Heat-stress-responsive HvHSFA2e gene regulates the heat and drought tolerance in barley through modulation of phytohormone and secondary metabolic pathways.

KEY MESSAGE: The heat stress transcription factor HSFA2e regulates both temperature and drought response via hormonal and secondary metabolism alterations. High temperature and drought are the primary yield-limiting environmental constraints for staple food crops. Heat shock transcription factors (HSF) terminally regulate the plant abiotic stress responses to maintain growth and development under extreme environmental conditions. HSF genes of subclass A2 predominantly express under heat stress (HS) and activate the transcriptional cascade of defense-related genes. In this study, a highly heat-inducible HSF, HvHSFA2e was constitutively expressed in barley (Hordeum vulgare L.) to investigate its role in abiotic stress response and plant development. Transgenic barley plants displayed enhanced heat and drought tolerance in terms of increased chlorophyll content, improved membrane stability, reduced lipid peroxidation, and less accumulation of ROS in comparison to wild-type (WT) plants. Transcriptome analysis revealed that HvHSFA2e positively regulates the expression of abiotic stress-related genes encoding HSFs, HSPs, and enzymatic antioxidants, contributing to improved stress tolerance in transgenic plants. The major genes of ABA biosynthesis pathway, flavonoid, and terpene metabolism were also upregulated in transgenics. Our findings show that HvHSFA2e-mediated upregulation of heat-responsive genes, modulation in ABA and flavonoid biosynthesis pathways enhance drought and heat stress tolerance.

Genome-wide identification, classification and expression analysis of the heat shock transcription factor family in Garlic (Allium sativum L.).

BACKGROUND: The heat shock transcription factor (HSF) plays a crucial role in the regulatory network by coordinating responses to heat stress as well as other stress signaling pathways. Despite extensive studies on HSF functions in various plant species, our understanding of this gene family in garlic, an important crop with nutritional and medicinal value, remains limited. In this study, we conducted a comprehensive investigation of the entire garlic genome to elucidate the characteristics of the AsHSF gene family. RESULTS: In this study, we identified a total of 17 AsHSF transcription factors. Phylogenetic analysis classified these transcription factors into three subfamilies: Class A (9 members), Class B (6 members), and Class C (2 members). Each subfamily was characterized by shared gene structures and conserved motifs. The evolutionary features of the AsHSF genes were investigated through a comprehensive analysis of chromosome location, conserved protein motifs, and gene duplication events. These findings suggested that the evolution of AsHSF genes is likely driven by both tandem and segmental duplication events. Moreover, the nucleotide diversity of the AsHSF genes decreased by only 0.0002% from wild garlic to local garlic, indicating a slight genetic bottleneck experienced by this gene family during domestication. Furthermore, the analysis of cis-acting elements in the promoters of AsHSF genes indicated their crucial roles in plant growth, development, and stress responses. qRT-PCR analysis, co-expression analysis, and protein interaction prediction collectively highlighted the significance of Asa6G04911. Subsequent experimental investigations using yeast two-hybridization and yeast induction experiments confirmed its interaction with HSP70/90, reinforcing its significance in heat stress. CONCLUSIONS: This study is the first to unravel and analyze the AsHSF genes in garlic, thereby opening up new avenues for understanding their functions. The insights gained from this research provide a valuable resource for future investigations, particularly in the functional analysis of AsHSF genes.

Metformin induction of heat shock factor 1 activation and the mitochondrial unfolded protein response alleviate cardiac remodeling in spontaneously hypertensive rats.

Heart failure and cardiac remodeling are both characterized by mitochondrial dysfunction. Healthy mitochondria are required for adequate contractile activity and appropriate regulation of cell survival. In the mammalian heart, enhancement of the mitochondrial unfolded protein response (UPRmt) is cardioprotective under pressure overload conditions. We explored the UPRmt and the underlying regulatory mechanism in terms of hypertension-induced cardiac remodeling and the cardioprotective effect of metformin. Male spontaneously hypertensive rats and angiotensin II-treated neonatal rat cardiomyocytes were used to induce cardiac hypertrophy. The results showed that hypertension induced the formation of aberrant mitochondria, characterized by a reduced mtDNA/nDNA ratio and swelling, as well as lower levels of mitochondrial complexes I to V and inhibition of the expression of one protein subunit of each of complexes I to IV. Such changes eventually enlarged cardiomyocytes and increased cardiac fibrosis. Metformin treatment increased the mtDNA/nDNA ratio and regulated the UPRmt, as indicated by increased expression of activating transcription factor 5, Lon protease 1, and heat shock protein 60, and decreased expression of C/EBP homologous protein. Thus, metformin improved mitochondrial ultrastructure and function in spontaneously hypertensive rats. In vitro analyses revealed that metformin reduced the high levels of angiotensin II-induced mitochondrial reactive oxygen species in such animals and stimulated nuclear translocation of heat shock factor 1 (HSF1). Moreover, HSF1 small-interfering RNA reduced the metformin-mediated improvements in mitochondrial morphology and the UPRmt by suppressing hypertrophic signals and cardiomyocyte apoptosis. These results suggest that HSF1/UPRmt signaling contributes to the beneficial effects of metformin. Metformin-mediated targeting of mitochondrial protein homeostasis and modulation of HSF1 levels have potential therapeutic implications in terms of cardiac remodeling.

The temperature sensor TWA1 is required for thermotolerance in Arabidopsis.

Plants exposed to incidences of excessive temperatures activate heat-stress responses to cope with the physiological challenge and stimulate long-term acclimation1,2. The mechanism that senses cellular temperature for inducing thermotolerance is still unclear3. Here we show that TWA1 is a temperature-sensing transcriptional co-regulator that is needed for basal and acquired thermotolerance in Arabidopsis thaliana. At elevated temperatures, TWA1 changes its conformation and allows physical interaction with JASMONATE-ASSOCIATED MYC-LIKE (JAM) transcription factors and TOPLESS (TPL) and TOPLESS-RELATED (TPR) proteins for repressor complex assembly. TWA1 is a predicted intrinsically disordered protein that has a key thermosensory role functioning through an amino-terminal highly variable region. At elevated temperatures, TWA1 accumulates in nuclear subdomains, and physical interactions with JAM2 and TPL appear to be restricted to these nuclear subdomains. The transcriptional upregulation of the heat shock transcription factor A2 (HSFA2) and heat shock proteins depended on TWA1, and TWA1 orthologues provided different temperature thresholds, consistent with the sensor function in early signalling of heat stress. The identification of the plant thermosensors offers a molecular tool for adjusting thermal acclimation responses of crops by breeding and biotechnology, and a sensitive temperature switch for thermogenetics.

Deactivation of the Unfolded Protein Response Aggravated Renal AA Amyloidosis in HSF1 Deficiency Mice.

Systemic amyloid A (AA) amyloidosis, which is considered the second most common form of systemic amyloidosis usually takes place several years prior to the occurrence of chronic inflammation, generally involving the kidney. Activated HSF1, which alleviated unfolded protein response (UPR) or enhanced HSR, is the potential therapeutic target of many diseases. However, the effect of HSF1 on AA amyloidosis remains unclear. This study focused on evaluating effect of HSF1 on AA amyloidosis based on HSF1 knockout mice. As a result, aggravated amyloid deposits and renal dysfunction have been found in HSF1 knockout mice. In progressive AA amyloidosis, HSF1 deficiency enhances serum amyloid A production might to lead to severe AA amyloid deposition in mice, which may be related to deactivated unfolded protein response as well as enhanced inflammation. Thus, HSF1 plays a significant role on UPR related pathway impacting AA amyloid deposition, which can mitigate amyloidogenic proteins from aggregation pathologically and is the possible way for intervening with the pathology of systemic amyloid disorder. In conclusion, HSF1 could not only serve as a new target for AA amyloidosis treatment in the future, but HSF1 knockout mice also can be considered as a valuable novel animal model for renal AA amyloidosis.

Genome-wide identification and role of HSFs in antioxidant response of hot water treated zucchini fruit during cold storage.

Zucchini squashes are cold-sensitive and vulnerable to chilling injury (CI) resulting from reactive oxygen species (ROS) and hot water (HW) immersing effectively reduce CI symptoms during cold storage. However, mechanism involved in reduced ROS due to HW treatment has not been characterized well. In this study, tender green zucchini fruit were treated with HW for 15 min at 45 ± 1 °C and stored for 15 d at 4 ± 1 °C and above 90 % relative humidity. Results showed substantial reduction in CI index, electrolyte leakage, malonaldehyde (MDA) contents and ROS accumulation along with increased activity of ROS-scavenging enzymes due to HW treatment. To gain insight into the molecular mechanism involved in antioxidant defense system, transcriptomic analysis revealed that heat shock factors (HSF) accumulated due to HW treatment regulated the ROS pathway during cold stress. CpHSFA4a was one of the highly expressed transcription factors (TF) due to HW treatment that regulated the transcription of ROS enzymes related genes. CpHSFA4a bind actively with heat shock element (HSE) in promoter regions of CpSOD, CpCAT, CpAPX1, CpAPX2, and CpAPX3, activated and increased the expression of these genes. In conclusion, HW treatment alleviated the CI by maintaining ROS homeostasis through CpHSFA4a mediated ROS pathway in zucchini squashes during cold storage.

Heat shock factor 1 inhibition enhances the effects of modulated electro hyperthermia in a triple negative breast cancer mouse model.

Female breast cancer is the most diagnosed cancer worldwide. Triple negative breast cancer (TNBC) is the most aggressive type and there is no existing endocrine or targeted therapy. Modulated electro-hyperthermia (mEHT) is a non-invasive complementary cancer therapy using an electromagnetic field generated by amplitude modulated 13.56 MHz frequency that induces tumor cell destruction. However, we have demonstrated a strong induction of the heat shock response (HSR) by mEHT, which can result in thermotolerance. We hypothesized that inhibition of the heat shock factor 1 (HSF1) can synergize with mEHT and enhance tumor cell-killing. Thus, we either knocked down the HSF1 gene with a CRISPR/Cas9 lentiviral construct or inhibited HSF1 with a specific small molecule inhibitor: KRIBB11 in vivo. Wild type or HSF1-knockdown 4T1 TNBC cells were inoculated into the mammary gland's fat pad of BALB/c mice. Four mEHT treatments were performed every second day and the tumor growth was followed by ultrasound and caliper. KRIBB11 was administrated intraperitoneally at 50 mg/kg daily for 8 days. HSF1 and Hsp70 expression were assessed. HSF1 knockdown sensitized transduced cancer cells to mEHT and reduced tumor growth. HSF1 mRNA expression was significantly reduced in the KO group when compared to the empty vector group, and consequently mEHT-induced Hsp70 mRNA upregulation diminished in the KO group. Immunohistochemistry (IHC) confirmed the inhibition of Hsp70 upregulation in mEHT HSF1-KO group. Demonstrating the translational potential of HSF1 inhibition, combined therapy of mEHT with KRIBB11 significantly reduced tumor mass compared to either monotherapy. Inhibition of Hsp70 upregulation by mEHT was also supported by qPCR and IHC. In conclusion, we suggest that mEHT-therapy combined with HSF1 inhibition can be a possible new strategy of TNBC treatment with great translational potential.

Atypical heat shock transcription factor HSF5 is critical for male meiotic prophase under non-stress conditions.

Meiotic prophase progression is differently regulated in males and females. In males, pachytene transition during meiotic prophase is accompanied by robust alteration in gene expression. However, how gene expression is regulated differently to ensure meiotic prophase completion in males remains elusive. Herein, we identify HSF5 as a male germ cell-specific heat shock transcription factor (HSF) for meiotic prophase progression. Genetic analyzes and single-cell RNA-sequencing demonstrate that HSF5 is essential for progression beyond the pachytene stage under non-stress conditions rather than heat stress. Chromatin binding analysis in vivo and DNA-binding assays in vitro suggest that HSF5 binds to promoters in a subset of genes associated with chromatin organization. HSF5 recognizes a DNA motif different from typical heat shock elements recognized by other canonical HSFs. This study suggests that HSF5 is an atypical HSF that is required for the gene expression program for pachytene transition during meiotic prophase in males.

Hsf1 and Hsf2 in normal, healthy human tissues: Immunohistochemistry provokes new questions.

The heat shock transcription factors heat shock transcription factor 1 and Hsf2 have been studied for many years, mainly in the context of stress response and in malignant cells. Their physiological function in nonmalignant human cells under nonstress conditions is still largely unknown. To approach this important issue, Joutsen et al. present immunohistochemical staining data on Hsf1 and Hsf2 in 80 nonpathological human tissue samples. The wealth of these data elicits many interesting questions that will spur many future research projects.

Intermolecular Interactions between Cysteine and Aromatic Amino Acids with a Phenyl Moiety in the DNA-Binding Domain of Heat Shock Factor 1 Regulate Thermal Stress-Induced Trimerization.

In this study, we investigated the trimerization mechanism and structure of heat shock factor 1 (HSF1) using western blotting, tryptophan (Trp) fluorescence spectroscopy, and molecular modeling. First, we examined the DNA-binding domains of human (Homo sapiens), goldfish (Carassius auratus), and walleye pollock (Gadus chalcogrammus) HSF1s by mutating key residues (36 and 103) that are thought to directly affect trimer formation. Human, goldfish, and walleye pollock HSF1s contain cysteine at residue 36 but cysteine (C), tyrosine (Y), and phenylalanine (F), respectively, at residue 103. The optimal trimerization temperatures for the wild-type HSF1s of each species were found to be 42, 37, and 20 °C, respectively. Interestingly, a mutation experiment revealed that trimerization occurred at 42 °C when residue 103 was cysteine, at 37 °C when it was tyrosine, and at 20 °C when it was phenylalanine, regardless of the species. In addition, it was confirmed that when residue 103 of the three species was mutated to alanine, trimerization did not occur. This suggests that in addition to trimerization via disulfide bond formation between the cysteine residues in human HSF1, trimerization can also occur via the formation of a different type of bond between cysteine and aromatic ring residues such as tyrosine and phenylalanine. We also confirmed that at least one cysteine is required for the trimerization of HSF1s, regardless of its position (residue 36 or 103). Additionally, it was shown that the trimer formation temperature is related to growth and survival in fish.

Coronary Artery Disease Risk Variant Dampens the Expression of CALCRL by Reducing HSF Binding to Shear Stress Responsive Enhancer in Endothelial Cells In Vitro.

BACKGROUND: CALCRL (calcitonin receptor-like) protein is an important mediator of the endothelial fluid shear stress response, which is associated with the genetic risk of coronary artery disease. In this study, we functionally characterized the noncoding regulatory elements carrying coronary artery disease that risks single-nucleotide polymorphisms and studied their role in the regulation of CALCRL expression in endothelial cells. METHODS: To functionally characterize the coronary artery disease single-nucleotide polymorphisms harbored around the gene CALCRL, we applied an integrative approach encompassing statistical, transcriptional (RNA-seq), and epigenetic (ATAC-seq [transposase-accessible chromatin with sequencing], chromatin immunoprecipitation assay-quantitative polymerase chain reaction, and electromobility shift assay) analyses, alongside luciferase reporter assays, and targeted gene and enhancer perturbations (siRNA and clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9) in human aortic endothelial cells. RESULTS: We demonstrate that the regulatory element harboring rs880890 exhibits high enhancer activity and shows significant allelic bias. The A allele was favored over the G allele, particularly under shear stress conditions, mediated through alterations in the HSF1 (heat shock factor 1) motif and binding. CRISPR deletion of rs880890 enhancer resulted in downregulation of CALCRL expression, whereas HSF1 knockdown resulted in a significant decrease in rs880890-enhancer activity and CALCRL expression. A significant decrease in HSF1 binding to the enhancer region in endothelial cells was observed under disturbed flow compared with unidirectional flow. CALCRL knockdown and variant perturbation experiments indicated the role of CALCRL in mediating eNOS (endothelial nitric oxide synthase), APLN (apelin), angiopoietin, prostaglandins, and EDN1 (endothelin-1) signaling pathways leading to a decrease in cell proliferation, tube formation, and NO production. CONCLUSIONS: Overall, our results demonstrate the existence of an endothelial-specific HSF (heat shock factor)-regulated transcriptional enhancer that mediates CALCRL expression. A better understanding of CALCRL gene regulation and the role of single-nucleotide polymorphisms in the modulation of CALCRL expression could provide important steps toward understanding the genetic regulation of shear stress signaling responses.

CsHSFA1d Promotes Drought Stress Tolerance by Increasing the Content of Raffinose Family Oligosaccharides and Scavenging Accumulated Reactive Oxygen Species in Cucumber.

Drought is the most severe form of stress experienced by plants worldwide. Cucumber is a vegetable crop that requires a large amount of water throughout the growth period. In our previous study, we identified that overexpression of CsHSFA1d could improve cold tolerance and the content of endogenous jasmonic acid in cucumber seedlings. To explore the functional diversities of CsHSFA1d, we treat the transgenic plants under drought conditions. In this study, we found that the heat shock transcription factor HSFA1d (CsHSFA1d) could improve drought stress tolerance in cucumber. CsHSFA1d overexpression increased the expression levels of galactinol synthase (CsGolS3) and raffinose synthase (CsRS) genes, encoding the key enzymes for raffinose family oligosaccharide (RFO) biosynthesis. Furthermore, the lines overexpressing CsHSFA1d showed higher enzymatic activity of GolS and raffinose synthase to increase the content of RFO. Moreover, the CsHSFA1d-overexpression lines showed lower reactive oxygen species (ROS) accumulation and higher ROS-scavenging enzyme activity after drought treatment. The expressions of antioxidant genes CsPOD2, CsAPX1 and CsSOD1 were also upregulated in CsHSFA1d-overexpression lines. The expression levels of stress-responsive genes such as CsRD29A, CsLEA3 and CsP5CS1 were increased in CsHSFA1d-overexpression lines after drought treatment. We conclude that CsHSFA1d directly targets and regulates the expression of CsGolS3 and CsRS to promote the enzymatic activity and accumulation of RFO to increase the tolerance to drought stress. CsHSFA1d also improves ROS-scavenging enzyme activity and gene expression indirectly to reduce drought-induced ROS overaccumulation. This study therefore offers a new gene target to improve drought stress tolerance in cucumber and revealed the underlying mechanism by which CsHSFA1d functions in the drought stress by increasing the content of RFOs and scavenging the excessive accumulation of ROS.

Comprehensive analysis of human tissues reveals unique expression and localization patterns of HSF1 and HSF2.

Heat shock factors (HSFs) are the main transcriptional regulators of the evolutionarily conserved heat shock response. Beyond cell stress, several studies have demonstrated that HSFs also contribute to a vast variety of human pathologies, ranging from metabolic diseases to cancer and neurodegeneration. Despite their evident role in mitigating cellular perturbations, the functions of HSF1 and HSF2 in physiological proteostasis have remained inconclusive. Here, we analyzed a comprehensive selection of paraffin-embedded human tissue samples with immunohistochemistry. We demonstrate that both HSF1 and HSF2 display distinct expression and subcellular localization patterns in benign tissues. HSF1 localizes to the nucleus in all epithelial cell types, whereas nuclear expression of HSF2 was limited to only a few cell types, especially the spermatogonia and the urothelial umbrella cells. We observed a consistent and robust cytoplasmic expression of HSF2 across all studied smooth muscle and endothelial cells, including the smooth muscle cells surrounding the vasculature and the high endothelial venules in lymph nodes. Outstandingly, HSF2 localized specifically at cell-cell adhesion sites in a broad selection of tissue types, such as the cardiac muscle, liver, and epididymis. To the best of our knowledge, this is the first study to systematically describe the expression and localization patterns of HSF1 and HSF2 in benign human tissues. Thus, our work expands the biological landscape of these factors and creates the foundation for the identification of specific roles of HSF1 and HSF2 in normal physiological processes.

pH Dependence of HSF1 trimerization is shaped by intramolecular interactions.

Heat shock factor 1 (HSF1) primarily regulates various cellular stress responses. Previous studies have shown that low pH within the physiological range directly activates HSF1 function in vitro. However, the detailed molecular mechanisms remain unclear. This study proposes a molecular mechanism based on the trimerization behavior of HSF1 at different pH values. Extensive mutagenesis of human and goldfish HSF1 revealed that the optimal pH for trimerization depended on the identity of residue 103. In particular, when residue 103 was occupied by tyrosine, a significant increase in the optimal pH was observed, regardless of the rest of the sequence. This behavior can be explained by the protonation state of the neighboring histidine residues, His101 and His110. Residue 103 plays a key role in trimerization by forming disulfide or non-covalent bonds with Cys36. If tyrosine resides at residue 103 in an acidic environment, its electrostatic interactions with positively charged histidine residues prevent effective trimerization. His101 and His110 are neutralized at a higher pH, which releases Tyr103 to interact with Cys36 and drives the effective trimerization of HSF1. This study showed that the protonation state of a histidine residue can regulate the intramolecular interactions, which consequently leads to a drastic change in the oligomerization behavior of the entire protein.

Distinct induction pathways of heat shock protein 27 in human keratinocytes: Heat stimulation or capsaicin through phosphorylation of heat shock factor 1 at serine 326 and/or suppression of ΔNp63.

Epidermal keratinocytes, forming the outermost layer of the human body, serve as a crucial barrier against diverse external stressors such as ultraviolet radiation. Proper keratinocyte differentiation and effective responses to external stimuli are pivotal for maintaining barrier integrity. Heat is one such stimulus that triggers the synthesis of heat shock proteins (HSPs) when cells are exposed to temperatures above 42 °C. Additionally, activation of the transient receptor potential cation channel subfamily V member 1 (TRPV1) occurs at 42 °C. Here, we explore the interplay between TRPV1 signaling and HSP induction in human keratinocytes. Both heat and capsaicin, a TRPV1 agonist, induce expression of HSP27, HSP70, and HSP90 in keratinocytes. Interestingly, pharmacological inhibition of TRPV1 attenuates heat-induced HSP27 expression, but not that of HSP70 or HSP90. Furthermore, both heat and capsaicin stimulation result in distinct phosphorylation patterns of heat shock factor 1 (HSF1), with phosphorylation at serine 326 being a common feature. Notably, genetic manipulation to mimic dephosphorylation of HSF1 at serine 326 reduces HSP27 levels. Additionally, ΔNp63, a key regulator of epidermal differentiation, negatively modulates HSP27 expression independently of HSF1 phosphorylation status. While heat stimulation has no effect on ΔNp63 expression, capsaicin reduces its levels. The precise role of TRPV1 signaling in keratinocytes warrants further investigation for a comprehensive understanding of its impact on barrier function.

A wheat heat shock transcription factor gene, TaHsf-7A, regulates seed dormancy and germination.

Heat shock transcription factors (Hsfs) play multifaceted roles in plant growth, development, and responses to environmental factors. However, their involvement in seed dormancy and germination processes has remained elusive. In this study, we identified a wheat class B Hsf gene, TaHsf-7A, with higher expression in strong-dormancy varieties compared to weak-dormancy varieties during seed imbibition. Specifically, TaHsf-7A expression increased during seed dormancy establishment and subsequently declined during dormancy release. Through the identification of a 1-bp insertion (ins)/deletion (del) variation in the coding region of TaHsf-7A among wheat varieties with different dormancy levels, we developed a CAPS marker, Hsf-7A-1319, resulting in two allelic variations: Hsf-7A-1319-ins and Hsf-7A-1319-del. Notably, the allele Hsf-7A-1319-ins correlated with a reduced seed germination rate and elevated dormancy levels, while Hsf-7A-1319-del exhibited the opposite trend across 175 wheat varieties. The association of TaHsf-7A allelic status with seed dormancy and germination levels was confirmed in various genetically modified species, including Arabidopsis, rice, and wheat. Results from the dual luciferase assay demonstrated notable variations in transcriptional activity among transformants harboring distinct TaHsf-7A alleles. Furthermore, the levels of abscisic acid (ABA) and gibberellin (GA), along with the expression levels of ABA and GA biosynthesis genes, showed significant differences between transgenic rice lines carrying different alleles of TaHsf-7A. These findings represent a significant step towards a comprehensive understanding of TaHsf-7A's involvement in the dormancy and germination processes of wheat seeds.

Early signaling enhance heat tolerance in Arabidopsis through modulating jasmonic acid synthesis mediated by HSFA2.

Given the detrimental impact of global warming on crop production, it is particularly important to understand how plants respond and adapt to higher temperatures. Using the non-invasive micro-test technique and laser confocal microscopy, we found that the cascade process of early signals (K+, H2O2, H+, and Ca2+) ultimately resulted in an increase in the cytoplasmic Ca2+ concentration when Arabidopsis was exposed to heat stress. Quantitative real-time PCR demonstrated that heat stress significantly up-regulated the expression of CAM1, CAM3 and HSFA2; however, after CAM1 and CAM3 mutation, the upregulation of HSFA2 was reduced. In addition, heat stress affected the expression of LOX3 and OPR3, which was not observed when HSFA2 was mutated. Luciferase reporter gene expression assay and electrophoretic mobility shift assay showed that HSFA2 regulated the expression of both genes. Determination of jasmonic acid (JA) content showed that JA synthesis was promoted by heat stress, but was damaged when HSFA2 and OPR3 were mutated. Finally, physiological experiments showed that JA reduced the relative electrical conductivity of leaves, enhanced chlorophyll content and relative water content, and improved the survival rate of Arabidopsis under heat stress. Together, our results reveal a new pathway for Arabidopsis to sense and transmit heat signals; HSFA2 is involved in the JA synthesis, which can act as a defensive compound improving Arabidopsis heat tolerance.

Cloning and characterization of heat shock transcription factor 1 and its functional role for Hsp70 production in the sea slug Onchidium reevesii.

To investigate the regulatory role of heat shock transcription factor 1 of sea slug Onchidium reevesii (OrHSF1) on Hsp70 expression in the sea slug under stress , the OrHSF1 gene was cloned and bioinformatics analysis was performed, then the gene and protein expressions by RNA interference (RNAi) mediated knockdown of OrHSF1 expression were measured to clarify the regulatory relationship between OrHSF1 and Hsp70 under low-frequency noise (LFN) stress. Our study was the first to clone a 1572 bp sequence of the OrHSF1 gene, with the sequence coding for amino acids (CDS) being 729 bp, encoding 243 amino acids. O. reevesii shared a close evolutionary relationship with mollusks such as the Aplysia californica. OrHSF1 gene is widely expressed in different tissues of sea slugs, with the highest expression in the intestine and the lowest in the reproductive glands. Furthermore, we used RNA interference (RNAi) as a tool to silence the OrHSF1 gene in the central nervous system (CNS) and the results indicated that gene silencing was occurring systematically in the CNS and the suppression of OrHSF1 expression by RNAi-mediated gene silencing altered the expression of Hsp70; besides, the expression trends of OrHSF1 gene and Hsp70 were consistent in the 3 and 5-day RNAi experiment. Moreover, in sea slugs injected with siHSF1 and exposed to LFN, the mRNA expression and protein expression of Hsp70 in the CNS were significantly decreased compared to the low-frequency noise group (P < 0.05). This study demonstrated that OrHSF1 regulates Hsp70 expression in marine mollusks under low-frequency noise, and HSF1-Hsp70 axis plays a key role in stress response.

Deletion of the transcription factors Hsf1, Msn2 and Msn4 in yeast uncovers transcriptional reprogramming in response to proteotoxic stress.

The response to proteotoxic stresses such as heat shock allows organisms to maintain protein homeostasis under changing environmental conditions. We asked what happens if an organism can no longer react to cytosolic proteotoxic stress. To test this, we deleted or depleted, either individually or in combination, the stress-responsive transcription factors Msn2, Msn4, and Hsf1 in Saccharomyces cerevisiae. Our study reveals a combination of survival strategies, which together protect essential proteins. Msn2 and 4 broadly reprogram transcription, triggering the response to oxidative stress, as well as biosynthesis of the protective sugar trehalose and glycolytic enzymes, while Hsf1 mainly induces the synthesis of molecular chaperones and reverses the transcriptional response upon prolonged mild heat stress (adaptation).

Cellular HSF1 expression is induced during HIV-1 infection by activation of its promoter mediated through the cooperative interaction of HSF1 and viral Nef protein.

The Human Immunodeficiency Virus-1 (HIV-1) tends to activate cellular promoters driving expression of pro-viral genes by complex host-virus interactions for productive infection. We have previously demonstrated that expression of such a positive host factor HSF1 (heat shock factor 1) is elevated during HIV-1 infection; however, the mechanism remains to be elucidated. In the present study, we therefore examined whether HSF1 promoter is induced during HIV-1 infection leading to up-regulation of hsf1 gene expression. We mapped the putative transcription start site (TSS) predicted by Eukaryotic promoter database and deletion constructs of the predicted promoter region were tested through luciferase assay to identify the active promoter. The 347 bp upstream to 153 bp downstream region around the putative TSS displayed the highest activity and both Sp1 (stimulating protein 1) and HSF1 itself were identified to be important for its basal activation. Activity of HSF1 promoter was further stimulated during HIV-1 infection in CD4+ T cells, where interestingly the HSF1-site itself seems to play a major role. In addition, HIV-1 protein Nef (negative factor) was also observed to be responsible for the virus-mediated induction of hsf1 gene expression. Chromatin-immunoprecipitation assays further demonstrate that Nef and HSF1 are co-recruited to the HSF1-binding site and cooperatively act on this promoter. The interplay between host HSF1 and viral Nef on HSF1 promoter eventually leads to increase in HSF1 expression during HIV-1 infection. Understanding the mechanism of HSF1 up-regulation during HIV-1 infection might contribute to future antiviral strategies as HSF1 is a positive regulator of virus replication.