Selection of new HSF1 and HSF2 DNA-binding sites reveals difference in trimer cooperativity

Chilo suppressalis heat shock proteins are regulated by heat shock factor 1 during heat stress

Heat shock factor 1 (HSF1) functions to maintain cellular and organismal homeostasis by regulating the expression of target genes, including those encoding heat shock proteins (HSPs). In the present study, the gene encoding HSF1 was cloned from the rice pest Chilo suppressalis, and designated Cshsf1. The deduced protein product, CsHSF1, contained conserved domains typical of the HSF1 family, including a DNA-binding domain, two hydrophobic heptad repeat domains, and a C-terminal transactivation domain. Real-time quantitative PCR showed that Cshsf1 was highly expressed in hemocytes. Expression analysis in different developmental stages of C. suppressalis revealed that Cshsf1 was most highly expressed in male adults. RNAi-mediated silencing of Cshsf1 expression reduced C. suppressalis survival at high temperatures. To investigate the regulatory interactions between Cshsf1 and Cshsps, the promoters and expression patterns of 18 identified Cshsps in C. suppressalis were analysed; four types of heat shock elements (HSEs) were identified in promoter regions including canonical, tail-tail, head-head, and step/gap. The expression of Cshsp19.0, Cshsp21.7B, Cshsp60, Cshsp70 and Cshsp90 was positively regulated by Cshsf1; however, Cshsp22.8, Cshsp702, Cshsp705 and Cshsp706 gene expression was not altered. This study provides a foundation for future studies of HSF1 in insects during thermal stress.

Chromosome Y pericentric heterochromatin is a primary target of HSF1 in male cells

The heat shock factor 1 (HSF1)-dependent transcriptional activation of human pericentric heterochromatin in heat-shocked cells is the most striking example of transcriptional activation of heterochromatin. Until now, pericentric heterochromatin of chromosome 9 has been identified as the primary target of HSF1, in both normal and tumor heat-shocked cells. Transcriptional awakening of this large genomic region results in the nuclear accumulation of satellite III (SATIII) noncoding RNAs (ncRNAs) and the formation in cis of specific structures known as nuclear stress bodies (nSBs). Here, we show that, in four different male cell lines, including primary human fibroblasts and amniocytes, pericentric heterochromatin of chromosome Y can also serve as a unique primary site of HSF1-dependent heterochromatin transcriptional activation, production of SATIII ncRNA, and nucleation of nuclear stress bodies (nSBs) upon heat shock. Our observation suggests that the chromosomal origin of SATIII transcripts in cells submitted to heat shock is not a determinant factor as such, but that transcription of SATIII repetitive units or the SATIII ncRNA molecules is the critical element of HSF1-dependent transcription activation of constitutive heterochromatin.

Heat Shock Factor Is Involved in Regulating the Transcriptional Expression of Two Potential Hsps (AhHsp70 and AhsHsp21) and Its Role in Heat Shock Response of Agasicles hygrophila

Heat shock proteins are molecular chaperones that are involved in numerous normal cellular processes and stress responses, and heat shock factors are transcriptional activators of heat shock proteins. Heat shock factors and heat shock proteins are coordinated in various biological processes. The regulatory function of heat shock factors in the expression of genes encoding heat shock proteins (Hsps) has been documented in some model insects, however, the role of transcription factors in modulating Hsps in other insects is still limited. In this study, one heat shock factor gene (AhHsf) was isolated and its two potential target genes (AhHsp70 and AhsHsp21) were confirmed from Agasicles hygrophila. AhHsf sequence analysis indicated that it belongs to the Hsfs gene family. RT-qPCR showed that expression levels of heat shock factors and of two heat shock proteins significantly increased under heat stress. Injection with double-stranded Hsf RNA in freshly emerged adult beetles significantly inhibited expression of AhHsp70 and AhsHsp21, shortened the adult survival, drastically reduced egg production, and ultimately led to a decrease in fecundity. RNA interference (RNAi)-mediated suppression of AhHsp70 or AhsHsp21 expression also significantly affected expression of AhHsf. Our findings revealed a potential transcriptional function of AhHsf to regulate expression of AhHsp70 and AhsHsp21, which may play a key role in A. hygrophila thermotolerance. Our results improve our understanding of the molecular mechanisms of the AhHsf - AhHsps signaling pathway in A. hygrophila.

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.

Heat-Triggered Remote Control of CRISPR-dCas9 for Tunable Transcriptional Modulation

CRISPR-associated proteins (Cas) are enabling powerful new approaches to control mammalian cell functions, yet the lack of spatially defined, noninvasive modalities limits their use as biological tools. Here, we integrate thermal gene switches with dCas9 complexes to confer remote control of gene activation and suppression with short pulses of heat. Using a thermal switch constructed from the heat shock protein A6 (HSPA6) locus, we show that a single heat pulse 3-5 °C above basal temperature is sufficient to trigger expression of dCas9 complexes. We demonstrate that dCas9 fused to the transcriptional activator VP64 is functional after heat activation, and, depending on the number of heat pulses, drives transcription of endogenous genes GzmB and CCL21 to levels equivalent to that achieved by a constitutive viral promoter. Across a range of input temperatures, we find that downstream protein expression of GzmB closely correlates with transcript levels (R² = 0.99). Using dCas9 fused with the transcriptional suppressor KRAB, we show that longitudinal suppression of the reporter d2GFP depends on key thermal input parameters including pulse magnitude, number of pulses, and dose fractionation. In living mice, we extend our study using photothermal heating to spatially target implanted cells to suppress d2GFP in vivo. Our study establishes a noninvasive and targeted approach to harness Cas-based proteins for modulation of gene expression to complement current methods for remote control of cell function.

p53-mediated miR-18 repression activates HSF2 for IGF-IIR-dependent myocyte hypertrophy in hypertension-induced heart failure

Hypertension-induced cardiac hypertrophy and attenuated cardiac function are the major characteristics of early stage heart failure. Cardiomyocyte death in pathological cardiac conditions is the primary cause of heart failure and mortality. Our previous studies found that heat shock factor 1 (HSF1) protected cardiomyocytes from death by suppressing the IGF-IIR signaling pathway, which is critical for hypertensive angiotensin II-induced cardiomyocyte apoptosis. However, the role of heat shock factor 2 (HSF2) in hypertension-induced cardiac hypertrophy is unknown. We identified HSF2 as a miR-18 target for cardiac hypertrophy. p53 activation in angiotensin II (ANG II)-stimulated NRVMs is responsible for miR-18 downregulation both in vitro and in vivo, which triggers HSF2 expression and the activation of IGF-IIR-induced cardiomyocyte hypertrophy. Finally, we provide genetic evidence that miR-18 is required for cardiomyocyte functions in the heart based on the gene transfer of cardiac-specific miR-18 via adenovirus-associated virus 2 (AAV2). Transgenic overexpression of miR-18 in cardiomyocytes is sufficient to protect against dilated cardiomyopathy during hypertension-induced heart failure. Our results demonstrated that the p53-miR-18-HSF2-IGF-IIR axis was a critical regulatory pathway of cardiomyocyte hypertrophy in vitro and in vivo, suggesting that miR-18 could be a therapeutic target for the control of cardiac functions and the alleviation of cardiomyopathy during hypertension-induced heart failure.

The Heat Shock Transcription Factor HSF1 Induces Ovarian Cancer Epithelial-Mesenchymal Transition in a 3D Spheroid Growth Model

Ovarian cancer is the most lethal gynecological cancer, with over 200,000 women diagnosed each year and over half of those cases leading to death. The proteotoxic stress-responsive transcription factor HSF1 is frequently overexpressed in a variety of cancers and is vital to cellular proliferation and invasion in some cancers. Upon analysis of various patient data sets, we find that HSF1 is frequently overexpressed in ovarian tumor samples. In order to determine the role of HSF1 in ovarian cancer, inducible HSF1 knockdown cell lines were created. Knockdown of HSF1 in SKOV3 and HEY ovarian cancer cell lines attenuates the epithelial-to-mesenchymal transition (EMT) in cells treated with TGFβ, as determined by western blot and quantitative RT-PCR analysis of multiple EMT markers. To further explore the role of HSF1 in ovarian cancer EMT, we cultured multicellular spheroids in a non-adherent environment to simulate early avascular tumors. In the spheroid model, cells more readily undergo EMT; however, EMT inhibition by HSF1 becomes more pronounced in the spheroid model. These findings suggest that HSF1 is important in the ovarian cancer TGFβ response and in EMT.

E2F coregulates an essential HSF developmental program that is distinct from the heat-shock response

Heat-shock factor (HSF) is the master transcriptional regulator of the heat-shock response (HSR) and is essential for stress resilience. HSF is also required for metazoan development; however, its function and regulation in this process are poorly understood. Here, we characterize the genomic distribution and transcriptional activity of Caenorhabditis elegans HSF-1 during larval development and show that the developmental HSF-1 transcriptional program is distinct from the HSR. HSF-1 developmental activation requires binding of E2F/DP to a GC-rich motif that facilitates HSF-1 binding to a heat-shock element (HSE) that is degenerate from the consensus HSE sequence and adjacent to the E2F-binding site at promoters. In contrast, induction of the HSR is independent of these promoter elements or E2F/DP and instead requires a distinct set of tandem canonical HSEs. Together, E2F and HSF-1 directly regulate a gene network, including a specific subset of chaperones, to promote protein biogenesis and anabolic metabolism, which are essential in development.

Purification, crystallization and X-ray diffraction analysis of the DNA-binding domain of human heat-shock factor 2

Cells respond to various proteotoxic stimuli and maintain protein homeostasis through a conserved mechanism called the heat-shock response, which is characterized by the enhanced synthesis of heat-shock proteins. This response is mediated by heat-shock factors (HSFs). Four genes encoding HSF1-HSF4 exist in the genome of mammals. In this protein family, HSF1 is the orthologue of the single HSF in lower eukaryotic organisms and is the major regulator of the heat-shock response, while HSF2, which shows low sequence homology to HSF1, serves as a developmental regulator. Increasing evidence has revealed biochemical properties and functional roles that are unique to HSF2, such as its DNA-binding preference and sumoylation patterns, which are distinct from those of HSF1. The structural basis for such differences, however, is poorly understood owing to the lack of available mammalian HSF structures. The N-terminal DNA-binding domain (DBD) is the most conserved functional module and is the only crystallizable domain in HSFs. To date, only HSF1 homologue structures from yeast and fruit fly have been determined. Along with extensive studies of the HSF family, more structural information, particularly from members with a remoter phylogenic relationship to the reported structures, e.g. HSF2, is needed in order to better understand the detailed mechanisms of HSF biology. In this work, the recombinant DBD (residues 7-112) from human HSF2 was produced in Escherichia coli and crystallized. An X-ray diffraction data set was collected to 1.32 Å resolution from a crystal belonging to space group P212121 with unit cell-parameters a = 65.66, b = 67.26, c = 93.25 Å. The data-evaluation statistics revealed good quality of the collected data, thus establishing a solid basis for the determination of the first structure at atomic resolution in this protein family.

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

The genus Trichoderma contains fungi with high relevance for humans, with applications in enzyme production for plant cell wall degradation and use in biocontrol. Here, we provide a broad, comprehensive overview of the genomic content of these species for "hot topic" research aspects, including CAZymes, transport, transcription factors, and development, along with a detailed analysis and annotation of less-studied topics, such as signal transduction, genome integrity, chromatin, photobiology, or lipid, sulfur, and nitrogen metabolism in T. reesei, T. atroviride, and T. virens, and we open up new perspectives to those topics discussed previously. In total, we covered more than 2,000 of the predicted 9,000 to 11,000 genes of each Trichoderma species discussed, which is >20% of the respective gene content. Additionally, we considered available transcriptome data for the annotated genes. Highlights of our analyses include overall carbohydrate cleavage preferences due to the different genomic contents and regulation of the respective genes. We found light regulation of many sulfur metabolic genes. Additionally, a new Golgi 1,2-mannosidase likely involved in N-linked glycosylation was detected, as were indications for the ability of Trichoderma spp. to generate hybrid galactose-containing N-linked glycans. The genomic inventory of effector proteins revealed numerous compounds unique to Trichoderma, and these warrant further investigation. We found interesting expansions in the Trichoderma genus in several signaling pathways, such as G-protein-coupled receptors, RAS GTPases, and casein kinases. A particularly interesting feature absolutely unique to T. atroviride is the duplication of the alternative sulfur amino acid synthesis pathway.

Loss of function of myosin chaperones triggers Hsf1-mediated transcriptional response in skeletal muscle cells

Background

Mutations in myosin chaperones Unc45b and Hsp90aa1.1 as well as in the Unc45b-binding protein Smyd1b impair formation of myofibrils in skeletal muscle and lead to the accumulation of misfolded myosin. The concomitant transcriptional response involves up-regulation of the three genes encoding these proteins, as well as genes involved in muscle development. The transcriptional up-regulation of unc45b, hsp90aa1.1 and smyd1b is specific to zebrafish mutants with myosin folding defects, and is not triggered in other zebrafish myopathy models.

Results

By dissecting the promoter of unc45b, we identify a Heat shock factor 1 (Hsf1) binding element as a mediator of unc45b up-regulation in myofibers lacking myosin folding proteins. Loss-of-function of Hsf1 abolishes unc45b up-regulation in mutants with defects in myosin folding.

Conclusions

Taken together, our data show that skeletal muscle cells respond to defective myosin chaperones with a complex gene program and suggest that this response is mediated by Hsf1 activation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0825-8) contains supplementary material, which is available to authorized users.

Multifaceted roles of HSF1 in cancer

Heat shock transcription factor 1 (HSF1) is the master regulator of the heat shock response. Accumulating evidence shows that HSF1 is overexpressed in a variety of human cancers, is associated with cancer aggressiveness, and could serve as an independent diagnostic or prognostic biomarker. In this review, we will provide an overview of the multifaceted roles of HSF1 in cancer, with a special focus on the four underlying molecular mechanisms involved. First, HSF1 regulates the expression of heat shock proteins (HSPs) including HSP90, HSP70, and HSP27. Second, HSF1 regulates cellular metabolism, including glycolysis and lipid metabolism. Third, HSF1 serves as a regulator of different signaling pathways, such as HuR-HIF-1, Slug, protein kinase C (PKC), nuclear factor-kappaB (NF-κB), PI3K-AKT-mTOR, and mitogen-activated protein kinase (MAPK) pathways. Finally, HSF1 regulates microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Overall, HSF1 plays many important roles in cancer via regulating cell proliferation, anti-apoptosis, epithelial-mesenchymal transition (EMT), migration, invasion, and metastasis and may be a potential therapeutic target for human cancers.

Transcription factor cooperativity with heat shock factor 1

The heat shock response has been characterized by the induction of major heat shock proteins that suppress protein aggregation by facilitating protein folding. Recently, we found that mammalian heat shock factor 1, a master regulator of HSP genes, regulates non-HSP genes that suppress protein aggregation by controlling protein degradation in cooperation with the transcription factor NFAT.

Selection and characterization of a DNA aptamer that can discriminate between cJun/cJun and cJun/cFos

The AP-1 family of transcriptional activators plays pivotal roles in regulating a wide range of biological processes from the immune response to tumorigenesis. Determining the roles of specific AP-1 dimers in cells, however, has remained challenging because common molecular biology techniques are unable to distinguish between the role of, for example, cJun/cJun homodimers versus cJun/cFos heterodimers. Here we used SELEX (systematic evolution of ligands by exponential enrichment) to identify and characterize DNA aptamers that are >100-fold more specific for binding cJun/cJun compared to cJun/cFos, setting the foundation to investigate the biological functions of different AP-1 dimer compositions.

Akt phosphorylates and activates HSF-1 independent of heat shock, leading to Slug overexpression and epithelial-mesenchymal transition (EMT) of HER2-overexpressing breast cancer cells

Epithelial-mesenchymal transition (EMT) is an essential step for tumor progression, although the mechanisms driving EMT are still not fully understood. In an effort to investigate these mechanisms, we observed that heregulin-mediated activation of HER2, or HER2 overexpression, resulted in EMT, which is accompanied with increased expression of a known EMT regulator Slug, but not TWIST or Snail. We then investigated how HER2 induced Slug expression and found, for the first time, that there are four consensus HSF Sequence-binding Elements (HSEs), the binding sites for heat shock factor-1 (HSF-1), located in the Slug promoter. HSF-1 bound to and transactivated the Slug promoter independent of heat shock, leading to Slug expression in breast cancer cells. Mutation of the putative HSEs ablated Slug transcriptional activation induced by heregulin or HSF-1 overexpression. Knockdown of HSF-1 expression by siRNA reduced Slug expression and heregulin-induced EMT. The positive association between HSF-1 and Slug was confirmed by immunohistochemical staining of a cohort of 100 invasive breast carcinoma specimens. While investigating how HER2 activated HSF-1 independent of heat shock, we observed that HER2 activation resulted in concurrent phosphorylation of Akt and HSF-1. We then observed, also for the first time, that Akt directly interacted with HSF-1 and phosphorylated HSF-1 at S326. Inhibition of Akt using siRNA, dominant-negative Akt mutant, or small molecule inhibitors prevented heregulin-induced HSF-1 activation and Slug expression. Conversely, constitutively active Akt induced HSF-1 phosphorylation and Slug expression. HSF-1 knockdown reduced the ability of Akt to induce Slug expression, indicating an essential that HSF-1 plays in Akt-induced Slug upregulation. Together, our study uncovered the existence of a novel Akt-HSF-1 signaling axis that leads to Slug upregulation and EMT, and potentially contributes to progression of HER2-positive breast cancer.

Transcription regulation of HYPK by Heat Shock Factor 1

HYPK (Huntingtin Yeast Partner K) was originally identified by yeast two-hybrid assay as an interactor of Huntingtin, the protein mutated in Huntington's disease. HYPK was characterized earlier as an intrinsically unstructured protein having chaperone-like activity in vitro and in vivo. HYPK has the ability of reducing rate of aggregate formation and subsequent toxicity caused by mutant Huntingtin. Further investigation revealed that HYPK is involved in diverse cellular processes and required for normal functioning of cells. In this study we observed that hyperthermia increases HYPK expression in human and mouse cells in culture. Expression of exogenous Heat Shock Factor 1 (HSF1), upon heat treatment could induce HYPK expression, whereas HSF1 knockdown reduced endogenous as well as heat-induced HYPK expression. Putative HSF1-binding site present in the promoter of human HYPK gene was identified and validated by reporter assay. Chromatin immunoprecipitation revealed in vivo interaction of HSF1 and RNA polymerase II with HYPK promoter sequence. Additionally, acetylation of histone H4, a known epigenetic marker of inducible HSF1 binding, was observed in response to heat shock in HYPK gene promoter. Overexpression of HYPK inhibited cells from lethal heat-induced death whereas knockdown of HYPK made the cells susceptible to lethal heat shock-induced death. Apart from elevated temperature, HYPK was also upregulated by hypoxia and proteasome inhibition, two other forms of cellular stress. We concluded that chaperone-like protein HYPK is induced by cellular stress and under transcriptional regulation of HSF1.

HSF1-mediated regulation of tumor cell apoptosis: a novel target for cancer therapeutics

Programmed cell death/apoptosis is a genetically conserved phenomenon involved in many biological processes including reconstruction of multicellular organisms and elimination of old or damaged cells. It is regulated by the activation/deactivation of PKC in response to exogenous and endogenous stimuli. PKC is activated under stress by a series of downstream signaling cascades, which ultimately induce HSF1 activation, which results in overexpression of heat shock proteins. Overexpression of heat shock proteins interferes in the apoptotic pathway, while their blocking results in apoptosis. Therefore, HSF1 could be a novel therapeutic target against a variety of tumors. Several pharmacological inhibitors of PKC have been demonstrated to exert inhibitory effects on the activation of HSF1 and, therefore, induce apoptosis in tumor cells. However, studies regarding the role of pharmacological inhibitors in the regulation of apoptosis and possible anti-tumor therapeutic intervention are still unknown or in their infancy. Therefore, an attempt has been made to delineate the precise role of HSF1 in the regulation of apoptosis and its prospects in cancer therapeutics.

Fractal genome sequences

The existence of fractal sets of DNA sequences have long been suspected on the basis of statistical analyses of genome data. In this article we identify for the first time explicitly the GA-sequences as a class of fractal genomic sequences that are easy to recognize and to extract, and are scattered densely throughout the chromosomes of a large number of genomes from different species and kingdoms including the human genome. Their existence and their fractality may have significant consequences for our understanding of the origin and evolution of genomes. Furthermore, as universal and natural markers they may be used to chart and explore the non-coding regions.

Monitoring the induction of heat shock factor 1/heat shock protein 70 expression following 17-allylamino-demethoxygeldanamycin treatment by positron emission tomography and optical reporter gene imaging

The cell response to proteotoxic cell stresses is mediated primarily through activation of heat shock factor 1 (HSF1). This transcription factor plays a major role in the regulation of the heat shock proteins (HSPs), including HSP70. We demonstrate that an [124I]iodide-pQHNIG70 positron emission tomography (PET) reporter system that includes an inducible HSP70 promoter can be used to image and monitor the activation of the HSF1/HSP70 transcription factor in response to drug treatment (17-allylamino-demethoxygeldanamycin [17-AAG]). We developed a dual imaging reporter (pQHNIG70) for noninvasive imaging of the heat shock response in cell culture and living animals previously and now study HSF1/HSP70 reporter activation in both cell culture and tumor-bearing animals following exposure to 17-AAG. 17-AAG (10-1,000 nM) induced reporter expression; a 23-fold increase was observed by 60 hours. Good correspondence between reporter expression and HSP70 protein levels were observed. MicroPET imaging based on [124I]iodide accumulation in pQHNIG70-transduced RG2 xenografts showed a significant 6.2-fold reporter response to 17-AAG, with a corresponding increase in tumor HSP70 and in tumor human sodium iodide symporter and green fluorescent protein reporter proteins. The HSF1 reporter system can be used to screen anticancer drugs for induction of cytotoxic stress and HSF1 activation both in vitro and in vivo.

Structure, Expression, and Function of ICAM-5

Cell adhesion is of utmost importance in normal development and cellular functions. ICAM-5 (intercellular adhesion molecule-5, telencephalin, TLN) is a member of the ICAM family of adhesion proteins. As a novel cell adhesion molecule, ICAM-5 shares many structural similarities with the other members of IgSF, especially the ICAM subgroup; however, ICAM-5 has several unique properties compared to the other ICAMs. With its nine extracellular Ig domains, ICAM-5 is the largest member of ICAM subgroup identified so far. Therefore, it is much more complex than the other ICAMs. The expression of ICAM-5 is confined to the telencephalic neurons of the central nervous system whereas all the other ICAM members are expressed mostly by cells in the immune and blood systems. The developmental appearance of ICAM-5 parallels the time of dendritic elongation and branching, and synapse formation in the telencephalon. As a somatodendrite-specific adhesion molecule, ICAM-5 not only participates in immune-nervous system interactions, it could also participate in neuronal activity, Dendrites' targeting signals, and cognition. It would not be surprising if future investigations reveal more binding partners and other related functions of ICAM-5.

Regulation of HSF1 function in the heat stress response: implications in aging and disease

To dampen proteotoxic stresses and maintain protein homeostasis, organisms possess a stress-responsive molecular machinery that detects and neutralizes protein damage. A prominent feature of stressed cells is the increased synthesis of heat shock proteins (Hsps) that aid in the refolding of misfolded peptides and restrain protein aggregation. Transcriptional activation of the heat shock response is orchestrated by heat shock factor 1 (HSF1), which rapidly translocates to hsp genes and induces their expression. Although the role of HSF1 in protecting cells and organisms against severe stress insults is well established, many aspects of how HSF1 senses qualitatively and quantitatively different forms of stresses have remained poorly understood. Moreover, recent discoveries that HSF1 controls life span have prompted new ways of thinking about an old transcription factor. Here, we review the established role of HSF1 in counteracting cell stress and prospect the role of HSF1 as a regulator of disease states and aging.

Deletion of a subgroup of ribosome-related genes minimizes hypoxia-induced changes and confers hypoxia tolerance

Hypoxia is a widely occurring condition experienced by diverse organisms under numerous physiological and disease conditions. To probe the molecular mechanisms underlying hypoxia responses and tolerance, we performed a genome-wide screen to identify mutants with enhanced hypoxia tolerance in the model eukaryote, the yeast Saccharomyces cerevisiae. Yeast provides an excellent model for genomic and proteomic studies of hypoxia. We identified five genes whose deletion significantly enhanced hypoxia tolerance. They are RAI1, NSR1, BUD21, RPL20A, and RSM22, all of which encode functions involved in ribosome biogenesis. Further analysis of the deletion mutants showed that they minimized hypoxia-induced changes in polyribosome profiles and protein synthesis. Strikingly, proteomic analysis by using the iTRAQ profiling technology showed that a substantially fewer number of proteins were changed in response to hypoxia in the deletion mutants, compared with the parent strain. Computational analysis of the iTRAQ data indicated that the activities of a group of regulators were regulated by hypoxia in the wild-type parent cells, but such regulation appeared to be diminished in the deletion strains. These results show that the deletion of one of the genes involved in ribosome biogenesis leads to the reversal of hypoxia-induced changes in gene expression and related regulators. They suggest that modifying ribosomal function is an effective mechanism to minimize hypoxia-induced specific protein changes and to confer hypoxia tolerance. These results may have broad implications in understanding hypoxia responses and tolerance in diverse eukaryotes ranging from yeast to humans.

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.

Diversity in DNA recognition by heat shock transcription factors (HSFs) from model organisms

Heat shock transcription factor (HSF), an evolutionarily conserved heat-responsive regulator, binds to heat shock elements (HSEs) comprising continuous inverted repeats of the pentamer nGAAn. Here, we analyzed DNA-binding ability, particularly for the discontinuously arranged nGAAn units, of HSFs from various organisms, including Arabidopsis thaliana, Caenorhabditis elegans, Drosophila melanogaster, and Danio rerio. Among these, only C. elegans HSF failed to bind the discontinuous nGAAn units, which suggests that the target genes of HSFs in many, but not all, organisms contain discontinuous HSEs, as well as continuous HSEs. Further analysis of alternatively spliced HSF isoforms showed the importance of the C-terminal region in HSF-HSE interaction.

Meta-analysis of heat- and chemically upregulated chaperone genes in plant and human cells

Molecular chaperones are central to cellular protein homeostasis. In mammals, protein misfolding diseases and aging cause inflammation and progressive tissue loss, in correlation with the accumulation of toxic protein aggregates and the defective expression of chaperone genes. Bacteria and non-diseased, non-aged eukaryotic cells effectively respond to heat shock by inducing the accumulation of heat-shock proteins (HSPs), many of which molecular chaperones involved in protein homeostasis, in reducing stress damages and promoting cellular recovery and thermotolerance. We performed a meta-analysis of published microarray data and compared expression profiles of HSP genes from mammalian and plant cells in response to heat or isothermal treatments with drugs. The differences and overlaps between HSP and chaperone genes were analyzed, and expression patterns were clustered and organized in a network. HSPs and chaperones only partly overlapped. Heat-shock induced a subset of chaperones primarily targeted to the cytoplasm and organelles but not to the endoplasmic reticulum, which organized into a network with a central core of Hsp90s, Hsp70s, and sHSPs. Heat was best mimicked by isothermal treatments with Hsp90 inhibitors, whereas less toxic drugs, some of which non-steroidal anti-inflammatory drugs, weakly expressed different subsets of Hsp chaperones. This type of analysis may uncover new HSP-inducing drugs to improve protein homeostasis in misfolding and aging diseases.

Novel aspects of heat shock factors: DNA recognition, chromatin modulation and gene expression

Heat shock factor (HSF) is an evolutionarily conserved stress-response regulator that activates the transcription of heat shock protein genes, whose products maintain protein homeostasis under normal physiological conditions, as well as under conditions of stress. The promoter regions of the target genes contain a heat shock element consisting of multiple inverted repeats of the pentanucleotide sequence nGAAn. A single HSF of yeast can bind to heat shock elements that differ in the configuration of the nGAAn units and can regulate the transcription of various genes that function not only in stress resistance, but also in a broad range of biological processes. Mammalian cells have four HSF family members involved in different, but in some cases similar, biological functions, including stress resistance, cell differentiation and development. Mammalian HSF family members exhibit differential specificity for different types of heat shock elements, which, together with cell type-specific expression of HSFs is important in determining the target genes of each HSF. This minireview focuses on the molecular mechanisms of DNA recognition, chromatin modulation and gene expression by yeast and mammalian HSFs.

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.

Metamotifs--a generative model for building families of nucleotide position weight matrices

Background

Development of high-throughput methods for measuring DNA interactions of transcription factors together with computational advances in short motif inference algorithms is expanding our understanding of transcription factor binding site motifs. The consequential growth of sequence motif data sets makes it important to systematically group and categorise regulatory motifs. It has been shown that there are familial tendencies in DNA sequence motifs that are predictive of the family of factors that binds them. Further development of methods that detect and describe familial motif trends has the potential to help in measuring the similarity of novel computational motif predictions to previously known data and sensitively detecting regulatory motifs similar to previously known ones from novel sequence.

Results

We propose a probabilistic model for position weight matrix (PWM) sequence motif families. The model, which we call the 'metamotif' describes recurring familial patterns in a set of motifs. The metamotif framework models variation within a family of sequence motifs. It allows for simultaneous estimation of a series of independent metamotifs from input position weight matrix (PWM) motif data and does not assume that all input motif columns contribute to a familial pattern. We describe an algorithm for inferring metamotifs from weight matrix data. We then demonstrate the use of the model in two practical tasks: in the Bayesian NestedMICA model inference algorithm as a PWM prior to enhance motif inference sensitivity, and in a motif classification task where motifs are labelled according to their interacting DNA binding domain.

Conclusions

We show that metamotifs can be used as PWM priors in the NestedMICA motif inference algorithm to dramatically increase the sensitivity to infer motifs. Metamotifs were also successfully applied to a motif classification problem where sequence motif features were used to predict the family of protein DNA binding domains that would interact with it. The metamotif based classifier is shown to compare favourably to previous related methods. The metamotif has great potential for further use in machine learning tasks related to especially de novo computational sequence motif inference. The metamotif methods presented have been incorporated into the NestedMICA suite.

Roles of heat shock factor 1 and 2 in response to proteasome inhibition: consequence on p53 stability

A single heat shock factor (HSF), mediating the heat shock response, exists from yeast to Drosophila, whereas several related HSFs have been found in mammals. This raises the question of the specific or redundant functions of the different members of the HSF family and in particular of HSF1 and HSF2, which are both ubiquitously expressed. Using immortalized mouse embryonic fibroblasts (iMEFs) derived from wild-type, Hsf1(-/-), Hsf2(-/-) or double-mutant mice, we observed the distinctive behaviors of these mutants with respect to proteasome inhibition. This proteotoxic stress reduces to the same extent the viability of Hsf1(-/-)- and Hsf2(-/-)-deficient cells, but through different underlying mechanisms. Contrary to Hsf2(-/-) cells, Hsf1(-/-) cells are unable to induce pro-survival heat shock protein expression. Conversely, proteasome activity is lower in Hsf2(-/-) cells and the expression of some proteasome subunits, such as Psmb5 and gankyrin, is decreased. As gankyrin is an oncoprotein involved in p53 degradation, we analyzed the status of p53 in HSF-deficient iMEFs and observed that it was strongly stabilized in Hsf2(-/-) cells. This study points a new role for HSF2 in the regulation of protein degradation and suggests that pan-HSF inhibitors could be valuable tools to reduce chemoresistance to proteasome inhibition observed in cancer therapy.

Chaperone networks: tipping the balance in protein folding diseases

Adult-onset neurodegeneration and other protein conformational diseases are associated with the appearance, persistence, and accumulation of misfolded and aggregation-prone proteins. To protect the proteome from long-term damage, the cell expresses a highly integrated protein homeostasis (proteostasis) machinery to ensure that proteins are properly expressed, folded, and cleared, and to recognize damaged proteins. Molecular chaperones have a central role in proteostasis as they have been shown to be essential to prevent the accumulation of alternate folded proteotoxic states as occurs in protein conformation diseases exemplified by neurodegeneration. Studies using invertebrate models expressing proteins associated with Huntington's disease, Alzheimer's disease, ALS, and Parkinson's disease have provided insights into the genetic networks and stress signaling pathways that regulate the proteostasis machinery to prevent cellular dysfunction, tissue pathology, and organismal failure. These events appear to be further amplified by aging and provide evidence that age-related failures in proteostasis may be a common element in many diseases.

Refined methods for propagating vesicular stomatitis virus vectors that are defective for G protein expression

Propagation-defective vesicular stomatitis virus (VSV) vectors that encode a truncated G protein (VSV-Gstem) or lack the G gene entirely (VSV-DeltaG) are attractive vaccine vectors because they are immunogenic, cannot replicate and spread after vaccination, and do not express many of the epitopes that elicit neutralizing anti-VSV immunity. To consider advancing non-propagating VSV vectors towards clinical assessment, scalable technology that is compliant with human vaccine manufacturing must be developed to produce clinical trial material. Accordingly, two propagation methods were developed for VSV-Gstem and VSV-DeltaG vectors encoding HIV gag that have the potential to support large-scale production. One method is based on transient expression of G protein after electroporating plasmid DNA into Vero cells and the second is based on a stable Vero cell line that contains a G gene controlled by a heat shock-inducible transcription unit. Both methods reproducibly supported production of 1 x 10(7) to 1 x 10(8) infectious units (I.U.s) of vaccine vector per milliliter. Results from these studies also showed that optimization of the G gene is necessary for abundant G protein expression from electroporated plasmid DNA or from DNA integrated in the genome of a stable cell line, and that the titers of VSV-Gstem vectors generally exceeded VSV-DeltaG.

Mutational analysis of human heat-shock transcription factor 1 reveals a regulatory role for oligomerization in DNA-binding specificity

HSF (heat-shock transcription factor) trimers bind to the HSE (heat-shock element) regulatory sequence of target genes and regulate gene expression. A typical HSE consists of at least three contiguous inverted repeats of the 5-bp sequence nGAAn. Yeast HSF is able to recognize discontinuous HSEs that contain gaps in the array of the nGAAn sequence; however, hHSF1 (human HSF1) fails to recognize such sites in vitro, in yeast and in HeLa cells. In the present study, we isolated suppressors of the temperature-sensitive growth defect of hHSF1-expressing yeast cells. Intragenic suppressors contained amino acid substitutions in the DNA-binding domain of hHSF1 that enabled hHSF1 to regulate the transcription of genes containing discontinuous HSEs. The substitutions facilitated hHSF1 oligomerization, suggesting that the DNA-binding domain is important for this conformational change. Furthermore, other oligomerization-prone derivatives of hHSF1 were capable of recognizing discontinuous HSEs. These results suggest that modulation of oligomerization is important for the HSE specificity of hHSF1 and imply that hHSF1 possesses the ability to bind to and regulate gene expression via various types of HSEs in diverse cellular processes.

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.

The analysis of entire gene promoters by surface plasmon resonance

We demonstrate that the biophysical technique of surface plasmon resonance (SPR) analysis, which has previously been used to measure transcription factor binding to short DNA molecules, can also be used to characterize interactions involving entire gene promoters. This discovery has two main implications that relate, respectively, to novel qualitative and quantitative uses of the SPR technique. Firstly, SPR analysis can be used qualitatively to test the capacity of any transcription factor to interact physically with its putative target genes. This application should prove particularly useful for the confirmation of predicted transcriptional interactions in model species, and for comparative studies of non-model species in which transcriptional interactions are not amenable to study by other methods. Secondly, SPR may be used quantitatively to characterize interactions between transcription factors and gene promoters containing multiple cis-acting sites. This application should prove useful for the detailed dissection of promoter function in known target genes. The qualitative and quantitative applications of the SPR analysis of whole promoters combine to make this a uniquely powerful technique, which should prove particularly useful in systems biology, evolutionary developmental biology and various branches of applied biology.

A DNA sequence directed mutual transcription regulation of HSF1 and NFIX involves novel heat sensitive protein interactions

BACKGROUND

Though the Nuclear factor 1 family member NFIX has been strongly implicated in PDGFB-induced glioblastoma, its molecular mechanisms of action remain unknown. HSF1, a heat shock-related transcription factor is also a powerful modifier of carcinogenesis by several factors, including PDGFB. How HSF1 transcription is controlled has remained largely elusive.

METHODOLOGY/PRINCIPAL FINDINGS

By combining microarray expression profiling and a yeast-two-hybrid screen, we identified that NFIX and its interactions with CGGBP1 and HMGN1 regulate expression of HSF1. We found that CGGBP1 organizes a bifunctional transcriptional complex at small CGG repeats in the HSF1 promoter. Under chronic heat shock, NFIX uses CGGBP1 and HMGN1 to get recruited to this promoter and in turn affects their binding to DNA. Results show that the interactions of NFIX with CGGBP1 and HMGN1 in the soluble fraction are heat shock sensitive due to preferential localization of CGGBP1 to heterochromatin after heat shock. HSF1 in turn was found to bind to the NFIX promoter and repress its expression in a heat shock sensitive manner.

CONCLUSIONS/SIGNIFICANCE

NFIX and HSF1 exert a mutual transcriptional repressive effect on each other which requires CGG repeat in HSF1 promoter and HSF1 binding site in NFIX promoter. We unravel a unique mechanism of heat shock sensitive DNA sequence-directed reciprocal transcriptional regulation between NFIX and HSF1. Our findings provide new insights into mechanisms of transcription regulation under stress.

Outline of a genome navigation system based on the properties of GA-sequences and their flanks

Introducing a new method to visualize large stretches of genomic DNA (see Appendix S1) the article reports that most GA-sequences [1] shared chains of tetra-GA-motifs and contained upstream poly(A)-segments. Although not integral parts of them, Alu-elements were found immediately upstream of all human and chimpanzee GA-sequences with an upstream poly(A)-segment. The article hypothesizes that genome navigation uses these properties of GA-sequences in the following way. (1) Poly(A) binding proteins interact with the upstream poly(A)-segments and arrange adjacent GA-sequences side-by-side ('GA-ribbon'), while folding the intervening DNA sequences between them into loops ('associated DNA-loops'). (2) Genome navigation uses the GA-ribbon as a search path for specific target genes that is up to 730-fold shorter than the full-length chromosome. (3) As to the specificity of the search, each molecule of a target protein is assumed to catalyze the formation of specific oligomers from a set of transcription factors that recognize tetra-GA-motifs. Their specific combinations of tetra-GA motifs are assumed to be present in the particular GA-sequence whose associated loop contains the gene for the target protein. As long as the target protein is abundant in the cell it produces sufficient numbers of such oligomers which bind to their specific GA-sequences and, thereby, inhibit locally the transcription of the target protein in the associated loop. However, if the amount of target protein drops below a certain threshold, the resultant reduction of specific oligomers leaves the corresponding GA-sequence 'denuded'. In response, the associated DNA-loop releases its nucleosomes and allows transcription of the target protein to proceed. (4) The Alu-transcripts may help control the general background of protein synthesis proportional to the number of transcriptionally active associated loops, especially in stressed cells. (5) The model offers a new mechanism of co-regulation of protein synthesis based on the shared segments of different GA-sequences.

Proteasome inhibitor MG132 induces BAG3 expression through activation of heat shock factor 1

BAG3 protein, a member of the BAG co-chaperones family, sustains cell survival in a variety of normal and neoplastic cell types, via its interaction with a variety of partners, such as the heat shock protein (HSP) 70, Bcl-2, Raf-1 and others. Expression of BAG3 is induced by some stressful stimuli, such as heat shock, heavy metal exposure. We have reported that proteasome inhibitors can also induce BAG3 expression at the transcriptional level and the induction of BAG3 compromises proteasome inhibitors-mediated apoptosis. However, the molecular mechanism of BAG3 upregulation has not been elucidated. In the current study, we provide evidence that heat shock transcription factor 1 (HSF1) is involved in BAG3 induction by proteasome inhibitor MG132. Using a series of varying lengths of 5'-flanking region of the BAG3 gene into luciferase reporter vectors, we found that MG132 stimulated the promoter activity via the -326/-233 and -825/-689 regions, which contains one putative heat shock-responsive element (HSE) for HSF1-binding, respectively. Site-directed deletion of the sites abrogated the enhanced reporter activity in response to MG132 treatment. Chromatin immunoprecipitation assay demonstrated that HSF1 directly bound to the MG132-responsive site on the BAG3 promoter. Activation of HSF1 occurred with MG132 along with BAG3 upregulation. Furthermore, knockdown HSF1 by small interfering RNA attenuated the BAG3 upregulation due to MG132.These results indicate that the proteasome inhibitor MG132 induces BAG3 expression through HSF1 activation.

Properties and distribution of pure GA-sequences of mammalian genomes

The article describes DNA sequences of mammalian genomes that are longer than 50 bases, but consist exclusively of G's and A's (‘pure GA-sequences’). Although their frequency of incidence should be 10⁻¹⁶ or smaller, the chromosomes of human, chimpanzee, dog, cat, rat, and mouse contained many tens of thousands of them ubiquitously located along the chromosomes with a species-dependent density, reaching sizes of up to 1300 [b]. With the exception of a small number of poly-A-, poly-G-, poly-GA-, and poly-GAAA-sequences (combined <0.5%), all pure GA-sequences of the mammals tested were unique individuals, contained several repeated short GA-containing motifs, and shared a common hexa-nucleotide spectrum. At most 2% of the human GA-sequences were transcribed into mRNAs; all others were not coding for proteins. Although this could have made them less subject to natural selection, they contained 160 times fewer point mutations than one should expect from the genome at large. As to the presence of other sequences with similarly restricted base contents, there were approximately as many pure TC-sequences as pure GA-sequences, but many fewer pure AC-, TA, and TG-sequences. There were practically no pure GC-sequences. The functions of pure GA-sequences are not known. Supported by a number of observations related to heat shock phenomena, the article speculates that they serve as genomic sign posts which may help guide polymerases and transcription factors to their proper targets, and/or as spatial linkers that help generate the 3-dimensional organization of chromatin.

Isolation and characterization of two cytoplasmic hsp90s from Mytilus galloprovincialis (Mollusca: Bivalvia) that contain a complex promoter with a p53 binding site

The commercially important marine bivalve Mytilus galloprovincialis (Mediterranean mussel) is considered a valuable bioindicator, due to its exposure to various pollutants and extreme environmental conditions. Environmental responsive genes, such as the hsp90s, protect the structure and function of cells and accomplish a significant task in cellular homeostasis. To study the hsp90s in M. galloprovincialis a genomic library was screened and two hsp90s were isolated. Sequence analysis revealed that the two genes exhibit great similarities in both the 5' non-coding and the coding region but differ in the 3' non-coding region, as well as in three introns, due to the presence of repeated sequences. Few synonymous substitutions in the coding region of the genes result to an identical predicted polypeptide, which belongs to the cytoplasmic HSP90 subfamily. The 5' non-coding region contains a non-translated exon and multiple binding sites for various transcription factors. The presence of a p53 binding site in the promoter of the isolated genes raises questions about the possible implication of hsp90s in the molluscan leukemia.

Urotensin II: lessons from comparative studies for general endocrinology

The importance of combining studies across vertebrates to provide insights into the functionality of hormone systems is considered, using recent advances in Urotensin II (UII) biology to illustrate this. The impact of genome analyses on understanding ligand and UII receptor (UT) structures is reviewed, noting their high conservation from fish to mammals. The early linkage of UII with fish osmoregulatory physiology drove our investigation of possible renal actions of UII in mammals. The kidney is a potential major source of UII in mammals and endogenous peptide appears to have tonal influence over renal excretion of water and electrolytes. Blockade of UII actions by administration of UT receptor antagonist, urantide, in anaesthetised rats, indicates that endogenous UII lowers renal filtration rates and excretion of water and ions. These effects are considered in relation to apparent association of UII with a number of human cardiovascular and renal disorders. Following up the sequencing of UT in mammals here we contrast the first fish UT sequences with those in other species. It is now evident that UT expression in fish osmoregulatory tissues, such as the gill and kidney, exhibits considerable plasticity in response to physiological challenge, providing an important component of the adaptive organismal responses. A number of areas of UII research, which will continue to benefit from moving questions between appropriate vertebrate groups, have been highlighted. These comparative approaches will yield improved understanding and further novel actions of this intriguing endocrine and paracrine system, so highly conserved across the vertebrate series.

Heat Shock Factor 1 as a Coordinator of Stress and Developmental Pathways

The transition from normal growth conditions to stressful conditions is accompanied by a robust upregulation of heat shock proteins, which dampen the cytotoxicity caused by misfolded and denatured proteins. The most prominent part of this transition occurs on the transcriptional level. In mammals, protein-damaging stress leads to the activation of heat shock factor 1 (HSF1), which binds to upstream regulatory sequences in the promoters of heat shock genes. The activation of HSF1 proceeds through a multi-step pathway, involving a monomer-to-trimer transition, nuclear accumulation and extensive posttranslational modifications. In addition to its established role as the main regulator of heat shock genes, new data link HSF 1 to developmental pathways. In this chapter, we examine the established stress-related functions and prospect the intriguing role of HSF 1 as a developmental coordinator.

Heat shock transcription factor 1 down-regulates spermatocyte-specific 70 kDa heat shock protein expression prior to the induction of apoptosis in mouse testes

Expression of constitutively active heat shock transcription factor 1 (HSF1) in mouse spermatocytes induces apoptosis and leads to male infertility. We report here that prior to the onset of massive apoptosis caused by expression of active HSF1 in spermatocytes a marked reduction in spermatocyte-specific Hsp70.2 mRNA and protein levels occurs. In addition, HSP70.2 protein relocalizes from a predominant cytoplasmic to a nuclear position in developing spermatocytes that express active HSF1. Later in the developmental stages, cells undergoing HSF1-induced apoptosis essentially lack the HSP70.2 protein. The down-regulation of Hsp70.2 gene expression by HSF1 is paradoxical because HSF1 is the prototypical activator of HSP genes. Furthermore, HSF1-mediated repression neither involved a heat shock element (HSE)-like sequence adjacent to the Hsp70.2 gene nor were Hsp70.2 promoter sequences associated directly with HSF1. Interestingly, other spermatocyte- and spermatid-specific transcripts are also down-regulated in testes of transgenic mice expressing active HSF1, suggesting involvement of a putative HSF1-dependent block of development of spermatogenic cells. Importantly however, transcription of the Hsp70.2 gene is down-regulated in testes of wild-type mice subjected to a hyperthermia that induces transient activation of HSF1, indicating that the spermatocyte-specific activity of HSF1 might misdirect a network of transcription factors required for proper regulation of Hsp70.2.

Interaction between heat shock transcription factors (HSFs) and divergent binding sequences: binding specificities of yeast HSFs and human HSF1

The target genes of the heat shock transcription factor (HSF) contain a cis-acting sequence, the heat shock element (HSE), which consists of multiple inverted repeats of the sequence 5'-nGAAn-3'. Using data acquired in this and a previous study, we have identified the HSEs in 59 of 62 target genes of Saccharomyces cerevisiae Hsf1. The Hsf1 protein recognizes continuous and discontinuous repeats of the nGAAn unit; the nucleotide sequences and configuration of the units diverge slightly among functional HSEs. When Schizosaccharomyces pombe HSF was expressed in S. cerevisiae cells, heat shock induced S. pombe HSF to bind to various HSE types, which properly activated transcription from almost all target genes, suggesting that the S. pombe genome also contains divergent HSEs. Human HSF1 induced the heat shock response via HSEs with continuous units in S. cerevisiae cells but failed to do so via HSEs with discontinuous units. Binding of human HSF1 to the discontinuous type of HSE was observed in vitro but was significantly inhibited in vivo. These results show that human HSF1 recognizes HSEs in a slightly different way than yeast HSFs and suggest that the configuration of the unit is an important determinant for HSF-HSE interactions.