Expression of heat shock proteins and heat shock protein messenger ribonucleic acid in human prostate carcinoma in vitro and in tumors in vivo

Protein expression profiling in esophageal adenocarcinoma patients indicates association of heat-shock protein 27 expression and chemotherapy response

PURPOSE

To identify pretherapeutic predictive biomarkers in tumor biopsies of patients with locally advanced esophageal adenocarcinomas treated with neoadjuvant chemotherapy, we used an explorative proteomic approach to correlate pretherapeutic protein expression profiles with tumor response to neoadjuvant chemotherapy.

EXPERIMENTAL DESIGN

Thirty-four patients with locally advanced esophageal adenocarcinomas who received neoadjuvant platin/5-fluorouracil-based chemotherapy before surgical resection were enrolled in this study. Response to chemotherapy was determined (a) by the amount of decline of [18F]fluorodeoxyglucose tumor uptake 2 weeks after the start of chemotherapy measured by positron emission tomography and (b) by histopathologic evaluation of tumor regression after surgical resection. Explorative quantitative and qualitative protein expression analysis was done through a quantitative differential protein expression analysis that used dual-isotope radioactive labeling of protein extracts. Selected identified biomarkers were validated by immunohistochemistry and quantitative real time reverse transcription-PCR.

RESULTS

Proteomic analysis revealed four cellular stress response-associated proteins [heat-shock protein (HSP) 27, HSP60, glucose-regulated protein (GRP) 94, GRP78] and a number of cytoskeletal proteins whose pretherapeutic abundance was significantly different (P < 0.001) between responders and nonresponders. Immunohistochemistry and gene expression analysis confirmed these data, showing a significant association between low HSP27 expression and nonresponse to neoadjuvant chemotherapy (P = 0.049 and P = 0.032, respectively).

CONCLUSIONS

Albeit preliminary, our encouraging data suggest that protein expression profiling may distinguish cancers with a different response to chemotherapy. Our results suggest that response to chemotherapy may be related to a different activation of stress response and inflammatory biology in general. Moreover, the potential of HSPs and GRPs as biomarkers of chemotherapy response warrants further validation.

Hsf1 is required for the nuclear translocation of p53 tumor suppressor

Although the p53 tumor suppressor is most frequently inactivated by genetic mutations, exclusion from the nucleus is also seen in human tumors. We have begun to examine p53 nuclear importation by isolating a series of mutant cells in which the temperature-sensitive murine p53(Val135) mutant is sequestered in the cytoplasm. We previously showed that that three of them (ALTR12, ALTR19, and ALTR25) constituted a single complementation group. Here, we found that ALTR12 cells are more sensitive to heat stress than either ALTR19 or ALTR25 and that there was a complete lack of induction of Hsp70 in response to heat shock. Western blot analysis showed no expression of the Hsf1 transcription factor, and neither heat shock nor azetidine could induce p53 nuclear localization in ALTR12 cells but did in parental A1-5 cells. Suppression of Hsf1 in A1-5 cells with quercetin or an Hsf1 siRNA reduced p53 nuclear importation and inhibited p53-mediated activation of a p21 reporter. Most convincingly, p53 nuclear importation could be restored in ALTR12 cells by introducing an exogenous Hsf1 gene. Collectively, our result suggests that Hsf1 is required for p53 nuclear importation and activation and implies that heat shock factors play a role in the regulation of p53.

Heat-shock proteins in cancer vaccines: agents of antigen cross-presentation

Heat-shock proteins (HSPs) derived from tumors are capable of eliciting an anticancer immune response by facilitating antigen cross-presentation in antigen-presenting cells (APCs). This process involves the ability of such chaperones to bind tumor antigens and facilitate their uptake by APCs. Recent evidence reveals that HSP-tumor antigen complexes bind cell surface proteins on APCs that mediate complex internalization and antigen-processing events, as well as inducing an innate immune response. Binding of HSPs to surface receptors is, thus, an imposing gateway to the induction of tumor-specific immune responses. Extensive studies in animals have indicated the usefulness of such HSP-based immunotherapy in killing established tumors and causing tumor regression. Currently, one HSP, the endoplasmic reticulum stress-response protein Gp96 is undergoing clinical trials for cancer treatment and has yielded promising results, including the induction of anti-tumor immunity and some benefit for patients when administered as part of a multidose regimen. Future advances in HSP-based immunotherapy will be aided by an understanding of the mechanisms by which HSP-peptide complexes induce innate and adaptive immunity to tumor cells and target the killing of primary and metastatic cancer cells.

The HspA2 protein localizes in nucleoli and centrosomes of heat shocked cancer cells

The human HSPA2 gene, which belongs to the HSP70 family of heat shock genes, is a counterpart of rodent testis-specific HspA2 gene. Rodent genes are expressed mainly in pachytene spermatocytes, while transcripts of human HSPA2 gene have been detected in various normal somatic tissues, albeit translation of the messenger RNA into corresponding protein has not been yet unambiguously demonstrated, except for several cancer cell lines. The aim of our work, a first step in search for HspA2 function in cancer cells, was to establish its intracellular localization at physiological temperature and during heat shock. First, we used qRT-PCR and a highly specific antibody to select cell lines with the highest expression of the HspA2 protein, which turned out to be A549 and NCI-H1299 lines originating from non-small cell lung carcinoma (NSCLC). Significant expression of the HspA2 was also detected by immunohistochemistry in primary NSCLC specimens. Intracellular localization of the HspA2 was studied using both the specific anti-HspA2 polyclonal antibody and transfection of cells with fusion proteins HspA2-EGFP and mRFP-HspA2. We found that, at physiological temperature, the HspA2 was localized primarily in cytoplasm whereas, during heat shock, localization shifted to nucleus and nucleoli. Moreover, we demonstrate that in heat-shocked cells HspA2 accumulated in centrosomes. Our results suggest that the HspA2, like Hsp70 protein, can be involved in protecting nucleoli and centrosomes integrity in cancer cells subjected to heat shock and, possibly, other cellular stressors.

Heat shock factor 1 represses estrogen-dependent transcription through association with MTA1

Heat shock factor 1 (HSF1), the transcriptional activator of the heat shock genes, is increasingly implicated in cancer. We have shown that HSF1 binds to the corepressor metastasis-associated protein 1 (MTA1) in vitro and in human breast carcinoma samples. HSF1-MTA1 complex formation was strongly induced by the transforming ligand heregulin and complexes incorporated a number of additional proteins including histone deacetylases (HDAC1 and 2) and Mi2alpha, all components of the NuRD corepressor complex. These complexes were induced to assemble on the chromatin of MCF7 breast carcinoma cells and associated with the promoters of estrogen-responsive genes. Such HSF1 complexes participate in repression of estrogen-dependent transcription in breast carcinoma cells treated with heregulin and this effect was inhibited by MTA1 knockdown. Repression of estrogen-dependent transcription may contribute to the role of HSF1 in cancer.

Heat shock proteins: stress proteins with Janus-like properties in cancer

Heat shock proteins (HSPs) were first identified as stress proteins that confer resistance to physical stresses such as elevated temperatures in all cellular organisms. HSPs are rapidly elevated after stress and confer a temperature resistant phenotype. Temperature resistance is dependent on the ability of HSPs to function as molecular chaperones and prevent aggregation and on the capacity of Hsp27 and Hsp70 to act as wide spectrum inhibitors of the cell death pathways. HSP expression becomes deregulated in cancer leading to elevated expression. Elevated HSP expression promotes cancer by inhibiting programmed cell death (Hsp27, Hsp70) and by promoting autonomous growth (Hsp90) and leads to resistance to chemotherapy and hyperthermia. Tumor HSPs have another property that can be exploited in therapy. They are immunogenic and can be used to form the basis of anticancer vaccines. Elevation in HSP levels may thus have competing effects in tumor growth, being required for tumor cell survival but conferring a hazard for cancer cells due to their immunogenic properties. This dichotomy is also reflected by the approaches used to target HSP in therapy. Pharmacological approaches are being employed to inhibit activity or expression of tumor HSP. Immunological approaches aim at increasing HSP levels in cells and tissues with the aim of increasing tumor antigen presentation to the immune system.

Expression and clinical significance of glucose regulated proteins GRP78 (BiP) and GRP94 (GP96) in human adenocarcinomas of the esophagus

Background

Glucose regulated proteins (GRPs) are main regulators of cellular homeostasis due to their role as molecular chaperones. Moreover, the functions of GRPs suggest that they also may play important roles in cancer biology. In this study we investigated the glucose regulated proteins GRP78 (BiP) and GRP94 (GP96) in a series of human esophageal adenocarcinomas to determine their implications in cancer progression and prognosis.

Methods

Formalin-fixed, paraffin-embedded tissues of primary resected esophageal (Barrett) adenocarcinomas (n = 137) and corresponding normal tissue were investigated. mRNA-gene expression levels of GRP78 and GRP94 were determined by quantitative real-time RT-PCR after mRNA extraction. Protein expression analysis was performed with immunohistochemical staining of the cases, assembled on a tissue micorarray. The results were correlated with pathologic features (pT, pN, G) and overall survival.

Results

GRP78 and GRP94 mRNA were expressed in all tumors. The relative gene expression of GRP78 was significantly higher in early cancers (pT1m and pT1sm) as compared to more advanced stages (pT2 and pT3) and normal tissue (p = 0.031). Highly differentiated tumors showed also higher GRP78 mRNA levels compared to moderate and low differentiated tumors (p = 0.035). In addition, patients with higher GRP78 levels tended to show a survival benefit (p = 0.07). GRP94 mRNA-levels showed no association to pathological features or clinical outcome.

GRP78 and GRP94 protein expression was detectable by immunohistochemistry in all tumors. There was a significant correlation between a strong GRP78 protein expression and early tumor stages (pT1m and pT1sm, p = 0.038). For GRP94 low to moderate protein expression was significantly associated with earlier tumor stage (p = 0.001) and less lymph node involvement (p = 0.036). Interestingly, the patients with combined strong GRP78 and GRP94 protein expression exclusively showed either early (pT1m or pT1sm) or advanced (pT3) tumor stages and no pT2 stage (p = 0.031).

Conclusion

We could demonstrate an association of GRP78 and GRP94 mRNA and protein expression with tumor stage and behaviour in esophageal adenocarcinomas. Increased expression of GRP78 may be responsible for controlling local tumor growth in early tumor stages, while high expression of GRP78 and GRP94 in advanced stages may be dependent from other factors like cellular stress reactions due to glucose deprivation, hypoxia or the hosts' immune response.

Targeting Cdc37 inhibits multiple signaling pathways and induces growth arrest in prostate cancer cells

Members of the 90-kDa heat shock protein (HSP90) family are known to bind and stabilize intermediates in a wide variety of cell signaling pathways and contribute to their dysregulation in cancer. An important intracellular cofactor for HSP90 is Cdc37, a protein with a broad role in fostering the activities of protein kinases. By targeting Cdc37 using RNA interference, we have shown that the loss of Cdc37 function induces irreversible growth arrest in androgen receptor-positive and -negative prostate carcinoma cells. In contrast to HSP90-directed agents, Cdc37 targeting seems to affect cancer cells through a distinct mechanism and does not significantly deplete the intracellular levels of most known HSP90 client proteins. Instead, Cdc37 depletion inhibits cellular kinase activity and flux through growth-promoting signal transduction cascades. We show that the loss of Cdc37 leads to reduced activity of the Erk, Akt, mTOR, and androgen-induced pathways. We have also discovered synergistic interactions between Cdc37 inactivation and the HSP90-inhibitory anticancer drug 17-(allylamino)-17-demethoxygeldanamycin (17AAG). These interactions involve enhanced degradation of proteins essential for growth and inhibition of 17AAG-induced expression of the antiapoptotic HSP70. Thus, Cdc37 is essential for maintaining prostate tumor cell growth and may represent a novel target in the search for multitargeted therapies based on the HSP90 chaperone system.

Heat shock factor 1 is a powerful multifaceted modifier of carcinogenesis

Heat shock factor 1 (HSF1) is the master regulator of the heat shock response in eukaryotes, a very highly conserved protective mechanism. HSF1 function increases survival under a great many pathophysiological conditions. How it might be involved in malignancy remains largely unexplored. We report that eliminating HSF1 protects mice from tumors induced by mutations of the RAS oncogene or a hot spot mutation in the tumor suppressor p53. In cell culture, HSF1 supports malignant transformation by orchestrating a network of core cellular functions including proliferation, survival, protein synthesis, and glucose metabolism. The striking effects of HSF1 on oncogenic transformation are not limited to mouse systems or tumor initiation; human cancer lines of diverse origins show much greater dependence on HSF1 function to maintain proliferation and survival than their nontransformed counterparts. While it enhances organismal survival and longevity under most circumstances, HSF1 has the opposite effect in supporting the lethal phenomenon of cancer.

Can the stress protein response be controlled by 'membrane-lipid therapy'?

In addition to high temperature, other stresses and clinical conditions such as cancer and diabetes can lead to the alteration of heat-shock protein (HSP) levels in cells. Moreover, HSPs can associate with either specific lipids or with areas of special membrane topology (such as lipid rafts), and changes in the physical state of cellular membranes can alter hsp gene expression. We propose that membrane microheterogeneity is important for regulating the HSP response. In support of this hypothesis, when particular membrane intercalating compounds are used to alter membrane properties, the simultaneous normalization of dysregulated expression of HSPs causes beneficial responses to disease states. Therefore, these compounds (such as hydroxylamine derivatives) have the potential to become a new class of pharmaceuticals for use in 'membrane-lipid therapy'.

Molecular chaperones regulate p53 and suppress senescence programs

Many types of cancer cells constitutively express major molecular chaperones at high levels. Recent findings demonstrate that specific depletion of individual chaperones, including various members of the Hsp70 family, small heat shock proteins, or VCP/p97, leads to activation of p53 pathway and subsequently triggers cellular senescence. Here, we discuss a possibility that in cancer cells high levels of chaperones serve to keep the p53 signaling under control, thus allowing cancer cells to evade the default senescence and form tumors.

Heat shock protein 70 is secreted from tumor cells by a nonclassical pathway involving lysosomal endosomes

Heat shock protein (HSP)70 can be released from tumor cells and stimulate a potent antitumor immune response. However, HSP70 does not contain a consensus secretory signal and thus cannot traverse the plasma membrane by conventional mechanisms. We have observed HSP70 release from intact human prostate carcinoma cell lines (PC-3 and LNCaP) by a mechanism independent of de novo HSP70 synthesis or cell death. This pathway is similar to one used by the leaderless protein IL-1beta. Our studies show that HSP70 release involves transit though an endolysosomal compartment and is inhibited by lysosomotropic compounds. In addition, the rate of HSP70 secretion correlates well with the appearance of the lysosomal marker LAMP1 on the cell surface, further suggesting the role for endolysosomes. The entry of HSP70 into this secretory compartment appears to involve the ABC family transporter proteins and ABC transporter inhibitor glibenclamide antagonizes secretion. Although the cell signals involved in triggering stress induced HSP70 release though this lysosomal pathway are largely unknown, our experiments suggest a regulatory role for extracellular ATP. These mechanisms appear to be shared by IL-1beta secretion. Following release, we observed the binding of extracellular HSP70 to the cell surface of the prostate carcinoma cells. These findings suggest that secreted HSP70 can take part in paracrine or autocrine interactions with adjacent cell surfaces. Our experiments therefore suggest a mechanism for HSP70 secretion and binding to the surface of other cells that may be involved in recognition of the tumor cells by the immune system.

Role of scavenger receptors in the binding and internalization of heat shock protein 70

Extracellular heat shock protein 70 (Hsp70) exerts profound effects both in mediating tumor rejection by Hsp70-based vaccines and in autoimmunity. Further progress in this area, however, awaits the identification of the cell surface receptors for extracellular Hsp70 that mediate its immune functions. We have examined a wide range of candidate Hsp70 receptors and find significant binding through two main families of cell surface proteins, including 1) the scavenger receptor (SR) family and 2) C-type lectins of the NK family. In addition, given that the anticancer effects of Hsp70 vaccines have been shown to involve uptake of Ags by APC exposed to Hsp70-tumor Ag complexes, we have examined the ability of the receptors identified here to internalize Hsp70-peptide complexes. Our findings indicate that three members of the SR family (lectin-like oxidized low density lipoprotein receptor 1; fasciclin, epidermal growth factor-like, laminin-type epidermal growth factor-like, and link domain-containing scavenger receptor-1; and SR expressed by endothelial cells-1) are able to bind Hsp70-peptide complexes and mediate its efficient internalization. Indeed, each of the SR was able to mediate efficient uptake of Hsp70 when transfected into Chinese hamster ovary cells previously null for uptake. Curiously, Hsp70 internalization occurs independently of the intracellular domains of the SR, and Hsp70 uptake could be detected when the entire intracellular domain of lectin-like oxidized low density lipoprotein receptor 1 or SR expressed by endothelial cells-1 was truncated. The existence of a wide repertoire of cell surface Hsp70-binding structures may permit intracellular responses to extracellular Hsp70 that are cell specific and discriminate between Hsp70 family members.

Enhanced immunogenicity of heat shock protein 70 peptide complexes from dendritic cell-tumor fusion cells

We have developed a molecular chaperone-based tumor vaccine that reverses the immune tolerance of cancer cells. Heat shock protein (HSP) 70 extracted from fusions of dendritic (DC) and tumor cells (HSP70.PC-F) possess superior properties such as stimulation of DC maturation and T cell proliferation over its counterpart from tumor cells. More importantly, immunization of mice with HSP70.PC-F resulted in a T cell-mediated immune response including significant increase of CD8 T cells and induction of the effector and memory T cells that was able to break T cell unresponsiveness to a nonmutated tumor Ag and provide protection of mice against challenge with tumor cells. By contrast, the immune response to vaccination with HSP70-PC derived from tumor cells is muted against such nonmutated tumor Ag. HSP70.PC-F complexes differed from those derived from tumor cells in a number of key manners, most notably, enhanced association with immunologic peptides. In addition, the molecular chaperone HSP90 was found to be associated with HSP70.PC-F as indicated by coimmunoprecipitation, suggesting ability to carry an increased repertoire of antigenic peptides by the two chaperones. Significantly, activation of DC by HSP70.PC-F was dependent on the presence of an intact MyD88 gene, suggesting a role for TLR signaling in DC activation and T cell stimulation. These experiments indicate that HSP70-peptide complexes (PC) derived from DC-tumor fusion cells have increased their immunogenicity and therefore constitute an improved formulation of chaperone protein-based tumor vaccine.

Expression of BAG-1 protein correlates with aggressive behavior of prostate cancers

BACKGROUND

Differences in tumor behavior, ranging from indolent to aggressive, create a need for novel prognostic biomarkers. BAG-1 is a co-chaperone that regulates the activity of Hsp70, Bcl-2, Raf-1, growth factor, and steroid receptors (e.g., the Androgen Receptor).

METHODS

Using immunohistochemical method, we explored BAG-1 expression in prostate cancers and its association with clinicopathological parameters.

RESULTS

BAG-1 immunostaining was elevated in prostate cancer compared to normal prostatic epithelium. Higher nuclear BAG-1 in hormone-refractory (n = 34) compared to localized untreated tumors (n = 58) (P < 0.0001) suggested that upregulation of the nuclear isoform may contribute to disease progression. In 64 early-stage patients (T2N0M0) treated with external-beam irradiation, cytosolic BAG-1 correlated with higher pretreatment levels of serum Prostate specific antigen (P = 0.04) and shorter time to disease progression (P = 0.00004).

CONCLUSIONS

Increased cytosolic and nuclear BAG-1 expression may denote more aggressive variants of prostate cancer.

Heat shock proteins in cancer: diagnostic, prognostic, predictive, and treatment implications

Heat shock proteins (Hsps) are overexpressed in a wide range of human cancers and are implicated in tumor cell proliferation, differentiation, invasion, metastasis, death, and recognition by the immune system. We review the current status of the role of Hsp expression in cancer with special emphasis on the clinical setting. Although Hsp levels are not informative at the diagnostic level, they are useful biomarkers for carcinogenesis in some tissues and signal the degree of differentiation and the aggressiveness of some cancers. In addition, the circulating levels of Hsp and anti-Hsp antibodies in cancer patients may be useful in tumor diagnosis. Furthermore, several Hsp are implicated with the prognosis of specific cancers, most notably Hsp27, whose expression is associated with poor prognosis in gastric, liver, and prostate carcinoma, and osteosarcomas, and Hsp70, which is correlated with poor prognosis in breast, endometrial, uterine cervical, and bladder carcinomas. Increased Hsp expression may also predict the response to some anticancer treatments. For example, Hsp27 and Hsp70 are implicated in resistance to chemotherapy in breast cancer, Hsp27 predicts a poor response to chemotherapy in leukemia patients, whereas Hsp70 expression predicts a better response to chemotherapy in osteosarcomas. Implication of Hsp in tumor progression and response to therapy has led to its successful targeting in therapy by 2 main strategies, including: (1) pharmacological modification of Hsp expression or molecular chaperone activity and (2) use of Hsps in anticancer vaccines, exploiting their ability to act as immunological adjuvants. In conclusion, the present times are of importance for the field of Hsps in cancer, with great contributions to both basic and clinical cancer research.

Triptolide, an Inhibitor of the Human Heat Shock Response That Enhances Stress-induced Cell Death

Molecular chaperones, inducible by heat shock and a variety of other stresses, have critical roles in protein homeostasis, balancing cell stress with adaptation, survival, and cell death mechanisms. In transformed cells and tumors, chaperones are frequently overexpressed, with constitutive activation of the heat shock transcription factor HSF1 implicated in tumor formation. Here, we describe the activity of triptolide, a diterpene triepoxide from the plant Triptergium wilfordii, as an inhibitor of the human heat shock response. Triptolide treatment of human tissue culture cells prevented the inducible expression of heat shock genes, shown by suppression of an HSP70 promoter-reporter construct and by suppression of endogenous HSP70 gene expression. Upon examining the steps in the HSF1 activation pathway, we found that triptolide abrogates the transactivation function of HSF1 without interfering in the early events of trimer formation, hyperphosphorylation, and DNA binding. The ability of triptolide to inhibit the heat shock response renders these cells sensitive to stress-induced cell death, which may be of great relevance to cancer treatments.

Heat shock proteins in cancer: chaperones of tumorigenesis

The heat shock proteins (HSPs) induced by cell stress are expressed at high levels in a wide range of tumors and are closely associated with a poor prognosis and resistance to therapy. The increased transcription of HSPs in tumor cells is due to loss of p53 function and to higher expression of the proto-oncogenes HER2 and c-Myc, and is crucial to tumorigenesis. The HSP family members play overlapping, essential roles in tumor growth both by promoting autonomous cell proliferation and by inhibiting death pathways. The HSPs have thus become targets for rational anti-cancer drug design: HSP90 inhibitors are currently showing much promise in clinical trials, whereas the increased expression of HSPs in tumors is forming the basis of chaperone-based immunotherapy.

Message in a bottle: role of the 70-kDa heat shock protein family in anti-tumor immunity

Extracellular heat shock protein 70 (HSP70) is a potent agent for tumor immunotherapy, which can break tolerance to tumor-associated antigens and cause specific tumor cell killing by cytotoxic CD8+ T cells. The pro-immune effects of extracellular HSP70 are, to some extent, extensions of its molecular properties as an intracellular stress protein. The HSP70 are characterized by massive inducibility after stress, preventing cell death by inhibiting aggregation of cell proteins and directly antagonizing multiple cell death pathways. HSP70 family members possess a domain in the C terminus that chaperones unfolded proteins and peptides, and a N-terminal ATPase domain that controls the opening and closing of the peptide binding domain. These properties not only enable intracellular HSP70 to inhibit tumor apoptosis, but also promote formation of stable complexes with cytoplasmic tumor antigens that can then escape intact from dying cells to interact with antigen-processing cells (APC) and stimulate anti-tumor immunity. HSP70 may be released from tumors undergoing therapy at high local extracellular concentrations, and send a danger signal to the host leading to APC activation. Extracellular HSP70 bind to high-affinity receptors on APC, leading to activation of maturation and re-presentation of the peptide antigen cargo of HSP70 by the APC. The ability of HSP70-peptide complexes (HSP70-PC) to break tolerance and cause tumor regression employs these dual properties as signaling ligand and antigen transporter. HSP70-PC thus coordinately activate innate immune responses and deliver antigens for re-presentation by MHC class I and II molecules on the APC cell surface, leading to specific anti-tumor immunity.

Induction of heat shock proteins by heregulin beta1 leads to protection from apoptosis and anchorage-independent growth

Elevation of heat shock protein (HSP) levels is widespread in cancer and predicts a poor prognosis and resistance to therapy. We show that HSP elevation in tumor cells can be induced by the highly malignant factor heregulin beta1 (HRGbeta1), which induces HSP expression through heat shock transcription factor 1 (HSF1). Inactivation of the hsf1 gene prevents HSP induction by HRGbeta1. HSP expression is induced through a cascade response initiated by HRGbeta1 binding to c-erbB receptors on the cell surface and which leads to the inhibition of intracellular HSF1 antagonist glycogen synthase kinase 3. HSF1 activated by this pathway plays a key role in the protection of cells from apoptosis and the mediation of anchorage independent growth by HRGbeta1, indicating a role for HSF1 in this tumorigenic pathway.