Hsp90 inhibition accelerates cell lysis. Anti-Hsp90 ribozyme reveals a complex mechanism of Hsp90 inhibitors involving both superoxide- and Hsp90-dependent events

Hsp90: From Cellular to Organismal Proteostasis

Assuring a healthy proteome is indispensable for survival and organismal health. Proteome disbalance and the loss of the proteostasis buffer are hallmarks of various diseases. The essential molecular chaperone Hsp90 is a regulator of the heat shock response via HSF1 and a stabilizer of a plethora of signaling proteins. In this review, we summarize the role of Hsp90 in the cellular and organismal regulation of proteome maintenance.

Four-protein model for predicting prognostic risk of lung cancer

Patients with lung cancer at the same stage may have markedly different overall outcome and a lack of specific biomarker to predict lung cancer outcome. Heat-shock protein 90 β (HSP90β) is overexpressed in various tumor cells. In this study, the ELISA results of HSP90β combined with CEA, CA125, and CYFRA21-1 were used to construct a recursive partitioning decision tree model to establish a four-protein diagnostic model and predict the survival of patients with lung cancer. Survival analysis showed that the recursive partitioning decision tree could distinguish the prognosis between high- and low-risk groups. Results suggested that the joint detection of HSP90β, CEA, CA125, and CYFRA21-1 in the peripheral blood of patients with lung cancer is plausible for early diagnosis and prognosis prediction of lung cancer.

New targets of morphine postconditioning protection of the myocardium in ischemia/reperfusion injury: Involvement of HSP90/Akt and C5a/NF-κB

Background

Activation of the complement component 5a (C5a) and nuclear factor κB (NF-κB) signaling is an important feature of myocardial ischemia/reperfusion (I/R) injury and recent studies show that morphine postconditioning (MP) attenuates the myocardial injury. However, the mediating cardioprotective mechanisms remain unclear. The present study explores the role and interaction of heat shock protein 90 (HSP90), Akt, C5a, and NF-κB in MP-induced cardioprotection.

Methods

Male Sprague Dawley rats (n = 160) were randomized into eight groups (n = 20 per group). Rats in the sham group underwent thoracotomy, passing the ligature through the heart but without tying it (150 min), and the other seven groups were subjected to 30 min of anterior descending coronary artery occlusion followed by 2 h of reperfusion and the following treatments: I/R (30 min of ischemia and followed by 2 h of reperfusion); ischemic postconditioning (IPostC, 30 s of ischemia altered with 30 s of reperfusion, repeated for three cycles, and followed by reperfusion for 2 h); MP (0.3 mg/kg morphine administration 10 min before reperfusion); MP combined with the HSP90 inhibitor geldanamycin (GA, 1 mg/kg); MP combined with the Akt inhibitor GSK-690693 (GSK, 20 mg/kg); and MP combined with the C5a inhibitor PMX205 (PMX, 1 mg/kg/day, administration via drinking water for 28 days) and MP combined with the NF-κB inhibitor EVP4593 (QNZ, 1 mg/kg). All inhibitors were administered 10 min before morphine and followed by 2 h reperfusion.

Results

MP significantly reduced the I/R-induced infarct size, the apoptosis, and the release of cardiac troponin I, lactate dehydrogenase (LDH), and creatine kinase-MB. These beneficial effects were accompanied by increased expression of HSP90 and p-Akt, and decreased expression of C5a, NF-κB, tumor necrosis factor α, interleukin-1β, and intercellular cell adhesion molecule 1. However, HSP90 inhibitor GA or Akt inhibitor GSK increased the expression of C5a and NF-κB and prevented MP-induced cardioprotection. Furthermore, GA inhibited the MP-induced upregulation of p-Akt, while GSK did not affect HSP90, indicating that p-Akt acts downstream of HSP90 in MP-induced cardioprotection. In addition, C5a inhibitor PMX enhanced the MP-induced downregulation of NF-κB, while NF-κB inhibitor QNZ had no effect on C5a, indicating that the C5a/NF-κB signaling pathway is involved in MP-induced cardioprotection.

Conclusion

HSP90 is critical for MP-mediated cardioprotection possibly by promoting the phosphorylation of Akt and inhibiting the activation of C5a and NF-κB signaling and the subsequent myocardial inflammation, ultimately attenuating the infarct size and cardiomyocyte apoptosis.

HSP90-Mediates Liraglutide Preconditioning-Induced Cardioprotection by Inhibiting C5a and NF-κB

OBJECTIVE

We previously showed that HSP90 is involved in postconditioning cardioprotection by inhibiting complement C5a. Here, we investigated whether HSP90-mediated C5a/NF-κB inhibition is responsible for the cardioprotection conferred by liraglutide.

METHODS

Rat hearts underwent a 30 min occlusion of the anterior descending coronary artery, after which reperfusion was performed for 2 h. A total of 100 rats were randomly assigned to the following groups: ischemia/reperfusion (I/R), sham, liraglutide preconditioning (LP, liraglutide, 0.18 mg/kg, intravenously, 12 h before ischemia), HSP90 inhibitor geldanamycin (GA, 1 mg/kg, intraperitoneally, 30 min before ischemia) plus LP, and C5a receptor antagonist PMX53 (1 mg/kg, intravenously, 30 min before ischemia) plus LP. Cardiac injury, C5a/NF-κB activation, and inflammation were investigated.

RESULTS

LP significantly attenuated I/R-induced cardiomyocyte apoptosis, infarct size, and secretion of creatine kinase-MB, lactate dehydrogenase and cardiac troponin I. These effects were complemented by decreased C5a levels, nuclear factor (NF)-κB signaling, inflammatory cytokine expression, and increased HSP90 levels. GA, an HSP90 inhibitor, promotes C5a activation, NF-κB signaling, and inflammation and suppresses cardioprotection by LP. By contrast, PMX53, a C5a inhibitor, suppressed C5a activation, NF-κB signaling, and inflammation, and enhanced cardioprotection by LP.

CONCLUSION

HSP90 markedly contributes to LP cardioprotection by inhibiting inflammatory responsesand C5a/NF-κB signaling , ultimately attenuating I/R-induced cardiomyocyte apoptosis by suppressing the proapoptotic factor Bax, and inducing the anti-apoptotic factor Bcl2.

New weapons to fight a new enemy: A systematic review of drug combinations against the drug-resistant fungus Candida auris

Candida auris is an emerging and drug-resistant pathogen. Drug combination is a promising approach against such pathogens. This study was conducted to provide an overview of all the studied drug combinations against C. auris. Relevant articles reporting results of any drug/non-drug combinations against C. auris were found by a systematic search in PubMed, Scopus and Web of Science (ISI), and in Google Scholar up to 1 October 2020. From 187 articles retrieved in the primary search, 23 met the inclusion criteria. In total, 124 different combinations including antifungal with antifungal (45), antifungal with other antimicrobials (11), antifungal with non-antimicrobials (32), antifungal with natural compounds (25) and between natural compounds (11) have been reported. Complete or partial synergistic effects have been reported for 3 out of 45 (6.67%) combinations of two antifungal agents, 8 out of 11 (72.73%) combinations involving antifungal agents and antimicrobials, 15 out of 32 (46.88%) of combinations between antifungal agents with non-antimicrobials, 16 out of 25 (64%) of combinations involving antifungal agents and natural compounds, and 3 out of 11 (22.27%) of combinations involving multiple natural compounds. Antagonistic interactions have been reported for 1 out of 32 (3.13%) and 8 out of 25 (32%) of combinations between antifungal drugs with non-antimicrobials and with natural compounds, respectively. Different drugs/compounds could potentiate the activity of antifungal drugs using this approach. However, despite the availability of this promising initial data, many more studies will be required to elucidate whether favourable interactions observed in vitro might translate into tangible clinical benefits.

Effect of a fever in viral infections — the ‘Goldilocks’ phenomenon?

Acute infections, including those due to Coronaviridae and other viruses, often stimulate a febrile response. A mild fever appears to improve outcome; it appears to diminish viral replication by several mechanisms, including virion entry into host cells and genome transcription, and improving host defence mechanisms against the pathogen. However, a fever may also damage host cellular and tissue function and increase metabolic demands. At temperatures at the lower end of the febrile range, the benefit of the fever appears to outweigh the detrimental effects. However, at higher temperatures, the outcome worsens, suggesting that the disadvantages of fever on the host predominate. A non-infective fever is associated with a worse outcome at lower temperatures, suggesting that hyperthermia carries less benefit in the absence of infection. This review discusses the risks and benefits of a fever on the host response, focusing on the effects of a fever on viral replication and host response, and the detrimental effect on the host.

Are Hsp90 inhibitors good candidates against Covid-19?

Drug reposition, or repurposing, has become a promising strategy in therapeutics due to its advantages in several aspects of drug therapy. General drug development is expensive and can take more than 10 years to go through the designing, development, and necessary approval steps. However, established drugs have already overcome these steps and thus a potential candidate may be already available decreasing the risks and costs involved. Viruses invade cells, usually provoking biochemical changes, leading to tissue damage, alteration of normal physiological condition in organisms and can even result in death. Inside the cell, the virus finds the machinery necessary for its multiplication, as for instance the protein quality control system, which involves chaperones and Hsps (heat shock proteins) that, in addition to physiological functions, help in the stabilization of viral proteins. Recently, many inhibitors of Hsp90 have been developed as therapeutic strategies against diseases such as the Hsp90 inhibitors used in anticancer therapy. Several shreds of evidence indicate that these inhibitors can also be used as therapeutic strategies against viruses. Therefore, since a drug treatment for COVID-19 is urgently needed, this review aims to discuss the potential use of Hsp90 inhibitors in the treatment of this globally threatening disease.

The matrix metalloproteinase 7 (MMP7) links Hsp90 chaperone with acquired drug resistance and tumor metastasis

BACKGROUND

Cancer emergence is associated with a series of cellular transformations that include acquired drug resistance followed by tumor metastasis. Matrix metalloproteinases (MMPs) and Hsp90 chaperone are implicated in tumor progression, however, they are not studied in the context of drug resistance.

AIMS

In the present study, we aimed at understanding the cross-talk between acquired drug resistance and tumor progression, linking MMP7 and Hsp90.

METHODS AND RESULTS

We have developed an in vitro model system for acquired drug resistance and studied the correlation between MMP7 and Hsp90. We demonstrate that enhanced drug efflux activity correlates with the induced expression and activity of MMP7, and enhanced metastatic potential of cells, however, in Hsp90-dependent manner. The MMP7 overexpression alone could enhance the drug efflux activity marginally, and metastasis significantly. However, challenging these cells with 17AAG has significantly increased the drug efflux activity and, in contrast, decreased the metastatic potential. Evaluating our in vitro findings in mice xenografts revealed that MMP7 overexpression facilitates altered homing properties. However, these cells, in response to 17AAG treatment, exhibited increased localized tumor growth but decreased tumor metastasis.

CONCLUSION

We demonstrated a cross-talk between Hsp90 and MMP7 in regulating the acquired drug resistance and tumor progression. Our findings provide novel insights on targeting drug resistant-tumors.

Hsp90 facilitates acquired drug resistance of tumor cells through cholesterol modulation however independent of tumor progression

Acquired multidrug resistance of cancer cells challenges the chemotherapeutic interventions. To understand the role of molecular chaperone, Hsp90 in drug adapted tumor cells, we have used in vitro drug adapted epidermoid tumor cells as a model system. We found that chemotherapeutic drug adaptation of tumor cells is mediated by induced activities of both Hsp90 and P-glycoprotein (P-gp). Although the high-affinity conformation of Hsp90 has correlated with the enhanced drug efflux activity, we did not observe a direct interaction between P-gp and Hsp90. The enrichment of P-gp and Hsp90 at the cholesterol-rich membrane microdomains is found obligatory for enhanced drug efflux activity. Since inhibition of cholesterol biosynthesis is not interfering with the drug efflux activity, it is presumed that the net cholesterol redistribution mediated by Hsp90 regulates the enhanced drug efflux activity. Our in vitro cholesterol and Hsp90 interaction studies have furthered our presumption that Hsp90 facilitates cholesterol redistribution. The drug adapted cells though exhibited anti-proliferative and anti-tumor effects in response to 17AAG treatment, drug treatment has also enhanced the drug efflux activity. Our findings suggest that drug efflux activity and metastatic potential of tumor cells are independently regulated by Hsp90 by distinct mechanisms. We expose the limitations imposed by Hsp90 inhibitors against multidrug resistant tumor cells.

Antibodies to Heat Shock Proteins 90α and 90β in Psoriasis

One of many hypotheses of psoriasis pathogenesis supposes an overexpression of heat shock proteins (Hsps) in different skin layers and systemic immunologic response to them. Hsp90 is one of the most abundant chaperone in eukaryotic cells. The number of studies concerning the role of Hsp90 and anti-Hsp90 antibodies in etiopathogenesis of various diseases is also constantly expanding. Still, there are not many reports concerning potential involvement of this Hsp family or anti-Hsp90 immunization in pathomechanism of psoriasis. The aim of the study was the estimation of anti-Hsp90α and anti-Hsp90β IgG antibodies in the sera of the psoriatic patients at different phases of disease activity in comparison to the sera of healthy individuals. The study material consisted of sera from psoriasis patients (n = 80) in active phase and in the remission phase and healthy individuals (n = 80). Concentrations of anti-Hsp90α and anti-Hsp90β IgG antibodies were determined using ELISA technique. In the patients with psoriasis (both in the active phase of the disease and in the remission phase) concentrations of anti-Hsp90α antibodies were significantly higher than in healthy individuals and they correlated positively with psoriasis area severity index values. The mean concentrations of anti-Hsp90β antibodies in the psoriatic patients and healthy controls were comparable. The obtained results indicate an existence of increased immunological response to Hsp90α in psoriasis. It may suggest the role of the extracellular form of this chaperone and/or anti-Hsp90α antibodies in etiopathogenesis of this dermatosis. The inhibition of Hsp90α may represent a novel therapeutic approach to treat psoriasis.

Involvement of HSP90 in ischemic postconditioning-induced cardioprotection by inhibition of the complement system, JNK and inflammation

Purpose

To investigate whether heat shock protein 90 (HSP90) is involved in complement regulation in ischemic postconditioning (IPC).

Methods

The left coronary artery of rats underwent 30 min of occlusion, followed by 120 min of reperfusion and treatment with IPC via 3 cycles of 30s reperfusion and 30s occlusion. The rats were injected intraperitoneally with 1 mg/kg HSP90 inhibitor geldanamycin (GA) after anesthesia. Eighty rats were randomly divided into four groups: sham, ischemia-reperfusion (I/R), IPC and IPC + GA. Myocardial infarct size, apoptosis index and the expression of HSP90, C3, C5a, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1β and c-Jun N-terminal kinase (JNK) were assessed.

Results

Compared with the I/R injury, the IPC treatment significantly reduced infarct size, release of troponin T, creatine kinase-MB, and lactate dehydrogenase, and cardiomyocyte apoptosis. These beneficial effects were accompanied by a decrease in TNF-α, IL-1β, C3, C5a and JNK expression levels. However, all these effects were abrogated by administration of the HSP90 inhibitor GA.

Conclusion

HSP90 exerts a profound effect on IPC cardioprotection, and may be linked to the inhibition of the complement system and JNK, ultimately attenuating I/R-induced myocardial injury and apoptosis.

Interaction of Hsp90 with phospholipid model membranes

Heat shock protein 90 (Hsp90) is an essential molecular chaperone with versatile functions in cell homeostatic control under both normal and stress conditions. Hsp90 has been found to be expressed on the cell surface, but the mechanism of Hsp90 association to the membrane remains obscure. In this study, the direct interaction of Hsp90 and phospholipid vesicles was characterized, and the role of Hsp90 on membrane physical state was explored. Using surface plasmon resonance (SPR), we observed a strong interaction between Hsp90 and different compositions of lipid. Hsp90 had a preference to bind with more unsaturated phospholipid species and the affinity was higher with negatively charged lipids than zwitterionic lipids. Increasing the mole fraction of cholesterol in the phospholipid led to a decrease of binding affinity to Hsp90. Circular dichroism (CD) spectroscopy of Hsp90 in PC membranes showed more α-helix structure than in aqueous buffer. The differential scanning calorimeter (DSC) and fluorescence polarization results showed Hsp90 could affect the transition temperature and fluidity of the bilayer. We postulate from these results that the association between Hsp90 and membranes may involve both electrostatic and hydrophobic force, and constitute a possible mechanism that modulates membrane lipid order during thermal fluctuations.

HSP90 inhibitor 17-DMAG exerts anticancer effects against gastric cancer cells principally by altering oxidant-antioxidant balance

Heat shock protein 90 (HSP90) stabilizes numerous oncoproteins and, therefore, its inhibition has emerged as a promising antineoplastic strategy for diverse malignancies. In this study, we determined the therapeutic effects and mechanisms of action of a specific HSP90 inhibitor, 17-dimethylamino-ethylamino-17-demethoxygeldanamycin (17-DMAG), in gastric cancer cell lines (AGS, SNU-1, and KATO-III), patient-derived tissues, and a mouse xenograft model. 17-DMAG exerted anticancer effects against gastric cancer cells, manifested by significantly decreased proliferation rates (P < 0.05) and increased expression of apoptotic markers. Flow cytometry using dichlorofluorescein (DCF) diacetate revealed that 17-DMAG dose-dependently increases reactive oxygen species (ROS) levels in gastric cancer cells. Inhibition of ROS by N-acetyl-L-cysteine (NAC) abrogated the proapoptotic effects of 17-DMAG, as demonstrated by the decreased expression of proapoptotic proteins. In addition, 17-DMAG dose- and time-dependently reduced the expression of antioxidants such as catalase and glutathione peroxidase (GPx). Moreover, 17-DMAG reduced the expression of nuclear respiratory factor (NRF)-1 and NRF-2, and prevented them from migrating from the cytoplasm to the nucleus dose-dependently. Finally, in a nude mouse xenograft model, the shrinkage of tumors was more prominent in mice treated with 17-DMAG than in control mice (P < 0.05). Taken altogether, our results suggest that 17-DMAG exerts potent antineoplastic activity against gastric cancer cells primarily by promoting ROS generation and suppressing antioxidant enzyme activities.

Effects of Argentilactone on the Transcriptional Profile, Cell Wall and Oxidative Stress of Paracoccidioides spp

Paracoccidioides spp., a dimorphic pathogenic fungus, is the etiologic agent of paracoccidioidomycosis (PCM). PCM is an endemic disease that affects at least 10 million people in Latin America, causing severe public health problems. The drugs used against pathogenic fungi have various side effects and limited efficacy; therefore, there is an inevitable and urgent medical need for the development of new antifungal drugs. In the present study, we evaluated the transcriptional profile of Paracoccidioides lutzii exposed to argentilactone, a constituent of the essential oil of Hyptis ovalifolia. A total of 1,058 genes were identified, of which 208 were up-regulated and 850 were down-regulated. Cell rescue, defense and virulence, with a total of 26 genes, was a functional category with a large number of genes induced, including heat shock protein 90 (hsp90), cytochrome c peroxidase (ccp), the hemoglobin ligand RBT5 (rbt5) and superoxide dismutase (sod). Quantitative real-time PCR revealed an increase in the expression level of all of those genes. An enzymatic assay showed a significant increase in SOD activity. The reduced growth of Pbhsp90-aRNA, Pbccp-aRNA, Pbsod-aRNA and Pbrbt5-aRNA isolates in the presence of argentilactone indicates the importance of these genes in the response of Paracoccidioides spp. to argentilactone. The response of the P. lutzii cell wall to argentilactone treatment was also evaluated. The results showed that argentilactone caused a decrease in the levels of polymers in the cell wall. These results suggest that argentilactone is a potential candidate for antifungal therapy.

Paracoccidioidomycosis (PCM) is a neglected human systemic mycosis caused by Paracoccidioides spp. fungus that invades the host’s lungs and can disseminate to many other organs. Treatment usually involves amphotericin B, sulfadiazine, trimethoprim-sulfamethoxazole, itraconazole, ketoconazole or fluconazole for six months to two years. In this way, many adverse effects are associated with treatment, and patients can have many co-morbidities and difficulties in complying with treatment. For those reasons, more effective and less toxic drugs are needed. The discovery of a potentially bioactive molecule and its correlation with a biological target is an important step in the research and development of drugs. One of the ways in which cells adjust to environmental change is by changing the pattern of gene expression. Thus, the transcriptome is potential experimental strategy to elucidate the mode of action of bioactive molecules. Here, Paracoccidoides spp. altered the expression of genes, leading to a further understanding of the action of the compound argentilactone in the fungal cells. Argentilactone seems to be able to modulate cellular targets, to induce oxidative stress and to interfere with the biosynthesis of the P. lutzii cell wall.

HSP90 Inhibitor Geldanamycin as a Radiation Response Modificator in Human Blood Cells

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone, involved in the folding, assembly, stabilization and activation of numerous proteins with unrelated amino acid sequences and functions. Geldanamycin (GA), a natural benzoquinone, can inhibit the chaperone activity of Hsp90. It has been shown that GA can produce superoxide anions and increase the intracellular oxidative stress, which, in addition to the direct inhibition of Hsp90, might also contribute to the modifying effects of the inhibitor on the early response in human mononuclear cells exposed to ionizing radiation. The present study shows that GA antagonizes the radiation-induced suppression on MnSOD and catalase, key enzymes of the radical scavenging systems. By significantly up-regulating catalase levels over the entire range of doses from 0.5 to 4 Gy, the inhibitor of Hsp90 exerted adaptive protection and modified the early radiation response of the human blood cells.

Prediction of dual agents as an activator of mutant p53 and inhibitor of Hsp90 by docking, molecular dynamic simulation and virtual screening

Heat shock protein90s (Hsp90s) play a crucial role in the development of cancer, and their inhibitors are a main target for tumor suppression. P53 also is a tumor suppressor, but in cancer cells, mutations in the p53 gene lead to the inactivation and accumulation of protein. For instance, the ninth p53 cancer mutation, Y220C, destabilizes the p53 core domain. Small molecules have been assumed to bind to Y220C DNA-binding domain and reactivate cellular mutant p53 functions. In this study, one of the mutant p53 activators is suggested as an Hsp90 inhibitor according to a pyrazole scaffold. To confirm a new ligand as a dual agent, molecular docking and molecular dynamic simulations were performed on both proteins (p53 and Hsp90). Molecular dynamic simulations were also conducted to evaluate the obtained results on the other two pyrazole structures, one known as Hsp90 inhibitor and the other as the reported mutant p53 activator. The findings indicate that the new ligand was stable in the active site of both proteins. Finally, a virtual screening was performed on ZINC database, and a set of new dual agents was proposed according to the new ligand scaffold.

Oxygen regulates molecular mechanisms of cancer progression and metastasis

Oxygen is the basic molecule which supports life and it truly is "god's gift to life." Despite its immense importance, research on "oxygen biology" has never received the light of the day and has been limited to physiological and biochemical studies. It seems that in modern day biology, oxygen research is summarized in one word "hypoxia." Scientists have focused on hypoxia-induced transcriptomics and molecular-cellular alterations exclusively in disease models. Interestingly, the potential of oxygen to control the basic principles of biology like homeostatic maintenance, transcription, replication, and protein folding among many others, at the molecular level, has been completely ignored. Here, we present a perspective on the crucial role played by oxygen in regulation of basic biological phenomena. Our conclusion highlights the importance of establishing novel research areas like oxygen biology, as there is great potential in this field for basic science discoveries and clinical benefits to the society.

High-level expression of Hsp90β is associated with poor survival in resectable non-small-cell lung cancer patients

AIMS

The aim of this study was to investigate the expression of Hsp90β and GRP94, and elucidate the clinical significance of their expression, in patients with resectable non-small-cell lung cancer (NSCLC).

METHODS AND RESULTS

Surgical tissue specimens were obtained from 208 patients with NSCLC who underwent surgical resection. The expression levels of Hsp90β and GRP94 were assessed with tissue microarrays and immunohistochemistry. No correlations were observed between Hsp90β or GRP94 expression and several clinicopathological factors. The high-Hsp90β group [median overall survival (OS) 20.4 months; 95% confidence interval (CI) 0.000-40.864] showed a significant decrease in OS as compared with the low-Hsp90β group (median OS not reached; P = 0.003). In contrast to the Hsp90β analysis, the GRP94 analysis did not show a difference in OS. Moreover, in subgroup analyses of patients with squamous cell carcinoma histology, OS (P = 0.012) and relapse-free survival (P = 0.044) were significantly worse in the high-Hsp90β group than in the low-Hsp90β group. Multivariate analysis suggested that old age [hazard ratio (HR) 1.568; 95% CI 1.019-2.412; P = 0.041], advanced disease (HR 2.066; 95% CI 1.218-3.502; P = 0.007) and high Hsp90β expression (HR 1.802; 95% CI 1.061-3.060; P = 0.029) were independent poor prognostic factors for OS.

CONCLUSIONS

Hsp90β expression might be a useful marker of poor OS, although further large prospective studies are warranted to validate our findings.

Thioredoxin-1 redox signaling regulates cell survival in response to hyperoxia

The most common form of newborn chronic lung disease, bronchopulmonary dysplasia (BPD), is thought to be caused by oxidative disruption of lung morphogenesis, which results in decreased pulmonary vasculature and alveolar simplification. Although cellular redox status is known to regulate cellular proliferation and differentiation, redox-sensitive pathways associated with these processes in developing pulmonary epithelium are unknown. Redox-sensitive pathways are commonly regulated by cysteine thiol modifications. Therefore two thiol oxidoreductase systems, thioredoxin and glutathione, were chosen to elucidate the roles of these pathways on cell death. Studies herein indicate that thiol oxidation contributes to cell death through impaired activity of glutathione-dependent and thioredoxin (Trx) systems and altered signaling through redox-sensitive pathways. Free thiol content decreased by 71% with hyperoxic (95% oxygen) exposure. Increased cell death was observed during oxygen exposure when either the Trx or the glutathione-dependent system was pharmacologically inhibited with aurothioglucose (ATG) or buthionine sulfoximine, respectively. However, inhibition of the Trx system yielded the smallest decrease in free thiol content (1.44% with ATG treatment vs 21.33% with BSO treatment). Although Trx1 protein levels were unchanged, Trx1 function was impaired during hyperoxic treatment as indicated by progressive cysteine oxidation. Overexpression of Trx1 in H1299 cells utilizing an inducible construct increased cell survival during hyperoxia, whereas siRNA knockdown of Trx1 during oxygen treatment reduced cell viability. Overall, this indicated that a comparatively small pool of proteins relies on Trx redox functions to mediate cell survival in hyperoxia, and the protective functions of Trx1 are progressively lost by its oxidative inhibition. To further elucidate the role of Trx1, potential Trx1 redox protein-protein interactions mediating cytoprotection and cell survival pathways were determined by utilizing a substrate trap (mass action trapping) proteomics approach. With this method, known Trx1 targets were detected, including peroxiredoxin-1as well as novel targets, including two HSP90 isoforms (HSP90AA1 and HSP90AB1). Reactive cysteines within the structure of HSP90 are known to modulate its ATPase-dependent chaperone activity through disulfide formation and S-nitrosylation. Whereas HSP90 expression is unchanged at the protein level during hyperoxic exposure, siRNA knockdown significantly increased hyperoxic cell death by 2.5-fold, indicating cellular dependence on HSP90 chaperone functions in response to hyperoxic exposure. These data support the hypothesis that hyperoxic impairment of Trx1 has a negative impact on HSP90-oxidative responses critical to cell survival, with potential implications for pathways implicated in lung development and the pathogenesis of BPD.

Heat shock protein 90 is a potential therapeutic target for ameliorating skeletal muscle abnormalities in Parkinson's disease

Previous studies have confirmed that heat shock protein 90 overexpression can lead to dopaminergic neuronal death. This study was designed to further investigate what effects are produced by heat shock protein 90 after endurance exercise training. Immunohistochemistry results showed that exercise training significantly inhibited heat shock protein 90 overexpression in the soleus and gastrocnemius in Parkinson's disease rats, which is a potential therapeutic target for ameliorating skeletal muscle abnormalities in Parkinson's disease.

Down-regulation of heat shock protein HSP90ab1 in radiation-damaged lung cells other than mast cells

Ionizing radiation (IR) leads to fibrosing alveolitis (FA) after a lag period of several weeks to months. In a rat model, FA starts at 8 weeks after IR. Before that, at 5.5 weeks after IR, the transcription factors Sp1 (stimulating protein 1) and AP-1 (activator protein 1) are inactivated. To find genes/proteins that were down-regulated at that time, differentially expressed genes were identified in a subtractive cDNA library and verified by quantitative RT-PCR (reverse transcriptase polymerase chain reaction), western blotting and immunohistochemistry (IH). The mRNA of the molecular chaperone HSP90AB1 (heat shock protein 90 kDa alpha, class B member 1) was down-regulated 5.5 weeks after IR. Later, when FA manifested, HSP90ab1 protein was down-regulated by more than 90% in lung cells with the exception of mast cells. In most mast cells of the normal lung, both HSP90ab1 and HSP70, another major HSP, show a very low level of expression. HSP70 was massively up-regulated in all mast cells three months after irradiation whereas HSP90AB1 was up-regulated only in a portion of mast cells. The strong changes in the expression of central molecular chaperones may contribute to the well-known disturbance of cellular functions in radiation-damaged lung tissue.

Hemolytic anemia in two patients with glioblastoma multiforme: A possible interaction between vorinostat and dapsone

Patients undergoing treatment for glioblastoma multiforme are routinely placed on prophylactic treatment for Pneumocystis jirovecii pneumonia because of significant therapy-induced lymphopenia. In patients with sulfa allergies, dapsone prophylaxis is often used due to its efficacy, long half-life, cost effectiveness, and general safety at low doses. However, dapsone may uncommonly induce a hemolytic anemia, particularly in patients deficient of glucose-6-phosphate dehydrogenase. This hemolysis is thought to be a result of oxidative stress on red blood cells induced by dapsone metabolites which produce reactive oxygen species that disrupt the red blood cell membrane and promote splenic sequestration. A single case report of dapsone-induced hemolytic anemia in a patient with glioblastoma multiforme has been reported. We present two patients with glioblastoma multiforme who developed severe hemolytic anemia shortly after initiating therapy with vorinostat, a pan-active histone deacetylase inhibitor, while on prophylactic dapsone. There are several potential mechanisms by which histone deacetylase inhibition may alter dapsone metabolism including changes in hepatic acetylation or N-glucuronidation leading to an increase in the bioavailability of dapsone’s hematotoxic metabolites. In addition, vorinostat may lead to increased hemolysis through inhibition of heat shock protein-90, a chaperone protein that maintains the integrity of the red blood cell membrane cytoskeleton. The potential interaction between dapsone and vorinostat may have important clinical implications as more than 10 clinical trials evaluating drug combinations with vorinostat in patients with malignant glioma are either ongoing or planned in North America.

Involvement of calcium-mediated reactive oxygen species in inductive GRP78 expression by geldanamycin in 9L rat brain tumor cells

Treatment with geldanamycin (GA) leads to an increase in [Ca2+]c and the production of reactive oxygen species (ROS) in rat brain tumor 9L RBT cells. GA-exerted calcium signaling was blocked by BAPTA/AM and EGTA. The effect of GA on [Ca2+]c was significantly reduced in the presence of thapsigargin (TG) and ruthenium red (RR). GA-induced GRP78 expression is significantly decreased in the presence of BAPTA/AM, EGTA and RR, suggesting that the calcium influx from the extracellular space and intracellular calcium store oscillations are contributed to by the calcium mobilization and GRP78 expression induced by GA. The induced GRP78 expression is sensitive to added U73122 and Ro-31-8425, pinpointing the involvement of phospholipase C (PLC) and protein kinase C (PKC) in GA-induced endoplasmic reticulum (ER) stress. The antioxidants N-acetylcysteine (NAC), BAPTA/AM, EGTA and H7 also have significant inhibitory effects on ROS generation. Finally, neither H7 nor NAC was able to affect the calcium response elicited by GA. Our results suggest that the causal signaling cascade during GA-inducted GRP78 expression occurs via a pathway that connects PLC to cytoplasmic calcium increase, PKC activation and, then, finally, ROS generation. Our data provides new insights into the influence of GA on ER stress response in 9L RBT cells.

Cardiomyocyte ryanodine receptor degradation by chaperone-mediated autophagy

AIMS

Chaperone-mediated autophagy (CMA) is a selective mechanism for the degradation of soluble cytosolic proteins bearing the sequence KFERQ. These proteins are targeted by chaperones and delivered to lysosomes where they are translocated into the lysosomal lumen and degraded via the lysosome-associated membrane protein type 2A (LAMP-2A). Mutations in LAMP2 that inhibit autophagy result in Danon disease characterized by hypertrophic cardiomyopathy. The ryanodine receptor type 2 (RyR2) plays a key role in cardiomyocyte excitation-contraction and its dysfunction can lead to cardiac failure. Whether RyR2 is degraded by CMA is unknown.

METHODS AND RESULTS

To induce CMA, cultured neonatal rat cardiomyocytes were treated with geldanamycin (GA) to promote protein degradation through this pathway. GA increased LAMP-2A levels together with its redistribution and colocalization with Hsc70 in the perinuclear region, changes indicative of CMA activation. The inhibition of lysosomes but not proteasomes prevented the loss of RyR2. The recovery of RyR2 content after incubation with GA by siRNA targeting LAMP-2A suggests that RyR2 is degraded via CMA. In silico analysis also revealed that the RyR2 sequence harbours six KFERQ motifs which are required for the recognition Hsc70 and its degradation via CMA. Our data suggest that presenilins are involved in RyR2 degradation by CMA.

CONCLUSION

These findings are consistent with a model in which oxidative damage of the RyR2 targets it for turnover by presenilins and CMA, which could lead to removal of damaged or leaky RyR2 channels.

Involvement of the 90 kDa heat shock protein during adaptation of Paracoccidioides brasiliensis to different environmental conditions

HSP90 is a molecular chaperone that participates in folding, stabilization, activation, and assembly of several proteins, all of which are key regulators in cell signaling. In dimorphic pathogenic fungi such as Paracoccidioides brasiliensis, the adaptation to a higher temperature, acid pH and oxidative stress, is an essential event for fungal survival and also for the establishing of the infectious process. To further understand the role of this protein, we used antisense RNA technology to generate a P. brasiliensis isolate with reduced PbHSP90 gene expression (PbHSP90-aRNA). Reduced expression of HSP90 decreased yeast cell viability during batch culture growth and increased susceptibility to acid pH environments and imposed oxidative stress. Also, PbHSP90-aRNA yeast cells presented reduced viability upon interaction with macrophages. The findings presented here suggest a protective role for HSP90 during adaptation to hostile environments, one that promotes survival of the fungus during host-pathogen interactions.

Hsp90 regulates Paracoccidioides brasiliensis proliferation and ROS levels under thermal stress and cooperates with calcineurin to control yeast to mycelium dimorphism

Paracoccidioidomycosis is a systemic human mycosis in Latin America caused by Paracoccidioides brasiliensis, a dimorphic pathogenic fungus that lives as a mold in the environment and as yeast during infections of human lungs. In this work, we provide evidence that the inhibition of Hsp90 by geldanamycin (GDA) impairs the proliferation of the yeast, but has no effect on mycelial development. Treatment with cyclosporin A (CsA), an inhibitor of the Hsp90 client protein calcineurin, did not increase the effect of GDA. In contrast, GDA prevented mycelial to yeast differentiation through a mechanism partially dependent on calcineurin, whereas differentiation from yeast to mycelia occurred independent of GDA or CsA. A significant increase in reactive oxygen species (ROS) levels was detected in GDA-treated yeast at 42°C. However, the levels of ROS remained unchanged in GDA-treated yeast or mycelia incubated at 37°C, suggesting that Hsp90 plays different roles under normal and thermal stress conditions. We propose that Hsp90 strengthens the stress response of P. brasiliensis at 37°C through a mechanism that does not involve ROS. Moreover, we suggest that Hsp90 has calcineurin-dependent functions in this organism.

17AAG Treatment Accelerates Doxorubicin Induced Cellular Senescence: Hsp90 Interferes with Enforced Senescence of Tumor Cells

Hsp90 chaperone has been identified as an attractive pharmacological target to combat cancer. However, some metastatic tumors either fail to respond to Hsp90 inhibition or show recovery necessitating irreversible therapeutic strategies. In response to this enforced senescence has been proposed as an alternate strategy. Here, we demonstrate that inhibiting Hsp90 with 17AAG sensitizes human neuroblastoma to DNA damage response mediated cellular senescence. Among individual and combination drug treatments, 17AAG pre-treatment followed by doxorubicin treatment exhibited senescence-like characteristics such as increased nucleus to cytoplasm ratio, cell cycle arrest, SA-β-gal staining and the perpetual increase in SAHF. Doxorubicin induced senescence signaling was mediated by p53-p21(CIP/WAF-1) and was accelerated in the absence of functional Hsp90. Sustained p16(INK4a) and H3K4me3 expressions correlating with unaffected telomerase activation annulled replicative senescence and appraised stress induced senescence. Despite increases in [(ROS)i] and [(Ca(2+))i], a concomitant increase in cellular antioxidant defense system suggested oxidation independent senescence activation. Sustained activation of survival (Akt) and proliferative (ERK1/2) kinases fosters robustness of cells. Invigorating senescent cells with growth factor or snooping with mTOR or PI3 kinase inhibitors compromised cell survival but not senescence. Intriguingly, senescence-associated secretory factors from the senescence cells manifested established senescence in neuroblastoma, which offers clinical advantage to our approach. Our study discusses tumor selective functions of Hsp90 and discusses irrefutable strategies of Hsp90 inhibition in anticancer treatments.

Redox properties and thiol reactivity of geldanamycin and its analogues in aqueous solutions

Geldanamycin (GM), a benzoquinone ansamycin antibiotic, is a natural product inhibitor of Hsp90 with potent and broad anticancer properties, but with unacceptable levels of hepatotoxicity. Less toxic C17-substituted analogues have been synthesizedincluding 17-(allylamino)-17-demethoxygeldanamycin (17-AAG) and the water-soluble 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG). Redox properties and thiol reactivity are central to the therapeutic and toxicologic effects of quinones, and the question arises as whether the extent of toxicity of GM, 17-AAG, and 17-DMAG is related to their redox potentials. Using pulse radiolysis, the one-electron redox potentials (vs NHE) at pH 7.0 of GM and 17-AAG have been determined to be -62 ± 7 mV and -273 ± 8 mV, respectively, whereas a value of -194 ± 6 mV has been previously published for 17-DMAG. The rate constants of the reaction of GM and its analogues with glutathione, cysteine, or dithiothreitol under anoxia at pH 7.4 followed the order GM > 17-DMAG > 17-AAG, which correlates with the order of the redox potential of the quinone/semiquinone couple. Thus, GM reacts much faster with thiols compared to the less toxic 17-DMAG and 17-AAG, and is also expected to be more readily reduced by reductases to the respective semiquinone radical, which either decomposes to yield the respective hydroquinone or reduces oxygen to superoxide. Because both redox cycling and thiol reactivity have been associated with quinone toxicity, it is concluded that the toxicity of benzoquinone ansamycins is directly related to the redox potential of the quinone/semiquinone couple.

Exploiting cancer cell vulnerabilities to develop a combination therapy for ras-driven tumors

Ras-driven tumors are often refractory to conventional therapies. Here we identify a promising targeted therapeutic strategy for two Ras-driven cancers: Nf1-deficient malignancies and Kras/p53 mutant lung cancer. We show that agents that enhance proteotoxic stress, including the HSP90 inhibitor IPI-504, induce tumor regression in aggressive mouse models, but only when combined with rapamycin. These agents synergize by promoting irresolvable ER stress, resulting in catastrophic ER and mitochondrial damage. This process is fueled by oxidative stress, which is caused by IPI-504-dependent production of reactive oxygen species, and the rapamycin-dependent suppression of glutathione, an important endogenous antioxidant. Notably, the mechanism by which these agents cooperate reveals a therapeutic paradigm that can be expanded to develop additional combinations.

The role of stress proteins in prostate cancer

The development of therapeutic resistance, after hormone or chemotherapy for example, is the underlying basis for most cancer deaths. Exposure to anticancer therapies induces expression of many stress related proteins, including small heat shock proteins (HSPs). HSPs interact with various client proteins to assist in their folding and enhance the cellular recovery from stress, thus restoring protein homeostasis and promoting cell survival. The vents of cell stress and cell death are linked, as the induction of molecular chaperones appears to function at key regulatory points in the control of apoptosis. On the basis of these observations and on the role of molecular chaperones in the regulation of steroid receptors, kinases, caspases, and other protein remodelling events involved in chromosome replication and changes in cell structure, it is not surprising that molecular chaperones have been implicated in the control of cell growth and in resistance to various anticancer treatments that induce apoptosis. Recently, several molecular chaperones such as Clusterin and HSP27 have been reported to be involved in development and progression of hormone-refractory prostate cancer. In this review, we address some of the molecular and cellular events initiated by treatment induced stress, and discuss the potential role of chaperone proteins as targets for prostate cancer treatment.

Repercussion of Mitochondria Deformity Induced by Anti-Hsp90 Drug 17AAG in Human Tumor Cells

Inhibiting Hsp90 chaperone roles using 17AAG induces cytostasis or apoptosis in tumor cells through destabilization of several mutated cancer promoting proteins. Although mitochondria are central in deciding the fate of cells, 17AAG induced effects on tumor cell mitochondria were largely unknown. Here, we show that Hsp90 inhibition with 17AAG first affects mitochondrial integrity in different human tumor cells, neuroblastoma, cervical cancer and glial cells. Using human neuroblastoma tumor cells, we found the early effects associated with a change in mitochondrial membrane potential, elongation and engorgement of mitochondria because of an increased matrix vacuolization. These effects are specific to Hsp90 inhibition as other chemotherapeutic drugs did not induce similar mitochondrial deformity. Further, the effects are independent of oxidative damage and cytoarchitecture destabilization since cytoskeletal disruptors and mitochondrial metabolic inhibitors also do not induce similar deformity induced by 17AAG. The 1D PAGE LC MS/MS mitochondrial proteome analysis of 17AAG treated human neuroblastoma cells showed a loss of 61% proteins from membrane, metabolic, chaperone and ribonucleoprotein families. About 31 unmapped protein IDs were identified from proteolytic processing map using Swiss-Prot accession number, and converted to the matching gene name searching the ExPASy proteomics server. Our studies display that Hsp90 inhibition effects at first embark on mitochondria of tumor cells and compromise mitochondrial integrity.

A new feature of the stress response: increase in endocytosis mediated by Hsp70

The expression of heat shock proteins (HSP) is a conserved cellular response to a variety of stresses. These proteins have been found to refold denatured polypeptides and stabilize critical cellular processes. In this study, we introduce a new component of the stress response: the increase of receptor-mediated uptake of macromolecules from the external environment. We observed that endocytosis of transferrin, which is involved in the delivery of iron to the cell, was increased after stress induced by heat shock or after incubation with inhibitors of Hsp90 function. In both cases, the increase in endocytosis was reverted by inhibition of transcription, suggesting that gene expression is required. Transfection of cells with Hsp70 gene or inhibition of its expression by siRNA confirmed the role of this HSP in the increase of endocytosis. The mechanism for the enhancement of transferrin uptake was related to an accelerated internalization of the ligand-receptor complex as well as an increase in receptor recycling. These observations constitute a new paradigm for the cellular protection induced by HSP.

Sperm protein 17 is a novel marker for predicting cisplatin response in esophageal squamous cancer cell lines

Expression of sperm protein 17 (Sp17) mRNA has been reported in various malignancies. In an earlier study, we reported the upregulation of Sp17 transcripts in primary esophageal squamous cell carcinomas (ESCCs) using differential display and detected Sp17 transcripts in 86% of ESCCs by RT-PCR, whereas no transcripts were detected in the paired normal esophageal tissues. Herein we hypothesized that Sp17 might be used as a marker for detecting the response of anticancer therapies in ESCCs. Our results indicated that Sp17 protein levels in esophageal squamous cancer cell lines decreased in response to treatment with (i) the HSP90 activity inhibitor geldanamycin, (ii) the tyrosine kinase inhibitor erlotinib and (iii) cisplatin (chemotherapeutic agent commonly used in management of ESCC). In contrast, the Sp17 levels did not decrease in response to radiation therapy and treatment with the chemotherapeutic agent, gemcitabine. Further investigations showed that cisplatin induced decrease in Sp17 levels was due to transcriptional inhibition and cisplatin-resistant cell lines did not show this decrease in Sp17 levels in response to cisplatin treatment. In addition, we also carried our mass spectophotometric analysis to identify the binding partners of Sp17 to characterize its possible involvement in esophageal tumorigenesis and chemoresistance.

Role of oxidative stress in geldanamycin-induced cytotoxicity and disruption of Hsp90 signaling complex

Heat shock protein 90 (Hsp90) is a chaperone protein regulating PC-12 cell survival by binding and stabilizing Akt, Raf-1, and Cdc37. Hsp90 inhibitor geldanamycin (GA) cytotoxicity has been attributed to the disruption of Hsp90 binding, and the contribution of oxidative stress generated by its quinone group has not been studied in this context. Reactive oxygen species (ROS) and cell survival were assessed in PC-12 cells exposed to GA or menadione (MEN), and Akt, Raf-1, and Cdc37 expression and binding to Hsp90 were determined. GA disrupted Hsp90 binding and increased ROS production starting at 1 h, and cell death occurred at 6 h, inhibited by N-acetylcysteine (NAC) without preventing dissociation of proteins. At 24 h, NAC prevented cytotoxicity and Hsp90 complex disruption. However, MnTBAP antioxidant treatment failed to inhibit GA cytotoxicity, suggesting that NAC acts by restoring glutathione. In contrast, 24 h MEN treatment induced cytotoxicity without disrupting Hsp90 binding. GA and MEN decreased Hsp90-binding protein expression, and proteasomal inhibition prevented MEN-, but not GA-induced degradation. In conclusion, whereas MEN cytotoxicity is mediated by ROS and proteasomal degradation, GA-induced cytotoxicity requires ROS but induces Hsp90 complex dissociation and proteasome-independent protein degradation. These differences between MEN- and GA-induced cytotoxicity may allow more specific targeting of cancer cells.

Control mechanisms of differential translation of Hsp90 isoforms in 9L rat gliosarcoma cells

Although the differential expression of heat shcok proteins, Hsp90alpha and Hsp90beta was extensively studied in many kinds of cells, the post-transcriptional regulation of Hsp90 isoforms remains unclear. In control and GA-treated rat gliosarcoma cells, it has been reported that the translational efficiency of hsp90alpha is higher than hsp90beta. In this study, we present evidences identifying the roles for leaky scanning and 5'-UTR sequence in translational regulation of Hsp90beta. The result of in vitro transcription and translation (IVTT) experiment showed that hsp90alpha exhibited higher translation efficiency than hsp90beta. Sequence analysis revealed that there is an out-of-frame downstream AUG codon in hsp90beta gene. However, elimination of the downstream AUG by site-directly mutagenesis or introducing Kozak context sequence around the initiator AUG of hsp90beta open reading frame increased its translational efficiency, which indicated that leaky scanning might be a possible mechanism regulating hsp90beta. Furthermore, we also constructed a firefly luciferase reporter system to verify the effect of subsequent translation at the downstream out-of-frame AUG codon in 9L and A549 cells. Furthermore, it is believed that 5'-untranslated region (5'-UTR) also plays a significant role in translational control. We showed hsp90beta 5'-UTR gives rise to the reduction of the translation efficiency in IVTT experiment. Additionally, the reductive effect of hsp90beta 5'-UTR was further confirmed by luciferase reporter assay using truncated deletion analyses of 5'-UTR of hsp90beta. Our results support the hypothesis that ribosome leaky scanning mechanism and 5'-UTR sequence acts as negative regulators in hsp90beta mRNA.

Heat shock protein 90 is involved in regulation of hypoxia-driven proliferation of embryonic neural stem/progenitor cells

Hypoxia may regulate the proliferation of diverse stem cells. Our previous study showed that hypoxia promoted the proliferation of embryonic neural stem/progenitor cells (NPCs) and that hypoxia inducible factor-1(HIF-1) was critical in this process. HIF-1 could be stabilized under hypoxic conditions, and heat shock protein 90 (HSP90) is an essential protein that controls the activity and stabilization of HIF-1alpha. In the present work, we investigate whether HSP90 is involved in proliferation of NPCs under hypoxia by regulating HIF-1alpha stabilization. Geldanamycin (GA), an HSP90 inhibitor, decreased the expression of HIF-1alpha in NPCs during hypoxia-driven proliferation and reduced the expression level of HIF-1alpha protein under hypoxia in a time-dependent manner. The proliferation of NPCs induced by hypoxia was inhibited after GA treatment for 24 h. Another HSP90 inhibitor, radicicol, had the same effect on NPCs as GA. Furthermore, the expression of erythropoietin (EPO) and vascular endothelial growth factor (VEGF) in NPCs under hypoxia was suppressed by GA. The above data indicated that HSP90 might be involved in regulation of hypoxia-driven proliferation.

The stress responsive and morphologically regulated hsp90 gene from Paracoccidioides brasiliensis is essential to cell viability

Background

Paracoccidioides brasiliensis is a dimorphic fungus that causes the most prevalent systemic mycosis in Latin America. The response to heat shock is involved in pathogenesis, as this pathogen switches from mycelium to yeast forms in a temperature dependent fashion that is essential to establish infection. HSP90 is a molecular chaperone that helps in the folding and stabilization of selected polypeptides. HSP90 family members have been shown to present important roles in fungi, especially in the pathogenic species, as an immunodominant antigen and also as a potential antifungal therapeutic target.

Results

In this work, we decided to further study the Pbhsp90 gene, its expression and role in cell viability because it plays important roles in fungal physiology and pathogenesis. Thus, we have sequenced a Pbhsp90 cDNA and shown that this gene is present on the genome as a single copy. We have also confirmed its preferential expression in the yeast phase and its overexpression during dimorphic transition and oxidative stress. Treatment of the yeast with the specific HSP90 inhibitors geldanamycin and radicicol inhibited growth at 2 and 10 μM, respectively.

Conclusion

The data confirm that the Pbhsp90 gene encodes a morphologically regulated and stress-responsive protein whose function is essential to cell viability of this pathogen. This work also enforces the potential of HSP90 as a target for antifungal therapies, since the use of HSP90 inhibitors is lethal to the P. brasiliensis yeast cells in a dose-responsive manner.

Using metabolomics to monitor anticancer drugs

The metabolome of a cancer cell is likely to show changes after responding to an anticancer drug. These changes could be used to decide whether to continue treatment or, in the context of a drug trial, to indicate whether the drug is working and perhaps its mechanism of action. (Nuclear) magnetic resonance spectroscopy (NMR/MRS) methods can offer important insights into novel anticancer agents in order to accelerate the drug development process including time-course studies on the effect of a drug on its site of action (termed pharmacodynamics), in this case the cancer. In addition, some classes of anticancer agents currently under development (e.g. antiangiogenics) are designed to be used in combination with other drugs and will not cause tumour shrinkage when used as single agents in Phase 1 clinical trials. Thus NMR/MRS may have a special role in monitoring the pharmacodynamic actions of such drugs in early-phase clinical trials. This review focuses on the use of ex vivo NMR and in vivo MRS methods for monitoring the effect of some novel anticancer drugs on the cancer metabolome. Ex vivo NMR methods are complementary to in vivo measurements, as they can provide additional information and help in the interpretation of the in vivo data.

Live Cell Imaging of Outward and Inward Vesiculation Induced by the Complement C5b-9 Complex

Cells resist death induced by the complement membrane attack complex (MAC, C5b-9) by removal of the MAC from their surface by an outward and/or inward vesiculation. To gain an insight into the route of MAC removal, human C9 was tagged with Alexa Fluor 488 and traced within live cells. Tagged C9-AF488 was active in lysis of erythrocytes and K562 cells. Upon treatment of K562 cells with antibody and human serum containing C9-AF488, C9-AF488 containing MAC bound to the cells. Within 5-10 min, the cells started shedding C5b-9-loaded vesicles (0.05-1 mum) by outward vesiculation. Concomitantly, C9-AF488 entered the cells and accumulated in a perinuclear, late recycling compartment, co-localized with endocytosed transferrin-Texas Red. Similar results were obtained with fixed cells in which the MAC was labeled with antibodies directed to a C5b-9 neoepitope. Inhibition of protein kinase C reduced endocytosis of C5b-9. Kinetic analysis demonstrated that peripheral, trypsin-sensitive C5b-9 was cleared from cells at a slower rate relative to fully inserted, trypsin-resistant C5b-9. MAC formation is controlled by CD59, a ubiquitously expressed membrane complement regulator. Analysis at a cell population level showed that the amount of C5b-9-AF488 bound to K562 cells after complement activation was highly heterogeneous and inversely correlated with the CD59 level of expression. Efficient C9-AF488 vesiculation was observed in cells expressing low CD59 levels, suggesting that the protective impact of MAC elimination by vesiculation increases as the level of expression of CD59 decreases.