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PubMedDate not supplied

[Heat capacity of hydrated and dehydrated globular proteins. The denaturing increment of heat capacity].

Absolute values of heat capacity for some hydrated globular proteins (11S globulin, ovalbumin, ribonuclease A, and lysozyme) have been studied by differential scanning calorimetry. It has been found that for proteins with bound water, as in the case of protein solutions, the heat capacity of denatured proteins is higher then prior to denaturation. Depending on temperature and humidity, the denatured proteins can be either in high-elastic or glass state. Specific heat capacities for these two states have the same values for all proteins and depend only on temperature with a characteristic increment of 0.55 J.g-1.K-1 at glass transition. The glass transitions were observed not only in denatured but also in native proteins. Our results indicate that the main contribution to the heat capacity increment at denaturation is connected with the thermal motion in the protein globule, which is contrast with the commonly accepted ideas.

Calorimetry, Differential Scanning↗

PubMed1977

[Growth and heat resistance of rats repeatedly exposed to heat during early ontogenesis].

The influence of a 10-fold heat training from the 1st to the 10th to the 20th, and from the 20th to the 30th days after birth on further growth and resistance of the animals to the high temperature was investigated. The growth and survival of rats was found to depend on the regimen of heat training. The animals aged 10 to 20 days proved to be most sensitive to the action of high temperature. Heat resistance of these rats turned out to be maximally increased at the period of primary sexual maturation, and the growth rate was retarded in comparison with the animals subjected to heat training at other age periods.

Adaptation, Physiological↗

PubMed1996

Temperature change in the pulp chamber during application of heat to composite and amalgam cores and its returning time to oral heat.

Protection of vital tissue, especially pulp tissue, is essential to any restorative dental procedure. This study observed the temperature changes in the pulp chamber one minute after application of heat of different degrees to composite and amalgam cores and period of time necessary for the temperature measured in the pulp one minute after heat application to return to 36 degrees C. For this, twelve extracted, morphologically intact human teeth were chosen. Four pins were placed in each of the teeth. Amalgam and composite cores were prepared. All specimens were placed in a water bath at 36 degrees C. Heat of 0 degree C, 40 degrees C, 60 degrees C, 80 degrees C was applied to the cores on the teeth and the temperature of the pulp was measured one minute later by means of a thermocouple. For both amalgam and composite cores, the lowest increase in the pulp temperature was established after the 40 degrees C heat application.

Body Temperature↗

PubMed1998

Examination for heat-labile, heat-stable, and Shiga-like toxins and for the eaeA gene in Escherichia coli isolates obtained from dogs dying with diarrhea: 122 cases (1992-1996).

OBJECTIVE: To examine Escherichia coli isolates obtained from dogs dying with diarrhea for heat-labile, heat-stable, and Shiga-like toxins and for the eaeA gene, which is associated with attaching and effacing lesions. DESIGN: Retrospective study. ANIMALS: 122 dogs. PROCEDURE: E coli isolates were tested by means of dot-blot hybridization of DNA extracts of cultured bacteria. Medical records of dogs from which E coli isolates with virulence genes had been isolated were examined, and histologic findings and evidence of intercurrent bacterial and viral infections were recorded. RESULTS: None of the E coli isolates obtained from these dogs produced heat-labile, heat-stable, or Shiga-like toxins; however, E coli isolates from 44 of 122 dogs were found to have the eaeA gene. Histologically, multifocal bacterial adherence to the epithelium and epithelial necrosis and detachment were seen in colonic specimens from 20 of 44 (45%) dogs. Escherichia coli was the sole pathogen identified in 15 of 44 (34%) dogs. Intercurrent pathogens, including canine parvovirus (n = 19), Clostridium perfringens (8), rotavirus (5), hookworms (3), coccidia (3), and Salmonella agona (1), were identified in the remaining 29 (66%) dogs. CLINICAL IMPLICATIONS: Attaching and effacing E coli can be a primary or secondary pathogen in dogs with diarrhea. Antibiotic treatment is indicated in dogs with diarrhea because of the possibility that it is primarily bacterial in origin and because, even if it is primarily viral in origin, there may be secondary bacterial infection.

Adhesins, Bacterial↗

PubMedDate not supplied

The heat sink and its relationship to reducing heat during pin-reduction procedures.

When self-threading pins are used in the restoration of teeth, the heat generated by cutting these pins to the correct length may traumatize the pulp. This study evaluated cotton forceps and a mosquito hemostat used as a heat sink and at different positions on the pin to determine any change in heat transferred to the tooth. Three hundred self-threading pins (Whaledent TMS System: 100 each of the Regular, Minim, and Minikin sizes) were inserted into freshly extracted teeth and sectioned. The temperature change at the apical end of the pin was measured using a thermistor probe. The results indicated that metal supporting instruments can be effective in reducing heat transferred to the apical aspect of the pin during pin reduction.

Dental Pins↗

PubMed1999

Regulatory domain of human heat shock transcription factor-2 is not regulated by hemin or heat shock.

Heat shock transcription factor 2 (HSF-2) activates transcription of heat shock proteins in response to hemin in the human erythroleukemia cell line, K562. To understand the regulation of HSF-2 activation, a series of deletion mutants of HSF-2 fused to the GAL-4 DNA binding domain were generated. We have found that human HSF-2 has a regulatory domain located in the carboxyl-terminal portion of the protein which represses the activity of its activation domain under normal physiological conditions. The repressive effects of this domain can be eliminated by its deletion in GAL4-HSF-2 fusion constructs. The regulatory domain of HSF-2 can also repress a heterologous chimeric activator that contains a portion of the VP16 activation domain. The activation domain of HSF-2 is a segment of approximately 77 amino acids located proximal to the carboxyl-terminal hydrophobic heptad repeat (leucine zipper 4) of the molecule. Interestingly, the GAL4-HSF-2 fusion protein and the 77 amino acids activation domain are inactive and are not activated by pretreatment of cells with either hemin or elevated temperature. Our data suggest that regulation of HSF-2 differs from HSF-1 in that its regulatory domain is not responsive to hemin or heat directly.

Base Sequence↗

PubMed2006

Heat shock transcription factor (Hsf)-4b recruits Brg1 during the G1 phase of the cell cycle and regulates the expression of heat shock proteins.

Human brahma-related gene 1(Brg1) is a subunit of the switching/sucrose non-fermenting (SWI/SNF) chromatin-remodeling complex and regulates transcription during cell growth and differentiation and has been found to be mutated in many types of human cancers. Mammalian heat shock factor 1 (Hsf1), which binds conserved sequences on the promoter of the hsp70 gene when cells are exposed to various stress stimuli, utilizes Brg1-SWI/SNF complexes and stimulates transcription in vitro at the level of initiation and elongation. In contrast to the stress-inducibility of Hsf1, in vitro transcribed/translated Hsf4b binds to the heat shock element (HSE) constitutively and loses its ability to bind HSEs following stress. The regulation of Hsf4b transcriptional activity in vivo remains unclear. Here, we present evidence that Hsf4b recruits Brg1 complexes to the promoters of heat shock proteins (HSPs) under physiological growth conditions. Furthermore, in an asynchronous cell population, the association of Hsf4b with Brg1 complexes is regulated in response to activation/inactivation of the extracellular signal regulated protein kinase 1/2 (ERK1/2) signaling pathway. Since Brg1 is also the target of mitogen-activated protein (MAP) kinases and other protein kinases and it is hyperphosphorylated and inactivated during the G2/M phase of the cell cycle, we tested whether the association of Hsf4b with Brg1 complexes is altered during the cell cycle. The results indicate that association of Hsf4b with Brg1 complexes is undetectable during G2/M; however, an Hsf4b interaction with Brg1 complexes is evident at 1-3 h after progression of cells into G1, where chromatin structure is presumed to be more accessible to transcriptional regulatory proteins. At this time, Hsf4b exhibits increased DNA-binding activity and is detectable on promoters of multiple Hsps. To determine the unique role of Hsf4b in stimulating the expression of Hsps during the cell cycle, experiments were conducted with mouse embryo fibroblasts (MEFs) deficient in individual Hsfs. The results indicate that in the absence of Hsf1 and Hsf2, Hsf4b expression in cells leads to increased ability of Hsf4b to bind HSE during G1, leading to enhanced synthesis of inducible Hsp70.

Animals↗

PubMed1999

Evidence for a novel set of small heat-shock proteins that associates with the mitochondria of murine PC12 cells and protects NADH:ubiquinone oxidoreductase from heat and oxidative stress.

Several previously unreported small heat-shock proteins (sHsps) were detected in mitochondria from heat-stressed rat PC12 cells, but not in unstressed controls. Functional inactivation of the mitochondrial sHsps with murine Hsp25 antibody indicated that these sHsps protect NADH:ubiquinone oxidoreductase and NADH dehydrogenase activity (i.e., complex I) in submitochondrial vesicles during heat and oxidative stress. These results (i) confirm the existence of multiple sHsps in mammals and indicate that several of these sHsps associate with the mitochondria, (ii) indicate a conserved function between plant and mammalian mitochondrial sHsps in protecting electron transport during stress, and (iii) suggest that these sHsps may play an important role in diseases whose etiology is based upon oxidative damage of complex I.

Animals↗

PubMed1997

Time course of tolerance to ischemia-reperfusion injury and induction of heat shock protein 72 by heat stress in the rat heart.

We compared the time course of tolerance to myocardial ischemia-reperfusion injury with the time course of heat shock protein 72 (hsp72; inducible form) induction after heat stress in a rat model. The size of the infarct resulting from ischemia-reperfusion was increased 12 h after whole-body hyperthermia (42 degrees C for 15 min), but was significantly decreased 48 and 72 h after hyperthermia, compared with the sham control. The infarct size was decreased as late as 96 h after hyperthermia, although the infarct-limiting effect was smaller at that time. The myocardial content of hsp72 was markedly increased for 3-72 h after hyperthermic treatment, and was decreased after 72 h in association with an increase in the infarct size. The hsp72 content remained elevated during the period of tolerance to ischemia-reperfusion injury, but the infarct size decreased after the hsp72 content peaked. Pretreatment with a protein kinase C (PKC) inhibitor, chelerythrine chloride, immediately before hyperthermia, significantly suppressed the delayed cardioprotective effect of hyperthermia and reduced hsp72 induction. These results suggest that newly synthesized hsp72 through PKC activation after heat stress may have to be post-translationally modified and compartmentalized prior to assuming to the development of the delayed tolerance to ischemia-reperfusion injury in rats.

Animals↗

PubMed1996

The transcriptional regulation of heat shock genes: a plethora of heat shock factors and regulatory conditions.

The inducible regulation of heat shock gene transcription is mediated by a family of heat shock factors (HSF) that respond to diverse forms of physiological and environmental stress including elevated temperature, amino acid analogs, heavy metals, oxidative stress, anti-inflammatory drugs, arachidonic acid, and a number of pathophysiological disease states. The vertebrate genome encodes a family of HSFs which are expressed ubiquitously, yet the DNA binding properties of each factor are negatively regulated and activated in response to specific conditions. This chapter will discuss the regulation of the HSF multi-gene family and the role of these transcriptional activators in the inducible expression of genes encoding heat shock proteins and molecular chaperones.

DNA-Binding Proteins↗

PubMed2000

Trichomonas vaginalis: analysis of a heat-inducible member of the cytosolic heat-shock-protein 70 multigene family.

A 2253-nucleotide (nt) transcript for a Trichomonas vaginalis heat-shock protein 70, TVCHSP70, has been isolated that encodes for a protein of 659 amino acids with a predicted molecular weight of 71.3 kDa. TVCHSP70 has a short (10-nt) 5' untranslated region (UTR), and the 263-nt 3' UTR is the longest reported for a Trichomonas peptide. Amino-acid sequence analysis and phylogenetic comparison identifies TVCHSP70 as a member of the heat-inducible cytoplasmic HSP70 gene family. Southern-blot data indicate that T. vaginalis contains at least four members of the cytoplasmic HSP70 gene family. Members of the TVCHSP70 family are expressed as 2.3-kb transcripts at low levels during 37 degrees C culture, and their expression is significantly up-regulated at 43 degrees C. Slot-blot analysis of seven T. vaginalis clinical isolates demonstrated a 3- to 44-fold up-regulation of TVCHSP70 under conditions of heat shock (43 degrees C) or oxidative stress (500 microm H2O2) as compared with controls (37 degrees C).

Animals↗

PubMed2004

The gene for the heat-shock protein HSP100 is induced by blue light and heat-shock in the fungus Phycomyces blakesleeanus.

We cloned and sequenced the Phycomyces hspA gene. The hspA gene product is a 901-amino-acid protein member of the clpB/HSP100 family. HSP100 proteins are ATPases involved in high-temperature tolerance, proteolysis, and protein disaggregation. Phycomyces HSP100 is composed of a domain presumably involved in protein-protein interactions and two ATP-binding domains. The hspA promoter contains three heat-shock elements that are presumably involved in the activation of hspA after heat-shock. In addition, four short sequences are present in the hspA promoter and in the promoter of the photoinducible genes carB and carRA; and these are candidates as binding sites for light-regulated transcription factors. Blue light can increase transcription of the hspA gene 10-fold, with a threshold of 1 J/m2. The threshold for hspA photoactivation is 10(4) times higher than the thresholds for blue-light regulation of sporangiophore development and photocarotenogenesis, which suggests that there are differences in the photosensory systems for gene photoactivation and mycelial photoresponses. A heat-shock of 30 min at 34 degrees C or 42 degrees C increased hspA gene activity 160-fold. The differences in maximum hspA gene transcription by blue light and heatshock suggest the presence of different regulatory mechanisms.

Adenosine Triphosphatases↗

PubMed2000

Heat and chemical shock potentiation of glucocorticoid receptor transactivation requires heat shock factor (HSF) activity. Modulation of HSF by vanadate and wortmannin.

Heat shock and other forms of stress increase glucocorticoid receptor (GR) activity in cells, suggesting cross-talk between the heat shock and GR signal pathways. An unresolved question concerning this cross-talk is whether heat shock factor (HSF1) activity is required for this response. We addressed this issue by modulating HSF1 activity with compounds acting by distinct mechanisms: sodium vanadate (SV), an inhibitor of protein phosphatases; and wortmannin, an inhibitor of DNA-dependent protein kinase. Using HSF1- and GR-responsive CAT reporters, we demonstrate that SV inhibits both HSF1 activity and the stress potentiation of GR, while having no effect on the hormone-free GR or HSF1. Paradoxically, SV increased hormone-induced GR activity in the absence of stress. In contrast, wortmannin increased HSF1 activity in stressed cells and had no effect on HSF1 in the absence of stress. Using the pMMTV-CAT reporter containing the negative regulatory element 1 site for DNA-dependent protein kinase, wortmannin was found to increase the GR response. However, in cells expressing a minimal promoter lacking negative regulatory element 1 sites, wortmannin had no effect on the GR in the absence of stress but increased the stress potentiation of GR. Our results show that the mechanism by which GR activity is increased in stressed cells requires intrinsic HSF1 activity.

3T3 Cells↗

PubMed1996

Response of two heat shock genes to selection for knockdown heat resistance in Drosophila melanogaster.

To identify genes involved in stress resistance and heat hardening, replicate lines of Drosophila melanogaster were selected for increased resistance to knockdown by a 39 degrees heat stress. Two selective regimes were used, one with and one without prior hardening. Mean knockdown times were increased from approximately 5 min to > 20 min after 18 generations. Initial realized heritabilities were as high as 10% for lines selected without hardening, and crosses between lines indicated simple additive gene effects for the selected phenotypes. To survey allelic variation and correlated selection responses in two candidate stress genes, hsr-omega and hsp68, we applied denaturing gradient gel electrophoresis to amplified DNA sequences from small regions of these genes. After eight generations of selection, allele frequencies at both loci showed correlated responses for selection following hardening, but not without hardening. The hardening process itself was associated with a hsp68 frequency change in the opposite direction to that associated with selection that followed hardening. These stress loci are closely linked on chromosome III, and the hardening selection established a disequilibrium, suggesting an epistatic effect on resistance. The data indicate that molecular variation in both hsr-omega and.hsp68 contribute to natural heritable variation for hardened heat resistance.

Alcohol Dehydrogenase↗

PubMed1994

Fine structure analyses of the Drosophila and Saccharomyces heat shock factor--heat shock element interactions.

Heat shock genes are activated by the binding of the heat shock transcription factor (HSF) to heat shock elements (HSEs), consisting of arrays of the 5-bp unit NGAAN arranged as inverted repeats. Here, we have investigated the interaction of the 5-bp unit with HSFs of Drosophila and Saccharomyces. Mutations within the conserved, central trinucleotide GAA reduce the relative binding affinity of both HSFs. In addition, the base at position 1 (N1) also influences binding, with a strong preference for an A at this position. Methylation interference initially indicated that HSF contacts A1 in the minor groove, but interacts with the immediately adjacent base G2 in the major groove. Further characterization of this apparently abrupt minor to major groove transition by substitution of A1 with an inosine, shows that HSF contacts A1 in the major groove. We offer an explanation for this apparent contradiction and propose that HSF recognizes the HSE primarily through contacts within the major groove of the DNA helix. Finally, based on these observations and a re-evaluation of the base frequencies and criteria for consensus sequence assignment, we propose that the sequence AGAAN more accurately represents the consensus HSE motif.

Animals↗

PubMed1994

CIRCE, a novel heat shock element involved in regulation of heat shock operon dnaK of Bacillus subtilis.

The dnaK and groESL operons of Bacillus subtilis are preceded by a potential sigma 43 promoter sequence (recognized by the vegetative sigma factor) and by an inverted repeat (IR) consisting of 9 bp separated by a 9-bp spacer. Since this IR has been found in many bacterial species, we suspected that it might be involved in heat shock regulation. In order to test this hypothesis, three different mutational alterations of three bases were introduced within the IR preceding the dnaK operon. These mutations were crossed into the chromosome of B. subtilis, and expression of the dnaK and of the unlinked groESL operons was studied. The dnaK operon exhibited increased expression at low temperature and a reduction in the stimulation after temperature upshift. Furthermore, these mutations reduced expression of the groESL operon at low temperature by 50% but did not interfere with stimulation after heat shock. These experiments show that the IR acts as a negative cis element of the dnaK operon. This conclusion was strengthened by the observation that the IR reduced expression of two different transcriptional fusions significantly after its insertion between the promoter and the reporter gene. Since this IR has been described in many bacterial species as preceding only genes of the dnaK and groESL operons, both encoding molecular chaperones (39 cases are documented so far), we designated this heat shock element CIRCE (controlling IR of chaperone expression). Furthermore, we suggest that this novel mechanism is more widespread among eubacteria than the regulation mechanism described for Escherichia coli and has a more ancient origin.

Bacillus subtilis↗

PubMed1993

Mouse heat shock transcription factors 1 and 2 prefer a trimeric binding site but interact differently with the HSP70 heat shock element.

To understand the function of multiple heat shock transcription factors in higher eukaryotes, we have characterized the interaction of recombinant mouse heat shock transcription factors 1 and 2 (mHSF1 and mHSF2) with their binding site, the heat shock element (HSE). For our analysis, we utilized the human HSP70 HSE, which consists of three perfect 5'-nGAAn-3' sites (1, 3, and 4) and two imperfect sites (2 and 5) arranged as tandem inverted repeats. Recombinant mHSF1 and mHSF2, which exist as trimers in solution, both bound specifically to this HSE and stimulated transcription of a human HSP70-CAT construct in vitro. Footprinting analyses revealed differential binding of mHSF1 and mHSF2 to the HSP70 HSE. Specifically, mHSF1 bound all five pentameric sites, whereas mHSF2 failed to interact with the first site of the HSE but bound to sites 2 to 5. Missing-nucleoside analysis demonstrated that the third and fourth nGAAn sites were essential for mHSF1 and mHSF2 binding. The binding of the initial mHSF1 trimer to the HSE exhibited preference for sites 3, 4, and 5, and then binding of a second trimer occurred at sites 1 and 2. These results suggest that HSF may recognize its binding site through the dyad symmetry of sites 3 and 4 but requires an adjacent site for stable interaction. Our data demonstrate that mHSF1 and mHSF2 bind specifically to the HSE through major groove interactions. Methidiumpropyl-EDTA footprinting revealed structural differences in the first and third repeats of the HSE, suggesting that the DNA is distorted in this region. The possibility that the HSE region is naturally distorted may assist in understanding how a trimer of HSF can bind to what is essentially an inverted repeat binding site.

Animals↗

PubMed2004

Evidence for a role of heat shock factor 1 in inhibition of NF-kappaB pathway during heat shock response-mediated lung protection.

Heat shock transcription factor (HSF)-1 is recognized as a central component of the heat shock response, which protects against various harmful conditions. However, the mechanisms underlying the protection and the role of HSF-1 in these mechanisms have not yet been clearly elucidated. Using HSF-1 knockout mice (Hsf1(-/-)), we examined whether heat shock response-mediated lung protection involved an inhibition of the proinflammatory pathway via an interaction between HSF-1 and NF-kappaB, in response to cadmium insult. The HSF-1-dependent protective effect against intranasal instillation of cadmium (10 and 100 microg/mouse) was demonstrated by the higher protein content (1.2- and 1.4-fold), macrophage (1.6- and 1.9-fold), and neutrophil (2.6- and 1.8-fold) number in bronchoalveolar fluids, higher lung wet-to-dry weight ratio, and more severe lung damage evaluated by histopathology in Hsf1(-/-) compared with wild-type animals. These responses were associated with higher granulocyte/macrophage colony-stimulating factor (GM-CSF; 1.7-fold) but not TNF-alpha concentrations in bronchoalveolar fluids of Hsf1(-/-) mice compared with those of wild-type animals, indicating that HSF-1 behaved as a repressor of specific cytokine production in our model. To further investigate the mechanism of GM-CSF repression, we analyzed the NF-kappaB activity and IkappaB stability. The DNA binding NF-kappaB activity, in particular p50 homodimer activity, was higher in Hsf1(-/-) mice than in wild-type mice after cadmium exposure. These results provide a first line of evidence that mechanisms of lung protection depending on HSF-1 involve specific cytokine repression via inhibition of NF-kappaB activation in vivo.

Administration, Intranasal↗