Cathelicidins Target HSP60 To Restrict CVB3 Transmission via Disrupting the Exosome and Reducing Cardiomyocyte Apoptosis.

Cathelicidin antimicrobial peptides (mouse, CRAMP; human, LL-37) have broad-spectrum antiviral activities against enveloped viruses, but their mechanisms of action against nonenveloped viruses remain to be elucidated. Coxsackievirus B3 (CVB3), a member of nonenveloped virus belonging to the Enterovirus genus of Picornaviridae, is an important pathogen of viral myocarditis and dilated cardiomyopathy. Here, we observed that cardiac CRAMP expression was significantly upregulated in mice after CVB3 infection. The administration of CRAMP or LL-37 markedly suppressed CVB3 infection in mice, and CRAMP deficiency increased the susceptibility of mice to CVB3. CRAMP and LL-37 inhibited CVB3 replication in primary cardiomyocytes. However, they did not inactivate CVB3 particles and did not regulate the response of cardiomyocytes against CVB3 infection. Intriguingly, they inhibited CVB3 transmission through the exosome, but not virus receptor. In detail, CRAMP and LL-37 directly induced the lysis of exosomes by interfering with exosomal heat shock protein 60 (HSP60) and then blocked the diffusion of exosomes to recipient cells and inhibited the establishment of productive infection by exosomes. In addition, the interaction of CRAMP and LL-37 with HSP60 simultaneously inhibited HSP60-induced apoptosis in cardiomyocytes and reduced HSP60-enhanced CVB3 replication. Our findings reveal a novel mechanism of cathelicidins against viral infection and provide a new therapeutic strategy for CVB3-induced viral myocarditis. IMPORTANCE The relative mechanisms that cathelicidin antimicrobial peptides use to influence nonenveloped virus infection are unclear. We show here that cathelicidin antimicrobial peptides (CRAMP and LL-37) directly target exosomal HSP60 to destroy exosomes, which in turn block the diffusion of exosomes to recipient cardiomyocytes and reduced HSP60-induced apoptosis, thus restricting coxsackievirus B3 infection. Our results provide new insights into the mechanisms cathelicidin antimicrobial peptides use against viral infection.

Exploiting the HSP60/10 chaperonin system as a chemotherapeutic target for colorectal cancer.

Over the past few decades, an increasing variety of molecular chaperones have been investigated for their role in tumorigenesis and as potential chemotherapeutic targets; however, the 60 kDa Heat Shock Protein (HSP60), along with its HSP10 co-chaperone, have received little attention in this regard. In the present study, we investigated two series of our previously developed inhibitors of the bacterial homolog of HSP60/10, called GroEL/ES, for their selective cytotoxicity to cancerous over non-cancerous colorectal cells. We further developed a third "hybrid" series of analogs to identify new candidates with superior properties than the two parent scaffolds. Using a series of well-established HSP60/10 biochemical screens and cell-viability assays, we identified 24 inhibitors (14%) that exhibited > 3-fold selectivity for targeting colorectal cancer over non-cancerous cells. Notably, cell viability EC50 results correlated with the relative expression of HSP60 in the mitochondria, suggesting a potential for this HSP60-targeting chemotherapeutic strategy as emerging evidence indicates that HSP60 is up-regulated in colorectal cancer tumors. Further examination of five lead candidates indicated their ability to inhibit the clonogenicity and migration of colorectal cancer cells. These promising results are the most thorough analysis and first reported instance of HSP60/10 inhibitors being able to selectively target colorectal cancer cells and highlight the potential of the HSP60/10 chaperonin system as a viable chemotherapeutic target.

Analogs of nitrofuran antibiotics are potent GroEL/ES inhibitor pro-drugs.

In two previous studies, we identified compound 1 as a moderate GroEL/ES inhibitor with weak to moderate antibacterial activity against Gram-positive and Gram-negative bacteria including Bacillus subtilis, methicillin-resistant Staphylococcus aureus, Klebsiella pneumonia, Acinetobacter baumannii, and SM101 Escherichia coli (which has a compromised lipopolysaccharide biosynthetic pathway making bacteria more permeable to drugs). Extending from those studies, we developed two series of analogs with key substructures resembling those of known antibacterials, nitroxoline (hydroxyquinoline moiety) and nifuroxazide/nitrofurantoin (bis-cyclic-N-acylhydrazone scaffolds). Through biochemical and cell-based assays, we identified potent GroEL/ES inhibitors that selectively blocked E. faecium, S. aureus, and E. coli proliferation with low cytotoxicity to human colon and intestine cells in vitro. Initially, only the hydroxyquinoline-bearing analogs were found to be potent inhibitors in our GroEL/ES-mediated substrate refolding assays; however, subsequent testing in the presence of an E. coli nitroreductase (NfsB) in situ indicated that metabolites of the nitrofuran-bearing analogs were potent GroEL/ES inhibitor pro-drugs. Consequently, this study has identified a new target of nitrofuran-containing drugs, and is the first reported instance of such a unique class of GroEL/ES chaperonin inhibitors. The intriguing results presented herein provide impetus for expanded studies to validate inhibitor mechanisms and optimize this antibacterial class using the respective GroEL/ES chaperonin systems and nitroreductases from E. coli and the ESKAPE bacteria.

COVID-19 and hypertension: is the HSP60 culprit for the severe course and worse outcome?

The 60-kDa heat shock protein (HSP60) is a chaperone essential for mitochondrial proteostasis ensuring thus sufficient aerobic energy production. In pathological conditions, HSP60 can be translocated from the mitochondria and excreted from the cell. In turn, the extracellular HSP60 has a strong ability to trigger and enhance inflammatory response with marked proinflammatory cytokine induction, which is mainly mediated by Toll-like receptor binding. Previous studies have found increased circulating levels of HSP60 in hypertensive patients, as well as enhanced HSP60 expression and membrane translocation in the hypertrophic myocardium. These observations are of particular interest, since they could provide a possible pathophysiological explanation of the severe course and worse outcome of severe acute respiratory syndrome coronavirus 2 infection in hypertensive patients, repeatedly reported during the recent coronavirus disease 2019 (COVID-19) pandemic and related to hyperinflammatory response and cytokine storm development during the third phase of the disease. In this regard, pharmacological inhibition of HSP60 could attract attention to potentially ameliorate inappropriate inflammatory reaction in severe COVID-19 patients. Among HSP60 antagonizing drugs, mizoribine is the most intriguing, since it is clinically approved and exerts antiviral activity. However, this topic requires to be further scrutinized.

Differential scanning fluorimetry (DSF) screen to identify inhibitors of Hsp60 protein-protein interactions.

There are relatively few methods available for discovering inhibitors of the protein-protein interactions (PPIs) that hold together homo-oligomers. We envisioned that Differential Scanning Fluorimetry (DSF) might be a versatile way to discover this type of inhibitor because oligomers are often more thermally stable than monomers. Using the homo-heptameric chaperonin, Hsp60, as a model, we screened ∼5000 diverse compounds in 384-well plates by DSF, revealing molecules that partially inhibited oligomerization. Because DSF does not require protein labeling or structural information, we propose that it could be a versatile way to uncover PPI inhibitors.

HSP60-regulated Mitochondrial Proteostasis and Protein Translation Promote Tumor Growth of Ovarian Cancer.

Ovarian cancer (OC) is the most lethal gynecological carcinoma due to the lack of diagnostic markers and effective drug targets. Discovery of new therapeutic targets in OC to improve the treatment outcome is urgently needed. We performed proteomic analysis of OC specimens and the paired normal tissues and revealed that proteins associated with mitochondrial proteostasis and protein translation were highly expressed in ovarian tumor tissues, indicating that mitochondria are required for tumor progression of OC. Heat shock protein 60 (HSP60), an important mitochondrial chaperone, was upregulated in ovarian tumors. HSP60 silencing significantly attenuated growth of OC cells in both cells and mice xenografts. Proteomic analysis revealed that HSP60 silencing downregulated proteins involved in mitochondrial functions and protein synthesis. Metabolomic analysis revealed that HSP60 silencing resulted in a more than 100-fold increase in cellular adenine levels, leading to increased adenosine monophosphate and an activated AMPK pathway, and consequently reduced mTORC1-mediated S6K and 4EBP1 phosphorylation to inhibit protein synthesis that suppressed the proliferation of OC cells. These results suggest that HSP60 knockdown breaks mitochondrial proteostasis, and inactivates the mTOR pathway to inhibit OC progression, suggesting that HSP60 is a potential therapeutic target for OC treatment.

pH-activated heat shock protein inhibition and radical generation enhanced NIR luminescence imaging-guided photothermal tumour ablation.

Photothermal therapy had great potential in being a new approach of tumour ablation due to their high selectivity and low side effect. However, the shallow penetration depth of near-infrared (NIR) irradiation resulted in the limited curative effect. Herein, a novel nanomedicine was developed based on the indocyanine green-loaded vanadium oxide nanocomposites (VO2-ICG) for pH-activated NIR luminescence imaging-guided enhanced photothermal tumour ablation. In acidic tumour microenvironment, the VO2 NPs were decomposed and released VO2+, which could not only inhibit the function of 60 kDa heat shock protein (HSP60), but also generate hydroxyl radical (OH) by catalysing intratumoral H2O2. Furthermore, the ICG was also released in the decomposition process of VO2 NPs, allowing the pH-activated NIR luminescence imaging and photothermal therapy. The inhibition of HSP60 down-regulated the heat tolerance of cells and the generation of OH up-regulated the intracellular oxidative stress, which enhanced the photothermal therapeutic efficiency. Our work demonstrated a promised method to enhance photothermal therapeutic effect, highlighting the importance of HSP inhibition and OH generation in promoting cell apoptosis under mild hyperthermia.

Modulatory effects of curcumin on heat shock proteins in cancer: A promising therapeutic approach.

Cancer metastasis represents a multistep process, including alteration of cell adhesion/motility in the microenvironment and sustained angiogenesis, which is essential for supporting cancer growth in tissues that are distant from the primary tumor. There is growing evidence suggesting that heat shock proteins (HSPs) (also known as heat stress proteins), which constitute a family of stress-inducible proteins, may be involved in the pathogenesis of cancer. Curcumin (diferuloylmethane) is a potent anti-inflammatory, antioxidant, antimicrobial, and antitumor agent. Curcumin has been shown to regulate different members of HSPs including HSP27, HSP40, HSP60, HSP70, and HSP90 in cancer. Here, we present extent findings suggesting that curcumin may act as a potential therapeutic agent for the treatment of cancer through its regulation of HSPs.

(-)-Epicatechin attenuates hepatic sinusoidal obstruction syndrome by inhibiting liver oxidative and inflammatory injury.

Hepatic sinusoidal obstruction syndrome (HSOS) is a rare liver disease with considerable morbidity and mortality. (-)-Epicatechin (EPI) is a natural flavonol. This study aims to investigate the protection of EPI against monocrotaline (MCT)-induced HSOS and its engaged mechanism. Results of serum alanine/aspartate aminotransferases (ALT/AST) activities, total bilirubin (TBil) and bile acids (TBA) amounts, liver histological evaluation, scanning electron microscope observation and hepatic metalloproteinase-9 (MMP-9) expression all demonstrated the protection by EPI against MCT-induced HSOS in rats. EPI attenuated liver oxidative injury induced by MCT. EPI enhanced the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) and increased the expression of its downstream antioxidant genes in rats. Molecular docking results implied the potential interaction of EPI with the Nrf2 binding site in kelch-like ECH-associated protein-1 (Keap1). The EPI-provided protection against MCT-induced HSOS was diminished in Nrf2 knock-out mice when mice were treated with MCT for 24 h but not for 48 h. However, EPI reduced the increased liver myeloperoxidase (MPO) activity, hepatic infiltration of immune cells, pro-inflammatory cytokines expression and nuclear factor κB (NFκB) activation in both wild-type and Nrf2 knock-out mice when mice were treated with MCT for 48 h. EPI reduced the elevated serum heat shock protein 60 (HSP60) content, and reversed the decreased mitochondria expression of HSP60 and Lon in livers from MCT-treated rats. Furthermore, the MCT-induced HSOS was markedly alleviated in mice treated with anti-HSP60 antibody. Taken together, this study demonstrates that EPI attenuates MCT-induced HSOS by reducing liver oxidative injury via activating Nrf2 antioxidant pathway and inhibiting liver inflammatory injury through abrogating NFκB signaling pathway initiated by HSP60.

HSP60/10 chaperonin systems are inhibited by a variety of approved drugs, natural products, and known bioactive molecules.

All living organisms contain a unique class of molecular chaperones called 60 kDa heat shock proteins (HSP60 - also known as GroEL in bacteria). While some organisms contain more than one HSP60 or GroEL isoform, at least one isoform has always proven to be essential. Because of this, we have been investigating targeting HSP60 and GroEL chaperonin systems as an antibiotic strategy. Our initial studies focused on applying this antibiotic strategy for treating African sleeping sickness (caused by Trypanosoma brucei parasites) and drug-resistant bacterial infections (in particular Methicillin-resistant Staphylococcus aureus - MRSA). Intriguingly, during our studies we found that three known antibiotics - suramin, closantel, and rafoxanide - were potent inhibitors of bacterial GroEL and human HSP60 chaperonin systems. These findings prompted us to explore what other approved drugs, natural products, and known bioactive molecules might also inhibit HSP60 and GroEL chaperonin systems. Initial high-throughput screening of 3680 approved drugs, natural products, and known bioactives identified 161 hit inhibitors of the Escherichia coli GroEL chaperonin system (4.3% hit rate). From a purchased subset of 60 hits, 29 compounds (48%) re-confirmed as selective GroEL inhibitors in our assays, all of which were nearly equipotent against human HSP60. These findings illuminate the notion that targeting chaperonin systems might be a more common occurrence than we previously appreciated. Future studies are needed to determine if the in vivo modes of action of these approved drugs, natural products, and known bioactive molecules are related to GroEL and HSP60 inhibition.

Green synthesis of ultra-small VOx nanodots for acidic-activated HSP60 inhibition and therapeutic enhancement.

Using metal oxide semiconductor nanomaterials for synergistic cancer treatment has recently attracted the attention of numerous researchers. Herein, oxygen-defective vanadium oxide nanodots (VOx NDs) with ultra-small size and great dispersibility were synthesized via a novel user-friendly method, and then doxorubicin was loaded onto the VOx NDs surfaces. The VOx NDs had great photothermal conversion efficiency and stability. Doxorubicin-loaded VOx NDs can simultaneously serve as therapeutic agent and tumor microenvironment-activable HSP60 inhibitor, resulting in improved efficacy of photothermal therapy and released active doxorubicin for chemotherapy. Finally, we show that synergistic treatment achieved significant therapeutic effects in mice. These results provided a promising strategy for developing novel methods of synthesizing metal oxide semiconductors for enhanced synergistic cancer treatment.

Inhibiting expression of HSP60 and TLR4 attenuates paraquat-induced microglial inflammation.

Accumulating evidences suggest that heat shock protein 60 (HSP60) and toll-like receptor 4 (TLR4) are involved in triggering inflammatory response in microglia. Paraquat (PQ) evokes microglial inflammation by up-regulating expression of HSP60-TLR4-myeloid differentiation factor 88 (Myd88)-nuclear factor-kappa B (NF-κB) in vitro. The aim of this study is to investigate the potential modulatory roles of HSP60 and TLR4 in PQ-induced inflammation. Before treated with PQ, microglia BV2 cells were pretreated using siRNA to knockdown HSP60 or with specific inhibitor to inhibit TLR4 expression. Expression of TLR4 and MyD88, and nuclear translocation of NF-κB subunit p65 were studied with immunoblotting and immunofluorescence, respectively. Expression of pro-inflammatory factors was assessed with quantitative real-time PCR. Knockdown of HSP60 or inhibition of TLR4 significantly reduced the expression of TLR4 and MyD88 and decreased the accumulation of NF-κB p65 in the nucleus. Gene expression of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1ß), interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS) were also significantly decreased in response to PQ. These results suggest that HSP60 and TLR4 can modulate intracellular signaling of PQ-induced inflammation. Inhibiting HSP60 or TLR4 reduces significantly the intensity of inflammation in PQ-activated microglia.

Inhibitors and chemical probes for molecular chaperone networks.

The molecular chaperones are central mediators of protein homeostasis. In that role, they engage in widespread protein-protein interactions (PPIs) with each other and with their "client" proteins. Together, these PPIs form the backbone of a network that ensures proper vigilance over the processes of protein folding, trafficking, quality control, and degradation. The core chaperones, such as the heat shock proteins Hsp60, Hsp70, and Hsp90, are widely expressed in most tissues, yet there is growing evidence that the PPIs among them may be re-wired in disease conditions. This possibility suggests that these PPIs, and perhaps not the individual chaperones themselves, could be compelling drug targets. Indeed, recent efforts have yielded small molecules that inhibit (or promote) a subset of inter-chaperone PPIs. These chemical probes are being used to study chaperone networks in a range of models, and the successes with these approaches have inspired a community-wide objective to produce inhibitors for a broader set of targets. In this Review, we discuss progress toward that goal and point out some of the challenges ahead.

Probing the mechanism of inhibition of amyloid-ß(1-42)-induced neurotoxicity by the chaperonin GroEL.

The human chaperonin Hsp60 is thought to play a role in the progression of Alzheimer's disease by mitigating against intracellular ß-amyloid stress. Here, we show that the bacterial homolog GroEL (51% sequence identity) reduces the neurotoxic effects of amyloid-ß(1-42) (Aß42) on human neural stem cell-derived neuronal cultures. To understand the mechanism of GroEL-mediated abrogation of neurotoxicity, we studied the interaction of Aß42 with GroEL using a variety of biophysical techniques. Aß42 binds to GroEL as a monomer with a lifetime of ∼1 ms, as determined from global analysis of multiple relaxation-based NMR experiments. Dynamic light scattering demonstrates that GroEL dissolves small amounts of high-molecular-weight polydisperse aggregates present in fresh soluble Aß42 preparations. The residue-specific transverse relaxation rate profile for GroEL-bound Aß42 reveals the presence of three anchor-binding regions (residues 16-21, 31-34, and 40-41) located within the hydrophobic GroEL-consensus binding sequences. Single-molecule FRET analysis of Aß42 binding to GroEL results in no significant change in the FRET efficiency of a doubly labeled Aß42 construct, indicating that Aß42 samples a random coil ensemble when bound to GroEL. Finally, GroEL substantially slows down the disappearance of NMR visible Aß42 species and the appearance of Aß42 protofibrils and fibrils as monitored by electron and atomic force microscopies. The latter observations correlate with the effect of GroEL on the time course of Aß42-induced neurotoxicity. These data provide a physical basis for understanding how Hsp60 may serve to slow down the progression of Alzheimer's disease.

Hydroxybiphenylamide GroEL/ES Inhibitors Are Potent Antibacterials against Planktonic and Biofilm Forms of Staphylococcus aureus.

We recently reported the identification of a GroEL/ES inhibitor (1, N-(4-(benzo[ d]thiazol-2-ylthio)-3-chlorophenyl)-3,5-dibromo-2-hydroxybenzamide) that exhibited in vitro antibacterial effects against Staphylococcus aureus comparable to vancomycin, an antibiotic of last resort. To follow up, we have synthesized 43 compound 1 analogs to determine the most effective functional groups of the scaffold for inhibiting GroEL/ES and killing bacteria. Our results identified that the benzothiazole and hydroxyl groups are important for inhibiting GroEL/ES-mediated folding functions, with the hydroxyl essential for antibacterial effects. Several analogs exhibited >50-fold selectivity indices between antibacterial efficacy and cytotoxicity to human liver and kidney cells in cell culture. We found that MRSA was not able to easily generate acute resistance to lead inhibitors in a gain-of-resistance assay and that lead inhibitors were able to permeate through established S. aureus biofilms and maintain their bactericidal effects.

Sulfonamido-2-arylbenzoxazole GroEL/ES Inhibitors as Potent Antibacterials against Methicillin-Resistant Staphylococcus aureus (MRSA).

Extending from a study we recently published examining the antitrypanosomal effects of a series of GroEL/ES inhibitors based on a pseudosymmetrical bis-sulfonamido-2-phenylbenzoxazole scaffold, here, we report the antibiotic effects of asymmetric analogs of this scaffold against a panel of bacteria known as the ESKAPE pathogens ( Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). While GroEL/ES inhibitors were largely ineffective against K. pneumoniae, A. baumannii, P. aeruginosa, and E. cloacae (Gram-negative bacteria), many analogs were potent inhibitors of E. faecium and S. aureus proliferation (Gram-positive bacteria, EC50 values of the most potent analogs were in the 1-2 µM range). Furthermore, even though some compounds inhibit human HSP60/10 biochemical functions in vitro (IC50 values in the 1-10 µM range), many of these exhibited moderate to low cytotoxicity to human liver and kidney cells (CC50 values > 20 µM).

Heat shock protein 60 involvement in vascular smooth muscle cell proliferation.

AIM: Heat shock protein 60 (Hsp60) is a mediator of stress-induced vascular smooth muscle cell (VSMC) proliferation. This study will determine, first, if the mitochondrial or cytoplasmic localization of Hsp60 is critical to VSMC proliferation and, second, the mechanism of Hsp60 induction of VSMC proliferation with a focus on modification of nucleocytoplasmic trafficking. METHODS AND RESULTS: Hsp60 was overexpressed in primary rabbit VSMCs with or without a mitochondrial targeting sequence (AdHsp60mito-). Both interventions induced an increase in VSMC PCNA expression and proliferation. The increase in VSMC PCNA expression and growth was not observed after siRNA-mediated knockdown of Hsp60 expression. Nuclear protein import in VSMC was measured by fluorescent microscopy using a microinjected fluorescent import substrate. Nuclear protein import was stimulated by both AdHsp60 and AdHsp60mito- treatments. AdHsp60 treatment also induced increases in nucleoporin (Nup) 62, Nup153, importin-α, importin-ß and Ran expression as well as cellular ATP levels compared to control. AdHsp60mito- treatment induced an up-regulation in importin-α, importin-ß and Ran expression compared to control. Hsp60 knockdown did not change nuclear protein import nor the expression of any nuclear transport receptors or nucleoporins. Both heat shock treatment and Hsp60 overexpression promoted the interaction of Ran with Hsp60. CONCLUSIONS: VSMC proliferation can be modulated via an Hsp60 dependent, cytosol localized mechanism that in part involves a stimulation of nuclear protein import through an interaction with Ran. This novel cellular signaling role for Hsp60 may be important in growth-based vascular pathologies like atherosclerosis and hypertension.

Multiplexed Thiol Reactivity Profiling for Target Discovery of Electrophilic Natural Products.

Electrophilic groups, such as Michael acceptors, expoxides, are common motifs in natural products (NPs). Electrophilic NPs can act through covalent modification of cysteinyl thiols on functional proteins, and exhibit potent cytotoxicity and anti-inflammatory/cancer activities. Here we describe a new chemoproteomic strategy, termed multiplexed thiol reactivity profiling (MTRP), and its use in target discovery of electrophilic NPs. We demonstrate the utility of MTRP by identifying cellular targets of gambogic acid, an electrophilic NP that is currently under evaluation in clinical trials as anticancer agent. Moreover, MTRP enables simultaneous comparison of seven structurally diversified α,ß-unsaturated γ-lactones, which provides insights into the relative proteomic reactivity and target preference of diverse structural scaffolds coupled to a common electrophilic motif and reveals various potential druggable targets with liganded cysteines. We anticipate that this new method for thiol reactivity profiling in a multiplexed manner will find broad application in redox biology and drug discovery.

Exosomal HSP60: a potentially useful biomarker for diagnosis, assessing prognosis, and monitoring response to treatment.

INTRODUCTION: Cell-to-cell communication is imperative for life and it is mediated by sending and receiving information via the secretion and subsequent receptor-mediated detection of biological molecules. Exosomes (EXs) secreted from cells to the extracellular environment play an important role in intercellular communication in normal and pathological conditions. Areas covered: New evidence indicates that tumor cells-derived EXs contribute to cancer progression through the modulation of tumor microenvironment. The exosomal heat shock protein 60 (HSP60) is very likely a key player in intercellular cross-talk, particularly during the progress of diseases, such as cancer. Many studies have focused on the extracellular roles played by HSP60 that pertain to cancer development and immune system stimulation. Our experimental data in vitro and in vivo demonstrated that HSP60 occurs on the surface of EXs secreted by tumour cells. Expert commentary: Exosomal HSP60 has great potential for clinical applications, as a 'liquid biopsy', including its use as biomarker for diagnostics, assessing prognosis, and monitoring disease progression and response to treatment, particularly in cancer.

Mitochondrial Chaperonin HSP60 Is the Apoptosis-Related Target for Myrtucommulone.

The acylphloroglucinol myrtucommulone A (MC) causes mitochondrial dysfunctions by direct interference leading to apoptosis in cancer cells, but the molecular targets involved are unknown. Here, we reveal the chaperonin heat-shock protein 60 (HSP60) as a molecular target of MC that seemingly modulates HSP60-mediated mitochondrial functions. Exploiting an unbiased, discriminative protein fishing approach using MC as bait and mitochondrial lysates from leukemic HL-60 cells as target source identified HSP60 as an MC-binding protein. MC prevented HSP60-mediated reactivation of denatured malate dehydrogenase in a protein refolding assay. Interference of MC with HSP60 was accompanied by aggregation of two proteins in isolated mitochondria under heat shock that were identified as Lon protease-like protein (LONP) and leucine-rich PPR motif-containing protein (LRP130). Together, our results reveal HSP60 as a direct target of MC, proposing MC as a valuable tool for studying HSP60 biology and for evaluating its value as a target in related diseases, such as cancer.