Cells are continuously exposed to a variety of physiological and environmental stresses that can lead to protein aggregation and/or denaturation, and eventually cell death. In order to ensure survival, cells have evolved a stress response that monitors, detects, and responds to changes within the cellular environment. The stress response is characterized by the up-regulation of heat shock protein (hsp) genes whose products can mediate the assembly and/or degradation of misfolded or aggregated proteins within the cell. This stress-induced upregulation of heat shock protein encoding genes is under the regulation of heat shock transcription factor 1 (HSF1) and its associated proteins that together form what is known as the HSF1 heterocomplex. In eukaryotic cells, HSF1 exists as a non-DNA binding monomer in the absence of stress. Upon exposure to stress, HSF1 undergoes trimerization and acquires the ability to bind heat shock elements (HSEs) located upstream of all hsp genes and after further modification, can become converted into a transcriptionally active form. Following prolonged stress or after removal of stress, HSF1 loses its ability to bind DNA and transcription ceases in a process termed attenuation. <p>Several studies have suggested that the DNA-binding and transcriptional activities of HSF1 are regulated by phosphorylation and dephosphorylation events and by chaperone-based folding mechanisms similar to those involved in the regulation of glucocorticoid receptors. Protein phosphatase 5 (PP5) has been identified as a member of the glucocorticoid receptor chaperone complex and its phosphatase activity has been shown to regulate the maturation and activation of the receptor. It has been suggested that PP5 may regulate HSF1 in a manner similar to that of glucocorticoid receptors however it has not yet been determined how PP5 interacts with the HSF1 heterocomplex or if PP5 functions to regulate HSF1-DNA binding and/or HSF1 transactivation.<p>Utilizing the Xenopus model system, I tested the hypothesis that PP5 regulates the DNA binding and transcriptional activities of HSF1 through interactions with the HSF1 heterocomplex. Increasing the activity of PP5, either through the elevation of PP5 protein levels or by activating endogenous PP5, resulted in decreased HSF1-DNA binding as well as accelerated attenuation after the removal of stress. Conversely, inhibiting the phosphatase activity of PP5 using okadaic acid or by immunotargetting, where an antibody recognizing PP5 was microinjected into the nuclei of oocytes, resulted in delayed HSF1 attenuation. Transcription assays performed using activated PP5 also demonstrated that PP5 acts to decrease HSF1-mediated transcription. Immunoprecipitation and gel mobility supershift assays were also used to show that PP5 interacts with the HSF1 heterocomplex and PP5-HSP90 binding mutants illustrated that PP5 may exert its repressive effects independently of binding directly to HSP90.

Cells are continuously exposed to a variety of physiological and environmental stresses that can lead to protein aggregation and/or denaturation, and eventually cell death. In order to ensure survival, cells have evolved a stress response that monitors, detects, and responds to changes within the cellular environment. The stress response is characterized by the up-regulation of heat shock protein (hsp) genes whose products can mediate the assembly and/or degradation of misfolded or aggregated proteins within the cell. This stress-induced upregulation of heat shock protein encoding genes is under the regulation of heat shock transcription factor 1 (HSF1) and its associated proteins that together form what is known as the HSF1 heterocomplex. In eukaryotic cells, HSF1 exists as a non-DNA binding monomer in the absence of stress. Upon exposure to stress, HSF1 undergoes trimerization and acquires the ability to bind heat shock elements (HSEs) located upstream of all hsp genes and after further modification, can become converted into a transcriptionally active form. Following prolonged stress or after removal of stress, HSF1 loses its ability to bind DNA and transcription ceases in a process termed attenuation. <p>Several studies have suggested that the DNA-binding and transcriptional activities of HSF1 are regulated by phosphorylation and dephosphorylation events and by chaperone-based folding mechanisms similar to those involved in the regulation of glucocorticoid receptors. Protein phosphatase 5 (PP5) has been identified as a member of the glucocorticoid receptor chaperone complex and its phosphatase activity has been shown to regulate the maturation and activation of the receptor. It has been suggested that PP5 may regulate HSF1 in a manner similar to that of glucocorticoid receptors however it has not yet been determined how PP5 interacts with the HSF1 heterocomplex or if PP5 functions to regulate HSF1-DNA binding and/or HSF1 transactivation.<p>Utilizing the Xenopus model system, I tested the hypothesis that PP5 regulates the DNA binding and transcriptional activities of HSF1 through interactions with the HSF1 heterocomplex. Increasing the activity of PP5, either through the elevation of PP5 protein levels or by activating endogenous PP5, resulted in decreased HSF1-DNA binding as well as accelerated attenuation after the removal of stress. Conversely, inhibiting the phosphatase activity of PP5 using okadaic acid or by immunotargetting, where an antibody recognizing PP5 was microinjected into the nuclei of oocytes, resulted in delayed HSF1 attenuation. Transcription assays performed using activated PP5 also demonstrated that PP5 acts to decrease HSF1-mediated transcription. Immunoprecipitation and gel mobility supershift assays were also used to show that PP5 interacts with the HSF1 heterocomplex and PP5-HSP90 binding mutants illustrated that PP5 may exert its repressive effects independently of binding directly to HSP90.

The heat-shock response is one of the many complex physiological systems that organisms have developed in order to protect their cells against stress. This response is initiated by the binding of heat shock factor 1 (HSF1) to the promoters of genes containing heat-shock elements (HSEs,) which results in the expression of several proteins, among them the proteo-protective inducible heat-shock protein (hsp70i). Due to HSF1s critical role in this process, an active area of research is trying to understand of how HSF1 executes its function. Considering the rapidity with which the field of cell biology is expanding, in particular the sub-field of nuclear compartmentalization, this study seeks to understand how nuclear structure affects the function of HSF1. Specifically, this study investigates the potential role for the interaction between HSF1 and the translocated promoter region protein (Tpr,) a structural component of the nuclear pore, an interaction initially identified by yeast two-hybrid analysis, in the transcription of hsp70i. Due to Tprs location and its putative function in nucleo-cytoplasmic trafficking, this works seeks to answer to the question, Does Tpr play a role in the export of HSF1-driven mRNAs? In a similar vein, heat-shock transcription factor 2 (HSF2,) a less well-understood member of the heat-shock transcription factor family, also interacts with Tpr in the yeast two-hybrid assay. HSF2 has recently been shown to have an active role during mitosis, when the hsp70i gene is being bookmarked for potential expression that might be needed in early G1, when most genes are unable to be expressed. This body of work also seeks to answer the question of, Does the Tpr/HSF2 interaction have a role in positioning the gene in relation to the nuclear pore after mitosis? This study was performed using both novel and standard in vivo and in vitro molecular biology techniques. It ultimately aims to clarify the less understood, although much broader, subject of how does transcription occur in the three-dimensional space of the nucleus.

Sous conditions de stress métabolique ou environnemental, l’activation instantanée de voies moléculaires puissantes permet aux cellules de prévenir la formation et l’accumulation d’agrégats protéiques toxiques. HSF1 (Heat Shock Factor 1) est le facteur de transcription majeur capable d’orchestrer cette réponse cellulaire au stress et cela via l’activation de protéines au rôle protecteur nommées chaperonnes. Cependant, il est aujourd’hui évident que les fonctions initialement attribuées au facteur HSF1 s’étendent bien au-delà de l’activation de la transcription de chaperonnes. En effet, il a été démontré que HSF1 joue un rôle essentiel dans l’activation et le remodelage de régions répétées appartenant à l’hétérochromatine péricentromérique sous stress thermique et plus récemment qu’HSF1 contribuerait significativement au processus de tumorigenèse dans différents types de cancers. Dans cette étude, nous avons identifié pour la première fois les régions subtélomériques comme étant une nouvelle cible génomique d’HSF1 sous conditions de stress thermique. Nous avons démontré, que la liaison directe et spécifique d’HSF1 avec plusieurs de ces régions sous stress thermique est à l’origine d’une surexpression de longs ARNs non codants issus des télomères, aussi connus sous le nom de TERRA. De façon intéressante nous avons trouvé que cette transcription était corrélée à un enrichissement de la marque épigénétique répressive H3K9me3 au niveau télomérique. De plus, nos données ont permis de démontrer que l’intégrité de la chromatine télomérique était significativement atteinte sous conditions de stress thermique. Nous observons à la fois, une dissociation partielle de la protéine TRF2 (Telomeric repeat-binding factor 2) et une accumulation de dommages à l’ADN détectés grâce au marqueur moléculaire H2AX-P, au niveau des télomères. Finalement, nos résultats ont également permis de souligner un rôle d’HSF1 dans le maintien de cette intégrité télomérique. L’ensemble de ce travail établit un premier lien entre la voie cellulaire puissante de réponse au stress, son acteur majeur HSF1 et les régions de l’hétérochromatine télomérique, dans des lignées de cellules humaines cancéreuses. Ces données fournissent des indications précieuses sur une voie de maintien de télomères sous stress et nous permettant de proposer un modèle dans lequel cette nouvelle fonction d’HSF1 aux télomères pourrait être étroitement liée à l’expression des ARNs non codants télomériques. Sur la base de nos données ainsi que sur les multiples publications démontrant l’implication d’HSF1 dans la tumorigenèse, la définition exacte du rôle d’HSF1 au niveau de l’intégrité des télomères dans un contexte pathologique comme le cancer apparait aujourd’hui comme un défi prometteur. / In response to metabolic or environmental stress, cells rapidly activate powerful defense mechanisms to prevent the formation and accumulation of toxic protein aggregates. The main orchestrator of this cellular response is HSF1 (Heat Shock Factor 1), a transcription factor involved in the up-regulation of protein-coding genes with protective roles. However, it is now becoming clear, that HSF1 function extends beyond what was previously predicted and that HSF1 can contribute to pericentromeric heterochromatin remodeling and activation as well as to efficiently support malignancy. In this study, we identify subtelomeric DNA as a new genomic target of HSF1 upon heat shock (HS). We show that HSF1 binding to subtelomeric regions plays an essential role in the upregulation of TERRA lncRNAs transcription and in the accumulation of repressive H3K9me3 histone mark at telomeres upon HS. Additionally, we demonstrate that HS significantly affects telomere capping and telomere integrity. We bring evidence of a partial TRF2 telomeric-binding factor dissociation and we reveal an accumulation of DNA damage at telomeres using the DNA damage marker H2A.X-P. In line with this, we bring solid evidences that under heat shock, HSF1 contributes to preserve telomere integrity by significantly limiting telomeric DNA damage accumulation. Altogether, our findings therefore reveal a new direct and essential function of HSF1 in transcription activation of TERRA and in telomere protection upon stress in human cancer cell lines. This work provides new insights into how telomeres are preserved under stressful heat shock conditions and allow us to propose a model where HSF1 may exert its protective function at telomeres via the expression of TERRA ncRNAs. Based on our results and given the important role of HSF1 in tumor development, defining the role of HSF1 with regard to telomere stability in tumor development already emerges as a promising challenge.

La majorité des études sur la dynamique des facteurs de transcription en cellules vivantes s'accordent sur une dynamique rapide. Il existe cependant quelques exceptions, comme la dynamique du facteur de transcription HSF « Heat Shock Factor », sur les chromosomes polyténiques de drosophile. Notre projet a consisté à étudier la dynamique d'HSF1 dans des cellules humaines. L'exposition des cellules à un stress tel qu'un choc thermique induit une réponse ubiquitaire et transitoire, dont la fonction est de protéger les cellules contre les effets délétères du stress. Au cours d'un choc thermique, plusieurs phénomènes se produisent : i) un arrêt global de la transcription excepté pour certains gènes tels que ceux codant pour les protéines de choc thermique (HSPs), dont l'expression est sous le contrôle du facteur de transcription HSF1. ii) une activation d'HSF1 qui se relocalise de façon rapide et transitoire sur les corps nucléaires de stress (nSBs), où il induit la transcription des séquences satellite III. Les nSBs forment un site d'activité naturellement amplifié et visible en microscopie. Nous avons utilisé deux techniques complémentaires pour étudier la dynamique d'HSF1 en cellules vivantes : le recouvrement de fluorescence après photoblanchiment (FRAP) et la spectroscopie à corrélation de fluorescence multi-confocale (mFCS), qui permet l'analyse FCS en plusieurs points simultanément. En cellules HeLa, la protéine HSF1-eGFP présente une dynamique rapide qui est significativement ralentie suite à un choc thermique. En mFCS, nous avons obtenu des constantes de diffusion de 14 µm²/s avant choc thermique et de 10 µm²/s après choc thermique. En FRAP, le temps de demi-recouvrement est de 0,2 s avant choc thermique, 2,6 s après choc thermique dans le nucléoplasme et 65 s sur les corps nucléaires de stress. Le ralentissement de la dynamique d'HSF1 s'explique par deux phénomènes : i) la formation de complexes de haut poids moléculaire, ii) une augmentation des interactions avec la chromatine. Pour mieux caractériser le changement de dynamique d'HSF1 après choc thermique, plusieurs mutants ont été analysés. Le domaine de trimérisation est indispensable pour le changement de dynamique après choc thermique, alors que le domaine de liaison à l'ADN et le domaine de transactivation n'ont que peu d'effet sur le changement de dynamique. Il ne peut donc pas être expliqué uniquement par les interactions directes à la chromatine du domaine de liaison à l'ADN, ni même par les liaisons indirectes du domaine de transactivation via d'autres protéines. La protéine HSF1 pourrait interagir de façon aspécifique avec la chromatine lors de la recherche de site de liaison, ou d'autres protéines via d'autres domaines pourraient entrainer des interactions indirectes avec la chromatine. / The majority of studies made on transcription factors dynamics on living cells agree with a fast dynamics process. However, there is some exceptions such as the dynamics of the transcription factor HSF “Heat Shock Factor” on drosophila polytenic chromosome. My project is to study HSF1 dynamics in human living cells. Cells exposure to a stress such as heat shock induces a transient and ubiquitous response that function's to protect cells against the deleterious effect of stress. During the course of a heat shock, several phenomenons take place: i) a global arrest of transcription, with the exception of some genes, such as those coding for the heat shock proteins (hsp), which expression is under the control of HSF1. ii) Activation of HSF1 that relocalize in a fast and transient way to nuclear stress bodies (nSBs), where it induces satellite III transcription. nSBs act as a natural amplification gene array, visible on microscopy. We have used two complementary techniques to look at HSF1 dynamics in living cells: Fluorescence recovery after photobleaching (FRAP) and multiconfocal fluorescence correlation spectroscopy (mFCS) that allow FCS analysis at several position simultaneously. On HeLa cells, HSF1-eGFP protein has a fast dynamics which is significantly slowed down following heat shock. On mFCS, we obtained a diffusion constant of 14 µm²/s before heat shock, and 10 µm²/s after heat shock. On FRAP, the half recovery time is 0.2 s before heat shock, 2.6 s after heat shock in the nucleoplasm and 65 s in nuclear stress bodies. HSF1 dynamics slowing down may be explain by two phenomenons: i) formation of high molecular mass complexes, ii) rise of interaction of HSF1 with chromatin. To better characterize changes in HSF1 dynamics after heat shock, several mutants have been analyzed. The trimerization domain of HSF1 is essential for dynamics changes after heat shock, while DNA binding domain (DBD) and transactivation domain (TAD) have only little effects on dynamics changes. These changes cannot only be explained by direct interaction of DNA binding domain with chromatin, neither by indirect interaction of the transactivation domain with other protein partners. HSF1 could be able to interact non-specifically with chromatin during the search for specific binding sites. Also other proteins via other domains might induce indirect binding to chromatin.

Cellular stress invokes a protective response in which heat shock factor 1 (HSF1) is activated to increase heat shock protein (Hsp) expression. HSF1 exists as a latent monomer in unstressed cells. Upon stress HSF1 forms homotrimers, increasing its affinity for the heat shock DNA element upstream of all Hsp genes. A second conformational change is required for HSF1 to gain transcriptional competence. During prolonged heat shock or following the resumption of normal conditions HSF1 DNA-binding and transcriptional activities are reduced and HSF1 returns to the monomeric state in a process called attenuation. During the activation/deactivation cycle HSF1 is modified by small ubiquitin-related modifier (SUMO-1) conjugation and undergoes several phosphorylation and dephosphorylation events that modulate HSF1 activity. Hyperphosphorylation of HSF1 is hypothesized to trigger HSF1 transcriptional activity. HSF1 also interacts with a dynamic series of Hsp90/Hsp70-based chaperone heterocomplexes that negatively regulate DNA-binding, and transcriptional activity, and promote attenuation. This thesis was aimed at characterizing the mechanisms regulating HSF1 DNA-binding, and transcriptional activity. Expression of human HSF1 in Xenopus oocytes altered the set-point of DNA-binding in response to heat indicating that both the cellular environment and innate properties of the molecule allow HSF1 to set its activation/deactivation set-point in response to stress in vivo. HSF1 DNA-binding but not transcription was activated in oocytes treated with a high temperature heat shock. Further characterization of this observation determined that HSF1 activated by a brief high temperature heat shock inhibited transcriptionally competent HSF1 from activating transcription. It was hypothesized that this phenomenon exists to ensure the eventual death of the cell due to the accumulation of excessive damage and potential mutation caused by severe stress. The most significant observation made in this thesis is that Hsp expression was detected in oocytes injected with reporter plasmid only during recovery from a high temperature heat shock. These results led to the proposal of a model in which HSF1 trimers are either assembled in a transcriptionally incompetent form or one that has the potential to become transcriptionally competent during stress, prior to DNA-binding. The identity of HSF1-binding proteins that interact with HSF1 at different stages of activation/deactivation was characterized in an effort to assign regulatory roles to these proteins. HSF1 was detected in a high molecular weight complex (350-600 kDa) during all phases of the activation/deactivation cycle. HSF1 at different stages of activation was tested for interaction with specific molecular chaperones by electrophoretic mobility supershift analysis. Hsp90, p23, FKBP52, Hip and Hop are all associated with transcriptionally active and inactive HSF1 suggesting that interaction of HSF1 with any of these molecules does not activate HSF1 transcriptional activity. These results do not exclude the possibility that the function of these molecular chaperones may change during activation of HSF1 transcription or that post-translational modifications may be the primary mechanism that drives HSF1 from a transcriptionally inactive to active form.

Cellular stress invokes a protective response in which heat shock factor 1 (HSF1) is activated to increase heat shock protein (Hsp) expression. HSF1 exists as a latent monomer in unstressed cells. Upon stress HSF1 forms homotrimers, increasing its affinity for the heat shock DNA element upstream of all Hsp genes. A second conformational change is required for HSF1 to gain transcriptional competence. During prolonged heat shock or following the resumption of normal conditions HSF1 DNA-binding and transcriptional activities are reduced and HSF1 returns to the monomeric state in a process called attenuation. During the activation/deactivation cycle HSF1 is modified by small ubiquitin-related modifier (SUMO-1) conjugation and undergoes several phosphorylation and dephosphorylation events that modulate HSF1 activity. Hyperphosphorylation of HSF1 is hypothesized to trigger HSF1 transcriptional activity. HSF1 also interacts with a dynamic series of Hsp90/Hsp70-based chaperone heterocomplexes that negatively regulate DNA-binding, and transcriptional activity, and promote attenuation. This thesis was aimed at characterizing the mechanisms regulating HSF1 DNA-binding, and transcriptional activity. Expression of human HSF1 in Xenopus oocytes altered the set-point of DNA-binding in response to heat indicating that both the cellular environment and innate properties of the molecule allow HSF1 to set its activation/deactivation set-point in response to stress in vivo. HSF1 DNA-binding but not transcription was activated in oocytes treated with a high temperature heat shock. Further characterization of this observation determined that HSF1 activated by a brief high temperature heat shock inhibited transcriptionally competent HSF1 from activating transcription. It was hypothesized that this phenomenon exists to ensure the eventual death of the cell due to the accumulation of excessive damage and potential mutation caused by severe stress. The most significant observation made in this thesis is that Hsp expression was detected in oocytes injected with reporter plasmid only during recovery from a high temperature heat shock. These results led to the proposal of a model in which HSF1 trimers are either assembled in a transcriptionally incompetent form or one that has the potential to become transcriptionally competent during stress, prior to DNA-binding. The identity of HSF1-binding proteins that interact with HSF1 at different stages of activation/deactivation was characterized in an effort to assign regulatory roles to these proteins. HSF1 was detected in a high molecular weight complex (350-600 kDa) during all phases of the activation/deactivation cycle. HSF1 at different stages of activation was tested for interaction with specific molecular chaperones by electrophoretic mobility supershift analysis. Hsp90, p23, FKBP52, Hip and Hop are all associated with transcriptionally active and inactive HSF1 suggesting that interaction of HSF1 with any of these molecules does not activate HSF1 transcriptional activity. These results do not exclude the possibility that the function of these molecular chaperones may change during activation of HSF1 transcription or that post-translational modifications may be the primary mechanism that drives HSF1 from a transcriptionally inactive to active form.

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. These poor statistics are related to a lack of early symptoms and inadequate screening techniques. This results in the cancer going undetected until later stages when the tumor has metastasized through a process that requires the epithelial to mesenchymal transition (EMT). In lieu of traditional monolayer cell culture, EMT and cancer progression in general is best characterized through the use of 3D spheroid models. In this study, we examine gene expression changes through microarray analysis in spheroid versus monolayer ovarian cancer cells treated with TGFβ to induce EMT. Transcripts that included Coiled-Coil Domain Containing 80 (CCDC80), Solute Carrier Family 6 (Neutral Amino Acid Transporter), Member 15 (SLC6A15), Semaphorin 3E (SEMA3E) and PIF1 5'-To-3' DNA Helicase (PIF1) were downregulated more than 10-fold in the 3D cells while Inhibitor Of DNA Binding 2, HLH Protein (ID2), Regulator Of Cell Cycle (RGCC), Protease, Serine 35 (PRSS35), and Aldo-Keto Reductase Family 1, Member C1 (AKR1C1) were increased more than 50-fold. Interestingly, stress responses and epigenetic processes were significantly affected by 3D growth. The heat shock response and the oxidative stress response were also identified as transcriptome responses that showed significant changes upon 3D growth. Subnetwork enrichment analysis revealed that DNA integrity (e.g. DNA damage, genetic instability, nucleotide excision repair, and the DNA damage checkpoint pathway) were altered in the 3D spheroid model. In addition, two epigenetic processes, DNA methylation and histone acetylation, were increased with 3D growth. These findings support the hypothesis that three dimensional ovarian cell culturing is physiologically different from its monolayer counterpart. 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-tomesenchymal 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 knockdown becomes more pronounced in the spheroid model. These findings suggest that HSF1 is important in the ovarian cancer TGFβ response and in EMT.

No description available.

Lors d'un stress, les cellules activent un mécanisme de défense appelé “la réponse au stress”. Ce mécanisme empêche notamment l'accumulation de protéines mal enroulées grâce à la synthèse des protéines du choc thermique, les HSPs (Heat Shock Proteins),via l'activation du facteur de transcription HSF1 (Heat Shock Factor 1). Les HSPs empêchent l'agrégation des protéines et aident au repliement protéique. Deux partenaires associés à HSF1 ont récemment été identifiés : le chaperon moléculaire VCP (Valosin Containing Protein) et l'histone déacétylase 6 (HDAC6). Notre projet était d'étudier les rôles d'HDAC6 et de VCP dans la réponse au stress thermique. Nous avons mis en évidence un rôle prépondérant du domaine de fixation à l'ubiquitine d'HDAC6 dans la régulation de la durée d'activation d'HSF1 suite à un choc thermique. Lorsque HDAC6 ne peut pas se fixer à l'ubiquitine, VCP favorise une inactivation rapide de HSF1 empêchant la transcription du chaperon HSP25. Ces travaux montrent également que la réponse activée suite à un stress dépend de la nature de celui-ci. En effet, nous avons montré que les mécanismes activés dans la réponse au stress suite à un choc thermique sont différents de ceux activés suite à une inhibition du protéasome. La myopathie à corps d'inclusion associée à la maladie osseuse de Paget et à une démence fronto-temporale, appelée IBMPFD, Inclusion Body Myopathy associated with Paget disease of the bone and Frontotemporal Dementia, est une maladie autosomale dominante rare. La myopathie est la caractéristique clinique la plus commune parmi celles qui sont causées par des mutations de VCP. La perturbation de la fonction de VCP entraîne l'accumulation de protéines poly-ubiquitinées et la formation de corps d'inclusion en partie responsables de la pathogenèse de l'IBMPFD. Nous avons montré que l'activation de la réponse au stress via un choc thermique dans des cellules murines déficientes en VCP mimant le phénotype de l'IBMPFD, entraîne une diminution du taux de cellules ayant des agrégats de protéines poly-ubiquitinées. Nos résultats préliminaires montrent que HSF1 ne serait pas à l'origine de cette diminution des agrégats au contraire de HSP90 et HDAC6 qui interviendraient suite à l'activation de la réponse au stress. Cette stratégie est actuellement en cours de test sur des modèles murins. / Under stress, cells activate a defense mechanism named “cellular stress response”. This mechanism prevents especially unfolded proteins accumulation thanks to Heat Shock Proteins (HSPs) synthesis through the activation of Heat Shock Factor 1 (HSF1) transcription factor. HSPs prevent aggregation and help protein refolding. Two partners associated to HSF1, have recently been identified: the molecular chaperone, VCP (Valosin Containing Protein) and the Histone DeACetylase 6 (HDAC6). Our project was to characterize the roles of HDAC6 and VCP in the Heat Shock Response (HSR). We have highlighted a preponderant role for the HDAC6 ubiquitin binding domain in the HSF1 activation time regulation after a heat shock. When HDAC6 can't bind ubiquitin, VCP promotes a rapid HSF1 inactivation preventing HSP25 chaperone transcription. This work also emphasizes a stimulus-dependent stress response. Indeed, we showed that mechanisms activated during the stress response following a heat shock differ from those activated after a proteasome inhibition. Inclusion Body Myopathy, Paget disease of the bone, and Frontotemporal Dementia (IBMPFD) is a rare autosomal dominant disorder. Myopathy is the most common clinical feature of IBMPFD. It is caused by mutations of VCP. Alteration of VCP function leads to the accumulation of poly-ubiquitinated proteins and to the formation of inclusion bodies thought to be responsible, at least in part, for the pathogenesis of IBMPFD. We have shown that activation of the heat shock stress response in mouse cells VCP deficient mimicking IBMPFD phenotype, results in the decrease of cells with ubiquitinated protein aggregates. Our preliminary results show that HSF1 is not responsible for this decrease unlike HSP90 and HDAC6 that seems to intervene following the stress response activation. This strategy is currently tested on mouse models.