Inhibiting the transcription factor HSF1 as an anticancer strategy

Chemical probes and drug leads from advances in synthetic planning and methodology

Screening of small-molecule libraries is a productive method for identifying both chemical probes of disease-related targets and potential starting points for drug discovery. In this article, we focus on strategies such as diversity-oriented synthesis that aim to explore novel areas of chemical space efficiently by populating small-molecule libraries with compounds containing structural features that are typically under-represented in commercially available screening collections. Drawing from more than a decade's worth of examples, we highlight how the design and synthesis of such libraries have been enabled by modern synthetic chemistry, and we illustrate the impact of the resultant chemical probes and drug leads in a wide range of diseases.

Heat Shock Factor 1 Epigenetically Stimulates Glutaminase-1-Dependent mTOR Activation to Promote Colorectal Carcinogenesis

Heat shock factor 1 (HSF1) generally exhibits its properties under stress conditions. In tumors, HSF1 has a pleiotropic feature in regulating growth, survival, and aggressiveness of cancer cells. In this study, we found HSF1 was increased in colorectal cancer (CRC) and had a positive correlation with shorter disease-free survival (DFS). Knockdown of HSF1 in CRC cells attenuated their growth while inhibiting mTOR activation and glutamine metabolism. HSF1 inhibited the expression of microRNA137 (MIR137), which targeted GLS1 (glutaminase 1), thus stimulating GLS1 protein expression to promote glutaminolysis and mTOR activation. HSF1 bound DNA methyltransferase DNMT3a and recruited it to the promoter of lncRNA MIR137 host gene (MIR137HG), suppressing the generation of primary MIR137. The chemical inhibitor of HSF1 also reduced cell growth, increased apoptosis, and impaired glutamine metabolism in vitro. Moreover, both chemical inhibition and genetic knockout of HSF1 succeeded in increasing MIR137 expression, reducing GLS1 expression, and alleviating colorectal tumorigenesis in azoxymethane (AOM)/dextran sulfate sodium (DSS) mice. In conclusion, HSF1 expression was increased and associated with poor prognosis in CRC. By recruiting DNMT3a to suppress the expression of MIR137 that targets GLS1 mRNA, HSF1 stimulated GLS1-dependent mTOR activation to promote colorectal carcinogenesis. Therefore, targeting HSF1 to attenuate glutaminolysis and mTOR activation could be a promising approach for CRC treatment.

Discovering a Reliable Heat-Shock Factor-1 Inhibitor to Treat Human Cancers: Potential Opportunity for Phytochemists

Heat-shock factor-1 (HSF-1) is an important transcription factor that regulates pathogenesis of many human diseases through its extensive transcriptional regulation. Especially, it shows pleiotropic effects in human cancer, and hence it has recently received increased attention of cancer researchers. After myriad investigations on HSF-1, the field has advanced to the phase where there is consensus that finding a potent and selective pharmacological inhibitor for this transcription factor will be a major break-through in the treatment of various human cancers. Presently, all reported inhibitors have their limitations, made evident at different stages of clinical trials. This brief account summarizes the advances with tested natural products as HSF-1 inhibitors and highlights the necessity of phytochemistry in this endeavor of discovering a potent pharmacological HSF-1 inhibitor.

Tuning Hsf1 levels drives distinct fungal morphogenetic programs with depletion impairing Hsp90 function and overexpression expanding the target space

The capacity to respond to temperature fluctuations is critical for microorganisms to survive within mammalian hosts, and temperature modulates virulence traits of diverse pathogens. One key temperature-dependent virulence trait of the fungal pathogen Candida albicans is its ability to transition from yeast to filamentous growth, which is induced by environmental cues at host physiological temperature. A key regulator of temperature-dependent morphogenesis is the molecular chaperone Hsp90, which has complex functional relationships with the transcription factor Hsf1. Although Hsf1 controls global transcriptional remodeling in response to heat shock, its impact on morphogenesis remains unknown. Here, we establish an intriguing paradigm whereby overexpression or depletion of C. albicans HSF1 induces morphogenesis in the absence of external cues. HSF1 depletion compromises Hsp90 function, thereby driving filamentation. HSF1 overexpression does not impact Hsp90 function, but rather induces a dose-dependent expansion of Hsf1 direct targets that drives overexpression of positive regulators of filamentation, including Brg1 and Ume6, thereby bypassing the requirement for elevated temperature during morphogenesis. This work provides new insight into Hsf1-mediated environmentally contingent transcriptional control, implicates Hsf1 in regulation of a key virulence trait, and highlights fascinating biology whereby either overexpression or depletion of a single cellular regulator induces a profound developmental transition.

For human pathogens, the capacity to respond to elevated temperature is required for survival, with elevated temperature in the form of fever as a conserved host response to defend against infection. One of the leading fungal pathogens of humans in Candida albicans, which is capable of growing in both a yeast and filamentous state. The ability to transition between these forms is a key virulence trait, and one that is highly temperature-dependent. A pivotal regulator of filamentous growth is the temperature-responsive molecular chaperone Hsp90, which has complex relationships with the transcription factor Hsf1. Although Hsf1 regulates changes in gene expression in response to heat shock, its impact on morphogenesis remains unknown. Here, we uncover an intriguing phenomenon whereby overexpression or depletion of C. albicans HSF1 induces morphogenesis. We observe that HSF1 depletion compromises Hsp90 function, thereby driving filamentation. In contrast, HSF1 overexpression induces a dose-dependent expansion of its transcriptional targets that drives overexpression of positive regulators of filamentous growth. This work illuminates novel mechanisms through which tuning the levels of an environmentally contingent transcription factor drives a key developmental program.

Upregulation of HSF1 in estrogen receptor positive breast cancer

Heat shock transcription factor 1 (HSF1), a key regulator of the heat-shock response, is deregulated in many cancers. HSF1 can mediate cancer cell survival and metastasis. High levels of HSF1 have been associated with poor prognosis in breast cancer. The nature of HSF1 upregulation needs to be validated in different cohorts to further validate its prognostic utility in breast cancer.

We first evaluated its expression in a cohort of breast cancer tissue microarrays with Oncotype DX recurrence scores available using immunohistochemistry. To further confirm the clinical relevance and prognostic impact, mutational and methylation status of the gene were also assessed in The Cancer Genome Atlas and publically available microarray datasets.

Immunohistochemical analysis showed that HSF1 expression is independent of Oncotype DX high recurrence score in ER-positive node-negative patients. Analysis of The Cancer Genome Atlas data revealed upregulation of HSF1 is not due to methylation or mutation. HSF1 copy number variations and amplifications (15%) were not associated with survival. In publicly available microarray datasets, a prognostic impact was observed in ER-positive tumors, but not in ER-negative tumors. Patients with ER-positive tumors with high HSF1 levels were associated with shorter overall survival (P = 0.00045) and relapse-free survival (P = 0.0057). In multivariable analysis, HSF1 remained a significant prognostic parameter.

The mRNA expression levels of HSF1 in ER-positive breast cancer are associated with both shorter relapse-free and overall survival. This prognostic impact is specific to mRNA expression, but stayed insignificant by protein expression or by analyzing amplification events.

Bortezomib-induced heat shock response protects multiple myeloma cells and is activated by heat shock factor 1 serine 326 phosphorylation

Proteasome inhibitors such as bortezomib are highly active in multiple myeloma by affecting signaling cascades and leading to a toxic buildup of misfolded proteins. Bortezomib-treated cells activate the cytoprotective heat shock response (HSR), including upregulation of heat shock proteins (HSPs). Here we inhibited the bortezomib-induced HSR by silencing its master regulator, Heat Shock Factor 1 (HSF1). HSF1 silencing led to bortezomib sensitization. In contrast, silencing of individual and combination HSPs, except HSP40β, did not result in significant bortezomib sensitization. However, HSP40β did not entirely account for increased bortezomib sensitivity upon HSF1 silencing. To determine the mechanism of HSF1 activation, we assessed phosphorylation and observed bortezomib-inducible phosphorylation in cell lines and patient samples. We determined that this bortezomib-inducible event is phosphorylation at serine 326. Prior clinical use of HSP inhibitors in combination with bortezomib has been disappointing in multiple myeloma therapy. Our results provide a rationale for targeting HSF1 activation in combination with bortezomib to enhance multiple myeloma treatment efficacy.

Clinical Evaluation and Biomarker Profiling of Hsp90 Inhibitors

Inhibitors of the molecular chaperone heat shock protein 90 (Hsp90) have been in clinical development as anticancer agents since 1998. There have been 18 Hsp90 inhibitors (Hsp90i) that have entered the clinic, all of which, though structurally distinct, target the ATP-binding Bergerat fold of the chaperone N-terminus. Currently, there are five Hsp90 inhibitors in clinical trial and no approved drug in this class. One impediment to development of a clinically efficacious Hsp90 inhibitor has been the very low percentage of clinical trials that have codeveloped a predictive or pharmacodynamic marker of the anticancer activity inherent in this class of drugs. Here, we provide an overview of the clinical development of Hsp90 inhibitors, review the pharmacodynamic assays that have been employed in the past, and highlight new approaches to Hsp90 inhibitor clinical development.

Targeting Heat Shock Proteins in Cancer: A Promising Therapeutic Approach

Heat shock proteins (HSPs) are a large family of chaperones that are involved in protein folding and maturation of a variety of "client" proteins protecting them from degradation, oxidative stress, hypoxia, and thermal stress. Hence, they are significant regulators of cellular proliferation, differentiation and strongly implicated in the molecular orchestration of cancer development and progression as many of their clients are well established oncoproteins in multiple tumor types. Interestingly, tumor cells are more HSP chaperonage-dependent than normal cells for proliferation and survival because the oncoproteins in cancer cells are often misfolded and require augmented chaperonage activity for correction. This led to the development of several inhibitors of HSP90 and other HSPs that have shown promise both preclinically and clinically in the treatment of cancer. In this article, we comprehensively review the roles of some of the important HSPs in cancer, and how targeting them could be efficacious, especially when traditional cancer therapies fail.

A pyrrole-based natural small molecule mitigates HSP90 expression in MDA-MB-231 cells and inhibits tumor angiogenesis in mice by inactivating HSF-1

Heat shock proteins (HSPs), molecular chaperones, are crucial for the cancer cells to facilitate proper functioning of various oncoproteins involved in cell survival, proliferation, migration, and tumor angiogenesis. Tumor cells are said to be "addicted" to HSPs. HSPs are overexpressed in many cancers due to upregulation of transcription factor Heat-shock factor 1 (HSF-1), the multifaceted master regulator of heat shock response. Therefore, pharmacological targeting of HSPs via HSF-1 is an effective strategy to treat malignant cancers like triple negative breast cancer. In the current study, we evaluated the efficacy of a pyrrole derivative [bis(2-ethylhexyl)1H-pyrrole-3,4-dicarboxylate], TCCP, purified from leaves of Tinospora cordifolia for its ability to suppress heat shock response and angiogenesis using MDA-MB-231 cells and the murine mammary carcinoma: Ehrlich ascites tumor model. HSP90 was downregulated by TCCP by inactivation of HSF-1 resulting in inhibition of tumor cell proliferation, VEGF-induced cell migration, and concomitant decrease in tumor burden and neo-angiogenesis in vivo. The mechanism of suppression of HSPs involves inactivation of PI3K/Akt and phosphorylation on serine 307 of HSF-1 by the activation of ERK1. HSF-1 and HSP90 and 70 localization and expression were ascertained by immunolocalization, immunoblotting, and qPCR experiments. The anti-angiogenic effect of TCCP was studied in vivo in tumor-bearing mice and ex vivo using rat corneal micro-pocket assay. All the results thus corroborate the logic behind inactivating HSF-1 using TCCP as an alternative approach for cancer therapy.

piR-823 contributes to colorectal tumorigenesis by enhancing the transcriptional activity of HSF1

Piwi-interacting RNAs (piRNAs), a novel class of small non-coding RNAs, were first discovered in germline cells and are thought to silence transposons in spermatogenesis. Recently, piRNAs have also been identified in somatic tissues, and aberrant expression of piRNAs in tumor tissues may be implicated in carcinogenesis. However, the function of piR-823 in colorectal cancer (CRC) remains unclear. Here, we first found that piR-823 was significantly upregulated in CRC tissues compared with its expression in the adjacent tissues. Inhibition of piR-823 suppressed cell proliferation, arrested the cell cycle in the G1 phase and induced cell apoptosis in CRC cell lines HCT116 and DLD-1, whereas overexpression of piR-823 promoted cell proliferation in normal colonic epithelial cell line FHC. Interestingly, Inhibition of piR-823 repressed the expression of heat shock protein (HSP) 27, 60, 70. Furthermore, elevated HSPs expression partially abolished the effect of piR-823 on cell proliferation and apoptosis. In addition, we further demonstrated that piR-823 increased the transcriptional activity of HSF1, the common transcription factor of HSPs, by binding to HSF1 and promoting its phosphorylation at Ser326. Our study reveals that piR-823 plays a tumor-promoting role by upregulating phosphorylation and transcriptional activity of HSF1 and suggests piR-823 as a potential therapeutic target for CRC.

Regulation of the mammalian heat shock factor 1

Living organisms are endowed with the capability to tackle various forms of cellular stress due to the presence of molecular chaperone machinery complexes that are ubiquitous throughout the cell. During conditions of proteotoxic stress, the transcription factor heat shock factor 1 (HSF1) mediates the elevation of heat shock proteins, which are crucial components of the chaperone complex machinery and function to ameliorate protein misfolding and aggregation and restore protein homeostasis. In addition, HSF1 orchestrates a versatile transcriptional programme that includes genes involved in repair and clearance of damaged macromolecules and maintenance of cell structure and metabolism, and provides protection against a broad range of cellular stress mediators, beyond heat shock. Here, we discuss the structure and function of the mammalian HSF1 and its regulation by post-translational modifications (phosphorylation, sumoylation and acetylation), proteasomal degradation, and small-molecule activators and inhibitors.

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.

Ugi Reaction-Derived α-Acyl Aminocarboxamides Bind to Phosphatidylinositol 3-Kinase-Related Kinases, Inhibit HSF1-Dependent Heat Shock Response, and Induce Apoptosis in Multiple Myeloma Cells

Heat shock transcription factor 1 (HSF1) has been identified as a therapeutic target for pharmacological treatment of multiple myeloma (MM). However, direct therapeutic targeting of HSF1 function seems to be difficult due to the shortage of clinically suitable pharmacological inhibitors. We utilized the Ugi multicomponent reaction to create a small but smart library of α-acyl aminocarboxamides and evaluated their ability to suppress heat shock response (HSR) in MM cells. Using the INA-6 cell line as the MM model and the strictly HSF1-dependent HSP72 induction as a HSR model, we identified potential HSF1 inhibitors. Mass spectrometry-based affinity capture experiments with biotin-linked derivatives revealed a number of target proteins and complexes, which exhibit an armadillo domain. Also, four members of the tumor-promoting and HSF1-associated phosphatidylinositol 3-kinase-related kinase (PIKK) family were identified. The antitumor activity was evaluated, showing that treatment with the anti-HSF1 compounds strongly induced apoptotic cell death in MM cells.

Nuclear inclusion bodies of mutant and wild-type p53 in cancer: a hallmark of p53 inactivation and proteostasis remodelling by p53 aggregation

Although p53 protein aggregates have been observed in cancer cell lines and tumour tissue, their impact in cancer remains largely unknown. Here, we extensively screened for p53 aggregation phenotypes in tumour biopsies, and identified nuclear inclusion bodies (nIBs) of transcriptionally inactive mutant or wild-type p53 as the most frequent aggregation-like phenotype across six different cancer types. p53-positive nIBs co-stained with nuclear aggregation markers, and shared molecular hallmarks of nIBs commonly found in neurodegenerative disorders. In cell culture, tumour-associated stress was a strong inducer of p53 aggregation and nIB formation. This was most prominent for mutant p53, but could also be observed in wild-type p53 cell lines, for which nIB formation correlated with the loss of p53's transcriptional activity. Importantly, protein aggregation also fuelled the dysregulation of the proteostasis network in the tumour cell by inducing a hyperactivated, oncogenic heat-shock response, to which tumours are commonly addicted, and by overloading the proteasomal degradation system, an observation that was most pronounced for structurally destabilized mutant p53. Patients showing tumours with p53-positive nIBs suffered from a poor clinical outcome, similar to those with loss of p53 expression, and tumour biopsies showed a differential proteostatic expression profile associated with p53-positive nIBs. p53-positive nIBs therefore highlight a malignant state of the tumour that results from the interplay between (1) the functional inactivation of p53 through mutation and/or aggregation, and (2) microenvironmental stress, a combination that catalyses proteostatic dysregulation. This study highlights several unexpected clinical, biological and therapeutically unexplored parallels between cancer and neurodegeneration. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Discovery of a Chemical Probe Bisamide (CCT251236): An Orally Bioavailable Efficacious Pirin Ligand from a Heat Shock Transcription Factor 1 (HSF1) Phenotypic Screen

Phenotypic screens, which focus on measuring and quantifying discrete cellular changes rather than affinity for individual recombinant proteins, have recently attracted renewed interest as an efficient strategy for drug discovery. In this article, we describe the discovery of a new chemical probe, bisamide (CCT251236), identified using an unbiased phenotypic screen to detect inhibitors of the HSF1 stress pathway. The chemical probe is orally bioavailable and displays efficacy in a human ovarian carcinoma xenograft model. By developing cell-based SAR and using chemical proteomics, we identified pirin as a high affinity molecular target, which was confirmed by SPR and crystallography.

Serum Heat Shock Protein 70, as a Potential Biomarker for Small Cell Lung Cancer

The 70 kDa heat shock protein (Hsp70) is a highly conservative molecular chaperone, that has important role in cell integrity. Recently considerable amount of data are accumulating on the potential role of Hsp70 in carcinogenesis and tumor progression. Most papers are focusing on intracellular or membrane bound protein, however very limited data exist on serum Hsp70, that can also induce innate and adaptive immune response. Previously we have published data on the correlation between coloretal cancer progression and serum Hsp70 concentration. The objective of this study was to compare the serum Hsp70 level in patients with small cell lung cancer (SCLC n = 70) and age matched healthy controlls (n = 121) and correlate Hsp70 level with other known serum biomarkers (LDH and NSE) of the disease. We found that the serum level of Hsp70 was significantly higher in SCLC patients compared to control subjects (mean value 6.91 vs 2.47 ng/ml, p = 0.001). The highest Hsp70 concentration was measured in stage IV advanced SCLC (Stage IV versus Stage I-III disease: 9.91 vs 4.38 ng/ml, p = 0.003). The serum Hsp70 level correlated with serum LDH (r = 0.426, p < 0,001) and NSE level (r = 0.455, p < 0,001). We found that high serum Hsp70 level predicted unfavorable survival, risk of death within 1 year was more than 3 times higher in patients with high baseline Hsp70 level (HR:3.509, CI: 1.066-11.562; p = 0.039). Our observations indicate that serum Hsp70 could be a valuable diagnostic and prognostic marker in small cell lung cancer.

Selective killing of cancer cells by small molecules targeting heat shock stress response

HSF1 heat shock response has emerged as a valuable non-oncogenetic intervention point in targeted cancer therapy. Current reporter based high throughput screening has led to the discovery of several compounds or chemotypes that are effective in the growth inhibition of multiple cancer cell lines and relevant animal tumor models. However, some intrinsic limitations of reporter based assays can potentially lead to biased results. Using a previously validated high content image based assay, we performed a phenotypic screen targeting HSF1 heat shock pathway with a chemically diversified library of over 100,000 compounds. Several novel functional inhibitors of HSF1 pathway were identified with different chemotypes. Western blot analysis confirmed that selective compounds inhibit phosphorylation of HSF1, followed by reduced expression of HSP proteins. Moreover, HeLa cells stably transfected with HSF1 shRNA were more resistant to the compound treatment under lethal temperature than cells containing HSF1, validating HSF1 dependent mechanism of action. These compounds demonstrate nanomolar potency toward multiple cancer cell lines with relatively low cytotoxicity to normal cells. Further SAR and target identification study will pave the way for the potential development of next generation anticancer drugs.

Tonantzitlolone cytotoxicity toward renal cancer cells is PKCθ- and HSF1-dependent

Elucidating the targets and mechanism of action of natural products is strategically important prior to drug development and assessment of potential clinical applications. In this report, we elucidated the main targets and mechanism of action of the natural product tonantzitlolone (TZL) in clear cell renal cell carcinoma (CCRCC). We identified TZL as a dual PKCα and PKCθ activator in vitro, although in CCRCC cells its activity was mostly PKCθ-dependent. Through activation of PKCθ, TZL induced an insulin resistant phenotype by inhibiting IRS1 and the PI3K/Akt pathway. Simultaneously, TZL activated the heat shock factor 1 (HSF1) transcription factor driving glucose dependency. Thus, similar to the selective PKCθ activator englerin A, TZL induces a metabolic catastrophe in CCRCC, starving cells of glucose while simultaneously increasing their glycolytic dependency.

Everolimus downregulates estrogen receptor and induces autophagy in aromatase inhibitor-resistant breast cancer cells

Background

mTOR inhibition of aromatase inhibitor (AI)-resistant breast cancer is currently under evaluation in the clinic. Everolimus/RAD001 (Afinitor®) has had limited efficacy as a solo agent but is projected to become part of combination therapy for AI-resistant breast cancer. This study was conducted to investigate the anti-proliferative and resistance mechanisms of everolimus in AI-resistant breast cancer cells.

Methods

In this study we utilized two AI-resistant breast cancer cell lines, MCF-7:5C and MCF-7:2A, which were clonally derived from estrogen receptor positive (ER+) MCF-7 breast cancer cells following long-term estrogen deprivation. Cell viability assay, colony formation assay, cell cycle analysis and soft agar anchorage-independent growth assay were used to determine the efficacy of everolimus in inhibiting the proliferation and tumor forming potential of MCF-7, MCF-7:5C, MCF-7:2A and MCF10A cells. Confocal microscopy and transmission electron microscopy were used to evaluate LC3-II production and autophagosome formation, while ERE-luciferase reporter, Western blot, and RT-PCR analyses were used to assess ER expression and transcriptional activity.

Results

Everolimus inhibited the proliferation of MCF-7:5C and MCF-7:2A cells with relatively equal efficiency to parental MCF-7 breast cancer cells. The inhibitory effect of everolimus was due to G1 arrest as a result of downregulation of cyclin D1 and p21. Everolimus also dramatically reduced estrogen receptor (ER) expression (mRNA and protein) and transcriptional activity in addition to the ER chaperone, heat shock protein 90 protein (HSP90). Everolimus restored 4-hydroxy-tamoxifen (4OHT) sensitivity in MCF-7:5C cells and enhanced 4OHT sensitivity in MCF-7 and MCF-7:2A cells. Notably, we found that autophagy is one method of everolimus insensitivity in MCF-7 breast cancer cell lines.

Conclusion

This study provides additional insight into the mechanism(s) of action of everolimus that can be used to enhance the utility of mTOR inhibitors as part of combination therapy for AI-resistant breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2490-z) contains supplementary material, which is available to authorized users.

Intracellular MMP3 Promotes HSP Gene Expression in Collaboration With Chromobox Proteins

Matrix metalloproteinases (MMPs) are crucial factors in tumor progression, inflammatory/immune responses and tissue development/regeneration. Of note, it has been known that MMPs promote genome instability, epithelial-mesenchymal transition, invasion, and metastasis in tumor progression. We previously reported that human MMP3 could translocate into cellular nuclei and control transcription in human chondrosarcoma-derived cells and in articular cartilage (Eguchi et al. [2008] Mol Cell Biol 28(7):2391-2413); however, further transcriptional target genes and cofactors of intranuclear MMP3 have not been uncovered. In this paper, we used transcriptomics analysis in order to examine novel transcriptional target genes regulated by intracellular MMP3. We found that mRNA levels of HSP family members (HSP70B', HSP72, HSP40/DNAJ, and HSP20/CRYAB) are upregulated by the intracellular MMP3 overload. Bioinformatic analysis predicted several transcription factors that possibly interact with MMP3. Among these factors, heat shock factor 1 (HSF1) cooperated with the MMP3 to activate the HSP70B' gene promoter in reporter gene assays, while a dominant negative HSF1 blocked the role for MMP3 in the trans-activation. The hemopexin-like repeat (PEX) domain of the human MMP3 was essential for transcriptional induction of the HSP70B' gene. In addition, chromobox proteins CBX5/HP1α and CBX3/HP1γ cooperated with the PEX domain in induction of HSP70B' mRNA. Taken together, this study newly clarified that intracellular MMP3 cooperate with CBXs/HP1s in transcriptional promotion of HSP genes. J. Cell. Biochem. 118: 43-51, 2017. © 2016 Wiley Periodicals, Inc.

αB-crystallin: Portrait of a malignant chaperone as a cancer therapeutic target

αB-crystallin is a widely expressed member of the small heat shock protein family that protects cells from stress by its dual function as a molecular chaperone to preserve proteostasis and as a cell death antagonist that negatively regulates components of the conserved apoptotic cell death machinery. Deregulated expression of αB-crystallin occurs in a broad array of solid tumors and has been linked to tumor progression and poor clinical outcomes. This review will focus on new insights into the molecular mechanisms by which oncogenes, oxidative stress, matrix detachment and other tumor microenvironmental stressors deregulate αB-crystallin expression. We will also review accumulating evidence pointing to an essential role for αB-crystallin in the multi-step metastatic cascade whereby tumor cells colonize distant organs by circumventing a multitude of barriers to cell migration and survival. Finally, we will evaluate emerging strategies to therapeutically target αB-crystallin and/or interacting proteins to selectively activate apoptosis and/or derail the metastatic cascade in an effort to improve outcomes for patients with metastatic disease.

protonation behavior of histidine during HSF1 activation by physiological acidification

The expression of eukaryotic molecular chaperones (heat shock proteins, HSPs) is triggered in response to a wide range of environmental stresses, including: heat shock, hydrogen peroxide, heavy metal, low-pH, or virus infection. Biochemical and genetic studies have clearly shown the fundamental roles of heat shock factor 1 (HSF1) in stress-inducible HSP gene expression, resistance to stress-induced cell death, carcinogenesis, and other biological phenomena. Previous studies show that acidic pH changes within the physiological range directly activate the HSF1 function in vitro. However, the detailed mechanism is unclear. Though computational pKa-predications of the amino acid side-chain, acidic-pH induced protonation of a histidine residue was found to be most-likely involved in this process. The histidine 83 (His83) residue, which could be protonated by mild decrease in pH, causes mild acidic-induced HSF1 activation (including in-vitro trimerization, DNA binding, in-vivo nuclear accumulation, and HSPs expression). His83, which is located in the loop region of the HSF1 DNA binding domain, was suggested to enhance the intermolecular force with Arginine 79, which helps HSF1 form a DNA-binding competent. Therefore, low-pH-induced activation of HSF1 by the protonation of histidine can help us better to understand the HSF1 mechanism and develop more therapeutic applications (particularly in cancer therapy). J. Cell. Biochem. 116: 977-984, 2015. © 2015 Wiley Periodicals, Inc.

Transportable, Chemical Genetic Methodology for the Small Molecule-Mediated Inhibition of Heat Shock Factor 1

Proteostasis in the cytosol is governed by the heat shock response. The master regulator of the heat shock response, heat shock factor 1 (HSF1), and key chaperones whose levels are HSF1-regulated have emerged as high-profile targets for therapeutic applications ranging from protein misfolding-related disorders to cancer. Nonetheless, a generally applicable methodology to selectively and potently inhibit endogenous HSF1 in a small molecule-dependent manner in disease model systems remains elusive. Also problematic, the administration of even highly selective chaperone inhibitors often has the side effect of activating HSF1 and thereby inducing a compensatory heat shock response. Herein, we report a ligand-regulatable, dominant negative version of HSF1 that addresses these issues. Our approach, which required engineering a new dominant negative HSF1 variant, permits dosable inhibition of endogenous HSF1 with a selective small molecule in cell-based model systems of interest. The methodology allows us to uncouple the pleiotropic effects of chaperone inhibitors and environmental toxins from the concomitantly induced compensatory heat shock response. Integration of our method with techniques to activate HSF1 enables the creation of cell lines in which the cytosolic proteostasis network can be up- or down-regulated by orthogonal small molecules. Selective, small molecule-mediated inhibition of HSF1 has distinctive implications for the proteostasis of both chaperone-dependent globular proteins and aggregation-prone intrinsically disordered proteins. Altogether, this work provides critical methods for continued exploration of the biological roles of HSF1 and the therapeutic potential of heat shock response modulation.

Human Heat shock protein 40 (Hsp40/DnaJB1) promotes influenza A virus replication by assisting nuclear import of viral ribonucleoproteins

A unique feature of influenza A virus (IAV) life cycle is replication of the viral genome in the host cell nucleus. The nuclear import of IAV genome is an indispensable step in establishing virus infection. IAV nucleoprotein (NP) is known to mediate the nuclear import of viral genome via its nuclear localization signals. Here, we demonstrate that cellular heat shock protein 40 (Hsp40/DnaJB1) facilitates the nuclear import of incoming IAV viral ribonucleoproteins (vRNPs) and is important for efficient IAV replication. Hsp40 was found to interact with NP component of IAV RNPs during early stages of infection. This interaction is mediated by the J domain of Hsp40 and N-terminal region of NP. Drug or RNAi mediated inhibition of Hsp40 resulted in reduced nuclear import of IAV RNPs, diminished viral polymerase function and attenuates overall viral replication. Hsp40 was also found to be required for efficient association between NP and importin alpha, which is crucial for IAV RNP nuclear translocation. These studies demonstrate an important role for cellular chaperone Hsp40/DnaJB1 in influenza A virus life cycle by assisting nuclear trafficking of viral ribonucleoproteins.

Structures of HSF2 reveal mechanisms for differential regulation of human heat-shock factors

Heat Shock Transcription Factor (HSF) family members function in stress protection and in human disease including proteopathies, neurodegeneration and cancer. The mechanisms that drive distinct post-translational modifications, co-factor recruitment and target gene activation for specific HSF paralogs are unknown. We present high-resolution crystal structures of the human HSF2 DNA-binding domain (DBD) bound to DNA, revealing an unprecedented view of HSFs that provides insights into their unique biology. The HSF2 DBD structures resolve a novel carboxyl-terminal helix that directs the coiled-coil domain to wrap around DNA, exposing paralog-specific sequences of the DBD surface, for differential post-translational modifications and co-factor interactions. We further demonstrate a direct interaction between HSF1 and HSF2 through their coiled-coil domains. Together, these features provide a new model for HSF structure as the basis for differential and combinatorial regulation to influence the transcriptional response to cellular stress.

Heat shock factor 1, an inhibitor of non-homologous end joining repair

A novel role for HSF1 as an inhibitor of non-homologous end joining (NHEJ) repair activity was identified. HSF1 interacted directly with both of the N-terminal sequences of the Ku70 and Ku86 proteins, which inhibited the endogenous heterodimeric interaction between Ku70 and Ku86. The blocking of the Ku70 and Ku86 interaction by HSF1 induced defective NHEJ repair activity and ultimately activated genomic instability after ionizing radiation (IR), which was similar to effects seen in Ku70 or Ku80 knockout cells. The binding activity between HSF1 and Ku70 or Ku86 was dependent on DNA damage response such as IR exposure, but not on the heat shock mediated transcriptional activation of HSF1. Moreover, the posttranslational modification such as phosphorylation, acetylation and sumoylation of HSF1 did not alter the binding activities of HSF1-Ku70 or HSF1-Ku86. Furthermore, the defect in DNA repair activity by HSF1 was observed regardless of p53 status. Rat mammary tumors derived using dimethylbenz(a)anthracence revealed that high levels of HSF1 expression which correlate with aggressive malignancy, interfered with the binding of Ku70-Ku80. This data suggests that HSF1 interacts with both Ku70 and Ku86 to induce defective NHEJ repair activity and genomic instability, which in turn suggests a novel mechanism of HSF1-mediated cellular carcinogenesis.

Direct link between metabolic regulation and the heat-shock response through the transcriptional regulator PGC-1α

In recent years an extensive effort has been made to elucidate the molecular pathways involved in metabolic signaling in health and disease. Here we show, surprisingly, that metabolic regulation and the heat-shock/stress response are directly linked. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a critical transcriptional coactivator of metabolic genes, acts as a direct transcriptional repressor of heat-shock factor 1 (HSF1), a key regulator of the heat-shock/stress response. Our findings reveal that heat-shock protein (HSP) gene expression is suppressed during fasting in mouse liver and in primary hepatocytes dependent on PGC-1α. HSF1 and PGC-1α associate physically and are colocalized on several HSP promoters. These observations are extended to several cancer cell lines in which PGC-1α is shown to repress the ability of HSF1 to activate gene-expression programs necessary for cancer survival. Our study reveals a surprising direct link between two major cellular transcriptional networks, highlighting a previously unrecognized facet of the activity of the central metabolic regulator PGC-1α beyond its well-established ability to boost metabolic genes via its interactions with nuclear hormone receptors and nuclear respiratory factors. Our data point to PGC-1α as a critical repressor of HSF1-mediated transcriptional programs, a finding with possible implications both for our understanding of the full scope of metabolically regulated target genes in vivo and, conceivably, for therapeutics.

Defective heat shock factor 1 inhibits the growth of fibrosarcoma derived from simian virus 40/T antigen‑transformed MEF cells

Heat shock factor 1 (Hsf1) serves an important role in regulating the proliferation of human tumor cell lines in vitro and tissue specific tumorigenesis in certain mouse models. However, its role in viral‑oncogenesis remains to be fully elucidated. In the current study, the role of Hsf1 in fibroblastoma derived from simian virus 40/T antigen (SV40/TAG)‑transformed mouse embryonic fibroblast (MEF) cell lines was investigated. Knockout of Hsf1 inhibited MEF cell proliferation in vitro and fibroblastoma growth and metastasis to the lungs in vivo in nude mice. Knockout of Hsf1 increased the protein expression levels of p53 and phosphorylated retinoblastoma protein (pRb), however reduced the expression of heat shock protein 25 (Hsp25) in addition to the expression of the angiogenesis markers vascular endothelial growth factor, cluster of differentiation 34 and factor VIII related antigen. Furthermore, immunoprecipitation indicated that knockout of Hsf1 inhibited the association between SV40/TAG and p53 or pRb. These data suggest that Hsf1 is involved in the regulation of SV40/TAG‑derived fibroblastoma growth and metastasis by modulating the association between SV40/TAG and tumor suppressor p53 and pRb. The current study provides further evidence that Hsf1 may be a novel therapeutic target in the treatment of cancer.

High-throughput screening system for inhibitors of human Heat Shock Factor 2

Development of novel anti-cancer drug leads that target regulators of protein homeostasis is a formidable task in modern pharmacology. Finding specific inhibitors of human Heat Shock Factor 1 (hHSF1) has proven to be a challenging task, while screening for inhibitors of human Heat Shock Factor 2 (hHSF2) has never been described. We report the development of a novel system based on an in vivo cell growth restoration assay designed to identify specific inhibitors of human HSF2 in a high-throughput format. This system utilizes a humanized yeast strain in which the master regulator of molecular chaperone genes, yeast HSF, has been replaced with hHSF2 with no detrimental effect on cell growth. This replacement preserves the general regulatory patterns of genes encoding major molecular chaperones including Hsp70 and Hsp90. The controlled overexpression of hHSF2 creates a slow-growth phenotype, which is the basis of the growth restoration assay used for high-throughput screening. The phenotype is most robust when cells are cultured at 25 °C, while incubation at temperatures greater than 30 °C leads to compensation of the phenotype. Overexpression of hHSF2 causes overexpression of molecular chaperones which is a likely cause of the slowed growth. Our assay is characterized by two unique advantages. First, screening takes place in physiologically relevant, in vivo conditions. Second, hits in our screen will be of medically relevant potency, as compounds that completely inhibit hHSF2 function will further inhibit cell growth and therefore will not be scored as hits. This caveat biases our screening system for compounds capable of restoring hHSF2 activity to a physiologically normal level without completely inhibiting this essential system.

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.

Regulating the master regulator: Controlling heat shock factor 1 as a chemotherapy approach

Described is the role that heat shock factor 1 (HSF1) plays in regulating cellular stress. Focusing on the current state of the HSF1 field in chemotherapeutics we outline the cytoprotective role of HSF1 in the cell. Summarizing the mechanism by which HSF1 regulates the unfolded proteins that are generated under stress conditions provides the background on why HSF1, the master regulator, is such an important protein in cancer cell growth. Summarizing siRNA knockdown results and current inhibitors provides a comprehensive evaluation on HSF1 and its current state. One set of molecules stands out, in that they completely obliterate the levels of HSF1, while simultaneously inhibiting heat shock protein 90 (Hsp90). These molecules are extremely promising as chemotherapeutic agents and as tools that may ultimately provide the connection between Hsp90 inhibition and HSF1 protein levels.

When Cancer Fights Back: Multiple Myeloma, Proteasome Inhibition, and the Heat-Shock Response

Multiple myeloma is a plasma cell malignancy with an estimated 26,850 new cases and 11,240 deaths in 2015 in the United States. Two main classes of agents are the mainstays of therapy-proteasome inhibitors (PI) and immunomodulatory drugs (IMiD). Other new targets are emerging rapidly, including monoclonal antibodies and histone deacetylase (HDAC) inhibitors. These therapeutic options have greatly improved overall survival, but currently only 15% to 20% of patients experience long-term progression-free survival or are cured. Therefore, improvement in treatment options is needed. One potential means of improving clinical options is to target resistance mechanisms for current agents. For example, eliminating the cytoprotective heat-shock response that protects myeloma cells from proteasome inhibition may enhance PI-based therapies. The transcription factor heat-shock factor 1 (HSF1) is the master regulator of the heat-shock response. HSF1 is vital in the proteotoxic stress response, and its activation is controlled by posttranslational modifications (PTM). This review details the mechanisms of HSF1 regulation and discusses leveraging that regulation to enhance PI activity.

FBXW7 modulates cellular stress response and metastatic potential through ​HSF1 post-translational modification

Heat-shock factor 1 (HSF1) orchestrates the heat-shock response in eukaryotes. Although this pathway has been evolved to help cells adapt in the presence of challenging conditions, it is co-opted in cancer to support malignancy. However, the mechanisms that regulate HSF1 and thus cellular stress response are poorly understood. Here we show that the ubiquitin ligase FBXW7 α interacts with HSF1 through a conserved motif phosphorylated by GSK3β and ERK1. FBXW7α ubiquitylates HSF1 and loss of FBXW7α results in impaired degradation of nuclear HSF1 and defective heat-shock response attenuation. FBXW7α is either mutated or transcriptionally downregulated in melanoma and HSF1 nuclear stabilization correlates with increased metastatic potential and disease progression. FBXW7α deficiency and subsequent HSF1 accumulation activates an invasion-supportive transcriptional program and enhances the metastatic potential of human melanoma cells. These findings identify a post-translational mechanism of regulation of the HSF1 transcriptional program both in the presence of exogenous stress and in cancer.

Heat shock factor 2 is a stress-responsive mediator of neuronal migration defects in models of fetal alcohol syndrome

Fetal alcohol spectrum disorder (FASD) is a frequent cause of mental retardation. However, the molecular mechanisms underlying brain development defects induced by maternal alcohol consumption during pregnancy are unclear. We used normal and Hsf2-deficient mice and cell systems to uncover a pivotal role for heat shock factor 2 (HSF2) in radial neuronal migration defects in the cortex, a hallmark of fetal alcohol exposure. Upon fetal alcohol exposure, HSF2 is essential for the triggering of HSF1 activation, which is accompanied by distinctive post-translational modifications, and HSF2 steers the formation of atypical alcohol-specific HSF1-HSF2 heterocomplexes. This perturbs the in vivo binding of HSF2 to heat shock elements (HSEs) in genes that control neuronal migration in normal conditions, such as p35 or the MAPs (microtubule-associated proteins, such as Dclk1 and Dcx), and alters their expression. In the absence of HSF2, migration defects as well as alterations in gene expression are reduced. Thus, HSF2, as a sensor for alcohol stress in the fetal brain, acts as a mediator of the neuronal migration defects associated with FASD.

ASF1 and the SWI/SNF complex interact functionally during nucleosome displacement, while FACT is required for nucleosome reassembly at yeast heat shock gene promoters during sustained stress

Histone chaperones are an integral part of the transcription regulatory machinery. We investigated the involvement of histone chaperones and their functional interactions with ATP-dependent chromatin remodeling complexes in the regulation of yeast heat shock genes. Strong functional interaction between the histone chaperone ASF1 and the ATP-dependent chromatin remodeling complex SWI/SNF is exhibited in synergistic diminishment of nucleosome displacement during heat shock in the ΔASF1/ΔSNF2 strain in comparison to individual ASF1 or SNF2 inactivation. A similar but less pronounced effect was observed for ISW1/ASF1 inactivation but not for ASF1/STH1 (RSC complex) combinatorial inactivation. The depletion of Spt16, which is a major subunit of the FACT histone chaperone complex, leads to a severe growth defect phenotype associated with unusual thermotolerance. The acquired thermotolerance in the Spt16-depleted strain is associated with a defect in the reassembly of nucleosomes at the promoters of heat shock genes during sustained heat stress, leading to increased recruitment of the transcriptional activator HSF and RNA polymerase II. The defect in nucleosome assembly associated with Spt16 depletion also leads to an increased tolerance to stress due to an increased concentration of NaCl.

Heat shock factor 1 in protein homeostasis and oncogenic signal integration

Heat shock factor 1 (HSF1) is a stress-inducible transcription factor and has been described as a multi-faceted modulator of tumorigenesis. Heat shock, accumulation of misfolded proteins, or malignant transformation promotes the activation and nuclear translocation of HSF1, where it binds to the promoters of heat shock proteins and an array of nonheat shock-regulated proteins to upregulate their transcription. These stress-responsive and tumor-promoting genes in turn alter the ability of tumor cells to respond to a variety of stresses and enable them to thrive in less than favorable growth conditions. Although a direct role for HSF1 in promoting mRNA transcription of tumor-promoting genes has been suggested, it appears that this property is context- and cell-type dependent. Furthermore, recent studies have demonstrated a direct involvement of mTOR signaling in regulating HSF1-mediated transcription, thus establishing a direct link between protein translation and HSF1 activity. Interestingly, there is a growing understanding of the signaling pathways that are modulated by HSF1 in a variety of tumor types and the co-option of these survival pathways by HSF1 to promote tumorigenesis. This review will focus on the role of HSF1 in protein homeostasis and HSF1-mediated oncogenic signaling pathways that together promote tumorigenesis.

Misfolded proteins: from little villains to little helpers in the fight against cancer

The application of cytostatic drugs targeting the high proliferation rates of cancer cells is currently the most commonly used treatment option in cancer chemotherapy. However, severe side effects and resistance mechanisms may occur as a result of such treatment, possibly limiting the therapeutic efficacy of these agents. In recent years, several therapeutic strategies have been developed that aim at targeting not the genomic integrity and replication machinery of cancer cells but instead their protein homeostasis. During malignant transformation, the cancer cell proteome develops vast aberrations in the expression of mutated proteins, oncoproteins, drug- and apoptosis-resistance proteins, etc. A complex network of protein quality-control mechanisms, including chaperoning by heat shock proteins (HSPs), not only is essential for maintaining the extravagant proteomic lifestyle of cancer cells but also represents an ideal cancer-specific target to be tackled. Furthermore, the high rate of protein synthesis and turnover in certain types of cancer cells can be specifically directed by interfering with the proteasomal and autophagosomal protein recycling and degradation machinery, as evidenced by the clinical application of proteasome inhibitors. Since proteins with loss of their native conformation are prone to unspecific aggregations and have proved to be detrimental to normal cellular function, specific induction of misfolded proteins by HSP inhibitors, proteasome inhibitors, hyperthermia, or inducers of endoplasmic reticulum stress represents a new method of cancer cell killing exploitable for therapeutic purposes. This review describes drugs - approved, repurposed, or under investigation - that can be used to accumulate misfolded proteins in cancer cells, and particularly focuses on the molecular aspects that lead to the cytotoxicity of misfolded proteins in cancer cells.

The reprogramming of tumor stroma by HSF1 is a potent enabler of malignancy

Stromal cells within the tumor microenvironment are essential for tumor progression and metastasis. Surprisingly little is known about the factors that drive the transcriptional reprogramming of stromal cells within tumors. We report that the transcriptional regulator heat shock factor 1 (HSF1) is frequently activated in cancer-associated fibroblasts (CAFs), where it is a potent enabler of malignancy. HSF1 drives a transcriptional program in CAFs that complements, yet is completely different from, the program it drives in adjacent cancer cells. This CAF program is uniquely structured to support malignancy in a non-cell-autonomous way. Two central stromal signaling molecules-TGF-β and SDF1-play a critical role. In early-stage breast and lung cancer, high stromal HSF1 activation is strongly associated with poor patient outcome. Thus, tumors co-opt the ancient survival functions of HSF1 to orchestrate malignancy in both cell-autonomous and non-cell-autonomous ways, with far-reaching therapeutic implications.

An RNA aptamer specific to Hsp70-ATP conformation inhibits its ATPase activity independent of Hsp40

The highly conserved and ubiquitous molecular chaperone heat shock protein 70 (Hsp70) plays a critical role in protein homeostasis (proteostasis). Controlled by its ATPase activity, Hsp70 cycles between two conformations, Hsp70-ATP and Hsp70-ADP, to bind and release its substrate. Chemical tools with distinct modes of action, especially those capable of modulating the ATPase activity of Hsp70, are being actively sought after in the mechanistic dissection of this system. Here, we report a conformation-specific RNA aptamer that binds only to Hsp70-ATP but not to Hsp70-ADP. We have refined this aptamer and demonstrated its inhibitory effect on Hsp70's ATPase activity. We have also shown that this inhibitory effect on Hsp70 is independent of its interaction with the Hsp40 co-chaperone. As Hsp70 is increasingly being recognized as a drug target in a number of age related diseases such as neurodegenerative, protein misfolding diseases and cancer, this aptamer is potentially useful in therapeutic applications. Moreover, this work also demonstrates the feasibility of using aptamers to target ATPase activity as a general therapeutic strategy.

Mutant p53 Amplifies Epidermal Growth Factor Receptor Family Signaling to Promote Mammary Tumorigenesis

The EGFR family (ErbB2/Her2 and EGFR/ErbB1/Her1) often modulates the transcriptional program involved in promoting mammary tumorigenesis. In humans, the majority of ErbB2-positive sporadic breast cancers harbor p53 mutations, which correlate with poor prognosis. Also, the extremely high incidence of ErbB2-positive breast cancer in women with p53 germline mutations (Li-Fraumeni syndrome) suggests a key role of mutant p53 specifically in ErbB2-mediated mammary tumorigenesis. To examine the role of mutant p53 during ErbB2-mediated mammary tumorigenesis, a mutant p53 allele (R172H) was introduced into the (MMTV)-ErbB2/Neu mouse model system. Interestingly, we show in heterozygous p53 mice that mutant p53 R172H is a more potent activator of ErbB2-mediated mammary tumorigenesis than simple loss of p53. The more aggressive disease in mutant p53 animals was reflected by earlier tumor onset, increased mammary tumor multiplicity, and shorter survival. These in vivo and in vitro data provide mechanistic evidence that mutant p53 amplifies ErbB2 and EGFR signaling to promote the expansion of mammary stem cells and induce cell proliferation.

IMPLICATIONS

This study identifies mutant p53 as an essential player in ErbB2 and EGFR-mediated mammary tumorigenesis and indicates the potential translational importance of targeting mutant p53 in this subset of patients with breast cancer.

Obesity depresses the anti-inflammatory HSP70 pathway, contributing to NAFLD progression

OBJECTIVES

To evaluate whether reduced activity of the anti-inflammatory HSP70 pathway correlates with nonalcoholic fatty liver disease (NAFLD) progression and with markers of oxidative stress because obesity activates inflammatory JNKs, whereas HSP70 exerts the opposite effect.

METHODS

Adult obese patients (N = 95) undergoing bariatric surgery were divided into steatosis (ST), steatohepatitis (SH), and fibrosis (SH+F) groups. The levels of HSP70, its major transcription factor, HSF1, and JNKs were assessed by immunoblotting hepatic and visceral adipose tissue; data were confirmed by immunohistochemistry. Plasma biochemistry (lipids, HbA1c , HOMA, hepatic enzymes, and redox markers) was also evaluated.

RESULTS

In both liver and adipose tissue, decreased HSP70 levels, paralleled by similar reductions in HSF1 and reduced plasma antioxidant enzyme activities, correlated with insulin resistance and with NAFLD progression (expression levels were as follows: ST > SH > SH + F). The immunohistochemistry results suggested Kupffer cells as a site of HSP70 inhibition. Conversely, JNK1 content and phosphorylation increased.

CONCLUSIONS

Decreased HSF1 levels in the liver and fat of obese patients correlated with impairment of HSP70 in an NAFLD stage-dependent manner. This impairment may affect HSP70-dependent anti-inflammation, with consequent oxidative stress and insulin resistance in advanced stages of NAFLD. Possible causal effects of fat cell senescence are discussed.

Celastrol, an oral heat shock activator, ameliorates multiple animal disease models of cell death

Protein homeostatic regulators have been shown to ameliorate single, loss-of-function protein diseases but not to treat broader animal disease models that may involve cell death. Diseases often trigger protein homeostatic instability that disrupts the delicate balance of normal cellular viability. Furthermore, protein homeostatic regulators have been delivered invasively and not with simple oral administration. Here, we report the potent homeostatic abilities of celastrol to promote cell survival, decrease inflammation, and maintain cellular homeostasis in three different disease models of apoptosis and inflammation involving hepatocytes and cardiomyocytes. We show that celastrol significantly recovers the left ventricular function and myocardial remodeling following models of acute myocardial infarction and doxorubicin-induced cardiomyopathy by diminishing infarct size, apoptosis, and inflammation. Celastrol prevents acute liver dysfunction and promotes hepatocyte survival after toxic doses of thioacetamide. Finally, we show that heat shock response (HSR) is necessary and sufficient for the recovery abilities of celastrol. Our observations may have dramatic clinical implications to ameliorate entire disease processes even after cellular injury initiation by using an orally delivered HSR activator.

Mutant p53 - Heat Shock Response Oncogenic Cooperation: A New Mechanism of Cancer Cell Survival

The main tumor suppressor function of p53 as a "guardian of the genome" is to respond to cellular stress by transcriptional activation of apoptosis, growth arrest, or senescence in damaged cells. Not surprisingly, mutations in the p53 gene are the most frequent genetic alteration in human cancers. Importantly, mutant p53 (mutp53) proteins not only lose their wild-type tumor suppressor activity but also can actively promote tumor development. Two main mechanisms accounting for mutp53 proto-oncogenic activity are inhibition of the wild-type p53 in a dominant-negative fashion and gain of additional oncogenic activities known as gain-of-function (GOF). Here, we discuss a novel mechanism of mutp53 GOF, which relies on its oncogenic cooperation with the heat shock machinery. This coordinated adaptive mechanism renders cancer cells more resistant to proteotoxic stress and provides both, a strong survival advantage to cancer cells and a promising means for therapeutic intervention.