Stressiproteiinien merkitys ja käyttö lääkekehityksen kohdemolekyyleinä

Proteiinihomeostaasi eli solujen kyky ylläpitää proteiinimolekyylien oikeaa laskostumista ja toiminnallisuutta on erottamattomasti yhteydessä ihmisen terveyteen. Ikääntyminen, fysiologinen stressi ja mutatoituneiden proteiinien ilmentyminen haastavat solun proteiinihomeostaasin, minkä seurauksena riski sairastua laskostumisvirheistä ja proteiinikertymistä johtuviin sairauksiin lisääntyy. Molekyylikaitsijat eli stressiproteiinit, kuten lämpösokkiproteiinit, ovat proteiinihomeostaasin keskeisimpiä säätelijöitä, ja niiden tehtävä on ohjata proteiinien laskostumista, sijaintia ja hajotusta. Virheellisesti säätynyt stressivaste ja yleinen proteiinien laadunvarmistuskoneiston heikkeneminen on yhdistetty useisiin kroonisiin tautitiloihin, kuten hermoston rappeumatauteihin ja syöpiin. Siksi stressivasteiden farmakologisesta säätelystä odotetaan apua yhä laajenevan sairausjoukon hoitoon.</p

Global SUMOylation on active chromatin is an acute heat stress response restricting transcription

ArticleBackground Cells have developed many ways to cope with external stress. One distinctive feature in acute proteotoxic stresses, such as heat shock (HS), is rapid post-translational modification of proteins by SUMOs (small ubiquitin-like modifier proteins; SUMOylation). While many of the SUMO targets are chromatin proteins, there is scarce information on chromatin binding of SUMOylated proteins in HS and the role of chromatin SUMOylation in the regulation of transcription. Results We mapped HS-induced genome-wide changes in chromatin occupancy of SUMO-2/3-modified proteins in K562 and VCaP cells using ChIP-seq. Chromatin SUMOylation was further correlated with HS-induced global changes in transcription using GRO-seq and RNA polymerase II (Pol2) ChIP-seq along with ENCODE data for K562 cells. HS induced a rapid and massive rearrangement of chromatin SUMOylation pattern: SUMOylation was gained at active promoters and enhancers associated with multiple transcription factors, including heat shock factor 1. Concomitant loss of SUMOylation occurred at inactive intergenic chromatin regions that were associated with CTCF-cohesin complex and SETDB1 methyltransferase complex. In addition, HS triggered a dynamic chromatin binding of SUMO ligase PIAS1, especially onto promoters. The HS-induced SUMOylation on chromatin was most notable at promoters of transcribed genes where it positively correlated with active transcription and Pol2 promoter-proximal pausing. Furthermore, silencing of SUMOylation machinery either by depletion of UBC9 or PIAS1 enhanced expression of HS-induced genes. Conclusions HS-triggered SUMOylation targets promoters and enhancers of actively transcribed genes where it restricts the transcriptional activity of the HS-induced genes. PIAS1-mediated promoter SUMOylation is likely to regulate Pol2-associated factors in HS.Publisher’s pd

Heat Shock Factor 2 Protects against Proteotoxicity by Maintaining Cell-Cell Adhesion

Maintenance of protein homeostasis, through inducible expression of molecular chaperones, is essential for cell survival under protein-damaging conditions. The expression and DNA-binding activity of heat shock factor 2 (HSF2), a member of the heat shock transcription factor family, increase upon exposure to prolonged proteotoxicity. Nevertheless, the specific roles of HSF2 and the global HSF2-dependent gene expression profile during sustained stress have remained unknown. Here, we found that HSF2 is critical for cell survival during prolonged proteotoxicity. Strikingly, our RNA sequencing (RNA-seq) analyses revealed that impaired viability of HSF2-deficient cells is not caused by inadequate induction of molecular chaperones but is due to marked downregulation of cadherin superfamily genes. We demonstrate that HSF2-dependent maintenance of cadherin-mediated cell-cell adhesion is required for protection against stress induced by proteasome inhibition. This study identifies HSF2 as a key regulator of cadherin superfamily genes and defines cell-cell adhesion as a determinant of proteotoxic stress resistance

Stress biology:Complexity and multifariousness in health and disease

Preserving and regulating cellular homeostasis in the light of changing environmental conditions or developmental processes is of pivotal importance for single cellular and multicellular organisms alike. To counteract an imbalance in cellular homeostasis transcriptional programs evolved, called the heat shock response, unfolded protein response, and integrated stress response, that act cell-autonomously in most cells but in multicellular organisms are subjected to cell-nonautonomous regulation. These transcriptional programs downregulate the expression of most genes but increase the expression of heat shock genes, including genes encoding molecular chaperones and proteases, proteins involved in the repair of stress-induced damage to macromolecules and cellular structures. Sixty-one years after the discovery of the heat shock response by Ferruccio Ritossa, many aspects of stress biology are still enigmatic. Recent progress in the understanding of stress responses and molecular chaperones was reported at the 12th International Symposium on Heat Shock Proteins in Biology, Medicine and the Environment in the Old Town Alexandria, VA, USA from 28th to 31st of October 2023.</p

Regulation of cellular stress proteins in physiology and disease

All cells in a human body are constantly exposed to environmental fluctuations to which the cells must respond. Most of the cellular responses are mediated by proteins that are specifically regulated according to the distinct requirements of the cell. Among various protein regulatory mechanisms, modulation by post-translational modifications (PTMs), such as phosphorylation or sumoylation, provides an efficient and rapid means to alter protein function. PTMs have an incredibly vast selection of target substrates and thus are involved in nearly every aspect of cells´ life. The fast modulation of cellular response pathways is particularly important during stress, which often poses a threat to cell survival unless mitigated appropriately. One of the most extensively studied cellular stress response pathways is called the heat shock response, which is initiated upon exposure to protein damaging conditions. Heat shock response is mediated by heat shock transcription factors (HSFs), which assist in the restoration of protein homeostasis, by activating the transcription of genes encoding for molecular chaperones. Of the mammalian HSFs, HSF1 is considered the main regulator of heat shock response. During its activation-attenuation cycle, HSF1 is extensively modified by PTMs, which accompany the acquisition of transcriptional activity. For this, the modifications are considered as a prerequisite for HSF1 activity, though their exact importance has not been conclusively examined. Due to its ability to potently enhance cell survival during stress, HSF1 is regarded as a powerful enabler of carcinogenesis and high HSF1 expression has been detected in multiple human cancer types. HSF2, on the other hand, is mainly recognized as an important regulator of other differentiation and developmental programs, but its role in proteotoxic stress and in human malignancies is currently uncharacterized. In the first study of this thesis, I focus on sumoylation as a post-translational regulator of protein function and describe a novel method to examine sumoylated proteins in vivo in cells. The method is based on engineered human SUMO1 and can be utilized in the identification of novel sumoylation substrates. The second study examines HSF1 phosphorylation and aims at understanding the importance of this modification as a regulator of HSF1 activity. The results presented in this thesis show that hyperphosphorylation is not required for HSF1 activity, but functions more as a fine-tuning mechanism for heat shock response. In the third study, we aimed at expanding our understanding on the role of HSFs in human malignancies. The study demonstrates that in contrast to oncogenic HSF1, HSF2 functions as a suppressor of prostate cancer invasion and shows that HSF2 downregulation promotes metastatic behavior of prostate cancer cells. Finally, the fourth study examines the role of HSF2 in proteasome inhibition-induced prolonged proteotoxic stress and establishes HSF2 as an essential cell survival factor in these conditions. Moreover, the work identifies HSF2-dependent expression of cadherins as a key determinant of cellular sensitivity to proteotoxic stress and thus greatly expands our knowledge regarding HSFs as factors promoting cell survival. Taken together, the work presented in this thesis elaborates on HSF-mediated cellular survival pathways and lays a ground for future studies regarding HSFs as important regulators of human physiology and disease

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Heat Shock Factor 2 Protects against Proteotoxicity by Maintaining Cell-Cell Adhesion

International audienceMaintenance of protein homeostasis, through inducible expression of molecular chaperones, is essential for cell survival under protein-damaging conditions. The expression and DNA-binding activity of heat shock factor 2 (HSF2), a member of the heat shock transcription factor family, increase upon exposure to prolonged proteotoxicity. Nevertheless, the specific roles of HSF2 and the global HSF2-dependent gene expression profile during sustained stress have remained unknown. Here, we found that HSF2 is critical for cell survival during prolonged proteotoxicity. Strikingly, our RNA sequencing (RNA-seq) analyses revealed that impaired viability of HSF2-deficient cells is not caused by inadequate induction of molecular chaperones but is due to marked downregulation of cadherin superfamily genes. We demonstrate that HSF2-dependent maintenance of cadherin-mediated cell-cell adhesion is required for protection against stress induced by proteasome inhibition. This study identifies HSF2 as a key regulator of cadherin superfamily genes and defines cell-cell adhesion as a determinant of proteotoxic stress resistance