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Lea Sistonen - One of the best experts on this subject based on the ideXlab platform.

  • Heat-shock factor 2 is a suppressor of prostate cancer invasion
    Oncogene, 2016
    Co-Authors: Johanna K. Björk, Jenny Joutsen, M C Puustinen, Malin Akerfelt, Lea Sistonen, F. Cheng, Matthias Nees
    Abstract:

    Heat-shock factors (HSFs) are key transcriptional regulators in cell survival. Although HSF1 has been identified as a driver of carcinogenesis, HSF2 has not been explored in malignancies. Here, we report that HSF2 suppresses tumor invasion of prostate cancer (PrCa). In three-dimensional organotypic cultures and the in vivo xenograft chorioallantoic membrane model HSF2 knockdown perturbs organoid differentiation and promotes invasiveness. Gene expression profiling together with functional studies demonstrated that the molecular mechanism underlying the effect on tumor progression originates from HSF2 steering the switch between acinar morphogenesis and invasion. This is achieved by the regulation of genes connected to, for example, GTPase activity, cell adhesion, extracellular matrix and actin cytoskeleton dynamics. Importantly, low HSF2 expression correlates with high Gleason score, metastasis and poor survival of PrCa patients, highlighting the clinical relevance of our findings. Finally, the study was expanded beyond PrCa, revealing that the expression of HSF2 is decreased in a wide range of cancer types. This study provides the first evidence for HSF2 acting as a suppressor of invasion in human malignancies.

  • expression of hsf2 decreases in mitosis to enable stress inducible transcription and cell survival
    Journal of Cell Biology, 2014
    Co-Authors: Alexandra N. Elsing, Pia Roosmattjus, Camilla Aspelin, Heidi A Bergman, Samu V Himanen, Johanna K. Björk, Marko J Kallio, Lea Sistonen
    Abstract:

    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.

  • Transcriptional response to stress in the dynamic chromatin environment of cycling and mitotic cells.
    Proceedings of the National Academy of Sciences of the United States of America, 2013
    Co-Authors: Anniina Vihervaara, Christian Sergelius, Jenni Vasara, Malin A. H. Blom, Alexandra N. Elsing, Pia Roos-mattjus, Lea Sistonen
    Abstract:

    Heat shock factors (HSFs) are the master regulators of transcription under protein-damaging conditions, acting in an environment where the overall transcription is silenced. We determined the genomewide transcriptional program that is rapidly provoked by HSF1 and HSF2 under acute stress in human cells. Our results revealed the molecular mechanisms that maintain cellular homeostasis, including HSF1-driven induction of polyubiquitin genes, as well as HSF1- and HSF2-mediated expression patterns of cochaperones, transcriptional regulators, and signaling molecules. We characterized the genomewide transcriptional response to stress also in mitotic cells where the chromatin is tightly compacted. We found a radically limited binding and transactivating capacity of HSF1, leaving mitotic cells highly susceptible to proteotoxicity. In contrast, HSF2 occupied hundreds of loci in the mitotic cells and localized to the condensed chromatin also in meiosis. These results highlight the importance of the cell cycle phase in transcriptional responses and identify the specific mechanisms for HSF1 and HSF2 in transcriptional orchestration. Moreover, we propose that HSF2 is an epigenetic regulator directing transcription throughout cell cycle progression.

  • Heat shock factors: integrators of cell stress, development and lifespan
    Nature Reviews Molecular Cell Biology, 2010
    Co-Authors: Malin Akerfelt, Richard I. Morimoto, Lea Sistonen
    Abstract:

    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. Heat shock factors (HSFs) are essential for all organisms to survive exposures to stress, as they bind heat shock elements to induce transcription of heat shock proteins (HSPs). In addition, the HSFs are important regulators involved in development, lifespan and disease, thereby integrating pathways of stress responses and normal physiology. The mammalian HSF family consists of four members: HSF1, HSF2, HSF3 and HSF4. Distinct HSFs possess unique and overlapping functions, with a great variation in expression patterns, post-translational modifications (PTMs) and interacting protein partners. HSFs are composed of functional domains, of which the DNA-binding domain is best preserved. The HSF1 activation–attenuation cycle involves trimerization, strict regulation by multiple PTMs, such as acetylation, phosphorylation and sumoylation, and feedback from HSPs. Functional crosstalk between HSF family members facilitates the fine-tuning of HSF-mediated gene regulation. HSF-knockout mouse models have made it possible to identify many targets, which have further extended the impact of HSFs in developmental processes, such as oogenesis, corticogenesis and spermatogenesis. The ability to sense and respond to environmental challenges is important for lifespan, and HSF1 is a longevity factor that prevents global instability of the proteome during ageing. The life-promoting function of HSF1 is strictly controlled by the insulin and insulin-like signalling pathway in Caenorhabditis elegans . HSF1 is a potent modifier of tumorigenesis and HSF1 deficiency in mice counteracts tumour initiation and progression. HSF1 is therefore a potential cancer drug target. As many human, age-related pathologies are associated with stress and misfolded proteins, several small-molecule activators and inhibitors of HSFs could be used for pharmacologic modulation of HSF-mediated gene regulation. Heat shock factors (HSFs) are essential for survival in a stressful environment. HSFs mediate the heat shock response by binding heat shock elements present in heat shock protein (HSP) genes, thereby mediating their transcription. They are also important regulators of development, lifespan and disease.

  • Heterotrimerization of Heat-Shock Factors 1 and 2 Provides a Transcriptional Switch in Response to Distinct Stimuli
    Molecular Biology of the Cell, 2009
    Co-Authors: Anton Sandqvist, Caroline Jolly, Zhanna Chitikova, Claire Vourc'h, Yvonne Nymalm, Malin Akerfelt, Johanna K. Björk, Tiina A. Salminen, Alexei Grichine, Lea Sistonen
    Abstract:

    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.

Richard I. Morimoto - One of the best experts on this subject based on the ideXlab platform.

  • Heat shock factors: integrators of cell stress, development and lifespan
    Nature Reviews Molecular Cell Biology, 2010
    Co-Authors: Malin Akerfelt, Richard I. Morimoto, Lea Sistonen
    Abstract:

    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. Heat shock factors (HSFs) are essential for all organisms to survive exposures to stress, as they bind heat shock elements to induce transcription of heat shock proteins (HSPs). In addition, the HSFs are important regulators involved in development, lifespan and disease, thereby integrating pathways of stress responses and normal physiology. The mammalian HSF family consists of four members: HSF1, HSF2, HSF3 and HSF4. Distinct HSFs possess unique and overlapping functions, with a great variation in expression patterns, post-translational modifications (PTMs) and interacting protein partners. HSFs are composed of functional domains, of which the DNA-binding domain is best preserved. The HSF1 activation–attenuation cycle involves trimerization, strict regulation by multiple PTMs, such as acetylation, phosphorylation and sumoylation, and feedback from HSPs. Functional crosstalk between HSF family members facilitates the fine-tuning of HSF-mediated gene regulation. HSF-knockout mouse models have made it possible to identify many targets, which have further extended the impact of HSFs in developmental processes, such as oogenesis, corticogenesis and spermatogenesis. The ability to sense and respond to environmental challenges is important for lifespan, and HSF1 is a longevity factor that prevents global instability of the proteome during ageing. The life-promoting function of HSF1 is strictly controlled by the insulin and insulin-like signalling pathway in Caenorhabditis elegans . HSF1 is a potent modifier of tumorigenesis and HSF1 deficiency in mice counteracts tumour initiation and progression. HSF1 is therefore a potential cancer drug target. As many human, age-related pathologies are associated with stress and misfolded proteins, several small-molecule activators and inhibitors of HSFs could be used for pharmacologic modulation of HSF-mediated gene regulation. Heat shock factors (HSFs) are essential for survival in a stressful environment. HSFs mediate the heat shock response by binding heat shock elements present in heat shock protein (HSP) genes, thereby mediating their transcription. They are also important regulators of development, lifespan and disease.

  • Stress-Specific Activation and Repression of Heat Shock Factors 1 and 2
    Molecular and Cellular Biology, 2001
    Co-Authors: Anu Mathew, Caroline Jolly, Sameer K. Mathur, Richard I. Morimoto
    Abstract:

    Vertebrate cells express a family of heat shock transcription factors (HSF1 to HSF4) that coordinate the inducible regulation of heat shock genes in response to diverse signals. HSF1 is potent and activated rapidly though transiently by heat shock, whereas HSF2 is a less active transcriptional regulator but can retain its DNA binding properties for extended periods. Consequently, the differential activation of HSF1 and HSF2 by various stresses may be critical for cells to survive repeated and diverse stress challenges and to provide a mechanism for more precise regulation of heat shock gene expression. Here we show, using a novel DNA binding and detection assay, that HSF1 and HSF2 are coactivated to different levels in response to a range of conditions that cause cell stress. Above a low basal activity of both HSFs, heat shock preferentially activates HSF1, whereas the amino acid analogue azetidine or the proteasome inhibitor MG132 coactivates both HSFs to different levels and hemin preferentially induces HSF2. Unexpectedly, we also found that heat shock has dramatic adverse effects on HSF2 that lead to its reversible inactivation coincident with relocalization from the nucleus. The reversible inactivation of HSF2 is specific to heat shock and does not occur with other stressors or in cells expressing high levels of heat shock proteins. These results reveal that HSF2 activity is negatively regulated by heat and suggest a role for heat shock proteins in the positive regulation of HSF2.

  • heat shock response and protein degradation regulation of hsf2 by the ubiquitin proteasome pathway
    Molecular and Cellular Biology, 1998
    Co-Authors: Anu Mathew, Sameer K. Mathur, Richard I. Morimoto
    Abstract:

    Mammalian cells coexpress a family of heat shock factors (HSFs) whose activities are regulated by diverse stress conditions to coordinate the inducible expression of heat shock genes. Distinct from HSF1, which is expressed ubiquitously and activated by heat shock and other stresses that result in the appearance of nonnative proteins, the stress signal for HSF2 has not been identified. HSF2 activity has been associated with development and differentiation, and the activation properties of HSF2 have been characterized in hemintreated human K562 erythroleukemia cells. Here, we demonstrate that a stress signal for HSF2 activation occurs when the ubiquitin-proteasome pathway is inhibited. HSF2 DNA-binding activity is induced upon exposure of mammalian cells to the proteasome inhibitors hemin, MG132, and lactacystin, and in the mouse ts85 cell line, which carries a temperature sensitivity mutation in the ubiquitin-activating enzyme (E1) upon shift to the nonpermissive temperature. HSF2 is labile, and its activation requires both continued protein synthesis and reduced degradation. The downstream effect of HSF2 activation by proteasome inhibitors is the induction of the same set of heat shock genes that are induced during heat shock by HSF1, thus revealing that HSF2 affords the cell with a novel heat shock gene-regulatory mechanism to respond to changes in the protein-degradative machinery.

  • Function and regulation of heat shock factor 2 during mouse embryogenesis
    Proceedings of the National Academy of Sciences of the United States of America, 1997
    Co-Authors: Murielle Rallu, Michel Morange, Marie Thérèse Loones, Y. Lallemand, Richard I. Morimoto, Valérie Mezger
    Abstract:

    The spontaneous expression of heat shock genes during development is well documented in many animal species, but the mechanisms responsible for this developmental regulation are only poorly understood. In vertebrates, additional heat shock transcription factors, distinct from the heat shock factor 1 (HSF1) involved in the stress response, were suggested to be involved in this developmental control. In particular, the mouse HSF2 has been found to be active in testis and during preimplantation development. However, the role of HSF2 and its mechanism of activation have remained elusive due to the paucity of data on its expression during development. In this study, we have examined HSF2 expression during the postimplantation phase of mouse development. Our data show a developmental regulation of HSF2, which is expressed at least until 15.5 days of embryogenesis. It becomes restricted to the central nervous system during the second half of gestation. It is expressed in the ventricular layer of the neural tube which contains mitotically active cells but not in postmitotic neurons. Parallel results were obtained for mRNA, protein, and activity levels, demonstrating that the main level of control was transcriptional. The detailed analysis of the activity of a luciferase reporter gene under the control of the hsp70.1 promoter, as well as the description of the protein expression patterns of the major heat shock proteins in the central nervous system, show that HSF2 and heat shock protein expression domains do not coincide. This result suggests that HFS2 might be involved in other regulatory developmental pathways and paves the way to new functional approaches.

  • Regulatory differences in the stress response of hippocampal neurons and glial cells after heat shock
    The Journal of Neuroscience, 1996
    Co-Authors: Charles J. Marcuccilli, Richard I. Morimoto, Sameer K. Mathur, Richard J. Miller
    Abstract:

    During periods of stress, cells depend on a transient, highly conserved, and regulated response to maintain homeostasis. This "heat shock response" is mediated transcriptionally by a multigene family of heat shock factors (HSF). The presence of multiple HSF suggests that activation of a given HSF is stress-specific. Using Western blot analysis, we have demonstrated the inability of primary cultured rat hippocampal neurons to induce a heat shock response after hyperthermia. In contrast, secondary cultured rat glial cells demonstrated a robust response. Examination of whole-cell extracts from the two cell types with gel shift mobility analysis and Western blot analysis revealed that although glial cells express HSF1 and HSF2, hippocampal neurons only express HSF2. Incubation of whole-cell extracts with monoclonal antisera raised against HSF1 and HSF2 before gel shift mobility analysis demonstrated HSF1 DNA-binding activity in glial cells and HSF2 DNA-binding activity in neurons. HSF1 has been shown to be the principal mediator of heat-induced heat shock gene expression. These results suggest that the deficient heat shock response of hippocampal neurons at this developmental stage is attributable to a lack of HSF1 expression. Furthermore, these results suggest that considerations of selective neuronal vulnerability to environmental stress should include the principal mediators of the stress response, the HSF.

Kevin D. Sarge - One of the best experts on this subject based on the ideXlab platform.

  • RNA Polymerase II interacts with the Hspa1b Promoter in Mouse Epididymal Spermatozoa
    Reproduction, 2009
    Co-Authors: Dennis Charles Wilkerson, Kevin D. Sarge
    Abstract:

    The Hspa1b (Hsp70.1) gene is one of the first genes expressed after fertilization, with expression occurring during the minor zygotic genome activation in the absence of stress. This expression can take place in the male pronucleus as early as the one-cell stage of embryogenesis. The importance of HSPA1B for embryonic viability during times of stress is supported by studies showing that depletion of this protein results in a significant reduction in embryos developing to the blastocyte stage. Recently we began addressing the mechanism responsible for allowing expression of Hspa1b during the minor ZGA and found that HSF1 and HSF2 bind the Hspa1b promoter during late spermatogenesis. In this report, we have extended those studies using western blots and chromatin immunoprecipitation assays and found that RNA Polymerase II is present in epididymal spermatozoa and bound to the Hspa1b promoter. These present results, in addition to our previous results, support a model in which the binding of HSF1, HSF2, Sp1, and RNA Polymerase II to the promoter of Hspa1b would allow the rapid formation of a transcription-competent state during the minor ZGA, thereby allowing Hspa1b expression.

  • interaction of HSF1 and hsf2 with the hspa1b promoter in mouse epididymal spermatozoa
    Biology of Reproduction, 2008
    Co-Authors: Dennis Charles Wilkerson, Lynea A Murphy, Kevin D. Sarge
    Abstract:

    The Hspa1b gene is one of the first genes expressed after fertilization, with expression observed in the male pronucleus as early as the one-cell stage of embryogenesis. This expression can occur in the absence of stress and is initiated during the minor zygotic genome activation. There is a significant reduction in the number of embryos developing to the blastocyte stage when HSPA1B levels are depleted, which supports the importance of this protein for embryonic viability. However, the mechanism responsible for allowing expression of Hspa1b during the minor zygotic genome activation (ZGA) is unknown. In this report, we investigated the role of HSF1 and HSF2 in bookmarking Hspa1b during late spermatogenesis. Western blot results show that both HSF1 and HSF2 are present in epididymal spermatozoa, and immunofluorescence analysis revealed that some of the HSF1 and HSF2 proteins in these cells overlap the 4′,6′-diamidino-2-phenylindole-stained DNA region. Results from chromatin immunoprecipitation assays showed that HSF1, HSF2, and SP1 are bound to the Hspa1b promoter in epididymal spermatozoa. Furthermore, we observed an increase in HSF2 binding to the Hspa1b promoter in late spermatids versus early spermatids, suggesting a likely period during spermatogenesis when transcription factor binding could occur. These results support a model in which the binding of HSF1, HSF2, and SP1 to the promoter of Hspa1b would allow the rapid formation of a transcription-competent state during the minor ZGA, thereby allowing Hspa1b expression.

  • prc1 associates with the hsp70i promoter and interacts with hsf2 during mitosis
    Experimental Cell Research, 2008
    Co-Authors: Lynea A Murphy, Dennis Charles Wilkerson, Yiling Hong, Kevin D. Sarge
    Abstract:

    Mitosis is a series of events leading to division of a cell by the process known as cytokinesis. Protein regulating cytokinesis 1 (PRC1) is a CDK substrate that associates with the mitotic spindle and functions in microtubule bundling. Previous studies revealed that loss of PRC1 is associated with chromosomal mis-segregation and atypical chromosome alignment. HSF2 is a DNA binding protein that we previously showed bookmarks the hsp70i gene during mitosis, an epigenetic mechanism which allows the hsp70i gene to re-establish transcriptional competence early in G1. Another study demonstrated that HSF2−/− mouse embryonic fibroblasts (MEFs) exhibit increased numbers of multinucleated cells vs. wild-type MEFs. This suggests that HSF2 is important for proper cytokinesis, but the mechanism was unknown. Here we report the existence of a direct interaction between HSF2 and PRC1. HSF2 and PRC1 associate during mitosis and co-localize during this phase of the cell cycle. PRC1 does not interact with the related protein HSF1, indicating the specificity of the HSF2-PRC1 interaction. Intriguingly, PRC1 is associated with the hsp70i promoter during mitosis. These results provide a potential mechanistic basis for the defective cytokinesis phenotype exhibited by HSF2−/− cells, as well as suggest a potential role for PRC1 in HSF2-mediated gene bookmarking.

  • Identification of Xenopus heat shock transcription factor-2: conserved role of sumoylation in regulating deoxyribonucleic acid-binding activity of heat shock transcription factor-2 proteins.
    Cell Stress & Chaperones, 2004
    Co-Authors: Roland S. Hilgarth, Lynea A Murphy, Colleen M. O'connor, James A. Clark, Ok Kyong Park-sarge, Kevin D. Sarge
    Abstract:

    Heat shock transcription factor (Hsf)-1 and Hsf2 are members of the heat shock factor (HSF) protein family involved in heat shock protein (hsp) gene regulation, a regulation that is critical for the ability of cells to survive exposure to stress conditions. Although the role of HSF1 in binding and activating transcription of hsp gene promoters in response to cell stress is well established, how Hsf2 enhances stress-induced hsp expression is not understood. To gain an insight into the critical conserved features of the regulation and function of Hsf2, we have identified and characterized the Hsf2 protein from Xenopus laevis. We found that, similar to its human counterpart, Xenopus Hsf2 is sumoylated at lysine 82 and that, as it does in human Hsf2, the modification event of the small ubiquitin-related modifier 1 functions to increase the deoxyribonucleic acid-binding activity of this transcription factor in Xenopus. These results indicate that sumoylation is an evolutionarily conserved modification of Hsf2 proteins, supporting the position of this modification as a critical regulator of Hsf2 function.

  • characterization of constitutive hsf2 dna binding activity in mouse embryonal carcinoma cells
    Molecular and Cellular Biology, 1994
    Co-Authors: Shawn P. Murphy, Kevin D. Sarge, Jacek J Gorzowski, Benette Phillips
    Abstract:

    Two distinct murine heat shock transcription factors, HSF1 and HSF2, have been identified. HSF1 mediates the transcriptional activation of heat shock genes in response to environmental stress, while the function of HSF2 is not understood. Both factors can bind to heat shock elements (HSEs) but are maintained in a non-DNA-binding state under normal growth conditions. Mouse embryonal carcinoma (EC) cells are the only mammalian cells known to exhibit HSE-binding activity, as determined by gel shift assays, even when maintained at normal physiological temperatures. We demonstrate here that the constitutive HSE-binding activity present in F9 and PCC4.aza.R1 EC cells, as well as a similar activity found to be present in mouse embryonic stem cells, is composed predominantly of HSF2. HSF2 in F9 EC cells is trimerized and is present at higher levels than in a variety of nonembryonal cell lines, suggesting a correlation of these properties with constitutive HSE-binding activity. Surprisingly, transcription run-on assays suggest that HSF2 in unstressed EC cells does not stimulate transcription of two putative target genes, hsp70 and hsp86. Genomic footprinting analysis indicates that HSF2 is not bound in vivo to the HSE of the hsp70 promoter in unstressed F9 EC cells, although HSF2 is present in the nucleus and the promoter is accessible to other transcription factors and to HSF1 following heat shock. Thus trimerization and nuclear localization of HSF2 do not appear to be sufficient for in vivo binding of HSF2 to the HSE of the hsp70 promoter in unstressed F9 EC cells.

Valérie Mezger - One of the best experts on this subject based on the ideXlab platform.

  • Heat shock factor 2 is required for maintaining proteostasis against febrile-range thermal stress and polyglutamine aggregation
    Molecular Biology of the Cell, 2011
    Co-Authors: Toyohide Shinkawa, Eiichi Takaki, Mitsuaki Fujimoto, Ramachandran Prakasam, Ryosuke Takii, Sachiye Inouye, Naoki Hayashida, Kaoru Yamamoto, Valérie Mezger
    Abstract:

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

  • Heat Shock Factors at a Crossroad between Stress and Development
    Annals of the New York Academy of Sciences, 2007
    Co-Authors: Malin Akerfelt, Diane Trouillet, Valérie Mezger, Lea Sistonen
    Abstract:

    : Organisms must be able to sense and respond rapidly to changes in their environment in order to maintain homeostasis and survive. Induction of heat shock proteins (Hsps) is a common cellular defense mechanism for promoting survival in response to various stress stimuli. Heat shock factors (HSFs) are transcriptional regulators of Hsps, which function as molecular chaperones in protecting cells against proteotoxic damage. Mammals have three different HSFs that have been considered functionally distinct: HSF1 is essential for the heat shock response and is also required for developmental processes, whereas HSF2 and HSF4 are important for differentiation and development. Specifically, HSF2 is involved in corticogenesis and spermatogenesis, and HSF4 is needed for maintenance of sensory organs, such as the lens and the olfactory epithelium. Recent evidence, however, suggests a functional interplay between HSF1 and HSF2 in the regulation of Hsp expression under stress conditions. In lens formation, HSF1 and HSF4 have been shown to have opposite effects on gene expression. In this chapter, we present the different roles of the mammalian HSFs as regulators of cellular stress and developmental processes. We highlight the interaction between different HSFs and discuss the discoveries of novel target genes in addition to the classical Hsps.

  • heat shock factor 2 hsf2 contributes to inducible expression of hsp genes through interplay with HSF1
    Journal of Biological Chemistry, 2007
    Co-Authors: Paivi Ostling, Valérie Mezger, Pia Roosmattjus, Johanna K. Björk, Lea Sistonen
    Abstract:

    Abstract The heat shock response is a defense reaction activated by proteotoxic damage induced by physiological or environmental stress. Cells respond to the proteotoxic damage by elevated expression of heat shock proteins (Hsps) that function as molecular chaperones and maintain the vital homeostasis of protein folds. Heat shock factors (HSFs) are the main transcriptional regulators of the stress-induced expression of hsp genes. Mammalian HSF1 was originally identified as the transcriptional regulator of the heat shock response, whereas HSF2 has not been implicated a role in the stress response. Previously, we and others have demonstrated that HSF1 and HSF2 interact through their trimerization domains, but the functional consequence of this interaction remained unclear. We have now demonstrated on chromatin that both HSF1 and HSF2 were able to bind the hsp70 promoter not only in response to heat shock but also during hemin-induced differentiation of K562 erythroleukemia cells. In both cases an intact HSF1 was required in order to reach maximal levels of promoter occupancy, suggesting that HSF1 influences the DNA binding activity of HSF2. The functional consequence of the HSF1-HSF2 interplay was demonstrated by real-time reverse transcription-PCR analyses, which showed that HSF2 was able to modulate the HSF1-mediated expression of major hsp genes. Our results reveal, contrary to the predominant model, that HSF2 indeed participates in the transcriptional regulation of the heat shock response.

  • Phenotypic characterization of mouse embryonic fibroblasts lacking heat shock factor 2.
    Journal of Cellular and Molecular Medicine, 2003
    Co-Authors: Liliana Paslaru, Michel Morange, Valérie Mezger
    Abstract:

    In murine cells, the heat shock response is regulated by a transcription factor, HSF1, which triggers the transcription of heat shock genes. HSF2 has been shown to be involved in meiosis and mouse brain development. We characterized the effects of the absence of HSF2 in mouse embryonic fibroblasts (MEFs). The temperature threshold of the heat shock response appeared lowered in Hsf2-/- MEFS as monitored by the synthesis of heat shock protein HSP70. In contrast to unstressed wild type MEFS, HSP70 and HSF1 are localized in the nucleus of unstressed Hsf2-/- MEFS, a characteristic of stressed cells. HSF1 is not activated for DNA-binding at unstressed temperature in Hsf2-/- MEFS. Therefore, the absence of HSF2 induces some but not all of the characteristics of the stress response. In addition, Hsf2-/- MEFS exhibited proliferation defects, altered morphology, remodeling of the fibronectin network.

  • Phenotypic characterization of mouse embryonic fibroblasts lacking heat shock factor 2.
    Journal of Cellular and Molecular Medicine, 2003
    Co-Authors: Liliana Paslaru, Michel Morange, Valérie Mezger
    Abstract:

    In murine cells, the heat shock response is regulated by a transcription factor, HSF1, which triggers the transcription of heat shock genes. HSF2 has been shown to be involved in meiosis and mouse brain development. We characterized the effects of the absence of HSF2 in mouse embryonic fibroblasts (MEFs). The temperature threshold of the heat shock response appeared lowered in Hsf2-/- MEFS as monitored by the synthesis of heat shock protein HSP70. In contrast to unstressed wild type MEFS, HSP70 and HSF1 are localized in the nucleus of unstressed Hsf2-/- MEFS, a characteristic of stressed cells. HSF1 is not activated for DNA-binding at unstressed temperature in Hsf2-/- MEFS. Therefore, the absence of HSF2 induces some but not all of the characteristics of the stress response. In addition, Hsf2-/- MEFS exhibited proliferation defects, altered morphology, remodeling of the fibronectin network.

Yves Le Dréan - One of the best experts on this subject based on the ideXlab platform.

  • Unraveling Complex Interplay between Heat Shock Factor 1 and 2 Splicing Isoforms
    PLOS ONE, 2013
    Co-Authors: Sylvain Lecomte, Léa Reverdy, Catherine Le Quément, Florent Le Masson, Pascale Le Goff, Denis Michel, Elisabeth Christians, Axelle Amon, Yves Le Dréan
    Abstract:

    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.

  • Roles of heat shock factor 1 and 2 in response to proteasome inhibition: consequence on p53 stability.
    Oncogene, 2010
    Co-Authors: Sylvain Lecomte, Florent Le Masson, Pascale Le Goff, Denis Michel, Elisabeth Christians, Fabienne Desmots, Yves Le Dréan
    Abstract:

    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.

  • implication of HSF1 and hsf2 in cellular response to proteasome inhibition
    Conférences Jacques Monod "New ideas for an old family: Heat Shock Factors at crossroads between stress epigenetics and development", 2008
    Co-Authors: Sylvain Lecomte, Denis Michel, Elisabeth Christians, Fabien Loison, Le F Masson, Pascale Le Goff, Fabienne Desmots, Yves Le Dréan
    Abstract:

    Inhibition of proteasome induces the intracellular accumulation of misfolded proteins that would otherwise be degraded. Cells adapt to proteasome inhibitor treatment by overexpressing chaperone proteins and proteasome subunits. Using clusterin, a secreted chaperone protein, as a model; we found that its overexpression involves interplay between HSF1 and HSF2. Proteasome inhibition activated HSF1 and HSF2 by different mechanisms involving phosphorylation and stabilization, respectively, then these two transcription factors interact and form heterotrimer on the heat shock element within the clusterin gene promoter. We have further studied the role of HSF1 and HSF2 interplay in the cellular response to proteasome inhibition, by using immortalized Mouse Embryonic Fibroblast (iMEF) derived from knock-out HSF1 and/or Hsf2 mice. We found that cells deleted for either HSF1 or HSF2 are more sensitive to proteasome inhibition than wild type cells. Moreover, using real-time reverse transcription-PCR analyses, we assessed the level of expression of HSFs target genes, and found that cells deleted in HSF1 and/or HSF2 present defect in transcriptional response to proteasome inhibitor. All together, these results confirm that both HSFs are important for cellular response to proteasome inhibitor treatment. Furthermore, to establish the relationship between proteasome and HSFs, the basal expression of ten proteasome subunits was measured in KO iMEF. We found that two catalytic subunits, beta 2 and beta 5, which support trypsin-like and chymotrypsin-like activity respectively, were present at lower level in Hsf2-/- and HSF1-/- & Hsf2-/- iMEF. Moreover, the subunits alpha 1, PSMC4 and PSMD10 also display a lower expression in absence of HSF2, whereas the other proteasome subunits tested are not affected. In agreement with this observation, we found a significant decrease of the proteasome activity in HSF2 deleted cells. In conclusion, our data show that HSF1 and HSF2 form a functional complex in response to proteasome inhibition. Moreover, we found that HSF2 is more directly involved in some proteasome subunits basal expression. In HSF2 deficient iMEF, decrease expression of these subunits have a direct influence in cell physiology, with a decrease of catalytic activity of the proteasome.

  • Role of Heat Shock Factor 2 in proteasome subunits genes expression
    2008
    Co-Authors: Sylvain Lecomte, Florent Le Masson, Denis Michel, Elisabeth Christians, Fabienne Desmots, Yves Le Dréan
    Abstract:

    Heat Shock Factors (HSF) form the main family of transcription factors involved in response to proteotoxic stress. Five HSF are currently described in vertebrate, but only HSF1 and HSF2 are for the moment, well documented. HSF1 is considered as the bona-fide stress-induced transcription factor, whereas HSF2 is more described for its implication in gametogenesis and embryonic development. However, recent studies have shown that HSF2 can have additional roles in response to protein denaturation1,2 and in bookmarking of several stress-related genes 3,4. We have studied the specific role of HSF1 and HSF2 in the cellular response to proteasome inhibition. Using immortalized Mouse Embryonic Fibroblast (iMEF) derived from knock-out HSF1 and/or Hsf2 mice, we found that cells deleted for either HSF1 or HSF2 are more sensitive to proteasome inhibition than wild type cells. This result suggests that both HSFs are important for cellular response to proteasome inhibitor treatment. To establish the relationship between the proteasome and these transcription factors, several tests were performed using knock-out cells. First, we found a significant decrease of the chymotrypsin-like activity of the proteasome in Hsf2-/- and in HSF1-/- & Hsf2-/- iMEF. Secondly, the basal expression of ten proteasome subunits was measured by real time PCR. In agreement with our measure of proteasome activity, we found that two catalytic subunits, PSMB2 and PSMB5 which support trypsin-like and chymotrypsin-like activity respectively, were present at lower level in HSF2 deleted iMEF. Moreover, PSMA1, PSMC4 and PSMD10 also display a lower expression in absence of HSF2, whereas the other proteasome subunits tested are not affected. In conclusion, our data showed that HSF2 is involved in some proteasome subunits basal expression. In HSF2 deficient iMEF, decrease expression of these subunits have a direct influence in cell physiology with a decrease of catalytic activity of the proteasome. These results could open a new field in cancer therapy: development of HSF2 inhibitors could improve the action and reduce chemoresistance to proteasome inhibitors such as bortezomib.

  • up regulation of the clusterin gene after proteotoxic stress implication of HSF1 hsf2 heterocomplexes
    Biochemical Journal, 2006
    Co-Authors: Fabien Loison, Denis Michel, Pascale Le Goff, Laure Debure, Philippe Nizard, Yves Le Dréan
    Abstract:

    Clusterin is a secreted protein chaperone up-regulated in several pathologies, including cancer and neurodegenerative diseases. The present study shows that accumulation of aberrant proteins, caused by the proteasome inhibitor MG132 or the incorporation of the amino acid analogue AZC (L-azetidine-2-carboxylic acid), increased both clusterin protein and mRNA levels in the human glial cell line U-251 MG. Consistently, MG132 treatment was capable of stimulating a 1.3 kb clusterin gene promoter. Promoter deletion and mutation studies revealed a critical MG132-responsive region between −218 and −106 bp, which contains a particular heat-shock element, named CLE for ‘clusterin element’. Gel mobility-shift assays demonstrated that MG132 and AZC treatments induced the formation of a protein complex that bound to CLE. As shown by supershift and chromatin-immunoprecipitation experiments, CLE is bound by HSF1 (heat-shock factor 1) and HSF2 upon proteasome inhibition. Furthermore, co-immunoprecipitation assays indicated that these two transcription factors interact. Gel-filtration analyses revealed that the HSF1–HSF2 heterocomplexes bound to CLE after proteasome inhibition have the same apparent mass as HSF1 homotrimers after heat shock, suggesting that HSF1 and HSF2 could heterotrimerize. Therefore these studies indicate that the clusterin is a good candidate to be part of a cellular defence mechanism against neurodegenerative diseases associated with misfolded protein accumulation or decrease in proteasome activity.