Conformational change of Bax: a question of life or death

Evidence for additionally increased apoptosis in the peripheral blood mononuclear cells of major depressive patients with a high risk for suicide

Several studies have suggested a pathophysiological role of blood cell apoptosis in major depressive disorder (MDD). The aim of this study was to evaluate mRNA expression levels of Bcl-2, Bax, and Fas in peripheral blood mononuclear cells (PBMCs) of MDD patients with a high risk for suicide relative to those without a high risk for suicide as well as healthy subjects. The mRNA expression of Bcl-2, Bax, and Fas as well as the Bcl-2/Bax ratio was examined in the PBMCs of 30 MDD patients with a high risk for suicide, 30 MDD patients without a high risk for suicide, and 30 healthy controls. The mRNA expression of target genes was measured using real-time quantitative Polymerase Chain Reaction (PCR). FAS mRNA expression was significantly increased, and Bcl-2 mRNA expression and the Bcl-2/Bax expression ratio were significantly decreased, in the PBMCs of MDD patients with or without a high risk for suicide attempts compared to healthy controls (p < .001). However, Bax mRNA expression was significantly increased only in MDD patients with a high risk for suicide. Moreover, MDD patients with a high risk for suicide had increased Bax and FAS mRNA expression and decreased Bcl-2 and Bcl-2/Bax ratio when compared to patients without risk for suicide (p < .001). Our findings may support the role of both internal and external apoptotic pathways in the interplay between the immune system and depressive symptoms, especially in patients with a high risk for suicide.

A Chemical Modulator of p53 Transactivation that Acts as a Radioprotective Agonist

Inhibiting p53-dependent apoptosis by inhibitors of p53 is an effective strategy for preventing radiation-induced damage in hematopoietic lineages, while p53 and p21 also play radioprotective roles in the gastrointestinal epithelium. We previously identified some zinc(II) chelators, including 8-quinolinol derivatives, that suppress apoptosis in attempts to discover compounds that target the zinc-binding site in p53. We found that 5-chloro-8-quinolinol (5CHQ) has a unique p53-modulating activity that shifts its transactivation from proapoptotic to protective responses, including enhancing p21 induction and suppressing PUMA induction. This p53-modulating activity also influenced p53 and p53-target gene expression in unirradiated cells without inducing DNA damage. The specificity of 5CHQ for p53 and p21 was demonstrated by silencing the expression of each protein. These effects seem to be attributable to the sequence-specific alteration of p53 DNA-binding, as evaluated by chromatin immunoprecipitation and electrophoretic mobility shift assays. In addition, 5-chloro-8-methoxyquinoline itself had no antiapoptotic activity, indicating that the hydroxyl group at the 8-position is required for its antiapoptotic activity. We applied this remarkable agonistic activity to protecting the hematopoietic and gastrointestinal system in mouse irradiation models. The dose reduction factors of 5CHQ in total-body and abdominally irradiated mice were about 1.2 and 1.3, respectively. 5CHQ effectively protected mouse epithelial stem cells from a lethal dose of abdominal irradiation. Furthermore, the specificity of 5CHQ for p53 in reducing the lethality induced by abdominal irradiation was revealed in Trp53-KO mice. These results indicate that the pharmacologic upregulation of radioprotective p53 target genes is an effective strategy for addressing the gastrointestinal syndrome. Mol Cancer Ther; 17(2); 432-42. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Association of glycogen synthase kinase-3β with Parkinson's disease (review)

Glycogen synthase kinase-3 (GSK-3) is a pleiotropic serine/threonine protein kinase found in almost all eukaryotes. It is structurally highly conserved and has been identified as a multifaceted enzyme affecting a wide range of biological functions, including gene expression and cellular processes. There are two closely related isoforms of GSK-3; GSK-3α and GSK-3β. The latter appears to play crucial roles in regulating the pathogenesis of diverse diseases, including neurodegenerative disease. The present review focuses on the involvement of this protein in Parkinson’s disease (PD), a common neurodegenerative disorder characterized by the gradually progressive and selective loss of dopaminergic neurons, and by intracellular inclusions known as Lewy bodies (LBs) expressed in surviving neurons of the substantia nigra (SN). GSK-3β is involved in multiple signaling pathways and has several phosphorylation targets. Numerous apoptotic conditions can be facilitated by the GSK-3β signaling pathways. Studies have shown that GSK-3β inhibition protects the dopaminergic neurons from various stress-induced injuries, indicating the involvement of GSK-3β in PD pathogenesis. However, the underlying mechanisms of the protective effect of GSK-3β inhibition on dopaminergic neurons in PD is not completely understood. Multiple pathological events have been recognized to be responsible for the loss of dopaminergic neurons in PD, including mitochondrial dysfunction, oxidative stress, protein aggregation and neuroinflammation. The present review stresses the regulatory roles of GSK-3β in these events and in dopaminergic neuron degeneration, in an attempt to gain an improved understanding of the underlying mechanisms and to provide a potential effective therapeutic target for PD.

Impact of heart failure on the behavior of human neonatal stem cells in vitro

Background

Clinical cardiac cell therapy using autologous somatic stem cells is restricted by age and disease-associated impairment of stem cell function. Juvenile cells possibly represent a more potent alternative, but the impact of patient-related variables on such cell products is unknown. We therefore evaluated the behavior of neonatal cord blood mesenchymal stem cells (CB-MSC) in the presence of serum from patients with advanced heart failure (HF).

Methods

Human serum was obtained from patients with severe HF (n = 21) and from healthy volunteers (n = 12). To confirm the systemic quality of HF in the sera, TNF-α and IL-6 were quantified. CB-MSC from healthy neonates were cultivated for up to 14 days in medium supplemented with 10% protein-normalized human HF or control serum or fetal calf serum (FCS).

Results

All HF sera contained increased cytokine concentrations (IL-6, TNF-α). When exposed to HF serum, CB-MSC maintained basic MSC properties as confirmed by immunophenotyping and differentiation assays, but clonogenic cells were reduced in number and gave rise to substantially smaller colonies in the CFU-F assay. Cell cycle analysis pointed towards G1 arrest. CB-MSC metabolic activity and proliferation were significantly impaired for up to 3 days as measured by MTS turnover, BrdU incorporation and DAPI + nuclei counting. On day 5, however, CB-MSC growth kinetics approached control serum levels, though protein expression of cell cycle inhibitors (p21, p27), and apoptosis marker Caspase 3 remained elevated. Signal transduction included the stress and cytokine-induced JNK and ERK1/2 MAP kinase pathways.

Conclusions

Heart failure temporarily inhibits clonality and proliferation of “healthy” juvenile MSC in vitro. Further studies should address the in vivo and clinical relevance of this finding.

Dissociation of progressive dopaminergic neuronal death and behavioral impairments by Bax deletion in a mouse model of Parkinson's diseases

Parkinson's disease (PD) is a common, late-onset movement disorder with selective degeneration of dopaminergic (DA) neurons in the substantia nigra (SN). Although the neurotoxin 6-hydroxydopamine (6-OHDA) has been used to induce progressive degeneration of DA neurons in various animal models of PD, the precise molecular pathway and the impact of anti-apoptotic treatment on this neurodegeneration are less understood. Following a striatal injection of 6-OHDA, we observed atrophy and progressive death of DA neurons in wild-type mice. These degenerating DA neurons never exhibited signs of apoptosis (i.e., caspase-3 activation and cytoplasmic release of cytochrome C), but rather show nuclear translocation of apoptosis-inducing factor (AIF), a hallmark of regulated necrosis. However, mice with genetic deletion of the proapoptotic gene Bax (Bax-KO) exhibited a complete absence of 6-OHDA-induced DA neuron death and nuclear translocation of AIF, indicating that 6-OHDA-induced DA neuronal death is mediated by Bax-dependent AIF activation. On the other hand, DA neurons that survived in Bax-KO mice exhibited marked neuronal atrophy, without significant improvement of PD-related behavioral deficits. These findings suggest that anti-apoptotic therapy may not be sufficient for PD treatment, and the prevention of Bax-independent neuronal atrophy may be an important therapeutic target.

Mitochondrial ceramide-rich macrodomains functionalize Bax upon irradiation

Background

Evidence indicates that Bax functions as a “lipidic” pore to regulate mitochondrial outer membrane permeabilization (MOMP), the apoptosis commitment step, through unknown membrane elements. Here we show mitochondrial ceramide elevation facilitates MOMP-mediated cytochrome c release in HeLa cells by generating a previously-unrecognized mitochondrial ceramide-rich macrodomain (MCRM), which we visualize and isolate, into which Bax integrates.

Methodology/Principal Findings

MCRMs, virtually non-existent in resting cells, form upon irradiation coupled to ceramide synthase-mediated ceramide elevation, optimizing Bax insertion/oligomerization and MOMP. MCRMs are detected by confocal microscopy in intact HeLa cells and isolated biophysically as a light membrane fraction from HeLa cell lysates. Inhibiting ceramide generation using a well-defined natural ceramide synthase inhibitor, Fumonisin B1, prevented radiation-induced Bax insertion, oligomerization and MOMP. MCRM deconstruction using purified mouse hepatic mitochondria revealed ceramide alone is non-apoptogenic. Rather Bax integrates into MCRMs, oligomerizing therein, conferring 1–2 log enhanced cytochrome c release. Consistent with this mechanism, MCRM Bax isolates as high molecular weight “pore-forming” oligomers, while non-MCRM membrane contains exclusively MOMP-incompatible monomeric Bax.

Conclusions/Significance

Our recent studies in the C. elegans germline indicate that mitochondrial ceramide generation is obligate for radiation-induced apoptosis, although a mechanism for ceramide action was not delineated. Here we demonstrate that ceramide, generated in the mitochondrial outer membrane of mammalian cells upon irradiation, forms a platform into which Bax inserts, oligomerizes and functionalizes as a pore. We posit conceptualization of ceramide as a membrane-based stress calibrator, driving membrane macrodomain organization, which in mitochondria regulates intensity of Bax-induced MOMP, and is pharmacologically tractable in vitro and in vivo.

Tocopheryl quinones and mitochondria

In the past, the role of tocopherols and tocopheryl hydroquinones as antioxidants in mitochondria has been examined. However, structural properties of tocopherols and tocopheryl quinones (arrangement of polar/apolar moieties) have also been recognized as being crucial for the selective transport of RRR-alpha-congeners compared with other tocopherols in the cell, suggesting that these properties might be generally important for the binding of vitamin E-related compounds to proteins and enzymes in mitochondria. Therefore, direct modulation of mitochondrial activities, such as bioenergetics, production of reactive oxygen species and apoptosis, not exclusively related to the redox activity of these compounds is increasingly studied. This overview focuses on the influence of alpha-/gamma-tocopheryl quinones and their parent alpha-/gamma-tocopherols on mitochondrial functions, including formation of tocopheryl quinones, their analytical aspects, their potential as alternative substrates and their inhibitory activity for some mitochondrial functions. It is shown that the understanding of how tocopheryl quinones and tocopherols interfere with mitochondrial functions on the molecular level is still incomplete and that a better comprehension requires further research activities.

Sodium orthovanadate inhibits p53-mediated apoptosis

Sodium orthovanadate (vanadate) inhibits the DNA-binding activity of p53, but its precise effects on p53 function have not been examined. Here, we show that vanadate exerts a potent antiapoptotic activity through both transcription-dependent and transcription-independent mechanisms relative to other p53 inhibitors, including pifithrin (PFT) alpha. We compared the effects of vanadate to PFTalpha and PFTmicro, an inhibitor of transcription-independent apoptosis by p53. Vanadate suppressed p53-associated apoptotic events at the mitochondria, including the loss of mitochondrial membrane potential, the conformational change of Bax and Bak, the mitochondrial translocation of p53, and the interaction of p53 with Bcl-2. Similarly, vanadate suppressed the apoptosis-inducing activity of a mitochondrially targeted temperature-sensitive p53 in stable transfectants of SaOS-2 cells. In radioprotection assays, which rely on p53, vanadate completely protected mice from a sublethal dose of 8 Gy and partially from a lethal dose of 12 Gy. Together, our findings indicated that vanadate effectively suppresses p53-mediated apoptosis by both transcription-dependent and transcription-independent pathways, and suggested that both pathways must be inhibited to completely block p53-mediated apoptosis.

D-beta-hydroxybutyrate prevents MPP+-induced neurotoxicity in PC12 cells

Numerous studies show that D-beta-Hydroxybutyrate (DbetaHB) is neuroprotective. The present study was to explore the neuroprotective effects of DbetaHB against the cell death and apoptosis induced by 1-methyl-4-phenylpyridinium ion (MPP+) in PC12 cells. PC12 cells were pretreated with DbetaHB and followed by MPP+ exposure. The cell viability was determined by MTT assay. The morphological characteristics of apoptosis was observed by Acridine Orange (AO) staining and apoptotic rates were measured by flow cytometer. The product of lipid peroxidation, malondialdehyde (MDA), was measured using thiobarbituric acid method. The mitochondrial membrane potential (MMP), intracellular ROS and total glutathione were detected by microplate reader. In PC12 cells, pretreatment with DbetaHB significantly reduced MPP+-induced the decrease of cell viability. AO staining and flow cytometric analysis found DbetaHB inhibited MPP+-induced apoptosis. The measurement of MDA formation showed that DbetaHB alleviated lipid peroxidation induced by MPP+. The loss of MMP induced by MPP+ was preventive by DbetaHB. The changes of intracellular ROS and total glutathione induced by MPP+ were reversed by DbetaHB. DbetaHB protected PC12 cells against MPP+-induced death and apoptosis.

Mitochondrial targeting of tBid/Bax: a role for the TOM complex?

The release of pro-apoptotic proteins from the mitochondria is a key event in cell death signaling that is regulated by Bcl-2 family proteins. For example, cleavage of the BH3-only protein, Bid, by multiple proteases leads to the formation of truncated Bid that, in turn, promotes the insertion/oligomerization of Bax into the mitochondrial outer membrane, resulting in pore formation and the release of proteins residing in the intermembrane space. Bax, a monomeric protein in the cytosol is targeted to the mitochondria by a yet unknown mechanism. Several proteins of the outer mitochondrial membrane have been proposed to act as receptors for Bax, among them the voltage-dependent anion channel, VDAC, and the mitochondrial protein translocase of the outer membrane, the TOM complex. Alternatively, the unique mitochondrial phospholipid, cardiolipin, has been ascribed a similar function. Here, we review recent work on the mechanisms of activation and the targeting of Bax to the mitochondria and discuss the advantages and limitations of the methods used to study this process.

Involvment of cytosolic and mitochondrial GSK-3beta in mitochondrial dysfunction and neuronal cell death of MPTP/MPP-treated neurons

Aberrant mitochondrial function appears to play a central role in dopaminergic neuronal loss in Parkinson's disease (PD). 1-methyl-4-phenylpyridinium iodide (MPP⁺), the active metabolite of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), is a selective inhibitor of mitochondrial complex I and is widely used in rodent and cell models to elicit neurochemical alterations associated with PD. Recent findings suggest that Glycogen Synthase Kinase-3β (GSK-3β), a critical activator of neuronal apoptosis, is involved in the dopaminergic cell death. In this study, the role of GSK-3β in modulating MPP⁺-induced mitochondrial dysfunction and neuronal death was examined in vivo, and in two neuronal cell models namely primary cultured and immortalized neurons. In both cell models, MPTP/MPP⁺ treatment caused cell death associated with time- and concentration-dependent activation of GSK-3β, evidenced by the increased level of the active form of the kinase, i.e. GSK-3β phosphorylated at tyrosine 216 residue. Using immunocytochemistry and subcellular fractionation techniques, we showed that GSK-3β partially localized within mitochondria in both neuronal cell models. Moreover, MPP⁺ treatment induced a significant decrease of the specific phospho-Tyr216-GSK-3β labeling in mitochondria concomitantly with an increase into the cytosol. Using two distinct fluorescent probes, we showed that MPP⁺ induced cell death through the depolarization of mitochondrial membrane potential. Inhibition of GSK-3β activity using well-characterized inhibitors, LiCl and kenpaullone, and RNA interference, prevented MPP⁺-induced cell death by blocking mitochondrial membrane potential changes and subsequent caspase-9 and -3 activation. These results indicate that GSK-3β is a critical mediator of MPTP/MPP⁺-induced neurotoxicity through its ability to regulate mitochondrial functions. Inhibition of GSK-3β activity might provide protection against mitochondrial stress-induced cell death.

Conformational changes and protein stability of the pro-apoptotic protein Bax

Pro-apoptotic Bax is a soluble and monomeric protein under normal physiological conditions. Upon its activation substantial structural rearrangements occur: The protein inserts into the mitochondrial outer membrane and forms higher molecular weight oligomers. Subsequently, the cells can undergo apoptosis. In our studies, we focused on the structural rearrangements of Bax during oligomerization and on the protein stability. Both protein conformations exhibit high stability against thermal denaturation, chemically induced unfolding and proteolytic processing. The oligomeric protein is stable up to 90 degrees C as well as in solutions of 8 M urea or 6 M guanidinium hydrochloride. Helix 9 appears accessible in the monomer but hidden in the oligomer assessed by proteolysis. Tryptophan fluorescence indicates that the environment of the C-terminal protein half becomes more apolar upon oligomerization, whereas the loop region between helices 1 and 2 gets solvent exposed.

Repeated unpredictable stress and antidepressants differentially regulate expression of the bcl-2 family of apoptotic genes in rat cortical, hippocampal, and limbic brain structures

Apoptosis has been proposed as a contributing cellular mechanism to the structural alterations that have been observed in stress-related mood disorders. Antidepressants, on the other hand, are hypothesized to exert trophic and/or neuroprotective actions. The present study examined the regulation of the major antiapoptotic (Bcl-2, Bcl-xl) and proapoptotic (Bax) genes by repeated unpredictable stress (an animal model of depression) and antidepressant treatments (ADT). In adult rats, exposure to unpredictable stress reduced Bcl-2 mRNA levels in the central nucleus of the amygdala (CeA), cingulate (Cg), and frontal (Fr) cortices. Bcl-xl mRNA was significantly decreased in hippocampal subfields. In contrast, chronic administration of clinically effective antidepressants from four different classes, ie fluoxetine, reboxetine, tranylcypromine, and electroconvulsive seizures (ECS) upregulated Bcl-2 mRNA expression in the Cg, Fr, and CeA. Reboxetine, tranylcypromine, and ECS selectively increased Bcl-xl, but not Bcl-2 mRNA expression in the hippocampus. Chemical ADT but not ECS, robustly enhanced Bcl-2 expression in the medial amygdaloid nucleus and ventromedial hypothalamus. Fluoxetine did not influence Bcl-xl expression in the hippocampus, but it was the only ADT that decreased Bax expression in this region. In the CeA, again in direct contrast to the stress effects, exposure to all classes of ADTs significantly increased Bcl-2 mRNA. The selective regulation of Bcl-xl and Bax in hippocampal subfields and of Bcl-2 in the Cg cortex, amygdala, and hypothalamus suggests that these cellular adaptations contribute to the long-term neural plastic adaptations to stress and ADTs in cortical, hypothalamic, and limbic brain structures.

Melatonin antagonizes the intrinsic pathway of apoptosis via mitochondrial targeting of Bcl-2

We have recently shown that melatonin antagonizes damage-induced apoptosis by interaction with the MT-1/MT-2 plasma membrane receptors. Here, we show that melatonin interferes with the intrinsic pathway of apoptosis at the mitochondrial level. In response to an apoptogenic stimulus, melatonin allows mitochondrial translocation of the pro-apoptotic protein Bax, but it impairs its activation/dimerization The downstream apoptotic events, i.e. cytochrome c release, caspase 9 and 3 activation and nuclear vesiculation are equally impaired, indicating that melatonin interferes with Bax activation within mitochondria. Interestingly, we found that melatonin induces a strong re-localization of Bcl-2, the main Bax antagonist to mitochondria, suggesting that Bax activation may in fact be antagonized by Bcl-2 at the mitochondrial level. Indeed, we inhibit the melatonin anti-apoptotic effect (i) by silencing Bcl-2 with small interfering RNAs, or with small-molecular inhibitors targeted at the BH3 binding pocket in Bcl-2 (i.e. the one interacting with Bax); and (ii) by inhibiting melatonin-induced Bcl-2 mitochondrial re-localization with the MT1/MT2 receptor antagonist luzindole. This evidence provides a mechanism that may explain how melatonin through interaction with the MT1/MT2 receptors, elicits a pathway that interferes with the Bcl-2 family, thus modulating the cell life/death balance.

RRR-gamma-tocopherol induces human breast cancer cells to undergo apoptosis via death receptor 5 (DR5)-mediated apoptotic signaling

Goal of this study was to investigate the pro-apoptotic properties of RRR-gamma-tocopherol (gammaT) in human breast cancer cells. gammaT was shown to induce cancer cells but not normal cells to undergo apoptosis, sensitize cancer cells to Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL)-induced apoptosis, and increase death receptor 5 (DR5) mRNA, protein and cell surface expression. Knockdown of DR5 attenuated gammaT-induced apoptosis. Investigations of post-receptor signaling showed: caspase-8, Bid and Bax activation, increases in mitochondria permeability, cytochrome c release and caspase-9 activation. Thus, gammaT is a potent pro-apoptotic agent for human breast cancer cells inducing apoptosis via activation of DR5-mediated apoptotic pathway.

Hierarchical recruitment by AMPA but not staurosporine of pro-apoptotic mitochondrial signaling in cultured cortical neurons: evidence for caspase-dependent/independent cross-talk

Excitotoxicity mediated via the (S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) subtype of receptor for l-glutamate contributes to various neuropathologies involving acute brain injury and chronic degenerative disorders. In this study, AMPA-induced neuronal injury and staurosporine (STS)-mediated apoptosis were compared in primary neuronal cultures of murine cerebral cortex by analyzing indices up- and downstream of mitochondrial activation. AMPA-mediated apoptosis involved induction of Bax, loss of mitochondrial transmembrane potential (deltapsi(m)), early release of cytochrome c (cyt c), and more delayed release of second mitochondrial activator of caspases (SMAC), Omi, and apoptosis-inducing factor (AIF) with early calpain and minor late activation of caspase 3. STS-induced apoptosis was characterized by a number of differences, a more rapid time course, non-involvement of deltapsi(m), and relatively early recruitment of SMAC and caspase 3. The AMPA-induced rise in intracellular calcium appeared insufficient to evoke feltapsi(m) as release of cyt c preceded mitochondrial depolarization, which was followed by the cytosolic translocation of SMAC, Omi, and AIF. Bax translocation preceded cyt c release for both stimuli inferring its involvement in apoptotic induction. Inclusion of the broad spectrum caspase inhibitor zVAD-fmk reduced the AMPA-induced release of cyt c, SMAC, and AIF, while only affecting the redistribution of Omi and AIF in the STS-treated neurons. Only AIF release was affected by a calpain inhibitor (calpastatin) which exerted relatively minor effects on the progression of cellular injury. AMPA-mediated release of apoptogenic proteins was more hierarchical relative to STS with its calpain activation and caspase-dependent AIF redistribution arguing for a model with cross-talk between caspase-dependent/independent apoptosis.

Two molecular pathways initiate mitochondria-dependent dopaminergic neurodegeneration in experimental Parkinson's disease

Dysfunction of mitochondrial complex I is associated with a wide spectrum of neurodegenerative disorders, including Parkinson's disease (PD). In rodents, inhibition of complex I leads to degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNpc), as seen in PD, through activation of mitochondria-dependent apoptotic molecular pathways. In this scenario, complex I blockade increases the soluble pool of cytochrome c in the mitochondrial intermembrane space through oxidative mechanisms, whereas activation of pro-cell death protein Bax is actually necessary to trigger neuronal death by permeabilizing the outer mitochondrial membrane and releasing cytochrome c into the cytosol. Activation of Bax after complex I inhibition relies on its transcriptional induction and translocation to the mitochondria. How complex I deficiency leads to Bax activation is currently unknown. Using gene-targeted mice, we show that the tumor suppressor p53 mediates Bax transcriptional induction after PD-related complex I blockade in vivo, but it does not participate in Bax mitochondrial translocation in this model, either by a transcription-independent mechanism or through the induction of BH3-only proteins Puma or Noxa. Instead, Bax mitochondrial translocation in this model relies mainly on the JNK-dependent activation of the BH3-only protein Bim. Targeting either Bax transcriptional induction or Bax mitochondrial translocation results in a marked attenuation of SNpc dopaminergic cell death caused by complex I inhibition. These results provide further insight into the pathogenesis of PD neurodegeneration and identify molecular targets of potential therapeutic significance for this disabling neurological illness.

Protein kinase C-dependent mitochondrial translocation of proapoptotic protein Bax on activation of inducible nitric-oxide synthase in rostral ventrolateral medulla mediates cardiovascular depression during experimental endotoxemia

Sympathetic premotor neurons for the maintenance of vasomotor tone are located in rostral ventrolateral medulla (RVLM). We demonstrated previously that overproduction of nitric oxide (NO) by inducible NO synthase (iNOS) in RVLM, leading to caspase 3-dependent apoptotic cell death, plays a pivotal role in cardiovascular depression during endotoxemia induced by intravenous administration of Escherichia coli lipopolysaccharide. The interposing intracellular events remain unknown. We evaluated the hypothesis that these events encompass protein kinase C (PKC) activation, which triggers activation and translocation of Bax that opens mitochondrial permeability transition pore by interacting with adenine nucleotide translocase (ANT) or voltage-dependent anion protein (VDAC), followed by cytosolic release of cytochrome c. In Sprague-Dawley rats, coimmunoprecipitation and Western blot analyses revealed sequential manifestations during endotoxemia of membrane-bound translocation of PKC, dissociation of cytosolic PKC/Bax complex, mitochondrial translocation of activated Bax, augmented Bax/ANT or Bax/VDAC association, elevated cytosolic cytochrome c and caspase 3, and DNA fragmentation in ventrolateral medulla. Microinjection of iNOS inhibitor into bilateral RVLM significantly retarded PKC and Bax activation. The induced association of translocated Bax with ANT or VDAC and the triggered mitochondrial apoptotic signaling cascade were blunted by blockade in RVLM of PKC, mitochondrial translocation of Bax, Bax channels, ANT, or caspase 3, alongside significant amelioration of cardiovascular depression. We conclude that formation of mitochondrial Bax/ANT or Bax/VDAC complex that initiates caspase 3-dependent apoptosis in the RVLM as a result of PKC-dependent mitochondrial translocation of activated Bax activated by iNOS-derived NO plays a pivotal role in the manifestation of endotoxin-induced cardiovascular depression.

A mitochondrial protein affects cell morphology, mitochondrial segregation and virulence in Leishmania

The single mitochondrion of kinetoplastids divides in synchrony with the nucleus and plays a crucial role in cell division. However, despite its importance and potential as a drug target, the mechanism of mitochondrial division and segregation and the molecules involved are only partly understood. In our quest to identify novel mitochondrial proteins in Leishmania, we constructed a hidden Markov model from the targeting motifs of known mitochondrial proteins as a tool to search the Leishmania major genome. We show here that one of the 17 proteins of unknown function that we identified, designated mitochondrial protein X (MIX), is an oligomeric protein probably located in the inner membrane and expressed throughout the Leishmania life cycle. The MIX gene appears to be essential. Moreover, even deletion of one allele from L. major led to abnormalities in cell morphology, mitochondrial segregation and, importantly, to loss of virulence. MIX is unique to kinetoplastids but its heterologous expression in Saccharomyces cerevisiae produced defects in mitochondrial morphology. Our data show that a number of mitochondrial proteins are unique to kinetoplastids and some, like MIX, play a central role in mitochondrial segregation and cell division, as well as virulence.

Modulation of apoptosis in the mouse brain after morphine treatments and morphine withdrawal

We have examined the effects of acute or chronic morphine and naltrexone-precipitated withdrawal on mouse brain apoptotic cell death. The associated changes in the expression of apoptosis regulatory proteins were also analyzed. After a single dose of morphine, no apoptotic cells were detected by TUNEL or active caspase-3 immunocytochemistry. Concurrently, a down-regulation of the proapoptotic proteins FasL and Bad was detected in cortical lysates. On the other hand, the brains of chronic-morphine-treated mice and abstinent mice exhibited scattered apoptotic neurons and astrocytes throughout the brain. This neurotoxic effect was accompanied by up-regulation of the proapoptotic proteins FasL, Fas, and Bad and the active fragments of caspases-8 and -3 in cortical and hippocampal lysates. Abstinent mice also displayed a reduced expression of the antiapoptotic protein Bcl-2. No changes on t-Bid expression were detected under any experimental condition. These results suggest a neurotoxic effect exerted by chronic, but not acute, morphine and its withdrawal by activating both the intrinsic and the extrinsic apoptotic pathways. The possible clinical implications of our findings are discussed.

α-TEA inhibits survival and enhances death pathways in cisplatin sensitive and resistant human ovarian cancer cells

RRR-alpha-tocopherol ether linked acetic acid analog (alpha-TEA), is a potential chemotherapeutic agent for ovarian cancer. Pro-death and pro-life signaling pathways were studied to understand the anti-cancer actions of alpha-TEA on cisplatin-sensitive (A2780S) and -resistant (A2780/cp70R) human ovarian cancer cells. Both cell lines were refractory to Fas; whereas, alpha-TEA sensitized them to Fas signaling. alpha-TEA increased levels of Fas message, protein and membrane-associated Fas. Neutralizing antibodies to Fas or Fas L partially blocked alpha-TEA-induced apoptosis. alpha-TEA induced prolonged activation of c-Jun N-terminal kinase (JNK) and its substrate c-Jun; Bax conformational change; and cleavage of Bid and caspases-8, -9 and -3. Chemical inhibitors of JNK, and caspases blocked alpha-TEA-induced apoptosis. alpha-TEA decreased phosphorylation of protein kinase B (Akt/PKB) and extracellular signal-regulated kinase (ERK1/2), as well as cellular FLICE-like inhibitory protein (c-FLIP) and Survivin protein levels. Knockdown of Akt and ERK activity using phosphoinositide- 3-kinase (PI3K) and mitogen-activated protein kinase kinase (MKK1) inhibitors enhanced alpha-TEA-induced apoptosis. Over-expression of constitutively active Akt2 and MKK1 blocked alpha-TEA-induced apoptosis. Collectively, data show alpha-TEA to be a potent apoptotic inducer of both cisplatin-sensitive and -resistant human ovarian cancer cells via activating death receptor Fas signaling and suppressing anti-apoptotic AKT and ERK targets.

Proapoptotic BCL-2 family members and mitochondrial dysfunction during ischemia/reperfusion injury, a study employing cardiac HL-1 cells and GFP biosensors

The objective of this study was to evaluate mitochondrial alterations in a cell-based model of myocardial ischemia/reperfusion (I/R) injury. Using GFP-biosensors and fluorescence deconvolution microscopy, we investigated mitochondrial morphology in relation to Bax and Bid activation in the HL-1 cardiac cell line. Mitochondria underwent extensive fragmentation during ischemia. Bax translocation from cytosol to mitochondria was initiated during ischemia and proceeded during reperfusion. However, Bax translocation was not sufficient to induce cell death or mitochondrial dysfunction. Bid processing was caspase-8 dependent, and Bid translocation to mitochondria occurred after Bax translocation and clustering, and minutes before cell death. Clustering of Bax into distinct regions on mitochondria could be prevented by CsA, an inhibitor of the mitochondrial permeability transition pore, and also by SB203580, an inhibitor of p38 MAPK. Surprisingly, mitochondrial fragmentation which occurred during ischemia and before Bax translocation could be reversed by the addition of the p38 inhibitor SB203580 at reperfusion. Taken together, these results implicate p38 MAPK in the mitochondrial remodeling response to I/R that facilitates Bax recruitment to mitochondria.

Sodium orthovanadate suppresses DNA damage-induced caspase activation and apoptosis by inactivating p53

We previously reported that p42/SETbeta is a substrate for caspase-7 in irradiated MOLT-4 cells, and that treating the cells with sodium orthovanadate (vanadate) inhibits p42/SETbeta's caspase-mediated cleavage. Here, we initially found that the inhibitory effect of vanadate was due to the suppression of caspase activation but not of caspase activity. Further investigations revealed that vanadate suppressed upstream of apoptotic events, such as the loss of mitochondrial membrane potential, the conformational change of Bax, and p53 transactivation, although the accumulation, total phosphorylation, and phosphorylation of six individual sites of p53 were not affected. Importantly, vanadate suppressed p53-dependent apoptosis, but not p53-independent apoptosis. Finally, gel-shift and chromatin immunoprecipitation assays conclusively demonstrated that vanadate inhibits the DNA-binding activity of p53. Vanadate is conventionally used as an inhibitor of protein tyrosine phosphatases (PTPs); however, we recommend that the influence of vanadate not only on PTPs but also on p53 be considered before using it.

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.

Impact of pH on Bax α conformation, oligomerisation and mitochondrial integration

The change in the conformation of Bax at the onset of apoptosis is a determinant for the execution of this cell death programme. However, very few models can account for this modification and the factors involved in this process remain elusive. We have analysed the modifications in the conformation induced by a variation in pH using a cell-free assay. We show that a moderate basic or acidic pH can induce apoptotic-like changes in the conformation of Bax, such as the exposure of the N-terminal or the BH3 domain. These changes in the conformation are associated with the binding of Bax to mitochondria and an enhanced Bax homo- and oligomerisation. Our results suggest that variations in the pH, in a range consistent with that often observed during apoptosis, are sufficient to trigger Bax translocation to mitochondria and the subsequent release of apoptogenic factors from this organelle.

Mitochondrial proteins in neuronal degeneration

In this review, we highlight recent findings about the role of some mitochondrial proteins in neurological diseases. Studies in mice gene-deleted for Omi/HtrA2 and AIF showed the involvement of these mitochondrial proteins in selective cell degeneration in the spinal cord and brain. In humans, mutations in the mitochondrial protein, Paraplegin, cause an autosomal form of hereditary spastic paraplegia with an enhanced sensitivity to oxidative stress. Reactive oxygen species and decreased respiratory chain activity in mitochondria also contribute to common neurological diseases. The mitochondrial uncoupling protein, Ucp-2, was found to be neuroprotective in experimental stroke and brain trauma. Recent proteomic and profiling studies have revealed the existence of additional mitochondrial proteins with unknown functions. The elucidation of the physiological functions of mitochondrial proteins may lead to new insights into the role of these organelles in cell degeneration and to identification of novel drug targets for the prevention and treatment of different diseases.

Involvement of proapoptotic Bcl-2 family members in parthenolide-induced mitochondrial dysfunction and apoptosis

Parthenolide is a sesquiterpene lactone responsible for the bioactivities of Feverfew. Besides its potent anti-inflammatory effect, this compound has recently been reported to induce apoptosis in cancer cells, possibly through mitochondrial dysfunction. In the present study, we attempted to examine parthenolide-mediated cell death signaling pathway by focusing on the involvement of Bcl-2 family members. Using a human colorectal cancer cell line COLO205, we first demonstrated that parthenolide acted through the cell death receptor pathway to activate caspase 8. Following caspase 8 activation, Bid, a proapoptotic Bcl-2 member, was cleaved and this cleavage then triggered Bax conformational changes and Bax translocation from cytosol to mitochondrial membrane. Meanwhile, another proapoptotic protein, Bak, was up-regulated and oligomerized on the mitochondrial membrane. All these alterations were found to be prerequisite for the subsequent release of proapopototic mitochondrial proteins, including cytochrome c and Samc, in parthenolide-treated cells. Moreover, selective inhibition of caspase 8 activity by a synthetic caspase inhibitor (IETD-FMK) or overexpression of a viral protein (CrmA) suppressed the cleavage of Bid, conformational changes of Bax, cytochrome c release, and apoptosis. Therefore, the proapoptotic Bcl-2 family members are important mediators relaying the cell death signaling elicited by parthenolide from caspase 8 to downstream effector caspases such as caspase 3, and eventually to cell death.

Viral Bcl-2 homologs and their role in virus replication and associated diseases

Cellular Bcl-2 family proteins regulate a critical step in the mammalian programmed cell death pathway by modulating mitochondrial permeability and function. Bcl-2 family proteins are also encoded by several large DNA viruses, including all known gamma herpesviruses, adenoviruses, and several other unrelated viruses. Viral Bcl-2 proteins can prevent cell death but often escape cellular regulatory mechanisms that govern their cellular counterparts. By evading the "altruistic" suicide of infected cells, viruses can ensure replication and propagation in the infected host, but sometimes in surprising ways. Many human cancers and other disorders are associated with viruses that encode Bcl-2 homologs. Here we consider the available mechanistic data for viral compared to cellular Bcl-2 protein function along with relevance to the virus life cycle and human disease states.

Induction of apoptosis by enediyne antibiotic calicheamicin ϑII proceeds through a caspase-mediated mitochondrial amplification loop in an entirely Bax-dependent manner

Calicheamicin thetaII is a member of the enediyne class of antitumor antibiotics that bind to DNA and induce apoptosis. These compounds differ, however, from conventional anticancer drugs as they bind in a sequence-specific manner noncovalently to DNA and cause sequence-selective oxidation of deoxyriboses and bending of the DNA helix. Calicheamicin is clinically employed as immunoconjugate to antibodies directed against, for example, CD33 in the case of gemtuzumab ozogamicin. Here, we show by the use of the unconjugated drug that calicheamicin-induced apoptosis is independent from death-receptor/FADD-mediated signals. Moreover, calicheamicin triggers apoptosis in a p53-independent manner as shown by the use of p53 knockout cells. Cell death proceeds via activation of mitochondrial permeability transition, cytochrome c release and activation of caspase-9 and -3. The overexpression of Bcl-x(L) or Bcl-2 strongly inhibited calicheamicin-induced apoptosis. Knockout of Bax abrogated cell death after calicheamicin treatment. Thus, the activation of mitochondria and execution of cell death occur through a fully Bax-dependent mechanism. Interestingly, caspase inhibition by the pancaspase-inhibitor zVAD-fmk interfered with mitochondrial activation by calicheamicin. This places caspase activation upstream of the mitochondria and indicates that calicheamicin-triggered apoptosis is enhanced through death receptor-independent activation of the caspase cascade, that is, an amplification loop that is required for full activation of the mitochondrial pathway.

Bax conformational change is a crucial step for PUMA-mediated apoptosis in human leukemia

The BH3-only protein, PUMA, plays an important role in p53-mediated apoptosis. The apoptotic effect of PUMA on the mitochondria was studied using a p53-negative, human leukemia K562 cell line. Overexpression of PUMA was accompanied by an increased Bax expression, Bax conformational change, and translocation to mitochondria. A PUMA-BH3 peptide can induce Bax conformational change, cytochrome c release, and reduction in the mitochondrial membrane potential (DeltaPsi(m)) in isolated K562 mitochondria and can be inhibited by Bcl-XL. The homo-dimer of Bax/Bax was also weakly shown after mitochondria were treated with PUMA-BH3 peptide but may not be lethal for PUMA-induced apoptosis in K562 cells. Our results suggest that PUMA-induced Bax conformational change and Bax translocation to mitochondria can be separate events and the conformational change in Bax is crucial for PUMA-induced mitochondrial dysfunction.

Increase in Bcl-2 phosphorylation and reduced levels of BH3-only Bcl-2 family proteins in kainic acid-mediated neuronal death in the rat brain

Kainic acid induces excitotoxicity and nerve cell degeneration in vulnerable regions of rat brain, most markedly in hippocampus and amygdala. Part of the cell death following kainic acid is apoptotic as shown by caspase 3 activation and chromatin condensation. Here we have studied the regulation of pro- and anti-apoptotic proteins belonging to the Bcl-2 family in rat hippocampus and amygdala by kainic acid in relationship to ensuing neuronal death. The pro-apoptotic protein Bax was up-regulated in hippocampus 6 h after kainic acid administration. The increase in Bax was followed by the appearance of TdT-mediated dUTP nick end labelling-positive cells which were prominent at 24 h. Immunohistochemistry for active Bax revealed a punctuated labelling of neurons in the CA3 and hilar regions of hippocampus as well as in amygdala. Double staining for NeuN, a marker for nerve cells, and TdT-mediated dUTP nick end labelling showed that mainly neurons undergo degeneration after kainic acid treatment. In contrast to Bax, the pro-apoptotic BH3-only Bcl-2 proteins Bim and Harakiri/DP5 were down-regulated by kainic acid. This was also observed for the anti-apoptotic proteins Bcl-x and Bcl-w. Immunoreactive Bcl-2 was up-regulated in hippocampus after kainic acid together with an increase in the phosphorylation of serine-87 in Bcl-2, suggesting a post-transcriptional modification of the protein. This was confirmed using immunoprecipitation of total Bcl-2 from hippocampus and amygdala which revealed an increase in serine-87 phospho-Bcl-2 after kainic acid. Inhibition of the c-jun N-terminal protein kinase pathway reduced both serine-87 phosphorylation and cell death after kainic acid. This indicates an important role of Bcl-2 phosphorylation in controlling neuronal death after kainic acid. In contrast to the situation in trophic factor-deprived neurons, no up-regulation of Bim or Harakiri/DP5 proteins occurred after kainic acid, suggesting alternative pathways for regulation of cell death in excitotoxicity. The results indicate that not only the relative levels of Bcl-2 family proteins but also conformation changes and post-translational modifications contribute to neuronal death following kainic acid.

Investigation of the role of the C-terminus of Bax and of tc-Bid on Bax interaction with yeast mitochondria

Because of structural homology with the transmembrane domain of Bcl-2, the proapoptotic protein Bax has been proposed to be anchored to the outer membrane of mitochondria through its carboxy-terminal end (CT). We took advantage of the absence of Bcl-2 family members in yeast to further investigate the role of Bax CT in its mitochondrial association and function. The complete deletion or the addition of a C-terminal c-myc tag as well as the replacement of CT by a random coiled sequence enhanced membrane insertion of Bax. It has previously been suggested that conformational change in the N-terminal end of Bax would allow the C-terminal end to play its anchoring function. We found that a mutant truncated in both N- and C-termini still exhibited a strong binding activity to mitochondria. In mammals, Bax interaction with the caspase-8-generated truncated form of Bid (tc-Bid) is believed to promote a conformational change necessary for the insertion of Bax into mitochondria. We coexpressed Bax and tc-Bid in yeast and found that native Bax functions are not stimulated by tc-Bid, whereas functions of an active variant with a modified CT are. We propose that Bax CT has to undergo a conformational change to allow the insertion of Bax in mitochondria but, contrary to current views, is not a bona fide membrane anchor.

Mutational analysis of N-Bak reveals different structural requirements for antiapoptotic activity in neurons and proapoptotic activity in nonneuronal cells

N-Bak, a neuron-specific BH3-only splice variant of Bak, is proapoptotic when overexpressed in nonneuronal cells, but antiapoptotic in NGF-deprived sympathetic neurons. We generated mutants of N-Bak and compared their activities in COS-7 or Neuro2A cells to those in NGF-deprived sympathetic neurons. A C-terminal deletion shortly after the BH3 domain of N-Bak compromised its neuroprotective activity but had little effect on its cytotoxic activity in nonneuronal cells. Amino acid changes in the BH3 domain of N-Bak differently affected its function in nonneuronal cells and in neurons. The same changes in the BH3 domain of longer Bak isoform affected its function similarly in nonneuronal cells and neurons. C-terminally truncated Bax, a structural analogue of N-Bak, was also neuroprotective, whereas Blk, a different BH3-only protein was apoptotic in neurons. Thus, neuron-specific antiapoptotic interactions require a "N-Bak-type" conformation, not just a BH3 domain, whereas the presence of a BH3 domain in the Bak protein is sufficient to kill nonneuronal cells.

Involvement of the N-terminus of Bax in its intracellular localization and function

We have identified, using site-directed mutagenesis, a proline located at position 13 of Baxalpha (Bax) as crucial for the maintenance of its cytosolic conformation. The substitution of this proline by a valine results in a strong binding of Bax to mitochondria and to conformational changes monitored by a decreased sensitivity of Bax to mild proteolysis and the enhancement of its oligomerization state. Deletion of the C-terminus of Bax does not modify its intracellular localization. On the other hand, the pro-apoptotic activity of Bax is enhanced by a deletion of the C-terminus in the absence of the N-terminus but is decreased in its presence. These results suggest that both extremities functionally interact to control the activity but not the subcellular localization of Bax.

Lipoxygenases and their involvement in programmed cell death

Lipoxygenases are a family of enzymes which dioxygenate unsaturated fatty acids, thus initiating lipoperoxidation of membranes and the synthesis of signaling molecules. Consequently, they induce structural and metabolic changes in the cell in a number of pathophysiological conditions. Recently, a pro-apoptotic effect of lipoxygenase, and of the hydroperoxides produced thereof, has been reported in different cells and tissues, leading to cell death. Anti-apoptotic effects of lipoxygenases have also been reported; however, this has often been based on the use of enzyme inhibitors. Here we review the characteristics of the lipoxygenase family and its involvement in the initiation of oxidative stress-induced apoptosis. Finally, we discuss the role of lipoxygenase activation in apoptosis of animal and plant cells, suggesting a common signal transduction pathway in cell death conserved through evolution of both kingdoms.