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Transcriptional responses of cancer cells to heat shock-inducing stimuli involve amplification of robust HSF1 binding

ABSTRACT: Background. The Heat Shock Response (HSR) is an evolutionarily conserved mechanism that helps cells adapt to environmental stresses. Heat Shock Factor 1 (HSF1) is a master HSR transcription factor that is long known to bind at promoters of its target HSP genes to rapidly activate their transcription. However, recent genome-wide studies revealed HSF1 binding at thousands of sites outside of heat-shock responsive gene promoters, implying a broader role of HSF1 in HSR. Results. We asked how the widespread HSF1 binding is established and to what extent it may be related to transcription activation. To answer these questions, we examined responses of two different human cancer cell lines to two stimuli that induce HSR, exposure to 42C and inorganic arsenic at the ambient temperature, by manually integrating ChIP-sequencing against HSF1, RNA Pol II, H3K4Me3 with nascent RNA- and ATAC-sequencing datasets in cells before and during HSR induced by these two stimuli. We show that widespread HSF1 binding is a temperature-agnostic hallmark of HSR whose genome-wide patterns combine cell type specificity with robustness to the nature of a stimulus and magnitude of activation. Mechanistically, HSR involves amplification of pre-existing low level HSF1 binding with few changes in accessible chromatin. HSF1 binding patterns show more stability than transcriptionally activated genes both between conditions and between cell lines. Conclusions. Comparing responses of distant cell lines to two HSR-inducing stimuli allowed us to define several features of HSR. Genome-wide HSF1 binding is a sensitive readout of HSR whose genome-wide patterns retain cell type identity across a broad dynamic range. The pre-existing genomic architecture is retained during HSR down to individual loci. Context-specific transcription involving common HSF1 binding favors a model of regulation by combinatory interplay of rigid transcription factor patterns.

ORGANISM(S): Homo sapiens

PROVIDER: GSE209675 | GEO | 2023/10/30

REPOSITORIES: GEO

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Project description:Huntington’s disease (HD) is a neurodegenerative disorder that is associated with the deposition of proteinaceous aggregates in the brains of HD patients and mouse models. Previous studies have suggested that wide-scale disruption of protein homeostasis occurs in protein folding diseases. Protein homeostasis can be maintained by activation of the heat shock response (HSR) via the transcription factor heat shock factor 1 (HSF1), the pharmacological activation of which can be achieved by Hsp90 inhibition and has been demonstrated to be beneficial in cell and invertebrate models of HD. Whether the HSR is functional in HD and whether its activation has therapeutic potential in mammalian HD models is currently unknown. To address these issues, we used a novel, brain penetrant Hsp90 inhibitor to activate the HSR in brain after systemic administration. Microarrays, quantitative PCR and western blotting showed that the HSR becomes impaired with disease progression in two mouse models of HD and that this originates at the level of transcription. Huntington’s disease (HD) is a neurodegenerative disorder that is associated with the deposition of proteinaceous aggregates in the brains of HD patients and mouse models. Previous studies have suggested that wide-scale disruption of protein homeostasis occurs in protein folding diseases. Protein homeostasis can be maintained by activation of the heat shock response (HSR) via the transcription factor heat shock factor 1 (HSF1), the pharmacological activation of which can be achieved by Hsp90 inhibition and has been demonstrated to be beneficial in cell and invertebrate models of HD. Whether the HSR is functional in HD and whether its activation has therapeutic potential in mammalian HD models is currently unknown. To address these issues, we used a novel, brain penetrant Hsp90 inhibitor to activate the HSR in brain after systemic administration. Microarrays, quantitative PCR and western blotting showed that the HSR becomes impaired with disease progression in two mouse models of HD and that this originates at the level of transcription.

Project description:Heat shock response (HSR) is critical for survival of organisms undergoing proteotoxic stress. Heat shock factor 1 (HSF1) is widely believed to be the master regulator of this response. Here, we examined the kinetics of the transcriptional response and HSF1 binding changes genome-wide after heat shock (HS) with high sensitivity and high spatial and temporal resolution using PRO-seq and ChIP-seq assays respectively in wild type and in hsf1-deletion mouse embryonic fibroblasts. The transcriptional response is rapid, dynamic, and extensive with activation of several hundred genes and repression of several thousands of genes. Although HSF1 is critically required for classical inducible Heat Shock Protein (HSP) genes, it is not required for the majority of gene activation. HSF1 acts mechanistically to promote RNA polymerase II (Pol II) release from the promoter-proximal pause, while recruitment and initiation of Pol II are predominantly HSF1-independent. Surprisingly, a major class of cytoskeleton genes is immediately (within 2.5 minutes) and transiently activated in an HSF1-independent manner. A second wave of regulation is characterized by robust activation or repression of new sets of genes. The broad repression of thousands of genes, a quarter of which are repressed immediately upon HS and the rest are repressed in the second wave of regulation, is mediated at the level of decreasing Pol II pause release and not at prior steps of Pol II recruitment or initiation. Notably, heat shock does not induce transcription of some previously defined HSP genes, and HSF2 â a homolog of HSF1 â does not compensate for the lack of HSF1. Together, these findings indicate that mammalian cells cope with stress by rapidly inducing pervasive and dramatic changes in transcription that are largely modulated at the step of pause release, and only a fraction of this regulation is HSF1-dependent. Examination of transcriptional regulation before and after heat shock in WT, HSF1-/-, and HSF1&2-/- MEFs

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Transcriptional responses of cancer cells to heat shock-inducing stimuli involve amplification of robust HSF1 binding

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