Heat Shock Factor 1 Function Research Articles

Age-dependent heat shock hormesis to HSF-1 deficiency suggests a compensatory mechanism mediated by the unfolded protein response and innate immunity in young Caenorhabditis elegans.

The transcription factor HSF-1 (heat shock factor 1) acts as a master regulator of heat shock response in eukaryotic cells to maintain cellular proteostasis. The protein has a protective role in preventing cells from undergoing ageing, and neurodegeneration, and also mediates tumorigenesis. Thus, modulating HSF-1 activity in humans has a promising therapeutic potential for treating these pathologies. Loss of HSF-1 function is usually associated with impaired stress tolerance. Contrary to this conventional knowledge, we show here that inactivation of HSF-1 in the nematode Caenorhabditis elegans results in increased thermotolerance at young adult stages, whereas HSF-1 deficiency in animals passing early adult stages indeed leads to decreased thermotolerance, as compared to wild-type. Furthermore, a gene expression analysis supports that in young adults, distinct cellular stress response and immunity-related signaling pathways become induced upon HSF-1 deficiency. We also demonstrate that increased tolerance to proteotoxic stress in HSF-1-depleted young worms requires the activity of the unfolded protein response of the endoplasmic reticulum and the SKN-1/Nrf2-mediated oxidative stress response pathway, as well as an innate immunity-related pathway, suggesting a mutual compensatory interaction between HSF-1 and these conserved stress response systems. A similar compensatory molecular network is likely to also operate in higher animal taxa, raising the possibility of an unexpected outcome when HSF-1 activity is manipulated in humans.

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.

Heat shock factor 1 directly regulates transsulfuration pathway to promote prostate cancer proliferation and survival

There are limited therapeutic options for patients with advanced prostate cancer (PCa). We previously found that heat shock factor 1 (HSF1) expression is increased in PCa and is an actionable target. In this manuscript, we identify that HSF1 regulates the conversion of homocysteine to cystathionine in the transsulfuration pathway by altering levels of cystathionine-β-synthase (CBS). We find that HSF1 directly binds the CBS gene and upregulates CBS mRNA levels. Targeting CBS decreases PCa growth and induces tumor cell death while benign prostate cells are largely unaffected. Combined inhibition of HSF1 and CBS results in more pronounced inhibition of PCa cell proliferation and reduction of transsulfuration pathway metabolites. Combination of HSF1 and CBS knockout decreases tumor size for a small cell PCa xenograft mouse model. Our study thus provides new insights into the molecular mechanism of HSF1 function and an effective therapeutic strategy against advanced PCa.

Heat Shock Factor 1 Inhibition: A Novel Anti-Cancer Strategy with Promise for Precision Oncology.

Heat shock factor 1 (HSF1) is a transcription factor crucial for regulating heat shock response (HSR), one of the significant cellular protective mechanisms. When cells are exposed to proteotoxic stress, HSF1 induces the expression of heat shock proteins (HSPs) to act as chaperones, correcting the protein-folding process and maintaining proteostasis. In addition to its role in HSR, HSF1 is overexpressed in multiple cancer cells, where its activation promotes malignancy and leads to poor prognosis. The mechanisms of HSF1-induced tumorigenesis are complex and involve diverse signaling pathways, dependent on cancer type. With its important roles in tumorigenesis and tumor progression, targeting HSF1 offers a novel cancer treatment strategy. In this article, we examine the basic function of HSF1 and its regulatory mechanisms, focus on the mechanisms involved in HSF1's roles in different cancer types, and examine current HSF1 inhibitors as novel therapeutics to treat cancers.

Abstract 4817: Protein aggregation promotes HSF1 activity enhancing cell survival during metastatic breast cancer colonization

Abstract Breast cancer is the most commonly diagnosed cancer in women and is the second leading cause of cancer-related deaths in women. Approximately 20-30% of patients will develop metastases and metastasis is responsible for greater than 90% of breast cancer deaths. Metastasis is a complex process in which the cells combat many forces to survive and spread to different areas of the body. Metastatic colonization is the rate-limiting step of metastasis and is an inefficient process in which most cells die and only a small fraction of those that survive can form metastases. We have previously shown that heat shock factor 1 (HSF1) promoted epithelial-to-mesenchymal transition (EMT) and the breast cancer stem-like population, potentially linking HSF1 to metastasis. Utilizing an HSF1 gene expression signature that assesses HSF1 transcriptional activity, we further found that patients with high HSF1 activity have significantly worse metastasis-free survival. The physiological function of HSF1 is the master regulator of the heat shock response wherein it upregulates chaperone proteins under stress conditions. Because of these functions and the fact that the process of metastatic colonization is known to involve the stem cell population and incur external stressors, we hypothesized that HSF1 may function in metastatic colonization. To test this, we subjected human breast cancer MDA- MB-231 cells with or without HSF1 knockdown to intracardiac injections in nude mice. This model injects cells directly into the circulation allowing for assessment of metastatic tumor formation in which the major barrier will be metastatic colonization. Mice receiving cells with knockdown of HSF1 had a significantly reduced metastatic burden, indicating HSF1 is necessary for the completion of metastasis and colonization. Consistent with these findings, bone metastatic tumor specimens from patients show increased HSF1 activation compared to their matched primary breast tumors. The mechanism by which HSF1 enables metastatic colonization is unknown. Metastatic colonization likely requires at least two stages that include tumor initiation (or early colonization) characterized by the seeding of a tumor followed by tumor expansion (or late colonization) characterized by rapid proliferation and an increase in tumor size. We observed increased protein amyloid aggregates that correlate with an increase in HSF1 activity during mammosphere formation, suggesting that colonization induces aggregation leading to HSF1 activation that promotes a cell survival response. Overall, my results indicate that HSF1 activity increased during breast cancer metastasis and HSF1 is necessary for colonization. Going forward, I want to understand what controls HSF1 activation during metastasis, which I hypothesize that protein aggregation is increased leading to HSF1 activation. Citation Format: Natasha Hockaden, Gabi Leriger, John Wang, Haimanti Ray, Richard Carpenter. Protein aggregation promotes HSF1 activity enhancing cell survival during metastatic breast cancer colonization. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4817.

The Emerging Role of Heat Shock Factor 1 (HSF1) and Heat Shock Proteins (HSPs) in Ferroptosis.

Cells employ a well-preserved physiological stress response mechanism, termed the heat shock response, to activate a certain type of molecular chaperone called heat shock proteins (HSPs). HSPs are activated by transcriptional activators of heat shock genes known as heat shock factors (HSFs). These molecular chaperones are categorized as the HSP70 superfamily, which includes HSPA (HSP70) and HSPH (HSP110) families; the DNAJ (HSP40) family; the HSPB family (small heat shock proteins (sHSPs)); chaperonins and chaperonin-like proteins; and other heat-inducible protein families. HSPs play a critical role in sustaining proteostasis and protecting cells against stressful stimuli. HSPs participate in folding newly synthesized proteins, holding folded proteins in their native conformation, preventing protein misfolding and accumulation, and degrading denatured proteins. Ferroptosis is a recently identified type of oxidative iron-dependent cell demise. It was coined recently in 2012 by Stockwell Lab members, who described a special kind of cell death induced by erastin or RSL3. Ferroptosis is characterized by alterations in oxidative status resulting from iron accumulation, increased oxidative stress, and lipid peroxidation, which are mediated by enzymatic and non-enzymatic pathways. The process of ferroptotic cell death is regulated at multiple, and it is involved in several pathophysiological conditions. Much research has emerged in recent years demonstrating the involvement of HSPs and their regulator heat shock factor 1 (HSF1) in ferroptosis regulation. Understanding the machinery controlling HSF1 and HSPs in ferroptosis can be employed in developing therapeutic interventions for ferroptosis occurrence in a number of pathological conditions. Therefore, this review comprehensively summarized the basic characteristics of ferroptosis and the regulatory functions of HSF1 and HSPs in ferroptosis.

Targeting HSF1 for cancer treatment: mechanisms and inhibitor development.

Heat Shock Factor 1 (HSF1) is a master regulator of heat shock responsive signaling. In addition to playing critical roles in cellular heat shock response, emerging evidence suggests that HSF1 also regulates a non-heat shock responsive transcriptional network to handle metabolic, chemical, and genetic stress. The function of HSF1 in cellular transformation and cancer development has been extensively studied in recent years. Due to important roles for HSF1 for coping with various stressful cellular states, research on HSF1 has been very active. New functions and molecular mechanisms underlying these functions have been continuously discovered, providing new targets for novel cancer treatment strategies. In this article, we review the essential roles and mechanisms of HSF1 action in cancer cells, focusing more on recently discovered functions and their underlying mechanisms to reflect the new advances in cancer biology. In addition, we emphasize new advances with regard to HSF1 inhibitors for cancer drug development.

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.

Temporal requirements of SKN-1/NRF as a regulator of lifespan and proteostasis in Caenorhabditis elegans.

Lowering the activity of the Insulin/IGF-1 Signaling (IIS) cascade results in elevated stress resistance, enhanced protein homeostasis (proteostasis) and extended lifespan of worms, flies and mice. In the nematode Caenorhabditis elegans (C. elegans), the longevity phenotype that stems from IIS reduction is entirely dependent upon the activities of a subset of transcription factors including the Forkhead factor DAF-16/FOXO (DAF-16), Heat Shock Factor-1 (HSF-1), SKiNhead/Nrf (SKN-1) and ParaQuat Methylviologen responsive (PQM-1). While DAF-16 determines lifespan exclusively during early adulthood and governs proteostasis in early adulthood and midlife, HSF-1 executes these functions foremost during development. Despite the central roles of SKN-1 as a regulator of lifespan and proteostasis, the temporal requirements of this transcription factor were unknown. Here we employed conditional knockdown techniques and discovered that in C. elegans, SKN-1 is primarily important for longevity and proteostasis during late larval development through early adulthood. Our findings indicate that events that occur during late larval developmental through early adulthood affect lifespan and proteostasis and suggest that subsequent to HSF-1, SKN-1 sets the conditions, partially overlapping temporally with DAF-16, that enable IIS reduction to promote longevity and proteostasis. Our findings raise the intriguing possibility that HSF-1, SKN-1 and DAF-16 function in a coordinated and sequential manner to promote healthy aging.

HSF-1 displays nuclear stress body formation in multiple tissues in Caenorhabditis elegans upon stress and following the transition to adulthood.

The transcription factor heat shock factor-1 (HSF-1) regulates the heat shock response (HSR), a cytoprotective response induced by proteotoxic stresses. Data from model organisms has shown that HSF-1 also has non-stress biological roles, including roles in the regulation of development and longevity. To better study HSF-1 function, we created a C. elegans strain containing HSF-1 tagged with GFP at its endogenous locus utilizing CRISPR/Cas9-guided transgenesis. We show that the HSF-1::GFP CRISPR worm strain behaves similarly to wildtype worms in response to heat and other stresses, and in other physiological processes. HSF-1 was expressed in all tissues assayed. Immediately following the initiation of reproduction, HSF-1 formed nuclear stress bodies, a hallmark of activation, throughout the germline. Upon the transition to adulthood, of HSF-1 nuclear stress bodies appeared in most somatic cells. Genetic loss of the germline suppressed nuclear stress body formation with age, suggesting that the germline influences HSF-1 activity. Interestingly, we found that various neurons did not form nuclear stress bodies after transitioning to adulthood. Therefore, the formation of HSF-1 nuclear stress bodies upon the transition to adulthood does not occur in a synchronous manner in all cell types. In sum, these studies enhance our knowledge of the expression and activity of the aging and proteostasis factor HSF-1 in a tissue-specific manner with age.

Pan-Cancer Analysis of the Prognostic and Immunological Role of HSF1: A Potential Target for Survival and Immunotherapy.

Emerging evidence revealed the significant roles of heat shock factor 1 (HSF1) in cancer initiation, development, and progression, but there is no pan-cancer analysis of HSF1. The present study first comprehensively investigated the expression profiles and prognostic significance of HSF1 and the relationship of HSF1 with clinicopathological parameters and immune cell infiltration using bioinformatic techniques. HSF1 is significantly upregulated in various common cancers, and it is associated with prognosis. Pan-cancer Cox regression analysis indicated that the high expression of HSF1 was associated with poor overall survival (OS), disease-specific survival (DSS), and progression-free interval (PFI) in cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), head and neck squamous cell carcinoma (HNSC), and kidney renal papillary cell carcinoma (KIRP) patients. The methylation of HSF1 DNA was decreased in most cancers and negatively correlated with the HSF1 expression. Increased phosphorylation of S303, S307, and S363 in HSF1 was observed in some cancers. HSF1 remarkably correlated with the levels of infiltrating cells and immune checkpoint genes. Our pan-cancer analysis provides a deep understanding of the functions of HSF1 in oncogenesis and metastasis in different cancers.

Detailed protocol for optimised expression and purification of functional monomeric human Heat Shock Factor 1

Heat Shock Factor 1 (HSF1) is the master regulator of the heat shock response, a universal survival mechanism throughout eukaryotic species used to buffer potentially lethal proteotoxic conditions. HSF1's function in vivo is regulated by several factors, including post translational modifications and elevated temperatures, whereupon it forms trimers to bind with heat shock elements in DNA. Unsurprisingly, HSF1 is also extremely sensitive to elevated temperatures in vitro, which poses specific technical challenges when producing HSF1 using a recombinant expression system. Although there are several useful publications which outline steps taken for HSF1 expression and purification, studies that describe specific strategies and detailed protocols to overcome HSF1 trimerisation and degradation are currently lacking. Herein, we have reported our detailed experimental protocol for the expression and purification of monomeric human HSF1 (HsHSF1) as a major species. We also propose a refined method of inducing HsHSF1 activation in vitro, that we consider more accurately mimics HsHSF1 activation in vivo and is therefore more physiologically relevant.

Hop depletion reduces HSF1 levels and activity and coincides with reduced stress resilience

Heat-shock factor 1 (HSF1) regulates the transcriptional response to stress and controls expression of molecular chaperones required for cell survival. Here we report that HSF1 is regulated by the abundance of the Hsp70-Hsp90 organizing protein (Hop/STIP1). HSF1 levels were significantly reduced in Hop-depleted HEK293T cells. HSF1 transcriptional activity at the Hsp70 promoter, and binding of a biotinylated HSE oligonucleotide under both basal and heat-shock conditions were significantly reduced. Hop-depleted HEK293T cells were more sensitive to the HSF1 inhibitor KRIBB11 and showed reduced short-term proliferation, and reduced long-term survival under basal and heat-shock conditions. HSF1 nuclear localization was reduced in response to heat-shock and the nuclear staining pattern in Hop-depleted cells was punctate. Taken together, these data suggest that Hop regulates HSF1 function under both basal and stress conditions through a mechanism involving changes in levels, activity and subcellular localization, and coincides with reduced cellular fitness.

The Multifaceted Role of HSF1 in Tumorigenesis.

Heat Shock Factor 1 (HSF1), the master transcriptional regulator of the heat shock response (HSR), was first cloned more than 30years ago. Most early research interrogating the role that HSF1 plays in biology focused on its cytoprotective functions, as a factor that promotes the survival of organisms by protecting against the proteotoxicity associated with neurodegeneration and other pathological conditions. However, recent studies have revealed a deleterious role of HSF1, as a factor that is co-opted by cancer cells to promote their own survival to the detriment of the organism. In cancer, HSF1 operates in a multifaceted manner to promote oncogenic transformation, proliferation, metastatic dissemination, and anti-cancer drug resistance. Here we review our current understanding of HSF1 activation and function in malignant progression and discuss the potential for HSF1 inhibition as a novel anticancer strategy. Collectively, this ever-growing body of work points to a prominent role of HSF1 in nearly every aspect of carcinogenesis.

HSF1 as a Cancer Biomarker and Therapeutic Target.

Heat shock factor 1 (HSF1) was discovered in 1984 as the master regulator of the heat shock response. In this classical role, HSF1 is activated following cellular stresses such as heat shock that ultimately lead to HSF1-mediated expression of heat shock proteins to protect the proteome and survive these acute stresses. However, it is now becoming clear that HSF1 also plays a significant role in several diseases, perhaps none more prominent than cancer. HSF1 appears to have a pleiotropic role in cancer by supporting multiple facets of malignancy including migration, invasion, proliferation, and cancer cell metabolism among others. Because of these functions, and others, of HSF1, it has been investigated as a biomarker for patient outcomes in multiple cancer types. HSF1 expression alone was predictive for patient outcomes in multiple cancer types but in other instances, markers for HSF1 activity were more predictive. Clearly, further work is needed to tease out which markers are most representative of the tumor promoting effects of HSF1. Additionally, there have been several attempts at developing small molecule inhibitors to reduce HSF1 activity. All of these HSF1 inhibitors are still in preclinical models but have shown varying levels of efficacy at suppressing tumor growth. The growth of research related to HSF1 in cancer has been enormous over the last decade with many new functions of HSF1 discovered along the way. In order for these discoveries to reach clinical impact, further development of HSF1 as a biomarker or therapeutic target needs to be continued.

Heat shock factor 1 protects germ cell proliferation during early ovarian differentiation in medaka

The heat shock response is important for the viability of all living organisms. It involves the induction of heat shock proteins whose expression is mainly regulated by heat shock factor 1 (HSF1). Medaka (Oryzias latipes) is a teleost fish with an XX/XY sex determination system. High water temperature (HT) inhibits the female-type proliferation of germ cells and induces the masculinisation of XX medaka in some cases during gonadal sex differentiation. Here, we investigated the roles of HSF1 on the proliferation of germ cells using HSF1 knockout medaka. Loss of HSF1 function under HT completely inhibited the female-type proliferation of germ cells, induced the expression of the anti-Mullerian hormone receptor type 2 (amhr2) and apoptosis-related genes, and suppressed that of the dead end (dnd) and heat shock protein-related genes. Moreover, the loss of HSF1 and AMHR2 function under HT recovered female-type proliferation in germ cells, while loss of HSF1 function under HT induced gonadal somatic cell apoptosis during early sex differentiation. These results strongly suggest that HSF1 under the HT protects the female-type proliferation of germ cells by inhibiting amhr2 expression in gonadal somatic cells. These findings provide new insights into the molecular mechanisms underlying environmental sex determination.

Heat shock factor 1 in cancer-associated fibroblasts is a potential prognostic factor and drives progression of oral squamous cell carcinoma.

Heat shock factor 1 (HSF1) is highly expressed in various malignancies and is a potential modulator of tumor progression. Emerging evidence suggests that HSF1 activation in stromal cells is closely related to poor patient prognosis. However, the role of HSF1 in oral squamous cell carcinoma (OSCC) remains elusive. We aimed to investigate the function of HSF1 in cancer‐associated fibroblasts (CAFs) of the tumor microenvironment (TME) and in tumor development. In the present study, we found that HSF1 was highly expressed in both CAFs and tumor cells, and was significantly correlated with poor prognosis and overall survival. Moreover, HSF1 overexpression in CAFs resulted in a fibroblast‐like phenotype of Cal27 cells, induced epithelial‐mesenchymal transition (EMT), and promoted proliferation, migration and invasion in Cal27 cells. HSF1 knockdown attenuated features of CAFs and reduced EMT, proliferation, migration and invasion in Cal27 cells. Furthermore, HSF1 in CAFs promoted tumor growth in nude mice. Taken together, these data suggest that HSF1 expression in CAFs drive OSCC progression, and could serve as an independent prognostic marker of patients with OSCC. Thus, HSF1 is a potent mediator of OSCC malignancy.

Heat Shock Factor 1 Inhibits the Expression of Suppressor of Cytokine Signaling 3 in Cerulein-Induced Acute Pancreatitis.

Heat shock factor 1 (HSF1), an important transcriptional molecule in the heat shock process, can regulate the expression of a lot of inflammatory mediators in addition to heat shock proteins. This study evaluated the inhibitive function of HSF1 on the expression of suppressor of cytokine signaling 3 in cerulein-induced acute pancreatitis. After HSF1 mice, HSF1 mice, and AR42J cells were treated with cerulein, histopathological score, expression of SOCS3 mRNA, and protein levels were analyzed by using RT-PCR, quantitative real-time RT-PCR, and western blotting, respectively. DNA binding and transcription activity of HSF1 to the SOCS3 promoter were detected by chromatin immunoprecipitation and luciferase reporter assays. The histopathological scores of the pancreas decreased significantly in the cerulein-induced HSF1 mice compared with the cerulein-induced HSF1 mice. SOCS3 mRNA and protein level decreased in the pancreas of the unstimulated HSF1 and HSF1 mice, whereas increased in the pancreas of the cerulein-induced HSF1 and HSF1 mice, with higher in the pancreas of cerulein-induced HSF1mice. In the pcDNA3.1-transfected AR42J cells, SOCS3 protein decreased and was upregulated after the cerulein stimulation, whereas HSF1 overexpression inhibited the upregulation. In the scramble-transfected AR42J cells, SOCS3 protein decreased and was upregulated after the cerulein stimulation, whereas HSF1-RNAi further promoted the upregulation. EMSA and chromatin immunoprecipition showed that HSF1 could directly bind to SOCS3 promoter region. Reporter assays showed that HSF1 could inhibit the transcriptional activity on SOCS3 promoter. HSF1 can protect AR42J cells from cerulein-induced pancreatitis through inhibiting the expression of SOCS3.

The Role of HSF2 in Human Malignancies

Heat‐Shock Factor 1 (HSF1) is the master transcriptional regulator of the heat shock response (HSR), an ancient survival mechanism that is conserved from yeast to humans. In the HSR, proteotoxic stress activates HSF1 to induce expression of heat shock protein genes, including HSP70 and HSP90, to maintain protein homeostasis. In cancer, HSF1 is highly expressed, and drives a transcriptional program distinct from the HSR. Genes in the HSF1 cancer program are involved in a broad range of cellular activities that include protein folding, but also include cell proliferation, cell adhesion, apoptosis, and energy metabolism. To better understand HSF1 function in cancer cells, we used a multifaceted strategy to identify HSF1‐interacting proteins. We found that Heat‐Shock Factor 2 (HSF2), an HSF1 paralog, was among the strongest HSF1 interacting proteins. However, the role of HSF2 in cancer cells and its influence on HSF1 activity is not well understood. We performed RNA‐Seq and ChIP‐Seq to identify the HSF2 cancer program. We used CRISPR‐Cas9 mediated genome editing to knock out HSF2 and HSF1 in a diverse panel of common human cancer cell lines. We found that HSF2 and HSF1 exhibit distinctive effects on transcription, despite sharing a high degree of genomic co‐occupancy. These transcriptional effects were affected by the type of cancer cell line. Lastly, we characterized the HSF2 cancer phenotype in vitro and in vivo. In vitro, we found that the loss of HSF2 affects cell migration and invasion. In vivo, loss of HSF2 affects tumor formation and growth. Our findings suggest a complex interplay between HSF1 and HSF2 that ultimately impacts malignant progression.Support or Funding InformationNIH/NCI R00 CA175293‐03, Kimmel Scholars Program SKF‐16‐135, Lynn Sage FoundationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Heat Shock Factor 1 Predicts Poor Prognosis of Gastric Cancer.

PurposeHeat shock factor 1 (HSF1) is a key regulator of the heat shock response and plays an important role in various cancers. However, the role of HSF1 in gastric cancer is still unknown. The present study evaluated the function of HSF1 and related mechanisms in gastric cancer.Materials and MethodsThe expression levels of HSF1 in normal and gastric cancer tissues were compared using cDNA microarray data from the NCBI Gene Expression Omnibus (GEO) dataset. The proliferation of gastric cancer cells was analyzed using the WST assay. Transwell migration and invasion assays were used to evaluate the migration and invasion abilities of gastric cancer cells. Protein levels of HSF1 were analyzed using immunohistochemical staining of tissue microarrays from patients with gastric cancer.ResultsHSF1 expression was significantly higher in gastric cancer tissue than in normal tissue. Knockdown of HSF1 reduced the proliferation, migration, and invasion of gastric cancer cells, while HSF1 overexpression promoted proliferation, migration, and invasion of gastric cancer cells. Furthermore, HSF1 promoted the proliferation of gastric cancer cells in vivo. In Kaplan-Meier analysis, high levels of HSF1 were associated with poor prognosis for patients with gastric cancer (p=0.028).ConclusionHSF1 may be closely associated with the proliferation and motility of gastric cancer cells and poor prognosis of patients with gastric cancer. Accordingly, HSF1 could serve as a prognostic marker for gastric cancer.