Apoptosis: mitochondria resurrected?

AM-18002, a derivative of natural anmindenol A, enhances radiosensitivity in mouse breast cancer cells

Natural anmindenol A isolated from the marine-derived bacteria Streptomyces sp. caused potent inhibition of inducible nitric oxide synthase without any significant cytotoxicity. This compound consists of a structurally unique 3,10-dialkylbenzofulvene skeleton. We previously synthesized and screened the novel derivatives of anmindenol A and identified AM-18002, an anmindenol A derivative, as a promising anticancer agent. The combination of AM-18002 and ionizing radiation (IR) improved anticancer effects, which were exerted by promoting apoptosis and inhibiting the proliferation of FM3A mouse breast cancer cells. AM-18002 increased the production of reactive oxygen species (ROS) and was more effective in inducing DNA damage. AM-18002 treatment was found to inhibit the expansion of myeloid-derived suppressor cells (MDSC), cancer cell migration and invasion, and STAT3 phosphorylation. The AM-18002 and IR combination synergistically induced cancer cell death, and AM-18002 acted as a potent anticancer agent by increasing ROS generation and blocking MDSC-mediated STAT3 activation in breast cancer cells.

ROS Induced by KillerRed Targeting Mitochondria (mtKR) Enhances Apoptosis Caused by Radiation via Cyt c/Caspase-3 Pathway

During radiotherapy, reactive oxygen species- (ROS-) induced apoptosis is one of the main mechanism of radiation. Based on KillerRed which can induce ROS burst in different cell substructures, here we hypothesized that KillerRed targeting mitochondria (mtKR) could induce ROS to enhance apoptosis by radiation. In this study, empty vector, mtKR, and mtmCherry plasmids were successfully constructed, and mitochondrial localization were detected in COS-7 and HeLa cells. After HeLa cells were transfected and irradiated by visible light and X-rays, ROS levels, mitochondrial membrane potential (Δψ_m), ATPase activities, adenosine triphosphate (ATP) content, apoptosis, and the expressions of mRNA and protein were measured, respectively. Data demonstrated that the ROS levels significantly increased after light exposure, and adding extra radiation, voltage-dependent anion channel 1 (VDAC1) protein increased in the mitochondria, while Na⁺-K⁺ and Ca²⁺-Mg²⁺ ATPase activities, ATP content, and Δψ_m significantly reduced. Additionally, the cell apoptotic rates dramatically increased, which referred to the increase of cytochrome c (Cyt c), caspase-9, and caspase-3 mRNA expressions, and Cyt c protein was released from the mitochondria into the cytoplasm; caspase-9 and -3 were activated. These results indicated that mtKR can increase the production of ROS, enhance mitochondrial dysfunction, and strengthen apoptosis by radiation via Cyt c/caspase-3 pathway.

The cAMP analogs have potent anti-proliferative effects on medullary thyroid cancer cell lines

The oncogenic activation of the rearranged during transfection (RET) proto-oncogene has a main role in the pathogenesis of medullary thyroid cancer (MTC). Several lines of evidence suggest that RET function could be influenced by cyclic AMP (cAMP)-dependent protein kinase A (PKA) activity. We evaluated the in vitro anti-tumor activity of 8-chloroadenosine-3',5'-cyclic monophosphate (8-Cl-cAMP) and PKA type I-selective cAMP analogs [equimolar combination of the 8-piperidinoadenosine-3',5'-cyclic monophosphate (8-PIP-cAMP) and 8-hexylaminoadenosine-3',5'-cyclic monophosphate (8-HA-cAMP) in MTC cell lines (TT and MZ-CRC-1)]. 8-Cl-cAMP and the PKA I-selective cAMP analogs showed a potent anti-proliferative effect in both cell lines. In detail, 8-Cl-cAMP blocked significantly the transition of TT cell population from G2/M to G0/G1 phase and from G0/G1 to S phase and of MZ-CRC-1 cells from G0/G1 to S phase. Moreover, 8-Cl-cAMP induced apoptosis in both cell lines, as demonstrated by FACS analysis for annexin V-FITC/propidium iodide, the activation of caspase-3 and PARP cleavage. On the other hand, the only effect induced by PKA I-selective cAMP analogs was a delay in G0/G1-S and S-G2/M progression in TT and MZ-CRC-1 cells, respectively. In conclusion, these data demonstrate that cAMP analogs, particularly 8-Cl-cAMP, significantly suppress in vitro MTC proliferation and provide rationale for a potential clinical use of cAMP analogs in the treatment of advanced MTC.

Increased expression but not sensitivity to Fas/CD95 in glioblastoma cells depleted of mitochondrial DNA

Mitochondria and Fas (CD95) play a role in tumorigenicity and apoptosis. In the present study, the functional relationship of mitochondria to Fas in mediating apoptosis was investigated. Glioblastoma cells (DBTRGO5MG, U87) were depleted of mitochondrial DNA (mtDNA) by treatment with ethidium bromide (Rho(-) cells). Compared to Rho(+) cells, Rho(-) cells showed enhanced expression of Fas at the cell surface. Indeed, when Rho(+) cells were treated with mitochondrial respiratory chain complex inhibitors, Fas cell surface expression was noted to increase in a similar fashion to the depletion of mtDNA in both cell lines. However, when cells were evaluated for sensitivity to apoptosis using Fas-engagement, there was no difference between the Rho(+) and Rho(-) cells in either cell line. By contrast, sensitivity to the cytotoxic agent cis-diammine-dichloroplatinum (cisplatin) was markedly increased in the Rho(-) cells, which expressed higher levels of cell surface Fas. Expression of Fas is increased with the depletion of mtDNA and respiratory complex inhibitors. However, this increase in expression does not necessarily translate to an increase in sensitivity to Fas-engagement, although there is an increase in the sensitivity of depleted cells to cytotoxic agents such as cisplatin.

Approaches for targeting mitochondria in cancer therapy

The recognition of the role that mitochondria play in human health and disease is evidenced by the emergence in recent decades of a whole new field of "Mitochondrial Medicine". Molecules located on or inside mitochondria are considered prime pharmacological targets and a wide range of efforts are underway to exploit these targets to develop targeted therapies for various diseases including cancer. However the concept of targeting, while seemingly simple in theory, has multiple subtly different practical approaches. The focus of this article is to highlight these differences in the context of a discussion on the current status of various mitochondria-targeted approaches to cancer therapy.

Bacterial induction of early response genes and activation of proapoptotic factors in pleural mesothelial cells

In bacterial empyema the pleural mesothelium is constantly exposed to microorganisms. Staphylococcus aureus (S. aureus) is one of the most frequent pathogens associated with empyema. In an earlier study we demonstrated that S. aureus induced barrier dysfunction in pleural mesothelial cell monolayers. In the present study we report that S. aureus activates the early response genes c-fos and c-jun and activator protein-1 (AP-1), and induces proapoptosis genes Bad and Bak in primary mouse pleural mesothelial cells (PMCs). Our data indicate that in PMCs S. aureus induces apoptosis in a time- and multiplicity of infection (MOI)-dependent manner. Staphylococcus aureus induced Bcl (2), Bcl-X (L), c-fos, c-jun, and AP-1 expression in PMCs during the initial phase of infection. In S. aureus-infected PMCs, Bad and Bak gene expression was increased and correlated with DNA fragmentation and cytochrome-c release. Bcl (2) and Bcl-X (L) gene expression was significantly lower in S. aureus-infected PMCs than in uninfected PMCs 12 h postinfection. We conclude that at the initial stage of infection S. aureus modulates expression of early response genes c-fos and c-jun, and in the late phase of infection S. aureus induces expression of proapoptotic genes Bak and Bad in PMCs. Silencing AP-1 significantly inhibited S. aureus-induced Bak and Bad expression in PMCs. The upregulation of early response genes during the early phase of infection may contribute to the activation of proapoptotic genes Bak and Bad and release of cytochrome-c, caspase-3 thereby resulting in apoptosis in PMCs.

Phenotypical characteristics, biochemical pathways, molecular targets and putative role of nitric oxide-mediated programmed cell death in Leishmania

Nitric oxide (NO) has been demonstrated to be the principal effector molecule mediating intracellular killing of Leishmania, both in vitro and in vivo. We investigated the type of cell death process induced by NO for the intracellular amastigote stage of the protozoa Leishmania. Specific detection methods revealed a rapid and extensive cell death with morphological features of apoptosis in axenic amastigotes exposed to NO donors, in intracellular amastigotes inside in vitro - activated mouse macrophages and also in activated macrophages of regressive lesions in a leishmaniasis-resistant mouse model. We extended our investigations to the dog, a natural host-reservoir of Leishmania parasites, by demonstrating that co-incubation of infected macrophages with autologous lymphocytes derived from dogs immunised with purified excreted-secreted antigens of Leishmania resulted in a significant NO-mediated apoptotic cell death of intracellular amastigotes. From the biochemical point of view, NO-mediated Leishmania amastigotes apoptosis did not seem to be controlled by caspase activity as indicated by the lack of effect of cell permeable inhibitors of caspases and cysteine proteases, in contrast to specific proteasome inhibitors, such as lactacystin or calpain inhibitor I. Moreover, addition of the products of two NO molecular targets, cis-aconitase and glyceraldehyde-3-phosphate dehydrogenase, also had an inhibitory effect on the cell death induced by NO. Interestingly, activities of these two enzymes plus 6-phosphogluconate dehydrogenase, parasitic enzymes involved in both glycolysis and respiration processes, are overexpressed in amastigotes selected for their NO resistance. This review focuses on cell death of the intracellular stage of the pathogen Leishmania induced by nitrogen oxides and gives particular attention to the biochemical pathways and the molecular targets potentially involved. Questions about the role of Leishmania amastigotes NO-mediated apoptosis in the overall infection process are raised and discussed.

G-CSF modulates LPS-induced apoptosis and IL-8 in human microvascular endothelial cells: involvement of calcium signaling

Microvascular endothelial cells (mECs) circulate at higher numbers in patients with severe sepsis and hemophagocytic syndromes. Although these blood mECs might stem from damaged microvasculature, they are perfectly viable and lead to the establishment of cell lines. Such mECs were cultured in low-dose human serum pools (0.5%) and MEM-alpha medium. Antigenic profiling revealed the expression of CD36, factor VIIIa, CD95-ligand, and CD44, but also CD146. We studied the antioxidative effect of the hematopoietic growth factor G-CSF(1) after in vitro stimulation with LPS from E. coli 0111:B4; the growth factor appeared to exhibit a protective effect on organ function in patients with SIRS. mECs were stimulated with 1 micro g/mL of LPS for 24 h and 48 h with and without G-CSF (3x10(3) U/mL) preincubation. After 24 h, supernatants of the stimulated mEC were tested for IL-8 by ELISA, and cells were tested for hemoxygenase-1 (HO-1, Hsp32) by immunohistochemistry and flow cytometry using OSA110 (mAb, Stressgene). Stimulation with LPS upregulated IL-8 by a factor of 2 to 10 in mEC. Preincubation with G-CSF markedly downregulated the LPS-induced IL-8 secretion (20-50%), but IL-6 production was not affected. Upon 48 h of LPS stimulation, mECs developed massive signs of apoptosis and concomitant caspase 3 activation. Caspase 3 activity induced by LPS (24 h) or by staurosporin (6 h) was found to be dramatically downregulated by the G-CSF preincubation protocol.

Sensitive and reliable JC-1 and TOTO-3 double staining to assess mitochondrial transmembrane potential and plasma membrane integrity: interest for cell death investigations

BACKGROUND

Apoptosis is currently studied by flow cytometry with mitochondrial membrane potential (Deltapsimt) and membrane integrity fluorochromes. Rhodamine 123 and DiOC6(3) remain controversial to identify cells displaying a low Deltapsimt. JC-1 constitutes a good Deltapsimt indicator, due to a fluorescence shift from green to orange emission, according to the increase in Deltapsimt. Nevertheless, it is not feasible to analyze it simultaneously with propidium iodide. Among available fluorescent probes, TOTO-3 seems to be a good candidate for double staining with JC-1.

METHODS

Cell death of HaCaT cells was induced by H2O2 and FasL. Samples were stained with DiOC6(3)/IP or JC-1/TOTO-3 then analyzed by flow cytometry. Results were supported by confocal microscopy analyses of mitochondrial membrane potential. Moreover, cell morphology was determined on the sorted subpopulations defined on the basis of staining (JC-1 versus TOTO-3).

RESULTS

We found that JC-1 is a more efficient mitochondrial probe than DiOC6(3). After stress induction, the fluorescence level of JC-1 and TOTO-3 clearly defined three fluorescent subpopulations, respectively: (1) JC-1high and TOTO-3low, (2) JC-1low and TOTO-3medium, and (3) JC-1low and TOTO-3high. Their morphologic aspects after cell sorting indicated that they corresponded to three functional states (intact, apoptotic, and necrotic cells), and data were supported by caspase activity measurements.

CONCLUSIONS

We propose a reliable and efficient staining, with JC-1 and TOTO-3 to discriminate three functional cellular states: intact, apoptotic, and necrotic/late apoptotic cells by flow cytometry.

Nitric oxide and differential effects of ATP on mitochondrial permeability transition

The mitochondrial permeability transition pore (PTP) undergoes a calcium-dependent transition (MPT) that disrupts membrane potential and releases apoptogenic proteins. Because PTP opening is enhanced by oxidation of thiols at the so-called "S-site," we hypothesized that nitrogen monoxide (NO*) could enhance the open probability of the PTP, e.g., by S-nitrosylation or S-thiolation. At low NO donor concentrations (1 to 20 microM), PTP opening in succinate-energized liver mitochondria at nonlimiting calcium was delayed or unaffected, while it was accelerated by NO donors at 20 to 100 microM. At low donor concentrations, PTP opening was facilitated twofold by adenosine triphosphate (ATP), which normally delays PTP opening. Among NO donors, the oxatriazole GEA 3162, with an activation constant (Ka) of 1.9 microM at 500 microM ATP was more effective at enhancing pore transition than SIN-1 or SNAP. NO donor effects were superseded by diamide, which induces disulfide formation, but independent of SH-adduct formation by alkylation. NO-related changes in PTP function were accompanied by protein mixed disulfide formation, inhibited by dithiothreitol (DTT), and reversed by DTT after donor addition. PTP opening was stimulated in the presence of ATP by L-arginine-dependent NO production, i.e., mitochondrial NOS activity. ATP-facilitated pore opening was sensitive to atractyloside and depended on nucleotide interactions but not on hydrolysis, because specific nonhydrolyzable ATP analogs accelerated pore opening. These data indicate NO can influence pore transition by oxidation of thiols that produce conformational changes governing the ATP interaction at the adenine nucleotide transporter.

Programmed cell death in the unicellular protozoan parasite Leishmania

In the present study we have demonstrated some features characterizing programmed cell death (PCD) in the unicellular protozoan parasite Leishmania donovani, the causative agent of visceral Leishmaniasis. We report that PCD is initiated in stationary phase cultures of promastigotes and both in actively growing cultures of axenic amastigotes and promastigotes upon treatment with anti Leishmanial drugs (Pentostam and amphotericin B). However, the two cell types respond to antileishmanial drugs differently. The features of PCD in L. donovani promastigotes are nuclear condensation, nicked DNA in the nucleus, DNA ladder formation, increase in plasma membrane permeability, decrease in the mitochondrial membrane potential (DeltaPsi m) and induction of a PhiPhiLux (PPL)-cleavage activity. PCD in both stationary phase culture and upon induction by amphotericin B resulted first in the decrease of mitochondrial membrane potential followed by simultaneous change in plasma membrane permeability and induction of PPL-cleavage activity. Of the total PPL-cleavage activity, several caspase inhibitors inhibited a significant amount (21-34%). Inhibitors of cathepsin or calpain did not inhibit PPL-cleavage activity. Taken together this study demonstrates that the characteristic features of PCD exist in unicellular protozoan Leishmania donovani. The implication of PCD on the Leishmania pathogenesis is discussed.

The effect of drugs and toxins on the process of apoptosis

In this review we examine the modifying effect of specific drugs on apoptosis. Apoptosis is a type of cell death prevalent during many physiological and pathological conditions, consisting of several steps, namely, initiating stimuli, transduction pathways, effector mechanisms, nuclear fragmentation, and phagocytosis. Pharmacological substances such as glucocorticoids can either induce or inhibit the process of apoptosis in various cells depending on the type of drug and its concentration. Understanding the mechanisms of interaction of drugs with cells undergoing apoptosis could encourage novel therapeutic approaches to human diseases in which apoptosis has a critical role.

Serum suppresses myeloid progenitor apoptosis by regulating iron homeostasis

The growth and survival of committed hematopoietic progenitors is dependent upon cytokine signaling. However, serum is also required for optimal growth of these progenitors in culture ex vivo. Here we report that serum withdrawal leads to myeloid progenitor cell apoptosis. Although serum deprivation-induced cell death has many hallmarks typical of apoptosis, these cell deaths were not inhibited by hemopoietins, survival factors such as IGF-I, or treatment with a broad-spectrum caspase inhibitor. Rather, apoptosis due to serum withdrawal was associated with damage to mitochondria. Surprisingly the serum factor required for myeloid cell survival was identified as iron, and loss of iron led to marked reductions in ATP production. Furthermore, supplementing serum-deprived myeloid cells with bound or free iron promoted cell survival and prevented mitochondrial damage. Therefore, serum suppresses hematopoietic cell apoptosis by providing an obligate source of iron and iron homeostasis is critical for proper myeloid cell metabolism and survival.

Nuclear apoptosis induced by isolated mitochondria

We isolated and purified mitochondria from mouse livers and spinach leaves. When added into egg extracts of Xenopus laevis, they caused nuclei of mouse liver to undergo apoptotic changes. Chromatin condensation, margination and DNA ladder were observed. After incubating isolated mitochondria in some hypotonic solutions, and centrifuging these mixtures at high speed, we got mitochondrial supernatants. It was found that in the absence of cytosolic factor, the supernatant alone was able to induce apoptotic changes in nuclei. The effective components were partly of protein. DNA fragmentation was partly inhibited by caspase inhibitors AC-DEVD-CHO and AC-YVAD-CHO. Meanwhile, caspase inhibitors fully blocked chromatin condensation. Primary characterization of the nuclear endonuclease(s) induced by mitochondrial supernatants was also conducted. It was found that this endonuclease is different from endonuclease G, cytochrome c-induced nuclease, or Ca2+-activated endonuclease.

The local control of cytosolic Ca2+ as a propagator of CNS communication--integration of mitochondrial transport mechanisms and cellular responses

Ca2+ signals propagate in wave form along individual cells of the central nervous system (CNS) and through networks of connected cells of neuronal and multiple glial cell types. In order for wave fronts to convey information, signaling mechanisms are required that allow waves to propagate reproducibly and without decrement in signal strength over long distances. CNS Ca2+ waves are under specific integrated local control, made possible by interactions at local subcellular microdomains between endoplasmic reticulum and mitochondria. Active mitochondria located near the mouth of inositol trisphosphate receptor (InsP3R) channel clusters in glia take up Ca2+, which may prevent a buildup of Ca2+ around the InsP3R channel, thereby decreasing the rate of Ca2+-induced receptor inactivation, and prolonging channel open time. Mitochondria may amplify InsP3-dependent Ca2+ signals by a transient permeability transition in response to Ca2+ uptake into the mitochondrion. Other evidence suggests privileged access into mitochondria for Ca2+ entering neurons by glutamatergic receptor channels. This enables specific signal modulation as the Ca2+ wave is propagated into neurons, such that mitochondria located close to glutamate channels can prolong the neuronal cytosolic response time by successive uptake and release of Ca2+. Disruption of mitochondrial function deregulates the ability of CNS-derived cells to undergo normal Ca2+ signaling and wave propagation.

Oxidative stress and adenine nucleotide control of mitochondrial permeability transition

Mitochondria can initiate apoptosis by releasing cytochrome c after undergoing a calcium-dependent permeability transition (MPT). Although the MPT is enhanced by oxidative stress and prevented by adenine nucleotides such as adenosine 5'-diphosphate (ADP), the hypothesis has not been tested that oxidants regulate the effects of exogenous adenine nucleotides on the MPT and cytochrome c release. We found that cytochrome c release from intact rat liver mitochondria depended strictly on pore opening and not on membrane potential, and that MPT-enhancing oxidative stress also augmented cytochrome c release. At low oxidative stress, micromolar (ADP) and low adenosine 5'-triphosphate (ATP)/ADP ratio inhibited the MPT and cytochrome c release, whereas ATP or high ATP/ADP had only a slight effect. In freshly isolated mitochondria, the time to half-maximal MPT was related to the log of the ATP/ADP ratio. This function was shifted to shorter times by oxidative stress which decreased ADP protection and caused ATP to accelerate the calcium-dependent MPT. By comparison, mitochondria treated with reducing agents and those isolated from septic rats were protected from the MPT by both nucleotides. These results indicate that oxidation-sensitive site(s) in the membrane regulate the effects of adenine nucleotides on the MPT. The oxidant-based differences in the effects of ADP and ATP on the pore support the novel hypothesis that failure of the cell to consume ATP and provide adequate ADP at the adenine nucleotide transporter during oxidative stress predisposes to cytochrome c release and initiation of apoptosis.

The wst gene regulates multiple forms of thymocyte apoptosis

Mice homozygous for the autosomal recessive mutation Wasted (wst/wst) display a disease characterized by immunodeficiency, cerebellar dysfunction, and sensitivity of their hematopoeitic cells to gamma radiation. Wasted mice die by 30 days of age. In this report, we show that the Wasted thymus shows evidence of dramatically increased apoptosis in situ. Moreover, wst/wst thymocytes are more sensitive to apoptosis induced by gamma radiation, heat shock, alpha-CD3 stimulation, and dexamethasone treatment in vitro. Thus, wst gene is a regulator of thymocyte apoptosis both in vitro and in vivo. The elevated levels of thymocyte apoptosis may be a major contributor to the lymphoid dysfunction and ultimate death in wst/wst mice.

Regulation of macrophage gene expression by Mycobacterium tuberculosis: down-regulation of mitochondrial cytochrome c oxidase

We have investigated changes in gene expression in mouse peritoneal macrophages following infection with virulent Mycobacterium tuberculosis. Using differential-display reverse transcription-PCR (RT-PCR), we have identified a gene that was markedly down-regulated within 6 h of infection and remained so for the duration of the experiment (5 days). On sequencing, this gene was found to encode the murine cytochrome c oxidase subunit VIIc (COX VIIc). Down-regulation of COX VIIc during M. tuberculosis infection was confirmed by three independent techniques: limiting-dilution RT-PCR, RNase protection assay, and Northern analysis. Limiting-dilution RT-PCR and Northern analysis were also used to analyze the specificity of this regulation; heat-killed M. tuberculosis, Mycobacterium bovis BCG, and latex beads had no effect on expression of COX VIIc. Down-regulation of this enzyme was also confirmed by using adherent cells isolated from spleens of M. tuberculosis-infected mice. These ex vivo macrophages showed apoptotic features, suggesting a possible involvement of cytochrome c oxidase in the programmed cell death of the host cells.

Selective induction of interleukin-1 production and tumor killing activity of macrophages through apoptosis by the inhibition of oxidative respiration

Suppression of mitochondrial respiration and increased glycolysis are characteristic features of activated macrophages. We show here that antimycin A, a respiratory inhibitor, induced interleukin-1 synthesis and tumoricidal activity without inducing tumor necrosis factor or nitric oxide. The induction of tumoricidal activity was resistant to inhibitors of tyrosine-specific protein kinases and intracellular glycoprotein transport. The cognate interaction between macrophages and target cells was not a prerequisite for the tumoricidal activity. In contrast, lipopolysaccharide induced the production of interleukin-1, tumor necrosis factor and nitric oxide, the induction of tumoricidal activity being sensitive to genistein and brefeldin A. Antimycin A, like lipopolysaccharide, induced the release of a cytoplasmic enzyme and apoptosis of macrophages. Antimycin A showed anti-metastatic activity in vivo. These results suggest that the inhibition of oxidative respiration would induce apoptosis and the resultant release of soluble effector molecules of macrophages which inhibit tumor metastasis in vivo.

Flow cytometric measurement of mitochondrial mass and function: a novel method for assessing chemoresistance

BACKGROUND

Chemotherapeutic agents induce apoptosis in cancer cells. Drugs failing to induce apoptosis are likely to have decreased clinical efficacy. We hypothesize that (1) chemotherapeutic agents induce mitochondrial changes and apoptosis through mechanisms associated with reactive oxidant species production; (2) the anti-apoptotic protein Bcl-2 prevents drug-induced mitochondrial changes, reactive oxygen species (ROS) production, and apoptosis; and (3) the assay of drug-induced mitochondrial changes can reflect drug-specific chemoresistance in a given cancer cell line.

METHODS

A stable Bcl-2 transfectant of the Bcl-2 negative breast cancer cell line SKBr3 was created (SKBr3/Bcl2-2). Both SKBr3 and SKBr3/Bcl2-2 cells were treated with Herbimycin A (300 ng/mL) or vehicle (1% DMSO). Cell cycle changes were assessed by BRDU staining. Apoptosis was determined by electron microscopy, TUNEL (TdT-mediated dUTP-biotin nick end labeling) staining, and diphenylamine assay of DNA fragmentation. Changes in mitochondrial mass and transmembrane potential (deltapsi(m)) were assessed by flow cytometric assessment of JC-1 fluorescence. Reactive oxygen species production was measured by 2',7'-dichlorodihydrofluorescein diacetate (DCFH) fluorescence.

RESULTS

Both SKBr3 and SKBr3/Bcl2-2 cells show cell cycle arrest after Herbimycin treatment. However, SKBr3 cells, but not SKBr3/Bcl2-2 cells, undergo apoptosis. Herbimycin-treated SKBr3 cells show increased mitochondrial mass (JC-1 green fluorescence), with no corresponding increase in deltapsi(m) (JC-1 red fluorescence). By contrast, Herbimycin-treated SKBr3/Bcl2-2 cells show no change in mitochondrial mass or deltapsi(m). Similarly, drug-treated SKBr3 cells, but not SKBr3/Bcl2-2 cells, demonstrate increased reactive oxygen species (ROS) production concomitant with the development of apoptosis.

CONCLUSION

SKBr3 cells undergoing apoptosis demonstrate mitochondrial changes associated with ROS production. Bcl-2 transfection prevents these changes because it prevents apoptosis and induces chemoresistance to Herbimycin in SKBr3. Flow cytometric measurement of drug induced mitochondrial changes and ROS production may facilitate in vitro assessment of chemosensitivity or chemoresistance in breast cancer.

The caspase-3 precursor has a cytosolic and mitochondrial distribution: implications for apoptotic signaling

Caspase-3-mediated proteolysis is a critical element of the apoptotic process. Recent studies have demonstrated a central role for mitochondrial proteins (e.g., Bcl-2 and cytochrome c) in the activation of caspase-3, by a process that involves interaction of several protein molecules. Using antibodies that specifically recognize the precursor form of caspase-3, we demonstrate that the caspase-3 proenzyme has a mitochondrial and cytosolic distribution in nonapoptotic cells. The mitochondrial caspase-3 precursor is contained in the intermembrane space. Delivery of a variety of apoptotic stimuli is accompanied by loss of mitochondrial caspase-3 precursor staining and appearance of caspase-3 proteolytic activity. We propose that the mitochondrial subpopulation of caspase-3 precursor molecules is coupled to a distinct subset of apoptotic signaling pathways that are Bcl-2 sensitive and that are transduced through multiple mitochondrion-specific protein interactions.

Role of mitochondrial Ca2+ regulation in neuronal and glial cell signalling

It is becoming increasingly clear that mitochondrial Ca2+ uptake from and release into the cytosol has important consequences for neuronal and glial activity. Ca2+ regulates mitochondrial metabolism, and mitochondrial Ca2+ uptake and release modulate physiological and pathophysiological cytosolic responses. In glial cells, inositol 1,4,5-trisphosphate-dependent Ca2+ responses are faithfully translated into elevations in mitochondrial Ca2+ levels, which modifies cytosolic Ca2+ wave propagation and may activate mitochondrial enzymes. The location of mitochondria within neurones may partially determine their role in Ca2+ signalling. Neuronal death due to NMDA-evoked Ca2+ entry can be delayed by an inhibitor of the mitochondrial permeability transition pore, and mitochondrial dysfunction is being increasingly implicated in a number of neurodegenerative conditions. These findings are illustrative of an emerging realization by neuroscientists of the importance of mitochondrial Ca2+ regulation as a modulator of cellular energetics, endoplasmic reticulum Ca2+ release and neurotoxicity.

Mitochondrial cytochrome c release in apoptosis occurs upstream of DEVD-specific caspase activation and independently of mitochondrial transmembrane depolarization

Mitochondrial cytochrome c, which functions as an electron carrier in the respiratory chain, translocates to the cytosol in cells undergoing apoptosis, where it participates in the activation of DEVD-specific caspases. The apoptosis inhibitors Bcl-2 or Bcl-xL prevent the efflux of cytochrome c from mitochondria. The mechanism responsible for the release of cytochrome c from mitochondria during apoptosis is unknown. Here, we report that cytochrome c release from mitochondria is an early event in the apoptotic process induced by UVB irradiation or staurosporine treatment in CEM or HeLa cells, preceding or at the time of DEVD-specific caspase activation and substrate cleavage. A reduction in mitochondrial transmembrane potential (Deltapsim) occurred considerably later than cytochrome c translocation and caspase activation, and was not necessary for DNA fragmentation. Although zVAD-fmk substantially blocked caspase activity, a reduction in Deltapsim and cell death, it failed to prevent the passage of cytochrome c from mitochondria to the cytosol. Thus the translocation of cytochrome c from mitochondria to cytosol does not require a mitochondrial transmembrane depolarization.

Imaging the mitochondrial permeability transition pore in intact cells

The involvement of mitochondrial permeability transition pore (MTP) in cellular processes is generally investigated by indirect means, such as changes in mitochondrial membrane potential or pharmacological inhibition. However, such effects could not be related univocally to MTP. In addition, source of errors could be represented by the increased retention of membrane potential probes induced by cyclosporin A (CsA) and the interactions between fluorescent probes. We developed a direct technique for monitoring MTP. Cells were co-loaded with calcein-AM and CoCl2, resulting in the quenching of the cytosolic signal without affecting the mitochondrial fluorescence. MTP inducers caused a rapid decrease in mitochondrial calcein fluorescence which, however, was not completely prevented by CsA. Besides the large and rapid efflux of calcein induced by MTP agonists, we also observed a constant and spontaneous decrease of mitochondrial calcein which was completely prevented by CsA. Thus, MTP likely fluctuates between open and closed states in intact cells.

Mitochondrial ultracondensation, but not swelling, is involved in TNF alpha-induced apoptosis in human T-lymphoblastic leukaemic cells

Mitochondrial permeability transition (PT) pore opening and mitochondrial swelling have been reported in association with apoptosis. Conformational alterations of mitochondria induced by tumour necrosis factor-alpha (TNF alpha), and the association with TNF alpha-induced apoptosis, were, therefore, studied in the human acute T-lymphoblastic leukaemia (T-ALL) cell line, CCRF-CEM and its vinblastine-resistant CEM/VLB100 cell line by transmission electron microscopy (TEM). The CEM/VLB100 cell line possessed more condensed (C phase) mitochondria in the resting state compared with its parental cell line, consistent with increased activity of the mitochondrial electron transport chain (ETC). Following exposure to TNF alpha, conformational alterations of mitochondria occurred in both apoptotic and non-apoptotic cells. Orthodox (O phase) mitochondria in non-apoptotic cells underwent C-phase, transitional O-phase and slightly swollen (S-phase) conformational changes. TNF alpha-induced mitochondrial swelling was a late event and was found to a far lesser extent than mitochondrial condensation. No swollen mitochondria were observed in apoptotic cells. Ultracondensed (UC phase) mitochondria were observed in cells undergoing both TNF alpha-induced and spontaneous apoptosis and were seen when TNF alpha-induced apoptosis was inhibited by 3-methyladenine (3MA). The structural integrity of UC phase mitochondria persisted through the apoptotic process. We conclude that TNF alpha-induced mitochondrial swelling and apoptosis are separate events. Mitochondrial ultracondensation is associated with the processes signalling apoptosis and is not a result of TNF alpha-induced apoptotic shrinkage.

Mitochondrial proliferation and paradoxical membrane depolarization during terminal differentiation and apoptosis in a human colon carcinoma cell line

Herbimycin A, a tyrosine kinase inhibitor, induces cellular differentiation and delayed apoptosis in Colo-205 cells, a poorly differentiated human colon carcinoma cell line. Cell cycle analysis in conjunction with end labeling of DNA fragments revealed that G2 arrest preceded apoptotic cell death. Ultrastructural examination of herbimycin-treated cells demonstrated morphologic features of epithelial differentiation, including formation of a microvillar apical membrane and lateral desmosome adhesions. A marked accumulation of mitochondria was also observed. Fluorometric analysis using the mitochondrial probes nonyl-acridine orange and JC-1 confirmed a progressive increase in mitochondrial mass. However these cells also demonstrated a progressive decline in unit mitochondrial transmembrane potential (DeltaPsim) as determined by the DeltaPsim-sensitive fluorescent probes rhodamine 123 and JC-1 analyzed for red fluorescence. In concert with these mitochondrial changes, Colo-205 cells treated with herbimycin A produced increased levels of reactive oxygen species as evidenced by oxidation of both dichlorodihydrofluorescein diacetate and dihydroethidium. Cell-free assays for apoptosis using rat-liver nuclei and extracts of Colo-205 cells at 24 h showed that apoptotic activity of Colo-205 lysates requires the early action of mitochondria. Morphological and functional mitochondrial changes were observed at early time points, preceding cleavage of poly (ADP-ribose) polymerase. These results suggest that apoptosis in differentiated Colo-205 cells involves unrestrained mitochondrial proliferation and progressive membrane dysfunction, a novel mechanism in apoptosis.

Death of Bystander Cells by a Novel Pathway Involving Early Mitochondrial Damage in Human Immunodeficiency Virus–Related Lymphadenopathy

Destruction of immune cells in peripheral lymphoid tissues plays presumably a pivotal role in acquired immune deficiency syndrome pathogenesis. We found that cell suspensions obtained from lymph nodes of eight human immunodeficiency virus (HIV)-infected individuals contained variable proportions (2.1% to 18.3%, median 11.2%) of dead lymphocytes permeable to supravital dyes, represented by CD4+, CD8+, and B cells. The frequency of dead cells correlated directly (R = 0.847) with the amount of HIV provirus in the cell populations, and HIV provirus was enriched in the dead cell fractions. Similar proportions of dead cells were observed in cell suspensions from lymphadenopathic lymph nodes of HIV− donors, but not from small resting HIV− lymph nodes. Electron microscopic and flow cytometric analyses revealed that most dead cells from HIV+ lymph nodes lacked internucleosomal DNA fragmentation but displayed combined features of apoptosis and necrosis, eg, chromatin condensation and mitochondrial swelling. Cells with similar morphology were readily identified in lymph node tissue sections, and marked mitochondrial swelling could be occasionally observed in cells with otherwise normal morphology. Our findings have two major implications. One is that the in vivo cell death in HIV-infected lymph nodes occurs predominantly through a novel pathway, related to but distinct from classical apoptosis and characterised by early and severe mitochondrial damage. The second implication is that HIV-related lymphadenopathy is accompanied in vivo by massive destruction of uninfected lymph node cells. Comparable levels of cell death were observed in other inflammatory lymphadenopathies not related to HIV; however, the uniquely endless and generalized nature of HIV lymphadenopathy might render this “inflammatory” cell destruction a powerful pathogenetic mechanism, accounting for the progressive disruption and depletion of lymphoid tissues seen in HIV infection.

Death of Bystander Cells by a Novel Pathway Involving Early Mitochondrial Damage in Human Immunodeficiency Virus–Related Lymphadenopathy

Destruction of immune cells in peripheral lymphoid tissues plays presumably a pivotal role in acquired immune deficiency syndrome pathogenesis. We found that cell suspensions obtained from lymph nodes of eight human immunodeficiency virus (HIV)-infected individuals contained variable proportions (2.1% to 18.3%, median 11.2%) of dead lymphocytes permeable to supravital dyes, represented by CD4+, CD8+, and B cells. The frequency of dead cells correlated directly (R = 0.847) with the amount of HIV provirus in the cell populations, and HIV provirus was enriched in the dead cell fractions. Similar proportions of dead cells were observed in cell suspensions from lymphadenopathic lymph nodes of HIV− donors, but not from small resting HIV− lymph nodes. Electron microscopic and flow cytometric analyses revealed that most dead cells from HIV+ lymph nodes lacked internucleosomal DNA fragmentation but displayed combined features of apoptosis and necrosis, eg, chromatin condensation and mitochondrial swelling. Cells with similar morphology were readily identified in lymph node tissue sections, and marked mitochondrial swelling could be occasionally observed in cells with otherwise normal morphology. Our findings have two major implications. One is that the in vivo cell death in HIV-infected lymph nodes occurs predominantly through a novel pathway, related to but distinct from classical apoptosis and characterised by early and severe mitochondrial damage. The second implication is that HIV-related lymphadenopathy is accompanied in vivo by massive destruction of uninfected lymph node cells. Comparable levels of cell death were observed in other inflammatory lymphadenopathies not related to HIV; however, the uniquely endless and generalized nature of HIV lymphadenopathy might render this “inflammatory” cell destruction a powerful pathogenetic mechanism, accounting for the progressive disruption and depletion of lymphoid tissues seen in HIV infection.

Regulation of macrophage gene expression following invasion by Mycobacterium tuberculosis

INTRODUCTION

Mycobacteria are intracellular pathogens which survive and grow in host macrophages. M. tuberculosis bacilli enter the macrophage via binding to several distinct cell surface molecules. Following phagocytosis, sustained intracellular bacterial growth depends on the ability to avoid destruction by macrophage-mediated host defences such as lysosomal enzymes, reactive oxygen and the reactive nitrogen intermediates. We used differential display reverse transcription polymerase chain reaction (DD RT-PCR) to identify host genes which are regulated during infection and hence which might be involved in the host-parasite cross talk.

RESULTS

Live M. tuberculosis (strain H37Rv) was used to infect Balb/c peritoneal murine macrophages. mRNA from infected and uninfected macrophages was isolated at different time intervals after phagocytosis and subjected to DD RT-PCR. Oligo dT12NV and random 10mer primers were used for PCR amplification of cDNA. Macrophage genes which appeared to be differently regulated during infection were subjected to further reamplification by PCR in order to clone and sequence them. The differential expression of the selected bands was further analysed by an RNA protection assay and a Northern blot.

RESULTS

Several differentially regulated bands were identified. One band, of 158 bp, was down regulated after infection. Sequencing of this band revealed a high level of homology (95% identity) to mouse cytochrome c oxidase subunit VIIc. The downregulation was specific for live virulent Mtb, while live BCG, heat killed Mtb and latex beads-mediated phagocytosis did not affect the transcriptional level of this enzyme.

CONCLUSIONS

The cytochrome oxidase enzyme complex of the inner mytochondrial membrane catalyzes the reaction between ferrocytochrome c and oxygen. The reaction is the terminal event in the electron transport scheme. Downregulation of cytochrome c oxidase subunit VIIc could interfere with: (1) the host apoptotic programme; or (2) the host respiratory burst.

Bcl-x(L) can inhibit apoptosis in cells that have undergone Fas-induced protease activation

Programmed cell death or apoptosis provides an irreversible mechanism for the elimination of excess or damaged cells. Several recent studies have implicated the activation of the interleukin 1beta-converting enzyme/Ced-3 (ICE/Ced-3) family of proteases as the "point of no return" in apoptotic cell death, while others have suggested that loss of mitochondrial membrane potential (delta psi(m)) is the ultimate determinant of cell death. The temporal relationship of these two events during apoptosis and the role of Bcl-2 proteins in inhibiting these steps has not been defined. To examine these issues, control and Bcl-x(L)-transfected Jurkat T cells were treated with Fas antibodies in the presence and absence of the ICE protease inhibitor zVAD-FMK. ICE/Ced-3 protease activity was monitored by following the cleavage of poly(ADP-ribose) polymerase (PARP) and delta psi(m) was followed by rhodamine 123 fluorescence. Although Bcl-x(L) expression did not block Fas-induced protease activation, it substantially inhibited the subsequent loss of delta psi(m) and cell death in Fas-treated cells. In contrast, zVAD-FMK blocked PARP cleavage as well as loss of delta psi(m) and cell death. Together these data demonstrate that Bcl-x(L) can maintain cell viability by preventing the loss of mitochondrial membrane potential that occurs as a consequence of ICE/Ced-3 protease activation.

Murine thioredoxin peroxidase delays neuronal apoptosis and is expressed in areas of the brain most susceptible to hypoxic and ischemic injury

Thioredoxin peroxidase (TPx) is an antioxidant protein that limits the activity of reactive oxygen species (ROS). We cloned the cDNA encoding the mouse homolog of TPx from an E14.5 brain cDNA library and analyzed its distribution and function in murine tissues. Comparison of the amino acid sequence of mouse TPx with those of other species revealed that TPx was highly conserved across all species. Mouse TPx had broad tissue distribution, but its expression was especially marked in cells that metabolize oxygen molecules at high levels such as erythroid cells, renal tubular cells, cardiac and skeletal muscle cells, and certain types of neurons. Levels of increased expression of TPx in the brain were coincident with regions known to be especially sensitive to hypoxic and ischemic injury in humans. Models of erythroid differentiation and neuronal survival were employed to study the function of TPx. Murine erythroleukemia cells (MEL cells) increased TPx transcription when in a chemically differentiated state. Furthermore, expression of mouse TPx in PC12 pheochromocytoma cells prolonged their survival in the absence of nerve growth factor (NGF) and serum, indicating that TPx could promote neuronal cell survival. We propose that TPx contributes to antioxidant defense in erythrocytes and neuronal cells by limiting the destructive capacity of oxygen radicals. These findings identify a novel gene that appears to be relevant to hypoxic brain injury and may be of importance in development of new approaches to abrogate the effects of ischemic- and hypoxic-related injury in the central nervous system (CNS).

The accumulation of non-replicative, non-functional, senescent T cells with age is avoided in calorically restricted mice by an enhancement of T cell apoptosis

Peripheral blood lymphocytes of elderly humans show an increased percentage of T cells with characteristics of replicative senescence. Similarly, the overall decrease in T cell proliferation in aged mice reflects a progressively increasing proportion of non-functional cells rather than a uniform decline in function by all cells. The improved immune function of calorically restricted (CR) animals is, paradoxically, accompanied by a relative lymphopenia. To test whether the reduction in lymphocyte number in the CR mice might reflect more efficient elimination of T cells, we measured apoptosis in young, old and CR old mice. T cell apoptosis induced by irradiation, Staurosporine, anti-CD3, and heat shock was reduced by 62, 42, 32, and 30%, respectively, in old compared with young mice. Caloric restriction normalized apoptosis in T cells from aged mice. Enhanced elimination of non-functional T cells in CR mice may be, at least in part, responsible for their improved immune functional status relative to non-CR mice of the same age.