BAX-dependent transport of cytochrome c reconstituted in pure liposomes

Heat-induced programmed cell death in Leishmania infantum is reverted by Bcl-X(L) expression

An increasing number of reports indicate that single-celled organisms are able to die following what seems to be an ordered program of cell death with strong similarities to apoptosis from higher eukaryotes. DNA degradation and several other apoptotic-like processes have also been described in the parasitic protozoa Leishmania. However, the existence of an apoptotic death in this parasite is still a matter of controversy. Our results indicate that most of the processes of macromolecular degradation and organelle dysfunction observed in mammalian cells during apoptosis can also be reproduced in promastigotes of the genus Leishmania when incubated at temperatures above 38 degrees C. These processes can be partially reversed by the expression of the anti-apoptotic mammalian gene Bcl-X(L), which suggests that this family of apoptosis-regulating proteins was present very early in the evolution of eukaryotic cells.

Neuroprotection against ischaemic brain injury by a GluR6-9c peptide containing the TAT protein transduction sequence

It is well documented that N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors play a pivotal role in ischaemic brain injury. Recent studies have shown that kainate (KA) receptors are involved in neuronal cell death induced by seizure, which is mediated by the GluR6*PSD-95*MLK3 signalling module and subsequent c-Jun N-terminal kinase (JNK) activation. Here we investigate whether GluR6 mediated JNK activation is correlated with ischaemic brain injury. Our results show that cerebral ischaemia followed by reperfusion can enhance the assembly of the GluR6*PSD-95*MLK3 signalling module and JNK activation. As a result, activated JNK can not only phosphorylate the transcription factor c-Jun and up-regulate Fas L expression but can also phosphorylate 14-3-3 and promote Bax translocation to mitochondria, increase the release of cytochrome c and increase caspase-3 activation. These results indicate that GluR6 mediated JNK activation induced by ischaemia/reperfusion ultimately results in neuronal cell death via nuclear and non-nuclear pathways. Furthermore, the peptides we constructed, Tat-GluR6-9c, show a protective role against neuronal death induced by cerebral ischaemia/reperfusion through inhibiting the GluR6 mediated signal pathway. In summary, our results indicate that the KA receptor subunit GluR6 mediated JNK activation is involved in ischaemic brain injury and provides a new approach for stroke therapy.

BCL-XL Dimerization by Three-dimensional Domain Swapping

Dimeric interactions among anti- and pro-apoptotic members of the BCL-2 protein family are dynamically regulated and intimately involved in survival and death functions. We report the structure of a BCL-X(L) homodimers a 3D-domain swapped dimer (3DDS). The X-ray crystal structure demonstrates the mutual exchange of carboxy-terminal regions including BH2 (Bcl-2 homology 2) between monomer subunits, with the hinge region occurring at the hairpin turn between the fifth and sixth alpha helices. Both BH3 peptide-binding hydrophobic grooves are unoccupied in the 3DDS dimer and available for BH3 peptide binding, as confirmed by sedimentation velocity analysis. BCL-X(L) 3DDS dimers have increased pore-forming activity compared to monomers, suggesting that 3DDS dimers may act as intermediates in membrane pore formation. Chemical crosslinking studies of Cys-substituted BCL-X(L) proteins demonstrate that 3DDS dimers form in synthetic lipid vesicles.

Lewy bodies

Lewy bodies (LB) in the substantia nigra are a cardinal pathological feature of Parkinson's disease, but they occur in a number of neurodegenerative diseases and can be widespread in the nervous system. The characteristics, locations, and composition of LB are reviewed, with particular attention to alpha-synuclein (alpha-SYN), which appears to be the major component of LB. The propensity for alpha-SYN, a presynaptic protein widely expressed in the brain, to aggregate is because of an amyloidogenic central region. The factors that favor the aggregation of alpha-SYN and mechanisms of toxicity are examined, and a mechanism through which aggregates of alpha-SYN could induce mitochondrial dysfunction and/or release of proapoptotic molecules is proposed.

Molecular dynamics simulation and automated docking of the pro-apoptotic bax protein and its complex with a peptide designed from the Bax-binding domain of anti-apoptotic Ku70

Bax, a multi-domain protein belonging to the large family of Bcl-2 proteins, has a pivotal role for the initiation of the cytochrome c-mediated apoptosis, a vital physiologic process to eliminate damaged or unwanted cells. In response to specific stimuli Bax translocates from cytosol to mitochondria outer membrane where a process of oligomerization occurs with pore formation through which cytochrome c and other death molecules escape. The pro-death action of Bax is regulated by the interaction with other pro-survival proteins. However, the conformational changes and the structural details necessary for homo and hetero interaction with other regulating proteins are largely unknown. This article reports a combined investigation of molecular dynamics (MD) simulation and automated docking that evidence the molecular regions of Bax involved in the binding with anti-apoptotic exapeptide (Bip) designed from Ku70, a subunit of the protein complex essential for non-homologous DNA repair but that inhibits also the Bax translocation to mitochondria. Since Bip suppresses apoptosis induced by several anti-cancer drugs, it appears relevant to achieve a better understanding of the structural and dynamical aspects that characterize the Bip-Bax complex in view of potential therapeutic implications. The present results show that the Bax region with the highest affinity for Bip is located in proximity of BH3 homology domain of Bax and also involves the alpha-helices 1 and 8. Moreover, the comparison of essential motions of Bax at 300 and 400 K before and after the formation of the complex with Bip evidences how the binding with the exa-peptide affects the collective motions of specific molecular districts of Bax considered to have functional relevance.

Acid destabilization of the solution conformation of Bcl-xL does not drive its pH-dependent insertion into membranes

Regulation of programmed cell death by Bcl-xL is dependent on both its solution and integral membrane conformations. A conformational change from solution to membrane is also important in this regulation. This conformational change shows a pH-dependence similar to the translocation domain of diphtheria toxin, where an acid-induced molten globule conformation in the absence of lipid vesicles mediates the change from solution to membrane conformations. By contrast, Bcl-xL deltaTM in the absence of lipid vesicles exhibits no gross conformational changes upon acidification as observed by near- and far-UV circular dichroism spectropolarimetry. Additionally, no significant local conformational changes upon acidification were observed by heteronuclear NMR spectroscopy of Bcl-xL deltaTM. Under conditions that favor the solution conformation (pH 7.4), the free energy of folding for Bcl-xL deltaTM (deltaG(o)) was determined to be 15.8 kcal x mol(-1). Surprisingly, under conditions that favor a membrane conformation (pH 4.9), deltaG(o) was 14.6 kcal x mol(-1). These results differ from those obtained with many other membrane-insertable proteins where acid-induced destabilization is important. Therefore, other contributions must be necessary to destabilize the solution conformation Bcl-xL and favor the membrane conformation at pH 4.9. Such contributions might include the presence of a negatively charged membrane or an electrostatic potential across the membrane. Thus, for proteins that adopt both solution and membrane conformations, an obligatory molten globule intermediate may not be necessary. The absence of a molten globule intermediate might have evolved to protect Bcl-xL from intracellular proteases as it undergoes this conformational change essential for its activity.

N-methyl-D-aspartate blocks activation of JNK and mitochondrial apoptotic pathway induced by potassium deprivation in cerebellar granule cells

During the postnatal development of cerebellum, lack of excitatory innervation from the mossy fibers results in cerebellar granule cell (CGC) apoptosis during the migration of the cells toward the internal granule cell layer. Accordingly, CGCs die by apoptosis when cultured in physiological KCl concentrations (5 mm; K5), and they survive in the presence of depolarizing conditions such as high KCl concentration (25 mm; K25) or N-methyl-D-aspartate (NMDA). We have recently shown that NMDA is able to exert a long lasting neuroprotective effect when added to immature (2 days in vitro) CGC cultures by inhibition of caspase-3 activity. Here we show that NMDA- and K25-mediated neuroprotection is associated with an increase in the levels of Bcl-2, an inhibition of K5-mediated increase in Bax, and the inhibition of the release of apoptogenic factors from mitochondria such as Smac/DIABLO and cytochrome c. Moreover, we have shown that similar effects are observed when c-Jun N-terminal kinases (JNKs) are inhibited and that treatment of CGC cultures with NMDA blocks K5-mediated JNK activation. These results allow us to postulate that the inhibition of JNK-mediated release of apoptogenic factors from mitochondria is involved in the NMDA protection from K5-mediated apoptosis of CGCs.

Sphingosine forms channels in membranes that differ greatly from those formed by ceramide

Ceramide channels formed in the outer membrane of mitochondria have been proposed to be the pathways by which proapoptotic proteins are released from mitochondria during the early stages of apoptosis. We report that sphingosine also forms channels in membranes, but these differ greatly from the large oligomeric barrel-stave channels formed by ceramide. Sphingosine channels have short open lifetimes and have diameters less than 2 nm, whereas ceramide channels have long open lifetimes, enlarge in size reaching diameters in excess of 10 nm. Unlike ceramide, sphingosine forms channels in erythrocyte plasma membranes that vary in size with concentration, but with a maximum possible channel diameter of 2 nm. In isolated mitochondria, a large proportion of the added sphingosine was rapidly metabolized to ceramide in the absence of externally added fatty acids or fatty-acyl-CoAs. The ceramide synthase inhibitor, fumonisin B1 failed to prevent sphingosine metabolism to ceramide and actually increased it. However, partial inhibition of conversion to ceramide was achieved in the presence of ceramidase inhibitors, indicating that reverse ceramidase activity is at least partially responsible for sphingosine metabolism to ceramide. A small amount of cytochrome c release was detected. It correlated with the level of ceramide converted from sphingosine. Thus, sphingosine channels, unlike ceramide channels, are not large enough to allow the passage of proapoptotic proteins from the intermembrane space of mitochondria to the cytoplasm.

Smac/DIABLO and cytochrome c are released from mitochondria through a similar mechanism during UV-induced apoptosis

During apoptosis, a key event is the release of Smac/DIABLO (an inhibitor of XIAP) and cytochrome c (Cyt-c, an activator of caspase-9) from mitochondria to cytosol. It was not clear, however, whether the releasing mechanisms of these two proteins are the same. Using a combination of single living-cell analysis and immunostaining techniques, we investigated the dynamic process of Smac and Cyt-c release during UV-induced apoptosis in HeLa cells. We found that YFP-labeled Smac and GFP-labeled Cyt-c were released from mitochondria in the same time window, which coincided with the mitochondrial membrane potential depolarization. Furthermore, using immunostaining, we found that the endogenous Smac and Cyt-c were always released together within an individual cell. Finally, when cells were pre-treated with caspase inhibitor (z-VAD-fmk) to block caspase activation, the process of Smac release, like that of Cyt-c, was not affected. This was true for both YFP-labeled Smac and endogenous Smac. These results suggest that in HeLa cells, both Smac and Cyt-c are released from mitochondria during UV-induced apoptosis through the same permeability transition mechanism, which we believe is triggered by the aggregation of Bax in the outer mitochondrial membrane to form lipid-protein complex.

Survival and cell death in cells constitutively unable to synthesize glutathione

We examined the role of GSH in survival and cell death using GCS-2 cells that are deficient in glutamate cysteine ligase (gamma-glutamyl cysteine synthetase, gammaGCS), an enzyme essential for GSH synthesis. Cells maintained in 2.5 mM GSH have GSH levels that are approximately 2% of wild type and grow indefinitely; however, they express both pro- and anti-apoptotic Bcl-2 family members and have detectable levels of cytoplasmic cytochrome C. Withdrawal of GSH from the medium results in a fall in intracellular GSH to undetectable levels, decreased mitochondrial dehydrogenase activity, decreased anti-apoptotic factor RNAs, increased pro-apoptotic factor RNAs, additional cytochrome C release, and a fall in ATP levels; however, cells continue to grow for another 24h. At 48 h, these trends continue with the exception that mitochondrial membrane potential and ATP levels rise; DNA fragmentation begins at 48 h. Thus, severe reduction of GSH to 2% of wild type produces a metastable state compatible with survival, but complete absence of GSH triggers apoptosis.

Bax channel inhibitors prevent mitochondrion-mediated apoptosis and protect neurons in a model of global brain ischemia

Ischemic injuries are associated with several pathological conditions, including stroke and myocardial infarction. Several studies have indicated extensive apoptotic cell death in the infarcted area as well as in the penumbra region of the infarcted tissue. Studies with transgenic animals suggest that the mitochondrion-mediated apoptosis pathway is involved in ischemia-related cell death. This pathway is triggered by activation of pro-apoptotic Bcl-2 family members such as Bax. Here, we have identified and synthesized two low molecular weight compounds that block Bax channel activity. The Bax channel inhibitors prevented cytochrome c release from mitochondria, inhibited the decrease in the mitochondrial membrane potential, and protected cells against apoptosis. The Bax channel inhibitors did not affect the conformational activation of Bax or its translocation and insertion into the mitochondrial membrane in cells undergoing apoptosis. Furthermore, the compounds protected neurons in an animal model of global brain ischemia. The protective effect in the animal model correlated with decreased cytochrome c release in the infarcted area. This is the first demonstration that Bax channel activity is required in apoptosis.

Pharmacological manipulation of Bcl-2 family members to control cell death

The commitment to programmed cell death involves complex interactions among pro- and antiapoptotic members of the Bcl-2 family of proteins. The physiological result of a decision by these proteins to undergo cell death is permeabilization of the mitochondrial outer membrane. Pharmacologic manipulation of proteins in this family appears both feasible and efficacious, whether the goal is decreased cell death, as in ischemia of the myocardium or brain, or increased cell death, as in cancer.

Newcomers in the process of mitochondrial permeabilization

Under stress conditions, apoptogenic factors normally sequestered in the mitochondrial intermembrane space are released into the cytosol, caspases are activated and cells die by apoptosis. Although the precise mechanism that leads to the permeabilization of mitochondria is still unclear, the activation of multidomain pro-apoptotic proteins of the Bcl-2 family, such as Bax and Bak, is evidently crucial. Regulation of Bax and Bak by other members of the family has been known for a long time, but recent evidence suggests that additional unrelated proteins participate in the process, both as inhibitors and activators. The important rearrangements mitochondrial lipids undergo during apoptosis play a role in the permeabilization process and this role is probably more central than first envisioned.

Susceptibility of cholangiocarcinoma cells to parthenolide-induced apoptosis

Cholangiocarcinomas are intrahepatic bile duct carcinomas that are known to have a poor prognosis. Sesquiterpene lactone parthenolide, which is the principal active component in medicinal plants, has been used to treat tumors. Parthenolide effectively induced apoptosis in all four cholangiocarcinoma cell lines in a dose-dependent manner. However, the sarcomatous SCK cells were more sensitive to parthenolide than the other adenomatous cholangiocarcinoma cells. Therefore, this study investigated whether or not the expression of p53, the Fas/Fas ligand (FasL), Bcl-2/Bcl-X(L) determines the enhanced drug susceptibility of SCK cells. The results showed that Bcl-2 family molecules, such as Bid, Bak, and Bax, are involved in the parthenolide-induced apoptosis and that the defective expression of Bcl-X(L) might contribute to the higher parthenolide sensitivity in the SCK cells than in the other adenomatous cholangiocarcinoma cells. SCK cells, which stably express Bcl-X(L), were resistant to parthenolide, whereas Bcl-X(L)-positive Choi-CK cells transfected with the antisense Bcl-X(L) showed a higher parthenolide sensitivity than the vector control cells. Molecular dissection revealed that Bcl-X(L) inhibited the translocation of Bax to the mitochondria, decreased the generation of intracellular reactive oxygen species, reduced the mitochondrial transmembrane potential (deltapsi(m)), decreased the release of cytochrome c, decreased the cleavage of poly(ADP-ribose) polymerase, and eventually inhibited apoptotic cell death. These results suggest that parthenolide effectively induces oxidative stress-mediated apoptosis, and that the susceptibility to parthenolide in cholangiocarcinoma cells might be modulated by Bcl-X(L) expression in association with Bax translocation to the mitochondria.

Interactions of Bax and tBid with Lipid Monolayers

The release of cytochrome c from mitochondria to the cytosol is a crucial step of apoptosis that involves interactions of Bax and tBid proteins with the mitochondrial membrane. We investigated Bax and tBid interactions with (i) phosphatidylcholine (PC) monolayer as the main component of the outer leaflet of the outer membrane, (ii) with phosphatidylethanolamine (PE) and phosphatidylserine (PS) that are present in the inner leaflet and (iii) with a mixed PC/PE/Cardiolipin (CL) monolayer of the contact sites between the outer and inner membranes. These interactions were studied by measuring the increase of the lipidic monolayer surface pressure induced by the proteins. Our measurements suggest that tBid interacts strongly with the POPC/DOPE/CL, whereas Bax interaction with this monolayer is about 12 times weaker. Both tBid and Bax interact moderately half as strongly with negatively charged DOPS and non-lamellar DOPE monolayers. TBid also slightly interacts with DOPC. Our results suggest that tBid but not Bax interacts with the PC-containing outer membrane. Subsequent insertion of these proteins may occur at the PC/PE/CL sites of contact between the outer and inner membranes. It was also shown that Bax and tBid being mixed in solution inhibit their insertion into POPC/DOPE/CL monolayer. The known 3-D structures of Bax and Bid allowed us to propose a structural interpretation of these experimental results.

Cytochrome C release from CNS mitochondria and potential for clinical intervention in apoptosis-mediated CNS diseases

Apoptosis is critical for normal development and tissue homeostasis. However, its abnormal occurrence has been implicated in a number of disorders, including neurodegenerative diseases and stroke. Translocation of cytochrome c (Cyt c) from mitochondria to the cytoplasm is a key step in the initiation and/or amplification of apoptosis. Here we discuss Cyt c release in apoptosis with its impact on the CNS and review our studies of Cyt c release from isolated rat brain mitochondria in response to several insults. Calcium-induced Cyt c release, as occurs in neurons during stroke and ischemia, involves rupture of the mitochondrial outer membrane (MOM) and can be blocked by inhibitors of the mitochondrial permeability transition (mPT). Thus, inhibitors of the mPT have shown efficacy in animal models of ischemia. In contrast, proapoptotic proteins, such as BID, BAX, and BAK, induce Cyt c release independently of the mPT without lysing the MOM. Several inhibitors of BAX-induced Cyt c release have shown promise in models of CNS apoptosis. Because of their distinct mechanisms for Cyt c release, both the mPT and proapoptotic proteins should be targeted for effective clinical intervention in CNS disorders involving apoptosis.

Cytochrome c is released in a single step during apoptosis

Release of cytochrome c from mitochondria is a central event in apoptotic signaling. In this study, we utilized a cytochrome c fusion that binds fluorescent biarsenical ligands (cytochrome c-4CYS (cyt. c-4CYS)) as well as cytochrome c-green fluorescent protein (cyt. c-GFP) to measure its release from mitochondria in different cell types during apoptosis. In single cells, the kinetics of cyt. c-4CYS release was indistinguishable from that of cyt. c-GFP in apoptotic cells expressing both molecules. Lowering the temperature by 7 degrees C did not affect this corelease, but further separated cytochrome c release from the subsequent decrease in mitochondrial membrane potential (DeltaPsi(m)). Cyt. c-GFP rescued respiration in cells lacking endogenous cytochrome c, and the duration of cytochrome c release was approximately 5 min in a variety of cell types induced to die by various forms of cellular stress. In addition, we could observe no evidence of caspase-dependent amplification of cytochrome c release or changes in DeltaPsi(m) preceding the release of cyt. c-GFP. We conclude that there is a general mechanism responsible for cytochrome c release that proceeds in a single step that is independent of changes in DeltaPsi(m).

Anaplasma phagocytophilum inhibits human neutrophil apoptosis via upregulation of bfl-1, maintenance of mitochondrial membrane potential and prevention of caspase 3 activation

The inhibition of neutrophil apoptosis plays a central role in human granulocytic anaplasmosis. Intracellular signalling pathways through which the obligatory intracellular bacterium Anaplasma phagocytophilum inhibits the spontaneous apoptosis of human peripheral blood neutrophils were investigated. bfl-1 mRNA levels in uninfected neutrophils after 12 h in culture were reduced to approximately 5-25% of 0 h levels, but remained high in infected neutrophils. The eukaryotic RNA synthesis inhibitor, actinomycin D, prevented the maintenance of bfl-1 mRNA levels by A. phagocytophilum. Differences in mcl-1, bax, bcl-w, bad or bak mRNA levels in infected versus uninfected neutrophils were not remarkable. By using mitochondrial fluorescent dyes, Mitotracker Red and JC-1, it was found that most uninfected neutrophils lost mitochondrial membrane potential after 10-12 h incubation, whereas A. phagocytophilum-infected neutrophils maintained high membrane potential. Caspase 3 activity and the degree of apoptosis were lower in dose-dependent manner in A. phagocytophilum-infected neutrophils at 16 h post infection, as compared to uninfected neutrophils. Anti-active caspase 3 antibody labelling showed less positively stained population in infected neutrophils compared to those in uninfected neutrophils after 12 h incubation. These results suggest that A. phagocytophilum inhibits human neutrophil apoptosis via transcriptional upregulation of bfl-1 and inhibition of mitochondria-mediated activation of caspase 3.

Induction of Apoptosis in Mouse Liver by Microcystin-LR

Microcystins (MCs) are a family of cyclic heptapeptide hepatotoxins produced by freshwater species of cyanobacteria that have been implicated in the development of liver cancer, necrosis, and even deadly intrahepatic bleeding. MC-LR, the most toxic MC variant, is also the most commonly encountered in a contaminated aquatic system. This study presents the first data in the toxicological research of MCs that combines the use of standard apoptotic assays with transcriptomics, proteomic technologies, and computer simulations. By using histochemistry, DNA fragmentation assays, and flow cytometry analysis, we determined that MC-LR causes rapid, dose-dependent apoptosis in mouse liver when BALB/c mice are treated with MC-LR for 24 h at doses of either 50, 60, or 70 microg/kg of body weight. We then used gene expression profiling to demonstrate differential expressions (>2-fold) of 61 apoptosis-related genes in cells treated with MC-LR. Further proteomic analysis identified a total of 383 proteins of which 35 proteins were up-regulated and 30 proteins were down-regulated more than 2.5-fold when compared with controls. Combining computer simulations with the transcriptomic and proteomic data, we found that low doses (50 microg/kg) of MC-LR lead to apoptosis primarily through the BID-BAX-BCL-2 pathway, whereas high doses of MC-LR (70 microg/kg) caused apoptosis via a reactive oxygen species pathway. These results indicated that MC-LR exposure can cause apoptosis in mouse liver and revealed two independent pathways playing a major regulatory role in MC-LR-induced apoptosis, thereby contributing to a better understanding of the hepatotoxicity and the tumor-promoting mechanisms of MCs.

Mitochondrial carrier homolog 2 is a target of tBID in cells signaled to die by tumor necrosis factor alpha

BID, a proapoptotic BCL-2 family member, plays an essential role in the tumor necrosis factor alpha (TNF-alpha)/Fas death receptor pathway in vivo. Activation of the TNF-R1 receptor results in the cleavage of BID into truncated BID (tBID), which translocates to the mitochondria and induces the activation of BAX or BAK. In TNF-alpha-activated FL5.12 cells, tBID becomes part of a 45-kDa cross-linkable mitochondrial complex. Here we describe the biochemical purification of this complex and the identification of mitochondrial carrier homolog 2 (Mtch2) as part of this complex. Mtch2 is a conserved protein that is similar to members of the mitochondrial carrier protein family. Our studies with mouse liver mitochondria indicate that Mtch2 is an integral membrane protein exposed on the surface of mitochondria. Using blue-native gel electrophoresis we revealed that in viable FL5.12 cells Mtch2 resides in a protein complex of ca. 185 kDa and that the addition of TNF-alpha to these cells leads to the recruitment of tBID and BAX to this complex. Importantly, this recruitment was partially inhibited in FL5.12 cells stably expressing BCL-X(L). These results implicate Mtch2 as a mitochondrial target of tBID and raise the possibility that the Mtch2-resident complex participates in the mitochondrial apoptotic program.

The mitochondrial death pathway and cardiac myocyte apoptosis

Apoptosis has been causally linked to the pathogenesis of myocardial infarction and heart failure in rodent models. This death process is mediated by two central pathways, an extrinsic pathway involving cell surface receptors and an intrinsic pathway using mitochondria and the endoplasmic reticulum. Each of these pathways has been implicated in myocardial pathology. In this review, we summarize recent advances in the understanding of the intrinsic pathway and how it relates to cardiac myocyte death and heart disease.

Bcl-XL disrupts death-inducing signal complex formation in plasma membrane induced by hypoxia/reoxygenation

Hypoxia/reoxygenation (H/R) causes cellular injury and death. The cell death pathways induced by H/R remain incompletely understood. H/R can induce Bid and Bax mitochondrial translocation and cytochrome c release. Using mouse lung endothelial cells (MLEC), we examined the role of Bcl-X(L), an anti-apoptotic Bcl-2-related protein, in H/R-induced cell death. The expression of Bcl-X(L) protected MLEC against H/R-induced cell death by blocking Bax and Bid translocation and inhibiting mitochondrial cytochrome c release. Bcl-X(L) expression inhibited caspase-8 cleavage and death-inducing signal complex (DISC) formation in plasma membrane. By isolating mitochondrial, nuclear, and Golgi fractions, we found that H/R induced DISC formation in these organelles. Bcl-X(L) expression inhibited DISC formation in the nuclear and Golgi fractions relative to LacZ-infected controls. In contrast, DISC formation was elevated in the mitochondrial fraction of Bcl-X(L)-infected cells. GRASP65, a Golgi-associated protein, physically associated with Fas and caspase-8; Bcl-X(L) expression decreased these associations. Bcl-X(L) expression also up-regulated FLIP, a caspase-8 inhibitor. In conclusion, Bcl-X(L) may inactivate caspase-8 by decreasing DISC formation in the plasma membrane, nucleus, and Golgi complex while diverting DISC formation to the mitochondria. The inhibitory effects of Bcl-X(L) on DISC formation may play significant roles in protecting endothelial cells from H/R-induced cell death.

Jasmonates: novel anticancer agents acting directly and selectively on human cancer cell mitochondria

We reported previously that jasmonates can kill human cancer cells. Many chemotherapeutic drugs induce mitochondrial membrane permeability transition, membrane depolarization, osmotic swelling, and release of cytochrome c, involving the opening of the permeability transition pore complex (PTPC). Because jasmonates exert their cytotoxic effects independent of transcription, translation, and p53 expression, we hypothesized that these compounds may act directly on mitochondria. Mitochondrial membrane depolarization was determined by flow cytometry, and cytochrome c release by Western blotting. Mitochondria were isolated by mechanical lysis and differential centrifugation. Cytotoxicity was measured by a tetrazolium-based assay, and mitochondrial swelling by spectrophotometry. Jasmonates induced membrane depolarization and cytochrome c release in intact human cancer cell lines. Jasmonates induced swelling in mitochondria isolated from Hep 3B hepatoma cells, but not in mitochondria isolated from 3T3 nontransformed cells or from normal lymphocytes, in a PTPC-mediated manner. Methyl jasmonate induced the release of cytochrome c from mitochondria isolated from cancer cell lines in a PTPC-mediated manner, but not from mitochondria isolated from normal lymphocytes. A correlation was found between cytotoxicity of methyl jasmonate and the percentage of leukemic cells in the blood of patients with chronic lymphocytic leukemia (CLL). Jasmonates induced membrane depolarization in CLL cells, and swelling and release of cytochrome c in mitochondria isolated from these cells. In conclusion, jasmonates act directly on mitochondria derived from cancer cells in a PTPC-mediated manner, and could therefore bypass premitochondrial apoptotic blocks. Jasmonates are promising candidates for the treatment of CLL and other types of cancer.

Peptides derived from apoptotic Bax and Bid reproduce the poration activity of the parent full-length proteins

Bax and Bid are proapoptotic proteins of the Bcl-2 family that regulate the release of apoptogenic factors from mitochondria. Although they localize constitutively in the cytoplasm, their apoptotic function is exerted at the mitochondrial outer membrane, and is related to their ability to form transbilayer pores. Here we report the poration activity of fragments from these two proteins, containing the first alpha-helix of a colicinlike hydrophobic hairpin (alpha-helix 5 of Bax and alpha-helix 6 of Bid). Both peptides readily bind to synthetic lipid vesicles, where they adopt predominantly alpha-helical structures and induce the release of entrapped calcein. In planar lipid membranes they form ion conducting channels, which in the case of the Bax-derived peptide are characterized by a two-stage pattern, a large conductivity and lipid-charge-dependent ionic selectivity. These features, together with the influence of intrinsic lipid curvature on the poration activity and the existence of two helical stretches of different orientations for the membrane-bound peptide, suggest that it forms mixed lipidic/peptidic pores of toroidal structure. In contrast, the assayed Bid fragment shows a markedly different behavior, characterized by the formation of discrete, steplike channels in planar lipid bilayers, as expected for a peptidic pore lined by a bundle of helices.

Oligomeric Bax is a component of the putative cytochrome c release channel MAC, mitochondrial apoptosis-induced channel

Bcl-2 family proteins regulate apoptosis, in part, by controlling formation of the mitochondrial apoptosis-induced channel (MAC), which is a putative cytochrome c release channel induced early in the intrinsic apoptotic pathway. This channel activity was never observed in Bcl-2-overexpressing cells. Furthermore, MAC appears when Bax translocates to mitochondria and cytochrome c is released in cells dying by intrinsic apoptosis. Bax is a component of MAC of staurosporine-treated HeLa cells because MAC activity is immunodepleted by Bax antibodies. MAC is preferentially associated with oligomeric, not monomeric, Bax. The single channel behavior of recombinant oligomeric Bax and MAC is similar. Both channel activities are modified by cytochrome c, consistent with entrance of this protein into the pore. The mean conductance of patches of mitochondria isolated after green fluorescent protein-Bax translocation is significantly higher than those from untreated cells, consistent with onset of MAC activity. In contrast, the mean conductance of patches of mitochondria indicates MAC activity is present in apoptotic cells deficient in Bax but absent in apoptotic cells deficient in both Bax and Bak. These findings indicate Bax is a component of MAC in staurosporine-treated HeLa cells and suggest Bax and Bak are functionally redundant as components of MAC.

Promises and challenges of targeting Bcl-2 anti-apoptotic proteins for cancer therapy

Cancer cells with elevated levels of BCL-2 and related survival proteins are broadly resistant to cytotoxic agents. Antisense oligodeoxynucleotides, and more recently small molecule ligands for BCL-2 and BCL-XL, are directly cytotoxic or synergistic with standard cytotoxic agents, and in some cases, may demonstrate selectivity for tumor cells. The usual issues for rational drug discovery are writ large upon BCL-2-targeted therapeutics. The molecular functions of BCL-2 are not well understood, such that validation of cytotoxic mechanisms related to BCL-2 as well as identification of surrogate markers for BCL-2 function are significant obstacles for drug development. Despite these problems, a substantial number of small molecules that bind to BCL-2 or BCL-XL are now available for pre-clinical testing; in turn, basic studies with these reagents should yield new insights about optimal strategies to disrupt BCL-2 survival functions.

Phosphorothioate oligodeoxynucleotides and G3139 induce apoptosis in 518A2 melanoma cells

In a previous study, we showed that G3139, an antisense phosphorothioate oligonucleotide that down-regulates the expression of Bcl-2 protein, did not cause chemosensitization of 518A2 melanoma cells. In this work, we show that G3139, and the 2-base mismatch, G4126, can initiate apoptosis in this and other melanoma cell lines as shown by increased cell surface Annexin V expression, typical nuclear phenotypic changes as assessed by 4′,6-diamidino-2-phenylindole staining, activation of caspase-3 (but not caspase-8) and Bid, appearance of DEVDase (but not IETDase) activity, and cleavage of poly(ADP-ribose)-polymerase 1. Depolarization of the mitochondrial membrane occurs as a relatively late event. All of these processes seem to be substantially, but perhaps not totally, Bcl-2 independent as shown by experiments employing an anti-Bcl-2 small interfering RNA, which as shown previously down-regulated Bcl-2 protein expression but did not produce apoptosis or chemosensitization in melanoma cells. In fact, these G3139-induced molecular events were not dramatically altered in cells that forcibly overexpressed high levels of Bcl-2 protein. Addition of irreversible caspase inhibitors (e.g., the pan-caspase inhibitor zVAD-fmk) to G3139-treated cells almost completely blocked cytotoxicity. Examination of the time course of the appearance of caspase-3 and cleaved poly(ADP-ribose)-polymerase 1 showed that this could be correlated with the release of cytochrome c from the mitochondria, an event that begins only ∼4 hours after the end of the oligonucleotide/LipofectAMINE 2000 5-hour transfection period. Thus, both G3139 and cytotoxic chemotherapy activate the intrinsic pathway of apoptosis in these cells, although Bcl-2 expression does not seem to contribute strongly to chemoresistance. These findings suggest that the attainment of G3139-induced chemosensitization in these cells will be difficult.

Role of the permeability transition pore in cytochrome C release from mitochondria during ischemia-reperfusion in rat liver

Ischemia and reperfusion cause mitochondrial dysfunctions that initiate the mitochondrial apoptosis pathway. They involve the release of cytochrome C and the activation of the caspase cascade but the mechanism(s) leading to cytochrome C release is(are) poorly understood. The aim of this study was to analyse the relation between cytochrome C release and the opening of the permeability transition pore (PTP) during in situ liver ischemia and reperfusion. Liver ischemia was induced for 30, 60 and 120 min and blood re-flow was subsequently restored for 30 and 180 min. Ischemia hugely altered mitochondrial functions, i.e., oxidative phosphorylation and membrane potential, and was accompanied by a time-dependent mitochondrial release of cytochrome C into the cytosol and by activations of caspases-3 and -9. PTP opening was not observed during ischemia, as demonstrated by the absence of effect of an in vivo pre-treatment of rats with cyclosporin A (CsA), a potent PTP inhibitor. Cytochrome C release was due neither to a direct effect of caspases onto mitochondria nor to an interaction of Bax or Bid with the mitochondrial membrane but could be related to a direct effect of oxygen deprivation. In contrast, during reperfusion, CsA pre-treatment inhibits cytochrome C release, PTP opening and caspase activation. At this step, cytochrome C release is likely to occur as a consequence of PTP opening. In conclusion, our study reveals that cytochrome C release, and thus the induction of the mitochondrial cell death pathway, occur successively independently and dependent on PTP opening during liver ischemia and reperfusion, respectively.

Evidence for dimer formation by an amphiphilic heptapeptide that mediates chloride and carboxyfluorescein release from liposomes

Heptapeptides having dioctadecyl, N-terminal hydrocarbon chains insert in phospholipid bilayer membranes and form pores through which at least chloride ions pass. Although amphiphilic, these compounds do not typically form vesicles themselves. They insert in the bilayers of phospholipid vesicles and mediate the release of carboxyfluorescein. Hill analysis indicates that at least two molecules of the amphiphile are involved in pore formation. In CD2Cl2, dimer formation is detected by NMR chemical shift changes. The anion release activity of individual anion transporters is increased by linking them covalently at the C-terminus or, even more, by linking them at the N-terminus. Evidence is presented that either linked molecule releases chloride from liposomes more effectively and rapidly than the individual transporter molecule at a comparable concentration.

Apoptosis of tail muscle during amphibian metamorphosis involves a caspase 9-dependent mechanism

The climax of amphibian metamorphosis is marked by thyroid hormone-dependent tadpole tail resorption, implicating apoptosis of multiple cell types, including epidermal cells, fibroblasts, nerve cells, and muscles. The molecular cascades leading to and coordinating the death of different cell types are not fully elucidated. It is known that the mitochondrial pathway, and in particular the Bax and XR11 genes, regulates the balance between apoptosis and survival in muscle. However, the down-stream factors modulated by changes in mitochondrial permeability have not been studied in a functional context. To investigate further the mitochondrial-dependent pathway, we analyzed the regulation and the role of caspase 9 in Xenopus tadpoles. We report that caspase 9 mRNA is expressed in the tail before metamorphosis and increases before and during climax. Similarly, at the protein level, the production of active forms of caspase 9 increases in muscle tissue as metamorphosis progresses. To assess the functional role of caspase 9, we designed a dominant-negative protein. Overexpression of this dominant-negative abrogates both Bax-induced cell death in vitro and muscle apoptosis in vivo during natural metamorphosis. These findings consolidate a model of metamorphic muscle death that directly implicates the mitochondrial pathway and the apoptosome.

Tumor necrosis factor-α-induced changes in insulin-producing β-cells

The migration of macrophages and lymphocytes that produce cytokines such as tumor necrosis factor-alpha (TNF-alpha) causes beta-cell death, leading to type 1 diabetes. Similarly, in type 2 diabetes, the adipocyte-derived cytokines including TNF-alpha are elevated in the circulation, causing inflammation and insulin resistance. Thus, the studies described in this article using TNF-alpha are relevant to furthering our understanding of the pathogenesis of diabetes mellitus. We used RINr1046-38 (RIN) insulin-producing beta-cells, which constitutively express calbindin-D(28k), to characterize the effect of TNF-alpha on apoptosis, replication, insulin release, and gene and protein expression. Western blots of TNF-alpha-treated RIN cells revealed a decrease in calbindin-D(28k). By ELISA, TNF-alpha-treated beta-cells had 47% less calbindin-D(28k) than controls. In association with the decline in calbindin-D(28k), TNF-alpha treatment of RIN cells led to a 73% greater increase in changes in intracellular calcium concentration (Delta[Ca(2+)](i)) in TNF-alpha-treated cells as compared to that in control RIN cells upon treatment with 50 mM KCl; caused a greater increase in the [Ca(2+)](i) following the addition of 5.5 microM ionomycin; increased by more than threefold the apoptotic rate, expressed as the percentage of TUNEL-positive nuclei to total nuclei; decreased the rate of cell replication by 36%; and increased and decreased selectively the expression of specific genes as determined by microarray analysis. The subcellular localizations of Bcl-2, an antiapoptotic protein, and Bax, a proapoptotic protein, within RIN cells were altered with TNF-alpha treatment such that the two were colocalized with mitochondria in the perinuclear region. We conclude that the proapoptotic action of TNF-alpha on beta-cells is manifested via decreased expression of calbindin-D(28k) and is mediated at least in part by [Ca(2+)](i).

The C- and N-Terminal Residues of Synthetic Heptapeptide Ion Channels Influence Transport Efficacy Through Phospholipid Bilayers

The synthetic peptide, R(2)N-COCH(2)OCH(2)CO-Gly-Gly-Gly-Pro-Gly-Gly-Gly-OR', was shown to be selective for Cl(-) over K(+) when R is n-octadecyl and R' is benzyl. Nineteen heptapeptides have now been prepared in which the N-terminal and C-terminal residues have been varied. All of the N-terminal residues are dialkyl but the C-terminal chains are esters, 2 degrees amides, or 3 degrees amides. The compounds having varied N-terminal anchors and C-terminal benzyl groups are as follows: 1, R = n-propyl; 2, R = n-hexyl; 3, R = n-octyl; 4, R = n-decyl; 5, R = n-dodecyl; 6, R = n-tetradecyl; 7, R = n-hexadecyl; 8, R = n-octadecyl. Compounds 9-19 have R = n-octadecyl and C-terminal residues as follows: 9, OR' = OCH(2)CH(3); 10, OR' = OCH(CH(3))(2); 11, OR' = O(CH(2))(6)CH(3); 12, OR' = OCH(2)-c-C(6)H(11); 13, OR' = O(CH(2))(9)CH(3); 14, OR' = O (CH(2))(17)CH(3); 15, NR'(2) = N[(CH(2))(6)CH(3)](2); 16, NHR' = NH(CH(2))(9)CH(3); 17, NR'(2) = N[(CH(2))(9)CH(3)](2); 18, NHR' = NH(CH(2))(17)CH(3); 19, NR'(2) = N[(CH(2))(17)CH(3)](2). The highest anion transport activities were observed as follows. For the benzyl esters whose N-terminal residues were varied, i.e.1-8, compound 3 was most active. For the C(18) anchored esters 10-14, n-heptyl ester 11 was most active. For the C(18) anchored, C-terminal amides 15-19, di-n-decylamide 17 was most active. It was concluded that both the C- and N-terminal anchors were important for channel function in the bilayer but that activity was lost unless only one of the two anchoring groups was dominant.

Anion Transport in Liposomes Responds to Variations in the Anchor Chains and the Fourth Amino Acid of Heptapeptide Ion Channels

Seven heptapeptide derivatives have been prepared. The peptide structure is (Gly)(3)Xxx(Gly)(3) in which Xxx stands for a variable amino acid. The amino acid variations include azetidine carboxylic acid, pipecolic acid, meta-aminobenzoic acid, proline, and leucine. All seven compounds have a C-terminal benzyl group. In all cases, the heptapeptide's N-terminus was linked to diglycolic acid and a dialkylamine. In five cases, the N-terminal group was didecylamine and in two cases, N-ethyl-N-decyl. Chloride and carboxyfluorescein release from phospholipid vesicles was studied with the result that C(10)H(21)N(C(2)H(5)) COCH(2)OCH(2)CO-NH-(Gly)(3)Leu(Gly)(3)-OCH(2)Ph was the most active. Hill analysis showed that this compound involves pore formation by four monomer units rather than two, as previously found for other members of this family.

Regulation of caspase-3 and -9 activation in oxidant stress to RTE by forkhead transcription factors, Bcl-2 proteins, and MAP kinases

Cytotoxicity to renal tubular epithelial cells (RTE) is dependent on the relative response of cell survival and cell death signals triggered by the injury. Forkhead transcription factors, Bcl-2 family member Bad, and mitogen-activated protein kinases are regulated by phosphorylation that plays crucial roles in determining cell fate. We examined the role of phosphorylation of these proteins in regulation of H2O2-induced caspase activation in RTE. The phosphorylation of FKHR, FKHRL, and Bcl-2 family member Bad was markedly increased in response to oxidant injury, and this increase was associated with elevated levels of basal phosphorylation of Akt/protein kinase B. Phosphoinositol (PI) 3-kinase inhibitors abolished this phosphorylation and also decreased expression of antiapoptotic proteins Bcl-2 and BclxL. Inhibition of phosphorylation of forkhead proteins resulted in a marked increase in the proapoptotic protein Bim. These downstream effects of PI 3-kinase inhibition promoted the oxidant-induced activation of caspase-3 and -9, but not caspase-8 and -1. The impact of enhanced activation of caspases by PI 3-kinase inhibition was reflected on accelerated oxidant-induced cell death. Oxidant stress also induced marked phosphorylation of ERK1/2, P38, and JNK kinases. Inhibition of ERK1/2 phosphorylation but not P38 and JNK kinase increased caspase-3 and -9 activation; however, this activation was far less than induced by inhibition of Akt phosphorylation. Thus the Akt-mediated phosphorylation pathway, ERK signaling, and the antiapoptotic Bcl-2 proteins distinctly regulate caspase activation during oxidant injury to RTE. These studies suggest that enhancing renal-specific survival signals may lead to preservation of renal function during oxidant injury.

Initiation of mitochondrial-mediated apoptosis during cardiac reperfusion

Reperfusion of myocardial tissue can result in programmed cell death. Nevertheless, relatively little information exists concerning pathways initiated in vivo that ultimately commit cardiac cells to apoptosis during ischemia/reperfusion. The goal of the present study was to determine whether mitochondrial-mediated mechanisms of apoptosis are initiated during in vivo cardiac ischemia/reperfusion. We provide evidence that the content of cytochrome c in the cytosol increases exclusively during reperfusion. Over the same time interval Bax, a pro-apoptotic protein implicated in release of cytochrome c from mitochondria, was found to disappear from cytosolic extracts. This was associated with the appearance of tightly associated Bax in the mitochondrial fraction. Cytochrome c from reperfused cytosolic extracts is present as a high molecular weight oligomer consistent with formation of the apoptosome. In addition, pro-caspase-9 was found to disappear exclusively during reperfusion. Therefore, the results of the current study indicate that the mitochondrial-mediated pathway of apoptosis is initiated as a result of in vivo cardiac ischemia/reperfusion.

Implication ofbaxinXenopus laevistail regression at metamorphosis

Apoptosis is fundamental to normal vertebrate development. A dramatic example of postembryonic development involving apoptosis is tail regression during amphibian metamorphosis. Earlier studies led us to propose a functional role for the pro-apoptotic protein Bax in tadpole tail regression. However, its physiological relevance has never been analyzed. We have now cloned a cDNA encoding Xenopus laevis bax (xlbax) and used in vivo gene transfer in tail muscle to analyze the effects of xlbax overexpression. Furthermore, by using an antisense strategy in a similar experimental paradigm, xlbax antisense mRNA was shown to block the apoptotic effects of xlbax and protect against apoptosis in metamorphosing tadpoles. Our results suggest that xlbax is a regulator of muscle fiber death in the regressing tail during metamorphosis.

VDAC: the channel at the interface between mitochondria and the cytosol

The mitochondrial outer membrane is not just a barrier but a site of regulation of mitochondrial function. The VDAC family of proteins are the major pathways for metabolite flux through the outer membrane. These can be regulated in a variety of ways and the integration of these regulatory inputs allows mitochondrial metabolism to be adjusted to changing cellular conditions. This includes total blockage of the flux of anionic metabolites leading to permeabilization of the outer membrane to small proteins followed by apoptotic cell death.

Gonadotropin-releasing hormone antagonist antide inhibits apoptosis of preovulatory follicle cells in rat ovary

Analogs of GnRH, including agonists (GnRH-a) and antagonists (GnRH-ant), have been widely used to inhibit gonadotropin pituitary release. Aside from the effect of GnRH analogs on the pituitary-gonadal axis, studies have shown that GnRH has extrapituitary effects, particularly on rat and human ovaries. In the present study, we evaluated the direct in vivo effects of the GnRH-a, leuprolide acetate (LA), or the GnRH-ant, Antide (Ant), either singly or together, on ovarian follicular development in prepubertal eCG-treated rats. LA significantly decreased ovarian weight, whereas Ant increased ovarian weight compared with controls; however, coinjection of both compounds had no effect. In addition, LA increased the number of preantral follicles (PFs) and atretic follicles, and decreased the number of early antral follicles (EAFs) and preovulatory follicles (POFs). Coinjection of Ant interfered with this LA effect. Ant alone increased the number of POFs compared with that of controls. Analysis of apoptosis has shown that LA increases the percentage of apoptotic cells in PFs, EAFs, and POFs; however, Ant prevented this effect. In addition, Ant alone decreased the percentage of apoptotic cells in EAFs and POFs. Data have shown that Ant per se inhibited BAX translocation from cytosol to mitochondria and retained cytochrome C in the mitochondria, whereas LA induced cytochrome C release. We conclude that Ant inhibits apoptosis in preovulatory follicles through a decrease of BAX translocation to mitochondria, suggesting that GnRH may act as a physiological intraovarian modulator factor that is able to interfere with follicular development through an increase in apoptotic events mediated by an imbalance among the BCL-2 family members.

Bax-inhibiting peptide derived from mouse and rat Ku70

Bax is a proapoptotic protein that plays a key role in the induction of apoptosis. Ku70 has activities to repair DNA damage in the nucleus and to suppress apoptosis by inhibiting Bax in the cytosol. We previously designed peptides based on the amino acid sequence of Bax-binding domain of human Ku70, and showed that these peptides bind Bax and inhibit cell death in human cell lines. In the present report, we examined the biological activities of other pentapeptides, VPTLK and VPALR, derived from mouse and rat Ku70. Cells in culture accumulated FITC-labeled VPTLK and VPALR, indicating that these peptides are cell permeable (human, mouse, rat, and porcine cells were examined). These peptides bound to Bax and suppressed cell death in various cell types including primary cultured cells. These data suggest that such Bax inhibiting peptides from three mammalian species may be used to protect healthy cells from apoptotic injury under pathological conditions.

Bcl-2 and Bax exert opposing effects on Ca2+ signaling, which do not depend on their putative pore-forming region

Recent work has shown that Bcl-2 and other anti-apoptotic proteins partially deplete the endoplasmic reticulum (ER) Ca(2+) store and that this alteration of Ca(2+) signaling reduces cellular sensitivity to apoptotic stimuli. We expressed in HeLa cells Bcl-2, Bax, and Bcl-2/Bax chimeras in which the putative pore-forming domains of the two proteins (alpha 5-alpha 6) were mutually swapped, comparing the effects on Ca(2+) signaling of the two proteins and relating them to defined molecular domains. The results showed that only Bcl-2 reduces ER Ca(2+) levels and that this effect does not depend on the alpha 5-alpha 6 helices of this oncoprotein. Soon after its expression, Bax increased ER Ca(2+) loading, with ensuing potentiation of mitochondrial Ca(2+) responses. Then the cells progressed into an apoptotic phenotype (which included drastic reductions of cytosolic and mitochondrial Ca(2+) responses and alterations of organelle morphology). These results provide a coherent scenario that high-lights a primary role of Ca(2+) signals in deciphering apoptotic stimuli.

Mechanism of hepatocytes apoptosis induced by the proapoptosis protein Bid

OBJECTIVE

To investigate the mechanism of hepatocyte apoptosis induced by the proapoptosis protein Bid.

METHODS

Mouse primary hepatocytes were isolated from wild-type and Bid-deficient mice and treated with tumor necrosis factor-alpha (TNF-alpha) or anti-Fas antibody to induce cell apoptosis. Immunofluorescence staining of Bax was performed to recognize Bax translocation and its conformational change. The wild-type mice or wild-type mice transfected with the adenovirus carried DN-FADD (Dominant Negative-Fas Associated Death Domain) and the Bid-deficient mice were injected with anti-Fas antibody 2 h before being killed. Caspase 3 and 8 activities were measured. Bands of Bid cleavage and Bax conformational change were detected by Western blot.

RESULTS

Death receptors, including TNF-alpha and anti-Fas antibody, induced hepatocytes apoptosis, Bax translocation and conformational change through activation of Bid, which caused Bax to be inserted into the mitochondrial membrane of hepatocytes. The translocation and insertion of Bax were blocked when Bid was knocked out or blocked, and hepatocyte apoptosis was delayed or inhibited.

CONCLUSION

Hepatocyte apoptosis induced by death receptors is regulated by Bid and the translocation and insertion of Bax are also dependent on Bid.

Neuronal pathology in Parkinson?s disease

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra leading to the major clinical and pharmacological abnormalities of PD. In order to establish causal or protective treatments for PD, it is necessary to identify the cascade of deleterious events that lead to the dysfunction and death of dopaminergic neurons. Based on genetic, neuropathological, and biochemical data in patients and experimental animal models, dysfunction of the ubiquitin-proteasome pathway, protein aggregation, mitochondrial dysfunction, oxidative stress, activation of the c-Jun N-terminal kinase pathway, and inflammation have all been identified as important pathways leading to excitotoxic and apoptotic death of dopaminergic neurons. Toxin-based and genetically engineered animal models allow (1) the study of the significance of these aspects and their interaction with each other and (2) the development of causal treatments to stop disease progression.

Bax interacts with the voltage-dependent anion channel and mediates ethanol-induced apoptosis in rat hepatocytes

Acute ethanol exposure induces oxidative stress and apoptosis in primary rat hepatocytes. Previous data indicate that the mitochondrial permeability transition (MPT) is essential for ethanol-induced apoptosis. However, the mechanism by which ethanol induces the MPT remains unclear. In this study, we investigated the role of Bax, a proapoptotic Bcl-2 family protein, in acute ethanol-induced hepatocyte apoptosis. We found that Bax translocates from the cytosol to mitochondria before mitochondrial cytochrome c release. Bax translocation was oxidative stress dependent. Mitochondrial Bax formed a protein complex with the mitochondrial voltage-dependent anion channel (VDAC). Prevention of Bax-VDAC interactions by a microinjection of anti-VDAC antibody effectively prevented hepatocyte apoptosis by ethanol. In conclusion, these data suggest that Bax translocation from the cytosol to mitochondria leads to the subsequent formation of a Bax-VDAC complex that plays a crucial role in acute ethanol-induced hepatocyte apoptosis.

The mitochondrial apoptosis-induced channel (MAC) corresponds to a late apoptotic event

We have investigated the mechanism responsible for mitochondria permeabilization occurring during cell apoptosis. We have developed an in vivo model of apoptotic rat liver. Mitochondria appeared as an homogenous population in control liver. On the contrary, mitochondria varied in size, morphology, and the matrical density in apoptotic liver. Mitochondria were purified from control and apoptotic livers. In control conditions, a single mitochondrial population was identified; whereas three populations of mitochondria were purified from apoptotic liver. Our data show that these apoptotic populations correspond to early, intermediate, and late apoptotic mitochondria, which are characterized by an increasing extent of permeabilization of their outer membrane and a gradual enrichment in oligomerized Bax protein. Remarkably, a new ionic channel was observed in apoptotic but not in control mitochondria. The biophysical and pharmacological properties of this channel are in good agreement with those reported for a previously described mitochondrial apoptosis-induced channel (MAC) (Pavlov, E. V., Priault, M., Pietkiewicz, D., Cheng, E. H., Antonsson, B., Manon, S., Korsmeyer, S. J., Mannella, C. A., and Kinnally, K. W. (2001) J. Cell Biol. 155, 725-731). However, MAC activity was only observed in the late apoptotic mitochondrial population. Thus, our study establishes that MAC activity is related to the overall apoptotic process but corresponds to a late event.

Bcl-2-family proteins and the role of mitochondria in apoptosis

Mitochondria are central to many forms of cell death, usually via the release of pro-apoptotic proteins from the mitochondrial intermembrane space. Some intermembrane space proteins, including cytochrome c, Smac/DIABLO, and Omi/Htra2, can induce or enhance caspase activation, whereas others, such as AIF and endonuclease G, might act in a caspase-independent manner. Intermembrane space protein release is often regulated by Bcl-2-family proteins. Recent evidence suggests that pro-apoptotic members of this family, by themselves, can permeabilize the outer mitochondrial membrane without otherwise damaging mitochondria. Mitochondria can contribute to cell death in other ways. For example, they can respond to calcium release from the endoplasmic reticulum by undergoing the mitochondrial permeability transition, which in turn causes outer membrane rupture and the release of intermembrane space proteins. Bcl-2-family proteins can influence the levels of releasable Ca(2+) in the endoplasmic reticulum, and thus determine whether the released Ca(2+) is sufficient to overload mitochondria and induce cell death.

Some amphiphilic cations block the mitochondrial apoptosis-induced channel, MAC

The mitochondrial apoptosis-induced channel (MAC) forms in the outer membrane of mitochondria early in apoptosis and this activity is altered by physiological levels of cytochrome c. While cyclosporine A and lidocaine have no effect, dibucaine induces a fast blockade of MAC with an IC(50) of 39 microM. In contrast, the IC(50) for propranolol and trifluoperazine are 52 and 0.9 microM, respectively, and these drugs likely destabilize the open state of MAC. These agents, and others not yet identified, should be valuable tools in the study of apoptosis. Profiling MAC's pharmacology may generate novel therapeutic regimes for disease.

Role of mitochondrial membrane permeabilization in apoptosis and cancer

The release of proteins from the intermembrane space of mitochondria is one of the pivotal events in the apoptotic process, which can lead to the activation of caspases and the ultimate demise of the cell. How these proteins exit the mitochondria is still a matter of intense debate. Here, we discuss the possible mechanisms behind the release of apoptogenic proteins, the ways in which cancer cells subvert these mechanisms, and the therapeutic regimens that aim to promote the timely loss of integrity of the outer mitochondrial membrane.