Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Mitochondrial Membrane Permeabilization in Cell Death

Mitochondria are the cells' powerhouse, but also their suicidal weapon store. Dozens of lethal signal transduction pathways converge on mitochondria to cause the permeabilization of the mitochondrial outer membrane, leading to the cytosolic release of pro-apoptotic proteins and to the impairment of the bioenergetic functions of mitochondria. The mitochondrial metabolism of cancer cells is deregulated owing to the use of glycolytic intermediates, which are normally destined for oxidative phosphorylation, in anabolic reactions. Activation of the cell death machinery in cancer cells by inhibiting tumour-specific alterations of the mitochondrial metabolism or by stimulating mitochondrial membrane permeabilization could therefore be promising therapeutic approaches.

/pdf/targeting-mitochondria-for-cancer-therapy-2ezqvlkpfu.pdf

Targeting mitochondria for cancer therapy

https://www.cell.com/developmental-cell/pdf/S1534-5807(07)00475-3.pdf

Chemical inhibition of the mitochondrial division dynamin reveals its role in Bax/Bak-dependent mitochondrial outer membrane permeabilization.

Molecular effectors of multiple cell death pathways initiated by photodynamic therapy

Cell death was once viewed as unregulated. It is now clear that at least a portion of cell death is a regulated cell suicide process. This type of death can exhibit multiple morphologies. One of these, apoptosis, has long been recognized to be actively mediated, and many of its underlying mechanisms have been elucidated. Moreover, necrosis, the traditional example of unregulated cell death, is also regulated in some instances. Autophagy is usually a survival mechanism but can occur in association with cell death. Little is known, however, about how autophagic cells die. Apoptosis, necrosis, and autophagy occur in cardiac myocytes during myocardial infarction, ischemia/reperfusion, and heart failure. Pharmacological and genetic inhibition of apoptosis and necrosis lessens infarct size and improves cardiac function in these disorders. The roles of autophagy in ischemia/reperfusion and heart failure are unresolved. A better understanding of these processes and their interrelationships may allow for the development of novel therapies for the major heart syndromes.

Cell Death in the Pathogenesis of Heart Disease: Mechanisms and Significance

How do Bax and Bak lead to permeabilization of the outer mitochondrial membrane

Immunotoxins are antibody-toxin bifunctional molecules that rely on intracellular toxin action to kill target cells. Target specificity is determined via the binding attributes of the chosen antibody. Mostly, but not exclusively, immunotoxins are purpose-built to kill cancer cells as part of novel treatment approaches. Other applications for immunotoxins include immune regulation and the treatment of viral or parasitic diseases. Here we discuss the utility of protein toxins, of both bacterial and plant origin, joined to antibodies for targeting cancer cells. Finally, while clinical goals are focused on the development of novel cancer treatments, much has been learned about toxin action and intracellular pathways. Thus toxins are considered both medicines for treating human disease and probes of cellular function.

Immunotoxins: The Role of the Toxin

Conformation of BCL-XL upon Membrane Integration

Pseudomonas exotoxin (PE)-based immunotoxins (antibody-toxin fusion proteins) have achieved frequent complete remissions in patients with hairy cell leukemia but far fewer objective responses in other cancers. To address possible mechanisms of resistance, we investigated immunotoxin activity in a model system using the colon cancer cell line, DLD1. Despite causing complete inhibition of protein synthesis, there was no evidence that an immunotoxin targeted to the transferrin receptor caused apoptosis in these cells. To address a possible protective role of prosurvival Bcl-2 proteins, the BH3-only mimetic, ABT-737, was tested alone or in combination with immunotoxins. Neither the immunotoxin nor ABT-737 alone activated caspase 3, whereas the combination exhibited substantial activation. In other epithelial cell lines, ABT-737 enhanced the cytotoxicity of PE-related immunotoxins by as much as 20-fold, but did not enhance diphtheria toxin or cycloheximide. Because PE translocates to the cytosol via the endoplasmic reticulum (ER) and the other toxins do not, ABT-737-mediated effects on the ER were investigated. ABT-737 treatment stimulated increased levels of ER stress response factor, ATF4. Because of its activity in the ER, ABT-737 might be particularly well suited for enhancing the activity of immunotoxins that translocate from the ER to the cell cytosol.

https://mct.aacrjournals.org/content/molcanther/9/7/2007.full.pdf

Antonella Antignani

Papers

How do Bax and Bak lead to permeabilization of the outer mitochondrial membrane

Immunotoxins: The Role of the Toxin

Conformation of BCL-XL upon Membrane Integration

ABT-737 overcomes resistance to immunotoxin-mediated apoptosis and enhances the delivery of pseudomonas exotoxin-based proteins to the cell cytosol.

Bax activates endophilin B1 oligomerization and lipid membrane vesiculation.