Heat Shock Factor-1 Signaling Research Articles

Abstract 3063: Canonical And Noncanonical Heat Shock Factor 1 Signaling In Smooth Muscle Cells Promote Atherosclerotic Plaque Burden

Smooth muscle cells (SMCs) in atherosclerotic plaques undergo complex phenotypic modulation, characterized by migration from the aortic medial layer to the intima, proliferation, de-differentiation, and variable increases in molecular markers characteristic of macrophages, fibroblasts, osteogenic cells and mesenchymal stem cells. This transition is driven in part by cholesterol entering the endoplasmic reticulum (ER) and activating ER stress. The importance of ER stress-driven PERK signaling in atherosclerosis is underscored by the observation that SMC-specific deletion of Perk reduces lesion size by ~70% in hypercholesterolemic (HC) mice. HC mice harboring either an SM α-actin ( ACTA2 ) missense variant or SMC-specific deletion of the centrosomal scaffolding protein pericentrin ( PCNT ) have increased augmented plaque burden compared to their HC wildtype (WT) counterparts, despite having comparable serum lipid levels. We went on to demonstrate that both these genetic alterations increase SMC cytosolic stress and activation of canonical heat shock factor 1 (HSF1) signaling, which in turn increases HMG-CoA reductase (HMGCR) activity and cholesterol biosynthesis, ER stress, PERK signaling, SMC phenotypic modulation and finally, augments the plaque burden. We also noted another distinct pro-atherogenic form of HSF1 activation in SMCs: SMCs in culture exposed to high levels of exogenous cholesterol activate PERK signaling, but also consistently activate HSF1, and blocking PERK signaling prevents HSF1 activation, suggesting “noncanonical” HSF1 activation. While global loss of Hsf1 in HC mice reduces plaque burden, we generated tamoxifen-inducible SMC-specific Hsf1 -deficient mice ( Hsf1 SMC-/- ) to assess the role of HSF1 signaling in SMCs of HC mice. Hyperlipidemia was induced in these mice by a single injection of AAV- PCSK9 DY followed by a high fat diet for 12 weeks. En face aortic Oil Red O staining demonstrated that Hsf1 SMC-/- mice had 67% reduction in plaque size in the whole aorta (p=0.0007), compared to HC WT mice, similar to the results seen with SMC-specific Perk deficiency. These data suggest distinct roles of canonical and noncanonical HSF1 signaling in SMCs that contribute to atherosclerotic plaque burden.

Specific Activation of Yamanaka Factors via HSF1 Signaling in the Early Stage of Zebrafish Optic Nerve Regeneration.

In contrast to the case in mammals, the fish optic nerve can spontaneously regenerate and visual function can be fully restored 3-4 months after optic nerve injury (ONI). However, the regenerative mechanism behind this has remained unknown. This long process is reminiscent of the normal development of the visual system from immature neural cells to mature neurons. Here, we focused on the expression of three Yamanaka factors (Oct4, Sox2, and Klf4: OSK), which are well-known inducers of induced pluripotent stem (iPS) cells in the zebrafish retina after ONI. mRNA expression of OSK was rapidly induced in the retinal ganglion cells (RGCs) 1-3 h after ONI. Heat shock factor 1 (HSF1) mRNA was most rapidly induced in the RGCs at 0.5 h. The activation of OSK mRNA was completely suppressed by the intraocular injection of HSF1 morpholino prior to ONI. Furthermore, the chromatin immunoprecipitation assay showed the enrichment of OSK genomic DNA bound to HSF1. The present study clearly showed that the rapid activation of Yamanaka factors in the zebrafish retina was regulated by HSF1, and this sequential activation of HSF1 and OSK might provide a key to unlocking the regenerative mechanism of injured RGCs in fish.

Crosstalk between heat shock factor 1 and signal transducer and activator of transcription 3 mediated by interleukin-8 autocrine signaling maintains the cancer stem cell phenotype in liver cancer.

Liver cancer stem cells (LCSCs) cause therapeutic refractoriness and relapse in hepatocellular carcinoma. Heat shock factor 1 (HSF1) plays versatile roles in multiple cancers. However, the role of HSF1 in LCSCs is not well understood. This study investigated the function and signal mechanisms of HSF1 in maintaining LCSC phenotypes. We established two LCSC lines, HepG2-R and HuH-7-R. Constitutive activation of HSF1 was observed in these LCSCs. Specific short hairpin RNAs (shRNAs) and chemical inhibitors were used to identify the relationship between HSF1 expression and LCSCs phenotypes. We revealed a concomitant activation modality involving HSF1 and STAT3 in LCSCs and liver cancer tissues. We also found that liver cancer patients whose HSF1 and STAT3 mRNA expression levels were high presented with unfavorable clinicopathological characteristics. Moreover, the secretion of interleukin-8 (IL-8) was elevated in the LCSC medium and was directly regulated by HSF1 at the transcriptional level. In turn, IL-8 activated HSF1 and STAT3 signaling, and a neutralizing IL-8 antibody inhibited HSF1 and STAT3 activity, reduced cancer stem cell marker expression, and decreased LCSC microsphere formation. Simultaneous intervention with HSF1 and STAT3 led to synergistically suppressed stemness acquisition and growth suppression in the LCSCs in vivo and in vitro. Our study indicates that IL-8 mediates the crosstalk between the HSF1 and Stat3 signaling pathways in LCSCs and that the combined targeting of HSF1 and STAT3 is a promising treatment strategy for patients with advanced liver cancer.

Abstract 15254: Acta2 Missense Variant Increases Atherosclerotic Plaque Burdern by Heat Shock Factor 1-Driven Augmented Phenotypic Modulation of Smooth Muscle Cells

ACTA2 encodes the contractile protein smooth muscle α-actin expressed in smooth muscle cells (SMCs). A heterozygous pathogenic variant in ACTA2 , p.R149C, predisposes to premature coronary artery disease (CAD) in the absence of risk factors. Recent studies have determined that SMCs contribute to atherosclerotic plaque formation after undergoing phenotypic modulation, characterized by de-differentiation and increased expression of macrophage, fibroblast, stem, and osteogenic markers. This SMC modulation is driven in part by exogenous cholesterol entering the endoplasmic reticulum (ER) and activating ER stress, specifically PERK signaling. To determine how a mutation in SM α-actin predisposes to atherosclerosis, Acta2 R149C/+ mice were crossed into Apoe -/- mice and fed a high fat diet for 3 months. Despite no differences in serum lipid levels, the Acta2 R149C/+ Apoe -/- mice have a 3-fold increased plaque burden compared to Apoe -/- mice. SMCs explanted from Acta2 R149C/+ mice have phenotypic modulation at baseline while WT SMCs do not. We determined that misfolding of the R149C SMα-actin activates heat shock factor 1 (HSF1), which increases endogenous cholesterol biosynthesis through increasing HMG-CoA reductase expression. The increase in endogenous cholesterol levels induces ER stress, activates PERK, and augments both modulation of SMCs and atherosclerotic plaque formation. ScRNA sequencing confirms increased HSF1 and PERK signaling and modulation in SMCs in the mutant mice. Importantly, pravastatin treatment dramatically lowers plaque burden to similar low levels of plaque burden in both the Acta2 R149C/+ Apoe -/- and Apoe -/- mice (Fig. 1a) . These studies identify a novel mechanism by which mutant SM α-actin increases endogenous cholesterol biosynthesis and drives atherosclerotic plaque formation, a mechanism that also informs as to why statins are effective in individuals at risk for CAD who do not have elevated plasma cholesterol levels (Fig. 1b) .

Inhibition of Heat Shock Factor 1 Signaling Decreases Hepatoblastoma Growth via Induction of Apoptosis

Although rare compared with adult liver cancers, hepatoblastoma (HB) is the most common pediatric liver malignancy, and its incidence is increasing. Currently, the treatment includes surgical resection with or without chemotherapy, and in severe cases, liver transplantation in children. The effort to develop more targeted, HB-specific therapies has been stymied by the lack of fundamental knowledge about HB biology. Heat shock factor 1 (HSF1), a transcription factor, is a canonical inducer of heat shock proteins, which act as chaperone proteins to prevent or undo protein misfolding. Recent work has shown a role for HSF1 in cancer beyond the canonical heat shock response. The current study found increased HSF1 signaling in HB versus normal liver. It showed that less differentiated, more embryonic tumors had higher levels of HSF1 than more differentiated, more fetal-appearing tumors. Most strikingly, HSF1 expression levels correlated with mortality. This study used a mouse model of HB to test the effect of inhibiting HSF1 early in tumor development on cancer growth. HSF1 inhibition resulted in fewer and smaller tumors, suggesting HSF1 is needed for aggressive tumor growth. Moreover, HSF1 inhibition also increased apoptosis in tumor foci. These data suggest that HSF1 may be a viable pharmacologic target for HB treatment.

Circadian disruption enhances HSF1 signaling and tumorigenesis in Kras-driven lung cancer.

Disrupted circadian rhythmicity is a prominent feature of modern society and has been designated as a probable carcinogen by the World Health Organization. However, the biological mechanisms that connect circadian disruption and cancer risk remain largely undefined. We demonstrate that exposure to chronic circadian disruption [chronic jetlag (CJL)] increases tumor burden in a mouse model of KRAS-driven lung cancer. Molecular characterization of tumors and tumor-bearing lung tissues revealed that CJL enhances the expression of heat shock factor 1 (HSF1) target genes. Consistently, exposure to CJL disrupted the highly rhythmic nuclear trafficking of HSF1 in the lung, resulting in an enhanced accumulation of HSF1 in the nucleus. HSF1 has been shown to promote tumorigenesis in other systems, and we find that pharmacological or genetic inhibition of HSF1 reduces the growth of KRAS-mutant human lung cancer cells. These findings implicate HSF1 as a molecular link between circadian disruption and enhanced tumorigenesis.

HSF1 Signaling Inhibits Apoptosis in Hepatoblastoma

IntroductionHepatoblastoma (HB) is the most common pediatric liver malignancy. While relatively rare, its incidence is increasing. Currently surgical resection with or without chemotherapy is the main treatment for the tumor though in severe cases children require liver transplantation. Development of precision therapy for the tumor has been hampered by gaps in fundamental knowledge about how the tumor develops and grows. Heat shock factor 1 (HSF1) is the master regulator of the heat shock response, which classically mediates cellular stress from heat but it likely has a cancer specific. Recent work has shown that HSF1 controls a suite of genes in cancer related to apoptosis, cell cycle signaling, DNA repair, energy metabolism and extracellular matrix formation. Previously, we conducted a meta‐analysis of six human HB transcriptomic data sets, which found expression levels of HSF1 was higher in tumors versus normal liver. Intriguingly, we found higher levels of HSF1 expression in tumors correlated with mortality. We wanted to investigate how inhibiting HSF1 impacted tumor growth in our lab’s mouse model of hepatoblastoma based on transfection with constitutively active forms of β‐catenin and yes‐associated protein 1 (Yap1). This model induces tumors that genetically and histologically resemble human hepatoblastoma. The objective of this study was to investigate the specific role of HSF1 signaling in the development of hepatoblastoma. Our hypothesis is inhibiting HSF1 in our mouse model of hepatoblastoma leads to increased apoptosis in tumor cells and thus decreased tumor size and number.MethodsWe inhibited HSF1 signaling in mice by co‐transfecting a dominant negative HSF1 (dnHSF1) plasmid along with β‐catenin and Yap1 plasmids. The dnHSF1 forms a truncated form of the protein that cannot initiate transcription of target genes. Mice injected with just β‐catenin and Yap1 plasmids served as controls. Eight weeks after transfection, the mice were harvested and the livers were preserved for analysis. Liver and body weights of each mouse was measured to calculate liver‐to‐body weight ratio, an index of tumor burden. At least three mice per condition was assessed.ResultsWe found transfection with the dnHSF1 lead to decreased liver‐to‐body weight ratio compared to control mice transfected with just the β‐catenin and Yap1 plasmids (p‐value<0.05)(Figure 1). What few tumor foci remained featured larger, more differentiated cells. Indeed, these foci showed positive staining via immunohistochemistry (IHC) for both activated mTORC1 and glutamine synthetase, markers seen early in tumor development. Next, we assessed apoptosis by conducting IHC for cleaved caspase 3 and by performing a TUNEL assay on liver sections from both dnHSF1/β‐catenin/Yap1 mice and from control β‐catenin/Yap1 animals. Staining for both markers was increased nearly three times in dnHSF1 treated animals versus control(p‐value<0.05)(Figure 2).ConclusionsWe conclude inhibiting HSF1 signaling in burgeoning hepatoblastoma cells leads to smaller, more differentiated tumors via increased apoptosis. More work is needed to determine if HSF1 is a viable pharmacologic target for hepatoblastoma.

PLOD1 acts as a tumor promoter in glioma via activation of the HSF1 signaling pathway.

Procollagen-lysine, 2-oxoglutarate 5-dioxygenase 1 (PLOD1) is a collagen-related lysyl hydroxylase and its prognostic value in glioma patients was verified. However, its biological function in glioma has yet to be fully investigated. The PLOD1 mRNA status and clinical significance in gliomas were assessed via the GEPIA database. Overexpression or targeted depletion of PLOD1 was carried out in the human glioma cell line U87 and verified by western blotting. CCK8 and colony formation assays were implemented to examine the impact of PLOD1 on the proliferative and colony-forming phenotypes of U87 cells. Luciferase reporter assays and HSF1-specific pharmacologic inhibitors (KRIBB11) were employed to determine the regulatory relationship between PLOD1 and heat shock factor 1 (HSF1). High expression of PLOD1 was observed in tissue samples of glioblastoma multiforme (GBM) and brain lower-grade glioma (LGG). GEPIA overall survival further demonstrated that both GBM and LGG patients with high PLOD1 displayed worse clinical outcomes compared with those with low PLOD1. Overexpression and targeted depletion of PLOD1 enhanced and suppressed U87 cell proliferation and colony formation, respectively. Luciferase reporter assays showed that PLOD1 significantly enhanced the transcriptional activity of HSF1 in HEK293T cells. PLOD1 deficiency in U87 cells inhibited HSF1-induced survivin accumulation, whereas KRIBB11 also blocked the PLOD1-overexpressing induced survivin expression. An inhibitor of HSF1 signaling events abolishedthe increased clonogenic potential caused by PLOD1 overexpression in U87 cells. High expression of PLOD1 can increase the proliferation and colony formation of U87 cells by activating the HSF1 signaling pathway. This study suggested PLOD1/HSF1 as an effective therapeutic target for gliomas.

Thrombospondin 4/integrin \u03b12/HSF1 axis promotes proliferation and cancer stem-like traits of gallbladder cancer by enhancing reciprocal crosstalk between cancer-associated fibroblasts and tumor cells

BackgroundCancer-associated fibroblasts (CAFs), the primary component of tumor stroma in tumor microenvironments, are well-known contributors to the malignant progression of gallbladder cancer (GBC). Thrombospondins (THBSs or TSPs) comprise a family of five adhesive glycoproteins that are overexpressed in many types of cancers. However, the expression and potential roles of TSPs in the crosstalk between CAFs and GBC cells has remained unclear.MethodsPeritumoral fibroblasts (PTFs) and CAFs were extracted from GBC tissues. Thrombospondin expression in GBC was screened by RT-qPCR. MTT viability assay, colony formation, EdU incorporation assay, flow cytometry analysis, Transwell assay, tumorsphere formation and western blot assays were performed to investigate the effects of CAF-derived TSP-4 on GBC cell proliferation, EMT and cancer stem-like features. Subcutaneous tumor formation models were established by co-implanting CAFs and GBC cells or GBC cells overexpressing heat shock factor 1 (HSF1) to evaluate the roles of TSP-4 and HSF1 in vivo. To characterize the mechanism by which TSP-4 is involved in the crosstalk between CAFs and GBC cells, the levels of a variety of signaling molecules were detected by coimmunoprecipitation, immunofluorescence staining, and ELISA assays.ResultsIn the present study, we showed that TSP-4, as the stromal glycoprotein, is highly expressed in CAFs from GBC and that CAF-derived TSP-4 induces the proliferation, EMT and cancer stem-like features of GBC cells. Mechanistically, CAF-secreted TSP-4 binds to the transmembrane receptor integrin α2 on GBC cells to induce the phosphorylation of HSF1 at S326 and maintain the malignant phenotypes of GBC cells. Moreover, the TSP-4/integrin α2 axis-induced phosphorylation of HSF1 at S326 is mediated by Akt activation (p-Akt at S473) in GBC cells. In addition, activated HSF1 signaling increased the expression and paracrine signaling of TGF-β1 to induce the transdifferentiation of PTFs into CAFs, leading to their recruitment into GBC and increased TSP-4 expression in CAFs, thereby forming a positive feedback loop to drive the malignant progression of GBC.ConclusionsOur data indicate that a complex TSP-4/integrin α2/HSF1/TGF-β cascade mediates reciprocal interactions between GBC cells and CAFs, providing a promising therapeutic target for gallbladder cancer patients.

HSB-1/HSF-1 pathway modulates histone H4 in mitochondria to control mtDNA transcription and longevity.

Heat shock factor-1 (HSF-1) is a master regulator of stress responses across taxa. Overexpression of HSF-1 or genetic ablation of its conserved negative regulator, heat shock factor binding protein 1 (HSB-1), results in robust life-span extension in Caenorhabditis elegans Here, we found that increased HSF-1 activity elevates histone H4 levels in somatic tissues during development, while knockdown of H4 completely suppresses HSF-1-mediated longevity. Moreover, overexpression of H4 is sufficient to extend life span. Ablation of HSB-1 induces an H4-dependent increase in micrococcal nuclease protection of both nuclear chromatin and mitochondrial DNA (mtDNA), which consequently results in reduced transcription of mtDNA-encoded complex IV genes, decreased respiratory capacity, and a mitochondrial unfolded protein response-dependent life-span extension. Collectively, our findings reveal a previously unknown role of HSB-1/HSF-1 signaling in modulation of mitochondrial function via mediating histone H4-dependent regulation of mtDNA gene expression and concomitantly acting as a determinant of organismal longevity.

17β-Estradiol Activates HSF1 via MAPK Signaling in ERα-Positive Breast Cancer Cells.

Heat Shock Factor 1 (HSF1) is a key regulator of gene expression during acute environmental stress that enables the cell survival, which is also involved in different cancer-related processes. A high level of HSF1 in estrogen receptor (ER)-positive breast cancer patients correlated with a worse prognosis. Here we demonstrated that 17β-estradiol (E2), as well as xenoestrogen bisphenol A and ERα agonist propyl pyrazole triol, led to HSF1 phosphorylation on S326 in ERα positive but not in ERα-negative mammary breast cancer cells. Furthermore, we showed that MAPK signaling (via MEK1/2) but not mTOR signaling was involved in E2/ERα-dependent activation of HSF1. E2­activated HSF1 was transcriptionally potent and several genes essential for breast cancer cells growth and/or ERα action, including HSPB8, LHX4, PRKCE, WWC1, and GREB1, were activated by E2 in a HSF1-dependent manner. Our findings suggest a hypothetical positive feedback loop between E2/ERα and HSF1 signaling, which may support the growth of estrogen-dependent tumors.

Skeletal muscle interleukin-6 regulation in hyperthermia

We previously reported that IL-6 production is acutely elevated in skeletal muscles exposed to ≥41°C, but the regulatory pathways are poorly understood. The present study characterizes the heat-induced transcriptional control of IL-6 in C2C12 muscle fibers. Hyperthermia exposure (42°C for 1 h) induced transcription from an IL-6 promoter-luciferase reporter plasmid. Heat shock factor-1 (HSF-1), a principal mediator of the heat shock response, was then tested for its role in IL-6 regulation. Overexpression of a constitutively active HSF-1 construct increased basal (37°C) promoter activity, whereas overexpression of a dominant negative HSF-1 reduced IL-6 promoter activity during basal and hyperthermia conditions. Since hyperthermia also induces stress-activated protein kinase (SAPK) signaling, we tested whether mutation of a transcription site downstream of SAPK, (i.e., activator protein-1, AP-1) influences IL-6 transcription in hyperthermia. The mutation had no effect on baseline reporter activity but completely inhibited heat-induced activity. We then tested whether pharmacologically induced states of protein stress, characteristic of cellular responses to hyperthermia and known to induce SAPKs and HSF-1, would induce IL-6 production in the absence of heat. The proteasome was inhibited with MG-132 in one set of experiments, and the unfolded protein response was stimulated with dithiothreitol, thapsigargin, tunicamycin, or castanospermine in other experiments. All treatments stimulated IL-6 protein secretion in the absence of hyperthermia. These studies demonstrate that IL-6 regulation in hyperthermia is directly controlled by HSF-1 and AP-1 signaling and that the IL-6 response in C2C12 myotubes is sensitive to categories of protein stress that reflect accumulation of damaged or unfolded proteins.

Heat Shock Factor 1 (HSF1) Controls Chemoresistance and Autophagy through Transcriptional Regulation of Autophagy-related Protein 7 (ATG7)

Heat shock factor 1 (HSF1), a master regulator of heat shock responses, plays an important role in tumorigenesis. In this study we demonstrated that HSF1 is required for chemotherapeutic agent-induced cytoprotective autophagy through transcriptional up-regulation of autophagy-related gene ATG7. Interestingly, this is independent of the HSF1 heat shock response function. Treatment of cancer cells with the FDA-approved chemotherapeutic agent carboplatin induced autophagy and growth inhibition, which were significantly increased upon knockdown of HSF1. Mechanistic studies revealed that HSF1 regulates autophagy by directly binding to ATG7 promoter and transcriptionally up-regulating its expression. Significantly, breast cancer patient sample study revealed that a higher ATG7 expression level is associated with poor patient survival. This novel finding was further confirmed by analysis of two independent patient databases, demonstrating a prognostic value of ATG7. Furthermore, a strong positive correlation was observed between levels of HSF1 and ATG7 in triple-negative breast cancer patient samples, thus validating our in vitro findings. This is the first study identifying a critical role for HSF1 in controlling cytoprotective autophagy through regulation of ATG7, which is distinct from the HSF1 function in the heat shock response. This is also the first study demonstrating a prognostic value of ATG7 in breast cancer patients. These findings strongly argue that combining chemotherapeutic agents with autophagy inhibition by repressing HSF1/ATG7 axis represents a promising strategy for future cancer treatment.

Netrin-1 protects hypoxia-induced mitochondrial apoptosis through HSP27 expression via DCC- and integrin α6β4-dependent Akt, GSK-3β, and HSF-1 in mesenchymal stem cells

Netrin (Ntn) has the potential to be successfully applied as an anti-apoptotic agent with a high affinity for tissue, for therapeutic strategies of umbilical cord blood-derived mesenchymal stem cells (UCB-MSC), although the mechanism by which Ntn-1 protects hypoxic injury has yet to be identified. Therefore, the present study examined the effect of Ntn-1 on hypoxia-induced UCB-MSC apoptosis, as well as the potential underlying mechanisms of its protective effect. Hypoxia (72 h) reduced cell viability (MTT reduction, and [3H]-thymidine incorporation) and cell number, and induced apoptosis (annexin and/or PI positive), which were reversed by Ntn-1 (10 ng/ml). Moreover, Ntn-1 decreased the increase of hypoxia-induced Bax, cleaved caspase-9, and -3, but blocked the decrease of hypoxia-reduced Bcl-2. Next, in order to examine the Ntn-1-related signaling cascade in the protection of hypoxic injury, we analyzed six Ntn receptors in UCB-MSC. We identified deleted in colorectal cancer (DCC) and integrin (IN) α6β4, except uncoordinated family member (UNC) 5A–C, and neogenin. Among them, IN α6β4 only was detected in lipid raft fractions. In addition, Ntn-1 induced the dissociation of DCC and APPL-1 complex, thereby stimulating the formation of APPL-1 and Akt2 complex. Ntn-1 also reversed the hypoxia-induced decrease of Akt and glycogen synthase kinase 3β (GSK-3β) phosphorylation, which is involved in heat shock factor-1 (HSF-1) expression. Ntn-1-induced phospho-Akt and -GSK-3β were inhibited by DCC function-blocking antibody, IN a6b4 function-blocking antibody, and the Akt inhibitor. Hypoxia and/or Ntn-1 stimulated heat shock protein (HSP)27 expression, which was blocked by HSF-1-specific small interfering RNA (siRNA). Furthermore, HSP27-specific siRNA reversed the Ntn-1-induced increase of phospho-Akt. Additionally, HSP27-specific siRNA attenuated the Ntn-1-reduced loss of mitochondrial membrane injury via the inhibition of cytochrome c (cyt c) release and formation of cyt c and HSP27 complex. Moreover, the inhibition of each signaling protein attenuated Ntn-1-induced blockage of apoptosis. In conclusion, Ntn-1-induced HSP27 protected hypoxic injury-related UCB-MSC apoptosis through DCC- and IN α6β4-dependent Akt, GSK-3β, and HSF-1 signaling pathways.

Manipulating Heat Shock Factor-1 in Xenopus Tadpoles: Neuronal Tissues Are Refractory to Exogenous Expression

BackgroundThe aging related decline of heat shock factor-1 (HSF1) signaling may be causally related to protein aggregation diseases. To model such disease, we tried to cripple HSF1 signaling in the Xenopus tadpole.ResultsOver-expression of heat shock factor binding protein-1 did not inhibit the heat shock response in Xenopus. RNAi against HSF1 mRNA inhibited the heat shock response by 70% in Xenopus A6 cells, but failed in transgenic tadpoles. Expression of XHSF380, a dominant-negative HSF1 mutant, was embryonic lethal, which could be circumvented by delaying expression via a tetracycline inducible promoter. HSF1 signaling is thus essential for embryonic Xenopus development. Surprisingly, transgenic expression of the XHSF380 or of full length HSF1, whether driven by a ubiquitous or a neural specific promoter, was not detectable in the larval brain.ConclusionsOur finding that the majority of neurons, which have little endogenous HSF1, refused to accept transgene-driven expression of HSF1 or its mutant suggests that HSF1 levels are strictly controlled in neuronal tissue.