Tumor necrosis factor-associated protein 1 (TRAP-1) protects cells from oxidative stress and apoptosis

Hsp90 regulation of mitochondrial protein folding: from organelle integrity to cellular homeostasis

Although essential for energy production and cell fate decisions, the mechanisms that govern protein homeostasis, or proteostasis, in mitochondria are only recently beginning to emerge. Fresh experimental evidence has uncovered a role of molecular chaperones of the heat shock protein 90 (Hsp90) family in overseeing the protein folding environment in mitochondria. Initially implicated in protection against cell death, there is now evidence that Hsp90-directed protein quality control in mitochondria connects to hosts of cellular homeostatic networks that become prominently exploited in human cancer.

Role of TRAP1 and estrogen receptor alpha in patients with ovarian cancer -a study of the OVCAD consortium

BACKGROUND

The role of the tumor necrosis factor receptor associated protein 1 (TRAP1) - supposed to be involved in protection of cells from apoptosis and oxidative stress - has just started to be investigated in ovarian cancer. TRAP1 has been shown to be estrogen up-regulated in estrogen receptor α (ERα) positive ovarian cancer cells. The clinical impact of TRAP1 is not clear so far and the significance of ERα expression as therapeutic and prognostic marker is still controversial. Therefore, we investigated the importance of TRAP1 together with ERα in regard to clinicopathological parameters, chemotherapy response, and survival.

METHODS AND RESULTS

Expressions of TRAP1 and ERα were evaluated by immunohistochemical staining of tissue microarrays comprised of 208 ovarian cancer samples. TRAP1 was highly expressed in 55% and ERα was expressed in 52% of all cases. High TRAP1 expression correlated significantly with ERα (p<0.001) but high TRAP1 expression was also found in 42% of ERα negative cases. High TRAP1 expression correlated significantly with favorable chemotherapy-response (HR = 0.48; 95%CI 0.24-0.96, p=0.037) and showed a significant impact on overall survival (OS) (HR = 0.65; 95%CI 0.43-0.99, p = 0.044). ERα expression was a favorable prognostic factor for OS in univariate and multivariate analyses. Interestingly, the combined pattern (ERα positive and/or TRAP1-high) revealed the strongest independent and significant positive influence on OS (HR=0.41; 95%CI 0.27-0.64).

CONCLUSION

Immunohistochemical evaluation of TRAP1 together with ERα provides significant prognostic information. TRAP1 alone is significantly associated with chemotherapy response and overall survival, rendering TRAP1 as interesting scientific and therapeutic target.

Quantitative proteomic analysis of mitochondrial proteins reveals prosurvival mechanisms in the perpetuation of radiation-induced genomic instability

Radiation-induced genomic instability is a well-studied phenomenon that is measured as mitotically heritable genetic alterations observed in the progeny of an irradiated cell. The mechanisms that perpetuate this instability are unclear; however, a role for chronic oxidative stress has consistently been demonstrated. In the chromosomally unstable LS12 cell line, oxidative stress and genomic instability were correlated with mitochondrial dysfunction. To clarify this mitochondrial dysfunction and gain insight into the mechanisms underlying radiation-induced genomic instability we have evaluated the mitochondrial subproteome and performed quantitative mass spectrometry analysis of LS12 cells. Of 98 quantified mitochondrial proteins, 17 met criteria for fold changes and reproducibility; and 11 were statistically significant in comparison with the stable parental GM10115 cell line. Previous observations implicated defects in the electron transport chain (ETC) in the LS12 cell mitochondrial dysfunction. Proteomic analysis supports these observations, demonstrating significantly reduced levels of mitochondrial cytochrome c, the intermediary between complexes III and IV of the ETC. Results also suggest that LS12 cells compensate for ETC dysfunction and oxidative stress through increased levels of tricarboxylic acid cycle enzymes and upregulation of proteins that protect against oxidative stress and apoptosis. More than one cellular defect is likely to contribute to the genomic instability phenotype, and evaluation of gene and microRNA expression suggests that epigenetics play a role in the phenotype. These data suggest that LS12 cells have adapted mechanisms that allow survival under suboptimal conditions of oxidative stress and compromised mitochondrial function to perpetuate genomic instability.

TRAP1 regulation of mitochondrial life or death decision in cancer cells and mitochondria-targeted TRAP1 inhibitors

Hsp90 is one of the most conserved molecular chaperones ubiquitously expressed in normal cells and over-expressed in cancer cells. A pool of Hsp90 was found in cancer mitochondria and the expression of the mitochondrial Hsp90 homolog, TRAP1, was also elevated in many cancers. The mitochondrial pool of chaperones plays important roles in regulating mitochondrial integrity, protecting against oxidative stress, and inhibiting cell death. Pharmacological inactivation of the chaperones induced mitochondrial dysfunction and concomitant cell death selectively in cancer cells, suggesting they can be target proteins for the development of cancer therapeutics. Several drug candidates targeting TRAP1 and Hsp90 in the mitochondria have been developed and have shown strong cytotoxic activity in many cancers, but not in normal cells in vitros and in vivo. In this review, recent developments in the study of mitochondrial chaperones and the mitochondria-targeted chaperone inhibitors are discussed.

Chaperone-protease networks in mitochondrial protein homeostasis

As essential organelles, mitochondria are intimately integrated into the metabolism of a eukaryotic cell. The maintenance of the functional integrity of the mitochondrial proteome, also termed protein homeostasis, is facing many challenges both under normal and pathological conditions. First, since mitochondria are derived from bacterial ancestor cells, the proteins in this endosymbiotic organelle have a mixed origin. Only a few proteins are encoded on the mitochondrial genome, most genes for mitochondrial proteins reside in the nuclear genome of the host cell. This distribution requires a complex biogenesis of mitochondrial proteins, which are mostly synthesized in the cytosol and need to be imported into the organelle. Mitochondrial protein biogenesis usually therefore comprises complex folding and assembly processes to reach an enzymatically active state. In addition, specific protein quality control (PQC) processes avoid an accumulation of damaged or surplus polypeptides. Mitochondrial protein homeostasis is based on endogenous enzymatic components comprising a diverse set of chaperones and proteases that form an interconnected functional network. This review describes the different types of mitochondrial proteins with chaperone functions and covers the current knowledge of their roles in protein biogenesis, folding, proteolytic removal and prevention of aggregation, the principal reactions of protein homeostasis. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.

Cisplatin resistance: a cellular self-defense mechanism resulting from multiple epigenetic and genetic changes

Cisplatin is one of the most effective broad-spectrum anticancer drugs. Its effectiveness seems to be due to the unique properties of cisplatin, which enters cells via multiple pathways and forms multiple different DNA-platinum adducts while initiating a cellular self-defense system by activating or silencing a variety of different genes, resulting in dramatic epigenetic and/or genetic alternations. As a result, the development of cisplatin resistance in human cancer cells in vivo and in vitro by necessity stems from bewilderingly complex genetic and epigenetic changes in gene expression and alterations in protein localization. Extensive published evidence has demonstrated that pleiotropic alterations are frequently detected during development of resistance to this toxic metal compound. Changes occur in almost every mechanism supporting cell survival, including cell growth-promoting pathways, apoptosis, developmental pathways, DNA damage repair, and endocytosis. In general, dozens of genes are affected in cisplatin-resistant cells, including pathways involved in copper metabolism as well as transcription pathways that alter the cytoskeleton, change cell surface presentation of proteins, and regulate epithelial-to-mesenchymal transition. Decreased accumulation is one of the most common features resulting in cisplatin resistance. This seems to be a consequence of numerous epigenetic and genetic changes leading to the loss of cell-surface binding sites and/or transporters for cisplatin, and decreased fluid phase endocytosis.

The mitochondrial chaperone protein TRAP1 mitigates α-Synuclein toxicity

Overexpression or mutation of α-Synuclein is associated with protein aggregation and interferes with a number of cellular processes, including mitochondrial integrity and function. We used a whole-genome screen in the fruit fly Drosophila melanogaster to search for novel genetic modifiers of human [A53T]α-Synuclein-induced neurotoxicity. Decreased expression of the mitochondrial chaperone protein tumor necrosis factor receptor associated protein-1 (TRAP1) was found to enhance age-dependent loss of fly head dopamine (DA) and DA neuron number resulting from [A53T]α-Synuclein expression. In addition, decreased TRAP1 expression in [A53T]α-Synuclein-expressing flies resulted in enhanced loss of climbing ability and sensitivity to oxidative stress. Overexpression of human TRAP1 was able to rescue these phenotypes. Similarly, human TRAP1 overexpression in rat primary cortical neurons rescued [A53T]α-Synuclein-induced sensitivity to rotenone treatment. In human (non)neuronal cell lines, small interfering RNA directed against TRAP1 enhanced [A53T]α-Synuclein-induced sensitivity to oxidative stress treatment. [A53T]α-Synuclein directly interfered with mitochondrial function, as its expression reduced Complex I activity in HEK293 cells. These effects were blocked by TRAP1 overexpression. Moreover, TRAP1 was able to prevent alteration in mitochondrial morphology caused by [A53T]α-Synuclein overexpression in human SH-SY5Y cells. These results indicate that [A53T]α-Synuclein toxicity is intimately connected to mitochondrial dysfunction and that toxicity reduction in fly and rat primary neurons and human cell lines can be achieved using overexpression of the mitochondrial chaperone TRAP1. Interestingly, TRAP1 has previously been shown to be phosphorylated by the serine/threonine kinase PINK1, thus providing a potential link of PINK1 via TRAP1 to α-Synuclein.

Sorcin induces a drug-resistant phenotype in human colorectal cancer by modulating Ca(2+) homeostasis

The Ca(2+)-binding protein sorcin regulates intracellular calcium homeostasis and plays a role in the induction of drug resistance in human cancers. Recently, an 18 kDa mitochondrial isoform of sorcin was reported to participate in antiapoptosis in human colorectal cancer (CRC), but information remains lacking about the functional role of the more abundant 22 kDa isoform of sorcin expressed in CRC. We found the 22 kDa isoform to be widely expressed in human CRC cells, whether or not they were drug resistant. Its upregulation in drug-sensitive cells induced resistance to 5-fluorouracil, oxaliplatin, and irinotecan, whereas its downregulation sensitized CRC cells to these chemotherapeutic agents. Sorcin enhances the accumulation of Ca(2+) in the endoplasmic reticulum (ER), preventing ER stress, and, in support of this function, we found that the 22 kDa isoform of sorcin was upregulated under conditions of ER stress. In contrast, RNAi-mediated silencing of sorcin activated caspase-3, caspase-12, and GRP78/BiP, triggering apoptosis through the mitochondrial pathway. Our findings establish that CRC cells overexpress sorcin as an adaptive mechanism to prevent ER stress and escape apoptosis triggered by chemotherapeutic agents, prompting its further investigation as a novel molecular target to overcome MDR.

TRAP1 and the proteasome regulatory particle TBP7/Rpt3 interact in the endoplasmic reticulum and control cellular ubiquitination of specific mitochondrial proteins

Tumor necrosis factor receptor-associated protein-1 (TRAP1) is a mitochondrial (MITO) antiapoptotic heat-shock protein. The information available on the TRAP1 pathway describes just a few well-characterized functions of this protein in mitochondria. However, our group's use of mass-spectrometric analysis identified TBP7, an AAA-ATPase of the 19S proteasomal subunit, as a putative TRAP1-interacting protein. Surprisingly, TRAP1 and TBP7 colocalize in the endoplasmic reticulum (ER), as demonstrated by biochemical and confocal/electron microscopic analyses, and interact directly, as confirmed by fluorescence resonance energy transfer analysis. This is the first demonstration of TRAP1's presence in this cellular compartment. TRAP1 silencing by short-hairpin RNAs, in cells exposed to thapsigargin-induced ER stress, correlates with upregulation of BiP/Grp78, thus suggesting a role of TRAP1 in the refolding of damaged proteins and in ER stress protection. Consistently, TRAP1 and/or TBP7 interference enhanced stress-induced cell death and increased intracellular protein ubiquitination. These experiments led us to hypothesize an involvement of TRAP1 in protein quality control for mistargeted/misfolded mitochondria-destined proteins, through interaction with the regulatory proteasome protein TBP7. Remarkably, expression of specific MITO proteins decreased upon TRAP1 interference as a consequence of increased ubiquitination. The proposed TRAP1 network has an impact in vivo, as it is conserved in human colorectal cancers, is controlled by ER-localized TRAP1 interacting with TBP7 and provides a novel model of the ER-mitochondria crosstalk.

TRAP-1, the mitochondrial Hsp90

Protein folding quality control does not occur randomly in cells, but requires the action of specialized molecular chaperones compartmentalized in subcellular microenvironments and organelles. Fresh experimental evidence has now linked a mitochondrial-specific Heat Shock Protein-90 (Hsp90) homolog, Tumor Necrosis Factor Receptor-Associated Protein-1 (TRAP-1) to pleiotropic signaling circuitries of organelle integrity and cellular homeostasis. TRAP-1-directed compartmentalized protein folding is broadly exploited in cancer and neurodegenerative diseases, presenting new opportunities for therapeutic intervention in humans. This article is part of a Special Issue entitled: Heat Shock Protein 90 (Hsp90).

Transcriptional modulation of a human monocytic cell line exposed to PM(10) from an urban area

Insight into the mechanisms by which ambient air particulate matter mediates adverse health effects is needed to provide biological plausibility to epidemiological studies demonstrating an association between PM(10) exposure and increased morbidity and mortality. In vitro studies of the effects of air pollution on human cells help to establish conditions for the analysis of cause-effect relationships. One of the major challenges is to test native atmosphere in its complexity, rather than the various components individually. We have developed an in vitro system in which human monocyte-macrophage U937 cells are directly exposed to filters containing different amounts of PM(10) collected in the city of Rome. Transcriptional profiling obtained after short exposure (1h) of cells to a filter containing 1666μg PM(10) (77.6μg/cm(2)) using a macroarray panel of 1176 genes reveals a significant change in the mRNA level (>2 fold) for 87 genes relative to cells exposed to a control filter. Overall, 9 out of 87 modulated genes were annotated as "lung cancer". qRT-PCR confirmed the induction of relevant genes involved in DNA repair and apoptosis, specifically: ERCC1, TDG, DAD1 and MCL1. In cells exposed for 10min, 1h and 3h to different amounts of PM(10), transcription of TNFα and TRAP1, which code for a key pro-inflammatory cytokine and a mitochondrial protein involved in cell protection from oxidative stress, respectively, was shown to be modulated in a time-dependent, but not a dose-dependent manner. Taken together, these data indicate that it is possible to analyze the effects of untreated particulate matter on human cells by the direct-exposure approach we have developed, possibly providing new clues to traffic-related health hazard.

Global gene expression and Ingenuity biological functions analysis on PCBs 153 and 138 induced human PBMC in vitro reveals differential mode(s) of action in developing toxicities

Several reports have indicated that low level of polychlorinated biphenyl (PCB) exposure can adversely affect a multitude of physiological disorders and diseases in in vitro, in vivo, and as reported in epidemiological studies. This investigation is focused on the possible contribution of two most prevalent PCB congeners in vitro in developing toxicities. We used PCBs 138 and 153 at the human equivalence level as model agents to test their specificity in developing toxicities. We chose a global approach using oligonucleotide microarray technology to investigate modulated gene expression for biological effects, upon exposure of PCBs, followed by Ingenuity Pathway Analysis (IPA), to understand the underlying consequence in developing disease and disorders. We performed in vitro studies with human peripheral blood mononuclear cells (PBMC), where PBMC cells were exposed to respective PCBs for 48 h. Overall, our observation on gene expression indicated that PCB produces a unique signature affecting different pathways, specific for each congener. While analyzing these data through IPA, the prominent and interesting disease and disorders were neurological disease, cancer, cardiovascular disease, respiratory disease, as well as endocrine system disorders, genetic disorders, and reproductive system disease. They showed strong resemblances with in vitro, in vivo, and in the epidemiological studies. A distinct difference was observed in renal and urological diseases, organisimal injury and abnormalities, dental disease, ophthalmic disease, and psychological disorders, which are only revealed by PCB 138 exposure, but not in PCB 153. The present study emphasizes the challenges of global gene expression in vitro and was correlated with the results of exposed human population. The microarray results give a molecular mechanistic insight and functional effects, following PCB exposure. The extent of changes in genes related to several possible mode(s) of action highlights the changes in cellular functions and signaling pathways that play major roles. In addition to understanding the pathways related to mode of action for chemicals, these data could lead to the identification of genomic signatures that could be used for screening of chemicals for their potential to cause disease and developmental disorders.

Acquired loss of renal nuclease activity is restricted to DNaseI and is an organ-selective feature in murine lupus nephritis

An acquired loss of renal DNaseI promotes transformation of mild mesangial lupus nephritis into membranoproliferative end-stage organ disease. In this study, we analyzed expression profiles of DNaseI in other organs of lupus-prone (NZB×NZW)F1 mice during disease progression to determine whether silencing of the renal DNaseI gene is an organ-specific feature or whether loss of DNaseI reflects a systemic error in mice with sever lupus nephritis. The present results demonstrate normal or elevated levels of DNaseI mRNA and enzyme activity in liver, spleen, and serum samples from (NZB×NZW)F1 mice throughout all the stages of lupus nephritis. DNaseI activity was dramatically reduced only in kidneys of mice with sever nephritis and was the only nuclease that was down-regulated, whereas six other nucleases (DNaseII1 to 3, caspase-activated DNase, Dnase2a, and endonuclease G) were approximately normally expressed in kidneys, liver, and spleen. Loss of renal DNaseI was not accompanied by changes in serum DNaseI activity, suggesting independent mechanisms of DNaseI regulation in circulation and in kidneys and an absence of compensatory up-regulation of serum DNaseI activity in the case of renal DNaseI deficiency. Thus, silencing of renal DNaseI is a unique renal feature in membranoproliferative lupus nephritis. Determining the mechanism(s) responsible for DNaseI down-regulation might lead to the generation of new therapeutic targets to treat and prevent progressive lupus nephritis.

In situ kinetic trapping reveals a fingerprint of reversible protein thiol oxidation in the mitochondrial matrix

Reactive oxygen species (ROS) are released at the mitochondrial inner membrane by the electron transport chain (ETC). Increasing evidence suggests that mitochondrial H2O2 acts as a signaling molecule and participates in the (feedback) regulation of mitochondrial activity and turnover. It seems likely that key mitochondrial components contain redox-sensitive thiols that help to adapt protein function to changes in electron flow. However, the identity of most redox-regulated mitochondrial proteins remains to be defined. Thioredoxin 2 (Trx2) is the major protein-thiol-reducing oxidoreductase in the mitochondrial matrix. We used in situ mechanism-based kinetic trapping to identify disulfide-exchange interactions of Trx2 within functional mitochondria of intact cells. Mass spectrometry successfully identified known and suspected Trx2 target proteins and, in addition, revealed a set of new candidate target proteins. Our results suggest that the mitochondrial protein biosynthesis machinery is a major target of ETC-derived ROS. In particular, we identified mitochondrial methionyl-tRNA synthetase (mtMetRS) as one of the most prominent Trx2 target proteins. We show that an increase in ETC-derived oxidants leads to an increase in mtMetRS oxidation in intact cells. In conclusion, we find that in situ kinetic trapping provides starting points for future functional studies of intramitochondrial redox regulation.

Proteomic identification of the differentially expressed proteins in human lung epithelial cells by airborne particulate matter

Exposure to airborne PM₁₀, particulate matter with a median aerodynamic diameter of less than 10 µm, is known to be associated with a number of adverse health effects. To gain a better understanding of the cytotoxic mechanism and to develop protein biomarker candidates for PM₁₀-induced toxicity, proteomic analyses were performed in human lung epithelial cells. Two-dimensional gel electrophoresis (2-DE) was followed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) to analyze the proteins differentially expressed by exposure to PM₁₀. Analysis of 2-DE gels revealed more than 1270 protein spots in the cells, of which 36 showed changes of more than 2-fold on exposure to PM₁₀ (up-regulation, n = 6; down-regulation, n = 30). The glycolytic enzyme pyruvate kinase, which also plays a role in tumor metabolism, showed a marked increase in expression, whereas the cytoskeleton-related vinculin and anti-inflammatory annexin 1 showed marked decreases in expression.

Targeted inhibition of mitochondrial Hsp90 suppresses localised and metastatic prostate cancer growth in a genetic mouse model of disease

Background:

The molecular chaperone heat shock protein-90 (Hsp90) is a promising cancer drug target, but current Hsp90-based therapy has so far shown limited activity in the clinic.

Methods:

We tested the efficacy of a novel mitochondrial-targeted, small-molecule Hsp90 inhibitor, Gamitrinib (GA mitochondrial matrix inhibitor), in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model. The TRAMP mice receiving 3-week or 5-week systemic treatment with Gamitrinib were evaluated for localised or metastatic prostate cancer, prostatic intraepithelial neoplasia (PIN) or localised inflammation using magnetic resonance imaging, histology and immunohistochemistry. Treatment safety was assessed histologically in organs collected at the end of treatment. The effect of Gamitrinib on mitochondrial dysfunction was studied in RM1 cells isolated from TRAMP tumours.

Results:

Systemic administration of Gamitrinib to TRAMP mice inhibited the formation of localised prostate tumours of neuroendocrine or adenocarcinoma origin, as well as metastatic prostate cancer to abdominal lymph nodes and liver. The Gamitrinib treatment had no effect on PIN or prostatic inflammation, and caused no significant animal weight loss or organ toxicity. Mechanistically, Gamitrinib triggered acute mitochondrial dysfunction in RM1 cells, with loss of organelle inner membrane potential and release of cytochrome-c in the cytosol.

Conclusions:

The Gamitrinib has pre-clinical activity and favourable tolerability in a genetic model of localised and metastatic prostate cancer in immunocompetent mice. Selective targeting of mitochondrial Hsp90 could provide novel molecular therapy for patients with advanced prostate cancer.

Preclinical characterization of mitochondria-targeted small molecule hsp90 inhibitors, gamitrinibs, in advanced prostate cancer

PURPOSE

This study aimed to characterize the preclinical activity of the first class of combinatorial, mitochondria-targeted, small molecule heat shock protein-90 (Hsp90) inhibitors, gamitrinibs, in models of hormone-refractory, drug-resistant, localized, and bone metastatic prostate cancer in vivo.

EXPERIMENTAL DESIGN

Mitochondrial permeability transition, apoptosis, and changes in metabolic activity were examined by time-lapse videomicroscopy, multiparametric flow cytometry, MTT, and analysis of isolated mitochondria. Drug-resistant prostate cancer cells were generated by chronic exposure of hormone-refractory PC3 cells to the Hsp90 inhibitor 17-allylaminogeldanamycin (17-AAG). The effect of gamitrinibs on s.c. or intratibial prostate cancer growth was studied in xenograft models. Bone metastatic tumor growth and bone parameters were quantified by micro-computed tomography imaging.

RESULTS

In the NCI 60-cell line screening, gamitrinibs were active against all tumor cell types tested, and efficiently killed metastatic, hormone-refractory, and multidrug-resistant prostate cancer cells characterized by overexpression of the ATP binding cassette transporter P-glycoprotein. Mechanistically, gamitrinibs, but not 17-AAG, induced acute mitochondrial dysfunction in prostate cancer cells with loss of organelle membrane potential, release of cytochrome c, and caspase activity, independently of proapoptotic Bcl-2 proteins Bax and Bak. Systemic administration of gamitrinibs to mice was well tolerated, and inhibited s.c. or bone metastatic prostate cancer growth in vivo.

CONCLUSIONS

Gamitrinibs have preclinical activity and favorable safety in models of drug-resistant and bone metastatic prostate cancer in vivo.

Gaining insights into the Bcr-Abl activity-independent mechanisms of resistance to imatinib mesylate in KCL22 cells: a comparative proteomic approach

Imatinib mesylate is a potent inhibitor of Bcr-Abl tyrosine kinase, an oncoprotein that plays a key role in the development of chronic myeloid leukemia. Consequently, imatinib is used as front-line therapy for this disease. A major concern in imatinib treatment is the emergence of resistance to the drug. Here we used the imatinib-resistant KCL22R and imatinib-sensitive KCL22S cells in which none of the known resistance mechanisms has been detected and hence novel Bcr-Abl activity-independent mechanisms could be envisaged. We characterized proteins that were differentially expressed between the KCL22R and KCL22S cells. Using two-dimensional differential gel electrophoresis coupled with mass spectrometry and Western blot analysis we identified 51 differentially expressed proteins: 27 were over-expressed and 24 were under-expressed in KCL22R versus KCL22S cells. Several of these proteins are likely to be involved in such survival mechanisms as modulation of redox balance and activation of anti-apoptotic pathways mediated by NF-kappaB and Ras-MAPK signaling. The data reported may be useful for further studies on mechanisms of imatinib resistance and for the screening of biomarkers to develop new combinatorial therapeutic approaches.

Effects of lovastatin on breast cancer cells: a proteo-metabonomic study

INTRODUCTION

Statins are cholesterol-lowering drugs with pleiotropic activities including inhibition of isoprenylation and reduction of signals driving cell proliferation and survival responses.

METHODS

In this study we evaluated the effects of lovastatin acid and lactone on breast cancer MDAMB231 and MDAMB468 cells using a combination of proteomic and metabonomic profiling techniques.

RESULTS

Lovastatin inhibited proliferation of breast cancer cell lines. MDAMB231 cells were more sensitive to its effects, and in most cases lovastatin acid showed more potency towards the manipulation of protein expression than lovastatin lactone. Increased expression of Rho inhibitor GDI-2 stabilized the non-active Ras homolog gene family member A (RhoA) leading to a decreased expression of its active, membrane-bound form. Its downstream targets cofilin, CDC42 and G3BP1 are members of the GTPase family affected by lovastatin. Our data indicated that lovastatin modulated the E2F1-pathway through the regulation of expression of prohibitin and retinoblastoma (Rb). This subsequently leads to changes of E2F-downstream targets minichromosome maintenance protein 7 (MCM7) and MutS homolog 2 (MSH2). Lovastatin also regulated the AKT-signaling pathway. Increased phosphatase and tensin homolog (PTEN) and decreased DJ-1 expression lead to a down-regulation of the active pAkt. Lovastatin's involvement in the AKT-signaling pathway was confirmed by an upregulation of its downstream target, tumor progressor NDRG1. Metabolic consequences to lovastatin exposure included suppression of glycolytic and Krebs cycle activity, and lipid biosynthesis.

CONCLUSIONS

The combination of proteomics and metabonomics enabled us to identify several key targets essential to the antitumor activity of lovastatin. Our results imply that lovastatin has the potential to reduce the growth of breast cancer cells.

Anti-dsDNA antibodies promote initiation, and acquired loss of renal Dnase1 promotes progression of lupus nephritis in autoimmune (NZBxNZW)F1 mice

Background

Lupus nephritis is characterized by deposition of chromatin fragment-IgG complexes in the mesangial matrix and glomerular basement membranes (GBM). The latter defines end-stage disease.

Methodology/Principals

In the present study we determined the impact of antibodies to dsDNA, renal Dnase1 and matrix metalloprotease (MMP) mRNA levels and enzyme activities on early and late events in murine lupus nephritis. The major focus was to analyse if these factors were interrelated, and if changes in their expression explain basic processes accounting for lupus nephritis.

Findings

Early phases of nephritis were associated with chromatin-IgG complex deposition in the mesangial matrix. A striking observation was that this event correlated with appearance of anti-dsDNA antibodies and mild or clinically silent nephritis. These events preceded down-regulation of renal Dnase1. Later, renal Dnase1 mRNA level and enzyme activity were reduced, while MMP2 mRNA level and enzyme activity increased. Reduced levels of renal Dnase1 were associated in time with deficient fragmentation of chromatin from dead cells. Large fragments were retained and accumulated in GBM. Also, since chromatin fragments are prone to stimulate Toll-like receptors in e.g. dendritic cells, this may in fact explain increased expression of MMPs.

Significance

These scenarios may explain the basis for deposition of chromatin-IgG complexes in glomeruli in early and late stages of nephritis, loss of glomerular integrity and finally renal failure.

Cytoprotective mitochondrial chaperone TRAP-1 as a novel molecular target in localized and metastatic prostate cancer

Molecular chaperones of the heat shock protein-90 (Hsp90) family promote cell survival, but the molecular requirements of this pathway in tumor progression are not understood. Here, we show that a mitochondria-localized Hsp90 chaperone, tumor necrosis factor receptor-associated protein-1 (TRAP-1), is abundantly and ubiquitously expressed in human high-grade prostatic intraepithelial neoplasia, Gleason grades 3 through 5 prostatic adenocarcinomas, and metastatic prostate cancer, but largely undetectable in normal prostate or benign prostatic hyperplasia in vivo. Prostate lesions formed in genetic models of the disease, including the transgenic adenocarcinoma of the mouse prostate and mice carrying prostate-specific deletion of the phosphatase tensin homolog tumor suppressor (Pten(pc-/-)), also exhibit high levels of TRAP-1. Expression of TRAP-1 in nontransformed prostatic epithelial BPH-1 cells inhibited cell death, whereas silencing of TRAP-1 in androgen-independent PC3 or DU145 prostate cancer cells by small interfering RNA enhanced apoptosis. Targeting TRAP-1 with a novel class of mitochondria-directed Hsp90 inhibitors, ie, Gamitrinibs, caused rapid and complete killing of androgen-dependent or -independent prostate cancer, but not BPH-1 cells, whereas reintroduction of TRAP-1 in BPH-1 cells conferred sensitivity to Gamitrinib-induced cell death. These data identify TRAP-1 as a novel mitochondrial survival factor differentially expressed in localized and metastatic prostate cancer compared with normal prostate. Targeting this pathway with Gamitrinibs could be explored as novel molecular therapy in patients with advanced prostate cancer.

Heat shock proteins, cell survival and drug resistance: the mitochondrial chaperone TRAP1, a potential novel target for ovarian cancer therapy

BACKGROUND

Protein homeostasis is a highly complex network of molecular interactions governing the health and life span of the organism. Molecular chaperones, mainly heat shock proteins (HSP) and other stress-inducible proteins abundantly expressed in multiple compartments of the cell, are major modulators of protein homeostasis. TRAP1 is a mitochondrial HSP involved in protection against oxidant-induced DNA damage and apoptosis. It was recently described as a component of a mitochondrial pathway selectively up-regulated in tumor cells which antagonizes the proapoptotic activity of cyclophilin D, a mitochondrial permeability transition pore regulator, and is responsible for the maintenance of mitochondrial integrity, thus favoring cell survival. Interestingly, novel TRAP1 antagonists cause sudden collapse of mitochondrial function and selective tumor cell death, suggesting that this pathway may represent a novel molecular target to improve anticancer therapy. Preliminary data suggest that TRAP1 may be a valuable biomarker in ovarian cancers: in fact, TRAP1 levels are significantly higher in cisplatin-resistant ovarian tumors and ovarian carcinoma cell lines.

CONCLUSIONS

While major advances have been made in understanding the genetics and molecular biology of cancer, given the considerable heterogeneity of ovarian cancer, the introduction of novel targeted therapies and the consequent selection of treatments based on the molecular profile of each tumor may have a major impact on the management of this malignancy and might contribute to building a new era of personalized medicine.

Adaptation to oxidative stress, chemoresistance, and cell survival

The discovery of some additional properties and functions of reactive oxygen species (ROS), beyond their toxic effects, provides a novel scenario for the molecular basis and cell regulation of several pathophysiologic processes. ROS are generated by redox-sensitive, prosurvival signaling pathways and function as second messengers in the transduction of several extracellular signals. A complex intracellular redox buffering network has developed to adapt and protect cells against the dangerous effects of oxidative stress. However, pathways involved in ROS-adaptive response may also play a critical role in protecting cells against cytotoxic effects of anticancer agents, thus supporting the hypothesis of a correlation between adaptation/resistance to oxidative stress and resistance to anticancer drugs. This review summarizes the main systems involved in the adaptive responses: an overview on the pathophysiologic relevance of mitochondria on redox-sensitive transcription factors and genes and main antioxidant networks in tumor cells is provided. One of the major aims is to highlight the adaptive mechanisms and their interplay in the intricate connection between oncogenic signaling, oxidative stress, and chemoresistance. Clarification of these mechanisms has tremendous application potential, in terms of developing novel molecular-targeted anticancer therapies and innovative strategies for rational combination of these agents with chemotherapeutic or tumor-specific biologic drugs.

Compartmentalized cancer drug discovery targeting mitochondrial Hsp90 chaperones

There is a plethora of attractive drug targets in cancer, but their therapeutic exploitation proved more difficult than expected, and only rarely truly successful. One possibility not often considered in drug discovery is that cancer signaling pathways are not randomly arranged in cells, but orchestrated in specialized subcellular compartments. The identification of heat shock protein-90 (Hsp90) chaperones in mitochondria of tumors, but not most normal tissues, provides an example of a compartmentalized network of cell survival, opening fresh prospects for novel, subcellularly targeted cancer drug discovery.

TRAP1, a novel mitochondrial chaperone responsible for multi-drug resistance and protection from apoptotis in human colorectal carcinoma cells

TRAP1 is a component of a pro-survival mitochondrial pathway up-regulated in tumor cells. The evaluation of TRAP1 expression in 26 human colorectal carcinomas showed up-regulation in 17/26 tumors. Accordingly, TRAP1 levels were increased in HT-29 colorectal carcinoma cells resistant to 5-fluorouracil, oxaliplatin and irinotecan. Thus, we investigated the role of TRAP1 in multi-drug resistance in human colorectal cancer. Interestingly, TRAP1 overexpression leads to 5-fluorouracil-, oxaliplatin- and irinotecan-resistant phenotypes in different neoplastic cells. Conversely, the inhibition of TRAP1 activity by TRAP1 ATPase antagonist, shepherdin, increased the sensitivity to oxaliplatin and irinotecan in colorectal carcinoma cells resistant to the single agents. These results suggest that the increased expression of TRAP1 could be part of a pro-survival pathway responsible for multi-drug resistance.

Mitochondrial dysregulation of osteoarthritic human articular chondrocytes analyzed by proteomics: a decrease in mitochondrial superoxide dismutase points to a redox imbalance

Mitochondria are involved in many cellular processes; mitochondrial dysfunctions have been associated with apoptosis, aging, and a number of pathological conditions, including osteoarthritis (OA). Mitochondrial proteins are attractive targets for the study of metabolism of the chondrocyte, the unique cell type present in mature cartilage, and its role in tissue degradation. Using a proteomics approach based on two-dimensional DIGE and MALDI-TOF/TOF mass spectrometric identification of mitochondria- enriched protein fractions from human articular chondrocytes, we analyzed mitochondrial protein changes that are characteristic of OA chondrocytes. A total of 73 protein forms were unambiguously identified as significantly altered in OA; 23 of them have been previously described as mitochondrial. An extensive statistical and cluster analysis of the data revealed a mitochondrial protein profile characteristic for OA. This pattern includes alterations in energy production, maintenance of mitochondrial membrane integrity, and free radical detoxification. Real time PCR, Western blot, and immunohistofluorescence assays confirmed a significant decrease of the major mitochondrial antioxidant protein manganese-superoxide dismutase (SOD2) in the superficial layer of OA cartilage. As possible outputs for this antioxidant deficiency, we found an increase of intracellular reactive oxygen species generation in OA chondrocytes and also verified an OA-dependent increase in the mitochondrial tumor necrosis factor-alpha receptor-associated protein 1 (TRAP1), a chaperone with a reported reactive oxygen species antagonist role. Our results describe the differences between the mitochondrial protein profiles of normal and OA chondrocytes, demonstrating that mitochondrial dysregulation occurs in cartilage cells during OA and highlighting redox imbalance as a key factor in OA pathogenesis.