Activation of heat shock factor 1 DNA binding precedes stress-induced serine phosphorylation. Evidence for a multistep pathway of regulation

Protein Misfolding Releases Human HSF1 from HSP70 Latency Control

Heat shock factor 1 (HSF1) responds to stress to mount the heat shock response (HSR), a conserved transcriptional program that allows cells to maintain proteostasis by upregulating heat shock proteins (HSPs). The homeostatic stress regulation of HSF1 plays a key role in human physiology and health but its mechanism has remained difficult to pinpoint. Recent work in the budding yeast model has implicated stress-inducible chaperones of the HSP70 family as direct negative regulators of HSF1 activity. Here, we have investigated the latency control and activation of human HSF1 by HSP70 and misfolded proteins. Purified oligomeric HSF1-HSP70 (HSPA1A) complexes exhibited basal DNA binding activity that was inhibited by increasing the levels of HSP70 and, importantly, misfolded proteins reverted the inhibitory effect. Using site-specific UV photo-crosslinking, we monitored HSP70-HSF1 complexes in HEK293T cells. While HSF1 was bound by the substrate binding domain of HSP70 in unstressed cells, activation of HSF1 by heat shock as well as by inducing the misfolding of newly synthesized proteins resulted in release of HSF1 from the chaperone. Taken our results together, we conclude that latent HSF1 populate dynamic complexes with HSP70, which are sensitive to increased levels of misfolded proteins that compete for binding to the HSP70 substrate binding domain. Thus, human HSF1 is activated by various stress conditions that all titrate available HSP70.

HSF1, Aging, and Neurodegeneration

Heat shock factor 1 (HSF1) is a master transcription regulator that mediates the induction of heat shock protein chaperones for quality control (QC) of the proteome and maintenance of proteostasis as a protective mechanism in response to stress. Research in this particular area has accelerated dramatically over the past three decades following successful isolation, cloning, and characterization of HSF1. The intricate multi-protein complexes and transcriptional activation orchestrated by HSF1 are fundamental processes within the cellular QC machinery. Our primary focus is on the regulation and function of HSF1 in aging and neurodegenerative diseases (ND) which represent physiological and pathological states of dysfunction in protein QC. This chapter presents an overview of HSF1 structural, functional, and energetic properties in healthy cells while addressing the deterioration of HSF1 function viz-à-viz age-dependent and neuron-specific vulnerability to ND. We discuss the structural domains of HSF1 with emphasis on the intrinsically disordered regions and note that disease proteins associated with ND are often structurally disordered and exquisitely sensitive to changes in cellular environment as may occur during aging. We propose a hypothesis that age-dependent changes of the intrinsically disordered proteome likely hold answers to understand many of the functional, structural, and organizational changes of proteins and signaling pathways in aging - dysfunction of HSF1 and accumulation of disease protein aggregates in ND included.Structured AbstractsIntroduction: Heat shock factor 1 (HSF1) is a master transcription regulator that mediates the induction of heat shock protein chaperones for quality control (QC) of the proteome as a cyto-protective mechanism in response to stress. There is cumulative evidence of age-related deterioration of this QC mechanism that contributes to disease vulnerability.

OBJECTIVES

Herein we discuss the regulation and function of HSF1 as they relate to the pathophysiological changes of protein quality control in aging and neurodegenerative diseases (ND).

METHODS

We present an overview of HSF1 structural, functional, and energetic properties in healthy cells while addressing the deterioration of HSF1 function vis-à-vis age-dependent and neuron-specific vulnerability to neurodegenerative diseases.

RESULTS

We examine the impact of intrinsically disordered regions on the function of HSF1 and note that proteins associated with neurodegeneration are natively unstructured and exquisitely sensitive to changes in cellular environment as may occur during aging.

CONCLUSIONS

We put forth a hypothesis that age-dependent changes of the intrinsically disordered proteome hold answers to understanding many of the functional, structural, and organizational changes of proteins - dysfunction of HSF1 in aging and appearance of disease protein aggregates in neurodegenerative diseases included.

Interplay between mammalian heat shock factors 1 and 2 in physiology and pathology

The heat-shock factors (HSFs) belong to an evolutionary conserved family of transcription factors that were discovered already over 30 years ago. The HSFs have been shown to a have a broad repertoire of target genes, and they also have crucial functions during normal development. Importantly, HSFs have been linked to several disease states, such as neurodegenerative disorders and cancer, highlighting their importance in physiology and pathology. However, it is still unclear how HSFs are regulated and how they choose their specific target genes under different conditions. Posttranslational modifications and interplay among the HSF family members have been shown to be key regulatory mechanisms for these transcription factors. In this review, we focus on the mammalian HSF1 and HSF2, including their interplay, and provide an updated overview of the advances in understanding how HSFs are regulated and how they function in multiple processes of development, aging, and disease. We also discuss HSFs as therapeutic targets, especially the recently reported HSF1 inhibitors.

Functional diversification of heat shock factors

Heat shock transcription factors (HSFs) are widely known as master regulators of the heat shock response. In invertebrates, a single heat shock factor, HSF1, is responsible for the maintenance of protein homeostasis. In vertebrates, seven members of the HSF family have been identified, namely HSF1, HSF2, HSF3, HSF4, HSF5, HSFX, and HSFY, of which HSF1 and HSF2 are clearly associated with heat shock response, while HSF4 is involved in development. Other members of the family have not yet been studied as extensively. Besides their role in cellular proteostasis, HSFs influence a plethora of biological processes such as aging, development, cell proliferation, and cell differentiation, and they are implicated in several pathologies such as neurodegeneration and cancer. This is achieved by regulating the expression of a great variety of genes including chaperones. Here, we review our current knowledge on the function of HSF family members and important aspects that made possible the functional diversification of HSFs.

Lessons Learned from Two Decades of Modeling the Heat-Shock Response

The Heat Shock Response (HSR) is a highly conserved genetic system charged with protecting the proteome in a wide range of organisms and species. Experiments since the early 1980s have elucidated key elements in these pathways and revealed a canonical mode of regulation, which relies on a titration feedback. This system has been subject to substantial modeling work, addressing questions about resilience, design and control. The compact core regulatory circuit, as well as its apparent conservation, make this system an ideal ‘hydrogen atom’ model for the regulation of stress response. Here we take a broad view of the models of the HSR, focusing on the different questions asked and the approaches taken. After 20 years of modeling work, we ask what lessons had been learned that would have been hard to discover without mathematical models. We find that while existing models lay strong foundations, many important questions that can benefit from quantitative modeling are still awaiting investigation.

HSF-1: Guardian of the Proteome Through Integration of Longevity Signals to the Proteostatic Network

Discoveries made in the nematode Caenorhabditis elegans revealed that aging is under genetic control. Since these transformative initial studies, C. elegans has become a premier model system for aging research. Critically, the genes, pathways, and processes that have fundamental roles in organismal aging are deeply conserved throughout evolution. This conservation has led to a wealth of knowledge regarding both the processes that influence aging and the identification of molecular and cellular hallmarks that play a causative role in the physiological decline of organisms. One key feature of age-associated decline is the failure of mechanisms that maintain proper function of the proteome (proteostasis). Here we highlight components of the proteostatic network that act to maintain the proteome and how this network integrates into major longevity signaling pathways. We focus in depth on the heat shock transcription factor 1 (HSF1), the central regulator of gene expression for proteins that maintain the cytosolic and nuclear proteomes, and a key effector of longevity signals.

Development of a genetically modified hepatoma cell line with heat-inducible high liver function

Hepatoma cells are a promising cell source for the construction of bioartificial liver (BAL) systems owing to their high proliferative capability. However, their low liver function compared with primary hepatocytes is a major problem. In a previous study, we established a genetically modified hepatoma cell line, Hepa/8F5, in which eight liver-enriched transcription factor (LETF) genes were transduced into mouse hepatoma Hepa1-6 cells using a drug-inducible transactivator system. These cells proliferate actively under normal culture conditions, meaning that large quantities can be prepared easily. When the overexpression of the LETFs is induced by the addition of an inducer drug, cell growth stops and cell morphology changes with concomitant high expression of liver functions. However, the liver functions largely depend on the presence of the inducer drug, which must be continuously added to maintain these enhanced functions. In the present study, we attempted to modify the method of induction of LETF overexpression in Hepa/8F5 cells to remove the requirement for continual drug addition. To this end, we constructed a system in which the artificial transactivator was transcribed and amplified under the control of a heat-shock protein promoter, and introduced the system into the genome of Hepa/8F5 cells. In our modified cell line, heat-triggered LETF expression was confirmed to induce high liver function. After drug-screening of transfected cells, we established a hepatoma cell line (Hepa/HS), which exhibited high, heat-inducible liver functions. The Hepa/HS cells may represent a new cell source for hepatic studies such as the construction of BAL systems.

Supplementary Information

The online version of this article (10.1007/s10616-021-00457-4) contains supplementary material, which is available to authorized users.

Multifactorial Attenuation of the Murine Heat Shock Response With Age

Age-dependent perturbation of the cellular stress response affects proteostasis and other key functions relevant to cellular action and survival. Central to age-related changes in the stress response is loss of heat shock factor 1 (HSF1)-DNA binding and transactivation properties. This report elucidates how age alters different checkpoints of HSF1 activation related to posttranslational modification and protein interactions. When comparing liver extracts from middle aged (12 M) and old (24 M) mice, significant differences are found in HSF1 phosphorylation and acetylation. HSF1 protein levels and messenger RNA decline with age, but its protein levels are stress-inducible and exempt from age-dependent changes. This surprising adaptive change in the stress response has additional implications for aging and chronic physiological stress that might explain an age-dependent dichotomy of HSF1 protein levels that are low in neurodegeneration and elevated in cancer.

Cloning and identification of grass carp transcription factor HSF1 and its characterization involving the production of fish HSP70

In mammals, heat shock transcription factor 1 (HSF1) is well documented as the critical transcript factor to regulate heat shock protein 70 (HSP70) expression under different stresses, such as heat shock or bacterial infection. In fish, Hsf1 responses to physiological and environmental stresses and regulates Hsp70 expression under thermal exposure. However, the functional role of Hsf1 in Hsp70 production is still elusive under bacterial infection. In the present study, a coding sequence of grass carp hsf1 (gchsf1) gene was cloned and identified. Using Ctenopharyngodon idellus kidney (CIK) cells as the model, we found that lipopolysaccharide (LPS) exerted stimulatory effects on the expression of grass carp hsp70 (gchsp70) and hsf1, implying possible relationship of Hsp70 and Hsf1 under immune stimulation in fish. To validate the hypothesis, overexpression of gcHsf1 was performed in CIK cells, and the effects of overexpressing gcHsf1 on the expression of gcHsp70 in the absence or presence of LPS were examined. Results showed that LPS significantly upregulated the transcription and protein synthesis of gcHsp70, and these stimulatory effects were further amplified when overexpression of gcHsf1 was performed. Furthermore, luciferase reporter assays in CIK cells revealed that both overexpression of Hsf1 and LPS upregulated gchsp70 transcription, and their combined treatment further enhanced the gchsp70 promoter activity. Moreover, the regions responsive to these treatments were mapped to the promoter of gchsp70. Besides transcriptional level and cellular protein contents, gcHsp70 secretion was measured by competitive ELISA, uncovering that gcHsf1 enhanced the release of gcHsp70 induced by LPS in the same cells. These data not only demonstrated the enhancement of Hsf1 in Hsp70 production but also initially revealed the involvement of Hsf1-Hsp70 axis in mediating inflammatory response in fish.

Hsf1 on a leash - controlling the heat shock response by chaperone titration

Heat shock factor 1 (Hsf1) is an ancient transcription factor that monitors protein homeostasis (proteostasis) and counteracts disturbances by triggering a transcriptional programme known as the heat shock response (HSR). The HSR is transiently activated and upregulates the expression of core proteostasis genes, including chaperones. Dysregulation of Hsf1 and its target genes are associated with disease; cancer cells rely on a constitutively active Hsf1 to promote rapid growth and malignancy, whereas Hsf1 hypoactivation in neurodegenerative disorders results in formation of toxic aggregates. These central but opposing roles highlight the importance of understanding the underlying molecular mechanisms that control Hsf1 activity. According to current understanding, Hsf1 is maintained latent by chaperone interactions but proteostasis perturbations titrate chaperone availability as a result of chaperone sequestration by misfolded proteins. Liberated and activated Hsf1 triggers a negative feedback loop by inducing the expression of key chaperones. Until recently, Hsp90 has been highlighted as the central negative regulator of Hsf1 activity. In this review, we focus on recent advances regarding how the Hsp70 chaperone controls Hsf1 activity and in addition summarise several additional layers of activity control.

Serotonin signaling by maternal neurons upon stress ensures progeny survival

Germ cells are vulnerable to stress. Therefore, how organisms protect their future progeny from damage in a fluctuating environment is a fundamental question in biology. We show that in Caenorhabditis elegans, serotonin released by maternal neurons during stress ensures the viability and stress resilience of future offspring. Serotonin acts through a signal transduction pathway conserved between C. elegans and mammalian cells to enable the transcription factor HSF1 to alter chromatin in soon-to-be fertilized germ cells by recruiting the histone chaperone FACT, displacing histones, and initiating protective gene expression. Without serotonin release by maternal neurons, FACT is not recruited by HSF1 in germ cells, transcription occurs but is delayed, and progeny of stressed C. elegans mothers fail to complete development. These studies uncover a novel mechanism by which stress sensing by neurons is coupled to transcription response times of germ cells to protect future offspring.

Protein level variability determines phenotypic heterogeneity in proteotoxic stress response

Cell-to-cell variability in stress response is a bottleneck for the construction of accurate and predictive models which could guide clinical diagnosis and treatment of certain diseases, for example, cancer. Indeed, such phenotypic heterogeneity can lead to fractional killing and persistence of a subpopulation of cells which are resistant to a given treatment. The heat shock response network plays a major role in protecting the proteome against several types of injuries. Here, we combine high-throughput measurements and mathematical modeling to unveil the molecular origin of the phenotypic variability in the heat shock response network. Although the mean response coincides with known biochemical measurements, we found a surprisingly broad diversity in single-cell dynamics with a continuum of response amplitudes and temporal shapes for several stimulus strengths. We theoretically predict that the broad phenotypic heterogeneity is due to network ultrasensitivity together with variations in the expression level of chaperones controlled by the transcription factor heat shock factor 1. Furthermore, we experimentally confirm this prediction by mapping the response amplitude to chaperone and heat shock factor 1 expression levels.

HSP70 and HSP90 in neurodegenerative diseases

Molecular chaperones have a role to stabilize proteins or assist them in reaching their native fold. Heat shock proteins (HSPs) are a family of molecular chaperons that protect proteins from cellular stress during the assembly of protein complexes and also prevent the proteins from aggregation and disassembly. The immediate increase of HSPs is crucial for cellular adaptation to environmental changes and protection of other proteins from denaturation, thereby maintaining the cellular homeostasis and increasing the longevity of an organism. HSP70 and HSP90 are the most studied HSPs in this very large HSP family. Notably, HSP90 also stabilizes the disease-related proteins in neurodegenerative disorders. Therefore, small molecules that inhibit the HSP90 but also increase the HSP70 has been tested as potential drugs for neurodegenerative disorders.

Proteomics analysis of proteins interacting with heat shock factor 1 in squamous cell carcinoma of the cervix

Protein interactions are crucial for maintaining homeostasis. Heat shock factor 1 (HSF1), a transcription factor that interacts with various proteins, is highly expressed in squamous cell carcinoma (SCC) of the cervix. The aim of the present study was to investigate the protein interaction profile of HSF1 in cervical SCC. Proteins interacting with HSF1 in SCC tissue and non-cancerous control (Ctrl) tissue were obtained by immunoprecipitation, separated by SDS-PAGE, identified by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry and analyzed using bioinformatics methods. A total of 220 and 241 proteins were identified by mass spectrometry in the tissues of Ctrl and SCC samples, respectively, among which 172 were detected exclusively in SCC (Pro-S), 151 exclusively in Ctrl (Pro-C) and 69 in both groups (Pro-B). The protein interaction profiles were different in each group; the STRING database identified three proteins that interacted with HSF1 directly, including insulin-like growth factor 1 receptor and small nuclear RNA-activating protein complex subunit 4 in Pro-C and small ubiquitin-related modifier 1 in Pro-S. Functional enrichment analysis of Gene Ontology revealed that the top terms were alternative splicing in Pro-S and polymorphism in Pro-C. In Pro-S, more categories were related to protein modification, such as phosphorylation, ubiquitination and acetylation. Therefore, HSF1 may influence the occurrence and development of cervical SCC by interacting with specific proteins.

Regulation of the Hsf1-dependent transcriptome via conserved bipartite contacts with Hsp70 promotes survival in yeast

Protein homeostasis and cellular fitness in the presence of proteotoxic stress is promoted by heat shock factor 1 (Hsf1), which controls basal and stress-induced expression of molecular chaperones and other targets. The major heat shock proteins and molecular chaperones Hsp70 and Hsp90, in turn, participate in a negative feedback loop that ensures appropriate coordination of the heat shock response with environmental conditions. Features of this regulatory circuit in the budding yeast Saccharomyces cerevisiae have been recently defined, most notably regarding direct interaction between Hsf1 and the constitutively expressed Hsp70 protein Ssa1. Here, we sought to further examine the Ssa1/Hsf1 regulation. We found that Ssa1 interacts independently with both the previously defined CE2 site in the Hsf1 C-terminal transcriptional activation domain and with an additional site that we identified within the N-terminal activation domain. Consistent with both sites bearing a recognition signature for Hsp70, we demonstrate that Ssa1 contacts Hsf1 via its substrate-binding domain and that abolishing either regulatory site results in loss of Ssa1 interaction. Removing Hsp70 regulation of Hsf1 globally dysregulated Hsf1 transcriptional activity, with synergistic effects on both gene expression and cellular fitness when both sites are disrupted together. Finally, we report that Hsp70 interacts with both transcriptional activation domains of Hsf1 in the related yeast Lachancea kluyveri Our findings indicate that Hsf1 transcriptional activity is tightly regulated to ensure cellular fitness and that a general and conserved Hsp70-HSF1 feedback loop regulates cellular proteostasis in yeast.

Magnetically triggered transgene expression in mammalian cells by localized cellular heating of magnetic nanoparticles

To develop a remote control system of transgene expression through localized cellular heating of magnetic nanoparticles, a heat-inducible transgene expression system was introduced into mammalian cells. Cells were labeled with magnetic nanoparticles and exposed to an alternating magnetic field. The magnetically labeled cells expressed the transgene in a monolayer and multilayered cell sheets in which cells were heated around the magnetic nanoparticles without an apparent temperature increase in the culture medium. Magnetic cells were also generated by genetically engineering with a ferritin gene, and transgene expression could be induced by exposure to an alternating magnetic field. This approach may be applicable to the development of novel gene therapies in cell-based medicine.

Tailoring of Proteostasis Networks with Heat Shock Factors

Heat shock factors (HSFs) are the main transcriptional regulators of the heat shock response and indispensable for maintaining cellular proteostasis. HSFs mediate their protective functions through diverse genetic programs, which are composed of genes encoding molecular chaperones and other genes crucial for cell survival. The mechanisms that are used to tailor HSF-driven proteostasis networks are not yet completely understood, but they likely comprise from distinct combinations of both genetic and proteomic determinants. In this review, we highlight the versatile HSF-mediated cellular functions that extend from cellular stress responses to various physiological and pathological processes, and we underline the key advancements that have been achieved in the field of HSF research during the last decade.

Circadian transcription factor HSF1 regulates differential HSP70 gene transcription during the arousal-torpor cycle in mammalian hibernation

Mammalian hibernation is a seasonal phenomenon. The hibernation season consists of torpor periods with a reduced body temperature (Tb), interrupted by euthermic arousal periods (interbout arousal, IBA). The physiological changes associated with hibernation are assumed to be under genetic control. However, the molecular mechanisms that govern hibernation-associated gene regulation are still unclear. We found that HSP70 transcription is upregulated in the liver of nonhibernating (summer-active) chipmunks compared with hibernating (winter-torpid) ones. In parallel, HSF1, the major transcription factor for HSP70 expression, is abundant in the liver-cell nuclei of nonhibernating chipmunks, and disappears from the nuclei of hibernating ones. Moreover, during IBA, HSF1 reappears in the nuclei and drives HSP70 transcription. In mouse liver, HSF1 is regulated by the daily Tb rhythm, and acts as a circadian transcription factor. Taken together, chipmunks similarly use the Tb rhythm to regulate gene expression via HSF1 during the torpor-arousal cycle in the hibernation season.

Heat shock protein 72 regulates hepatic lipid accumulation

Induction of the chaperone heat shock protein 72 (HSP72) through heat treatment (HT), exercise, or overexpression improves glucose tolerance and mitochondrial function in skeletal muscle. Less is known about HSP72 function in the liver where lipid accumulation can result in insulin resistance and nonalcoholic fatty liver disease (NAFLD). The purpose of this study was 1) to determine whether weekly in vivo HT induces hepatic HSP72 and improves glucose tolerance in rats fed a high-fat diet (HFD) and 2) to determine the ability of HSP72 to protect against lipid accumulation and mitochondrial dysfunction in primary hepatocytes. Male Wistar rats were fed an HFD for 15 wk and were given weekly HT (41°C, 20 min) or sham treatments (37°C, 20 min) for the final 7 wk. Glucose tolerance and insulin sensitivity were assessed, along with HSP72 induction and triglyceride storage, in the skeletal muscle and liver. The effect of an acute loss of HSP72 in primary hepatocytes was examined via siRNA. Weekly in vivo HT improved glucose tolerance, elevated muscle and hepatic HSP72 protein content, and reduced muscle triglyceride storage. In primary hepatocytes, mitochondrial morphology was changed, and fatty acid oxidation was reduced in small interfering HSP72 (siHSP72)-treated hepatocytes. Lipid accumulation following palmitate treatment was increased in siHSP72-treated hepatocytes. These data suggest that HT may improve systemic metabolism via induction of hepatic HSP72. Additionally, acute loss of HSP72 in primary hepatocytes impacts mitochondrial health as well as fat oxidation and storage. These findings suggest therapies targeting HSP72 in the liver may prevent NAFLD.

Oncogenic hijacking of the stress response machinery in T cell acute lymphoblastic leukemia

Cellular transformation is accompanied by extensive re-wiring of many biological processes leading to augmented levels of distinct types of cellular stress, including proteotoxic stress. Cancer cells critically depend on stress-relief pathways for their survival. However, the mechanisms underlying the transcriptional initiation and maintenance of the oncogenic stress response remain elusive. Here, we show that the expression of heat shock transcription factor 1 (HSF1) and the downstream mediators of the heat shock response is transcriptionally upregulated in T-cell acute lymphoblastic leukemia (T-ALL). Hsf1 ablation suppresses the growth of human T-ALL and eradicates leukemia in mouse models of T-ALL, while sparing normal hematopoiesis. HSF1 drives a compact transcriptional program and among the direct HSF1 targets, specific chaperones and co-chaperones mediate its critical role in T-ALL. Notably, we demonstrate that the central T-ALL oncogene NOTCH1 hijacks the cellular stress response machinery by inducing the expression of HSF1 and its downstream effectors. The NOTCH1 signaling status controls the levels of chaperone/co-chaperone complexes and predicts the response of T-ALL patient samples to HSP90 inhibition. Our data demonstrate an integral crosstalk between mediators of oncogene and non-oncogene addiction and reveal critical nodes of the heat shock response pathway that can be targeted therapeutically.

Poly(ADP-Ribose) Polymerase 1 Promotes the Human Heat Shock Response by Facilitating Heat Shock Transcription Factor 1 Binding to DNA

The heat shock response (HSR) is characterized by the rapid and robust induction of heat shock proteins (HSPs), including HSP70, in response to heat shock and is regulated by heat shock transcription factor 1 (HSF1) in mammalian cells. Poly(ADP-ribose) polymerase 1 (PARP1), which can form a complex with HSF1 through the scaffold protein PARP13, has been suggested to be involved in the HSR. However, its effects on and the regulatory mechanisms of the HSR are not well understood. Here we show that prior to heat shock, the HSF1-PARP13-PARP1 complex binds to the HSP70 promoter. In response to heat shock, activated and auto-PARylated PARP1 dissociates from HSF1-PARP13 and is redistributed throughout the HSP70 locus. Remarkably, chromatin in the HSP70 promoter is initially PARylated at high levels and decondensed, whereas chromatin in the gene body is moderately PARylated afterwards. Activated HSF1 then binds to the promoter efficiently and promotes the HSR. Chromatin PARylation and HSF1 binding to the promoter are also facilitated by the phosphorylation-dependent dissociation of PARP13. Furthermore, the HSR and proteostasis capacity are reduced by pretreatment with genotoxic stresses, which disrupt the ternary complex. These results illuminate one of the priming mechanisms of the HSR that facilitates the binding of HSF1 to DNA during heat shock.

Hsf1 and Hsp70 constitute a two-component feedback loop that regulates the yeast heat shock response

Models for regulation of the eukaryotic heat shock response typically invoke a negative feedback loop consisting of the transcriptional activator Hsf1 and a molecular chaperone. Previously we identified Hsp70 as the chaperone responsible for Hsf1 repression and constructed a mathematical model that recapitulated the yeast heat shock response (Zheng et al., 2016). The model was based on two assumptions: dissociation of Hsp70 activates Hsf1, and transcriptional induction of Hsp70 deactivates Hsf1. Here we validate these assumptions. First, we severed the feedback loop by uncoupling Hsp70 expression from Hsf1 regulation. As predicted by the model, Hsf1 was unable to efficiently deactivate in the absence of Hsp70 transcriptional induction. Next, we mapped a discrete Hsp70 binding site on Hsf1 to a C-terminal segment known as conserved element 2 (CE2). In vitro, CE2 binds to Hsp70 with low affinity (9 µM), in agreement with model requirements. In cells, removal of CE2 resulted in increased basal Hsf1 activity and delayed deactivation during heat shock, while tandem repeats of CE2 sped up Hsf1 deactivation. Finally, we uncovered a role for the N-terminal domain of Hsf1 in negatively regulating DNA binding. These results reveal the quantitative control mechanisms underlying the heat shock response.

NF‑κB regulates HSF1 and c‑Jun activation in heat stress‑induced intestinal epithelial cell apoptosis

Heat stress may induce intestinal epithelial cell apoptosis; however, the molecular mechanisms have not yet been identified. The present study used IEC‑6 rat small intestinal epithelial cells to investigate heat stress‑induced production of reactive oxygen species (ROS), which may be involved in nuclear factor (NF)‑κB activation during heat stress. IEC‑6 cells were transfected with NF‑κB p65‑specific small interfering RNA (siRNA), and observed a significant increase in cell apoptosis and caspase‑3 cleavage; however, in cells transfected with adenovirus that constitutively overexpressed p65, the opposite results were obtained. Furthermore, p65 knockdown increased the heat stress‑induced expression and activity of heat shock transcription factor 1 (HSF1); conversely, p65 overexpression slightly decreased HSF1 activity. The levels of heat stress‑induced c‑Jun phosphorylation were also examined: Knockdown of p65 resulted in a reduction of c‑Jun phosphorylation, whereas p65 overexpression resulted in increased phosphorylation. Furthermore, siRNA‑mediated knockdown of HSF1 in IEC‑6 cells significantly increased heat stress‑induced apoptosis. Cells pretreated with c‑Jun peptide, an inhibitor of c‑Jun activation, exhibited a significant reduction in apoptosis. These findings indicated that heat stress stimulation in IEC‑6 cells induced the pro‑apoptotic role of NF‑κB by regulating HSF1 and c‑Jun activation.

Hikeshi modulates the proteotoxic stress response in human cells: Implication for the importance of the nuclear function of HSP70s

Hikeshi mediates the heat stress-induced nuclear import of heat-shock protein 70 (HSP70s: HSP70/HSC70). Dysfunction of Hikeshi causes some serious effects in humans; however, the cellular function of Hikeshi is largely unknown. Here, we investigated the effects of Hikeshi depletion on the survival of human cells after proteotoxic stress and found opposite effects in HeLa and hTERT-RPE1 (RPE) cells; depletion of Hikeshi reduced the survival of HeLa cells, but increased the survival of RPE cells in response to proteotoxic stress. Hikeshi depletion sustained heat-shock transcription factor 1 (HSF1) activation in HeLa cells after recovery from stress, but introduction of a nuclear localization signal-tagged HSC70 in Hikeshi-depleted HeLa cells down-regulated HSF1 activity. In RPE cells, the HSF1 was efficiently activated, but the activated HSF1 was not sustained after recovery from stress, as in HeLa cells. Additionally, we found that p53 and subsequent up-regulation of p21 were higher in the Hikeshi-depleted RPE cells than in the wild-type cells. Our results indicate that depletion of Hikeshi renders HeLa cells proteotoxic stress-sensitive through the abrogation of the nuclear function of HSP70s required for HSF1 regulation. Moreover, Hikeshi depletion up-regulates p21 in RPE cells, which could be a cause of its proteotoxic stress resistant.

Vitexin confers HSF-1 mediated autophagic cell death by activating JNK and ApoL1 in colorectal carcinoma cells

Heat shock transcription factor-1 (HSF-1) guards the cancerous cells proteome against the alterations in protein homeostasis generated by their hostile tumor microenvironment. Contrasting with the classical induction of heat shock proteins, the pro-oncogenic activities of HSF-1 remains to be explored. Therefore, cancer's fragile proteostatic pathway governed by HSF-1 could be a potential therapeutic target and novel biomarker by natural compounds. Vitexin, a natural flavonoid has been documented as a potent anti-tumor agent on various cell lines. However, in the present study, when human colorectal carcinoma HCT-116 cells were exposed to vitexin, the induction of HSF-1 downstream target proteins, such as heat shock proteins were suppressed. We identified HSF-1 as a potential molecular target of vitexin that interact with DNA-binding domain of HSF-1, which inhibited HSF-1 oligomerization and activation (in silico). Consequently, HSF-1 hyperphosphorylation mediated by JNK operation causes transcriptional inactivation of HSF-1, and supported ROS-mediated autophagy induction. Interestingly, in HSF-1 immunoprecipitated and silenced HCT-116 cells, co-expression of apolipoprotein 1 (ApoL1) and JNK was observed which promoted the caspase independent autophagic cell death accompanied by p62 downregulation and increased LC3-I to LC3-II conversion. Finally, in vivo findings confirmed that vitexin suppressed tumor growth through activation of autophagic cascade in HCT-116 xenograft model. Taken together, our study insights a probable novel association between HSF-1 and ApoL-1 was established in this study, which supports HSF-1 as a potential target of vitexin to improve treatment outcome in colorectal cancer.

piR-823 contributes to colorectal tumorigenesis by enhancing the transcriptional activity of HSF1

Piwi-interacting RNAs (piRNAs), a novel class of small non-coding RNAs, were first discovered in germline cells and are thought to silence transposons in spermatogenesis. Recently, piRNAs have also been identified in somatic tissues, and aberrant expression of piRNAs in tumor tissues may be implicated in carcinogenesis. However, the function of piR-823 in colorectal cancer (CRC) remains unclear. Here, we first found that piR-823 was significantly upregulated in CRC tissues compared with its expression in the adjacent tissues. Inhibition of piR-823 suppressed cell proliferation, arrested the cell cycle in the G1 phase and induced cell apoptosis in CRC cell lines HCT116 and DLD-1, whereas overexpression of piR-823 promoted cell proliferation in normal colonic epithelial cell line FHC. Interestingly, Inhibition of piR-823 repressed the expression of heat shock protein (HSP) 27, 60, 70. Furthermore, elevated HSPs expression partially abolished the effect of piR-823 on cell proliferation and apoptosis. In addition, we further demonstrated that piR-823 increased the transcriptional activity of HSF1, the common transcription factor of HSPs, by binding to HSF1 and promoting its phosphorylation at Ser326. Our study reveals that piR-823 plays a tumor-promoting role by upregulating phosphorylation and transcriptional activity of HSF1 and suggests piR-823 as a potential therapeutic target for CRC.

The Nuclear Proteome of White and Gray Matter from Schizophrenia Postmortem Brains

Schizophrenia (SCZ) is a serious neuropsychiatric disorder that manifests through several symptoms from early adulthood. Numerous studies over the last decades have led to significant advances in increasing our understanding of the factors involved in SCZ. For example, mass spectrometry-based proteomic analysis has provided important insights by uncovering protein dysfunctions inherent to SCZ. Here, we present a comprehensive analysis of the nuclear proteome of postmortem brain tissues from corpus callosum (CC) and anterior temporal lobe (ATL). We show an overview of the role of deregulated nuclear proteins in these two main regions of the brain: the first, mostly composed of glial cells and axons of neurons, and the second, represented mainly by neuronal cell bodies. These samples were collected from SCZ patients in an attempt to characterize the role of the nucleus in the disease process. With the ATL nucleus enrichment, we found 224 proteins present at different levels, and 76 of these were nuclear proteins. In the CC analysis, we identified 119 present at different levels, and 24 of these were nuclear proteins. The differentially expressed nuclear proteins of ATL are mainly associated with the spliceosome, whereas those of the CC region are associated with calcium/calmodulin signaling.

Mechanisms of Hsp90 regulation

Heat shock protein 90 (Hsp90) is a molecular chaperone that is involved in the activation of disparate client proteins. This implicates Hsp90 in diverse biological processes that require a variety of co-ordinated regulatory mechanisms to control its activity. Perhaps the most important regulator is heat shock factor 1 (HSF1), which is primarily responsible for upregulating Hsp90 by binding heat shock elements (HSEs) within Hsp90 promoters. HSF1 is itself subject to a variety of regulatory processes and can directly respond to stress. HSF1 also interacts with a variety of transcriptional factors that help integrate biological signals, which in turn regulate Hsp90 appropriately. Because of the diverse clientele of Hsp90 a whole variety of co-chaperones also regulate its activity and some are directly responsible for delivery of client protein. Consequently, co-chaperones themselves, like Hsp90, are also subject to regulatory mechanisms such as post translational modification. This review, looks at the many different levels by which Hsp90 activity is ultimately regulated.

Regulation of the mammalian heat shock factor 1

Living organisms are endowed with the capability to tackle various forms of cellular stress due to the presence of molecular chaperone machinery complexes that are ubiquitous throughout the cell. During conditions of proteotoxic stress, the transcription factor heat shock factor 1 (HSF1) mediates the elevation of heat shock proteins, which are crucial components of the chaperone complex machinery and function to ameliorate protein misfolding and aggregation and restore protein homeostasis. In addition, HSF1 orchestrates a versatile transcriptional programme that includes genes involved in repair and clearance of damaged macromolecules and maintenance of cell structure and metabolism, and provides protection against a broad range of cellular stress mediators, beyond heat shock. Here, we discuss the structure and function of the mammalian HSF1 and its regulation by post-translational modifications (phosphorylation, sumoylation and acetylation), proteasomal degradation, and small-molecule activators and inhibitors.

Regulatory Mechanisms of Hsp90

The ability of Hsp90 to activate a disparate clientele implicates this chaperone in diverse biological processes. To accommodate such varied roles, Hsp90 requires a variety of regulatory mechanisms that are coordinated in order to modulate its activity appropriately. Amongst these, the master-regulator heat shock factor 1 (HSF1) is critically important in upregulating Hsp90 during stress, but is also responsible, through interaction with specific transcription factors (such as STAT1 and Strap/p300) for the integration of a variety of biological signals that ultimately modulate Hsp90 expression. Additionally, transcription factors, such as STAT1, STAT3 (including STAT1-STAT3 oligomers), NF-IL6, and NF-kB, are known to influence Hsp90 expression directly. Co-chaperones offer another mechanism for Hsp90 regulation, and these can modulate the chaperone cycle appropriately for specific clientele. Co-chaperones include those that deliver specific clients to Hsp90, and others that regulate the chaperone cycle for specific Hsp90-client complexes by modulating Hsp90s ATPase activity. Finally, post-translational modification (PTM) of Hsp90 and its co-chaperones helps too further regulate the variety of different Hsp90 complexes found in cells.

Molecular cloning of hsf1 and hsbp1 cDNAs, and the expression of hsf1, hsbp1 and hsp70 under heat stress in the sea cucumber Apostichopus japonicus

The heat shock response (HSR) is known for the elevated synthesis of heat shock proteins (HSPs) under heat stress, which is mediated primarily by heat shock factor 1 (HSF1). Heat shock factor binding protein 1 (HSBP1) and feedback control of heat shock protein 70 (HSP70) are major regulators of the activity of HSF1. We obtained full-length cDNA of genes hsf1 and hsbp1 in the sea cucumber Apostichopus japonicus, which are the second available for echinoderm (after Strongylocentrotus purpuratus), and the first available for holothurian. The full-length cDNA of hsf1 was 2208bp, containing a 1326bp open reading frame encoding 441 amino acids. The full-length cDNA of hsbp1 was 2850bp, containing a 225bp open reading frame encoding 74 amino acids. The similarities of A. japonicus HSF1 with other species are low, and much higher similarity identities of A. japonicus HSBP1 were shared. Phylogenetic trees showed that A. japonicus HSF1 and HSBP1 were clustered with sequences from S. purpuratus, and fell into distinct clades with sequences from mollusca, arthropoda and vertebrata. Analysis by real-time PCR showed hsf1 and hsbp1 mRNA was expressed constitutively in all tissues examined. The expression of hsf1, hsbp1 and hsp70 in the intestine at 26°C was time-dependent. The results of this study might provide new insights into the regulation of heat shock response in this species.

Loss of function of myosin chaperones triggers Hsf1-mediated transcriptional response in skeletal muscle cells

Background

Mutations in myosin chaperones Unc45b and Hsp90aa1.1 as well as in the Unc45b-binding protein Smyd1b impair formation of myofibrils in skeletal muscle and lead to the accumulation of misfolded myosin. The concomitant transcriptional response involves up-regulation of the three genes encoding these proteins, as well as genes involved in muscle development. The transcriptional up-regulation of unc45b, hsp90aa1.1 and smyd1b is specific to zebrafish mutants with myosin folding defects, and is not triggered in other zebrafish myopathy models.

Results

By dissecting the promoter of unc45b, we identify a Heat shock factor 1 (Hsf1) binding element as a mediator of unc45b up-regulation in myofibers lacking myosin folding proteins. Loss-of-function of Hsf1 abolishes unc45b up-regulation in mutants with defects in myosin folding.

Conclusions

Taken together, our data show that skeletal muscle cells respond to defective myosin chaperones with a complex gene program and suggest that this response is mediated by Hsf1 activation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0825-8) contains supplementary material, which is available to authorized users.

Heat shock protein 70 induction by glutamine increases the α-synuclein degradation in SH-SY5Y neuroblastoma cells

Functional defects in heat shock proteins (HSPs), e.g. Hsp70, have been reported to have a key role in Parkinson's disease (PD). Overexpressed Hsp70 re‑folds aggregated α‑synuclein to generate the non‑toxic and non‑aggregated form. Thus, Hsp70 is a well‑defined therapeutic target, and Hsp70 promotion is an efficient strategy to prevent or even reverse the α‑synuclein‑induced toxicity in PD. The present study investigated the promotion of Hsp70 expression in SH‑SY5Y neuroblastoma cells by glutamine (Gln), which has recently been recognized to induce Hsp70 expression. Furthermore, the role of heat shock factor (HSF)‑1 in the Gln‑mediated upregulation of Hsp70 expression was investigated. In addition, the regulatory role of Gln in α‑synuclein degradation in α‑synuclein‑overexpressing SH‑SY5Y cells was determined. The results of the present study demonstrated that Gln treatment significantly upregulated Hsp70 expression at the mRNA as well as the protein level in a dose‑dependent and time‑dependent manner. Gln‑induced Hsp70 upregulation was found to be HSF‑1‑dependent, as HSF‑1 knockdown abrogated the Hsp70 upregulation by Gln in α‑synuclein‑overexpressing SH‑SY5Y cells. In conclusion, present study confirmed that Gln upregulates Hsp70 expression in SH‑SY5Y neuroblastoma cells in an HSF‑1‑dependent manner. The upregulation of Hsp70 by Gln increases the α‑synuclein degradation. Therefore, Gln may be a potential therapeutic agent to prevent α‑synuclein aggregation in PD.

Acetyl salicylic acid protected against heat stress damage in chicken myocardial cells and may associate with induced Hsp27 expression

We investigated whether acetyl salicylic acid (ASA) protects chicken myocardial cells from heat stress-mediated damage in vivo and whether the induction of Hsp27 expression is connected with this function. Pathological changes, damage-related enzyme levels, and Hsp27 expression were studied in chickens following heat stress (40 ± 1 °C for 0, 1, 2, 3, 5, 7, 10, 15, or 24 h, respectively) with or without ASA administration (1 mg/kg BW, 2 h prior). Appearance of pathological lesions such as degenerations and karyopyknosis as well as the myocardial damage-related enzyme activation indicated that heat stress causes considerable injury to the myocardial cells in vivo. Myocardial cell injury was most serious in chickens exposed to heat stress without prior ASA administration; meanwhile, ASA pretreatment acted protective function against high temperature-induced injury. Hsp27 expression was induced under all experimental conditions but was one-fold higher in the ASA-pretreated animals (0.3138 ± 0.0340 ng/mL) than in untreated animals (0.1437 ± 0.0476 ng/mL) 1 h after heat stress exposure, and such an increase was sustained over the length of the experiment. Our findings indicate that pretreatment with ASA protects chicken myocardial cells from acute heat stress in vivo with almost no obvious side effects, and this protection may involve an enhancement of Hsp27 expression. However, the detailed mechanisms underlying this effect require further investigation.

Inhibition of viral protein translation by indomethacin in vesicular stomatitis virus infection: role of eIF2α kinase PKR

Indomethacin, a cyclooxygenase‐1 and ‐2 inhibitor widely used in the clinic for its potent anti‐inflammatory/analgesic properties, possesses antiviral activity against several viral pathogens; however, the mechanism of antiviral action remains elusive. We have recently shown that indomethacin activates the double‐stranded RNA (dsRNA)‐dependent protein kinase R (PKR) in human colon cancer cells. Because of the important role of PKR in the cellular defence response against viral infection, herein we investigated the effect of indomethacin on PKR activity during infection with the prototype rhabdovirus vesicular stomatitis virus. Indomethacin was found to activate PKR in an interferon‐ and dsRNA‐independent manner, causing rapid (< 5 min) phosphorylation of eukaryotic initiation factor‐2 α‐subunit (eIF2α). These events resulted in shutting off viral protein translation and blocking viral replication (IC₅₀ = 2 μM) while protecting host cells from virus‐induced damage. Indomethacin did not affect eIF2α kinases PKR‐like endoplasmic reticulum‐resident protein kinase (PERK) and general control non‐derepressible‐2 (GCN2) kinase, and was unable to trigger eIF2α phosphorylation in the presence of PKR inhibitor 2‐aminopurine. In addition, small‐interfering RNA‐mediated PKR gene silencing dampened the antiviral effect in indomethacin‐treated cells. The results identify PKR as a critical target for the antiviral activity of indomethacin and indicate that eIF2α phosphorylation could be a key element in the broad spectrum antiviral activity of the drug.

Uncoupling Stress-Inducible Phosphorylation of Heat Shock Factor 1 from Its Activation

In mammals the stress-inducible expression of genes encoding heat shock proteins is under the control of the heat shock transcription factor 1 (HSF1). Activation of HSF1 is a multistep process, involving trimerization, acquisition of DNA-binding and transcriptional activities, which coincide with several posttranslational modifications. Stress-inducible phosphorylation of HSF1, or hyperphosphorylation, which occurs mainly within the regulatory domain (RD), has been proposed as a requirement for HSF-driven transcription and is widely used for assessing HSF1 activation. Nonetheless, the contribution of hyperphosphorylation to the activity of HSF1 remains unknown. In this study, we generated a phosphorylation-deficient HSF1 mutant (HSF1Δ∼PRD), where the 15 known phosphorylation sites within the RD were disrupted. Our results show that the phosphorylation status of the RD does not affect the subcellular localization and DNA-binding activity of HSF1. Surprisingly, under stress conditions, HSF1Δ∼PRD is a potent transactivator of both endogenous targets and a reporter gene, and HSF1Δ∼PRD has a reduced activation threshold. Our results provide the first direct evidence for uncoupling stress-inducible phosphorylation of HSF1 from its activation, and we propose that the phosphorylation signature alone is not an appropriate marker for HSF1 activity.

The Chlamydomonas heat stress response

Heat waves occurring at increased frequency as a consequence of global warming jeopardize crop yield safety. One way to encounter this problem is to genetically engineer crop plants toward increased thermotolerance. To identify entry points for genetic engineering, a thorough understanding of how plant cells perceive heat stress and respond to it is required. Using the unicellular green alga Chlamydomonas reinhardtii as a model system to study the fundamental mechanisms of the plant heat stress response has several advantages. Most prominent among them is the suitability of Chlamydomonas for studying stress responses system-wide and in a time-resolved manner under controlled conditions. Here we review current knowledge on how heat is sensed and signaled to trigger temporally and functionally grouped sub-responses termed response elements to prevent damage and to maintain cellular homeostasis in plant cells.

Fever, immunity, and molecular adaptations

The heat shock response (HSR) is an ancient and highly conserved process that is essential for coping with environmental stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms temporarily subject themselves to thermal stress in the face of infections. We review the phylogenetically conserved mechanisms that regulate fever and discuss the effects that febrile-range temperatures have on multiple biological processes involved in host defense and cell death and survival, including the HSR and its implications for patients with severe sepsis, trauma, and other acute systemic inflammatory states. Heat shock factor-1, a heat-induced transcriptional enhancer is not only the central regulator of the HSR but also regulates expression of pivotal cytokines and early response genes. Febrile-range temperatures exert additional immunomodulatory effects by activating mitogen-activated protein kinase cascades and accelerating apoptosis in some cell types. This results in accelerated pathogen clearance, but increased collateral tissue injury, thus the net effect of exposure to febrile range temperature depends in part on the site and nature of the pathologic process and the specific treatment provided.

A direct regulatory interaction between chaperonin TRiC and stress-responsive transcription factor HSF1

Heat shock transcription factor 1 (HSF1) is an evolutionarily conserved transcription factor that protects cells from protein-misfolding-induced stress and apoptosis. The mechanisms by which cytosolic protein misfolding leads to HSF1 activation have not been elucidated. Here, we demonstrate that HSF1 is directly regulated by TRiC/CCT, a central ATP-dependent chaperonin complex that folds cytosolic proteins. A small-molecule activator of HSF1, HSF1A, protects cells from stress-induced apoptosis, binds TRiC subunits in vivo and in vitro, and inhibits TRiC activity without perturbation of ATP hydrolysis. Genetic inactivation or depletion of the TRiC complex results in human HSF1 activation, and HSF1A inhibits the direct interaction between purified TRiC and HSF1 in vitro. These results demonstrate a direct regulatory interaction between the cytosolic chaperone machine and a critical transcription factor that protects cells from proteotoxicity, providing a mechanistic basis for signaling perturbations in protein folding to a stress-protective transcription factor.

Heat-inducible gene expression system by applying alternating magnetic field to magnetic nanoparticles

By combining synthetic biology with nanotechnology, we demonstrate remote controlled gene expression using a magnetic field. Magnetite nanoparticles, which generate heat under an alternating magnetic field, have been developed to label cells. Magnetite nanoparticles and heat-induced therapeutic genes were introduced into tumor xenografts. The magnetically triggered gene expression resulted in tumor growth inhibition. This system shows great potential for controlling target gene expression in a space and time selective manner and may be used for remote control of cell functions via gene expression.

Dissecting the heat stress response in Chlamydomonas by pharmaceutical and RNAi approaches reveals conserved and novel aspects

To study how conserved fundamental concepts of the heat stress response (HSR) are in photosynthetic eukaryotes, we applied pharmaceutical and antisense/amiRNA approaches to the unicellular green alga Chlamydomonas reinhardtii. The Chlamydomonas HSR appears to be triggered by the accumulation of unfolded proteins, as it was induced at ambient temperatures by feeding cells with the arginine analog canavanine. The protein kinase inhibitor staurosporine strongly retarded the HSR, demonstrating the importance of phosphorylation during activation of the HSR also in Chlamydomonas. While the removal of extracellular calcium by the application of EGTA and BAPTA inhibited the HSR in moss and higher plants, only the addition of BAPTA, but not of EGTA, retarded the HSR and impaired thermotolerance in Chlamydomonas. The addition of cycloheximide, an inhibitor of cytosolic protein synthesis, abolished the attenuation of the HSR, indicating that protein synthesis is necessary to restore proteostasis. HSP90 inhibitors induced a stress response when added at ambient conditions and retarded attenuation of the HSR at elevated temperatures. In addition, we detected a direct physical interaction between cytosolic HSP90A/HSP70A and heat shock factor 1, but surprisingly this interaction persisted after the onset of stress. Finally, the expression of antisense constructs targeting chloroplast HSP70B resulted in a delay of the cell's entire HSR, thus suggesting the existence of a retrograde stress signaling cascade that is desensitized in HSP70B-antisense strains.

Role of drug-independent stress factors in liver injury associated with diclofenac intake

Although a basic understanding of the chemical and biological events leading to idiosyncratic drug toxicity is still lacking, it appears that drug-independent risk factors that increase reactive metabolite formation or alter cellular stress and immune response may be critical determinants in the response to an otherwise non-toxic drug. Thus, we were interested to determine the impact of various drug-independent stress factors - lipopolysaccharide (LPS), poly I:C (PIC) or glutathione depletion via buthionine sulfoximine (BSO) - on the toxicity of diclofenac (Dcl), a model drug associated with rare but significant cases of serious hepatotoxicity, and to understand if enhanced toxicity occurs through alterations of drug metabolism and/or modulation of stress response pathways. Co-treatment of rats repeatedly given therapeutic doses of Dcl for 7 days with a single dose of LPS 2h before the last Dcl dose resulted in severe liver toxicity. Neither LPS nor diclofenac alone or in combination with PIC or BSO had such an effect. While it is thought that bioactivation to reactive Dcl acyl glucuronides (AG) and subsequent protein adduct formation contribute to Dcl induced liver injury, LC-MS/MS analyses did not reveal increased formation of 4'- and 5-hydroxy-Dcl, Dcl-AG or Dcl-AG dependent protein adducts in animals treated with LPS/Dcl. Hepatic gene expression analysis suggested enhanced activation of NFκB and MAPK pathways and up-regulation of co-stimulatory molecules (IL-1β, TNF-α, CINC-1) by LPS/Dcl and PIC/Dcl, while protective factors (HSPs, SOD2) were down-regulated. LPS/Dcl led to extensive release of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, TNF-α) and factors thought to constitute danger signals (HMGB1, CINC-1) into plasma. Taken together, our results show that Dcl enhanced the inflammatory response induced by LPS - and to a lesser extent by PIC - through up-regulation of pro-inflammatory molecules and down-regulation of protective factors. This suggests sensitization of cells to cellular stress mediated by non-drug-related risk factors by therapeutic doses of Dcl, rather than potentiation of Dcl toxicity by the stress factors.

Genetic selection for constitutively trimerized human HSF1 mutants identifies a role for coiled-coil motifs in DNA binding

Human heat shock transcription factor 1 (HSF1) promotes the expression of stress-responsive genes and is a critical factor for the cellular protective response to proteotoxic and other stresses. In response to stress, HSF1 undergoes a transition from a repressed cytoplasmic monomer to a homotrimer, accumulates in the nucleus, binds DNA, and activates target gene transcription. Although these steps occur as sequential and highly regulated events, our understanding of the full details of the HSF1 activation pathway remains incomplete. Here we describe a genetic screen in humanized yeast that identifies constitutively trimerized HSF1 mutants. Surprisingly, constitutively trimerized HSF1 mutants do not bind to DNA in vivo in the absence of stress and only become DNA binding competent upon stress exposure, suggesting that an additional level of regulation beyond trimerization and nuclear localization may be required for HSF1 DNA binding. Furthermore, we identified a constitutively trimerized and nuclear-localized HSF1 mutant, HSF1 L189P, located in LZ3 of the HSF1 trimerization domain, which in response to proteotoxic stress is strongly compromised for DNA binding at the Hsp70 and Hsp25 promoters but readily binds to the interleukin-6 promoter, suggesting that HSF1 DNA binding is in part regulated in a locus-dependent manner, perhaps via promoter-specific differences in chromatin architecture. Furthermore, these results implicate the LZ3 region of the HSF1 trimerization domain in a function beyond its canonical role in HSF1 trimerization.

Fever, hyperthermia and the heat shock response

The heat shock response is a highly conserved primitive response that is essential for survival against a wide range of stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms raise their core body temperature and temporarily subject themselves to thermal stress in the face of infections. The present review documents studies showing the potential overlap between the febrile response and the heat shock response and how both activate the same common transcriptional programme (although with different magnitudes) including the stress-activated transcription factor, heat shock factor-1, to modify host defences in the context of infection, inflammation and injury. The review focuses primarily on how hyperthermia within the febrile range that often accompanies infections and inflammation acts as a biological response modifier and modifies innate immune responses. The characteristic 2-3 °C increase in core body temperature during fever activates and utilises elements of the heat shock response pathway to modify cytokine and chemokine gene expression, cellular signalling and immune cell mobilisation to sites of inflammation, infection and injury. Interestingly, typical proinflammatory agonists such as Toll-like receptor agonists modify the heat shock-induced transcriptional programme and expression of HSP genes following co-exposure to febrile range hyperthermia or heat shock, suggesting a complex reciprocal regulation between the inflammatory pathway and the heat shock response pathway.

HSP-72 accelerated expression in mononuclear cells induced in vivo by acetyl salicylic acid can be reproduced in vitro when combined with H2O2

Background

Among NSAIDs acetyl salicylic acid remains as a valuable tool because of the variety of benefic prophylactic and therapeutic effects. Nevertheless, the molecular bases for these responses have not been complete understood. We explored the effect of acetyl salicylic acid on the heat shock response.

Results

Peripheral blood mononuclear cells from rats challenged with acetyl salicylic acid presented a faster kinetics of expression of HSP-72 messenger RNA and protein in response to in vitro heat shock. This effect reaches its maximum 2 h after treatment and disappeared after 5 h. On isolated peripheral blood mononuclear cells from untreated rats, incubation with acetyl salicylic acid was ineffective to produce priming, but this effect was mimicked when the cells were incubated with the combination of H₂O₂+ ASA.

Conclusions

Administration of acetyl salicylic acid to rats alters HSP-72 expression mechanism in a way that it becomes more efficient in response to in vitro heat shock. The fact that in vitro acetyl salicylic acid alone did not induce this priming effect implies that in vivo other signals are required. Priming could be reproduces in vitro with the combination of acetyl salicylic acid+H₂O₂.

Heat-inducible transgene expression with transcriptional amplification mediated by a transactivator

PURPOSE

Control of therapeutic gene expression in tumours is a major goal of gene therapy research, as it can restrict cytotoxic gene expression in cancer cells. In addition, the combination of hyperthermia with gene therapy through the application of heat-inducible vectors can result in considerable improvements in therapeutic efficiency. In this study, to combine heat-inducibility with high-level transgene expression, we developed a heat-inducible transgene expression system with transcriptional amplification mediated by a tetracycline-responsive transactivator.

MATERIALS AND METHODS

A hybrid promoter was generated by placing the heat shock protein (HSP) 70B' promoter under the tetracycline-repressor responsive element sequence, and a reporter/therapeutic gene expression plasmid was constructed by placing a reporter/therapeutic gene under the control of this hybrid promoter.

RESULTS

When the transactivator expression plasmid harbouring an expression cassette of the tetracycline-responsive transactivator gene was co-transfected with a reporter gene expression plasmid, the reporter gene expression was controlled by heat treatment. With this system, high levels of heat-induced transgene expression were observed compared to that from the HSP promoter alone without the transactivator. Evaluation of in vitro therapeutic effects using cancer cell lines revealed that therapeutic gene expression effectively caused cell death in a greater percentage of the cells.

CONCLUSION

These findings indicate that this strategy improves the efficacy of cancer gene therapy.

Dietary supplementation of Zingiber officinale and Zingiber zerumbet to heat-stressed broiler chickens and its effect on heat shock protein 70 expression, blood parameters and body temperature

The present study was conducted to assess the effects of dietary supplementation of Zingiber officinale and Zingiber zerumbet and to heat-stressed broiler chickens on heat shock protein (HSP) 70 density, plasma corticosterone concentration (CORT), heterophil to lymphocyte ratio (HLR) and body temperature. Beginning from day 28, chicks were divided into five dietary groups: (i) basal diet (control), (ii) basal diet +1%Z. zerumbet powder (ZZ1%), (iii) basal diet +2%Z. zerumbet powder (ZZ2%), (iv) basal diet +1%Z. officinale powder (ZO1%) and (v) basal diet +2%Z. officinale powder (ZO2%). From day 35-42, heat stress was induced by exposing birds to 38±1°C and 80% RH for 2 h/day. Irrespective of diet, heat challenge elevated HSP70 expression, CORT and HLR on day 42. On day 42, following heat challenge, the ZZ1% birds showed lower body temperatures than those of control, ZO1% and ZO2%. Neither CORT nor HLR was significantly affected by diet. The ZO2% and ZZ2% diets enhanced HSP70 expression when compared to the control groups. We concluded that dietary supplementation of Z. officinale and Z. zerumbet powder may induce HSP70 reaction in broiler chickens exposed to heat stress.