Voltage-dependent Anion Channel 1 Oligomerization Research Articles

VDAC1 in the diseased myocardium and the effect of VDAC1-interacting compound on atrial fibrosis induced by hyperaldosteronism

The voltage-dependent anion channel 1 (VDAC1) is a key player in mitochondrial function. VDAC1 serves as a gatekeeper mediating the fluxes of ions, nucleotides, and other metabolites across the outer mitochondrial membrane, as well as the release of apoptogenic proteins initiating apoptotic cell death. VBIT-4, a VDAC1 oligomerization inhibitor, was recently shown to prevent mitochondrial dysfunction and apoptosis, as validated in mouse models of lupus and type-2 diabetes. In the present study, we explored the expression of VDAC1 in the diseased myocardium of humans and rats. In addition, we evaluated the effect of VBIT-4 treatment on the atrial structural and electrical remodeling of rats exposed to excessive aldosterone levels. Immunohistochemical analysis of commercially available human cardiac tissues revealed marked overexpression of VDAC1 in post-myocardial infarction patients, as well as in patients with chronic ventricular dilatation\\dysfunction. In agreement, rats exposed to myocardial infarction or to excessive aldosterone had a marked increase of VDAC1 in both ventricular and atrial tissues. Immunofluorescence staining indicated a punctuated appearance typical for mitochondrial-localized VDAC1. Finally, VBIT-4 treatment attenuated the atrial fibrotic load of rats exposed to excessive aldosterone without a notable effect on the susceptibility to atrial fibrillation episodes induced by burst pacing. Our results indicate that VDAC1 overexpression is associated with myocardial abnormalities in common pathological settings. Our data also indicate that inhibition of the VDAC1 can reduce excessive fibrosis in the atrial myocardium, a finding which may have important therapeutic implications. The exact mechanism\\s of this beneficial effect need further studies.

VDAC upregulation and αTAT1‑mediated α‑tubulin acetylation contribute to tanespimycin‑induced apoptosis in Calu‑1 cells.

Voltage‑dependent anion channel 1 (VDAC1) functions as a porin in the mitochondrial outer membrane (MOM) and plays important roles in mitochondria‑mediated cell apoptosis. VDAC1 interacts with a variety of proteins, such as Bcl‑2 family proteins, hexose kinase (HK), adenine nucleotide translocase (ANT) and α‑tubulin. However, the association between VDAC1 and α‑tubulin, particularly between VDAC1 and acetylated α‑tubulin (Ac‑α‑tubulin), in apoptosis remains unclear. The present study revealed that the heat shock protein 90 inhibitor, tanespimycin, induced VDAC1 upregulation and α‑tubulin acetylation during Calu‑1 cell apoptosis in human lung cancer. Hsp90 mediated the expression level of VDAC1, and the acetylation of α‑tubulin was enhanced in an α‑tubulin acetyltransferase 1 (αTAT1)‑dependent manner following an increase in VDAC1 expression. Docetaxel, as an inhibitor of microtubules, augmented the expression of Ac‑α‑tubulin, VDAC1 and Bax induced by tanespimycin and increased the degree of caspase activation. Immunoprecipitation (IP) experiments revealed that Ac‑α‑tubulin, α‑tubulin and VDAC1 were co‑precipitated in the IP complex, in which α‑tubulin expression was decreased and VDAC1 proteins were oligomerized, and that the p‑AKT/glycogen synthase kinase 3β (GSK3β) signalling pathway mediated the opening of VDAC1. Therefore, it can be asserted that the acetylation of α‑tubulin and VDAC1 upregulation or oligomerization induced by tanespimycin may lead to mitochondrial permeability and consequently induce the apoptosis of lung cancer cells. These findings provide evidence for the use of a combination of drugs that target VDAC1 and tubulin to induce tumour cell apoptosis.

Modulation of the mitochondrial voltage-dependent anion channel (VDAC) by hydrogen peroxide and its recovery by curcumin.

The Voltage-Dependent Anion Channel (VDAC) plays a vital role in mitochondria-mediated transport of ions and metabolites. It is well established that mitochondria are a site for production of hydrogen peroxide (H2O2). Excess production of H2O2 is toxic to the cell and causes oxidative stress. Therefore, the effect of H2O2 on the single-channel conductance of VDAC was investigated. In vitro bilayer electrophysiology experiments were performed on VDAC isolated from rat brain mitochondria, which consists predominately of the isoform VDAC1. VDAC was treated with H2O2 on a planar bilayer membrane (BLM). The conductance of VDAC increased upon H2O2 treatment, whereas the same concentration of H2O2 was unable to affect the BLM (without protein) over a long period of time. Subsequently, the sequential addition of curcumin to H2O2-treated VDAC reduced the conductance. Experimental results (bilayer electrophysiology) demonstrate the role of curcumin in the restoration of the activity of VDAC affected by H2O2. In silico docking studies enables identification of the probable binding site of H2O2 on VDAC. We further find that the oligomerization of VDAC that results in its increased conductance is an effect of lipid oxidation by H2O2.

Oligomerization of VDAC1 promotes mtDNA release and lupus‐like disease

Mitochondrial stress releases mitochondrial DNA (mtDNA) into the cytosol, triggering immunostimulatory pathways such as the type‐Ι interferon response. Pores formed in the outer membrane of mitochondria (OMM) can promote mtDNA release; however, the identity of such a pore in living cells is not well characterized. Here, we provide genetic and biochemical evidence demonstrating that the oligomerization of voltage‐dependent anion channel 1 (VDAC1) in the OMM promotes mtDNA release and triggers the type‐Ι interferon response in living cells. In addition to forming OMM pores, VDAC1 interacts with mtDNA via its positively charged residues in the N‐terminal domain and increases both VDAC1 oligomerization and type‐Ι interferon response. VBIT‐4, which inhibits VDAC1 oligomerization, decreases mtDNA release, type‐Ι interferon signaling, neutrophil extracellular traps, and disease severity in a mouse model of systemic lupus erythematosus. These findings suggest that VDAC1 oligomerization is a potential therapeutic target for lupus.Support or Funding InformationSupported by the Intramural Research Program of the National Heart Lung and Blood Institute, National Institute of Arthritis and Musculoskeletal and Skin Diseases, and National Institute of Allergy and Infectious Diseases and by a grant from the National Institute for Biotechnology in the Negev (V.S.‐B.) and by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health and Welfare, Republic of Korea (grant number HI14C1176) and a grant from the KRIBB Research Initiative Program (Korean Biomedical Scientist Fellowship Program), Korea Research Institute of Bioscience and Biotechnology, Republic of Korea.VDAC oligomers form mitochondrial pores to release mtDNA fragments.Figure 1

VDAC oligomers form mitochondrial pores to release mtDNA fragments and promote lupus-like disease.

Mitochondrial stress releases mitochondrial DNA (mtDNA) into the cytosol, thereby triggering the type Ι interferon (IFN) response. Mitochondrial outer membrane permeabilization, which is required for mtDNA release, has been extensively studied in apoptotic cells, but little is known about its role in live cells. We found that oxidatively stressed mitochondria release short mtDNA fragments via pores formed by the voltage-dependent anion channel (VDAC) oligomers in the mitochondrial outer membrane. Furthermore, the positively charged residues in the N-terminal domain of VDAC1 interact with mtDNA, promoting VDAC1 oligomerization. The VDAC oligomerization inhibitor VBIT-4 decreases mtDNA release, IFN signaling, neutrophil extracellular traps, and disease severity in a mouse model of systemic lupus erythematosus. Thus, inhibiting VDAC oligomerization is a potential therapeutic approach for diseases associated with mtDNA release.

Inhibition of VDAC1 Protects Against Glutamate-Induced Oxytosis and Mitochondrial Fragmentation in Hippocampal HT22 Cells.

The involvement of glutamate in neuronal cell death in neurodegenerative diseases and neurotrauma is mediated through excitotoxicity or oxytosis. The latter process induces oxidative stress via glutamate-mediated inhibition of cysteine transporter xCT, leading to depletion of the cellular glutathione pool. Mitochondrial damage, loss of mitochondrial membrane potential (MMP), and depletion of energy metabolites have been shown in this process. The Voltage-Dependent Anion Channel-1 (VDAC1) is one of the main components of the mitochondrial outer membrane and plays a gatekeeping role in mitochondria-cytoplasm transport of metabolites. In this study, we explored the possible participation of VDAC-1 in the pathophysiology of oxytosis. Administration of glutamate in HT22 cells that lack the glutamate ionotropic receptors induced an upregulation and oligomerization of VDAC1. This was associated with an increase in ROS and loss of cell survival. Glutamate-mediated oxytosis in this model also decreased MMP and promoted ATP depletion, resulting in translocation of cytochrome c (cyt C) and apoptosis inducing factor (AIF) from mitochondria into the cytosol. This was also accompanied by cleavage of AIF to form truncated AIF. Inhibition of VDAC1 oligomerization using 4,4'-Diisothiocyanatostilbene-2,2'-disulfonate (DIDS), significantly improved the cell survival, decreased the ROS levels, improved mitochondrial functions, and decreased the mitochondrial damage. Notably, DIDS also inhibited the mitochondrial fragmentation caused by glutamate, indicating the active role of VDAC1 oligomerization in the process of mitochondrial fragmentation in oxytosis. These results suggest a critical role for VDAC1 in mitochondrial fragmentation and its potential therapeutic value against glutamate-mediated oxidative neurotoxicity.

Peroxynitrite nitrates adenine nucleotide translocase and voltage-dependent anion channel 1 and alters their interactions and association with hexokinase II in mitochondria

Cardiac ischemia and reperfusion (IR) injury induces excessive emission of deleterious reactive O2 and N2 species (ROS/RNS), including the non-radical oxidant peroxynitrite (ONOO−) that can cause mitochondria dysfunction and cell death. In this study, we explored whether IR injury in isolated hearts induces tyrosine nitration of adenine nucleotide translocase (ANT) and alters its interaction with the voltage-dependent anion channel 1 (VDAC1). We found that IR injury induced tyrosine nitration of ANT and that exposure of isolated cardiac mitochondria to ONOO− induced ANT tyrosine, Y81, nitration. The exposure of isolated cardiac mitochondria to ONOO− also led ANT to form high molecular weight proteins and dissociation of ANT from VDAC1. We found that IR injury in isolated hearts, hypoxic injury in H9c2 cells, and ONOO− treatment of H9c2 cells and isolated mitochondria, each decreased mitochondrial bound-hexokinase II (HK II), which suggests that ONOO− caused HK II to dissociate from mitochondria. Moreover, we found that mitochondria exposed to ONOO− induced VDAC1 oligomerization which may decrease its binding with HK II. We have reported that ONOO− produced during cardiac IR injury induced tyrosine nitration of VDAC1, which resulted in conformational changes of the protein and increased channel conductance associated with compromised cardiac function on reperfusion. Thus, our results imply that ONOO− produced during IR injury and hypoxic stress impeded HK II association with VDAC1. ONOO− exposure nitrated mitochondrial proteins and also led to cytochrome c (cyt c) release from mitochondria. In addition, in isolated mitochondria exposed to ONOO− or obtained after IR, there was significant compromise in mitochondrial respiration and delayed repolarization of membrane potential during oxidative (ADP) phosphorylation. Taken together, ONOO− produced during cardiac IR injury can nitrate tyrosine residues of two key mitochondrial membrane proteins involved in bioenergetics and energy transfer to contribute to mitochondrial and cellular dysfunction.

Human erythrocytes release ATP by a novel pathway involving VDAC oligomerization independent of pannexin-1

We previously demonstrated that the translocase protein TSPO2 together with the voltage-dependent anion channel (VDAC) and adenine nucleotide transporter (ANT) were involved in a membrane transport complex in human red blood cells (RBCs). Because VDAC was proposed as a channel mediating ATP release in RBCs, we used TSPO ligands together with VDAC and ANT inhibitors to test this hypothesis. ATP release was activated by TSPO ligands, and blocked by inhibitors of VDAC and ANT, while it was insensitive to pannexin-1 blockers. TSPO ligand increased extracellular ATP (ATPe) concentration by 24–59% over the basal values, displaying an acute increase in [ATPe] to a maximal value, which remained constant thereafter. ATPe kinetics were compatible with VDAC mediating a fast but transient ATP efflux. ATP release was strongly inhibited by PKC and PKA inhibitors as well as by depleting intracellular cAMP or extracellular Ca2+, suggesting a mechanism involving protein kinases. TSPO ligands favoured VDAC polymerization yielding significantly higher densities of oligomeric bands than in unstimulated cells. Polymerization was partially inhibited by decreasing Ca2+ and cAMP contents. The present results show that TSPO ligands induce polymerization of VDAC, coupled to activation of ATP release by a supramolecular complex involving VDAC, TSPO2 and ANT.

VDAC1 as a Player in Mitochondria-Mediated Apoptosis and Target for Modulating Apoptosis.

The voltage-dependent anion channel 1 (VDAC1), an outer mitochondria membrane protein, functions as a mitochondrial governor, controlling transport of metabolites in and out of the mitochondria and energy production, while also coordinating glycolysis and oxidative phosphorylation. VDAC1 plays a key role in mitochondria-mediated apoptosis by functioning in the release of apoptotic proteins located in the inter-membranal space and due to its association with pro- and anti-apoptotic proteins. Thus, VDAC1 is considered as a promising target for controlling apoptosis. We reviewed published data presenting accumulated evidence suggesting that VDAC1 oligomerization represents an important step in the intrinsic mitochondria-mediated apoptosis pathway. The published data support the proposal that VDAC1 oligomerization leads to the formation of a large pore that allows the release of pro-apoptotic proteins to the cytosol, thereby, activation of apoptosis. Evidence for the relationship between VDAC1 expression levels and induction of apoptosis are presented. This includes the finding that almost all apoptosis stimuli induce VDAC1 over-expression shifting VDAC1 from a monomeric to an oligomeric assembly, corresponding to the Cyto c release channel. Compounds or conditions inducing VDAC1 over-expression, VDAC1 oligomerization and apoptosis are presented. Likewise, VDAC1-interacting molecules, that inhibit both VDAC1 oligomerization and apoptosis are also presented. This review highlights the findings about VDAC1 oligomerization as a potential target for controlling apoptosis, specifically using drugs to induce apoptotic cell death in cancer and inhibit apoptosis in neurodegenerative diseases, as well as possible VDAC1-based therapeutic applications.

Protonation state of glutamate 73 regulates the formation of a specific dimeric association of mVDAC1

The voltage-dependent anion channel (VDAC) is the most abundant protein in the outer mitochondrial membrane and constitutes the primary pathway for the exchange of ions and metabolites between the cytosol and the mitochondria. There is accumulating evidence supporting VDAC's role in mitochondrial metabolic regulation and apoptosis, where VDAC oligomerization has been implicated with these processes. Herein, we report a specific pH-dependent dimerization of murine VDAC1 (mVDAC1) identified by double electron-electron resonance and native mass spectrometry. Intermolecular distances on four singly spin-labeled mVDAC1 mutants were used to generate a model of the low-pH dimer, establishing the presence of residue E73 at the interface. This dimer arrangement is different from any oligomeric state previously described, and it forms as a steep function of pH with an apparent pKa of 7.4. Moreover, the monomer-dimer equilibrium affinity constant was determined using native MS, revealing a nearly eightfold enhancement in dimerization affinity at low pH. Mutation of E73 to either alanine or glutamine severely reduces oligomerization, demonstrating the role of protonated E73 in enhancing dimer formation. Based on these results, and the known importance of E73 in VDAC physiology, VDAC dimerization likely plays a significant role in mitochondrial metabolic regulation and apoptosis in response to cytosolic acidification during cellular stress.

98 - Lysosomal Permeabilization Facilitate Mitochondria-mediated Cell Death in Ferroptosis and Oxytosis

The central role of mitochondria in energy production is associated with generation of reactive oxygen species (ROS). Energy failure and increased ROS levels induce autophagy or regulated cell death (RCD). Apoptosis is a well-studied form of RCD that is identified by the release of mitochondrial content into cytoplasm, through mitochondrial permeability transition pore (PTP) and activation of caspase cascade. One component of PTP is the voltage-dependent anion channel 1 (VDAC1) that has been shown to be upregulated and oligomerized in apoptosis. In this study we examined the response of neuronal VDAC1 in Oxytosis and ferroptosis, two caspase-independent models of RCD. In these models, glutathione is depleted from the cells leading to excessive oxidative stress and cell death. Results VDAC1 was highly upregulated in a time dependent manner in immortalized hippocampal neurons (HT22) in response to inducers of oxytosis and ferroptosis, glutamate and erastin, respectively and was associated with significant cell death. Application of N-acetylcysteine decreased cell death, indicating the involvement of oxidative stress. Further analysis of VDAC1 revealed that oxytosis and ferroptosis lead to VDAC1 oligomerization, which are known to induce mitochondrial membrane permeabilization, as confirmed by cytochrome C and A poptosis I nducing F actor (AIF) release, leading to cell death. Pharmacological inhibitor of VDAC1, DIDS or function-blocking antibody against VDAC1 showed significant protection against glutamate and erastin induced cytotoxicity. Incidentally, we observed that pretreatment of cells with cathepsin B inhibitor (CA-074me) significantly improved cell viability. These results suggest that lysosomal permeability may facilitate mitochondrial damage and VDAC1 oligomerization, and identify VDAC1 as a potential therapeutic target in neurogenerative diseases where oxidative stress plays a key role in progression of disease.

Crystal structural characterization reveals novel oligomeric interactions of human voltage-dependent anion channel 1.

Voltage-dependent anion channel 1 (VDAC1), which is located in the outer mitochondrial membrane, plays important roles in various cellular processes. For example, oligomerization of VDAC1 is involved in the release of cytochrome c to the cytoplasm, leading to apoptosis. However, it is unknown how VDAC1 oligomerization occurs in the membrane. In the present study, we determined high-resolution crystal structures of oligomeric human VDAC1 (hVDAC1) prepared by using an Escherichia coli cell-free protein synthesis system, which avoided the need for denaturation and refolding of the protein. Broad-range screening using a bicelle crystallization method produced crystals in space groups C222 and P221 21 , which diffracted to a resolution of 3.10 and 3.15 Å, respectively. Each crystal contained two hVDAC1 protomers in the asymmetric unit. Dimer within the asymmetrical unit of the crystal in space group C222 were oriented parallel, whereas those of the crystal in space group P221 21 were oriented anti-parallel. From a model of the crystal in space group C222, which we constructed by using crystal symmetry operators, a heptameric structure with eight patterns of interaction between protomers, including hydrophobic interactions with β-strands, hydrophilic interactions with loop regions, and protein-lipid interactions, was observed. It is possible that by having multiple patterns of interaction, VDAC1 can form homo- or hetero-oligomers not only with other VDAC1 protomers but also with other proteins such as VDAC2, VDAC3 and apoptosis-regulating proteins in the Bcl-2 family.

The Mitochondrial Voltage-Dependent Anion Channel 1, Ca2+ Transport, Apoptosis, and Their Regulation

In the outer mitochondrial membrane, the voltage-dependent anion channel 1 (VDAC1) functions in cellular Ca2+ homeostasis by mediating the transport of Ca2+ in and out of mitochondria. VDAC1 is highly Ca2+-permeable and modulates Ca2+ access to the mitochondrial intermembrane space. Intramitochondrial Ca2+ controls energy metabolism by enhancing the rate of NADH production via modulating critical enzymes in the tricarboxylic acid cycle and fatty acid oxidation. Mitochondrial [Ca2+] is regarded as an important determinant of cell sensitivity to apoptotic stimuli and was proposed to act as a “priming signal,” sensitizing the organelle and promoting the release of pro-apoptotic proteins. However, the precise mechanism by which intracellular Ca2+ ([Ca2+]i) mediates apoptosis is not known. Here, we review the roles of VDAC1 in mitochondrial Ca2+ homeostasis and in apoptosis. Accumulated evidence shows that apoptosis-inducing agents act by increasing [Ca2+]i and that this, in turn, augments VDAC1 expression levels. Thus, a new concept of how increased [Ca2+]i activates apoptosis is postulated. Specifically, increased [Ca2+]i enhances VDAC1 expression levels, followed by VDAC1 oligomerization, cytochrome c release, and subsequently apoptosis. Evidence supporting this new model suggesting that upregulation of VDAC1 expression constitutes a major mechanism by which apoptotic stimuli induce apoptosis with VDAC1 oligomerization being a molecular focal point in apoptosis regulation is presented. A new proposed mechanism of pro-apoptotic drug action, namely Ca2+-dependent enhancement of VDAC1 expression, provides a platform for developing a new class of anticancer drugs modulating VDAC1 levels via the promoter and for overcoming the resistance of cancer cells to chemotherapy.

Quinocetone induces mitochondrial apoptosis in HepG2 cells through ROS-dependent promotion of VDAC1 oligomerization and suppression of Wnt1/β-catenin signaling pathway

Quinocetone (QCT) has been used as an animal feed additive in China since 2003. However, investigations indicate that QCT has potential toxicity due to the fact that it shows cytotoxicity, genotoxicity, hepatotoxicity, nephrotoxicity and immunotoxicity in vitro and animal models. Although QCT-induced mitochondrial apoptosis has been established, the molecular mechanism remains unclear. This study was aimed to investigate the role of voltage-dependent anion channel 1 (VDAC1) oligomerization and Wnt/β-catenin pathway in QCT-induced mitochondrial apoptosis. The results showed VDAC inhibitor 4, 4-diisothiocyano stilbene-2, 2-disulfonic acid (DIDS) partly compromised QCT-induced cell viability decrease (from 34.1% to 68.5%) and mitochondrial apoptosis accompanied by abating VDAC1 oligomerization, cytochrome c (Cyt c) release and the expression levels of cleaved caspase-9, -3 and poly (ADP-ribose) polymerase (PARP). Meanwhile, overexpression VDAC1 exacerbated QCT-induced VDAC1 oligomerization and Cyt c release. In addition, lithium chloride (LiCl), an activator of Wnt/β-catenin pathway, markedly attenuated QCT-induced mitochondrial apoptosis by partly restoring the expression levels of Wnt1 and β-catenin. Finally, reactive oxygen species (ROS) scavenger N-acetyl-l-cysteine (NAC) obviously blocked QCT-induced VDAC1 oligomerization and the inhibition of Wnt1/β-catenin pathway. Taken together, our results reveal that QCT induces mitochondrial apoptosis by ROS-dependent promotion of VDAC1 oligomerization and suppression of Wnt1/β-catenin pathway.

Ph-Induced Oligomerization of the Voltage Dependent Anion Channel

The Voltage-Dependent Anion Channel (VDAC) is the most abundant protein in the outer mitochondrial membrane facilitating the passage of ions and metabolites between the cytoplasm and the intermembrane space. In addition to its critical role in bioenergetics, VDAC is capable of modulating the organelle's permeability, implicating VDAC in metabolic stress and mitochondria-mediated apoptotic cell death. VDAC functions as a monomer but exhibits various oligomeric states, as shown by electron microscopy and atomic force microscopy. Oligomerization of VDAC can be linked to apoptosis and therefore is crucial for understanding mitochondrial regulation. Double Electron-Electron Resonance (DEER) on 4 singly spin-labeled mutants of mVDAC1 revealed a specific pH-induced dimerization. These inter-molecular distances were used to generate a model of a dimer interface that contains Glutamate 73. Mutation of Glutamate 73, to either Alanine or Glutamine, prevented pH induced oligomerization confirming the vital role of this residue. This dimer, induced by acidification, differs from any oligomeric form of VDAC previously described and likely plays a significant role in mitochondrial regulation and apoptosis in the response to cytosolic acidification during cellular stress.

Novel Compounds Targeting the Mitochondrial Protein VDAC1 Inhibit Apoptosis and Protect against Mitochondrial Dysfunction

Apoptosis is thought to play a critical role in several pathological processes, such as neurodegenerative diseases (i.e. Parkinson's and Alzheimer's diseases) and various cardiovascular diseases. Despite the fact that apoptotic mechanisms are well defined, there is still no substantial therapeutic strategy to stop or even slow this process. Thus, there is an unmet need for therapeutic agents that are able to block or slow apoptosis in neurodegenerative and cardiovascular diseases. The outer mitochondrial membrane protein voltage-dependent anion channel 1 (VDAC1) is a convergence point for a variety of cell survival and death signals, including apoptosis. Recently, we demonstrated that VDAC1 oligomerization is involved in mitochondrion-mediated apoptosis. Thus, VDAC1 oligomerization represents a prime target for agents designed to modulate apoptosis. Here, high-throughput compound screening and medicinal chemistry were employed to develop compounds that directly interact with VDAC1 and prevent VDAC1 oligomerization, concomitant with an inhibition of apoptosis as induced by various means and in various cell lines. The compounds protected against apoptosis-associated mitochondrial dysfunction, restoring dissipated mitochondrial membrane potential, and thus cell energy and metabolism, decreasing reactive oxidative species production, and preventing detachment of hexokinase bound to mitochondria and disruption of intracellular Ca2+ levels. Thus, this study describes novel drug candidates with a defined mechanism of action that involves inhibition of VDAC1 oligomerization, apoptosis, and mitochondrial dysfunction. The compounds VBIT-3 and VBIT-4 offer a therapeutic strategy for treating different diseases associated with enhanced apoptosis and point to VDAC1 as a promising target for therapeutic intervention.

VDAC1-interacting anion transport inhibitors inhibit VDAC1 oligomerization and apoptosis

Mitochondria-mediated apoptosis involves pro-apoptotic protein release from the mitochondria to the cytosol, triggering apoptosis. However, the mechanisms by which apoptotic initiators cross the outer mitochondrial membrane (OMM) remain unclear. The voltage-dependent anion channel 1 (VDAC1), an OMM protein, is central to mitochondria-mediated apoptosis. In previous work, we demonstrated that apoptosis induction is associated with VDAC1 oligomerization, forming a mega-pore that mediates pro-apoptotic protein release. Here, we demonstrated that several known anion transport inhibitors, DIDS, SITS, H2DIDS, DNDS, and DPC, all interact with VDAC1, as revealed by micro-scale thermophoresis and decreased conductance of bilayer-reconstituted VDAC1. These compounds inhibited apoptosis stimuli-induced release of mitochondrial pro-apoptotic proteins, apoptosis and VDAC1 oligomerization, as monitored by chemical cross-linking or in living cells by BRET2. Moreover, the compounds inhibited VDAC1 oligomerization in isolated mitochondria and as induced by VDAC1 over-expression, suggesting that the inhibitory effect of the tested compounds involved VDAC1.Finally, the compounds also inhibited apoptosis-associated increases in intracellular Ca2+, ([Ca2+]i), ROS production, mitochondria membrane potential dissipation and the increase in VDAC1 expression levels. The results presented here explored a new mechanism of action for DIDS and its analogs. All inhibited apoptosis via direct interaction with VDAC1 to inhibit its oligomerization and subsequent Cyto c release and apoptosis. Such results may allow the development of a VDAC1-specific inhibitor that would offer substantial insight into the function of VDAC1 in controlling metabolism, energy production, cholesterol transport and apoptosis. Finally, inhibitors of apoptosis could serve in pathological conditions where enhanced apoptosis is found, such as neurodegenerative diseases.

The Voltage-dependent Anion Channel 1 Mediates Amyloid β Toxicity and Represents a Potential Target for Alzheimer Disease Therapy

The voltage-dependent anion channel 1 (VDAC1), found in the mitochondrial outer membrane, forms the main interface between mitochondrial and cellular metabolisms, mediates the passage of a variety of molecules across the mitochondrial outer membrane, and is central to mitochondria-mediated apoptosis. VDAC1 is overexpressed in post-mortem brains of Alzheimer disease (AD) patients. The development and progress of AD are associated with mitochondrial dysfunction resulting from the cytotoxic effects of accumulated amyloid β (Aβ). In this study we demonstrate the involvement of VDAC1 and a VDAC1 N-terminal peptide (VDAC1-N-Ter) in Aβ cell penetration and cell death induction. Aβ directly interacted with VDAC1 and VDAC1-N-Ter, as monitored by VDAC1 channel conductance, surface plasmon resonance, and microscale thermophoresis. Preincubated Aβ interacted with bilayer-reconstituted VDAC1 and increased its conductance ∼ 2-fold. Incubation of cells with Aβ resulted in mitochondria-mediated apoptotic cell death. However, the presence of non-cell-penetrating VDAC1-N-Ter peptide prevented Aβ cellular entry and Aβ-induced mitochondria-mediated apoptosis. Likewise, silencing VDAC1 expression by specific siRNA prevented Aβ entry into the cytosol as well as Aβ-induced toxicity. Finally, the mode of Aβ-mediated action involves detachment of mitochondria-bound hexokinase, induction of VDAC1 oligomerization, and cytochrome c release, a sequence of events leading to apoptosis. As such, we suggest that Aβ-mediated toxicity involves mitochondrial and plasma membrane VDAC1, leading to mitochondrial dysfunction and apoptosis induction. The VDAC1-N-Ter peptide targeting Aβ cytotoxicity is thus a potential new therapeutic strategy for AD treatment.

Mitochondrial ATF2 translocation contributes to apoptosis induction and BRAF inhibitor resistance in melanoma through the interaction of Bim with VDAC1.

The mitochondrial accumulation of ATF2 is involved in tumor suppressor activities via cytochrome c release in melanoma cells. However, the signaling pathways that connect mitochondrial ATF2 accumulation and cytochrome c release are not well documented. Several melanoma cell lines, B16F10, K1735M2, A375 and A375-R1, were treated with paclitaxel and vemurafenib to test the function of mitochondrial ATF2 and its connection to Bim and voltage-dependent anion channel 1 (VDAC1). Immunoprecipitation analysis was performed to investigate the functional interaction between the involved proteins. VDAC1 oligomerization was evaluated using an EGS-based crosslinking assay. The expression and migration of ATF2 to the mitochondria accounted for paclitaxel stimuli and acquired resistance to BRAF inhibitors. Mitochondrial ATF2 facilitated Bim stabilization through the inhibition of its degradation by the proteasome, thereby promoting cytochrome c release and inducing apoptosis in B16F10 and A375 cells. Studies using B16F10 and A375 cells genetically modified for ATF2 indicated that mitochondrial ATF2 was able to dissociate Bim from the Mcl-1/Bim complex to trigger VDAC1 oligomerization. Immunoprecipitation analysis revealed that Bim interacts with VDAC1, and this interaction was remarkably enhanced during apoptosis. These results reveal that mitochondrial ATF2 is associated with the induction of apoptosis and BRAF inhibitor resistance through Bim activation, which might suggest potential novel therapies for the targeted induction of apoptosis in melanoma therapy.

Role of annexin a5 on mitochondria-dependent apoptosis induced by tetramethoxystilbene in human breast cancer cells.

We have previously shown that 2,4,3′,5′-tetramethoxystilbene (TMS), a trans-stilbene analogue, induces apoptosis in human cancer cells. However, the detailed mechanisms of mitochondria-dependent apoptosis induced by TMS are not fully understood. In the present study, the possible roles of annexin A5 in TMS-mediated apoptosis were investigated in MCF7 human breast cancer cells. Quantitative real-time PCR analysis and Western blot analysis showed that the expression of annexin A5 was strongly increased in TMS-treated cells. TMS caused a strong translocation of annexin A5 from cytosol into mitochondria. Confocal laser scanning microscopic analysis clearly showed that TMS induced translocation of annexin A5 into mitochondria. TMS increased the expression and oligomerization of voltage-dependent anion channel (VDAC) 1, which may promote mitochondria-dependent apoptosis through disruption of mitochondrial membrane potential. When cells were treated with TMS, the levels of Bax, and Bak as well as annexin A5 were strongly enhanced. Moreover, we found that the cytosolic release of apoptogenic factors such as cytochrome c, or apoptosis-inducing factor (AIF) in mitochondria was markedly increased. Annexin A5 depletion by siRNA led to decreased proapoptotic factors such as Bax, Bak, and annexin A5. Taken together, our results indicate that annexin A5 may play an important role in TMS-mediated mitochondrial apoptosis through the regulation of proapoptotic proteins and VDAC1 expression.