Targeting tumor proteostasis has emerged as a promising strategy in anticancer therapy, particularly through Hsp90 inhibition, which has shown clinical potential. However, the efficacy of Hsp90 inhibitors is limited by the activation of HSF1, a master regulator of the heat shock response (HSR), which mitigates proteotoxic stress by inducing protective chaperones. To address this limitation, we investigated the role of HSF1 SUMOylation in modulating its activity and its impact on Hsp90 inhibitor efficacy. We generated HSF1 mutants with lysine-to-arginine substitutions at five SUMOylation sites and studied their function in H1299 lung carcinoma cells with HSF1/HSF2 knockout, which lack a functional HSR. Unexpectedly, these mutants retained full transcriptional activity during the early phase of the heat shock response, mimicking the initial stress response of wild-type HSF1. SUMOylation inhibition using Subasumstat also led to altered nuclear stress bodies morphology but did not impair Hsp70 induction or enhance Hsp90 inhibitor cytotoxicity. Our findings reveal that SUMOylation is dispensable for HSF1 activation and transactivation capacity during the early phase of HSR. These results refine our understanding of HSF1 regulation and suggest that alternative strategies targeting HSF1 stability and degradation may enhance the therapeutic efficacy of proteostasis-targeting cancer therapies.

• Klíčová slova
• Cancer, HSF1, Heat shock response, SUMOylation, Stress, Subasumstat,
• MeSH
• aktivace transkripce * MeSH
• lidé MeSH
• nádorové buněčné linie MeSH
• proteiny tepelného šoku HSP90 metabolismus   antagonisté a inhibitory   MeSH
• reakce na tepelný šok * genetika   MeSH
• sumoylace * MeSH
• transkripční faktory tepelného šoku * metabolismus   genetika   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• HSF1 protein, human MeSH Prohlížeč
• proteiny tepelného šoku HSP90 MeSH
• transkripční faktory tepelného šoku * MeSH

Stress responses play a vital role in cellular survival against environmental challenges, often exploited by cancer cells to proliferate, counteract genomic instability, and resist therapeutic stress. Heat shock factor protein 1 (HSF1), a central transcription factor in stress response pathways, exhibits markedly elevated activity in cancer. Despite extensive research into the transcriptional role of HSF1, the mechanisms underlying its activation remain elusive. Upon exposure to conditions that induce protein damage, monomeric HSF1 undergoes rapid conformational changes and assembles into trimers, a key step for DNA binding and transactivation of target genes. This study investigates the role of HSF1 as a sensor of proteotoxic stress conditions. Our findings reveal that purified HSF1 maintains a stable monomeric conformation independent of molecular chaperones in vitro. Moreover, while it is known that heat stress triggers HSF1 trimerization, a notable increase in trimerization and DNA binding was observed in the presence of protein-based crowders. Conditions inducing protein misfolding and increased protein crowding in cells directly trigger HSF1 trimerization. In contrast, proteosynthesis inhibition, by reducing denatured proteins in the cell, prevents HSF1 activation. Surprisingly, HSF1 remains activated under proteotoxic stress conditions even when bound to Hsp70 and Hsp90. This finding suggests that the negative feedback regulation between HSF1 and chaperones is not directly driven by their interaction but is realized indirectly through chaperone-mediated restoration of cytoplasmic proteostasis. In summary, our study suggests that HSF1 serves as a molecular crowding sensor, trimerizing to initiate protective responses that enhance chaperone activities to restore homeostasis.

• MeSH
• DNA vazebné proteiny metabolismus   chemie   genetika   MeSH
• lidé MeSH
• multimerizace proteinu MeSH
• proteiny tepelného šoku HSP70 metabolismus   chemie   MeSH
• reakce na tepelný šok MeSH
• sbalování proteinů * MeSH
• transkripční faktory tepelného šoku * metabolismus   genetika   chemie   MeSH
• transkripční faktory metabolismus   chemie   MeSH
• vazba proteinů MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• DNA vazebné proteiny MeSH
• HSF1 protein, human MeSH Prohlížeč
• proteiny tepelného šoku HSP70 MeSH
• transkripční faktory tepelného šoku * MeSH
• transkripční faktory MeSH

BACKGROUND: The heat shock transcription factor, HSF1, is the main regulator of the proteotoxic stress response that orchestrates the adaptation of cells to stress conditions such as elevated temperature, oxidative stress, and proteotoxic stress. As such, HSF1 regulates a large number of stress response-related genes, primarily those encoding heat shock proteins (HSPs). HSPs are molecular chaperones involved in the acquisition of native protein conformations and the prevention of protein degradation, and they also contribute to the removal of denatured proteins via the proteasome. Representative members of the HSP family are HSP70 and HSP90. The stress response is a highly conserved mechanism across all eukaryotes, and HSF1 has been linked to a number of physiological processes (ribosomal biogenesis, translation, transcription, cell cycle, and metabolism) and pathological disorders (neurodegenerative disorders such as Parkinson´s and Alzheimer´s diseases). HSF1 activation is also prominent in different types of cancer (prostate, breast, colorectal carcinoma etc.) where it correlates with tumor aggressiveness and poor prognosis. HSF1 is therefore considered a diagnostic and prognostic marker and is currently being targeted to develop new cancer therapies. Several inhibitors of HSF1 have already been synthesized, but their molecular mechanism (s) of action, specificity those of HSF1, nontoxicity in healthy tissues, and their efficacy in targeting tumor cells remain to be elucidated. PURPOSE: This review summarizes known mechanisms of HSF1 regulation and activation, the role of HSF1 during malignant transformation, and the potential of designing small molecule HSF1 inhibitors for cancer therapy. Key words: HSF1 transcription factor - molecular chaperones - cellular stress - tumor transformation - cancer This work was supported by the project MEYS - NPS I - LO1413. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Accepted: 10. 8. 2018.

• Klíčová slova
• HSF1 transcription factor - molecular chaperones - cellular stress - tumor transformation - cancer This work was supported by the project MEYS - NPS I - LO1413. The authors declare they have no potential conflicts of interest concerning drugs, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Accepted: 10. 8. 2018, products,
• MeSH
• lidé MeSH
• nádorová transformace buněk * MeSH
• nádory diagnóza   farmakoterapie   metabolismus   MeSH
• transkripční faktory tepelného šoku antagonisté a inhibitory   fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• HSF1 protein, human MeSH Prohlížeč
• transkripční faktory tepelného šoku MeSH

Response of tumours to Hsp90 inhibitors is highly variable and their clinical effects are unpredictable, emphasising the need for a predictive marker. We postulated that sensitivity to Hsp90 inhibitors is connected to basal proteotoxic stress that makes cells dependent on Hsp90. Therefore, we assessed HSF1 as a general sensor of proteotoxic stress and correlated its activity with sensitivity to three separate small molecule Hsp90 inhibitors in seven breast cancer cell lines representing each of the different cancer subtypes. Flow cytometry was used to analyse the viability of breast cancer cell lines after Hsp90 inhibition. HSF1 activity was characterised by Ser326 phosphorylation and the transactivation capacity of HSF1 was determined by qPCR analysis of the ratios of HSF1-dependent (HOP, Hsp70) and HSF1-independent (CHIP) chaperones and cochaperone mRNAs. We show that the sensitivity of breast cancer cell lines to Hsp90 inhibition is highly variable. The basal levels of phosphorylated HSF1 also vary between cell lines and the magnitude of change in HSF1 phosphorylation after Hsp90 inhibition showed a negative correlation with sensitivity to Hsp90 inhibitors. Similarly, the basal transactivation capacity of HSF1, determined by the ratio of Hsp70 or HOP mRNA to CHIP mRNA level, is directly proportional to sensitivity to Hsp90 inhibitors. Increasing basal HSF1 activity by prior heat shock sensitised cells to Hsp90 inhibition. These results demonstrate that endogenous HSF1 activity varies between individual cancer cell lines and inversely reflects their sensitivity to Hsp90 inhibitors, suggesting that basal proteotoxic stress is an important and generalised predictor of response. Mechanistically, the data indicate that high endogenous proteotoxic stress levels sensitise to Hsp90 inhibition due to the inability to respond adequately to further proteotoxic stress. HSF1 activity therefore represents a potential biomarker for therapy with Hsp90 inhibitors, which may be useful for the rational design of future clinical studies.

• MeSH
• biologické markery metabolismus   MeSH
• fosforylace účinky léků   MeSH
• knihovny malých molekul farmakologie   MeSH
• lidé MeSH
• MFC-7 buňky MeSH
• molekulární chaperony genetika   MeSH
• nádorové buněčné linie MeSH
• nádory prsu farmakoterapie   metabolismus   MeSH
• proliferace buněk účinky léků   MeSH
• proteiny tepelného šoku HSP90 antagonisté a inhibitory   MeSH
• reakce na tepelný šok MeSH
• transkripční faktory tepelného šoku metabolismus   MeSH
• viabilita buněk účinky léků   MeSH
• Check Tag
• lidé MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• biologické markery MeSH
• HSF1 protein, human MeSH Prohlížeč
• knihovny malých molekul MeSH
• molekulární chaperony MeSH
• proteiny tepelného šoku HSP90 MeSH
• transkripční faktory tepelného šoku MeSH

BACKGROUND: The proteome of eukaryotic cells represents a complex system. Its components are exposed to various intrinsic and extrinsic stresses. Therefore, the function of the cellular proteome is dependent on the existence of compensatory mechanisms balancing the inner protein homeostasis - proteostasis. These mechanisms involve the network of molecular chaperones and transcriptional program regulating their expression. The process of cancerogenesis is accompanied by significant changes in the intracellular milieu of cancer cells - temperature, pH, availability of nutrients. On the one hand, these changes represent a consequence of the deregulated growth of the tumor tissue; on the other hand, they can be a source of selection pressure, which allows the emergence of resistant and aggressive tumor cell populations. Description of the proteostatic apparatus components and the mechanism of their involvement in the tumor tissue development is provided in this review article. AIM: This review focuses on the description of two causally linked groups of proteostatic events; their mutual coordination is crucial to the process of tumor cell and by extension the entire tumor tissue response to environmental and internal stress factors. The first group of these processes is represented by the "executory" role of molecular chaperones from HSP70, HSP90 and so-called small molecular chaperone protein families. These proteins are involved in maintaining stability of cellular proteins essential for proliferation, apoptosis, senescence, migration and phenotypic plasticity of tumor cells. The second group of the described processes comprises the posttranslational control of the "systemic" role of the transcription factor HSF1 in regulating the gene expression of molecular chaperones and other genes specifically regulated by this transcription factor in the tumor and stromal cells.Key words: molecular chaperones - heat-shock factor 1 - cancer - protein homeostasisThis work was supported by the project MEYS - NPS I - LO1413.The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study.The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers.Submitted: 15. 5. 2016Accepted: 25. 5. 2016.

• MeSH
• DNA vazebné proteiny metabolismus   MeSH
• homeostáza * MeSH
• lidé MeSH
• molekulární chaperony metabolismus   MeSH
• nádorová transformace buněk genetika   metabolismus   MeSH
• nádorové proteiny metabolismus   MeSH
• nádory metabolismus   MeSH
• proteiny teplotního šoku metabolismus   MeSH
• proteom metabolismus   MeSH
• regulace genové exprese u nádorů MeSH
• transkripční faktory tepelného šoku MeSH
• transkripční faktory metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• DNA vazebné proteiny MeSH
• HSF1 protein, human MeSH Prohlížeč
• molekulární chaperony MeSH
• nádorové proteiny MeSH
• proteiny teplotního šoku MeSH
• proteom MeSH
• transkripční faktory tepelného šoku MeSH
• transkripční faktory MeSH

Ocular lens morphogenesis is a model for investigating mechanisms of cellular differentiation, spatial and temporal gene expression control, and chromatin regulation. Brg1 (Smarca4) and Snf2h (Smarca5) are catalytic subunits of distinct ATP-dependent chromatin remodeling complexes implicated in transcriptional regulation. Previous studies have shown that Brg1 regulates both lens fiber cell differentiation and organized degradation of their nuclei (denucleation). Here, we employed a conditional Snf2h(flox) mouse model to probe the cellular and molecular mechanisms of lens formation. Depletion of Snf2h induces premature and expanded differentiation of lens precursor cells forming the lens vesicle, implicating Snf2h as a key regulator of lens vesicle polarity through spatial control of Prox1, Jag1, p27(Kip1) (Cdkn1b) and p57(Kip2) (Cdkn1c) gene expression. The abnormal Snf2h(-/-) fiber cells also retain their nuclei. RNA profiling of Snf2h(-/) (-) and Brg1(-/-) eyes revealed differences in multiple transcripts, including prominent downregulation of those encoding Hsf4 and DNase IIβ, which are implicated in the denucleation process. In summary, our data suggest that Snf2h is essential for the establishment of lens vesicle polarity, partitioning of prospective lens epithelial and fiber cell compartments, lens fiber cell differentiation, and lens fiber cell nuclear degradation.

• Klíčová slova
• Brg1, Cataract, Denucleation, Lens, Smarca4, Smarca5, Snf2h, Terminal differentiation,
• MeSH
• adenosintrifosfatasy metabolismus   MeSH
• autofagie MeSH
• biologické modely MeSH
• buněčná diferenciace * MeSH
• buněčné jádro metabolismus   MeSH
• buněčný cyklus MeSH
• chromozomální proteiny, nehistonové metabolismus   MeSH
• DNA vazebné proteiny metabolismus   MeSH
• DNA-helikasy metabolismus   MeSH
• embryo savčí metabolismus   MeSH
• epitelové buňky cytologie   metabolismus   MeSH
• jaderné proteiny metabolismus   MeSH
• kompartmentace buňky MeSH
• mitofagie MeSH
• mutace genetika   MeSH
• myši knockoutované MeSH
• oční čočka cytologie   embryologie   MeSH
• restrukturace chromatinu * MeSH
• transkripční faktor PAX6 metabolismus   MeSH
• transkripční faktory tepelného šoku MeSH
• transkripční faktory metabolismus   MeSH
• transkriptom genetika   MeSH
• vývojová regulace genové exprese MeSH
• zvířata MeSH
• Check Tag
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• adenosintrifosfatasy MeSH
• chromozomální proteiny, nehistonové MeSH
• DNA vazebné proteiny MeSH
• DNA-helikasy MeSH
• Hsf4 protein, mouse MeSH Prohlížeč
• jaderné proteiny MeSH
• Pax6 protein, mouse MeSH Prohlížeč
• Smarca4 protein, mouse MeSH Prohlížeč
• Smarca5 protein, mouse MeSH Prohlížeč
• transkripční faktor PAX6 MeSH
• transkripční faktory tepelného šoku MeSH
• transkripční faktory MeSH

Activation of the Hsp90 chaperone system is a characteristic of cancer cells. The regulation of chaperone activities involves their interaction with cochaperones; therefore we investigated the expression of Hsp70 and Hsp90 and their specific co-chaperones HOP and CHIP in cancer cell lines and primary cancers. Inhibition of Hsp90 by 17AAG increased the levels of Hsp70, Hsp90 and HOP but not CHIP mRNA in cancer cells. These changes are linked to activation of the HSF1 transcription factor and we show that the HOP promoter contains HSF1 binding sites, and that HSF1 binding to the HOP promoter is increased following 17AAG. The lack of alteration in the co-chaperone CHIP is explained by a lack of HSF response elements in the CHIP promoter. Non-proliferating cells expressed higher levels of CHIP and lower HOP, Hsp70 and Hsp90 levels compared to proliferating cells. Decreased expression of CHIP in proliferating cancer cells is in keeping with its proposed tumor suppressor properties, while over-expression of HOP in proliferating cells may contribute to excessive Hsp90 activity and stabilization of client proteins in tumors. In a panel of colorectal cancer samples, increased expression of Hsp70 and an increased ratio of HOP to CHIP were found, and were associated with decreased median survival. These data indicate that multiple changes occur in the chaperone/co-chaperone system in cancer that impact patient survival. It is likely that the ability to identify individual alterations to this system will be beneficial for treatment strategy decisions, particularly those that employ chaperone inhibitors.

• MeSH
• benzochinony farmakologie   MeSH
• DNA vazebné proteiny genetika   metabolismus   MeSH
• HCT116 buňky MeSH
• homeodoménové proteiny genetika   metabolismus   MeSH
• Kaplanův-Meierův odhad MeSH
• lidé MeSH
• makrocyklické laktamy farmakologie   MeSH
• nádorové supresorové proteiny genetika   metabolismus   MeSH
• nádory tračníku metabolismus   MeSH
• prognóza MeSH
• proliferace buněk účinky léků   MeSH
• promotorové oblasti (genetika) účinky léků   MeSH
• proteiny tepelného šoku HSP70 genetika   metabolismus   MeSH
• proteiny tepelného šoku HSP90 antagonisté a inhibitory   genetika   metabolismus   MeSH
• regulace genové exprese u nádorů účinky léků   MeSH
• responzivní elementy genetika   MeSH
• transkripční faktory tepelného šoku MeSH
• transkripční faktory genetika   metabolismus   MeSH
• ubikvitinligasy genetika   metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• benzochinony MeSH
• DNA vazebné proteiny MeSH
• homeodoménové proteiny MeSH
• HOPX protein, human MeSH Prohlížeč
• HSF1 protein, human MeSH Prohlížeč
• makrocyklické laktamy MeSH
• nádorové supresorové proteiny MeSH
• proteiny tepelného šoku HSP70 MeSH
• proteiny tepelného šoku HSP90 MeSH
• STUB1 protein, human MeSH Prohlížeč
• tanespimycin MeSH Prohlížeč
• transkripční faktory tepelného šoku MeSH
• transkripční faktory MeSH
• ubikvitinligasy MeSH