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

Heat shock and caloric restriction have a synergistic effect on the heat shock response in a sir2.1-dependent manner in Caenorhabditis elegans

The heat shock response (HSR) is responsible for maintaining cellular and organismal health through the regulation of proteostasis. Recent data demonstrating that the mammalian HSR is regulated by SIRT1 suggest that this response may be under metabolic control. To test this hypothesis, we have determined the effect of caloric restriction in Caenorhabditis elegans on activation of the HSR and have found a synergistic effect on the induction of hsp70 gene expression. The homolog of mammalian SIRT1 in C. elegans is Sir2.1. Using a mutated C. elegans strain with a sir2.1 deletion, we show that heat shock and caloric restriction cooperate to promote increased survivability and fitness in a sir2.1-dependent manner. Finally, we show that caloric restriction increases the ability of heat shock to preserve movement in a polyglutamine toxicity neurodegenerative disease model and that this effect is dependent on sir2.1.

Heat shock protein 25-enriched plasma transfusion preconditions the heart against doxorubicin-induced dilated cardiomyopathy in mice

Extracellular heat shock proteins (eHsps) in the circulation have recently been found to activate both apoptotic and protective signaling in the heart. However, the role of eHsps in doxorubicin (Dox)-induced heart failure has not yet been studied. The objective of the present study was to determine how Dox affects circulating eHsp25 in blood plasma and how eHsp25 affects Dox-induced dilated cardiomyopathy. Wild-type mice [HSF-1(+/+)] were pretreated with 100 μl of heterozygous heat shock factor-1 [HSF-1(+/-)] mouse plasma (which contained 4-fold higher eHsp25 compared with wild-type mice), HSF-1(+/+) plasma, or saline, before treatment with Dox (6 mg/kg). After 4 weeks of this treatment protocol, HSF-1(+/-) plasma-pretreated mice showed increased eHsp25 in plasma and improved cardiac function (percentage of fractional shortening 37.3 ± 2.1 versus 26.4 ± 4.0) and better life span (31 ± 2 versus 22 ± 3 days) compared with the HSF-1(+/+) plasma or saline-pretreated mice. Preincubation of isolated adult cardiomyocytes with HSF-1(+/-) plasma or recombinant human Hsp27 (rhHsp27) significantly reduced Dox-induced activation of nuclear factor-κB and cytokine release and delayed cardiomyocyte death. Moreover, when cardiomyocytes were incubated with fluorescence-tagged rhHsp27, a saturation in binding was observed, suggesting that eHsp25 can bind to surface receptors. Competitive assays with a Toll-like receptor 2 (TLR2) antibody reduced the rhHSP27 binding, indicating that Hsp25 interacts with TLR2. In conclusion, transfusion of Hsp25-enriched blood plasma protected the heart from Dox-induced cardiotoxicity. Hsp25 antagonized Dox binding to the TLR2 receptor on cardiomyocytes.

Temporal requirements of heat shock factor-1 for longevity assurance

Reducing the activity of the insulin/IGF-1 signaling pathway (IIS) modifies development, elevates stress resistance, protects from toxic protein aggregation (proteotoxicity), and extends lifespan (LS) of worms, flies, and mice. In the nematode Caenorhabditis elegans, LS extension by IIS reduction is entirely dependent upon the activity of the transcription factors DAF-16 and the heat shock factor-1 (HSF-1). While DAF-16 determines LS exclusively during early adulthood, it is required for proteotoxicity protection also during late adulthood. In contrast, HSF-1 protects from proteotoxicity during larval development. Despite the critical requirement for HSF-1 for LS extension, the temporal requirements for this transcription factor as a LS determinant are unknown. To establish the temporal requirements of HSF-1 for longevity assurance, we conditionally knocked down hsf-1 during larval development and adulthood of C. elegans and found that unlike daf-16, hsf-1 is foremost required for LS determination during early larval development, required for a lesser extent during early adulthood and has small effect on longevity also during late adulthood. Our findings indicate that early developmental events affect LS and suggest that HSF-1 sets during development of the conditions that enable DAF-16 to promote longevity during reproductive adulthood. This study proposes a novel link between HSF-1 and the longevity functions of the IIS.

Celastrol analogues as inducers of the heat shock response. Design and synthesis of affinity probes for the identification of protein targets

The natural product celastrol (1) possesses numerous beneficial therapeutic properties and affects numerous cellular pathways. The mechanism of action and cellular target(s) of celastrol, however, remain unresolved. While a number of studies have proposed that the activity of celastrol is mediated through reaction with cysteine residues, these observations have been based on studies with specific proteins or by in vitro analysis of a small fraction of the proteome. In this study, we have investigated the spatial and structural requirements of celastrol for the design of suitable affinity probes to identify cellular binding partners of celastrol. Although celastrol has several potential sites for modification, some of these were not synthetically amenable or yielded unstable analogues. Conversion of the carboxylic acid functionality to amides and long-chain analogues, however, yielded bioactive compounds that induced the heat shock response (HSR) and antioxidant response and inhibited Hsp90 activity. This led to the synthesis of biotinylated celastrols (23 and 24) that were used as affinity reagents in extracts of human Panc-1 cells to identify Annexin II, eEF1A, and β-tubulin as potential targets of celastrol.

HSF-1 regulators DDL-1/2 link insulin-like signaling to heat-shock responses and modulation of longevity

Extended longevity is often correlated with increased resistance against various stressors. Insulin/IGF-1-like signaling (IIS) is known to have a conserved role in aging and cellular mechanisms against stress. In C. elegans, genetic studies suggest that heat-shock transcription factor HSF-1 is required for IIS to modulate longevity. Here, we report that the activity of HSF-1 is regulated by IIS. This regulation occurs at an early step of HSF-1 activation via two HSF-1 regulators, DDL-1 and DDL-2. Inhibition of DDL-1/2 increases longevity and thermotolerance in an hsf-1-dependent manner. Furthermore, biochemical analyses suggest that DDL-1/2 negatively regulate HSF-1 activity by forming a protein complex with HSF-1. The formation of this complex (DHIC) is affected by the phosphorylation status of DDL-1. Both the formation of DHIC and the phosphorylation of DDL-1 are controlled by IIS. Our findings point to DDL-1/2 as a link between IIS and the HSF-1 pathway.

Regulation of survival gene hsp70

Rapid expression of the survival gene, inducible heat shock protein 70 (hsp70), is critical for mounting cytoprotection against severe cellular stress, like elevated temperature. Hsp70 protein chaperones the refolding of heat-denatured peptides to minimize proteolytic degradation as a part of an eukaryotically conserved phenomenon referred to as the heat shock response. The physiologic stress associated with exercise, which can include elevated temperature, mechanical damage, hypoxia, lowered pH, and reactive oxygen species generation, may promote protein unfolding, leading to hsp70 gene expression in skeletal myofibers. Although the pre-transcriptional activation of hsp70 gene expression has been thoroughly reviewed, discussion of downstream hsp70 gene regulation is less extensive. The purpose of this brief review was to examine all levels of hsp70 gene regulation in response to heat stress and exercise with a special focus on skeletal myofibers where data are available. In general, while heat stress represses bulk gene expression, hsp70 mRNA expression is enhanced. Post-transcriptionally, intronless hsp70 mRNA circumvents a host of decay pathways, as well as heat stress-repressed pre-mRNA splicing and nuclear export. Pre-translationally, hsp70 mRNA is excluded from stress granules and preferentially translated during heat stress-repressed global cap-dependent translation. Post-translationally, nascent Hsp70 protein is thermodynamically stable at elevated temperatures, allowing for the commencement of chaperoning activity early after synthesis to attenuate the heat shock response and protect against subsequent injury. This review demonstrates that hsp70 mRNA expression is closely coupled with functional protein translation.

Proteomic signatures of human oral epithelial cells in HIV-infected subjects

The oral epithelium, the most abundant structural tissue lining the oral mucosa, is an important line of defense against infectious microorganisms. HIV infected subjects on highly active antiretroviral therapy (HAART) are susceptible to comorbid viral, bacterial and fungal infections in the oral cavity. To provide an assessment of the molecular alterations of oral epithelia potentially associated with susceptibility to comorbid infections in such subjects, we performed various proteomic studies on over twenty HIV infected and healthy subjects. In a discovery phase two Dimensional Difference Gel Electrophoresis (2-D DIGE) analyses of human oral gingival epithelial cell (HOEC) lysates were carried out; this identified 61 differentially expressed proteins between HIV-infected on HAART subjects and healthy controls. Down regulated proteins in HIV-infected subjects include proteins associated with maintenance of protein folding and pro- and anti-inflammatory responses (e.g., heat-shock proteins, Cryab, Calr, IL-1RA, and Galectin-3-binding protein) as well as proteins involved in redox homeostasis and detoxification (e.g., Gstp1, Prdx1, and Ero1). Up regulated proteins include: protein disulfide isomerases, proteins whose expression is negatively regulated by Hsp90 (e.g., Ndrg1), and proteins that maintain cellular integrity (e.g., Vimentin). In a verification phase, proteins identified in the protein profiling experiments and those inferred from Ingenuity Pathway Analysis were analyzed using Western blotting analysis on separate HOEC lysate samples, confirming many of the discovery findings. Additionally in HIV-infected patient samples Heat Shock Factor 1 is down regulated, which explains the reduced heat shock responses, while activation of the MAPK signal transduction cascade is observed. Overall, HAART therapy provides an incomplete immune recovery of the oral epithelial cells of the oral cavity for HIV-infected subjects, and the toxic side effects of HAART and/or HIV chronicity silence expression of multiple proteins that in healthy subjects function to provide robust innate immune responses and combat cellular stress.

Inducible hsp70 in the regulation of cancer cell survival: analysis of chaperone induction, expression and activity

Understanding the mechanisms that control stress is central to realize how cells respond to environmental and physiological insults. All the more important is to reveal how tumour cells withstand their harsher growth conditions and cope with drug-induced apoptosis, since resistance to chemotherapy is the foremost complication when curing cancer. Intensive research on tumour biology over the past number of years has provided significant insights into the molecular events that occur during oncogenesis, and resistance to anti-cancer drugs has been shown to often rely on stress response and expression of inducible heat shock proteins (HSPs). However, with respect to the mechanisms guarding cancer cells against proteotoxic stresses and the modulatory effects that allow their survival, much remains to be defined. Heat shock proteins are molecules responsible for folding newly synthesized polypeptides under physiological conditions and misfolded proteins under stress, but their role in maintaining the transformed phenotype often goes beyond their conventional chaperone activity. Expression of inducible HSPs is known to correlate with limited sensitivity to apoptosis induced by diverse cytotoxic agents and dismal prognosis of several tumour types, however whether cancer cells survive because of the constitutive expression of heat shock proteins or the ability to induce them when adapting to the hostile microenvironment remains to be elucidated. Clear is that tumours appear nowadays more "addicted" to heat shock proteins than previously envisaged, and targeting HSPs represents a powerful approach and a future challenge for sensitizing tumours to therapy. This review will focus on the anti-apoptotic role of heat shock 70kDa protein (Hsp70), and how regulatory factors that control inducible Hsp70 synthesis, expression and activity may be relevant for response to stress and survival of cancer cells.

Transthiocarbamoylation of proteins by thiolated isothiocyanates

Isothiocyanates, membrane-permeable electrophiles that form adducts with thiols, have been suggested to have important medical benefits. Here we shed light on isothiocyanate-thiol conjugates and studied their electrophilic potential transferring an isothiocyanate moiety to cellular proteins. When we examined the effect of sulfhydryl molecules on cellular response induced by 6-methylsulfinylhexyl isothiocyanate (6-HITC), an analog of sulforaphane isolated from broccoli, we observed significant induction of heme oxygenase-1 by 6-HITC even in the presence of N-acetyl-L-cysteine or glutathione (GSH). In addition, the authentic 6-HITC-β-mercaptoethanol (6-HITC-ME) conjugate markedly up-regulated the enzyme expression, suggesting the electrophilic potential of thiolated isothiocyanates. To gain a chemical insight into the cellular response induced by thiolated isothiocyanates, we studied the occurrence of transthiocarbamoylation of sulfhydryl molecules by 6-HITC-ME and observed that, upon incubation of 6-HITC-ME with GSH, a single product corresponding to the GSH conjugate of 6-HITC was generated. To test the functional ability of thiolated isothiocyanates to thiocarbamoylate proteins in living cells, we designed a novel probe, combining an isothiocyanate-reactive group and an alkyne functionality, and revealed that the transthiocarbamoylation of proteins occurred in the cells upon exposure to 6-HITC-ME. The target of thiocarbamoylation included heat shock protein 90 β (Hsp90β), a chaperone ATPase of the Hsp90 family implicated in protein maturation and targeting. To identify the sites of the Hsp90β modification, we utilized nano-LC/MALDI-TOF MS/MS and suggested that a thiol group on the peptide containing Cys-521 reacted with 6-HITC, resulting in a covalent adduct in a 6-HITC-treated recombinant Hsp90β in vitro. The site-selective binding to Cys-521 was supported by in silico modeling. Further study on the thiocarbamoylation of Hsp90β suggested that the formation of 6-HITC-Hsp90β conjugate might cause activation of heat shock factor-1, rapidly signaling a potential heat shock response. These data suggest that thiolated isothiocyanates are an active metabolite that could contribute to cellular responses through transthiocarbamoylation of cellular proteins.

Lipid peroxidation, antioxidant activities and stress protein (HSP72/73, GRP94) expression in kidney and liver of rats under lithium treatment

The present work was aimed at studying the effects of a subchronic lithium treatment on rat liver and kidneys, paying attention to the relationship between lithium toxicity, oxidative stress, and stress protein expression. Male rats were submitted to lithium treatment by adding 2 g of lithium carbonate/kg of food for different durations up to 1 month. This treatment led to serum concentrations ranging from 0.5 mM (day 7) to 1.34 mM (day 28) and renal insufficiency highlighted by an increase of blood creatinine and urea levels and a decrease of urea excretion. Lithium treatment was found to trigger an oxidative stress both in kidney and liver, leading to an increase of lipid peroxidation level (TBARS) and of superoxide dismutase and catalase activities. Conversely, glutathione peroxidase activity was reduced. Constitutive HSP73 (heat shock protein 73) expression was not modified by lithium treatment, whereas inducible HSP72 was down-regulated in kidney. GRP94 (glucose regulated protein 94) appeared as two isoforms of 92 and 98 kDa: the 98-kDa protein being overexpressed in kidney by lithium treatment whereas 92-kDa protein was underexpressed both in kidney and liver.

Heat shock proteins in stabilization of spontaneously restored sinus rhythm in permanent atrial fibrillation patients after mitral valve surgery

A spontaneously restored sinus rhythm in permanent atrial fibrillation patients has been often observed after mitral valve (MV) surgery, but persisting duration in sinus rhythm varies from patient to patient. Heat shock proteins (Hsps) may be involved in pathogenesis of atrial fibrillation. We hypothesized that stabilization of restored sinus rhythm is associated with expression of Hsps in the atria. To test this hypothesis, clinical data, biopsies of right atrial appendage, and blood samples were collected from 135 atrial fibrillation patients who spontaneously restored sinus rhythm after conventional isolated MV replacement. Comparison was made between patients who had recurrence of atrial fibrillation within 7 days (AF) vs. patients with persisted sinus rhythm for more than 7 days (SR). Results showed that SR patients had higher activity of heat shock transcription factor 1 (HSF1) as well as upregulated expressions of heat shock cognate 70, Hsp70, and Hsp27 in the tissues. The activation of HSF1-Hsps pathway was associated with less-aggressive pathogenesis as reflected by lower rates of myolysis, apoptosis, interstitial fibrosis, and inflammation in SR patients. However, Hsp60 was lower in both tissue and plasma in SR patients, and was positively correlated with apoptosis, interstitial fibrosis, and inflammation. These findings suggest that the Hsps play important roles in stabilization of restored sinus rhythm after MV surgery by inhibiting AF-related atrial remodeling and arrhythmogenic substrates in atrial fibrillation patients. Low circulating Hsp60 levels preoperatively might predict a stable spontaneously restored sinus rhythm postoperatively.

Heat shock factor 2 is required for maintaining proteostasis against febrile-range thermal stress and polyglutamine aggregation

HSF2 regulates proteostasis capacity against febrile-range thermal stress, which provides temperature-dependent mechanisms of cellular adaptation to thermal stress. Furthermore, HSF2 has a strong impact on disease progression of Huntington's disease R6/2 mice, suggesting that it could be a promising therapeutic target for protein misfolding diseases.

Heat shock response is characterized by the induction of heat shock proteins (HSPs), which facilitate protein folding, and non-HSP proteins with diverse functions, including protein degradation, and is regulated by heat shock factors (HSFs). HSF1 is a master regulator of HSP expression during heat shock in mammals, as is HSF3 in avians. HSF2 plays roles in development of the brain and reproductive organs. However, the fundamental roles of HSF2 in vertebrate cells have not been identified. Here we find that vertebrate HSF2 is activated during heat shock in the physiological range. HSF2 deficiency reduces threshold for chicken HSF3 or mouse HSF1 activation, resulting in increased HSP expression during mild heat shock. HSF2-null cells are more sensitive to sustained mild heat shock than wild-type cells, associated with the accumulation of ubiquitylated misfolded proteins. Furthermore, loss of HSF2 function increases the accumulation of aggregated polyglutamine protein and shortens the lifespan of R6/2 Huntington's disease mice, partly through αB-crystallin expression. These results identify HSF2 as a major regulator of proteostasis capacity against febrile-range thermal stress and suggest that HSF2 could be a promising therapeutic target for protein-misfolding diseases.

Cellular heat shock factor 1 positively regulates human immunodeficiency virus-1 gene expression and replication by two distinct pathways

Human immunodeficiency virus-1 (HIV-1) infection leads to changes in cellular gene expression, which in turn tend to modulate viral gene expression and replication. Cellular heat shock proteins (HSPs) are induced upon heat shock, UV irradiation and microbial or viral infections. We have reported earlier Nef-dependent induction of HSP40 leading to increased HIV-1 gene expression; however, the mechanism of induction remained to be elucidated. As expression of HSPs is regulated by heat shock factors (HSFs), we have now studied the role of HSF1 not only in Nef-dependent HSP40 induction but also in HIV-1 gene expression. Our results show that HSF1 is also induced during HIV-1 infection and it positively regulates HIV-1 gene expression by two distinct pathways. First, along with Nef it activates HSP40 promoter which in turn leads to increased HIV-1 gene expression. Second, HSF1 directly interacts with newly identified HSF1 binding sequence on HIV-1 LTR promoter and induces viral gene expression and replication. Thus, the present work not only identifies a molecular basis for HSF1-mediated enhancement of viral replication but also provides another example of how HIV-1 uses host cell machinery for its successful replication in the host.

Distinct, gene-specific effect of heat shock on heat shock factor-1 recruitment and gene expression of CXC chemokine genes

The heat shock (HS) response, a phylogenetically conserved ubiquitous response to stress, is generally characterized by the induced expression of heat shock protein (HSP) genes. Our earlier studies showed that the stress-activated transcription factor, heat shock factor-1 (HSF1), activated at febrile range or HS temperatures also modified expression of non-HSP genes including cytokine and chemokine genes. We also showed by in silico analysis that 28 among 29 human and mouse CXC chemokine genes had multiple putative heat shock response elements (HSEs) present in their gene promoters. To further determine whether these potential HSEs were functional and bound HSF1, we analyzed the recruitment of HSF1 to promoters of 5 human CXC chemokine genes (CXCL-1, 2, 3, 5 and 8) by chromatin immunoprecipitation (ChIP) assay and analyzed the effect of HS exposure on tumor necrosis factor-α (TNFα)-induced expression of these genes in human lung epithelial-like A549 cells. HSF1 ChIP analysis showed that HSF1 was recruited to all but one of these CXC chemokine genes (CXCL-3) and HS caused a significant increase in recruitment of HSF1 to one or multiple HSEs present in the promoters of CXCL-1, 2, 5 and 8 genes. However, the effect of HS exposure on expression of these genes showed a variable gene-specific effect. For example, CXCL8 expression was markedly enhanced (p<0.05) whereas CXCL5 expression was significantly repressed (p<0.05) in cells exposed to HS coincident with TNFα stimulation. In contrast, expression of CXCL1 and CXCL2, despite HSF1 recruitment to their promoters, was not affected by HS exposure. Our results indicate that some, if not all, putative HSEs present in the CXC chemokine gene promoters are functional and recruit HSF1 in vivo but the effects on gene expression are variable and gene specific. We speculate, the physical proximity and interactions of other transcription factors and co-regulators with HSF1 could be critical to determining the effects of HS on the expression of these genes.

RNA granules: the good, the bad and the ugly

Processing bodies (PBs) and Stress Granules (SGs) are the founding members of a new class of RNA granules, known as mRNA silencing foci, as they harbour transcripts circumstantially excluded from the translationally active pool. PBs and SGs are able to release mRNAs thus allowing their translation. PBs are constitutive, but respond to stimuli that affect mRNA translation and decay, whereas SGs are specifically induced upon cellular stress, which triggers a global translational silencing by several pathways, including phosphorylation of the key translation initiation factor eIF2alpha, and tRNA cleavage among others. PBs and SGs with different compositions may coexist in a single cell. These macromolecular aggregates are highly conserved through evolution, from unicellular organisms to vertebrate neurons. Their dynamics is regulated by several signaling pathways, and depends on microfilaments and microtubules, and the cognate molecular motors myosin, dynein, and kinesin. SGs share features with aggresomes and related aggregates of unfolded proteins frequently present in neurodegenerative diseases, and may play a role in the pathology. Virus infections may induce or impair SG formation. Besides being important for mRNA regulation upon stress, SGs modulate the signaling balancing apoptosis and cell survival. Finally, the formation of Nuclear Stress Bodies (nSBs), which share components with SGs, and the assembly of additional cytosolic aggregates containing RNA -the UV granules and the Ire1 foci-, all of them induced by specific cell damage factors, contribute to cell survival.

Deciphering human heat shock transcription factor 1 regulation via post-translational modification in yeast

Heat shock transcription factor 1 (HSF1) plays an important role in the cellular response to proteotoxic stresses. Under normal growth conditions HSF1 is repressed as an inactive monomer in part through post-translation modifications that include protein acetylation, sumoylation and phosphorylation. Upon exposure to stress HSF1 homotrimerizes, accumulates in nucleus, binds DNA, becomes hyper-phosphorylated and activates the expression of stress response genes. While HSF1 and the mechanisms that regulate its activity have been studied for over two decades, our understanding of HSF1 regulation remains incomplete. As previous studies have shown that HSF1 and the heat shock response promoter element (HSE) are generally structurally conserved from yeast to metazoans, we have made use of the genetically tractable budding yeast as a facile assay system to further understand the mechanisms that regulate human HSF1 through phosphorylation of serine 303. We show that when human HSF1 is expressed in yeast its phosphorylation at S303 is promoted by the MAP-kinase Slt2 independent of a priming event at S307 previously believed to be a prerequisite. Furthermore, we show that phosphorylation at S303 in yeast and mammalian cells occurs independent of GSK3, the kinase primarily thought to be responsible for S303 phosphorylation. Lastly, while previous studies have suggested that S303 phosphorylation represses HSF1-dependent transactivation, we now show that S303 phosphorylation also represses HSF1 multimerization in both yeast and mammalian cells. Taken together, these studies suggest that yeast cells will be a powerful experimental tool for deciphering aspects of human HSF1 regulation by post-translational modifications.

KRIBB11 inhibits HSP70 synthesis through inhibition of heat shock factor 1 function by impairing the recruitment of positive transcription elongation factor b to the hsp70 promoter

Heat shock factor 1 (HSF1) is the master switch for heat shock protein (HSP) expression in eukaryotes. A synthetic chemical library was screened to identify inhibitors of HSF1 using a luciferase reporter under the control of a heat shock element. A compound named KRIBB11 (N(2)-(1H-indazole-5-yl)-N(6)-methyl-3-nitropyridine-2,6-diamine) was identified for its activity in abolishing the heat shock-induced luciferase activity with an IC(50) of 1.2 μmol/liter. When the cells were exposed to heat shock in the presence of KRIBB11, the induction of HSF1 downstream target proteins such as HSP27 and HSP70 was blocked. In addition, treatment of HCT-116 cells with KRIBB11 induced growth arrest and apoptosis. Markers of apoptosis, such as cleaved poly(ADP-ribose) polymerase, were detected after KRIBB11 treatment. Biotinyl-KRIBB11 was synthesized as an affinity probe for the identification of KRIBB11 target proteins. Using affinity chromatography and competition assays, KRIBB11 was shown to associate with HSF1 in vitro. Chromatin immunoprecipitation analysis showed that KRIBB11 inhibited HSF1-dependent recruitment of p-TEFb (positive transcription elongation factor b) to the hsp70 promoter. Finally, intraperitoneal treatment of nude mice with KRIBB11 at 50 mg/kg resulted in a 47.4% (p < 0.05) inhibition of tumor growth without body weight loss. Immunoblotting assays showed that the expression of HSP70 was lower in KRIBB11-treated tumor tissue than in control tissues. Because HSPs are expressed at high levels in a wide range of tumors, these results strengthen the rationale for targeting HSF1 in cancer therapy.

Protein kinase A binds and activates heat shock factor 1

BACKGROUND

Many inducible transcription factors are regulated through batteries of posttranslational modifications that couple their activity to inducing stimuli. We have studied such regulation of Heat Shock Factor 1 (HSF1), a key protein in control of the heat shock response, and a participant in carcinogenisis, neurological health and aging. As the mechanisms involved in the intracellular regulation of HSF1 in good health and its dysregulation in disease are still incomplete we are investigating the role of posttranslational modifications in such regulation.

METHODOLOGY/PRINCIPAL FINDINGS

In a proteomic study of HSF1 binding partners, we have discovered its association with the pleiotropic protein kinase A (PKA). HSF1 binds avidly to the catalytic subunit of PKA, (PKAcα) and becomes phosphorylated on a novel serine phosphorylation site within its central regulatory domain (serine 320 or S320), both in vitro and in vivo. Intracellular PKAcα levels and phosphorylation of HSF1 at S320 were both required for HSF1 to be localized to the nucleus, bind to response elements in the promoter of an HSF1 target gene (hsp70.1) and activate hsp70.1 after stress. Reduction in PKAcα levels by small hairpin RNA led to HSF1 exclusion from the nucleus, its exodus from the hsp70.1 promoter and decreased hsp70.1 transcription. Likewise, null mutation of HSF1 at S320 by alanine substitution for serine led to an HSF1 species excluded from the nucleus and deficient in hsp70.1 activation.

CONCLUSIONS

These findings of PKA regulation of HSF1 through S320 phosphorylation add to our knowledge of the signaling networks converging on this factor and may contribute to elucidating its complex roles in the stress response and understanding HSF1 dysregulation in disease.

Beta-N-acetylglucosamine (O-GlcNAc) is part of the histone code

Dynamic posttranslational modification of serine and threonine residues of nucleocytoplasmic proteins by β-N-acetylglucosamine (O-GlcNAc) is a regulator of cellular processes such as transcription, signaling, and protein-protein interactions. Like phosphorylation, O-GlcNAc cycles in response to a wide variety of stimuli. Although cycling of O-GlcNAc is catalyzed by only two highly conserved enzymes, O-GlcNAc transferase (OGT), which adds the sugar, and β-N-acetylglucosaminidase (O-GlcNAcase), which hydrolyzes it, the targeting of these enzymes is highly specific and is controlled by myriad interacting subunits. Here, we demonstrate by multiple specific immunological and enzymatic approaches that histones, the proteins that package DNA within the nucleus, are O-GlcNAcylated in vivo. Histones also are substrates for OGT in vitro. We identify O-GlcNAc sites on histones H2A, H2B, and H4 using mass spectrometry. Finally, we show that histone O-GlcNAcylation changes during mitosis and with heat shock. Taken together, these data show that O-GlcNAc cycles dynamically on histones and can be considered part of the histone code.

Overexpression of Colligin 2 in Glioma Vasculature is Associated with Overexpression of Heat Shock Factor 2

In previous studies we found expression of the protein colligin 2 (heat shock protein 47 (HSP47), SERPINH1) in glioma neovasculature while not in normal brain tissue. Generally, the regulation of heat shock gene expression in eukaryotes is mediated by heat shock factors (HSF). In mammals, three heat shock transcription factors, HSF-1, -2, and -4, have been isolated. Here we investigated the relation between the expression of colligin 2 and these heat shock factors at the mRNA level using real-time reverse transcriptase PCR (qRT-PCR) in different grades of astrocytic tumorigenesis, viz., low-grade glioma and glioblastoma. Endometrium samples, representing physiological angiogenesis, were included as controls. Since colligin 2 is a chaperon for collagens, the gene expression of collagen I (COL1A1) was also investigated. The blood vessel density of the samples was monitored by expression of the endothelial marker CD31 (PECAM1). Because NG2-immunopositive pericytic cells are involved in glioma neovascularization, the expression of NG2 (CSPG4) was also measured.

We demonstrate overexpression of HSF2 in both stages of glial tumorigenesis (reaching significance only in low-grade glioma) and also minor elevated levels of HSF1 as compared to normal brain. There were no differences in expression of HSF4 between low-grade glioma and normal brain while HSF4 was downregulated in glioblastoma. In the endometrium samples, none of the HSFs were upregulated. In the low-grade gliomas SERPINH appeared to be slightly overexpressed with a parallel 4-fold upregulation of COL1A1, while in glioblastoma there was over 5-fold overexpression of SERPINH1 and more than 150-fold overexpression of COL1A1. In both the lowgrade gliomas and the glioblastomas overexpression of CSPG4 was found and overexpression of PECAM1 was only found in the latter. Our data suggest that the upregulated expression of colligin 2 in glioma is accompanied by upregulation of COL1A1, CSPG4, HSF2 and to a lesser extent, HSF1. Further studies will unravel the association of these factors with colligin 2 expression, possibly leading to keys for therapeutic intervention.

Heat shock factor 1 protects mice from rapid death during Listeria monocytogenes infection by regulating expression of tumor necrosis factor alpha during fever

Heat shock factor 1 (HSF1) is a stress-induced transcription factor that promotes expression of genes that protect mammalian cells from the lethal effects of severely elevated temperatures (>42°C). However, we recently showed that HSF1 is activated at a lower temperature (39.5°C) in T cells, suggesting that HSF1 may be important for preserving T cell function during pathogen-induced fever responses. To test this, we examined the role of HSF1 in clearance of Listeria monocytogenes, an intracellular bacterial pathogen that elicits a strong CD8(+) T cell response in mice. Using temperature transponder microchips, we showed that the core body temperature increased approximately 2°C in L. monocytogenes-infected mice and that the fever response was maintained for at least 24 h. HSF1-deficient mice cleared a low-dose infection with slightly slower kinetics than did HSF1(+/+) littermate controls but were significantly more susceptible to challenges with higher doses of bacteria. Surprisingly, HSF1-deficient mice did not show a defect in CD8(+) T cell responses following sublethal infection. However, when HSF1-deficient mice were challenged with high doses of L. monocytogenes, increased levels of serum tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ) compared to those of littermate control mice were observed, and rapid death of the animals occurred within 48 to 60 h of infection. Neutralization of TNF-α enhanced the survival of HSF1-deficient mice. These results suggest that HSF1 is needed to prevent the overproduction of proinflammatory cytokines and subsequent death due to septic shock that can result following high-dose challenge with bacterial pathogens.

Anaphase-promoting complex/cyclosome participates in the acute response to protein-damaging stress

The ubiquitin E3 ligase anaphase-promoting complex/cyclosome (APC/C) drives degradation of cell cycle regulators in cycling cells by associating with the coactivators Cdc20 and Cdh1. Although a plethora of APC/C substrates have been identified, only a few transcriptional regulators are described as direct targets of APC/C-dependent ubiquitination. Here we show that APC/C, through substrate recognition by both Cdc20 and Cdh1, mediates ubiquitination and degradation of heat shock factor 2 (HSF2), a transcription factor that binds to the Hsp70 promoter. The interaction between HSF2 and the APC/C subunit Cdc27 and coactivator Cdc20 is enhanced by moderate heat stress, and the degradation of HSF2 is induced during the acute phase of the heat shock response, leading to clearance of HSF2 from the Hsp70 promoter. Remarkably, Cdc20 and the proteasome 20S core α2 subunit are recruited to the Hsp70 promoter in a heat shock-inducible manner. Moreover, the heat shock-induced expression of Hsp70 is increased when Cdc20 is silenced by a specific small interfering RNA (siRNA). Our results provide the first evidence for participation of APC/C in the acute response to protein-damaging stress.

Sulforaphane activates heat shock response and enhances proteasome activity through up-regulation of Hsp27

It is conceivable that stimulating proteasome activity for rapid removal of misfolded and oxidized proteins is a promising strategy to prevent and alleviate aging-related diseases. Sulforaphane (SFN), an effective cancer preventive agent derived from cruciferous vegetables, has been shown to enhance proteasome activities in mammalian cells and to reduce the level of oxidized proteins and amyloid β-induced cytotoxicity. Here, we report that SFN activates heat shock transcription factor 1-mediated heat shock response. Specifically, SFN-induced expression of heat shock protein 27 (Hsp27) underlies SFN-stimulated proteasome activity. SFN-induced proteasome activity was significantly enhanced in Hsp27-overexpressing cells but absent in Hsp27-silenced cells. The role of Hsp27 in regulating proteasome activity was further confirmed in isogenic REG cells, in which SFN-induced proteasome activation was only observed in cells stably overexpressing Hsp27, but not in the Hsp27-free parental cells. Finally, we demonstrated that phosphorylation of Hsp27 is irrelevant to SFN-induced proteasome activation. This study provides a novel mechanism underlying SFN-induced proteasome activity. This is the first report to show that heat shock response by SFN, in addition to the antioxidant response mediated by the Keap1-Nrf2 pathway, may contribute to cytoprotection.

Prostaglandin E2 potentiates heat shock-induced heat shock protein 72 expression in A549 cells

The heat shock (HS) response is an important cytoprotective response comprising the expression of heat shock proteins (HSPs) and orchestrated by the heat/stress-induced transcription factor, heat shock factor-1 (HSF-1). Previous studies suggest that the activation threshold and magnitude of the HS response may be modified by treatment with arachidonic acid (AA). We analyzed the effect of exogenous AA and its metabolites, PGE(2), LTD(4), and 15-HETE on HSF-1-dependent gene expression in A549 human respiratory epithelial-like cells. When added at 1microM, PGE(2) much more than LTD(4), but not 15-HETE increased activity of a synthetic HSF-1-dependent reporter after HS exposure (42 degrees C for 2h), but had no effect in the absence of HS. Exposing A549 cells to HS stimulated the release of PGE(2) and treatment with the cyclooxygenase inhibitor, ibuprofen, reduced HS-induced HSF-1-dependent transcription. PGE(2) increased HS-induced HSP72 mRNA and protein expression but EMSA and Western blot analysis failed to show an effect on HSF-1 DNA binding activity or post-translational modification. In summary, we showed that HS stimulates the generation of PGE(2), which augments the generation of HSPs. The clinical consequences of this pathway have yet to be determined.

Heat shock transcription factor 1 localizes to sex chromatin during meiotic repression

Heat shock factor 1 (HSF1) is an important transcription factor in cellular stress responses, cancer, aging, and developmental processes including gametogenesis. Disruption of Hsf1, together with another HSF family member, Hsf2, causes male sterility and complete lack of mature sperm in mice, but the specific role of HSF1 in spermatogenesis has remained unclear. Here, we show that HSF1 is transiently expressed in meiotic spermatocytes and haploid round spermatids in mouse testis. The Hsf1(-/-) male mice displayed regions of seminiferous tubules containing only spermatogonia and increased morphological abnormalities in sperm heads. In search for HSF1 target genes, we identified 742 putative promoters in mouse testis. Among them, the sex chromosomal multicopy genes that are expressed in postmeiotic cells were occupied by HSF1. Given that the sex chromatin mostly is repressed during and after meiosis, it is remarkable that HSF1 directly regulates the transcription of sex-linked multicopy genes during postmeiotic repression. In addition, our results show that HSF1 localizes to the sex body prior to the meiotic divisions and to the sex chromocenter after completed meiosis. To the best of our knowledge, HSF1 is the first known transcription factor found at the repressed sex chromatin during meiosis.

Heat shock factors: integrators of cell stress, development and lifespan

Heat shock factors (HSFs) are essential for all organisms to survive exposures to acute stress. They are best known as inducible transcriptional regulators of genes encoding molecular chaperones and other stress proteins. Four members of the HSF family are also important for normal development and lifespan-enhancing pathways, and the repertoire of HSF targets has thus expanded well beyond the heat shock genes. These unexpected observations have uncovered complex layers of post-translational regulation of HSFs that integrate the metabolic state of the cell with stress biology, and in doing so control fundamental aspects of the health of the proteome and ageing.

SR and SR-related proteins redistribute to segregated fibrillar components of nucleoli in a response to DNA damage

Pre-mRNA splicing factors are often redistributed to nucleoli in response to physiological conditions and cell stimuli. In telophase nuclei, serine-arginine rich (SR) proteins, which usually reside in nuclear speckles, localize transiently to active ribosomal DNA (rDNA) transcription sites called nucleolar organizing region-associated patches (NAPs). Here, we show that ultraviolet light and DNA damaging chemicals induce the redistribution of SR and SR-related proteins to areas around nucleolar fibrillar components in interphase nuclei that are similar to, but distinct from, NAPs, and these areas have been termed DNA damage-induced NAPs (d-NAPs). In vivo labeling of nascent RNA distinguished d-NAPs from NAPs in that d-NAPs were observed even after full rDNA transcriptional arrest as a result of DNA damage. Studies under a variety of conditions revealed that d-NAP formation requires both RNA polymerase II-dependent transcriptional arrest and nucleolar segregation, in particular, the disorganization of the granular nucleolar components. Despite the redistribution of SR proteins, splicing factor-enriched nuclear speckles were not disrupted because other nuclear speckle components, such as nuclear poly(A) RNA and the U5-116K protein, remained in DNA-damaged cells. These data suggest that the selective redistribution of splicing factors contributes to the regulation of specific genes via RNA metabolism. Finally, we demonstrate that a change in alternative splicing of apoptosis-related genes is coordinated with the occurrence of d-NAPs. Our results reveal a novel response to DNA damage that involves the dynamic redistribution of splicing factors to nucleoli.

Nuclear stress bodies

Nuclear stress bodies (nSBs) are unique subnuclear organelles which form in response to heat shock. They are initiated through a direct interaction between heat shock transcription factor 1 (HSF1) and pericentric tandem repeats of satellite III sequences and correspond to active transcription sites for noncoding satellite III transcripts. Given their unusual features, nSBs are distinct from other known transcription sites. In stressed cells, they are thought to participate in rapid, transient, and global reprogramming of gene expression through different types of mechanisms including chromatin remodeling and trapping of transcription and splicing factors. The analysis of these atypical and intriguing structures uncovers new facets of the relationship between nuclear organization and nuclear function.

Systems analysis of protein modification and cellular responses induced by electrophile stress

Biological electrophiles result from oxidative metabolism of exogenous compounds or endogenous cellular constituents, and they contribute to pathophysiologies such as toxicity and carcinogenicity. The chemical toxicology of electrophiles is dominated by covalent addition to intracellular nucleophiles. Reaction with DNA leads to the production of adducts that block replication or induce mutations. The chemistry and biology of electrophile−DNA reactions have been extensively studied, providing in many cases a detailed understanding of the relation between adduct structure and mutational consequences. By contrast, the linkage between protein modification and cellular response is poorly understood.

In this Account, we describe our efforts to define the chemistry of protein modification and its biological consequences using lipid-derived α,β-unsaturated aldehydes as model electrophiles. In our global approach, two large data sets are analyzed: one represents the identity of proteins modified over a wide range of electrophile concentrations, and the second comprises changes in gene expression observed under similar conditions. Informatics tools show theoretical connections based primarily on transcription factors hypothetically shared between the two data sets, downstream of adducted proteins and upstream of affected genes. This method highlights potential electrophile-sensitive signaling pathways and transcriptional processes for further evaluation.

Peroxidation of cellular phospholipids generates a complex mixture of both membrane-bound and diffusible electrophiles. The latter include reactive species such as malondialdehyde, 4-oxononenal, and 4-hydroxynonenal (HNE). Enriching HNE-adducted proteins for proteomic analysis was a technical challenge, solved with click chemistry that generated biotin-tagged protein adducts. For this purpose, HNE analogues bearing terminal azide or alkyne functionalities were synthesized. Cellular lysates were first exposed to a single type of HNE analogue (azido- or alkynyl-HNE), and then click reactions were performed against the cognate alkynyl- and azido-biotin derivative. The resulting biotin-labeled proteins were captured and enriched over a streptavidin matrix for subsequent mass spectrometric analysis. We thereby identified a multitude of HNE targets. Simultaneous microarray analysis of changes in gene expression triggered by HNE also produced an abundance of data. Functional analysis of both data sets generated the hypothesis that an important pathway of cellular response derives from electrophile modification of protein chaperones, resulting in the release of transcription factors that are their clients. Informatic analysis of the protein modification and microarray data sets identified several transcription factors as potential mediators of the cellular response to HNE-adducted proteins. Among these, heat shock factor 1 (HSF1) was confirmed as a sensitive and robust effector of HNE-induced changes in gene expression. Activation of HSF1 appears, in part, to be mediated by the electrophilic adduction of Hsp70 and Hsp90, which normally maintain HSF1 in an inactive cytosolic complex.

The identification of HSF1 as a mediator of biological effects downstream of HSF1 has provided new opportunities for research, illustrating the potential of our systems-based approach. Accordingly, we characterized HSF1-mediated gene expression in protecting against electrophile-induced toxicity. Among the genes induced by HSF1, Bcl-2- associated athanogene 3 (BAG3) is notable for its actions in promoting cell survival through stabilization of antiapoptotic Bcl-2 proteins, appearing to have a critical role in mediating cellular protection against electrophile-induced death.

Heat shock protein 70 is upregulated in the intestine of intrauterine growth retardation piglets

The objective of this study is to investigate the expression and distribution of heat shock protein 70 (Hsp70) in the intestine of intrauterine growth retardation (IUGR) piglets. Samples from the duodenum, prejejunum, distal jejunum, ileum, and colon of IUGR and normal-body-weight (NBW) piglets were collected at birth. The results indicated that the body and intestine weight of IUGR piglets were significantly lower than NBW piglets. The villus height and villus/crypt ratio in jejunum and ileum of IUGR piglets were significantly reduced compared to NBW piglets. These results indicated that IUGR causes abnormal gastrointestinal morphologies and gastrointestinal dysfunction. The mRNA of hsp70 was increased in prejejunum (P < 0.05), distal jejunum (P < 0.05), and colon in IUGR piglets. However, the hsp70 mRNA in ileum of piglets with IUGR was decreased. Similar to hsp70 mRNA, the protein levels of Hsp70 in prejejunum (P < 0.05), distal jejunum, and colon (P < 0.05) in IUGR piglets were higher than those in NBW piglets. These results indicated that the expression of Hsp70 in the intestinal piglets was upregulated by IUGR, and different intestinal sites had different responses to stress. Meanwhile, the localization of Hsp70 in the epithelial cells of the whole villi and intestinal gland rather than in the lamina propria and myenteron suggested that Hsp70 has a cytoprotective role in epithelial cell function and structure.

Temporal requirements of insulin/IGF-1 signaling for proteotoxicity protection

Toxic protein aggregation (proteotoxicity) is a unifying feature in the development of late-onset human neurodegenerative disorders. Reduction of insulin/IGF-1 signaling (IIS), a prominent lifespan, developmental and reproductive regulatory pathway, protects worms from proteotoxicity associated with the aggregation of the Alzheimer’s disease-linked Aβ peptide. We utilized transgenic nematodes that express human Aβ and found that late life IIS reduction efficiently protects from Aβ toxicity without affecting development, reproduction or lifespan. To alleviate proteotoxic stress in the animal, the IIS requires heat shock factor (HSF)-1 to modulate a protein disaggregase, while DAF-16 regulates a presumptive active aggregase, raising the question of how these opposing activities could be co-regulated. One possibility is that HSF-1 and DAF-16 have distinct temporal requirements for protection from proteotoxicity. Using a conditional RNAi approach, we found an early requirement for HSF-1 that is distinct from the adult functions of DAF-16 for protection from proteotoxicity. Our data also indicate that late life IIS reduction can protect from proteotoxicity when it can no longer promote longevity, strengthening the prospect that IIS reduction might be a promising strategy for the treatment of neurodegenerative disorders caused by proteotoxicity.

A novel transcriptional repressor, Rhit, is involved in heat-inducible and age-dependent expression of Mpv17-like protein, a participant in reactive oxygen species metabolism

Mpv17-like protein (M-LP) is a protein that has been suggested to be involved in the metabolism of reactive oxygen species. The two M-LP isoforms in mouse, M-LP(S) and M-LP(L), are generated by the alternative usage of promoters. M-LP(S) is expressed exclusively in kidneys after the age of 6 weeks, whereas M-LP(L) is expressed ubiquitously. To elucidate the molecular basis of M-LP(S) expression, we searched for cis-regulatory elements in the promoter region of M-LP(S) and identified heat shock element half-sites as positive elements and a Tramtrack 69K (Ttk 69K) binding site as a negative element. Furthermore, we isolated a novel transcription repressor, Rhit (regulator of heat-induced transcription), that binds to the Ttk 69K binding site within the M-LP(S) promoter by DNA affinity chromatography and confirmed its participation in the transcriptional regulation of M-LP(S) by RNA interference (RNAi). Sequence analysis revealed that Rhit contains a KRAB (Krüppel-associated box) domain and a DNA-binding domain composed of eight C(2)H(2)-type zinc fingers. Interestingly, exposure to heat shock stress resulted in the upregulation of M-LP(S) expression concurrent with the downregulation of Rhit expression. Moreover, the age-dependent expression of M-LP(S) was inversely correlated with that of Rhit. These observations strongly suggest that Rhit acts as a repressor in the heat-induced and age-dependent transcriptional regulation of M-LP(S).

LPS-induced cytokine levels are repressed by elevated expression of HSP70 in rats: possible role of NF-kappaB

Heat shock protein (HSP)70 provides a spectrum of protection against any of a variety of stresses, preventing damage measured at the level of molecules, cells, as well as whole organism. We have previously reported that lipopolysaccharide (LPS)-induced lethality in rats is prevented by a previous exposure to a mild thermal stress and that a thermal stress sufficient to induce HSP70 expression in the liver is accompanied by an inhibition of endotoxin-mediated cytokines and modulation of febrile response. However, the effect of HSP70 upregulation on cytokine expression in animals is unknown. The aim of the present study was to demonstrate the effect of HSP70 overexpression with adenovirus administration on LPS-induced increase in cytokines levels in animals. In the present study, Sprague-Dawley rats were infected with either the control AdTrack or Ad70 virus that directs the expression of human HSP70. After a 5-day incubation, animals were injected with either saline alone or LPS (50 microg/kg). Four hours later, blood samples were drawn and plasma levels of interleukin (IL)-6 or tumor necrosis factor (TNF)-alpha were measured by enzyme-linked immunosorbent assay. Our data demonstrate for the first time that HSP70 overexpression with adenovirus injection prevented the LPS-induced increase in TNF-alpha and IL-6 levels in rats. Repression of LPS-induced cytokines expressions by HSP70 upregulation was associated with inhibited IkappaBalpha degradation and nuclear factor kappa-B (NF-kappaB) p65 nuclear translocation in liver, suggesting that HSP70 overexpression may regulate LPS-induced cytokines expression through NF-kappaB pathway. We conclude that the effects of heat stress-induced increase in HSP70 protein expression on LPS-induced cytokine elaboration in whole animals can be reproduced by the actions of a single gene product.

A novel mouse HSF3 has the potential to activate nonclassical heat-shock genes during heat shock

HSF1 is a master regulator of the heat-shock response in mammalian cells, whereas in avian cells, HSF3, which was considered as an avian-specific factor, is required for the expression of classical heat-shock genes. Here, the authors identify mouse HSF3, and demonstrate that it has the potential to activate only nonclassical heat-shock genes.

The heat-shock response is characterized by the expression of a set of classical heat-shock genes, and is regulated by heat-shock transcription factor 1 (HSF1) in mammals. However, comprehensive analyses of gene expression have revealed very large numbers of inducible genes in cells exposed to heat shock. It is believed that HSF1 is required for the heat-inducible expression of these genes although HSF2 and HSF4 modulate some of the gene expression. Here, we identified a novel mouse HSF3 (mHSF3) translocated into the nucleus during heat shock. However, mHSF3 did not activate classical heat-shock genes such as Hsp70. Remarkably, overexpression of mHSF3 restored the expression of nonclassical heat-shock genes such as PDZK3 and PROM2 in HSF1-null mouse embryonic fibroblasts (MEFs). Although down-regulation of mHSF3 expression had no effect on gene expression or cell survival in wild-type MEF cells, it abolished the moderate expression of PDZK3 mRNA and reduced cell survival in HSF1-null MEF cells during heat shock. We propose that mHSF3 represents a unique HSF that has the potential to activate only nonclassical heat-shock genes to protect cells from detrimental stresses.

Proteotoxic stress increases nuclear localization of ataxin-3

Spinocerebellar ataxia type 3 (SCA3)/Machado Joseph disease results from expansion of the polyglutamine domain in ataxin-3 (Atx3). Atx3 is a transcriptional co-repressor, as well as a deubiquitinating enzyme that appears to function in cellular pathways involved in protein homeostasis. In this study, we show that interactions of Atx3 with valosin-containing protein and hHR23B are dynamic and modulated by proteotoxic stresses. Heat shock, a general proteotoxic stress, also induced wild-type and pathogenic Atx3 to accumulate in the nucleus. Mapping studies showed that two regions of Atx3, the Josephin domain and the C-terminus, regulated heat shock-induced nuclear localization. Heat shock-induced nuclear localization of Atx3 was not affected by a casein kinase-2 inhibitor or by mutating a predicted nuclear localization signal. However, serine-111 of Atx3 was required for nuclear localization of the Josephin domain and regulated nuclear localization of full-length Atx3. Atx3 null cells were more sensitive to toxic effects of heat shock suggesting that Atx3 had a protective function in the cellular response to heat shock. Importantly, we found that oxidative stress also induced nuclear localization of Atx3; both wild-type and pathogenic Atx3 accumulated in the nucleus of SCA3 patient fibroblasts following oxidative stress. Heat shock and oxidative stress are the first processes identified that increase nuclear localization of Atx3. Observations in this study provide new and important insights for understanding SCA3 pathology as the nucleus is likely a key site for early pathogenesis.

Regulation of the heat shock response under anoxia in the turtle, Trachemys scripta elegans

The effects of 20 h of anoxic submergence in cold water and 5 h of aerobic recovery on the heat shock response were analyzed in four organs of the anoxia-tolerant turtle Trachemys scripta elegans. Immunoblotting was used to analyze levels of active and inactive forms of the heat shock transcription factor 1 (HSF1), nuclear translocation of HSF1, and the levels of six heat shock proteins (HSPs). PCR was also used to retrieve the turtle HSF1 nucleotide sequence; its deduced amino acid sequence showed 97% identity with chicken HSF1. White skeletal muscle showed a strong fivefold increase in the amount of active HSF1 under anoxic conditions as well as an 80% increase in nuclear localization. This was accompanied by upregulation of five HSPs by 1.8- to 2.9-fold: Hsp25, Hsp40, Hsp70, Hsc70, and Hsp90, the latter two remained elevated after 5 h of aerobic recovery. Kidney and liver showed little change in active HSF1 content during anoxia and recovery, but a significant increase in the nuclear localization of HSF1 during anoxia. This supported enhanced expression of three HSPs in kidney (Hsp40, Hsc70, and Hsp90) and four in liver (Hsp40, Hsp60, Hsp70, Hsc70). Heart displayed a strong increase in active HSF1 during anoxia and recovery (6.6- to 6.8-fold higher than control) and increased nuclear localization but heart HSP levels did not rise. The data demonstrate organ-specific regulation of HSPs during anoxia exposure and aerobic recovery in T. s. elegans and suggest that the heat shock response is an important aspect of cytoprotection during facultative anaerobiosis, particularly with regard to underwater hibernation of turtles in cold water.

Hyperthermia in the febrile range induces HSP72 expression proportional to exposure temperature but not to HSF-1 DNA-binding activity in human lung epithelial A549 cells

Expression of heat shock proteins (HSPs) is classically activated at temperatures above the physiologic range (>or=42 degrees C) via activation of the stress-activated transcription factor, heat shock factor-1 (HSF-1). Several studies suggest that less extreme hyperthermia, especially within the febrile range, as occurs during fever and exertional/environmental hyperthemia, can also activate HSF-1 and enhance HSP expression. We compared HSP72 protein and mRNA expression in human A549 lung epithelial cells continuously exposed to 38.5 degrees C, 39.5 degrees C, or 41 degrees C or exposed to a classic heat shock (42 degrees C for 2 h). We found that expression of HSP72 protein and mRNA increased linearly as incubation temperature was increased from 37 degrees C to 41 degrees C, but increased abruptly when the incubation temperature was raised to 42 degrees C. A similar response in luciferase activity was observed using A549 cells stably transfected with an HSF-1-responsive luciferase reporter plasmid. However, activation of intranuclear HSF-1 DNA-binding activity was comparable at 38.5 degrees C, 39.5 degrees C, and 41 degrees C and only modestly greater at 42 degrees C but the mobility of HSF1 protein on a denaturing gel was altered with increasing exposure temperature and was distinctly different at 42 degrees C. These findings indicate that the proportional changes in HSF-1-dependent HSP72 expression at febrile-range temperatures are dependent upon exposure time and temperature but not on the degree of HSF-1 DNA-binding activity. Instead, HSF-1-mediated HSP expression following hyperthermia and heat shock appears to be mediated, in addition to HSF-1 activation, by posttranslational modifications of HSF-1 protein.

Reinvestigation of the effect of carbenoxolone on the induction of heat shock proteins

Carbenoxolone (CBX) is a semisynthetic derivative of the licorice root substance glycyrrhizinic acid and has been previously reported to induce only heat shock protein 70 [Hsp70, HSPA1A (the systematic name of heat shock protein is given in the parenthesis after each HSP, according to the recent nomenclature guidelines, Kampinga et al., Cell Stress Chaperones, 14:105-111, 2008) but not other heat shock proteins (HSPs) (Nagayama et al., Life Sci. 69:2867-2873, 2001). In this study, we reinvestigated the effect of CBX on the induction of HSPs in HeLa and human neuroblastoma (A-172) cells. CBX clearly induced not only Hsp70 but also Hsp90 (HSPC1), Hsp40 (DNAJB1), and Hsp27 (HSPB1) at concentrations of 10 to 800 microM for 16 h incubation. At higher concentrations (more than 400 microM), however, CBX appeared to be toxic. Treatment of cells with CBX resulted in enhanced phosphorylation and acquisition of DNA-binding ability of heat shock transcription factor 1 (HSF1). Furthermore, characteristic HSF1 granules were formed in the nucleus, suggesting that the induction of HSPs by CBX is mediated by the activation of HSF1. Furthermore, thermotolerance was induced by CBX treatment, as determined by clonogenic survival. Although the precise target of CBX is not known at present, these results indicate that CBX is one of the molecular chaperone inducers and suggest that some pharmacological activities of CBX might be ascribable in part to its molecular chaperone-inducing property.

Thiazolides, a new class of anti-influenza molecules targeting viral hemagglutinin at the post-translational level

The emergence of highly contagious influenza A virus strains, such as the new H1N1 swine influenza, represents a serious threat to global human health. Efforts to control emerging influenza strains focus on surveillance and early diagnosis, as well as development of effective vaccines and novel antiviral drugs. Herein we document the anti-influenza activity of the anti-infective drug nitazoxanide and its active circulating-metabolite tizoxanide and describe a class of second generation thiazolides effective against influenza A virus. Thiazolides inhibit the replication of H1N1 and different other strains of influenza A virus by a novel mechanism: they act at post-translational level by selectively blocking the maturation of the viral hemagglutinin at a stage preceding resistance to endoglycosidase H digestion, thus impairing hemagglutinin intracellular trafficking and insertion into the host plasma membrane, a key step for correct assembly and exit of the virus from the host cell. Targeting the maturation of the viral glycoprotein offers the opportunity to disrupt the production of infectious viral particles attacking the pathogen at a level different from the currently available anti-influenza drugs. The results indicate that thiazolides may represent a new class of antiviral drugs effective against influenza A infection.

Stress-inducible regulation of heat shock factor 1 by the deacetylase SIRT1

Heat shock factor 1 (HSF1) is essential for protecting cells from protein-damaging stress associated with misfolded proteins and regulates the insulin-signaling pathway and aging. Here, we show that human HSF1 is inducibly acetylated at a critical residue that negatively regulates DNA binding activity. Activation of the deacetylase and longevity factor SIRT1 prolonged HSF1 binding to the heat shock promoter Hsp70 by maintaining HSF1 in a deacetylated, DNA-binding competent state. Conversely, down-regulation of SIRT1 accelerated the attenuation of the heat shock response (HSR) and release of HSF1 from its cognate promoter elements. These results provide a mechanistic basis for the requirement of HSF1 in the regulation of life span and establish a role for SIRT1 in protein homeostasis and the HSR.

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

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

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

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

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

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

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

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

Hsf1 is required for the nuclear translocation of p53 tumor suppressor

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

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

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

The insulin paradox: aging, proteotoxicity and neurodegeneration

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

HSF1 as a mitotic regulator: phosphorylation of HSF1 by Plk1 is essential for mitotic progression

Previously, heat shock factor 1 (HSF1) had been reported to induce genomic instability and aneuploidy by interaction with Cdc20. Here, we have further examined the functions of HSF1 in the regulation of mitosis. A null mutant or knockdown of HSF1 caused defective mitotic progression. By monitoring chromosomes in living cells, we determined that HSF1 was localized to the centrosome in mitosis and especially to the spindle poles in metaphase. HSF1 was phosphorylated by Plk1 at Ser(216) of the DSGXXS motif during the timing of mitosis and a phospho-defective mutant form of HSF1 inhibited mitotic progression. Phosphorylated HSF1 during spindle pole localization underwent ubiquitin degradation through the SCF(beta-TrCP) pathway. However, binding of HSF1 with Cdc20 stabilized the phosphorylation of HSF1. Moreover, SCF(beta-TrCP)-mediated degradation only occurred when phosphorylated HSF1 was released from Cdc20. HSF1 phosphorylation at Ser(216) occurred in the early mitotic period with simultaneous binding of Cdc20. The interaction of HSF1 with SCF(beta-TrCP) was followed and then the interaction of APC/Cdc20 was subsequently observed. From these findings, it was shown that Plk1 phosphorylates HSF1 in early mitosis and that the binding of phosphorylated HSF1 with Cdc20 and ubiquitin degradation by SCF(beta-TrCP) regulates mitotic progression.

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

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

Heat shock factor 1 regulates lifespan as distinct from disease onset in prion disease

Prion diseases are fatal, transmissible, neurodegenerative diseases caused by the misfolding of the prion protein (PrP). At present, the molecular pathways underlying prion-mediated neurotoxicity are largely unknown. We hypothesized that the transcriptional regulator of the stress response, heat shock factor 1 (HSF1), would play an important role in prion disease. Uninoculated HSF1 knockout (KO) mice used in our study do not show signs of neurodegeneration as assessed by survival, motor performance, or histopathology. When inoculated with Rocky Mountain Laboratory (RML) prions HSF1 KO mice had a dramatically shortened lifespan, succumbing to disease approximately 20% faster than controls. Surprisingly, both the onset of home-cage behavioral symptoms and pathological alterations occurred at a similar time in HSF1 KO and control mice. The accumulation of proteinase K (PK)-resistant PrP also occurred with similar kinetics and prion infectivity accrued at an equal or slower rate. Thus, HSF1 provides an important protective function that is specifically manifest after the onset of behavioral symptoms of prion disease.