VDAC in Retinal Health and Disease

The retina, a tissue of the central nervous system, is vital for vision as its photoreceptors capture light and transform it into electrical signals, which are further processed before they are sent to the brain to be interpreted as images. The retina is unique in that it is continuously exposed to light and has the highest metabolic rate and demand for energy amongst all the tissues in the body. Consequently, the retina is very susceptible to oxidative stress. VDAC, a pore in the outer membrane of mitochondria, shuttles metabolites between mitochondria and the cytosol and normally protects cells from oxidative damage, but when a cell's integrity is greatly compromised it initiates cell death. There are three isoforms of VDAC, and existing evidence indicates that all three are expressed in the retina. However, their precise localization and function in each cell type is unknown. It appears that most retinal cells express substantial amounts of VDAC2 and VDAC3, presumably to protect them from oxidative stress. Photoreceptors express VDAC2, HK2, and PKM2-key proteins in the Warburg pathway that also protect these cells. Consistent with its role in initiating cell death, VDAC is overexpressed in the retinal degenerative diseases retinitis pigmentosa, age related macular degeneration (AMD), and glaucoma. Treatment with antioxidants or inhibiting VDAC oligomerization reduced its expression and improved cell survival. Thus, VDAC may be a promising therapeutic candidate for the treatment of these diseases.

Bombyx mori voltage-dependent anion-selective channel induces programmed cell death to defend against Bombyx mori nucleopolyhedrovirus infection

BACKGROUND

Voltage-dependent anion-selective channels (VDACs) serve as pore proteins within the mitochondrial membrane, aiding in the regulation of cell life and cell death. Although the occurrence of cell death is crucial for defense against virus infection, the function played by VDAC in Bombyx mori, in response to the influence of Bombyx mori nucleopolyhedrovirus (BmNPV), remains unclear.

RESULTS

BmVDAC was found to be relatively highly expressed both during embryonic development, and in the Malpighian tubule and midgut. Additionally, the expression levels of BmVDAC were found to be different among silkworm strains with varying levels of resistance to BmNPV, strongly suggesting a connection between BmVDAC and virus infection. To gain further insight into the function of BmVDAC in BmNPV, we employed RNA interference (RNAi) to silence and overexpress it by pIZT/V5-His-mCherry. The results revealed that BmVDAC is instrumental in developing the resistance of host cells to BmNPV infection in BmN cell-line cells, which was further validated as likely to be associated with initiating programmed cell death (PCD). Furthermore, we evaluated the function of BmVDAC in another insect, Spodoptera exigua. Knockdown of the BmVDAC homolog in S. exigua, SeVDAC, made the larvae more sensitive to BmNPV.

CONCLUSION

We have substantiated the pivotal role of BmVDAC in conferring resistance against BmNPV infection, primarily associated with the initiation of PCD. The findings of this study shine new light on the molecular mechanisms governing the silkworm's response to BmNPV infection, thereby supporting innovative approaches for pest biocontrol. © 2024 Society of Chemical Industry.

The Promoting Role of HK II in Tumor Development and the Research Progress of Its Inhibitors

Increased glycolysis is a key characteristic of malignant cells that contributes to their high proliferation rates and ability to develop drug resistance. The glycolysis rate-limiting enzyme hexokinase II (HK II) is overexpressed in most tumor cells and significantly affects tumor development. This paper examines the structure of HK II and the specific biological factors that influence its role in tumor development, as well as the potential of HK II inhibitors in antitumor therapy. Furthermore, we identify and discuss the inhibitors of HK II that have been reported in the literature.

Combining nano-differential scanning fluorimetry and microscale thermophoresis to investigate VDAC1 interaction with small molecules

The mitochondrial voltage-dependent anion channel 1 (VDAC1) plays a central role in metabolism and apoptosis, which makes it a promising therapeutic target. Nevertheless, molecular mechanisms governing VDAC1 functioning remain unclear. Small-molecule ligands specifically interacting with the channel provide an attractive way of exploring its structure-function relationships and can possibly be used as founding stones for future drug-candidates. While around 30 VDAC1 ligands have been identified over the years, various techniques have been used by research teams, making a fair and direct comparison between compounds impossible. To tackle this issue, we performed ligand-binding assays on a representative set of seventeen known VDAC1 ligands using nano-differential scanning fluorimetry and microscale thermophoresis. While all the compounds have been confirmed as VDAC1 ligands by at least one method, combining both technologies lead to the selection of four molecules (cannabidiol, curcumin, DIDS and VBIT4) as chemical starting points for future design of VDAC1 selective ligands.

Hexokinase dissociation from mitochondria promotes oligomerization of VDAC that facilitates NLRP3 inflammasome assembly and activation

NLRP3 inflammasome activation is a highly regulated process for controlling secretion of the potent inflammatory cytokines IL-1β and IL-18 that are essential during bacterial infection, sterile inflammation, and disease, including colitis, diabetes, Alzheimer's disease, and atherosclerosis. Diverse stimuli activate the NLRP3 inflammasome, and unifying upstream signals has been challenging to identify. Here, we report that a common upstream step in NLRP3 inflammasome activation is the dissociation of the glycolytic enzyme hexokinase 2 from the voltage-dependent anion channel (VDAC) in the outer membrane of mitochondria. Hexokinase 2 dissociation from VDAC triggers activation of inositol triphosphate receptors, leading to release of calcium from the ER, which is taken up by mitochondria. This influx of calcium into mitochondria leads to oligomerization of VDAC, which is known to form a macromolecule-sized pore in the outer membranes of mitochondria that allows proteins and mitochondrial DNA (mtDNA), often associated with apoptosis and inflammation, respectively, to exit the mitochondria. We observe that VDAC oligomers aggregate with NLRP3 during initial assembly of the multiprotein oligomeric NLRP3 inflammasome complex. We also find that mtDNA is necessary for NLRP3 association with VDAC oligomers. These data, together with other recent work, help to paint a more complete picture of the pathway leading to NLRP3 inflammasome activation.

Apoptotic proteins with non-apoptotic activity: expression and function in cancer

Apoptosis is a process of programmed cell death in which a cell commits suicide while maintaining the integrity and architecture of the tissue as a whole. Apoptosis involves activation of one of two major pathways: the extrinsic pathway, where extracellular pro-apoptotic signals, transduced through plasma membrane death receptors, activate a caspase cascade leading to apoptosis. The second, the intrinsic apoptotic pathway, where damaged DNA, oxidative stress, or chemicals, induce the release of pro-apoptotic proteins from the mitochondria, leading to the activation of caspase-dependent and independent apoptosis. However, it has recently become apparent that proteins involved in apoptosis also exhibit non-cell death-related physiological functions that are related to the cell cycle, differentiation, metabolism, inflammation or immunity. Such non-conventional activities were predominantly reported in non-cancer cells although, recently, such a dual function for pro-apoptotic proteins has also been reported in cancers where they are overexpressed. Interestingly, some apoptotic proteins translocate to the nucleus in order to perform a non-apoptotic function. In this review, we summarize the unconventional roles of the apoptotic proteins from a functional perspective, while focusing on two mitochondrial proteins: VDAC1 and SMAC/Diablo. Despite having pro-apoptotic functions, these proteins are overexpressed in cancers and this apparent paradox and the associated pathophysiological implications will be discussed. We will also present possible mechanisms underlying the switch from apoptotic to non-apoptotic activities although a deeper investigation into the process awaits further study.

Pro-Apoptotic and Anti-Cancer Activity of the Vernonanthura Nudiflora Hydroethanolic Extract

The mitochondrial voltage-dependent anion channel 1 (VDAC1) protein is involved in several essential cancer hallmarks, including energy and metabolism reprogramming and apoptotic cell death evasion. In this study, we demonstrated the ability of hydroethanolic extracts from three different plants, Vernonanthura nudiflora (Vern), Baccharis trimera (Bac), and Plantago major (Pla), to induce cell death. We focused on the most active Vern extract. We demonstrated that it activates multiple pathways that lead to impaired cell energy and metabolism homeostasis, elevated ROS production, increased intracellular Ca²⁺, and mitochondria-mediated apoptosis. The massive cell death generated by this plant extract's active compounds involves the induction of VDAC1 overexpression and oligomerization and, thereby, apoptosis. Gas chromatography of the hydroethanolic plant extract identified dozens of compounds, including phytol and ethyl linoleate, with the former producing similar effects as the Vern hydroethanolic extract but at 10-fold higher concentrations than those found in the extract. In a xenograft glioblastoma mouse model, both the Vern extract and phytol strongly inhibited tumor growth and cell proliferation and induced massive tumor cell death, including of cancer stem cells, inhibiting angiogenesis and modulating the tumor microenvironment. Taken together, the multiple effects of Vern extract make it a promising potential cancer therapeutic.

Site-specific ubiquitination of VDAC1 restricts its oligomerization and mitochondrial DNA release in liver fibrosis

Mitochondrial DNA (mtDNA) released through protein oligomers, such as voltage-dependent anion channel 1 (VDAC1), triggers innate immune activation and thus contributes to liver fibrosis. Here, we investigated the role of Parkin, an important regulator of mitochondria, and its regulation of VDAC1-mediated mtDNA release in liver fibrosis. The circulating mitochondrial DNA (mtDNA) and protein levels of liver Parkin and VDAC1 were upregulated in patients with liver fibrosis. A 4-week CCl₄ challenge induced release of mtDNA, activation of STING signaling, a decline in autophagy, and apoptosis in mouse livers, and the knockout of Parkin aggravated these effects. In addition, Parkin reduced mtDNA release and prevented VDAC1 oligomerization in a manner dependent on its E3 activity in hepatocytes. We found that site-specific ubiquitination of VDAC1 at lysine 53 by Parkin interrupted VDAC1 oligomerization and prevented mtDNA release into the cytoplasm under stress. The ubiquitination-defective VDAC1 K53R mutant predominantly formed oligomers that resisted suppression by Parkin. Hepatocytes expressing VDAC1 K53R exhibited mtDNA release and thus activated the STING signaling pathway in hepatic stellate cells, and this effect could not be abolished by Parkin. We propose that the ubiquitination of VDAC1 at a specific site by Parkin confers protection against liver fibrosis by interrupting VDAC1 oligomerization and mtDNA release.

Balancing life and death: BCL-2 family members at diverse ER-mitochondrial contact sites

The outer mitochondrial membrane is a busy place. One essential activity for cellular survival is the regulation of membrane integrity by the BCL-2 family of proteins. Another critical facet of the outer mitochondrial membrane is its close approximation with the endoplasmic reticulum. These mitochondrial-associated membranes (MAMs) occupy a significant fraction of the mitochondrial surface and serve as key signaling hubs for multiple cellular processes. Each of these pathways may be considered as forming their own specialized MAM subtype. Interestingly, like membrane permeabilization, most of these pathways play critical roles in regulating cellular survival and death. Recently, the pro-apoptotic BCL-2 family member BOK has been found within MAMs where it plays important roles in their structure and function. This has led to a greater appreciation that multiple BCL-2 family proteins, which are known to participate in numerous functions throughout the cell, also have roles within MAMs. In this review, we evaluate several MAM subsets, their role in cellular homeostasis, and the contribution of BCL-2 family members to their functions.

The Potential Role of Voltage-Dependent Anion Channel in the Treatment of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease second only to Alzheimer’s disease in terms of prevalence. Previous studies have indicated that the occurrence and progression of PD are associated with mitochondrial dysfunction. Mitochondrial dysfunction is one of the most important causes for apoptosis of dopaminergic neurons. Therefore, maintaining the stability of mitochondrial functioning is a potential strategy in the treatment of PD. Voltage-dependent anion channel (VDAC) is the main component in the outer mitochondrial membrane, and it participates in a variety of biological processes. In this review, we focus on the potential roles of VDACs in the treatment of PD. We found that VDACs are involved in PD by regulating apoptosis, autophagy, and ferroptosis. VDAC1 oligomerization, VDACs ubiquitination, regulation of mitochondrial permeability transition pore (mPTP) by VDACs, and interaction between VDACs and α-synuclein (α-syn) are all promising methods for the treatment of PD. We proposed that inhibition of VDAC1 oligomerization and promotion of VDAC1 ubiquitination as an effective approach for the treatment of PD. Previous studies have proven that the expression of VDAC1 has a significant change in PD models. The expression levels of VDAC1 are decreased in the substantia nigra (SN) of patients suffering from PD compared with the control group consisting of normal individuals by using bioinformatics tools. VDAC2 is involved in PD mainly through the regulation of apoptosis. VDAC3 may have a similar function to VDAC1. It can be concluded that the functional roles of VDACs contribute to the therapeutic strategy of PD.

How Do Hexokinases Inhibit Receptor-Mediated Apoptosis?

Simple Summary

In multicellular animals, cells autonomously respond to lethal stress by inducing cell death programs. The most common regulated cell death is apoptosis. Cells protect their neighbors from damage by their cell contents or infection through this process. Apoptosis can occur as a result of intrinsic stress or induced by surface receptors, for example, by immune cells. In most cases, receptor-mediated apoptosis also requires the intrinsic signaling pathway. Intrinsic apoptosis is controlled by proteins of the B-cell lymphoma 2 (BCL-2) family. Pro-apoptotic BCL-2 proteins are inhibited by retrotranslocation from the mitochondria into the cytosol until the cell commits to apoptosis. Increasingly, discoveries show that BCL-2 proteins are regulated by proteins that are not themselves members of the BCL-2 family. Here, we discuss the selective inhibition of the link between death receptors activation and intrinsic apoptosis by hexokinases. These enzymes funnel glucose into the cellular metabolism. Independently, hexokinases retrotranslocate BCL-2 proteins and thereby protect cells from receptor-mediated apoptosis.

Abstract

The regulated cell death apoptosis enables redundant or compromised cells in ontogeny and homeostasis to remove themselves receptor-dependent after extrinsic signaling or after internal stress by BCL-2 proteins on the outer mitochondrial membrane (OMM). Mitochondrial BCL-2 proteins are also often needed for receptor-mediated signaling in apoptosis. Then, the truncated BH3-only protein BID (tBID) blocks retrotranslocation of the pro-apoptotic BCL-2 proteins BAX and BAK from the mitochondria into the cytosol. BAX and BAK in turn permeabilize the OMM. Although the BCL-2 proteins are controlled by a complex regulatory network, a specific mechanism for the inhibition of tBID remained unknown. Curiously, it was suggested that hexokinases, which channel glucose into the metabolism, have an intriguing function in the regulation of apoptosis. Recent analysis of transient hexokinase interactions with BAX revealed its participation in the inhibition of BAX and also BAK by retrotranslocation from mitochondria to the cytosol. In contrast to general apoptosis inhibition by anti-apoptotic BCL-2 proteins, hexokinase I and hexokinase 2 specifically inhibit tBID and thus the mitochondrial apoptosis pathway in response to death receptor signaling. Mitochondrial hexokinase localization and BH3 binding of cytosolic hexokinase domains are prerequisites for protection against receptor-mediated cell death, whereas glucose metabolism is not. This mechanism protects cells from apoptosis induced by cytotoxic T cells.

Voltage-Dependent Anion Selective Channel 3: Unraveling Structural and Functional Features of the Least Known Porin Isoform

Voltage-dependent anion-selective channels (VDAC) are pore-forming proteins located in the outer mitochondrial membrane. Three isoforms are encoded by separate genes in mammals (VDAC1-3). These proteins play a crucial role in the cell, forming the primary interface between mitochondrial and cellular metabolisms. Research on the role of VDACs in the cell is a rapidly growing field, but the function of VDAC3 remains elusive. The high-sequence similarity between isoforms suggests a similar pore-forming structure. Electrophysiological analyzes revealed that VDAC3 works as a channel; however, its gating and regulation remain debated. A comparison between VDAC3 and VDAC1-2 underlines the presence of a higher number of cysteines in both isoforms 2 and 3. Recent mass spectrometry data demonstrated that the redox state of VDAC3 cysteines is evolutionarily conserved. Accordingly, these residues were always detected as totally reduced or partially oxidized, thus susceptible to disulfide exchange. The deletion of selected cysteines significantly influences the function of the channel. Some cysteine mutants of VDAC3 exhibited distinct kinetic behavior, conductance values and voltage dependence, suggesting that channel activity can be modulated by cysteine reduction/oxidation. These properties point to VDAC3 as a possible marker of redox signaling in the mitochondrial intermembrane space. Here, we summarize our current knowledge about VDAC3 predicted structure, physiological role and regulation, and possible future directions in this research field.

The Molecular Mechanism of Human Voltage-Dependent Anion Channel 1 Blockade by the Metallofullerenol Gd@C82(OH)22: An In Silico Study

The endohedral metallofullerenol Gd@C₈₂(OH)₂₂ has been identified as a possible antineoplastic agent that can inhibit both the growth and metastasis of cancer cells. Despite these potentially important effects, our understanding of the interactions between Gd@C₈₂(OH)₂₂ and biomacromolecules remains incomplete. Here, we study the interaction between Gd@C₈₂(OH)₂₂ and the human voltage-dependent anion channel 1 (hVDAC1), the most abundant porin embedded in the mitochondrial outer membrane (MOM), and a potential druggable target for novel anticancer therapeutics. Using in silico approaches, we observe that Gd@C₈₂(OH)₂₂ molecules can permeate and form stable interactions with the pore of hVDAC1. Further, this penetration can occur from either side of the MOM to elicit blockage of the pore. The binding between Gd@C₈₂(OH)₂₂ and hVDAC1 is largely driven by long-range electrostatic interactions. Analysis of the binding free energies indicates that it is thermodynamically more favorable for Gd@C₈₂(OH)₂₂ to bind to the hVDAC1 pore when it enters the channel from inside the membrane rather than from the cytoplasmic side of the protein. Multiple factors contribute to the preferential penetration, including the surface electrostatic landscape of hVDAC1 and the unique physicochemical properties of Gd@C₈₂(OH)₂₂. Our findings provide insights into the potential molecular interactions of macromolecular biological systems with the Gd@C₈₂(OH)₂₂ nanodrug.

Coronavirus Infection-Associated Cell Death Signaling and Potential Therapeutic Targets

COVID-19 is the name of the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection that occurred in 2019. The virus-host-specific interactions, molecular targets on host cell deaths, and the involved signaling are crucial issues, which become potential targets for treatment. Spike protein, angiotensin-converting enzyme 2 (ACE2), cathepsin L-cysteine peptidase, transmembrane protease serine 2 (TMPRSS2), nonstructural protein 1 (Nsp1), open reading frame 7a (ORF7a), viral main protease (3C-like protease (3CLpro) or Mpro), RNA dependent RNA polymerase (RdRp) (Nsp12), non-structural protein 13 (Nsp13) helicase, and papain-like proteinase (PLpro) are molecules associated with SARS-CoV infection and propagation. SARS-CoV-2 can induce host cell death via five kinds of regulated cell death, i.e., apoptosis, necroptosis, pyroptosis, autophagy, and PANoptosis. The mechanisms of these cell deaths are well established and can be disrupted by synthetic small molecules or natural products. There are a variety of compounds proven to play roles in the cell death inhibition, such as pan-caspase inhibitor (z-VAD-fmk) for apoptosis, necrostatin-1 for necroptosis, MCC950, a potent and specific inhibitor of the NLRP3 inflammasome in pyroptosis, and chloroquine/hydroxychloroquine, which can mitigate the corresponding cell death pathways. However, NF-κB signaling is another critical anti-apoptotic or survival route mediated by SARS-CoV-2. Such signaling promotes viral survival, proliferation, and inflammation by inducing the expression of apoptosis inhibitors such as Bcl-2 and XIAP, as well as cytokines, e.g., TNF. As a result, tiny natural compounds functioning as proteasome inhibitors such as celastrol and curcumin can be used to modify NF-κB signaling, providing a responsible method for treating SARS-CoV-2-infected patients. The natural constituents that aid in inhibiting viral infection, progression, and amplification of coronaviruses are also emphasized, which are in the groups of alkaloids, flavonoids, terpenoids, diarylheptanoids, and anthraquinones. Natural constituents derived from medicinal herbs have anti-inflammatory and antiviral properties, as well as inhibitory effects, on the viral life cycle, including viral entry, replication, assembly, and release of COVID-19 virions. The phytochemicals contain a high potential for COVID-19 treatment. As a result, SARS-CoV-2-infected cell death processes and signaling might be of high efficacy for therapeutic targeting effects and yielding encouraging outcomes.

VDACs Post-Translational Modifications Discovery by Mass Spectrometry: Impact on Their Hub Function

VDAC (voltage-dependent anion selective channel) proteins, also known as mitochondrial porins, are the most abundant proteins of the outer mitochondrial membrane (OMM), where they play a vital role in various cellular processes, in the regulation of metabolism, and in survival pathways. There is increasing consensus about their function as a cellular hub, connecting bioenergetics functions to the rest of the cell. The structural characterization of VDACs presents challenging issues due to their very high hydrophobicity, low solubility, the difficulty to separate them from other mitochondrial proteins of similar hydrophobicity and the practical impossibility to isolate each single isoform. Consequently, it is necessary to analyze them as components of a relatively complex mixture. Due to the experimental difficulties in their structural characterization, post-translational modifications (PTMs) of VDAC proteins represent a little explored field. Only in recent years, the increasing number of tools aimed at identifying and quantifying PTMs has allowed to increase our knowledge in this field and in the mechanisms that regulate functions and interactions of mitochondrial porins. In particular, the development of nano-reversed phase ultra-high performance liquid chromatography (nanoRP-UHPLC) and ultra-sensitive high-resolution mass spectrometry (HRMS) methods has played a key role in this field. The findings obtained on VDAC PTMs using such methodologies, which permitted an in-depth characterization of these very hydrophobic trans-membrane pore proteins, are summarized in this review.

Adverse Effects of Metformin From Diabetes to COVID-19, Cancer, Neurodegenerative Diseases, and Aging: Is VDAC1 a Common Target?

Metformin has been used for treating diabetes mellitus since the late 1950s. In addition to its antihyperglycemic activity, it was shown to be a potential drug candidate for treating a range of other diseases that include various cancers, cardiovascular diseases, diabetic kidney disease, neurodegenerative diseases, renal diseases, obesity, inflammation, COVID-19 in diabetic patients, and aging. In this review, we focus on the important aspects of mitochondrial dysfunction in energy metabolism and cell death with their gatekeeper VDAC1 (voltage-dependent anion channel 1) as a possible metformin target, and summarize metformin’s effects in several diseases and gut microbiota. We question how the same drug can act on diseases with opposite characteristics, such as increasing apoptotic cell death in cancer, while inhibiting it in neurodegenerative diseases. Interestingly, metformin’s adverse effects in many diseases all show VDAC1 involvement, suggesting that it is a common factor in metformin-affecting diseases. The findings that metformin has an opposite effect on various diseases are consistent with the fact that VDAC1 controls cell life and death, supporting the idea that it is a target for metformin.

Cellular Interactome of Mitochondrial Voltage-Dependent Anion Channels: Oligomerization and Channel (Mis)Regulation

Voltage-dependent anion channels (VDACs) of the outer mitochondrial membrane are known conventionally as metabolite flux proteins. However, research findings in the past decade have revealed the multifaceted regulatory roles of VDACs, from governing cellular physiology and mitochondria-mediated apoptosis to directly regulating debilitating cancers and neurodegenerative diseases. VDACs achieve these diverse functions by establishing isoform-dependent stereospecific interactomes in the cell with the cytosolic constituents and endoplasmic reticulum complexes, and the machinery of the mitochondrial compartments. VDACs are now increasingly recognized as regulatory hubs of the cell. Not surprisingly, even the transient misregulation of VDACs results directly in mitochondrial dysfunction. Additionally, human VDACs are now implicated in interaction with aggregation-prone cytosolic proteins, including Aβ, tau, and α-synuclein, contributing directly to the onset of Alzheimer's and Parkinson's diseases. Deducing the interaction dynamics and mechanisms can lead to VDAC-targeted peptide-based therapeutics that can alleviate neurodegenerative states. This review succinctly presents the latest findings of the VDAC interactome, and the mode(s) of VDAC-dependent regulation of biochemical physiology. We also discuss the relevance of VDACs in pathophysiological states and aggregation-associated diseases and address how VDACs will facilitate the development of next-generation precision medicines.

Enhancing the Cell-Free Expression of Native Membrane Proteins by In Silico Optimization of the Coding Sequence-An Experimental Study of the Human Voltage-Dependent Anion Channel

Membrane proteins are involved in many aspects of cellular biology; for example, they regulate how cells interact with their environment, so such proteins are important drug targets. The rapid advancement in the field of immune effector cell therapy has been expanding the horizons of synthetic membrane receptors in the areas of cell-based immunotherapy and cellular medicine. However, the investigation of membrane proteins, which are key constituents of cells, is hampered by the difficulty and complexity of their in vitro synthesis, which is of unpredictable yield. Cell-free synthesis is herein employed to unravel the impact of the expression construct on gene transcription and translation, without the complex regulatory mechanisms of cellular systems. Through the systematic design of plasmids in the immediacy of the start of the target gene, it was possible to identify translation initiation and the conformation of mRNA as the main factors governing the cell-free expression efficiency of the human voltage-dependent anion channel (VDAC), which is a relevant membrane protein in drug-based therapy. A simple translation initiation model was developed to quantitatively assess the expression potential for the designed constructs. A scoring function that quantifies the feasibility of the formation of the translation initiation complex through the ribosome–mRNA hybridization energy and the accessibility of the mRNA segment binding to the ribosome is proposed. The scoring function enables one to optimize plasmid sequences and semi-quantitatively predict protein expression efficiencies. This scoring function is publicly available as webservice XenoExpressO at University of Vienna, Austria.

The impact of Zika virus exposure on the placental proteomic profile

Zika virus (ZIKV) infection has caused severe unexpected clinical outcomes in neonates and adults during the recent outbreak in Latin America, particularly in Brazil. Congenital malformations associated with ZIKV have been frequently reported; nevertheless, the mechanism of vertical transmission and the involvement of placental cells remains unclear. In this study, we applied quantitative proteomics analysis in a floating explant model of chorionic villi of human placental tissues incubated with ZIKV and with ZIKV pre-adsorbed with anti-ZIKV envelope protein. Proteomic data are available via ProteomeXchange with identifier PXD025764. Altered levels of proteins were involved in cell proliferation, apoptosis, inflammatory processes, and the integrin-cytoskeleton complex. Antibody-opsonized ZIKV particles differentially modulated the pattern of protein expression in placental cells; this phenomenon may play a pivotal role in determining the course of infection and the role of mixed infections. The expression of specific proteins was also evaluated by immunoperoxidase assays. These data fill gaps in our understanding of early events after ZIKV placental exposure and help identify infection control targets.

Advances in Intracellular Calcium Signaling Reveal Untapped Targets for Cancer Therapy

Intracellular Ca2+ distribution is a tightly regulated process. Numerous Ca2+ chelating, storage, and transport mechanisms are required to maintain normal cellular physiology. Ca2+-binding proteins, mainly calmodulin and calbindins, sequester free intracellular Ca2+ ions and apportion or transport them to signaling hubs needing the cations. Ca2+ channels, ATP-driven pumps, and exchangers assist the binding proteins in transferring the ions to and from appropriate cellular compartments. Some, such as the endoplasmic reticulum, mitochondria, and lysosomes, act as Ca2+ repositories. Cellular Ca2+ homeostasis is inefficient without the active contribution of these organelles. Moreover, certain key cellular processes also rely on inter-organellar Ca2+ signaling. This review attempts to encapsulate the structure, function, and regulation of major intracellular Ca2+ buffers, sensors, channels, and signaling molecules before highlighting how cancer cells manipulate them to survive and thrive. The spotlight is then shifted to the slow pace of translating such research findings into anticancer therapeutics. We use the PubMed database to highlight current clinical studies that target intracellular Ca2+ signaling. Drug repurposing and improving the delivery of small molecule therapeutics are further discussed as promising strategies for speeding therapeutic development in this area.

Mitochondrial Voltage-Dependent Anion Channel 1-Hexokinase-II Complex-Targeted Strategy for Melanoma Inhibition Using Designed Multiblock Peptide Amphiphiles

Targeted therapies of melanoma are of urgent need considering the resistance of this aggressive type of cancer to chemotherapeutics. The voltage-dependent anion channel 1 (VDAC1)-hexokinase-II (HK-II) complex is an emerging target for novel anticancer therapies based on induced mitochondria-mediated apoptosis. The low cell membrane permeability of the anticancer 12-mer peptide N-Ter (RDVFTKGYGFGL) derived from the N-terminal fragment of the VDAC1 protein impedes the intracellular targeting. Here, novel multiblock VDAC1-derived cationic amphiphilic peptides (referred to as Pal-N-Ter-TAT, pFL-N-Ter-TAT, and Pal-pFL-N-Ter-TAT) are designed with a self-assembly propensity and cell-penetrating properties. The created multiblock amphiphilic peptides of partial α-helical conformations form nanoparticles of ellipsoid-like shapes and are characterized by enhanced cellular uptake. The amphiphilic peptides can target mitochondria and dissociate the VDAC1-HK-II complex at the outer mitochondrial membrane, which result in mitochondria-mediated apoptosis. The latter is associated with decrease of the mitochondrial membrane potential, cytochrome c release, and changes of the expression levels of the apoptotic proteins in A375 melanoma cells. Importantly, the mitochondrial VDAC1-derived amphiphilic peptides have a comparable IC₅₀ value for melanoma cells to a small-molecule drug, sorafenib, which has been previously used in clinical trials for melanoma. These results demonstrate the potential of the designed peptide constructs for efficient melanoma inhibition.

Metabolic Reprogramming: A Friend or Foe to Cancer Therapy?

Drug resistance is a major cause of cancer treatment failure, effectively driven by processes that promote escape from therapy-induced cell death. The mechanisms driving evasion of apoptosis have been widely studied across multiple cancer types, and have facilitated new and exciting therapeutic discoveries with the potential to improve cancer patient care. However, an increasing understanding of the crosstalk between cancer hallmarks has highlighted the complexity of the mechanisms of drug resistance, co-opting pathways outside of the canonical "cell death" machinery to facilitate cell survival in the face of cytotoxic stress. Rewiring of cellular metabolism is vital to drive and support increased proliferative demands in cancer cells, and recent discoveries in the field of cancer metabolism have uncovered a novel role for these programs in facilitating drug resistance. As a key organelle in both metabolic and apoptotic homeostasis, the mitochondria are at the forefront of these mechanisms of resistance, coordinating crosstalk in the event of cellular stress, and promoting cellular survival. Importantly, the appreciation of this role metabolism plays in the cytotoxic response to therapy, and the ability to profile metabolic adaptions in response to treatment, has encouraged new avenues of investigation into the potential of exploiting metabolic addictions to improve therapeutic efficacy and overcome drug resistance in cancer. Here, we review the role cancer metabolism can play in mediating drug resistance, and the exciting opportunities presented by imposed metabolic vulnerabilities.

Cell Death in Coronavirus Infections: Uncovering Its Role during COVID-19

Cell death mechanisms are crucial to maintain an appropriate environment for the functionality of healthy cells. However, during viral infections, dysregulation of these processes can be present and can participate in the pathogenetic mechanisms of the disease. In this review, we describe some features of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and some immunopathogenic mechanisms characterizing the present coronavirus disease (COVID-19). Lymphopenia and monocytopenia are important contributors to COVID-19 immunopathogenesis. The fine mechanisms underlying these phenomena are still unknown, and several hypotheses have been raised, some of which assign a role to cell death as far as the reduction of specific types of immune cells is concerned. Thus, we discuss three major pathways such as apoptosis, necroptosis, and pyroptosis, and suggest that all of them likely occur simultaneously in COVID-19 patients. We describe that SARS-CoV-2 can have both a direct and an indirect role in inducing cell death. Indeed, on the one hand, cell death can be caused by the virus entry into cells, on the other, the excessive concentration of cytokines and chemokines, a process that is known as a COVID-19-related cytokine storm, exerts deleterious effects on circulating immune cells. However, the overall knowledge of these mechanisms is still scarce and further studies are needed to delineate new therapeutic strategies.

Structural basis of complex formation between mitochondrial anion channel VDAC1 and Hexokinase-II

Complex formation between hexokinase-II (HKII) and the mitochondrial VDAC1 is crucial to cell growth and survival. We hypothesize that HKII first inserts into the outer membrane of mitochondria (OMM) and then interacts with VDAC1 on the cytosolic leaflet of OMM to form a binary complex. To systematically investigate this process, we devised a hybrid approach. First, we describe membrane binding of HKII with molecular dynamics (MD) simulations employing a membrane mimetic model with enhanced lipid diffusion capturing membrane insertion of its H-anchor. The insertion depth of the H-anchor was then used to derive positional restraints in subsequent millisecond-scale Brownian dynamics (BD) simulations to preserve the membrane-bound pose of HKII during the formation of the HKII/VDAC1 binary complex. Multiple BD-derived structural models for the complex were further refined and their structural stability probed with additional MD simulations, resulting in one stable complex. A major feature in the complex is the partial (not complete) blockade of VDAC1's permeation pathway, a result supported by our comparative electrophysiological measurements of the channel in the presence and absence of HKII. We also show how VDAC1 phosphorylation disrupts HKII binding, a feature that is verified by our electrophysiology recordings and has implications in mitochondria-mediated cell death.

OsUEV1B, an Ubc enzyme variant protein, is required for phosphate homeostasis in rice

Phosphorus is a crucial macronutrient for plant growth and development. The mechanisms for maintaining inorganic phosphate (Pi) homeostasis in rice are not well understood. The ubiquitin-conjugating enzyme variant protein OsUEV1B was previously found to interact with OsUbc13 and mediate lysine63-linked polyubiquitination. In the present study, we found OsUEV1B was specifically inhibited by Pi deficiency, and was localized in the nucleus and cytoplasm. Both osuev1b mutant and OsUEV1B-RNA interference (RNAi) lines displayed serious symptoms of toxicity due to Pi overaccumulation. Some Pi starvation inducible and phosphate transporter genes were upregulated in osuev1b mutant and OsUEV1B-RNAi plants in association with enhanced Pi acquisition, and representative Pi starvation responses, including stimulation of acid phosphatase activity and root hair growth, were also activated in the presence of sufficient Pi. A yeast two-hybrid screen revealed an interaction between OsUEV1B and OsVDAC1, which was confirmed by bimolecular fluorescence complementation and firefly split-luciferase complementation assays. OsVDAC1 encoded a voltage-dependent anion channel protein localized in the mitochondria, and OsUbc13 was shown to interact with OsVDAC1 via yeast two-hybrid and bimolecular fluorescence complementation assays. Under sufficient Pi conditions, similar to osuev1b, a mutation in OsVDAC1 resulted in significantly greater Pi concentrations in the roots and second leaves, improved acid phosphatase activity, and enhanced expression of the Pi starvation inducible and phosphate transporter genes compared with wild-type DongJin, whereas overexpression of OsVDAC1 had the opposite effects. OsUEV1B or OsVDAC1 knockout reduced the mitochondrial membrane potential and adenosine triphosphate levels. Moreover, overexpression of OsVDAC1 in osuev1b partially restored its high Pi concentration to a level between those of osuev1b and DongJin. Our results indicate that OsUEV1B is required for rice phosphate homeostasis.

Intersection between Redox Homeostasis and Autophagy: Valuable Insights into Neurodegeneration

Autophagy, a main degradation pathway for maintaining cellular homeostasis, and redox homeostasis have recently been considered to play protective roles in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Increased levels of reactive oxygen species (ROS) in neurons can induce mitochondrial damage and protein aggregation, thereby resulting in neurodegeneration. Oxidative stress is one of the major activation signals for the induction of autophagy. Upon activation, autophagy can remove ROS, damaged mitochondria, and aggregated proteins from the cells. Thus, autophagy can be an effective strategy to maintain redox homeostasis in the brain. However, the interaction between redox homeostasis and autophagy is not clearly elucidated. In this review, we discuss recent studies on the relationship between redox homeostasis and autophagy associated with neurodegenerative diseases and propose that autophagy induction through pharmacological intervention or genetic activation might be a promising strategy to treat these disorders.

Dynamic Interplay between Copper Toxicity and Mitochondrial Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder, affecting millions of people worldwide, a number expected to exponentially increase in the future since no effective treatments are available so far. AD is characterized by severe cognitive dysfunctions associated with neuronal loss and connection disruption, mainly occurring in specific brain areas such as the hippocampus, cerebral cortex, and amygdala, compromising memory, language, reasoning, and social behavior. Proteomics and redox proteomics are powerful techniques used to identify altered proteins and pathways in AD, providing relevant insights on cellular pathways altered in the disease and defining novel targets exploitable for drug development. Here, we review the main results achieved by both -omics techniques, focusing on the changes occurring in AD mitochondria under oxidative stress and upon copper exposure. Relevant information arises by the comparative analysis of these results, evidencing alterations of common mitochondrial proteins, metabolic cycles, and cascades. Our analysis leads to three shared mitochondrial proteins, playing key roles in metabolism, ATP generation, oxidative stress, and apoptosis. Their potential as targets for development of innovative AD treatments is thus suggested. Despite the relevant efforts, no effective drugs against AD have been reported so far; nonetheless, various compounds targeting mitochondria have been proposed and investigated, reporting promising results.

Bcl-2 Family of Proteins in the Control of Mitochondrial Calcium Signalling: An Old Chap with New Roles

Bcl-2 family proteins are considered as one of the major regulators of apoptosis. Indeed, this family is known to control the mitochondrial outer membrane permeabilization (MOMP): a central step in the mitochondrial pathway of apoptosis. However, in recent years Bcl-2 family members began to emerge as a new class of intracellular calcium (Ca²⁺) regulators. At mitochondria-ER contacts (MERCs) these proteins are able to interact with major Ca²⁺ transporters, thus controlling mitochondrial Ca²⁺ homeostasis and downstream Ca²⁺ signalling pathways. Beyond the regulation of cell survival, this Bcl-2-dependent control over the mitochondrial Ca²⁺ dynamics has far-reaching consequences on the physiology of the cell. Here, we review how the Bcl-2 family of proteins mechanistically regulate mitochondrial Ca²⁺ homeostasis and how this regulation orchestrates cell death/survival decisions as well as the non-apoptotic process of cell migration.

The role of Bcl-2 proteins in modulating neuronal Ca2+ signaling in health and in Alzheimer's disease

The family of B-cell lymphoma-2 (Bcl-2) proteins exerts key functions in cellular health. Bcl-2 primarily acts in mitochondria where it controls the initiation of apoptosis. However, during the last decades, it has become clear that this family of proteins is also involved in controlling intracellular Ca²⁺ signaling, a critical process for the function of most cell types, including neurons. Several anti- and pro-apoptotic Bcl-2 family members are expressed in neurons and impact neuronal function. Importantly, expression levels of neuronal Bcl-2 proteins are affected by age. In this review, we focus on the emerging roles of Bcl-2 proteins in neuronal cells. Specifically, we discuss how their dysregulation contributes to the onset, development, and progression of neurodegeneration in the context of Alzheimer's disease (AD). Aberrant Ca²⁺ signaling plays an important role in the pathogenesis of AD, and we propose that dysregulation of the Bcl-2-Ca²⁺ signaling axis may contribute to the progression of AD and that herein, Bcl-2 may constitute a potential therapeutic target for the treatment of AD.

Metabolic programs define dysfunctional immune responses in severe COVID-19 patients

It is unclear why some SARS-CoV-2 patients readily resolve infection while others develop severe disease. By interrogating metabolic programs of immune cells in severe and recovered coronavirus disease 2019 (COVID-19) patients compared with other viral infections, we identify a unique population of T cells. These T cells express increased Voltage-Dependent Anion Channel 1 (VDAC1), accompanied by gene programs and functional characteristics linked to mitochondrial dysfunction and apoptosis. The percentage of these cells increases in elderly patients and correlates with lymphopenia. Importantly, T cell apoptosis is inhibited in vitro by targeting the oligomerization of VDAC1 or blocking caspase activity. We also observe an expansion of myeloid-derived suppressor cells with unique metabolic phenotypes specific to COVID-19, and their presence distinguishes severe from mild disease. Overall, the identification of these metabolic phenotypes provides insight into the dysfunctional immune response in acutely ill COVID-19 patients and provides a means to predict and track disease severity and/or design metabolic therapeutic regimens.

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T cells with a unique metabolic profile are expanded in acute COVID-19

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These T cells are prone to mitochondrial apoptosis, correlating with lymphopenia

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Metabolically distinct myeloid-derived suppressor cells increase in acute COVID-19

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The presence of these M-MDSCs in acute COVID-19 correlates with disease severity

Selective Host Cell Death by Staphylococcus aureus: A Strategy for Bacterial Persistence

Host cell death programs are fundamental processes that shape cellular homeostasis, embryonic development, and tissue regeneration. Death signaling and downstream host cell responses are not only critical to guide mammalian development, they often act as terminal responses to invading pathogens. Here, we briefly review and contrast how invading pathogens and specifically Staphylococcus aureus manipulate apoptotic, necroptotic, and pyroptotic cell death modes to establish infection. Rather than invading host cells, S. aureus subverts these cells to produce diffusible molecules that cause death of neighboring hematopoietic cells and thus shapes an immune environment conducive to persistence. The exploitation of cell death pathways by S. aureus is yet another virulence strategy that must be juxtaposed to mechanisms of immune evasion, autophagy escape, and tolerance to intracellular killing, and brings us closer to the true portrait of this pathogen for the design of effective therapeutics and intervention strategies.

VDAC1 at the Intersection of Cell Metabolism, Apoptosis, and Diseases

The voltage-dependent anion channel 1 (VDAC1) protein, is an important regulator of mitochondrial function, and serves as a mitochondrial gatekeeper, with responsibility for cellular fate. In addition to control over energy sources and metabolism, the protein also regulates epigenomic elements and apoptosis via mediating the release of apoptotic proteins from the mitochondria. Apoptotic and pathological conditions, as well as certain viruses, induce cell death by inducing VDAC1 overexpression leading to oligomerization, and the formation of a large channel within the VDAC1 homo-oligomer. This then permits the release of pro-apoptotic proteins from the mitochondria and subsequent apoptosis. Mitochondrial DNA can also be released through this channel, which triggers type-Ι interferon responses. VDAC1 also participates in endoplasmic reticulum (ER)-mitochondria cross-talk, and in the regulation of autophagy, and inflammation. Its location in the outer mitochondrial membrane, makes VDAC1 ideally placed to interact with over 100 proteins, and to orchestrate the interaction of mitochondrial and cellular activities through a number of signaling pathways. Here, we provide insights into the multiple functions of VDAC1 and describe its involvement in several diseases, which demonstrate the potential of this protein as a druggable target in a wide variety of pathologies, including cancer.

Pharmacodynamic modeling of synergistic birinapant/paclitaxel interactions in pancreatic cancer cells

Background

For most patients, pancreatic adenocarcinoma responds poorly to treatment, and novel therapeutic approaches are needed. Standard-of-care paclitaxel (PTX), combined with birinapant (BRP), a bivalent mimetic of the apoptosis antagonist SMAC (second mitochondria-derived activator of caspases), exerts synergistic killing of PANC-1 human pancreatic adenocarcinoma cells.

Methods

To investigate potential mechanisms underlying this synergistic pharmacodynamic interaction, data capturing PANC-1 cell growth, apoptosis kinetics, and cell cycle distribution were integrated with high-quality IonStar-generated proteomic data capturing changes in the relative abundance of more than 3300 proteins as the cells responded to the two drugs, alone and combined.

Results

PTX alone (15 nM) elicited dose-dependent G2/M-phase arrest and cellular polyploidy. Combined BRP/PTX (150/15 nM) reduced G2/M by 35% and polyploid cells by 45%, and increased apoptosis by 20%. Whereas BRP or PTX alone produced no change in the pro-apoptotic protein pJNK, and a slight increase in the anti-apoptotic protein Bcl2, the drug combination increased pJNK and decreased Bcl2 significantly compared to the vehicle control. A multi-scale, mechanism-based mathematical model was developed to investigate integrated birinapant/paclitaxel effects on temporal profiles of key proteins involved in kinetics of cell growth, death, and cell cycle distribution.

Conclusions

The model, consistent with the observed reduction in the Bcl2/BAX ratio, suggests that BRP-induced apoptosis of mitotically-arrested cells is a major contributor to the synergy between BRP and PTX. Coupling proteomic and cellular response profiles with multi-scale pharmacodynamic modeling provides a quantitative mechanistic framework for evaluating pharmacodynamically-based drug-drug interactions in combination chemotherapy, and could potentially guide the development of promising drug regimens.

Regulation of Cell Death by Mitochondrial Transport Systems of Calcium and Bcl-2 Proteins

Mitochondria represent the fundamental system for cellular energy metabolism, by not only supplying energy in the form of ATP, but also by affecting physiology and cell death via the regulation of calcium homeostasis and the activity of Bcl-2 proteins. A lot of research has recently been devoted to understanding the interplay between Bcl-2 proteins, the regulation of these interactions within the cell, and how these interactions lead to the changes in calcium homeostasis. However, the role of Bcl-2 proteins in the mediation of mitochondrial calcium homeostasis, and therefore the induction of cell death pathways, remain underestimated and are still not well understood. In this review, we first summarize our knowledge about calcium transport systems in mitochondria, which, when miss-regulated, can induce necrosis. We continue by reviewing and analyzing the functions of Bcl-2 proteins in apoptosis. Finally, we link these two regulatory mechanisms together, exploring the interactions between the mitochondrial Ca2+ transport systems and Bcl-2 proteins, both capable of inducing cell death, with the potential to determine the cell death pathway-either the apoptotic or the necrotic one.

Mitochondrial Oxidative and Nitrosative Stress and Alzheimer Disease

Oxidative and nitrosative stress are widely recognized as critical factors in the pathogenesis and progression of Alzheimer disease (AD) and its earlier stage, amnestic mild cognitive impairment (MCI). A major source of free radicals that lead to oxidative and nitrosative damage is mitochondria. This review paper discusses oxidative and nitrosative stress and markers thereof in the brain, along with redox proteomics, which are techniques that have been pioneered in the Butterfield laboratory. Selected biological alterations in-and oxidative and nitrosative modifications of-mitochondria in AD and MCI and systems of relevance thereof also are presented. The review article concludes with a section on the implications of mitochondrial oxidative and nitrosative stress in MCI and AD with respect to imaging studies in and targeted therapies toward these disorders. Taken together, this review provides support for the notion that brain mitochondrial alterations in AD and MCI are key components of oxidative and nitrosative stress observed in these two disorders, and as such, they provide potentially promising therapeutic targets to slow-and hopefully one day stop-the progression of AD, which is a devastating dementing disorder.

The activating transcription factor 2: an influencer of cancer progression

In contrast to the continuous increase in survival rates for many cancer entities, colorectal cancer (CRC) and pancreatic cancer are predicted to be ranked among the top 3 cancer-related deaths in the European Union by 2025. Especially, fighting metastasis still constitutes an obstacle to be overcome in CRC and pancreatic cancer. As described by Fearon and Vogelstein, the development of CRC is based on sequential mutations leading to the activation of proto-oncogenes and the inactivation of tumour suppressor genes. In pancreatic cancer, genetic alterations also attribute to tumour development and progression. Recent findings have identified new potentially important transcription factors in CRC, among those the activating transcription factor 2 (ATF2). ATF2 is a basic leucine zipper protein and is involved in physiological and developmental processes, as well as in tumorigenesis. The mutation burden of ATF2 in CRC and pancreatic cancer is rather negligible; however, previous studies in other tumours indicated that ATF2 expression level and subcellular localisation impact tumour progression and patient prognosis. In a tissue- and stimulus-dependent manner, ATF2 is activated by upstream kinases, dimerises and induces target gene expression. Dependent on its dimerisation partner, ATF2 homodimers or heterodimers bind to cAMP-response elements or activator protein 1 consensus motifs. Pioneering work has been performed in melanoma in which the dual role of ATF2 is best understood. Even though there is increasing interest in ATF2 recently, only little is known about its involvement in CRC and pancreatic cancer. In this review, we summarise the current understanding of the underestimated ‘cancer gene chameleon’ ATF2 in apoptosis, epithelial-to-mesenchymal transition and microRNA regulation and highlight its functions in CRC and pancreatic cancer. We further provide a novel ATF2 3D structure with key phosphorylation sites and an updated overview of all so-far available mouse models to study ATF2 in vivo.

The mystery of mitochondria-ER contact sites in physiology and pathology: A cancer perspective

Mitochondria-associated membranes (MAM), physical platforms that enable communication between mitochondria and the endoplasmic reticulum (ER), are enriched with many proteins and enzymes involved in several crucial cellular processes, such as calcium (Ca²⁺) homeostasis, lipid synthesis and trafficking, autophagy and reactive oxygen species (ROS) production. Accumulating studies indicate that tumor suppressors and oncogenes are present at these intimate contacts between mitochondria and the ER, where they influence Ca²⁺ flux between mitochondria and the ER or affect lipid homeostasis at MAM, consequently impacting cell metabolism and cell fate. Understanding these fundamental roles of mitochondria-ER contact sites as important domains for tumor suppressors and oncogenes can support the search for new and more precise anticancer therapies. In the present review, we summarize the current understanding of basic MAM biology, composition and function and discuss the possible role of MAM-resident oncogenes and tumor suppressors.

Bcl-2-Protein Family as Modulators of IP3 Receptors and Other Organellar Ca2+ Channels

The pro- and antiapoptotic proteins belonging to the B-cell lymphoma-2 (Bcl-2) family exert a critical control over cell-death processes by enabling or counteracting mitochondrial outer membrane permeabilization. Beyond this mitochondrial function, several Bcl-2 family members have emerged as critical modulators of intracellular Ca²⁺ homeostasis and dynamics, showing proapoptotic and antiapoptotic functions. Bcl-2 family proteins specifically target several intracellular Ca²⁺-transport systems, including organellar Ca²⁺ channels: inositol 1,4,5-trisphosphate receptors (IP₃Rs) and ryanodine receptors (RyRs), Ca²⁺-release channels mediating Ca²⁺ flux from the endoplasmic reticulum, as well as voltage-dependent anion channels (VDACs), which mediate Ca²⁺ flux across the mitochondrial outer membrane into the mitochondria. Although the formation of protein complexes between Bcl-2 proteins and these channels has been extensively studied, a major advance during recent years has been elucidating the complex interaction of Bcl-2 proteins with IP₃Rs. Distinct interaction sites for different Bcl-2 family members were identified in the primary structure of IP₃Rs. The unique molecular profiles of these Bcl-2 proteins may account for their distinct functional outcomes when bound to IP₃Rs. Furthermore, Bcl-2 inhibitors used in cancer therapy may affect IP₃R function as part of their proapoptotic effect and/or as an adverse effect in healthy cells.

The VDAC1-based R-Tf-D-LP4 Peptide as a Potential Treatment for Diabetes Mellitus

Diabetes mellitus is a metabolic disorder approaching epidemic proportions. Non-alcoholic fatty liver disease (NAFLD) regularly coexists with metabolic disorders, including type 2 diabetes, obesity, and cardiovascular disease. Recently, we demonstrated that the voltage-dependent anion channel 1 (VDAC1) is involved in NAFLD. VDAC1 is an outer mitochondria membrane protein that serves as a mitochondrial gatekeeper, controlling metabolic and energy homeostasis, as well as crosstalk between the mitochondria and the rest of the cell. It is also involved in mitochondria-mediated apoptosis. Here, we demonstrate that the VDAC1-based peptide, R-Tf-D-LP4, affects several parameters of a NAFLD mouse model in which administration of streptozotocin (STZ) and high-fat diet 32 (STZ/HFD-32) led to both type 2 diabetes (T2D) and NAFLD phenotypes. We focused on diabetes, showing that R-Tf-D-LP4 peptide treatment of STZ/HFD-32 fed mice restored the elevated blood glucose back to close to normal levels, and increased the number and average size of islets and their insulin content as compared to untreated controls. Similar results were obtained when staining the islets for glucose transporter type 2. In addition, the R-Tf-D-LP4 peptide decreased the elevated glucose levels in a mouse displaying obese, diabetic, and metabolic symptoms due to a mutation in the obese (ob) gene. To explore the cause of the peptide-induced improvement in the endocrine pancreas phenotype, we analyzed the expression levels of the proliferation marker, Ki-67, and found it to be increased in the islets of STZ/HFD-32 fed mice treated with the R-Tf-D-LP4 peptide. Moreover, peptide treatment of STZ/HFD-32 fed mice caused an increase in the expression of β-cell maturation and differentiation PDX1 transcription factor that enhances the expression of the insulin-encoding gene, and is essential for islet development, function, proliferation, and maintenance of glucose homeostasis in the pancreas. This increase occurred mainly in the β-cells, suggesting that the source of their increased number after R-Tf-D-LP4 peptide treatment was most likely due to β-cell proliferation. These results suggest that the VDAC1-based R-Tf-D-LP4 peptide has potential as a treatment for diabetes.

Exosomal transfer of miR-15b-3p enhances tumorigenesis and malignant transformation through the DYNLT1/Caspase-3/Caspase-9 signaling pathway in gastric cancer

Background

Exosomes are essential for tumor growth, metastasis, and are used as novel signaling molecules in targeted therapies. Therefore, exosomal miRNAs can be used in new diagnostic and therapeutic approaches due to their involvement in the development of cancers. However, the detailed biological function, potential molecular mechanism and clinical application of exo-miR-15b-3p in gastric cancer (GC) remains unclear.

Methods

miR-15b-3p mRNA levels in tissues, serum, cells and exosomes were analyzed using qRT-PCR assays. qRT-PCR, immunohistochemical and western blotting analyses were utilized for the determination of DYNLT1 expression. The interrelationship connecting miR-15b-3p with DYNLT1 was verified using Dual-luciferase report, western blotting and qRT-PCR assays. Fluorescent PKH-26 or GFP-Lv-CD63 labeled exosomes, as well as Cy3-miR-15b-3p, were utilized to determine the efficacy of the transfer of exo-miR-15b-3p between BGC-823 and recipient cells. Several in vitro assays and xenograft tumor models were conducted to determine exo-miR-15b-3p impact on GC progression.

Results

This is the first study to confirm high miR-15b-3p expression in GC cell lines, tissues and serum. Exosomes obtained from 108 GC patient serum samples and GC cell-conditioned medium were found to show upregulation of exo-miR-15b-3p, with the area under the ROC curve (AUC) being 0.820 [0.763–0.876], which is superior to the AUC of tissues and serum miR-15b-3p (0.674 [0.600–0.748] and 0.642 [0.499–0.786], respectively). In addition, high exo-miR-15b-3p expression in serum was found to accurately predict worse overall survival. SGC-7901 and GES-1 cells are capable of internalizing BGC-823 cell-derived exosomes, allowing the transfer of miR-15b-3p. Migration, invasion, proliferation and inhibition of apoptosis in vitro and in vivo were enhanced by exo-miR-15b-3p, by restraining DYNLT1, Cleaved Caspase-9 and Caspase-3 expression.

Conclusions

This study identified a previously unknown regulatory pathway, exo-miR-15b-3p/DYNLT1/Caspase-3/Caspase-9, which promotes GC development and GES-1 cell malignant transformation. Therefore, serum exo-miR-15b-3p may be a potential GC diagnosis and prognosis biomarker, which can be used in precise targeted GC therapy.

The Structural Basis for Low Conductance in the Membrane Protein VDAC upon β-NADH Binding and Voltage Gating

The voltage-dependent anion channel (VDAC) forms the primary diffusion pore of the outer mitochondrial membrane. In its apo form, VDAC adopts an open conformation with high conductance. States of lower conductance can be induced by ligand binding or the application of voltage. Here, we clarify at the atomic level how β-NADH binding leads to a low-conductance state and characterize the role of the VDAC N-terminal helix in voltage gating. A high-resolution NMR structure of human VDAC-1 with bound NADH, combined with molecular dynamics simulation show that β-NADH binding reduces the pore conductance sterically without triggering a structural change. Electrophysiology recordings of crosslinked protein variants and NMR relaxation experiments probing different time scales show that increased helix dynamics is present in the open state and that motions of the N-terminal helices are involved in the VDAC voltage gating mechanism.

Cancer-Related Increases and Decreases in Calcium Signaling at the Endoplasmic Reticulum-Mitochondria Interface (MAMs)

Endoplasmic reticulum (ER)-mitochondria regions are specialized subdomains called also mitochondria-associated membranes (MAMs). MAMs allow regulation of lipid synthesis and represent hubs for ion and metabolite signaling. As these two organelles can module both the amplitude and the spatiotemporal patterns of calcium (Ca²⁺) signals, this particular interaction controls several Ca²⁺-dependent pathways well known for their contribution to tumorigenesis, such as metabolism, survival, sensitivity to cell death, and metastasis. Mitochondria-mediated apoptosis arises from mitochondrial Ca²⁺ overload, permeabilization of the mitochondrial outer membrane, and the release of mitochondrial apoptotic factors into the cytosol. Decreases in Ca²⁺ signaling at the ER-mitochondria interface are being studied in depth as failure of apoptotic-dependent cell death is one of the predominant characteristics of cancer cells. However, some recent papers that linked MAMs Ca²⁺ crosstalk-related upregulation to tumor onset and progression have aroused the interest of the scientific community.In this review, we will describe how different MAMs-localized proteins modulate the effectiveness of Ca²⁺-dependent apoptotic stimuli by causing both increases and decreases in the ER-mitochondria interplay and, specifically, by modulating Ca²⁺ signaling.

Effects of ABT-737 combined with irradiation treatment on uterine cervical cancer cells

The aim of the present study was to examine the role of ABT-737, an inhibitor of B-cell lymphoma 2 (Bcl-2), in enhancing the effect of irradiation on uterine cervical cancer. Based on The Cancer Genomic Atlas (TCGA), Bcl-2 mRNA expression was associated with the Tumor-Node-Metastasis stage of cervical cancer. Therefore, it was hypothesized that Bcl-2 inhibition may decrease the progression of cervical cancer. ABT-737 was added to irradiation treatment to evaluate its effectiveness in inhibiting cancer cell progression. SiHa and CaSki cervical cancer cells were selected for in vitro assays. Patients with advanced stage III uterine cancer had slightly increased mRNA expression levels of Bcl-2 compared with patients with stage I cancer, although the difference was not significant. ABT-737 and radiation administration induced a synergistic cytotoxic effect based on the MTT assay and flow cytometry results, where an increase in apoptosis was observed. The apoptotic percentages were significantly increased in the cells treated with a combination of ABT-737 and irradiation. Loss of mitochondrial membrane potential and gain of reactive oxygen species (ROS) were detected by flow cytometry in CaSki and SiHa cells treated with ABT-737 and radiation. Additionally, the protein expression levels of the cleaved forms of poly ADP ribose polymerase and caspase-7 were increased following the combined treatment. In conclusion, ABT-737 and irradiation may induce apoptosis via loss of mitochondrial membrane potential and a ROS-dependent apoptotic pathway in CaSki and SiHa cells. The present study indicates that ABT-737 may be a potential irradiation adjuvant when treating cervical cancer.

A VDAC1-Derived N-Terminal Peptide Inhibits Mutant SOD1-VDAC1 Interactions and Toxicity in the SOD1 Model of ALS

Mutations in superoxide dismutase (SOD1) are the second most common cause of familial amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease caused by the death of motor neurons in the brain and spinal cord. SOD1 neurotoxicity has been attributed to aberrant accumulation of misfolded SOD1, which in its soluble form binds to intracellular organelles, such as mitochondria and ER, disrupting their functions. Here, we demonstrate that mutant SOD1 binds specifically to the N-terminal domain of the voltage-dependent anion channel (VDAC1), an outer mitochondrial membrane protein controlling cell energy, metabolic and survival pathways. Mutant SOD1^G93A and SOD1^G85R, but not wild type SOD1, directly interact with VDAC1 and reduce its channel conductance. No such interaction with N-terminal-truncated VDAC1 occurs. Moreover, a VDAC1-derived N-terminal peptide inhibited mutant SOD1-induced toxicity. Incubation of motor neuron-like NSC-34 cells expressing mutant SOD1 or mouse embryonic stem cell-derived motor neurons with different VDAC1 N-terminal peptides resulted in enhanced cell survival. Taken together, our results establish a direct link between mutant SOD1 toxicity and the VDAC1 N-terminal domain and suggest that VDAC1 N-terminal peptides targeting mutant SOD1 provide potential new therapeutic strategies for ALS.

VDAC1 and the TSPO: Expression, Interactions, and Associated Functions in Health and Disease States

The translocator protein (TSPO), located at the outer mitochondrial membrane (OMM), serves multiple functions and contributes to numerous processes, including cholesterol import, mitochondrial metabolism, apoptosis, cell proliferation, Ca²⁺ signaling, oxidative stress, and inflammation. TSPO forms a complex with the voltage-dependent anion channel (VDAC), a protein that mediates the flux of ions, including Ca²⁺, nucleotides, and metabolites across the OMM, controls metabolism and apoptosis and interacts with many proteins. This review focuses on the two OMM proteins TSPO and VDAC1, addressing their structural interaction and associated functions. TSPO appears to be involved in the generation of reactive oxygen species, proposed to represent the link between TSPO activation and VDAC, thus playing a role in apoptotic cell death. In addition, expression of the two proteins in healthy brains and diseased states is considered, as is the relationship between TSPO and VDAC1 expression. Both proteins are over-expressed in in brains from Alzheimer’s disease patients. Finally, TSPO expression levels were proposed as a biomarker of some neuropathological settings, while TSPO-interacting ligands have been considered as a potential basis for drug development.

High glucose induces apoptosis of HUVECs in a mitochondria-dependent manner by suppressing hexokinase 2 expression

Hyperglycemia in patients with diabetes induces vascular endothelial cell apoptosis and subsequent vasculopathy. The aim of the current study was to investigate the pathological mechanism of hyperglycemia-induced endothelial cell apoptosis and vasculopathy using human umbilical vein endothelial cells. As high glucose-induced apoptosis is caused by elevated mitochondrial permeability-mediated release of mitochondrial cytochrome c, the current study examined voltage-dependent anion channel (VDAC1), the controller of mitochondrial permeability, and its regulators, hexokinase2 (HK2), Bcl-2 and Bax. The current study demonstrated that HK2 may be involved in high glucose-induced cell apoptosis, as HK2 overexpression partially reversed high glucose-induced downregulation of mitochondrial/cellular HK2 and Bcl-2 as well as upregulation of mitochondrial Bax. These results suggest that HK2 overexpression partially reversed the reduced binding of HK2 and Bcl-2 and the enhanced binding of Bax to VDAC1, which reduced the high mitochondrial permeability observed under high-glucose conditions. Furthermore, high glucose reduced HK2 transcription via down-regulation of the HK2 transcriptional factor, peroxisome proliferator activated receptor γ (PPARγ). Taken together, these results suggest that PPARγ/HK2 may be novel targets for the prevention of diabetic vasculopathy.

Strategies for targeting energy metabolism in Kirsten rat sarcoma viral oncogene homolog -mutant colorectal cancer

Alterations in cellular energy metabolism play critical roles in colorectal cancer (CRC). These alterations, which correlate to KRAS mutations, have been identified as energy metabolism signatures. This review summarizes the relationship between colorectal tumors associated with mutated KRAS and energy metabolism, especially for the deregulated energy metabolism that affects tumor cell proliferation, invasion, and migration. Furthermore, this review will concentrate on the role of metabolic genes, factors and signaling pathways, which are coupled with the primary energy source connected with the KRAS mutation that induces metabolic alterations. Strategies for targeting energy metabolism in mutated KRAS CRC are also introduced. In conclusion, deregulated energy metabolism has a close relationship with KRAS mutations in colorectal tumors. Therefore, selective inhibitors, agents against metabolic targets or KRAS signaling, may be clinically useful for colorectal tumor treatment through a patient-personalized approach.

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.