Disruption of the HSF3 gene results in the severe reduction of heat shock gene expression and loss of thermotolerance

HSF1 is required for cellular adaptation to daily temperature fluctuations

The heat shock response (HSR) is a universal mechanism of cellular adaptation to elevated temperatures and is regulated by heat shock transcription factor 1 (HSF1) or HSF3 in vertebrate endotherms, such as humans, mice, and chickens. We here showed that HSF1 and HSF3 from egg-laying mammals (monotremes), with a low homeothermic capacity, equally possess a potential to maximally induce the HSR, whereas either HSF1 or HSF3 from birds have this potential. Therefore, we focused on cellular adaptation to daily temperature fluctuations and found that HSF1 was required for the proliferation and survival of human cells under daily temperature fluctuations. The ectopic expression of vertebrate HSF1 proteins, but not HSF3 proteins, restored the resistance in HSF1-null cells, regardless of the induction of heat shock proteins. This function was associated with the up-regulation of specific HSF1-target genes. These results indicate the distinct role of HSF1 in adaptation to thermally fluctuating environments and suggest association of homeothermic capacity with functional diversification of vertebrate HSF genes.

Heat Shock Response and Heat Shock Proteins: Current Understanding and Future Opportunities in Human Diseases

The heat shock response is an evolutionarily conserved mechanism that protects cells or organisms from the harmful effects of various stressors such as heat, chemicals toxins, UV radiation, and oxidizing agents. The heat shock response triggers the expression of a specific set of genes and proteins known as heat shock genes/proteins or molecular chaperones, including HSP100, HSP90, HSP70, HSP60, and small HSPs. Heat shock proteins (HSPs) play a crucial role in thermotolerance and aiding in protecting cells from harmful insults of stressors. HSPs are involved in essential cellular functions such as protein folding, eliminating misfolded proteins, apoptosis, and modulating cell signaling. The stress response to various environmental insults has been extensively studied in organisms from prokaryotes to higher organisms. The responses of organisms to various environmental stressors rely on the intensity and threshold of the stress stimuli, which vary among organisms and cellular contexts. Studies on heat shock proteins have primarily focused on HSP70, HSP90, HSP60, small HSPs, and ubiquitin, along with their applications in human biology. The current review highlighted a comprehensive mechanism of heat shock response and explores the function of heat shock proteins in stress management, as well as their potential as therapeutic agents and diagnostic markers for various diseases.

Involvement of the heat shock response (HSR) regulatory pathway in cadmium-elicited cerebral damage

The heat shock response (HSR) is a cellular protective mechanism that is characterized by the induction of heat shock transcription factors (HSFs) and heat shock proteins (HSPs) in response to diverse cellular and environmental stressors, including cadmium (Cd). However, little is known about the relationship between the damaging effects of Cd and the HSR pathway in the chicken cerebrum following Cd exposure. To explore whether Cd exposure elicits cerebral damage and triggers the HSR pathway, chicks were exposed to Cd in the daily diet at different concentrations (35, 70, or 140 mg/kg feed) for 90 days, while a control group was fed the standard diet without Cd. Histopathological examination of cerebral tissue from Cd-exposed chickens showed neuronal damage, as evidenced by swelling and degeneration of neurons, loss of neurons, and capillary damage. Cd exposure significantly increased mRNA expression of HSF1, HSF2, and HSF3, and mRNA and protein expression of three major stress-inducible HSPs (HSP60, HSP70, and HSP90). Moreover, Cd exposure differentially modulated mRNA expression of small HSP (sHSPs), most notably reducing expression of HSP27 (HSPB1). Furthermore, Cd exposure increased TUNEL-positive neuronal apoptotic cells and up-regulated protein expression of caspase-1, caspase-8, caspase-3, and p53, leading to apoptosis. Taken together, these data demonstrate that activation of the HSR and apoptotic pathways by Cd exposure is involved in Cd-elicited cerebral damage in the chicken. Synopsis for the graphical abstract Cadmium (Cd)-induced neuronal damage triggers the heat shock response (HSR) by activating heat shock transcription factors (HSFs) and subsequent induction of major heat shock proteins (notably, HSP60, HSP70, and HSP90). Moreover, Cd exposure activates caspase-1, caspase-8, caspase-3, and p53 protein, thereby resulting in neuronal apoptosis in the chicken brain.

Role of Heat Shock Factors in Stress-Induced Transcription: An Update

Heat shock proteins (HSP) are rapidly induced after proteotoxic stresses such as heat shock and accumulate at high concentrations in cells. HSP induction involves primarily a family of heat shock transcription factors (HSF) that bind the heat shock elements of the HSP genes and mediate transcription in trans. We discuss methods for the study of HSP binding to HSP promoters and the consequent increases in HSP gene expression in vitro and in vivo.

Impacts of Embryonic Thermal Programming on the Expression of Genes Involved in Foie gras Production in Mule Ducks

Embryonic thermal programming has been shown to improve foie gras production in overfed mule ducks. However, the mechanisms at the origin of this programming have not yet been characterized. In this study, we investigated the effect of embryonic thermal manipulation (+1°C, 16 h/24 h from embryonic (E) day 13 to E27) on the hepatic expression of genes involved in lipid and carbohydrate metabolisms, stress, cell proliferation and thyroid hormone pathways at the end of thermal manipulation and before and after overfeeding (OF) in mule ducks. Gene expression analyses were performed by classic or high throughput real-time qPCR. First, we confirmed well-known results with strong impact of OF on the expression of genes involved in lipid and carbohydrates metabolisms. Then we observed an impact of OF on the hepatic expression of genes involved in the thyroid pathway, stress and cell proliferation. Only a small number of genes showed modulation of expression related to thermal programming at the time of OF, and only one was also impacted at the end of the thermal manipulation. For the first time, we explored the molecular mechanisms of embryonic thermal programming from the end of heat treatment to the programmed adult phenotype with optimized liver metabolism.

Physiological Functions of Heat Shock Proteins

Heat shock proteins (HSPs) are molecular chaperones involved in a variety of life activities. HSPs function in the refolding of misfolded proteins, thereby contributing to the maintenance of cellular homeostasis. Heat shock factor (HSF) is activated in response to environmental stresses and binds to heat shock elements (HSEs), promoting HSP translation and thus the production of high levels of HSPs to prevent damage to the organism. Here, we summarize the role of molecular chaperones as anti-heat stress molecules and their involvement in immune responses and the modulation of apoptosis. In addition, we review the potential application of HSPs to cancer therapy, general medicine, and the treatment of heart disease.

Dietary supplementation of dried plum: a novel strategy to mitigate heat stress in broiler chickens

Background

Heat stress is a significant problem in the poultry industry, causing a severe economic loss due to its detrimental effects on chickens’ health and performance. Dried plum (DP) is a good source of minerals, vitamins, antioxidants, and phenolic compounds. Studies have suggested that DP has several health benefits, such as maintaining the body’s redox system, immune status, and calcium hemostasis. Based on the health benefits of DP, we hypothesized that the dietary supplementation of DP would alleviate the detrimental effects of heat stress on broiler chickens.

Results

To test the hypothesis, day-old broiler chicks (n = 72) were randomly allocated to three treatment groups (n = 24/group): no heat stress (NHS), heat stress (HS), and heat stress with dried plum (HS + DP), and reared under standard conditions. The inclusion of 2.5% DP in the feed of the HS + DP group was made during the treatment period, while birds in other groups were provided with a standard finisher diet. After 21 days, birds in the HS and HS + DP groups were exposed to cyclic heat stress conditions (33 °C for 8 h during daytime) for 3 weeks, while those in the NHS group were reared under normal conditions (22–24 °C). Weekly body weight and feed intake were recorded to calculate the average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR). Heat stress significantly decreased the final body weight, ADG, ADFI, and increased FCR compared to the NHS group, whereas dietary supplementation of DP significantly improved these growth performance parameters compared to the HS group. Furthermore, supplementation of DP significantly increased the expression of heat shock protein-related genes (HSF1, HSF3, HSP70, and HSP90), antioxidant-related genes (SOD1, SOD2, GPX1, GPX3, PRDX1, and TXN), tight junction-related genes (CLDN1, and OCLN), and immune-related genes (IL4, MUC2) in the ileum as compared to the HS group. The microbiota analysis showed significant enrichment of Bacillales, Christensenellaceae, Bacillaceae, Peptostreptococcaceae, and Anaerotruncus in heat-stressed birds supplemented with DP as compared to the HS group. Further, DP supplementation also significantly increased the concentration of acetate, propionate, and total VFA in the cecal digesta of the HS + DP group as compared to the HS group.

Conclusion

These findings suggest that DP supplementation effectively improved the growth performances and gut health parameters in the heat-stressed birds. Thus, dried plum can be a potential feed supplement to mitigate heat stress in broiler chickens.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00571-5.

Enriched environment housing improved the laying hen's resistance to transport stress via modulating the heat shock protective response and inflammation

An enriched environment can promote adaptability of animals to cope with complex environments. A total of 18-week-old 216 laying hens were randomly divided into 2 groups; of which, one group was housed in conventional battery cages (CC, n = 36), and the others were housed in furnished cages (FC, n = 180). At the end of 64 wk of age, 24 chickens of each group were selected for 4-hour transport treatment. The spleen tissues of laying hens were collected before transportation (BT), immediately after transportation, and at 48 h after transportation to detect the expression of the heat shock protective response signaling pathway and inflammatory factors. Serum samples were collected to detect the content of immune cytokines. Transport stress decreased heat shock proteins (HSP; including Small HSP, HSP27, HSP40, HSP60, HS70, HSP90, HSP110) in the CC group (P < 0.05), whereas there was no significant difference in the expression of HSP (except for Small HSP and HSP40) in the FC group (P > 0.05) immediately after transportation. At 48 h after transportation, mRNA levels of HSP (except for Small HSP and HSP40) in the FC group were upregulated, which were higher than those at BT (P < 0.05). The changes in HSP60, HSP70, and HSP90 protein levels had similar tendencies. The results showed that housing in furnished cages alleviated the inhibition of expression of HSP in the hens' spleen induced by transport stress. In addition, the hens housed in the FC group had lower expression levels of proinflammatory factors (nuclear transcription factor-kappa B, inducible nitric oxide synthase, cyclooxygenase-2, prostaglandin E synthase, inflammatory cytokines [IL-1β and IL-6], and tumor necrosis factor alpha) (P < 0.05). We suggest that the enriched environment can reduce transport stress damage in laying hens and improve resistance to transport stress by regulating expression of heat shock response proteins and inflammatory cytokines.

HSF3 and Hsp70 Expression during Post-Hatch Cold Stress in Broiler Chickens Subjected to Embryonic Thermal Manipulation

Decades of selective breeding for commercial purposes have rendered the broiler chicken (Gallus gallus domesticus) highly susceptible to heat and cold stress. A multitude of studies have documented the effects of thermal manipulation (TM) on broiler thermotolerance during periods of post-hatch heat stress, but very few have focused on the effect of TM on a broiler’s ability to withstand cold stress. Therefore, the primary objective of the current study is to determine the effects of TM on the acquisition of thermotolerance in broilers via their expression of the stress-associated 70 kilodalton heat shock protein (Hsp70) gene and heat shock factor 3 (HSF3) gene. Briefly, Hubbard broiler embryos were subject to TM by increasing the incubation temperature to 39 °C and 65% relative humidity (RH) for 18 h daily, from embryonic days (ED) 10 to 18. Broilers were then exposed to cold stress by decreasing the room temperature to 16 °C during post-hatch days 32 to 37. After thermal challenge, broilers were euthanized and hepatic and splenic tissues were collected. Our results showed that TM decreased the hatchability rate and body temperature but improved the body weight gain. TM generally decreased the hepatic expression but did not change the splenic expression of HSF3 during cold stress. In contrast, both hepatic and splenic Hsp70 expression decreased during cold stress. The results of the present study may suggest that TM significantly affects a broiler’s genetic response to cold stress.

The "HSF connection": Pleiotropic regulation and activities of Heat Shock Factors shape pathophysiological brain development

The Heat Shock Factors (HSFs) have been historically identified as a family of transcription factors that are activated and work in a stress-responsive manner, after exposure to a large variety of stimuli. However, they are also critical in normal conditions, in a life long manner, in a number of physiological processes that encompass gametogenesis, embryonic development and the integrity of adult organs and organisms. The importance of such roles is emphasized by the devastating impact of their deregulation on health, ranging from reproductive failure, neurodevelopmental disorders, cancer, and aging pathologies, including neurodegenerative disorders. Here, we provide an overview of the delicate choreography of the regulation of HSFs during neurodevelopment, at prenatal and postnatal stages. The regulation of HSFs acts at multiple layers and steps, and comprises the control of (i) HSF mRNA and protein levels, (ii) HSF activity in terms of DNA-binding and transcription, (iii) HSF homo- and hetero-oligomerization capacities, and (iv) HSF combinatory set of post-translational modifications. We also describe how these regulatory mechanisms operate in the normal developing brain and how their perturbation impact neurodevelopment under prenatal or perinatal stress conditions. In addition, we put into perspective the possible role of HSFs in the evolution of the vertebrate brains and the importance of the HSF pathway in a large variety of neurodevelopmental disorders.

Tailoring of Proteostasis Networks with Heat Shock Factors

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

Co-enzyme Q10 protects chicken hearts from in vivo heat stress via inducing HSF1 binding activity and Hsp70 expression

In this report, we investigated the protective function of co-enzyme Q10 on chicken hearts during in vivo heat stress (HS) and the relationship with Hsp70 expression. The concentration of co-enzyme Q10 (Q10) in the serum indicated that Q10 exogenously added prior HS was fully absorbed by chickens and is maintained at high levels during HS. The level of heart and oxidative damage-associated enzymes in the serum revealed that treatment with Q10 decreased the activity of CK-MB, CK, and LDH compared with the HS group; moreover, oxidative injury was also alleviated by Q10 according to the level of SOD, MDA, and T-AOC in the serum compared with HS group during heat stress. A pathological examination indicated that the chicken hearts suffered serious damage during HS, including hemorrhage, granular changes, karyopyknosis, and cardiac muscle fiber disorder; however, the extent of heart damage was reduced in HS + Q10 group. Our results indicated that the addition of Q10 could upregulate the expression of Hsp70 during HS compared with the HS group. Compared with the HS group, the addition of Q10 significantly increased the gene expression of hsf1 during HS and hsf3 at 5 h of HS. The expression of hsf2 and hsf4 was not influenced by HS. Q10 could only accelerate the trimerization of HSF1 as well binding activities to Hsp70 HSE according to native page and ChIP assays. These findings suggest that co-enzyme Q10 can protect chicken hearts from in vivo HS by inducing HSF1 binding activity and Hsp70 expression.

Gordon H. Dixon's trace in my personal career and the quantic jump experienced in regulatory information

Even before Rosalin Franklin had discovered the DNA double helix, in her impressive X-ray diffraction image pattern, Erwin Schröedinger, described, in his excellent book, What is Life, how the finding of aperiodic crystals in biological systems surprised him (an aperiodic crystal, which, in my opinion is the material carrier of life). In the 21st century and still far from being able to define life, we are attending to a quick acceleration of knowledge on regulatory information. With the discovery of new codes and punctuation marks, we will greatly increase our understanding in front of an impressive avalanche of genomic sequences. Trifonov et al. defined a genetic code as a widespread DNA sequence pattern that carries a message with an impact on biology. These patterns are largely captured in transcribed messages that give meaning and identity to the particular cells. In this review, I will go through my personal career in and after my years of work in the laboratory of Gordon H. Dixon, extending toward the impressive acquisition of new knowledge on regulatory information and genetic codes provided by remarkable scientists in the field. Abbreviations: CA II: carbonic anhydridase II (chicken); Car2: carbonic anhydridase 2 (mouse); CpG islands: short (>0.5 kb) stretches of DNA with a G+C content ≥55%; DNMT1: DNA methyltransferases 1; DNMT3b: DNA methyltransferases 3B; DSB: double-strand DNA breaks; ERT: endogenous retrotransposon; ERV: endogenous retroviruses; ES cells: embryonic stem cells; GAPDH: glyceraldehide phosphate dehydrogenase; H1: histone H1; HATs: histone acetyltransferases; HDACs: histone deacetylases; H3K4me3: histone 3 trimethylated at lys 4; H3K79me2: histone 3 dimethylated at lys 79; HMG: high mobility group proteins; HMT: histone methyltransferase; HP1: heterochromatin protein 1; HR: homologous recombination; HSE: heat-shock element; ICRs: imprinted control regions; IRF: interferon regulatory factor; LDH-A/-B: lactate dehydrogenase A/B; LTR: long terminal repeats; MeCP2: methyl CpG binding protein 2; OCT4: octamer-binding transcription factor 4; PAF1: RNA Polymerase II associated factor 1; piRNA: PIWI-interacting RNA; poly(A) tails: poly-adenine tails; PRC2: polycomb repressive complex 2; PTMs: post-translational modifications; SIRT 1: sirtuin 1, silent information regulator; STAT3: signal transducer and activator of transcription; tRNAs: transfer RNA; tRFs: tRNA-derived fragments; TSS: transcription start site; TE: transposable elements; UB I: polyubiquitin I; UB II: polyubiquitin II; UBE 2N: ubiquitin conjugating enzyme E2N; 5'-UTR: 5'-untranslated sequences; 3'-UTR: 3'-untranslated sequences.

Inhibition of heat stress-related apoptosis of chicken myocardial cells through inducing Hsp90 expression by aspirin administration in vivo

1. This experiment investigated the anti-apoptosis effects and the mechanism of aspirin action in the heat shock response of chicken myocardial cells in vivo, via changes in the heat stress (HS) protein Hsp90 and the rate of apoptosis. Broiler chickens were administered aspirin (1 mg/kg body weight) 2 h before exposure to HS, and then exposed to 40 ± 1°C for 0, 1, 2, 3, 5, 7, 10, 15 and 24 h. 2. The induction and consumption of the HS factor heat shock factor (HSF)-1, and reductions of HSF-2 and HSF-3 induced by HS led to a delay in Hsp90 expression. HSF-1, 2 and 3 regulation of hsp90 expression in turn inhibited the synthesis and activation of protein kinase β (Akt), which resulted in a significant increase in caspase-3 at 2 and 10 h, caspase-9 from 1 to 7 h (except at 5 h), and the heat-stressed apoptosis of the myocardial cells. 3. Administration of aspirin changed the expression patterns of HSF-1, 2 and 3 such that the expression of Hsp90 protein was significantly upregulated (by 2.3-4.1 times compared with that of the non-treated cells). The resultant increase in Akt expression and activation, compared with the HS group, inhibited caspase-3 and caspase-9 activities and reduced the myocardial cells apoptosis rate (by 2.14-2.56 times). 4. Aspirin administration could inhibit heat-stressed apoptosis of myocardial cells in vivo and may be closely associated with its promotion of HS response of chicken hearts, especially Hsp90 expression.

Sexual Dimorphism and Aging Differentially Regulate Adaptive Homeostasis

External and internal stimuli cause modifications to gene and biochemical pathways. In turn, demonstrating that biological systems continuously make short-term adaptations both to set-points, and to the range of "normal" capacity, due to mild conditional changes, or to subtoxic, nondamaging levels of chemical agents. This is termed as "Adaptive Homeostasis," defined with the following: "The transient expansion or contraction of the homeostatic range in response to exposure to sub-toxic, nondamaging, signaling molecules or events, or the removal or cessation of such molecules or events." Research from several laboratories, including our own, found that adaptive homeostasis declines with age in organisms as diverse as worms, flies, and mammals, and decreases with senescence in mammalian cell cultures. We suggest that diminishing adaptive homeostasis may play a causal role as a factor responsible for the aging phenotype. Furthermore, although studies of humans, animals, and model organisms are often limited to a single sex, and cell culture studies may even be conducted with lines whose donor's sex was unknown, studies reveal distinct sexual dimorphism in adaptive homeostasis. Interestingly, although young males and females may exhibit dramatic differences in adaptive capacities and/or preferences, these distinctions are lost with age as adaptive homeostasis patterns converge.

Role of Heat Shock Factors in Stress-Induced Transcription

Heat shock proteins (HSP) are rapidly induced after stresses such as heat shock and accumulate at high concentrations in cells. HSP induction involves primarily a family of heat shock transcription factors (HSF) that bind the heat shock elements of the HSP genes and mediate transcription in trans. We discuss methods for the study of HSP binding to HSP promoters and the consequent increases in HSP gene expression in vitro and in vivo.

Heat stress induces expression of HSP genes in genetically divergent chickens

BACKGROUND

Chickens are animals that are sensitive to thermal stress, which may decrease their production level in terms that it affects feed intake and thus, decreasing body weight gain. The Heat Shock Factors (HSF) and Heat Shock Proteins (HSP) genes are involved in the key cellular defense mechanisms during exposure in hot environments. Aimed with this study to analyze the expression of HSF1, HSF3, HSP70 and HSP90 genes in two local breeds (Peloco and Caneluda) and a commercial broiler line (Cobb 500®) to verify differences in resistance of these chicken to Heat stress treatment. Chicken were submitted to heat stress under an average temperature of 39°C ± 1.

RESULTS

Under stress environment, the HSP70 and HSP90 genes were more expressed in backyard chickens than in broiler. There was a difference in HSP70 and HSP90 expression between Caneluda and Cobb and between Peloco and Cobb under stress and comfort environment respectively. HSP70 expression is higher in local breeds during heat stress than in a commercial broiler line. No significant differences were observed in the expression of HSF1 and HSF3 genes between breeds or environments.

CONCLUSIONS

HSP70 and HSP90 genes are highly expressed, HSF1 and HSF3 genes did not have high expression in all genetic groups. HSP70 and HSP90 are highly expressed in Peloco and Caneluda within heat stress, these breeds proved to be very resistant to high temperature.

HSF1 and HSF3 cooperatively regulate the heat shock response in lizards

Cells cope with temperature elevations, which cause protein misfolding, by expressing heat shock proteins (HSPs). This adaptive response is called the heat shock response (HSR), and it is regulated mainly by heat shock transcription factor (HSF). Among the four HSF family members in vertebrates, HSF1 is a master regulator of HSP expression during proteotoxic stress including heat shock in mammals, whereas HSF3 is required for the HSR in birds. To examine whether only one of the HSF family members possesses the potential to induce the HSR in vertebrate animals, we isolated cDNA clones encoding lizard and frog HSF genes. The reconstructed phylogenetic tree of vertebrate HSFs demonstrated that HSF3 in one species is unrelated with that in other species. We found that the DNA-binding activity of both HSF1 and HSF3 in lizard and frog cells was induced in response to heat shock. Unexpectedly, overexpression of lizard and frog HSF3 as well as HSF1 induced HSP70 expression in mouse cells during heat shock, indicating that the two factors have the potential to induce the HSR. Furthermore, knockdown of either HSF3 or HSF1 markedly reduced HSP70 induction in lizard cells and resistance to heat shock. These results demonstrated that HSF1 and HSF3 cooperatively regulate the HSR at least in lizards, and suggest complex mechanisms of the HSR in lizards as well as frogs.

Co-enzyme Q10 and acetyl salicylic acid enhance Hsp70 expression in primary chicken myocardial cells to protect the cells during heat stress

We investigated the effects of co-enzyme Q10 (Q10) and acetyl salicylic acid (ASA) on expression of Hsp70 in the protection of primary chicken myocardial cells during heat stress. Western blot analysis showed that Q10 and ASA accelerated the induction of Hsp70 when chicken myocardial cells were exposed to hyperthermia. In the absence of heat stress, however, neither Q10 nor ASA are able to upregulate Hsp70 expression. Analysis of enzymes that respond to cellular damage and pathological examination revealed that ectopic expression of ASA and Q10 alleviate cellular damage during heat stress. Quantification of heat shock factors (HSF) indicated that treatment of ASA increased the expression of HSF-1 and HSF-3 during heat stress. Treatment with Q10 resulted in the elevation of HSF-1 expression. Expression of HSF-2 and HSF-4 was not affected by ASA or Q10. Subcellular distribution analysis of HSF-1 and HSF-3 showed that in response to heat stress ASA promoted nuclear translocation of HSF-1 and HSF-3, while Q10 promoted only HSF-1 nuclear translocation. Chromatin immunoprecipitation (ChIP) analysis indicated that HSF-1 occupies the Hsp70 promoter in chicken primary myocardial cells during heat stress and under normal conditions, while HSF-3 occupies the Hsp70 promoter only during heat stress. Real-time PCR analysis revealed that ASA induces HSF-1 and HSF-3 binding to Hsp70 HSE, while Q10 only induces HSF1 binding to Hsp70 HSE, in agreement with the impact of HSF1 and HSF3 silencing on Hsp70 expression. These data demonstrate that ASA and Q10 both induce the expression of Hsp70 to protect chicken primary myocardial cells during heat stress, but through distinct pathways.

Chicken IL-6 is a heat-shock gene

The febrile response is elicited by pyrogenic cytokines including IL-6 in response to microorganism infections and diseases in vertebrates. Mammalian HSF1, which senses elevations in temperature, negatively regulates the response by suppressing pyrogenic cytokine expression. We here showed that HSF3, an avian ortholog of mammalian HSF1, directly binds to and activates IL-6 during heat shock in chicken cells. Other components of the febrile response mechanism, such as IL-1β and ATF3, were also differently regulated in mammalian and chicken cells. These results suggest that the febrile response is exacerbated by a feed-forward circuit composed of the HSF3-IL-6 pathway in birds.

Targeting heat-shock-protein 90 (Hsp90) by natural products: geldanamycin, a show case in cancer therapy

Covering 2005 to 2013. In this review recent progress in the development of heat shock proteins (Hsp90) in oncogenesis is illuminated. Particular emphasis is put on inhibitors such as geldanamycin and analogues that serve as a natural product show case. Hsp90 has emerged as an important target in cancer therapy and/or against pathogenic cells which elicit abnormal Hsp patterns. Competition for ATP by geldanamycin and related compounds abrogate the chaperone function of Hsp90. In this context, this account pursues three topics in detail: a) Hsp90 and its biochemistry, b) Hsp90 and its role in oncogenesis and c) strategies to create compound libraries of structurally complex inhibitors like geldanamycin on which SAR studies and the development of drugs that are currently in different stages of clinical testing rely.

Disruption of heat shock factor 1 reduces the formation of conidia and thermotolerance in the mycoparasitic fungus Coniothyrium minitans

Coniothyrium minitans is a bio-control agent of Sclerotinia spp., and has the ability to produce abundant conidia to infect the host fungi. Mediation of heat shock factors (HSFs) is required to adapt to the acute temperatures, and to regulate the expression of heat shock proteins (HSPs) to function as molecular chaperones to assist in development, protein folding and stability. A heat shock factor 1 (HSF1) gene was identified from a T-DNA insertion mutant that lost the ability to form conidia in liquid culture as well as on solid media. Null mutants lacking CmHSF1 were constructed by gene disruption strategy. Mutants lacking CmHSF1 had reduced in conidial production and displayed decreased tolerance to heat and other abiotic stresses as compared to the wild type parent. Over-expression strains could recover faster from heat and abiotic stresses such as, ethanol, oxidative or osmotic stresses with or without heat shock. In over-expression strains, conidial germination was increased, and parasitic ability on sclerotia of Sclerotinia sclerotiorum was enhanced by 0.42-5.92% compared to the wild type strain. Increased expression levels in wild strain ZS-1 were observed when the fungus was grown at 37°C or 45°C with other abiotic stresses. CmHSF1 plays an important role in conidial production, conidial germination, and tolerance against heat and other abiotic stresses.

Zebrafish HSF4: a novel protein that shares features of both HSF1 and HSF4 of mammals

Heat-shock proteins (hsps) have important roles in the development of the eye lens. We previously demonstrated that knockdown of hsp70 gene expression using morpholino antisense technology resulted in an altered lens phenotype in zebrafish embryos. A less severe phenotype was seen with knockdown of heat-shock factor 1 (HSF1), suggesting that, while it likely plays a role in hsp70 regulation during lens formation, other regulatory factors are also involved. Heat-shock factor 4 plays an important role in mammalian lens development, and an expressed sequence tag encoding zebrafish HSF4 has been identified. The deduced amino acid sequence shares structural similarities with mammalian HSF4 including the lack of an HR-C domain. However, the HR-C domain is absent due to a severe C-terminal truncation within zebrafish HSF4 (zHSF4) relative to the mammalian protein. Surprisingly, the amino acid composition of the zHSF4 DNA binding domain shares a greater degree of identity with HSF1 proteins than it does with mammalian HSF4 proteins. Consistent with this, the binding affinity of in vitro synthesized zHSF4 for discontinuous heat-shock response element sequences is more limited, similar to what has been previously observed for HSF1 proteins. Hsf4 mRNA is expressed in zebrafish adult eye tissue but is only observed in developing embryonic tissue at 60 h post-fertilization or later. This, together with the lack of an observable phenotype following morpholino-based antisense knockdown of hsf4, suggests that zHSF4 is unlikely to play a role in regulating early embryonic lens development.

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.

The role of heat shock factors in stress-induced transcription

Heat shock proteins (HSPs) are rapidly induced after stresses, such as heat shock, and accumulate at high concentrations in cells. HSP induction involves a family of heat shock transcription factors that bind the heat shock elements of the HSP genes and mediate transcription in trans. We discuss methods for the study of HSP binding to HSP promoters and the consequent increases in HSP gene expression in vitro and in vivo.

The heat shock factor family and adaptation to proteotoxic stress

The heat shock response was originally characterized as the induction of a set of major heat shock proteins encoded by heat shock genes. Because heat shock proteins act as molecular chaperones that facilitate protein folding and suppress protein aggregation, this response plays a major role in maintaining protein homeostasis. The heat shock response is regulated mainly at the level of transcription by heat shock factors (HSFs) in eukaryotes. HSF1 is a master regulator of the heat shock genes in mammalian cells, as is HSF3 in avian cells. HSFs play a significant role in suppressing protein misfolding in cells and in ameliorating the progression of Caenorhabditis elegans, Drosophila and mouse models of protein-misfolding disorders, by inducing the expression of heat shock genes. Recently, numerous HSF target genes were identified, such as the classical heat shock genes and other heat-inducible genes, called nonclassical heat shock genes in this study. Importance of the expression of the nonclassical heat shock genes was evidenced by the fact that mouse HSF3 and chicken HSF1 play a substantial role in the protection of cells from heat shock without inducing classical heat shock genes. Furthermore, HSF2 and HSF4, as well as HSF1, shown to have roles in development, were also revealed to be necessary for the expression of certain nonclassical heat shock genes. Thus, the heat shock response regulated by the HSF family should consist of the induction of classical as well as of nonclassical heat shock genes, both of which might be required to maintain protein homeostasis.

Heat shock factor 1 ameliorates proteotoxicity in cooperation with the transcription factor NFAT

Heat shock transcription factor 1 (HSF1) is an important regulator of protein homeostasis (proteostasis) by controlling the expression of major heat shock proteins (Hsps) that facilitate protein folding. However, it is unclear whether other proteostasis pathways are mediated by HSF1. Here, we identified novel targets of HSF1 in mammalian cells, which suppress the aggregation of polyglutamine (polyQ) protein. Among them, we show that one of the nuclear factor of activated T cells (NFAT) proteins, NFATc2, significantly inhibits polyQ aggregation in cells and is required for HSF1-mediated suppression of polyQ aggregation. NFAT deficiency accelerated disease progression including aggregation of a mutant polyQ-huntingtin protein and shortening of lifespan in R6/2 Huntington's disease mice. Furthermore, we found that HSF1 and NFAT cooperatively induce the expression of the scaffold protein PDZK3 and αB-crystallin, which facilitate the degradation of polyQ protein. These results show the first mechanistic basis for the observation that HSF1 has a much more profound effect on proteostasis than individual Hsp or combination of different Hsps, and suggest a new pathway for ameliorating protein-misfolding diseases.

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.

Analysis of HSF4 binding regions reveals its necessity for gene regulation during development and heat shock response in mouse lenses

Heat shock transcription factors (HSFs) regulate gene expression in response to heat shock and in physiological conditions. In mammals, HSF1 is required for heat-mediated induction of classic heat shock genes; however, we do not know the molecular mechanisms by which HSF4 regulates gene expression or the biological consequences of its binding to chromatin. Here, we identified that HSF4 binds to various genomic regions, including the introns and distal parts of protein-coding genes in vivo in mouse lenses, and a substantial numbers of the regions were also occupied by HSF1 and HSF2. HSF4 regulated expression of some genes at a developmental stage when HSF1 and HSF2 expression decreased. Although HSF4 binding did not affect expression of many genes, it induces demethylated status of histone H3K9 on the binding regions. Unexpectedly, a lot of HSF4 targets were induced by heat shock treatment, and HSF4 is required for induction of a set of non-classic heat shock genes in response to heat shock, in part by facilitating HSF1 binding through chromatin modification. These results suggest novel mechanisms of gene regulation controlled by HSF4 in non-classic heat shock response and in lens development.

Heat shock transcription factor 1 is required for maintenance of ciliary beating in mice

Heat shock transcription factors (HSFs) maintain protein homeostasis through regulating expression of heat shock proteins, especially in stressed conditions. In addition, HSFs are involved in cellular differentiation and development by regulating development-related genes, as well as heat shock genes. Here, we showed chronic sinusitis and mild hydrocephalus in postnatal HSF1-null mice, which are associated with impaired mucociliary clearance and cerebrospinal flow, respectively. Analysis of ciliary beating revealed that the amplitude of the beating was significantly reduced, and ciliary beat frequencies were lower in the respiratory epithelium, ependymal cells, oviduct, and trachea of HSF1-null mice than those of wild-type mice. Cilia possess a common axonema structure composed of microtubules of alpha- and beta-tubulin. We found a marked reduction in alpha- and ciliary betaiv-tubulin in the HSF1-null cilia, which is developmentally associated with reduced Hsp90 expression in HSF1-null mice. Treatment of the respiratory epithelium with geldanamycin resulted in rapid reduction of ciliary beating in a dose-dependent manner. Furthermore, Hsp90 was physically associated with ciliary betaiv-tubulin, and Hsp90 stabilizes tubulin polymerization in vitro. These results indicate that HSF1 is required to maintain ciliary beating in postnatal mice, probably by regulating constitutive expression of Hsp90 that is important for tubulin polymerization.

Heat shock transcription factor 1 opens chromatin structure of interleukin-6 promoter to facilitate binding of an activator or a repressor

Heat shock transcription factor 1 (HSF1) not only regulates expression of heat shock genes in response to elevated temperature, but is also involved in developmental processes by regulating genes such as cytokine genes. However, we did not know how HSF1 regulates non-heat shock genes. Here, we show that constitutive HSF1 binding to the interleukin (IL)-6 promoter is necessary for its maximal induction by lipopolysaccharide (LPS) stimulation in mouse embryo fibroblasts and peritoneal macrophages. Lack of HSF1 inhibited LPS-induced in vivo binding of an activator NF-kappaB and a repressor ATF3 to IL-6 promoter. Neither NF-kappaB nor ATF3 binds to the IL-6 promoter in unstimulated HSF1-null cells even if they were overexpressed. Treatment with histone deacetylase inhibitor or a DNA methylation inhibitor restored LPS-induced IL-6 expression in HSF1-null cells, and histone modification enzymes were recruited on the IL-6 promoter in the presence of HSF1. Consistently, chromatin structure of the IL-6 promoter in the presence of HSF1 was more open than that in its absence. These results indicate that HSF1 partially opens the chromatin structure of the IL-6 promoter for an activator or a repressor to bind to it, and provides a novel mechanism of gene regulation by HSF1.

Chaperone regulation of the heat shock protein response

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

A novel HSF1-mediated death pathway that is suppressed by heat shock proteins

Heat shock response is an adoptive response to proteotoxic stress, and a major heat shock transcription factor 1 (HSF1) has been believed to protect cells from cell death by inducing heat shock proteins (Hsps) that assist protein folding and prevent protein denaturation. However, it is revealed recently that HSF1 also promotes cell death of male germ cells. Here, we found a proapoptotic Tdag51 (T-cell death associated gene 51) gene as a direct target gene of HSF1. Heat shock and other stresses induced different levels of Hsps and Tdag51, which depend on cell types. Hsps bound directly to the N-terminal pleckstrin-homology like (PHL) domain of Tdag51, and suppressed death activity of the C-terminal proline/glutamine/histidine-rich domain. Tdag51, but not major Hsps, were induced in male germ cells exposed to high temperatures. Analysis of Tdag51-null testes showed that Tdag51 played substantial roles in promoting heat shock-induced cell death in vivo. These data suggest that cell fate on proteotoxic condition is determined at least by balance between Hsp and Tdag51 levels, which are differently regulated by HSF1.

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

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

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

BACKGROUND

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

SCOPE

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

Thermoprotection of synaptic transmission in aDrosophilaheat shock factor mutant is accompanied by increased expression of Hsp83 and DnaJ-1

In Drosophila larvae, acquired synaptic thermotolerance after heat shock has previously been shown to correlate with the induction of heat shock proteins (Hsps) including HSP70. We tested the hypothesis that synaptic thermotolerance would be significantly diminished in a temperature-sensitive strain ( Drosophila heat shock factor mutant hsf4), which has been reported not to be able to produce inducible Hsps in response to heat shock. Contrary to our hypothesis, considerable thermoprotection was still observed at hsf4larval synapses after heat shock. To investigate the cause of this thermoprotection, we conducted DNA microarray experiments to identify heat-induced transcript changes in these organisms. Transcripts of the hsp83, dnaJ-1 ( hsp40), and glutathione- S-transferase gstE1 genes were significantly upregulated in hsf4larvae after heat shock. In addition, increases in the levels of Hsp83 and DnaJ-1 proteins but not in the inducible form of Hsp70 were detected by Western blot analysis. The mode of heat shock administration differentially affected the relative transcript and translational changes for these chaperones. These results indicate that the compensatory upregulation of constitutively expressed Hsps, in the absence of the synthesis of the major inducible Hsp, Hsp70, could still provide substantial thermoprotection to both synapses and the whole organism.

Depletion of hsp90beta induces multiple defects in B cell receptor signaling

Hsp90 participates in many distinct aspects of cellular functions and accomplishes these roles by interacting with multiple client proteins. To gain insight into the interactions between Hsp90 and its clients, here we have reduced the protein level of Hsp90 in avian cells by gene targeting in an attempt to elicit the otherwise undetectable (because of the vast amount of cellular Hsp90) Hsp90-interacting proteins. Hsp90beta-deficient cells can grow, albeit more slowly than wild-type cells. B cell antigen receptor signaling is multiply impaired in these mutant cells; in particular, the amount of immunoglobulin M heavy chain protein is markedly reduced. Furthermore, serum activation does not promote ERK phosphorylation in Hsp90beta-deficient cells. These multifaceted depressive effects seem to be provoked independently of each other and possibly recapitulate the proteome-wide in vivo functions of Hsp90. Reintroduction of the Hsp90beta gene efficiently restores all of the defects. Unexpectedly, however, introducing the Hsp90alpha gene is also effective in restoration; thus, these defects might be caused by a reduction in the total expression of Hsp90 rather than by loss of Hsp90beta-specific function.

Clustering of heat-shock factors

Clusterin is a ubiquitous glycoprotein found in most physiological fluids and tissues. Although not fully understood, the function of clusterin seems to be related to its ability to bind a wide variety of molecules. Since clusterin has been found associated with extracellular protein aggregates, a role as a molecular chaperone has been proposed. In this issue of the Biochemical Journal, Le Dréan and colleagues demonstrate an up-regulation of clusterin in neuronal cells exposed to proteotoxic stress that results in unfolded protein accumulation and proteasome impairment, both commonly associated with neurodegenerative diseases. Interestingly, expression of clusterin was found to be regulated by two members of the HSF (heat-shock factor) family, HSF1 and HSF2, which possibly form a trimeric complex on the clusterin promoter. The study proposes clusterin as a player in a cellular defence mechanism against harmful protein accumulation, and highlights the importance of elucidating further the exact role of clusterin and the intriguing interaction between HSF1 and HSF2.

Feedback regulation of the heat shock response

The heat shock response is triggered primarily by nonnative proteins accumulating in a stressed cell and results in increased expression of heat shock proteins (Hsps), i.e., of chaperones capable of participating in the refolding or elimination of nonnative proteins. Best known is the transcriptional part of this response that is mediated predominantly by heat shock factor 1 (HSF1). HSF1 activity is regulated at different levels by Hsps and co-chaperones and is modulated further by a number of mechanisms involving other stress-regulated aspects of cell metabolism.

HSFs in development

Heat shock transcription factors, as well as heat shock proteins, are involved in different steps in differentiation and development, in addition to their role in adaptation to stress. This has already been demonstrated in the case of the single heat shock factor present in Drosophila. Over the last 6 years, similar observations have accumulated from the progressive inactivation of the different hsf genes in mammals, the use of double-null animals, and the slow characterization of their complex phenotypes. Although these studies are not yet complete, the data so far can be used to draw some conclusions. All hsf genes contribute to development in mammals and to normal functions at the adult stage, by controlling the expression of Hsp and non-Hsp genes. Reproduction, the immune response and aging are the processes that are the most deeply affected. An attractive hypothesis would be that these new functions have been recruited during evolution in order to coordinate these processes: HSFs may occupy a central place in the trade off that organisms make between reproduction and maintenance, in response to the variations in the environment.

Radiosensitization by hyperthermia in the chicken B-lymphocyte cell line DT40 and its derivatives lacking nonhomologous end joining and/or homologous recombination pathways of DNA double-strand break repair

Hyperthermia has a radiosensitizing effect, which is one of the most important biological bases for its use in cancer therapy with radiation. Although the mechanism of this effect has not been clarified in molecular terms, possible involvement of either one or both of two major DNA double-strand break (DSB) repair pathways, i.e. nonhomologous end joining (NHEJ) and homologous recombination (HR), has been speculated. To test this possibility, we examined cells of the chicken B-lymphocyte cell line DT40 and its derivatives lacking NHEJ and/or HR: KU70(-/-), DNA-PKcs(-/-/-), RAD54(-/-) and KU70(-/-)/RAD54(-/-). Radiosensitization by hyperthermia could be seen in all of the mutants, including KU70(-/-)/RAD54(-/-), which lacked both NHEJ and HR. Therefore, radiosensitization by hyperthermia cannot be explained simply by its inhibitory effects, if any, on NHEJ and/or HR alone. However, in NHEJ-defective KU70(-/-) and DNA-PKcs(-/-/-), consisting of two subpopulations with distinct radiosensitivity, the radiosensitive subpopulation, which is considered to be cells in G(1) and early S, was not sensitized. Substantial sensitization was seen only in the radioresistant subpopulation, which is considered to be cells in late S and G(2), capable of repairing DSBs through HR. This observation did not exclude possible involvement of NHEJ in G(1) and early S phase and also suggested inhibitory effects of hyperthermia on HR. Thus partial contribution of NHEJ and HR in radiosensitization by hyperthermia, especially that depending on the cell cycle stage, remains to be considered.

HSF4 is required for normal cell growth and differentiation during mouse lens development

The heat shock transcription factor (HSF) family consists of three members in mammals and regulates expression of heat shock genes via a heat shock element. HSF1 and HSF2 are required for some developmental processes, but it is unclear how they regulate these processes. To elucidate the mechanisms of developmental regulation by HSFs, we generated mice in which the HSF4 gene is mutated. HSF4-null mice had cataract with abnormal lens fiber cells containing inclusion-like structures, probably due to decreased expression of gamma-crystallin, which maintains protein stability. Furthermore, we found increased proliferation and premature differentiation of the mutant lens epithelial cells, which is associated with increased expression of growth factors, FGF-1, FGF-4, and FGF-7. Unexpectedly, HSF1 competed with HSF4 for the expression of FGFs not only in the lens but also in other tissues. These findings reveal the lens-specific role of HSF4, which activates gamma-crystallin genes, and also indicate that HSF1 and HSF4 are involved in regulating expression of growth factor genes, which are essential for cell growth and differentiation.

Hsp25, a member of the Hsp30 family, promotes inclusion formation in response to stress

Protein aggregates are oligomeric complexes of misfolded proteins, and serve as the seeds of inclusion bodies termed aggresomes in the cells. Heat shock proteins (Hsps) prevent misfolding and aggregate formation. Here, we found that only avian Hsp25 dominantly accumulated in the aggresomes induced by proteasome inhibition. Molecular cloning of chicken Hsp25 (cHsp25) revealed that it belongs to the Hsp30 family, which is a subfamily of the alpha-crystallin/small Hsp gene family. Unexpectedly, overexpression of cHsp25 into HeLa cells promoted inclusion formation whereas overexpression of mouse Hsp27 and its chicken homologue did not. These results suggest that cHsp25 acts differently from other small Hsps on protein aggregates.

Cloning and characterization of two distinct isoforms of rainbow trout heat shock factor 1

To elucidate the molecular mechanism underlying the heat shock response in cold-water fish species, genes encoding heat shock transcription factors (HSFs) were cloned from RTG-2 cells of the rainbow trout Oncorhynchus mykiss. Consequently, two distinct HSF1 genes, named HSF1a and HSF1b, were identified. The predicted amino acid sequence of HSF1a shows 86.4% identity to that of HSF1b. The two proteins contained the general structural motifs of HSF1, i.e. a DNA-binding domain, hydrophobic heptad repeats and nuclear localization signals. Southern blot analysis showed that each HSF1 is encoded by a distinct gene. The two HSF1 mRNAs were coexpressed in unstressed rainbow trout RTG-2 cells and in various tissues. In an electrophoretic mobility shift assay, each in vitro translated HSF1 bound to the heat shock element. Chemical cross-linking and immunoprecipitation analysis showed that HSF1a and HSF1b form heterotrimers as well as homotrimers. Taken together, these results demonstrate that in rainbow trout cells there are two distinct HSF1 isoforms that can form heterotrimers, suggesting that a unique molecular mechanism underlies the stress response in tetraploid and/or cold-water fish species.