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

Activation of the heat shock transcription factor Hsf1 is essential for the full virulence of the fungal pathogen Candida albicans

Peer reviewedPublisher PD

Compound A, a selective glucocorticoid receptor modulator, enhances heat shock protein Hsp70 gene promoter activation

Compound A possesses glucocorticoid receptor (GR)-dependent anti-inflammatory properties. Just like classical GR ligands, Compound A can repress NF-kappa B-mediated gene expression. However, the monomeric Compound A-activated GR is unable to trigger glucocorticoid response element-regulated gene expression. The heat shock response potently activates heat shock factor 1 (HSF1), upregulates Hsp70, a known GR chaperone, and also modulates various aspects of inflammation. We found that the selective GR modulator Compound A and heat shock trigger similar cellular effects in A549 lung epithelial cells. With regard to their anti-inflammatory mechanism, heat shock and Compound A are both able to reduce TNF-stimulated I kappa B alpha degradation and NF-kappa B p65 nuclear translocation. We established an interaction between Compound A-activated GR and Hsp70, but remarkably, although the presence of the Hsp70 chaperone as such appears pivotal for the Compound A-mediated inflammatory gene repression, subsequent novel Hsp70 protein synthesis is uncoupled from an observed CpdA-induced Hsp70 mRNA upregulation and hence obsolete in mediating CpdA's anti-inflammatory effect. The lack of a Compound A-induced increase in Hsp70 protein levels in A549 cells is not mediated by a rapid proteasomal degradation of Hsp70 or by a Compound A-induced general block on translation. Similar to heat shock, Compound A can upregulate transcription of Hsp70 genes in various cell lines and BALB/c mice. Interestingly, whereas Compound A-dependent Hsp70 promoter activation is GR-dependent but HSF1-independent, heat shock-induced Hsp70 expression alternatively occurs in a GR-independent and HSF1-dependent manner in A549 lung epithelial cells

Unleashing the full potential of Hsp90 inhibitors as cancer therapeutics through simultaneous inactivation of Hsp90, Grp94, and TRAP1

Cancer therapeutics: Extending a drug's reach A new drug that blocks heat shock proteins (HSPs), helper proteins that are co-opted by cancer cells to promote tumor growth, shows promise for cancer treatment. Several drugs have targeted HSPs, since cancer cells are known to hijack these helper proteins to shield themselves from destruction by the body. However, the drugs have had limited success. Hye-Kyung Park and Byoung Heon Kang at Ulsan National Institutes of Science and Technology in South Korea and coworkers noticed that the drugs were not absorbed into mitochondria, a key cellular compartment, and HSPs in this compartment were therefore not being blocked. They identified a new HSP inhibitor that can reach every cellular compartment and inhibit all HSPs. Testing in mice showed that this inhibitor effectively triggered death of tumor cells, and therefore shows promise for anti-cancer therapy. The Hsp90 family proteins Hsp90, Grp94, and TRAP1 are present in the cell cytoplasm, endoplasmic reticulum, and mitochondria, respectively; all play important roles in tumorigenesis by regulating protein homeostasis in response to stress. Thus, simultaneous inhibition of all Hsp90 paralogs is a reasonable strategy for cancer therapy. However, since the existing pan-Hsp90 inhibitor does not accumulate in mitochondria, the potential anticancer activity of pan-Hsp90 inhibition has not yet been fully examined in vivo. Analysis of The Cancer Genome Atlas database revealed that all Hsp90 paralogs were upregulated in prostate cancer. Inactivation of all Hsp90 paralogs induced mitochondrial dysfunction, increased cytosolic calcium, and activated calcineurin. Active calcineurin blocked prosurvival heat shock responses upon Hsp90 inhibition by preventing nuclear translocation of HSF1. The purine scaffold derivative DN401 inhibited all Hsp90 paralogs simultaneously and showed stronger anticancer activity than other Hsp90 inhibitors. Pan-Hsp90 inhibition increased cytotoxicity and suppressed mechanisms that protect cancer cells, suggesting that it is a feasible strategy for the development of potent anticancer drugs. The mitochondria-permeable drug DN401 is a newly identified in vivo pan-Hsp90 inhibitor with potent anticancer activity

Adenine Nucleotide Translocase 1 Expression is Coupled to the HSP27-Mediated TLR4 Signaling in Cardiomyocytes

The cardiac-specific overexpression of the adenine nucleotide translocase 1 (ANT1) has cardioprotective effects in various experimental heart disease models. Here, we analyzed the link between ANT1 expression and heat shock protein 27 (HSP27)-mediated toll-like receptor 4 (TLR4) signaling, which represents a novel communication pathway between mitochondria and the extracellular environment. The interaction between ANT1 and HSP27 was identified by co-immunoprecipitation from neonatal rat cardiomyocytes. ANT1 transgenic (ANT1-TG) cardiomyocytes demonstrated elevated HSP27 expression levels. Increased levels of HSP27 were released from the ANT1-TG cardiomyocytes under both normoxic and hypoxic conditions. Extracellular HSP27 stimulated TLR4 signaling via protein kinase B (AKT). The HSP27-mediated activation of the TLR4 pathway was more pronounced in ANT1-TG cardiomyocytes than in wild-type (WT) cardiomyocytes. HSP27-specific antibodies inhibited TLR4 activation and the expression of HSP27. Inhibition of the HSP27-mediated TLR4 signaling pathway with the TLR4 inhibitor oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (OxPAPC) reduced the mitochondrial membrane potential (∆ψm) and increased caspase 3/7 activity, which are both markers for cell stress. Conversely, treating cardiomyocytes with recombinant HSP27 protein stimulated TLR4 signaling, induced HSP27 and ANT1 expression, and stabilized the mitochondrial membrane potential. The activation of HSP27 signaling was verified in ischemic ANT1-TG heart tissue, where it correlated with ANT1 expression and the tightness of the inner mitochondrial membrane. Our study shows a new mechanism by which ANT1 is part of the cardioprotective HSP27-mediated TLR4 signaling

Neuronal Protection by a Novel C-terminal Hsp90 Modulator

Alzheimer's disease (AD), like most neurodegenerative disorders, is characterized by accumulation of misfolded and aggregated proteins, indicating that the protein quality control machinery is compromised. Enhancing the activity of molecular chaperones such as the `heat shock' proteins (Hsp's) that re-fold or signal degradation of damaged proteins may help remove protein oligomers/aggregates and prevent cell death. The goal of our studies was to characterize a novel, non-toxic Hsp90 modulator, KU-32, which protects primary cortical neurons against Aβ1-42, a toxic peptide found in AD brain. Pharmacokinetic studies indicated that KU-32 is blood brain barrier permeable and orally bioavailable. Using two AD mouse models, JNPL3 and rTg4510, which both contain the P301L Tau mutation and develop aberrant Tau tangles as well as cognitive impairments, we assessed KU-32 treatment in vivo. The JNPL3 mice were treated with 20 mg/kg of KU-32 or with 12.5% Captisol® (vehicle) five times a week for six months. Immunohistochemical studies indicated significant decreases of hyperphosphorylated Tau in the cortical region. The rTg4510 mice were treated with 60 mg/kg of KU-32 or with vehicle (5% Captisol®) twice a week for 10 weeks. Immunofluorescent analyses demonstrated significant protection against dendritic pathology and neuronal death in KU-32-treated vs vehicle-treated rTg4510 mice. Further studies were conducted to examine the potential mechanisms of drug action. We hypothesized that KU-32 activated the heat shock response leading to an increase in molecular chaperones involved in protein quality control such as Hsp70. Our data suggest that KU-32 is not acting through this mechanism, and further studies are needed to elucidate the mechanism. Overall, our in vivo results suggest that the novel Hsp90 modulator, KU-32, may have therapeutic potential for treatment of AD

Heat shock protein 70-mediated sensitization of cells to apoptosis by Carboxyl-Terminal Modulator Protein

<p>Abstract</p> <p>Background</p> <p>The serine/threonine protein kinase B (PKB/Akt) is involved in insulin signaling, cellular survival, and transformation. Carboxyl-terminal modulator protein (CTMP) has been identified as a novel PKB binding partner in a yeast two-hybrid screen, and appears to be a negative PKB regulator with tumor suppressor-like properties. In the present study we investigate novel mechanisms by which CTMP plays a role in apoptosis process.</p> <p>Results</p> <p>CTMP is localized to mitochondria. Furthermore, CTMP becomes phosphorylated following the treatment of cells with pervanadate, an insulin-mimetic. Two serine residues (Ser37 and Ser38) were identified as novel <it>in vivo </it>phosphorylation sites of CTMP. Association of CTMP and heat shock protein 70 (Hsp70) inhibits the formation of complexes containing apoptotic protease activating factor 1 and Hsp70. Overexpression of CTMP increased the sensitivity of cells to apoptosis, most likely due to the inhibition of Hsp70 function.</p> <p>Conclusion</p> <p>Our data suggest that phosphorylation on Ser37/Ser38 of CTMP is important for the prevention of mitochondrial localization of CTMP, eventually leading to cell death by binding to Hsp70. In addition to its role in PKB inhibition, CTMP may therefore play a key role in mitochondria-mediated apoptosis by localizing to mitochondria.</p

A Small Molecule Modulator of Hsp90 Improves Experimental Diabetic Neuropathy

Background: Current Hsp90 inhibitors are therapeutically problematic. Although they induce a pro-survival heat shock response that promotes the refolding of damaged proteins, a confounding issue is that at these concentrations the inhibitors are cytotoxic, due to their ability to decrease the maturation of newly synthesized client proteins. KU-32 contains a novobiocin-based scaffold that binds to the C-terminal of Hsp90 and induces a pro-survival heat shock response at a concentration ~10,000 fold lower than that needed to induce neurotoxicity. This creates an optimal therapeutic window in which to operate, providing promise towards the development of novel neuroprotective agents. Objective: To evaluate whether the induction of the heat shock response through Hsp90 modulation could decrease or reverse the pathophysiological progression of diabetic peripheral neuropathy in Type-1 diabetic mice. Hypothesis: A small molecule modulator of Hsp90 will improve experimental diabetic neuropathy. Methods: After 8-12 weeks of diabetes induced by streptozotocin, the effects of weekly doses of KU-32 on several standard indices of diabetic neuropathy were measured. Results: Initial toxicity studies employing the weekly intraperitoneal administration of 2 or 20 mg/kg KU-32 to non-diabetic mice over 6 week duration did not alter motor or sensory nerve conduction velocity (MNCV/SNCV), mechanical or thermal sensitivity, or intra-epidermal nerve fiber density. Thus, the drug alone had no effect on altering common measures of neuropathy. In a 12-week intervention study, wild-type C57 Bl/6 animals receiving a weekly treatment regimen of 20 mg/kg KU-32 for 6 weeks exhibited a steady recovery to control levels in thermal and mechanical sensitivity, MNCV, and SNCV. KU-32 did not alter metabolic control. As Hsp70 is hypothesized to be a major target for KU-32, its necessity in neuroprotection was examined using Hsp70 double knockout mice (Hsp70.1/Hsp70.3). In a 12-week intervention study, Hsp70 knockout mice receiving a weekly treatment regimen of 20 mg/kg for 6 weeks displayed no improvements in thermal and mechanical sensitivity, MNCV, and SNCV. In 8-week intervention studies, animals demonstrated recoveries in sensory hypoalgesia and nerve conduction velocity deficits in a dose-dependent manner. KU-32 did not alter sensory nerve fiber innervation. Conclusions: These data suggest that hyperglycemia may adversely impact the ability of neurons to promote refolding or decrease unfolding of mildly damaged proteins. C-terminal Hsp90 modulators can improve several standard clinical indices of negative symptoms associated with small and large fiber dysfunction in the absence of improving overall metabolic control. The affects of KU-32 appear to be dose-dependent and require the presence of inducible Hsp70 for efficacy. Inducible Hsp70 is not required for the pathophysiological progression of diabetic neuropathy