Modulation of mitochondrial Ca(2+) homeostasis by Bcl-2

Hemichannels contribute to mitochondrial Ca2+ and morphology alterations evoked by ethanol in astrocytes

Alcohol, a toxic and psychoactive substance with addictive properties, severely impacts life quality, leading to significant health, societal, and economic consequences. Its rapid passage across the blood-brain barrier directly affects different brain cells, including astrocytes. Our recent findings revealed the involvement of pannexin-1 (Panx1) and connexin-43 (Cx43) hemichannels in ethanol-induced astrocyte dysfunction and death. However, whether ethanol influences mitochondrial function and morphology in astrocytes, and the potential role of hemichannels in this process remains poorly understood. Here, we found that ethanol reduced basal mitochondrial Ca2+ but exacerbated thapsigargin-induced mitochondrial Ca2+ dynamics in a concentration-dependent manner, as evidenced by Rhod-2 time-lapse recordings. Similarly, ethanol-treated astrocytes displayed increased mitochondrial superoxide production, as indicated by MitoSox labeling. These effects coincided with reduced mitochondrial membrane potential and increased mitochondrial fragmentation, as determined by MitoRed CMXRos and MitoGreen quantification, respectively. Crucially, inhibiting both Cx43 and Panx1 hemichannels effectively prevented all ethanol-induced mitochondrial abnormalities in astrocytes. We speculate that exacerbated hemichannel activity evoked by ethanol may impair intracellular Ca2+ homeostasis, stressing mitochondrial Ca2+ with potentially damaging consequences for mitochondrial fusion and fission dynamics and astroglial bioenergetics.

Probing the Mechanism of Action of Bis(phenolato) Amine (ONO Donor Set) Titanium(IV) Anticancer Agents

The need for anticancer therapies that overcome metallodrug resistance while minimizing adverse toxicities is targeted, herein, using titanium coordination complexes. Octahedral titanium(IV) trans,mer-[Ti{R1N(CH2-2-MeO-4-R1-C6H2)2}2] [R1 = Et, allyl, n-Pr, CHO, F, CH2(morpholino), the latter from the formyl derivative; R2 = Me, Et; not all combinations] are attained from Mannich reactions of commercial 2-methoxyphenols (27-74% overall yield, 2 steps). These crystalline (four X-ray structures) Ti(IV)-complexes are active against MCF-7, HCT-116, HT-29, PANC-1, and MDA-MB-468 cancer cell lines (GI50 = 0.5-38 μM). Their activity and cancer selectivity (vs nontumor MRC-5 cells) typically exceeds that of cisplatin (up to 16-fold). Proteomic analysis (in MCF-7) supported by other studies (G2/M cell cycle arrest, ROS generation, γH2AX production, caspase activation, annexin positivity, western blot, and kinase screens in MCF-7 and HCT-116) suggest apoptosis elicited by more than one mechanism of action. Comparison of these data to the modes of action proposed for salan Ti(IV) complexes is made.

Kinase signalling adaptation supports dysfunctional mitochondria in disease

Mitochondria form a critical control nexus which are essential for maintaining correct tissue homeostasis. An increasing number of studies have identified dysregulation of mitochondria as a driver in cancer. However, which pathways support and promote this adapted mitochondrial function? A key hallmark of cancer is perturbation of kinase signalling pathways. These pathways include mitogen activated protein kinases (MAPK), lipid secondary messenger networks, cyclic-AMP-activated (cAMP)/AMP-activated kinases (AMPK), and Ca2+/calmodulin-dependent protein kinase (CaMK) networks. These signalling pathways have multiple substrates which support initiation and persistence of cancer. Many of these are involved in the regulation of mitochondrial morphology, mitochondrial apoptosis, mitochondrial calcium homeostasis, mitochondrial associated membranes (MAMs), and retrograde ROS signalling. This review will aim to both explore how kinase signalling integrates with these critical mitochondrial pathways and highlight how these systems can be usurped to support the development of disease. In addition, we will identify areas which require further investigation to fully understand the complexities of these regulatory interactions. Overall, this review will emphasize how studying the interaction between kinase signalling and mitochondria improves our understanding of mitochondrial homeostasis and can yield novel therapeutic targets to treat disease.

Notch1 Modulation of Cellular Calcium Regulates Mitochondrial Metabolism and Anti-Apoptotic Activity in T-Regulatory Cells

As the major hub of metabolic activity and an organelle sequestering pro-apoptogenic intermediates, mitochondria lie at the crossroads of cellular decisions of death and survival. Intracellular calcium is a key regulator of these outcomes with rapid, uncontrolled uptake into mitochondria, activating pro-apoptotic cascades that trigger cell death. Here, we show that calcium uptake and mitochondrial metabolism in murine T-regulatory cells (Tregs) is tuned by Notch1 activity. Based on analysis of Tregs and the HEK cell line, we present evidence that modulation of cellular calcium dynamics underpins Notch1 regulation of mitochondrial homeostasis and consequently anti-apoptotic activity. Targeted siRNA-mediated ablations reveal dependency on molecules controlling calcium release from the endoplasmic reticulum (ER) and the chaperone, glucose-regulated protein 75 (Grp75), the associated protein Voltage Dependent Anion Channel (VDAC)1 and the Mitochondrial Calcium Uniporter (MCU), which together facilitate ER calcium transfer and uptake into the mitochondria. Endogenous Notch1 is detected in immune-complexes with Grp75 and VDAC1. Deficits in mitochondrial oxidative and survival in Notch1 deficient Tregs, were corrected by the expression of recombinant Notch1 intracellular domain, and in part by recombinant Grp75. Thus, the modulation of calcium dynamics and consequently mitochondrial metabolism underlies Treg survival in conditions of nutrient stress. This work positions a key role for Notch1 activity in these outcomes.

Crosstalk between Mitochondria and Cytoskeleton in Cardiac Cells

Elucidation of the mitochondrial regulatory mechanisms for the understanding of muscle bioenergetics and the role of mitochondria is a fundamental problem in cellular physiology and pathophysiology. The cytoskeleton (microtubules, intermediate filaments, microfilaments) plays a central role in the maintenance of mitochondrial shape, location, and motility. In addition, numerous interactions between cytoskeletal proteins and mitochondria can actively participate in the regulation of mitochondrial respiration and oxidative phosphorylation. In cardiac and skeletal muscles, mitochondrial positions are tightly fixed, providing their regular arrangement and numerous interactions with other cellular structures such as sarcoplasmic reticulum and cytoskeleton. This can involve association of cytoskeletal proteins with voltage-dependent anion channel (VDAC), thereby, governing the permeability of the outer mitochondrial membrane (OMM) to metabolites, and regulating cell energy metabolism. Cardiomyocytes and myocardial fibers demonstrate regular arrangement of tubulin beta-II isoform entirely co-localized with mitochondria, in contrast to other isoforms of tubulin. This observation suggests the participation of tubulin beta-II in the regulation of OMM permeability through interaction with VDAC. The OMM permeability is also regulated by the specific isoform of cytolinker protein plectin. This review summarizes and discusses previous studies on the role of cytoskeletal proteins in the regulation of energy metabolism and mitochondrial function, adenosine triphosphate (ATP) production, and energy transfer.

Acaricidal Mechanism of Scopoletin Against Tetranychus cinnabarinus

Scopoletin is a promising acaricidal botanical natural compound against Tetranychus cinnabarinus, and its acaricidal mechanism maybe involve calcium overload according to our previous study. To seek potential candidate target genes of calcium overload induced by scopoletin in T. cinnabarinus, RNA-seq was utilized to detect changes in transcription levels. 24 and 48 h after treatment, 70 and 102 differentially expressed genes were obtained, respectively. Target genes included 3 signal transduction genes, 4 cell apoptosis genes, 4 energy metabolism genes, and 2 transcription factor genes. The role of 3 calcium signaling pathway-related genes, namely, G-protein-coupled neuropeptide receptor, Bcl-2 protein and guanylate kinase (designated TcGPCR, TcBAG, and TcGUK, respectively) in the calcium overload were investigated in this study. RT-qPCR detection showed that scopoletin treatment upregulated the expression level of TcGPCR and downregulated the expression level of TcBAG and TcGUK. The result of RNAi indicated that downregulation of TcGPCR decreased susceptibility to scopoletin, and downregulation of TcBAG and TcGUK enhanced susceptibility to scopoletin. Functional expression in Chinese hamster ovary cells showed that scopoletin induced a significant increase in intracellular free calcium [Ca2+]i levels by activating TcGPCR. These results demonstrated that the acaricidal mechanism of scopoletin was via disrupting intracellular Ca2+ homeostasis and calcium signaling pathway mediated by GPCR, BAG, and GUK.

BH3 mimetic-elicited Ca2+ signals in pancreatic acinar cells are dependent on Bax and can be reduced by Ca2+-like peptides

BH3 mimetics are small-molecule inhibitors of B-cell lymphoma-2 (Bcl-2) and Bcl-xL, which disrupt the heterodimerisation of anti- and pro-apoptotic Bcl-2 family members sensitising cells to apoptotic death. These compounds have been developed as anti-cancer agents to counteract increased levels of Bcl-2 proteins often present in cancer cells. Application of a chemotherapeutic drug supported with a BH3 mimetic has the potential to overcome drug resistance in cancers overexpressing anti-apoptotic Bcl-2 proteins and thus increase the success rate of the treatment. We have previously shown that the BH3 mimetics, BH3I-2' and HA14-1, induce Ca²⁺ release from intracellular stores followed by a sustained elevation of the cytosolic Ca²⁺ concentration. Here we demonstrate that loss of Bax, but not Bcl-2 or Bak, inhibits this sustained Ca²⁺ elevation. What is more, in the absence of Bax, thapsigargin-elicited responses were decreased; and in two-photon-permeabilised bax^-/- cells, Ca²⁺ loss from the ER was reduced compared to WT cells. The Ca²⁺-like peptides, CALP-1 and CALP-3, which activate EF hand motifs of Ca²⁺-binding proteins, significantly reduced excessive Ca²⁺ signals and necrosis caused by two BH3 mimetics: BH3I-2' and gossypol. In the presence of CALP-1, cell death was shifted from necrotic towards apoptotic, whereas CALP-3 increased the proportion of live cells. Importantly, neither of the CALPs markedly affected physiological Ca²⁺ signals elicited by ACh, or cholecystokinin. In conclusion, the reduction in passive ER Ca²⁺ leak in bax^-/- cells as well as the fact that BH3 mimetics trigger substantial Ca²⁺ signals by liberating Bax, indicate that Bax may regulate Ca²⁺ leak channels in the ER. This study also demonstrates proof-of-principle that pre-activation of EF hand Ca²⁺-binding sites by CALPs can be used to ameliorate excessive Ca²⁺ signals caused by BH3 mimetics and shift necrotic death towards apoptosis.

Intermediate Filaments as Organizers of Cellular Space: How They Affect Mitochondrial Structure and Function

Intermediate filaments together with actin filaments and microtubules form the cytoskeleton, which is a complex and highly dynamic 3D network. Intermediate filaments are the major mechanical stress protectors but also affect cell growth, differentiation, signal transduction, and migration. Using intermediate filament-mitochondrial crosstalk as a prominent example, this review emphasizes the importance of intermediate filaments as crucial organizers of cytoplasmic space to support these functions. We summarize observations in different mammalian cell types which demonstrate how intermediate filaments influence mitochondrial morphology, subcellular localization, and function through direct and indirect interactions and how perturbations of these interactions may lead to human diseases.

NF-kB as a key player in regulation of cellular radiation responses and identification of radiation countermeasures

Nuclear factor (NF)-κB is a transcription factor that plays significant role in immunity, cellular survival and inhibition of apoptosis, through the induction of genetic networks. Depending on the stimulus and the cell type, the members of NF-κB related family (RelA, c-Rel, RelB, p50, and p52), forms different combinations of homo and hetero-dimers. The activated complexes (Es) translocate into the nucleus and bind to the 10bp κB site of promoter region of target genes in stimulus specific manner. In response to radiation, NF-κB is known to reduce cell death by promoting the expression of anti-apoptotic proteins and activation of cellular antioxidant defense system. Constitutive activation of NF-κB associated genes in tumour cells are known to enhance radiation resistance, whereas deletion in mice results in hypersensitivity to IR-induced GI damage. NF-κB is also known to regulate the production of a wide variety of cytokines and chemokines, which contribute in enhancing cell proliferation and tissue regeneration in various organs, such as the GI crypts stem cells, bone marrow etc., following exposure to IR. Several other cytokines are also known to exert potent pro-inflammatory effects that may contribute to the increase of tissue damage following exposure to ionizing radiation. Till date there are a series of molecules or group of compounds that have been evaluated for their radio-protective potential, and very few have reached clinical trials. The failure or less success of identified agents in humans could be due to their reduced radiation protection efficacy. In this review we have considered activation of NF-κB as a potential marker in screening of radiation countermeasure agents (RCAs) and cellular radiation responses. Moreover, we have also focused on associated mechanisms of activation of NF-κB signaling and their specified family member activation with respect to stimuli. Furthermore, we have categorized their regulated gene expressions and their function in radiation response or modulation. In addition, we have discussed some recently developed radiation countermeasures in relation to NF-κB activation

Calcium signaling alterations, oxidative stress, and autophagy in aging

SIGNIFICANCE

Aging is a multi-factorial process that may be associated with several functional and structural deficits which can evolve into degenerative diseases. In this review, we present data that may depict an expanded view of molecular aging theories, beginning with the idea that reactive oxygen species (ROS) are the major effectors in this process. In addition, we have correlated the importance of autophagy as a neuroprotective mechanism and discussed a link between age-related molecules, Ca(2+) signaling, and oxidative stress.

RECENT ADVANCES

There is evidence suggesting that alterations in Ca(2+) homeostasis, including mitochondrial Ca(2+) overload and alterations in electron transport chain (ETC) complexes, which increase cell vulnerability, are linked to oxidative stress in aging. As much as Ca(2+) signaling is altered in aged cells, excess ROS can be produced due to an ineffective coupling of mitochondrial respiration. Damaged mitochondria might not be removed by the macroautophagic system, which is hampered in aging by lipofuscin accumulation, boosting ROS generation, damaging DNA, and, ultimately, leading to apoptosis.

CRITICAL ISSUES

This process can lead to altered protein expression (such as p53, Sirt1, and IGF-1) and progress to cell death. This cycle can lead to increased cell vulnerability in aging and contribute to an increased susceptibility to degenerative processes.

FUTURE DIRECTIONS

A better understanding of Ca(2+) signaling and molecular aging alterations is important for preventing apoptosis in age-related diseases. In addition, caloric restriction, resveratrol and autophagy modulation appear to be predominantly cytoprotective, and further studies of this process are promising in age-related disease therapeutics.

Canonical Wnt signaling protects hippocampal neurons from Aβ oligomers: role of non-canonical Wnt-5a/Ca(2+) in mitochondrial dynamics

Alzheimer's disease (AD) is the most common type of age-related dementia. The disease is characterized by a progressive loss of cognitive abilities, severe neurodegeneration, synaptic loss and mitochondrial dysfunction. The Wnt signaling pathway participates in the development of the central nervous system and growing evidence indicates that Wnts also regulate the function of the adult nervous system. We report here, that indirect activation of canonical Wnt/β-catenin signaling using Bromoindirubin-30-Oxime (6-BIO), an inhibitor of glycogen synthase kinase-3β, protects hippocampal neurons from amyloid-β (Aβ) oligomers with the concomitant blockade of neuronal apoptosis. More importantly, activation with Wnt-5a, a non-canonical Wnt ligand, results in the modulation of mitochondrial dynamics, preventing the changes induced by Aβ oligomers (Aβo) in mitochondrial fission-fusion dynamics and modulates Bcl-2 increases induced by oligomers. The canonical Wnt-3a ligand neither the secreted Frizzled-Related Protein (sFRP), a Wnt scavenger, did not prevent these effects. In contrast, some of the Aβ oligomer effects were blocked by Ryanodine. We conclude that canonical Wnt/β-catenin signaling controls neuronal survival, and that non-canonical Wnt/Ca(2+)signaling modulates mitochondrial dysfunction. Since mitochondrial dysfunction is present in neurodegenerative diseases, the therapeutic possibilities of the activation of Wnt signaling are evident.

Non-apoptotic roles of Bcl-2 family: the calcium connection

The existence of the bcl-2 (B-cell lymphoma-2) gene was reported nearly 30 years ago. Yet, Bcl-2 family group of proteins still surprises us with their structural and functional diversity. Since the discovery of the Bcl-2 family of proteins as one of the main apoptosis judges, the precise mechanism of their action remains a hot topic of intensive scientific research and debates. Although extensive work has been performed on the role of mitochondria in apoptosis, more and more studies point out an implication of the endoplasmic reticulum in this process. Interestingly, Bcl-2 family proteins could be localized to both the mitochondria and the endoplasmic reticulum highlighting their crucial role in apoptosis control. In particular, in these organelles Bcl-2 proteins seem to be involved in calcium homeostasis regulation although the mechanisms underlying this function are still misunderstood. We now assume with high degree of certainty that the majority of Bcl-2 family members take part not only in apoptosis regulation but also in other processes important for the cell physiology briefly denominated as "non-apoptotic" functions. Drawing a complete and comprehensive image of Bcl-2 family requires the understanding of their implications in all cellular processes. Here, we review the current knowledge on the control of calcium homeostasis by the Bcl-2 family at the endoplasmic reticulum and at the mitochondria. Then we focus on the non-apoptotic functions of the Bcl-2 proteins in relation with the regulation of this versatile intracellular messenger. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

Signaling cascades initiated by TSLP-mediated signals in different cell types

Thymic stromal lymphopoietin (TSLP) has been well characterized as a consequence of its ability to modulate allergic and neoplastic diseases. However, downstream signaling mediated by TSLP varies significantly between the cell type and species examined. Since this observation is often overlooked and in some cases ignored, this review aims to consolidate the molecular pathways activated by TSLP receptors expressed by various human and mouse cell types.

Bcl-2 protein family members: versatile regulators of calcium signaling in cell survival and apoptosis

Bcl-2 family members are important regulators of cell survival and cell death. Researchers have focused mainly on mitochondria, where both proapoptotic and antiapoptotic family members function to regulate the release of cytochrome c and other mediators of apoptosis. However, as reviewed here, Bcl-2 family members also operate on another front, the endoplasmic reticulum (ER), to both positively and negatively regulate the release of Ca2+. There is abundant evidence that Ca2+ signals trigger apoptosis in response to a wide variety of agents and conditions. Conversely, Ca2+ signals can also mediate cell survival. Recent findings indicate that Bcl-2 interacts with inositol 1,4,5-trisphosphate (IP3) receptor Ca2+ channels on the ER, regulating their opening in response to IP3- and thus inhibiting IP3-mediated Ca2+ signals that induce apoptosis while enhancing Ca2+ signals that support cell survival.

Contribuição na prevenção da isquemia cerebral pelo cilostazol, um inibidor da fosfodiesterase III: revisão de literatura

Esta revisão bibliográfica objetiva expor estas pesquisas sobre as ações do cilostazol no sistema nervoso central. O cilostazol é uma droga que demonstrou exercer inibição seletiva e potente da fosfodiesterase tipo III, ocasionando o aumento de adenosina cíclica -3',5'-monofosfato nas plaquetas, nas células endoteliais e nas células musculares lisas, sendo classificado como vasodilatador, antiagregante plaquetário e antitrombótico. É o fármaco de primeira escolha na claudicação intermitente devido à doença arterial obstrutiva periférica. Além disso, há evidências de que o cilostazol é eficaz no processo aterosclerótico cerebral, promovendo aumento do fluxo e volume sangüíneos e prevenindo infartos, especialmente lacunares e recorrentes, por diminuir a morte celular devido à apoptose e ao estresse oxidativo nas substâncias branca e parda.

Mitochondrial DNA-dependent effects of valproate on mitochondrial calcium levels in transmitochondrial cybrids

Calcium plays important roles in various cellular processes. Using transmitochondrial hybrid cells (cybrids) carrying fluorescent calcium indicators, we previously found two mitochondrial DNA (mtDNA) polymorphism sites, 8701 and 10398, that alter intracellular calcium signalling and mitochondrial pH. The 10398A polymorphism is reportedly associated with bipolar disorder, Parkinson's disease, Alzheimer's disease, and cancer, whereas 10398G is associated with longevity. In bipolar disorder, elevation of intracellular calcium levels in the platelets and lymphocytes is a well-replicated finding. Thus, we examined whether two mood stabilizers, lithium and valproate, affect the intracellular calcium signalling in cybrids with these mtDNA polymorphisms. After cybrids with 8701A/10398A and 8701G/10398G (three cell lines for each) derived from healthy controls were pretreated with lithium (0.75 mm or 1.5 mm) or valproate (0.6 mm or 1.2 mm) for 7 d, they were stimulated by 10 mum histamine. Valproate decreased mitochondrial calcium levels, compared with untreated cybrids, only in cybrids with 8701A/10398A. Moreover, valproate decreased cytosolic calcium levels at plateau after stimulation in cybrids with 8701A/10398A. These finding suggest that valproate may stabilize intracellular calcium only in cells with high mitochondrial calcium levels.

The cellular concentration of Bcl-2 determines its pro- or anti-apoptotic effect

Bcl-2 is an oncoprotein that is widely known to promote cell survival by inhibiting apoptosis. We explored the consequences of different expression paradigms on the cellular action of Bcl-2. Using either transient or stable transfection combined with doxycycline-inducible expression, we titrated the cellular concentration of Bcl-2. With each expression paradigm Bcl-2 was correctly targeted to the endoplasmic reticulum and mitochondria. However, with protocols that generated the greatest cellular concentrations of Bcl-2 the structure of these organelles was dramatically altered. The endoplasmic reticulum appeared to be substantially fragmented, whilst mitochondria coalesced into dense perinuclear structures. Under these conditions of high Bcl-2 expression, cells were not protected from pro-apoptotic stimuli. Rather Bcl-2 itself caused a significant amount of spontaneous cell death, and sensitised the cells to apoptotic agents such as staurosporine or ceramide. We observed a direct correlation between Bcl-2 concentration and spontaneous apoptosis. Expression of calbindin, a calcium buffering protein, or an enzyme that inhibited inositol 1,4,5-trisphosphate-mediated calcium release, significantly reduced cell death caused by Bcl-2 expression. We further observed that high levels of Bcl-2 expression caused lipid peroxidation and that the deleterious effects of Bcl-2 could be abrogated by the reactive oxygen species (ROS) scavenger Trolox. When stably expressed at low levels, Bcl-2 did not corrupt organelle structure or trigger spontaneous apoptosis. Rather, it protected cells from pro-apoptotic stimuli. These data reveal that high cellular concentrations of Bcl-2 lead to a calcium- and ROS-dependent induction of death. Selection of the appropriate expression paradigm is therefore crucial when investigating the biological role of Bcl-2.

IP3 receptors in cell survival and apoptosis: Ca2+ release and beyond

Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) serve to discharge Ca(2+) from ER stores in response to agonist stimulation. The present review summarizes the role of these receptors in models of Ca(2+)-dependent apoptosis. In particular we focus on the regulation of IP(3)Rs by caspase-3 cleavage, cytochrome c, anti-apoptotic proteins and Akt kinase. We also address the evidence that some of the effects of IP(3)Rs in apoptosis may be independent of their ion-channel function. The role of IP(3)Rs in delivering Ca(2+) to the mitochondria is discussed from the perspective of the factors determining inter-organellar dynamics and the spatial proximity of mitochondria and ER membranes.

TNF provokes cardiomyocyte apoptosis and cardiac remodeling through activation of multiple cell death pathways

Transgenic mice with cardiac-restricted overexpression of secretable TNF (MHCsTNF) develop progressive LV wall thinning and dilation accompanied by an increase in cardiomyocyte apoptosis and a progressive loss of cytoprotective Bcl-2. To test whether cardiac-restricted overexpression of Bcl-2 would prevent adverse cardiac remodeling, we crossed MHCsTNF mice with transgenic mice harboring cardiac-restricted overexpression of Bcl-2. Sustained TNF signaling resulted in activation of the intrinsic cell death pathway, leading to increased cytosolic levels of cytochrome c, Smac/Diablo and Omi/HtrA2, and activation of caspases -3 and -9. Cardiac-restricted overexpression of Bcl-2 blunted activation of the intrinsic pathway and prevented LV wall thinning; however, Bcl-2 only partially attenuated cardiomyocyte apoptosis. Subsequent studies showed that c-FLIP was degraded, that caspase-8 was activated, and that Bid was cleaved to t-Bid, suggesting that the extrinsic pathway was activated concurrently in MHCsTNF hearts. As expected, cardiac Bcl-2 overexpression had no effect on extrinsic signaling. Thus, our results suggest that sustained inflammation leads to activation of multiple cell death pathways that contribute to progressive cardiomyocyte apoptosis; hence the extent of such programmed myocyte cell death is a critical determinant of adverse cardiac remodeling.

The attenuating effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in human neuroblastoma SH-SY5Y cells

Memantine, a clinically used N-methyl-D-aspartate (NMDA)-receptor antagonist, has been shown to prevent apoptotic neuronal damage connected with the over-activity of NMDA receptors. In the present study, we examined the effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in the SH-SY5Y cell line which does not possess functional NMDA receptors. Electrophysiological recordings and toxicity studies showed no response to NMDA-evoked currents in this cell line, irrespective of the stage of its neuronal differentiation. Memantine (0.1-2 microM) attenuated staurosporine-induced apoptosis as evidenced by reversal of the changes in mitochondrial membrane potential (DeltaPsi(m)) and decreased caspase-3 activity, lactate dehydrogenase (LDH) release and DNA fragmentation. Wortmannin (10 nM) and LY 294002 (10 microM) (inhibitors of phosphatidylinositol-3-kinase, PI3-K) reversed the inhibitory effect of memantine on the staurosporine-induced LDH release, suggesting that the PI3-K/Akt prosurvival pathway is a possible target for antiapoptotic action of memantine. Memantine at low micromolar concentrations also attenuated salsolinol- and doxorubicin-induced LDH release and DNA fragmentation, but only in the case of salsolinol was this effect accompanied by a decrease in caspase-3 activity. The present data indicate that memantine attenuates the toxic effects of various proapoptotic agents and the cytoprotective effect of memantine does not seem to be connected with its action on NMDA receptor but rather with its influence on intracellular pathways engaged in cellular survival/apoptotic processes.

Role of the unfolded protein response in cell death

Unfolded protein response (UPR) is an important genomic response to endoplasmic reticulum (ER) stress. The ER chaperones, GRP78 and Gadd153, play critical roles in cell survival or cell death as part of the UPR, which is regulated by three signaling pathways: PERK/ATF4, IRE1/XBP1 and ATF6. During the UPR, accumulated unfolded protein is either correctly refolded, or unsuccessfully refolded and degraded by the ubiquitin-proteasome pathway. When the unfolded protein exceeds a threshold, damaged cells are committed to cell death, which is mediated by ATF4 and ATF6, as well as activation of the JNK/AP-1/Gadd153-signaling pathway. Gadd153 suppresses activation of Bcl-2 and NF-kappaB. UPR-mediated cell survival or cell death is regulated by the balance of GRP78 and Gadd153 expression, which is coregulated by NF-kappaB in accordance with the magnitude of ER stress. Less susceptibility to cell death upon activation of the UPR may contribute to tumor progression and drug resistance of solid tumors.

Mitochondrial Ca2+ as a key regulator of cell life and death

Mitochondrial Ca(2+) homeostasis is today at the center of wide interest in the scientific community because of its role both in the modulation of numerous physiological responses and because of its involvement in cell death. In this review, we briefly summarize a few basic features of mitochondrial Ca(2+) handling in vitro and within living cells, and its involvement in the modulation of Ca(2+)-dependent signaling. We then discuss the role of mitochondrial Ca(2+) in the control of apoptotic death, focusing in particular on the effects of pro- and anti-apoptotic proteins of the Bcl-2 family. Finally, the potential involvement of Ca(2+) and mitochondria in the development of two diseases, Ullrich muscular dystrophy and familial Alzheimer's disease, is briefly discussed.

Estrogen protects neuronal cells from amyloid beta-induced apoptosis via regulation of mitochondrial proteins and function

BACKGROUND

Neurodegeneration in Alzheimer's disease is associated with increased apoptosis and parallels increased levels of amyloid beta, which can induce neuronal apoptosis. Estrogen exposure prior to neurotoxic insult of hippocampal neurons promotes neuronal defence and survival against neurodegenerative insults including amyloid beta. Although all underlying molecular mechanisms of amyloid beta neurotoxicity remain undetermined, mitochondrial dysfunction, including altered calcium homeostasis and Bcl-2 expression, are involved in neurodegenerative vulnerability.

RESULTS

In this study, we investigated the mechanism of 17beta-estradiol-induced prevention of amyloid beta-induced apoptosis of rat hippocampal neuronal cultures. Estradiol treatment prior to amyloid beta exposure significantly reduced the number of apoptotic neurons and the associated rise in resting intracellular calcium levels. Amyloid beta exposure provoked down regulation of a key antiapoptotic protein, Bcl-2, and resulted in mitochondrial translocation of Bax, a protein known to promote cell death, and subsequent release of cytochrome c. E2 pretreatment inhibited the amyloid beta-induced decrease in Bcl-2 expression, translocation of Bax to the mitochondria and subsequent release of cytochrome c. Further implicating the mitochondria as a target of estradiol action, in vivo estradiol treatment enhanced the respiratory function of whole brain mitochondria. In addition, estradiol pretreatment protected isolated mitochondria against calcium-induced loss of respiratory function.

CONCLUSION

Therefore, we propose that estradiol pretreatment protects against amyloid beta neurotoxicity by limiting mitochondrial dysfunction via activation of antiapoptotic mechanisms.

Effects of methotrexate on calcium flux in rat liver mitochondria, microsomes and plasma membrane vesicles

The metabolic effects of methotrexate in perfused livers are similar to those exerted by hormones acting through Ca(2+)-dependent mechanisms. The aim of the present study was to determine whether the effects of methotrexate are mediated by a direct action on cellular Ca(2+) fluxes. Methotrexate did not affect the ATP-dependent (45)Ca(2+) uptake by mitochondria, microsomes and inside-out plasma membrane vesicles and Ca(2+) efflux from plasma membrane vesicles. However, methotrexate was able to stimulate (45)Ca(2+) release from preloaded microsomes. The amount of Ca(2+) released by methotrexate was similar to that induced by IP(3). Methotrexate could be acting through the capacitative calcium entry mechanism.

Bcl-2 overexpression prevents calcium overload and subsequent apoptosis in dystrophic myotubes

Duchenne muscular dystrophy (DMD) is a lethal disease caused by the lack of the cytoskeletal protein dystrophin. Altered calcium homoeostasis and increased calcium concentrations in dystrophic fibres may be responsible for the degeneration of muscle occurring in DMD. In the present study, we used subsarcolemmal- and mitochondrial-targeted aequorin to study the effect of the antiapoptotic Bcl-2 protein overexpression on carbachol-induced near-plasma membrane and mitochondrial calcium responses in myotubes derived from control C57 and dystrophic (mdx) mice. We show that Bcl-2 overexpression decreases subsarcolemmal and mitochondrial calcium overload that occurs during activation of nicotinic acetylcholine receptors in dystrophic myotubes. Moreover, our results suggest that overexpressed Bcl-2 protein may prevent near-plasma membrane and mitochondrial calcium overload by inhibiting IP3Rs (inositol 1,4,5-trisphosphate receptors), which we have shown previously to be involved in abnormal calcium homoeostasis in dystrophic myotubes. Most likely as a consequence, the inhibition of IP3R function by Bcl-2 also inhibits calcium-dependent apoptosis in these cells.

Neuroprotection by cilostazol, a phosphodiesterase type 3 inhibitor, against apoptotic white matter changes in rat after chronic cerebral hypoperfusion

In the present study, we elucidated effect of cilostazol to prevent the occurrence of vacuolation and rarefaction of the white matter in association with apoptosis induced by bilateral occlusion of common carotid arteries in the male Wistar rats. Rats orally received vehicle (DMSO) or 60 mg kg(-1) day(-1) (orally) cilostazol for 3, 7, 14 or 30 days. In the vehicle group, increased vacuolation and rarefactions in the white matter were accompanied by extensive activation of both microglial and astroglial cells with suppression of oligodendrocytes in association with increased TNF-alpha production, caspase-3 immunoreactivity and TUNEL-positive cells in the white matter including optic tract. Post-treatment with cilostazol (60 mg kg(-1) day(-1)) strongly suppressed not only elevated activation of astroglia and microglia but also diminished oligodendrocytes following chronic cerebral hypoperfusion. In conclusion, cilostazol (60 mg kg(-1) day(-1), orally) significantly reduced the apoptotic cell death in association with decreased TNF-alpha production and caspase-3-positive cells in the white matter of rat brains subjected to bilateral occlusion of common carotid arteries, consequently ameliorating vacuoles and rarefaction changes in the white matter.

Don't lose heart--therapeutic value of apoptosis prevention in the treatment of cardiovascular disease

Cardiovascular disease is a leading cause of death worldwide. Loss of function or death of cardiomyocytes is a major contributing factor to these diseases. Cell death in conditions such as heart failure and myocardial infarction is associated with apoptosis. Apoptotic pathways have been well studied in non-myocytes and it is thought that similar pathways exist in cardiomyocytes. These pathways include death initiated by ligation of membrane-bound death receptors, release of pro-apoptotic factors from mitochondria or stress at the endoplasmic reticulum. The key regulators of apoptosis include inhibitors of caspases (IAPs), the Bcl-2 family of proteins, growth factors, stress proteins, calcium and oxidants. The highly organized and predictive nature of apoptotic signaling means it is amenable to manipulation. A thorough understanding of the apoptotic process would facilitate intervention at the most suitable points, alleviating myocardium decline and dysfunction. This review summarizes the mechanisms underlying apoptosis and the mediators/regulators involved in these signaling pathways. We also discuss how the potential therapeutic value of these molecules could be harnessed.

Bcl-2 mediated inhibition of erucylphosphocholine-induced apoptosis depends on its subcellular localisation

The synthetic phospholipid derivative erucylphosphocholine (ErPC) is a potent inducer of apoptosis in human tumor cell lines. This membrane-targeted drug induces apoptosis independently from death receptor signaling through a mitochondrial pathway that is inhibited by over-expression of Bcl-2. Within the cell, Bcl-2 resides in membranes of mitochondria, endoplasmic reticulum (ER) and the nucleus. However, the importance of its subcellular localisation in distinct organelles for protection against apoptosis is not completely understood. To investigate the impact of Bcl-2 localised at defined subcellular compartments on its protective effects against ErPC-induced apoptosis, Bcl-2 expression was directed to the outer membrane of the mitochondria or the ER of Jurkat T Lymphoma cells, using Bcl-2 mutants with modified membrane anchors. The mitochondrial insertion sequence of ActA directed Bcl-2 to the mitochondria (Bcl-2/MT), the ER-specific sequence of cytochrome b5 to the ER (Bcl-2/ER). Additionally, Jurkat cells expressing wild-type Bcl-2 (Bcl-2/WT) or a transmembrane domain-lacking mutant (Bcl-2/DeltaTM) were employed. While restricted expression of Bcl-2 either at membranes of the mitochondria or the ER strongly interfered with ErPC-induced mitochondrial damage and apoptosis, cytosolic Bcl-2/DeltaTM exhibited only reduced protection. Thus, membrane localisation of Bcl-2 is a prerequisite for substantial protection against ErPC-induced apoptosis. For efficient long-term inhibition of ErPC-induced apoptosis Bcl-2 had to be present in the membranes of both compartments, the ER and the mitochondria. The finding that ER-targeted Bcl-2 interferes with ErPC-induced mitochondrial damage points to an involvement of the ER in apoptosis signaling upstream of the mitochondria and to a crosstalk between both compartments.

G1P3, an interferon inducible gene 6-16, is expressed in gastric cancers and inhibits mitochondrial-mediated apoptosis in gastric cancer cell line TMK-1 cell

Expression of an interferon inducible gene 6-16, G1P3, increases not only in type I interferon-treated cells but also in human senescent fibroblasts. However, the function of 6-16 protein is unknown. Here we report that 6-16 is 34 kDa glycosylated protein and localized at mitochondria. Interestingly, 6-16 is expressed at high levels in gastric cancer cell lines and tissues. One of exceptional gastric cancer cell line, TMK-1, which do not express detectable 6-16, is sensitive to apoptosis induced by cycloheximide (CHX), 5-fluorouracil (5-FU) and serum-deprivation. Ectopic expression of 6-16 gene restored the induction of apoptosis and inhibited caspase-3 activity in TMK-1 cells. Thus 6-16 protein has anti-apoptotic function through inhibiting caspas-3. This anti-apoptotic function is expressed through inhibition of the depolarization of mitochondrial membrane potential and release of cytochrome c. By two-hybrid screening, we found that 6-16 protein interacts with calcium and integrin binding protein, CIB/KIP/Calmyrin (CIB), which interacts with presenilin 2, a protein involved in Alzheimer's disease. These protein interactions possibly play a pivotal role in the regulation of apoptosis, for which further detailed analyses are need. These results overall indicate that 6-16 protein may have function as a cell survival protein by inhibiting mitochondrial-mediated apoptosis.

Mitochondrial dysfunction is related to necrosis-like programmed cell death induced by A23187 in CEM cells

We have previously reported that calcium ionophore A23187 differentially induces necrosis in CEM cells, a T-lymphoblastic leukemia cell line, and apoptosis in HL60 cells, a promyelocytic leukemia cell line. Stimulation with VP16, however, induces typical apoptosis in both cell lines. Necrosis in CEM cells, characterized by cell shrinkage and clustering, began within 5 min of treatment. Swelling of the mitochondria, lumpy chromatin condensation and intact plasma membranes were evident by electron microscopy. These A23187-mediated changes in CEM cells were suppressed by clonazepam or CGP37157, inhibitors of the mitochondrial Na(+)/Ca(2+) exchanger. The changes, however, were not affected by cyclosporin A, an inhibitor of the mitochondrial permeability transition pore. In both CEM and HL60 cells, intra-cellular calcium increased with similar amplitude within 1 min of treatment with 2 microM A23187. Intra-mitochondrial calcium increased with clonazepam pre-treatment alone in both CEM and HL60 cells. However, intra-mitochondrial calcium did not change drastically in response to A23187 in CEM or HL60 cells, either untreated or pre-treated with clonazepam. A23187 induces necrosis in CEM cells concurrent with mitochondrial dysfunction, which is independent of the mitochondrial permeability transition, but affected by intra-mitochondrial calcium, while HL60 cells lack these early changes. Differences in the responses to A23187 between these two cell lines might derive from differences in the susceptibility of the mitochondrial membrane to rapid increases in intra-cellular calcium.

Lack of a Gender Difference in Post-Traumatic Neurodegeneration in the Mouse Controlled Cortical Impact Injury Model

Recent studies using a mouse model of weight-drop-induced "diffuse" traumatic brain injury (TBI) have demonstrated a substantial gender difference in the time course and magnitude of post-traumatic neurodegeneration following a severe level of injury. The time of maximal damage, as assessed by the de Olmos aminocupric silver staining method, occurred at 72 h in male mice, whereas the peak of neurodegeneration was not observed until 14 days in females and was less in magnitude compared to males. This difference, favoring females, has been postulated to relate to the neuroprotective actions of estrogen and progesterone. In the presently reported experiments, we compared the time course and peak of neurodegeneration in male and female mice after a severe level of "focal" controlled cortical impact (CCI; 1 mm, 3.5 m/sec) TBI using the same strain (CF-1) and weight (29-31 g) as employed in the "diffuse" TBI study. The volume of silver staining was measured using image analysis methods at 24, 48, and 72 h, and 1, 2 and 4 weeks. In male and female mice, a significant increase in neurodegeneration was observed at 24 h, and the volume was not significantly different between the two genders. In both gender groups, the maximal neurodegeneration was seen at 48 h after injury. Although the female mice exhibited a trend toward higher mean volumes of silver staining, this difference was not significantly different compared to males. Furthermore, the rate of resolution of staining between 48 h and 4 weeks was similar. However, injured females still exhibited a significantly higher volume of staining compared to sham, non-injured females at 4 weeks, whereas the difference in staining volume between sham and injured males was no longer significant at that time point. These results show that, following a "focal" CCI, there is no gender difference that favors females, in contrast to that seen with the "diffuse" injury paradigm. The disparity between the effects of gender in the two models may be due to the fact that, in the "focal" CCI model, the timing of post-traumatic neurodegeneration is significantly more rapid than that seen in the "diffuse" model, which may overwhelm the neuroprotective effects of estrogen and progesterone and obscure the appearance of a gender difference.

Calcium buffering activity of mitochondria controls basal growth hormone secretion and modulates specific neuropeptide signaling

Goldfish somatotropes contain multiple functionally distinct classes of non-mitochondrial intracellular Ca(2+) stores. In this study, we investigated the role of mitochondrial Ca(2+) handling in the control of hormone secretion. Inhibition of mitochondrial Ca(2+) uptake with 10 microM ruthenium red (RR) and 10 microM carbonyl cyanide m-chlorophenylhydrazone (CCCP) caused a small and reversible increase in cytosolic [Ca(2+)]. Despite relatively modest global Ca(2+) signals, RR and CCCP stimulated robust GH secretion under basal culture conditions. CCCP-stimulated hormone release was abolished in cells pre-incubated with 50 microM BAPTA-AM, suggesting that elevations in cytosolic [Ca(2+)] mediate this release of GH. Both caffeine-sensitive intracellular Ca(2+) stores and L-type Ca(2+) channels can be the source of the Ca(2+) buffered by mitochondria in somatotropes. The stimulatory effect of RR on caffeine-stimulated GH release was enhanced dramatically in the presence of ryanodine, pointing to a complex interaction between these three Ca(2+) stores. Inhibition of mitochondrial Ca(2+) uptake with RR augmented GH release evoked by only one of the two endogenous gonadotropin-releasing hormones. Thus, we provide the first evidence that mitochondrial Ca(2+) buffering is differentially involved in specific agonist Ca(2+) signaling pathways and plays an important role in the control of basal GH release.

Human T lymphotropic virus type 1 accessory protein p12I modulates calcium-mediated cellular gene expression and enhances p300 expression in T lymphocytes

Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent of adult T cell leukemia/lymphoma (ATLL), an aggressive CD4+ T lymphocyte malignancy. Activation of T lymphocytes is required for effective retroviral integration into the host cell genome and subsequent viral replication, but the molecular mechanisms involved in HTLV-1-mediated T cell activation remain unclear. HTLV-1 encodes various accessory proteins such as p12I, which has been demonstrated to be critical for HTLV-1 infectivity in vivo in rabbits and in vitro in quiescent primary human T lymphocytes. This hydrophobic protein localizes in the endoplasmic reticulum, increases intracellular calcium, and activates nuclear factor of activated T cell-mediated transcription. To further elucidate the role of p12I in regulation of cellular gene expression, we performed gene array analysis on stable p12I-expressing Jurkat T cells, using Affymetrix U133A arrays. Our data indicate that p12I altered the expression of genes associated with a network of interrelated pathways including T cell signaling, cell proliferation, and apoptosis. Expression of several calcium-regulated genes was found to be altered by p12I, consistent with known properties of the viral protein. Gene array findings were confirmed by semiquantitative RT-PCR in Jurkat T cells and primary CD4+ T lymphocytes. Furthermore, dose-dependent expression of p12I in Jurkat T cells resulted in significant increases in p300 and p300-dependent transcription. This is the first report of a viral protein influencing the transcription of p300, a rate-limiting coadapter critical in HTLV-1-mediated T cell activation. Collectively, our data strongly indicate that HTLV-1 p12I modulates cellular gene expression patterns to hasten the activation of T lymphocytes and thereby promote efficient viral infection.

Regulation of Ca2+-induced permeability transition by Bcl-2 is antagonized by Drp1 and hFis1

The regulation of mitochondrial permeability transition (MPT) is essential for cell survival. Un-controlled opening of the MPT pore is often associated with cell death. Anti-death protein Bcl-2 can block MPT as assessed by the enhanced capacity of mitochondria to accumulate and retain Ca2+. We report here that two proteins of the mitochondrial fission machinery, dynamin-related protein (Drp1) and human mitochondrial fission protein (hFis1), have an antagonistic effect on Bcl-2. Drp1, with the assistance of hFis1, sensitizes cells to MPT by reducing the mitochondrial Ca2+ retention capacity (CRC). While the reduction of CRC by Drp1/hFis1 is linked to mitochondrial fission, the antagonism between Bcl-2 and Drp1 appears to be mediated by mutually exclusive interactions of the two proteins with hFis1 . The complexity of protein-protein interactions demonstrated in the present study suggests that in addition to the previously described role of Bcl-2 in the control of apoptosis, Bcl-2 may also participate directly or indirectly in the regulation of mitochondrial fission.

Methyl protodioscin induces G2/M arrest and apoptosis in K562 cells with the hyperpolarization of mitochondria

Methyl protodioscin is a furostanol bisglycoside with antitumor properties. The present study investigated its effects on human chronic myelogenous leukemia K562 cells. Cell cycle analysis showed that methyl protodioscin caused distinct G2/M arrest, with the appearance of polyploidy population. The levels of cyclin B1 decreased, whereas Cdc2 kept at a steady level. Subsequent apoptosis after G2/M blockage was demonstrated through DNA fragmentation and the annexin V staining assay. Methyl protodioscin induced a biphasic alteration (i.e. an early hyperpolarization, followed by depolarization) in mitochondrial membrane potential of K562 cells. The transient decline of intracellular Ca2+ concentration was observed at early stage. The generation of reactive oxygen species was also detected. The anti-apoptotic Bcl-x(L) transiently increased and then decreased. And the pro-apoptotic Bax was markedly up-regulated. Taken together, these data demonstrated that methyl protodioscin inhibits K562 cell proliferation via G2/M arrest and apoptosis, with mitochondrial hyperpolarization and the disruption of Ca2+ homeostasis playing important roles.

Anti-apoptotic action of (2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378) by suppression of the phosphatase and tensin homolog deleted from chromosome 10 phosphorylation and increased phosphorylation of casein kinase2/Akt/ cyclic AMP response element binding protein via maxi-K channel opening in neuronal cells

This study shows the signaling pathway by which (2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378) prevents tumor necrosis factor (TNF)-alpha-induced neuronal cell death. KR-31378 restored TNF-alpha-induced decreased cell viability of SK-N-SH. U87-MG cells (PTEN-null glioblastoma cell line) transfected with expression vectors for sense PTEN (phosphatase and tensin homolog deleted from chromosome 10) showed significantly decreased cell viability, which was restored by KR-31378. TNF-alpha-induced increased PTEN phosphorylation and decreased phosphorylation of Akt/cyclic AMP response element-binding protein (CREB) in SK-N-SH cells were concentration-dependently reversed by KR-31378, those of which were antagonized by iberiotoxin, a maxi-K channel blocker. TNF-alpha and apigenin, a casein kinase2 (CK2) inhibitor, showed decreased CK2 phosphorylation and increased PTEN phosphorylation, which were reversed by KR-31378. KR-31378 increased K(+) currents by activating the maxi-K channels in SK-N-SH cells, with suppression of TNF-alpha-induced increase in cytosolic Ca(2+) and elevation of suppressed mitochondrial membrane potential, all of which were antagonized by iberiotoxin. It is suggested that increase in cell viability by KR-31378 is ascribed to the maxi-K channel opening-coupled upregulation of CK2/Akt/CREB phosphorylation and downregulation of PTEN phosphorylation in association with increased Bcl-2 and decreased Bax levels.

P2Y2 receptors activate neuroprotective mechanisms in astrocytic cells

Mechanical or ischemic trauma to the CNS causes the release of nucleotides and other neurotransmitters into the extracellular space. Nucleotides can activate nucleotide receptors that modulate the expression of genes implicated in cellular adaptive responses. In this investigation, we used human 1321N1 astrocytoma cells expressing a recombinant P2Y2 receptor to assess the role of this receptor in the regulation of anti-apoptotic (bcl-2 and bcl-xl) and pro-apoptotic (bax) gene expression. Acute treatment with the P2Y2 receptor agonist UTP up-regulated bcl-2 and bcl-xl, and down-regulated bax, gene expression. Activation of P2Y2 receptors was also coupled to the phosphorylation of cyclic AMP responsive element binding protein that positively regulates bcl-2 and bcl-xl gene expression. Cyclic AMP responsive element decoy oligonucleotides markedly attenuated the UTP-induced increase in bcl-2 and bcl-xl mRNA levels. Activation of P2Y2 receptors induced the phosphorylation of the pro-apoptotic factor Bad and caused a reduction in bax/bcl-2 mRNA expression ratio. All these signaling pathways are known to be involved in cell survival mechanisms. Using cDNA microarray analysis and RT-PCR, P2Y2 receptors were found to up-regulate the expression of genes for neurotrophins, neuropeptides and growth factors including nerve growth factor 2; neurotrophin 3; glia-derived neurite-promoting factor, as well as extracellular matrix proteins CD44 and fibronectin precursor--genes known to regulate neuroprotection. Consistent with this observation, conditioned media from UTP-treated 1321N1 cells expressing P2Y2 receptors stimulated the outgrowth of neurites in PC-12 cells. Taken together, our results suggest an important novel role for the P2Y2 receptor in survival and neuroprotective mechanisms under pathological conditions.

Bcl-2 functionally interacts with inositol 1,4,5-trisphosphate receptors to regulate calcium release from the ER in response to inositol 1,4,5-trisphosphate

Inositol 1,4,5-trisphosphate (InsP3) receptors (InsP3Rs) are channels responsible for calcium release from the endoplasmic reticulum (ER). We show that the anti-apoptotic protein Bcl-2 (either wild type or selectively localized to the ER) significantly inhibited InsP3-mediated calcium release and elevation of cytosolic calcium in WEHI7.2 T cells. This inhibition was due to an effect of Bcl-2 at the level of InsP3Rs because responses to both anti-CD3 antibody and a cell-permeant InsP3 ester were decreased. Bcl-2 inhibited the extent of calcium release from the ER of permeabilized WEHI7.2 cells, even at saturating concentrations of InsP3, without decreasing luminal calcium concentration. Furthermore, Bcl-2 reduced the open probability of purified InsP3Rs reconstituted into lipid bilayers. Bcl-2 and InsP3Rs were detected together in macromolecular complexes by coimmunoprecipitation and blue native gel electrophoresis. We suggest that this functional interaction of Bcl-2 with InsP3Rs inhibits InsP3R activation and thereby regulates InsP3-induced calcium release from the ER.

Diosgenin induces cell cycle arrest and apoptosis in human leukemia K562 cells with the disruption of Ca2+ homeostasis

PURPOSE

Diosgenin is a steroidal sapogenin with estrogenic and antitumor properties. In order to elucidate the mechanism of its antiproliferative activity, we investigated its effects on the cell cycle and apoptosis in human chronic myelogenous leukemia K562 cells.

METHODS

Cell viability was assessed via an MTT assay. Apoptosis was investigated in terms of nuclear morphology, DNA fragmentation, and phosphatidylserine externalization. Cell cycle analysis was performed via PI staining and flow cytometry (FCM). Western blotting and immunofluorescence methods were used to determine the levels of p53, cell cycle-related proteins and Bcl-2 family members. FCM was also used to estimate the changes in mitochondrial membrane potential (MMP), intracellular Ca2+ concentration and reactive oxygen species (ROS) generation.

RESULTS

Cell cycle analysis showed that diosgenin caused G2/M arrest independently of p53. The levels of cyclin B1 and p21Cip1/Waf1 were decreased, whereas cdc2 levels were increased. Subsequent apoptosis was demonstrated with the dramatic activation of caspase-3. A dramatic decline in intracellular Ca2+ concentration was observed as an initiating event in the process of cell cycle arrest and apoptosis, which was followed by the hyperpolarization and depolarization of MMP. Generation of ROS was observed in the progression of apoptosis. The antiapoptotic Bcl-2 and Bcl-xL proteins were downregulated, whereas the proapoptotic Bax was upregulated.

CONCLUSIONS

Diosgenin inhibits K562 cell proliferation via cell cycle G2/M arrest and apoptosis, with disruption of Ca2+ homeostasis and mitochondrial dysfunction playing vital roles.

Bcl-2 and calcium: controversy beneath the surface

The function of Bcl-2 family members on the endoplasmic reticulum has received increasing attention in recent years. The endoplasmic reticulum is the major organelle involved in intracellular calcium homeostasis and calcium signaling, including calcium signals that mediate apoptosis induction by anticancer drugs. But currently a controversy exists regarding reported effects of Bcl-2 on the calcium concentration within the lumen of the endoplasmic reticulum. Although several prominent reports indicate that Bcl-2 overexpression is associated with a decrease in luminal calcium, there are a large number of reports indicating that Bcl-2 either does not decrease luminal calcium or actually increases luminal calcium. This review summarizes this vast array of conflicting findings, and analyses potential reasons why different conclusions have been reached by different laboratories. Future directions are emphasized that might bring clarity to this important area of apoptosis biology.

Raising intracellular calcium attenuates neuronal apoptosis triggered by staurosporine or oxygen-glucose deprivation in the presence of glutamate receptor blockade

The relationship between intracellular Ca(2+) ([Ca(2+)](i)) regulation and programmed cell death is not well-defined; both increases and decreases in [Ca(2+)](i) have been observed in cells undergoing apoptosis. We determined [Ca(2+)](i) in cultured murine cortical neurons undergoing apoptosis after exposure to staurosporine or following oxygen-glucose deprivation in the presence of glutamate receptor antagonists. Neuronal [Ca(2+)](i) was decreased 1-4 h after exposure to staurosporine (30 nM). A [Ca(2+)](i) decrease was also observed 1 h after the end of the oxygen-glucose deprivation period when MK-801 and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were added to the bathing medium during the deprivation period. A similar decrease in [Ca(2+)](i) produced by reducing extracellular Ca(2+) or chelating intracellular Ca(2+) was sufficient to induce neuronal apoptosis. Raising [Ca(2+)](i) either by activating voltage-sensitive Ca(2+) channels with (-) Bay K8644 or by application of low concentrations of kainate attenuated both staurosporine and oxygen-glucose deprivation-induced apoptosis.

Activation of K+ channels: an essential pathway in programmed cell death

Cell apoptosis and proliferation are two counterparts in sharing the responsibility for maintaining normal tissue homeostasis. In recent years, the process of the programmed cell death has gained much interest because of its influence on malignant cell growth and other pathological states. Apoptosis is characterized by a distinct series of morphological and biochemical changes that result in cell shrinkage, DNA breakdown, and, ultimately, phagocytic death. Diverse external and internal stimuli trigger apoptosis, and enhanced K+ efflux has been shown to be an essential mediator of not only early apoptotic cell shrinkage, but also of downstream caspase activation and DNA fragmentation. The goal of this review is to discuss the role(s) played by K+ transport or flux across the plasma membrane in the regulation of the apoptotic volume decrease and apoptosis. Attention has also been paid to the role of inner mitochondrial membrane ion transport in the regulation of mitochondrial permeability and apoptosis. We provide specific examples of how deregulation of the apoptotic process contributes to pulmonary arterial medial hypertrophy, a major pathological feature in patients with pulmonary arterial hypertension. Finally, we discuss the targeting of K+ channels as a potential therapeutic tool in modulating apoptosis to maintain the balance between cell proliferation and cell death that is essential to the normal development and function of an organism.

F16, a Mitochondriotoxic Compound, Triggers Apoptosis or Necrosis Depending on the Genetic Background of the Target Carcinoma Cell

Mutations that lead to the emergence of resistance to apoptosis are commonly observed among tumor cells. Some of the proteins affected are integral parts of the apoptotic cascade such as pro- and antiapoptotic members of the Bcl-2 family. F16 is a small molecule that accumulates in mitochondria of a variety of tumor cells and interferes with their physiological function. Because this interference ultimately triggers apoptosis in many affected cell lines, we examined the effect of antiapoptotic Bcl-2 overexpression on the response of cells to F16. Our results showed that high levels of Bcl-2 did not block the ability of F16 to induce cell death. However, unlike the apoptotic response that followed F16 treatment of cells with moderate Bcl-2 levels, cells resistant to a variety of apoptotic stimuli by virtue of Bcl-2 overexpression succumbed to F16 by necrosis. Thus, this dual ability of the mitochondriotoxic compound F16 to induce apoptosis and necrosis may represent an added advantage by expanding its spectrum of action toward genetically altered tumor cells incapable of apoptosis.

Mitochondrial control of neuron death and its role in neurodegenerative disorders

Genetic or functional mitochondrial alterations can result in the initiation of cell death programs that are believed to contribute to cell death in diabetes, ageing and neurodegenerative disorders. Mitochondria are being considered the main link between cellular stress signals activated during acute and chronic nerve cell injury, and the execution of nerve cell death. This second function of mitochondria is regulated by several families of proteins that can trigger an increase in permeability of the outer and/or inner mitochondrial membrane. One example of this is the formation of the mitochondrial permeability transition pore (MPTP). This process can trigger the release of cell death-inducing factors from mitochondria, as well as a dissipation of the mitochondrial transmembrane potential, depletion of ATP, and increased free radical formation. Among the factors released from mitochondria are cytochrome c, the apoptosis inductor factor (AIF), and caspases. We review the role of the MPTP in diverse physiological and pathological processes, including neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis (ALS). The design of drugs that could interfere with the functions of the MPTP could allow novel therapeutic approaches for the treatment of acute and chronic nerve cell injury.

Naproxen affects Ca2+ fluxes in mitochondria, microsomes and plasma membrane vesicles

There is substantial evidence that nonsteroidal anti-inflammatory drugs (NSAIDs) affect cellular processes regulated by Ca(2+) ions, including the metabolic responses of the liver to Ca(2+)-dependent hormones. The aim of the present study was to determine whether the effects of naproxen are mediated by a direct action on cellular Ca(2+) fluxes. The effects of naproxen on 45Ca(2+) fluxes in mitochondria, microsomes and inside-out plasma membrane vesicles were examined. Naproxen strongly impaired the mitochondrial capacity to retain 45Ca(2+) and inhibited also ATP-dependent 45Ca(2+) uptake by microsomes. Naproxen did not modify 45Ca(2+) uptake by inside-out plasma membrane vesicles, but it inhibited the hexokinase/glucose-induced Ca(2+) efflux from preloaded vesicles. Additional assays performed in isolated mitochondria revealed that naproxen causes mitochondrial uncoupling and swelling in the presence of Ca(2+) ions. These effects were prevented by EGTA, ruthenium red and cyclosporin A, indicating that naproxen acts synergistically with Ca(2+) ions by promoting the mitochondrial permeability transition. The experimental results suggest that naproxen may impair the metabolic responses to Ca(2+)-dependent hormones acting by at least two mechanisms: (1) by interfering with the supply of external Ca(2+) through a direct action on the plasma membrane Ca(2+) influx, and (2) by affecting the refilling of the agonist-sensitive internal stores, including endoplasmic reticulum and mitochondria.

Regulation of apoptosis by endoplasmic reticulum pathways

Apoptotic programmed cell death pathways are activated by a diverse array of cell extrinsic and intrinsic signals, most of which are ultimately coupled to the activation of effector caspases. In many instances, this involves an obligate propagation through mitochondria, causing egress of critical proapoptotic regulators to the cytosol. Central to the regulation of the mitochondrial checkpoint is a complex three-way interplay between members of the BCL-2 family, which are comprised of an antiapoptotic subgroup including BCL-2 itself, and the proapoptotic BAX,BAK and BH3-domain-only subgroups. Constituents of all three of these BCL-2 classes, however, also converge on the endoplasmic reticulum (ER), an organelle whose critical contributions to apoptosis is only now becoming apparent. In addition to propagating death-inducing stress signals itself, the ER also contributes in a fundamental way to Fas-mediated apoptosis and to p53-dependent pathways resulting from DNA damage and oncogene expression. Mobilization of ER calcium stores can initiate the activation of cytoplasmic death pathways as well as sensitize mitochondria to direct proapoptotic stimuli. Additionally, the existence of BCL-2-regulated initiator procaspase activation complexes at the ER membrane has also been described. Here, we review the potential underlying mechanisms involved in these events and discuss pathways for ER-mitochondrial crosstalk pertinent to a number of cell death stimuli.