Heat shock proteins and macrophage resistance to the toxic effects of nitric oxide

Nitric oxide (NO) functions as a pathophysiological mediator in mammalian tissues. Activated macrophages produce NO as a non-specific immune response directed against invading bacteria or micro-organisms. The same macrophages that initiate the production of NO also can be toxically affected by NO. Incubation of RAW 264.7 macrophages with lipopolysaccharide (LPS) and/or interferon-gamma (INF-gamma) induced the formation of NO by the activation of a cytokine-inducible NO synthase (NOS). The viability of these macrophages was inversely correlated with the formation of nitrite, a final NO-oxidation product measurable in the incubation medium. The addition of an NOS inhibitor, NG-monomethyl-L-arginine, diminished NO formation and preserved cell viability in a dose- and time-dependent fashion. Treatment of macrophages with ten cycles of non-lethal doses of LPS and INF-gamma, each followed by subculturing of the surviving cells, resulted in cell resistance to the NO toxic insult induced by LPS and INF-gamma. These resistant macrophages showed a 2-fold increase in the expression of the constitutive heat shock protein (HSC 70) which is known to be involved in protecting cells against the action of various metabolic insults. Our results establish a link between cell resistance to the toxic effects of NO, and the expression of heat shock proteins in RAW 264.7 macrophages.

The heat shock/oxidative stress connection. Relevance to Alzheimer disease

Involvement of free-radical oxidations in the aging process has been a topic of interest since Harman's original contribution. Because of the close association between aging and Alzheimer disease (AD) and the qualitative similarity in the neuropathology of both conditions, it has been proposed by many investigators that oxidative stress may be important in Ad. If such modality of injury was indeed involved, one should expect to find markers of oxidation and heat shock (since free radicals are key mediators of heat-shock induction) in brains of patients with AD. In fact, several studies documented abnormal expression of antioxidant enzymes and heat-shock proteins (HSP) along with other markers of oxidation in AD brains. We showed that abnormally expressed antioxidant enzymes are topographically associated with senile plaques and neurofibrillary tangles, and that the activity of these enzymes is (contrary to what one would expect) markedly reduced. These findings have recently been confirmed by other investigators. Despite a large amount of evidence that suggests an association between oxidative stress and the pathogenesis of AD, it is not yet known whether oxidative stress is a cause or consequence of the disorder. Future research efforts regarding the oxidative stress hypothesis of AD should include attempts at generating AD pathology by oxidative means in laboratory animals, determining the role and integrity of the heat-shock response in AD, as well as that of various antioxidant systems, growth factors, and hormones with antioxidant and neuroprotective properties.

Membrane lipid perturbation modifies the set point of the temperature of heat shock response in yeast

Addition of a saturated fatty acid (SFA) induced a strong increase in heat shock (HS) mRNA transcription when cells were heat-shocked at 37 degrees C, whereas treatment with an unsaturated fatty acid (UFA) reduced or eliminated the level of HS gene transcription at 37 degrees C. Transcription of the delta 9-desaturase gene (Ole1) of Histoplasma capsulatum, whose gene product is responsible for the synthesis of UFA, is up-regulated in a temperature-sensitive strain. We show that when the L8-14C mutant of Saccharomyces cerevisiae, which has a disrupted Ole1 gene, is complemented with its own Ole1 coding region under control of its own promoter or Ole1 promoters of H. capsulatum, the level of HS gene transcription depends on the activity of the promoters. Fluorescence anisotropy of mitochondrial membranes of completed strains corresponded to the different activity of the Ole1 promoter used. We propose that the SFA/UFA ratio and perturbation of membrane lipoprotein complexes are involved in the perception of rapid temperature changes and under HS conditions disturbance of the preexisting membrane physical state causes transduction of a signal that induces transcription of HS genes.

Induction of heat shock proteins and their possible roles in macrophages during activation by macrophage colony-stimulating factor

(1) Treatment of resident peritoneal macrophages for 8 h with macrophage colony-stimulating factor (M-CSF) increased release of superoxide anion (O2-) stimulated by phorbol 12-myristate 13-acetate. Gel electrophoresis of pulse-labelled proteins with L-[35S]methionine showed that a number of proteins were induced during activation by M-CSF. Immunoblot analysis with antibody against heat shock protein (HSP) 90, HSP70, or HSP60 demonstrated that M-CSF induced these stress-inducible HSPs; the timing of induction and level of each HSP correlated with the increase in O2- production. The activated macrophages acquired resistance to H2O2-induced damage. M-CSF also stimulated the synthesis of a heat shock cognate protein (HSC70); however, the induction occurred at 1 h, when O2- production was not yet augmented, but at which time L-[35S]methionine incorporation into cell proteins was already enhanced. (2) Gel mobility shift assay with oligonucleotide coding for the heat shock element showed that M-CSF activated the heat shock factor within 15 min, and the activation continued for at least 8 h. Northern-blot analysis with a cDNA probe for human HSP70 or HSC70 showed that accumulations of HSP70 and HSC70 mRNAs coincided with the inductions of the respective proteins. (3) These results suggest that M-CSF may induce the transcriptional activation of heat shock genes, and that the stress-inducible HSPs as well as HSC70 may play an important role in the activation of macrophages by functioning as molecular chaperones and by protecting the macrophage against the auto-oxidative damage associated with the respiratory burst.

Relationship between stress response toward bile salts, acid and heat treatment in Enterococcus faecalis

Stress tolerance and cross-protection in Enterococcus faecalis ATCC19433 were examined after exposure to bile salts, acid or heat shock. Bile salts and heat adapted cells demonstrated induced homologous tolerance and cross-resistance. No cross-protection of heat adapted cells against acid stress is observed and pretreatment with bile salts even sensitized the cells to this challenge. Whole-cell protein extract analysis revealed that each treatment induced a battery of stress proteins. Some of these polypeptides are induced by more than one treatment. The greatest overlap is observed between bile salts and heat treatments. Eighteen stress proteins, including DnaK and GroEL, are common between these stresses.

Cell-specific heat-shock induction of Hsp23 in the eye of Drosophila melanogaster

The expression of two small heat shock proteins (sHsp), Hsp23 and Hsp27, was examined by immunological approaches in the eye of Drosophila melanogaster. Neither Hsp23 nor Hsp27 is detectable in unstressed (23 degrees C) eyes but both proteins are induced by heat shock (35 degrees C). In response to heat stress, Hsp27 is expressed in all cells of the ommatidium including the cone, pigment and photoreceptor cells. However, the heat-induced expression of Hsp23 is restricted to a single cell type of the ommatidium, the cone cells, suggesting that Hsp23 is regulated by specific mechanisms acting to inhibit the expression of this polypeptide in some ommatidial cells. The cell-specific induction of Hsp23 under stress conditions does not seem to be regulated by the Drosophila melanogaster heat shock transcriptional factor (DmHSF). In both unstressed and stressed conditions, DmHSF is detected in all the different types of ommatidial cells where it is found associated with the nucleus. These observations suggest that factors, other than the heat shock transcriptional factor, are involved in regulating the expression of the hsp23 gene under stress conditions.

The mitochondria are recognition organelles of cell stress

The cellular response to stress includes synthesis of specific stress proteins in the presence of a generalized suppression of protein synthesis. The response occurs in intact animals, individually stressed organs of intact animals, donor organs upon removal, regardless of preservation methods, and cells in culture. The molecular biology of stress protein induction is not understood. While stress proteins are beneficial, overall suppression of protein synthesis, if prolonged, is harmful. Since altered energy metabolism is integral to stress induction, we examined the mitochondria to determine if they could provide a possible molecular mechanism for initiating the response. Rat myoblasts were incubated at varying temperatures for up to 120 min in [35 S] methionine. Proteins were separated electrophoretically and newly synthesized proteins visualized autoradiographically. Isolated mitochondria from resting rat myoblasts were then stressed, label incorporation determined, and newly synthesized protein was visualized. Stress sharply suppressed protein synthesis in mitochondria but autoradiograms of stressed mitochondria showed that a single stress protein of 18 kDa was synthesized. Mitochondria independently respond to stress and synthesize a stress protein from their own DNA. This protein may provide an intermediary pathway that links stressful conditions in the environment to the overall response observed in the cell.

The cell cycle-coupled expression of topoisomerase IIalpha during S phase is regulated by mRNA stability and is disrupted by heat shock or ionizing radiation

Topoisomerase II is a multifunctional protein required during DNA replication, chromosome disjunction at mitosis, and other DNA-related activities by virtue of its ability to alter DNA supercoiling. The enzyme is encoded by two similar but nonidentical genes: the topoisomerase IIalpha and IIbeta genes. In HeLa cells synchronized by mitotic shake-off, topoisomeraseII alpha mRNA levels were found to vary as a function of cell cycle position, being 15-fold higher in late S phase (14 to 18 h postmitosis) than during G1 phase. Also detected was a corresponding increase in topoisomerase IIalpha protein synthesis at 14 to 18 h postmitosis which resulted in significantly higher accumulation of the protein during S and G2 phases. Topoisomerase IIalpha expression was not dependent on DNA synthesis during S phase, which could be inhibited without effect on the timing or level of mRNA expression. Mechanistically, topoisomerase IIalpha expression appears to be coupled to cell cycle position mainly through associated changes in mRNA stability. When cells are in S phase and mRNA levels are maximal, the half-life of topoisomerase IIalpha mRNA was determined to be approximately 30 min. A similar decrease in mRNA stability was also induced by two external factors known to delay cell cycle progression. Treatment of S-phase cells, at the time of maximum topoisomerase IIalpha mRNA stability, with either ionizing radiation (5 Gy) or heat shock (45 degrees C for 15 min) caused the accumulated topoisomerase IIalpha mRNA to decay. This finding suggests a potential relationship between stress-induced decreases in topoisomerase IIalpha expression and cell cycle progression delays in late S/G2.

The effect of gamma-radiation and heat shock on protein synthesis and antioxidant enzymes in the gastrointestinal parasite, Heligmosomoides polygyrus

Protein synthesis and antioxidant enzyme activities were investigated in gamma-irradiated (300 Gy) and heat shocked (42 degrees C) larval stages of the gastrointestinal parasite, Heligmosomoides polygyrus bakeri (H. polygyrus). No qualitative or quantitative differences were observed in the incorporation of (35S)-methionine into somatic proteins of unirradiated or irradiated exsheathed third-stage (L3) larvae at either 37 degrees C or 42 degrees C. The rate of protein synthesis doubled in L3 stages maintained at 42 degrees C compared with 37 degrees C, irrespective of whether the larvae had been irradiated or not. The composition of excretory/secretory (ES) proteins varied between unirradiated and irradiated exsheathed L3 larvae maintained under identical conditions. Prominent heat-inducible proteins of 26 and 17 kDa were synthesised and excreted at 42 degrees C by both unirradiated and irradiated L3 stages. No major differences in protein synthesis could be detected between unirradiated and irradiated fourth-stage (L4) larvae. Temperature elevation significantly reduced protein synthesis in L4 stages, most notably in unirradiated parasites. Heat-inducible proteins were not detected in response to either irradiation or temperature elevation in L4 larvae. Immune sera recognised a similar spectrum of antigens in both unirradiated and irradiated L4 somatic and ES preparations and reacted with antigens from irradiated L4 parasites with less intensity than with antigens from unirradiated L4 larvae. Catalase was the only antioxidant enzyme examined with activity that changed significantly in irradiated parasites, being reduced to approximately 36% of normal levels in irradiated L4 stages. No significant difference existed between irradiated and unirradiated parasites in the levels of activity of superoxide dismutase and glutathione reductase.

Glycosylation of rat NGF receptor ectodomain in the yeast Saccharomyces cerevisiae

Here we studied the glycosylation of a mammalian protein, the ectodomain of rat nerve growth factor receptor (NGFRe), in Saccharomyces cerevisiae. NGFRe is secreted to the culture medium of S. cerevisiae if it is fused to a polypeptide (hsp 150 delta) carrier. The hsp 150 delta-carrier has 95 serine and threonine residues, which were extensively O-glycosylated. In spite of 41 potential sites, NGFRe lacked O-glycans, whether fused to the carrier or not. Distortion of the conformation of NGFRe by inhibition of disulfide formation did not promote O-glycosylation, whereas N-glycosylation was enhanced. Thus, the serine and threonine residues of the hsp 150 delta-NGFRe fusion protein were highly selectively O-glycosylated.

Heat shock protein synthesis and trehalose accumulation are not required for induced thermotolerance in depressed Saccharomyces cerevisiae

Intrinsic and heat shock induced thermotolerance of Saccharomyces cerevisiae was investigated in cells grown on glucose and acetate supplemented media. Heat shocked cells (37 degrees C/30 min), in either medium, exhibited induced synthesis of heat shock proteins (hsp) and trehalose. In all cases, with the notable exception of repressed cells of a relatively thermosensitive strain, heat shock acquisition of thermotolerance also occurred in the absence of protein synthesis and coincident decrease in trehalose accumulation. Results indicted that the marked increase in thermotolerance exhibited by non-fermenting (acetate) cells compared with fermenting (glucose) cells was not closely correlated with levels of hsp or trehalose. It was concluded that mechanisms for intrinsic and induced thermotolerance appear to be different and that growth on acetate endows cells with a biochemical predisposition, other than hsp or trehalose, that confers intrinsic tolerance, a factor which may be subject to heat induced modification.

Increased expression of the HDJ-2 heat shock protein in biopsies of human rejected kidney

The presence of donor-specific alloreactive helper and cytotoxic T cells has been described in allograft biopsies obtained from individuals undergoing acute allograft rejection of various solid organs. However, not all of these lymphocytes demonstrated specificity to mismatched donor HLA antigens. The identity of the antigens to which these T cells are directed to is still unknown at present. The possibility that heat shock proteins (Hsp) could serve as antigenic determinants to which these T cells respond has been raised. We have recently cloned and characterized a novel Hsp of 45Kd molecular weight. In the present study we show that the synthesis of this Hsp (HDJ-2) as well as Hsp60 is significantly elevated in kidney biopsies from individuals undergoing acute and chronic rejection. No message was detected either for HDJ-2 or Hsp60 in biopsies obtained from normal pretransplant kidneys or posttransplant kidneys with no rejection. However, there was some increase in Hsp in miscellaneous causes of allograft dysfunction such as infection and drug allergy. But, this was not as consistent as that noted for allograft rejection. This marked increase in Hsp expression during allograft rejection suggests Hsps as potential candidates for antigenic determinants contributing to kidney rejection.

Co-induction of DNA relaxation and synthesis of DnaK and GroEL proteins in Escherichia coli by expression of LetD (CcdB) protein, an inhibitor of DNA gyrase encoded by the F factor

We examined the influence of overexpression of LetD (CcdB) protein, an inhibitor of DNA gyrase encoded by the F factor of Escherichia coli, on DNA supercoiling and induction of heat shock proteins. Cells were transformed with a plasmid carrying the structural gene for LetD protein under control of the tac promoter, and LetD protein was induced by adding isopropyl beta-D-thiogalactopyranoside (IPTG) to the culture medium. Analysis by agarose gel electrophoresis in the presence of chloroquine revealed relaxation of plasmid DNA in cells depending on the concentration of IPTG employed for induction. Protein pulse-labeling experiments with [35S]methionine and cysteine revealed that synthesis of DnaK and GroEL proteins was also induced by IPTG, and concentrations necessary for DNA relaxation and induction of the heat shock proteins were much the same. Expression of mutant LetD protein lacking two amino acid residues at the C-terminus induced neither DNA relaxation nor the synthesis of DnaK and GroEL proteins. Induction of wild-type LetD protein but not mutant LetD protein markedly enhanced synthesis of sigma32. We interpret these results to mean that DNA relaxation in cells caused by the expression of LetD protein induces heat shock proteins via increased synthesis of sigma32.

Comparison of the cell cycle regulated synthesis and phosphorylation of stress proteins, actin isoforms and a novel actin-like protein following drug administration in cultured rat lymphocytes

Administration of phytohemagglutinin initiated cycling of rat lymphocytes in vitro, and following treatment with this drug and other drugs in combination, lymphocytes were pulse labeled with [3H] leucine of [32P] phosphate. The nuclei were isolated from lymphocytes and collected from partitions of the cell cycle, and the proteins analyzed from fluorographs following gel electrophoresis for protein biomarkers after drug exposure. Stress proteins (sps) were dependent on a specific drug or drugs in combination (i.e., interleukin-2, bleomycin) for their synthesis that occurred only during the G1-phase of the cell cycle. An "actin-like" protein (A4) with electrophoretic mobilities similar to the actin complex, was synthesized in S and G2 phases and phosphorylated in all phases of the cell cycle only following the administration of drugs in combination. A4 exhibited a binding affinity for sp 24 that was cell cycle regulated (i.e., A4 from S phase did not bind with sp 24, but A4 from G2 phase did bind with the sp. Protein A4 appeared similar in some structural aspects to the nonmuscular actin isoform family but differed in epitope, suggesting a unique relationship and represented a stable protein, perhaps a product from the mutation of an actin gene. The dependence of certain sps and protein A4 for their induction by drugs in combination may serve as biomarkers of chemical interaction and toxicity.

Effect of combined alpha IFN and prostaglandin A1 treatment on vesicular stomatitis virus replication and heat shock protein synthesis in epithelial cells

The antiviral activity of prostaglandin A (PGA) and interferons (IFNs) has been widely described. In the present report, we investigated the effect of combined alpha IFN and PGA1 treatment on vesicular stomatitis virus (VSV) replication and on heat shock protein (HSP) induction in monkey epithelia cells. In uninfected cells, PGA1 caused a dose-dependent induction of HSP70, HSP90 and HSP110, while alpha IFN did not affect HSP synthesis. Alpha-IFN suppressed VSV replication dose-dependently, even when cells were treated after virus infection. VSV protein synthesis was not affected by alpha IFN, indicating a block at the level of virus assembly or maturation. PGA1 caused a dose-dependent inhibition of VSV replication, and suppressed VSV protein synthesis at concentrations which induced the synthesis of high levels of HSP70. The combined treatment with low doses of alpha IFN or PGA1, which only moderately inhibited VSV replication when administered separately, was found to suppress VSV production by more than 95%, and resulted in a 3-fold increase of HSP70 synthesis as compared to PGA1 alone. These results demonstrate a co-operative effect of PGA1 and alpha IFN against VSV infection and suggest that alpha IFN can potentiate the cellular response to HSP induction in virus-infected cells.

Alteration of gonococcal protein expression in acidic culture

We grew Neisseria gonorrhoeae under acidic, neutral, and alkaline conditions and noted altered expression of at least 12 outer membrane proteins between 31 and 100 kDa in size. One protein whose expression was upregulated under acidic conditions was gonococcal heat shock protein 63. These proteins may contribute to the pathogenesis of gonorrhea in the urogenital tract.

Constitutive expression of HSP 72 in swine heart

Stress-induced regulation of the 72 kD heat shock protein (HSP 72), the major stress inducible protein in mammalian cells, is mediated by the activation and binding of a heat shock transcription factor (HSF) to a specific sequence in the 5' region of the promoter termed the heat shock element (HSE). In agreement with this regulation, HSP 72 is absent in most cells under unstressed conditions but is rapidly synthesized following exposure to protein damaging stressors. An exception is the skeletal muscle, where HSP 72 is constitutively expressed in muscles that express the beta myosin heavy chain (beta-MHC) protein. Since beta-MHC is also expressed in the ventricles of large mammals, we have examined if HSP 72 was also constitutively expressed in beta-MHC positive hearts. Chambers of the heart muscle from Yorkshire swine were examined for alpha-MHC, beta-MHC and HSP 72 content. HSF:HSE activation was also assessed by gel shift analyses. In the swine heart, atria and ventricles differed in their alpha-MHC and beta-MHC protein content but all expressed a high HSP 72 content. Gel shift analyses demonstrated no HSF:HSE binding in extracts from unstressed swine hearts. These results indicate that HSP 72 is constitutively expressed in all portions of the swine heart and this expression may not be dependent on an HSF:HSE interaction.

Synthesis rates of cellular proteins involved in translation and protein folding are strongly altered in response to overproduction of basic fibroblast growth factor by recombinant Escherichia coli

The cellular response to temperature-induced production of human basic fibroblast growth (bFGF) factor by recombinant E. coli (bacteriophage lambda PRPL promoter/cI857 repressor expression system) was studied by one- and two-dimensional gel electrophoresis. Temperature shift from 30 to 42 degrees C caused the induction of heat-shock protein synthesis and the repression of synthesis of ribosomal proteins and the protein folding catalyst trigger factor. Compared to control cells, carrying the expression vector without structural bFGF gene cells, producing the heterologous protein exhibited a stronger increase in the synthesis rate of heat-shock proteins ClpB (HtpM), DnaK, HtpG, GroEL, GrpE, and IbpB (HtpE) in response to temperature upshift. Unexpectedly, formation of the chaperone heat-shock protein GroES was not detected after temperature shift to 42 degrees C in cells producing bFGF. In addition to amplified heat-shock protein formation, the syntheses of ribosomal proteins and of the protein folding catalyst trigger factor were more severely repressed after temperature upshift in cells producing bFGF. In conclusion, the normal cellular stress response caused by the high inducing temperature was strongly amplified by heterologous protein synthesis. In particular, syntheses of proteins involved in translation and protein folding were affected by the overproduction of the heterologous protein.

Thermoregulatory and heat-shock protein response deficits in cold-exposed diabetic mice

Cold-induced expression of heat-shock proteins (HSPs) has been suggested to facilitate thermogenesis in brown adipose tissue (BAT). However, the regulation of this response and the mechanism supporting this facilitation have not been established. Because of the significant role of insulin in maintaining BAT thermogenesis, we employed a transgenic mouse model of diabetes to investigate the regulation and function of HSPs in BAT thermogenesis. These transgenic mice overexpress a calmodulin minigene regulated by the rat insulin II promotor, resulting in severe diabetes characterized by elevated blood glucose and glucagon that coincides with reduced serum and pancreatic insulin. Body temperature (Tb) of diabetic mice dropped significantly faster during a 3-h cold exposure (6 degrees C) than Tb of similarly treated control littermates. Cold exposure resulted in increased levels of constitutive and inducible HSP70 transcripts in control mice, but only constitutive HSP70 mRNA transcripts were induced in diabetic mice. Diabetes did not affect uncoupling protein induction, but cold-induced expression of members of other HSP families was reduced. Correspondingly, heat-shock regulatory factors were not activated in diabetic mice even though these factors were present. Phenylephrine induced HSP70 expression in control and diabetic animals, indicating that alpha-receptor-coupled HSP induction remained intact in BAT of diabetic mice. Insulin replacement restored the Tb response of diabetic mice as well as the HSP response. From these results it is clear that physiological signals that regulate cold-induced activation of BAT also regulate HSP expression in this tissue. This diabetic model provides a novel system in which the HSP response to cold has been selectively knocked out, making it a useful tool for the study of HSP regulation and function in BAT.

AlphaB-crystallin protects glial cells from hypertonic stress

AlphaB-crystallin and the small stress protein, heat shock protein of 27 kDa (HSP27), share structural similarities and are coordinately induced by classical stress stimuli. We have recently observed that hypertonic stress produced by high NaCl concentrations selectively induces alphaB-crystallin in glial cells. To examine divergence of the functional properties of these two related proteins, we have constructed stable alphaB-crystallin-expressing glial cell lines from the U-251 MG glioma cells, which are normally deficient in alphaB-crystallin expression but constitutively express HSP27. These transfected cells lines are more resistant to acute hypertonic stress than the parental line from which they were derived. Moreover, the parental line acclimates to stepwise increases in hypertonicity and upregulates endogenous alphaB-crystallin in the process but not HSP27. The overexpression of HSP27 and alphaB-crystallin in NIH/3T3 fibroblasts, a cell line that normally expresses little alphaB-crystallin and no HSP27, does not result in increased survival. This suggests that alphaB-crystallin interacts with cell-type specific mechanisms to aid in protection from hypertonic stress.

Heat shock proteins increase resistance to apoptosis

Heat shock treatment of cells increases their survival and resistance to apoptosis. The kinetics of development of this resistance correlates with the kinetics of synthesis of heat shock proteins (hsps). U937 and Wehi-s cells were cultured for 1 h at 42 degrees C, conditions which induced the synthesis of heat shock proteins 27, 70, and 90. The cells were subsequently permitted to recover for a 2-h period, prior to exposure to the apoptosis inducing agents actinomycin-D (5 micrograms/ml), camptothecin (5 micrograms/ml), and etoposide (25 micrograms/ml). Apoptosis was determined by both DNA fragmentation and flow cytometric analysis. Heat-shocked cultures had a smaller number of apoptotic compared to control cultures when both were exposed to apoptosis inducing stimuli. Transfected Wehi-s cells constitutively overexpressing human hsp 70 or 27 were then examined for their resistance to apoptosis inducing by these drugs. Using the MTT assay, hsp 27 and 70 overexpressing cells exhibited an increased resistance to cell death when compared to the parental line. The parental line demonstrated features of apoptosis, that is, cell shrinkage and single- and double-strand DNA breaks. Taken together these results demonstrate that an increase in cellular levels of hsp 27 or 70, either by a mild heat shock treatment or by stable transfection, increases the resistance of U937 and Wehi-s cells to apoptotic cell death.

Tissue-specific posttranslational modification of the small heat shock protein HSP27 in Drosophila

Drosophila sHSPs (small heat shock proteins) are expressed in the absence of stress in specific regions of the central nervous system and in gonads of young adults flies. In these two organs, the sHSPs show a cell-specific and developmental stage-specific pattern of expression suggesting distinct regulation and function(s) of each individual sHSP (R. Marin et al., Dev. Genet. 14, 69-77, 1993). Since mammalian HSP27 has been reported to be phosphorylated through a complex novel cascade implicating distinct kinases, we examined whether two of the sHSPs (HSP27 and HSP23) exist in different isoforms as a result of posttranslational modification in vivo. HSP27 and HSP23 were analyzed in various tissues in unstressed and heat-shocked flies. Four isoforms of HSP27 were found to be constitutively expressed in the nervous system and in testes and two in ovaries. The proportion of these isoforms relative to each other was specific to a given tissue. In the case of HSP23, two isoforms were expressed in the heads and in testes of unstressed flies. In ovaries, a low level of a single isoform of HSP23 was found. Heat shock caused an increase in the amount of preexisting HSP27 and HSP23 and the appearance of additional isoforms in ovaries. Susceptibility to phosphatase treatment indicated that isoforms of HSP27 were phosphoproteins. This was further supported by in vitro experiments in which Drosophila sHSPs were incubated with purified Chinese hamster HSP27 kinase. Only HSP27 was shown to be a substrate of this mammalian HSP27 kinase. The present data suggest that tissue- and HSP-specific posttranslational modification systems may modulate the function of these proteins in different cell types. Furthermore, the signal transduction pathways leading to phosphorylation of the sHSPs are conserved between mammals and Drosophila, and the sHSP kinase cascade may be developmentally regulated.

Thermal response in murine L929 cells lacking alpha B-crystallin expression and alpha B-crystallin expressing L929 transfectants

We investigated the role of alpha B-crystallin expression in the development of thermotolerance in murine L929 cells. An initial heat-shock of 10 min at 45 degrees C induced thermotolerance in these cells to a heat challenge at 45 degrees C administered 24 h later. The thermotolerance ratio at 10(-1) isosurvival was 1.7. Expression of alpha B-crystallin gene was not detected during the 24 h incubation at 37 degrees C following heat shock by either northern or western blots. In contrast, inducible HSP70 synthesis was observed during this time period. Thus, this cell line provided an unique system in which to examine the effects of transfected alpha B-crystallin on thermoresistance and thermotolerance. Cells stably transfected with alpha B-crystallin under the control of an inducible promoter did not show a significant increase in the ability to develop thermotolerance. However, a stably transfected L929 clone expressing high levels of constitutive alpha B-crystallin exhibited an approximately 50% increase in thermal resistance over parental and control cells. Though expression of alpha B-crystallin is not requisite for the development of thermotolerance in L929 cells, overexpression of transfected alpha B-crystallin can contribute to increased thermoresistance.

Interaction of ethanol with inducers of glucose-regulated stress proteins. Ethanol potentiates inducers of grp78 transcription

GRP78, a molecular chaperone expressed in the endoplasmic reticulum, is a "glucose-regulated protein" induced by stress responses that deplete glucose or intracisternal calcium or otherwise disrupt glycoprotein trafficking. Previously we showed that chronic ethanol exposure increases the expression of GRP78. To further understand the mechanism underlying ethanol regulation of GRP78 expression, we studied the interaction between ethanol and classical modulators of GRP78 expression in NG108-15 neuroblastoma x glioma cells. We found that, in addition to increasing basal levels of GRP78 mRNA ("induction"), ethanol produced greater than additive increases in the induction of GRP78 mRNA by the "classical" GRP inducers A23187, brefeldin A, and thapsigargin ("potentiation"). Both the ethanol induction and potentiation responses modulated grp78 gene transcription as determined by stable transfection analyses with the rat grp78 promoter. Ethanol potentiated the action of all classical inducers of grp78 transcription that were studied. In contrast, co-treatment with the classical GRP inducers thapsigargin and tunicamycin produced only simple additive increases in grp78 promoter activity. Transient transfection studies with deletion mutants of the rat grp78 promoter showed that cis-acting promoter sequences required for ethanol induction differ from those mediating responses to classical GRP inducers. Furthermore, linker-scanning mutations of the grp78 promoter suggested that the ethanol potentiation response required a cis-acting promoter element different from those involved in induction by ethanol or classical inducing agents. While the ethanol induction response required 16-24 h to be detectable, ethanol potentiation of thapsigargin occurred within 6 h. The potentiation response also decayed rapidly after ethanol removal. In addition, the protein kinase A inhibitor Rp-cAMPS and protein phosphatase inhibitor okadaic acid both increased ethanol potentiation of thapsigargin while Sp-cAMPS, an activator of protein kinase A, decreased ethanol potentiation. Taken together, our findings suggest two mechanisms by which ethanol regulates grp78 transcription, both differing from the action of classical GRP inducers such as thapsigargin. One mechanism (potentiation) involves a protein phosphorylation cascade and potentiates the action of classical GRP inducers. In contrast, GRP78 induction by ethanol involves promoter sequences and a mechanistic pathway separate from that of the ethanol potentiation response or classical GRP78 inducers. These studies show that ethanol produces a novel and complex regulation of grp78 transcription which could be of particular importance during neuronal exposure to GRP-inducing stressors as might occur with central nervous system injury.