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Genome-wide maps of HSF1 phase separation in heat shock and non-heat shock cells

ABSTRACT: HSF1 binds DNA via the DBD domain, causing gene upregulation during HS. We assessed the effect of RD-mediated phase separation on chromatin targeting of HSF1 using Cut&Tag followed by high-throughput sequencing to map genome-wide binding of LLPS-competent versus LLPS-incompetent HSF1 mutants under both HS and NHS conditions. Comparing with WT HSF1 under NHS, both WT under HS and M1 under NHS showed increased and broad binding to enhancers and distal intergenic region, with binding most enriched in expected motifs of HSF-related transcription factors. To further assess the role for IDR-induced LLPS in chromatin targeting of HSF1, we used several additional strategies. First, the treatment of 1,6-hexanediol markedly decreased chromatin occupancy both of WT under HS and M1 under NHS conditions. Second, we interrogate chromatin binding of LLPS-deficient mutant M3. Cut&Tag analysis revealed that M3 showed decreased chromatin binding compared to WT under HS and M1 under NHS. The decreased chromatin binding of M3 to chromatin was not due to the loss of its DNA binding ability, as the EMSA assay revealed that M3 was still capable of binding HSE. Instead, the decreased chromatin binding reflects the loss of inter-molecular interaction between HSF1 that holds LLPS. Furthermore, M3 in heat shocked cells shows similar reduced genomic targeting and shallow binding pattern as NHS cells . Third, the enrichment of transcriptional apparatus RNA Pol II, CYCT1, BRD4 to HSF1 target genes also depend on whether HSF1 can phase separate at these sites. Lastly, we conducted live cell single molecule imaging to evaluate chromatin binding kinetics of LLPS-deficient mutant M3 relative to WT HSF1. Measurements of single molecule displacement and diffusion coefficient showed M3 to be significantly more mobile than WT under HS, which suggests M3 was less confined within phase-separated puncta compared with LLPS-competent HSF1. Consistent with this result, super resolution imaging of M3 also showed decreased cluster formation at HSP gene foci but maintained nSBs formation. Altogether, LLPS-forming capability of HSF1 is essential for the efficient recruitment of HSF1 and transcriptional apparatus to HSP gene loci.

ORGANISM(S): Homo sapiens

PROVIDER: GSE192370 | GEO | 2021/12/24

REPOSITORIES: GEO

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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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Genome-wide maps of HSF1 phase separation in heat shock and non-heat shock cells

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