Heat shock factor 1 is a powerful multifaceted modifier of carcinogenesis

Expression of heat shock proteins in classical Hodgkin lymphoma: correlation with apoptotic pathways and prognostic significance

AIMS

Heat shock proteins (HSPs), known to inhibit apoptosis and promote cellular survival, are overexpressed in many tumours. We analysed the expression of relevant HSPs and heat shock factor 1 (HSF1) in classical Hodgkin lymphoma (cHL) and their relationship with caspase signalling pathways and patient outcome.

METHODS AND RESULTS

Using tissue microarrays (TMAs), most cases showed strong immunohistochemical expression of HSPs [10, 27, 40, 60, 70, 90, 110, HO1, cell division cycle 37 homolog (CDC37) and HSF1, which points to cHL as a potential candidate to stress-response inhibitors. Active caspases 3, 8 and 9 were detected in 55.1%, 55.4% and 96.2% of cases although cleaved poly (ADP-ribose) polymerase (PARP) was observed in only 16.1%, suggesting an improper functioning of apoptosis. Statistical analysis showed associations of HSP70 with active caspase 3 (P = 0.000); HSP40 with active caspase 9 (P = 0.031) and p53 (P = 0.003); HO1 with p53 (P = 0.006) and p21 (P = 0.005); and p53 with p21 (P = 0.015).

CONCLUSIONS

Correlations between the expression of apoptotic markers and HSPs may suggest a role for the latter in modulating apoptosis in cHL, mainly through the HSP70-HSP40 system, and in the stabilization of p53. Survival analyses showed that absence of active caspase 8 and HO1 had a negative impact in patient outcome.

BAG3: a multifaceted protein that regulates major cell pathways

Bcl2-associated athanogene 3 (BAG3) protein is a member of BAG family of co-chaperones that interacts with the ATPase domain of the heat shock protein (Hsp) 70 through BAG domain (110–124 amino acids). BAG3 is the only member of the family to be induced by stressful stimuli, mainly through the activity of heat shock factor 1 on bag3 gene promoter. In addition to the BAG domain, BAG3 contains also a WW domain and a proline-rich (PXXP) repeat, that mediate binding to partners different from Hsp70. These multifaceted interactions underlie BAG3 ability to modulate major biological processes, that is, apoptosis, development, cytoskeleton organization and autophagy, thereby mediating cell adaptive responses to stressful stimuli. In normal cells, BAG3 is constitutively present in a very few cell types, including cardiomyocytes and skeletal muscle cells, in which the protein appears to contribute to cell resistance to mechanical stress. A growing body of evidence indicate that BAG3 is instead expressed in several tumor types. In different tumor contexts, BAG3 protein was reported to sustain cell survival, resistance to therapy, and/or motility and metastatization. In some tumor types, down-modulation of BAG3 levels was shown, as a proof-of-principle, to inhibit neoplastic cell growth in animal models. This review attempts to outline the emerging mechanisms that can underlie some of the biological activities of the protein, focusing on implications in tumor progression.

The possible prevention of cancer

The prevention of the infectious diseases was accomplished long before there was any understanding of the molecular biology of bacteria and viruses. As for cancer, the sharp drop in frequency of the once-commonest lethal cancer, stomach cancer, was achieved without any contribution from biological research, and the current drop in lung cancer is the end-result of the observation by epidemiologists that most lung cancer is caused by smoking. So the basis for both these triumphs was essentially empirical and owed nothing to biological research. This paper discusses how molecular biology can now offer the possibility of large-scale protection against cancer.

Implication of heat shock factors in tumorigenesis: therapeutical potential

Heat Shock Factors (HSF) form a family of transcription factors (four in mammals) which were named according to the discovery of their activation by a heat shock. HSFs trigger the expression of genes encoding Heat Shock Proteins (HSPs) that function as molecular chaperones, contributing to establish a cytoprotective state to various proteotoxic stresses and in pathological conditions. Increasing evidence indicates that this ancient transcriptional protective program acts genome-widely and performs unexpected functions in the absence of experimentally defined stress. Indeed, HSFs are able to re-shape cellular pathways controlling longevity, growth, metabolism and development. The most well studied HSF, HSF1, has been found at elevated levels in tumors with high metastatic potential and is associated with poor prognosis. This is partly explained by the above-mentioned cytoprotective (HSP-dependent) function that may enable cancer cells to adapt to the initial oncogenic stress and to support malignant transformation. Nevertheless, HSF1 operates as major multifaceted enhancers of tumorigenesis through, not only the induction of classical heat shock genes, but also of “non-classical” targets. Indeed, in cancer cells, HSF1 regulates genes involved in core cellular functions including proliferation, survival, migration, protein synthesis, signal transduction, and glucose metabolism, making HSF1 a very attractive target in cancer therapy. In this review, we describe the different physiological roles of HSFs as well as the recent discoveries in term of non-cogenic potential of these HSFs, more specifically associated to the activation of “non-classical” HSF target genes. We also present an update on the compounds with potent HSF1-modulating activity of potential interest as anti-cancer therapeutic agents.

Heat shock protein Hsp72 plays an essential role in Her2-induced mammary tumorigenesis

The major heat shock protein Hsp72 is expressed at elevated levels in many human cancers and its expression correlates with tumor progression. Here we investigated the role of Hsp72 in Her2 oncogene-induced neoplastic transformation and tumorigenesis. Expression of Her2 in untransformed MCF10A mammary epithelial cells caused transformation, as judged by foci formation in culture and tumorigenesis in xenografts. However, expression of Her2 in Hsp72-depleted cells failed to induce transformation. The anti-tumorigenic effects of Hsp72 downregulation were associated with cellular senescence due to accumulation of p21 and depletion of survivin. Accordingly, either knockdown of p21 or expression of survivin reversed this senescence process. Further, we developed an animal model of Hsp72-dependent breast cancer associated with expression of Her2. Knockout of Hsp72 almost completely suppressed tumorigenesis in the MMTVneu breast cancer mouse model. In young Hsp72 KO mice, expression of Her2 instead of mammary tissue hyperplasia led to suppression of duct development and blocked alveolar budding. These effects were due to massive cell senescence in mammary tissue, which was associated with upregulation of p21 and downregulation of survivin. Therefore Hsp72 plays an essential role in Her2-induced tumorigenesis by regulating oncogene-induced senescence pathways.

Autophagy facilitates glycolysis during Ras-mediated oncogenic transformation

The protumorigenic functions for autophagy are largely attributed to its ability to promote cancer cell survival in response to diverse stresses. Here we demonstrate an unexpected connection between autophagy and glucose metabolism that facilitates adhesion-independent transformation driven by a strong oncogenic insult-mutationally active Ras. In cells ectopically expressing oncogenic H-Ras as well as human cancer cell lines harboring endogenous K-Ras mutations, autophagy is induced following extracellular matrix detachment. Inhibiting autophagy due to the genetic deletion or RNA interference-mediated depletion of multiple autophagy regulators attenuates Ras-mediated adhesion-independent transformation and proliferation as well as reduces glycolytic capacity. Furthermore, in contrast to autophagy-competent cells, both proliferation and transformation in autophagy-deficient cells expressing oncogenic Ras are insensitive to reductions in glucose availability. Overall, increased glycolysis in autophagy-competent cells facilitates Ras-mediated adhesion-independent transformation, suggesting a unique mechanism by which autophagy may promote Ras-driven tumor growth in specific metabolic contexts.

Emerging metabolic targets in cancer therapy

Cancer cells are different from normal cells in their metabolic properties. Normal cells mostly rely on mitochondrial oxidative phosphorylation to produce energy. In contrast, cancer cells depend mostly on glycolysis, the aerobic breakdown of glucose into ATP. This altered energy dependency is known as the "Warburg effect" and is a hallmark of cancer cells. In recent years, investigating the metabolic changes within cancer cells has been a rapidly growing area. Emerging evidence shows that oncogenes that drive the cancer-promoting signals also drive the altered metabolism. Although the exact mechanisms underlying the Warburg effect are unclear, the existing evidence suggests that increased glycolysis plays an important role in support malignant behavior of cancer cells. A thorough understanding of the unique metabolism of cancer cells will help to design of more effective drugs targeting metabolic pathways, which will greatly impact the capacity to effectively treat cancer patients. Here we provide an overview of the current understanding of the Warburg effect upon tumor cell growth and survival, and discussion on the potential metabolic targets for cancer therapy.

Metallothionein and the biology of aging

Metallothionein (MT) is a low molecular weight protein with anti-apoptotic properties that has been demonstrated to scavenge free radicals in vitro. MT has not been extensively investigated within the context of aging biology. The purpose of this review, therefore, is to discuss findings on MT that are relevant to basic aging mechanisms and to draw attention to the possible role of MT in pro-longevity interventions. MT is one of just a handful of proteins that, when overexpressed, has been demonstrated to increase mouse lifespan. MT also protects against development of obesity in mice provided a high fat diet as well as diet-induced oxidative stress damage. Abundance of MT is responsive to caloric restriction (CR) and inhibition of the insulin/insulin-like signaling (IIS) pathway, and elevated MT gene expression has been observed in tissues from fasted and CR-fed mice, long-lived dwarf mice, worms maintained under CR conditions, and long-lived daf-2 mutant worms. The dysregulation of MT in these systems is likely to have tissue-specific effects on aging outcomes. Further investigation will therefore be needed to understand how MT contributes to the response of invertebrates and mice to CR and the endocrine mutations studied by aging researchers.

Heat shock proteins in breast cancer progression--a suitable case for treatment?

Heat shock proteins (HSP) and heat shock factor 1 (HSF1), key factors in the heat shock response (HSR) have been implicated in the etiology of breast cancer. At least two members of the HSP family, Hsp27 and Hsp70 undergo significant increases in cellular concentration during the transformation of mammary cells. These changes result in HSP-mediated inhibition of tumour cell inactivation through blockade of the apoptosis and replicative senescence pathways. The increases in HSP thus mediate two of the common hallmarks of cancer and favour cell birth over cell death. In addition, Hsp90 plays a role in facilitating transformation by stabilising the mutated and over-expressed oncoproteins found in breast tumours, and permitting the activation of growth stimulatory and transforming pathways in the absence of growth factors. HSF1 appears to play a similar role as a facilitator of transformation in mammary carcinoma. Induction of some facets of the HSR in breast cancer cells therefore leads to growth stimulation and inhibits cell death. Pharmacological targeting of HSP and HSF1 is therefore indicated and in the case of Hsp90, inhibitory drugs are undergoing clinical trial for treatment of breast carcinoma and other cancers.

Co-chaperones are limiting in a depleted chaperone network

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

KRIBB11 inhibits HSP70 synthesis through inhibition of heat shock factor 1 function by impairing the recruitment of positive transcription elongation factor b to the hsp70 promoter

Heat shock factor 1 (HSF1) is the master switch for heat shock protein (HSP) expression in eukaryotes. A synthetic chemical library was screened to identify inhibitors of HSF1 using a luciferase reporter under the control of a heat shock element. A compound named KRIBB11 (N(2)-(1H-indazole-5-yl)-N(6)-methyl-3-nitropyridine-2,6-diamine) was identified for its activity in abolishing the heat shock-induced luciferase activity with an IC(50) of 1.2 μmol/liter. When the cells were exposed to heat shock in the presence of KRIBB11, the induction of HSF1 downstream target proteins such as HSP27 and HSP70 was blocked. In addition, treatment of HCT-116 cells with KRIBB11 induced growth arrest and apoptosis. Markers of apoptosis, such as cleaved poly(ADP-ribose) polymerase, were detected after KRIBB11 treatment. Biotinyl-KRIBB11 was synthesized as an affinity probe for the identification of KRIBB11 target proteins. Using affinity chromatography and competition assays, KRIBB11 was shown to associate with HSF1 in vitro. Chromatin immunoprecipitation analysis showed that KRIBB11 inhibited HSF1-dependent recruitment of p-TEFb (positive transcription elongation factor b) to the hsp70 promoter. Finally, intraperitoneal treatment of nude mice with KRIBB11 at 50 mg/kg resulted in a 47.4% (p < 0.05) inhibition of tumor growth without body weight loss. Immunoblotting assays showed that the expression of HSP70 was lower in KRIBB11-treated tumor tissue than in control tissues. Because HSPs are expressed at high levels in a wide range of tumors, these results strengthen the rationale for targeting HSF1 in cancer therapy.

Protein kinase A binds and activates heat shock factor 1

BACKGROUND

Many inducible transcription factors are regulated through batteries of posttranslational modifications that couple their activity to inducing stimuli. We have studied such regulation of Heat Shock Factor 1 (HSF1), a key protein in control of the heat shock response, and a participant in carcinogenisis, neurological health and aging. As the mechanisms involved in the intracellular regulation of HSF1 in good health and its dysregulation in disease are still incomplete we are investigating the role of posttranslational modifications in such regulation.

METHODOLOGY/PRINCIPAL FINDINGS

In a proteomic study of HSF1 binding partners, we have discovered its association with the pleiotropic protein kinase A (PKA). HSF1 binds avidly to the catalytic subunit of PKA, (PKAcα) and becomes phosphorylated on a novel serine phosphorylation site within its central regulatory domain (serine 320 or S320), both in vitro and in vivo. Intracellular PKAcα levels and phosphorylation of HSF1 at S320 were both required for HSF1 to be localized to the nucleus, bind to response elements in the promoter of an HSF1 target gene (hsp70.1) and activate hsp70.1 after stress. Reduction in PKAcα levels by small hairpin RNA led to HSF1 exclusion from the nucleus, its exodus from the hsp70.1 promoter and decreased hsp70.1 transcription. Likewise, null mutation of HSF1 at S320 by alanine substitution for serine led to an HSF1 species excluded from the nucleus and deficient in hsp70.1 activation.

CONCLUSIONS

These findings of PKA regulation of HSF1 through S320 phosphorylation add to our knowledge of the signaling networks converging on this factor and may contribute to elucidating its complex roles in the stress response and understanding HSF1 dysregulation in disease.

The role of HDAC6 in cancer

Histone deacetylase 6 (HDAC6), a member of the HDAC family whose major substrate is α-tubulin, has become a target for drug development to treat cancer due to its major contribution in oncogenic cell transformation. Overexpression of HDAC6 correlates with tumorigenesis and improved survival; therefore, HDAC6 may be used as a marker for prognosis. Previous work demonstrated that in multiple myeloma cells, inhibition of HDAC6 results in apoptosis. Furthermore, HDAC6 is required for the activation of heat-shock factor 1 (HSF1), an activator of heat-shock protein encoding genes (HSPs) and CYLD, a cylindromatosis tumor suppressor gene. HDAC6 contributes to cancer metastasis since its upregulation increases cell motility in breast cancer MCF-7 cells and its interaction with cortactin regulates motility. HDAC6 also affects transcription and translation by regulating the heat-shock protein 90 (Hsp90) and stress granules (SGs), respectively. This review will discuss the role of HDAC6 in the pathogenesis and treatment of cancer.

The heat shock factor family and adaptation to proteotoxic stress

The heat shock response was originally characterized as the induction of a set of major heat shock proteins encoded by heat shock genes. Because heat shock proteins act as molecular chaperones that facilitate protein folding and suppress protein aggregation, this response plays a major role in maintaining protein homeostasis. The heat shock response is regulated mainly at the level of transcription by heat shock factors (HSFs) in eukaryotes. HSF1 is a master regulator of the heat shock genes in mammalian cells, as is HSF3 in avian cells. HSFs play a significant role in suppressing protein misfolding in cells and in ameliorating the progression of Caenorhabditis elegans, Drosophila and mouse models of protein-misfolding disorders, by inducing the expression of heat shock genes. Recently, numerous HSF target genes were identified, such as the classical heat shock genes and other heat-inducible genes, called nonclassical heat shock genes in this study. Importance of the expression of the nonclassical heat shock genes was evidenced by the fact that mouse HSF3 and chicken HSF1 play a substantial role in the protection of cells from heat shock without inducing classical heat shock genes. Furthermore, HSF2 and HSF4, as well as HSF1, shown to have roles in development, were also revealed to be necessary for the expression of certain nonclassical heat shock genes. Thus, the heat shock response regulated by the HSF family should consist of the induction of classical as well as of nonclassical heat shock genes, both of which might be required to maintain protein homeostasis.

α-Synuclein: membrane interactions and toxicity in Parkinson's disease

In the late 1990s, mutations in the synaptic protein &#x03B1;-synuclein (&#x03B1;-syn) were identified in families with hereditary Parkinson's disease (PD). Rapidly, &#x03B1;-syn became the target of numerous investigations that have transformed our understanding of the pathogenesis underlying this disorder. &#x03B1;-Syn is the major component of Lewy bodies (LBs), cytoplasmic protein aggregates that form in the neurons of PD patients. &#x03B1;-Syn interacts with lipid membranes and adopts amyloid conformations that deposit within LBs. Work in yeast and other model systems has revealed that &#x03B1;-syn-associated toxicity might be the consequence of abnormal membrane interactions and alterations in vesicle trafficking. Here we review evidence regarding &#x03B1;-syn's normal interactions with membranes and regulation of synaptic vesicles as well as how overexpression of &#x03B1;-syn yields global cellular dysfunction. Finally, we present a model linking vesicle dynamics to toxicity with the sincere hope that understanding these disease mechanisms will lead to the development of novel, potent therapeutics.

Overexpression of Colligin 2 in Glioma Vasculature is Associated with Overexpression of Heat Shock Factor 2

In previous studies we found expression of the protein colligin 2 (heat shock protein 47 (HSP47), SERPINH1) in glioma neovasculature while not in normal brain tissue. Generally, the regulation of heat shock gene expression in eukaryotes is mediated by heat shock factors (HSF). In mammals, three heat shock transcription factors, HSF-1, -2, and -4, have been isolated. Here we investigated the relation between the expression of colligin 2 and these heat shock factors at the mRNA level using real-time reverse transcriptase PCR (qRT-PCR) in different grades of astrocytic tumorigenesis, viz., low-grade glioma and glioblastoma. Endometrium samples, representing physiological angiogenesis, were included as controls. Since colligin 2 is a chaperon for collagens, the gene expression of collagen I (COL1A1) was also investigated. The blood vessel density of the samples was monitored by expression of the endothelial marker CD31 (PECAM1). Because NG2-immunopositive pericytic cells are involved in glioma neovascularization, the expression of NG2 (CSPG4) was also measured.

We demonstrate overexpression of HSF2 in both stages of glial tumorigenesis (reaching significance only in low-grade glioma) and also minor elevated levels of HSF1 as compared to normal brain. There were no differences in expression of HSF4 between low-grade glioma and normal brain while HSF4 was downregulated in glioblastoma. In the endometrium samples, none of the HSFs were upregulated. In the low-grade gliomas SERPINH appeared to be slightly overexpressed with a parallel 4-fold upregulation of COL1A1, while in glioblastoma there was over 5-fold overexpression of SERPINH1 and more than 150-fold overexpression of COL1A1. In both the lowgrade gliomas and the glioblastomas overexpression of CSPG4 was found and overexpression of PECAM1 was only found in the latter. Our data suggest that the upregulated expression of colligin 2 in glioma is accompanied by upregulation of COL1A1, CSPG4, HSF2 and to a lesser extent, HSF1. Further studies will unravel the association of these factors with colligin 2 expression, possibly leading to keys for therapeutic intervention.

Hyperthermia-induced Hsp90·eNOS preserves mitochondrial respiration in hyperglycemic endothelial cells by down-regulating Glut-1 and up-regulating G6PD activity

Uncoupling of NO production from NADPH oxidation by endothelial nitric-oxide synthase (eNOS) is enhanced in hyperglycemic endothelium, potentially due to dissociation of heat shock proteins 90 (Hsp90), and cellular glucose homeostasis is enhanced by a ROS-induced positive feed back mechanism. In this study we investigated how such an uncoupling impacts oxygen metabolism and how the oxidative phosphorylation can be preserved by heat shock (42 °C for 2 h, hyperthermia) in bovine aortic endothelial cells. Normal and heat-shocked bovine aortic endothelial cells were exposed to normoglycemia (NG, 5.0 mM) or hyperglycemia (30 mM). With hyperglycemia treatment, O(2) consumption rate was reduced (from V(O(2)max) = 7.51 ± 0.54 to 2.35 ± 0.27 mm Hg/min/10(6) cells), whereas in heat-shocked cells, O(2) consumption rate remained unaltered (8.19 ± 1.01 mm Hg/min/10 × 10(6) cells). Heat shock was found to enhance Hsp90/endothelial NOS interactions and produce higher NO. Moreover, ROS generation in the hyperglycemic condition was also reduced in heat-shocked cells. Interestingly, glucose uptake was reduced in heat-shocked cells as a result of decrease in Glut-1 protein level. Glucose phosphate dehydrogenase activity that gives rise to NADPH generation was increased by hyperthermia, and mitochondrial oxidative metabolism was preserved. In conclusion, the present study provides a novel mechanism wherein the reduced oxidative stress in heat-shocked hyperglycemic cells down-regulates Glut-1 and glucose uptake, and fine-tuning of this pathway may be a potential approach to use for therapeutic benefit of diabetes mellitus.

Heat shock proteins and Drosophila aging

Since their discovery in Drosophila, the heat shock proteins (Hsps) have been shown to regulate both stress resistance and life-span. Aging is characterized by increased oxidative stress and the accumulation of abnormal (malfolded) proteins, and these stresses induce Hsp gene expression through the transcription factor HSF. In addition, a subset of Hsps is induced by oxidative stress through the JNK signaling pathway and the transcription factor Foxo. The Hsps counteract the toxicity of abnormal proteins by facilitating protein refolding and turnover, and through other mechanisms including inhibition of apoptosis. The Hsps are up-regulated in tissue-specific patterns during aging, and their expression correlates with, and sometimes predicts, life span, making them ideal biomarkers of aging. The tools available for experimentally manipulating gene function and assaying healthspan in Drosophila provides an unparalleled opportunity to further study the role of Hsps in aging.

Transcriptional modulation of heat-shock protein gene expression

Heat-shock proteins (Hsps) are molecular chaperones that are ubiquitously expressed but are also induced in cells exposed to stressful stimuli. Hsps have been implicated in the induction and propagation of several diseases. This paper focuses on regulatory factors that control the transcription of the genes encoding Hsps. We also highlight how distinct transcription factors are able to interact and modulate Hsps in different pathological states. Thus, a better understanding of the complex signaling pathways regulating Hsp expression may lead to novel therapeutic targets.

Heat shock factor 1 ameliorates proteotoxicity in cooperation with the transcription factor NFAT

Heat shock transcription factor 1 (HSF1) is an important regulator of protein homeostasis (proteostasis) by controlling the expression of major heat shock proteins (Hsps) that facilitate protein folding. However, it is unclear whether other proteostasis pathways are mediated by HSF1. Here, we identified novel targets of HSF1 in mammalian cells, which suppress the aggregation of polyglutamine (polyQ) protein. Among them, we show that one of the nuclear factor of activated T cells (NFAT) proteins, NFATc2, significantly inhibits polyQ aggregation in cells and is required for HSF1-mediated suppression of polyQ aggregation. NFAT deficiency accelerated disease progression including aggregation of a mutant polyQ-huntingtin protein and shortening of lifespan in R6/2 Huntington's disease mice. Furthermore, we found that HSF1 and NFAT cooperatively induce the expression of the scaffold protein PDZK3 and αB-crystallin, which facilitate the degradation of polyQ protein. These results show the first mechanistic basis for the observation that HSF1 has a much more profound effect on proteostasis than individual Hsp or combination of different Hsps, and suggest a new pathway for ameliorating protein-misfolding diseases.

Heat shock transcription factor 1 localizes to sex chromatin during meiotic repression

Heat shock factor 1 (HSF1) is an important transcription factor in cellular stress responses, cancer, aging, and developmental processes including gametogenesis. Disruption of Hsf1, together with another HSF family member, Hsf2, causes male sterility and complete lack of mature sperm in mice, but the specific role of HSF1 in spermatogenesis has remained unclear. Here, we show that HSF1 is transiently expressed in meiotic spermatocytes and haploid round spermatids in mouse testis. The Hsf1(-/-) male mice displayed regions of seminiferous tubules containing only spermatogonia and increased morphological abnormalities in sperm heads. In search for HSF1 target genes, we identified 742 putative promoters in mouse testis. Among them, the sex chromosomal multicopy genes that are expressed in postmeiotic cells were occupied by HSF1. Given that the sex chromatin mostly is repressed during and after meiosis, it is remarkable that HSF1 directly regulates the transcription of sex-linked multicopy genes during postmeiotic repression. In addition, our results show that HSF1 localizes to the sex body prior to the meiotic divisions and to the sex chromocenter after completed meiosis. To the best of our knowledge, HSF1 is the first known transcription factor found at the repressed sex chromatin during meiosis.

Randomized phase II study of docetaxel and prednisone with or without OGX-011 in patients with metastatic castration-resistant prostate cancer

PURPOSE

To determine the clinical activity of OGX-011, an antisense inhibitor of clusterin, in combination with docetaxel/prednisone in patients with metastatic castration-resistant prostate cancer.

PATIENTS AND METHODS

Patients were randomly assigned 1:1 to receive docetaxel/prednisone either with (arm A) or without (arm B) OGX-011 640 mg intravenously weekly. The primary end point was the proportion of patients with a prostate-specific antigen (PSA) decline of ≥ 50% from baseline, with the experimental therapy being considered of interest if the proportion of patients with a PSA decline was more than 60%. Secondary end points were objective response rate, progression-free survival (PFS), overall survival (OS), and changes in serum clusterin.

RESULTS

Eighty-two patients were accrued, 41 to each arm. OGX-011 adverse effects included rigors and fevers. After cycle 1, median serum clusterin decreased by 26% in arm A and increased by 0.9% in arm B (P < .001). PSA declined by ≥ 50% in 58% of patients in arm A and 54% in arm B. Partial response occurred in 19% and 25% of patients in arms A and B, respectively. Median PFS and OS times were 7.3 months (95% CI, 5.3 to 8.8 months) and 23.8 months (95% CI, 16.2 months to not reached), respectively, in arm A and 6.1 months (95% CI, 3.7 to 8.6 months) and 16.9 months (95% CI, 12.8 to 25.8 months), respectively, in arm B. Baseline factors associated with improved OS on exploratory multivariate analysis were an Eastern Cooperative Oncology Group performance status of 0 (hazard ratio [HR], 0.27; 95% CI, 0.14 to 0.51), presence of bone or lymph node metastases only (HR, 0.45; 95% CI, 0.25 to 0.79), and treatment assignment to OGX-011 (HR, 0.50; 95% CI, 0.29 to 0.87).

CONCLUSION

Treatment with OGX-011 and docetaxel was well tolerated with evidence of biologic effect and was associated with improved survival. Further evaluation is warranted.

Activation of heat shock factor 1 plays a role in pyrrolidine dithiocarbamate-mediated expression of the co-chaperone BAG3

Adaptive responses to physical and inflammatory stressors are mediated by transcription factors and molecular chaperones. The transcription factor heat shock factor 1 (HSF1) has been implicated in extending lifespan in part by increasing expression of heat shock response genes. Pyrrolidine dithiocarbamate (PDTC) is a small thiol compound that exerts in vivo and in vitro anti-inflammatory properties through mechanisms that remain unclear. Here we report that PDTC induced the release of monomeric HSF1 from the molecular chaperone heat shock protein 90 (Hsp90), with concomitant increase in HSF1 trimer formation, translocation to the nucleus, and binding to promoter of target genes in human HepG2 cells. siRNA-mediated silencing of HSF1 blocked BAG3 gene expression by PDTC. The protein levels of the co-chaperone BAG3 and its interaction partner Hsp72 were stimulated by PDTC in a dose-dependent fashion, peaking at 6h. Inhibition of Hsp90 function by geldanamycin derivatives and novobiocin elicited a pattern of HSF1 activation and BAG3 expression that was similar to PDTC. Chromatin immunoprecipitation studies showed that PDTC and the inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin enhanced the binding of HSF1 to the promoter of several target genes, including BAG3, HSPA1A, HSPA1B, FKBP4, STIP1 and UBB. Cell treatment with PDTC increased significantly the level of Hsp90α thiol oxidation, a posttranslational modification known to inhibit its chaperone function. These results unravel a previously unrecognized mechanism by which PDTC and related compounds could confer cellular protection against inflammation through HSF1-induced expression of heat shock response genes.

Targeting the dynamic HSP90 complex in cancer

The molecular chaperone heat shock protein 90 (HSP90) has been used by cancer cells to facilitate the function of numerous oncoproteins, and it can be argued that cancer cells are 'addicted' to HSP90. However, although recent reports of the early clinical efficacy of HSP90 inhibitors are encouraging, the optimal use of HSP90-targeted therapeutics will depend on understanding the complexity of HSP90 regulation and the degree to which HSP90 participates in both neoplastic and normal cellular physiology.

Heat shock factors: integrators of cell stress, development and lifespan

Heat shock factors (HSFs) are essential for all organisms to survive exposures to acute stress. They are best known as inducible transcriptional regulators of genes encoding molecular chaperones and other stress proteins. Four members of the HSF family are also important for normal development and lifespan-enhancing pathways, and the repertoire of HSF targets has thus expanded well beyond the heat shock genes. These unexpected observations have uncovered complex layers of post-translational regulation of HSFs that integrate the metabolic state of the cell with stress biology, and in doing so control fundamental aspects of the health of the proteome and ageing.

Heat-shock transcription factor HSF1 has a critical role in human epidermal growth factor receptor-2-induced cellular transformation and tumorigenesis

The heat shock transcription factor HSF1 was recently demonstrated to play a key role in the development of tumors associated with activation of Ras or inactivation of p53. Here we show that HSF1 is required for cell transformation and tumorigenesis induced by HER2 oncogene responsible for aggressive breast tumors. Upon expression of HER2, untransformed human mammary epithelial cells MCF-10A underwent neoplastic transformation, formed foci in culture and tumors in nude mouse xenografts. However, expression of HER2 in MCF-10A cells with knockdown of HSF1 did not cause either foci formation or tumor growth in xenografts. The anti-tumorigenic effect of downregulation of HSF1 was associated with HER2-induced accumulation of the CDK inhibitor p21 and decrease of the mitotic regulator survivin, which resulted in growth inhibition and cell senescence. In fact, either knockout of p21 or overexpression of survivin alleviated these effects of HSF1 knockdown. Proliferation of certain human HER2-postitive breast cancer lines also requires HSF1, since its knockdown led to upregulation of p21 and/or drop of survivin, precipitating growth arrest. Similar effects were observed with a small molecular weight inhibitor of the heat shock response NZ28. Effects of HSF1 knockdown on growth arrest and senescence of HER2-expressing cells were associated with downregulation of Hsp72 and Hsp27. Therefore, HSF1 is critical for proliferation of HER2-expressing cells, most likely since it maintains levels of HSPs, which in turn control regulators of senescence p21 and survivin.

Major heat shock protein Hsp72 controls oncogene-induced senescence

Various heat shock proteins, including Hsp72, are strongly upregulated in cancers, but their significance for tumor emergence and growth is poorly understood. Here we review recent data from several labs to indicate that Hsps, including Hsp72, are critical for growth of transformed but not normal cells. By manipulating expression and activity of Hsp72 and several oncogenes, it was shown that Hsp72 suppresses oncogene-induced senescence, thus allowing proliferation of cancer cells. Importantly, Hsp72 is able to suppress both p53-dependent and p53-independent senescence pathways. We propose that targeting Hsp72 may be a promising approach toward development of novel cancer therapies.

Hsp90 as a gatekeeper of tumor angiogenesis: clinical promise and potential pitfalls

Tumor vascularization is an essential modulator of early tumor growth, progression, and therapeutic outcome. Although antiangiogenic treatments appear promising, intrinsic and acquired tumor resistance contributes to treatment failure. Clinical inhibition of the molecular chaperone heat shock protein 90 (Hsp90) provides an opportunity to target multiple aspects of this signaling resiliency, which may elicit more robust and enduring tumor repression relative to effects elicited by specifically targeted agents. This review highlights several primary effectors of angiogenesis modulated by Hsp90 and describes the clinical challenges posed by the redundant circuitry of these pathways. The four main topics addressed include (1) Hsp90-mediated regulation of HIF/VEGF signaling, (2) chaperone-dependent regulation of HIF-independent VEGF-mediated angiogenesis, (3) Hsp90-dependent targeting of key proangiogenic receptor tyrosine kinases and modulation of drug resistance, and (4) consideration of factors such as tumor microenvironment that pose several challenges for the clinical efficacy of anti-angiogenic therapy and Hsp90-targeted strategies.

Knocking down gene function with an RNA aptamer expressed as part of an intron

We developed a powerful expression system to produce aptamers and other types of functional RNA in yeast to examine their effects. Utilizing the intron homing process, the aptamer-coding sequences were integrated into hundreds of rRNA genes, and the aptamers were transcribed at high levels by RNA polymerase I without any additional promoter being introduced into the cell. We used this system to express an aptamer against the heat shock factor 1 (HSF1), a conserved transcription factor responsible for mobilizing specific genomic expression programs in response to stressful conditions such as elevated temperature. We observed a temperature sensitive growth retardation phenotype and specific decrease of heat shock gene expression. As HSF1 enables and promotes malignant growth and metastasis in mammals, and this aptamer binds yeast HSF1 and its mammalian ortholog with equal affinity, the results presented here attest to the potential of this aptamer as a specific and effective inhibitor of HSF1 activity.

Taspase1 functions as a non-oncogene addiction protease that coordinates cancer cell proliferation and apoptosis

Taspase1, the mixed lineage leukemia and TFIIAalpha-beta cleaving protease, enables cell proliferation and permits oncogenic initiation. Here, we show its critical role in cancer maintenance and thus offer a new anticancer target. Taspase1 is overexpressed in primary human cancers, and deficiency of Taspase1 in cancer cells not only disrupts proliferation but also enhances apoptosis. Mechanistically, loss of Taspase1 induces the levels of CDK inhibitors (CDKI: p16, p21, and p27) and reduces the level of antiapoptotic MCL-1. Therapeutically, deficiency of Taspase1 synergizes with chemotherapeutic agents and ABT-737, an inhibitor of BCL-2/BCL-X(L), to kill cancer cells. Taspase1 alone or in conjunction with MYC, RAS, or E1A fails to transform NIH/3T3 cells or primary mouse embryonic fibroblasts, respectively, but plays critical roles in cancer initiation and maintenance. Therefore, Taspase1 is better classified as a "non-oncogene addiction" protease, the inhibition of which may offer a novel anticancer therapeutic strategy. The reliance of oncogenes on subordinate non-oncogenes during tumorigenesis underscores the non-oncogene addiction hypothesis in which a large class of non-oncogenes functions to maintain cancer phenotypes and presents attractive anticancer therapeutic targets. The emergence of successful cancer therapeutics targeting non-oncogenes to which cancers are addicted supports the future development and potential application of small-molecule Taspase1 inhibitors for cancer therapy.

Roles of heat shock factor 1 and 2 in response to proteasome inhibition: consequence on p53 stability

A single heat shock factor (HSF), mediating the heat shock response, exists from yeast to Drosophila, whereas several related HSFs have been found in mammals. This raises the question of the specific or redundant functions of the different members of the HSF family and in particular of HSF1 and HSF2, which are both ubiquitously expressed. Using immortalized mouse embryonic fibroblasts (iMEFs) derived from wild-type, Hsf1(-/-), Hsf2(-/-) or double-mutant mice, we observed the distinctive behaviors of these mutants with respect to proteasome inhibition. This proteotoxic stress reduces to the same extent the viability of Hsf1(-/-)- and Hsf2(-/-)-deficient cells, but through different underlying mechanisms. Contrary to Hsf2(-/-) cells, Hsf1(-/-) cells are unable to induce pro-survival heat shock protein expression. Conversely, proteasome activity is lower in Hsf2(-/-) cells and the expression of some proteasome subunits, such as Psmb5 and gankyrin, is decreased. As gankyrin is an oncoprotein involved in p53 degradation, we analyzed the status of p53 in HSF-deficient iMEFs and observed that it was strongly stabilized in Hsf2(-/-) cells. This study points a new role for HSF2 in the regulation of protein degradation and suggests that pan-HSF inhibitors could be valuable tools to reduce chemoresistance to proteasome inhibition observed in cancer therapy.

Systems analysis of protein modification and cellular responses induced by electrophile stress

Biological electrophiles result from oxidative metabolism of exogenous compounds or endogenous cellular constituents, and they contribute to pathophysiologies such as toxicity and carcinogenicity. The chemical toxicology of electrophiles is dominated by covalent addition to intracellular nucleophiles. Reaction with DNA leads to the production of adducts that block replication or induce mutations. The chemistry and biology of electrophile−DNA reactions have been extensively studied, providing in many cases a detailed understanding of the relation between adduct structure and mutational consequences. By contrast, the linkage between protein modification and cellular response is poorly understood.

In this Account, we describe our efforts to define the chemistry of protein modification and its biological consequences using lipid-derived α,β-unsaturated aldehydes as model electrophiles. In our global approach, two large data sets are analyzed: one represents the identity of proteins modified over a wide range of electrophile concentrations, and the second comprises changes in gene expression observed under similar conditions. Informatics tools show theoretical connections based primarily on transcription factors hypothetically shared between the two data sets, downstream of adducted proteins and upstream of affected genes. This method highlights potential electrophile-sensitive signaling pathways and transcriptional processes for further evaluation.

Peroxidation of cellular phospholipids generates a complex mixture of both membrane-bound and diffusible electrophiles. The latter include reactive species such as malondialdehyde, 4-oxononenal, and 4-hydroxynonenal (HNE). Enriching HNE-adducted proteins for proteomic analysis was a technical challenge, solved with click chemistry that generated biotin-tagged protein adducts. For this purpose, HNE analogues bearing terminal azide or alkyne functionalities were synthesized. Cellular lysates were first exposed to a single type of HNE analogue (azido- or alkynyl-HNE), and then click reactions were performed against the cognate alkynyl- and azido-biotin derivative. The resulting biotin-labeled proteins were captured and enriched over a streptavidin matrix for subsequent mass spectrometric analysis. We thereby identified a multitude of HNE targets. Simultaneous microarray analysis of changes in gene expression triggered by HNE also produced an abundance of data. Functional analysis of both data sets generated the hypothesis that an important pathway of cellular response derives from electrophile modification of protein chaperones, resulting in the release of transcription factors that are their clients. Informatic analysis of the protein modification and microarray data sets identified several transcription factors as potential mediators of the cellular response to HNE-adducted proteins. Among these, heat shock factor 1 (HSF1) was confirmed as a sensitive and robust effector of HNE-induced changes in gene expression. Activation of HSF1 appears, in part, to be mediated by the electrophilic adduction of Hsp70 and Hsp90, which normally maintain HSF1 in an inactive cytosolic complex.

The identification of HSF1 as a mediator of biological effects downstream of HSF1 has provided new opportunities for research, illustrating the potential of our systems-based approach. Accordingly, we characterized HSF1-mediated gene expression in protecting against electrophile-induced toxicity. Among the genes induced by HSF1, Bcl-2- associated athanogene 3 (BAG3) is notable for its actions in promoting cell survival through stabilization of antiapoptotic Bcl-2 proteins, appearing to have a critical role in mediating cellular protection against electrophile-induced death.

Endoplasmic reticulum Ca2+ increases enhance mutant glucocerebrosidase proteostasis

Altering intracellular calcium levels is known to partially restore mutant enzyme homeostasis in several lysosomal storage diseases, but why? We hypothesize that endoplasmic reticulum (ER) calcium level increases enhance the folding, trafficking and function of these mutant misfolding/degradation-prone lysosomal enzymes by increasing chaperone function. Herein, we report that increasing ER calcium levels by reducing ER calcium efflux through the ryanodine receptor (antagonists or RNAi) or by promoting ER calcium influx by SERCA2b overexpression enhances mutant glucocerebrosidase (GC) homeostasis in Gaucher’s disease patient-derived cells. Post-translational regulation of the calnexin folding pathway by increasing the ER calcium concentration appears to enhance the capacity of this chaperone system to fold mutant misfolding-prone enzymes, increasing the folded mutant GC population that can engage the trafficking receptor at the expense of ER-associated degradation, increasing the lysosomal GC concentration.

Signal Transduction Pathways Leading to Heat Shock Transcription

Heat shock proteins (HSP) are essential for intracellular protein folding during stress and protect cells from denaturation and aggregation cascades that can lead to cell death. HSP genes are regulated at the transcriptional level by heat shock transcription factor 1 (HSF1) that is activated by stress and binds to heat shock elements in HSP genes. The activation of HSF1 during heat shock involves conversion from an inert monomer to a DNA binding trimer through a series of intramolecular folding rearrangements. However, the trigger for HSF1 at the molecular level is unclear and hypotheses for this process include reversal of feedback inhibition of HSF1 by molecular chaperones and heat-induced binding to large non-coding RNAs. Heat shock also causes a profound modulation in cell signaling pathways that lead to protein kinase activation and phosphorylation of HSF1 at a number of regulatory serine residues. HSP genes themselves exist in an accessible chromatin conformation already bound to RNA polymerase II. The RNA polymerase II is paused on HSP promoters after transcribing a short RNA sequence proximal to the promoter. Activation by heat shock involves HSF1 binding to the promoter and release of the paused RNA polymerase II followed by further rounds of transcriptional initiation and elongation. HSF1 is thus involved in both initiation and elongation of HSP RNA transcripts. Recent studies indicate important roles for histone modifications on HSP genes during heat shock. Histone modification occurs rapidly after stress and may be involved in promoting nucleosome remodeling on HSP promoters and in the open reading frames of HSP genes. Understanding these processes may be key to evaluating mechanisms of deregulated HSP expression that plays a key role in neurodegeneration and cancer.

Hyperthermia-associated carboplatin resistance: differential role of p53, HSF1 and Hsp70 in hepatoma cells

Due to substantial technical improvements, clinical application of heat as a co-adjuvant in cancer treatment is acquiring new interest. The effect of hyperthermia on hepatoma cell lines Hep3B (p53 defective) and HepG2 (p53 wild type) when investigated led to an interesting observation that Hep3B cells are more susceptible to heat stress than HepG2 cells. In addition, heat-induced carboplatin resistance was observed in HepG2 cells only. To investigate the reasons, heat shock response was explored and it was observed that heat stress augmented heat shock protein 70 (Hsp70) expression levels in HepG2 and not in Hep3B cells. Furthermore, in HepG2 cells, induced Hsp70 is regulated by both p53 and heat shock transcription factor 1 (HSF1) wherein HSF1 levels are modulated by p53. The data implies that Hep3B are more susceptible to death upon heat stress than HepG2 cells because of non-induction of Hsp70. In addition, it was observed that inhibition of heat-induced p53/HSF1 diminishes Hsp70 levels, thereby restoring the sensitivity of heat-stressed HepG2 cells to carboplatin-triggered cell death. Collectively, the present study establishes interplay of p53, HSF1, and Hsp70 upon heat stress in HepG2 cells and also defines novel strategies to overcome constraints of utility of hyperthermia in cancer therapy through p53/HSF1-targeted therapeutic intervention.

Role of lipid peroxidation in cellular responses to D,L-sulforaphane, a promising cancer chemopreventive agent

D,L-sulforaphane (SFN), a synthetic analogue of the broccoli-derived l-isomer, is a highly promising cancer chemopreventive agent substantiated by inhibition of chemically induced cancer in rodents and prevention of cancer development and distant site metastasis in transgenic mouse models of cancer. SFN is also known to inhibit growth of human cancer cells in association with cell cycle arrest and reactive oxygen species-dependent apoptosis, but the mechanism of these cellular responses to SFN exposure is not fully understood. Because 4-hydroxynonenal (4-HNE), a product of lipid peroxidation (LPO), the formation of which is regulated by hGSTA1-1, assumes a pivotal role in oxidative stress-induced signal transduction, we investigated its contribution in growth arrest and apoptosis induction by SFN using HL60 and K562 human leukemic cell lines as a model. The SFN-induced formation of 4-HNE was suppressed in hGSTA1-1-overexpressing cells, which also acquired resistance to SFN-induced cytotoxicity, cell cycle arrest, and apoptosis. While resistance to SFN-induced cell cycle arrest by ectopic expression of hGSTA1-1 was associated with changes in levels of G2/M regulatory proteins, resistance to apoptosis correlated with an increased Bcl-xL/Bax ratio, inhibition of nuclear translocation of AIF, and attenuated cytochrome c release in cytosol. The hGSTA1-1-overexpressing cells exhibited enhanced cytoplasmic export of Daxx, nuclear accumulation of transcription factors Nrf2 and HSF1, and upregulation of their respective client proteins, gamma-GCS and HSP70. These findings not only reveal a central role of 4-HNE in cellular responses to SFN but also reaffirm that 4-HNE contributes to oxidative stress-mediated signaling.

The miR-17-92 microRNA polycistron regulates MLL leukemia stem cell potential by modulating p21 expression

Despite advances in defining the critical molecular determinants for leukemia stem cell (LSC) generation and maintenance, little is known about the roles of microRNAs in LSC biology. Here, we identify microRNAs that are differentially expressed in LSC-enriched cell fractions (c-kit(+)) in a mouse model of MLL leukemia. Members of the miR-17 family were notably more abundant in LSCs compared with their normal counterpart granulocyte-macrophage progenitors and myeloblast precursors. Expression of miR-17 family microRNAs was substantially reduced concomitant with leukemia cell differentiation and loss of self-renewal, whereas forced expression of a polycistron construct encoding miR-17-19b miRNAs significantly shortened the latency for MLL leukemia development. Leukemias expressing increased levels of the miR-17-19b construct displayed a higher frequency of LSCs, more stringent block of differentiation, and enhanced proliferation associated with reduced expression of p21, a cyclin-dependent kinase inhibitor previously implicated as a direct target of miR-17 microRNAs. Knockdown of p21 in MLL-transformed cells phenocopied the overexpression of the miR-17 polycistron, including a significant decrease in leukemia latency, validating p21 as a biologically relevant and direct in vivo target of the miR-17 polycistron in MLL leukemia. Expression of c-myc, a crucial upstream regulator of the miR-17 polycistron, correlated with miR-17-92 levels, enhanced self-renewal, and LSC potential. Thus, microRNAs quantitatively regulate LSC self-renewal in MLL-associated leukemia in part by modulating the expression of p21, a known regulator of normal stem cell function.

IKK{gamma} protein is a target of BAG3 regulatory activity in human tumor growth

BAG3, a member of the BAG family of heat shock protein (HSP) 70 cochaperones, is expressed in response to stressful stimuli in a number of normal cell types and constitutively in a variety of tumors, including pancreas carcinomas, lymphocytic and myeloblastic leukemias, and thyroid carcinomas. Down-regulation of BAG3 results in cell death, but the underlying molecular mechanisms are still elusive. Here, we investigated the molecular mechanism of BAG3-dependent survival in human osteosarcoma (SAOS-2) and melanoma (M14) cells. We show that bag3 overexpression in tumors promotes survival through the NF-kappaB pathway. Indeed, we demonstrate that BAG3 alters the interaction between HSP70 and IKKgamma, increasing availability of IKKgamma and protecting it from proteasome-dependent degradation; this, in turn, results in increased NF-kappaB activity and survival. These results identify bag3 as a potential target for anticancer therapies in those tumors in which this gene is constitutively expressed. As a proof of principle, we show that treatment of a mouse xenograft tumor model with bag3siRNA-adenovirus that down-regulates bag3 results in reduced tumor growth and increased animal survival.

Role of heat shock factor-1 activation in the doxorubicin-induced heart failure in mice

Treating cancer patients with chemotherapeutics, such as doxorubicin (Dox), cause dilated cardiomyopathy and congestive heart failure because of oxidative stress. On the other hand, heat shock factor-1 (HSF-1), a transcription factor for heat shock proteins (Hsps), is also known to be activated in response to oxidative stress. However, the possible role of HSF-1 activation and the resultant Hsp25 in chemotherapeutic-induced heart failure has not been investigated. Using HSF-1 wild-type (HSF-1(+/+)) and knock-out (HSF-1(-/-)) mice, we tested the hypothesis that activation of HSF-1 plays a role in the development of Dox-induced heart failure. Higher levels of Hsp25 and its phosphorylated forms were found in the failing hearts of Dox-treated HSF-1(+/+) mice. More than twofold increase in Hsp25 mRNA level was found in Dox-treated hearts. Proteomic analysis showed that there is accumulation and aggregation of Hsp25 in Dox-treated failing hearts. Additionally, Hsp25 was found to coimmunoprecipitate with p53 and vice versa. Further studies indicated that the Dox-induced higher levels of Hsp25 transactivated p53 leading to higher levels of the pro-apoptotic protein Bax, but other p53-related proteins remained unaltered. Moreover, HSF-1(-/-) mice showed significantly reduced Dox-induced heart failure and higher survival rate, and there was no change in Bax upon treating with Dox in HSF-1(-/-) mice. From these results we propose a novel mechanism for Dox-induced heart failure: increased expression of Hsp25 because of oxidant-induced activation of HSF-1 transactivates p53 to increase Bax levels, which leads to heart failure.

A DNAJB chaperone subfamily with HDAC-dependent activities suppresses toxic protein aggregation

Misfolding and aggregation are associated with cytotoxicity in several protein folding diseases. A large network of molecular chaperones ensures protein quality control. Here, we show that within the Hsp70, Hsp110, and Hsp40 (DNAJ) chaperone families, members of a subclass of the DNAJB family (particularly DNAJB6b and DNAJB8) are superior suppressors of aggregation and toxicity of disease-associated polyglutamine proteins. The antiaggregation activity is largely independent of the N-terminal Hsp70-interacting J-domain. Rather, a C-terminal serine-rich (SSF-SST) region and the C-terminal tail are essential. The SSF-SST region is involved in substrate binding, formation of polydisperse oligomeric complexes, and interaction with histone deacetylases (HDAC4, HDAC6, SIRT2). Inhibiting HDAC4 reduced DNAJB8 function. DNAJB8 is (de)acetylated at two conserved C-terminal lysines that are not involved in substrate binding, but do play a role in suppressing protein aggregation. Combined, our data provide a functional link between HDACs and DNAJs in suppressing cytotoxic protein aggregation.

Arylamine N-acetyltransferase 1 gene regulation by androgens requires a conserved heat shock element for heat shock factor-1

Human arylamine N-acetyltransferase 1 (NAT1) is a widely distributed protein that has been implicated in a number of different cancers including breast and prostate. Previously, NAT1 gene expression was shown to be androgen dependent, although the effect of androgens was not due to direct activation of the NAT1 promoter. Here, we show that heat shock factor (HSF)1 is induced by androgen in androgen receptor-positive prostate 22Rv1 cells. It also binds to a heat shock element (HSE) in the NAT1 promoter located 776 bp upstream of the transcriptional start site. Mutation of the HSE inhibited androgen responsiveness and prevented direct upregulation of the NAT1 promoter by HSF1. Although HSF2 also bound to the HSE, it did not increase promoter activity. HSF1 induced endogenous NAT1 activity in this cell line in the absence of androgen. This could be attenuated by pretreating cells with HSF1-directed small interfering RNA but not by a scrambled sequence. Our results show that HSF1 is an important transcription factor for induction of NAT1 in human cells and is required for androgen activation of the NAT1 promoter.

Identification of inhibitors of HSF1 functional activity by high-content target-based screening

Cancer cells are known to experience a high level of stress and may require constant repair for survival and proliferation. Recent studies showed that inhibition of heat shock factor 1 (HSF1), the key regulator for the stress-activated transcription of heat shock protein (HSP), can reduce the tumorigenic potential of cancer cells. Such a "nononcogene addiction" phenomenon makes HSF1 an attractive cancer drug target. Here, the authors report an image-based high-content screening (HCS) assay for HSF1 functional inhibitors. A heat shock-based methodology was used to stimulate the stress response followed by quantitative measurement of HSF1/HSP70 granules for compound-induced inhibitory effects. The authors discovered a small molecule from a compound library that inhibits HSF1 granule formation substantially in heat-shocked HeLa cells with IC(50) at 80 nM. Electorphoretic mobility shift of HSF1 by this compound suggested significant inhibition of HSF1 phosphorylation, accompanied by reduced expression levels of HSP70 and HSP90 after heat induction. Importantly, HeLa cells stably transfected with HSF1 shRNA were more resistant to the compound treatment under lethal temperature than cells containing HSF1, further validating an HSF1-dependent mechanism of action. The HCS assay the authors developed was robust with a Z' factor of 0.65 in a 384-well plate format, providing a valuable method for identifying small-molecule functional inhibitors of HSF1 for potential cancer treatment.

Targeting the cytoprotective chaperone, clusterin, for treatment of advanced cancer

Many strategies used to kill cancer cells induce stress-responses that activate survival pathways to promote emergence of a treatment resistant phenotype. Secretory clusterin (sCLU) is a stress-activated cytoprotective chaperone up-regulated by many varied anticancer therapies to confer treatment resistance when overexpressed. sCLU levels are increased in several treatment recurrent cancers including castrate resistant prostate cancer, and therefore sCLU has become an attractive target in cancer therapy. sCLU is not druggable with small molecule inhibitors, therefore nucleotide-based strategies to inhibit sCLU at the RNA level are appealing. Preclinical studies have shown that antisense oligonucleotide (ASO) or siRNA knockdown of sCLU have preclinical activity in combination with hormone- and chemotherapy. Phase I and II clinical trial data indicate that the second generation ASO, custirsen (OGX-011), has biologic and clinical activity, suppressing sCLU expression in prostate cancer tissues by more than 90%. A randomized study comparing docetaxel-custirsen to docetaxel alone in men with castrate resistant prostate cancer reported improved survival by 7 months from 16.9 to 23.8 months. Strong preclinical and clinical proof-of-principle data provide rationale for further study of sCLU inhibitors in randomized phase III trials, which are planned to begin in 2010.

Heat shock factor 1 binds to and transcribes satellite II and III sequences at several pericentromeric regions in heat-shocked cells

Cells respond to stress by activating the synthesis of heat shock proteins (HSPs) which protect the cells against the deleterious effects of stress. This mechanism is controlled by the heat shock factor 1 (HSF1). In parallel to HSP gene transcription, in human cells, HSF1 also binds to and transcribes satellite III repeated sequences present in numerous copies in the 9q12 pericentromeric region of chromosome 9. These HSF1 accumulation sites are termed nuclear stress bodies (nSBs). In tumor cells, however, the number of nSBs is higher than the number of 9q12 copies, suggesting the existence of other HSF1 targets. In this paper, we were interested in characterizing these other HSF1 binding sites. We show that HSF1 indeed binds to the pericentromeric region of 14 chromosomes, thereby directing the formation of 'secondary nSBs'. The appearance of secondary nSBs depends on the number of satellite sequences present in the target locus, and on the cellular amount of HSF1 protein. Moreover, secondary nSBs also correspond to transcription sites, thus demonstrating that heat shock induces a genome-wide transcription of satellite sequences. Finally, by analyzing published transcriptomic data, we show that the derepression of these large heterochromatic blocks does not significantly affect the transcription of neighboring genes.

Modulation of heat shock transcription factor 1 as a therapeutic target for small molecule intervention in neurodegenerative disease

A yeast-based small molecule screen identifies a novel activator of human HSF1 and protein chaperone expression and which appears to alleviate the toxicity of protein misfolding diseases.

Neurodegenerative diseases such as Huntington disease are devastating disorders with no therapeutic approaches to ameliorate the underlying protein misfolding defect inherent to poly-glutamine (polyQ) proteins. Given the mounting evidence that elevated levels of protein chaperones suppress polyQ protein misfolding, the master regulator of protein chaperone gene transcription, HSF1, is an attractive target for small molecule intervention. We describe a humanized yeast-based high-throughput screen to identify small molecule activators of human HSF1. This screen is insensitive to previously characterized activators of the heat shock response that have undesirable proteotoxic activity or that inhibit Hsp90, the central chaperone for cellular signaling and proliferation. A molecule identified in this screen, HSF1A, is structurally distinct from other characterized small molecule human HSF1 activators, activates HSF1 in mammalian and fly cells, elevates protein chaperone expression, ameliorates protein misfolding and cell death in polyQ-expressing neuronal precursor cells and protects against cytotoxicity in a fly model of polyQ-mediated neurodegeneration. In addition, we show that HSF1A interacts with components of the TRiC/CCT complex, suggesting a potentially novel regulatory role for this complex in modulating HSF1 activity. These studies describe a novel approach for the identification of new classes of pharmacological interventions for protein misfolding that underlies devastating neurodegenerative disease.

The misfolding of proteins into a toxic state contributes to a variety of neurodegenerative diseases such as Huntington, Alzheimer, and Parkinson disease. Although no known cure exists for these afflictions, many studies have shown that increasing the levels of protein chaperones, proteins that assist in the correct folding of other proteins, can suppress the neurotoxicity of the misfolded proteins. As such, increasing the cellular concentration of protein chaperones might serve as a powerful therapeutic approach in treating protein misfolding diseases. Because the levels of protein chaperones in the cell are primarily controlled by the heat shock transcription factor 1 [HSF1], we have designed and implemented a pharmacological screen to identify small molecules that can promote human HSF1 activation and increase the expression of protein chaperones. Through these studies, we have identified HSF1A, a molecule capable of activating human HSF1, increasing the levels of protein chaperones and alleviating the toxicity of misfolded proteins in both cell culture as well as fruit fly models of neurodegenerative disease.

Anti-malaria drug blocks proteotoxic stress response: anti-cancer implications

The number of physical conditions and chemical agents induce accumulation of misfolded proteins creating proteotoxic stress. This leads to activation of adaptive pro-survival pathway, known as heat shock response (HSR), resulting in expression of additional chaperones. Several cancer treatment approaches, such as proteasome inhibitor Bortezomib and hsp90 inhibitor geldanamycin, involve activation of proteotoxic stress. Low efficacy of these therapies is likely due to the protective effects of HSR induced in treated cells, making this pathway an attractive target for pharmacological suppression. We found that the anti-malaria drugs quinacrine (QC) and emetine prevented HSR in cancer cells, as judged by induction of hsp70 expression. As opposed to emetine, which inhibited general translation, QC did not affect protein synthesis, but rather suppressed inducible HSF1-dependent transcription of the hsp70 gene in a relatively selective manner. The treatment of tumor cells in vitro with a combination of non-toxic concentrations of QC and proteotoxic stress inducers resulted in rapid induction of apoptosis. The effect was similar if QC was substituted by siRNA against hsp70, suggesting that the HSR inhibitory activity of QC was responsible for cell sensitization to proteotoxic stress inducers. QC was also found to enhance the antitumor efficacy of proteotoxic stress inducers in vivo: combinatorial treatment with 17-DMAG + QC resulted in suppression of tumor growth in two mouse syngeneic models. These results reveal that QC is an inhibitor of HSF1-mediated HSR. As such, this compound has significant clinical potential as an adjuvant in therapeutic strategies aimed at exploiting the cytotoxic potential of proteotoxic stress.

Heat shock factor 1-mediated aneuploidy requires a defective function of p53

Because heat shock factor 1 (HSF1) phosphorylation by Plk1 has been previously reported to be involved in mitotic regulation and p53 function may be involved in this mitotic regulation, we have further examined HSF1 functions in mitotic regulation according to p53 status. Nocodazole-mediated aneuploidy was increased in p53-defective (p53Mut) cells; however, it was not increased in p53 wild-type (p53WT) cells. Phosphorylation of HSF1 at Ser216 was increased in p53Mut cells with increased stability of securin and cyclin B1 in mitosis compared with p53WT cells. The interaction of p53 with Plk1 that was shown in p53WT cells and that induced normal mitotic checkpoint function was not observed in p53Mut cells; instead, the binding of HSF1 with Plk1 and HSF1 phosphorylation at Ser216 were seen in p53Mut cells, which resulted in increased aneuploidy production. Moreover, the interaction affinity of Cdc20 with Mad2 was inhibited in p53Mut cells, whereas the interaction between Cdc20 and HSF1 was increased. From the data, it was suggested that HSF1-mediated aneuploidy was more facilitated in p53-defective cells, indicating the importance of novel mechanisms for p53 function in HSF1-mediated mitotic regulation and genomic instability.