Heat shock-independent induction of multidrug resistance by heat shock factor 1

The cytotoxic activities of the major diterpene extracted from Salvia multicaulis (Bardakosh) are mediated by the regulation of heat-shock response and fatty acid metabolism pathways in human leukemia cells

BACKGROUND

Leukemia is one of the most lethal cancers worldwide and represents the sixth-leading cause of cancer deaths. The results of leukemia treatment have not been as positive as desired, and recurrence is common.

PURPOSE

Thus, there is an urgent requirement for the development of new therapeutic drugs. Salvia multicaulis (Bardakosh) is a widespread species that contains multiple phytochemical components with anti-cancer activities.

METHODS

We isolated and characterized the major diterpene candesalvone B methyl ester from S. multicaulis and investigated its action as a cytotoxic agent towards sensitive and drug-resistant leukemia cells by the resazurin reduction assay. Additionally, the targeted genes and the affected molecular mechanisms attributed to the potent cytotoxic activities were discovered by transcriptome-wide mRNA expression profiling. The targets predicted to be regulated by candesalvone B methyl ester in each cell line were confirmed by qRT-PCR, molecular docking, microscale thermophoresis, and western blotting. Moreover, cell cycle distribution and apoptosis were analyzed by flow cytometry.

RESULTS

Candesalvone B methyl ester was cytotoxic with IC50 values of 20.95 ± 0.15 µM against CCRF-CEM cells and 4.13 ± 0.10 µM against multidrug-resistant CEM/ADR5000 leukemia cells. The pathway enrichment analysis disclosed that candesalvone B methyl ester could regulate the heat-shock response signaling pathway via targeting heat shock factor 1 (HSF1) in CCRF-CEM cells and ELOVL fatty acid elongase 5 (ELOVL5) controls the fatty acid metabolism pathway in CEM/ADR5000 cells. Microscale thermophoresis showed the binding of candesalvone B methyl ester with HSF1 and ELOVL5, confirming the results of molecular docking analysis. Down-regulation of both HSF1 and ELOVL5 by candesalvone B methyl ester as detected by both western blotting and RT-qPCR was related to the reversal of drug resistance in the leukemia cells. Furthermore, candesalvone B methyl ester increased the arrest in the sub-G1 phase of the cell cycle in a dose-dependent manner from 1.3 % to 32.3 % with concomitant induction of apoptosis up to 29.0 % in CCRF-CEM leukemic cells upon inhibition of HSF1.

CONCLUSION

Candesalvone B methyl ester isolated from S. multicaulis exerted cytotoxicity by affecting apoptosis, cell division, and modulation of expression levels of genes contributing to the heat stress signaling and fatty acid metabolism pathways that could relieve drug resistance of leukemia cells.

Dominant-negative TP53 mutations potentiated by the HSF1-regulated proteostasis network

Protein mutational landscapes are sculpted by the impacts of the resulting amino acid substitutions on the protein's stability and folding or aggregation kinetics. These properties can, in turn, be modulated by the composition and activities of the cellular proteostasis network. Heat shock factor 1 (HSF1) is the master regulator of the cytosolic and nuclear proteostasis networks, dynamically tuning the expression of cytosolic and nuclear chaperones and quality control factors to meet demand. Chronic increases in HSF1 levels and activity are prominent hallmarks of cancer cells. One plausible explanation for this observation is that the consequent upregulation of proteostasis factors could biophysically facilitate the acquisition of oncogenic mutations. Here, we experimentally evaluate the impacts of chronic HSF1 activation on the mutational landscape accessible to the quintessential oncoprotein p53. Specifically, we apply quantitative deep mutational scanning of p53 to assess how HSF1 activation shapes the mutational pathways by which p53 can escape cytotoxic pressure conferred by the small molecule nutlin-3, which is a potent antagonist of the p53 negative regulator MDM2. We find that activation of HSF1 broadly increases the fitness of dominant-negative substitutions within p53. This effect of HSF1 activation was particularly notable for non-conservative, biophysically unfavorable amino acid substitutions within buried regions of the p53 DNA-binding domain. These results indicate that chronic HSF1 activation profoundly shapes the oncogenic mutational landscape, preferentially supporting the acquisition of cancer-associated substitutions that are biophysically destabilizing. Along with providing the first experimental and quantitative insights into how HSF1 influences oncoprotein mutational spectra, these findings also implicate HSF1 inhibition as a strategy to reduce the accessibility of mutations that drive chemotherapeutic resistance and metastasis.

ER Stress-Activated HSF1 Governs Cancer Cell Resistance to USP7 Inhibitor-Based Chemotherapy through the PERK Pathway

Ubiquitin-specific protease 7 inhibitors (USP7i) are considered a novel class of anticancer drugs. Cancer cells occasionally become insensitive to anticancer drugs, known as chemoresistance, by acquiring multidrug resistance, resulting in poor clinical outcomes in patients with cancer. However, the chemoresistance of cancer cells to USP7i (P22077 and P5091) and mechanisms to overcome it have not yet been investigated. In the present study, we generated human cancer cells with acquired resistance to USP7i-induced cell death. Gene expression profiling showed that heat stress response (HSR)- and unfolded protein response (UPR)-related genes were largely upregulated in USP7i-resistant cancer cells. Biochemical studies showed that USP7i induced the phosphorylation and activation of heat shock transcription factor 1 (HSF1), mediated by the endoplasmic reticulum (ER) stress protein kinase R-like ER kinase (PERK) signaling pathway. Inhibition of HSF1 and PERK significantly sensitized cancer cells to USP7i-induced cytotoxicity. Our study demonstrated that the ER stress-PERK axis is responsible for chemoresistance to USP7i, and inhibiting PERK is a potential strategy for improving the anticancer efficacy of USP7i.

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

BACKGROUND AND AIM

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Heat Shock Proteins and HSF1 in Cancer

Fitness of cells is dependent on protein homeostasis which is maintained by cooperative activities of protein chaperones and proteolytic machinery. Upon encountering protein-damaging conditions, cells activate the heat-shock response (HSR) which involves HSF1-mediated transcriptional upregulation of a group of chaperones - the heat shock proteins (HSPs). Cancer cells experience high levels of proteotoxic stress due to the production of mutated proteins, aneuploidy-induced excess of components of multiprotein complexes, increased translation rates, and dysregulated metabolism. To cope with this chronic state of proteotoxic stress, cancers almost invariably upregulate major components of HSR, including HSF1 and individual HSPs. Some oncogenic programs show dependence or coupling with a particular HSR factor (such as frequent coamplification of HSF1 and MYC genes). Elevated levels of HSPs and HSF1 are typically associated with drug resistance and poor clinical outcomes in various malignancies. The non-oncogene dependence ("addiction") on protein quality controls represents a pancancer target in treating human malignancies, offering a potential to enhance efficacy of standard and targeted chemotherapy and immune checkpoint inhibitors. In cancers with specific dependencies, HSR components can serve as alternative targets to poorly druggable oncogenic drivers.

Heat shock transcription factor HSF2 modulates the autophagy response through the BTG2-SOD2 axis

The heat shock transcription factor HSF1 regulates the inducible Hsp gene transcription, whereas HSF2 is involved in the constitutive transcription. HSFs can work for the non-heat shock genes transcription in a case-specific manner to facilitate normal cellular functions. Here, we demonstrate that HSF2 acts as an upstream regulator of heat shock-induced autophagy response in a rat histiocytoma. The heat-induced HSF2 transactivates the B-cell translocation gene-2 (BTG2) transcription, and the latter acts as a transcriptional coactivator for superoxide dismutase (SOD2). The altered HSF2 promoter occupancy on the BTG2 promoter enhances BTG2 transcription. Since SOD2 regulation is linked to mitochondrial redox sensing, HSF2 appears to act as a redox sensor in deciding the cell fate. The HSF2 shRNA or NFE2L2/BTG2 siRNA treatments have interfered with the autophagy response. We demonstrate that HSF2 is an upstream activator of autophagy response, and the HSF2-BTG2-SOD2 axis acts as a switch between the non-selective (micro/macro) and selective (chaperone-mediated) autophagy.

Targeting HSF1 as a Therapeutic Strategy for Multiple Mechanisms of EGFR Inhibitor Resistance in EGFR Mutant Non-Small-Cell Lung Cancer

Simple Summary

We attempted to identify target proteins and compounds that can be used to overcome EGFR-TKI resistance in NSCLC. To accomplish this, we generated EGFR inhibitor erlotinib-resistant HCC827-ErlR cells and obtained a list of differentially expressed genes. Then, we performed connectivity map analysis and identified heat shock factor 1 (HSF1) as a potential target protein to overcome erlotinib resistance. Using specific HSF1 shRNAs and KRIBB11 (N²-(1H-Indazol-5-yl)-N⁶-methyl-3-nitropyridine-2,6-diamine), we proved the effectiveness of HSF1 inhibition for overcoming erlotinib resistance in vitro. In addition, we proved the efficacy of emetine in inhibiting HSF1 activity and the tumor growth of erlotinib-resistant PC9-ErlR cells in a mouse model.

Abstract

Although EGFR-TKI treatment of NSCLC (non-small-cell lung cancer) patients often achieves profound initial responses, the efficacy is transient due to acquired resistance. Multiple receptor tyrosine kinase (RTK) pathways contribute to the resistance of NSCLC to first- and third-generation EGFR-TKIs, such as erlotinib and osimertinib. To identify potential targets for overcoming EGFR-TKI resistance, we performed a gene expression signature-based strategy using connectivity map (CMap) analysis. We generated erlotinib-resistant HCC827-ErlR cells, which showed resistance to erlotinib, gefitinib, osimertinib, and doxorubicin. A list of differentially expressed genes (DEGs) in HCC827-ErlR cells was generated and queried using CMap analysis. Analysis of the top 4 compounds from the CMap list suggested HSF1 as a potential target to overcome EGFR-TKI resistance. HSF1 inhibition by using HSF1 shRNAs or KRIBB11 decreased the expression of HSF1 downstream proteins, such as HSP70 and HSP27, and also decreased the expression of HSP90/HSP70/BAG3 client proteins, such as BCL2, MCL1, EGFR, MET, and AXL, causing apoptosis of EGFR-TKI-resistant cancer cells. Finally, we demonstrated the efficacy of the HSF1 inhibitor on PC9-ErlR cells expressing mutant EGFR (T790M) in vivo. Collectively, these findings support a targetable HSF1-(HSP90/HSP70/BAG3)-(BCL2/MCL1/EGFR/MET/AXL) pathway to overcome multiple mechanisms of EGFR-TKI resistance.

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 Chaperones in Osteosarcoma: Diagnosis and Therapeutic Issues

Osteosarcoma (OS) is the most common form of primary bone tumor affecting mainly children and young adults. Despite therapeutic progress, the 5-year survival rate is 70%, but it drops drastically to 30% for poor responders to therapies or for patients with metastases. Identifying new therapeutic targets is thus essential. Heat Shock Proteins (HSPs) are the main effectors of Heat Shock Response (HSR), the expression of which is induced by stressors. HSPs are a large family of proteins involved in the folding and maturation of other proteins in order to maintain proteostasis. HSP overexpression is observed in many cancers, including breast, prostate, colorectal, lung, and ovarian, as well as OS. In this article we reviewed the significant role played by HSPs in molecular mechanisms leading to OS development and progression. HSPs are directly involved in OS cell proliferation, apoptosis inhibition, migration, and drug resistance. We focused on HSP27, HSP60, HSP70 and HSP90 and summarized their potential clinical uses in OS as either biomarkers for diagnosis or therapeutic targets. Finally, based on different types of cancer, we consider the advantage of targeting heat shock factor 1 (HSF1), the major transcriptional regulator of HSPs in OS.

Antigiardial Activity of Acetylsalicylic Acid Is Associated with Overexpression of HSP70 and Membrane Transporters

Giardia lamblia is a flagellated protozoan responsible for giardiasis, a worldwide diarrheal disease. The adverse effects of the pharmacological treatments and the appearance of drug resistance have increased the rate of therapeutic failures. In the search for alternative therapeutics, drug repositioning has become a popular strategy. Acetylsalicylic acid (ASA) exhibits diverse biological activities through multiple mechanisms. However, the full spectrum of its activities is incompletely understood. In this study we show that ASA displayed direct antigiardial activity and affected the adhesion and growth of trophozoites in a time-dose-dependent manner. Electron microscopy images revealed remarkable morphological alterations in the membrane, ventral disk, and caudal region. Using mass spectrometry and real-time quantitative reverse transcription (qRT-PCR), we identified that ASA induced the overexpression of heat shock protein 70 (HSP70). ASA also showed a significant increase of five ATP-binding cassette (ABC) transporters (giABC, giABCP, giMDRP, giMRPL and giMDRAP1). Additionally, we found low toxicity on Caco-2 cells. Taken together, these results suggest an important role of HSPs and ABC drug transporters in contributing to stress tolerance and protecting cells from ASA-induced stress.

HSF1: Primary Factor in Molecular Chaperone Expression and a Major Contributor to Cancer Morbidity

Heat shock factor 1 (HSF1) is the primary component for initiation of the powerful heat shock response (HSR) in eukaryotes. The HSR is an evolutionarily conserved mechanism for responding to proteotoxic stress and involves the rapid expression of heat shock protein (HSP) molecular chaperones that promote cell viability by facilitating proteostasis. HSF1 activity is amplified in many tumor contexts in a manner that resembles a chronic state of stress, characterized by high levels of HSP gene expression as well as HSF1-mediated non-HSP gene regulation. HSF1 and its gene targets are essential for tumorigenesis across several experimental tumor models, and facilitate metastatic and resistant properties within cancer cells. Recent studies have suggested the significant potential of HSF1 as a therapeutic target and have motivated research efforts to understand the mechanisms of HSF1 regulation and develop methods for pharmacological intervention. We review what is currently known regarding the contribution of HSF1 activity to cancer pathology, its regulation and expression across human cancers, and strategies to target HSF1 for cancer therapy.

Roles of heat shock factor 1 beyond the heat shock response

Various stress factors leading to protein damage induce the activation of an evolutionarily conserved cell protective mechanism, the heat shock response (HSR), to maintain protein homeostasis in virtually all eukaryotic cells. Heat shock factor 1 (HSF1) plays a central role in the HSR. HSF1 was initially known as a transcription factor that upregulates genes encoding heat shock proteins (HSPs), also called molecular chaperones, which assist in refolding or degrading injured intracellular proteins. However, recent accumulating evidence indicates multiple additional functions for HSF1 beyond the activation of HSPs. Here, we present a nearly comprehensive list of non-HSP-related target genes of HSF1 identified so far. Through controlling these targets, HSF1 acts in diverse stress-induced cellular processes and molecular mechanisms, including the endoplasmic reticulum unfolded protein response and ubiquitin-proteasome system, multidrug resistance, autophagy, apoptosis, immune response, cell growth arrest, differentiation underlying developmental diapause, chromatin remodelling, cancer development, and ageing. Hence, HSF1 emerges as a major orchestrator of cellular stress response pathways.

Targeted production of reactive oxygen species in mitochondria to overcome cancer drug resistance

Multidrug resistance is a major challenge to cancer chemotherapy. The multidrug resistance phenotype is associated with the overexpression of the adenosine triphosphate (ATP)-driven transmembrane efflux pumps in cancer cells. Here, we report a lipid membrane-coated silica-carbon (LSC) hybrid nanoparticle that targets mitochondria through pyruvate, to specifically produce reactive oxygen species (ROS) in mitochondria under near-infrared (NIR) laser irradiation. The ROS can oxidize the NADH into NAD⁺ to reduce the amount of ATP available for the efflux pumps. The treatment with LSC nanoparticles and NIR laser irradiation also reduces the expression and increases the intracellular distribution of the efflux pumps. Consequently, multidrug-resistant cancer cells lose their multidrug resistance capability for at least 5 days, creating a therapeutic window for chemotherapy. Our in vivo data show that the drug-laden LSC nanoparticles in combination with NIR laser treatment can effectively inhibit the growth of multidrug-resistant tumors with no evident systemic toxicity.

Multidrug resistance is a major challenge in cancer therapy. Here, the authors develop a mitochondria-targeting nanoparticle system that inhibits adenosine triphosphate transporter activity via reactive oxygen species generation and can thus be used to target multidrug-resistant cancer.

A Novel Heat Shock Element (HSE) in Entamoeba histolytica that Regulates the Transcriptional Activation of the EhPgp5 Gene in the Presence of Emetine Drug

Transcriptional regulation of the multidrug resistance EhPgp5 gene in Entamoeba histolytica is induced by emetine stress. EhPgp5 overexpression alters the chloride-dependent currents that cause trophozoite swelling, diminishing induced programmed cell death (PCD) susceptibility. In contrast, antisense inhibition of P-glycoprotein (PGP) expression produces synchronous death of trophozoites and the enhancement of the biochemical and morphological characteristics of PCD induced by G418. Transcriptional gene regulation analysis identified a 59 bp region at position −170 to −111 bp promoter as putative emetine response elements (EREs). However, insights into transcription factors controlling EhPgp5 gene transcription are missing; to fill this knowledge gap, we used deletion studies and transient CAT activity assays. Our findings suggested an activating motif (−151 to −136 bp) that corresponds to a heat shock element (HSE). Gel-shift assays, UV-crosslinking, binding protein purification, and western blotting assays revealed proteins of 94, 66, 62, and 51 kDa binding to the EhPgp5 HSE that could be heat shock-like transcription factors that regulate the transcriptional activation of the EhPgp5 gene in the presence of emetine drug.

Pleiotropic role of HSF1 in neoplastic transformation

HSF1 (Heat Shock transcription Factor 1) is the main transcription factor activated in response to proteotoxic stress. Once activated, it induces an expression of heat shock proteins (HSPs) which enables cells to survive in suboptimal conditions. HSF1 could be also activated by altered kinase signaling characteristic for cancer cells, which is a probable reason for its high activity found in a broad range of tumors. There is rapidly growing evidence that HSF1 supports tumor initiation and growth, as well as metastasis and angiogenesis. It also modulates the sensitivity of cancer cells to therapy. Functions of HSF1 in cancer are connected with HSPs’ activity, which generally protects cells from apoptosis, but also are independent of its classical targets. HSF1-dependent regulation of non-HSPs genes plays a role in cell cycle progression, glucose metabolism, autophagy and drug efflux. HSF1 affects the key cell-survival and regulatory pathways, including p53, RAS/MAPK, cAMP/PKA, mTOR and insulin signaling. Although the exact mechanism of HSF1 action is still somewhat obscure, HSF1 is becoming an attractive target in anticancer therapies, whose inhibition could enhance the effects of other treatments.

Combined phosphoproteomics and bioinformatics strategy in deciphering drug resistant related pathways in triple negative breast cancer

Because of the absence of a clear therapeutic target for triple negative breast cancer (TNBC), conventional chemotherapy is the only available systemic treatment option for these patients. Despite chemotherapy treatment, TNBC patients still have worse prognosis when compared with other breast cancer patients. The study is to investigate unique phosphorylated proteins expressed in chemoresistant TNBC cell lines. In the current study, twelve TNBC cell lines were subjected to drug sensitivity assays against chemotherapy drugs docetaxel, doxorubicin, gemcitabine, and cisplatin. Based on their half maximal inhibitory concentrations, four resistant and two sensitive cell lines were selected for further analysis. The phosphopeptides from these cells were enriched with TiO2 beads and fractionated using strong cation exchange. 1,645 phosphoprotein groups and 9,585 unique phosphopeptides were identified by a high throughput LC-MS/MS system LTQ-Orbitrap. The phosphopeptides were further filtered with Ascore system and 1,340 phosphoprotein groups, 2,760 unique phosphopeptides, and 4,549 unique phosphosites were identified. Our study suggested that differentially phosphorylated Cdk5, PML, AP-1, and HSF-1 might work together to promote vimentin induced epithelial to mesenchymal transition (EMT) in the drug resistant cells. EGFR and HGF were also shown to be involved in this process.

Overexpression of Heat Shock Transcription Factor 1 enhances the resistance of melanoma cells to doxorubicin and paclitaxel

Background

Heat Shock Transcription Factor 1 (HSF1) is activated under stress conditions. In turn, it induces expression of Heat Shock Proteins (HSPs), which are well-known regulators of protein homeostasis. Elevated levels of HSF1 and HSPs were observed in many types of tumors. The aim of the present study was to determine whether HSF1 could have an effect on the survival of cancer cells treated with chemotherapeutic cytotoxic agents.

Methods

We constructed mouse (B16F10) and human (1205Lu, WM793B) melanoma cells overexpressing full or mutant form of human HSF1: a constitutively active one with a deletion in regulatory domain or a dominant negative one with a deletion in the activation domain. The impact of different forms of HSF1 on the expression of HSP and ABC genes was studied by RT-PCR and Western blotting. Cell cultures were treated with increasing amounts of doxorubicin, paclitaxel, cisplatin, vinblastine or bortezomib. Cell viability was determined by MTT, and IC₅₀ was calculated. Cellular accumulation of fluorescent dyes and side population cells were studied using flow cytometry.

Results

Cells overexpressing HSF1 and characterized by increased HSPs accumulation were more resistant to doxorubicin or paclitaxel, but not to cisplatin, vinblastine or bortezomib. This resistance correlated with the enhanced efflux of fluorescent dyes and the increased number of side population cells. The expression of constitutively active mutant HSF1, also resulting in HSPs overproduction, did not reduce the sensitivity of melanoma cells to drugs, unlike in the case of dominant negative form expression. Cells overexpressing a full or dominant negative form of HSF1, but not a constitutively active one, had higher transcription levels of ABC genes when compared to control cells.

Conclusions

HSF1 overexpression facilitates the survival of melanoma cells treated with doxorubicin or paclitaxel. However, HSF1-mediated chemoresistance is not dependent on HSPs accumulation but on an increased potential for drug efflux by ABC transporters. Direct transcriptional activity of HSF1 is not necessary for increased expression of ABC genes, which is probably mediated by HSF1 regulatory domain.

Heat shock proteins and heat shock factor 1 in carcinogenesis and tumor development: an update

Heat shock proteins (HSP) are a subset of the molecular chaperones, best known for their rapid and abundant induction by stress. HSP genes are activated at the transcriptional level by heat shock transcription factor 1 (HSF1). During the progression of many types of cancer, this heat shock transcriptional regulon becomes co-opted by mechanisms that are currently unclear, although evidently triggered in the emerging tumor cell. Concerted activation of HSF1 and the accumulation of HSPs then participate in many of the traits that permit the malignant phenotype. Thus, cancers of many histologies exhibit activated HSF1 and increased HSP levels that may help to deter tumor suppression and evade therapy in the clinic. We review here the extensive work that has been carried out and is still in progress aimed at (1) understanding the oncogenic mechanisms by which HSP genes are switched on, (2) determining the roles of HSF1/HSP in malignant transformation and (3) discovering approaches to therapy based on disrupting the influence of the HSF1-controlled transcriptome in cancer.

Heat shock factor-1 knockout induces multidrug resistance gene, MDR1b, and enhances P-glycoprotein (ABCB1)-based drug extrusion in the heart

Heat-shock factor 1 (HSF-1), a transcription factor for heat-shock proteins (HSPs), is known to interfere with the transcriptional activity of many oncogenic factors. In the present work, we have discovered that HSF-1 ablation induced the multidrug resistance gene, MDR1b, in the heart and increased the expression of P-glycoprotein (P-gp, ABCB1), an ATP binding cassette that is usually associated with multidrug-resistant cancer cells. The increase in P-gp enhanced the extrusion of doxorubicin (Dox) to alleviate Dox-induced heart failure and reduce mortality in mice. Dox-induced left ventricular (LV) dysfunction was significantly reduced in HSF-1(-/-) mice. DNA-binding activity of NF-κB was higher in HSF-1(-/-) mice. IκB, the NF-κB inhibitor, was depleted due to enhanced IκB kinase (IKK)-α activity. In parallel, MDR1b gene expression and a large increase in P-gp and lowering Dox loading were observed in HSF-1(-/-) mouse hearts. Moreover, application of the P-gp antagonist, verapamil, increased Dox loading in HSF-1(-/-) cardiomyocytes, deteriorated cardiac function in HSF-1(-/-) mice, and decreased survival. MDR1 promoter activity was higher in HSF-1(-/-) cardiomyocytes, whereas a mutant MDR1 promoter with heat-shock element (HSE) mutation showed increased activity only in HSF-1(+/+) cardiomyocytes. However, deletion of HSE and NF-κB binding sites diminished luminescence in both HSF-1(+/+) and HSF-1(-/-) cardiomyocytes, suggesting that HSF-1 inhibits MDR1 activity in the heart. Thus, because high levels of HSF-1 are attributed to poor prognosis of cancer, systemic down-regulation of HSF-1 before chemotherapy is a potential therapeutic approach to ameliorate the chemotherapy-induced cardiotoxicity and enhance cancer prognosis.

Inhibition of the heat shock response by PI103 enhances the cytotoxicity of arsenic trioxide

Heat shock factor 1 (HSF1) is a key regulator of the cytoprotective and anti-apoptotic heat shock response and can be activated by arsenite. Inhibition of HSF1 activation may therefore enhance the cytotoxicity of arsenic trioxide (ATO). We show that ATO induced HSF1 phosphorylation at serine 326 (S326) and induced HSF1-dependent expression of heat shock proteins (HSPs) 27 and 70 in cultured cells. HSF1 significantly reduced cell sensitivity to ATO by reducing apoptosis. Disruption of HSF1 function not only reduced ATO induction of HSP27 and 70 but also enhanced ATO cytotoxicity by elevating apoptosis. These results reveal that HSF1 activation and the resulting induction of HSPs may protect cells from ATO cytotoxicity. The diminished expression of HSPs and hypersensitivity to ATO in cells stably depleted of HSF1 was rescued by ectopic expression of wild-type HSF1 but not an S326A substitution mutant, indicating that phosphorylation at S326 was critical for the protective effect of HSF1. Simultaneous treatment of cells with ATO and PI103, an inhibitor of members of the phosphatidylinositol 3-kinase (PI3K) family, suppressed not only ATO-induced expression of an HSP70 promoter-reporter construct and endogenous HSP70 but also phosphorylation of HSF1 S326. PI103 considerably reduced HSF1 transactivation in ATO-treated cells but had only a limited effect on HSF1 nuclear translocation and DNA binding. Furthermore, PI103 enhanced ATO cytotoxicity in an HSF1-dependent manner. Thus, inhibition of S326 phosphorylation by PI103 blocks the transactivation of HSF1 and may consequently suppress ATO induction of the heat shock response and sensitize cells to ATO.

A dormant state modulated by osmotic pressure controls clonogenicity of prostate cancer cells

Cell dormancy constitutes a limiting step of the metastatic process by preventing the proliferation of isolated cancer cells disseminated at distant sites from the primary tumor. The study of cancer cell dormancy is severely hampered by the lack of biological samples so that the mechanisms that regulate cell dormancy have not been extensively explored. In this work, we describe the rapid induction in vitro of a dormant state in prostate cancer cells by exposure to a slightly hypertonic growth medium. This quiescence is observed only when cells are seeded at low density and, once established, requires additional stimuli besides osmotic pressure to be reversed. Media conditioned by cells grown at high density can partially prevent or reverse dormancy, a phenomenon which can be reproduced with citric acid. In addition to this role of small metabolites, inactivation of the p53 and smad pathways also counters the entry into dormancy, whereas exposure to activin A induces it to some extent. Thus, this easily inducible dormancy reproduces several features associated with the dormancy of stem cells and cancer cells in vivo.

Forced expression of heat shock protein 27 (Hsp27) reverses P-glycoprotein (ABCB1)-mediated drug efflux and MDR1 gene expression in Adriamycin-resistant human breast cancer cells

Mutant p53 accumulation has been shown to induce the multidrug resistance gene (MDR1) and ATP binding cassette (ABC)-based drug efflux in human breast cancer cells. In the present work, we have found that transcriptional activation of the oxidative stress-responsive heat shock factor 1 (HSF-1) and expression of heat shock proteins, including Hsp27, which is normally known to augment proteasomal p53 degradation, are inhibited in Adriamycin (doxorubicin)-resistant MCF-7 cells (MCF-7/adr). Such an endogenous inhibition of HSF-1 and Hsp27 in turn results in p53 mutation with gain of function in its transcriptional activity and accumulation in MCF-7/adr. Also, lack of HSF-1 enhances nuclear factor κB (NF-κB) DNA binding activity together with mutant p53 and induces MDR1 gene and P-glycoprotein (P-gp, ABCB1), resulting in a multidrug-resistant phenotype. Ectopic expression of Hsp27, however, significantly depleted both mutant p53 and NF-κB (p65), reversed the drug resistance by inhibiting MDR1/P-gp expression in MCF-7/adr cells, and induced cell death by increased G(2)/M population and apoptosis. We conclude from these results that HSF-1 inhibition and depletion of Hsp27 is a trigger, at least in part, for the accumulation of transcriptionally active mutant p53, which can either directly or NF-κB-dependently induce an MDR1/P-gp phenotype in MCF-7 cells. Upon Hsp27 overexpression, this pathway is abrogated, and the acquired multidrug resistance is significantly abolished so that MCF-7/adr cells are sensitized to Dox. Thus, clinical alteration in Hsp27 or NF-κB level will be a potential approach to circumvent drug resistance in breast cancer.

Co-chaperones are limiting in a depleted chaperone network

To probe the limiting nodes in the chaperoning network which maintains cellular proteostasis, we expressed a dominant negative mutant of heat shock factor 1 (dnHSF1), the regulator of the cytoplasmic proteotoxic stress response. Microarray analysis of non-stressed dnHSF1 cells showed a two- or more fold decrease in the transcript level of 10 genes, amongst which are the (co-)chaperone genes HSP90AA1, HSPA6, DNAJB1 and HSPB1. Glucocorticoid signaling, which requires the Hsp70 and the Hsp90 folding machines, was severely impaired by dnHSF1, but fully rescued by expression of DNAJA1 or DNAJB1, and partially by ST13. Expression of DNAJB6, DNAJB8, HSPA1A, HSPB1, HSPB8, or STIP1 had no effect while HSP90AA1 even inhibited. PTGES3 (p23) inhibited only in control cells. Our results suggest that the DNAJ co-chaperones in particular become limiting in a depleted chaperoning network. Our results also suggest a difference between the transcriptomes of cells lacking HSF1 and cells expressing dnHSF1.

Targeting the brain--surmounting or bypassing the blood-brain barrier

The constituents of the blood-brain barrier, including its efflux transporter system, can efficiently limit brain penetration of potential CNS therapeutics. Effective extrusion from the brain by transporters is a frequent reason for the pharmaceutical industry to exclude novel compounds from further development for CNS therapeutics. Moreover, high transporter expression levels that are present in individual patients or may be generally associated with the pathophysiology seem to be a major cause of therapeutic failure in a variety of CNS diseases including brain tumors, epilepsy, brain HIV infection, and psychiatric disorders. Increasing knowledge of the structure and function of the blood-brain barrier creates a basis for the development of strategies which aim to enhance brain uptake of beneficial pharmaceutical compounds. The different strategies discussed in this review aim to modulate blood-brain barrier function or to bypass constituents of the blood-brain barrier.

Transcriptional expression levels of cell stress marker genes in the Pacific oyster Crassostrea gigas exposed to acute thermal stress

During the annual cycle, oysters are exposed to seasonal slow changes in temperature, but during emersion at low tide on sunny summer days, their internal temperature may rise rapidly, resulting in acute heat stress. We experimentally exposed oysters to a 1-h acute thermal stress and investigated the transcriptional expression level of some genes involved in cell stress defence mechanisms, including chaperone proteins (heat shock proteins Hsp70, Hsp72 and Hsp90 (HSP)), regulation of oxidative stress (Cu-Zn superoxide dismutase, metallothionein (MT)), cell detoxification (glutathione S-transferase sigma, cytochrome P450 and multidrug resistance (MDR1)) and regulation of the cell cycle (p53). Gene mRNA levels were quantified by reverse transcription-quantitative polymerase chain reaction and expressed as their ratio to actin mRNA, used as a reference. Of the nine genes studied, HSP, MT and MDR1 mRNA levels increased in response to thermal stress. We compared the responses of oysters exposed to acute heat shock in summer and winter and observed differences in terms of magnitude and kinetics. A larger increase was observed in September, with recovery within 48 h, whereas in March, the increase was smaller and lasted more than 2 days. The results were also compared with data obtained from the natural environment. Though the functional molecule is the protein and information at the mRNA level only has limitations, the potential use of mRNAs coding for cell stress defence proteins as early sensitive biomarkers is discussed.

Association of human APOBEC3 cytidine deaminases with the generation of hepatitis virus B x antigen mutants and hepatocellular carcinoma

Human APOBEC3 (apolipoprotein B mRNA editing enzyme, catalytic polypeptide 3) cytidine deaminases have been shown to be potent inhibitors of diverse retroviruses including Vif-deficient human immunodeficiency virus 1 (HIV-1), hepatitis virus B (HBV), adeno-associated virus, and endogenous retroelements. Despite the fact that these enzymes are known to be potential DNA mutators and to target retroviral DNA for cytidine deamination, the pathological effects of their deregulated expression in human diseases are not yet clear. Mutants of the viral HBx protein have been implicated in the carcinogenesis of hepatocellular carcinoma (HCC); however, little is known about how or why such mutants are generated in the human liver. Here, we report that a number of APOBEC3 deaminases preferentially edit the HBx region of HBV DNA and generate C-terminally truncated HBx mutants. Our functional studies indicated that APOBEC3-mediated HBx mutants, especially the C-terminally truncated mutants, cause a gain of function that enhances the colony-forming ability and proliferative capacity of neoplastic cells. Furthermore, we detected G-to-A hypermutation-mediated HBx mutants in preneoplastic liver tissues of selected patients with active chronic HBV infections. We also observed that the APOBEC3B (A3B) cytidine deaminase was widely up-regulated in HCC tumor tissues; it also promoted the growth of neoplastic human HepG2 liver cells and up-regulated heat shock transcription factor1 (HSF1) expression.

CONCLUSION

These findings suggest that some of the APOBEC3 deaminases play a role in the carcinogenesis of HCC through the generation of HBx mutants, providing preneoplastic and neoplastic hepatocytes with a selective clonal growth advantage. Deregulated expression of A3B in liver tissues may also have the potential to promote genetic instability and tumorigenesis.

Ceramide and glucosylceramide upregulate expression of the multidrug resistance gene MDR1 in cancer cells

In the present study we used human breast cancer cell lines to assess the influence of ceramide and glucosylceramide (GC) on expression of MDR1, the multidrug resistance gene that codes for P-glycoprotein (P-gp), because GC has been shown to be a substrate for P-gp. Acute exposure (72 h) to C8-ceramide (5 microg/ml culture medium), a cell-permeable ceramide, increased MDR1 mRNA levels by 3- and 5-fold in T47D and in MDA-MB-435 cells, respectively. Acute exposure of MCF-7 and MDA-MB-231 cells to C8-GC (10 microg/ml culture medium), a cell-permeable analog of GC, increased MDR1 expression by 2- and 4- fold, respectively. Chronic exposure of MDA-MB-231 cells to C8-ceramide for extended periods enhanced MDR1 mRNA levels 45- and 390-fold at passages 12 and 22, respectively, and also elicited expression of P-gp. High-passage C8-ceramide-grown MDA-MB-231 (MDA-MB-231/C8cer) cells were more resistant to doxorubicin and paclitaxel. Incubation with [1-(14)C]C6-ceramide showed that cells converted short-chain ceramide into GC, lactosylceramide, and sphingomyelin. When challenged with 5 mug/ml [1-(14)C]C6-ceramide, MDA-MB-231, MDA-MB-435, MCF-7, and T47D cells took up 31, 17, 21, and 13%, respectively, and converted 82, 58, 62, and 58% of that to short-chain GC. Exposing cells to the GCS inhibitor, ethylenedioxy-P4, a substituted analog of 1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol, prevented ceramide's enhancement of MDR1 expression. These experiments show that high levels of ceramide and GC enhance expression of the multidrug resistance phenotype in cancer cells. Therefore, ceramide's role as a messenger of cytotoxic response might be linked to the multidrug resistance pathway.

Subcellular distribution of human RDM1 protein isoforms and their nucleolar accumulation in response to heat shock and proteotoxic stress

The RDM1 gene encodes a RNA recognition motif (RRM)-containing protein involved in the cellular response to the anti-cancer drug cisplatin in vertebrates. We previously reported a cDNA encoding the full-length human RDM1 protein. Here, we describe the identification of 11 human cDNAs encoding RDM1 protein isoforms. This repertoire is generated by alternative pre-mRNA splicing and differential usage of two translational start sites, resulting in proteins with long or short N-terminus and a great diversity in the exonic composition of their C-terminus. By using tagged proteins and fluorescent microscopy, we examined the subcellular distribution of full-length RDM1 (renamed RDM1alpha), and other RDM1 isoforms. We show that RDM1alpha undergoes subcellular redistribution and nucleolar accumulation in response to proteotoxic stress and mild heat shock. In unstressed cells, the long N-terminal isoforms displayed distinct subcellular distribution patterns, ranging from a predominantly cytoplasmic to almost exclusive nuclear localization, suggesting functional differences among the RDM1 proteins. However, all isoforms underwent stress-induced nucleolar accumulation. We identified nuclear and nucleolar localization determinants as well as domains conferring cytoplasmic retention to the RDM1 proteins. Finally, RDM1 null chicken DT40 cells displayed an increased sensitivity to heat shock, compared to wild-type (wt) cells, suggesting a function for RDM1 in the heat-shock response.

A stress regulatory network for co‐ordinated activation of proteasome expression mediated by yeast heat shock transcription factor

Heat shock transcription factor (HSF) mediates the transcriptional response of eukaryotic cells to heat, infection and inflammation, pharmacological agents, and other stresses. Although genes encoding heat shock proteins (HSPs) are the best characterized targets of HSF, recent genome-wide localization of Saccharomyces cerevisiae HSF revealed novel HSF targets involved in a wide range of cellular functions. One such target, the RPN4 gene, encodes a transcription factor that directly activates expression of a number of genes encoding proteasome subunits. Here we demonstrate that HSF co-ordinates a feed-forward gene regulatory circuit for RPN4 activation. We show that HSF activates expression of PDR3, encoding a multidrug resistance (MDR) transcription factor that also directly activates RPN4 gene expression. We demonstrate that the HSF binding site (HSE) in the RPN4 promoter is primarily responsible for heat- or methyl methanesulphonate induction of RPN4, with a minor contribution of Pdr3 binding sites (PDREs), while a Yap1 binding site (YRE) is responsible for RPN4 induction in response to oxidative stress. Furthermore, heat-induced expression of Rpn4 protein leads to expression of Rpn4 targets at later stages of heat stress, providing a temporal controlling mechanism for proteasome synthesis upon stress conditions that could result in irreversibly damaged proteins. In addition, the overlapping transcriptional regulatory networks involving HSF, Yap1 and Pdr3 suggest a close linkage between stress responses and pleiotropic drug resistance.