Feedback regulation of the heat shock response

Boric acid and Borax Supplementation Reduces Weight Gain in Overweight Rats and Alter L-Carnitine and IGF-I Levels

Abstract. The aim of this study was to investigate the effects of boric acid (BA) and borax (BX) on live weight and obesity associated molecules including leptin, L-carnitine, insulin-like growth factor 1 (IGF-I), and heat shock proteins 70 (HSP70) in rats fed with high-fat diet. A total of 60 rats were equally allocated as ND (normal diet), HF (high-fat diet), HF+BA, HF+BX, ND+BX, ND+BA. Body weight increases in HF+BA (85 g) and HF+BX (86 g) were significantly lower (p<0.05) compared to HF group (126 g). Boron treatment decreased serum L-carnitine level in high-fat diet (HF+BA 11.12 mg/L, HF+BX 10.51 mg/L, p<0.05) compared to HF group (15.57 mg/L), while no change was observed in groups ND+BA (7.55 mg/L) and ND+BX (7.57 mg/L) compared to group ND (8.29 mg/L). Neither BA nor BX supplementation in ND and HF groups altered the serum levels of HSP70 and leptin. BA and BX supplementation in rats fed HF resulted in a significant reduction in live weight. Boron compounds altered L-carnitine and IGF-1 levels in rats. These results indicate that boron compounds are beneficial in the treatment of obesity as well as in the prevention of high-fat diet-induced weight increase. Alterations in serum L-carnitine and IGF-1 levels in boron treated rats also indicate possible role of boron compounds in energy metabolism in response to high fat diet.

GLP-1 Analogue, Exendin-4, Modulates MAPKs Activity but not the Heat Shock Response in Human HepG2 Cells

PURPOSE

Glucagon-like peptide-1 (GLP-1) analogues reduce ER stress and inflammation in key metabolic organs, including the liver. However, their effects on heat shock response (HSR) and mitogen-activated protein kinases (MAPKs) have not yet been elucidated. In the present study, we investigate whether the GLP-1 analogue, exendin-4, triggers the expression of HSR and increases MAPK activity under metabolic stress.

EXPERIMENTAL DESIGN

The effects of exendin-4 in the presence or absence of palmitic acid (PA; 400 μm) or glucose (30 mm) in the HepG2 liver cell line are assessed using Western blots, quantitative real-time PCR, and label-free proteomics.

RESULTS

Heat shock proteins (HSP60, HSP72, HSP90, and GRP78) and other chaperones are not significantly affected by exendin-4 under the conditions tested. In contrast, the presence of exendin-4 alone increases the MAPK phosphorylation levels (JNK, ERK1/2, and p38). For short incubation periods, in the presence of PA or glucose, treatment with exendin-4 exhibits limited effects but significantly attenuates MAPK phosphorylation after a 24-h incubation. Interestingly, canonical signaling pathways, such as EIF2, ILK, PKA, and Rho, are modulated by exendin-4.

CONCLUSION AND CLINICAL RELEVANCE

Identifying new pathways modulated by GLP-1 analogues will provide further insights into their benefits beyond their currently recognized roles in glycemic control, such as MAPK activity, energy homeostasis, and body weight decrease.

A Novel Class of Hsp90 C-Terminal Modulators Have Pre-Clinical Efficacy in Prostate Tumor Cells Without Induction of a Heat Shock Response

BACKGROUND

While there is compelling rationale to use heat shock protein 90 (Hsp90) inhibitors for treatment of advanced prostate cancer, agents that target the N-terminal ATP-binding site of Hsp90 have shown little clinical benefit. These N-terminal binding agents induce a heat shock response that activates compensatory heat shock proteins, which is believed to contribute in part to the agents' lack of efficacy. Here, we describe the functional characterization of two novel agents, SM253 and SM258, that bind the N-middle linker region of Hsp90, resulting in reduced client protein activation and preventing C-terminal co-chaperones and client proteins from binding to Hsp90.

METHODS

Inhibition of Hsp90 activity in prostate cancer cells by SM253 and SM 258 was assessed by pull-down assays. Cell viability, proliferation and apoptosis were assayed in prostate cancer cell lines (LNCaP, 22Rv1, PC-3) cultured with N-terminal Hsp90 inhibitors (AUY922, 17-AAG), SM253 or SM258. Expression of HSR heat shock proteins, Hsp90 client proteins and co-chaperones was assessed by immunoblotting. Efficacy of the SM compounds was evaluated in human primary prostate tumors cultured ex vivo by immunohistochemical detection of Hsp70 and Ki67.

RESULTS

SM253 and SM258 exhibit antiproliferative and pro-apoptotic activity in multiple prostate cancer cell lines (LNCaP, 22Rv1, and PC-3) at low micromolar concentrations. Unlike the N-terminal inhibitors AUY922 and 17-AAG, these SM agents do not induce expression of Hsp27, Hsp40, or Hsp70, proteins that are characteristic of the heat shock response, in any of the prostate cell lines analyzed. Notably, SM258 significantly reduced proliferation within 2 days in human primary prostate tumors cultured ex vivo, without the significant induction of Hsp70 that was caused by AUY922 in the tissues.

CONCLUSIONS

Our findings provide the first evidence of efficacy of this class of C-terminal modulators of Hsp90 in human prostate tumors, and indicate that further evaluation of these promising new agents is warranted. Prostate 76:1546-1559, 2016. © 2016 Wiley Periodicals, Inc.

Alterations in gene expression levels provide early indicators of chemical stress during Xenopus laevis embryo development: A case study with perfluorooctane sulfonate (PFOS)

In the present study, Xenopus laevis embryos were exposed to a range of perfluorooctane sulfonate (PFOS) concentrations (0, 0.5, 6, 12, 24, 48 and 96mg/L) for 96h in laboratorial conditions to establish toxicity along with possible gene expression changes. Mortality and deformities were monitored daily and head-tail length was measured at the end of the assay as an indicator of growth. At 24 and 96h post-exposure (hpe), the mRNA expression levels of the genetic markers involved in general stress responses (hsp70, hsp47, crh-a and ucn1), oxidative stress (cat.2 and sod), lipid metabolism (ppard) and apoptosis (tp53 and bax) were analyzed by RT-qPCR. Malformations were significantly higher in the embryos exposed to the highest PFOS concentration (41.8% to 56.4%) compared to controls (5.5%) at 48, 72 and 96hpe. Growth inhibition was observed in the embryos exposed to PFOS concentrations≥48mg/L. At 24 hpe, a statistically significant up-regulation of genes hsp70, hsp47, ppard, tp53 and bax in relation to controls was found. Similar responses were found for genes hsp70, hsp47, crh-a, ucn1, sod and ppard at 96 hpe. Alterations in the mRNA expression levels indicated both a stress response to PFOS exposure during X. laevis embryo development, and alterations in the regulation of oxidative stress, apoptosis, and differentiation. These molecular alterations were detected at an earlier exposure time or at lower concentrations than those producing developmental toxicity. Therefore, these sensitive warning signals could be used together with other biomarkers to supplement alternative methods (i.e. the frog embryo test) for developmental toxicity safety evaluations, and as tools in amphibian risk assessments for PFOS and its potential substitutes.

Immunohistochemical profiling of the heat shock response in obese non-diabetic subjects revealed impaired expression of heat shock proteins in the adipose tissue

BACKGROUND

Obesity is characterized by a chronic low-grade inflammation and altered stress responses in key metabolic tissues. Impairment of heat shock response (HSR) has been already linked to diabetes and insulin resistance as reflected by decrease in heat shock proteins (HSPs) expression. However, the status of HSR in non-diabetic human obese has not yet been elucidated. The aim of the current study was to investigate whether obesity triggers a change in the HSR pattern and the impact of physical exercise on this pattern at protein and mRNA levels.

METHODS

Two groups of adult non-diabetic human subjects consisting of lean and obese (n = 47 for each group) were enrolled in this study. The expression pattern of HSP-27, DNAJB3/HSP-40, HSP-60, HSC-70, HSP72, HSP-90 and GRP-94 in the adipose tissue was primarily investigated by immunohistochemistry and then complemented by western blot and qRT-PCR in Peripheral blood mononuclear cells (PBMCs). HSPs expression levels were correlated with various physical, clinical and biochemical parameters. We have also explored the effect of a 3-month moderate physical exercise on the HSPs expression pattern in obese subjects.

RESULTS

Obese subjects displayed increased expression of HSP-60, HSC-70, HSP-72, HSP-90 and GRP-94 and lower expression of DNAJB3/HSP-40 (P < 0.05). No differential expression was observed for HSP-27 between the two groups. Higher levels of HSP-72 and GRP-94 proteins correlated positively with the indices of obesity (body mass index and percent body fat) and circulating levels of IFN-gamma-inducible protein 10 (IP-10) and RANTES chemokines. This expression pattern was concomitant with increased inflammatory response in the adipose tissue as monitored by increased levels of Interleukin-6 (IL-6), Tumor necrosis factor-α (TNF-α), and RANTES (P < 0.05). Physical exercise reduced the expression of various HSPs in obese to normal levels observed in lean subjects with a parallel decrease in the endogenous levels of IL-6, TNF-α, and RANTES.

CONCLUSION

Taken together, these data indicate that obesity triggers differential regulation of various components of the HSR in non-diabetic subjects and a 3-month physical moderate exercise was sufficient to restore the normal expression of HSPs in the adipose tissue with concomitant attenuation in the inflammatory response.

Dual-reporter in vivo imaging of transient and inducible heat-shock promoter activation

Gene promoter activity can be studied in vivo by molecular imaging methods using reporter gene technology. Transcription of the reporter and the reported genes occurs simultaneously. However, imaging depends on reporter protein translation, stability, and cellular fate that may differ among the various proteins. A double transgenic mouse strain expressing the firefly luciferase (lucF) and fluorescent mPlum protein under the transcriptional control of the thermo-inducible heat-shock protein (Hspa1b) promoter was generated allowing to follow up the reporter proteins by different and complementary in vivo imaging technologies. These mice were used for in vivo imaging by bioluminescence and epi fluorescence reflectance imaging (BLI & FRI) and as a source of embryonic fibroblast (MEF) for in vitro approaches. LucF, mPlum and endogenous Hsp70 mRNAs were transcribed simultaneously. The increase in mRNA was transient, peaking at 3 h and then returning to the basal level about 6 h after the thermal stimulations. The bioluminescent signal was transient and initiated with a 3 h delay versus mRNA expression. The onset of mPlum fluorescence was more delayed, increasing slowly up to 30 h after heat-shock and remaining for several days. This mouse allows for both bioluminescence imaging (BLI) and fluorescence reflectance imaging (FRI) of Hsp70 promoter activation showing an early and transient lucF activity and a retrospective and persistent mPlum fluorescence. This transgenic mouse will allow following the transient local induction of Hsp-70 promoter beyond its induction time-frame and relate into subsequent dynamic biological effects of the heat-shock response.

DNAJB3/HSP-40 cochaperone is downregulated in obese humans and is restored by physical exercise

Obesity is a major risk factor for a myriad of disorders such as insulin resistance and diabetes. The mechanisms underlying these chronic conditions are complex but low grade inflammation and alteration of the endogenous stress defense system are well established. Previous studies indicated that impairment of HSP-25 and HSP-72 was linked to obesity, insulin resistance and diabetes in humans and animals while their induction was associated with improved clinical outcomes. In an attempt to identify additional components of the heat shock response that may be dysregulated by obesity, we used the RT²-Profiler PCR heat shock array, complemented with RT-PCR and validated by Western blot and immunohistochemistry. Using adipose tissue biopsies and PBMC of non-diabetic lean and obese subjects, we report the downregulation of DNAJB3 cochaperone mRNA and protein in obese that negatively correlated with percent body fat (P = 0.0001), triglycerides (P = 0.035) and the inflammatory chemokines IP-10 and RANTES (P = 0.036 and P = 0.02, respectively). DNAJB positively correlated with maximum oxygen consumption (P = 0.031). Based on the beneficial effect of physical exercise, we investigated its possible impact on DNAJB3 expression and indeed, we found that exercise restored the expression of DNAJB3 in obese subjects with a concomitant decrease of phosphorylated JNK. Using cell lines, DNAJB3 protein was reduced following treatment with palmitate and tunicamycin which is suggestive of the link between the expression of DNAJB3 and the activation of the endoplasmic reticulum stress. DNAJB3 was also shown to coimmunoprecipiate with JNK and IKKβ stress kinases along with HSP-72 and thus, suggesting its potential role in modulating their activities. Taken together, these data suggest that DNAJB3 can potentially play a protective role against obesity.

Molecular chaperones as therapeutic targets to counteract proteostasis defects

The health of cells is preserved by the levels and correct folding states of the proteome, which is generated and maintained by the proteostasis network, an integrated biological system consisting of several cytoprotective and degradative pathways. Indeed, the health conditions of the proteostasis network is a fundamental prerequisite to life as the inability to cope with the mismanagement of protein folding arising from genetic, epigenetic, and micro-environment stress appears to trigger a whole spectrum of unrelated diseases. Here we describe the potential functional role of the proteostasis network in tumor biology and in conformational diseases debating on how the signaling branches of this biological system may be manipulated to develop more efficacious and selective therapeutic strategies. We discuss the dual strategy of these processes in modulating the folding activity of molecular chaperones in order to counteract the antithetic proteostasis deficiencies occurring in cancer and loss/gain of function diseases. Finally, we provide perspectives on how to improve the outcome of these disorders by taking advantage of proteostasis modeling.

Heat treatment increases the incidence of alopecia areata in the C3H/HeJ mouse model

Alopecia areata (AA) is a common autoimmune disease characterized by non-scarring hair loss. Previous studies have demonstrated an association between AA and physiological/psychological stress. In this study, we investigated the effects of heat treatment, a physiological stress, on AA development in C3H/HeJ mice. Whereas this strain of mice are predisposed to AA at low incidence by 18 months of age, we observed a significant increase in the incidence of hair loss in heat-treated 8-month-old C3H/HeJ mice compared with sham-treated mice. Histological analysis detected mononuclear cell infiltration in anagen hair follicles, a characteristic of AA, in heat-treated mouse skin. As expected, increased expression of induced HSPA1A/B (formerly called HSP70i) was detected in skin samples from heat-treated mice. Importantly, increased HSPA1A/B expression was also detected in skin samples from C3H/HeJ mice that developed AA spontaneously. Our results suggest that induction of HSPA1A/B may precipitate the development of AA in C3H/HeJ mice. For future studies, the C3H/HeJ mice with heat treatment may prove a useful model to investigate stress response in AA.

Heat-shock protein vaccines as active immunotherapy against human gliomas

Modern advances in cancer immunotherapy have led to the development of active immunotherapy that utilizes tumor-associated antigens to induce a specific immune response against the tumor. Current methods of immunotherapy implementation are based on the principle that tumor-associated antigens are capable of being processed by antigen-presenting cells and inducing an activated cytotoxic T-lymphocyte-specific immune response that targets the tumor cells. Antigen internalization and processing by antigen-presenting cells, such as dendritic cells, or macrophages results in their surface association with MHC class I molecules, which can be recognized by an antigen-specific cytotoxic T-lymphocyte adaptive immune response. With the aim of augmenting current immunotherapeutic modalities, much effort has been directed towards enhancing antigen-presenting cell activation and optimizing the processing of tumor-associated antigens and major histocompatibility molecules. The goal of these immunotherapy modifications is to ultimately improve the adaptive specific immune response in killing of tumor cells while sparing normal tissues. Immunotherapy has been actively studied and applied in glioblastomas. Preclinical animal models have shown the feasibility of an active immunotherapy approach through the utilization of tumor vaccines, and recently several clinical studies have also been initiated. Recently, endogenous heat-shock proteins have been implicated in the mediation of both the adaptive and innate immune responses. They are now being investigated as a potential modality and adjuvant to immunotherapy, and they represent a promising novel treatment for human glioblastomas.

Molecular characterization and expression analysis of a heat shock protein 90 gene from disk abalone (Haliotis discus)

Heat shock protein 90s (hsp90s) are chaperones that contribute to the proper folding of cellular proteins and help animals cope with the cellular protein damages in stress conditions. In this study, an hsp90 gene was isolated from disc abalone (Haliotis discus). The complete nucleotide sequence of the hsp90 gene contains an open reading frame of 2,184 base pairs, encoding an 84 kDa protein. Disk abalone hsp90 shares high sequence similarity with other hsp90 family proteins. Although the phylogenetic analysis did not classify it into the hsp90α group, the inductivity of this gene was confirmed by heat shock and lipopolysaccharide (LPS) challenge test. Disk abalone hsp90 gene displayed a rapid and reversible induction response to both an exposure of typical heat shock and the LPS challenge. Once given the sublethal heat shock treatment, the transcription of disk abalone hsp90 gene was significantly up-regulated. With a recovery of 12 h, the transcription of disk abalone hsp90 gene gradually attenuated to the control level. These observations reflected the feedback regulation of abalone heat shock responses faithfully. In response to LPS challenge, the transcription of disk abalone hsp90 gene was significantly increased within 2 h and it approached maximum induction at 4 h later and recovered finally the reference level in 24 h. Take all together, the cloning and expression analysis of disk abalone hsp90 gene provided useful molecular information of abalone responses in stress conditions and potential ways to monitor the chronic stressors in abalone culture environments and diagnose the animal health status.

Heat shock proteins in glioblastomas

Glioblastoma multiforme is the most common primary central nervous system tumor. The prognosis for these malignant brain tumors is poor, with a median survival of 14 months and a 5-year survival rate below 2%. Development of novel treatments is essential to improving survival and quality of life for these patients. Endogenous heat shock proteins have been implicated in mediation of both adaptive and innate immunity, and there is a rising interest in the use of this safe and multifaceted heat shock protein vaccine therapy as a promising treatment for human cancers, including glioblastoma multiforme.

Ubiquitin-mediated proteolysis of HuR by heat shock

The RNA-binding protein HuR regulates the stability and translation of numerous mRNAs encoding stress-response and proliferative proteins. Although its post-transcriptional influence has been linked primarily to its cytoplasmic translocation, here we report that moderate heat shock (HS) potently reduces HuR levels, thereby altering the expression of HuR target mRNAs. HS did not change HuR mRNA levels or de novo translation, but instead reduced HuR protein stability. Supporting the involvement of the ubiquitin-proteasome system in this process were results showing that (1) HuR was ubiquitinated in vitro and in intact cells, (2) proteasome inhibition increased HuR abundance after HS, and (3) the HuR kinase checkpoint kinase 2 protected against the loss of HuR by HS. Within a central, HS-labile approximately 110-amino-acid region, K182 was found to be essential for HuR ubiquitination and proteolysis as mutant HuR(K182R) was left virtually unubiquitinated and was refractory to HS-triggered degradation. Our findings reveal that HS transiently lowers HuR by proteolysis linked to K182 ubiquitination and that HuR reduction enhances cell survival following HS.

HTS-compatible beta-lactamase transcriptional reporter gene assay for interrogating the heat shock response pathway

Moderate environmental and physiological stressors are known to initiate protective heat shock response (HSR) leading to cell survival. HSR is largely mediated by the activation of heat shock factor (HSF), resulting in increased heat shock protein expression. Dysregulation of the HSR signaling has been associated with various diseases including cancer, inflammation and neurodegenerative disorders. Compounds that can modulate HSR have been pursued for the treatment of these diseases. To facilitate the discovery of HSR modulators, we developed a high-throughput amenable betalactamase transcriptional reporter gene assay for monitoring the function of HSF. HeLa cells were engineered to express the beta-lactamase reporter under the control of HSF response elements (HSE) present in the HSP70 gene promoter. The HSE-beta lactamase (HSE-bla) reporter gene assay was validated by using HSF-specific siRNAs and known small molecule modulators. Taking the advantage of fluorescence resonance energy transfer (FRET)-based cell permeable betalactamase substrate, this assay can be miniaturized into 1536-well format. Our results demonstrate that the assay is robust and can be applied to high-throughput screening (HTS) for modulators of HSR.

"Toxic memory" via chaperone modification is a potential mechanism for rapid Mallory-Denk body reinduction

The cytoplasmic hepatocyte inclusions, Mallory-Denk bodies (MDBs), are characteristic of several liver disorders, including alcoholic and nonalcoholic steatohepatitis. In mice, MDBs can be induced by long-term feeding with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) for 3 to 4 months or rapidly reformed in DDC-induced then recovered mice by DDC refeeding or exposure to a wide range of toxins for only 5 to 7 days. The molecular basis for such a rapid reinduction of MDBs is unknown. We hypothesized that protein changes retained after DDC priming contribute to the rapid MDB reappearance and associate with MDB formation in general terms. Two-dimensional differential-in-gel-electrophoresis coupled with mass spectrometry were used to characterize protein changes in livers from the various treatment groups. The alterations were assessed by real-time reverse-transcription polymerase chain reaction and confirmed by immunoblotting. DDC treatment led to pronounced charged isoform changes in several chaperone families, including Hsp25, 60, 70, GRP58, GRP75, and GRP78, which lasted at least for 1 month after discontinuation of DDC feeding, whereas changes in other proteins normalized during recovery. DDC feeding also resulted in altered expression of Hsp72, GRP75, and Hsp25 and in functional impairment of Hsp60 and Hsp70 as determined using a protein complex formation and release assay. The priming toward rapid MDB reinduction lasts for at least 3 months after DDC discontinuation, but becomes weaker after prolonged recovery. MDB reinduction parallels the rapid increase in p62 and Hsp25 levels as well as keratin 8 cross-linking that is normally associated with MDB formation.

CONCLUSION

Persistent posttranslational modifications in chaperone proteins, coupled with protein cross-linking and altered chaperone expression and function likely contribute to the "toxic memory" of DDC-primed mice. We hypothesize that similar changes are important contributors to inclusion body formation in several diseases.

Differential display of DNA-binding proteins reveals heat-shock factor 1 as a circadian transcription factor

The circadian clock enables the anticipation of daily recurring environmental changes by presetting an organism's physiology and behavior. Driven and synchronized by a central pacemaker in the brain, circadian output genes fine-tune a wide variety of physiological parameters in peripheral organs. However, only a subset of circadianly transcribed genes seems to be directly regulated by core clock proteins. Assuming that yet unidentified transcription factors may exist in the circadian transcriptional network, we set out to develop a novel technique, differential display of DNA-binding proteins (DDDP), which we used to screen mouse liver nuclear extracts. In addition to several established circadian transcription factors, we found DNA binding of heat-shock factor 1 (HSF1) to be highly rhythmic. HSF1 drives the expression of heat-shock proteins at the onset of the dark phase, when the animals start to be behaviorally active. Furthermore, Hsf1-deficient mice have a longer free-running period than wild-type littermates, suggesting a combined role for HSF1 in the mammalian timekeeping and cytoprotection systems. Our results also suggest that the new screening method DDDP is not limited to the identification of circadian transcription factors but can be applied to discover novel transcriptional regulators in various biological systems.

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.

Inhibitors of the heat shock response: biology and pharmacology

A number of human diseases can be linked to aberrations in protein folding which cause an imbalance in protein homeostasis. Molecular chaperones, including heat shock proteins, act to assist protein folding, stability and activity in the cell. Attention has begun to focus on modulating the expression and/or activity of this group of proteins for the treatment of a wide variety of human diseases. This review will describe the progress made to date in developing pharmacological modulators of the heat shock response, including both agents which affect the entire heat shock response and those that specifically target the HSP70 and HSP90 chaperone families.

Crystal structure of the archaeal heat shock regulator from Pyrococcus furiosus: a molecular chimera representing eukaryal and bacterial features

We report here the crystal structure of a protein from Pyrococcus furiosus (Phr) that represents the first characterized heat shock transcription factor in archaea. Phr specifically represses the expression of heat shock genes at physiological temperature in vitro and in vivo but is released from the promoters upon heat shock response. Structure analysis revealed a stable homodimer, each subunit consisting of an N-terminal winged helix DNA-binding domain (wH-DBD) and a C-terminal antiparallel coiled coil helical domain. The overall structure shows as a molecular chimera with significant folding similarity of its DBD to the bacterial SmtB/ArsR family, while its C-terminal part was found to be a remote homologue of the eukaryotic BAG domain. The dimeric protein recognizes a palindromic DNA sequence. Molecular docking and mutational analyses suggested a novel binding mode in which the major specific contacts occur at the minor groove interacting with the strongly basic wing containing a cluster of three arginine residues.