Activation of heat shock gene transcription by heat shock factor 1 involves oligomerization, acquisition of DNA-binding activity, and nuclear localization and can occur in the absence of stress

Delivery of HSF1(+) protein using HIV-1 TAT protein transduction domain

HSF1 is the major transcription factor of HSPs (heat shock proteins) in response to various stresses. Wild type HSF1 (heat shock transcriptional factor 1) is normally inactive, while a constitutively active form of HSF1 (HSF1(+)) can activate downstream HSP expression in the absence of stresses. Here we generated the eukaryotic vectors that expresses HSF1(+) fusion proteins, and found that HSF1(+)-TAT fusion protein was expressed and activated HSP expression. TAT, as a trans-acting factor of HIV-1, has been demonstrated to deliver functional cargo protein into living cells. HSF1(+)-TAT fusion protein was expressed in E. coli, purified, incubated with A549 cells for 8 h, Western blot analysis and luciferase reporter assay showed that HSF1(+) fusion protein was delivered into A549 cells successfully, and the accumulation of HSF1(+)-TAT fusion protein in A549 cells up-regulated HSP70 expression.

Heat shock proteins in diabetes and wound healing

The heat shock proteins (HSPs), originally identified as heat-inducible gene products, are a highly conserved family of proteins that respond to a wide variety of stress. Although HSPs are among the most abundant intracellular proteins, they are expressed at low levels under normal physiological conditions, and show marked induction in response to various stressors. HSPs function primarily as molecular chaperones, facilitating the folding of other cellular proteins, preventing protein aggregation, or targeting improperly folded proteins to specific pathways for degradation. By modulating inflammation, wound debris clearance, cell proliferation, migration and collagen synthesis, HSPs are essential for normal wound healing of the skin. In this review, our goal is to discuss the role and clinical implications of HSP with respect to skin wound healing and diabetes. The numerous defects in the function of HSPs associated with diabetes could contribute to the commonly observed complications and delayed wound healing in diabetics. Several physical, pharmacological and genetic approaches may be considered to address HSP-directed therapies both in the laboratory and in the clinics.

Exercise can increase small heat shock proteins (sHSP) and pre- and post-synaptic proteins in the hippocampus

The molecular events mediating the complex interaction between exercise and cognition are not well-understood. Although many aspects of the signal transduction pathways mediate exercise induced improvement in cognition are elucidated, little is known about the molecular events interrelating physiological stress with synaptic proteins, following physical exercise. Small heat shock proteins (sHSP), HSP27 and alpha-B-crystallin are co-localized to synapses and astrocytes, but their role in the brain is not well-understood. We investigated whether their levels in the hippocampus were modulated by exercise, using a well characterized voluntary exercise paradigm. Since sHSP are known to be regulated by many intracellular signaling molecules in other cells types outside the brain, we investigated whether similar regulation may serve a role in the brain by measuring protein kinase B (PKB/Akt), pGSK3 and the mitogen activated protein (MAP) kinases, p38, phospho-extracellular signal-regulated kinase (pERK) and phospho-c-Jun kinase (pJNK). Results demonstrated exercise-dependent increases in HSP27 and alpha-B-crystallin levels. We observed that increases in sHSP coincided with robust elevations in the presynaptic protein, SNAP25 and the post-synaptic proteins NR2b and PSD95. Exercise had a differential impact on kinases, significantly reducing pAkt and pERK, while increasing p38 MAPK. In conclusion, we demonstrate four early novel hippocampal responses to exercise that have not been identified previously: the induction of (1) sHSPs (2) the synaptic proteins SNAP-25, NR2b, and PSD-95, (3) the MAP kinase p38 and (4) the immediate early gene product MKP1. We speculate that sHSP may play a role in synaptic plasticity in response to exercise.

Proteasome inhibitor MG132 induces BAG3 expression through activation of heat shock factor 1

BAG3 protein, a member of the BAG co-chaperones family, sustains cell survival in a variety of normal and neoplastic cell types, via its interaction with a variety of partners, such as the heat shock protein (HSP) 70, Bcl-2, Raf-1 and others. Expression of BAG3 is induced by some stressful stimuli, such as heat shock, heavy metal exposure. We have reported that proteasome inhibitors can also induce BAG3 expression at the transcriptional level and the induction of BAG3 compromises proteasome inhibitors-mediated apoptosis. However, the molecular mechanism of BAG3 upregulation has not been elucidated. In the current study, we provide evidence that heat shock transcription factor 1 (HSF1) is involved in BAG3 induction by proteasome inhibitor MG132. Using a series of varying lengths of 5'-flanking region of the BAG3 gene into luciferase reporter vectors, we found that MG132 stimulated the promoter activity via the -326/-233 and -825/-689 regions, which contains one putative heat shock-responsive element (HSE) for HSF1-binding, respectively. Site-directed deletion of the sites abrogated the enhanced reporter activity in response to MG132 treatment. Chromatin immunoprecipitation assay demonstrated that HSF1 directly bound to the MG132-responsive site on the BAG3 promoter. Activation of HSF1 occurred with MG132 along with BAG3 upregulation. Furthermore, knockdown HSF1 by small interfering RNA attenuated the BAG3 upregulation due to MG132.These results indicate that the proteasome inhibitor MG132 induces BAG3 expression through HSF1 activation.

Heterotrimerization of heat-shock factors 1 and 2 provides a transcriptional switch in response to distinct stimuli

Organisms respond to circumstances threatening the cellular protein homeostasis by activation of heat-shock transcription factors (HSFs), which play important roles in stress resistance, development, and longevity. Of the four HSFs in vertebrates (HSF1-4), HSF1 is activated by stress, whereas HSF2 lacks intrinsic stress responsiveness. The mechanism by which HSF2 is recruited to stress-inducible promoters and how HSF2 is activated is not known. However, changes in the HSF2 expression occur, coinciding with the functions of HSF2 in development. Here, we demonstrate that HSF1 and HSF2 form heterotrimers when bound to satellite III DNA in nuclear stress bodies, subnuclear structures in which HSF1 induces transcription. By depleting HSF2, we show that HSF1-HSF2 heterotrimerization is a mechanism regulating transcription. Upon stress, HSF2 DNA binding is HSF1 dependent. Intriguingly, when the elevated expression of HSF2 during development is mimicked, HSF2 binds to DNA and becomes transcriptionally competent. HSF2 activation leads to activation of also HSF1, revealing a functional interdependency that is mediated through the conserved trimerization domains of these factors. We propose that heterotrimerization of HSF1 and HSF2 integrates transcriptional activation in response to distinct stress and developmental stimuli.

Increased temperature and protein oxidation lead to HSP72 mRNA and protein accumulation in the in vivo exercised rat heart

Expression of myocardial heat shock protein 72 (HSP72), mediated by its transcription factor, heat shock factor 1 (HSF1), increases following exercise. However, the upstream stimuli governing exercise-induced HSF1 activation and subsequent Hsp72 gene expression in the whole animal remain unclear. Exercise-induced increases in body temperature may promote myocardial radical production, leading to protein oxidation. Conceivably, myocardial protein oxidation during exercise may serve as an important signal to promote nuclear HSF1 migration and activation of Hsp72 expression. Therefore, these experiments tested the hypothesis that prevention of exercise-induced increases in body temperature attenuates cardiac protein oxidation, diminishes HSF1 activation and decreases HSP72 expression in vivo. To test this hypothesis, in vivo exercise-induced changes in body temperature were manipulated by exercising male rats in either cold (4 degrees C) or warm ambient conditions (22 degrees C). Warm exercise increased both body temperature (+3 degrees C) and myocardial protein oxidation, whereas these changes were attenuated by cold exercise. Interestingly, exercise in both conditions did not significantly increase myocardial nuclear localized phosphorylated HSF1. Nonetheless, warm exercise elevated left-ventricular HSP72 mRNA by ninefold and increased myocardial HSP72 protein levels by threefold compared with cold-exercised animals. Collectively, these data indicate that elevated body temperature and myocardial protein oxidation promoted exercise-induced cardiac HSP72 mRNA expression and protein accumulation following in vivo exercise. However, these results suggest that exercise-induced myocardial HSP72 protein accumulation is not a result of nuclear-localized, phosphorylated HSF1, indicating that other transcriptional or post-transcriptional regulatory mechanisms are involved in exercise-induced HSP72 expression.

Heat shock proteins and exercise: a primer

Heat shock proteins (HSPs) are, in general, prosurvival molecules within the cellular environment, and the overexpression of even just 1 family of HSPs can lead to protection against and improvements after a variety of stressors. Not surprisingly, a fertile area of study has grown out of efforts to exploit the innate biologic behaviour of HSPs. Exercise, because of the inherent physiologic stresses associated with it, is but 1 stimulus that can result in a robust increase in various HSPs in several tissues, not the least of which happen to be the heart and skeletal muscle. The purpose of this review is to introduce the reader to the major HSP families, the control of their expression, and some of their biologic functions, specifically with respect to the influence of exercise. Moreover, as the first in a series of reviews from a common symposium, we will briefly introduce the concepts presented by the other authors, which include the effects of different exercise paradigms on skeletal muscle HSPs in the adult and aged systems, HSPs as regulators of inflammation, and the ion channel stabilizing effects of HSPs.

Hsf1 is required for the nuclear translocation of p53 tumor suppressor

Although the p53 tumor suppressor is most frequently inactivated by genetic mutations, exclusion from the nucleus is also seen in human tumors. We have begun to examine p53 nuclear importation by isolating a series of mutant cells in which the temperature-sensitive murine p53(Val135) mutant is sequestered in the cytoplasm. We previously showed that that three of them (ALTR12, ALTR19, and ALTR25) constituted a single complementation group. Here, we found that ALTR12 cells are more sensitive to heat stress than either ALTR19 or ALTR25 and that there was a complete lack of induction of Hsp70 in response to heat shock. Western blot analysis showed no expression of the Hsf1 transcription factor, and neither heat shock nor azetidine could induce p53 nuclear localization in ALTR12 cells but did in parental A1-5 cells. Suppression of Hsf1 in A1-5 cells with quercetin or an Hsf1 siRNA reduced p53 nuclear importation and inhibited p53-mediated activation of a p21 reporter. Most convincingly, p53 nuclear importation could be restored in ALTR12 cells by introducing an exogenous Hsf1 gene. Collectively, our result suggests that Hsf1 is required for p53 nuclear importation and activation and implies that heat shock factors play a role in the regulation of p53.

Biochemical insights into the mechanisms central to the response of mammalian cells to cold stress and subsequent rewarming

Mammalian cells cultured in vitro are able to recover from cold stress. However, the mechanisms activated during cold stress and recovery are still being determined. We here report the effects of hypothermia on cellular architecture, cell cycle progression, mRNA stability, protein synthesis and degradation in three mammalian cell lines. The cellular structures examined were, in general, well maintained during mild hypothermia (27-32 degrees C) but became increasingly disrupted at low temperatures (4-10 degrees C). The degradation rates of all mRNAs and proteins examined were much reduced at 27 degrees C, and overall protein synthesis rates were gradually reduced with temperature down to 20 degrees C. Proteins involved in a range of cellular activities were either upregulated or downregulated at 32 and 27 degrees C during cold stress and recovery. Many of these proteins were molecular chaperones, but they did not include the inducible heat shock protein Hsp72. Further detailed investigation of specific proteins revealed that the responses to cold stress and recovery are at least partially controlled by modulation of p53, Grp75 and eIF3i levels. Furthermore, under conditions of severe cold stress (4 degrees C), lipid-containing structures were observed that appeared to be in the process of being secreted from the cell that were not observed at less severe cold stress temperatures. Our findings shed light on the mechanisms involved and activated in mammalian cells upon cold stress and recovery.

Alcohol exposure regulates heat shock transcription factor binding and heat shock proteins 70 and 90 in monocytes and macrophages: implication for TNF-alpha regulation

Immunomodulatory effects of alcohol use involve regulation of innate immune cell function leading to liver disease. Alteration of inflammatory responses by alcohol is linked to dysregulated TNF-alpha production. Alcohol-induced oxidative stress also contributes to alterations in inflammatory cell activity. Heat shock proteins (hsps) and the heat shock transcription factor-1 (HSF-1) induced by oxidative stress regulate NF-kappaB activation and TNF-alpha gene expression in monocytes and macrophages. Here, we report that in vitro alcohol treatment induced and augmented LPS-induced HSF-1 nuclear translocation and DNA-binding activity in monocytes and macrophages. Supershift analysis revealed that alcohol regulated HSF-1- and not HSF-2-binding activity. Hsp70, a target gene induced by HSF-1, was transiently increased within 24 h by alcohol, but extended alcohol exposure decreased hsp70 in macrophages. The alcohol-induced alteration of hsp70 correlated with a concomitant change in hsp70 promoter activity. Hsp90, another HSF-1 target gene, was decreased during short-term alcohol but increased after prolonged alcohol exposure. Decreased hsp90-HSF-1 complexes after short-term alcohol indicated dissociation of HSF-1 from hsp90. On the other hand, hsp90 interacted with client protein IkappaB kinase beta, a signaling intermediate of the LPS pathway, followed by IkappaBalpha degradation and increased NF-kappaB activity after chronic alcohol exposure, indicating that hsp90 plays an important role in supporting inflammatory cytokine production. Inhibition of hsp90 using geldanamycin prevented prolonged alcohol-induced elevation in LPS-induced NF-kappaB and TNF-alpha production. These results suggest that alcohol exposure differentially regulates hsp70 and hsp90 via HSF-1 activation. Further, hsp90 regulates TNF-alpha production in macrophages contributing to alcohol-induced inflammation.

The insulin paradox: aging, proteotoxicity and neurodegeneration

Distinct human neurodegenerative diseases share remarkably similar temporal emergence patterns, even though different toxic proteins are involved in their onset. Typically, familial neurodegenerative diseases emerge during the fifth decade of life, whereas sporadic cases do not exhibit symptoms earlier than the seventh decade. Recently, mechanistic links between the aging process and toxic protein aggregation, a common hallmark of neurodegenerative diseases, have been revealed. The insulin/insulin-like growth factor 1 (IGF1) signalling pathway - a lifespan, metabolism and stress-resistance regulator - links neurodegeneration to the aging process. Thus, although a reduction of insulin signalling can result in diabetes, its reduction can also increase longevity and delay the onset of protein-aggregation-mediated toxicity. Here we review this apparent paradox and delineate the therapeutic potential of manipulating the insulin/IGF1 signalling pathway for the treatment of neurodegenerative diseases.

Hsp70 inhibits aminoglycoside-induced hair cell death and is necessary for the protective effect of heat shock

Sensory hair cells of the inner ear are sensitive to death from aging, noise trauma, and ototoxic drugs. Ototoxic drugs include the aminoglycoside antibiotics and the antineoplastic agent cisplatin. Exposure to aminoglycosides results in hair cell death that is mediated by specific apoptotic proteins, including c-Jun N-terminal kinase (JNK) and caspases. Induction of heat shock proteins (Hsps) is a highly conserved stress response that can inhibit JNK- and caspase-dependent apoptosis in a variety of systems. We have previously shown that heat shock results in a robust upregulation of Hsps in the hair cells of the adult mouse utricle in vitro. In addition, heat shock results in significant inhibition of both cisplatin- and aminoglycoside-induced hair cell death. In our system, Hsp70 is the most strongly induced Hsp, which is upregulated over 250-fold at the level of mRNA 2 h after heat shock. Therefore, we have begun to examine the role of Hsp70 in mediating the protective effect of heat shock. To determine whether Hsp70 is necessary for the protective effect of heat shock against aminoglycoside-induced hair cell death, we utilized utricles from Hsp70.1/3 (-/-) mice. While heat shock inhibited gentamicin-induced hair cell death in wild-type utricles, utricles from Hsp70.1/3 (-/-) mice were not protected. In addition, we have examined the role of the major heat shock transcription factor, Hsf1, in mediating the protective effect of heat shock. Utricles from Hsf1 (-/-) mice and wild-type littermates were exposed to heat shock followed by gentamicin. The protective effect of heat shock on aminoglycoside-induced hair cell death was only observed in wild-type mice and not in Hsf1 (-/-) mice. To determine whether Hsp70 is sufficient to protect hair cells, we have utilized transgenic mice that constitutively overexpress Hsp70. Utricles from Hsp70-overexpressing mice and wild-type littermates were cultured in the presence of varying neomycin concentrations for 24 h. The Hsp70-overexpressing utricles were significantly protected against neomycin-induced hair cell death at moderate to high doses of neomycin. This protective effect was achieved without a heat shock. Taken together, these data indicate that Hsp70 and Hsf1 are each necessary for the protective effect of heat shock against aminoglycoside-induced death. Furthermore, overexpression of Hsp70 alone significantly inhibits aminoglycoside-induced hair cell death.

Metabolic and molecular stress responses of sublittoral bearded horse musselModiolus barbatusto warming sea water: implications for vertical zonation

The present study set out to investigate the thermal limits of the Mediterranean bivalve Modiolus barbatus, acclimated to various temperatures, and includes a comparison of laboratory determined limits with its temperature-dependent restriction to deeper water layers in its natural habitat. Thermal responses and limits were determined by integrating information from various levels of biological organization, including the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases, p38 mitogen-activated protein kinase (p38 MAPK) and cJun-N-terminal kinases (JNKs) as well as metabolic adjustments. The latter were assessed by examining temperature effects on the activity of the key glycolytic enzyme pyruvate kinase (PK). The expression of Hsp70 and Hsp90 was activated when mussels were acclimated to temperatures above 20°C. Increased phosphorylation of p38 MAPK and JNKs at about the same temperatures indicate activation of MAPK signaling cascades and their potential involvement in the induction of Hsp genes. As indicated by the activity of PK, Modiolus barbatus maintains some aerobic capacity when acclimated to temperatures up to 24°C, while further warming probably caused metabolic depression and a shift from aerobic to anaerobic metabolism. An increase in mortality occurred in parallel, during acclimation to temperatures above 24°C. Our results indicate that both the biochemical stress indicators and metabolic status respond in parallel once hypoxemia becomes extreme. Comparison with our previous study of thermal limits and vertical distribution in M. galloprovincialis dwelling in shallow waters emphasizes the relevance of maintained aerobic scope over that of passive tolerance for permanent vertical zonation at higher temperatures in the field. These findings and conclusions are in line with the concept of oxygen and capacity limited thermal tolerance and the associated systemic to molecular hierarchy of thermal limitation.

Concerted actions of multiple transcription elements confer differential transactivation of HSP90 isoforms in geldanamycin-treated 9L rat gliosarcoma cells

HSP90 chaperones are transducer proteins of many signaling pathways in cells. Using a highly specific inhibitor, geldanamycin (GA), an increasing number of the HSP90 client proteins have been identified. Nevertheless, there is little information on the differential transactivation of the two isoforms of the hsp90 genes, hsp90alpha and beta, in cells under stress conditions. Here, we demonstrate the differential expression of the HSP90 isoforms, HSP90alpha and beta, in rat gliosarcoma 9L cells using a modified SDS-PAGE system that allowed us to distinguish the isoforms. We subsequently assessed the transcriptional controls involving the transcription elements located in the promoter regions of the hsp90 genes. At the protein level, HSP90alpha is more responsive to GA in terms of rate of de novo synthesis and amount of accumulation, as shown by metabolic-labeling and Western-blotting analyses. Upregulation of the hsp90 genes was demonstrated by real-time qPCR. The promoter elements hsp90alpha-HSE2 and hsp90beta-HSE1 were also identified to be the major transcription elements involved in GA-activated gene expression, as shown by EMSA, whereas the results of supershift showed that the transcription factor HSF1 is also involved. Moreover, EMSA results of analysis of the GC box showed differences in both the initial amounts and inductive response of hsp90s transcripts, whereas analysis of the TATA box showed GA responsiveness in hsp90alpha only. Collectively, these results indicate that GA exerts its regulatory effects through transcription elements including heat-shock elements (HSEs), GC boxes and TATA boxes, resulting in differential transactivation of hsp90alpha and hsp90beta in rat gliosarcoma 9L cells.

CoREST represses the heat shock response mediated by HSF1

The stress response in cells involves a rapid and transient transcriptional activation of stress genes. It has been shown that Hsp70 limits its own transcriptional activation functioning as a corepressor of heat shock factor 1 (HSF1) during the attenuation of the stress response. Here we show that the transcriptional corepressor CoREST interacts with Hsp70. Through this interaction, CoREST represses both HSF1-dependent and heat shock-dependent transcriptional activation of the hsp70 promoter. In cells expressing short hairpin RNAs directed against CoREST, Hsp70 cannot repress HSF1-dependent transcription. A reduction of CoREST levels also provoked a significant increase of Hsp70 protein levels and an increase of HSF1-dependent transactivation of hsp70 promoter. Via chromatin immunoprecipitation assays we show that CoREST is bound to the hsp70 gene promoter under basal conditions and that its binding increases during heat shock response. In conclusion, we demonstrated that CoREST is a key regulator of the heat shock stress response.

Riluzole increases the amount of latent HSF1 for an amplified heat shock response and cytoprotection

Background

Induction of the heat shock response (HSR) and increased expression of the heat shock proteins (HSPs) provide mechanisms to ensure proper protein folding, trafficking, and disposition. The importance of HSPs is underscored by the understanding that protein mis-folding and aggregation contribute centrally to the pathogenesis of neurodegenerative diseases.

Methodology/Principal Findings

We used a cell-based hsp70-luciferease reporter gene assay system to identify agents that modulate the HSR and show here that clinically relevant concentrations of the FDA-approved ALS drug riluzole significantly increased the heat shock induction of hsp70-luciferse reporter gene. Immuno-Western and -cytochemical analysis of HSF1 show that riluzole increased the amount of cytosolic HSF1 to afford a greater activation of HSF1 upon heat shock. The increased HSF1 contributed centrally to the cytoprotective activity of riluzole as hsf1 gene knockout negated the synergistic activity of riluzole and conditioning heat shock to confer cell survival under oxidative stress. Evidence of a post-transcriptional mechanism for the increase in HSF1 include: quantitation of mRNA^hsf1 by RT-PCR showed no effect of either heat shock or riluzole treatment; riluzole also increased the expression of HSF1 from a CMV-promoter; analysis of the turnover of HSF1 by pulse chase and immunoprecipitation show that riluzole slowed the decay of [³⁵S]labeled-HSF1. The effect of riluzole on HSF1 was qualitatively different from that of MG132 and chloroquine, inhibitors of the proteasome and lysosome, respectively, and appeared to involve the chaperone-mediated autophagy pathway as RNAi-mediated knockdown of CMA negated its effect.

Conclusion/Significance

We show that riluzole increased the amount of HSF1 to amplify the HSR for cytoprotection. Our study provides novel insight into the mechanism that regulates HSF1 turnover, and identifies the degradation of HSF1 as a target for therapeutics intervention.

Interaction of HSF1 and HSF2 with the Hspa1b promoter in mouse epididymal spermatozoa

The Hspa1b gene is one of the first genes expressed after fertilization, with expression observed in the male pronucleus as early as the one-cell stage of embryogenesis. This expression can occur in the absence of stress and is initiated during the minor zygotic genome activation. There is a significant reduction in the number of embryos developing to the blastocyte stage when HSPA1B levels are depleted, which supports the importance of this protein for embryonic viability. However, the mechanism responsible for allowing expression of Hspa1b during the minor zygotic genome activation (ZGA) is unknown. In this report, we investigated the role of HSF1 and HSF2 in bookmarking Hspa1b during late spermatogenesis. Western blot results show that both HSF1 and HSF2 are present in epididymal spermatozoa, and immunofluorescence analysis revealed that some of the HSF1 and HSF2 proteins in these cells overlap the 4',6'-diamidino-2-phenylindole-stained DNA region. Results from chromatin immunoprecipitation assays showed that HSF1, HSF2, and SP1 are bound to the Hspa1b promoter in epididymal spermatozoa. Furthermore, we observed an increase in HSF2 binding to the Hspa1b promoter in late spermatids versus early spermatids, suggesting a likely period during spermatogenesis when transcription factor binding could occur. These results support a model in which the binding of HSF1, HSF2, and SP1 to the promoter of Hspa1b would allow the rapid formation of a transcription-competent state during the minor ZGA, thereby allowing Hspa1b expression.

HSP70 and constitutively active HSF1 mediate protection against CDCrel-1-mediated toxicity

Defects in cellular quality control mechanisms are thought to contribute to the neuropathology of Parkinson's disease (PD). Overexpressing heat shock proteins (HSPs) may constitute a powerful therapeutic strategy for PD, because they boost the ability of the cell to eliminate unwanted proteins. We investigated the neuroprotective potential of HSP70, HSP40, and H-BH, a constitutively active form of heat shock factor 1, in a rat model of PD based on adeno-associated virus (AAV) vector-mediated overexpression of CDCrel-1, a parkin substrate known to be toxic to dopaminergic neurons. AAV vector-mediated overexpression of H-BH and of HSP70 afforded similar levels of protection against CDCrel-1 toxicity, with approximately 20% improvement in survival of dopaminergic neurons as compared to the controls. The assessment of protection conferred was made using tyrosine hydroxylase (TH) and HuC/D immunohistochemistry and Fluoro-Gold retrograde tracing, and by observing the extent of preservation of spontaneous function and also the extent of drug-induced motor function. In contrast to H-BH and HSP70, HSP40 overexpression exacerbated CDCrel-1-mediated cell death. Real-time reverse transcriptase (RT)-PCR analysis showed that H-BH had the effect of upregulating endogenous HSP70 and HSP40 mRNA levels 10-fold and 4-fold over basal levels, respectively, whereas AAV vector-mediated HSP70 and HSP40 mRNA levels were over 100-fold higher. Our results suggest that a comparatively modest upregulation of multiple HSPs may be an effective approach for achieving significant neuroprotection in PD.

Heat shock factor activation in human muscles following a demanding intermittent exercise protocol is attenuated with hyperthermia

AIM

The present study investigated whether increased activation of heat shock factors (HSF) following exercise relates primarily to the increased muscle temperature or to exercise in general.

METHODS

Six subjects completed 40 min of intermittent cycling (15s:15s exercise:recovery at 300 +/- 22 W) at an ambient temperature of either 20.0 +/- 1.3 or 40.3 +/- 0.7 degrees C. Muscle biopsies were taken prior to and immediately following the exercise protocol with samples analysed for HSF DNA binding by electrophoretic mobility shift assay.

RESULTS

Exercise at 40 degrees C resulted in significantly increased oesophageal (39.3 +/- 0.2 degrees C) and muscle temperature (40.0 +/- 0.2 degrees C) at the end of the exercise protocol compared with 20 degrees C (oesophageal, 38.1 +/- 0.1 degrees C; muscle, 38.9 +/- 0.2 degrees C). However, an increased DNA binding of HSF was not evident following exercise at 40 degrees C (reduced by 21 +/- 22%) whereas it increased by 29 +/- 51% following exercise at 20 degrees C.

CONCLUSION

It appears that increased temperature is not the major factor responsible for activation of HSF DNA binding.

Heat shock co-activates interleukin-8 transcription

The heat shock (HS) response is a phylogenetically ancient cellular response to stress, including heat, that shifts gene expression to a set of conserved HS protein (HSP) genes. In our earlier studies, febrile-range hyperthermia (FRH) not only activated HSP gene expression, but also increased expression of CXC chemokines in mice, leading us to hypothesize that the CXC chemokine family of genes might be HS-responsive. To address this hypothesis we analyzed the effect of HS on the expression of IL-8/CXCL-8, a member of the human CXC family of ELR(+) chemokines. HS markedly enhanced TNF-alpha-induced IL-8 secretion in human A549 respiratory epithelial-like cells and in primary human small airway epithelial cells. IL-8 mRNA was also up-regulated by HS, but the stability of IL-8 mRNA was not affected. TNF-alpha-induced reporter activity of an IL-8 promoter construct IL8(-1471/+44)-luc stably transfected in A549 cells was also enhanced by HS. Electrophoretic mobility and chromatin immunoprecipitation assays showed that the stress-activated transcription factor heat shock factor-1 (HSF-1) binds to at least two putative heat shock response elements (HSE) present in the IL-8 promoter. Deletional reporter constructs lacking either one or both of these sites showed reduced HS responsiveness. Furthermore, depletion of HSF-1 using siRNA also reduced the effects HS on TNF-alpha-induced IL-8 expression, demonstrating that HSF-1 could also act to regulate IL-8 gene transcription. We speculate that during evolution the CXC chemokine genes may have co-opted elements of the HS response to amplify their expression and enhance neutrophil delivery during febrile illnesses.

Heat shock protein accumulation and heat shock transcription factor activation in rat skeletal muscle during compensatory hypertrophy

AIM

To assess the stress/heat shock protein (HSP) and heat shock factor activation response in overloaded (hypertrophied) plantaris muscles.

METHODS

Male Sprague-Dawley rats (n = 5 per time point) underwent unilateral removal of the left gastrocnemius muscle. After 1, 2, 3, 5, 7, 14 and 28 days, plantaris muscles were removed, weighted rapidly frozen in liquid nitrogen. Total protein content was determined and HSP 25 and HSP 72 contents were assessed by Western blotting. Heat shock transcription factor (HSF) activation was assessed by electrophoretic mobility shift assay (EMSA).

RESULTS

While plantaris muscle mass was significantly increased 3 days after the imposition of overload and remained elevated thereafter confirming muscle hypertrophy, muscle protein content was not increased until 7 days after the imposition of overload. HSP 72 content was significantly increased at 3 days, while HSP 25 content was not significantly increased until 7 days after synergistic muscle removal. HSF activation was detected at 1, 2 and 3 days of overload but undetectable thereafter. The addition of HSF1- and HSF2-specific antibodies to extracts prior to EMSA failed to supershift the HSF-heat shock element complex.

CONCLUSION

The temporal pattern of both HSF activation and HSP expression in skeletal muscle undergoing hypertrophy suggests the increased level of the observed HSPs may be both a consequence of both the immediate stress of overload and the hypertrophic process. The inability of HSF1- and HSF2-specific antibodies to cause supershifts suggests the HSF detected during overload may not be HSF1 or HSF2.

Heat shock proteins and toll-like receptors

Researchers have only just begun to elucidate the relationship between heat shock proteins (HSP) and Toll-like receptors (TLR). HSP were originally described as an intracellular molecular chaperone of naïve, aberrantly folded, or mutated proteins and primarily implicated as a cytoprotective protein when cells are exposed to stressful stimuli. However, recent studies have ascribed novel functions to the Hsp70 protein depending on its localization: Surface-bound Hsp70 specifically activate natural killer (NK) cells, while Hsp70 released into the extracellular milieu specifically bind to Toll-like receptors (TLR) 2 and 4 on antigen-presenting cells (APC) and exerts immunoregulatory effects, including upregulation of adhesion molecules, co-stimulatory molecule expression, and cytokine and chemokine release-a process known as the chaperokine activity of Hsp70. This chapter discusses the most recent advances in the understanding of heat shock protein (HSP) and TLR interactions in general and highlights recent findings that demonstrate Hsp70 is a ligand for TLR and its biological significance.

Cellular and molecular mechanisms of heat stress-induced up-regulation of occludin protein expression: regulatory role of heat shock factor-1

The heat stress (HS)-induced increase in occludin protein expression has been postulated to be a protective response against HS-induced disruption of the intestinal epithelial tight junction barrier. The aim of this study was to elucidate the cellular and molecular processes that mediate the HS-induced up-regulation of occludin expression in Caco-2 cells. Exposure to HS (39 degrees C or 41 degrees C) resulted in increased expression of occludin protein; this was preceded by an increase in occludin mRNA transcription and promoter activity. HS-induced activation of heat shock factor-1 (HSF-1) resulted in cytoplasmic-to-nuclear translocation of HSF-1 and binding to its binding motif in the occludin promoter region. HSF-1 activation was associated with an increase in occludin promoter activity, mRNA transcription, and protein expression; which were abolished by the HSF-1 inhibitor quercetin. Targeted HSF-1 knock-down by siRNA transfection inhibited the HSF-1-induced increase in occulin expression and junctional localization of occulin protein. Site-directed mutagenesis of the HSF-1 binding motif in the occludin promoter region inhibited HS-induced binding of HSF-1 to the occludin promoter region and subsequent promoter activity. In conclusion, our data show for the first time that the HS-induced increase in occludin protein expression is mediated by HSF-1 activation and subsequent binding of HSF-1 to the occludin promoter, which initiates a series of molecular and cellular events culminating in increased junctional localization of occludin protein.

Heat Shock Factor 1 Attenuates 4-Hydroxynonenal-mediated Apoptosis

Lipid peroxidation is a consequence of both normal physiology and oxidative stress that generates various reactive metabolites, a principal end product being 4-hydroxynonenal (HNE). As a diffusible electrophile, HNE reacts extensively with cellular nucleophiles. Consequently, HNE alters cellular signaling and activates the intrinsic apoptotic cascade. We have previously demonstrated that in addition to promoting apoptosis, HNE activates stress response pathways, including the antioxidant, endoplasmic reticulum stress, DNA damage, and heat shock responses. Here we demonstrate that activation of the heat shock response by HNE is dependent on the expression and nuclear translocation of heat shock factor 1 (HSF1), which promotes the expression of heat shock protein 40 (Hsp40) and Hsp70-1. Ectopic expression and immunoprecipitation of c-Myc-tagged Hsp70-1 indicates that HNE disrupts the inhibitory interaction between Hsp70-1 and HSF1, leading to the activation heat shock gene expression. Using siRNA to silence HSF1 expression, we observe that HSF1 is necessary for the induction of Hsp40 and Hsp70-1 by HNE, and the lack of Hsp expression is correlated with an increase in apoptosis. Nrf2, the transcription factor that mediates the antioxidant response, was also silenced using siRNA. Silencing Nrf2 also enhanced the cytotoxicity of HNE, but not as effectively as HSF1. Silencing HSF1 expression facilitates the activation of JNK pro-apoptotic signaling and selectively decreases expression of the anti-apoptotic Bcl-2 family member Bcl-X(L). Overexpression of Bcl-X(L) attenuates HNE-mediated apoptosis in HSF1-silenced cells. Overall, activation of HSF1 and stabilization of Bcl-X(L) mediate a protective response that may contribute significantly to the cellular biology of lipid peroxidation.

Exercise-mediated regulation of Hsp70 expression following aerobic exercise training

An issue central to understanding the biological benefits associated with regular exercise training is to elucidate the intracellular mechanisms governing exercise-conferred cardioprotection. Heat shock proteins (HSPs), most notably the inducible 70-kDa HSP family member Hsp70, are believed to participate in the protection of the myocardium during cardiovascular stress. Following acute exercise, activation of PKA mediates the suppression of an intermediary protein kinase, ERK1/2, which phosphorylates and suppresses the activation of the heat shock transcription factor 1 (HSF1). However, following exercise training, ERK1/2 has been reported to regulate the transcriptional activation of several genes involved in cell growth and proliferation and has been shown to be associated with training-mediated myocardial hypertrophy. The present project examined the transcriptional activation of hsp70 gene expression in acutely exercised (60 min at 30 m/min) naïve sedentary and aerobically trained (8 wk, low intensity) male Sprague-Dawley rats. Following acute exercise stress, no significant differences were demonstrated in the expression of myocardial Hsp70 mRNA and activation of PKA between sedentary and trained animals. However, trained animals elicited expression of the hsp70 gene (P < 0.05) in the presence of elevated ERK1/2 activation. Given the association of ERK1/2 and the suppression of hsp70 gene expression following acute exercise in naïve sedentary rats, these results suggest that training results in adaptations that allow for the simultaneous initiation of both proliferative and protective responses. While it is unclear what factors are associated with this training-related shift, increases in HSF1 DNA binding affinity (P < 0.05) and posttranscriptional modifications of the Hsp70 transcript are suggested.

Chaperone regulation of the heat shock protein response

The heat shock protein response appears to be triggered primarily by nonnative proteins accumulating in a stressed cell and results in increased expression of heat shock proteins (HSPs). Many heat shock proteins prevent protein aggregation and participate in refolding or elimination of misfolded proteins in their capacity as chaperones. Even though several mechanisms exist to regulate the abundance of cytosolic and nuclear chaperones, activation of heat shock transcription factor 1 (HSF1) is an essential aspect of the heat shock protein response. HSPs and co-chaperones that are assembled into multichaperone complexes regulate HSF1 activity at different levels. HSP90-containing multichaperone complexes appear to be the most relevant repressors of HSF1 activity. Because HSP90-containing multichaperone complexes interact not only specifically with client proteins including HSF1 but also generically with nonnative proteins, the concentration of nonnative proteins influences assembly on HSF1 of HSP90-containing complexes that repress activation, and may play a role in inactivation, of the transcription factor. Proteins that are unable to achieve stable tertiary structures and remain chaperone substrates are targeted for proteasomal degradation through polyubiquitination by co-chaperone CHIP. CHIP can activate HSF1 to regulate the protein quality control system that balances protection and degradation of chaperone substrates.

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.

Behavioral, metabolic, and molecular stress responses of marine bivalve Mytilus galloprovincialis during long-term acclimation at increasing ambient temperature

The present study aimed to determine the thermal response of the Mediterranean mussel Mytilus galloprovincialis by integrating information from various levels of biological organization including behavior, metabolic adjustments, heat shock protein expression, and protein kinase activity. Behavioral responses were determined by examining the effect of warming on valve closure and opening. Metabolic impacts were assessed by examining the activity of the key glycolytic enzyme pyruvate kinase (PK). Molecular responses were addressed through the expression of Hsp70 and Hsp90 and the phosphorylation of stress-activated protein kinases, p38 mitogen-activated protein kinase (p38 MAPK) and cJun-N-terminal kinases (JNKs). Mussels increased the duration of valve closure by about sixfold when acclimated to 24°C rather than to 17°C. As indicated by the activity of PK, such behavior caused metabolic depression and probably a shift from aerobic to anaerobic metabolism. Acclimation to temperatures higher than 24°C caused an increase in mortality and induced the expression of Hsp72. Increased phosphorylation of p38 MAPK and JNKs indicated activation of MAPK signaling cascades. The potential involvement of MAPKs in the induction of Hsp genes in the tissues of M. galloprovincialis is discussed. In conclusion, it seems that M. galloprovincialis lives close to its acclimation limits and incipient lethal temperature and that a small degree of warming will elicit stress responses at whole organism and molecular levels.

Cytoprotective effect of Podophyllum hexandrum against gamma radiation is mediated via hemopoietic system stimulation and up-regulation of heme-oxygenase-1 and the prosurvival multidomain protein Bcl-2

The radioprotective effect of a hydroalcoholic extracted material (REC-2000) from the rhizome of Podophyllum hexandrum was studied in mice exposed to lethal gamma radiation (10 Gy). The extract (REC-2000) was found to restore the hemoglobin content (14.73 +/- 0.33) and total leukocyte count (TLC) (4166.66 +/- 0.02) in lethally (10 Gy) gamma-irradiated mice on the 15th day in comparison to the radiation control mice. The hemoglobin content of the drug + radiation group was observed to be significantly (21.25%) higher than the radiation control group on the 10th day. Similarly, the TLC was significantly increased (83.33 times) in the drug + radiation group as compared to a radiation (10 Gy) only group on the 10th day. Enhanced expression of heme-oxygenase-1 and Bcl-2 protein observed by Western blotting further supports the observation of hemopoietic recovery in irradiated mice. These findings indicate that the bioactive constituents present in REC-2000 exert the radioprotective effect by modulating the hemopoietic system.

Cell stress induced HSP are targets of regulatory T cells: A role for HSP inducing compounds as anti-inflammatory immuno-modulators?

T cell responses to heat shock proteins (HSP) have disease suppressive activities through production of anti-inflammatory cytokines in patients and in models of inflammatory diseases. There is evidence that the anti-inflammatory activity of HSP-specific T cells depends on their recognition of endogenous HSP epitopes as expressed by stressed cells at sites of inflammation. Previously, we have demonstrated that such T cells can be induced by conserved sequences of microbial HSP. Now we propose that drug induced up-regulation of endogenous HSP can contribute to anti-inflammatory T cell regulation.

CXC chemokines: a new family of heat-shock proteins?

The heat shock (HS) response is a generalized stress response that is characterized by the induced synthesis of a family of proteins referred to as heat shock proteins (HSPs). These proteins protect cells from a myriad of stressful insults in part by functioning as chaperones for denatured proteins. Increasing evidence suggests that the stress response is not limited to the HSP family of genes, but includes numerous other genes that are regulated by HS through the activation of the stress-activated transcription factor, heat shock factor-1 (HSF-1). Based on observations from our own in vivo hyperthermia models, we hypothesized that the CXC chemokine family of neutrophil activators and chemoattractants might be a previously unrecognized class of HS-responsive genes. Analysis of the promoters of the CXC family of chemokines in both human and mouse showed that they share a common promoter organization in which multiple copies of the HSF-1 binding sequence (heat shock response element, HRE) are present in the 5'-upstream flanking region of each of these genes. We have reviewed previous work from our own laboratory and others demonstrating a strong correlation between activation of HSPs and generation of CXC chemokines. Although rigorous experimental evidence is still required to support this hypothesis, this strong and consistent correlation between expression of HSPs and CXC chemokines in vivo and in vitro model systems suggests that the putative HREs present in the CXC chemokine genes are functionally active. We speculate that the activation of the HS response during febrile range hyperthermia, inflammation, infection and injury directly enhances expression of the CXC chemokines, thereby augmenting neutrophil delivery to sites of infection and injury during febrile illnesses.

Different Mechanisms Are Involved in the Transcriptional Activation by Yeast Heat Shock Transcription Factor through Two Different Types of Heat Shock Elements

The hydrophobic repeat is a conserved structural motif of eukaryotic heat shock transcription factor (HSF) that enables HSF to form a homotrimer. Homotrimeric HSF binds to heat shock elements (HSEs) consisting of three inverted repeats of the sequence nGAAn. Sequences consisting of four or more nGAAn units are bound cooperatively by two HSF trimers. We show that in Saccharomyces cerevisiae cells oligomerization-defective Hsf1 is not able to bind HSEs with three units and is not extensively phosphorylated in response to stress; it is therefore unable to activate genes containing this type of HSE. Several lines of evidence indicate that oligomerization is a prerequisite for stress-induced hyperphosphorylation of Hsf1. In contrast, oligomerization and hyperphosphorylation are not necessary for gene activation via HSEs with four units. Intragenic suppressor screening of oligomerization-defective hsf1 showed that an interface between adjacent DNA-binding domains is important for the binding of Hsf1 to the HSE. We suggest that Saccharomyces cerevisiae HSEs with different structures are regulated differently; HSEs with three units require Hsf1 to be both oligomerized and hyperphosphorylated, whereas HSEs with four or more units do not require either.

The role of chromatin structure in regulating stress-induced transcription in Saccharomyces cerevisiae

All cells, whether free-living or part of a multicellular organism, must contend with a variety of environmental fluctuations that can be harmful or lethal to the cell. Cells exposed to different kinds of environmental stress rapidly alter gene transcription, resulting in the immediate downregulation of housekeeping genes, while crucial stress-responsive transcription is drastically increased. Common cis-acting elements within many stress-induced promoters, such as stress response elements and heat shock elements, allow for coordinated expression in response to many different stresses. However, specific promoter architectures, i.e., specific combinations of high- and low-affinity stress-responsive cis elements embedded in a particular chromatin environment, allow for unique expression patterns that are responsive to the individual type and degree of stress. The coordination of transcriptional stress responses and the role that chromatin structure plays in the regulation and kinetics of such responses is discussed. The interplay among global and gene-specific stress responses is illustrated using the constitutive and stress-induced transcriptional regulation of HSP82 as a model. This review also investigates evidence suggesting that stress-induced transcription is globally synchronized with the stress-induced repression of housekeeping gene via 2 distinct mechanisms of facilitating the binding of TATA-binding protein (TBP): TFIID and SAGA-mediated TBP binding.

Increased temperature, not cardiac load, activates heat shock transcription factor 1 and heat shock protein 72 expression in the heart

The expression of myocardial heat shock protein 72 (HSP72) postexercise is initiated by the activation of heat shock transcription factor 1 (HSF1). However, it remains unknown which physiological stimuli govern myocardial HSF1 activation during exercise. These experiments tested the hypothesis that thermal stress and mechanical load, concomitant with simulated exercise, provide independent stimuli for HSF1 activation and ensuing cardiac HSP72 gene expression. To elucidate the independent roles of increased temperature and cardiac workload in the exercise-mediated upregulation of left-ventricular HSP72, hearts from adult male Sprague-Dawley rats were randomly assigned to one of five simulated exercise conditions. Upon reaching a surgical plane of anesthesia, each experimental heart was isolated and perfused using an in vitro working heart model, while independently varying temperatures (i.e., 37°C vs. 40°C) and cardiac workloads (i.e., low preload and afterload vs. high preload and afterload) to mimic exercise responses. Results indicate that hyperthermia, independent of cardiac workload, promoted an increase in nuclear translocation and phosphorylation of HSF1 compared with normothermic left ventricles. Similarly, hyperthermia, independent of workload, resulted in significant increases in cardiac levels of HSP72 mRNA. Collectively, these data suggest that HSF1 activation and HSP72 gene transcriptional competence during simulated exercise are linked to elevated heart temperature and are not a direct function of increased cardiac workload.

Manipulation of protein kinases reveals different mechanisms for upregulation of heat shock proteins in motor neurons and non-neuronal cells

Motor neurons have a high threshold for induction of heat shock proteins (Hsps) in response to stress, a property associated with impaired ability to activate heat shock transcription factor 1 (Hsf1). Hyperphosphorylation of Hsf1 has been established as a requirement for transactivation of heat shock genes. This study demonstrated that the impaired heat shock response in motor neurons is not due to altered phosphorylation of Hsf1 by kinases previously shown to affect activation of Hsf1 in other cells (PKC, GSK3beta, ERK1, CaMKIIalpha). However, a constitutively active form of CaMKIV induced robust expression of Hsp70, as well as transcription of a GFP reporter gene driven by the human inducible Hsp70 promoter in unstressed motor neurons, but not in mouse embryonic fibroblasts. The results point to novel mechanisms of activation of heat shock genes in motor neurons that have relevance to exploitation of endogenous stress responses therapeutically.

Human sat III and Drosophila hsr omega transcripts: a common paradigm for regulation of nuclear RNA processing in stressed cells

Exposure of cells to stressful conditions elicits a highly conserved defense mechanism termed the heat shock response, resulting in the production of specialized proteins which protect the cells against the deleterious effects of stress. The heat shock response involves not only a widespread inhibition of the ongoing transcription and activation of heat shock genes, but also important changes in post-transcriptional processing. In particular, a blockade in splicing and other post-transcriptional processing has been described following stress in different organisms, together with an altered spatial distribution of the proteins involved in these activities. However, the specific mechanisms that regulate these activities under conditions of stress are little understood. Non-coding RNA molecules are increasingly known to be involved in the regulation of various activities in the cell, ranging from chromatin structure to splicing and RNA degradation. In this review, we consider two non-coding RNAs, the hsrω transcripts in Drosophila and the sat III transcripts in human cells, that seem to be involved in the dynamics of RNA-processing factors in normal and/or stressed cells, and thus provide new paradigms for understanding transcriptional and post-transcriptional regulations in normal and stressed cells.

Reciprocal activation of HSF1 and HSF3 in brain and blood tissues: is redundancy developmentally related?

Transcriptional induction of heat-shock genes in response to temperature elevation and other stresses is mediated by heat-shock transcription factors (HSFs). Avian cells express two redundant heat-shock responsive factors, HSF1 and HSF3, which differ in their activation kinetics and threshold induction temperature. Unlike the ubiquitous activation of HSF1, the DNA-binding activity of HSF3 is restricted to undifferentiated avian cells and embryonic tissues. Herein, we report a reciprocal activation of HSF1 and HSF3 in vivo. Whereas HSF1 mediates transcriptional activity only in the brain upon severe heat shock, HSF3 is exclusively activated in blood cells upon light, moderate, and severe heat shock, promoting induction of heat-shock genes. Although not activated, HSF1 is expressed in blood cell nuclei in a granular appearance, suggesting regulation of genes other than heat-shock genes. Intraspecific comparison of heat-sensitive and heat-resistant fowl strains indicates that the unique activation pattern of HSF3 in blood tissue is a general phenomenon, not related to thermal history. Taken together, HSF1 and HSF3 mediate transcriptional activity of adult tissues and differentiated cells in a nonredundant manner. Instead, an exclusive, tissue-specific activation is observed, implying that redundancy may be developmentally related. The physiological and developmental implications are discussed.

Differential effects of mitochondrial heat shock protein 60 and related molecular chaperones to prevent intracellular beta-amyloid-induced inhibition of complex IV and limit apoptosis

Defects in mitochondrial oxidative metabolism, in particular decreased activity of cytochrome c oxidase, have been reported in Alzheimer disease tissue and in cultured cells that overexpress amyloid precursor protein. Mitochondrial dysfunction contributes to neurodegeneration in Alzheimer disease partly through formation of reactive oxygen species and the release of sequestered molecules that initiate programmed cell death pathways. The heat shock proteins (HSP) are cytoprotective against a number of stressors, including accumulations of misfolded proteins and reactive oxygen species. We reported on the property of Hsp70 to protect cultured neurons from cell death caused by intraneuronal beta-amyloid. Here we demonstrate that Hsp60, Hsp70, and Hsp90 both alone and in combination provide differential protection against intracellular beta-amyloid stress through the maintenance of mitochondrial oxidative phosphorylation and functionality of tricarboxylic acid cycle enzymes. Notably, beta-amyloid was found to selectively inhibit complex IV activity, an effect selectively neutralized by Hsp60. The combined effect of HSPs was to reduce the free radical burden, preserve ATP generation, decrease cytochrome c release, and prevent caspase-9 activation, all important mediators of beta-amyloid-induced neuronal dysfunction and death.

Could heat shock transcription factors function as hydrogen peroxide sensors in plants?

BACKGROUND

Heat shock transcription factors (Hsfs) are modular transcription factors encoded by a large gene family in plants. They bind to the consensus sequence 'nGAAnnTCCn' found in the promoters of many defence genes, and are thought to function as a highly redundant and flexible gene network that controls the response of plants to different environmental stress conditions, including biotic and abiotic stresses. Hsf proteins encoded by different genes exhibit a high degree of complexity in their interactions. They can potentially bind and activate their own promoters, as well as the promoters of other members of their gene family, and they can form homo- or heterotrimers resulting in altered nuclear localization, as well as enhanced or suppressed transcription.

SCOPE

In this review, we summarize recent studies on Hsf function in Arabidopsis and tomato and present evidence obtained from microarray expression studies in Arabidopsis that the Hsf gene network is highly flexible and specialized, with specific members and/or member combinations controlling the response of plants to particular stress conditions. In addition, we describe recent studies that support the hypothesis that certain Hsfs function as molecular sensors that directly sense reactive oxygen species (ROS) and control the expression of oxidative stress response genes during oxidative stress.

Benzo(a)pyrene inhibits expression of inducible heat shock protein 70 in vascular endothelial cells

Benzo(a)pyrene (BaP), a ubiquitous environmental pollutant known to cause many diseases including atherosclerosis, induces a dose-dependent reduction in the levels of the inducible Hsp70. To explore the mechanism underlying the reduction of Hsp70, we measured the levels of Hsp70, cytoplasmic and nuclear heat shock factor 1 (HSF1) in porcine aortic endothelial cells using Western blot, and then further characterized the binding ability of HSF1 and heat shock element (HSE) by electrophoretic mobility shift assay. We found that when porcine aortic endothelial cells were treated by 0.1-10 microM of BaP for 24 h, there was a significant reduction of Hsp70, cytoplasmic and nuclear HSF1 and the binding rate of HSF1 and HSE at 5, 10 microM of BaP but less effective at lower concentrations. The effect of BaP on the Hsp70 expression level was markedly attenuated by co-treatment with phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC). Staurosporine (STP), an inhibitor of PKC, blocked the effect of PMA treatment in combination with BaP. These results suggest that BaP might inhibit Hsp70 levels by reducing the expression of HSF1 and decreasing binding of HSF1 and HSE via PKC-dependent signaling pathways that might be involved in the regulation of Hsp70 gene expression under BaP.

The maize heat shock factor-binding protein paralogs EMP2 and HSBP2 interact non-redundantly with specific heat shock factors

The heat shock response (HSR) is a conserved mechanism by which transcripts of heat shock protein (hsp) genes accumulate following mobilization of heat shock transcription factors (HSFs) in response to thermal stress. Studies in animals identified the heat shock factor-binding protein1 (HSBP1) that interacts with heat shock transcription factor1 (HSF1) during heat shock attenuation; overexpression analyses revealed that the coiled-coil protein HSBP1 functions as a negative regulator of the HSR. Zea mays contains two HSBP paralogs, EMP2 and HSBP2, which exhibit differential accumulation during the HSR and plant development. Embryo-lethal recessive emp2 mutations revealed that EMP2 is required for the down-regulation of hsp transcription during embryogenesis, whereas accumulation of HSBP2 is induced in seedlings following heat shock. Notwithstanding, no interaction has yet been demonstrated between a plant HSBP and a plant HSF. In this report 22 maize HSF isoforms are identified comprising three structural classes: HSF-A, HSF-B and HSF-C. Phylogenetic analysis of Arabidopsis, maize and rice HSFs reveals that at least nine ancestral HSF isoforms were present prior to the separation of monocot and eudicots, followed by differential amplification of HSF members in these lineages. Yeast two-hybrid analyses show that EMP2 and HSBP2 interact non-redundantly with specific HSF-A isoforms. Site-specific mutagenesis of HSBP2 reveals that interactions between hydrophobic residues within the coiled coil are required for HSF::HSBP2 binding; domain swapping demonstrate that the isoform specificity of HSF::HSBP interaction is conferred by residues outside of the coiled coil. These data suggest that the non-redundant functions of the maize HSBPs may be explained, at least in part, by the specificity of HSBP::HSF interactions during plant development.