Heat shock factor 1 (HSF1) is essential for protecting cells from protein-damaging stress associated with misfolded proteins and regulates the insulin-signaling pathway and aging. Here, we show that human HSF1 is inducibly acetylated at a critical residue that negatively regulates DNA binding activity. Activation of the deacetylase and longevity factor SIRT1 prolonged HSF1 binding to the heat shock promoter Hsp70 by maintaining HSF1 in a deacetylated, DNA–binding competent state. Conversely, down-regulation of SIRT1 accelerated the attenuation of the heat shock response (HSR) and release of HSF1 from its cognate promoter elements. These results provide a mechanistic basis for the requirement of HSF1 in the regulation of life span and establish a role for SIRT1 in protein homeostasis and the HSR.

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Thousands of organic micropollutants and their transformation products occur in water. Although often present at low concentrations, individual compounds contribute to mixture effects. Cell-based bioassays that target health-relevant biological endpoints may therefore complement chemical analysis for water quality assessment. The objective of this study was to evaluate cell-based bioassays for their suitability to benchmark water quality and to assess efficacy of water treatment processes. The selected bioassays cover relevant steps in the toxicity pathways including induction of xenobiotic metabolism, specific and reactive modes of toxic action, activation of adaptive stress response pathways and system responses. Twenty laboratories applied 103 unique in vitro bioassays to a common set of 10 water samples collected in Australia, including wastewater treatment plant effluent, two types of recycled water (reverse osmosis and ozonation/activated carbon filtration), stormwater, surface water, and drinking water. Sixty-five bioassays (63%) showed positive results in at least one sample, typically in wastewater treatment plant effluent, and only five (5%) were positive in the control (ultrapure water). Each water type had a characteristic bioanalytical profile with particular groups of toxicity pathways either consistently responsive or not responsive across test systems. The most responsive health-relevant endpoints were related to xenobiotic metabolism (pregnane X and aryl hydrocarbon receptors), hormone-mediated modes of action (mainly related to the estrogen, glucocorticoid, and antiandrogen activities), reactive modes of action (genotoxicity) and adaptive stress response pathway (oxidative stress response). This study has demonstrated that selected cell-based bioassays are suitable to benchmark water quality and it is recommended to use a purpose-tailored panel of bioassays for routine monitoring.

Alterations in protein folding and the regulation of conformational states have become increasingly important to the functionality of key molecules in signaling, cell growth, and cell death. Molecular chaperones, because of their properties in protein quality control, afford conformational flexibility to proteins and serve to integrate stress-signaling events that influence aging and a range of diseases including cancer, cystic fibrosis, amyloidoses, and neurodegenerative diseases. We describe here characteristics of celastrol, a quinone methide triterpene and an active component from Chinese herbal medicine identified in a screen of bioactive small molecules that activates the human heat shock response. From a structure/function examination, the celastrol structure is remarkably specific and activates heat shock transcription factor 1 (HSF1) with kinetics similar to those of heat stress, as determined by the induction of HSF1 DNA binding, hyperphosphorylation of HSF1, and expression of chaperone genes. Celastrol can activate heat shock gene transcription synergistically with other stresses and exhibits cytoprotection against subsequent exposures to other forms of lethal cell stress. These results suggest that celastrols exhibit promise as a new class of pharmacologically active regulators of the heat shock response.

The disruption of protein folding quality control results in the accumulation of non-native protein species that can form oligomers, aggregates, and inclusions indicative of neurodegenerative disease. Likewise for over 100 other human diseases of protein conformation, a common feature may be the formation of off-pathway folding intermediates that are unstable, self-associate, and with time lead to a chronic imbalance in protein homeostasis with deleterious consequences on cellular function. This has led to a hypothesis that enhancement of components of the cellular quality control machinery, specifically the levels and activities of molecular chaperones, suppress aggregation and toxicity phenotypes to allow cellular function to be restored. This review addresses the regulation of molecular chaperones and components of protein homeostasis by heat shock transcription factor 1 (HSF1), the master stress-inducible regulator, and our current understanding of pharmacologically active small molecule regulators of the heat shock response as a therapeutic strategy for protein conformational diseases. Heat Shock Proteins: Functions in Normal and Disease StatesThe heat shock response (HSR) 2 is an ordered genetic response to diverse environmental and physiological stressors that results in the immediate induction of genes encoding molecular chaperones, proteases, and other proteins essential for protection and recovery from cellular damage associated with the expression of misfolded proteins (Fig. 1). The list of "stressors" that activate transcription of these heat shock genes is large and includes various acute and chronic conditions such as elevated temperatures, heavy metals, small molecule chemical toxicants, infection, and oxidative stress. Mutations and environmental influences including inflammation, ischemia, tissue wounding and repair, cancer, and neurodegenerative diseases are also associated with the aberrant expression of heat shock proteins.The heat shock gene superfamily is organized by molecular size and functional class, including the Hsp100, Hsp90, Hsp70, Hsp60, Hsp40 (J-domain proteins), and small heat shock protein (sHsp) families. Many of these proteins function as molecular chaperones to guide conformational states critical in the synthesis, folding, translocation, assembly, and degradation of proteins (1, 2). As chaperones are also central components in many signal transduction pathways (3), the proper regulation of chaperone expression is critical to the health of the cell.Cytoprotection-Heat shock proteins function at the cellular level to protect cells against a wide array of acute and chronic stress conditions. Subacute activation of the HSR results in stress tolerance and cytoprotection against otherwise lethal exposures to stress-induced molecular damage. This protective and adaptive response, also known as induced thermotolerance, ensures that the cell responds rapidly to repeated sub-acute challenges by diverse conditions of cell stress (4). The ability of heat shock proteins to protect agai...

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Stress response pathways allow cells to sense and respond to environmental changes and adverse pathophysiological states. Pharmacological modulation of cellular stress pathways has implications in the treatment of human diseases, including neurodegenerative disorders, cardiovascular disease, and cancer. The quinone methide triterpene celastrol, derived from a traditional Chinese medicinal herb, has numerous pharmacological properties, and it is a potent activator of the mammalian heat shock transcription factor HSF1. However, its mode of action and spectrum of cellular targets are poorly understood. We show here that celastrol activates Hsf1 in Saccharomyces cerevisiae at a similar effective concentration seen in mammalian cells. Transcriptional profiling revealed that celastrol treatment induces a battery of oxidant defense genes in addition to heat shock genes. Celastrol activated the yeast Yap1 oxidant defense transcription factor via the carboxy-terminal redox center that responds to electrophilic compounds. Antioxidant response genes were likewise induced in mammalian cells, demonstrating that the activation of two major cell stress pathways by celastrol is conserved. We report that celastrol's biological effects, including inhibition of glucocorticoid receptor activity, can be blocked by the addition of excess free thiol, suggesting a chemical mechanism for biological activity based on modification of key reactive thiols by this natural product. INTRODUCTIONThe heat shock response (HSR) is an ancient and highly conserved cytoprotective mechanism. Production of heat shock proteins, including protein chaperones, is essential for the folding, repair, or triage of damaged proteins; thus, it serves to promote cellular viability under conditions that would otherwise induce apoptosis (McMillan et al., 1998;Christians et al., 2002). There is significant interest in the discovery and development of small molecules that modulate the HSR and parallel stress response pathways for therapeutic purposes (Morimoto and Santoro, 1998;Westerheide and Morimoto, 2005;Corson and Crews, 2007). The HSR is governed by the stress-inducible heat shock transcription factor HSF1, which plays a key regulatory role in response to environmental stress, development, and many pathophysiological conditions, including cancer, ischemia-reperfusion injury, diabetes, and aging (Morimoto and Santoro, 1998;Morano and Thiele, 1999a).Significant progress has been made in identifying HSF1-modulating compounds such as triptolide and quercetin, inhibitors of HSF1, and activators such as the protein synthesis inhibitor puromycin, the proteasome inhibitor MG132, the nonsteroidal anti-inflammatory drugs salicylate and indomethacin, and the heat shock protein (Hsp)90 inhibitors radicicol and geldanamycin (Hightower, 1980;Jurivich et al., 1992;Lee et al., 1995;Nagai et al., 1995;Bagatell et al., 2000;Holmberg et al., 2000;Westerheide et al., 2006). A large-scale screen for novel pharmacologically active compounds that may be beneficial in treating the neur...

BackgroundThe heat shock response, induced by cytoplasmic proteotoxic stress, is one of the most highly conserved transcriptional responses. This response, driven by the heat shock transcription factor HSF1, restores proteostasis through the induction of molecular chaperones and other genes. In addition to stress-dependent functions, HSF1 has also been implicated in various stress-independent functions. In C. elegans, the HSF1 homolog HSF-1 is an essential protein that is required to mount a stress-dependent response, as well as to coordinate various stress-independent processes including development, metabolism, and the regulation of lifespan. In this work, we have performed RNA-sequencing for C. elegans cultured in the presence and absence of hsf-1 RNAi followed by treatment with or without heat shock. This experimental design thus allows for the determination of both heat shock-dependent and -independent biological targets of HSF-1 on a genome-wide level.ResultsOur results confirm that C. elegans HSF-1 can regulate gene expression in both a stress-dependent and -independent fashion. Almost all genes regulated by HS require HSF-1, reinforcing the central role of this transcription factor in the response to heat stress. As expected, major categories of HSF-1-regulated genes include cytoprotection, development, metabolism, and aging. Within both the heat stress-dependent and -independent gene groups, significant numbers of genes are upregulated as well as downregulated, demonstrating that HSF-1 can both activate and repress gene expression either directly or indirectly. Surprisingly, the cellular process most highly regulated by HSF-1, both with and without heat stress, is cuticle structure. Via network analyses, we identify a nuclear hormone receptor as a common link between genes that are regulated by HSF-1 in a HS-dependent manner, and an epidermal growth factor receptor as a common link between genes that are regulated by HSF-1 in a HS-independent manner. HSF-1 therefore coordinates various physiological processes in C. elegans, and HSF-1 activity may be coordinated across tissues by nuclear hormone receptor and epidermal growth factor receptor signaling.ConclusionThis work provides genome-wide HSF-1 regulatory networks in C. elegans that are both heat stress-dependent and -independent. We show that HSF-1 is responsible for regulating many genes outside of classical heat stress-responsive genes, including genes involved in development, metabolism, and aging. The findings that a nuclear hormone receptor may coordinate the HS-induced HSF-1 transcriptional response, while an epidermal growth factor receptor may coordinate the HS-independent response, indicate that these factors could promote cell non-autonomous signaling that occurs through HSF-1. Finally, this work highlights the genes involved in cuticle structure as important HSF-1 targets that may play roles in promoting both cytoprotection as well as longevity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2837-5...