Defining the Essential Function of Yeast Hsf1 Reveals a Compact Transcriptional Program for Maintaining Eukaryotic Proteostasis
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ABSTRACT: We used the conditional chemical genetics approach known as “anchor away” (AA) to rapidly inactivate the essential yeast transcription factor Hsf1. We coupled Hsf1-AA to RNA-seq and NET-seq to define the genes whose expression depends on Hsf1 and performed Hsf1-3xFLAG-V5 ChIP-seq to validate direct targets. We also carried out a number of other perturbations to yeast stress pathways to show that most of the gene expression changes during heat shock are Hsf1-independent but depend on PKA signaling and the Msn2/4 general stress transcription factors. Finally, we generated RNA-seq in mouse ES cells and MEFs in wild type and hsf1-/- cells to define HSF1 targets in murine cells.
Project description:The heat shock response is an ancient and ubiquitous program allowing organisms to survive adverse environmental conditions. In S. cerevisiae, three transcription factors, Hsf1, Msn2 and Msn4, are thought to regulate the stress response. While Msn2/4 can be deleted, Hsf1 is essential. By combining the depletion of Hsf1 with the deletion of Msn2 and Msn4, we were able to switch off the central stress response. We show that the transcription factors Hsf1 and Msn2/4 follow different strategies and regimes: Whereas Msn2/4 are responsible for a broad metabolic response, Hsf1 triggers a direct chaperone response to stabilize and repair unfolded proteins. Exposure of cells lacking Msn2/4 and Hsf1 to thermal stress resulted in massive protein aggregation. Comparison with wildtype yeast revealed that among the proteins rescued by the stress response are many essential proteins.
Project description:We performed ChIP-seq of Hsf1 under non heat shock, 5-minute heat shock and 120 minute heat shock conditions. We used the conditional chemical genetics approach known as “anchor away” (AA) to rapidly inactivate Hsf1. We coupled Hsf1-AA to and nascent RNA seq (NAC)-seq to define the genes whose expression depends on Hsf1 during heat shock.
Project description:To ensure cell survival and growth during temperature increase, eukaryotic organisms respond with transcriptional activation that results in accumulation of proteins that protect against damage, and facilitate recovery. To define the global cellular adaptation response to heat stress, we performed a systematic genetic screen that yielded 277 yeast genes required for growth at high temperature. Of these, the Rpd3 histone deacetylase complex was enriched. Global gene expression analysis showed that Rpd3 partially regulated gene expression upon heat shock. The Hsf1 and Msn2/4 transcription factors are the main regulators of gene activation in response to heat stress. RPD3-deficient cells had impaired activation of Msn2/4-dependent genes, while activation of genes controlled by Hsf1 was deacetylase independent. Rpd3 bound to heat stress-dependent promoters through the Msn2/4 transcription factors, allowing entry of RNA Pol II and activation of transcription upon stress. Finally, we found that the large, but not the small Rpd3 complex regulated cell adaptation in response to heat stress.
Project description:To ensure cell survival and growth during temperature increase, eukaryotic organisms respond with transcriptional activation that results in accumulation of proteins that protect against damage, and facilitate recovery. To define the global cellular adaptation response to heat stress, we performed a systematic genetic screen that yielded 277 yeast genes required for growth at high temperature. Of these, the Rpd3 histone deacetylase complex was enriched. Global gene expression analysis showed that Rpd3 partially regulated gene expression upon heat shock. The Hsf1 and Msn2/4 transcription factors are the main regulators of gene activation in response to heat stress. RPD3-deficient cells had impaired activation of Msn2/4-dependent genes, while activation of genes controlled by Hsf1 was deacetylase independent. Rpd3 bound to heat stress-dependent promoters through the Msn2/4 transcription factors, allowing entry of RNA Pol II and activation of transcription upon stress. Finally, we found that the large, but not the small Rpd3 complex regulated cell adaptation in response to heat stress. Three independent 200 ml cultures of wild-type and rpd3Δ mutant strains were grown to mid-log phase in YPD rich medium at 25ºC (control) or at 39 ºC for 20 min (heat stressed). Results were analyzed comparing thermo-responsive gene expression respect to the control in each individual strain.
Project description:Transcriptional induction of Heat Shock Protein (HSP) genes in yeast is accompanied by dynamic changes in their 3D structure and spatial organization, yet the molecular basis for these phenomena remains unknown. Using chromosome conformation capture and single cell imaging, we show that genes transcriptionally activated by Heat Shock Factor 1 (Hsf1) specifically interact across chromosomes and coalesce into diffraction-limited intranuclear foci. Genes activated by the alternative stress regulators Msn2 and Msn4, in contrast, do not interact among themselves nor with Hsf1 targets. Likewise, constitutively expressed genes, even those interposed between HSP genes, show no detectable interaction. Hsf1 forms discrete subnuclear puncta when stressactivated, and these puncta dissolve in concert with transcriptional attenuation, paralleling the kinetics of HSP gene coalescence and dissolution. Nuclear Hsf1 and RNA Pol II are both necessary for intergenic HSP gene interactions, while DNA-bound Hsf1 is necessary and sufficient to drive coalescence of a heterologous gene. Our findings demonstrate that Hsf1 can dynamically restructure the yeast genome.
Project description:Samples GSM206658-GSM206693: Acquired Stress resistance in S. cerevisiae: NaCl primary and H2O2 secondary Transcriptional timecourses of yeast cells exposed to 0.7M NaCl alone, 0.5mM H2O2 alone, or 0.5mM H2O2 following 0.7M NaCl, all compared to an unstressed sample. Repeated using msn2∆ strain. Samples GSM291156-GSM291196: Transcriptional response to stress in strains lacking MSN2 and/or MSN4 Transcriptional timecourses of yeast cells (WT, msn2∆, msn4∆, or msn2∆msn4∆) exposed to 0.7M NaCl for 45 minutes or 30-37˚C Heat Shift for 15 min compared to an unstressed sample of the same strain. Keywords: Stress Response
Project description:The response to proteotoxic stresses such as heat shock is an ancient and ubiquitous transcriptional program allowing organisms to maintain protein homeostasis under changing environmental conditions. We depleted or deleted the three stress-specific transcription factors, Hsf1, Msn2 and Msn4, in S. cerevisiae and determined the effects on the transcriptome and proteome. Msn2/4 are responsible for a broad transcriptional reprogramming which includes i. a. the response to oxidative stress as well as biosynthesis of the protective sugar trehalose and glycolysis enzymes. Hsf1 activates the synthesis of molecular chaperones. In the absence of stress protection, thermal stress results in massive protein aggregation including many essential proteins. As a last resort to sustain life this triggers the transcriptomic induction of sporulation likely via the cell wall integrity signaling pathway.
Project description:The yeast PP2A-Cdc55 Serine/Threonine phosphatase regulates transcription under certain conditions. It is required for full activation of the environmental stress response mediated by the transcription factors Msn2 and Msn4. PP2A-Cdc55 contributes to sustained nuclear accumulation of Msn2 and Msn4 and extended chromatin recruitment under stress conditions such as hyperosmolarity stress. Transcript profiles of Msn2 and Msn4 double mutants are similar to cdc55 and the corresponding triple mutants. This argues for a Msn2/4 specific function of PP2A-Cdc55.