) is a highly conserved stress protein that is expressed in CNS cells and may play a role in protection from neural injury. We used a monoclonal antibody to HSP72 and immunocytochemistry to localize HSP72 in the rat brain 24 h following either 30 or 60 min of flurothyl-induced status epilepticus. Sprague-Dawley rats were anesthetized with halothane, paralyzed, and ventilated, and remained normotensive and well oxygenated for the duration of the seizures. Seizure activity was quantified via analysis of the scalp EEG pattern. HSP72-like immunoreactivity (HSP72-LI) was induced in specific brain regions in a graded fashion that correlated, in part, with the duration and degree of seizure activity. Milder seizures produced HSP72-LI limited to layers 2 and 3 of frontoparietal cortex, dentate hilus cells, and CA3 pyramidal neurons. More extensive seizures led to HSP72-LI in layers 2, 3 and 5 of frontoparietal and visual cortex, dentate hilus cells, CA1 and CA3 pyramidal neurons, and certain thalamic and amygdaloid nuclei. These are similar to many, but not all, of the brain regions known to be injured with this model. No HSP72-LI was observed in sham-treated controls or flurothyl-treated animals whose seizures were controlled with pentobarbital. HSP72-LI thus localizes to certain regions of seizure-induced injury, and may provide a sensitive method of detecting neuronal 'stress' or injury relatively soon after status epilepticus. Whether or not HSP72 synthesis plays a protective role in the pathogenesis of seizures, or is only a marker for cell injury, remains to be determined.

'Ischemic tolerance' phenomenon found in the brain

We investigated the possibility that neuronal cells given a mild ischemic treatment sufficient to perturb the cellular metabolism acquired tolerance to a subsequent, and what would be lethal, ischemic stress in vivo. Cerebral ischemia was produced in the gerbils by occlusion of both common carotids for 5 min, which consistently resulted in delayed neuronal death in the CA1 region of the hippocampus. Minor 2-min ischemia in this model depletes high-energy phosphate compounds and perturbs the protein synthesis, but never causes neuronal necrosis, and therefore was chosen as mild ischemic treatment. Single 2-min ischemia 1 day or 2 days before 5 min ischemia exhibited only partial protective effects against delayed neuronal death. However, two 2-min ischemic treatments at 1 day intervals 2 days before 5 min ischemia exhibited drastically complete protection against neuronal death. The duration and intervals of ischemic treatment, enough to perturb cellular metabolism and cause protein synthesis, were needed respectively, because neither 1-min ischemia nor 2-min ischemia received twice at short intervals exhibited protective effects. This 'ischemic tolerance' phenomenon induced by ischemic stress--which is unquestionably important--and frequent stress in clinical medicine, is intriguing and may open a new approach to investigate the pathophysiology of ischemic neuronal damage.

T lymphocyte stress response. I. Induction of heat shock protein synthesis at febrile temperatures is correlated with enhanced resistance to hyperthermic stress but not to heavy metal toxicity or dexamethasone-induced immunosuppression

We have investigated the effect of febrile temperatures (less than or equal to 41 degrees C) on T cell heat shock protein (hsp) synthesis and the acquisition of stress tolerance. Enhanced synthesis of hsps was detected in highly purified T cells and two cloned T cell lines representing helper T (D10) and cytotoxic T cell (Qa-2 128.38) subsets at temperatures as low as 39 degrees C with a maximal response at 41 degrees C. Three major hsps with approximate molecular weights of 110, 90, and 75 were detected in these T cell populations. Western blot analysis using a monoclonal antibody specific for hsp70 indicated that the 75-kDa protein represented hscp70, the cognate or constitutively produced member of the hsp70 family. Although the strongly heat-inducible hsp70 could not be detected in T cells incubated at 41 degrees C by immunoblot analysis, two-dimensional SDS-PAGE analysis did detect a modest induction of hsp70. Thus, hscp70 and not hsp70 was the major intracellular hsp70 member in T cells incubated at febrile temperatures. Enhanced hsp synthesis reflected augmented transcription of hsp genes which was contingent on the continued presence of hyperthermic stress. In order to determine whether induction of hsp synthesis conferred a state of increased resistance to thermal stress, splenic T cells were incubated at either 37 degrees or 41 degrees C (induction temperatures) and then subjected to a heat-shock challenge temperature. These studies revealed that following heat-shock challenge, mitogen-stimulated T cells preincubated at 41 degrees C synthesized DNA at an enhanced rate relative to controls (induction temperature, 37 degrees C). Thus, febrile temperatures were capable of inducing a state of acquired thermotolerance in T cells. However, the thermotolerant state did not protect T cell proliferation against other unrelated stressors such as cadmium and dexamethasone. Reconstitution experiments with accessory cells and interleukin-2-containing supernatants failed to reveal enhanced resistance in thermotolerant T cells to cadmium toxicity or the immunosuppressive activities of dexamethasone. The possibility that higher intracellular concentrations of hsps are required to demonstrate protection against these stressors was tested by the concurrent exposure of T cells to a febrile temperature (41 degrees C) and ethanol. This resulted in a synergistic increase in hsp90 and hsp70 synthesis; however, there was no evidence of enhanced resistance to cadmium- or dexamethasone-induced stress in T cells given this induction protocol. Similarly, alloreactive cytotoxic T lymphocyte responses were inhibited to the same extent in both control and thermotolerant T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of stress (heat shock) protein 70 and its mRNA in rat corneal epithelium by hyperthermia

Because stress proteins are believed to play an important role in cellular repair and survival mechanisms, we investigated accumulation of the 70-kilodalton stress protein (SP70) and its mRNA in the rat corneal epithelium after hyperthermia. In the corneal epithelium of control rats, in situ hydridization with a radioactive probe for SP70 mRNA followed by autoradiography revealed very few silver grains. Eighteen hours after the rats were subjected to hyperthermia, the density of silver grains was greatly increased and this elevated level of corneal epithelium SP70 expression continued through 50 hours after heat treatment. Immunostaining for SP70 in the corneal epithelium was consistent with the in situ hybridization, being weak and mainly confined to the basal cells in control rats and increasing by 18 hours in the heat-treated rats. At 50 hours post-heat treatment, the immunostaining was denser than control in all corneal epithelial cells, especially in the apical portions of the basal and wing cells. These results suggest that SP70 may be an important factor in the response of the corneal epithelium to adverse environmental changes.

Heat shock protein synthesis and thermotolerance in Salmonella typhimurium

The resistance of stationary phase Salmonella typhimurium to heating at 55 degrees C was greater in cells grown in nutritionally rich than in minimal media, but in all media tested resistance was enhanced by exposing cells to a primary heat shock at 48 degrees C. Chloramphenicol reduced the acquisition of thermotolerance in all media but did not completely prevent it in any. The onset of thermotolerance was accompanied by increased synthesis of major heat shock proteins of molecular weight about 83, 72, 64 and 25 kDa. When cells were shifted from 48 degrees C to 37 degrees C, however, thermotolerance was rapidly lost with no corresponding decrease in the levels of these proteins. There is thus no direct relationship between thermotolerance and the cellular content of the major heat shock proteins. One minor protein of molecular weight about 34 kDa disappeared rapidly following a temperature down-shift. Its presence in the cell was thus correlated with the thermotolerant state.

Pathogenic anti-DNA autoantibody-inducing T helper cell lines from patients with active lupus nephritis: isolation of CD4-8- T helper cell lines that express the gamma delta T-cell antigen receptor

The antigen responsible for autoimmunization in systemic lupus erythematosus is unknown. In spite of this obstacle, we show that T helper (Th) cell lines that are functionally relevant to this disease can be established in vitro. We derived a total of 396 interleukin 2-dependent T-cell lines from the in vivo activated T cells of five patients with lupus nephritis. Only 59 (approximately 15%) of these lines had the ability to selectively augment the production of pathogenic anti-DNA autoantibodies that were IgG in class, cationic in charge, specific for native DNA, and clonally restricted in spectrotype. Forty-nine of these autoantibody-inducing Th lines were CD4+ and expressed the alpha beta T-cell receptor (TCR). The other 10 were CD4-8- (double negative), 3 expressing the alpha beta TCR and 7 expressing the gamma delta TCR. All of the autoantibody-inducing Th lines responded to some endogenous antigen presented by autologous B cells. The autoreactive responses of the CD4+ Th lines were restricted to HLA class II antigens, whereas those of the double-negative cells were not. Endogenous heat shock or stress proteins of the HSP60 family that were expressed by the lupus patients' B cells were involved in stimulating an autoreactive proliferation of the gamma delta Th cells. These studies demonstrate a novel helper activity of certain gamma delta T cells in a spontaneous autoimmune response.

Increased transcription of a major stress gene in spontaneously hypertensive mice

Environmental stress factors, including temperature, modify the severity of hypertension, a genetic disease. Hypertensive animals and humans respond abnormally to heat exposure, and this abnormality is reflected at the cellular level by an increment in a major stress (heat-shock) gene expression. The present studies demonstrate that increased hsp70 gene expression is due to its heightened transcription rate. The genetic basis of environmental susceptibility to hypertension may thus involve an abnormal control of heat shock genes.

Interaction of Hsp 70 with newly synthesized proteins: implications for protein folding and assembly

The 70-kilodalton family of heat shock proteins (Hsp 70) has been implicated in posttranslational protein assembly and translocation. Binding of cytosolic forms of Hsp 70 (Hsp 72,73) with nascent proteins in the normal cell was investigated and found to be transient and adenosine triphosphate (ATP)-dependent. Interaction of Hsp 72,73 with newly synthesized proteins appeared to occur cotranslationally, because nascent polypeptides released prematurely from polysomes in vivo can be isolated in a complex with Hsp 72,73. Moreover, isolation of polysomes from short-term [35S]Met-labeled cells (pulsed) revealed that Hsp 72,73 associated with nascent polypeptide chains. In cells experiencing stress, newly synthesized proteins coimmunoprecipitated with Hsp 72,73; however, in contrast to normal cells, interaction with Hsp 72,73 was not transient. A model consistent with these data suggests that under normal growth conditions, cytosolic Hsp 72,73 interact transiently with nascent polypeptides to facilitate proper folding, and that metabolic stress interferes with these events.

Induction of cellular hsp70 expression by human cytomegalovirus

Expression of the cellular heat shock protein 70 gene (hsp70) is transiently induced by human cytomegalovirus (HCMV) infection of permissive human diploid fibroblasts. Induction of the cellular heat shock response during critical times of infection had previously been reported to alter the growth of HCMV in vitro. Thus, a potential interaction between heat shock proteins and HCMV expression was indicated. HCMV dramatically increased expression of hsp70 RNA within 8 h of infection. hsp70 RNA remained elevated at 24 and 48 h postinfection and decreased to low levels of 72 h postinfection. Induction of HSP70 protein occurred more slowly; inducible HSP70 protein encoded by this RNA increased within 16 h postinfection and continued to increase throughout infection until 72 h postinfection, when the highest abundance of inducible HSP70 protein was observed. Cells that received both heat (43 degrees C for 70 min) treatment and HCMV infection expressed hsp70 RNA to levels above the sum of levels present in cells given either treatment alone. Furthermore, hsp70 RNA induction occurred earlier and remained elevated longer than in cells infected with HCMV alone or in cells treated with heat alone, respectively. Nevertheless, the pattern of HCMV immediate-early transcript expression at 2, 4, and 6 h postinfection appeared to be unchanged by this prior heat treatment. Our results suggest that heat shock treatment and HCMV infection can act additively in stimulating hsp70 RNA expression. The previously reported stimulation of HCMV growth in vitro following the heat shock response apparently does not result from alterations in the steady-state expression of HCMV immediate-early transcripts.

Exercising mammals synthesize stress proteins

Spleen cells, peripheral lymphocytes, and soleus muscles were removed from male Sprague-Dawley rats that had been run on a treadmill (24 m/min) for either 20, 40, or 60 min or to exhaustion (86 +/- 41 min) and were labeled in vitro with [35S]methionine at 37 degrees C. Similar tissues from nonrunning control rats were labeled in vitro at either 37 or 43 degrees C (heat shock). Fluorographic analyses of one- and two-dimensional polyacrylamide gel electrophoretic separations of the proteins from cells and tissues of exercised rats demonstrate the new or enhanced synthesis of proteins of approximately 65, 72, 90, and 100 kDa. Although synthesis of these proteins is low or not detectable in tissues from control rats labeled at 37 degrees C, they are prominent products of similar tissues labeled under heat-shock conditions (43 degrees C) and, in fact, correspond in Mr and pI with the so-called heat-shock proteins. These results suggest that exercise is a sufficient stimulus to induce or enhance the synthesis of heat shock and/or stress proteins in mammalian cells and tissues.

Acquired thermotolerance and heat shock in the extremely thermophilic archaebacterium Sulfolobus sp. strain B12

The extreme thermophile Sulfolobus sp. strain B12 exhibits an acquired thermotolerance response. Thus, survival of cells from a 70 degrees C culture at the lethal temperature of 92 degrees C was enhanced by as much as 6 orders of magnitude over a 2-h period if the culture was preheated to 88 degrees C for 60 min or longer before being exposed to the lethal temperature. In eubacteria and eucaryotes, acquired thermotolerance correlates with the induced synthesis of a dozen or so proteins known as heat shock proteins. In this Sulfolobus species, it correlates with the preferential synthesis of primarily one major protein (55 kilodaltons) and, to a much lesser extent, two minor proteins (28 and 35 kilodaltons). Since the synthesis of all other proteins was radically reduced and these proteins were apparently not degraded or exported, their relative abundance within the cell increased during the time the cells were becoming thermotolerant. They could not yet be related to known heat shock proteins. In immunoassays, they were not cross-reactive with antibodies against heat shock proteins from Escherichia coli (DnaK and GroE), which are highly conserved between eubacteria and eucaryotes. However, it appears that if acquired thermotolerance depends on the synthesis of protective proteins, then in this extremely thermophilic archaebacterium it depends primarily on one protein.

Increased thermostability of thermotolerant CHL V79 cells as determined by differential scanning calorimetry

Heat shock denatures cellular protein and induces both a state of acquired thermotolerance, defined as resistance to a subsequent heat shock, and the synthesis of a category of proteins referred to as heat-shock proteins (HSPs). Thermotolerance may be due to the stabilization of thermolabile proteins that would ordinarily denature during heat shock, either by HSPs or some other factors. We show by differential scanning calorimetry (DSC) that mild heat shock irreversibly denatures a small fraction of Chinese hamster lung V79-WNRE cell protein (i.e., the enthalpy change, which is proportional to denaturation, on scanning to 45 degrees C at 1 degree C/min is approximately 2.3% of the total calorimetric enthalpy). Thermostability, defined by the extent of denaturation during heat shock and determined from DSC scans of whole cells, increases as the V79 cells become thermotolerant. Cellular stabilization appears to be due to an increase in the denaturation temperature of the most thermolabile proteins; there is no increase in the denaturation temperatures of the most thermally resistant proteins, i.e., those denaturing above 65 degrees C. Cellular stabilization is also observed in the presence of glycerol, which is known to increase resistance to heat shock and to stabilize proteins in vitro. A model is presented, based on a direct relationship between the extent of hyperthermic killing and the denaturation or inactivation of a critical target that defines the rate-limiting step in killing, which predicts a transition temperature (Tm) of the critical target for control V79-WNRE cells of 46.0 degrees C and a Tm of 47.3 degrees C for thermotolerant cells. This shift of 1.3 degrees C is consistent with the degree of stabilization detected by DSC.

Effects of heat shock on cytolysis mediated by NK cells, LAK cells, activated monocytes and TNFs alpha and beta

We have recently shown that a heat treatment of a murine target cell line, WEHI 164, induces resistance to lysis mediated by tumour necrosis factors alpha (TNF-alpha) and beta (TNF-beta). In the present study the effect of the heat shock of target cells on cytotoxicity mediated by natural killer cells (NK cells), lymphocyte-activated killer cells (LAK cells), activated monocytes, TNF-alpha, and TNF-beta was investigated. First, WEHI 164 cell line and six human cell lines (ME 180, K 562, U 937, HeLa, MCF7, and SK-OV 3) were screened for their sensitivity to different forms of lysis, and then sensitive cell lines were heat-treated. Pretreatment of target cells at 42 degrees C for 45-60 min also rendered human target cell lines more resistant to lysis by rTNFs, and the acquired resistance was accompanied by an increased resistance to activated monocytes, but not to NK cells or LAK cells. Thus, the heat-induced resistance mechanisms capable of protecting target cells from lysis by rTNFs and by activated monocytes do not elicit resistance to lysis by NK cells and LAK cells, supporting the hypothesis that mediators other than TNFs are involved in NK cell- and LAK cell-mediated killing.

Enhanced glycosyltransferase activity during thermotolerance development in mammalian cells

The cellular heat shock response leads to the enhanced synthesis of a family of heat shock proteins and the development of thermotolerance. In CHO cells, however, heat shock also leads to enhanced synthesis of a 50 kD glycoprotein and elevated activity of N-acetylgalactosaminyltransferase (GalNAcT). In this study we showed increased GalNAcT activity during thermotolerance expression in all of five mammalian cell lines included in the study. However, there was no simple correlation between cellular heat sensitivity of unheated control cells and basal levels of GalNAcT activity, measured toward the same exogenous acceptor apomucin. Although GalNAcT was elevated in thermotolerant cells, GalNAcT activity itself did not exhibit thermotolerance in terms of reduced sensitivity to heat inactivation. The increase in GalNAcT activity after heating was similar in exponentially growing and plateau-phase cultures and was inhibited neither by cycloheximide nor actinomycin D. However, the inhibitors by themselves also increased GalNAcT activity in unheated control cells. Chemical inducers of thermotolerance (arsenite and diamide) increased GalNAcT activity, but the increase was modest when compared to that following hyperthermia. In addition to GalNAcT, two other glycosyltransferases with specificity for O-glycans, alpha 1,2-fucosyltransferase and alpha 2,6-sialyltransferase, also showed increased activity after hyperthermia and during thermotolerance development. Together with previously published data, these results support the hypothesis that heat-induced activation of O-glycan-specific glycosyltransferases plays a physiological role in the cellular heat shock response and in thermotolerance development.

The adenovirus E1B 19-kilodalton protein stimulates gene expression by increasing DNA levels

In transient expression assays, the adenovirus E1B 19-kilodalton (19K) tumor antigen increases expression from viral promoters and the promoter for the cellular 70-kilodalton heat shock protein (hsp70). To study the mechanism of this effect, we constructed HeLa cell lines that contain stably integrated copies of the 19K gene. Compared with a 19K- control cell line, 19K+ cells produced a significantly higher level of expression from every promoter introduced into the cells by transfection. The 19K protein also increased expression of an RNA polymerase III-transcribed gene but did not affect the level of expression of the endogenous hsp70 gene. The rate of transcription from transfected promoters, as measured by a nuclear run-on assay, was higher in the 19K+ cells than in the 19K- control cells. Furthermore, the level of plasmid DNA remained higher in the 19K+ cell line, suggesting that the 19K protein stabilizes transfected plasmid DNA. The elevated DNA levels seemed to account in full for the increased transcription. The role of the 19K protein in increasing gene expression during viral infection was found to be due to a replication-dependent increase in viral DNA levels. Thus, the 19K protein activates transcription indirectly by producing a higher level of viral or plasmid DNA. The DNA stabilization function of the 19K protein is probably related to the protective role of the 19K protein during viral infection and represents the first example of a viral oncogene product that modulates gene expression by regulating viral and plasmid DNA levels.

Effects of heat and chemical stress on development

Similarities in the means by which developmental defects are induced in vertebrates and Drosophila suggest that some kinds of defects may be induced by similar mechanisms. The similarities include the fact that heat and a group of chemicals that induce synthesis of heat-shock proteins induce defects in mammals, chickens, and flies. Different kinds of defects are even produced in one type of animal, depending on the precise timing of the environmental insult. The effectiveness of the environmental treatment in inducing defects depends on the genetic background of the animal as well as on past exposure to chemicals and heat. Developmental defects induced by heat in mice, rats, and flies can all be prevented by thermotolerance-inducing treatments. The basis for these effects has been studied at the molecular level in Drosophila, and the evidence indicates that these teratogens and the thermotolerance-inducing treatments affect the level or timing of expression of specific genes during critical periods in the developmental program.

Longevity hormesis. A review

The phenomenon of longevity hormesis is reviewed. The life-prolonging effects of longevity hormesis are compared and contrasted with those resulting from depressed food intake. The use of age-specific mortality rate analysis as a tool to characterize the separate and distinct effects of longevity hormesis, cumulative toxicity and depressed food intake on the survival of laboratory animals is illustrated. Finally, model systems through which the mechanism(s) of longevity hormesis may be elucidated are discussed.

Involvement of protein synthesis in the development of thermotolerance using a CHO temperature-sensitive mutant

A Chinese hamster ovary temperature-sensitive mutant (CHO-tsH1) with defective leucyl-tRNA synthetase at temperatures greater than 39 degrees C was used to examine the importance of protein synthesis in the development of thermotolerance. Its wild-type parent CHO-SC1 was used as the control. At temperatures of 41.5 degrees C, 42 degrees C and 42.5 degrees C, SC1 showed the classical biphasic thermotolerant response while tsH1 showed no thermotolerance. When both cell lines were heated for 15 min at 45 degrees C, then allowed to incubate at the permissive temperature of 35 degrees C and finally challenged with another 25 min treatment at 45 degrees C, tolerance was expressed in both cell lines. When the development incubation temperature was raised from 35 degrees C to the non-permissive temperature of 40 degrees C, tolerance was also observed. Although both cell lines expressed tolerance under these conditions, the magnitude and duration of response of the mutant cell line were reduced. Heat-shock protein analysis using one-dimensional gel electrophoresis showed that, under permissive conditions, the mutant cell was able to express the full spectrum of heat-shock proteins as seen in the wild-type cells. Under non-permissive conditions, little or no detectable proteins were synthesized in the mutant cell. We therefore postulate that the synthesis of new cytosol proteins is not required for the initial onset of thermotolerance but is necessary for the sustenance of tolerance.

Changes in thermodependence of the tyrosine transaminating activity in mitochondria of Drosophila melanogaster larvae due to environmental stress

1. The form of Arrhenius plots of enzyme in mitochondria isolated from Drosophila melanogaster larvae exposed to heat shock, ethanol, or ethanol and heat shock, solubilized with charged detergents was analysed. 2. Heat shock and ethanol caused different changes in membrane microenvironment of the tyrosine transaminating activity, which found expression in different forms of Arrhenius plots, and different values of activation energy of enzyme. 3. The Arrhenius plots of the enzyme from mitochondria of larvae exposed both to ethanol and heat shock, solubilized with charged detergents, were similar to those observed for mitochondria from organisms exposed only to ethanol.

Expression of heat shock genes (hsp70) in the mammalian brain: distinguishing constitutively expressed and hyperthermia-inducible mRNA species

The mammalian genome contains both constitutively expressed and heat-shock-inducible members of the hsp70 gene family. Riboprobes derived from members of these two classes of heat shock genes were utilized in Northern blot studies to analyze brain mRNA isolated from control rabbits and rats and from animals subjected to hyperthermic treatment. A riboprobe derived from a constitutively expressed hsp70 gene detected a 2.5 kilobase (kb) mRNA in brain tissue from control rabbits and a 2.3 kb mRNA species in control rat brain. These brain mRNAs showed little change in abundance in animals which were subjected to hyperthermic treatment. A riboprobe derived from a heat-shock-inducible hsp70 gene detected an abundant 2.7 kb brain transcript in hyperthermic rabbits which was not apparent in control animals. A time course study revealed that the induction of this mRNA species was transient and paralleled the rise and fall in body temperature. Peak induction was observed at 1 hr. The level of this message had greatly decreased by 5 hr and only trace levels were present at 10 and 24 hr. In the rat brain the induced hsp70 mRNA species was slightly larger than that observed in rabbit (2.9 kb vs. 2.7 kb). The riboprobe which detected the hyperthermia-inducible mRNA species was highly specific and did not cross react to the constitutively expressed mRNA species under the conditions employed in the Northern blot studies.

Time course of induction of a heat shock gene (hsp70) in the rabbit cerebellum after LSD in vivo: involvement of drug-induced hyperthermia

In situ hybridization studies were carried out to determine whether induction of hsp70 mRNA in various cellular layers of the rabbit cerebellum was due to hyperthermic effects of the psychotropic drug LSD. Results indicated that induction was not present when LSD-induced hyperthermia was blocked. The pattern of induction of hsp70 mRNA in various cell types of the cerebellum was similar when hyperthermia was induced by either drug (LSD) or nondrug means (placement of animals in a warm incubator). A time course analysis of the induction of hsp70 mRNA following LSD-induced hyperthermia revealed maximal levels of mRNA at 1 hr in all cerebellar cell layers except the Purkinje layer where highest levels were attained at 5 hr. By 10 hr hsp70 mRNA had returned to constitutive levels in all cellular layers of the cerebellum.

The adenovirus E1B 19-kilodalton protein stimulates gene expression by increasing DNA levels

In transient expression assays, the adenovirus E1B 19-kilodalton (19K) tumor antigen increases expression from viral promoters and the promoter for the cellular 70-kilodalton heat shock protein (hsp70). To study the mechanism of this effect, we constructed HeLa cell lines that contain stably integrated copies of the 19K gene. Compared with a 19K- control cell line, 19K+ cells produced a significantly higher level of expression from every promoter introduced into the cells by transfection. The 19K protein also increased expression of an RNA polymerase III-transcribed gene but did not affect the level of expression of the endogenous hsp70 gene. The rate of transcription from transfected promoters, as measured by a nuclear run-on assay, was higher in the 19K+ cells than in the 19K- control cells. Furthermore, the level of plasmid DNA remained higher in the 19K+ cell line, suggesting that the 19K protein stabilizes transfected plasmid DNA. The elevated DNA levels seemed to account in full for the increased transcription. The role of the 19K protein in increasing gene expression during viral infection was found to be due to a replication-dependent increase in viral DNA levels. Thus, the 19K protein activates transcription indirectly by producing a higher level of viral or plasmid DNA. The DNA stabilization function of the 19K protein is probably related to the protective role of the 19K protein during viral infection and represents the first example of a viral oncogene product that modulates gene expression by regulating viral and plasmid DNA levels.

Stress proteins, arthritis, and autoimmunity

Stress proteins have been highly conserved during evolution not only because of their fundamental importance in the response of the cell to stressful assaults, but also because they have critical roles in cellular activation and cell growth, regulation of protein function, protein transport, and protein assembly. Research focusing on the basic cell biology of stress proteins is intense at present, and will surely continue to be for some time to come. Of particular interest to immunologists and rheumatologists is the convergence of data in several fields that suggest that stress proteins in microorganisms that commonly infect humans may be triggers of humoral and cellular autoimmune responses and consequent overt autoimmune disease expression. Thus, stress proteins of M tuberculosis and other bacteria are close homologs of stress proteins in mammals, and may be involved in the pathogenesis of adjuvant-induced arthritis in rats and, possibly, of RA and reactive arthritis in humans. A great deal of work remains to be done in this area, including (a) generation and propagation of specifically reactive T cell clones, (b) molecular delineation of the immune recognition elements and critical epitopes shared by microbial stress proteins and host proteins, (c) definition of the relative contribution of alpha beta and gamma delta TCRs to T cell reactivity to stress proteins, and (d) clarification of the circumstances that enable persistent T cell autoreactivity to stress proteins. The data at hand are sufficiently compelling, however, to suggest that vaccination against T cells that recognize stress proteins may eventually become part of our therapeutic armamentarium to prevent or cure some forms of arthritis.(ABSTRACT TRUNCATED AT 250 WORDS)

The cellular proteins which can associate specifically with polyomavirus middle T antigen in human 293 cells include the major human 70-kilodalton heat shock proteins

We compared the proteins which associate with middle T antigen (MT) of polyomavirus in human cells infected with Ad5(pymT), a recombinant adenovirus which directs the overexpression of MT, with the MT-associated proteins (MTAPs) previously identified in murine fibroblasts expressing MT. MTAPs of 27, 29, 36, and 63 kilodaltons (kDa) appeared to be fairly well conserved between the two species, as judged by comigration on two-dimensional gels. Several 61-kDa MTAP species detected in MT immunoprecipitates from both cell sources also comigrated on these gels. However, no protein comigrating precisely with the murine 85-kDa MTAP could be detected in the human cells. Furthermore, two proteins of 72 and 74 kDa associated with wild-type MT in the infected human cells but not in murine fibroblasts expressing MT. It had been previously reported for murine cells that the 70-kDa heat shock protein associates with a particular mutant MT but not with wild-type MT (G. Walter, A. Carbone, and W.J. Welch, J. Virol. 61:405-410, 1987). By the criteria of comigration on two-dimensional gels, tryptic peptide mapping, and immunoblotting, we showed that the 72- and 74-kDa proteins that associate with wild-type MT in human cells are the major human 70-kDa heat shock proteins.

Activation primes human B lymphocytes to respond to heat shock

Crosslinkage of the B cell antigen receptor by anti-mu beads or SAC results in the selective induction of hsp70. We have observed that activated cells, having enhanced expression of hsp70, survive lethal stimuli much better than their unactivated counterparts. These results are in accordance with the proposal that hsp70 is essential for cells to survive lethal environmental stresses. Moreover, the activation event itself primes B cells thereby enabling them to increase the expression of both hsp70 mRNA and protein. This is the first demonstration that triggering of B cells via crosslinkage of sIg is accompanied by the induction of thermotolerance without the need for a prior sublethal heat treatment.

Heat shock induces c-fos protein-like immunoreactivity in glial cells in adult rat brain

Heat shocking of anesthetized rats lead to a massive increase in c-fos protein-like immunoreactivity (FOS-IR) in glial-like cells in white and gray matter regions of the brain. Neuronal FOS-IR was not detectibly altered by heat shock. This induction of FOS-IR was present 1 h, but not 10 min or 24 h, after heat shock. These results demonstrate that c-fos protein is expressed in glial cells following thermal stress.

Rapidly reversible enzyme inhibition in a temperature-sensitive mammalian cell mutant lacks thermotolerance

The temperature-sensitive (ts) Chinese hamster ovary (CHO) cell mutant tsH1 contains a thermolabile leucyl-tRNA synthetase. Upon incubation at the nonpermissive temperature of 39.5 degrees C, the enzyme became reversibly inhibited over a period of minutes, and the cells lost viability over a period of many hours. However, killing of tsH1 by acute heating at 45 degrees C was identical to that of wild-type (SC) cells. In addition, the heat-induced inhibition of protein synthesis was similar for both cell types, as measured after acute heating at 45 degrees C. Furthermore, both killing and inhibition of protein synthesis showed thermotolerance in both cell types. In contrast to the effects at 45 degrees C, at 39.5 degrees C, neither the inhibition of leucyl-tRNA synthetase activity nor the killing of tsH1 expressed thermotolerance. Also, treatment of tsH1 at 39.5 degrees C did not induce thermotolerance to killing at 45 degrees C. The inhibition of leucyl-tRNA synthetase activity in tsH1 at 39.5 degrees C was further distinguished from the 45 degrees C-induced inhibition of protein synthesis in SC cells by a much more rapid reversal of the inhibition of leucyl-tRNA synthetase activity. Also, the rate of reversal of the inhibition of protein synthesis by 45 degrees C in SC cells was decreased by increased heat dose. Such was not true for the 39.5 degrees C inhibition of leucyl-tRNA synthetase activity in tsH1. The data indicate that there exist two distinct types of thermal inhibition--one slowly reversible type which was observed during and after heating at 45 degrees C and both induced and expressed thermotolerance, and a second, rapidly reversible type, which was evident only during heating of tsH1 at 39.5 degrees C and neither induced nor expressed thermotolerance.

Heat shock protects WEHI-164 target cells from the cytolysis by tumor necrosis factors alpha and beta

Elevated temperatures and a number of other types of stress induce synthesis of a small number of highly conserved proteins, the heat shock proteins, in a wide variety of cells. The structure and regulation of these proteins have been intensively studied but the question of the function of this universal response has remained unanswered. We studied the effect of heat shock on tumor necrosis factor-alpha (TNF-alpha)- and -beta (TNF-beta)-mediated cytolysis of WEHI-164 clone 13 target cells. One hour pretreatment of target cells at 42 degrees C decreased rTNF-alpha-mediated lysis by 65.3%, 50.5% and 44.8% and TNF-beta-mediated lysis by 61.9%, 43.2% and 38.9% at cytokine concentrations of 0.5 ng/ml, 5 ng/ml and 50 ng/ml, respectively, in an 18-h Cr-release assay. The effect was maximal when TNF-alpha was added 1 h after the heat shock and then gradually declined, being almost undetectable after 2 days. This pattern was found to roughly coincide with the kinetics of hsp68, the major heat-induced protein in murine cells. Heat shock treatment had no protective effect when given 1 h after addition of recombinant TNF-alpha. The heat-induced target cell resistance was not associated with decreased binding of recombinant TNF-alpha to its receptor. Inhibition of protein synthesis by cycloheximide diminished this effect by 76% and inhibition of transcription by actinomycin D abolished it completely, suggesting that de novo synthesized heat-induced proteins protect target cells from TNF-mediated lysis in heat shock-treated WEHI cells.

Heat shock resistance conferred by expression of the human HSP27 gene in rodent cells

Heat shock induces in cells the synthesis of specific proteins called heat shock proteins (HSPs) and a transient state of thermotolerance. The putative role of one of the HSPs, HSP27, as a protective molecule during thermal stress has been directly assessed by measuring the resistance to hyperthermia of Chinese hamster and mouse cells transfected with the human HSP27 gene contained in plasmid pHS2711. One- and two-dimensional gel electrophoresis of [3H]leucine- and [32P]orthophosphate-labeled proteins, coupled with immunological analysis using Ha27Ab and Hu27Ab, two rabbit antisera that specifically recognize the hamster and the human HSP27 protein respectively, were used to monitor expression and inducibility of the transfected and endogenous proteins. The human HSP27 gene cloned in pHS2711 is constitutively expressed in rodent cells, resulting in accumulation of the human HSP27 and all phosphorylated derivatives. No modification of the basal or heat-induced expression of endogenous HSPs is detected. The presence of additional HSP27 protein provides immediate protection against heat shock administered 48 h after transfection and confers a permanent thermoresistant phenotype to stable transfectant Chinese hamster and mouse cell lines. Mild heat treatment of the transfected cells results in an induction of the full complement of the endogenous heat shock proteins and a small increase in thermoresistance, but the level attained did not surpass that of heat-induced thermotolerant control cells. These results indicate that elevated levels of HSP27 is sufficient to give protection from thermal killing. It is concluded that HSP27 plays a major role in the increased thermal resistance acquired by cells after exposure to HSP inducers.

Induction of stress proteins in cultured human RPE-derived cells

The expression and induction of stress protein families were examined in cultured human fetal retinal pigment epithelial (RPE)-derived cells. These stress proteins (SPs) include the heat-shock proteins (HSPs) that have been shown to be highly inducible following treatment by heat, amino acid analogues, and various chemical oxidants. Three sets of proteins with molecular weights of 70, 84, and 110 kilodaltons were elevated simultaneously from constitutive levels after treatment with azetidine-2-carboxylic acid (AzC), an amino acid analogue of proline. Further experiments demonstrated that incubation of cultured human fetal RPE-derived cells with hydrogen peroxide (H2O2) at concentrations ranging from 10(-5) M to 10(-3) M for 30 minutes to 60 minutes did not elevate the levels of the common families of HSPs as with AzC. These results indicate that cultured human fetal RPE-derived cells are capable of elevated HSP biosynthesis after AzC exposure but appear resistant to H2O2 treatment.

Induction of a heat shock gene at the site of tissue injury in the rat brain

Our objective was to investigate whether localized tissue injury induces expression of a gene encoding the major 70 kd heat shock protein (hsp70) in the mammalian nervous system. A small surgical cut was made in the rat cerebral cortex. By 2 hr postsurgery a dramatic and highly localized induction of hsp70 mRNA was detected at the lesion site using in situ hybridization with labeled riboprobe. By 12 hr the intensity of the signal had diminished, and by 24 hr only a few cells along the walls of the cut demonstrated a high level of hsp70 mRNA. Both neurons and glial cells at the site of the surgical cut responded to tissue injury by induction of hsp70 mRNA. Induction was not observed in other brain regions, nor was the pattern of constitutive expression affected by the surgical procedure.

Will heat-stable proteins nonspecifically protect cells from thermal stress?

In cell-free systems, stress-resistant proteins nonspecifically stabilize stress-susceptible proteins. This mechanism has been suggested to contribute to thermotolerance in cells (Minton et al.: Proc. Natl. Acad. Sci. USA, 79: 7107-7117, 1982). To test this hypothesis, red-blood-cell-mediated microinjection was used to transfer macromolecules into monolayers of CHO cells. We introduced the heat-stable proteins fetuin and ovomucoid into RBCs during hypotonic hemolysis and then fused the RBCs to CHO cells with polyethylene glycol as fusogen. Fetuin and ovomucoid were successfully transferred into 36-55% of the CHO cells as demonstrated by fluorescence of FITC-conjugated proteins. The plating efficiency of these CHO cells after fusion ranged from 35% to 60%. Three hours after fusion, CHO cells microinjected with fetuin or ovomucoid were exposed to 43 degrees C for 0-180 min or 45 degrees C for 0-40 min, and thermal survival was determined. There was no difference in cell survival between control untreated cells, control cells fused with nonloaded RBCs, and cells fused with RBCs loaded with fetuin or ovomucoid. While our results do not support the hypothesis that heat-stable proteins nonspecifically protect cells from thermal stress, several possible explanations are provided for this observation.

The cdc2 kinase is a nuclear protein that is essential for mitosis in mammalian cells

A homolog of the fission yeast cdc2-encoded protein kinase (p34) is a component of M phase promoting factor in Xenopus oocytes. The homologous kinase in human HeLa cells is maximally active during mitosis, suggesting a mitotic role in mammalian somatic cells. This has been directly investigated by microinjection of anti-p34 antibodies into serum-stimulated rat fibroblasts. DNA synthesis was unaffected but cell division was quantitatively blocked in injected cells. Injection of antibodies against p13suc1, a component of the p34 kinase complex, did not block mitosis but caused mitotic abnormalities resulting in cells containing multiple micronuclei in the subsequent interphase. p34 localized in the nucleus during interphase. During mitosis, a fraction tightly associated with centrosomes. p13 was more evenly distributed between the nucleus and cytoplasm. These observations demonstrate that cdc2 is a nuclear and centrosomal protein that is required for mitosis in mammalian cells.

Heat shock protein expression in thermotolerant and thermosensitive lines of cotton

The expression of heat shock proteins (HSPs) was compared between genetically characterized heat tolerant and heat sensitive lines of cotton (Gossypium hirsutum andG. barbadense) using electrophoretic analysis ofin vivo labelled proteins. No differences were observed between the two lines with regard to: the temperature at which HSP synthesis was induced (37°C); the temperature at which HSP synthesis was maximal (45°C); the rates of recovery from HSP synthesis; the duration of HSP synthesis; or the major size classes of HSPs expressed in these two lines. Several HSPs were identified on 2D gels which were expressed uniquely in either the tolerant or sensitive cotton line. However, the HSP pattern displayed in a heat tolerant BC-3 individual was that of the heat sensitive parent.

Competitive inhibition of hsp70 gene expression causes thermosensitivity

A novel method has been developed for modulating the expression of an endogenous chromosomal gene in a higher eukaryote, by competitive inhibition at the level of gene transcription. The gene studied was the hsp70 gene, which encodes a 72-kilodalton (kD) heat shock protein that is synthesized after thermal stress. The 5' control region of the hsp70 gene was inserted on a plasmid containing the eukaryotic gene for dihydrofolate reductase. The hybrid plasmid was then introduced into a Chinese hamster ovary cell line and elevated in copy number approximately 20,000-fold by selection of cells with methotrexate. Heat-inducible expression from the intact hsp70 gene was reduced by at least 90% in the modified cells when compared with the induction in control cells, and the modified cells also displayed elevated thermosensitivity. The change in heat shock protein synthesis is presumably caused by competition among the increased number of binding sites for the heat-shock transcription factor, leading to altered expression from the native heat shock gene. These results support a role for heat shock protein in the recovery of mammalian cells from acute thermal stress.