Hsp90 inhibition transiently activates Src kinase and promotes Src-dependent Akt and Erk activation

Co-targeting HSP90 alpha and CDK7 overcomes resistance against HSP90 inhibitors in BCR-ABL1+ leukemia cells

HSP90 has emerged as an appealing anti-cancer target. However, HSP90 inhibitors (HSP90i) are characterized by limited clinical utility, primarily due to the resistance acquisition via heat shock response (HSR) induction. Understanding the roles of abundantly expressed cytosolic HSP90 isoforms (α and β) in sustaining malignant cells' growth and the mechanisms of resistance to HSP90i is crucial for exploiting their clinical potential. Utilizing multi-omics approaches, we identified that ablation of the HSP90β isoform induces the overexpression of HSP90α and extracellular-secreted HSP90α (eHSP90α). Notably, we found that the absence of HSP90α causes downregulation of PTPRC (or CD45) expression and restricts in vivo growth of BCR-ABL1+ leukemia cells. Subsequently, chronic long-term exposure to the clinically advanced HSP90i PU-H71 (Zelavespib) led to copy number gain and mutation (p.S164F) of the HSP90AA1 gene, and HSP90α overexpression. In contrast, acquired resistance toward other tested HSP90i (Tanespimycin and Coumermycin A1) was attained by MDR1 efflux pump overexpression. Remarkably, combined CDK7 and HSP90 inhibition display synergistic activity against therapy-resistant BCR-ABL1+ patient leukemia cells via blocking pro-survival HSR and HSP90α overexpression, providing a novel strategy to avoid the emergence of resistance against treatment with HSP90i alone.

A Coumarin-Imidazothiadiazole Derivative, SP11 Abrogates Tumor Growth by Targeting HSP90 and Its Client Proteins

Despite several treatment options for blood cancer, mortality remains high due to relapse and the disease's aggressive nature. Elevated levels of HSP90, a molecular chaperone essential for protein folding, are associated with poor prognosis in leukemia and lymphoma. HSP90 as a target for chemotherapy has been met with limited success due to toxicity and induction of heat shock. This study tested the activity of an HSP90 inhibitor, SP11, against leukemic cells, mouse lymphoma allograft, and xenograft models. SP11 induced cytotoxicity in vitro in leukemic cell lines and induced cell death via apoptosis, with minimal effect on normal cells. SP11 induced cell death by altering the status of HSP90 client proteins both in vitro and in vivo. SP11 reduced the tumor burden in allograft and xenograft mouse models without apparent toxicity. The half-life of SP11 in the plasma was approximately 2 h. SP11 binding was observed at both the N-terminal and C-terminal domains of HSP90. C-terminal binding was more potent than N-terminal binding of HSP90 in silico and in vitro using isothermal calorimetry. SP11 bioavailability and minimal toxicity in vivo make it a potential candidate to be developed as a novel anticancer agent.

Molecular determinants of Hsp90 dependence of Src kinase revealed by deep mutational scanning

Hsp90 is a molecular chaperone involved in the refolding and activation of numerous protein substrates referred to as clients. While the molecular determinants of Hsp90 client specificity are poorly understood and limited to a handful of client proteins, strong clients are thought to be destabilized and conformationally extended. Here, we measured the phosphotransferase activity of 3929 variants of the tyrosine kinase Src in both the presence and absence of an Hsp90 inhibitor. We identified 84 previously unknown functionally dependent client variants. Unexpectedly, many destabilized or extended variants were not functionally dependent on Hsp90. Instead, functionally dependent client variants were clustered in the αF pocket and β1-β2 strand regions of Src, which have yet to be described in driving Hsp90 dependence. Hsp90 dependence was also strongly correlated with kinase activity. We found that a combination of activation, global extension, and general conformational flexibility, primarily induced by variants at the αF pocket and β1-β2 strands, was necessary to render Src functionally dependent on Hsp90. Moreover, the degree of activation and flexibility required to transform Src into a functionally dependent client varied with variant location, suggesting that a combination of regulatory domain disengagement and catalytic domain flexibility are required for chaperone dependence. Thus, by studying the chaperone dependence of a massive number of variants, we highlight factors driving Hsp90 client specificity and propose a model of chaperone-kinase interactions.

HSP90β promotes osteoclastogenesis by dual-activation of cholesterol synthesis and NF-κB signaling

Heat shock protein 90β (Hsp90β, encoded by Hsp90ab1 gene) is the most abundant proteins in the cells and contributes to variety of biological processes including metabolism, cell growth and neural functions. However, genetic evidences showing Hsp90β in vivo functions using tissue specific knockout mice are still lacking. Here, we showed that Hsp90β exerted paralogue-specific role in osteoclastogenesis. Using myeloid-specific Hsp90ab1 knockout mice, we provided the first genetic evidence showing the in vivo function of Hsp90β. Hsp90β binds to Ikkβ and reduces its ubiquitylation and proteasomal degradation, thus leading to activated NF-κB signaling. Meanwhile, Hsp90β increases cholesterol biosynthesis by activating Srebp2. Both pathways promote osteoclastogenic genes expression. Genetic deletion of Hsp90ab1 in osteoclast or pharmacological inhibition of Hsp90β alleviates bone loss in ovariectomy-induced mice. Therefore, Hsp90β is a promising druggable target for the treatment of osteoporosis.

The Heat Shock Protein 90 (HSP90) Is Required for the IL-33-Induced Cytokine Production in Mast Cells (MCs)

The alarmin interleukin-33 (IL-33) is released upon cell stress and damage in peripheral tissues. The receptor for IL-33 is the Toll/Interleukin-1 receptor (TIR)-family member T1/ST2 (the IL-33R), which is highly and constitutively expressed on MCs. The sensing of IL-33 by MCs induces the MyD88-TAK1-IKK2-dependent activation of p65/RelA and MAP-kinases, which mediate the production of pro-inflammatory cytokines and amplify FcεRI-mediated MC-effector functions and the resulting allergic reactions. Therefore, the investigation of IL-33-induced signaling is of interest for developing therapeutic interventions effective against allergic reactions. Importantly, beside the release of IL-33, heat shock proteins (HSPs) are upregulated during allergic reactions. This maintains the biological functions of signaling molecules and/or cytokines but unfortunately also strengthens the severity of inflammatory reactions. Here, we demonstrate that HSP90 does not support the IL-33-induced and MyD88-TAK1-IKK2-dependent activation of p65/RelA and of mitogen-activated protein (MAP)-kinases. We found that HSP90 acts downstream of these signaling pathways, mediates the stability of produced cytokine mRNAs, and therefore facilitates the resulting cytokine production. These data show that IL-33 enables MCs to perform an effective cytokine production by the upregulation of HSP90. Consequently, HSP90 might be an attractive therapeutic target for blocking IL-33-mediated inflammatory reactions.

Hsp90 and phosphorylation of the Slt2(Mpk1) MAP kinase activation loop are essential for catalytic, but not non-catalytic, Slt2-mediated transcription in yeast

In yeast, the Slt2(Mpk1) stress-activated protein kinase directs the activation of two transcription factors, Rlm1 and Swi4/Swi6, in response to cell wall stress. Rlm1 is activated through a phosphorylation by Slt2, whereas the Swi4/Swi6 activation is noncatalytic and triggered by the binding of phosphorylated forms of both Slt2 and a catalytically inactive pseudokinase (Mlp1). Previous studies have delineated a role for the molecular chaperone Hsp90 in the activation of Slt2, but the involvement of Hsp90 in these events of catalytic versus non-catalytic cell integrity signaling has remained elusive. In cells lacking Mlp1, the Hsp90 inhibitor radicicol was found to inhibit the Slt2-mediated catalytic activation of Rlm1, but not the noncatalytic activation of Swi4/Swi6. Mutation of residues in the TEY motif of the Slt2 activation loop strongly impacted both Hsp90 binding and Rlm1-mediated transcription. In contrast, many of these same mutations had only modest effects on Swi4/6 (Slt2-mediated, non-catalytic) transcription, although one that blocked both the Slt2:Hsp90 interaction and Rlm1-mediated transcription (E191G) triggered a hyperactivation of Swi4/6. Taken together, our results cement the importance of the Slt2 activation loop for both the binding of Hsp90 by Slt2 and the catalytic activation of cell integrity signaling.

Procr functions as a signaling receptor and is essential for the maintenance and self-renewal of mammary stem cells

The protein C receptor (Procr) has been implicated as a stem cell surface marker in several tissues. It is unknown whether Procr acts as a functional signaling receptor in stem cells. Here, by conditional knockout in mammary stem cells (MaSCs), we demonstrate that Procr is essential for mammary gland development and homeostasis. Through proteomics profiling, we identify that, upon stimulation by the ligand protein C, Procr interacts with heat shock protein 90 (HSP90AA1) via its short cytoplasmic tail, recruiting Src and IGF1R to the complex at the plasma membrane. We show that Procr acts as a signaling receptor of protein C in regulation of MaSCs through HSP90, Src, and IGF1R in vitro. In vivo, IGF1R deletion in MaSCs displays similar phenotypes to Procr deletion. These findings illustrate the essential role of Procr signaling in MaSC maintenance, shedding light onto the molecular regulation by Procr in tissue stem cells.

Region-Specific Biomarkers and Their Mechanisms in the Treatment of Lung Adenocarcinoma: A Study of Panax quinquefolius from Wendeng, China

Panax quinquefolius, a popular medicinal herb, has been cultivated in China for many years. In this work, the region-specific profiles of metabolites in P. quinquefolius from Wendeng was investigated using liquid-chromatography-quadrupole-time-of-flight-(LC-Q-TOF)-based metabolomics analysis. The three most abundant biomarkers, identified as ginsenoside Rb₃, notoginsenoside R₁, and ginsenoside Rc, were the representative chemical components employed in the network pharmacology analysis. In addition, molecular docking and western blotting analyses revealed that the three compounds were effective binding ligands with Hsp90α, resulting in the inactivation of SRC and PI3K kinase, which eventually led to the inactivation of the Akt and ERK pathways and lung cancer suppression. The outcomes obtained herein demonstrated the intriguing chemical characteristics and potential functional activities of P. quinquefolius from Wendeng.

Inhibition of Hsp90 Counteracts the Established Experimental Dermal Fibrosis Induced by Bleomycin

Our previous study demonstrated that heat shock protein 90 (Hsp90) is overexpressed in the involved skin of patients with systemic sclerosis (SSc) and in experimental dermal fibrosis. Pharmacological inhibition of Hsp90 prevented the stimulatory effects of transforming growth factor-beta on collagen synthesis and the development of dermal fibrosis in three preclinical models of SSc. In the next step of the preclinical analysis, herein, we aimed to evaluate the efficacy of an Hsp90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), in the treatment of established experimental dermal fibrosis induced by bleomycin. Treatment with 17-DMAG demonstrated potent antifibrotic and anti-inflammatory properties: it decreased dermal thickening, collagen content, myofibroblast count, expression of transforming growth factor beta receptors, and pSmad3-positive cell counts, as well as leukocyte infiltration and systemic levels of crucial cytokines/chemokines involved in the pathogenesis of SSc, compared to vehicle-treated mice. 17-DMAG effectively prevented further progression and may induce regression of established bleomycin-induced dermal fibrosis to an extent comparable to nintedanib. These findings provide further evidence of the vital role of Hsp90 in the pathophysiology of SSc and characterize it as a potential target for the treatment of fibrosis with translational implications due to the availability of several Hsp90 inhibitors in clinical trials for other indications.

High-throughput proteomic profiling reveals mechanisms of action of AMG925, a dual FLT3-CDK4/6 kinase inhibitor targeting AML and AML stem/progenitor cells

FLT3 mutations, which are found in a third of patients with acute myeloid leukemia (AML), are associated with poor prognosis. Responses to currently available FLT3 inhibitors in AML patients are typically transient and followed by disease recurrence. Thus, FLT3 inhibitors with new inhibitory mechanisms are needed to improve therapeutic outcomes. AMG925 is a novel, potent, small-molecule dual inhibitor of FLT3 and CDK4/6. In this study. we determined the antileukemic effects and mechanisms of action of AMG925 in AML cell lines and primary samples, in particular AML stem/progenitor cells. AMG925 inhibited cell growth and promoted apoptosis in AML cells with or without FLT3 mutations. Reverse-phase protein array profiling confirmed its on-target effects on FLT3-CDK4/6-regulated pathways and identified unrevealed signaling network alterations in AML blasts and stem/progenitor cells in response to AMG925. Mass cytometry identified pathways that may confer resistance to AMG925 in phenotypically defined AML stem/progenitor cells and demonstrated that combined blockade of FLT3-CDK4/6 and AKT/mTOR signaling facilitated stem cell death. Our findings provide a rationale for the mechanism-based inhibition of FLT3-CDK4/6 and for combinatorial approaches to improve the efficacy of FLT3 inhibition in both FLT3 wild-type and FLT3-mutated AML.

Plasma Hsp90 levels in patients with systemic sclerosis and relation to lung and skin involvement: a cross-sectional and longitudinal study

Our previous study demonstrated increased expression of Heat shock protein (Hsp) 90 in the skin of patients with systemic sclerosis (SSc). We aimed to evaluate plasma Hsp90 in SSc and characterize its association with SSc-related features. Ninety-two SSc patients and 92 age-/sex-matched healthy controls were recruited for the cross-sectional analysis. The longitudinal analysis comprised 30 patients with SSc associated interstitial lung disease (ILD) routinely treated with cyclophosphamide. Hsp90 was increased in SSc compared to healthy controls. Hsp90 correlated positively with C-reactive protein and negatively with pulmonary function tests: forced vital capacity and diffusing capacity for carbon monoxide (DLCO). In patients with diffuse cutaneous (dc) SSc, Hsp90 positively correlated with the modified Rodnan skin score. In SSc-ILD patients treated with cyclophosphamide, no differences in Hsp90 were found between baseline and after 1, 6, or 12 months of therapy. However, baseline Hsp90 predicts the 12-month change in DLCO. This study shows that Hsp90 plasma levels are increased in SSc patients compared to age-/sex-matched healthy controls. Elevated Hsp90 in SSc is associated with increased inflammatory activity, worse lung functions, and in dcSSc, with the extent of skin involvement. Baseline plasma Hsp90 predicts the 12-month change in DLCO in SSc-ILD patients treated with cyclophosphamide.

The role of heat shock proteins in the regulation of fibrotic diseases

Heat shock proteins (HSPs) are key players to restore cell homeostasis and act as chaperones by assisting the folding and assembly of newly synthesized proteins and preventing protein aggregation. Recently, evidence has been accumulating that HSPs have been proven to have other functions except for the classical molecular chaperoning in that they play an important role in a wider range of fibrotic diseases via modulating cytokine induction and inflammation response, including lung fibrosis, liver fibrosis, and idiopathic pulmonary fibrosis. The recruitment of inflammatory cells, a large number of secretion of pro-fibrotic cytokines such as transforming growth factor-β1 (TGF-β1) and increased apoptosis, oxidative stress, and proteasomal system degradation are all events occurring during fibrogenesis, which might be associated with HSPs. However, their role on fibrotic process is not yet fully understood. In this review, we discuss new discoveries regarding the involvement of HSPs in the regulation of organ and tissue fibrosis, and note recent findings suggesting that HSPs may be a promising therapeutic target for improving the current frustrating outcome of fibrotic disorders.

Hsp90 interacts with Cdc37, is phosphorylated by PKA/PKC, and regulates Src phosphorylation in human sperm capacitation

BACKGROUND

Heat shock protein 90 (Hsp90) signaling pathways participate in protein phosphorylation during sperm capacitation. However, the underlying mechanism is largely unknown.

OBJECTIVE

The aim of this study was to explore the interaction between Hsp90 and its co-chaperone protein, cell division cycle protein Cdc37 (Cdc37), in human spermatozoa.

MATERIALS AND METHODS

We examined the effects of H-89 (a protein kinase A [PKA] inhibitor) and Go6983 (a protein kinase C [PKC] inhibitor) on the phosphorylation of serine, threonine, and tyrosine residues in Hsp90; the effect of 17-allylamino-17-demethoxygeldanamycin (17-AAG, Hsp90 inhibitor) on Y416-Src phosphorylation; and the effects of 17-AAG and geldanamycin on threonine phosphorylation during human sperm capacitation.

RESULTS

Hsp90 co-localized and interacted with Cdc37. During human sperm capacitation, Hsp90 phosphorylation at serine, threonine, and tyrosine residues was inhibited by H-89 and Go6983. In addition, phosphorylation of residue Y416 in the tyrosine kinase Src (its active site) was inhibited by 17-AAG, and the threonine phosphorylation levels of some proteins were decreased by 17-AAG and geldanamycin.

DISCUSSION AND CONCLUSION

Taken together, our data showed that the interaction of Hsp90 with Cdc37 regulates total protein threonine phosphorylation and Src phosphorylation via its serine, threonine, and tyrosine phosphorylation, which are controlled by PKA and PKC during human sperm capacitation. The results of this study help understand the mechanism underlying Hsp90 regulation of sperm function.

Nitration-induced ubiquitination and degradation control quality of ERK1

The mitogen-activated protein kinase ERK1/2 (ERKs, extracellular-regulated protein kinases) plays important roles in a wide spectrum of cellular processes and have been implicated in many disease states. The spatiotemporal regulation of ERK activity has been extensively studied. However, scarce information has been available regarding the quality control of the kinases to scavenge malfunctioning ERKs. Using site-specific mutagenesis and mass spectrometry, we found that the disruption of the conserved H-bond between Y210 and E237 of ERK1 through point mutation at or naturally occurring nitration on Y210 initiates a quality control program dependent on chaperon systems and CHIP (C-terminal of Hsp70-interacting protein)-mediated ubiquitination and degradation. The H-bond is also important for the quality control of ERK2, but through a distinct mechanism. These findings clearly demonstrate how malfunctioning ERKs are eliminated when cells are in certain stress conditions or unhealthy states, and could represent a general mechanism for scavenging malfunctioning kinases in stress conditions.

The effect of heat shock protein 90 inhibitors on histone 4 lysine 20 methylation in bladder cancer

Heat shock protein 90 (HSP90), an ATP-dependent molecular chaperone required for the stability and function of numerous oncogenic signaling, is one of the hallmarks of cancer. Recent years, the studies showed that HSP90 plays a pivotal role in epigenetic pathways. Epigenetic regulation plays an important role in the etiology of bladder cancer. The aim of the present study was to investigate the effect of HSP90 proteins on DNA methylation and the levels of inactivated histone methylation markers in bladder cancers. The cytotoxic effect of geldanamycin (GA), a HSP90-specific inhibitor, in human bladder cancer cell line, T24, was studied by using WST1 (both time and dose-dependent), qPCR for the expression aberration of target genes DNMT1 and WIF-1 and western blot for the protein levels of DNMT1, Histone H4, Histone 4 lysine monomethylation (H4K20me1), Histone 4 lysine trimethylation (H4K20me3), Akt1, pAkt1 (S473) and Lysine methyltransferase 5C (KMT5C). High-dose GA treatment decreased cell proliferation. After the GA treatment, DNMT1 decreased at both transcriptional and translational levels due to Akt1 and pAkt1 (S473) inhibition. Following the GA-induced decrease in DNMT1, re-expression of WIF-1 gene was found at mRNA. In addition, the GA treatment resulted in dose- and time-dependent upregulation/downregulation of histone post-translational modifications (H4K20me1 and H4K20me3) and the KMT5C enzyme responsible for these modifications. There was no significant change in the H4 protein level. These findings may offer a new approach for the determination of the molecular effect of HSP90 on epigenetic regulation and the identification of new molecular targets (HSP90 client proteins) for bladder cancer treatment.

Nck-associated protein 1 associates with HSP90 to drive metastasis in human non-small-cell lung cancer

Background

Metastatic lung cancer is a life-threatening condition that develops when cancer in another area of the body metastasizes, or spreads, to the lung. Despite advances in our understanding of primary lung oncogenesis, the biological basis driving the progression from primary to metastatic lung cancer remains poorly characterized.

Methods

Genetic knockdown of the particular genes in cancer cells were achieved by lentiviral-mediated interference. Invasion potential was determined by Matrigel and three-dimensional invasion. The secretion of matrix metalloproteinase 2 (MMP2) and MMP9 were measured by ELISA. Protein levels were assessed by Western blotting and immunohistochemistry. Protein-protein interactions were determined by immunoprecipitation. An experimental mouse model was generated to investigate the gene regulation in tumor growth and metastasis.

Results

Nck-associated protein 1 (NAP1/NCKAP1) is highly expressed in primary non-small-cell lung cancer (NSCLC) when compared with adjacent normal lung tissues, and its expression levels are strongly associated with the histologic tumor grade, metastasis and poor survival rate of NSCLC patients. Overexpression of NAP1 in lowly invasive NSCLC cells enhances MMP9 secretion and invasion potential, whereas NAP1 silencing in highly invasive NSCLC cells produces opposing effects in comparison. Mechanistic studies further reveal that the binding of NAP1 to the cellular chaperone heat shock protein 90 (HSP90) is required for its protein stabilization, and NAP1 plays an essential role in HSP90-mediated invasion and metastasis by provoking MMP9 activation and the epithelial-to-mesenchymal transition in NSCLC cells.

Conclusions

Our insights demonstrate the importance and functional regulation of the HSP90-NAP1 protein complex in cancer metastatic signaling, which spur new avenues to target this interaction as a novel approach to block NSCLC metastasis.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1124-0) contains supplementary material, which is available to authorized users.

17-allylamino-17-demethoxygeldanamycin impeded chemotherapy through antioxidant activation via reducing reactive oxygen species-induced cell death

Hyperthermia enhances the anticancer effects of thymidylate synthase (TYMS) inhibitors (raltitrexed, RTX) and improves the precise biochemical mechanisms partially through enhancement of intracellular drug absorption. Recent research focuses on the potential anticancer drug target Heat Shock Protein 90 (HSP90), which could increase the sensitivity of cancer cells to TYMS inhibitors; however, with different HSP90 inhibitors, several research studies finally showed a poor efficacy in preclinical or clinical research. Here, we showed that 17-allylamino-17-demethoxygeldanamycin (17-AAG, HSP90 inhibitor) affects the efficacy of chemotherapy through antioxidant activation-induced resistance. In this study, we found that RTX, alone or in combination with hyperthermia, triggers reactive oxygen species (ROS) exposure and thus induces cell death. Also, the addition of hyperthermia showed more ROS exposure and function. The pharmacologic inhibition of HSP90 reversed the effects of chemotherapeutical treatments, while the overexpression of HSP90 showed no relation with these effects, which demonstrated that dysregulation of HSP90 might have a significant impact on chemotherapeutic treatments. The addition of 17-AAG increased the activation of antioxidant with increased antioxidant enzymes, thus affecting the RTX efficacy.

Small Molecule-Mediated Activation of RAS Elicits Biphasic Modulation of Phospho-ERK Levels that Are Regulated through Negative Feedback on SOS1

Oncogenic mutation of RAS results in aberrant cellular signaling and is responsible for more than 30% of all human tumors. Therefore, pharmacologic modulation of RAS has attracted great interest as a therapeutic strategy. Our laboratory has recently discovered small molecules that activate Son of Sevenless (SOS)-catalyzed nucleotide exchange on RAS and inhibit downstream signaling. Here, we describe how pharmacologically targeting SOS1 induced biphasic modulation of RAS-GTP and ERK phosphorylation levels, which we observed in a variety of cell lines expressing different RAS-mutant isoforms. We show that compound treatment caused an increase in phosphorylation at ERK consensus motifs on SOS1 that was not observed with the expression of a non-phosphorylatable S1178A SOS1 mutant or after pretreatment with an ERK inhibitor. Phosphorylation at S1178 on SOS1 is known to inhibit the association between SOS1 and GRB2 and disrupt SOS1 membrane localization. Consistent with this, we show that wild-type SOS1 and GRB2 dissociated in a time-dependent fashion in response to compound treatment, and conversely, this interaction was enhanced with the expression of an S1178A SOS1 mutant. Furthermore, in cells expressing either S1178A SOS1 or a constitutively membrane-bound CAAX box tagged SOS1 mutant, we observed elevated RAS-GTP levels over time in response to compound, as compared with the biphasic changes in RAS-GTP exhibited in cells expressing wild-type SOS1. These results suggest that small molecule targeting of SOS1 can elicit a biphasic modulation of RAS-GTP and phospho-ERK levels through negative feedback on SOS1 that regulates the interaction between SOS1 and GRB2. Mol Cancer Ther; 17(5); 1051-60. ©2018 AACR.

Reactivation of ERK and Akt confers resistance of mutant BRAF colon cancer cells to the HSP90 inhibitor AUY922

Oncogenic mutations of BRAF occur in approximately 10% of colon cancers and are associated with their resistance to clinically available therapeutic drugs and poor prognosis of the patients. Here we report that colon cancer cells with mutant BRAF are also resistant to the heat shock protein 90 (HSP90) inhibitor AUY922, and that this is caused by rebound activation of ERK and Akt. Although AUY922 triggered rapid reduction in ERK and Akt activation in both wild-type and mutant BRAF colon cancer cells, activation of ERK and Akt rebounded shortly in the latter leading to resistance of the cells to AUY922-induced apoptosis. Reactivation of ERK was associated with the persistent expression of mutant BRAF, which, despite being a client of HSP90, was only partially degraded by AUY922, whereas reactivation of Akt was related to the activity of the HSP90 co-chaperone, cell division cycle 37 (CDC37), in that knockdown of CDC37 inhibited Akt reactivation in mutant colon cancer cells treated with AUY922. In support, as a HSP90 client protein, Akt was only diminished by AUY922 in wild-type but not mutant BRAF colon cancer cells. Collectively, these results reveal that reactivation of ERK and Akt associated respectively with the activity of mutant BRAF and CDC37 renders mutant BRAF colon cancer cells resistant to AUY922, with implications of co-targeting mutant BRAF and/or CDC37 and HSP90 in the treatment of mutant BRAF colon cancers.

Effect of 17-allylamino-17-demethoxygeldanamycin (17-AAG) on Akt protein expression is more effective in head and neck cancer cell lineages that retain PTEN protein expression

OBJECTIVES

The aim of this study was to evaluate the expression of Akt, PTEN, Mdm2 and p53 proteins in three different head and neck squamous cell carcinoma (HNSCC) cell lines (HN6, HN19 and HN30), all of them treated with epidermal growth factor (EGF) and 17-allylamino-17-demethoxygeldanamycin (17-AAG), an inhibitor of Hsp90 protein.

MATERIAL AND METHODS

Immunofluorescence and western blot were performed in order to analyze the location and quantification, respectively, of proteins under the action 17-AAG and EGF.

RESULTS

Treatment with EGF resulted in increased levels of Akt, PTEN and p53 in all cell lineages. The expression of Mdm2 was constant in HN30 and HN6 lineages, while in HN19 showed slightly decreased expression. Under the action 17-AAG, in HN6 and HN19, the expression of PTEN and p53 proteins was suppressed, while Akt and Mdm2 expression was reduced. Finally, in the HN30 cell lineage were absolute absence of expression of Akt, Mdm2 and p53 and decreased expression of PTEN.

CONCLUSION

These data allow us to speculate on the particular utility of 17-AAG for HNSCC treatment through the inhibition of Akt protein expression, especially in the cases that retain the expression of PTEN protein.

Unconventional Approaches to Modulating the Immunogenicity of Tumor Cells

For several years, it has been known that histone deacetylase inhibitors have the potential to alter the immunogenicity of tumor cells exposed to checkpoint inhibitory immunotherapy antibodies. HDAC inhibitors can rapidly reduce expression of PD-L1 and increase expression of MHCA in various tumor types that subsequently facilitate the antitumor actions of checkpoint inhibitors. Recently, we have discovered that drug combinations which cause a rapid and intense autophagosome formation also can modulate the expression of HDAC proteins that control tumor cell immunogenicity via their regulation of PD-L1 and MHCA. These drug combinations, in particular those using the irreversible ERBB1/2/4 inhibitor neratinib, can result in parallel in the internalization of growth factor receptors as well as fellow-traveler proteins such as mutant K-RAS and mutant N-RAS into autophagosomes. The drug-induced autophagosomes contain HDAC proteins/signaling proteins whose expression is subsequently reduced by lysosomal degradation processes. These findings argue that cancer therapies which strongly promote autophagosome formation and autophagic flux may facilitate the subsequent use of additional antitumor modalities using checkpoint inhibitor antibodies.

Cancer Stem Cell-Suppressing Activity of Chrysotoxine, a Bibenzyl from Dendrobium pulchellum

Cancer stem cells (CSCs) have been recognized as rare populations driving cancer progression, metastasis, and drug resistance in leading cancers. Attempts have been made toward identifying compounds that specifically target these CSCs. Therefore, investigations of novel therapeutic strategies for CSC targeting are required. The cytotoxic effects of chrysotoxine on human non-small cell lung cancer-derived H460 and H23 cells were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The effects of chrysotoxine suppression of CSC-like phenotypes were determined in CSC-rich populations and primary CSCs in three-dimensional (3D) culture and in an extreme limiting dilution assay. Expression of CSC markers and associated proteins was determined by Western blot analyse and flow cytometry. We have reported herein the CSC-suppressing activity of chrysotoxine, a bibenzyl compound isolated from Dendrobium pulchellum We have shown, to our knowledge for the first time, that chrysotoxine dramatically suppresses CSC-like phenotypes of H460 and H23 cells. Treatment with chrysotoxine significantly reduced the viability of 3D CSC-rich populations and concomitantly decreased known CSC markers. Chrysotoxine suppressed CSC phenotypes through downregulation of Src/protein kinase B (Akt) signaling. Active (phosphorylated Y416) Src was shown to regulate cancer stemness, since ectopic overexpression of Src strongly activated Akt and subsequently enhanced pluripotency transcription factor SRY (sex-determining region Y)-box 2 (Sox2)- mediating CSC phenotypes, whereas the short hairpin RNA of Src and an Src inhibitor (dasatinib) suppressed Akt, Sox2, and CSC properties. Importantly, chrysotoxine was shown to suppress active Src/Akt signaling and in turn depleted Sox2-mediated CSCs. Our findings indicate a novel CSC-targeted role of chrysotoxine and its regulation by Src/Akt and Sox2, which may be exploited for cancer treatment.

Proteomic profiling of human HepG2 cells treated with hesperidin using antibody array

Protein array technology not only identifies a large number of proteins but also determines their expression levels. In the present study, antibody array analysis is used to decipher the proteins involved in hesperidin-induced cell death in HepG2 cells. Altered proteins in hesperidin treated cells were compared with that of untreated control cells by using a RayBio® Label‑based (L series) human antibody array kit. The identified proteins were further confirmed using western blot analysis. STRING software based analysis was used to determine the protein‑protein interactions. Many proteins related to signal transduction, cellular mechanisms, cell growth and proliferation regulatory proteins were identified. Among the proteins identified Hsp90, Smac/DIABLO, Prdx6 and FRK were significantly reduced in hesperidin treated cells. To the best of the authors' knowledge, the present study is the first to use antibody array for identifying proteins marker in hesperidin‑induced cell death in HepG2 cells. The present study provides a novel insight into the anticancer mechanism of hesperidin.

Hyperglycemia and advanced glycation end products (AGEs) suppress the differentiation of 3T3-L1 preadipocytes

Aging is characterized by mild hyperglycemia and accumulation of advanced glycation end products (AGEs). Effects of chronic exposure to hyperglycemia or AGEs on the adipogenic differentiation of 3T3-L1 preadipocytes remain unclear. We examined the chronic effect of AGEs and high glucose on the differentiation of 3T3-L1 cells by culturing 3T3-L1 cells in the presence of AGEs or 25 mM glucose for 1 month. Chronic incubation of 3T3-L1 cells with AGEs or high glucose blocked their differentiation into mature adipocytes as evidenced by reduced levels of adipocyte markers such as accumulated oil droplets, GPDH, aP2, adiponectin and of adipogenesis regulators PPARγ and C/EBPα. Levels or activities of Src, PDK1, Akt, and NF-κB were higher in AGEs- and high glucose-treated cells than those in 3T3-L1 cells. Levels of Bcl-2 were elevated in AGEs- and high glucose-treated cells, and were attenuated by inhibitors of PI3-kinase, Akt and NF-κB. Moreover, adipogenesis was attenuated in 3T3-L1 cells stably expressing Bcl-2 or YAP. These results suggest that chronic AGEs and high glucose treatments up-regulate Bcl-2 and YAP via the Akt-NF-κB pathway and impair adipogenesis.

The Abl pathway bifurcates to balance Enabled and Rac signaling in axon patterning in Drosophila

The Abl tyrosine kinase signaling network controls cell migration, epithelial organization, axon patterning and other aspects of development. Although individual components are known, the relationships among them remain unresolved. We now use FRET measurements of pathway activity, analysis of protein localization and genetic epistasis to dissect the structure of this network in Drosophila We find that the adaptor protein Disabled stimulates Abl kinase activity. Abl suppresses the actin-regulatory factor Enabled, and we find that Abl also acts through the GEF Trio to stimulate the signaling activity of Rac GTPase: Abl gates the activity of the spectrin repeats of Trio, allowing them to relieve intramolecular repression of Trio GEF activity by the Trio N-terminal domain. Finally, we show that a key target of Abl signaling in axons is the WAVE complex that promotes the formation of branched actin networks. Thus, we show that Abl constitutes a bifurcating network, suppressing Ena activity in parallel with stimulation of WAVE. We suggest that the balancing of linear and branched actin networks by Abl is likely to be central to its regulation of axon patterning.

S100B raises the alert in subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating disease with high mortality and mobility, the novel therapeutic strategies of which are essentially required. The calcium binding protein S100B has emerged as a brain injury biomarker that is implicated in pathogenic process of SAH. S100B is mainly expressed in astrocytes of the central nervous system and functions through initiating intracellular signaling or via interacting with cell surface receptor, such as the receptor of advanced glycation end products. The biological roles of S100B in neurons have been closely associated with its concentrations, resulting in either neuroprotection or neurotoxicity. The levels of S100B in the blood have been suggested as a biomarker to predict the progress or the prognosis of SAH. The role of S100B in the development of cerebral vasospasm and brain damage may result from the induction of oxidative stress and neuroinflammation after SAH. To get further insight into mechanisms underlying the role of S100B in SAH based on this review might help us to find novel therapeutic targets for SAH.

Inhibition of HSP90 by AUY922 Preferentially Kills Mutant KRAS Colon Cancer Cells by Activating Bim through ER Stress

Oncogenic mutations of KRAS pose a great challenge in the treatment of colorectal cancer. Here we report that mutant KRAS colon cancer cells are nevertheless more susceptible to apoptosis induced by the HSP90 inhibitor AUY922 than those carrying wild-type KRAS. Although AUY922 inhibited HSP90 activity with comparable potency in colon cancer cells irrespective of their KRAS mutational statuses, those with mutant KRAS were markedly more sensitive to AUY922-induced apoptosis. This was associated with upregulation of the BH3-only proteins Bim, Bik, and PUMA. However, only Bim appeared essential, in that knockdown of Bim abolished, whereas knockdown of Bik or PUMA only moderately attenuated apoptosis induced by AUY922. Mechanistic investigations revealed that endoplasmic reticulum (ER) stress was responsible for AUY922-induced upregulation of Bim, which was inhibited by a chemical chaperone or overexpression of GRP78. Conversely, siRNA knockdown of GRP78 or XBP-1 enhanced AUY922-induced apoptosis. Remarkably, AUY922 inhibited the growth of mutant KRAS colon cancer xenografts through activation of Bim that was similarly associated with ER stress. Taken together, these results suggest that AUY922 is a promising drug in the treatment of mutant KRAS colon cancers, and the agents that enhance the apoptosis-inducing potential of Bim may be useful to improve the therapeutic efficacy.

Geldanamycin induces apoptosis in human gastric carcinomas by affecting multiple oncogenic kinases that have synergic effects with TNF-related apoptosis-inducing ligand

The aim of the present study was to evaluate the effect of geldanamycin (GA) on the treatment of human gastric carcinomas and to investigate the molecular mechanism that provides the basis for the combination of GA with the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induction strategy. The expression of target proteins at the mRNA level was determined using reverse transcription-polymerase chain reaction (RT-PCR), and apoptosis was evaluated with the terminal deoxynucleotidyl transferase mediated digoxigenin-dUTP nick-end labeling and Annexin V/propidium iodide (PI) staining methods. Phosphorylation of targeted kinases was studied using immunocytochemistry methods, and malignant phenotypes were studied using in vitro assays. GA treatment inhibits proliferation, migration and invasion, and induces apoptosis in human gastric cancer SGC-7901 cells, most likely by decreasing the expression of B-RAF and by phosphorylation of protein kinase B (AKT) and ERK. The inhibitory role of AKT in TRAIL regulation holds considerable potential for achieving a synergic effect in clinical therapy, using a combination of GA treatment and TRAIL induction. The present study provides a basis for the future application of heat shock protein 90 (Hsp90) inhibitors, such as GA, in the clinical treatment of gastric cancer, particularly in combination therapies with TRAIL inducers.

Immune microenvironment as a factor of breast cancer progression

Background

The rate of progression of the disease depends on various factors and the tumor microenvironment takes not the last place among them. One part of researchers argues that the presence of tumor-infiltrating leukocytes serves as a favorable marker of the disease. There exists a completely different point of view on the matter.

The investigation of the effects of the inflammatory infiltration on the course of breast cancer process.

Methods

We found a pronounced inflammatory infiltration in the tumor microenvironment in 24 cases. Nineteen cases of IDC without inflammatory infiltration were used as a control group. Immunohistochemical reaction showed expression of ERα, PR, HER2/neu, E-cadherin, Hsp90α, Bcl-2, CD3, CD79α, S100 and Myeloperoxidase receptors. Mathematical calculations were done using Microsoft Excel 2010 with 12.0.5 Attestat option.

Results

We have determined five variants of immune microenvironment: interstitial, trabecular, nodular, diffuse and mixed. We have established a direct correlation between the expression of ERα and PR and indirect correlation between the receptors of steroid hormones and HER2/neo in both groups of breast cancer. HER2/neo positive tumors in 100% of cases were accompanied by the presence of heat shock proteins. There was a combination of Bcl-2 presence with the steroid receptors expression in 90 % of cases. There was found the indirect correlation between the presence of B lymphocytes and expression of steroid receptors.

Conclusions

The presence of B lymphocytes in an inflammatory infiltrate leads to the disappearance of estrogen receptors and progesterone receptors. It provokes the accumulation of Hsp90 in a cell. It contributes to the stabilization of HER2/neu receptors and most proteins that promote tumor progression.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1362330168161694

Geldanamycin Enhances Retrograde Transport of Shiga Toxin in HEp-2 Cells

The heat shock protein 90 (Hsp90) inhibitor geldanamycin (GA) has been shown to alter endosomal sorting, diverting cargo destined for the recycling pathway into the lysosomal pathway. Here we investigated whether GA also affects the sorting of cargo into the retrograde pathway from endosomes to the Golgi apparatus. As a model cargo we used the bacterial toxin Shiga toxin, which exploits the retrograde pathway as an entry route to the cytosol. Indeed, GA treatment of HEp-2 cells strongly increased the Shiga toxin transport to the Golgi apparatus. The enhanced Golgi transport was not due to increased endocytic uptake of the toxin or perturbed recycling, suggesting that GA selectively enhances endosomal sorting into the retrograde pathway. Moreover, GA activated p38 and both inhibitors of p38 or its substrate MK2 partially counteracted the GA-induced increase in Shiga toxin transport. Thus, our data suggest that GA-induced p38 and MK2 activation participate in the increased Shiga toxin transport to the Golgi apparatus.

FAK is required for c-Met/β-catenin-driven hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the third most common cause of cancer death worldwide and most patients with HCC have limited treatment options. Focal adhesion kinase (FAK) is overexpressed in many HCC specimens, offering a potential target for HCC treatment. However, the role of FAK in hepatocarcinogenesis remains elusive. Establishing whether FAK expression plays a role in HCC development is necessary to determine whether it is a viable therapeutic target. In this study, we generated mice with hepatocyte-specific deletion of Fak and investigated the role of Fak in an oncogenic (c-MET/β-catenin, MET/CAT)-driven HCC model. We found that deletion of Fak in hepatocytes did not affect morphology, proliferation, or apoptosis. However, Fak deficiency significantly repressed MET/CAT-induced tumor development and prolonged survival of animals with MET/CAT-induced HCC. In mouse livers and HCC cell lines, Fak was activated by MET, which induced the activation of Akt/Erk and up-regulated cyclin D1 and tumor cell proliferation. CAT enhanced MET-stimulated FAK activation and synergistically induced the activation of the AKT/ERK-cyclin D1 signaling pathway in a FAK kinase-dependent manner. In addition, FAK was required for CAT-induced cyclin D1 expression in a kinase-independent fashion.

CONCLUSION

Fak is required for c-Met/β-catenin-driven hepatocarcinogenesis. Inhibition of FAK provides a potential strategy to treat HCC.

Heat shock protein 90 has roles in intracellular calcium homeostasis, protein tyrosine phosphorylation regulation, and progesterone-responsive sperm function in human sperm

Heat shock protein 90 plays critical roles in client protein maturation, signal transduction, protein folding and degradation, and morphological evolution; however, its function in human sperm is not fully understood. Therefore, our objective in this study was to elucidate the mechanism by which heat shock protein 90 exerts its effects on human sperm function. By performing indirect immunofluorescence staining, we found that heat shock protein 90 was localized primarily in the neck, midpiece, and tail regions of human sperm, and that its expression increased with increasing incubation time under capacitation conditions. Geldanamycin, a specific inhibitor of heat shock protein 90, was shown to inhibit this increase in heat shock protein 90 expression in western blotting analyses. Using a multifunctional microplate reader to examine Fluo-3 AM-loaded sperm, we observed for the first time that inhibition of heat shock protein 90 by using geldanamycin significantly decreased intracellular calcium concentrations during capacitation. Moreover, western blot analysis showed that geldanamycin enhanced tyrosine phosphorylation of several proteins, including heat shock protein 90, in a dose-dependent manner. The effects of geldanamycin on human sperm function in the absence or presence of progesterone was evaluated by performing chlortetracycline staining and by using a computer-assisted sperm analyzer. We found that geldanamycin alone did not affect sperm capacitation, hyperactivation, and motility, but did so in the presence of progesterone. Taken together, these data suggest that heat shock protein 90, which increases in expression in human sperm during capacitation, has roles in intracellular calcium homeostasis, protein tyrosine phosphorylation regulation, and progesterone-stimulated sperm function. In this study, we provide new insights into the roles of heat shock protein 90 in sperm function.

Contribution of chaperones to STAT pathway signaling

Aberrant STAT signaling is associated with the development and progression of many cancers and immune related diseases. Recent findings demonstrate that proteostasis modulators under clinical investigation for cancer therapy have a significant impact on STAT signaling, which may be critical for mediating their anti-cancer effects. Chaperones are critical for protein folding, stability and function and, thus, play an essential role in the maintenance of proteostasis. In this review we discuss the role of chaperones in STAT and tyrosine kinase (TK) protein folding, modulation of STAT and TK activity, and degradation of TKs. We highlight the important role of chaperones in STAT signaling, and how this knowledge has provided a framework for the development of new therapeutic avenues of targeting STAT signaling related pathologies.

Low dose Hsp90 inhibitor 17AAG protects neural progenitor cells from ischemia induced death

Stress adaptation effect provides cell protection against ischemia induced apoptosis. Whether this mechanism prevents other types of cell death in stroke is not well studied. This is an important question for regenerative medicine to treat stroke since other types of cell death such as necrosis are also prominent in the stroke brain apart from apoptosis. We report here that treatment with 17-N-Allylamino-17-demethoxygeldanamycin (17AAG), an Hsp90 inhibitor, protected neural progenitor cells (NPCs) against oxygen glucose deprivation (OGD) induced cell death in a dose dependent fashion. Cell death assays indicated that 17AAG not only ameliorated apoptosis, but also necrosis mediated by OGD. This NPC protection was confirmed by exposing cells to oxidative stress, a major stress signal prevalent in the stroke brain. Mechanistic studies demonstrated that 17AAG activated PI3K/Akt and MAPK cell protective pathways. More interestingly, these two pathways were activated in vivo by 17AAG and 17AAG treatment reduced infarct volume in a middle cerebral artery occlusion (MCAO) stroke model. These data suggest that 17AAG protects cells against major cell death pathways and thus might be used as a pharmacological conditioning agent for regenerative medicine for stroke.

Geldanamycin attenuates 3‑nitropropionic acid‑induced apoptosis and JNK activation through the expression of HSP 70 in striatal cells

Although selective striatal cell death is a characteristic hallmark in the pathogenesis of Huntington's disease (HD), the underlying mechanism of striatal susceptibility remains to be clarified. Heat shock proteins (HSPs) have been reported to suppress the aggregate formation of mutant huntingtin and concurrent striatal cell death. In a previous study, we observed that heat shock transcription factor 1 (HSF1), a major transcription factor of HSPs, significantly attenuated 3‑nitropropionic acid (3NP)‑induced reactive oxygen species (ROS) production and apoptosis through the expression of HSP 70 in striatal cells. To investigate the differential roles of HSPs in 3NP‑induced striatal cell death, the effect of geldanamycin (GA), an HSP 90 inhibitor, was examined in 3NP‑stimulated striatal cells. GA significantly attenuated 3NP‑induced striatal apoptosis and ROS production with an increased expression of HSP 70. Triptolide (TL), an HSP 70 inhibitor, abolished GA‑mediated protective effects in 3NP‑stimulated striatal cells. To understand the underlying mechanism by which GA‑mediated HSP 70 protects striatal cells against 3NP stimulation, the involvement of various signaling pathways was examined. GA significantly attenuated 3NP‑induced c‑Jun N‑terminal kinase (JNK) phosphorylation and subsequent c‑Jun phosphorylation in striatal cells. Taken together, the present study demonstrated that GA exhibits protective properties against 3NP‑induced apoptosis and JNK activation via the induction of HSP 70 in striatal cells, suggesting that expression of HSP 70 may be a valuable therapeutic target in the treatment of HD.

Targeted therapies in development for non-small cell lung cancer

The iterative discovery in various malignancies during the past decades that a number of aberrant tumorigenic processes and signal transduction pathways are mediated by "druggable" protein kinases has led to a revolutionary change in drug development. In non-small cell lung cancer (NSCLC), the ErbB family of receptors (e.g., EGFR [epidermal growth factor receptor], HER2 [human epidermal growth factor receptor 2]), RAS (rat sarcoma gene), BRAF (v-raf murine sarcoma viral oncogene homolog B1), MAPK (mitogen-activated protein kinase) c-MET (c-mesenchymal-epithelial transition), FGFR (fibroblast growth factor receptor), DDR2 (discoidin domain receptor 2), PIK3CA (phosphatidylinositol-4,5-bisphosphate3-kinase, catalytic subunit alpha)), PTEN (phosphatase and tensin homolog), AKT (protein kinase B), ALK (anaplastic lym phoma kinase), RET (rearranged during transfection), ROS1 (reactive oxygen species 1) and EPH (erythropoietin-producing hepatoma) are key targets of various agents currently in clinical development. These oncogenic targets exert their selective growth advantage through various intercommunicating pathways, such as through RAS/RAF/MEK, phosphoinositide 3-kinase/AKT/mammalian target of rapamycin and SRC-signal transduction and transcription signaling. The recent clinical studies, EGFR tyrosine kinase inhibitors and crizotinib were considered as strongly effective targeted therapies in metastatic NSCLC. Currently, five molecular targeted agents were approved for treatment of advanced NSCLC: Gefitinib, erlotinib and afatinib for positive EGFR mutation, crizotinib for positive echinoderm microtubule-associated protein-like 4 (EML4)-ALK translocation and bevacizumab. Moreover, oncogenic mutant proteins are subject to regulation by protein trafficking pathways, specifically through the heat shock protein 90 system. Drug combinations affecting various nodes in these signaling and intracellular processes are predicted and demonstrated to be synergistic and advantageous in overcoming treatment resistance compared with monotherapy approaches. Understanding the role of the tumor microenvironment in the development and maintenance of the malignant phenotype provided additional therapeutic approaches as well. More recently, improved knowledge on tumor immunology has set the stage for promising immunotherapies in NSCLC. This review will focus on the rationale for the development of targeted therapies in NSCLC and the various strategies employed in preventing or overcoming the inevitable occurrence of treatment resistance.

Tumor-intrinsic and tumor-extrinsic factors impacting hsp90- targeted therapy

In 1994 the first heat shock protein 90 (Hsp90) inhibitor was identified and Hsp90 was reported to be a target for anticancer therapeutics. In the past 18 years there have been 17 distinct Hsp90 inhibitors entered into clinical trial, and the small molecule Hsp90 inhibitors have been highly valuable as probes of the role of Hsp90 and its client proteins in cancer. Although no Hsp90 inhibitor has achieved regulatory approval, recently there has been significant progress in Hsp90 inhibitor clinical development, and in the past year RECIST responses have been documented in HER2-positive breast cancer and EML4-ALK-positive non-small cell lung cancer. All of the clinical Hsp90 inhibitors studied to date are specific in their target, i.e. they bind exclusively to Hsp90 and two related heat shock proteins. However, Hsp90 inhibitors are markedly pleiotropic, causing degradation of over 200 client proteins and impacting critical multiprotein complexes. Furthermore, it has only recently been appreciated that Hsp90 inhibitors can, paradoxically, cause transient activation of the protein kinase clients they are chaperoning, resulting in initiation of signal transduction and significant physiological events in both tumor and tumor microenvironment. An additional area of recent progress in Hsp90 research is in studies of the posttranslational modifications of Hsp90 itself and Hsp90 co-chaperone proteins. Together, a picture is emerging in which the impact of Hsp90 inhibitors is shaped by the tumor intracellular and extracellular milieu, and in which Hsp90 inhibitors impact tumor and host on a microenvironmental and systems level. Here we review the tumor intrinsic and extrinsic factors that impact the efficacy of small molecules engaging the Hsp90 chaperone machine.

Galleria mellonella infected with Bacillus thuringiensis involves Hsp90

Insects are good models for studying the innate immune response. We report that Galleria mellonella larvae infected with entomopathogenic bacteria Bacillus thuringiensis kurstaki show changes in the level of Hsp90. Our experimental approach was to pre-treat larvae with the Hsp90-binding compound, 17-DMAG, before infection with B. thuringiensis. We show that pre-treated animals display a higher level of immune response. This was mainly manifested by enhanced action of their hemolymph directed toward living bacteria as well as lysozyme activity digesting bacterial peptidoglycan. The observed phenomenon was due to the higher activity of antimicrobial peptides which, in contrast to healthy animals, was detected in the hemolymph of the immunestimulated larvae. Finally, the physiological significance of our observation was highlighted by the fact that G. mellonella pre-treated with 17-DMAG showed a prolonged survival rate after infection with B. thuringiensis than the control animals. Our report points to a role for Hsp90 in the immune response of G. mellonella after infection with B. thuringiensis at the optimal growth temperature.

DIDS inhibits Na-K-ATPase activity in porcine nonpigmented ciliary epithelial cells by a Src family kinase-dependent mechanism

The anion transport inhibitor DIDS is known to reduce aqueous humor secretion but questions remain about anion dependence of the effect. In some tissues, DIDS is reported to cause Na-K-ATPase inhibition. Here, we report on the ability of DIDS to inhibit Na-K-ATPase activity in nonpigmented ciliary epithelium (NPE) and investigate the underlying mechanism. Porcine NPE cells were cultured to confluence on permeable supports, treated with drugs added to both sides of the membrane, and then used for (86)Rb uptake measurements or homogenized to measure Na-K-ATPase activity or to detect protein phosphorylation. DIDS inhibited ouabain-sensitive (86)Rb uptake, activated Src family kinase (SFK), and caused a reduction of Na-K-ATPase activity. PP2, an SFK inhibitor, prevented the DIDS responses. In BCECF-loaded NPE, DIDS was found to reduce cytoplasmic pH (pHi). PP2-sensitive Na-K-ATPase activity inhibition, (86)Rb uptake suppression, and SFK activation were observed when a similar reduction of pHi was imposed by low-pH medium or an ammonium chloride withdrawal maneuver. PP2 and the ERK inhibitor U0126 prevented robust ERK1/2 activation in cells exposed to DIDS or subjected to pHi reduction, but U0126 did not prevent SFK activation or the Na-K-ATPase activity response. The evidence points to an inhibitory influence of DIDS on NPE Na-K-ATPase activity by a mechanism that hinges on SFK activation associated with a reduction of cytoplasmic pH.

Heat shock protein 90 (Hsp90) inhibition targets canonical TGF-β signalling to prevent fibrosis

OBJECTIVES

Targeted therapies for systemic sclerosis (SSc) and other fibrotic diseases are not yet available. We evaluated the efficacy of heat shock protein 90 (Hsp90) inhibition as a novel approach to inhibition of aberrant transforming growth factor (TGF)-β signalling and for the treatment of fibrosis in preclinical models of SSc.

METHODS

Expression of Hsp90 was quantified by quantitative PCR, western blot and immunohistochemistry. The effects of Hsp90 inhibition were analysed in cultured fibroblasts, in bleomycin-induced dermal fibrosis, in tight-skin (Tsk-1) mice and in mice overexpressing a constitutively active TGF-β receptor I (TβRI).

RESULTS

Expression of Hsp90β was increased in SSc skin and in murine models of SSc in a TGF-β-dependent manner. Inhibition of Hsp90 by 17-dimethylaminoethylamino-17-demethoxy-geldanamycin (17-DMAG) inhibited canonical TGF-β signalling and completely prevented the stimulatory effects of TGF-β on collagen synthesis and myofibroblast differentiation. Treatment with 17-DMAG decreased the activation of canonical TGF-β signalling in murine models of SSc and exerted potent antifibrotic effects in bleomycin-induced dermal fibrosis, in Tsk-1 mice and in mice overexpressing a constitutively active TβRI. Dermal thickness, number of myofibroblasts and hydroxyproline content were all significantly reduced on treatment with 17-DMAG. No toxic effects were observed with 17-DMAG at antifibrotic doses.

CONCLUSIONS

Hsp90 is upregulated in SSc and is critical for TGF-β signalling. Pharmacological inhibition of Hsp90 effectively blocks the profibrotic effects of TGF-β in cultured fibroblasts and in different preclinical models of SSc. These results have translational implications, as several Hsp90 inhibitors are in clinical trials for other indications.

Molecular chaperone TRAP1 regulates a metabolic switch between mitochondrial respiration and aerobic glycolysis

TRAP1 (TNF receptor-associated protein), a member of the HSP90 chaperone family, is found predominantly in mitochondria. TRAP1 is broadly considered to be an anticancer molecular target. However, current inhibitors cannot distinguish between HSP90 and TRAP1, making their utility as probes of TRAP1-specific function questionable. Some cancers express less TRAP1 than do their normal tissue counterparts, suggesting that TRAP1 function in mitochondria of normal and transformed cells is more complex than previously appreciated. We have used TRAP1-null cells and transient TRAP1 silencing/overexpression to show that TRAP1 regulates a metabolic switch between oxidative phosphorylation and aerobic glycolysis in immortalized mouse fibroblasts and in human tumor cells. TRAP1-deficiency promotes an increase in mitochondrial respiration and fatty acid oxidation, and in cellular accumulation of tricarboxylic acid cycle intermediates, ATP and reactive oxygen species. At the same time, glucose metabolism is suppressed. TRAP1-deficient cells also display strikingly enhanced invasiveness. TRAP1 interaction with and regulation of mitochondrial c-Src provide a mechanistic basis for these phenotypes. Taken together with the observation that TRAP1 expression is inversely correlated with tumor grade in several cancers, these data suggest that, in some settings, this mitochondrial molecular chaperone may act as a tumor suppressor.

Heat shock protein 90 (Hsp90) selectively regulates the stability of KDM4B/JMJD2B histone demethylase

The family of KDM4A-D histone demethylases selectively demethylates H3K9 and H3K36 and is implicated in key cellular processes including DNA damage response, transcription, cell cycle regulation, cellular differentiation, senescence, and carcinogenesis. Various human cancers exhibit elevated protein levels of KDM4A-D members, and their depletion impairs tumor formation, suggesting that their enhanced activity promotes carcinogenesis. However, the mechanisms regulating the KDM4 protein stability remain largely unknown. Here, we show that the molecular chaperon Hsp90 interacts with and stabilizes KDM4B protein. Pharmacological inhibition of Hsp90 with geldanamycin resulted in ubiquitin-dependent proteasomal degradation of KDM4B, but not of KDM4C, suggesting that the turnover of these demethylases is regulated by distinct mechanisms. This degradation was accompanied by increased methylation of H3K9. We further show that KDM4B is ubiquitinated on lysines 337 and 562; simultaneous substitution of these residues to arginine suppressed the geldanamycin-induced degradation of KDM4B, suggesting that the ubiquitination of Lys-337 and Lys-562 targets KDM4B for proteasomal degradation upon Hsp90 inhibition. These findings constitute a novel pathway by which Hsp90 activity alters the histone code via regulation of KDM4B stability. This pathway may prove a druggable target for the treatment of tumors driven by enhanced KDM4B activity.

The double edge of the HSP90-CDC37 chaperone machinery: opposing determinants of kinase stability and activity

The molecular chaperone HSP90, in concert with the co-chaperone CDC37, facilitates the maturation and modulates the activity of a variety of protein kinases. In this article, Gaude and colleagues described the dual activities of the HSP90-CDC37 chaperone machinery in maintaining the stability while inhibiting the activity of LKB1 kinase. LKB1 in complex with HSP90-CDC37 has a longer half-life but is incapable of autophosphorylation, and its kinase activity is increased upon HSP90 inhibition. Dissociation of HSP90 from LKB1 results in its interaction with HSP/HSC70. HSP/HSC70 recruits the ubiquitin ligase CHIP, which ubiquitinates LKB1, leading to its proteasome-mediated degradation. These data emphasize the versatile roles of molecular chaperones associated with LKB1 and warrant future studies to characterize the clinical relevance of these observations.

Heat shock protein 90α (HSP90α), a substrate and chaperone of DNA-PK necessary for the apoptotic response

The "apoptotic ring" is characterized by the phosphorylation of histone H2AX at serine 139 (γ-H2AX) by DNA-dependent protein kinase (DNA-PK). The γ-H2AX apoptotic ring differs from the nuclear foci patterns observed in response to DNA-damaging agents. It contains phosphorylated DNA damage response proteins including activated Chk2, activated ATM, and activated DNA-PK itself but lacks MDC1 and 53BP1, which are required to initiate DNA repair. Because DNA-PK can phosphorylate heat shock protein 90α (HSP90α) in biochemical assays, we investigated whether HSP90α is involved in the apoptotic ring. Here we show that HSP90α is phosphorylated by DNA-PK on threonines 5 and 7 early during apoptosis and that both phosphorylated HSP90α and DNA-PK colocalize in the apoptotic ring. We also show that DNA-PK is a client of HSP90α and that HSP90α is required for full DNA-PK activation, γ-H2AX formation, DNA fragmentation, and apoptotic body formation. In contrast, HSP90 inhibition by geldanamycin markedly enhances TRAIL-induced DNA-PK and H2AX activation. Together, our results reveal that HSP90α is a substrate and chaperone of DNA-PK in the apoptotic response. The response of phosphorylated HSP90α to TRAIL and its localization to the γ-H2AX ring represent epigenetic features of apoptosis that offer insights for studying and monitoring nuclear apoptosis.