Heat Shock Factor 1 as a Coordinator of Stress and Developmental Pathways

MONITTR allows real-time imaging of transcription and endogenous proteins in C. elegans

Maximizing cell survival under stress requires rapid and transient adjustments of RNA and protein synthesis. However, capturing these dynamic changes at both single-cell level and across an organism has been challenging. Here, we developed a system named MONITTR (MS2-embedded mCherry-based monitoring of transcription) for real-time simultaneous measurement of nascent transcripts and endogenous protein levels in C. elegans. Utilizing this system, we monitored the transcriptional bursting of fasting-induced genes and found that the epidermis responds to fasting by modulating the proportion of actively transcribing nuclei and transcriptional kinetics of individual alleles. Additionally, our findings revealed the essential roles of the transcription factors NHR-49 and HLH-30 in governing the transcriptional kinetics of fasting-induced genes under fasting. Furthermore, we tracked transcriptional dynamics during heat-shock response and ER unfolded protein response and observed rapid changes in the level of nascent transcripts under stress conditions. Collectively, our study provides a foundation for quantitatively investigating how animals spatiotemporally modulate transcription in various physiological and pathological conditions.

UPS-dependent strategies of protein quality control degradation

The degradation of damaged proteins is critical for tissue integrity and organismal health because damaged proteins have a high propensity to form aggregates. E3 ubiquitin ligases are key regulators of protein quality control (PQC) and mediate the selective degradation of damaged proteins, a process termed 'PQC degradation' (PQCD). The degradation signals (degrons) that trigger PQCD are based on hydrophobic sites that are normally buried within the native protein structure. However, an open question is how PQCD-specialized E3 ligases distinguish between transiently misfolded proteins, which can be efficiently refolded, and permanently damaged proteins, which must be degraded. While significant progress has been made in characterizing degradation determinants, understanding the key regulatory signals of cellular and organismal PQCD pathways remains a challenge.

Heat shock transcription factor 1 facilitates liver cancer progression by driving super-enhancer-mediated transcription of MYCN

BACKGROUND

Heat shock transcription factors (HSFs) play crucial roles in the development of malignancies. However, the specific roles of HSFs in hepatocellular carcinoma (HCC) have yet to be fully elucidated.

AIMS

To explore the involvement of the HSF family, particularly HSF1, in the progression and prognosis of HCC.

MATERIALS & METHODS

We conducted a thorough analysis of HSF expression and copy number variations across various cancer datasets. Specifically focusing on HSF1, we examined its expression levels and prognostic implications in HCC. In vitro and in vivo experiments were carried out to evaluate the impact of HSF1 on liver cancer cell proliferation. Additionally, we utilized CUT&Tag, H3K27 acetylation enrichment, and RNA sequencing (RNA-seq) to investigate the super-enhancer (SE) regulatory landscapes of HSF1 in liver cancer cell lines.

RESULTS

HSF1 expression is elevated in HCC and is linked to poor prognosis in several datasets. HSF1 stimulates liver cancer cell proliferation both in vitro and in vivo, partly through modulation of H3K27ac levels, influencing enhancer distribution. Mechanistically, our findings demonstrate that HSF1 transcriptionally activates MYCN expression by binding to its promoter and SE elements, thereby promoting liver cancer cell proliferation. Moreover, increased MYCN expression was detected in HCC tumors and correlated with unfavorable patient outcomes.

DISCUSSION

Our study sheds light on previously unexplored aspects of HSF1 biology, identifying it as a transcription factor capable of shaping the epigenetic landscape in the context of HCC. Given HSF1's potential as an epigenetic regulator, targeting the HSF1-MYCN axis could open up new therapeutic possibilities for HCC treatment.

CONCLUSION

The HSF1-MYCN axis constitutes a transcription-dependent regulatory mechanism that may function as both a prognostic indicator and a promising therapeutic target in liver cancer. Further exploration of this axis could yield valuable insights into novel treatment strategies for HCC.

Neuromuscular and gene signaling responses to passive whole-body heat stress in young adults

This study aimed to investigate whether acute passive heat stress 1) decreases muscle Maximal Voluntary Contraction (MVC); 2) increases peripheral muscle fatigue; 3) increases spinal cord excitability, and 4) increases key skeletal muscle gene signaling pathways in skeletal muscle. Examining the biological and physiological markers underlying passive heat stress will assist us in understanding the potential therapeutic benefits. MVCs, muscle fatigue, spinal cord excitability, and gene signaling were examined after control or whole body heat stress in an environmental chamber (heat; 82 °C, 10% humidity for 30 min). Heart Rate (HR), an indicator of stress response, was correlated to muscle fatigue in the heat group (R = 0.59; p < 0.05) but was not correlated to MVC, twitch potentiation, and H reflex suppression. Sixty-one genes were differentially expressed after heat (41 genes >1.5-fold induced; 20 < 0.667 fold repressed). A strong correlation emerged between the session type (control or heat) and principal components (PC1) (R = 0.82; p < 0.005). Cell Signal Transduction, Metabolism, Gene Expression and Transcription, Immune System, DNA Repair, and Metabolism of Proteins were pathway domains with the largest number of genes regulated after acute whole body heat stress. Acute whole-body heat stress may offer a physiological stimulus for people with a limited capacity to exercise.

HSF1, Aging, and Neurodegeneration

Heat shock factor 1 (HSF1) is a master transcription regulator that mediates the induction of heat shock protein chaperones for quality control (QC) of the proteome and maintenance of proteostasis as a protective mechanism in response to stress. Research in this particular area has accelerated dramatically over the past three decades following successful isolation, cloning, and characterization of HSF1. The intricate multi-protein complexes and transcriptional activation orchestrated by HSF1 are fundamental processes within the cellular QC machinery. Our primary focus is on the regulation and function of HSF1 in aging and neurodegenerative diseases (ND) which represent physiological and pathological states of dysfunction in protein QC. This chapter presents an overview of HSF1 structural, functional, and energetic properties in healthy cells while addressing the deterioration of HSF1 function viz-à-viz age-dependent and neuron-specific vulnerability to ND. We discuss the structural domains of HSF1 with emphasis on the intrinsically disordered regions and note that disease proteins associated with ND are often structurally disordered and exquisitely sensitive to changes in cellular environment as may occur during aging. We propose a hypothesis that age-dependent changes of the intrinsically disordered proteome likely hold answers to understand many of the functional, structural, and organizational changes of proteins and signaling pathways in aging - dysfunction of HSF1 and accumulation of disease protein aggregates in ND included.Structured AbstractsIntroduction: Heat shock factor 1 (HSF1) is a master transcription regulator that mediates the induction of heat shock protein chaperones for quality control (QC) of the proteome as a cyto-protective mechanism in response to stress. There is cumulative evidence of age-related deterioration of this QC mechanism that contributes to disease vulnerability.

OBJECTIVES

Herein we discuss the regulation and function of HSF1 as they relate to the pathophysiological changes of protein quality control in aging and neurodegenerative diseases (ND).

METHODS

We present an overview of HSF1 structural, functional, and energetic properties in healthy cells while addressing the deterioration of HSF1 function vis-à-vis age-dependent and neuron-specific vulnerability to neurodegenerative diseases.

RESULTS

We examine the impact of intrinsically disordered regions on the function of HSF1 and note that proteins associated with neurodegeneration are natively unstructured and exquisitely sensitive to changes in cellular environment as may occur during aging.

CONCLUSIONS

We put forth a hypothesis that age-dependent changes of the intrinsically disordered proteome hold answers to understanding many of the functional, structural, and organizational changes of proteins - dysfunction of HSF1 in aging and appearance of disease protein aggregates in neurodegenerative diseases included.

The Thermal Stress Coping Network of the Nematode Caenorhabditis elegans

Response to hyperthermia, highly conserved from bacteria to humans, involves transcriptional upregulation of genes involved in battling the cytotoxicity caused by misfolded and denatured proteins, with the aim of proteostasis restoration. C. elegans senses and responds to changes in growth temperature or noxious thermal stress by well-defined signaling pathways. Under adverse conditions, regulation of the heat shock response (HSR) in C. elegans is controlled by a single transcription factor, heat-shock factor 1 (HSF-1). HSR and HSF-1 in particular are proven to be central to survival under proteotoxic stress, with additional roles in normal physiological processes. For years, it was a common belief that upregulation of heat shock proteins (HSPs) by HSF-1 was the main and most important step toward thermotolerance. However, an ever-growing number of studies have shown that targets of HSF-1 involved in cytoskeletal and exoskeletal integrity preservation as well as other HSF-1 dependent and independent pathways are equally important. In this review, we follow the thermal stimulus from reception by the nematode nerve endings till the activation of cellular response programs. We analyze the different HSF-1 functions in HSR as well as all the recently discovered mechanisms that add to the knowledge of the heat stress coping network of C. elegans.

Hawthorn fruit extract ameliorates H2O2-induced oxidative damage in neuronal PC12 cells and prolongs the lifespan of Caenorhabditis elegans via the IIS signaling pathway

Hawthorn (Crataegus pinnatifida) fruit has a long history of use as traditional Chinese medicine and is shown to have many health benefits including antioxidant and anti-aging. In this study, the anti-aging mechanism of hawthorn fruit extract (HFE) is predicted by network pharmacology and further verified in H₂O₂-induced PC12 cells and Caenorhabditis elegans. Network pharmacology predicted that the antiaging mechanism of HFE is mainly involved in phosphoinositide 3-kinase (PI3K)/AKT and the insulin/insulin-like growth factor-1 (IIS) signaling pathway. HFE significantly improved cell viability, increased superoxide dismutase, catalase, and glutathione peroxidase activity, decreased lactate dehydrogenase release, the level of reactive oxygen species (ROS), and malondialdehyde content in H₂O₂-induced PC12 cells (p < 0.05). HFE significantly increased the mean lifespan of C. elegans by 28.43% (100 μg mL^-1) and enhanced the stress resistance to H₂O₂, paraquat, juglone, ultraviolet radiation, and heat shock. HFE also suppressed the accumulation of aging pigments, improved the body bending ability, increased antioxidant enzyme activities, and reduced the contents of ROS and malondialdehyde. In addition, relevant gene expression, lifespan experiments with mutant strains, and molecular docking studies supported the results that HFE might extend lifespan through the IIS signal pathway.

Knockdown of heat shock transcription factor 1 decreases temperature stress tolerance in Bemisia tabaci MED

The primary function of heat shock transcription factor (HSF) in the heat shock response is to activate the transcription of genes encoding heat shock proteins (HSPs). The phloem-feeding insect Bemisia tabaci (Gennadius) is an important pest of cotton, vegetables and ornamentals that transmits several plant viruses and causes enormous agricultural losses. In this study, the gene encoding HSF (Bthsf1) was characterized in MED B. tabaci. The full-length cDNA encoded a protein of 652 amino acids with an isoelectric point of 5.55. The BtHSF1 deduced amino acid sequence showed strong similarity to HSF in other insects. Expression analyses using quantitative real-time PCR indicated that Bthsf1 was significantly up-regulated in B. tabaci adults and pupae during thermal stress. Although Bthsf1 was induced by both hot and cold stress, the amplitude of expression was greater in the former. Bthsf1 had distinct, significant differences in expression pattern during different duration of high but not low temperature stress. Oral ingestion of dsBthsf1 repressed the expression of Bthsf1 and four heat shock proteins (Bthsp90, Bthsp70-3, Bthsp20 and Bthsp19.5) in MED B. tabaci during hot and cold stress. In conclusion, our results show that Bthsf1 is differentially expressed during high and low temperature stress and regulates the transcription of multiple hsps in MED B. tabaci.

Network Theoretical Approach to Explore Factors Affecting Signal Propagation and Stability in Dementia’s Protein-Protein Interaction Network

Dementia—a syndrome affecting human cognition—is a major public health concern given to its rising prevalence worldwide. Though multiple research studies have analyzed disorders such as Alzheimer’s disease and Frontotemporal dementia using a systems biology approach, a similar approach to dementia syndrome as a whole is required. In this study, we try to find the high-impact core regulating processes and factors involved in dementia’s protein–protein interaction network. We also explore various aspects related to its stability and signal propagation. Using gene interaction databases such as STRING and GeneMANIA, a principal dementia network (PDN) consisting of 881 genes and 59,085 interactions was achieved. It was assortative in nature with hierarchical, scale-free topology enriched in various gene ontology (GO) categories and KEGG pathways, such as negative and positive regulation of apoptotic processes, macroautophagy, aging, response to drug, protein binding, etc. Using a clustering algorithm (Louvain method of modularity maximization) iteratively, we found a number of communities at different levels of hierarchy in PDN consisting of 95 “motif-localized hubs”, out of which, 7 were present at deepest level and hence were key regulators (KRs) of PDN (HSP90AA1, HSP90AB1, EGFR, FYN, JUN, CELF2 and CTNNA3). In order to explore aspects of network’s resilience, a knockout (of motif-localized hubs) experiment was carried out. It changed the network’s topology from a hierarchal scale-free topology to scale-free, where independent clusters exhibited greater control. Additionally, network experiments on interaction of druggable genome and motif-localized hubs were carried out where UBC, EGFR, APP, CTNNB1, NTRK1, FN1, HSP90AA1, MDM2, VCP, CTNNA1 and GRB2 were identified as hubs in the resultant network (RN). We finally concluded that stability and resilience of PDN highly relies on motif-localized hubs (especially those present at deeper levels), making them important therapeutic intervention candidates. HSP90AA1, involved in heat shock response (and its master regulator, i.e., HSF1), and EGFR are most important genes in pathology of dementia apart from KRs, given their presence as KRs as well as hubs in RN.

Transcriptional regulation of small heat shock protein genes by heat shock factor 1 (HSF1) in Liriomyza trifolii under heat stress

Small heat shock proteins (sHSPs) function as molecular chaperones in multiple physiological processes and are active during thermal stress. sHSP expression is controlled by heat shock transcription factor (HSF); however, few studies have been conducted on HSF in agricultural pests. Liriomyza trifolii is an introduced insect pest of horticultural and vegetable crops in China. In this study, the master regulator, HSF1, was cloned and characterized from L. trifolii, and the expression levels of HSF1 and five sHSPs were studied during heat stress. HSF1 expression in L. trifolii generally decreased with rising temperatures, whereas expression of the five sHSPs showed an increasing trend that correlated with elevated temperatures. All five sHSPs and HSF1 showed an upward trend in expression with exposure to 40 ℃ without a recovery period. When a recovery period was incorporated after thermal stress, the expression patterns of HSF1 and sHSPs in L. trifolii exposed to 40 °C was significantly lower than expression with no recovery period. To elucidate potential interactions between HSF1 and sHSPs, double-stranded RNA was synthesized to knock down HSF1 in L. trifolii by RNA interference. The knockdown of HSF1 by RNAi decreased the survival rate and expression of HSP19.5, HSP20.8, and HSP21.3 during high-temperature stress. This study expands our understanding of HSF1-regulated gene expression in L. trifolii exposed to heat stress.

Role of a Heat Shock Transcription Factor and the Major Heat Shock Protein Hsp70 in Memory Formation and Neuroprotection

Heat shock proteins (Hsps) represent the most evolutionarily ancient, conserved, and universal system for protecting cells and the whole body from various types of stress. Among Hsps, the group of proteins with a molecular weight of 70 kDa (Hsp70) plays a particularly important role. These proteins are molecular chaperones that restore the native conformation of partially denatured proteins after exposure to proteotoxic forms of stress and are critical for the folding and intracellular trafficking of de novo synthesized proteins under normal conditions. Hsp70s are expressed at high levels in the central nervous system (CNS) of various animals and protect neurons from various types of stress, including heat shock, hypoxia, and toxins. Numerous molecular and behavioral studies have indicated that Hsp70s expressed in the CNS are important for memory formation. These proteins contribute to the folding and transport of synaptic proteins, modulate signaling cascades associated with synaptic activation, and participate in mechanisms of neurotransmitter release. In addition, HSF1, a transcription factor that is activated under stress conditions and mediates Hsps transcription, is also involved in the transcription of genes encoding many synaptic proteins, whose levels are increased in neurons under stress and during memory formation. Thus, stress activates the molecular mechanisms of memory formation, thereby allowing animals to better remember and later avoid potentially dangerous stimuli. Finally, Hsp70 has significant protective potential in neurodegenerative diseases. Increasing the level of endogenous Hsp70 synthesis or injecting exogenous Hsp70 reduces neurodegeneration, stimulates neurogenesis, and restores memory in animal models of ischemia and Alzheimer’s disease. These findings allow us to consider recombinant Hsp70 and/or Hsp70 pharmacological inducers as potential drugs for use in the treatment of ischemic injury and neurodegenerative disorders.

The Multifaceted Role of HSF1 in Pathophysiology: Focus on Its Interplay with TG2

The cellular environment needs to be strongly regulated and the maintenance of protein homeostasis is crucial for cell function and survival. HSF1 is the main regulator of the heat shock response (HSR), the master pathway required to maintain proteostasis, as involved in the expression of the heat shock proteins (HSPs). HSF1 plays numerous physiological functions; however, the main role concerns the modulation of HSPs synthesis in response to stress. Alterations in HSF1 function impact protein homeostasis and are strongly linked to diseases, such as neurodegenerative disorders, metabolic diseases, and different types of cancers. In this context, type 2 Transglutaminase (TG2), a ubiquitous enzyme activated during stress condition has been shown to promote HSF1 activation. HSF1-TG2 axis regulates the HSR and its function is evolutionary conserved and implicated in pathological conditions. In this review, we discuss the role of HSF1 in the maintenance of proteostasis with regard to the HSF1-TG2 axis and we dissect the stress response pathways implicated in physiological and pathological conditions.

Molecular Characterization of Heat-Induced HSP11.0 and Master-Regulator HSF from Cotesia chilonis and Their Consistent Response to Heat Stress

Simple Summary

Small heat shock proteins (sHSPs) are members of the heat shock protein (HSP) family that play an important role in heat stress, and heat shock factors (HSFs) are transcriptional activators that mainly regulate the expression of HSPs. Cotesia chilonis, the major endoparasitoid of Chilo suppressalis, widely distributes in China and other Asian regions. Previous studies have shown that C. chilonis has a certain thermal tolerance. Here, heat-induced HSP11.0 and master-regulator HSF were cloned and characterized from C. chilonis. The transcription patterns of them in response to different temperatures and time course after temperature treatment were analyzed. This study is the first report on the analysis on hsf gene of C. chilonis. The results of expression patterns will provide new insights into thermoregulation of C. chilonis in response to climate change.

Abstract

Small heat shock proteins (sHSPs) are members of the heat shock protein (HSP) family that play an important role in temperature stress, and heat shock factors (HSFs) are transcriptional activators that regulate HSP expression. Cotesia chilonis, the major endoparasitoid of Chilo suppressalis, modulates the C. suppressalis population in the field. In this study, we cloned and characterized two genes from C.chilonis: the heat-induced HSP11.0 gene (Cchsp11.0) that consisted of a 306-bp ORF, and the master regulator HSF (Cchsf) containing an 1875-bp ORF. CcHSP11.0 contained a chaperonin cpn10 signature motif that is conserved in other hymenopteran insects. CcHSF is a typical HSF and contains a DNA-binding domain, two hydrophobic heptad repeat domains, and a C-terminal trans-activation domain. Neither Cchsp11.0 or Cchsf contain introns. Real-time quantitative PCR revealed that Cchsp11.0 and Cchsf were highly induced at 36 °C and 6 °C after a 2-h exposure. Overall, the induction of Cchsf was lower than Cchsp11.0 at low temperatures, whereas the opposite was true at high temperatures. In conclusion, both Cchsp11.0 and Cchsf are sensitive to high and low temperature stress, and the expression pattern of the two genes were positively correlated during temperature stress.

HSP27 role in cardioprotection by modulating chemotherapeutic doxorubicin-induced cell death

The common phenomenon expected from any anti-cancer drug in use is to kill the cancer cells without any side effects to non-malignant cells. Doxorubicin is an anthracycline derivative anti-cancer drug active over different types of cancers with anti-cancer activity but attributed to unintended cytotoxicity and genotoxicity triggering mitogenic signals inducing apoptosis. Administration of doxorubicin tends to both acute and chronic toxicity resulting in cardiomyopathy (left ventricular dysfunction) and congestive heart failure (CHF). Cardiotoxicity is prevented through administration of different cardioprotectants along with the drug. This review elaborates on mechanism of drug-mediated cardiotoxicity and attenuation principle by different cardioprotectants, with a focus on Hsp27 as cardioprotectant by prevention of drug-induced oxidative stress, cell survival pathways with suppression of intrinsic cell death. In conclusion, Hsp27 may offer an exciting/alternating cardioprotectant, with a wider study being need of the hour, specifically on primary cell line and animal models in conforming its cardioprotectant behaviour.

Heat shock protein 90 inhibition and multi-target approach to maximize cardioprotection in ischaemic injury

Despite several advances in medicine, ischaemic heart disease remains a major cause of morbidity and mortality. The unravelling of molecular mechanisms underlying disease pathophysiology has revealed targets for pharmacological interventions. However, transfer of these pharmcological possibilities to clinical use has been disappointing. Considering the complexity of ischaemic disease at the cellular and molecular levels, an equally multifaceted treatment approach may be envisioned. The pharmacological principle of 'one target, one key' may fall short in such contexts, and optimal treatment may involve one or many agents directed against complementary targets. Here, we introduce a 'multi-target approach to cardioprotection' and propose heat shock protein 90 (HSP90) as a target of interest. We report on a member of a distinct class of HSP90 inhibitor possessing pleiotropic activity, which we found to exhibit potent infarct-sparing effects.

Consequences of HSF knockdown on gene expression during the heat shock response in Tigriopus californicus

Although the existence of a cellular heat shock response is nearly universal, its relationship to organismal thermal tolerance is not completely understood. Many of the genes involved are known to be regulated by the highly conserved heat shock transcription factor-1 (HSF-1), yet the regulatory network is not fully characterized. Here, we investigated the role of HSF-1 in gene expression following thermal stress using knockdown of HSF-1 by RNA interference in the intertidal copepod Tigriopus californicus We observed some evidence for decreased transcription of heat shock protein genes following knockdown, supporting the widely acknowledged role of HSF-1 in the heat shock response. However, the majority of differentially expressed genes between the control and HSF-1 knockdown groups were upregulated, suggesting that HSF-1 normally functions to repress their expression. Differential expression observed in genes related to chitin and cuticle formation lends support to previous findings that these processes are highly regulated following heat stress. We performed a genome scan and identified a set of 396 genes associated with canonical heat shock elements. RNA-seq data did not find those genes to be more highly represented in our HSF-1 knockdown treatment, indicating that requirements for binding and interaction of HSF-1 with a given gene are not simply predicted by the presence of HSF-1 binding sites. Further study of the pathways implicated by these results and future comparisons among populations of T. californicus may help us understand the role and importance of HSF-1 in the heat shock response and, more broadly, in organismal thermal tolerance.

p53 dynamics in single cells are temperature-sensitive

Cells need to preserve genome integrity despite varying cellular and physical states. p53, the guardian of the genome, plays a crucial role in the cellular response to DNA damage by triggering cell cycle arrest, apoptosis or senescence. Mutations in p53 or alterations in its regulatory network are major driving forces in tumorigenesis. As multiple studies indicate beneficial effects for hyperthermic treatments during radiation- or chemotherapy of human cancers, we aimed to understand how p53 dynamics after genotoxic stress are modulated by changes in temperature across a physiological relevant range. To this end, we employed a combination of time-resolved live-cell microscopy and computational analysis techniques to characterise the p53 response in thousands of individual cells. Our results demonstrate that p53 dynamics upon ionizing radiation are temperature dependent. In the range of 33 °C to 39 °C, pulsatile p53 dynamics are modulated in their frequency. Above 40 °C, which corresponds to mild hyperthermia in a clinical setting, we observed a reversible phase transition towards sustained hyperaccumulation of p53 disrupting its canonical response to DNA double strand breaks. Moreover, we provide evidence that mild hyperthermia alone is sufficient to induce a p53 response in the absence of genotoxic stress. These insights highlight how the p53-mediated DNA damage response is affected by alterations in the physical state of a cell and how this can be exploited by appropriate timing of combination therapies to increase the efficiency of cancer treatments.

A promoter variant in ZNF804A decreasing its expression increases the risk of autism spectrum disorder in the Han Chinese population

Synaptic pathology may be one of the cellular substrates underlying autism spectrum disorder (ASD). ZNF804A is a transcription factor that can affect or regulate the expression of many candidate genes involved in ASD. It also localizes at synapses and regulates neuronal and synaptic morphology. So far, few reports have addressed possible associations between ZNF804A polymorphisms and ASD. This study aimed to investigate whether ZNF804A genetic variants contribute to ASD susceptibility and its possible pathological role in the disorder. We analyzed the relationship of two polymorphisms (rs10497655 and rs34714481) in ZNF804A promoter region with ASD in 854 cases versus 926 controls. The functional analyses of rs10497655 were then performed using real-time quantitative polymerase chain reaction, electrophoretic mobility shift assays, chromatin immunoprecipitation and dual-luciferase assays. The variant rs10497655 was significantly associated with ASD (P = 0.007851), which had a significant effect on ZNF804A expression, with the T risk allele homozygotes related with reduced ZNF804A expression in human fetal brains. HSF2 acted as a suppressor by down-regulating ZNF804A expression and had a stronger binding affinity for the T allele of rs10497655 than for the C allele. This was the first experiment to elucidate the process in which a disease-associated SNP affects the level of ZNF804A expression by binding with the upstream regulation factor HSF2. This result indicates that the rs10497655 allelic expression difference of ZNF804A during the critical period of brain development may have an effect on postnatal phenotypes of ASD. It reveals new roles of ZNF804A polymorphisms in the pathogenesis of psychiatric disorders.

Inhibition of Heat Shock Factor 1 Enhances Repressive Molecular Mechanisms on the POMC Promoter

BACKGROUND

Cushing's disease (CD) is caused by adrenocorticotropic hormone (ACTH)-secreting pituitary tumours. They express high levels of heat shock protein 90 and heat shock factor 1 (HSF1) in comparison to the normal tissue counterpart, indicating activated cellular stress.

AIMS

Our objectives were: (1) to correlate HSF1 expression with clinical features and hormonal/radiological findings of CD, and (2) to investigate the effects of HSF1 inhibition as a target for CD treatment.

PATIENTS/METHODS

We examined the expression of total and pSer326HSF1 (marker for its transcriptional activation) by Western blot on eight human CD tumours and compared to the HSF1 status of normal pituitary. We screened a cohort of 45 patients with CD for HSF1 by immunohistochemistry and correlated the HSF1 immunoreactivity score with the available clinical data. We evaluated the effects of HSF1 silencing with RNA interference and the HSF1 inhibitor KRIBB11 in AtT-20 cells and four primary cultures of human corticotroph tumours.

RESULTS

We show that HSF1 protein is highly expressed and transcriptionally active in CD tumours in comparison to normal pituitary. The immunoreactivity score for HSF1 did not correlate with the typical clinical features of the disease. HSF1 inhibition reduced proopiomelanocortin (Pomc) transcription in AtT-20 cells. The HSF1 inhibitor KRIBB11 suppressed ACTH synthesis from 75% of human CD tumours in primary cell culture. This inhibitory action on Pomc transcription was mediated by increased glucocorticoid receptor and suppressed Nurr77/Nurr1 and AP-1 transcriptional activities.

CONCLUSIONS

These data show that HSF1 regulates POMC transcription. Pharmacological targeting of HSF1 may be a promising treatment option for the control of excess ACTH secretion in CD.

Dysregulation of Transcription Factors: A Key Culprit Behind Neurodegenerative Disorders

Neurodegenerative diseases (NDs) are considered heterogeneous disorders characterized by progressive pathological changes in neuronal systems. Transcription factors are protein molecules that are important in regulating the expression of genes. Although the clinical manifestations of NDs vary, the pathological processes appear similar with regard to neuroinflammation, oxidative stress, and proteostasis, to which, as numerous studies have discovered, transcription factors are closely linked. In this review, we summarized and reviewed the roles of transcription factors in NDs, and then we elucidated their functions during pathological processes, and finally we discussed their therapeutic values in NDs.

Heat shock factor 1 regulates heat shock proteins and immune-related genes in Penaeus monodon under thermal stress

Heat shock factors (HSFs) participate in the response to environmental stressors and regulate heat shock protein (Hsp) expression. This study describes the molecular characterization and expression of PmHSF1 in black tiger shrimp Penaeus monodon under heat stress. PmHSF1 expression was detected in several shrimp tissues: the highest in the lymphoid organ and the lowest in the eyestalk. Significant up-regulation of PmHSF1 expression was observed in hemocytes (p < 0.05) following thermal stress. The expression of several PmHsps was rapidly induced following heat stress. Endogenous PmHSF1 protein was expressed in all three types of shrimp hemocyte and strongly induced under heat stress. The suppression of PmHSF1 expression by dsRNA-mediated gene silencing altered the expression of PmHsps, several antimicrobial genes, genes involved in the melanization process, and an antioxidant gene (PmSOD). PmHSF1 plays an important role in the thermal stress response, regulating the expression of Hsps and immune-related genes in P. monodon.

The Disordered C-Terminus of Yeast Hsf1 Contains a Cryptic Low-Complexity Amyloidogenic Region

Response mechanisms to external stress rely on networks of proteins able to activate specific signaling pathways to ensure the maintenance of cell proteostasis. Many of the proteins mediating this kind of response contain intrinsically disordered regions, which lack a defined structure, but still are able to interact with a wide range of clients that modulate the protein function. Some of these interactions are mediated by specific short sequences embedded in the longer disordered regions. Because the physicochemical properties that promote functional and abnormal interactions are similar, it has been shown that, in globular proteins, aggregation-prone and binding regions tend to overlap. It could be that the same principle applies for disordered protein regions. In this context, we show here that a predicted low-complexity interacting region in the disordered C-terminus of the stress response master regulator heat shock factor 1 (Hsf1) protein corresponds to a cryptic amyloid region able to self-assemble into fibrillary structures resembling those found in neurodegenerative disorders.

Could Sirtuin Activities Modify ALS Onset and Progression?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with a complex etiology. Sirtuins have been implicated as disease-modifying factors in several neurological disorders, and in the past decade, attempts have been made to check if manipulating Sirtuin activities and levels could confer benefit in terms of neuroprotection and survival in ALS models. The efforts have largely focused on mutant SOD1, and while limited in scope, the results were largely positive. Here, the body of work linking Sirtuins with ALS is reviewed, with discussions on how Sirtuins and their activities may impact on the major etiological mechanisms of ALS. Moving forward, it is important that the potentially beneficial effect of Sirtuins in ALS disease onset and progression are assessed in ALS models with TDP-43, FUS, and C9orf72 mutations.

Repair or destruction-an intimate liaison between ubiquitin ligases and molecular chaperones in proteostasis

Cellular differentiation, developmental processes, and environmental factors challenge the integrity of the proteome in every eukaryotic cell. The maintenance of protein homeostasis, or proteostasis, involves folding and degradation of damaged proteins, and is essential for cellular function, organismal growth, and viability 1, 2. Misfolded proteins that cannot be refolded by chaperone machineries are degraded by specialized proteolytic systems. A major degradation pathway regulating cellular proteostasis is the ubiquitin (Ub)/proteasome system (UPS), which regulates turnover of damaged proteins that accumulate upon stress and during aging. Despite a large number of structurally unrelated substrates, Ub conjugation is remarkably selective. Substrate selectivity is mainly provided by the group of E3 enzymes. Several observations indicate that numerous E3 Ub ligases intimately collaborate with molecular chaperones to maintain the cellular proteome. In this review, we provide an overview of specialized quality control E3 ligases playing a critical role in the degradation of damaged proteins. The process of substrate recognition and turnover, the type of chaperones they team up with, and the potential pathogeneses associated with their malfunction will be further discussed.

Regulation of cell-non-autonomous proteostasis in metazoans

Cells have developed robust adaptation mechanisms to survive environmental conditions that challenge the integrity of their proteome and ensure cellular viability. These are stress signalling pathways that integrate extracellular signals with the ability to detect and efficiently respond to protein-folding perturbations within the cell. Within the context of an organism, the cell-autonomous effects of these signalling mechanisms are superimposed by cell-non-autonomous stress signalling pathways that allow co-ordination of stress responses across tissues. These transcellular stress signalling pathways orchestrate and maintain the cellular proteome at an organismal level. This article focuses on mechanisms in both invertebrate and vertebrate organisms that activate stress responses in a cell-non-autonomous manner. We discuss emerging insights and provide specific examples on how components of the cell-non-autonomous proteostasis network are used in cancer and protein-folding diseases to drive disease progression across tissues.

Targeting chaperones, heat shock factor-1, and unfolded protein response: Promising therapeutic approaches for neurodegenerative disorders

Protein misfolding, which is known to cause several serious diseases, is an emerging field that addresses multiple therapeutic areas. Misfolding of a disease-specific protein in the central nervous system ultimately results in the formation of toxic aggregates that may accumulate in the brain, leading to neuronal cell death and dysfunction, and associated clinical manifestations. A large number of neurodegenerative diseases in humans, including Alzheimer's, Parkinson's, Huntington's, and prion diseases, are primarily caused by protein misfolding and aggregation. Notably, the cellular system is equipped with a protein quality control system encompassing chaperones, ubiquitin proteasome system, and autophagy, as a defense mechanism that monitors protein folding and eliminates inappropriately folded proteins. As the intrinsic molecular mechanisms of protein misfolding become more clearly understood, the novel therapeutic approaches in this arena are gaining considerable interest. The present review will describe the chaperones network and different approaches as the therapeutic targets for neurodegenerative diseases. Current and emerging therapeutic approaches to combat neurodegenerative diseases, addressing the roles of molecular, chemical, and pharmacological chaperones, as well as heat shock factor-1 and the unfolded protein response, are also discussed in detail.

Loggerhead sea turtle embryos (Caretta caretta) regulate expression of stress response and developmental genes when exposed to a biologically realistic heat stress

Oviparous reptile embryos are expected to breach their critical thermal maxima if temperatures reach those predicted under current climate change models due to the lack of the maternal buffering processes and parental care. Heat-shock proteins (HSPs) are integral in the molecular response to thermal stress, and their expression is heritable, but the roles of other candidate families such as the heat-shock factors (HSFs) have not been determined in reptiles. Here, we subject embryonic sea turtles (Caretta caretta) to a biologically realistic thermal stress and employ de novo transcriptomic profiling of brain tissue to investigate the underlying molecular response. From a reference transcriptome of 302 293 transcripts, 179 were identified as differentially expressed between treatments. As anticipated, genes enriched in the heat-shock treatment were primarily associated with the Hsp families, or were genes whose products play similar protein editing and chaperone functions (e.g. bag3, MYOC and serpinh1). Unexpectedly, genes encoding the HSFs were not significantly upregulated under thermal stress, indicating their presence in unstressed cells in an inactive state. Genes that were downregulated under thermal stress were less well functionally defined but were associated with stress response, development and cellular organization, suggesting that developmental processes may be compromised at realistically high temperatures. These results confirm that genes from the Hsp families play vital roles in the thermal tolerance of developing reptile embryos and, in addition with a number of other genes, should be targets for evaluating the capacity of oviparous reptiles to respond adaptively to the effects of climate change.

Thermal stress in Danio rerio: a link between temperature, light, thermo-TRP channels, and clock genes

It is believed that the biological systems perceiving temperature and light daily cycles were subjected to the simultaneous selective pressures, which resulted in their co-evolutionary association. We investigated the influence of 1h 33°C heat shock on the expression of clock and heat shock protein genes, as well as the role of the thermo-TRP channel, TRPV1, in ZEM-2S cells of the teleost Danio rerio, in constant dark (DD) or light-dark cycles (LD). After heat shock, we observed an acute increase of hsp90 aa1 levels in both DD and LD conditions. Interestingly, the expression of hsp90 aa1 was two-fold lower in LD than in DD, what suggests an antagonistic effect of white light on heat shock action. Regarding clock genes, no effect was found in cells subjected to the heat shock in DD. When cells were kept in LD, the expression of per1, per2, cry1a, and cry1b increased in response to heat shock, indicating that heat shock only affects clock core of LD-synchronized ZEM-2S cells. We then evaluated whether TRPV1 played a role in heat-mediated hsp90 aa1 and per2 responses: hsp90 aa1 increase was unaffected whereas per2 increase was partially blocked by TRPV1 inhibitor, demonstrating the channel participation in clock gene regulation by heat shock. Taken together, our results open a novel investigative perspective regarding the relationship between temperature and clock genes, placing a new player in the regulation of this phenomenon: the TRPV1 channel.

Abnormal degradation of the neuronal stress-protective transcription factor HSF1 in Huntington's disease

Huntington's Disease (HD) is a neurodegenerative disease caused by poly-glutamine expansion in the Htt protein, resulting in Htt misfolding and cell death. Expression of the cellular protein folding and pro-survival machinery by heat shock transcription factor 1 (HSF1) ameliorates biochemical and neurobiological defects caused by protein misfolding. We report that HSF1 is degraded in cells and mice expressing mutant Htt, in medium spiny neurons derived from human HD iPSCs and in brain samples from patients with HD. Mutant Htt increases CK2α' kinase and Fbxw7 E3 ligase levels, phosphorylating HSF1 and promoting its proteasomal degradation. An HD mouse model heterozygous for CK2α' shows increased HSF1 and chaperone levels, maintenance of striatal excitatory synapses, clearance of Htt aggregates and preserves body mass compared with HD mice homozygous for CK2α'. These results reveal a pathway that could be modulated to prevent neuronal dysfunction and muscle wasting caused by protein misfolding in HD.

The myeloid heat shock transcription factor 1/β-catenin axis regulates NLR family, pyrin domain-containing 3 inflammasome activation in mouse liver ischemia/reperfusion injury

Heat shock transcription factor 1 (HSF1) has been implicated in the differential regulation of cell stress and disease states. β-catenin activation is essential for immune homeostasis. However, little is known about the role of macrophage HSF1-β-catenin signaling in the regulation of NLRP3 inflammasome activation during ischemia/reperfusion (I/R) injury (IRI) in the liver. This study investigated the functions and molecular mechanisms by which HSF1-β-catenin signaling influenced NLRP3-mediated innate immune response in vivo and in vitro. Using a mouse model of IR-induced liver inflammatory injury, we found that mice with a myeloid-specific HSF1 knockout (HSF1^M-KO ) displayed exacerbated liver damage based on their increased serum alanine aminotransferase levels, intrahepatic macrophage/neutrophil trafficking, and proinflammatory interleukin (IL)-1β levels compared to the HSF1-proficient (HSF1^FL/FL ) controls. Disruption of myeloid HSF1 markedly increased transcription factor X-box-binding protein (XBP1), NLR family, pyrin domain-containing 3 (NLRP3), and cleaved caspase-1 expression, which was accompanied by reduced β-catenin activity. Knockdown of XBP1 in HSF1-deficient livers using a XBP1 small interfering RNA ameliorated hepatocellular functions and reduced NLRP3/cleaved caspase-1 and IL-1β protein levels. In parallel in vitro studies, HSF1 overexpression increased β-catenin (Ser552) phosphorylation and decreased reactive oxygen species (ROS) production in bone-marrow-derived macrophages. However, myeloid HSF1 ablation inhibited β-catenin, but promoted XBP1. Furthermore, myeloid β-catenin deletion increased XBP1 messenger RNA splicing, whereas a CRISPR/CRISPR-associated protein 9-mediated XBP1 knockout diminished NLRP3/caspase-1.

CONCLUSION

The myeloid HSF1-β-catenin axis controlled NLRP3 activation by modulating the XBP1 signaling pathway. HSF1 activation promoted β-catenin, which, in turn, inhibited XBP1, leading to NLRP3 inactivation and reduced I/R-induced liver injury. These findings demonstrated that HSF1/β-catenin signaling is a novel regulator of innate immunity in liver inflammatory injury and implied the therapeutic potential for management of sterile liver inflammation in transplant recipients. (Hepatology 2016;64:1683-1698).

The genome-wide role of HSF-1 in the regulation of gene expression in Caenorhabditis elegans

BACKGROUND

The 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.

RESULTS

Our 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.

CONCLUSION

This 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.

Heat Shock Factor 1 Deficiency Affects Systemic Body Temperature Regulation

INTRODUCTION

Heat shock factor 1 (HSF1) is a ubiquitous heat-sensitive transcription factor that mediates heat shock protein transcription in response to cellular stress, such as increased temperature, in order to protect the organism against misfolded proteins. In this study, we analysed the effect of HSF1 deficiency on core body temperature regulation.

MATERIALS AND METHODS

Body temperature, locomotor activity, and food consumption of wild-type mice and HSF1-deficient mice were recorded. Prolactin and thyroid-stimulating hormone levels were measured by ELISA. Gene expression in brown adipose tissue was analysed by quantitative real-time PCR. Hypothalamic HSF1 and its co-localisation with tyrosine hydroxylase was analysed using confocal laser scanning microscopy.

RESULTS

HSF1-deficient mice showed an increase in core body temperature (hyperthermia), decreased overall locomotor activity, and decreased levels of prolactin in pituitary and blood plasma reminiscent of cold adaptation. HSF1 could be detected in various hypothalamic regions involved in temperature regulation, suggesting a potential role of HSF1 in hypothalamic thermoregulation. Moreover, HSF1 co-localises with tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, suggesting a potential role of HSF1 in the hypothalamic control of prolactin release. In brown adipose tissue, levels of prolactin receptor and uncoupled protein 1 were increased in HSF1-deficient mice, consistent with an up-regulation of heat production.

CONCLUSION

Our data suggest a role of HSF1 in systemic thermoregulation.

Heat shock proteins in hepatocellular carcinoma: Molecular mechanism and therapeutic potential

Heat shock proteins (HSPs) are highly conserved proteins, which are expressed at low levels under normal conditions, but significantly induced in response to cellular stresses. As molecular chaperones, HSPs play crucial roles in protein homeostasis, apoptosis, invasion and cellular signaling transduction. The induction of HSPs is an important part of heat shock response, which could help cancer cells to adapt to stress conditions. Because of the constant stress condition in tumor microenvironment, HSPs overexpression is widely reported in many human cancers. In light of the significance of HSPs for cancer cells to survive and obtain invasive phenotype under stress condition, HSPs are often associated with poor prognosis and treatment resistance in many types of human cancers. It has been described that upregulation of HSPs may serve as diagnostic and prognostic markers in hepatocellular carcinoma (HCC). Targeting HSPs with specific inhibitor alone or in combination with chemotherapy regimens holds promise for the improvement of outcomes for HCC patients. In this review, we summarize the expression profiles, functions and molecular mechanisms of HSPs (HSP27, HSP70 and HSP90) as well as a HSP-like protein (clusterin) in HCC. In addition, we address progression and challenges in targeting these HSPs as novel therapeutic strategies in HCC.

Global SUMOylation on active chromatin is an acute heat stress response restricting transcription

BACKGROUND

Cells have developed many ways to cope with external stress. One distinctive feature in acute proteotoxic stresses, such as heat shock (HS), is rapid post-translational modification of proteins by SUMOs (small ubiquitin-like modifier proteins; SUMOylation). While many of the SUMO targets are chromatin proteins, there is scarce information on chromatin binding of SUMOylated proteins in HS and the role of chromatin SUMOylation in the regulation of transcription.

RESULTS

We mapped HS-induced genome-wide changes in chromatin occupancy of SUMO-2/3-modified proteins in K562 and VCaP cells using ChIP-seq. Chromatin SUMOylation was further correlated with HS-induced global changes in transcription using GRO-seq and RNA polymerase II (Pol2) ChIP-seq along with ENCODE data for K562 cells. HS induced a rapid and massive rearrangement of chromatin SUMOylation pattern: SUMOylation was gained at active promoters and enhancers associated with multiple transcription factors, including heat shock factor 1. Concomitant loss of SUMOylation occurred at inactive intergenic chromatin regions that were associated with CTCF-cohesin complex and SETDB1 methyltransferase complex. In addition, HS triggered a dynamic chromatin binding of SUMO ligase PIAS1, especially onto promoters. The HS-induced SUMOylation on chromatin was most notable at promoters of transcribed genes where it positively correlated with active transcription and Pol2 promoter-proximal pausing. Furthermore, silencing of SUMOylation machinery either by depletion of UBC9 or PIAS1 enhanced expression of HS-induced genes.

CONCLUSIONS

HS-triggered SUMOylation targets promoters and enhancers of actively transcribed genes where it restricts the transcriptional activity of the HS-induced genes. PIAS1-mediated promoter SUMOylation is likely to regulate Pol2-associated factors in HS.

Regulation of protein turnover by heat shock proteins

Protein turnover reflects the balance between synthesis and degradation of proteins, and it is a crucial process for the maintenance of the cellular protein pool. The folding of proteins, refolding of misfolded proteins, and also degradation of misfolded and damaged proteins are involved in the protein quality control (PQC) system. Correct protein folding and degradation are controlled by many different factors, one of the most important of which is the heat shock protein family. Heat shock proteins (HSPs) are in the class of molecular chaperones, which may prevent the inappropriate interaction of proteins and induce correct folding. On the other hand, these proteins play significant roles in the degradation pathways, including endoplasmic reticulum-associated degradation (ERAD), the ubiquitin-proteasome system, and autophagy. This review focuses on the emerging role of HSPs in the regulation of protein turnover; the effects of HSPs on the degradation machineries ERAD, autophagy, and proteasome; as well as the role of posttranslational modifications in the PQC system.

Modulation of the maladaptive stress response to manage diseases of protein folding

Diseases of protein folding arise because of the inability of an altered peptide sequence to properly engage protein homeostasis components that direct protein folding and function. To identify global principles of misfolding disease pathology we examined the impact of the local folding environment in alpha-1-antitrypsin deficiency (AATD), Niemann-Pick type C1 disease (NPC1), Alzheimer's disease (AD), and cystic fibrosis (CF). Using distinct models, including patient-derived cell lines and primary epithelium, mouse brain tissue, and Caenorhabditis elegans, we found that chronic expression of misfolded proteins not only triggers the sustained activation of the heat shock response (HSR) pathway, but that this sustained activation is maladaptive. In diseased cells, maladaptation alters protein structure-function relationships, impacts protein folding in the cytosol, and further exacerbates the disease state. We show that down-regulation of this maladaptive stress response (MSR), through silencing of HSF1, the master regulator of the HSR, restores cellular protein folding and improves the disease phenotype. We propose that restoration of a more physiological proteostatic environment will strongly impact the management and progression of loss-of-function and gain-of-toxic-function phenotypes common in human disease.

Stress, inflammation, and defense of homeostasis

Inflammation is traditionally considered a defense response induced by infection or injury. However, inflammation can also be induced by tissue stress and malfunction in the absence of infection or overt tissue damage. Here we discuss the relationship between homeostasis, stress responses, and inflammation. Stress responses have cell-autonomous and cell-extrinsic components, the latter contributing to tissue level adaptation to stress conditions. Inflammation can be thought of as the extreme end of a spectrum that ranges from homeostasis to stress response to bona fide inflammatory response. Inflammation can be triggered by two types of stimuli: extreme deviations of homeostasis or challenges that cause a disruption of homeostasis. This perspective may help to explain qualitative differences and functional outcomes of diverse inflammatory responses.

Molecular chaperones and proteostasis regulation during redox imbalance

Free radicals originate from both exogenous environmental sources and as by-products of the respiratory chain and cellular oxygen metabolism. Sustained accumulation of free radicals, beyond a physiological level, induces oxidative stress that is harmful for the cellular homeodynamics as it promotes the oxidative damage and stochastic modification of all cellular biomolecules including proteins. In relation to proteome stability and maintenance, the increased concentration of oxidants disrupts the functionality of cellular protein machines resulting eventually in proteotoxic stress and the deregulation of the proteostasis (homeostasis of the proteome) network (PN). PN curates the proteome in the various cellular compartments and the extracellular milieu by modulating protein synthesis and protein machines assembly, protein recycling and stress responses, as well as refolding or degradation of damaged proteins. Molecular chaperones are key players of the PN since they facilitate folding of nascent polypeptides, as well as holding, folding, and/or degradation of unfolded, misfolded, or non-native proteins. Therefore, the expression and the activity of the molecular chaperones are tightly regulated at both the transcriptional and post-translational level at organismal states of increased oxidative and, consequently, proteotoxic stress, including ageing and various age-related diseases (e.g. degenerative diseases and cancer). In the current review we present a synopsis of the various classes of intra- and extracellular chaperones, the effects of oxidants on cellular homeodynamics and diseases and the redox regulation of chaperones.

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Free radicals originate from various sources and at physiological concentrations are essential for the modulation of cell signalling pathways.

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Abnormally high levels of free radicals induce oxidative stress and damage all cellular biomolecules, including proteins.

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Molecular chaperones facilitate folding of nascent polypeptides, as well as holding, folding, and/or degradation of damaged proteins.

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The expression and the activity of chaperones during oxidative stress are regulated at both the transcriptional and post-translational level.

Transcription regulation of HYPK by Heat Shock Factor 1

HYPK (Huntingtin Yeast Partner K) was originally identified by yeast two-hybrid assay as an interactor of Huntingtin, the protein mutated in Huntington's disease. HYPK was characterized earlier as an intrinsically unstructured protein having chaperone-like activity in vitro and in vivo. HYPK has the ability of reducing rate of aggregate formation and subsequent toxicity caused by mutant Huntingtin. Further investigation revealed that HYPK is involved in diverse cellular processes and required for normal functioning of cells. In this study we observed that hyperthermia increases HYPK expression in human and mouse cells in culture. Expression of exogenous Heat Shock Factor 1 (HSF1), upon heat treatment could induce HYPK expression, whereas HSF1 knockdown reduced endogenous as well as heat-induced HYPK expression. Putative HSF1-binding site present in the promoter of human HYPK gene was identified and validated by reporter assay. Chromatin immunoprecipitation revealed in vivo interaction of HSF1 and RNA polymerase II with HYPK promoter sequence. Additionally, acetylation of histone H4, a known epigenetic marker of inducible HSF1 binding, was observed in response to heat shock in HYPK gene promoter. Overexpression of HYPK inhibited cells from lethal heat-induced death whereas knockdown of HYPK made the cells susceptible to lethal heat shock-induced death. Apart from elevated temperature, HYPK was also upregulated by hypoxia and proteasome inhibition, two other forms of cellular stress. We concluded that chaperone-like protein HYPK is induced by cellular stress and under transcriptional regulation of HSF1.

Pendrin, a novel transcriptional target of the uroguanylin system

Guanylin (GN) and uroguanylin (UGN) are low-molecular-weight peptide hormones produced mainly in the intestinal mucosa in response to oral salt load. GN and UGN (guanylin peptides) induce secretion of electrolytes and water in both intestine and kidney. Thought to act as "intestinal natriuretic factors", GN and UGN modulate renal salt secretion by both endocrine mechanisms (linking the digestive system and kidney) and paracrine/autocrine (intrarenal) mechanisms. The cellular function of GN and UGN in intestine and proximal tubule is mediated by guanylyl cyclase C (GC-C)-, cGMP-, and G protein-dependent pathways, whereas, in principal cells of the cortical collecting duct (CCD), these peptide hormones act via GC-C-independent signaling through phospholipase A2 (PLA2). The Cl(-)/HCO(-)3 exchanger pendrin (SLC26A4), encoded by the PDS gene, is expressed in non-α intercalated cells of the CCD. Pendrin is essential for CCD bicarbonate secretion and is also involved in NaCl balance and blood pressure regulation. Our recent studies have provided evidence that pendrin-mediated anion exchange in the CCD is regulated at the transcriptional level by UGN. UGN exerts an inhibitory effect on the pendrin gene promoter likely via heat shock factor 1 (HSF1) action at a defined heat shock element (HSE) site. Recent studies have unraveled novel roles for guanylin peptides in several organ systems including involvement in appetite regulation, olfactory function, cell proliferation and differentiation, inflammation, and reproductive function. Both the guanylin system and pendrin have also been implicated in airway function. Future molecular research into the receptors and signal transduction pathways involved in the action of guanylin peptides and the pendrin anion exchanger in the kidney and other organs, and into the links between them, may facilitate discovery of new therapies for hypertension, heart failure, hepatic failure and other fluid retention syndromes, as well as for diverse diseases such as obesity, asthma, and cancer.

Eye-specific gene expression following embryonic ethanol exposure in zebrafish: roles for heat shock factor 1

The mechanisms through which ethanol exposure results in developmental defects remain unclear. We used the zebrafish model to elucidate eye-specific mechanisms that underlie ethanol-mediated microphthalmia (reduced eye size), through time-series microarray analysis of gene expression within eyes of embryos exposed to 1.5% ethanol. 62 genes were differentially expressed (DE) in ethanol-treated as compared to control eyes sampled during retinal neurogenesis (24-48 h post-fertilization). The EDGE (extraction of differential gene expression) algorithm identified >3000 genes DE over developmental time in ethanol-exposed eyes as compared to controls. The DE lists included several genes indicating a mis-regulated cellular stress response due to ethanol exposure. Combined treatment with sub-threshold levels of ethanol and a morpholino targeting heat shock factor 1 mRNA resulted in microphthalmia, suggesting convergent molecular pathways. Thermal preconditioning partially prevented ethanol-mediated microphthalmia while maintaining Hsf-1 expression. These data suggest roles for reduced Hsf-1 in mediating microphthalmic effects of embryonic ethanol exposure.