Complex expression of murine heat shock transcription factors

Comprehensive analysis of human tissues reveals unique expression and localization patterns of HSF1 and HSF2

Heat shock factors (HSFs) are the main transcriptional regulators of the evolutionarily conserved heat shock response. Beyond cell stress, several studies have demonstrated that HSFs also contribute to a vast variety of human pathologies, ranging from metabolic diseases to cancer and neurodegeneration. Despite their evident role in mitigating cellular perturbations, the functions of HSF1 and HSF2 in physiological proteostasis have remained inconclusive. Here, we analyzed a comprehensive selection of paraffin-embedded human tissue samples with immunohistochemistry. We demonstrate that both HSF1 and HSF2 display distinct expression and subcellular localization patterns in benign tissues. HSF1 localizes to the nucleus in all epithelial cell types, whereas nuclear expression of HSF2 was limited to only a few cell types, especially the spermatogonia and the urothelial umbrella cells. We observed a consistent and robust cytoplasmic expression of HSF2 across all studied smooth muscle and endothelial cells, including the smooth muscle cells surrounding the vasculature and the high endothelial venules in lymph nodes. Outstandingly, HSF2 localized specifically at cell-cell adhesion sites in a broad selection of tissue types, such as the cardiac muscle, liver, and epididymis. To the best of our knowledge, this is the first study to systematically describe the expression and localization patterns of HSF1 and HSF2 in benign human tissues. Thus, our work expands the biological landscape of these factors and creates the foundation for the identification of specific roles of HSF1 and HSF2 in normal physiological processes.

An Increase in HSF1 Expression Directs Human Mammary Epithelial Cells toward a Mesenchymal Phenotype

HSF1 is a well-known heat shock protein expression regulator in response to stress. It also regulates processes important for growth, development or tumorigenesis. We studied the HSF1 influence on the phenotype of non-tumorigenic human mammary epithelial (MCF10A and MCF12A) and several triple-negative breast cancer cell lines. MCF10A and MCF12A differ in terms of HSF1 levels, morphology, growth in Matrigel, expression of epithelial (CDH1) and mesenchymal (VIM) markers (MCF10A are epithelial cells; MCF12A resemble mesenchymal cells). HSF1 down-regulation led to a reduced proliferation rate and spheroid formation in Matrigel by MCF10A cells. However, it did not affect MCF12A proliferation but led to CDH1 up-regulation and the formation of better organized spheroids. HSF1 overexpression in MCF10A resulted in reduced CDH1 and increased VIM expression and the acquisition of elongated fibroblast-like morphology. The above-mentioned results suggest that elevated levels of HSF1 may direct mammary epithelial cells toward a mesenchymal phenotype, while a lowering of HSF1 could reverse the mesenchymal phenotype to an epithelial one. Therefore, HSF1 may be involved in the remodeling of mammary gland architecture over the female lifetime. Moreover, HSF1 levels positively correlated with the invasive phenotype of triple-negative breast cancer cells, and their growth was inhibited by the HSF1 inhibitor DTHIB.

Functional diversification of heat shock factors

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

Is there a role for HSF1 in viral infections?

Cells undergo numerous processes to adapt to new challenging conditions and stressors. Heat stress is regulated by a family of heat shock factors (HSFs) that initiate a heat shock response by upregulating the expression of heat shock proteins (HSPs) intended to counteract cellular damage elicited by increased environmental temperature. Heat shock factor 1 (HSF1) is known as the master regulator of the heat shock response and upon its activation induces the transcription of genes that encode for molecular chaperones, such as HSP40, HSP70, and HSP90. Importantly, an accumulating body of studies relates HSF1 with viral infections; the induction of fever during viral infection may activate HSF1 and trigger a consequent heat shock response. Here, we review the role of HSF1 in different viral infections and its impact on the health outcome for the host. Studying the relationship between HSF1 and viruses could open new potential therapeutic strategies given the availability of drugs that regulate the activation of this transcription factor.

Heat Shock Proteins in Oxidative Stress and Ischemia/Reperfusion Injury and Benefits from Physical Exercises: A Review to the Current Knowledge

Heat shock proteins (HSPs) are molecular chaperones produced in response to oxidative stress (OS). These proteins are involved in the folding of newly synthesized proteins and refolding of damaged or misfolded proteins. Recent studies have been focused on the regulatory role of HSPs in OS and ischemia/reperfusion injury (I/R) where reactive oxygen species (ROS) play a major role. ROS perform many functions, including cell signaling. Unfortunately, they are also the cause of pathological processes leading to various diseases. Biological pathways such as p38 MAPK, HSP70 and Akt/GSK-3β/eNOS, HSP70, JAK2/STAT3 or PI3K/Akt/HSP70, and HSF1/Nrf2-Keap1 are considered in the relationship between HSP and OS. New pathophysiological mechanisms involving ROS are being discovered and described the protein network of HSP interactions. Understanding of the mechanisms involved, e.g., in I/R, is important to the development of treatment methods. HSPs are multifunctional proteins because they closely interact with the antioxidant and the nitric oxide generation systems, such as HSP70/HSP90/NOS. A deficiency or excess of antioxidants modulates the activation of HSF and subsequent HSP biosynthesis. It is well known that HSPs are involved in the regulation of several redox processes and play an important role in protein-protein interactions. The latest research focuses on determining the role of HSPs in OS, their antioxidant activity, and the possibility of using HSPs in the treatment of I/R consequences. Physical exercises are important in patients with cardiovascular diseases, as they affect the expression of HSPs and the development of OS.

Heat Shock Factor 5 Is Essential for Spermatogenesis in Zebrafish

Heat shock factors (Hsfs) are transcription factors that regulate responses to heat shock and other environmental stimuli. Four heat shock factors (Hsf1-4) have been characterized from vertebrates to date. In addition to stress response, they also play important roles in development and gametogenesis. Here, we study the fifth member of heat shock factor family, Hsf5, using zebrafish as a model organism. Mutant hsf5^-/- males, generated by CRISPR/Cas9 technique, were infertile with drastically reduced sperm count, increased sperm head size, and abnormal tail architecture, whereas females remained fertile. We show that Hsf5 is required for progression through meiotic prophase 1 during spermatogenesis as suggested by the accumulation of cells in the leptotene and zygotene-pachytene stages and increased apoptosis in post-meiotic cells. hsf5^-/- mutants show gonadal misregulation of a substantial number of genes with roles in cell cycle, apoptosis, protein modifications, and signal transduction, indicating an important role of Hsf5 in early stages of spermatogenesis.

Characterizing the Role of TaWRKY13 in Salt Tolerance

The WRKY transcription factor superfamily is known to participate in plant growth and stress response. However, the role of this family in wheat (Triticum aestivum L.) is largely unknown. Here, a salt-induced gene TaWRKY13 was identified in an RNA-Seq data set from salt-treated wheat. The results of RT-qPCR analysis showed that TaWRKY13 was significantly induced in NaCl-treated wheat and reached an expression level of about 22-fold of the untreated wheat. Then, a further functional identification was performed in both Arabidopsis thaliana and Oryza sativa L. Subcellular localization analysis indicated that TaWRKY13 is a nuclear-localized protein. Moreover, various stress-related regulatory elements were predicted in the promoter. Expression pattern analysis revealed that TaWRKY13 can also be induced by polyethylene glycol (PEG), exogenous abscisic acid (ABA), and cold stress. After NaCl treatment, overexpressed Arabidopsis lines of TaWRKY13 have a longer root and a larger root surface area than the control (Columbia-0). Furthermore, TaWRKY13 overexpression rice lines exhibited salt tolerance compared with the control, as evidenced by increased proline (Pro) and decreased malondialdehyde (MDA) contents under salt treatment. The roots of overexpression lines were also more developed. These results demonstrate that TaWRKY13 plays a positive role in salt stress.

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.

The Role of Heat Shock Factors in Mammalian Spermatogenesis

Heat shock transcription factors (HSFs), as regulators of heat shock proteins (HSPs) expression, are well known for their cytoprotective functions during cellular stress. They also play important yet less recognized roles in gametogenesis. All HSF family members are expressed during mammalian spermatogenesis, mainly in spermatocytes and round spermatids which are characterized by extensive chromatin remodeling. Different HSFs could cooperate to maintain proper spermatogenesis. Cooperation of HSF1 and HSF2 is especially well established since their double knockout results in meiosis arrest, spermatocyte apoptosis, and male infertility. Both factors are also involved in the repackaging of the DNA during spermatid differentiation. They can form heterotrimers regulating the basal level of transcription of target genes. Moreover, HSF1/HSF2 interactions are lost in elevated temperatures which can impair the transcription of genes essential for spermatogenesis. In most mammals, spermatogenesis occurs a few degrees below the body temperature and spermatogenic cells are extremely heat-sensitive. Pro-survival pathways are not induced by heat stress (e.g., cryptorchidism) in meiotic and postmeiotic cells. Instead, male germ cells are actively eliminated by apoptosis, which prevents transition of the potentially damaged genetic material to the next generation. Such a response depends on the transcriptional activity of HSF1 which in contrary to most somatic cells, acts as a proapoptotic factor in spermatogenic cells. HSF1 activation could be the main trigger of impaired spermatogenesis related not only to elevated temperature but also to other stress conditions; therefore, HSF1 has been proposed to be the quality control factor in male germ cells.

Molecular cloning of orange-spotted grouper (Epinephelus coioides) heat shock transcription factor 1 isoforms and characterization of their expressions in response to nodavirus

Heat shock transcription factor 1 (HSF1) regulates heat shock proteins (HSPs), which assist in protein folding and inhibit protein denaturation following stress. HSF1 was firstly cloned from orange-spotted grouper and exists as two isoforms, one with (osgHSF1a) and one without (osgHSF1b) exon 11. Heat exposure increased the expression of osgHSF1b while cold exposure increased that of osgHSF1a. Both isoforms were mainly expressed in the brains, eyes, and fins. Expression of osgHSF1b was higher than osgHSF1a during development. Poly I:C and LPS could also induce osgHSF1 isoforms expression differentially. Exposure to nervous necrosis virus (NNV) increased the level of both osgHSF1 isoforms at 12 h. GF-1 cells with overexpression of osgHSF1 isoforms enhanced viral loads within 24 h, whereas both pharmacological inhibition and RNA interference of HSF1 reduced virus infection. This study shows that osgHSF1 can support the early stage of virus infection and provides a new insight into the molecular regulation of osgHSF1 between the influence of temperatures and immunity.

High-throughput screening system for inhibitors of human Heat Shock Factor 2

Development of novel anti-cancer drug leads that target regulators of protein homeostasis is a formidable task in modern pharmacology. Finding specific inhibitors of human Heat Shock Factor 1 (hHSF1) has proven to be a challenging task, while screening for inhibitors of human Heat Shock Factor 2 (hHSF2) has never been described. We report the development of a novel system based on an in vivo cell growth restoration assay designed to identify specific inhibitors of human HSF2 in a high-throughput format. This system utilizes a humanized yeast strain in which the master regulator of molecular chaperone genes, yeast HSF, has been replaced with hHSF2 with no detrimental effect on cell growth. This replacement preserves the general regulatory patterns of genes encoding major molecular chaperones including Hsp70 and Hsp90. The controlled overexpression of hHSF2 creates a slow-growth phenotype, which is the basis of the growth restoration assay used for high-throughput screening. The phenotype is most robust when cells are cultured at 25 °C, while incubation at temperatures greater than 30 °C leads to compensation of the phenotype. Overexpression of hHSF2 causes overexpression of molecular chaperones which is a likely cause of the slowed growth. Our assay is characterized by two unique advantages. First, screening takes place in physiologically relevant, in vivo conditions. Second, hits in our screen will be of medically relevant potency, as compounds that completely inhibit hHSF2 function will further inhibit cell growth and therefore will not be scored as hits. This caveat biases our screening system for compounds capable of restoring hHSF2 activity to a physiologically normal level without completely inhibiting this essential system.

Splice variants and seasonal expression of buffalo HSF genes

In eukaryotes, the heat shock factors (HSFs) are recognized as the master regulator of the heat shock response. In this respect, the genes encoding the heat shock factors seem to be important for adaptation to thermal stress in organisms. Despite this, only few mammalian HSFs has been characterized. In this study, four major heat shock factor genes viz. HSF-1, 2, 4, and 5 were studied. The main objective of the present study was to characterize the cDNA encoding using conserved gene specific primers and to investigate the expression status of these buffalo HSF genes. Our RT-PCR analysis uncovered two distinct variants of buffalo HSF-1 and HSF-2 gene transcripts. In addition, we identified a variant of the HSF5 transcript in buffalo lacking a DNA-binding domain. In silico analysis of deduced amino acid sequences for buffalo HSF genes showed domain architecture similar to other mammalian species. Changes in the gene expression profile were noted by quantitative real-time PCR (qRT-PCR) analysis. We detected the transcript of buffalo HSF genes in different tissues. We also evaluated the seasonal changes in the expression of HSF genes. Interestingly, the transcript level of HSF-1 gene was found upregulated in months of high and low ambient temperatures. In contrast, the expression of the HSF-4 and 5 genes was found to be downregulated in months of high ambient temperature. This suggests that the intricate balance of different HSFs is adjusted to minimize the effect of seasonal changes in environmental conditions. These findings advance our understanding of the complex, context-dependent regulation of HSF gene expression under normal and stressful conditions.

HSF1 at a glance

Heat shock factor 1 (HSF1) is an evolutionarily highly conserved transcription factor that coordinates stress-induced transcription and directs versatile physiological processes in eukaryotes. The central position of HSF1 in cellular homeostasis has been well demonstrated, mainly through its strong effect in transactivating genes that encode heat shock proteins (HSPs). However, recent genome-wide studies have revealed that HSF1 is capable of reprogramming transcription more extensively than previously assumed; it is also involved in a multitude of processes in stressed and non-stressed cells. Consequently, the importance of HSF1 in fundamental physiological events, including metabolism, gametogenesis and aging, has become apparent and its significance in pathologies, such as cancer progression, is now evident. In this Cell Science at a Glance article, we highlight recent advances in the HSF1 field, discuss the organismal control over HSF1, and present the processes that are mediated by HSF1 in the context of cell type, cell-cycle phase, physiological condition and received stimuli.

Expression of HSF2 decreases in mitosis to enable stress-inducible transcription and cell survival

In spite of global transcriptional inhibition, a decrease in HSF2 expression during mitosis allows for heat shock protein expression and protects cells against proteotoxicity.

Unless mitigated, external and physiological stresses are detrimental for cells, especially in mitosis, resulting in chromosomal missegregation, aneuploidy, or apoptosis. Heat shock proteins (Hsps) maintain protein homeostasis and promote cell survival. Hsps are transcriptionally regulated by heat shock factors (HSFs). Of these, HSF1 is the master regulator and HSF2 modulates Hsp expression by interacting with HSF1. Due to global inhibition of transcription in mitosis, including HSF1-mediated expression of Hsps, mitotic cells are highly vulnerable to stress. Here, we show that cells can counteract transcriptional silencing and protect themselves against proteotoxicity in mitosis. We found that the condensed chromatin of HSF2-deficient cells is accessible for HSF1 and RNA polymerase II, allowing stress-inducible Hsp expression. Consequently, HSF2-deficient cells exposed to acute stress display diminished mitotic errors and have a survival advantage. We also show that HSF2 expression declines during mitosis in several but not all human cell lines, which corresponds to the Hsp70 induction and protection against stress-induced mitotic abnormalities and apoptosis.

Genome-Wide Analysis of Heat-Sensitive Alternative Splicing in Physcomitrella patens

Plant growth and development are constantly influenced by temperature fluctuations. To respond to temperature changes, different levels of gene regulation are modulated in the cell. Alternative splicing (AS) is a widespread mechanism increasing transcriptome complexity and proteome diversity. Although genome-wide studies have revealed complex AS patterns in plants, whether AS impacts the stress defense of plants is not known. We used heat shock (HS) treatments at nondamaging temperature and messenger RNA sequencing to obtain HS transcriptomes in the moss Physcomitrella patens. Data analysis identified a significant number of novel AS events in the moss protonema. Nearly 50% of genes are alternatively spliced. Intron retention (IR) is markedly repressed under elevated temperature but alternative donor/acceptor site and exon skipping are mainly induced, indicating differential regulation of AS in response to heat stress. Transcripts undergoing heat-sensitive IR are mostly involved in specific functions, which suggests that plants regulate AS with transcript specificity under elevated temperature. An exonic GAG-repeat motif in these IR regions may function as a regulatory cis-element in heat-mediated AS regulation. A conserved AS pattern for HS transcription factors in P. patens and Arabidopsis (Arabidopsis thaliana) reveals that heat regulation for AS evolved early during land colonization of green plants. Our results support that AS of specific genes, including key HS regulators, is fine-tuned under elevated temperature to modulate gene regulation and reorganize metabolic processes.

Novel isoforms of heat shock transcription factor 1, HSF1γα and HSF1γβ, regulate chaperone protein gene transcription

The heat shock response, resulting in the production of heat shock proteins or molecular chaperones, is triggered by elevated temperature and a variety of other stressors. Its master regulator is heat shock transcription factor 1 (HSF1). Heat shock factors generally exist in multiple isoforms. The two known isoforms of HSF1 differ in the inclusion (HSF1α) or exclusion (HSF1β) of exon 11. Although there are some data concerning the differential expression patterns and transcriptional activities of HSF2 isoforms during development, little is known about the distinct properties of the HSF1 isoforms. Here we present evidence for two novel HSF1 isoforms termed HSF1γα and HSF1γβ, and we show that the HSF1 isoform ratio differentially regulates heat shock protein gene transcription. Hsf1γ isoforms are expressed in various mouse tissues and are translated into protein. Furthermore, after heat shock, HSF1γ isoforms are exported from the nucleus more rapidly or degraded more quickly than HSF1α or HSF1β. We also show that each individual HSF1 isoform is sufficient to induce the heat shock response and that expression of combinations of HSF1 isoforms, in particular HSF1α and HSF1β, results in a synergistic enhancement of the transcriptional response. In addition, HSF1γ isoforms potentially suppress the synergistic effect of HSF1α and HSF1β co-expression. Collectively, our observations suggest that the expression of HSF1 isoforms in a specific ratio provides an additional layer in the regulation of heat shock protein gene transcription.

Mice with an absent stress response are protected against ischemic renal injury

Inducible heat shock proteins (HSP), regulated by heat shock factor-1 (HSF-1), protect against renal cell injury in vitro. To determine whether HSPs ameliorate ischemic renal injury in vivo, HSF-1functional knock-out mice (HSF-KO) were compared with wild-type mice following bilateral ischemic renal injury. Following injury, the kidneys of wild-type mice had the expected induction of HSP70 and HSP25; a response absent in the kidneys of HSF-KO mice. Baseline serum creatinine was equivalent between strains. Serum creatinines at 24 hours reflow in HSF-KO mice were significantly lower than in the wild-type. Histology showed similar tubule injury in both strains after ischemic renal injury but increased medullary vascular congestion in wild-type compared with HSF-KO mice. Flow-cytometry of mononuclear cells isolated from kidneys showed no difference between strains in the number of CD4⁺ and CD8⁺ T cells in sham operated animals. At 1 hour of reflow, CD4⁺ and CD8⁺ cells were doubled in the kidneys of wild type but not HSF-KO mice. Foxp3⁺ T regulatory cells were significantly more abundant in the kidneys of sham-operated HSF-KO than wild-type mice. Suppression of CD25⁺Foxp3⁺ cells in HSF-KO kidneys with the anti-CD25 antibody PC61 reversed the protection against ischemic renal injury. Thus, HSF-KO mice are protected from ischemic renal injury by a mechanism that depends on an increase in the T regulatory cells in the kidney associated with altered T cell infiltration early in reflow. Hence, stress response activation may contribute to early injury by facilitating T cell infiltration into ischemic kidney.

Unraveling complex interplay between heat shock factor 1 and 2 splicing isoforms

Chaperone synthesis in response to proteotoxic stress is dependent on a family of transcription factors named heat shock factors (HSFs). The two main factors in this family, HSF1 and HSF2, are co-expressed in numerous tissues where they can interact and form heterotrimers in response to proteasome inhibition. HSF1 and HSF2 exhibit two alternative splicing isoforms, called α and β, which contribute to additional complexity in HSF transcriptional regulation, but remain poorly examined in the literature. In this work, we studied the transcriptional activity of HSF1 and HSF2 splicing isoforms transfected into immortalized Mouse Embryonic Fibroblasts (iMEFs) deleted for both Hsf1 and Hsf2, under normal conditions and after proteasome inhibition. We found that HSF1α is significantly more active than the β isoform after exposure to the proteasome inhibitor MG132. Furthermore, we clearly established that, while HSF2 had no transcriptional activity by itself, short β isoform of HSF2 exerts a negative role on HSF1β-dependent transactivation. To further assess the impact of HSF2β inhibition on HSF1 activity, we developed a mathematical modelling approach which revealed that the balance between each HSF isoform in the cell regulated the strength of the transcriptional response. Moreover, we found that cellular stress such as proteasome inhibition could regulate the splicing of Hsf2 mRNA. All together, our results suggest that relative amounts of each HSF1 and HSF2 isoforms quantitatively determine the cellular level of the proteotoxic stress response.

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.

HSFs and regulation of Hsp70.1 (Hspa1b) in oocytes and preimplantation embryos: new insights brought by transgenic and knockout mouse models

Gene encoding heat shock protein (Hsps) are induced following a thermal stress thanks to the activation of heat shock transcription factor (HSF) which interacts with heat shock elements (HSE) located within the sequence of Hsp promoters. This cellular and protective response (heat shock response (HSR)) is well known and evolutionarily conserved. Nevertheless, HSR does not function in all the cells produced during the life of a multicellular organism, e.g., early mouse embryos. Taking advantage of mouse transgenic and knockout models, we investigated the roles of trans (HSF 1 and 2) and cis (HSE) regulatory elements in the control of Hsp70.1 (Hspa1b) through several developmental steps from oocytes to blastocysts. Our studies confirm that, even in absence of any stress, HSF1 regulates Hsp70.1 in oocytes and early embryos. Our data emphasize the role of maternal and paternal HSFs in the developmentally regulated expression of Hsp70.1 observed when the zygotic genome activation occurs. Furthermore, in this unstressed developmental condition, affinity and binding to HSEs might be more permissive than in the stress response. Finally, submitting blastocyst to different stress conditions, we show that HSF2 is differentially required for Hsp expression and cell survival. Taken together, our findings indicate that the role of heat shock trans and cis regulatory elements evolve along the successive steps of early embryonic development.

Novel isoforms of heat shock transcription factor 1 are induced by hypoxia in the Pacific oyster Crassostrea gigas

The Pacific oyster Crassostrea gigas inhabits the intertidal zone and shows tolerance to various stress conditions such as hypoxia and heat shock. However, little is known about the cellular mechanism of responses to these stresses. Heat shock transcription factor 1 (HSF1) regulates the transcription of several genes, including heat shock proteins (HSPs). In this study, we cloned HSF1 from the oyster and investigated its response to air-exposure. The cDNA of oyster Hsf1 contains 2,931 bp, of which 1,389 bp encode a protein of 463 amino acid residues. Moreover, we found that the oyster has seven novel alternatively spliced isoforms, Hsf1b-h, consisting of insertion A with 48 bp, insertion B with 42 bp and/or insertion C with 42 bp. We determined the sequences of oyster genomic DNA containing Hsf1 insertions A, B and C. The results indicated that eight isoforms of Hsf1 are generated from a single Hsf1 gene by alternative splicing without frameshifting. Real-time PCR analysis showed that Hsf1a is expressed constitutively, and the expression of Hsf1b-h and Hsp70 mRNA is induced by air exposure and/or hypoxia. In addition, we found that 11 putative hypoxia response elements, which are hypoxia-inducible factor 1 (HIF-1) binding sequences, are located in the Hsf1 promoter region. These data suggest that the oyster has an HIF-HSF pathway in which HSPs are induced in an HIF-dependent manner, and that it also has a novel mechanism of alternative splicing of Hsf1 in response to hypoxia.

Roles of heat shock factors in gametogenesis and development

Heat shock factors form a family of transcription factors (four in mammals), which were named according to the first discovery of their activation by heat shock. As a result of the universality and robustness of their response to heat shock, the stress-dependent activation of heat shock factor became a ‘paradigm’: by binding to conserved DNA sequences (heat shock elements), heat shock factors trigger the expression of genes encoding heat shock proteins that function as molecular chaperones, contributing to establish a cytoprotective state to various proteotoxic stress and in several pathological conditions. Besides their roles in the stress response, heat shock factors perform crucial roles during gametogenesis and development in physiological conditions. First, during these process, in stress conditions, they are either proactive for survival or, conversely, for apoptotic process, allowing elimination or, inversely, protection of certain cell populations in a way that prevents the formation of damaged gametes and secure future reproductive success. Second, heat shock factors display subtle interplay in a tissue- and stage-specific manner, in regulating very specific sets of heat shock genes, but also many other genes encoding growth factors or involved in cytoskeletal dynamics. Third, they act not only by their classical transcription factor activities, but are necessary for the establishment of chromatin structure and, likely, genome stability. Finally, in contrast to the heat shock gene paradigm, heat shock elements bound by heat shock factors in developmental process turn out to be extremely dispersed in the genome, which is susceptible to lead to the future definition of ‘developmental heat shock element’.

Regulation of the members of the mammalian heat shock factor family

Regulation of gene expression is fundamental in all living organisms and is facilitated by transcription factors, the single largest group of proteins in humans. For cell- and stimulus-specific gene regulation, strict control of the transcription factors themselves is crucial. Heat shock factors are a family of transcription factors best known as master regulators of induced gene expression during the heat shock response. This evolutionary conserved cellular stress response is characterized by massive production of heat shock proteins, which function as cytoprotective molecular chaperones against various proteotoxic stresses. In addition to promoting cell survival under stressful conditions, heat shock factors are involved in the regulation of life span and progression of cancer and they are also important for developmental processes such as gametogenesis, neurogenesis and maintenance of sensory organs. Here, we review the regulatory mechanisms steering the activities of the mammalian heat shock factors 1–4.

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.

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.

Characterization of alternatively spliced transcripts encoding heat shock transcription factor in cultured cells of the cabbage armyworm, Mamestra brassicae

A gene encoding heat shock transcription factor (HSF) was cloned and sequenced from cultured cells of the cabbage armyworm, Mamestra brassicae. The cDNA potentially encoded a 699-aa protein, with a calculated molecular weight of 77.8 kDa. Deduced amino acid identities to HSFs from Aedes aegypti and Drosophila melanogaster were 36 and 34%, respectively. Analysis of the genomic DNA revealed eight exons and three optional exons: a, b, and c. Exon a contained a premature in-frame stop codon that would generate a truncated protein. When the cells were exposed to high temperature or cadmium, no particular alternative transcripts showed significant up- or down-regulated expression relative to the total amount of the transcripts. These results suggest that alternative splicing may not be a principal mechanism for regulation of M. brassicae HSF gene expression in response to heat shock and cadmium.

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.

Riluzole increases the amount of latent HSF1 for an amplified heat shock response and cytoprotection

Background

Induction of the heat shock response (HSR) and increased expression of the heat shock proteins (HSPs) provide mechanisms to ensure proper protein folding, trafficking, and disposition. The importance of HSPs is underscored by the understanding that protein mis-folding and aggregation contribute centrally to the pathogenesis of neurodegenerative diseases.

Methodology/Principal Findings

We used a cell-based hsp70-luciferease reporter gene assay system to identify agents that modulate the HSR and show here that clinically relevant concentrations of the FDA-approved ALS drug riluzole significantly increased the heat shock induction of hsp70-luciferse reporter gene. Immuno-Western and -cytochemical analysis of HSF1 show that riluzole increased the amount of cytosolic HSF1 to afford a greater activation of HSF1 upon heat shock. The increased HSF1 contributed centrally to the cytoprotective activity of riluzole as hsf1 gene knockout negated the synergistic activity of riluzole and conditioning heat shock to confer cell survival under oxidative stress. Evidence of a post-transcriptional mechanism for the increase in HSF1 include: quantitation of mRNA^hsf1 by RT-PCR showed no effect of either heat shock or riluzole treatment; riluzole also increased the expression of HSF1 from a CMV-promoter; analysis of the turnover of HSF1 by pulse chase and immunoprecipitation show that riluzole slowed the decay of [³⁵S]labeled-HSF1. The effect of riluzole on HSF1 was qualitatively different from that of MG132 and chloroquine, inhibitors of the proteasome and lysosome, respectively, and appeared to involve the chaperone-mediated autophagy pathway as RNAi-mediated knockdown of CMA negated its effect.

Conclusion/Significance

We show that riluzole increased the amount of HSF1 to amplify the HSR for cytoprotection. Our study provides novel insight into the mechanism that regulates HSF1 turnover, and identifies the degradation of HSF1 as a target for therapeutics intervention.

Promoter ChIP-chip analysis in mouse testis reveals Y chromosome occupancy by HSF2

The mammalian Y chromosome is essential for spermatogenesis, which is characterized by sperm cell differentiation and chromatin condensation for acquisition of correct shape of the sperm. Deletions of the male-specific region of the mouse Y chromosome long arm (MSYq), harboring multiple copies of a few genes, lead to sperm head defects and impaired fertility. Using chromatin immunoprecipitation on promoter microarray (ChIP-chip) on mouse testis, we found a striking in vivo MSYq occupancy by heat shock factor 2 (HSF2), a transcription factor involved in spermatogenesis. HSF2 was also found to regulate the transcription of MSYq resident genes, whose transcriptional regulation has been unknown. Importantly, disruption of Hsf2 caused a similar phenotype as the 2/3 deletion of MSYq, i.e., altered expression of the multicopy genes and increased mild sperm head abnormalities. Consequently, aberrant levels of chromatin packing proteins and more frequent DNA fragmentation were detected, implying that HSF2 is required for correct chromatin organization in the sperm. Our findings define a physiological role for HSF2 in the regulation of MSYq resident genes and the quality of sperm.

Neurospora crassa heat shock factor 1 Is an essential gene; a second heat shock factor-like gene, hsf2, is required for asexual spore formation

Appropriate responses of organisms to heat stress are essential for their survival. In eukaryotes, adaptation to high temperatures is mediated by heat shock transcription factors (HSFs). HSFs regulate the expression of heat shock proteins, which function as molecular chaperones assisting in protein folding and stability. In many model organisms a great deal is known about the products of hsf genes. An important exception is the filamentous fungus and model eukaryote Neurospora crassa. Here we show that two Neurospora crassa genes whose protein products share similarity to known HSFs play different biological roles. We report that heat shock factor 1 (hsf1) is an essential gene and that hsf2 is required for asexual development. Conidiation may be blocked in the hsf2 knockout (hsf2(KO)) strain because HSF2 is an integral element of the conidiation pathway or because it affects the availability of protein chaperones. We report that genes expressed during conidiation, for example fluffy, conidiation-10, and repressor of conidiation-1 show wild-type levels of expression in a hsf2(KO) strain. However, consistent with the lack of macroconidium development, levels of eas are much reduced. Cultures of the hsf2(KO) strain along with two other aconidial strains, the fluffy and aconidial-2 strains, took longer than the wild type to recover from heat shock. Altered expression profiles of hsp90 and a putative hsp90-associated protein in the hsf2(KO) strain after exposure to heat shock may in part account for its reduced ability to cope with heat stress.

Structure and alternative splicing of a heat shock transcription factor gene, MsHSF1, in Medicago sativa

Plant heat shock transcription factors (HSF) are highly complex. In this study, we identified an alfalfa HSF gene MsHSF1 that is composed of four exons and three introns in the encoding region. The intron1-exon2-intron2-exon3-intron3 as an intervening sequence was inserted at the conserved position that separates the coding region for the DNA-binding domain by single intron in other known plant HSF genes. Alternative splicing of MsHSF1 has generated five transcript isoforms. Spliced transcript MsHSF1b consisted of exon1 and exon4, encodes a class A1 HSF protein that can specifically bind to the heat shock elements in vitro. Other four spliced transcripts (MsHSF1a-1 to 4) consist of exon1, part of the intervening sequence and exon4. These transcripts carry the premature termination codon and are low-abundant. Apparently these transcripts are the targets of nonsense-mediated mRNA decay (NMD). These results provide new insight into roles in the expression regulation of plant HSF genes.

Promoter of the heat shock testis-specific Hsp70.2/Hst70 gene is active in nervous system during embryonic development of mice

The Hsp70.2/Hst70 gene is a unique member of the 70 kDa heat shock proteins multigene family whose activity is regulated developmentally; in adult mice and rats its expression is restricted mostly to meiotic and postmeiotic male germ cells. In aim to analyze activity of the Hsp70.2/Hst70 promoter in developing embryos we have constructed transgenic mice expressing EGFP reporter gene under control of the rat Hst70 promoter. The appearance of EGFP fluorescence coincides with series of major developmental events, such as extra-embryonic membranes formation, axial rotation, formation of neural tube and the primordium of central nervous system, formation of differentiated somites, extensive remodeling of the heart, development of fingers and toes, and sensory organs formation. Activity of the Hst70 promoter localizes mostly inside nervous system indicating the role of Hsp70.2/Hst70 gene in development of this system.

Role of heat-shock factor 2 in cerebral cortex formation and as a regulator of p35 expression

Heat-shock factors (HSFs) are associated with multiple developmental processes, but their mechanisms of action in these processes remain largely enigmatic. Hsf2-null mice display gametogenesis defects and brain abnormalities characterized by enlarged ventricles. Here, we show that Hsf2-/- cerebral cortex displays mispositioning of neurons of superficial layers. HSF2 deficiency resulted in a reduced number of radial glia fibers, the architectural guides for migrating neurons, and of Cajal-Retzius cells, which secrete the positioning signal Reelin. Therefore, we focused on the radial migration signaling pathways. The levels of Reelin and Dab1 tyrosine phosphorylation were reduced, suggesting that the Reelin cascade is affected in Hsf2-/- cortices. The expression of p35, an activator of cyclin-dependent kinase 5 (Cdk5), essential for radial migration, was dependent on the amount of HSF2 in gain- and loss-of-function systems. p39, another Cdk5 activator, displayed reduced mRNA levels in Hsf2-/- cortices, which, together with the lowered p35 levels, decreased Cdk5 activity. We demonstrate in vivo binding of HSF2 to the p35 promoter and thereby identify p35 as the first target gene for HSF2 in cortical development. In conclusion, HSF2 affects cellular populations that assist in radial migration and directly regulates the expression of p35, a crucial actor of radial neuronal migration.

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.

Alternative splicing regulates the transcriptional activity ofDrosophilaheat shock transcription factor in response to heat/cold stress

Heat shock transcription factor 1 (HSF1) mediates the induction of heat shock proteins in response to various types of stress. Although HSF1 activity is regulated by its post-translational modifications, alterations in mRNA expression have also been suggested. We here identified three new alternatively spliced isoforms of Drosophila HSF (dHSF) mRNA, named dHSFb, dHSFc, and dHSFd. We found that the ratio of dHSFb increases upon heat exposure, while that of dHSFd increases upon cold exposure. The dHSFc and dHSFd isoforms showed greater transcriptional activity than the other isoforms. Our findings suggest that alternative splicing regulates the transcriptional activity of dHSF.

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.

Location of promoter elements necessary and sufficient to direct testis-specific expression of the Hst70/Hsp70.2 gene

The rat Hst70 gene and its mouse counterpart Hsp70.2 are expressed specifically in pachytene primary spermatocytes and spermatids. Here we demonstrate that a 165 bp fragment of the Hst70 gene promoter, containing the T1 transcription start site region, entire exon 1 and 42 bp 5' region of the intron, is sufficient to drive testis-specific expression of the chloramphenicol acetyltransferase reporter gene in transgenic mice with the same developmentally regulated pattern as the endogenous Hsp70.2 gene. We show further that high-level tissue-specific gene expression requires additional sequences localized upstream of the T2 transcription start site. Electrophoretic mobility-shift assay analysis revealed that only testes of juvenile rats, when Hst70 gene expression is repressed, contain proteins that specifically bind to the Oct (octamer) sequence localized directly downstream of the T1 site.

In vivo heat-shock response in the brain: signalling pathway and transcription factor activation

We analysed the expression of the hsp70 gene, the phosphorylation status of different members of the mitogen-activated protein kinase (MAPK) family, the behaviour of the Akt-GSK3 pathway, as well as the DNA-binding activity of several transcription factors, potential targets of these kinases, in the brain of rats exposed to a fever-like increase in body temperature. Two different brain regions, the cerebellum and the hippocampus, were studied. Hyperthermia caused HSF activation and the induction of hsp70 mRNA and protein to a greater extent in the cerebellum than in the hippocampus. In the cerebellum, ERK1/2 and p38 MAPK phosphorylation were increased by hyperthermia and returned to basal levels during the recovery from heat stress, whereas JNK3 phosphorylation decreased and recovered to above control levels within 60 min of recovery. JNK1 phosphorylation was never modified. In the hippocampus, ERK phosphorylation did not increase but rather decreased, whereas the behaviour of p38 MAPK and JNK was similar to that observed in the cerebellum. Akt phosphorylation increased after hyperthermia and was accompanied by an increased phosphorylation of two substrates, GSK3 and FKHRL1, in both brain areas, with a major effect in the cerebellum. DNA-binding activities of AP-1, NF-kappaB, and MEF2 were activated by heat shock in the cerebellum, whereas only MEF2 was activated in the hippocampus. Our data indicate that a physiologically relevant increase in body temperature induces brain injury and survival response to it as demonstrated by induction of hsp70 gene expression and activation of specific signalling pathways. Reprogramming of gene expression, by the specific transcription factors activated, probably plays a central role in cell adaptation and survival to heat stress. The hippocampus shows less responsiveness to hyperthermia than the cerebellum.

Early transcriptional activation of the hsp70.1 gene by osmotic stress in one-cell embryos of the mouse

In fertilized mouse eggs, de novo transcription of embryonic genes is first observed during the S phase of the one-cell stage. This transcription, however, is mostly limited to the male pronucleus and possibly uncoupled from translation, making the functional meaning obscure. We found that one-cell mouse embryos respond to the osmotic shock of in vitro isolation with migration of HSF1, the canonical stress activator of mammalian heat shock genes, to pronuclei and by transient transcription of the hsp70.1, but not hsp70.3 and hsp90, heat shock genes. Isolated growing dictyate oocytes also display a nuclear HSF1 localization, but, in contrast with embryos, they transcribe both hsp70.1 and hsp70.3 genes only after heat shock. Intranuclear injection of double-stranded oligodeoxyribonucleotides containing HSE, GAGA box or GC box consensus sequences, and antibodies raised to transcription factors HSF1, HSF2, Drosophila melanogaster GAGA factor, or Sp1 demonstrated that hsp70.1 transcription depends on HSF1 in both oocytes and embryos and that Sp1 is dispensable in oocytes and inhibitory in the embryos. Hsp70.1 thus represents the first endogenous gene so far identified to be physiologically activated and tightly regulated after fertilization in mammals.

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.

Heat- and cold-inducible regulation of HSP70 expression in zebrafish ZF4 cells

Elevated temperature induces a rapid heat shock transcription factor (HSFs)-mediated expression of heat shock (hsp) genes. The effect of cold exposure on hsp gene expression has hardly been investigated, although ectothermic animals experience both cold and heat stress. We have previously shown in zebrafish that the expression of hsf1a and a unique isoform hsf1b vary in a tissue-specific manner upon heat stress. In the current study, using a zebrafish (Danio rerio) embryonic cell line (ZF4), we have compared the effects of heat shock (28-->37 degrees C) vs. cold shock (28-->20 degrees C) on the expression of ahsf1a, zhsf1b and hsp70. Concomitantly, the suitability of the ZF4 cells as a model system was verified. The expression pattern of HSP70 proteins following heat or cold exposure is distinct, and the total HSP70 level is upregulated or stable, respectively. Moreover, heat exposure specifically increases the ratio of zhsf1a/b expression (10-fold), whereas cold exposure decreases it to one half. These data suggest that the zhsf1a/zhsf1b ratio is regulated in a temperature-dependent manner, and the ratio may be indicative of the stressor-specific HSP70 expression. Furthermore, the response in ZF4 cells upon heat shock resembles the response observed in zebrafish liver and thus, supports the use of this cell line in stress response studies.

Regulation of uterine hsp90alpha, hsp72 and HSF-1 transcription in B6C3F1 mice by beta-estradiol and bisphenol A: involvement of the estrogen receptor and protein kinase C

We have previously demonstrated that bisphenol A (BPA)- and beta-estradiol (E2)-induced increases in uterine weight and heat shock protein (hsp) 90alpha and hsp72 levels are mediated through the estrogen receptor (ER). It is not, however, clear if BPA and E2 regulation of hsps is at the transcriptional or post-transcriptional level. Therefore, in this study we examined the ability of BPA and E2 to increase uterine weight and regulate transcription of these hsps and of heat shock factor (HSF)-1 in ovariectomized B6C3F1 mice at 6 or 24 h after a single subcutaneous injection of E2 (1 microg/kg) or BPA (100 mg/kg). The role of the ER and protein kinase C (PKC) in these E2 and BPA effects was evaluated by co-administration of the antiestrogen ICI 182,780 (5 mg/kg) or the PKC inhibitor GF 109203X (0.5 mg/kg), respectively. The results demonstrated ER involvement in uterine weight increases. Uterine hsp mRNA levels are increased by E2 and BPA through a direct effect on their transcription and/or, in the case of E2, through an increase in HSF-1 mRNA. PKC is involved in the BPA-induced increases in hsp90alpha mRNA levels. We conclude that E2 and BPA regulate hsp90alpha and hsp72alpha transcription via similar and distinct pathways.

Elevated expression of heat shock factor (HSF) 2A stimulates HSF1-induced transcription during stress

Heat shock factor 2 (HSF2) belongs to a family of structurally related transcription factors, which share the property of binding to heat shock elements in the promoters of hsp molecular chaperone genes. However, unlike HSF1, which is essential for hsp gene transcription, the cellular functions of HSF2 are not well known. Here we show that human HSF2, although an ineffective activator of the hsp70 promoter in vitro and in vivo in the absence of stress, participates in the activation of the hsp70 promoter by heat shock. HSF2 was not, however, activated by heat shock in cells deficient in functional HSF1, suggesting a requirement for HSF1 in HSF2-mediated transcriptional enhancement. In addition, HSF2 regulation involves differential activity of two isoforms, HSF2A and HSF2B, which arise from alternative splicing of a common hsf2 gene. Under basal conditions, both HSF2 isoforms are ineffective in activating the hsp70 transcription. However, heat shock differentially activates HSF2A in vivo. This phenomenon appears to be physiologically significant, as human myeloprogenitor cells differentiating along the erythroid lineage express HSF2A de novo and undergo a large increase in capacity to activate the hsp70 promoter. Our experiments further show that HSF1 is physically associated with HSF2 in the cell and that such binding is enhanced by heat shock. Our data suggest a mechanism involving the formation of heterocomplexes between HSF1 and HSF2 with enhanced activity to activate the hsp70 promoter when compared with HSF1 or HSF2 homotrimers.

A seed-specific heat-shock transcription factor involved in developmental regulation during embryogenesis in sunflower

We report the cloning and functional characterization of the first heat-shock transcription factor that is specifically expressed during embryogenesis in the absence of environmental stress. In sunflower embryos this factor, HaHSFA9, trans-activated promoters with poor consensus heat-shock cis-elements, including that of the seed-specific Hahsp17.6G1 gene. Mutations that improved the heat-shock cis-element consensus at the Hahsp17.7G4 promoter impaired transient activation by HaHSFA9 in sunflower embryos. The same mutations did not affect heat-shock-induced gene expression of this promoter in transgenic tobacco plants but reduced the developmental activation by endogenous heat-shock transcription factors (HSFs) in seeds. Sunflower, and perhaps other plants such as tobacco, differs from the vertebrate animal systems in having at least one specialized HSF with expression and (or) activation patterns strictly restricted to embryos. Our results strongly indicate that HaHSFA9 is a transcription factor critically involved in the developmental activation of Hahsp17.6G1 and in that of similar target genes as Hahsp17.7G4.

Heat shock transcription factor 2 is not essential for embryonic development, fertility, or adult cognitive and psychomotor function in mice

Members of the heat shock factor (HSF) family are evolutionarily conserved regulators that share a highly homologous DNA-binding domain. In mammals, HSF1 is the main factor controlling the stress-inducible expression of Hsp genes while the functions of HSF2 and HSF4 are less clear. Based on its developmental profile of expression, it was hypothesized that HSF2 may play an essential role in brain and heart development, spermatogenesis, and erythroid differentiation. To directly assess this hypothesis and better understand the underlying mechanisms that require HSF2, we generated Hsf2 knockout mice. Here, we report that Hsf2(-/-) mice are viable and fertile and exhibit normal life span and behavioral functions. We conclude that HSF2, most probably because its physiological roles are integrated into a redundant network of gene regulation and function, is dispensable for normal development, fertility, and postnatal psychomotor function.

A novel non-conventional heat shock element regulates expression of MDJ1 encoding a DnaJ homolog in Saccharomyces cerevisiae

The heat shock factor (HSF) is a pivotal transcriptional factor that regulates the expression of genes encoding heat shock proteins (HSPs) via heat shock elements (HSEs). nGAAnnTTCnnGAAn functions as the minimum consensus HSE (cHSE) in vivo. Here we show that the expression of Saccharomyces cerevisiae MDJ1 encoding a mitochondrial DnaJ homolog is regulated by HSF via a novel non-consensus HSE (ncHSE(MDJ1)), which consists of three separated pentameric nGAAn motifs, nTTCn-(11 bp)-nGAAn-(5 bp)-nGAAn. This is the first evidence to show that the immediate contact of nGAAn motifs is dispensable for regulation by HSF in vivo. ncHSE(MDJ1) confers different heat shock responses versus cHSE and, unlike cHSE, definitively requires a carboxyl-terminal activation domain of HSF in the expression. ncHSE(MDJ1)-like elements are found in promoter regions of some other DnaJ-related genes. The highly conserved HSF/HSE system suggests that similar ncHSEs may be used for the expression of HSP genes in other eukaryotes including humans.

Brain abnormalities, defective meiotic chromosome synapsis and female subfertility in HSF2 null mice

Heat shock factor 2, one of the four vertebrate HSFs, transcriptional regulators of heat shock gene expression, is active during embryogenesis and spermatogenesis, with unknown functions and targets. By disrupting the Hsf2 gene, we show that, although the lack of HSF2 is not embryonic lethal, Hsf2(-/-) mice suffer from brain abnormalities, and meiotic and gameto genesis defects in both genders. The disturbances in brain are characterized by the enlargement of lateral and third ventricles and the reduction of hippocampus and striatum, in correlation with HSF2 expression in proliferative cells of the neuroepithelium and in some ependymal cells in adults. Many developing spermatocytes are eliminated via apoptosis in a stage-specific manner in Hsf2(-/-) males, and pachytene spermatocytes also display structural defects in the synaptonemal complexes between homologous chromosomes. Hsf2(-/-) females suffer from multiple fertility defects: the production of abnormal eggs, the reduction in ovarian follicle number and the presence of hemorrhagic cystic follicles are consistent with meiotic defects. Hsf2(-/-) females also display hormone response defects, that can be rescued by superovulation treatment, and exhibit abnormal rates of luteinizing hormone receptor mRNAs.

Insights into regulation and function of the major stress-induced hsp70 molecular chaperone in vivo: analysis of mice with targeted gene disruption of the hsp70.1 or hsp70.3 gene

The murine hsp70 gene family includes the evolutionarily conserved hsp70.1 and hsp70.3 genes, which are the major proteins induced by heat and other stress stimuli. hsp70.1 and hsp70.3 encode identical proteins which protect cells and facilitate their recovery from stress-induced damage. While the hsp70 gene family has been widely studied and the roles of the proteins it encodes as molecular chaperones in a range of human pathologies are appreciated, little is known about the developmental regulation of hsp70.1 and hsp70.3 expression and the in vivo biological function of their products. To directly study the physiological role of these proteins in vivo, we have generated mice deficient in heat shock protein 70 (hsp70) by replacing the hsp70.1 or hsp70.3 gene with an in-frame beta-galactosidase sequence. We report here that the expression of hsp70.1 and hsp70.3 is developmentally regulated at the transcriptional level, and an overlapping expression pattern for both genes is observed during embryo development and in the tissues of adult mice. hsp70.1-/- or hsp70.3-/- mice are viable and fertile, with no obvious morphological abnormalities. In late embryonic stage and adult mice, both genes are expressed constitutively in tissues exposed directly to the environment (the epidermis and cornea) and in certain internal organs (the epithelium of the tongue, esophagus, and forestomach, and the kidney, bladder, and hippocampus). Exposure of mice to thermal stress results in the rapid induction and expression of hsp70, especially in organs not constitutively expressing hsp70 (the liver, pancreas, heart, lung, adrenal cortex, and intestine). Despite functional compensation in the single-gene-deficient mice by the intact homologous gene (i.e., hsp70.3 in hsp70.1-/- mice and vice versa), a marked reduction in hsp70 protein expression was observed in tissues under both normal and heat stress conditions. At the cellular level, inactivation of hsp70.1 or hsp70.3 resulted in deficient maintenance of acquired thermotolerance and increased sensitivity to heat stress-induced apoptosis. The additive or synergistic effects exhibited by coexpression of both hsp70 genes, and the evolutionary significance of the presence of both hsp70 genes, is hence underlined.