Heat shock factor 1 in protein homeostasis and oncogenic signal integration

Targeting the heat shock response induced by modulated electro-hyperthermia (mEHT) in cancer

The Heat Shock Response (HSR) is a cellular stress reaction crucial for cell survival against stressors, including heat, in both healthy and cancer cells. Modulated electro-hyperthermia (mEHT) is an emerging non-invasive cancer therapy utilizing electromagnetic fields to selectively target cancer cells via temperature-dependent and independent mechanisms. However, mEHT triggers HSR in treated cells. Despite demonstrated efficacy in cancer treatment, understanding the underlying molecular mechanisms for improved therapeutic outcomes remains a focus. This review examines the HSR induced by mEHT in cancer cells, discussing potential strategies to modulate it for enhanced tumor-killing effects. Approaches such as HSF1 gene-knockdown and small molecule inhibitors like KRIBB11 are explored to downregulate the HSR and augment tumor destruction. We emphasize the impact of HSR inhibition on cancer cell viability, mEHT sensitivity, and potential synergistic effects, addressing challenges and future directions. This understanding offers opportunities for optimizing treatment strategies and advancing precision medicine in cancer therapy.

RING induces cell cycle arrest and apoptosis in human breast cancer cells by regulating the HSF1/MT2A axis

It was reported that lowly expressed RING1 indicates poor prognosis in breast cancer (BC) patients, while the mechanism by which RING1 is involved in BC progression is not fully understood. Here, we found that RING1 was lowly expressed in BC tissues and cells than in normal mammary tissues and epithelial cells. Overexpression of RING1 suppressed the cell proliferative and colony formation abilities, and facilitated cell cycle arrest and cell apoptosis in BC cells (T47D and MCF-7 cells). Mechanistically, as an ubiquitin ligase, RING1 bound to HSF1 and induced its proteasome-dependent degradation. HSF1 could bind to the promoter region of MT2A to promote the transcriptional level of MT2A. While RING1 overexpression hindered the transcriptional activation of MT2A induced by HSF1. Moreover, ectopic expression of MT2A reversed the inhibitory effect of RING1 on cell proliferation and clonogenesis, and antagonized the promotion effect of RING1 on cell cycle arrest and apoptosis in BC cells. Additionally, T47D cells infected with or without lentivirus-mediated RING1 overexpression vector (LV-RING1) were injected subcutaneously into the right back of nude mice to evaluate tumorigenicity. And overexpression of RING1 impeded the growth of BC xenografts in mice. In conclusion, RING1 suppressed the transcriptional activation of MT2A induced by HSF1 by facilitating the ubiquitination degradation of HSF1, resulting in cell cycle arrest and apoptosis in BC cells.

Targeting N7-methylguanosine tRNA modification blocks hepatocellular carcinoma metastasis after insufficient radiofrequency ablation

Radiofrequency heat ablation is an ideal radical treatment for hepatocellular carcinoma (HCC). However, insufficient radiofrequency ablation (IRFA) could lead to high recurrence of HCC. N7-methylguanosine (m7G) on tRNAs, an evolutionally conservative modification in mammals and yeast, modulates heat stress responses and tumor progression, while its function in HCC recurrence after IRFA remains unknown. Here, we found that IRFA significantly upregulates the level of m7G tRNA modification and its methyltransferase complex components METTL1/WDR4 in multiple systems including HCC patient-derived xenograft (PDX) mouse, patients' HCC tissues, sublethal-heat-treated models of HCC cell lines, and organoids. Functionally, gain-/loss-of-function assays showed that METTL1-mediated m7G tRNA modification promotes HCC metastasis under sublethal heat exposure both in vitro and in vivo. Mechanistically, we found that METTL1 and m7G tRNA modification enhance the translation of SLUG/SNAIL in a codon frequency-dependent manner under sublethal heat stress. Overexpression of SLUG/SNAIL rescued the malignant potency of METTL1 knockdown HCC cells after sublethal heat exposure. Our study uncovers the key functions of m7G tRNA modification in heat stress responses and HCC recurrence after IRFA, providing molecular basis for targeting METTL1-m7G-SLUG/SNAIL axis to prevent HCC metastasis after radiofrequency heat ablation treatment.

NRF2 in Cancer: Cross-Talk with Oncogenic Pathways and Involvement in Gammaherpesvirus-Driven Carcinogenesis

Expanding knowledge of the molecular mechanisms at the basis of tumor development, especially the cross-talk between oncogenic pathways, will possibly lead to better tailoring of anticancer therapies. Nuclear factor erythroid 2-related factor 2 (NRF2) plays a central role in cancer progression, not only because of its antioxidant activity but also because it establishes cross-talk with several oncogenic pathways, including Heat Shock Factor1 (HSF1), mammalian target of rapamycin (mTOR), and mutant (mut) p53. Moreover, the involvement of NRF2 in gammaherpesvirus-driven carcinogenesis is particularly interesting. These viruses indeed hijack the NRF2 pathway to sustain the survival of tumor cells in which they establish a latent infection and to avoid a too-high increase of reactive oxygen species (ROS) when these cancer cells undergo treatments that induce viral replication. Interestingly, NRF2 activation may prevent gammaherpesvirus-driven oncogenic transformation, highlighting how manipulating the NRF2 pathway in the different phases of gammaherpesvirus-mediated carcinogenesis may lead to different outcomes. This review will highlight the mechanistic interplay between NRF2 and some oncogenic pathways and its involvement in gammaherpesviruses biology to recapitulate published evidence useful for potential application in cancer therapy.

Deregulation of HSF1-mediated endoplasmic reticulum unfolded protein response promotes cisplatin resistance in lung cancer cells

Mild hypothermia can induce apoptotic cell death in many cancer cells, but the underlying mechanisms remain unclear. In a genetic screen in Caenorhabditis elegans, we found that impaired endoplasmic reticulum unfolded protein response (UPR^ER ) increased animal survival after cold shock. Consistently, in normal human lung cells, decreasing culture temperature from 37 to 30 °C activated UPR^ER and promoted cell death. However, lung adenocarcinoma cells were impaired in UPR^ER induction and resistant to hypothermia-induced cell death. Mechanistically, hypothermic stress increased HSF1 levels, which in turn activated UPR^ER to promote apoptotic cell death. HSF1 expression was associated with UPR^ER genes in normal tissues, but such association was lost in many cancers, especially lung adenocarcinoma. Activating UPR^ER enhanced the cytotoxicity of chemotherapy drugs cisplatin preferentially in cancer cells. Consistently, cancer patients with higher UPR^ER expression had generally better prognosis. Together, our study on hypothermia has led to the discovery of HSF1-UPR^ER in the regulation of drug sensitivity in lung cancer cells, providing novel thoughts on developing new strategies against chemoresistance.

p53N236S Activates Autophagy in Response to Hypoxic Stress Induced by DFO

Hypoxia can lead to stabilization of the tumor suppressor gene p53 and cell death. However, p53 mutations could promote cell survival in a hypoxic environment. In this study, we found that p53N236S (p53N239S in humans, hereinafter referred to as p53S) mutant mouse embryonic fibroblasts (MEFs) resistant to deferoxamine (DFO) mimic a hypoxic environment. Further, Western blot and flow cytometry showed reduced apoptosis in p53S/S cells compared to WT after DFO treatment, suggesting an antiapoptosis function of p53S mutation in response to hypoxia-mimetic DFO. Instead, p53S/S cells underwent autophagy in response to hypoxia stress presumably through inhibition of the AKT/mTOR pathway, and this process was coupled with nuclear translocation of p53S protein. To understand the relationship between autophagy and apoptosis in p53S/S cells in response to hypoxia, the autophagic inhibitor 3-MA was used to treat both WT and p53S/S cells after DFO exposure. Both apoptotic signaling and cell death were enhanced by autophagy inhibition in p53S/S cells. In addition, the mitochondrial membrane potential (MMP) and the ROS level results indicated that p53S might initiate mitophagy to clear up damaged mitochondria in response to hypoxic stress, thus increasing the proportion of intact mitochondria and maintaining cell survival. In conclusion, the p53S mutant activates autophagy instead of inducing an apoptotic process in response to hypoxia stress to protect cells from death.

Curcumin and Ethanol Effects in Trembler-J Schwann Cell Culture

Charcot-Marie-Tooth (CMT) syndrome is the most common progressive human motor and sensory peripheral neuropathy. CMT type 1E is a demyelinating neuropathy affecting Schwann cells due to peripheral-myelin-protein-22 (PMP22) mutations, modelized by Trembler-J mice. Curcumin, a natural polyphenol compound obtained from turmeric (Curcuma longa), exhibits dose- and time-varying antitumor, antioxidant and neuroprotective properties, however, the neurotherapeutic actions of curcumin remain elusive. Here, we propose curcumin as a possible natural treatment capable of enhancing cellular detoxification mechanisms, resulting in an improvement of the neurodegenerative Trembler-J phenotype. Using a refined method for obtaining enriched Schwann cell cultures, we evaluated the neurotherapeutic action of low dose curcumin treatment on the PMP22 expression, and on the chaperones and autophagy/mammalian target of rapamycin (mTOR) pathways in Trembler-J and wild-type genotypes. In wild-type Schwann cells, the action of curcumin resulted in strong stimulation of the chaperone and macroautophagy pathway, whereas the modulation of ribophagy showed a mild effect. However, despite the promising neuroprotective effects for the treatment of neurological diseases, we demonstrate that the action of curcumin in Trembler-J Schwann cells could be impaired due to the irreversible impact of ethanol used as a common curcumin vehicle necessary for administration. These results contribute to expanding our still limited understanding of PMP22 biology in neurobiology and expose the intrinsic lability of the neurodegenerative Trembler-J genotype. Furthermore, they unravel interesting physiological mechanisms of cellular resilience relevant to the pharmacological treatment of the neurodegenerative Tremble J phenotype with curcumin and ethanol. We conclude that the analysis of the effects of the vehicle itself is an essential and inescapable step to comprehensibly assess the effects and full potential of curcumin treatment for therapeutic purposes.

Deciphering the Role of Pyrvinium Pamoate in the Generation of Integrated Stress Response and Modulation of Mitochondrial Function in Myeloid Leukemia Cells through Transcriptome Analysis

Pyrvinium pamoate, a widely-used anthelmintic agent, reportedly exhibits significant anti-tumor effects in several cancers. However, the efficacy and mechanisms of pyrvinium against myeloid leukemia remain unclear. The growth inhibitory effects of pyrvinium were tested in human AML cell lines. Transcriptome analysis of Molm13 myeloid leukemia cells suggested that pyrvinium pamoate could trigger an unfolded protein response (UPR)-like pathway, including responses to extracellular stimulus [p-value = 2.78 × 10^-6] and to endoplasmic reticulum stress [p-value = 8.67 × 10^-7], as well as elicit metabolic reprogramming, including sulfur compound catabolic processes [p-value = 2.58 × 10^-8], and responses to a redox state [p-value = 5.80 × 10^-5]; on the other hand, it could elicit a pyrvinium blunted protein folding function, including protein folding [p-value = 2.10 × 10^-8] and an ATP metabolic process [p-value = 3.95 × 10^-4]. Subsequently, pyrvinium was verified to induce an integrated stress response (ISR), demonstrated by activation of the eIF2α-ATF4 pathway and inhibition of mTORC1 signaling, in a dose- and time-dependent manner. Additionally, pyrvinium could co-localize with mitochondria and then decrease the mitochondrial basal oxidative consumption rate, ultimately dysregulating the mitochondrial function. Similar effects were observed in cabozantinib-resistant Molm13-XR cell lines. Furthermore, pyrvinium treatment retarded Molm13 and Molm13-XR xenograft tumor growth. Thus, we concluded that pyrvinium exerts anti-tumor activity, at least, via the modulation of the mitochondrial function and by triggering ISR.

The proteostasis guardian HSF1 directs the transcription of its paralog and interactor HSF2 during proteasome dysfunction

Protein homeostasis is essential for life in eukaryotes. Organisms respond to proteotoxic stress by activating heat shock transcription factors (HSFs), which play important roles in cytoprotection, longevity and development. Of six human HSFs, HSF1 acts as a proteostasis guardian regulating stress-induced transcriptional responses, whereas HSF2 has a critical role in development, in particular of brain and reproductive organs. Unlike HSF1, that is a stable protein constitutively expressed, HSF2 is a labile protein and its expression varies in different tissues; however, the mechanisms regulating HSF2 expression remain poorly understood. Herein we demonstrate that the proteasome inhibitor anticancer drug bortezomib (Velcade), at clinically relevant concentrations, triggers de novo HSF2 mRNA transcription in different types of cancers via HSF1 activation. Similar results were obtained with next-generation proteasome inhibitors ixazomib and carfilzomib, indicating that induction of HSF2 expression is a general response to proteasome dysfunction. HSF2-promoter analysis, electrophoretic mobility shift assays, and chromatin immunoprecipitation studies unexpectedly revealed that HSF1 is recruited to a heat shock element located at 1.397 bp upstream from the transcription start site in the HSF2-promoter. More importantly, we found that HSF1 is critical for HSF2 gene transcription during proteasome dysfunction, representing an interesting example of transcription factor involved in controlling the expression of members of the same family. Moreover, bortezomib-induced HSF2 was found to localize in the nucleus, interact with HSF1, and participate in bortezomib-mediated control of cancer cell migration. The results shed light on HSF2-expression regulation, revealing a novel level of HSF1/HSF2 interplay that may lead to advances in pharmacological modulation of these fundamental transcription factors.

Emerging roles of HSF1 in cancer: Cellular and molecular episodes

Heat shock factor 1 (HSF1) systematically guards proteome stability and proteostasis by regulating the expression of heat shock protein (HSP), thus rendering cancer cells addicted to HSF1. The non-canonical transcriptional programme driven by HSF1, which is distinct from the heat shock response (HSR), plays an indispensable role in the initiation, promotion and progression of cancer. Therefore, HSF1 is widely exploited as a potential therapeutic target in a broad spectrum of cancers. Various molecules and signals in the cell jointly regulate the activation and attenuation of HSF1. The high-level expression of HSF1 in tumours and its relationship with patient prognosis imply that HSF1 can be used as a biomarker for patient prognosis and a target for cancer treatment. In this review, we discuss the newly identified mechanisms of HSF1 activation and regulation, the diverse functions of HSF1 in tumourigenesis, and the feasibility of using HSF1 as a prognostic marker. Disrupting cancer cell proteostasis by targeting HSF1 represents a novel anti-cancer therapeutic strategy.

Cold-hearted: A case for cold stress in cancer risk

A negative correlation exists between environmental temperature and cancer risk based on both epidemiological and statistical analyses. Previously, cold stress was reported to be an effective cause of tumorigenesis. Several studies have demonstrated that cold temperature serves as a potential risk factor in cancer development. Most recently, a link was demonstrated between the effects of extreme cold climate on cancer incidence, pinpointing its impact on tumour suppressor genes by causing mutation. The underlying mechanism behind cold stress and its association with tumorigenesis is not well understood. Hence, this review intends to shed light on the role of associated factors, genetic and/or non-genetic, which are modulated by cold temperature, and eventually influence tumorigenic potential. While scrutinizing the effect of cold exposure on the body, the expression of certain genes, e.g. uncoupled proteins and heat-shock proteins, were elevated. Biological chemicals such as norepinephrine, thyroxine, and cholesterol were also elevated. Brown adipose tissue, which plays an essential role in thermogenesis, displayed enhanced activity upon cold exposure. Adaptive measures are utilized by the body to tolerate the cold, and in doing so, invites both epigenetic and genetic changes. Unknowingly, these adaptive strategies give rise to a lethal outcome i.e., genesis of cancer. Concisely, this review attempts to draw a link between cold stress, genetic and epigenetic changes, and tumorigenesis and aspires to ascertain the mechanism behind cold temperature-mediated cancer risk.

Heat Shock Proteins and Ovarian Cancer: Important Roles and Therapeutic Opportunities

Ovarian cancer is a serious cause of death in gynecological oncology. Delayed diagnosis and poor survival rates associated with late stages of the disease are major obstacles against treatment efforts. Heat shock proteins (HSPs) are stress responsive molecules known to be crucial in many cancer types including ovarian cancer. Clusterin (CLU), a unique chaperone protein with analogous oncogenic criteria to HSPs, has also been proven to confer resistance to anti-cancer drugs. Indeed, these chaperone molecules have been implicated in diagnosis, prognosis, metastasis and aggressiveness of various cancers. However, relative to other cancers, there is limited body of knowledge about the molecular roles of these chaperones in ovarian cancer. In the current review, we shed light on the diverse roles of HSPs as well as related chaperone proteins like CLU in the pathogenesis of ovarian cancer and elucidate their potential as effective drug targets.

Phosphorylation of HSF1 by PIM2 Induces PD-L1 Expression and Promotes Tumor Growth in Breast Cancer

Heat shock transcription factor 1 (HSF1) is the master regulator of the proteotoxic stress response, which plays a key role in breast cancer tumorigenesis. However, the mechanisms underlying regulation of HSF1 protein stability are still unclear. Here, we show that HSF1 protein stability is regulated by PIM2-mediated phosphorylation of HSF1 at Thr120, which disrupts the binding of HSF1 to the E3 ubiquitin ligase FBXW7. In addition, HSF1 Thr120 phosphorylation promoted proteostasis and carboplatin-induced autophagy. Interestingly, HSF1 Thr120 phosphorylation induced HSF1 binding to the PD-L1 promoter and enhanced PD-L1 expression. Furthermore, HSF1 Thr120 phosphorylation promoted breast cancer tumorigenesis in vitro and in vivo. PIM2, pThr120-HSF1, and PD-L1 expression positively correlated with each other in breast cancer tissues. Collectively, these findings identify PIM2-mediated HSF1 phosphorylation at Thr120 as an essential mechanism that regulates breast tumor growth and potential therapeutic target for breast cancer. SIGNIFICANCE: These findings identify heat shock transcription factor 1 as a new substrate for PIM2 kinase and establish its role in breast tumor progression.

Autophagy manipulation as a strategy for efficient anticancer therapies: possible consequences

Autophagy is a catabolic process whose activation may help cancer cells to adapt to cellular stress although, in some instances, it can induce cell death. Autophagy stimulation or inhibition has been considered an opportunity to treat cancer, especially in combination with anticancer therapies, although autophagy manipulation may be viewed as controversial. Thus, whether to induce or to inhibit autophagy may be the best option in the different cancer patients is still matter of debate. Her we will recapitulate the possible advantages or disadvantages of manipulating autophagy in cancer, not only with the aim to obtain cancer cell death and disable oncogenes, but also to evaluate its interplay with the immune response which is fundamental for the success of anticancer therapies.

Mutant p53 and Cellular Stress Pathways: A Criminal Alliance That Promotes Cancer Progression

The capability of cancer cells to manage stress induced by hypoxia, nutrient shortage, acidosis, redox imbalance, loss of calcium homeostasis and exposure to drugs is a key factor to ensure cancer survival and chemoresistance. Among the protective mechanisms utilized by cancer cells to cope with stress a pivotal role is played by the activation of heat shock proteins (HSP) response, anti-oxidant response induced by nuclear factor erythroid 2-related factor 2 (NRF2), the hypoxia-inducible factor-1 (HIF-1), the unfolded protein response (UPR) and autophagy, cellular processes strictly interconnected. However, depending on the type, intensity or duration of cellular stress, the balance between pro-survival and pro-death pathways may change, and cell survival may be shifted into cell death. Mutations of p53 (mutp53), occurring in more than 50% of human cancers, may confer oncogenic gain-of-function (GOF) to the protein, mainly due to its stabilization and interaction with the above reported cellular pathways that help cancer cells to adapt to stress. This review will focus on the interplay of mutp53 with HSPs, NRF2, UPR, and autophagy and discuss how the manipulation of these interconnected processes may tip the balance towards cell death or survival, particularly in response to therapies.

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.

Recent advances in searching c-Myc transcriptional cofactors during tumorigenesis

Background

The mechanism by which c-Myc exerts its oncogenic functions is not completely clear and different hypotheses are still under investigation. The knowledge of the capacity of c-Myc to bind exclusively E-box sequences determined the discrepancy between, on the one hand, genomic studies showing the binding of c-Myc to all active promoters and, on the other hand, the evidence that only 60% or less of the binding sites have E-box sequences.

Main body

In this review, we provide support to the hypothesis that the cooperation of c-Myc with transcriptional cofactors mediates c-Myc-induced cellular functions. We produce evidence that recently identified cofactors are involved in c-Myc control of survival mechanisms of cancer cells.

Conclusion

The identification of new c-Myc cofactors could favor the development of therapeutic strategies able to compensate the difficulty of targeting c-Myc.

Role of heat shock factor 1 expression in the microenvironment of intrahepatic cholangiocarcinomas

BACKGROUND AND AIM

Heat shock factor 1 (HSF1), a master regulator of heat shock response, has been shown to play a multifaceted role in cancer progression. However, the clinical significance and biological effect of HSF1 expression in intrahepatic cholangiocarcinoma (IHCC) remain unknown.

METHODS

Forty-nine patients with IHCC who underwent hepatic resection were enrolled in this study. HSF1 expression in tumor tissue was determined by immunohistochemistry, and patients were divided into two groups, those with high (n = 20) and low (n = 29) HSF1 expression. Clinicopathological factors including prognosis were compared in these two groups.

RESULTS

HSF1 expression was significantly higher in tumors than in normal tissue. The overall survival rate was significantly lower in patients with high than low HSF1. Multivariate analysis showed that high HSF1 expression was a factor independently prognostic of patient survival.

CONCLUSION

High HSF1 expression in tumor tissues may be a prognostic biomarker in patients with IHCC.

Genetic polymorphism and expression of HSF1 gene is significantly associated with breast cancer in Saudi females

The transcription factor, heat shock factor 1 (HSF1), influences the expression of heat shock proteins as well as other activities like the induction of tumor suppressor genes, signal transduction pathway, and glucose metabolism. We hypothesized that single nucleotide polymorphisms (SNPs) in HSF1 gene might affect its expression or function which might have an influence on the development of breast cancer. The study group included 242 individuals (146 breast cancer patients and 96 healthy controls). From the cancer patients, genomic DNA was extracted from 96 blood samples and 50 Formalin-Fixed Paraffin Embedded (FFPE) tissues, while from the controls DNA were extracted from blood only. Genotype was carried out for four SNPs in the HSF1 gene (rs78202224, rs35253356, rs4977219 and rs34404564) using Taqman genotyping assay method. The HSF1 expression was investigated using immunohistochemistry on FFPE tissues (cancer tissue and adjacent normal tissue). The SNP rs78202224 (G>T) was significantly associated with increased risk of breast cancer. The combined TT + GT genotype (OR: 6.91; p: 0.035) and the T allele showed high risk (OR: 5.81; p:0.0085) for breast cancer development. The SNP rs34404564 (A>G) had a protective effect against the development of breast cancer. The genotype AG (OR: 0.41; p = 0.0059) and GG+AG (OR: 0.52; p: 0.026) occurred at a significantly lower frequency in the breast cancer patients compared to the frequency in healthy controls. No significant relationship was identified between either rs35253356 (A>G) or rs4977219 (A>C) and breast cancer in Saudi. The HSF1 protein expression was higher in all invasive and in situ breast carcinoma compared to the normal tissue. A stronger positive staining for HSF1 was found in the nucleus compared to the cytoplasm. Our results show that HSF1 gene expression is elevated in breast cancer tissue and two of the studied SNPs correlate significantly with cancer development.

X66, a novel N-terminal heat shock protein 90 inhibitor, exerts antitumor effects without induction of heat shock response

Heat shock protein 90 (HSP90) is essential for cancer cells to assist the function of various oncoproteins, and it has been recognized as a promising target in cancer therapy. Although the HSP90 inhibitors in clinical trials have shown encouraging clinical efficacy, these agents induce heat shock response (HSR), which undermines their therapeutic effects. In this report, we detailed the pharmacologic properties of 4-(2-((1H-indol-3-yl)methylene)hydrazinyl)-N-(4-bromophenyl)-6-(3,5- dimethyl-1H -pyrazol-1-yl)-1,3,5-triazin-2-amine (X66), a novel and potent HSP90 inhibitor. X66 binds to the N-terminal domain in a different manner from the classic HSP90 inhibitors. Cellular study showed that X66 depleted HSP90 client proteins, resulted in cell cycle arrest and apoptosis, and inhibition of proliferation in cancer cell lines. X66 did not activate heat shock factor-1 (HSF-1) or stimulate transcription of HSPs. Moreover, the combination of X66 with HSP90 and proteasome inhibitors yielded synergistic cytotoxicity which was involved in X66-mediated abrogation of HSR through inhibition of HSF-1 activity. The intraperitoneal administration of X66 alone depleted client protein and inhibited tumor growth, and led to enhanced activity when combined with celastrol as compared to either agent alone in BT-474 xenograft model. Collectively, the HSP90 inhibitory action and the potent antitumor activity, with the anti-HSR action, promise X66 a novel HSP90-targeted agent, which merits further research and development.

Targeting protein quality control pathways in breast cancer

The efficient production, folding, and secretion of proteins is critical for cancer cell survival. However, cancer cells thrive under stress conditions that damage proteins, so many cancer cells overexpress molecular chaperones that facilitate protein folding and target misfolded proteins for degradation via the ubiquitin-proteasome or autophagy pathway. Stress response pathway induction is also important for cancer cell survival. Indeed, validated targets for anti-cancer treatments include molecular chaperones, components of the unfolded protein response, the ubiquitin-proteasome system, and autophagy. We will focus on links between breast cancer and these processes, as well as the development of drug resistance, relapse, and treatment.

Deregulated c-Myc requires a functional HSF1 for experimental and human hepatocarcinogenesis

Deregulated activity of the c-Myc protooncogene is a frequent molecular event underlying mouse and human hepatocarcinogenesis. Nonetheless, the mechanisms sustaining c-Myc oncogenic activity in liver cancer remain scarcely delineated. Recently, we showed that the mammalian target of rapamycin complex 1 (mTORC1) cascade is induced and necessary for c-Myc dependent liver tumor development and progression. Since the heat shock factor 1 (HSF1) transcription factor is a major positive regulator of mTORC1 in the cell, we investigated the functional interaction between HSF1 and c-Myc using in vitro and in vivo approaches. We found that ablation of HSF1 restrains the growth of c-Myc-derived mouse hepatocellular carcinoma (HCC) cell lines, where it induces downregulation of c-Myc levels. Conversely, silencing of c-Myc gene in human and mouse HCC cells led to downregulation of HSF1 expression. Most importantly, overexpression of a dominant negative form of HSF1 (HSF1dn) in the mouse liver via hydrodynamic gene delivery resulted in the complete inhibition of mouse hepatocarcinogenesis driven by overexpression of c-Myc. Altogether, the present results indicate that a functional HSF1 is necessary for c-Myc-driven hepatocarcinogenesis. Consequently, targeting HSF1 might represent a novel and effective therapeutic strategy for the treatment of HCC subsets with activated c-Myc signaling.

Targeting heat shock factor 1 as an antiviral strategy against dengue virus replication in vitro and in vivo

Fever onset is correlated with viremia in dengue virus (DENV) patients. Heat shock factor 1 (HSF1), a heat stress response host transcription factor, plays a crucial role in regulating multiple cellular functions, as well as the onset of infectious diseases. This study evaluated the role of HSF1 in DENV replication as a means of regulating DENV infection in vitro and in vivo. DENV infection activated HSF1 in both Ca²⁺ and protein kinase A-dependent manners. Inhibiting HSF1 effectively reduced DENV replication, not only in THP-1 cells but also in primary human monocytes. Activated HSF1 contributed to DENV replication by upregulating autophagy-related protein (Atg) 7, as autophagy is crucial for virus replication. Heat stress also activated HSF1, which in turn facilitated DENV replication. Activated HSF1, the increased Atg7, and autophagic induction were founded in the DENV-infected brains and pharmacologically inhibiting HSF1 reduced autophagy, viral protein expression, neuropathy, and mortality. These results provide new insight into HSF1 as a novel host factor for DENV infection through its role in facilitating autophagy-regulated viral replication in the brains.

Targeting HSF1 leads to an antitumor effect in human epithelial ovarian cancer

Late diagnosis and lack of specific therapeutic targets contribute to the low survival rate of patients with epithelial ovarian cancer (EOC), the most lethal gynecologic malignancy. Therefore, the screening of diagnostic markers and the identification of therapeutic targets are urgently required. Heat shock factor 1 (HSF1) has been demonstrated to be overexpressed in certain malignancies and to be involved in tumor initiation, development, transformation and metastasis. It is believed that HSF1 is a promising candidate for antitumor therapy. However, its expression pattern and function in ovarian cancer are far from being fully elucidated. Therefore, we examined the HSF1 expression in human EOC tissues, and evaluated its carcinogenesis-promoting activity in a xenograft tumor model. Examination of HSF1 expression in human EOC tissues was performed by immunohistochemical assay using ovarian tissue blots. Specific short hairpin RNA (shRNA) against HSF1 was employed to knockdown HSF1 in SKOV3 cells. Cell proliferative activity was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay; cell cycle distribution and apoptosis were determined by flow cytometric analysis. In normal ovarian tissues, HSF1 was barely detected, whereas, high expression of HSF1 was found in malignant EOC tissues, including serous, mucinous, endometrioid, and clear cell EOC tissues. Suppressed proliferative activity and intensified apoptosis were observed in HSF1-knockdown SKOV3 cells. In nude mouse xenografts, downregulation of HSF1 was found to cause reduced carinogenesis, indicating the antitumor effect induced by modulation of HSF1 against EOC. Our findings suggest that HSF1 may be considered as a potential candidate diagnostic marker of human EOC, and that modulation of HSF1 could be a promising therapeutic strategy against human EOC.

Inhibition of HSF1 suppresses the growth of hepatocarcinoma cell lines in vitro and AKT-driven hepatocarcinogenesis in mice

Upregulation of the heat shock transcription factor 1 (HSF1) has been described as a frequent event in many cancer types, but its oncogenic role in hepatocellular carcinoma (HCC) remains poorly delineated. In the present study, we assessed the function(s) of HSF1 in hepatocarcinogenesis via in vitro and in vivo approaches. In particular, we determined the importance of HSF1 on v-Akt murine thymoma viral oncogene homolog (AKT)-induced liver cancer development in mice. We found that knockdown of HSF1 activity via specific siRNA triggered growth restraint by suppressing cell proliferation and inducing massive cell apoptosis in human HCC cell lines. At the molecular level, HSF1 inhibition was accompanied by downregulation of the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) cascade and related metabolic pathways. Most importantly, overexpression of a dominant negative form of HSF1 (HSF1dn) in the mouse liver via hydrodynamic gene delivery led to the inhibition of mouse hepatocarcinogenesis driven by overexpression of AKT. In human liver cancer specimens, we detected that HSF1 is progressively induced from human non-tumorous surrounding livers to HCC, reaching the highest expression in the tumors characterized by the poorest outcome (as defined by the length of patients’ survival). In conclusion, HSF1 is an independent prognostic factor in liver cancer and might represent an innovative therapeutic target in HCC subsets characterized by activation of the AKT/mTOR pathway.

The novel combination of dual mTOR inhibitor AZD2014 and pan-PIM inhibitor AZD1208 inhibits growth in acute myeloid leukemia via HSF pathway suppression

Mammalian target of rapamycin (mTOR) signaling is a critical pathway in the biology of acute myeloid leukemia (AML). Proviral integration site for moloney murine leukemia virus (PIM) serine/threonine kinase signaling takes part in various pathways exerting tumorigenic properties. We hypothesized that the combination of a PIM kinase inhibitor with an mTOR inhibitor might have complementary growth-inhibitory effects against AML. The simultaneous inhibition of the PIM kinase by pan-PIM inhibitor AZD1208 and of mTOR by selective mTORC1/2 dual inhibitor AZD2014 exerted anticancer properties in AML cell lines and in cells derived from primary AML samples with or without supportive stromal cell co-culture, leading to suppressed proliferation and increased apoptosis. The combination of AZD1208 and AZD2014 rapidly activated AMPKα, a negative regulator of translation machinery through mTORC1/2 signaling in AML cells; profoundly inhibited AKT and 4EBP1 activation; and suppressed polysome formation. Inhibition of both mTOR and PIM counteracted induction of heat-shock family proteins, uncovering the master negative regulation of heat shock factor 1 (HSF1), the dominant transcription factor controlling cellular stress responses. The novel combination of the dual mTOR inhibitor and pan-PIM inhibitor synergistically inhibited AML growth by effectively reducing protein synthesis through heat shock factor pathway suppression.

Formaldehyde Is a Potent Proteotoxic Stressor Causing Rapid Heat Shock Transcription Factor 1 Activation and Lys48-Linked Polyubiquitination of Proteins

Endogenous and exogenous formaldehyde (FA) has been linked to cancer, neurotoxicity, and other pathophysiologic effects. Molecular and cellular mechanisms that underlie FA-induced damage are poorly understood. In this study, we investigated whether proteotoxicity is an important, unrecognized factor in cell injury caused by FA. We found that irrespective of their cell cycle phases, all FA-treated human cells rapidly accumulated large amounts of proteins with proteasome-targeting K48-linked polyubiquitin, which was comparable with levels of polyubiquitination in proteasome-inhibited MG132 controls. Both nuclear and cytoplasmic proteins were damaged and underwent K48-polyubiquitination. There were no significant changes in the nonproteolytic K63-polyubiquitination of soluble and insoluble cellular proteins. FA also rapidly induced nuclear accumulation and Ser326 phosphorylation of the main heat shock-responsive transcription factor HSF1, which was not a result of protein polyubiquitination. Consistent with the activation of the functional heat shock response, FA strongly elevated the expression of HSP70 genes. In contrast to the responsiveness of the cytoplasmic protein damage sensor HSF1, FA did not activate the unfolded protein response in either the endoplasmic reticulum or mitochondria. Inhibition of HSP90 chaperone activity increased the levels of K48-polyubiquitinated proteins and diminished cell viability after FA treatment. Overall, our results indicate that FA is a strong proteotoxic agent, which helps explain its diverse pathologic effects, including injury in nonproliferative tissues.

Targeting p97 to Disrupt Protein Homeostasis in Cancer

Cancer cells are addicted to numerous non-oncogenic traits that enable them to thrive. Proteotoxic stress is one such non-oncogenic trait that is experienced by all tumor cells owing to increased genomic abnormalities and the resulting synthesis and accumulation of non-stoichiometric amounts of cellular proteins. This imbalance in the amounts of proteins ultimately culminates in proteotoxic stress. p97, or valosin-containing protein (VCP), is an ATPase whose function is essential to restore protein homeostasis in the cells. Working in concert with the ubiquitin proteasome system, p97 promotes the retrotranslocation from cellular organelles and/or degradation of misfolded proteins. Consequently, p97 inhibition has emerged as a novel therapeutic target in cancer cells, especially those that have a highly secretory phenotype. This review summarizes our current understanding of the function of p97 in maintaining protein homeostasis and its inhibition with small molecule inhibitors as an emerging strategy to target cancer cells.

Heat Shock Factor 1 Mediates Latent HIV Reactivation

HSF1, a conserved heat shock factor, has emerged as a key regulator of mammalian transcription in response to cellular metabolic status and stress. To our knowledge, it is not known whether HSF1 regulates viral transcription, particularly HIV-1 and its latent form. Here we reveal that HSF1 extensively participates in HIV transcription and is critical for HIV latent reactivation. Mode of action studies demonstrated that HSF1 binds to the HIV 5'-LTR to reactivate viral transcription and recruits a family of closely related multi-subunit complexes, including p300 and p-TEFb. And HSF1 recruits p300 for self-acetylation is also a committed step. The knockout of HSF1 impaired HIV transcription, whereas the conditional over-expression of HSF1 improved that. These findings demonstrate that HSF1 positively regulates the transcription of latent HIV, suggesting that it might be an important target for different therapeutic strategies aimed at a cure for HIV/AIDS.