GSE209685
Transcriptional responses of cancer cells to heat shock-inducing stimuli involve amplification of robust HSF1 binding
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.     Overall design: Control cells, cells treated with heat shock at 42'C for 60 minutes, and cells treated with 500micromolar sodium metaarsenite for 60 minutes were subjected to ChIP-seq against total RNA pol II, histone H3 Lysine 4 trimethylation and total HSF1, ATAC-seq, and Precision Run-on sequencing (PRO-seq). Unless indicated, all treatments involve two independent biological replicates.