Enhanced constitutive expression of the 27-kDa heat shock proteins in heat-resistant variants from Chinese hamster cells

Expression and activation of mitogen-activated protein kinases in matured porcine oocytes under thermal stress

In this study, we determined the expression and activation of p38 MAPK in matured porcine oocytes subjected to heat shock (HS). When MII oocytes were heated, only the phosphorylated p38 levels relative to the total p38 levels decreased (P < 0.01) after HS, but no clear relationship with HS treatments was observed in the ERK, JNK and p90^rsk expressions of matured oocytes. To confirm p38 activation in matured oocytes, immunocytochemical staining was performed to localize its expression and distribution in the ooplasm, and the results were largely consistent with previous Western blot analyses. Moreover, when matured oocytes were co-cultured with a P38 MAPK inhibitor, SB203580, for 4 h at 41.5 C, the activation of its immediate downstream substrate MAPKAPK-2 was not inhibited within any of the treatment groups. It appears that the MAPKAPK2 levels increased only under prolonged culture (HS4h and C4h) compared with the control group. In conclusion, p38 activity in porcine oocytes was decreased after exposure to HS and prolonged culture. These alterations of p38 and activation of MAPKAPK2 may be associated with porcine oocyte viability under HS conditions, and a potential cross-talk between p38 MAPK and other signaling cascades may exist, which warrants additional investigation.

Ginkgo biloba extract decreases non-small cell lung cancer cell migration by downregulating metastasis-associated factor heat-shock protein 27

Heat-shock proteins (HSPs) are molecular chaperones that protect proteins from damage. HSP27 expression is associated with cancer transformation and invasion. Ginkgo biloba extract (EGb761), the most widely sold herbal supplement, has antiangiogenic effects and induces tumor apoptosis. Data regarding the effect of EGb761 on HSP expression is limited, particularly in cancer. HSP27 expression in paired tumors and normal lung tissues of 64 patients with non-small cell lung cancer (NSCLC) were detected by real-time PCR, western blotting, and immunohistochemistry. NSCLC cell lines (A549/H441) were used to examine the migratory abilities in vitro. NSCLC tissue showed higher HSP27 expression than normal lung tissue. Kaplan–Meier survival analysis showed that NSCLC patients with low HSP27 expression ratio (<1) had significantly longer survival time than those with a high expression ratio (>1) (p = 0.04). EGb761 inhibited HSP27 expression and migratory ability of A549/H441 cells, which is the same as HSP27-siRNA transfection effect. Moreover, EGb761 treatment activated the AKT and p38 pathways and did not affect the expression of PI3K, ERK, and JNK pathways. HSP27 is a poor prognostic indicator of NSCLC. EGb761 can decrease the migration ability of A549/H441 by inhibiting HSP27 expression most likely through AKT and p38 MAPK pathways activation.

Atypical heat shock response and acquisition of thermotolerance in P388D1 cells

Reports of atypical heat shock response in some tumour cell lines emphasize the possibilities of alternate stress response mechanisms. We demonstrate here that P388D1, a mouse macrophage tumour cell line, failed to induce heat shock proteins (HSPs) in response to either heat stress (42 °C, 1h) or to heavy metal stress induced by arsenic trioxide (5-20 μM). Heat shock transcriptional factor 1 (HSF1) that mediates transcriptional up regulation of HSPs during stress was found to be deficient in transactivation despite its binding to the promoter region of HSP genes. Interestingly, cells exhibited thermotolerance in the absence of induced HSPs. However, the tolerance was abrogated in cells treated with cycloheximide (250 ng/ml) suggested that thermotolerance was dependent on de novo protein synthesis.

Changes in Plasma Level of Heat Shock Protein 27 After Acute Coronary Syndrome

We assessed the association between serum heat shock protein 27 (Hsp-27)concentrations in patients with acute coronary syndrome (ACS) and compared them with healthy participants. Patients with ACS (n = 75) were recruited and their biochemical parameters were compared with 75 healthy participants. Heat shock protein 27 concentrations were measured from blood samples taken on admission and 12 hours after the onset of chest pain. In the patient group, Hsp-27 concentrations (31.62 [20.12-38.51] ng/mL) in the first blood samples were significantly ( P < .001) higher than in control samples (20.12 [16.67-28.17] ng/mL). In patients, serum Hsp-27 levels on admission were significantly ( P < .001) higher than for the samples collected 12 hours after the onset of chest pain (25.87 [15.52-31.62]); the latter did not differ significantly from samples of healthy controls. In conclusion, serum Hsp-27 concentrations are elevated in the early hours following ACS, but fall to levels near to those in healthy individuals after about 12 hours from the onset of chest pain.

The role of the cysteine residue in the chaperone and anti-apoptotic functions of human Hsp27

The small heat shock protein Hsp27 is a molecular chaperone and an anti-apoptotic protein. Human Hsp27 has one cysteine residue at position 137. We investigated the role of this cysteine residue in the chaperone and anti-apoptotic functions of Hsp27 by mutating the cysteine residue to an alanine (Hsp27(C137A)) and comparing it to wild-type protein (Hsp27(WT)). Both proteins were multi-subunit oligomers, but subunits of Hsp27(WT) were disulfide-linked unlike those of Hsp27(C137A), which were monomeric. Hsp27(C137A) was indistinguishable from Hsp27(WT) with regard to its secondary structure, surface hydrophobicity, oligomeric size and chaperone function. S-thiolation and reductive methylation of the cysteine residue had no apparent effect on the chaperone function of Hsp27(WT). The anti-apoptotic function of Hsp27(C137A) and Hsp27(WT) was studied by overexpressing them in CHO cells. No difference in the caspase-3 or -9 activity was observed in staurosporine-treated cells. The rate of apoptosis between Hsp27(C137A) and Hsp27(WT) overexpressing cells was similar whether the cells were treated with staurosporine or etoposide. However, the mutant protein was less protective relative to the wild-type protein in preventing caspase-3 and caspase-9 activation and apoptosis induced by 1 mM H(2)O(2) in CHO and HeLa cells. These data demonstrate that in human Hsp27, disulfide formation by the lone cysteine does not affect its chaperone function and anti-apoptotic function against chemical toxicants. However, oxidation of the lone cysteine in Hsp27 might at least partially affect the anti-apoptotic function against oxidative stress.

Increased monomerization of mutant HSPB1 leads to protein hyperactivity in Charcot-Marie-Tooth neuropathy

Small heat shock proteins are molecular chaperones capable of maintaining denatured proteins in a folding-competent state. We have previously shown that missense mutations in the small heat shock protein HSPB1 (HSP27) cause distal hereditary motor neuropathy and axonal Charcot-Marie-Tooth disease. Here we investigated the biochemical consequences of HSPB1 mutations that are known to cause peripheral neuropathy. In contrast to other chaperonopathies, our results revealed that particular HSPB1 mutations presented higher chaperone activity compared with wild type. Hyperactivation of HSPB1 was accompanied by a change from its wild-type dimeric state to a monomer without dissociation of the 24-meric state. Purification of protein complexes from wild-type and HSPB1 mutants showed that the hyperactive isoforms also presented enhanced binding to client proteins. Furthermore, we show that the wild-type HSPB1 protein undergoes monomerization during heat-shock activation, strongly suggesting that the monomer is the active form of the HSPB1 protein.

Comparison of Hsps expression after radio-frequency field exposure in three human glioma cell lines

OBJECTIVE

To investigate and compare the effect of radio-frequency (RF) field exposure on expression of heat shock proteins (Hsps) in three human glioma cell lines (MO54, A172, and T98).

METHODS

Cells were exposed to sham or 1950 MHz continuous-wave for 1 h. Specific absorption rates (SARs) were 1 and 10 W/kg. Localization and expression of Hsp27 and phosphorylated Hsp27 ((78) Ser) (p-Hsp27) were examined by immunocytochemistry. Expression levels of Hsp27, p-Hs27, and Hsp70 were determined by Western blotting.

RESULTS

The Hsp27 was primarily located within the cytoplasm, p-Hsp27 in both cytoplasm and nuclei of MO54, A172, and T98 cells. RF field exposure did not affect the distribution or expression of Hsp27. In addition, Western blotting showed no significant differences in protein expression of Hsp27 or Hsp70 between sham- and RF field-exposed cells at a SAR of 1 W/kg and 10 W/kg for 1 h in three cells lines. Exposure to RF field at a SAR of 10 W/kg for 1 h slightly decreased the protein level of phosphorylated Hsp27 in MO54 cells.

CONCLUSION

The 1950 MHz RF field has only little or no apparent effect on Hsp70 and Hsp27 expression in MO54, A172, and T98 cells.

HSP27 phosphorylation increases after 45°C or 41°C heat shocks but not after non-thermal TDMA or GSM exposures

PURPOSE

Experiments with cultured HeLa, S3 and E.A. Hy296 cells were performed to determine if exposure to acute (30 min at 45 degrees C) or chronic (2 h at 41 degrees C) heat shocks or to non-thermal exposures of radiofrequency radiation (RF) induce changes in HSP27 phosphorylation.

MATERIALS AND METHODS

The radiofrequency (RF) exposures used in this study were 847 MHz time division multiple access modulated (TDMA) at a specific absorption rate (SAR) of 5 W kg-1 for 1, 2 or 24 h or 900 MHz GSM modulated (GSM) at a SAR of 3.7 W kg-1 for 1, 2 or 5 h. HSP27 phosphorylation was evaluated by resolving the various phosphorylation forms using two-dimensional gel electrophoresis measuring the relative amount of each by densitometry. Alternatively, an antibody specific for phosphorylated HSP27 was used to detect changes in HSP27 phosphorylation levels. All heat shock and RF exposure conditions were analysed simultaneously along with a matched incubator control sample. Each experiment was repeated three times.

RESULTS

Following heat shock, the degree of phosphorylation of HSP27 varied with the heat dose, with acute hyperthermia (45 degrees C) having an increased proportion of higher phosphorylated forms. Exposure of HeLa S3 cells to 5 W kg-1 TDMA for 1, 2 or 24 h did not induce significant differences in the levels of HSP27 phosphorylation compared to incubator control or sham. Exposure of E.A. Hy926 cells to 3.7 W kg-1 900 MHz GSM for 1, 2 or 5 h did not induce significant differences in the levels of HSP27 phosphorylation compared to sham exposed.

CONCLUSIONS

Acute and moderate hyperthermia significantly increase HSP27 phosphorylation, but there was no significant change in the levels of HSP27 following non-thermal exposure to TDMA and GSM modulated RF radiations.

Role of Membrane Components in Thermal Injury of Cells and Development of Thermotolerance

Exposure of cells to hyperthermia induces a transient resistance to subsequent heat treatment. The specific mechanisms responsible for hyperthermic cell killing and thermotolerance development are not well understood. It seems that heat may induce at least two different states of thermotolerance, of which one is dependent on protein synthesis. The expression of thermotolerance may include multiple cytoplasmic and membrane components. A number of studies have indicated that membranes play an important role in governing the thermal injury of cells. It seems, therefore, that heat denatured plasma membrane proteins may be a potential target for thermal stress and a trigger for the induction of thermotolerance. The localization of heat shock proteins in the plasma membrane and the suggestion of thermal resistance in enucleate erythrocytes support this suggestion. However, a direct relationship between the plasma membrane and hyperthermic killing or development of thermotolerance has not been found.

Body cooling causes normalization of cardiac protein expression and function in a rat heatstroke model

Cardiac dysfunction contributes to heatstroke genesis, which can be ameliorated by whole body cooling. A comparative analysis using two-dimensional in-gel electrophoresis of cardiac protein patterns is performed in rat controls, untreated heatstroke rats, and whole body cooling-treated heatstroke rats. After the onset of heatstroke, animals display hypotension and altered cardiac protein profiles, which can be reversed by whole body cooling. Thus, the proteomic mechanisms exerted by body cooling during heatstroke are elucidated by the current results.

Comprehensive characterization of heat shock protein 27 phosphorylation in human endothelial cells stimulated by the microbial dithiole thiolutin

Thiolutin is a sulfur-based microbial compound with known activity as an angiogenesis inhibitor. Relative to previously studied angiogenesis inhibitors, thiolutin is a remarkably potent inducer of heat shock protein 27 (Hsp27) phosphorylation. This phosphorylation requires p38 kinase but is independent of increased p38 phosphorylation. To elucidate how thiolutin regulates Hsp27 phosphorylation and ultimately angiogenesis, Hsp27 was immunoprecipitated using nonphosphorylated and phospho-Ser78 specific antibodies from lysates of thiolutin treated and untreated human umbilical vein endothelial cells and analyzed by LC-MS. Separate LC-MS analyses of Lys-C, Lys-C plus trypsin, and Lys-C plus Glu-C digests provided 100% sequence coverage, including the identification of a very large 13 kDa Lys-C fragment using a special sample handling procedure (4 M guanidine HCl) prior to the LC-MS analysis to improve the large peptide recovery. The analysis revealed a novel post-translational modification of Hsp27 involving truncation of the N-terminal Met and acetylation of the penultimate Thr. Analysis of a Glu-C fragment containing two phosphorylation sites, Ser78 and Ser82, and a tryptic fragment containing the other phosphorylation site, Ser15, enabled quantitative stoichiometry of Hsp27 phosphorylation by LC-MS. The strategy revealed details of Hsp27 phosphorylation, including significant di-phosphorylation at both Ser78 and Ser82, that would be difficult to obtain by traditional approaches because oligomerization of the hydrophobic N-terminal region of the molecule prevents efficient enzymatic cleavage. The combination of Western blotting, immunoprecipation, and LC-MS provides a quantitative analysis of thiolutin-stimulated Hsp27 phosphorylation and further defines the role of Hsp27 in the antiangiogenic activities of thiolutin and related dithiolethiones.

Mechanisms of Activation and Regulation of the Heat Shock-Sensitive Signaling Pathways

Heat shock (HS), like many other stresses, induces specific and highly regulated signaling cascades that promote cellular homeostasis. The three major mitogen-activated protein kinases (MAPK) and protein kinase B (PKB/Akt) are the most notable of these HS-stimulated pathways. Their activation occurs rapidly and sooner than the transcriptional upregulation of heat shock proteins (Hsp), which generate a transient state of extreme resistance against subsequent thermal stress. The direct connection of these signaling pathways to cellular death or survival mechanisms suggests that they contribute importantly to the HS response. Some of them may counteract early noxious effects of heat, while others may bolster key apoptosis events. The triggering events responsible for activating these pathways are unclear. Protein denaturation, specific and nonspecific receptor activation, membrane alteration and chromatin structure perturbation are potential initiating factors.

Effects of a 2450 MHz high-frequency electromagnetic field with a wide range of SARs on the induction of heat-shock proteins in A172 cells

In this study, we investigated whether exposure to 2450 MHz high-frequency electromagnetic fields (HFEMFs) could act as an environmental insult to evoke a stress response in A172 cells, using HSP70 and HSP27 as stress markers. The cells were exposed to a 2450 MHz HFEMF with a wide range of specific absorption rates (SARs: 5-200 W/kg) or sham conditions. Because exposure to 2450 MHz HFEMF at 50-200 W/kg SAR causes temperature increases in culture medium, appropriate heat control groups (38-44 degrees C) were also included. The expression of HSP 70 and HSP 27, as well as the level of phosphorylated HSP 27 ((78)Ser) (p-HSP27), was determined by Western blotting. Our results showed that the expression of HSP 70 increased in a time and dose-dependent manner at >50 W/kg SAR for 1-3 h. A similar effect was also observed in corresponding heat controls. There was no significant change in HSP 27 expression caused by HFEMF at 5-200 W/kg or by comparable heating for 1-3 h. However, HSP 27 phosphorylation increased transiently at 100 and 200 W/kg to a greater extent than at 40-44 degrees C. Phosphorylation of HSP 27 reached a maximum after 1 h exposure at 100 W/kg HFEMF. Our results suggest that exposure to a 2450 MHz HFEMF has little or no apparent effect on HSP70 and HSP27 expression, but it may induce a transient increase in HSP27 Phosphorylation in A172 cells at very high SAR (>100 W/kg).

Heat shock protein 27: its potential role in vascular disease

Heat shock proteins are molecular chaperones that have an ability to protect proteins from damage induced by environmental factors such as free radicals, heat, ischaemia and toxins, allowing denatured proteins to adopt their native configuration. Heat shock protein-27 (Hsp27) is a member of the small Hsp (sHsp) family of proteins, and has a molecular weight of approximately 27 KDa. In addition to its role as a chaperone, it has also been reported to have many additional functions. These include effects on the apoptotic pathway, cell movement and embryogenesis. In this review, we have focused on its possible role in vascular disease.

Hsp70 accumulation and ultrastructural features of lung and liver induced by ethanol treatment with and without l-carnitine protection in rats

This study examined Hsp70 accumulation and the subcellular characteristics of liver and lung when exposed to ethanol (EtOH), with and without L-carnitine protection. Female Sprague-Dawley rats, 150-200 g body weight, were randomized into four groups: Control (CON), Alcohol (ALC), L-carnitine (CAR) and Alcohol-L-carnitine (ALC-CAR). EtOH was administered per os at a dose of 4 g/kg body weight (1 ml) daily for 4 weeks. Before alcohol intake, an oral dose of 500 mg/kg body weight of L-carnitine was also administered to the ALC-CAR group. The liver and lung samples were subjected to Hsp70 Western blot and ultrastructural analysis. The Hsp70 accumulation was higher in the liver than in the lung samples. Hepatic Hsp70 accumulation was similar for all groups in contrast to lung, where the Hsp70 accumulation depends on the group studied. The ultrastructural results showed lung but not liver alterations, evidencing a stressful condition and subsequent cellular injury for lung tissue but not for liver. The ALC-CAR group showed less lung damage than the non-protected group and resembles the general appearance of the CON and CAR groups. EtOH intoxication induced differential cellular response in liver and lung in a dose and tissue dependent manner. L-carnitine seems to reduce lung EtOH-induced subcellular damage. The promotion of heat shock or stress proteins might represent one of the mechanisms involved that need to be further investigated.

Overexpression of heat-shock protein 20 in rat heart myogenic cells confers protection against simulated ischemia/reperfusion injury

AIM

To explore whether overexpression of the small heat shock protein HSP20 in rat cardiomyocytes protects against simulated ischemia/reperfusion (SI/R) injury.

METHODS

Recombinant adenovirus expressing HSP20 was used to infect rat H9c2 cardiomyocytes at high efficiency, as assessed by green fluorescent protein. H9c2 cells were subjected to SI/R stress; survival was estimated through assessment of lactate dehydrogenase and cell apoptosis through caspase-3 activity.

RESULTS

Overexpression of HSP20 decreased lactate dehydrogenase release by 21.5% and caspase-3 activity by 58.8%. Pretreatment with the protein kinase C inhibitor Ro-31-8220 (0.1 micromol/L) for 30 min before SI/R canceled the protective effect of HSP20. The selective mitochondrial K+ATP channel inhibitor 5-hydroxydecanoate (100 micromol/L) had a similar effect. However, the non-selective K+ATP channel inhibitor glibenclamide (100 micromol/L) had no significant effect.

CONCLUSION

These data indicate that the protective effect of HSP20 in vitro is primarily due to reduced necrotic and apoptotic death of cardiomyocytes, possibly via the protein kinase C/mitochondrial K+ATP pathway.

Characterization of heat shock protein 27 phosphorylation sites in renal cell carcinoma

The phosphorylation of heat shock protein 27 (HSP27) occurs differently in human renal cell carcinoma (RCC) compared to homologous normal kidney tissue. Two-dimensional electrophoresis was used to separate and visualize HSP27, via immunostaining with anti-HSP27 antibody, in tumor and normal renal samples, obtained after surgery resection from patients with RCC. The mean number of protein species was 21 in RCC and 15 in normal tissues. Selected spots were in-gel digested with trypsin, extracted and analyzed by microcapillary liquid chromatography (LC) electrospray ionization tandem mass spectrometry to confirm HSP27 protein identity and reveal phosphorylation sites. Loss of phosphopeptides due to extensive plumbing and/or metal components in automated LC-systems was limited by manual loading of samples directly onto the LC system using a homemade pressure vessel. Mass spectrometry (MS) analysis revealed that in three of the HSP27 protein species phosphorylation occurred at Serine 15 and in five at Serine 82 in a different pattern. The phosphorylation of Serine 15 and 82 was also investigated by immunohistochemistry on tissue sections. The data obtained using anti-HSP27Serine82phos-antibody are consistent with MS results, while the variance between results achieved by anti-HSP27Serine15phos-antibody and by MS is probably due to the low specificity of the antibody. Knowledge of the diversity and modulation of HSP27 phosphorylation protein species might represent useful markers involved in the differentiation of RCC.

Essential Role of the NH2-terminal WD/EPF Motif in the Phosphorylation-activated Protective Function of Mammalian Hsp27

Hsp27 is expressed at high levels after mild heat shock and contributes to making cells extremely resistant to subsequent treatments. The activity of the protein is regulated at the transcriptional level, but also by phosphorylation, which occurs rapidly during stress and is responsible for causing the dissociation of large 700-kDa Hsp27 oligomers into dimers. We investigated the mechanism by which phosphorylation and oligomerization modulate the protective activity of Chinese hamster Hsp27. In contrast to oligomer dissociation, which only required Ser90 phosphorylation, activation of Hsp27 thermoprotective activity required the phosphorylation of both Ser90 and Ser15. Replacement of Ser90 by Ala90, which prevented the dissociation of the oligomer upon stress, did cause a severe defect in the protective activity. Dissociation was, however, not a sufficient condition to activate the protein because replacement of Ser15 by Ala15, which caused little effect in the oligomeric organization of the protein, also yielded an inactive protein. Analyzes of mutants with short deletions in the NH2 terminus identified the Hsp27 WD/EPF or PF-rich domain as essential for protection, maintenance of the oligomeric structure, and in vitro chaperone activity of the protein. In light of a three-dimensional model of Hsp27 based on the crystallographic structure of wheat Hsp16.9, we propose that the conserved WD/EPF motif of mammalian Hsp27 mediates important intramolecular interactions with hydrophic surfaces of the alpha-crystallin domain of the protein. These interactions are destabilized by Ser90 phosphorylation, making the motif free to interact with heterologous molecular targets upon the additional phosphorylation of the nearby Ser15.

Survival pathways regulating the apoptosis induced by tumour necrosis factor-alpha in primary cultured bovine endothelial cells

The aim of the present study was to identify biochemical pathways driving the resistance of endothelial cells to apoptosis induced by tumour necrosis factor-alpha (TNF). (1) Although nuclear factor-kappa B (NF-kappaB) was activated by TNF, its inhibition by MG-132 failed to sensitize these cells. (2) The activation of protein kinase C (PKC) by phorbol ester completely abolished the TNF-induced cell death. (3) The phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin (Wo) triggered apoptosis and enhanced the TNF-induced cell death. (4) The MEK inhibitor PD98059 did not affect the TNF-induced apoptotic process. (5) The p38 is activated by TNF and its inhibition by SB203580 sensitized the cells to TNF. This is correlated with the inhibition of phosphorylation of heat-shock protein of 27 kDa (HSP27). These results indicate that TNF activates NF-kappaB, which does not drive any anti-apoptotic response, and p38, which plays an anti-apoptotic function probably through HSP27 phosphorylation. Moreover, PKC and PI3K are involved in the control of survival pathways.

Stress protection by a fluorescent Hsp27 chimera that is independent of nuclear translocation or multimeric dissociation

A chimeric protein consisting of enhanced green fluorescent protein (EGFP) fused to the N-terminus of human Hsp27 conferred stress protection in human A549 lung carcinoma and murine L929 cells that were stably transfected to express the chimera constitutively. The resultant protection was comparable with that in the same cell lines when they were transfected to express corresponding levels of Hsp27. Unlike L929 cells, A549 cells exhibit endogenous Hsp27 expression, whose expression was inhibited in proportion to the amount of fluorescent chimera expressed, suggesting that the A549 cells recognized the latter as Hsp27. Upregulation of Hsp27 or chimeric Hsp27 in all transfected cell lines (stable or transient transfection) caused no measurable change in cellular glutathione levels, indicating that glutathione played no role in the stress protection associated with either protein. Chimeric Hsp27 had a monomeric molecular weight of 55 kDa (that of Hsp27 plus EGFP) in both cell types and formed a 16-mer complex twice as massive as that formed by Hsp27. Heat shock or sodium arsenite induced phosphorylation of both chimeric Hsp27 and Hsp27, which resulted in the disaggregation of Hsp27 multimers in both cell types and disaggregation of 20% of the chimeric multimers in L929 cells. But chimeric Hsp27 multimers did not disaggregate after stress in A549 cells. Epifluorescence and confocal microscopy demonstrated that chimeric Hsp27 was restricted to the cytoplasm under normal growth conditions and after heat shock in all cells. This study supports the conclusions that Hsp27 stress protection requires neither its translocation into the nucleus nor the dissociation of its multimeric complex. Furthermore, it demonstrates that fluorescent chimeras of heat shock proteins can be functional and used to observe the protein's distribution within living cells.

Activation of the mitogen-activated protein kinase pathways by heat shock

In addition to inducing new transcriptional activities that lead within a few hours to the accumulation of heat shock proteins (Hsps), heat shock activates within minutes the major signaling transduction pathways involving mitogen-activated protein kinases, extracellular signal-regulated kinase, stress-activated protein kinase 1 (SAPK1)-c-Jun N-terminal kinase, and SAPK2-p38. These kinases are involved in both survival and death pathways in response to other stresses and may, therefore, contribute significantly to the heat shock response. In the case of p38, the activation leads to the phosphorylation and activation of one of the Hsps, Hsp27. Phosphorylation occurs very early during stress, is tightly regulated, and results from the triggering of a highly specific heat shock-sensing pathway.

Heat shock protein 27 associates with basolateral cell boundaries in heat-shocked and ATP-depleted epithelial cells

Heat stress alters epithelial barrier function, and heat stress preconditioning protects epithelial function from injury. Hsp27 is a small stress protein that has previously been shown to modulate actin assembly. Thus, by regulating actin filaments associated with cell junctions, hsp27 could alter epithelial function. To begin to address this hypothesis, the regulation and distribution of a human hsp27-green fluorescence fusion protein ((EGFP)hHsp27) that is expressed in cultured renal epithelial cells was assessed. (EGFP)hHsp27, like the endogenous hsp27, associated with the cytoskeleton in heat-stressed and chemically ATP-depleted cells, and both proteins were regulated similarly. Confocal microscopy of intact and detergent-lysed cells revealed novel distribution patterns in which (EGFP)hHsp27 associated with basolateral, but not apical, cell borders in injured cells. Double labeling studies revealed (EGFP)hHsp27 and actin filament colocalization in ATP-depleted cells. However, during heat shock, granules of (EGFP)hHsp27 were found at sites of cell-cell contact and in the cell body, but colocalization with actin was not apparent. Thus, heat stress and ATP depletion induce distinct patterns of hsp27 redistribution in epithelial cells, and sites of cell-cell and cell-substrate attachment are unique in their ability to recruit hsp27 during injury. The association of (EGFP)hHsp27 with basolateral cell boundaries supports a potential role for hsp27 in protection or regulation of epithelial cell-cell and cell-substrate attachments.

Expression of inducible Hsp70 enhances the proliferation of MCF-7 breast cancer cells and protects against the cytotoxic effects of hyperthermia

Heat shock proteins (Hsps) are ubiquitous proteins that are induced following exposure to sublethal heat shock, are highly conserved during evolution, and protect cells from damage through their function as molecular chaperones. Some cancers demonstrate elevated levels of Hsp70, and their expression has been associated with cell proliferation, disease prognosis, and resistance to chemotherapy. In this study, we developed a tetracycline-regulated gene expression system to determine the specific effects of inducible Hsp70 on cell growth and protection against hyperthermia in MCF-7 breast cancer cells. MCF-7 cells expressing high levels of Hsp70 demonstrated a significantly faster doubling time (39 hours) compared with nonoverexpressing control cells (54 hours). The effect of elevated Hsp70 on cell proliferation was characterized further by 5-bromo-2'deoxyuridine labeling, which demonstrated a higher number of second and third division metaphases in cells at 42 and 69 hours, respectively. Estimates based on cell cycle analysis and mean doubling time indicated that Hsp70 may be exerting its growth-stimulating effect on MCF-7 cells primarily by shortening of the G0/G1 and S phases of the cell cycle. In addition to the effects on cell growth, we found that elevated levels of Hsp70 were sufficient to confer a significant level of protection against heat in MCF-7 cells. The results of this study support existing evidence linking Hsp70 expression with cell growth and cytoprotection in human cancer cells.

Heat shock proteins--modulators of apoptosis in tumour cells

Apoptosis is a genetically programmed, physiological method of cell destruction. A variety of genes are now recognised as positive or negative regulators of this process. Expression of inducible heat shock proteins (hsp) is known to correlate with increased resistance to apoptosis induced by a range of diverse cytotoxic agents and has been implicated in chemotherapeutic resistance of tumours and carcinogenesis. Intensive research on apoptosis over the past number of years has provided significant insights into the mechanisms and molecular events that occur during this process. The modulatory effects of hsps on apoptosis are well documented, however, the mechanisms of hsp-mediated protection against apoptosis remain to be fully defined, although several hypotheses have been proposed. Elucidation of these mechanisms should reveal novel targets for manipulating the sensitivity of leukaemic cells to therapy. This review aims to explain the currently understood process of apoptosis and the effects of hsps on this process. Several proposed mechanisms for hsp protection against apoptosis and the therapeutic implications of hsps in leukaemia are also discussed.

Two distinct forms of MAPKAP kinase-2 in adult cardiac ventricular myocytes

Hsp27 kinase activities were studied in adult rat ventricular myocytes following sequential chromatography on Mono Q and Mono S. A basal level of activity was present following cell isolation. FPLC on Mono Q revealed three peaks of activity, peaks 'a', 'b', and 'c'. A fourth peak, 'd', was detected upon subsequent chromatography of the Mono Q flow-through on Mono S. Immunoblotting revealed that peaks 'a', 'b', and 'c' contained predominantly a 49 kDa form of MAPKAP kinase-2. Peak 'd' contained a 43 kDa form. 'In-gel' kinase assays using hsp27 indicated both forms of MAPKAP kinase-2 were active. No other bands of hsp27 kinase activity were detected. Both forms of hsp27 kinase immunoprecipitated with a MAPKAP kinase-2 antibody and have therefore been named MAPKAP kinase-2alpha (p49) and MAPKAP kinase-2beta (p43). MAPKAP kinase-2beta chromatographed on Superose 12 as a 60.7 kDa monomer whereas the behavior of MAPKAP kinase-2alpha suggested both a 65.7 kDa monomer and higher molecular mass complexes. Both activities phosphorylated hsp27 on serine residues, and two-dimensional phosphopeptide mapping indicated the same sites were phosphorylated. A tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), stimulated both MAPKAP kinase-2alpha and MAPKAP kinase-2beta activity. Inhibition of MEK activation with PD 98059 or p38alpha/beta MAP kinase activity with SB203580 blocked activation by PMA. However, whereas PD 98059 inhibited only the PMA-stimulated activation, SB203580 inhibited both PMA-stimulated and basal hsp27 phosphorylation. These data demonstrate the presence of two forms of MAPKAP kinase-2 in adult ventricular myocytes. Both forms are activated indirectly by the ERK MAP kinase pathway and directly by p38 MAP kinase but independently regulated.

Molecular chaperone function of mammalian Hsp70 and Hsp40--a review

Virtually all organisms respond to up-shifts in temperature (heat shock) by synthesizing a set of proteins called heat shock proteins (HSPs). The HSPs are induced not only by heat shock but also by various other environmental stresses. Induction of HSPs is regulated by the trans-acting heat shock factors (HSFs) and cis-acting heat shock element (HSE) present at the promoter region of each heat shock gene. Usually, HSPs are also expressed constitutively at normal growth temperatures and have basic and indispensable functions in the life cycle of proteins as molecular chaperones, as well as playing a role in protecting cells from the deleterious stresses. Molecular chaperones are able to inhibit the aggregation of partially denatured proteins and refold them using the energy of ATP. Recently, there are expectations for the use of molecular chaperones for the protection against and therapeutic treatment of inherited diseases caused by protein misfolding. In this review, the focus will be on the mammalian Hsp40, a homologue of bacterial DnaJ heat shock protein, and the beneficial functions of molecular chaperones.

Modified expression of a carrot small heat shock protein gene, hsp17. 7, results in increased or decreased thermotolerancedouble dagger

We have determined that one small heat shock protein gene, encoding Hsp17.7, plays an important role in the ability of carrot cells and plants to survive thermal stress. Transgenic cells and regenerated plants were generated in which the carrot Hsp17.7 gene was either constitutively expressed (denoted CaS lines) or expressed as a heat inducible antisense RNA (denoted AH lines). Thermotolerance measurements demonstrated that CaS lines were more thermotolerant than vector controls and AH antisense lines were less thermo- tolerant than vector controls. RNA analysis demonstrated that Hsp17. 7 mRNA was detectable, but not abundant, prior to heat shock in CaS cells, but not in vector control cells. Conversely, RNA analysis of antisense cells showed that, after heat shock, the amounts of mRNA for Hsp17.7 was moderately less abundant in AH cells than in vector controls. Analysis of protein synthesis in CaS cells did not indicate substantial synthesis or accumulation of Hsp17.7, or any small Hsp, at 23 degrees C. However, in the most thermotolerant line, protein synthesis was maintained at a higher rate than in other cell lines at a more extreme heat shock (42 degrees C). In contrast, antisense AH cells showed reduced synthesis of many Hsp, large and small. These results suggest that the Hsp17.7 gene plays a critical, although as yet not understood, role in thermotolerance in carrot. This represents the first demonstration of the ability to both increase and decrease thermotolerance by the manipulation of expression of a single gene.

Increased heat shock protein expression after stress in Japanese quail

Heat shock proteins (HSPs) have been shown to provide information on the biological impact of environmental stress to organisms, yet none have investigated the HSP response to stress in birds. Japanese quail were exposed to seven different stressors (mild restraint, loud noise, inescapable irritation, cold temperature, isolation in darkness, and two stressful social situations) and expression of HSP30, 60, 70, and 90 in heart, liver, lung, kidney and gonads was examined. Tonic Immobility (TI) tests were also conducted to assess whether the stressors increased fear response. Increased expression of HSP70 was found in the myocardial tissue of birds exposed to loud noise, inescapable irritation, cold temperature, and isolation in darkness. Increased expression of other HSPs was not apparent in the heart or any of the other all tissues examined. Longer TI was observed only in birds exposed to the noise stress. Evidence is presented that a fairly wide range of stressors caused increased expression of HSP70 in the Japanese quail myocardial tissue and that HSPs may provide useful biomarkers for the study of environmental stress in birds.

Induction of the 27-kDa heat shock protein (Hsp27) in the rat medulla oblongata after vagus nerve injury

The 27-kDa heat shock protein (Hsp27) is constitutively expressed in motor and sensory neurons of the brainstem. Hsp27 is also rapidly induced in the nervous system following oxidative and cellular metabolic stress. In this study, we examined the distribution of Hsp27 in the rat medulla oblongata by means of immunohistochemistry after the vagus nerve was cut or crushed. After vagal injury, rats were allowed to survive for 6, 12, 24 h, 2, 4, 7, 10, 14, 30, or 90 days. Vagus nerve lesions resulted in a time-dependent up-regulation of Hsp27 in vagal motor and nodose ganglion sensory neurons that expressed Hsp27 constitutively and de novo induction in neurons that did not express Hsp27 constitutively. In the dorsal motor nucleus of the vagus nerve (DMV) and nucleus ambiguus, the levels of Hsp27 in motor neurons were elevated within 24 h of injury and persisted for up to 90 days. Vagal afferents to the nucleus of the tractus solitarius (NTS) and area postrema showed increases in Hsp27 levels within 4 days that were still present 90 days postinjury. In addition, increases in Hsp27 staining of axons in the NTS and DMV suggest that vagus nerve injury resulted in sprouting of afferent axons and spread into areas of the dorsal vagal complex not normally innervated by the vagus. Our observations are consistent with the possibility that Hsp27 plays a role in long-term survival of distinct subpopulations of injured vagal motor and sensory neurons.

Phosphorylation of alphaB-crystallin and HSP27 is induced by similar stressors in HeLa cells

Three members of the small heat shock protein family, alphaA-, alphaB-crystallin, and HSP27, confer thermoresistance upon their overexpression in mammalian cells. Phosphorylation, in conjunction with the molecular chaperone-like activity of these small HSPs, is believed to be important for this in situ functional property. We here report the influence of heat shock and other kinds of stress on the phosphorylation of alphaA-, alphaB-crystallin, and HSP27 in stably transfected HeLa cells. It is observed that alphaB-crystallin becomes phosphorylated upon exposure to the same inducers as is HSP27, although to a lesser extent. In contrast, phosphorylation of alphaA-crystallin is very low upon heat stress and even absent when other stressors are used. This indicates that phosphorylation is not in all instances essential for the stress protective functioning of the various small HSPs.

Heat shock protein and p53 expression in head and neck squamous cell carcinoma

BACKGROUND

Heat shock proteins have been associated with the mutant form of the tumor suppressor gene, TP53, and with resistance to cancer chemotherapy.

METHODS

Archival tissues from 50 patients with head and neck squamous cell carcinoma who received primary surgical resection were examined for p53, HSP27, and HSP70 by immunohistochemistry and correlated with tumor stage, grade, and 5-year survival (alive or deceased).

RESULTS

Both heat shock proteins were strongly expressed in normal mucosa and in small (T1 and T2) tumors. Thirty (60%) of tumors were positive for p53, 43 (86%) for HSP27, and 34 (68%) for HSP70, with no association between p53 and heat shock protein expression. Twenty-five patients were alive (4 with disease), and 25 patients were deceased (9 from other causes). p53 Protein overexpression correlated with low-grade tumors. Only primary tumor site (i.e., oral cavity > larynx > oropharynx/base of tongue) and N stage were significantly associated with survival.

CONCLUSIONS

Heat shock proteins are expressed in normal upper respiratory tract squamous mucosa, and their role in carcinoma remains unclear. None of the markers, p53, HSP27, or HSP70, demonstrated prognostic significance for 5-year survival. We confirm the recognized association of cervical lymph node metastases with decreased survival.

Small heat shock proteins and protection against ischemic injury in cardiac myocytes

BACKGROUND

Overexpression of the inducible hsp70 protects against ischemic cardiac damage. However, it is unclear whether the small heat shock proteins hsp27 and alphaB-crystallin protect against ischemic injury.

METHODS AND RESULTS

Our aim was to examine whether the overexpression of hsp27 and alphaB-crystallin in neonatal and adult rat cardiomyocytes would protect against ischemic injury. Recombinant adenovirus expressing hsp27 or alphaB-crystallin under the control of the cytomegalovirus promoter was used to infect cardiac myocytes at high efficiency as assessed by immunostaining. Overexpression was confirmed by Western blot analysis. Cardiomyocytes were subjected to simulated ischemic stress, and survival was estimated through assessment of lactate dehydrogenase and creatine phosphokinase release. The hsp27 overexpression decreased lactate dehydrogenase release by 45+/-7.5% in adult cardiomyocytes but had no effect in the neonatal cells. In contrast, alphaB-crystallin overexpression was associated with a decrease in cytosolic enzyme release in both adult (29+/-6.6%) and neonatal (32+/-5.4%) cardiomyocytes. Decreased endogenous hsp25 with an antisense adenovirus produced a 29+/-9.9% increase in damage with simulated ischemia. Overexpression of the inducible hsp70 in adult cardiomyocytes was associated with a 34+/-4.6% decrease in lactate dehydrogenase release and is in line with our previous results in neonatal cardiomyocytes.

CONCLUSIONS

The increased expression of hsp27 and alphaB-crystallin through an adenovirus vector system protects against ischemic injury in adult cardiomyocytes. Likewise, the overexpression of alphaB-crystallin protects against ischemic damage in neonatal cardiomyocytes. Decreasing the high levels of endogenous hsp25 present in neonatal cardiomyocytes renders them more susceptible to damage caused by simulated ischemia.

Molecular/cellular biology of the heat stress response and its role in agent-induced teratogenesis

Available data indicate that heat shock proteins act as chaperones under non-stress conditions by assisting in: (1) the folding of newly synthesized proteins, (2) the intracellular translocation of proteins, and (3) the function of other proteins. As we gain additional information concerning cellular physiology, we may find that heat shock proteins play a key role in many additional cellular functions. When cells experience thermal or chemical stress, heat shock proteins take on a new role, conserved from bacteria to humans, of protecting cells from the detrimental effects of stress. This latter role takes on added significance for the embryo in which the developmental program must be read linearly, with little opportunity to cycle backward to complete a missed segment of the program. Although circumstantial evidence clearly implicates heat shock proteins in protecting embryos from thermal stress, definitive evidence is still lacking. The challenge for the future is to obtain such definitive data. Ideally, such information will lead to new therapeutic paradigms that will afford protection to the human embryo/fetus exposed to thermal/chemical stress.

Phosphorylation of A 27-kDa protein correlates with survival of protein-synthesis-inhibited MCF-7 cells

Previously, we have shown that IGF-1, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and aurintricarboxylic acid (ATA) protected MCF-7 cells against death induced by the protein synthesis inhibitor cycloheximide (CHX). We proposed that phosphorylation of a putative cellular proteins(s) may be involved in this survival mechanism. In the present study we investigated the ability of several agents to induce phosphorylation of cellular proteins and correlated this ability to their survival effect. We found that TPA, ATA, and IGF-1 increased the degree of phosphorylation of a 27-kDa protein in a dose- and time-dependent manner in CHX-treated MCF-7 cells. The ED50 values observed were 25 ng/ml, 40 micrograms/ml and 15 ng/ml for TPA, ATA, and IGF-1, respectively. The effect was measured upon 10 min of cell treatment with each agent; it reached maximum at 60 min and thereafter decreased continuously to control levels. The 27-kDa protein was found in the cytosolic fraction as a phosphorylated serine residue. Further characterization with two-dimensional electrophoresis indicated that the 27-kDa phosphorylated serine residue. Further characterization with two-dimensional electrophoresis indicated that the 27-kDa phosphoprotein was resolved into two isoforms with pI 5.7 and 5.9. Such characteristics were observed for the small molecular weight heat shock protein HSP27. Indeed, a single band of 27 kDa was detected immunologically with rabbit polyclonal anti-human HSP27. The inactive phorbol ester alpha TPA, epidermal growth factor (EGF), and 8-bromoadenosine 3'5'-cyclic monophosphate (Br-cAMP) did not increase phosphorylation of the 27-kDa protein. Cell survival was measured by exposure of the CHX-pretreated cells to increasing concentrations of the various agents for 60 min, followed by a further incubation for 48 h in the presence of CHX only. TPA, ATA, and IGF-1 were found to enhance cell survival, whereas alpha-TPA, EGF and Br-cAMP did not. Our results indicate a correlation between phosphorylation of a 27-kDa protein, probably HSP27, and enhanced cell survival, suggesting a role for this phosphoprotein in the survival mechanism.

p75, a member of the heat shock protein family, undergoes tyrosine phosphorylation in response to oxidative stress

The combination of H2O2 and vanadate generates aqueous peroxovanadium (pV) species, which are effective cell-permeable oxidants, and potent inhibitors of protein-tyrosine phosphatases. As a result, treatment of intact cells with pV compounds significantly enhances protein Tyr phosphorylation. Here we demonstrate that treatment of intact rat hepatoma Fao cells with pV markedly enhances Tyr phosphorylation of a 75-kDa protein, termed pp75. Amino-terminal sequencing of pp75 revealed that this protein is a member of the 70-75-kDa heat shock protein family, which includes PBP-74, glucose-related protein (GRP)-75, and mortalin. Tyr phosphorylation of pp75 is selective, because other proteins that belong to the heat shock protein 70 family, such as GRP-72, Bip (GRP-78), and HSC-70 fail to undergo Tyr phosphorylation when cells are treated with pV. Our findings suggest that heat shock proteins such as pp75 may undergo tyrosine phosphorylation when intact cells are subjected to oxidative stress induced by pV compounds.

A novel 29-kDa chicken heat shock protein

The family of small heat shock proteins is the more variable among the highly conserved superfamily of heat shock proteins (HSP). Using a metabolic labeling procedure with tissue explants, we have detected in chickens a new member of the small HSP family with an apparent molecular weight of 29-kDa. This protein was induced in broiler chickens' heart muscle and lungs following an in vivo heat stress. The 29-kDa band appears after 3 h of heat stress, much later than the induction of HSP 90, HSP 70, and HSP 27. The late onset of induction suggests that HSP 29 plays a more specific role of a "second stage defense protein".

Induction of heat shock protein 27 in rat embryos exposed to hyperthermia

Previously we reported that eight proteins were reproducibly induced in postimplantation rat embryos exposed to a brief heat shock (43 degrees C, 15 min). The major heat-inducible rat embryo protein has now been identified as heat shock protein 72 (Hsp 72). In addition, the induction of Hsp 72 is temporally correlated with induction of thermotolerance. One of the other rat embryo proteins previously shown to be induced by elevated temperature is a heat shock protein of approximately 27 kilodaltons (Hsp 27). In this report we show that this protein is recognized by an antibody directed against a conserved peptide sequence of Hsp 27. Unlike Hsp 72, Hsp 27 is constitutively expressed in the rat embryo in the absence of any thermal stress; however, the level of Hsp 27 is increased approximately 2-3-fold after thermal stress (43 degrees C, 10 min). Immunohistochemical analysis revealed that the constitutively expressed Hsp 27 is localized primarily to cells of the heart, cells that are uniquely resistant to the cytotoxic effects of hyperthermia. After thermal stress, Hsp 27 is expressed in all tissues of the embryo. Finally, our data show that Hsp 27 exists in the rat embryo as three major isoforms indicative of different phosphorylation states. Furthermore, most Hsp 27 in the heart is phosphorylated, whereas in the rest of the embryo, nonphosporylated Hsp 27 predominates. After thermal stress, levels of phosphorylated isoforms increase dramatically in nonheart tissues of the embryo. Together, these results suggest that Hsp 27 may play a role in the development of thermotolerance in the postimplantation mammalian embryo.

HSP27 and HSP70 increase the survival of WEHI-S cells exposed to hyperthermia

Exposure of cells to hyperthermia and various other stress conditions induces synthesis of a small group of proteins, the heat shock proteins (HSPs). Synthesis of HSPs correlates with the development of thermotolerance, but little is known about the role of individual HSPs in this phenomenon. Using stably transfected WEHI-S murine fibrosarcoma cells we show that overexpression of either HSP27 or HSP70 clearly protects these cells from the toxic effect of elevated temperatures. Moreover, a clone expressing HSP70 mRNA in antisense orientation, and thereby reduced levels of endogenous HSP70 protein, is more thermosensitive than transfection control cells. Using indirect immunofluorescence we show that following heat treatment exogeneous HSP27 and HSP70 are relocated from the cytoplasm to the nucleus and nucleoli respectively. A similar pattern of localization was seen for the endogenous HSPs. Taken together, these results indicate that both HSP27 and HSP70 protect cells from heat mediated killing.

Heat shock protein expression in testis and bladder cancer cell lines exhibiting differential sensitivity to heat

Testis cancer cells are more sensitive than bladder and most other cancer cells to chemotherapeutic drugs both in the clinic and in vitro. In this study we show that they are also more sensitive than bladder cancer cells to heat. Since heat and drug sensitivity may be related to the ability of a cell to mount a stress response, constitutive and induced levels of heat shock proteins (HSPs) in three testis and three bladder human cancer cell lines were measured using Western blotting and scanning densitometry. No correlation between constitutive levels of HSP 90 or HSP 73/72 and cellular heat sensitivity was found. However, HSP 27 levels were much lower in the testis tumour cells, suggesting that low HSP 27 expression might contribute to heat sensitivity. Protein synthesis studies using [35S]methionine indicated that, for the same heat shocks, the kinetics of synthesis and decay of HSP 90 and HSP 73/72 in 833K (the most heat sensitive testis cells) was similar to or greater than that in HT1376 (the most heat-resistant bladder cells). Both 833K and HT1376 developed thermotolerance, and this followed an increase in synthesis of HSPs. These results indicate that, although there are differences in the constitutive levels of HSPs between testis and bladder cancer cells, both cell types are capable of mounting an induced heat shock response and can develop a similar degree of thermotolerance.

Hepatoma cells adapted to proliferate under normally lethal hyperthermic stress conditions show rapid decay of thermoresistance and heat shock protein synthesis when returned to 37 degrees C

H35 hepatoma cultures were adapted to sustained growth at 41.3 degrees C. In these variant cells the 'basic' levels of various heat shock proteins (hsps), especially those of hsp60, 70 and 100, are significantly raised. These cells exhibit a thermoresistance comparable with the induced thermotolerance in normal hepatoma cells heat shocked at 42.5 degrees C for 30 min. However, this resistance of variant cells shows a rapid, exponential decay with a half-time of 2.2 h when the temperature is lowered to 37 degrees C, with a concomitant decrease of the synthesis of hsp60 and 70. Heat shock experiments with variant cells grown at 41.3 degrees C lead to increased thermoresistance and synthesis of hsps when further incubation was performed at the original temperature but not at 37 degrees C. In the latter case, only a 3-h delay in the onset of decay of thermoresistance is observed. However, when the variant cells were incubated at 37 degrees C prior to heat stress normal induction of thermoresistance and hsp synthesis return inversely proportional to the progression of thermoresistance decay. Thermoresistant cells thus seem to be valuable tools in the study of the down-regulation of thermoresistance as well as of hsp synthesis.

An immunohistochemical study of heat shock protein-27 in the hippocampus in a gerbil model of cerebral ischemia and ischemic tolerance

Preconditioning of the gerbil brain with a 2-min period of sublethal ischemia protects against neuronal damage following a subsequent 3-min period of ischemia which normally damages CA1 neurons of the hippocampus (ischemic tolerance). In this study, we investigated the role of a small stress protein, heat shock protein-27, in the induction of ischemic tolerance. For this purpose, we used immunohistochemistry with an antibody against heat shock protein-27. Normal hippocampus contained very low levels of heat shock protein-27. The preconditioning ischemia for 2 min caused little changes in the heat shock protein-27 immunostaining in CA1 neurons but an increase in heat shock protein-27 immunostaining in a small number of astrocytes in the CA3 region and in many astrocytes in the dentate hilus. The second ischemia for 3 min caused no specific changes in heat shock protein-27 immunostaining in CA1 neurons both with and without tolerance in early reperfusion periods. After seven days, destruction of CA1 neurons occurred in animals without preconditioning and reactive astrocytes were intensely immunostained for heat shock protein-27. An intense heat shock protein-27 immunostaining was also seen in astrocytes in the dentate hilus after the second ischemia in both groups. Thus, we observed no temporal correlation between the induction of heat shock protein-27 and the manifestation of ischemic tolerance in the CA1 neurons. Most intense heat shock protein-27 immunostaining was observed in reactive astrocytes that accumulated in the damaged CA1 region and dentate hilus.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of heat shock protein HSP27 in human neurons and glial cells in culture

HSP27 expression was investigated in cultured neurons and glial cells isolated from fetal human brains using immunoblotting and immunocytochemistry. Under unstressed conditions, HSP27 was identified at a high level in astrocytes (> 99%), at a low level in neurons (7%), and at a minimally detectable level in microglia (< 1%), whereas it was undetectable in oligodendrocytes. Under these conditions, HSP27 was located in the cytoplasm, fractionated into the Triton X-100-soluble phase, and composed chiefly of the basic isoform (HSP27a). After exposure to heat stress (43 degrees C/90 min), the level of HSP27 expression was not altered in astrocytes but was elevated significantly in neurons (11-21%) and microglia (4-7%) during 8-48 hr postrecovery periods, while it remained undetectable in oligodendrocytes. In addition, various human neural cell lines exhibited differential patterns of HSP27 expression under unstressed and heat-stressed conditions. Following heat shock treatment (45 degrees C/30 min), granular aggregates of HSP27 were identified in the cytoplasm of astrocytes. Under heat-stressed conditions, HSP27 was distributed within the Triton X-100-insoluble fraction associated with an increase in two more acidic isoforms (HSP27b and HSP27c). HSP27 and alpha B-crystallin were coexpressed in astrocytes under unstressed and heat-stressed conditions. When astrocytes were exposed to known HSP27 inducers, hydrogen peroxide and cysteamine reduced the synthesis of HSP27, while estradiol showed no effects. The differential patterns of constitutive and heat-induced expression of HSP27 in cultured human neurons and glial cells suggest that the cellular mechanisms by which HSP27 expression is regulated are different among various cell types in the human central nervous system.

Effects of tumor necrosis factor-alpha on antimitogenicity and cell cycle-related proteins in MCF-7 cells

Tumor necrosis factor-alpha (TNF-alpha) demonstrated antimitogenic activity in MCF-7 cells (estrogen receptor-positive human breast cancer cells) in a dose- and time-dependent manner (EC-50 of 2.5 ng/ml). This antimitogenic effect of TNF-alpha was accompanied by a decreased number of cells in S phase in a dose- and time-dependent manner. Based on growth arrest experiments using aphidicolin, it is apparent that TNF-alpha acted in early G1 phase. It did not show antimitogenic effects once cells reentered the S phase based on [3H]thymidine incorporation into DNA and cell cycle analysis. Specificity of TNF-alpha was established by using monoclonal anti-human TNF-alpha antibody. On the basis of Western immunoblot analysis of Rb, p53 and cell cycle inhibitory protein (Cip1) (p21) proteins, TNF-alpha decreased Rb protein expression in a dose- and time-dependent manner whereas it increased the expression level of tumor suppressor p53 protein. TNF-alpha also increased the expression level of Cip1 (p21) protein in a dose-dependent manner. This induction of Cip1 (p21) protein was preceded by the induction of p53 protein in MCF-7 cells. Cip1 (p21) protein associated with cyclin D was also increased. Tumor suppressor Rb protein expression was increased during G1 to S phase progression. Cyclin D protein expression levels were not changed in response to TNF-alpha treatment, although serine/threonine kinase inhibitors such as H7 and the protein kinase C inhibitor staurosporine decreased cyclin D expression levels in MCF-7 cells. Based on experiments with staurosporine, it appears that TNF-alpha does not utilize a protein kinase C pathway in MCF-7 cells. Other cell cycle-related proteins such as Cdk2, Cdc2, and Cdk4 did not show any change in response to TNF-alpha. TNF-alpha did not affect complexes between cyclin D and Cdk2, Cdk4, and Rb proteins in MCF-7 cells. Taken together these results suggest that Rb, p53, and Cip1 (p21) proteins mediate TNF-alpha antimitogenic activity, and TNF-alpha induces growth arrest in the G1 phase in MCF-7 cells.

Transient acquired thermotolerance in Drosophila, correlated with rapid degradation of Hsp70 during recovery

Acquired thermotolerance, measured either as increased cell viability following a lethal heat shock or by translational thermotolerance, appears rapidly following a 'priming' heat treatment, but also decays rapidly. 4 hours after priming heating thermotolerance is reduced by > 50% and by 9 hours it is virtually undetectable. Heat-shock protein 70 (Hsp70) turns over with a half-life of approximately 2 hours, and the decline in its intracellular abundance parallels the loss of acquired thermotolerance. Continuous heat shock extends the half-life of Hsp70 to approximately 7 hours. When Hsp70 is expressed at normal temperature using a metallothionein promoter, only partial acquired translational thermotolerance results. The results suggest that acquired thermotolerance is tightly regulated in Drosophila and partly, but not wholly, determined by post-translational regulation of Hsp70 levels.

Isoelectric focusing as a tool for the investigation of post-translational processing and chemical modifications of proteins

It has been demonstrated that good agreement may be observed between computed and experimental isoelectric point (pI) values when proteins of known sequence are focused under denaturing conditions on immobilized pH gradient IPG slabs, at least in the pH range 4-7.5. Hence, discrepancies between expected and found in this experimental set-up may be reliably ascribed to some kind of post-transcriptional processing, or chemical modification, having taken place in the sample. This evaluation is made easier when the comparison is set between the pI of a parent molecule and that (or those) of one to several of its derivatives as resolved in a single experiment (for instance, as a spot row in two-dimensional maps); no previous knowledge is required in these cases about the amino acid composition of the primary structure. The effects on protein surface charge are discussed in this review mainly for two biologically relevant processes, glycosylation and phosphorylation. Then, the pI shifts are analysed for some protein modifications that may occur naturally but can also be artefactually elicited, such as NH2 terminus blocking, deamidation and thiol redox reactions. Finally, carboxymethylation and carbamylation are used to exemplify chemical treatments often applied in connection with electrophoretic techniques and involving charged residues. Procedures to be applied in order to verify whether a given modification has occurred, and often relying on the focusing of a treated specimen, are detailed in each section. Numerical examples on model proteins are also discussed. As an important field of application of the above concepts may be genetic engineering, an exhaustive bibliographic list dealing with pI evaluation and structural assessment on recombinant proteins is included.