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

Overexpression of the mitochondrial chaperone tumor necrosis factor receptor-associated protein 1 is associated with the poor prognosis of patients with colorectal cancer

Tumor necrosis factor receptor-associated protein-1 (TRAP-1), a mitochondrial chaperone, contributes significantly to the progression of cancer. However, the understanding of its involvement in the clinicopathological characteristics and prognosis of colorectal cancer (CRC) remains limited. The aim of the present study was to assess the significance of TRAP-1 expression in CRC. The expression of TRAP-1 was evaluated in corresponding cancerous, paracancerous, lymph node and distant metastatic tissues of 256 cases of CRC by immunohistochemistry. The associations between TRAP-1 expression and the clinicopathological parameters and survival rates of patients was assessed. Out of 256 patients with CRC, TRAP-1 expression was detected in 203 (79.3%). TRAP-1 expression was significantly increased in cancerous tissue compared with that in corresponding paracancerous tissues (P<0.001). Overexpression of TRAP-1 was significantly associated with differentiation (P=0.011), depth of invasion (P=0.006), lymph node metastasis (P<0.001) and tumor-node-metastasis stage (P<0.001). In patients with high TRAP-1 expression, the 5-year overall survival (OS) rate was 38.0%, in contrast to 56.5% in patients with low TRAP-1 expression (P=0.003). Similarly, the 5-year progression-free survival (PFS) was 26.6% for patients with high TRAP-1 expression and 53.3% for patients with low TRAP-1 expression (P<0.001). Multivariate analyses indicated the TRAP-1 expression is an independent prognostic factor for poorer OS [P=0.015; hazard ratio (HR), 1.914] and PFS (P<0.001; HR, 2.534). Thus, TRAP-1 may serve as a potential biomarker for predicting the prognosis of patients with CRC. Specifically, overexpression of TRAP-1 may predict progression and poor survival in cases of CRC.

Redox Aspects of Chaperones in Cardiac Function

Molecular chaperones are stress proteins that allow the correct folding or unfolding as well as the assembly or disassembly of macromolecular cellular components. Changes in expression and post-translational modifications of chaperones have been linked to a number of age- and stress-related diseases including cancer, neurodegeneration, and cardiovascular diseases. Redox sensible post-translational modifications, such as S-nitrosylation, glutathionylation and phosphorylation of chaperone proteins have been reported. Redox-dependent regulation of chaperones is likely to be a phenomenon involved in metabolic processes and may represent an adaptive response to several stress conditions, especially within mitochondria, where it impacts cellular bioenergetics. These post-translational modifications might underlie the mechanisms leading to cardioprotection by conditioning maneuvers as well as to ischemia/reperfusion injury. In this review, we discuss this topic and focus on two important aspects of redox-regulated chaperones, namely redox regulation of mitochondrial chaperone function and cardiac protection against ischemia/reperfusion injury.

TRiC controls transcription resumption after UV damage by regulating Cockayne syndrome protein A

Transcription-blocking DNA lesions are removed by transcription-coupled nucleotide excision repair (TC-NER) to preserve cell viability. TC-NER is triggered by the stalling of RNA polymerase II at DNA lesions, leading to the recruitment of TC-NER-specific factors such as the CSA–DDB1–CUL4A–RBX1 cullin–RING ubiquitin ligase complex (CRL^CSA). Despite its vital role in TC-NER, little is known about the regulation of the CRL^CSA complex during TC-NER. Using conventional and cross-linking immunoprecipitations coupled to mass spectrometry, we uncover a stable interaction between CSA and the TRiC chaperonin. TRiC’s binding to CSA ensures its stability and DDB1-dependent assembly into the CRL^CSA complex. Consequently, loss of TRiC leads to mislocalization and depletion of CSA, as well as impaired transcription recovery following UV damage, suggesting defects in TC-NER. Furthermore, Cockayne syndrome (CS)-causing mutations in CSA lead to increased TRiC binding and a failure to compose the CRL^CSA complex. Thus, we uncover CSA as a TRiC substrate and reveal that TRiC regulates CSA-dependent TC-NER and the development of CS.

An integrated network of chaperones and protein degradation machineries called the proteostasis network (PN) is required to maintain protein homeostasis. Here the authors show that one of the components of the PN, the chaperonin TRiC, interacts with the core transcription-coupled nucleotide excision repair protein CSA to ensure its assembly into the CRLCSA complex.

Proteomic analysis of chicken embryo fibroblast cells infected with recombinant H5N1 avian influenza viruses with and without NS1 eIF4GI binding domain

Non-structural 1 (NS1) protein is a key virulence factor that regulates replication of influenza virus. A recombinant H5N1 virus lacking the eIF4GI-binding domain of NS1 (rNS1-SD30) exhibits significantly lower pathogenicity than H5N1 virus with an intact eIF4GI-binding domain (rNS1-wt). To further investigate this phenomenon, we performed comparative proteomics analyses to profile host proteins in chicken embryo fibroblasts (CEFs) infected with rNS1-wt and rNS1-SD30 viruses. In total, 81 differentially expressed (DE) proteins were identified at 12, 24, and 36 h post-infection. These proteins are mainly involved in the cytoskeletal, apoptotic and stress responses, transcription regulation, transport and metabolic processes, mRNA processing and splicing, and cellular signal transduction. Overexpression of DE proteins revealed that ANXA7 suppresses propagation of rNS1-SD30, but not rNS1-wt viruses. Moreover, ALDH7A1, ANXA7, and DCTN2 strongly enhanced IFN-β promoter activity induced by chicken MDA5 (chMDA5), and in the case of ANXA7, also by the rNS1-SD30 viral strain. NS1-wt co-transfection suppressed the ANXA7-mediated increase in IFN-β promoter activity induced by chMDA5. These findings highlight the role of NS1 eIF4GI binding domain in H5N1 pathogenicity, and may contribute to the design of antiviral strategies to reduce the high morbidity and mortality associated with this pathogen.

TRAP1 protein signature predicts outcome in human metastatic colorectal carcinoma

TRAP1 is a HSP90 molecular chaperone upregulated in colorectal carcinomas and involved in control of intracellular signaling, cell cycle, apoptosis and drug resistance, stemness and bioenergetics through co-traslational regulation of a network of client proteins. Thus, the clinical significance of TRAP1 protein network was analyzed in human colorectal cancers. TRAP1 and/or its client proteins were quantified, by immunoblot analysis, in 60 surgical specimens of colorectal carcinomas at different stages and, by immunohistochemistry, in 9 colorectal adenomatous polyps, 11 in situ carcinomas and 55 metastatic colorectal tumors. TRAP1 is upregulated at the transition between low- and high-grade adenomas, in in situ carcinomas and in about 60% of human colorectal carcinomas, being downregulated only in a small cohort of tumors. The analysis of TCGA database showed that a subgroup of colorectal tumors is characterized by gain/loss of TRAP1 copy number, this correlating with its mRNA and protein expression. Interestingly, TRAP1 is co-expressed with the majority of its client proteins and hierarchical cluster analysis showed that the upregulation of TRAP1 and associated 6-protein signature (i.e., IF2α, eF1A, TBP7, MAD2, CDK1 and βCatenin) identifies a cohort of metastatic colorectal carcinomas with a significantly shorter overall survival (HR 5.4; 95% C.I. 1.1-26.6; p=0.037). Consistently, the prognostic relevance of TRAP1 was confirmed in a cohort of 55 metastatic colorectal tumors. Finally, TRAP1 positive expression and its prognostic value are more evident in left colon cancers. These data suggest that TRAP1 protein network may provide a prognostic signature in human metastatic colorectal carcinomas.

TRAP1 controls cell cycle G2-M transition through the regulation of CDK1 and MAD2 expression/ubiquitination

Regulation of tumour cell proliferation by molecular chaperones is still a complex issue. Here, the role of the HSP90 molecular chaperone TRAP1 in cell cycle regulation was investigated in a wide range of human breast, colorectal, and lung carcinoma cell lines, and tumour specimens. TRAP1 modulates the expression and/or the ubiquitination of key cell cycle regulators through a dual mechanism: (i) transcriptional regulation of CDK1, CYCLIN B1, and MAD2, as suggested by gene expression profiling of TRAP1-silenced breast carcinoma cells; and (ii) post-transcriptional quality control of CDK1 and MAD2, being the ubiquitination of these two proteins enhanced upon TRAP1 down-regulation. Mechanistically, TRAP1 quality control on CDK1 is crucial for its regulation of mitotic entry, since TRAP1 interacts with CDK1 and prevents CDK1 ubiquitination in cooperation with the proteasome regulatory particle TBP7, this representing the limiting factor in TRAP1 regulation of the G2-M transition. Indeed, TRAP1 silencing results in enhanced CDK1 ubiquitination, lack of nuclear translocation of CDK1/cyclin B1 complex, and increased MAD2 degradation, whereas CDK1 forced up-regulation partially rescues low cyclin B1 and MAD2 levels and G2-M transit in a TRAP1-poor background. Consistently, the CDK1 inhibitor RO-3306 is less active in a TRAP1-high background. Finally, a significant correlation was observed between TRAP1 and Ki67, CDK1 and/or MAD2 expression in breast, colorectal, and lung human tumour specimens. This study represents the first evidence that TRAP1 is relevant in the control of the complex machinery that governs cell cycle progression and mitotic entry and provides a strong rationale to regard TRAP1 as a biomarker to select tumours with deregulated cell cycle progression and thus likely poorly responsive to novel cell cycle inhibitors. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

TRAP1: a viable therapeutic target for future cancer treatments?

INTRODUCTION

HSP90 molecular chaperones (i.e., HSP90α, HSP90β, GRP94 and TRAP1) are potential therapeutic targets to design novel anticancer agents. However, despite numerous designed HSP90 inhibitors, most of them have failed due to unfavorable toxicity profiles and lack of specificity toward different HSP90 paralogs. Indeed, a major limitation in this field is the high structural homology between different HSP90 chaperones, which significantly limits our capacity to design paralog-specific inhibitors. Area covered: This review examines the relevance of TRAP1 in tumor development and progression, with an emphasis on its oncogenic/oncosuppressive role in specific human malignancies and its multifaceted and context-dependent functions in cancer cells. Herein, we discuss the rationale for considering TRAP1 as a potential molecular target and the strategies used to date, to achieve its compartmentalized inhibition directly in mitochondria. Expert opinion: TRAP1 targeting may represent a promising strategy for cancer therapy, based on the increasing and compelling evidence supporting TRAP1 involvement in human carcinogenesis. However, considering the complexity of TRAP1 biology, future strategies of drug discovery need to improve selectivity and specificity toward TRAP1 respect to other HSP90 paralogs. The characterization of specific human malignancies suitable for TRAP1 targeting is also mandatory.

The Chaperone TRAP1 As a Modulator of the Mitochondrial Adaptations in Cancer Cells

Mitochondria can receive, integrate, and transmit a variety of signals to shape many biochemical activities of the cell. In the process of tumor onset and growth, mitochondria contribute to the capability of cells of escaping death insults, handling changes in ROS levels, rewiring metabolism, and reprograming gene expression. Therefore, mitochondria can tune the bioenergetic and anabolic needs of neoplastic cells in a rapid and flexible way, and these adaptations are required for cell survival and proliferation in the fluctuating environment of a rapidly growing tumor mass. The molecular bases of pro-neoplastic mitochondrial adaptations are complex and only partially understood. Recently, the mitochondrial molecular chaperone TRAP1 (tumor necrosis factor receptor associated protein 1) was identified as a key regulator of mitochondrial bioenergetics in tumor cells, with a profound impact on neoplastic growth. In this review, we analyze these findings and discuss the possibility that targeting TRAP1 constitutes a new antitumor approach.

Stress-Adaptive Response in Ovarian Cancer Drug Resistance: Role of TRAP1 in Oxidative Metabolism-Driven Inflammation

Metabolic reprogramming is one of the most frequent stress-adaptive response of cancer cells to survive environmental changes and meet increasing nutrient requirements during their growth. These modifications involve cellular bioenergetics and cross talk with surrounding microenvironment, in a dynamic network that connect different molecular processes, such as energy production, inflammatory response, and drug resistance. Even though the Warburg effect has long been considered the main metabolic feature of cancer cells, recent reports identify mitochondrial oxidative metabolism as a driving force for tumor growth in an increasing number of cellular contexts. In recent years, oxidative phosphorylation has been linked to a remodeling of inflammatory response due to autocrine or paracrine secretion of interleukines that, in turn, induces a regulation of gene expression involving, among others, molecules responsible for the onset of drug resistance. This process is especially relevant in ovarian cancer, characterized by low survival, high frequency of disease relapse and chemoresistance. Recently, the molecular chaperone TRAP1 (tumor necrosis factor-associated protein 1) has been identified as a key junction molecule in these processes in ovarian cancer: in fact, TRAP1 mediates a metabolic switch toward oxidative phosphorylation that, in turn, triggers cytokines secretion, with consequent gene expression remodeling, finally leading to cisplatin resistance and epithelial-to-mesenchymal transition in ovarian cancer models. This review summarizes how metabolism, chemoresistance, inflammation, and epithelial-to-mesenchymal transition are strictly interconnected, and how TRAP1 stays at the crossroads of these processes, thus shedding new lights on molecular networks at the basis of ovarian cancer.

TRAP1 regulates stemness through Wnt/β-catenin pathway in human colorectal carcinoma

Colorectal carcinoma (CRC) is a common cause of cancer-related death worldwide. Indeed, treatment failures are triggered by cancer stem cells (CSCs) that give rise to tumor repopulation upon initial remission. Thus, the role of the heat shock protein TRAP1 in stemness was investigated in CRC cell lines and human specimens, based on its involvement in colorectal carcinogenesis, through regulation of apoptosis, protein homeostasis and bioenergetics. Strikingly, co-expression between TRAP1 and stem cell markers was observed in stem cells located at the bottom of intestinal crypts and in CSCs sorted from CRC cell lines. Noteworthy, TRAP1 knockdown reduced the expression of stem cell markers and impaired colony formation, being the CSC phenotype and the anchorage-independent growth conserved in TRAP1-rich cancer cells. Consistently, the gene expression profiling of HCT116 cells showed that TRAP1 silencing results in the loss of the stem-like signature with acquisition of a more-differentiated phenotype and the downregulation of genes encoding for activating ligands and target proteins of Wnt/β-catenin pathway. Mechanistically, TRAP1 maintenance of stemness is mediated by the regulation of Wnt/β-catenin signaling, through the modulation of the expression of frizzled receptor ligands and the control of β-catenin ubiquitination/phosphorylation. Remarkably, TRAP1 is associated with higher expression of β-catenin and several Wnt/β-catenin target genes in human CRCs, thus supporting the relevance of TRAP1 regulation of β-catenin in human pathology. This study is the first demonstration that TRAP1 regulates stemness and Wnt/β-catenin pathway in CRC and provides novel landmarks in cancer biology and therapeutics.

Targeting TRAP1 as a downstream effector of BRAF cytoprotective pathway: a novel strategy for human BRAF-driven colorectal carcinoma

The HSP90 chaperone TRAP1 is translational regulator of BRAF synthesis/ubiquitination, since BRAF down-regulation, ERK signaling inhibition and delay of cell cycle progression occur upon TRAP1 silencing/inhibition. Since TRAP1 is upregulated in human colorectal carcinomas (CRCs) and involved in protection from apoptosis and as human BRAF-driven CRCs are poorly responsive to anticancer therapies, the relationship between TRAP1 regulation of mitochondrial apoptotic pathway and BRAF antiapoptotic signaling has been further evaluated. This study reports that BRAF cytoprotective signaling involves TRAP1-dependent inhibition of the mitochondrial apoptotic pathway. It is worth noting that BRAF and TRAP1 interact and that the activation of BRAF signaling results in enhanced TRAP1 serine-phosphorylation, a condition associated with resistance to apoptosis. Consistently, a BRAF dominant-negative mutant prevents TRAP1 serine phosphorylation and restores drug sensitivity in BRAFV600E CRC drug-resistant cells with high TRAP1 levels. In addition, TRAP1 targeting by the mitochondria-directed HSP90 chaperones inhibitor gamitrinib induces apoptosis and inhibits colony formation in BRAF-driven CRC cells. Thus, TRAP1 is a downstream effector of BRAF cytoprotective pathway in mitochondria and TRAP1 targeting may represent a novel strategy to improve the activity of proapoptotic agents in BRAF-driven CRC cells.

TRAP1 regulates cell cycle and apoptosis in thyroid carcinoma cells

Tumor necrosis factor receptor-associated protein 1 (TRAP1) is a heat shock protein 90 (HSP90) molecular chaperone upregulated in several human malignancies and involved in protection from apoptosis and drug resistance, cell cycle progression, cell metabolism and quality control of specific client proteins. TRAP1 role in thyroid carcinoma (TC), still unaddressed at present, was investigated by analyzing its expression in a cohort of 86 human TCs and evaluating its involvement in cancer cell survival and proliferation in vitro Indeed, TRAP1 levels progressively increased from normal peritumoral thyroid gland, to papillary TCs (PTCs), follicular variants of PTCs (FV-PTCs) and poorly differentiated TCs (PDTCs). By contrast, anaplastic thyroid tumors exhibited a dual pattern, the majority being characterized by high TRAP1 levels, while a small subgroup completely negative. Consistently with a potential involvement of TRAP1 in thyroid carcinogenesis, TRAP1 silencing resulted in increased sensitivity to paclitaxel-induced apoptosis, inhibition of cell cycle progression and attenuation of ERK signaling. Noteworthy, the inhibition of TRAP1 ATPase activity by pharmacological agents resulted in attenuation of cell proliferation, inhibition of ERK signaling and reversion of drug resistance. These data suggest that TRAP1 inhibition may be regarded as potential strategy to target specific features of human TCs, i.e., cell proliferation and resistance to apoptosis.

S-nitrosylation of the Mitochondrial Chaperone TRAP1 Sensitizes Hepatocellular Carcinoma Cells to Inhibitors of Succinate Dehydrogenase

S-nitrosoglutathione reductase (GSNOR) represents the best-documented denitrosylase implicated in regulating the levels of proteins posttranslationally modified by nitric oxide on cysteine residues by S-nitrosylation. GSNOR controls a diverse array of physiologic functions, including cellular growth and differentiation, inflammation, and metabolism. Chromosomal deletion of GSNOR results in pathologic protein S-nitrosylation that is implicated in human hepatocellular carcinoma (HCC). Here we identify a metabolic hallmark of aberrant S-nitrosylation in HCC and exploit it for therapeutic gain. We find that hepatocyte GSNOR deficiency is characterized by mitochondrial alteration and by marked increases in succinate dehydrogenase (SDH) levels and activity. We find that this depends on the selective S-nitrosylation of Cys(501) in the mitochondrial chaperone TRAP1, which mediates its degradation. As a result, GSNOR-deficient cells and tumors are highly sensitive to SDH inhibition, namely to α-tocopheryl succinate, an SDH-targeting molecule that induced RIP1/PARP1-mediated necroptosis and inhibited tumor growth. Our work provides a specific molecular signature of aberrant S-nitrosylation in HCC, a novel molecular target in SDH, and a first-in-class therapy to treat the disease. Cancer Res; 76(14); 4170-82. ©2016 AACR.

Oxidative metabolism drives inflammation-induced platinum resistance in human ovarian cancer

Tumour cells have long been considered defective in mitochondrial respiration and mostly dependent on glycolytic metabolism. However, this assumption is currently challenged by several lines of evidence in a growing number of tumours. Ovarian cancer (OC) is one of the most lethal cancers worldwide, but it continues to be a poorly understood disease and its metabolic features are far to be elucidated. In this context, we investigated the role of tumour necrosis factor receptor-associated protein 1 (TRAP1), which is found upregulated in several cancer types and is a key modulator of tumour cell metabolism. Surprisingly, we found that TRAP1 expression inversely correlated with grade, stage and lower survival in a large cohort of OC patients. Accordingly, TRAP1 silencing induced resistance to cisplatin, resistant cells showed increased oxidative metabolism compared with their sensitive counterpart, and the bioenergetics cellular index of higher grade tumours indicated increased mitochondrial respiration. Strikingly, cisplatin resistance was reversible upon pharmacological inhibition of mitochondrial oxidative phosphorylation by metformin/oligomycin. At molecular level, increased oxidative metabolism in low TRAP1-expressing OC cells and tissues enhanced production of inflammatory mediators such as interleukin (IL)-6 and IL-8. Mechanistically, we identified members of the multidrug resistance complex (MDR) as key mediators of such metabolism-driven, inflammation-induced process. Indeed, treatment of OC cell lines with TNFα and IL6 induced a selective increase in the expression of TAP1 and multidrug resistance protein 1, whereas TAP1 silencing sensitized cells to cisplatin-induced apoptosis. Our results unveil a novel role for TRAP1 and oxidative metabolism in cancer progression and suggest the targeting of mitochondrial bioenergetics to increase cisplatin efficacy in human OC.

The genomic architecture of resistance to Campylobacter jejuni intestinal colonisation in chickens

BACKGROUND

Campylobacter is the leading cause of foodborne diarrhoeal illness in humans and is mostly acquired from consumption or handling of contaminated poultry meat. In the absence of effective licensed vaccines and inhibitors, selection for chickens with increased resistance to Campylobacter could potentially reduce its subsequent entry into the food chain. Campylobacter intestinal colonisation levels are influenced by the host genetics of the chicken. In the present study, two chicken populations were used to investigate the genetic architecture of avian resistance to colonisation: (i) a back-cross of two White Leghorn derived inbred lines [(61 x N) x N] known to differ in resistance to Campylobacter colonisation and (ii) a 9(th) generation advanced intercross (61 x N) line.

RESULTS

The level of colonisation with Campylobacter jejuni following experimental infection was found to be a quantitative trait. A back-cross experiment using 1,243 fully informative single nucleotide polymorphism (SNP) markers revealed quantitative trait loci (QTL) on chromosomes 7, 11 and 14. In the advanced intercross line study, the location of the QTL on chromosome 14 was confirmed and refined and two new QTLs were identified located on chromosomes 4 and 16. Pathway and re-sequencing data analysis of the genes located in the QTL candidate regions identified potential pathways, networks and candidate resistance genes. Finally, gene expression analyses were performed for some of the candidate resistance genes to support the results.

CONCLUSION

Campylobacter resistance in chickens is a complex trait, possibly involving the Major Histocompatibility Complex, innate and adaptive immune responses, cadherins and other factors. Two of the QTLs for Campylobacter resistance are co-located with Salmonella resistance loci, indicating that it may be possible to breed simultaneously for enhanced resistance to both zoonoses.

Mitochondrial Hsp90 is a ligand-activated molecular chaperone coupling ATP binding to dimer closure through a coiled-coil intermediate

Heat-shock protein of 90 kDa (Hsp90) is an essential molecular chaperone that adopts different 3D structures associated with distinct nucleotide states: a wide-open, V-shaped dimer in the apo state and a twisted, N-terminally closed dimer with ATP. Although the N domain is known to mediate ATP binding, how Hsp90 senses the bound nucleotide and facilitates dimer closure remains unclear. Here we present atomic structures of human mitochondrial Hsp90N (TRAP1N) and a composite model of intact TRAP1 revealing a previously unobserved coiled-coil dimer conformation that may precede dimer closure and is conserved in intact TRAP1 in solution. Our structure suggests that TRAP1 normally exists in an autoinhibited state with the ATP lid bound to the nucleotide-binding pocket. ATP binding displaces the ATP lid that signals the cis-bound ATP status to the neighboring subunit in a highly cooperative manner compatible with the coiled-coil intermediate state. We propose that TRAP1 is a ligand-activated molecular chaperone, which couples ATP binding to dramatic changes in local structure required for protein folding.

Cross Talk of Proteostasis and Mitostasis in Cellular Homeodynamics, Ageing, and Disease

Mitochondria are highly dynamic organelles that provide essential metabolic functions and represent the major bioenergetic hub of eukaryotic cell. Therefore, maintenance of mitochondria activity is necessary for the proper cellular function and survival. To this end, several mechanisms that act at different levels and time points have been developed to ensure mitochondria quality control. An interconnected highly integrated system of mitochondrial and cytosolic chaperones and proteases along with the fission/fusion machinery represents the surveillance scaffold of mitostasis. Moreover, nonreversible mitochondrial damage targets the organelle to a specific autophagic removal, namely, mitophagy. Beyond the organelle dynamics, the constant interaction with the ubiquitin-proteasome-system (UPS) has become an emerging aspect of healthy mitochondria. Dysfunction of mitochondria and UPS increases with age and correlates with many age-related diseases including cancer and neurodegeneration. In this review, we discuss the functional cross talk of proteostasis and mitostasis in cellular homeodynamics and the impairment of mitochondrial quality control during ageing, cancer, and neurodegeneration.

Localization of MRP-1 to the outer mitochondrial membrane by the chaperone protein HSP90β

Overexpression of plasma membrane multidrug resistance-associated protein 1 (MRP-1) in Ewing's sarcoma (ES) predicts poor outcome. MRP-1 is also expressed in mitochondria, and we have examined the submitochondrial localization of MRP-1 and investigated the mechanism of MRP-1 transport and role of this organelle in the response to doxorubicin. The mitochondrial localization of MRP-1 was examined in ES cell lines by differential centrifugation and membrane solubilization by digitonin. Whether MRP-1 is chaperoned by heat shock proteins (HSPs) was investigated by immunoprecipitation, immunofluorescence microscopy, and HSP knockout using small hairpin RNA and inhibitors (apoptozole, 17-AAG, and NVPAUY). The effect of disrupting mitochondrial MRP-1-dependent efflux activity on the cytotoxic effect of doxorubicin was investigated by counting viable cell number. Mitochondrial MRP-1 is glycosylated and localized to the outer mitochondrial membrane, where it is coexpressed with HSP90. MRP-1 binds to both HSP90 and HSP70, although only inhibition of HSP90β decreases expression of MRP-1 in the mitochondria. Disruption of mitochondrial MRP-1-dependent efflux significantly increases the cytotoxic effect of doxorubicin (combination index, <0.9). For the first time, we have demonstrated that mitochondrial MRP-1 is expressed in the outer mitochondrial membrane and is a client protein of HSP90β, where it may play a role in the doxorubicin-induced resistance of ES.-Roundhill, E., Turnbull, D., Burchill, S. Localization of MRP-1 to the outer mitochondrial membrane by the chaperone protein HSP90β.

The Mitochondrial Permeability Transition Pore: Channel Formation by F-ATP Synthase, Integration in Signal Transduction, and Role in Pathophysiology

The mitochondrial permeability transition (PT) is a permeability increase of the inner mitochondrial membrane mediated by a channel, the permeability transition pore (PTP). After a brief historical introduction, we cover the key regulatory features of the PTP and provide a critical assessment of putative protein components that have been tested by genetic analysis. The discovery that under conditions of oxidative stress the F-ATP synthases of mammals, yeast, and Drosophila can be turned into Ca(2+)-dependent channels, whose electrophysiological properties match those of the corresponding PTPs, opens new perspectives to the field. We discuss structural and functional features of F-ATP synthases that may provide clues to its transition from an energy-conserving into an energy-dissipating device as well as recent advances on signal transduction to the PTP and on its role in cellular pathophysiology.

Inhibition of succinate dehydrogenase by the mitochondrial chaperone TRAP1 has anti-oxidant and anti-apoptotic effects on tumor cells

TRAP1 is a mitochondrial chaperone highly expressed in many tumor types; it inhibits respiratory complex II, down-modulating its succinate dehydrogenase (SDH) enzymatic activity. SDH inhibition in turn leads to a pseudohypoxic state caused by succinate-dependent HIF1α stabilization and promotes neoplastic growth. Here we report that TRAP1 inhibition of SDH also shields cells from oxidative insults and from the ensuing lethal opening of the mitochondrial permeability transition pore. This anti-oxidant activity of TRAP1 protects tumor cells from death in conditions of nutrient paucity that mimic those encountered in the neoplasm during the process of malignant accrual, and it is required for in vitro tumorigenic growth. Our findings demonstrate that SDH inhibition by TRAP1 is oncogenic not only by inducing pseudohypoxia, but also by protecting tumor cells from oxidative stress.

Organelle-specific Hsp90 inhibitors

Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone that is involved in the folding, activation, and stabilization of numerous oncogenic proteins. It has become an attractive therapeutic target, especially for eradicating malignant cancers and overcoming chemotherapy resistance. The Hsp90 family in mammalian cells is composed of four major homologs: Hsp90α, Hsp90β, 94-kDa glucose-regulated protein (Grp94), and TNF receptor-associated protein 1 (Trap1). Hsp90α and Hsp90β are mainly localized in the cytoplasm, while Grp94 and Trap1 reside in the endoplasmic reticulum and the mitochondria, respectively. Additionally, some Hsp90 s are secreted from the cytoplasm, commonly called extracellular Hsp90. Interestingly, each Hsp90 isoform is localized in a particular organelle, possesses a unique biological function, and participates in various physiological and pathological processes. To inhibit the organelle-specific Hsp90 chaperone function, there have been significant efforts to accumulate Hsp90 inhibitors in particular cellular compartments. This review introduces current studies regarding the delivery of Hsp90 inhibitors to subcellular organelles, particularly to the extracellular matrix and the mitochondria, and discusses their biological insights and therapeutic implications.

N-terminal functional domain of Gasdermin A3 regulates mitochondrial homeostasis via mitochondrial targeting

BACKGROUND

The epidermis forms a critical barrier that is maintained by orchestrated programs of proliferation, differentiation, and cell death. Gene mutations that disturb this turnover process may cause skin diseases. Human GASDERMIN A (GSDMA) is frequently silenced in gastric cancer cell lines and its overexpression has been reported to induce apoptosis. GSDMA has also been linked with airway hyperresponsiveness in genetic association studies. The function of GSDMA in the skin was deduced by dominant mutations in mouse gasdermin A3 (Gsdma3), which caused skin inflammation and hair loss. However, the mechanism for the autosomal dominance of Gsdma3 mutations and the mode of Gsdma3's action remain unanswered.

RESULTS

We demonstrated a novel function of Gsdma3 in modulating mitochondrial oxidative stress. We showed that Gsdma3 is regulated by intramolecular fold-back inhibition, which is disrupted by dominant mutations in the C-terminal domain. The unmasked N-terminal domain of Gsdma3 associates with Hsp90 and is delivered to mitochondrial via mitochondrial importer receptor Tom70, where it interacts with the mitochondrial chaperone Trap1 and causes increased production of mitochondrial reactive oxygen species (ROS), dissipation of mitochondrial membrane potential, and mitochondrial permeability transition (MPT). Overexpression of the C-terminal domain of Gsdma3 as well as pharmacological interventions of mitochondrial translocation, ROS production, and MPT pore opening alleviate the cell death induced by Gsdma3 mutants.

CONCLUSIONS

Our results indicate that the genetic mutations in the C-terminal domain of Gsdma3 are gain-of-function mutations which unmask the N-terminal functional domain of Gsdma3. Gsdma3 regulates mitochondrial oxidative stress through mitochondrial targeting. Since mitochondrial ROS has been shown to promote epidermal differentiation, we hypothesize that Gsdma3 regulates context-dependent response of keratinocytes to differentiation and cell death signals by impinging on mitochondria.

TNFα Amplifies DNaseI Expression in Renal Tubular Cells while IL-1β Promotes Nuclear DNaseI Translocation in an Endonuclease-Inactive Form

We have demonstrated that the renal endonuclease DNaseI is up-regulated in mesangial nephritis while down-regulated during progression of the disease. To determine the basis for these reciprocal DNaseI expression profiles we analyse processes accounting for an early increase in renal DNaseI expression. Main hypotheses were that i. the mesangial inflammation and secreted pro-inflammatory cytokines directly increase DNaseI protein expression in tubular cells, ii. the anti-apoptotic protein tumor necrosis factor receptor-associated protein 1 (Trap 1) is down-regulated by increased expression of DNaseI due to transcriptional interference, and iii. pro-inflammatory cytokines promote nuclear translocation of a variant of DNaseI. The latter hypothesis emerges from the fact that anti-DNaseI antibodies stained tubular cell nuclei in murine and human lupus nephritis. The present study was performed on human tubular epithelial cells stimulated with pro-inflammatory cytokines. Expression of the DNaseI and Trap 1 genes was determined by qPCR, confocal microscopy, gel zymography, western blot and by immune electron microscopy. Results from in vitro cell culture experiments were analysed for biological relevance in kidneys from (NZBxNZW)F1 mice and human patients with lupus nephritis. Central data indicate that stimulating the tubular cells with TNFα promoted increased DNaseI and reduced Trap 1 expression, while TNFα and IL-1β stimulation induced nuclear translocation of the DNaseI. TNFα-stimulation resulted in 3 distinct effects; increased DNaseI and IL-1β gene expression, and nuclear translocation of DNaseI. IL-1β-stimulation solely induced nuclear DNaseI translocation. Tubular cells stimulated with TNFα and simultaneously transfected with IL-1β siRNA resulted in increased DNaseI expression but no nuclear translocation. This demonstrates that IL-1β promotes nuclear translocation of a cytoplasmic variant of DNaseI since translocation clearly was not dependent on DNaseI gene activation. Nuclear translocated DNaseI is shown to be enzymatically inactive, which may point at a new, yet unknown function of renal DNaseI.

Hurt, tired and queasy: Specific variants in the ATPase domain of the TRAP1 mitochondrial chaperone are associated with common, chronic "functional" symptomatology including pain, fatigue and gastrointestinal dysmotility

Functional disorders are common conditions with a substantial impact on a patients' wellbeing, and can be diagnostically elusive. There are bidirectional associations between functional disorders and mitochondrial dysfunction. In this study, provided clinical information and the exon sequence of the TRAP1 mitochondrial chaperone were retrospectively reviewed with a focus on the functional categories of chronic pain, fatigue and gastrointestinal dysmotility. Very-highly conserved TRAP1 variants were identified in 73 of 930 unrelated patients. Functional symptomatology is strongly associated with specific variants in the ATPase binding pocket. In particular, the combined presence of all three functional categories is strongly associated with p.Ile253Val (OR 7.5, P = 0.0001) and with two other interacting variants (OR 18, P = 0.0005). Considering a 1-2% combined variant prevalence and high odds ratios, these variants may be an important factor in the etiology of functional symptomatology.

Proteomic identification and characterization of Ctenopharyngodon idella tumor necrosis factor receptor-associated protein 1 (CiTrap1): an anti-apoptosis factor upregulated by grass carp reovirus infection

Human tumor necrosis factor receptor-associated protein 1 (Trap1) is a mitochondrial protein identical to heat shock protein 75 (HSP75) that plays an important role in protecting cells from oxidative stress and apoptosis. In this study, grass carp (Ctenopharyngodon idella) tumor necrosis factor receptor-associated protein 1 (designated as CiTrap1) was identified through two-dimensional electrophoresis (2-DE) analysis and its pattern of expression was investigated in grass carp kidney (CIK) cells infected with grass carp reovirus (GCRV). The full length cDNA of CiTrap1 contained an opening reading frame of 2157 bp that encoded a peptide of 718 amino acids. Phylogenetic analyses indicated that the CiTrap1 shared 87% identity with its homologue from zebrafish (Danio rerio). The transcriptional level of CiTrap1 in CIK cells was upregulated post virus infection as well as poly (I: C) stimulation. Following virus infection, grass carp PTEN-induced putative kinase 1 (PINK1) and Sorcin, whose coding proteins interact with Trap1 in human, were simultaneously upregulated with CiTrap1. Typical characteristics of apoptosis were observed in CIK cells infected with GCRV by DAPI staining, DNA ladder electrophoresis, TUNEL assay and Annexin Ⅴ labeling. RNAi-mediated silencing of CiTrap1 in CIK cells resulted in the increased rate of virus-induced apoptotic cells. The results of this study suggest that CiTrap1 is involved in the host's innate immune response to viral infection possibly through protecting infected cells from apoptosis.

Reprint of "The mitochondrial permeability transition pore and its adaptive responses in tumor cells"

This review covers recent progress on the nature of the mitochondrial permeability transition pore (PTP) – a key effector in the mitochondrial pathways to cell death – and on the adaptive responses of tumor cells that desensitize the PTP to Ca(2+) and reactive oxygen species (ROS), thereby playing an important role in the resistance of tumors to cell death. The discovery that the PTP forms from dimers of F-ATP synthase; and the definition of the Ca(2+)- and ROS-dependent signaling pathways affecting the transition of the F-ATP synthase from an energy-conserving to an energy-dissipating device open new perspectives for therapeutic intervention in cancer cells.

New interaction partners for Nek4.1 and Nek4.2 isoforms: from the DNA damage response to RNA splicing

BACKGROUND

Neks are serine-threonine kinases that are similar to NIMA, a protein found in Aspergillus nidulans which is essential for cell division. In humans there are eleven Neks which are involved in different biological functions besides the cell cycle control. Nek4 is one of the largest members of the Nek family and has been related to the primary cilia formation and in DNA damage response. However, its substrates and interaction partners are still unknown. In an attempt to better understand the role of Nek4, we performed an interactomics study to find new biological processes in which Nek4 is involved. We also described a novel Nek4 isoform which lacks a region of 46 amino acids derived from an insertion of an Alu sequence and showed the interactomics profile of these two Nek4 proteins.

RESULTS AND DISCUSSION

Isoform 1 and isoform 2 of Nek4 were expressed in human cells and after an immunoprecipitation followed by mass spectrometry, 474 interacting proteins were identified for isoform 1 and 149 for isoform 2 of Nek4. About 68% of isoform 2 potential interactors (102 proteins) are common between the two Nek4 isoforms. Our results reinforce Nek4 involvement in the DNA damage response, cilia maintenance and microtubule stabilization, and raise the possibility of new functional contexts, including apoptosis signaling, stress response, translation, protein quality control and, most intriguingly, RNA splicing. We show for the first time an unexpected difference between both Nek4 isoforms in RNA splicing control. Among the interacting partners, we found important proteins such as ANT3, Whirlin, PCNA, 14-3-3ε, SRSF1, SRSF2, SRPK1 and hNRNPs proteins.

CONCLUSIONS

This study provides new insights into Nek4 functions, identifying new interaction partners and further suggests an interesting difference between isoform 1 and isoform 2 of this kinase. Nek4 isoform 1 may have similar roles compared to other Neks and these roles are not all preserved in isoform 2. Besides, in some processes, both isoforms showed opposite effects, indicating a possible fine controlled regulation.

Up-regulation of mitochondrial chaperone TRAP1 in ulcerative colitis associated colorectal cancer

AIM: To characterize tumor necrosis factor receptor-associated protein 1 (TRAP1) expression in the progression of ulcerative colitis (UC)-associated colorectal cancer.

METHODS: Chronic UC is an inflammatory bowel disease that predisposes to colorectal cancer. Immunohistochemical analysis was used to evaluate TRAP1 expression on tissue microarrays containing colonic tissues from 42 UC progressors (patients with cancer or dysplasia) and 38 non-progressors (dysplasia/cancer free patients). Statistical analyses of the TRAP1 immunohistochemistry staining were performed using GraphPad Prism. Differences in the TRAP1 level between non-progressors and progressors were tested for statistical significance using the Mann-Whitney test. Receiver operating characteristic curve method was used to quantify marker performance in distinguishing diseased cases from controls.

RESULTS: TRAP1 was up-regulated in the colon tissues from UC progressors, but not in the colon tissues from UC non-progressors. Moreover, up-regulation of TRAP1 preceded the neoplastic changes: it was present in both the dysplastic and non-dysplastic tissues of UC progressors. When TRAP1 staining in rectal tissue was used as a diagnostic marker, it could distinguish progressors from non-progressors with 59% sensitivity and 80% specificity. Our study further showed that the increase of TRAP1 expression positively correlated with the degree of inflammation in the colorectal cancer tissues, which could be related to the increased oxidation present in the colonic mucosa from UC progressors. We then investigated the cellular proteome changes underlying oxidative stress, and found that oxidative stress could induce up-regulation of TRAP1 along with several other negative modulators of apoptosis.

CONCLUSION: These results suggest that oxidative stress in long standing UC could lead to the increase of cytoprotective protein TRAP1, which in turn could promote cancer progression by preventing or protecting the oxidative damaged epithelial cells from undergoing apoptosis. TRAP1 could be a potential diagnostic marker for UC associated colorectal cancer.

The mitochondrial permeability transition pore and its adaptive responses in tumor cells

This review covers recent progress on the nature of the mitochondrial permeability transition pore (PTP) - a key effector in the mitochondrial pathways to cell death - and on the adaptive responses of tumor cells that desensitize the PTP to Ca(2+) and reactive oxygen species (ROS), thereby playing an important role in the resistance of tumors to cell death. The discovery that the PTP forms from dimers of F-ATP synthase; and the definition of the Ca(2+)- and ROS-dependent signaling pathways affecting the transition of the F-ATP synthase from an energy-conserving to an energy-dissipating device open new perspectives for therapeutic intervention in cancer cells.

Crystallization and preliminary X-ray diffraction analysis of Trap1 complexed with Hsp90 inhibitors

Hsp90 is a molecular chaperone responsible for the assembly and regulation of many cellular client proteins. In particular, Trap1, a mitochondrial Hsp90 homologue, plays a pivotal role in maintaining mitochondrial integrity, protecting against apoptosis in cancer cells. The N (N-terminal)-M (middle) domain of human Trap1 was crystallized in complex with Hsp90 inhibitors (PU-H71 and BIIB-021) by the hanging-drop vapour-diffusion method at pH 6.5 and 293 K using 15% PEG 8K as a precipitant. Diffraction data were collected from crystals of the Trap1-PU-H71 (2.7 Å) and Trap1-BIIB-021 (3.1 Å) complexes to high resolution at a synchrotron-radiation source. Preliminary X-ray diffraction analysis revealed that both crystals belonged to space group P41212 or P43212, with unit-cell parameters a = b = 69.2, c = 252.5 Å, and contained one molecule per asymmetric unit according to Matthews coefficient calculations.

TRAP1 is involved in BRAF regulation and downstream attenuation of ERK phosphorylation and cell-cycle progression: a novel target for BRAF-mutated colorectal tumors

Human BRAF-driven tumors are aggressive malignancies with poor clinical outcome and lack of sensitivity to therapies. TRAP1 is a HSP90 molecular chaperone deregulated in human tumors and responsible for specific features of cancer cells, i.e., protection from apoptosis, drug resistance, metabolic regulation, and protein quality control/ubiquitination. The hypothesis that TRAP1 plays a regulatory function on the BRAF pathway, arising from the observation that BRAF levels are decreased upon TRAP1 interference, was tested in human breast and colorectal carcinoma in vitro and in vivo. This study shows that TRAP1 is involved in the regulation of BRAF synthesis/ubiquitination, without affecting its stability. Indeed, BRAF synthesis is facilitated in a TRAP1-rich background, whereas increased ubiquitination occurs upon disruption of the TRAP1 network that correlates with decreased protein levels. Remarkably, BRAF downstream pathway is modulated by TRAP1 regulatory activity: indeed, TRAP1 silencing induces (i) ERK phosphorylation attenuation, (ii) cell-cycle inhibition with cell accumulation in G0-G1 and G2-M transitions, and (iii) extensive reprogramming of gene expression. Interestingly, a genome-wide profiling of TRAP1-knockdown cells identified cell growth and cell-cycle regulation as the most significant biofunctions controlled by the TRAP1 network. It is worth noting that TRAP1 regulation on BRAF is conserved in human colorectal carcinomas, with the two proteins being frequently coexpressed. Finally, the dual HSP90/TRAP1 inhibitor HSP990 showed activity against the TRAP1 network and high cytostatic potential in BRAF-mutated colorectal carcinoma cells. Therefore, this novel TRAP1 function represents an attractive therapeutic window to target dependency of BRAF-driven tumors on TRAP1 translational/quality control machinery.

Expression of TRAP1 predicts poor survival of malignant glioma patients

TRAP1/Hsp75 (tumor necrosis factor receptor-associated protein 1), a paralogue of the Hsp90 family, has been recently described as a molecular marker and novel therapeutic target in local and metastatic prostate cancer. It has been proved to be associated with tumor invasion and metastasis in various human malignancies. In our study, the protein expression level of TRAP1 in 236 cases of glioma is investigated by immunohistochemistry assay. Statistical analysis was utilized to evaluate the association of TRAP1 with clinicopathological characteristics and prognosis of patients. It was proved that TRAP1 protein expression was increased in glioma compared with that in normal brain tissue. Moreover, TRAP1 immunohistochemical staining was correlated with World Health Organization (WHO) grade and Karnofsky performance score (KPS). Strong positive TRAP1 staining is more frequently detected in glioma of advanced grade or low KPS. It is also demonstrated that TRAP1 could be an independent negative prognostic factor in glioma, for patients with glioma of strong TRAP1 staining tend to have high risk of death. These results proved that TRAP1 is associated with prognosis of glioma, which may also suggest the potential role of TRAP1 in glioma management.

TRAP1 revisited: novel localizations and functions of a 'next-generation' biomarker (review)

In the last decade, the identification and characterization of novel molecular mechanisms and pathways involving the heat shock protein TRAP1/HSP75 in cancers and other diseases enhanced the scientific interest. Recent reports have shown that TRAP1 stays at the crossroad of multiple crucial processes in the onset of neoplastic transformation. In fact, TRAP1: i) contributes to the tumor's switch to aerobic glycolysis through the inhibition of succinate dehydrogenase, the complex II of the mitochondrial respiratory chain; ii) is part of a pro-survival signaling pathway aimed at evading the toxic effects of oxidants and anticancer drugs and protects mitochondria against damaging stimuli via a decrease of ROS generation; iii) controls protein homeostasis through a direct involvement in the regulation of protein synthesis and protein co-translational degradation. Therefore, TRAP1 seems to be a central regulatory protein with balancing functions at the intersection of different metabolic processes during the neoplastic transformation. For this reason, it can be considered at the same time an attractive target for the development of novel anticancer strategies and a promising study model to understand the biology of tumor cells at a systemic level. This review summarizes the most recent advances in TRAP1 biology and proposes a new comprehensive view of its functions.

TRAP1-dependent regulation of p70S6K is involved in the attenuation of protein synthesis and cell migration: relevance in human colorectal tumors

TNF receptor-associated protein 1 (TRAP1) is an HSP90 chaperone involved in stress protection and apoptosis in mitochondrial and extramitochondrial compartments. Remarkably, aberrant deregulation of TRAP1 function has been observed in several cancer types with potential new opportunities for therapeutic intervention in humans. Although previous studies by our group identified novel roles of TRAP1 in quality control of mitochondria-destined proteins through the attenuation of protein synthesis, molecular mechanisms are still largely unknown. To shed further light on the signaling pathways regulated by TRAP1 in the attenuation of protein synthesis, this study demonstrates that the entire pathway of cap-mediated translation is activated in cells following TRAP1 interference: consistently, expression and consequent phosphorylation of p70S6K and RSK1, two translation activating kinases, are increased upon TRAP1 silencing. Furthermore, we show that these regulatory functions affect the response to translational stress and cell migration in wound healing assays, processes involving both kinases. Notably, the regulatory mechanisms controlled by TRAP1 are conserved in colorectal cancer tissues, since an inverse correlation between TRAP1 and p70S6K expression is found in tumor tissues, thereby supporting the relevant role of TRAP1 translational regulation in vivo. Taken as a whole, these new findings candidate TRAP1 network for new anti-cancer strategies aimed at targeting the translational/quality control machinery of tumor cells.

Mitochondrial Hsp90s suppress calcium-mediated stress signals propagating from mitochondria to the ER in cancer cells

BACKGROUND

Resistance to cell death in the presence of stressful stimuli is one of the hallmarks of cancer cells acquired during multistep tumorigenesis, and knowledge of the molecular mechanism of stress adaptation can be exploited to develop cancer-selective therapeutics. Mitochondria and the endoplasmic reticulum (ER) are physically interconnected organelles that can sense and exchange various stress signals. Although there have been many studies on stress propagation from the ER to mitochondria, reverse stress signals originating from mitochondria have not been well reported.

METHODS

After inactivation of the proteins by pharmacologic and genetic methods, the signal pathways were analyzed by fluorescence microscopy, flow cytometry, MTT assay, and western blotting. A mouse xenograft model was used to examine synergistic anticancer activity and the action mechanism of drugs in vivo.

RESULTS

We show in this study that mitochondrial heat shock protein 90 (Hsp90) suppresses mitochondria-initiated calcium-mediated stress signals propagating into the ER in cancer cells. Mitochondrial Hsp90 inhibition triggers the calcium signal by opening the mitochondrial permeability transition pore and, in turn, the ER ryanodine receptor, via calcium-induced calcium release. Subsequent depletion of ER calcium activates unfolded protein responses in the ER lumen, thereby increasing the expression of a pro-apoptotic transcription factor, CEBP homologous protein (CHOP). Combined treatment with the ER stressor thapsigargin and the mitochondrial Hsp90 inhibitor gamitrinib augmented interorganelle stress signaling by elevating CHOP expression, and showed synergistic cytotoxic activity exclusively in cancer cells in vitro and in vivo.

CONCLUSIONS

Collectively, mitochondrial Hsp90s confer cell death resistance to cancer cells by suppressing the mitochondria-initiated calcium-mediated interorganelle stress response.

Mitochondrial oxidative phosphorylation TRAP(1)ped in tumor cells

Many tumors undergo a dramatic metabolic shift known as the Warburg effect in which glucose utilization is favored and oxidative phosphorylation is downregulated, even when oxygen availability is plentiful. However, the mechanistic basis for this switch has remained unclear. Recently several independent groups identified tumor necrosis factor receptor-associated protein 1 (TRAP1), a mitochondrial molecular chaperone of the heat shock protein 90 (Hsp90) family, as a key modulator of mitochondrial respiration. Although all reports agree that this activity of TRAP1 has important implications for neoplastic progression, data from the different groups only partially overlap, suggesting that TRAP1 may have complex and possibly contextual effects on tumorigenesis. In this review we analyze these recent findings and attempt to reconcile these observations.

Tumor Necrosis Factor-Associated Protein 1 (TRAP1) is Released from the Mitochondria Following 6-hydroxydopamine Treatment

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta. Most cases are sporadic and its etiology is incompletely understood. However, increasing evidence suggests that oxidative stress and mitochondrial dysfunction may be involved in the pathogenesis of Parkinson's disease. The aim of this study was to investigate changes in mitochondrial protein profiles during dopaminergic neuronal cell death using two-dimensional gel electrophoresis in conjunction with mass spectrometry. Several protein spots were found to be significantly altered following treatment of MN9D dopaminergic neuronal cells with 6-hydroxydopamine (6-OHDA). Among several identified candidates, TNF receptor-associated protein 1 (TRAP1), a mitochondrial molecular chaperone, was released from the mitochondria into the cytosol in MN9D cells as well as primary cultures of dopaminergic neurons following 6-OHDA treatment. This event was drug-specific in that such apoptotic inducers as staurosporine and etoposide did not cause translocation of TRAP1 into the cytosol. To our knowledge, the present study is the first to demonstrate the drug-induced subcellular translocation of TRAP1 during neurodegeneration. Further studies delineating cellular mechanism associated with this phenomenon and its functional consequence may provide better understanding of dopaminergic neurodegeneration that underlies PD pathogenesis.

TRAP1 regulates proliferation, mitochondrial function, and has prognostic significance in NSCLC

The TNF receptor-associated protein 1 (TRAP1) is a mitochondrial HSP that has been related to drug resistance and protection from apoptosis in colorectal and prostate cancer. Here, the effect of TRAP1 ablation on cell proliferation, survival, apoptosis, and mitochondrial function was determined in non-small cell lung cancer (NSCLC). In addition, the prognostic value of TRAP1 was evaluated in patients with NSCLC. These results demonstrate that TRAP1 knockdown reduces cell growth and clonogenic cell survival. Moreover, TRAP1 downregulation impairs mitochondrial functions such as ATP production and mitochondrial membrane potential as measured by TMRM (tetramethylrhodamine methylester) uptake, but it does not affect mitochondrial density or mitochondrial morphology. The effect of TRAP1 silencing on apoptosis, analyzed by flow cytometry and immunoblot expression (cleaved PARP, caspase-9, and caspase-3) was cell line and context dependent. Finally, the prognostic potential of TRAP1 expression in NSCLC was ascertained via immunohistochemical analysis which revealed that high TRAP1 expression was associated with increased risk of disease recurrence (univariate analysis, P = 0.008; multivariate analysis, HR: 2.554; 95% confidence interval, 1.085-6.012; P = 0.03). In conclusion, these results demonstrate that TRAP1 impacts the viability of NSCLC cells, and that its expression is prognostic in NSCLC.

IMPLICATIONS

TRAP1 controls NSCLC proliferation, apoptosis, and mitochondrial function, and its status has prognostic potential in NSCLC.

Combination of TRAP1 and ERCC1 Expression Predicts Clinical Outcomes in Metastatic Colorectal Cancer Treated with Oxaliplatin/5-Fluorouracil

PURPOSE

The novel heat shock protein tumor necrosis factor receptor-associated protein 1 (TRAP1) is associated with multidrug resistance in colorectal cancer (CRC) cells in vitro. Excision repair cross-complementation group 1 (ERCC1) expression levels in tumor tissues also predict clinical outcomes in metastatic CRC patients receiving combination oxaliplatin and 5-fluorouracil treatment. We investigated whether TRAP1 and ERCC1 protein expression by immunohistochemistry predict clinical outcomes in CRC patients.

MATERIALS AND METHODS

The study population consisted of 56 patients with metastatic CRC who received first-line oxaliplatin/5-fluorouracil therapy. Clinical response and overall survival (OS) by levels of the markers TRAP1 and ERCC1 were evaluated.

RESULTS

The rates of TRAP1 and ERCC1 expression were 21% and 52%, respectively. Patients negative for ERCC1 expression showed a tendency to respond to chemotherapy (p=0.066). Median OS was significantly longer in patients negative for TRAP1 than those positive for TRAP1 (p=0.023). Patients negative for ERCC1 expression also had a better OS than those positive for ERCC1 (p=0.021). The median OS was 30.9 months for patients negative for TRAP1 and ERCC1 compared to 13.2 months for those positive for TRAP1 and/or positive for ERCC1 expression (p=0.006). The combination of TRAP1 and ERCC1 expression was significantly associated with the response to chemotherapy (p=0.046) and independently predicted median OS in multivariate analysis (hazard ratio, 2.98; 95% confidence interval, 1.18 to 7.49).

CONCLUSION

The present study demonstrates that the combination of TRAP1 and ERCC1 expression predicts the survival of metastatic CRC patients who were treated with oxaliplatin/5-fluorouracil.

ER stress protection in cancer cells: the multifaceted role of the heat shock protein TRAP1

TRAP1 is an HSP90 chaperone, upregulated in human cancers and involved in organelles’ homeostasis and tumor cell metabolism. Indeed, TRAP1 is a key regulator of adaptive responses used by highly proliferative tumors to face the metabolic stress induced by increased demand of protein synthesis and hostile environments. Besides well-characterized roles in prevention of mitochondrial permeability transition pore opening and in regulating mitochondrial respiration, TRAP1 is involved in novel regulatory mechanisms: i) the attenuation of global protein synthesis, ii) the co-translational regulation of protein synthesis and ubiquitination of specific client proteins, and iii) the protection from Endoplasmic Reticulum stress. This provides a crucial role to TRAP1 in maintaining cellular homeostasis through protein quality control, by avoiding the accumulation of damaged or misfolded proteins and, likely, facilitating the synthesis of selective cancer-related proteins. Herein, we summarize how these regulatory mechanisms are part of an integrated network, which enables cancer cells to modulate their metabolism and to face, at the same time, oxidative and metabolic stress, oxygen and nutrient deprivation, increased demand of energy production and macromolecule biosynthesis. The possibility to undertake a new strategy to disrupt such networks of integrated control in cancer cells holds great promise for treatment of human malignancies.

Guardian of the furnace: mitochondria, TRAP1, ROS and stem cell maintenance

Mitochondria are key to eukaryotic cell survival and their activity is linked to generation of reactive oxygen species (ROS) which in turn acts as both an intracellular signal and an effective executioner of cells with regards to cellular senescence. The mitochondrial molecular chaperone tumor necrosis factor receptor associated protein 1 (TRAP1) is often termed the cytoprotective chaperone for its role in cancer cell survival and protection from apoptosis. Here, we hypothesize that TRAP1 serves to modulate mitochondrial activity in stem cell maintenance, survival and differentiation.

Translational control in the stress adaptive response of cancer cells: a novel role for the heat shock protein TRAP1

TNF receptor-associated protein 1 (TRAP1), the main mitochondrial member of the heat shock protein (HSP) 90 family, is induced in most tumor types and is involved in the regulation of proteostasis in the mitochondria of tumor cells through the control of folding and stability of selective proteins, such as Cyclophilin D and Sorcin. Notably, we have recently demonstrated that TRAP1 also interacts with the regulatory protein particle TBP7 in the endoplasmic reticulum (ER), where it is involved in a further extra-mitochondrial quality control of nuclear-encoded mitochondrial proteins through the regulation of their ubiquitination/degradation. Here we show that TRAP1 is involved in the translational control of cancer cells through an attenuation of global protein synthesis, as evidenced by an inverse correlation between TRAP1 expression and ubiquitination/degradation of nascent stress-protective client proteins. This study demonstrates for the first time that TRAP1 is associated with ribosomes and with several translation factors in colon carcinoma cells and, remarkably, is found co-upregulated with some components of the translational apparatus (eIF4A, eIF4E, eEF1A and eEF1G) in human colorectal cancers, with potential new opportunities for therapeutic intervention in humans. Moreover, TRAP1 regulates the rate of protein synthesis through the eIF2α pathway either under basal conditions or under stress, favoring the activation of GCN2 and PERK kinases, with consequent phosphorylation of eIF2α and attenuation of cap-dependent translation. This enhances the synthesis of selective stress-responsive proteins, such as the transcription factor ATF4 and its downstream effectors BiP/Grp78, and the cystine antiporter system xCT, thereby providing protection against ER stress, oxidative damage and nutrient deprivation. Accordingly, TRAP1 silencing sensitizes cells to apoptosis induced by novel antitumoral drugs that inhibit cap-dependent translation, such as ribavirin or 4EGI-1, and reduces the ability of cells to migrate through the pores of transwell filters. These new findings target the TRAP1 network in the development of novel anti-cancer strategies.

Resveratrol accelerates erythroid maturation by activation of FoxO3 and ameliorates anemia in beta-thalassemic mice

Resveratrol, a polyphenolic-stilbene, has received increased attention in the last decade due to its wide range of biological activities. Beta(β)-thalassemias are inherited red cell disorders, found worldwide, characterized by ineffective erythropoiesis and red cell oxidative damage with reduced survival. We evaluated the effects of low-dose-resveratrol (5 μM) on in vitro human erythroid differentiation of CD34(+) from normal and β-thalassemic subjects. We found that resveratrol induces accelerated erythroid-maturation, resulting in the reduction of colony-forming units of erythroid cells and increased intermediate and late erythroblasts. In sorted colony-forming units of erythroid cells resveratrol activates Forkhead-box-class-O3, decreases Akt activity and up-regulates anti-oxidant enzymes as catalase. In an in vivo murine model for β-thalassemia, resveratrol (2.4 mg/kg) reduces ineffective erythropoiesis, increases hemoglobin levels, reduces reticulocyte count and ameliorates red cell survival. In both wild-type and β-thalassemic mice, resveratrol up-regulates scavenging enzymes such as catalase and peroxiredoxin-2 through Forkhead-box-class-O3 activation. These data indicate that resveratrol inhibits Akt resulting in FoxO3 activation with upregulation of cytoprotective systems enabling the pathological erythroid precursors to resist the oxidative damage and continue to differentiate. Our data suggest that the dual effect of resveratrol on erythropoiesis through activation of FoxO3 transcriptional factor combined with the amelioration of oxidative stress in circulating red cells may be considered as a potential novel therapeutic strategy in treating β-thalassemia.

Genome-wide analysis of the Populus Hsp90 gene family reveals differential expression patterns, localization, and heat stress responses

Background

Members of the heat shock protein 90 (Hsp90) class of proteins are evolutionarily conserved molecular chaperones. They are involved in protein folding, assembly, stabilization, activation, and degradation in many normal cellular processes and under stress conditions. Unlike many other well-characterized molecular chaperones, Hsp90s play key roles in signal transduction, cell-cycle control, genomic silencing, and protein trafficking. However, no systematic analysis of genome organization, gene structure, and expression compendium has been performed in the Populus model tree genus to date.

Results

We performed a comprehensive analysis of the Populus Hsp90 gene family and identified 10 Populus Hsp90 genes, which were phylogenetically clustered into two major groups. Gene structure and motif composition are relatively conserved in each group. In Populus trichocarpa, we identified three paralogous pairs, among which the PtHsp90-5a/PtHsp90-5b paralogous pair might be created by duplication of a genome segment. Subcellular localization analysis shows that PtHsp90 members are localized in different subcellular compartments. PtHsp90-3 is localized both in the nucleus and in the cytoplasm, PtHsp90-5a and PtHsp90-5b are in chloroplasts, and PtHsp90-7 is in the endoplasmic reticulum (ER). Furthermore, microarray and semi-quantitative real-time RT-PCR analyses show that a number of Populus Hsp90 genes are differentially expressed upon exposure to various stresses.

Conclusions

The gene structure and motif composition of PtHsp90s are highly conserved among group members, suggesting that members of the same group may also have conserved functions. Microarray and RT-PCR analyses show that most PtHsp90s were induced by various stresses, including heat stress. Collectively, these observations lay the foundation for future efforts to unravel the biological roles of PtHsp90 genes.

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

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

Drosophila Trap1 protects against mitochondrial dysfunction in a PINK1/parkin model of Parkinson's disease

Mitochondrial dysfunction caused by protein aggregation has been shown to have an important role in neurological diseases, such as Parkinson's disease (PD). Mitochondria have evolved at least two levels of defence mechanisms that ensure their integrity and the viability of their host cell. First, molecular quality control, through the upregulation of mitochondrial chaperones and proteases, guarantees the clearance of damaged proteins. Second, organellar quality control ensures the clearance of defective mitochondria through their selective autophagy. Studies in Drosophila have highlighted mitochondrial dysfunction linked with the loss of the PTEN-induced putative kinase 1 (PINK1) as a mechanism of PD pathogenesis. The mitochondrial chaperone TNF receptor-associated protein 1 (TRAP1) was recently reported to be a cellular substrate for the PINK1 kinase. Here, we characterise Drosophila Trap1 null mutants and describe the genetic analysis of Trap1 function with Pink1 and parkin. We show that loss of Trap1 results in a decrease in mitochondrial function and increased sensitivity to stress, and that its upregulation in neurons of Pink1 mutant rescues mitochondrial impairment. Additionally, the expression of Trap1 was able to partially rescue mitochondrial impairment in parkin mutant flies; and conversely, expression of parkin rescued mitochondrial impairment in Trap1 mutants. We conclude that Trap1 works downstream of Pink1 and in parallel with parkin in Drosophila, and that enhancing its function may ameliorate mitochondrial dysfunction and rescue neurodegeneration in PD.

TRAP1 controls mitochondrial fusion/fission balance through Drp1 and Mff expression

Mitochondria are dynamic organelles that change in response to extracellular stimuli. These changes are essential for normal mitochondrial/cellular function and are controlled by a tight balance between two antagonistic pathways that promote fusion and fission. Although some molecules have been identified to mediate the mitochondrial fusion and fission process, the underlying mechanisms remain unclear. Tumor necrosis factor receptor-associated protein 1 (TRAP1) is a mitochondrial molecule that regulates a variety of mitochondrial functions. Here, we examined the role of TRAP1 in the regulation of morphology. Stable TRAP1 knockdown cells showed abnormal mitochondrial morphology, and we observed significant decreases in dynamin-related protein 1 (Drp1) and mitochondrial fission factor (Mff), mitochondrial fission proteins. Similar results were obtained by transient knockdown of TRAP1 in two different cell lines, SH-SY5Y neuroblastoma cells and KNS-42 glioma cells. However, TRAP1 knockdown did not affect expression levels of fusion proteins. The reduction in Drp1 and Mff protein levels was rescued following treatment with the proteasome inhibitor MG132. These results suggest that TRAP1 regulates the expression of fission proteins and controls mitochondrial fusion/fission, which affects mitochondrial/cellular function.

Correlation between mitochondrial TRAP-1 expression and lymph node metastasis in colorectal cancer

AIM: To evaluate the effect of mitochondrial tumor necrosis factor receptor-associated protein-1 (TRAP-1) on the lymph node metastasis (LNM) in Chinese colorectal cancer (CRC) patients, and develop potential LNM-associated biomarkers for CRC using quantitative real-time polymerase chain reaction (RT-PCR) analysis.

METHODS: Differences in mitochondrial TRAP-1 gene expression between primary CRC with LNM (LNM CRC) and without LNM (non-LNM CRC) were assessed in 96 Chinese colorectal carcinoma samples using quantitative RT-PCR analysis, Western blotting, and confirmed with immunohistochemical assay. The relationship between clinicopathological parameters and potential diagnostic biomarkers was also examined.

RESULTS: TRAP-1 was significantly upregulated in LNM CRC compared with non-LNM CRC, which was confirmed by RT-PCR, Western blotting and immunohistochemical assay. The expression of TRAP-1 in two different metastatic potential human colorectal cancer cell lines, LoVo and HT29, was analyzed with Western blotting. The expression level of TRAP-1 was dramatically higher in LoVo than in HT29. Overexpression of TRAP-1 was significantly associated with LNM (90.2% in LNM group vs 22% in non-LNM group, P < 0.001), the advanced tumor node metastasis stage (89.1% in LNM group vs 26.9% in non-LNM group, P < 0.001), the increased 5-year recurrence rate (82.7% in LNM group vs 22.6% in non-LNM group, P < 0.001) and the decreased 5-year overall survival rate (48.4% in LNM vs 83.2% in non-LNM group, P < 0.001). Univariate and multivariate analyses indicated that TRAP-1 expression was an independent prognostic factor for recurrence and survival of CRC patients (Hazard ratio of 2.445 in recurrence, P = 0.017; 2.867 in survival, P = 0.028).

CONCLUSION: Mitochondria TRAP-1 affects the lymph node metastasis in CRC, and may be a potential biomarker for LNM and a prognostic factor in CRC. Over-expression of TRAP-1 is a predictive factor for the poor outcome of colorectal cancer patients.