Benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethylketone (Z-VAD.FMK) inhibits apoptosis by blocking the processing of CPP32

Release of DNA from dead and dying lymphocyte and monocyte cell lines in vitro

DNA is a nuclear macromolecule that circulates in the blood where its levels can reflect the activity of inflammatory and malignant diseases. While dead and dying cells have usually been considered the source of blood DNA, the mechanisms for its release during apoptosis and necrosis are not well defined. To elucidate DNA release, an in vitro model system was used, assessing DNA in the media of living, apoptotic or necrotic Jurkat and U937 cells. Apoptosis was induced by etoposide, camptothecin or staurosporine, while necrosis was induced by heating at 56 degrees C. DNA release was measured by fluorometry with the dye PicoGreen while the extent of death was measured by fluorescence-activated cell sorter analysis with propidium iodide and annexin. Apoptotic Jurkat cells released significantly more DNA in the media than untreated cells while necrotic cells did not show significant DNA release. U937 cells showed similar findings. Pretreatment of Jurkat cells with z-VAD-fmk, a caspase inhibitor, reduced both apoptosis and DNA release. By gel electrophoresis, extracellular DNA from apoptotic cells showed laddering with low molecular weight fragments. These studies suggest that extracellular release of DNA is a consequence of apoptosis and may account for some of the DNA in the blood.

Prostaglandin F2α is protective for apoptosis stimulated synergistically with 12-O-tetradecanoyl phorbol-β-acetate and nordihydroguaiaretic acid in Madin-Darby canine kidney cells

We recently found that 12-O-tetradecanoyl phorbol-beta-acetate (TPA) induced apoptosis in cultured Madin-Darby canine kidney (MDCK) cells. The present study shows that the apoptosis was mediated by the activation of caspases including caspase-3 and -7. Moreover, nordihydroguaiaretic acid (NDGA), a general lipoxygenase (LOX) inhibitor, synergistically stimulated the TPA-induced apoptosis despite no activation with NDGA alone. TPA preferentially increased the transcription of cyclooxygenase (COX)-2 in MDCK cells, whereas the expression of LOXs was almost negligible. These findings suggested that the effect of NDGA was independent of the inhibition of LOXs. The study using a cell-permeable 2',7'-dichlorofluorescin diacetate confirmed the more remarked production of reactive oxygen species at 6 h after the cells were treated with a mixture of TPA and NDGA. Calcium ionophore A23187 was markedly effective to attenuate the TPA-induced apoptosis, indicating that elevated endogenous prostaglandins (PGs) served as survival factors through not only the activation of phospholipase A(2) by A23187 but also the induction of COX-2 by TPA. Consistent with this indication, exogenous addition of PGF(2alpha), a predominant prostanoid in MDCK cells, was the most potent to protect the cells from the apoptosis induced by a mixture of TPA and NDGA.

Susceptibility of mouse primary cortical neuronal cells to coxsackievirus B

Coxsackievirus B (CVB) is often associated with aseptic meningitis and encephalitis, but the six serotypes of CVB vary in their relative disease severity. To elucidate the detailed mechanisms of CVB-induced cytopathological effects, the morphological and biochemical characteristics caused by the CVB serotypes in mouse primary cortical neuronal cells were investigated. By 24 h post-infection, all CVB serotypes except CVB2 induced severe cytotoxic alterations, including a loss of neurites. Both fluorescence and transmission electron microscopy revealed CVB-induced morphological changes indicative of apoptosis, including heavily condensed nuclei, subsequent chromatin condensation into the periphery of the nuclei and oligonucleosomal DNA fragmentation. It was also found that infection with all six CVB serotypes led to productive virus replication, which was completed prior to an apoptotic signal. The caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone significantly inhibited nuclear changes associated with virus-induced apoptosis, but had less effect on virus-associated cytopathic effects and no effect on virus production. In contrast, the transcription inhibitor actinomycin D profoundly inhibited all three virus-induced events. Taken together, these findings demonstrate that all six CVB serotypes can efficiently replicate in mouse cortical neuronal cells and that productive replication of these CVBs, except for CVB2, induces multiple cytopathological effects, including apoptotic alterations.

Involvement of ras activation in toxic hair cell damage of the mammalian cochlea

To identify possible intracellular mediators of hair cell (HC) death due to ototoxins, we treated basal-turn, neonatal, rat HCs in vitro with several intracellular signaling inhibitors, prior to and during gentamicin exposure. The general guanine nucleotide-binding protein (G-protein) inhibitor, GDP-betaS (1 mM), provided potent HC protection, suggesting involvement of G-proteins in the intracellular pathway linking gentamicin exposure to HC death. ADP-betaS had minimal effect, indicating that the protection is specific to guanosine diphosphate (GDP)-binding, rather than a general reaction to nucleotides. Azido-GTP(32) photolabeling and gel electrophoresis indicated activation of an approximately 21 kDa G-protein in HCs after exposure to gentamicin. Spectroscopic analysis of peptide fragments from this band matched its sequence with H-Ras. The Ras inhibitors B581 (50 microM) and FTI-277 (10 microM) provided potent protection against damage and reduced c-Jun activation in HC nuclei, suggesting that activation of Ras is functionally involved in damage to these cells due to gentamicin.

Cognate MHC-TCR interaction leads to apoptosis of antigen-presenting cells

Antigen presentation to T lymphocytes has been characterized extensively in terms of T lymphocyte activation and eventual cell death. In contrast, little is known about the consequences of antigen presentation for the antigen-presenting cell (APC). We have determined the outcome of major histocompatibility complex class II-restricted peptide presentation to a specific T cell. We demonstrate that specific T lymphocyte interaction with peptide-presenting APCs led to apoptosis in the APC population. In contrast, T lymphocyte interaction with nonpeptide-loaded APCs or APCs loaded with monosubstituted peptide failed to induce T lymphocyte secretion of interleukin-2 and APC apoptosis. Phosphatidylserine externalization and mitochondrial depolarization were used to evaluate APC apoptosis. Fas/Fas ligand interactions were not required, but cytoskeletal integrity and caspase activation were essential for APC apoptosis. Antigen presentation leading to T lymphocyte activation is therefore coordinated with apoptosis in the APC population and could provide a mechanism of immune response regulation by eliminating APCs, which have fulfilled their role as specific ligands for T lymphocyte activation. This pathway may have particular importance for APCs, which are not sensitive to death receptor-induced apoptosis.

Antiviral activity of caspase inhibitors: effect on picornaviral 2A proteinase

Peptide-based fluoromethyl ketones have been considered for many years to be highly specific caspase inhibitors distinctly blocking the progress of apoptosis in a variety of systems. Here we demonstrate that these compounds can significantly reduce rhinovirus multiplication in cell culture. In their methylated forms they block eIF4GI cleavage in vivo and in vitro and inhibit the activity of picornaviral 2A proteinases.

Induction of caspase-dependent apoptosis in cultured rat oligodendrocytes by murine coronavirus is mediated during cell entry and does not require virus replication

Murine coronavirus mouse hepatitis virus (MHV) causes demyelination of the central nervous system (CNS) in rats and mice. Apoptotic oligodendrocytes have been detected in the vicinity of the CNS demyelinating lesions in these animals. However, whether MHV can directly induce oligodendrocyte apoptosis has not been documented. Here, we established a rat oligodendrocyte culture that is morphologically and phenotypically indistinguishable from the primary rat oligodendrocytes. Using this culture, we showed that mature rat oligodendrocytes were permissive to MHV infection but did not support productive virus replication. Significantly, oligodendrocytes infected with both live and ultraviolet light-inactivated viruses underwent apoptosis to a similar extent, which was readily detectable at 24 h postinfection as revealed by apoptotic bodies and DNA fragmentation, indicating that MHV-induced apoptosis is mediated during the early stages of the virus life cycle and does not require virus replication. Prior treatment of cells with the lysosomotropic agents NH(4)Cl and chloroquine as well as the vacuolar proton pump-ATPase inhibitor bafilomycin A1, all of which block the acidification of the endosome, prevented oligodendrocytes from succumbing to apoptosis induced by MHV mutant OBLV60, which enters cells via endocytosis, indicating that fusion between the viral envelope and cell membranes triggers the apoptotic cascade. Treatment with the pan-caspase inhibitor Z-VAD-fmk blocked MHV-induced apoptosis, suggesting an involvement of the caspase-dependent pathway. Our results, thus, for the first time provide unequivocal evidence that infection of oligodendrocytes with MHV directly results in apoptosis. This finding provides an explanation for the destruction of oligodendrocytes and the damage of myelin sheath in MHV-infected CNS and suggests that oligodendrocyte apoptosis may be one of the underlying mechanisms for the pathogenesis of MHV-induced demyelinating diseases in animals.

Carbohydrate-mediated phagocytic recognition of early apoptotic cells undergoing transient capping of CD43 glycoprotein

A novel mechanism of phagocytic recognition of apoptotic cells was found and characterized. Jurkat cells incubated with appropriate concentrations of etoposide or anti-Fas antibody transiently became susceptible to binding and phagocytosis by THP-1 cell-derived macrophages at 2 h. The bound Jurkat cells showed no chromatin condensation, but the binding was prevented by a caspase inhibitor, indicating that they were recognized at an early stage of apoptosis. The ligands recognized on the apoptotic cells were sialylpolylactosaminyl sugar chains because 1) the binding was inhibited by an oligosaccharide preparation of erythrocyte membrane, and its inhibitory activity was destroyed by polylactosaminoglycan-specific endo-beta-galactosidase or neuraminidase; 2) Jurkat cells pretreated with endo-beta-galactosidase or neuraminidase failed to be recognized; and 3) treatment of the apoptotic cells with polylactosaminoglycan-binding Datura stramonium agglutinin prevented recognition. The sialylpolylactosaminyl chains involved were most likely those of a major sialoglycoprotein CD43 because anti-CD43 antibody inhibited recognition. CD43 on apoptotic Jurkat cells was found to form a cap at 2 h, and the cap disappeared at 4 h. This transient capping of CD43 coincided with the transient increase in the susceptibility of the cells to macrophage recognition, suggesting that CD43 capping is responsible for generation of the carbohydrate ligands for recognition. Furthermore, microscopic observation suggested that the apoptotic cells were recognized at the CD43 cap. Taken together, we conclude that apoptotic Jurkat cells transiently undergo CD43 capping at an early stage of apoptosis and are recognized by macrophages through the cluster of sialylpolylactosaminyl chains of the capped CD43.

Intracellular determination of activated caspases (IDAC) by flow cytometry using a pancaspase inhibitor labeled with FITC

BACKGROUND

Flow cytometry-based methods of simultaneous detection of multiple activated caspases in single cells are of diagnostic value and remain to be fully explored.

METHODS

Genomic DNA fragmentation was determined by agarose gel electrophoresis and flow cytometry. Whole cells were incubated with the cell-permeable pancaspase inhibitor, FITC-Val-Ala-Asp-fluoro-methyl-Rerone (FITC-VAD-FMK), and propidium iodide (PI) and analyzed for intracellular activated caspases and plasma membrane integrity, respectively, by flow cytometry.

RESULTS

Two distinct populations of apoptotic cells were identified by flow cytometry: an early apoptotic population indicated by FITC-VAD-FMK binding and the late apoptotic cells characterized by FITC-VAD-FMK staining and permeability to PI. The binding of FITC-VAD-FMK to apoptotic cells was time dependent and concurred with DNA fragmentation. Pretreatment with the pancaspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-methyl-fluoro-methyl-kerone (Z-VAD (OMe)-FMK), coordinately attenuated apoptosis induction and activation of caspases. The pancaspase inhibitor also competitively blocked the binding of FITC-VAD-FMK to early apoptotic cells in vitro. Significantly, the use of FITC-VAD-FMK permitted apoptosis determination in a number of cell lines including the caspase-3 gene-deleted MCF-7 responding to various apoptotic stimuli.

CONCLUSIONS

Apoptosis detection based on FITC-VAD-FMK binding is specific and easily performed by flow cytometry in a variety of cells. This novel technique has implications for detecting apoptosis in pathophysiologic conditions.

Induction of caspase-dependent apoptosis in cultured rat oligodendrocytes by murine coronavirus is mediated during cell entry and does not require virus replication

Murine coronavirus mouse hepatitis virus (MHV) causes demyelination of the central nervous system (CNS) in rats and mice. Apoptotic oligodendrocytes have been detected in the vicinity of the CNS demyelinating lesions in these animals. However, whether MHV can directly induce oligodendrocyte apoptosis has not been documented. Here, we established a rat oligodendrocyte culture that is morphologically and phenotypically indistinguishable from the primary rat oligodendrocytes. Using this culture, we showed that mature rat oligodendrocytes were permissive to MHV infection but did not support productive virus replication. Significantly, oligodendrocytes infected with both live and ultraviolet light-inactivated viruses underwent apoptosis to a similar extent, which was readily detectable at 24 h postinfection as revealed by apoptotic bodies and DNA fragmentation, indicating that MHV-induced apoptosis is mediated during the early stages of the virus life cycle and does not require virus replication. Prior treatment of cells with the lysosomotropic agents NH(4)Cl and chloroquine as well as the vacuolar proton pump-ATPase inhibitor bafilomycin A1, all of which block the acidification of the endosome, prevented oligodendrocytes from succumbing to apoptosis induced by MHV mutant OBLV60, which enters cells via endocytosis, indicating that fusion between the viral envelope and cell membranes triggers the apoptotic cascade. Treatment with the pan-caspase inhibitor Z-VAD-fmk blocked MHV-induced apoptosis, suggesting an involvement of the caspase-dependent pathway. Our results, thus, for the first time provide unequivocal evidence that infection of oligodendrocytes with MHV directly results in apoptosis. This finding provides an explanation for the destruction of oligodendrocytes and the damage of myelin sheath in MHV-infected CNS and suggests that oligodendrocyte apoptosis may be one of the underlying mechanisms for the pathogenesis of MHV-induced demyelinating diseases in animals.

Shiga toxin induces decreased expression of the anti-apoptotic protein Mcl-1 concomitant with the onset of endothelial apoptosis

Shiga toxin (Stx) has been implicated in the pathogenesis of several human and animal disease states. A key host target of Stx is the endothelial cell. Stx induces endothelial cell apoptosis through a mechanism that remains unknown. In the present report, we demonstrate that Stx-1 and Stx-2 inhibit endothelial cell expression of the anti-apoptotic Bcl-2 family member, Mcl-1. Decreased expression of Mcl-1 preceded the onset of Stx-induced apoptosis. Further, Stx-1-induced decrements in Mcl-1 expression correlated in a dose-dependent manner with sensitization to Stx-1-induced apoptosis. Finally, inhibition of Mcl-1 degradation with the proteasome inhibitor, lactacystin, protected against Stx-1-induced apoptosis. These combined data suggest a role for Mcl-1 in protecting endothelial cells against Stx-1-induced apoptosis.

Ligation of Siglec-8: a selective mechanism for induction of human eosinophil apoptosis

Sialic acid binding immunoglobulin-like lectin 8 (Siglec-8), which exists in 2 isoforms including one possessing cytoplasmic tyrosine motifs, is expressed only on human eosinophils, basophils, and mast cells. Until now, its function was unknown. Here we define a novel function of Siglec-8 on eosinophils. Siglec-8 cross-linking with antibodies rapidly generated caspase-3-like activity and reduced eosinophil viability through induction of apoptosis. The pancaspase inhibitor benzyloxycarbonyl (Cbz)-Val-Ala-Asp-(Ome)-fluoromethyl ketone (zVAD-FMK) completely blocked this response, implicating caspases in Siglec-8 cross-linking-induced apoptosis. Eosinophil survival-promoting cytokines such as interleukin 5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF) failed to block apoptosis and instead enhanced the sensitivity of eosinophils to undergo apoptosis in response to Siglec-8 antibody. Siglec-8 activation may provide a useful therapeutic approach to reduce numbers of eosinophils (and perhaps basophils and mast cells) in disease states where these cells are important.

Membrane incorporation of 22-hydroxycholesterol inhibits chemokine receptor activity

Cell membrane exposure to oxysterols, such as 22-hydroxycholesterol (22-OHC), has previously been shown to induce a suppressive effect on lymphocyte activation. Based on our previous findings that chemokine binding was significantly inhibited by the extraction of membrane cholesterol, we sought to assess the effects of 22-OHC treatment on chemokine ligand-binding and receptor activity. Our results revealed that 22-OHC, but not nonoxidized cholesterol, significantly reduced the binding of both SDF-1alpha and MIP-1beta to human T-cell lines and PBMCs within 1 h of treatment. Incubating the treated cells at 37 degrees C for 1 h reversed a majority of the inhibitory effects on chemokine binding. 22-OHC also inhibited intracellular calcium mobilization and cell migration in response to SDF-1alpha treatment. Interestingly, while the presence of oxysterols in cell membranes significantly inhibits chemokine receptor function, this inhibitory effect does not involve alterations in receptor conformation, expression, or a direct antagonism of chemokine binding. We propose here a novel mechanism for oxysterol-mediated inhibition of chemokine receptor function and the implications for the presence of oxysterols on immune cells.

Calpain in the pathophysiology of spinal cord injury: neuroprotection with calpain inhibitors

Spinal cord injury (SCI) evokes an increase in intracellular free Ca(2+) level resulting in activation of calpain, a Ca(2+)-dependent cysteine protease, which cleaves many cytoskeletal and myelin proteins. Calpain is widely expressed in the central nervous system (CNS) and regulated by calpastatin, an endogenous calpain-specific inhibitor. Calpastatin degraded by overactivation of calpain after SCI may lose its regulatory efficiency. Evidence accumulated over the years indicates that uncontrolled calpain activity mediates the degradation of many cytoskeletal and membrane proteins in the course of neuronal death and contributes to the pathophysiology of SCI. Cleavage of the key cytoskeletal and membrane proteins by calpain is an irreversible process that perturbs the integrity and stability of CNS cells leading to cell death. Calpain in conjunction with caspases, most notably caspase-3, can cause apoptosis of the CNS cells following trauma. Aberrant Ca(2+) homeostasis following SCI inevitably activates calpain, which has been shown to play a crucial role in the pathophysiology of SCI. Therefore, calpain appears to be a potential therapeutic target in SCI. Substantial research effort has been focused upon the development of highly specific inhibitors of calpain and caspase-3 for therapeutic applications. Administration of cell permeable and specific inhibitors of calpain and caspase-3 in experimental animal models of SCI has provided significant neuroprotection, raising the hope that humans suffering from SCI may be treated with these inhibitors in the near future.

Enhancement of TRAIL/Apo2L-mediated apoptosis by adriamycin through inducing DR4 and DR5 in renal cell carcinoma cells

Renal cell carcinoma (RCC) is one of the most drug-resistant malignancies in humans. We show that adriamycin (ADR) and TNF-related apoptosis-inducing ligand (TRAIL)/Apo2L have a synergistic cytotoxic effect against RCC cells. This synergistic cytotoxicity was obtained in ACHN, A704, Caki-1 and Caki-2 human RCC cell lines and freshly derived RCC cells from 6 patients. This synergistic effect, however, was not achieved in 5 samples of freshly isolated normal kidney cells. We further explored the mechanisms underlying this synergistic effect and found that the synergistic cytotoxicity of TRAIL/Apo2L and ADR was realized by inducing apoptosis. Sequential treatment with ADR followed by TRAIL/Apo2L induced significantly more cytotoxicity than the reverse treatment. ADR increased the expression of DR4 and DR5 in RCC cells, but not in the normal kidney cells. Furthermore, the synergistic cytotoxicity was significantly inhibited by DR4:Fc and DR5:Fc fusion proteins, which inhibit TRAIL/Apo2L-mediated apoptosis. In addition, caspase activity assays and treatment of caspase inhibitors demonstrated that the combination treatment with ADR and TRAIL/Apo2L activated caspase cascade, including caspase-9, -8, -6 and -3, which were the downstream molecules of death receptors. These findings indicate that ADR sensitizes RCC cells to TRAIL/Apo2L-mediated apoptosis through induction of DR4 and DR5, suggesting that the combination therapy of TRAIL/Apo2L and ADR might be effective for RCC therapy.

Mechanism of action of interleukin-2 (IL-2)-Bax, an apoptosis-inducing chimaeric protein targeted against cells expressing the IL-2 receptor

The chimaeric protein interleukin-2 (IL-2)-Bax was designed to target and kill specific cell populations expressing the IL-2 receptor. However, it is not well understood how IL-2-Bax causes target cells to die. In the present study, we investigated the pathway of apoptosis evoked by IL-2-Bax and the possible involvement of endogenous Bax in this process. We report here that, upon internalization of IL-2-Bax into target cells, it is localized first mainly in the nucleus, and only later is it translocated to the mitochondria. Similarly, endogenous Bax is also partially localized in the nucleus, and accumulates mainly in this compartment soon after physiological triggering of apoptosis. Despite the fact that Bax has no nuclear localization sequence, our data suggest that Bax has one or more physiological roles and/or substrates within the nucleus. Indeed, a dramatic repression of nuclear Tax protein expression was induced following treatment of HUT-102 cells with IL-2-Bax, similar to what occurs following serum deprivation of these cells. Unexpectedly, induction of apoptosis using IL-2-Bax was preceded by enhanced expression of newly synthesized Bax protein and suppression of Bcl-2. This imbalance between the pro- and anti-apoptotic genes was associated with p53 induction, although IL-2-Bax activity was also evident in cells lacking p53 expression. By studying the mechanism of action of IL-2-Bax, we were able to follow the intrinsic events and their cascade that culminates in cell death. We have shown that the ability of IL-2-Bax to affect the intracellular apoptotic machinery within the target cells, and to cause the cells to die, uses a mechanism similar to that induced following a normal apoptotic signal.

Phosphatidylinositol 3-kinase regulates human immunodeficiency virus type 1 replication following viral entry in primary CD4+ T lymphocytes and macrophages

Human immunodeficiency virus (HIV) gp120 induces multiple cellular signaling pathways, including the phosphatidylinositol 3-kinase (PI3-kinase) pathway. The role of the PI3-kinase pathway in HIV-1 replication is not understood. Here we examined whether HIV-1 gp120 upregulates the PI3-kinase pathway and whether PI3-kinase activity plays a role in virus replication in primary human CD4(+) T cells and macrophages. Soluble and virion-associated HIV-1 gp120 induced calcium mobilization and phosphorylation of the PI3-kinase downstream effectors PKB/Akt and p70 S6 kinase. gp120-induced PI3-kinase activity and calcium mobilization were inhibited by pertussis toxin and blocking antibodies directed against CCR5 and CXCR4, suggesting that the signaling is mediated through the chemokine receptor. The PI3-kinase inhibitor LY294002 inhibited infection of CD4(+) T cells and macrophages with X4 and R5 HIV-1-pseudotyped viruses at concentrations that did not induce cell toxicity or downregulate HIV-1 coreceptor expression. When gp120-induced signaling was bypassed with the vesicular stomatitis virus G envelope protein, infection was still sensitive to PI3-kinase inhibition, suggesting that basal PI3-kinase activity is required for infection. LY294002 inhibited HIV-1 infection when added after viral entry and did not affect formation of the HIV-1 reverse transcriptase products R/U5 and long terminal repeat/Gag in the presence of the inhibitor. However, when the inhibitor was added after viral integration had occurred, no inhibition of HIV infection was observed. Our studies show that inhibition of the PI3-kinase signaling pathway suppresses virus infection post-viral entry and post-reverse transcription but prior to HIV gene expression. This type of host-virus interaction has implications for anti-HIV therapeutics that target cellular signaling machinery.

Cholesteryl-hemisuccinate-induced apoptosis of promyelocytic leukemia HL-60 cells through a cyclosporin A-insensitive mechanism

We reported previously that alpha-tocopheryl-succinate (VES) induced apoptosis of cultured human promyelocytic leukemia cells (HL-60) (Free Radic Res 2000;33:407-18). We have now studied the effect of cholesteryl-hemisuccinate (CS) on the fate of HL-60 cells to clarify whether CS has an effect similar to that of VES. CS inhibited the growth of HL-60 cells without differentiation to granulocytes and induced DNA fragmentation and ladder formation. CS inhibited the phosphorylation of pleckstrin homology domain-containing protein kinase B (Akt) and initiated the activation of a caspase cascade. CS triggered the reaction leading to the cleavage of Bid and also released cytochrome c (Cyt. c) from mitochondria. In addition, CS induced mitochondrial membrane depolarization and translocation of Bax to mitochondria in HL-60 cells. However, CS did not induce an increase in the concentration of intracellular calcium ions in HL-60 cells. The membrane depolarization, Cyt. c release, and DNA fragmentation were inhibited by z-VAD-fluoromethylketone (z-VAD-fmk), a pan-caspase inhibitor, but not by cyclosporin A, an inhibitor of membrane permeability transition. These results suggested that CS-induced apoptosis of HL-60 cells might be caused by inhibiting Akt phosphorylation following cleavage of Bid through caspase-8 activation and subsequently via an Apaf complex-caspase cascade pathway.

Poliovirus-induced apoptosis is reduced in cells expressing a mutant CD155 selected during persistent poliovirus infection in neuroblastoma cells

Poliovirus (PV) can establish persistent infections in human neuroblastoma IMR-32 cells. We previously showed that during persistent infection, specific mutations were selected in the first extracellular domain of the PV receptor (CD155) of these cells (N. Pavio, T. Couderc, S. Girard, J. Y. Sgro, B. Blondel, and F. Colbère-Garapin, Virology 274:331-342, 2000). These mutations included the Ala 67 --> Thr substitution, corresponding to a previously described allelic form of the PV receptor. The mutated CD155(Thr67) and the nonmutated IMR-32 CD155 (CD155(IMR)) were expressed independently in murine LM cells lacking the CD155 gene. Following infection of the cells with PV, we analyzed the death of cells expressing these two forms of CD155. Levels of DNA fragmentation, caspase activity, and cytochrome c release were lower in LM-CD155(Thr67) cells than in LM-CD155(IMR) cells. Thus, the level of apoptosis was lower in cells expressing mutated CD155 selected during persistent PV infection in IMR-32 than in cells expressing the wild-type receptor.

Implication of caspases during maedi-visna virus-induced apoptosis

Maedi-visna virus (MVV) causes encephalitis, pneumonia and arthritis in sheep. In vitro, MVV infection and replication lead to strong cytopathic effects characterized by syncytia formation and subsequent cellular lysis. It was demonstrated previously that MVV infection in vitro induces cell death of sheep choroid plexus cells (SCPC) by a mechanism that can be associated with apoptotic cell death. Here, the relative implication of several caspases during acute infection with MVV is investigated by employing diverse in vitro and in situ strategies. It was demonstrated using specific pairs of caspase substrates and inhibitors that, during in vitro infection of SCPC by MVV, the two major pathways of caspase activation (i.e. intrinsic and extrinsic pathways) were stimulated: significant caspase-9 and -8 activities, as well as caspase-3 activity, were detected. To study the role of caspases during MVV infection in vitro, specific, cell-permeable, caspase inhibitors were used. First, these results showed that both z-DEVD-FMK (a potent inhibitor of caspase-3-like activities) and z-VAD-FMK (a broad spectrum caspase inhibitor) inhibit caspase-9, -8 and -3 activities. Second, both irreversible caspase inhibitors, z-DEVD-FMK and z-VAD-FMK, delayed MVV-induced cellular lysis as well as virus growth. Third, during SCPC in vitro infection by MVV, cells were positively stained with FITC-VAD-FMK, a probe that specifically stains cells containing active caspases. In conclusion, these data suggest that MVV infection in vitro induces SCPC cell death by a mechanism that is strongly dependent on active caspases.

Shiga-like toxin inhibition of FLICE-like inhibitory protein expression sensitizes endothelial cells to bacterial lipopolysaccharide-induced apoptosis

Shiga-like toxin (SLT) has been implicated in the pathogenesis of hemolytic uremic syndrome and its attendant endothelial cell (EC) injury. Key serotypes of Escherichia coli produce SLT-1 in addition to another highly pro-inflammatory molecule, lipopolysaccharide (LPS). It has previously been established that SLT-1 induces EC apoptosis and that LPS enhances this effect. LPS alone has no affect on human EC viability, and the mechanism for this enhancement remains unknown. In the present report, we demonstrate that SLT-1 sensitizes EC to LPS-induced apoptosis. Pretreatment with SLT-1 sensitized EC to LPS-induced apoptosis, whereas pretreatment with LPS did not influence SLT-1-induced apoptosis. SLT-1 exposure resulted in decreased expression of FLICE-like inhibitory protein (FLIP), an anti-apoptotic protein that has previously been shown to block LPS-induced apoptosis. This SLT-1-mediated decrease in FLIP expression preceded the onset of apoptosis elicited by SLT-1 alone or in combination with LPS. SLT-1-mediated decrements in FLIP expression correlated in a dose- and time-dependent manner with sensitization to LPS-induced apoptosis. Finally, transient or stable overexpression of FLIP protected against LPS enhancement of SLT-1-induced apoptosis, and this protection corresponded with sustained expression of FLIP. Together, these data suggest that SLT-1 sensitizes EC to LPS-induced apoptosis by inhibiting FLIP expression.

The poststimulation program of CD4 versus CD8 T cells (death versus activation-induced nonresponsiveness)

Both CD8 and CD4 T cells undergo autocrine IL-2-induced proliferation and clonal expansion following stimulation with Ag and costimulation. The CD8 T cell response is transient because the cells rapidly become activation-induced nonresponsive (AINR) and exhibit split anergy. In these cells, the capacity for IL-2 production is lost, but TCR-mediated IFN-gamma production and cytotoxicity are maintained. At this point, the CTL become dependent on IL-2 provided by CD4 Th cells for continued expansion. If IL-2 is available to support expansion for a brief period, AINR is reversed and the cells regain the ability to produce IL-2. In this study, we show that CD4 T cells do not become AINR, but instead are rendered susceptible to Fas-mediated activation-induced cell death following stimulation through TCR and CD28. Using z-VAD-fmk or anti-Fas ligand mAb to inhibit cell death, we demonstrate that previously activated CD4 T cells retain the ability to up-regulate c-Jun N-terminal kinase activity and IL-2 mRNA levels upon TCR engagement and no longer require costimulation. This rewiring of signaling pathways is similar to that seen following reversal of AINR in CD8 T cells. Thus, CD8 and CD4 T cells appear to use distinct mechanisms, AINR and activation-induced cell death, respectively, to limit excessive clonal expansion following a productive response, while permitting important effector functions to be expressed.

An ex vivo murine model to study poliovirus-induced apoptosis in nerve cells

Paralytic poliomyelitis results from destruction of motor neurons owing to poliovirus (PV) replication. Using a mouse model, we have previously shown that PV kills neurons of the central nervous system (CNS) as a result of apoptosis (Girard et al., Journal of Virology 73, 6066-6072, 1999). We report the development of mixed mouse primary nerve cell cultures from the cerebral cortex of neonatal mice transgenic for the human PV receptor. These cultures contained all three main cell types of the CNS, i.e. neurons, astrocytes and oligodendrocytes. All three cell types were susceptible to PV infection and virus replication in the cultures led to DNA fragmentation characteristic of apoptosis. PV-induced apoptosis was inhibited by the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(O-Me) fluoromethyl ketone (Z-VAD.FMK), indicating that this process involved caspases. Thus, these mixed mouse primary nerve cell cultures are a new in vitro model for studying the molecular mechanisms of PV-induced apoptosis in nerve cells.

Blebs and apoptotic bodies are B cell autoantigens

Mounting evidence suggests that systemic lupus erythematosus autoantigens are derived from apoptotic cells. To characterize the potential interactions between apoptotic cells and B cells, the D56R/S76R variant of 3H9, a murine autoantibody that binds to DNA, chromatin, and anionic phospholipids, was compared with DNA4/1, a human anti-DNA autoantibody. Flow cytometry revealed that only D56R/S76R bound to Jurkat cells treated with either of three distinct proapoptotic stimuli, Ab binding was dependent on caspase activity, and immunoreactivity developed subsequent to annexin V binding. Confocal microscopy established a structural basis for the distinct kinetics of binding. D56R/S76R preferentially bound to membrane blebs of apoptotic cells, whereas annexin V binding did not require blebs. Inhibition of ROCK I kinase, an enzyme that stimulates nuclear fragmentation and fragment distribution into blebs, significantly reduced Ab binding. Because members of the collectin and pentraxin families of serum proteins bind to blebs on apoptotic cells and assist in the clearance of cellular remains, our results suggest that Abs to blebs could affect the recognition of apoptotic cells by cells of the innate immune system and thus modify tolerance to nuclear Ags.

Cloned Shiga toxin 2 B subunit induces apoptosis in Ramos Burkitt's lymphoma B cells

The Shiga toxins (Stx1 and Stx2), produced by Shigella dysenteriae type 1 and enterohemorrhagic Escherichia coli, consist of one A subunit and five B subunits. The Stx1 and Stx2 B subunits form a pentameric structure that binds to globotriaosylceramide (Gb3-Cer) receptors on eukaryotic cells and promotes endocytosis. The A subunit then inhibits protein biosynthesis, which triggers apoptosis in the affected cell. In addition to its Gb3-Cer binding activity, the data in the following report demonstrate that the Stx2 B pentamer induces apoptosis in Ramos Burkitt's lymphoma B cells independently of A subunit activity. Apoptosis was not observed in A subunit-free preparations of the Stx1 B pentamer which competitively inhibited Stx2 B pentamer-mediated apoptosis. The pancaspase inhibitor, Z-VAD-fmk, prevented apoptosis in Ramos cells exposed to the Stx2 B subunit, Stx1 or Stx2. Brefeldin A, an inhibitor of the Golgi transport system, also prevented Stx2 B subunit-mediated apoptosis. These observations suggest that the Stx2 B subunit must be internalized, via Gb3-Cer receptors, to induce Ramos cell apoptosis. Moreover, unlike the two holotoxins, Stx2 B subunit-mediated apoptosis does not involve inhibition of protein biosynthesis. This study provides further insight into the pathogenic potential of this family of potent bacterial exotoxins.

Caspase inhibition and N6-benzyladenosine-induced apoptosis in HL-60 cells

As an extension of our recently published work (Mlejnek and Kuglík [2000] J. Cell. Biochem. 77:6-17), the role of caspases in N(6)-benzylaminopurine riboside (BAPR)-induced apotosis in HL-60 cells was evaluated in this study. Here, BAPR-induced apoptosis was accompanied by activation of caspase-3 and caspase-9. However, when these caspases were selectively inhibited, the progression of BAPR-induced apoptosis was not markedly affected. Besides that, activation of caspase-3 and caspase-9 was found to be rather late event in apoptotic process. These results suggested that other caspases might be critically implicated. Indeed, pan-specific caspase inhibitor, Z-VAD-FMK, completely prevented DNA cleavage and apoptotic bodies formation. However, Z-VAD-FMK failed to prevent cell death and it was incapable to fully counteract the main apoptotic hallmark-chromatin condensation. Finally, our data indicate that cellular decision between apoptosis and necrosis is made upon the availability of both caspase proteases and intracellular ATP.

Transforming growth factor beta (TGFbeta) mediates Schwann cell death in vitro and in vivo: examination of c-Jun activation, interactions with survival signals, and the relationship of TGFbeta-mediated death to Schwann cell differentiation

In some situations, cell death in the nervous system is controlled by an interplay between survival factors and negative survival signals that actively induce apoptosis. The present work indicates that the survival of Schwann cells is regulated by such a dual mechanism involving the negative survival signal transforming growth factor beta (TGFbeta), a family of growth factors that is present in the Schwann cells themselves. We analyze the interactions between this putative autocrine death signal and previously defined paracrine and autocrine survival signals and show that expression of a dominant negative c-Jun inhibits TGFbeta-induced apoptosis. This and other findings pinpoint activation of c-Jun as a key downstream event in TGFbeta-induced Schwann cell death. The ability of TGFbeta to kill Schwann cells, like normal Schwann cell death in vivo, is under a strong developmental regulation, and we show that the decreasing ability of TGFbeta to kill older cells is attributable to a decreasing ability of TGFbeta to phosphorylate c-Jun in more differentiated cells.

Transforming growth factor beta (TGFbeta) mediates Schwann cell death in vitro and in vivo: examination of c-Jun activation, interactions with survival signals, and the relationship of TGFbeta-mediated death to Schwann cell differentiation

In some situations, cell death in the nervous system is controlled by an interplay between survival factors and negative survival signals that actively induce apoptosis. The present work indicates that the survival of Schwann cells is regulated by such a dual mechanism involving the negative survival signal transforming growth factor beta (TGFbeta), a family of growth factors that is present in the Schwann cells themselves. We analyze the interactions between this putative autocrine death signal and previously defined paracrine and autocrine survival signals and show that expression of a dominant negative c-Jun inhibits TGFbeta-induced apoptosis. This and other findings pinpoint activation of c-Jun as a key downstream event in TGFbeta-induced Schwann cell death. The ability of TGFbeta to kill Schwann cells, like normal Schwann cell death in vivo, is under a strong developmental regulation, and we show that the decreasing ability of TGFbeta to kill older cells is attributable to a decreasing ability of TGFbeta to phosphorylate c-Jun in more differentiated cells.

Human chondrocyte apoptosis in response to mechanical injury

OBJECTIVE

The effect of mechanical injury on chondrocyte viability and matrix degradation was studied. It was proposed that mechanical injury to human cartilage explants results in chondrocyte apoptosis with associated loss of glycosaminoglycans.

DESIGN

Full thickness human cartilage explants, 5 mm in diameter were subjected to a single static mechanical stress of 14 MPa for 500 ms under radially unconfined compression. Glycosaminoglycan (GAG) release and percentage of cells undergoing apoptosis were measured at 96 h after injury. To establish the time course of apoptosis, explants were subjected to 30% strain and cultured for varying intervals up to 7 days after injury. A group of loaded explants were also treated with the broad spectrum caspase inhibitor z-Vad.fmk after injury.

RESULTS

Internucleosomal DNA fragmentation as one indicator of apoptosis was observed in 34% (S.D.+/-11) of chondrocytes at 96 h in response to mechanical loading at 14 MPa, compared to 4% (S.D.+/-2) in the non-loaded explants. Evidence for cell death induction via apoptosis was also obtained by electron microscopy and caspase cleavage of cytokeratin. GAG release was also higher for the loaded explants, mean 1.9% (S.D.+/-0.14) of total GAG content, compared to control explants, mean 0.8% (S.D.+/-0.28). The percentage of apoptotic cells also correlated with the level of GAG release into the culture media. The percentage of apoptotic chondrocytes demonstrated a progressive increase from 6 h to 7 days post-injury. When loaded explants were cultured in z-Vad.fmk after injury, a 50% reduction in apoptosis rates was seen.

CONCLUSIONS

These results demonstrate that mechanical injury induces chondrocyte apoptosis and release of GAG from the matrix. The time course suggests that a therapeutic window may exist where apoptosis could be inhibited. This potentially identifies a new approach to chondroprotection.

Cladribine induces apoptosis in human leukaemia cells by caspase-dependent and -independent pathways acting on mitochondria

We have studied the role of caspases and mitochondria in apoptosis induced by 2-chloro-2'-deoxyadenosine (cladribine) in several human leukaemic cell lines. Cladribine treatment induced mitochondrial transmembrane potential (DeltaPsi(m)) loss, phosphatidylserine exposure, caspase activation and development of typical apoptotic morphology in JM1 (pre-B), Jurkat (T) and U937 (promonocytic) cells. Western-blot analysis of cell extracts revealed the activation of at least caspases 3, 6, 8 and 9. Co-treatment with Z-VAD-fmk (benzyloxy-carbonyl-Val-Ala-Asp-fluoromethylketone), a general caspase inhibitor, significantly prevented cladribine-induced death in JM1 and Jurkat cells for the first approximately 40 h, but not for longer times. Z-VAD-fmk also partly prevented some morphological and biochemical features of apoptosis in U937 cells, but not cell death. Co-incubation with selective caspase inhibitors Ac-DEVD-CHO (N-acetyl-Asp-Glu-Val-Asp-aldehyde), Ac-LEHD-CHO (N-acetyl-Leu-Glu-His-Asp-aldehyde) or Z-IETD-fmk (benzyloxycarbonyl-Ile-Glu-Thr-Asp-fluoromethylketone), inhibition of protein synthesis with cycloheximide or cell-cycle arrest with aphidicolin did not prevent cell death. Overexpression of Bcl-2, but not CrmA, efficiently prevented death in Jurkat cells. In all cell lines, death was always preceded by Delta Psi(m) loss and accompanied by the translocation of the protein apoptosis-inducing factor (AIF) from mitochondria to the nucleus. These results suggest that caspases are differentially involved in induction and execution of apoptosis depending on the leukaemic cell lineage. In any case, Delta Psi(m) loss marked the point of no return in apoptosis and may be caused by two different pathways, one caspase-dependent and the other caspase-independent. Execution of apoptosis was always performed after Delta Psi(m) loss by a caspase-9-triggered caspase cascade and the action of AIF.

Granulysin blocks replication of varicella-zoster virus and triggers apoptosis of infected cells

Granulysin, a lytic protein present in cytolytic granules of human natural killer and cytotoxic T cells, entered cells infected with varicella-zoster virus (VZV). Exposure to granulysin accelerated death of infected cells as assessed by apoptosis markers. The functional domain of granulysin that mediated its antiviral effects was amino acid 23-51; this domain also mediates the additional antitumor cell effects of granulysin. Because granulysin is a product of natural killer cells and T lymphocytes, it is possible that its antiviral activity may act as a mediator of innate and adaptive immune mechanisms.

Mechanism of apoptosis in HL-60 cells induced by n-3 and n-6 polyunsaturated fatty acids

The biochemical properties and specificity of n-3 and n-6 polyunsaturated fatty acids (PUFAs) are not well known. Because PUFAs induce apoptosis of different cells, we studied the effect of various PUFAs, such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosapentaenoic acid (DPA), on the fate of cultured human promyelocytic leukemia cells (HL-60) to elucidate the mechanism of apoptosis and the difference in action between n-3 and n-6 PUFAs. Fairly low concentrations of PUFAs inhibited the growth of HL-60 cells and induced their apoptosis by a mechanism that is sensitive to DMSO, an antioxidant, and z-Val-Ala-Asp(OMe)-fluoromethylketone (z-VAD-fmk), a pan-caspase inhibitor. PUFAs stimulated the generation of reactive oxygen species (ROS) and activated various types of caspase-like proteases, such as caspase-3, -6, -8, and -9, but not caspase-1. In addition, PUFAs triggered the reaction leading to the cleavage of Bid, a death agonist member of the Bcl-2 family, and also released cytochrome c from mitochondria into the cytosol. PUFAs also decreased the mitochondrial membrane potential of intact HL-60 cells. All of these actions of n-3 PUFAs were stronger than those of AA, an n-6 PUFA, although the mechanism is not known. PUFAs stimulate swelling and membrane depolarization of isolated mitochondria in a cyclosporin A-sensitive manner. The results indicated that PUFA-induced apoptosis of HL-60 cells may be caused, in part, by direct action on the cells and by activation of the caspase cascade through cytochrome c release coupled with mitochondrial membrane depolarization.

Impact of mechanical trauma on matrix and cells

Posttraumatic arthritis is one of the most common causes of secondary osteoarthritis. The contribution of cell death to matrix degradation has not been characterized fully. The current study was designed to determine the effect of mechanical injury on chondrocyte viability and matrix degradation. Full-thickness bovine and human cartilage explants, 5 mm in diameter were subjected to mechanical loads representative of traumatic joint injury. Glycosaminoglycan release and percent apoptotic cells were measured. Unilateral patellas in eight anesthetized rabbits were subjected to an impact load. Rabbits were euthanized at 96 hours after injury and patellar cartilage was harvested for analysis. The effect of a pan-caspase inhibitor, z-VAD.fmk [benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethylketone] in preventing chondrocyte apoptosis in human articular cartilage explants was determined. A significant increase in the number of apoptotic cells was observed in response to mechanical loading. The mean in vivo apoptotic rates were 1% in control rabbits and 15% in impacted patellas. Caspase inhibition reduced chondrocyte apoptosis from 34% to 25% after mechanical injury and was associated with reduction in glycosaminoglycan release. Mechanical injury induces chondrocyte apoptosis that is sensitive to pharmacologic inhibition. This identifies a new approach to limit traumatic cartilage injury and the subsequent development of secondary osteoarthritis.

Laser-beam-triggered microcavitation: a novel method for selective cell destruction

We describe a new method of cell destruction that may have potential for use in antitumor therapy. Cells are loaded by phagocytosis with microparticles (<1 microm) and irradiated with short laser pulses. Absorption of laser energy by the microparticles causes localized vaporization of the fluid surrounding the microparticles, leading to the generation of transient vapor bubbles (microcavitation) around the microparticles. Using cultures of bovine aortic endothelial cells, we demonstrate that induction of intralysosomal microcavitation is an efficient, rapid and selective method of cell killing that is dependent on the number of microparticles, the number of laser pulses, and the fluence of the laser pulses. Cell killing by microcavitation is a very selective process that is restricted to cells containing microparticles, leaving other cells unaffected. Intracytoplasmic release of lysosomal hydrolases is, in part, responsible for cell death, because the protease inhibitors E64d and TLCK diminished cell killing. Using the broad-specificity caspase inhibitor Z-VAD-fmk, we determined that lysosomal hydrolases could induce apoptosis in a caspase-independent manner. We also examined the possibility of microcavitation-induced delayed effects in the cells that survived the treatment. Using flow cytometry, we determined that there was no delayed cell death between 1 and 4 days after microcavitation. Moreover, we did not observe changes in the cell cycle, in expression of the proteins BCL2, HSP70 and HSP27, or in PARP degradation. In conclusion, microcavitation induces rapid and specific cells death (limited only to cells containing microparticles), without producing delayed effects among the surviving cells.

Investigation of a potential scintigraphic marker of apoptosis: radioiodinated Z-Val-Ala-DL-Asp(O-methyl)-fluoromethyl ketone

The imaging of apoptosis represents an attractive diagnostic goal in the area of tumor therapy, degenerative diseases and organ transplantation. Since caspases play a key role during the early period of the intracellular signal cascade of cells undergoing apoptosis we considered benzyloxycarbonyl-Val-Ala-DL-Asp(O-methyl)-fluoromethyl ketone [Z-VAD-fmk], a pan-caspase inhibitor, as a potential apoptosis imaging agent. Applying the Tl(TFA)(3)/[131I]iodide method Z-VAD-fmk was successfully labeled at the benzyloxycarbonyl protecting group. The success of radioiodination, however, depended on the presence of carrier iodide resulting in specific radioactivities of 2.6 GBq/micromol and the formation of a mixture of the 2- and 4-iodophenyl derivative (61%) which could not be separated by HPLC. Uptake measurements were performed with Morris hepatoma cells (MH3924Atk8) which showed expression of the Herpes Simplex Virus thymidine kinase (HSVtk) gene. Apoptosis was induced by treatment of the cells with 25 microM ganciclovir. The TUNEL assay revealed 1.3 +/-0.3 and 23 +/-1.1% apoptotic cells immediately and 24 h after therapy, respectively. A two-fold increase of [131I]IZ-VAD-fmk uptake was found at the end of treatment with the HSVtk/suicide system which constantly remained elevated for the following 4 hours. The slow cellular influx and lack of uptake saturation of [131I]IZ-VAD-fmk are evidence for simple diffusion as transport mechanism. In addition, the absolute cellular uptake of [131I]IZ-VAD-fmk was found to be low. This quality was related to the rather high lipophilicity of [131I]IZ-VAD-fmk causing unspecific binding to macromolecules in the medium. Instead of using an inhibitor, synthetic caspase substrates are currently investigated which may accumulate in the apoptotic cell by metabolic trapping thereby enhancing the imaging signal.

Differential involvement of caspases in hydroquinone-induced apoptosis in human leukemic hl-60 and jurkat cells

The benzene metabolite hydroquinone (HQ) is postulated to exert its myelotoxicity by bioactivation to reactive quinone derivatives in myeloperoxidase (MPO)-containing cells. In this study, the role of caspases in hydroquinone-induced apoptosis in MPO-rich HL-60 promyelocytic leukemia and MPO-deficient Jurkat T-lymphoblastic leukemia cells was investigated. HQ-induced apoptosis in both cell types was accompanied by phosphatidylserine (PS) exposure, caspases-3/-7 activation, PARP cleavage, DNA fragmentation, and ultrastructural changes as assessed by electron microscopy. In HL-60 cells, the general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone (Z-VAD.FMK) blocked activation of caspases-3/-7, cleavage of PARP, and DNA, but PS externalization and cytoplasmic changes were not significantly affected. In marked contrast, all features of apoptosis were completely inhibited by Z-VAD.FMK in HQ-treated Jurkat cells. These data provide evidence for Z-VAD.FMK-insensitive and caspases-3/-7-independent pathway(s) in the externalization of PS and cytoplasmic changes during HQ-induced apoptosis in HL-60 cells. In contrast, in Jurkat cells, all of these changes required caspase activation. The ability of HQ to induce equivalent apoptosis in both MPO-deficient Jurkat cells and MPO-rich HL-60 cells demonstrates that MPO-catalyzed bioactivation of HQ is not a prerequisite for toxicity. The differential mechanisms of apoptosis in HL-60 and Jurkat T cells may reflect the MPO activity of these cells and, as a result, the amount of reactive BQ and other metabolites that are generated.

Cutting edge: amelioration of kidney disease in a transgenic mouse model of lupus nephritis by administration of the caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-(beta-o-methyl)-fluoromethylketone

Systemic lupus erythematosus (SLE) is a common, potentially fatal, non-organ-specific autoimmune disorder. Immune complex-mediated kidney disease is the major cause of mortality. Apoptotic cells in the epidermis are a possible source of self Ags, and apoptosis of endothelial cells and lymphocytes is thought to contribute to end-organ damage. We have previously shown that female transgenic mice expressing IFN-gamma in the epidermis develop inflammatory skin disease and features of SLE that have striking parallels with the human condition. We have now tested the effects of a pan-caspase inhibitor, carbobenzoxy-valyl-alanyl-aspartyl-(beta-o-methyl)-fluoromethylketone, on disease progression. Daily s.c. administration of carbobenzoxy-valyl-alanyl-aspartyl-(beta-o-methyl)-fluoromethylketone to female transgenic mice over a 3-wk period resulted in significant amelioration of both glomerular and interstitial renal damage, independent of the effects on autoantibody levels or skin inflammation. We propose that apoptosis inhibitors could be beneficial in the treatment of human SLE.

Human blood-derived macrophages induce apoptosis in human plaque-derived vascular smooth muscle cells by Fas-ligand/Fas interactions

Human atherosclerotic plaques that rupture are characterized by relatively low vascular smooth muscle cell (VSMC) and high inflammatory cell contents. Ruptured plaques also contain higher numbers of apoptotic VSMCs than do stable lesions, suggesting that VSMC apoptosis may promote plaque rupture. We examined the ability of human monocytes/macrophages to induce apoptosis of VSMCs derived from human carotid plaque, aortic media, and coronary media. Macrophages, but not T lymphocytes, induced a dose-dependent apoptosis of VSMCs, which required monocyte maturation to macrophages and direct cell-cell contact/proximity. VSMC apoptosis was inhibited by neutralizing antibodies to Fas-ligand (Fas-L) or an Fas-Fc fusion protein, indicating the requirement for membrane-bound Fas and Fas-L. Monocyte maturation was associated with increased surface expression of Fas-L, coincident with the onset of cytotoxicity. VSMCs expressed surface Fas, which was increased in plaque VSMCs, and plaque VSMCs also underwent Fas-induced apoptosis. We conclude that human macrophages potently induce human VSMC apoptosis, which requires direct cell-cell interactions and is in part dependent on Fas/Fas-L interactions. Macrophage-induced VSMC apoptosis may therefore directly promote plaque rupture.

Proteasome inhibitor-induced apoptosis of B-chronic lymphocytic leukaemia cells involves cytochrome c release and caspase activation, accompanied by formation of an approximately 700 kDa Apaf-1 containing apoptosome complex

Proteasome inhibitors, including lactacystin and MG132 (carbobenzoxyl-leucinyl-leucinyl-leucinal), potently induce apoptosis in leukaemic B cells from patients with B cell chronic lymphocytic leukaemia (B-CLL). This pro-apoptotic effect occurs in cells from patients at all stages of the disease, including those resistant to conventional chemotherapy, suggesting that proteasome inhibitors may be useful for treatment of B-CLL. Following initial inhibition of proteasomal activity, these agents induce mitochondrial cytochrome c release and caspase-dependent apoptosis, involving cleavage/activation of caspases -2, -3, -7, -8 and -9. Pre-treatment with the cell permeable caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe)fluoromethyl ketone (Z-VAD.fmk), did not prevent the release of cytochrome c or partial processing of caspase-9 but prevented activation of effector caspases and the induction of apoptosis. These results suggest that the release of cytochrome c is caspase independent and that caspase-9 is the initiator caspase in proteasome inhibitor-induced apoptosis of B-CLL cells. Activation of B-CLL lysates with dATP results in the formation of an approximately 700 kDa caspase-activating apoptosome complex containing Apaf-1. We describe for the first time the formation of a similar approximately 700 kDa caspase-activating apoptosome complex in B-CLL cells induced to undergo apoptosis by proteasome inhibitors.

Apoptosis induction and cell cycle perturbation in established cell lines by peroxysomicine A1 (T-514)

Peroxysomicine A1, a novel potential anticancer compound induced cell death in established cell lines and in a primary culture of rat neonatal cardiomyocytes. Non-transformed cells are less sensitive to the compound than transformed cell lines. Fluorescent microscopy of dying cells stained with DNA-specific dyes revealed chromatin condensation and nuclear fragmentation as well as membrane blebbing characteristic of apoptosis. Flow cytometry of cells treated with peroxysomicine A1, demonstrated appearance of cells containing less than 2C DNA, that indicated degradation of nuclear DNA, another hallmark of apoptotic cell death. Z-VAD, a nonspecific caspase inhibitor, prevented DNA fragmentation but not cell death registered by permeabilization of cell outer membrane. Peroxysomicine A1 also inhibited proliferation of various cell lines. Flow cytometry analysis showed significant accumulation of dividing cells in G2/M phases of cell cycle indicating, most likely delay in G2. These results provide initial insight into the mechanisms of action of peroxysomicine A1 and suggest that peroxysomicine A1 is a potent inhibitor of cell proliferation and inducer of apoptosis and may be a useful antineoplastic chemotherapeutic agent.

A constitutive cytoprotective pathway protects endothelial cells from lipopolysaccharide-induced apoptosis

Lipopolysaccharide (LPS) has been implicated as the bacterial component responsible for much of the endothelial cell injury/dysfunction associated with Gram-negative bacterial infections. Protein synthesis inhibition is required to sensitize the endothelium to lipopolysaccharide-induced apoptosis, suggesting that a constitutive or inducible cytoprotective protein(s) is required for endothelial survival. We have identified two known endothelial anti-apoptotic proteins, c-FLIP and Mcl-1, the expression of which is decreased markedly in the presence of cycloheximide. Decreased expression of both proteins preceded apoptosis evoked by lipopolysaccharide + cycloheximide. Caspase inhibition protected against apoptosis, but not the decreased expression of c-FLIP and Mcl-1, suggesting that they exert protection upstream of caspase activation. Inhibition of the degradation of these two proteins with the proteasome inhibitor, lactacystin, prevented lipopolysaccharide + cycloheximide-induced apoptosis. Similarly, lactacystin protected against endothelial apoptosis induced by either tumor necrosis factor-alpha or interleukin-1beta in the presence of cycloheximide. That apoptosis could be blocked in the absence of new protein synthesis by inhibition of the proteasome degradative pathway implicates the requisite involvement of a constitutively expressed protein(s) in the endothelial cytoprotective pathway. Finally, reduction of FLIP expression with antisense oligonucleotides sensitized endothelial cells to LPS killing, demonstrating a definitive role for FLIP in the protection of endothelial cells from LPS-induced apoptosis.

Caspase-3 activity and carbonyl cyanide m-chlorophenylhydrazone-induced apoptosis in HL-60

The role of caspase proteases in carbonyl cyanide m-chlorophenylhydrazone (CCCP)-induced apoptosis of human promyelocytic HL-60 cells was examined. Treatment of HL-60 cells with micromolar concentrations of CCCP resulted in cell death, with typical apoptotic features such as chromatin condensation, formation of apoptotic bodies, nucleosomal fragmentation of DNA and a distinct increase in caspase-3 activity. The results, however, indicated that full caspase-3 inhibition by the selective inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp fluoromethyl ketone (Z-DEVD-FMK) did not prevent cell death, nor did it affect the manifestation of apoptotic hallmarks, including apoptotic bodies formation and nucleosomal DNA fragmentation. The only distinct effect that Z-DEVD-FMK exhibited was to retard the disruption of the plasma membrane. We therefore assume that caspase-3 activity itself is not essential for the manifestation of apoptotic features mentioned above. Similarly, the pan-specific caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone (Z-VAD-FMK) did not prevent cell death. On the contrary, Z-VAD-FMK completely prevented DNA cleavage and apoptotic body formation, but it failed to completely counteract chromatin condensation. Thus, in the presence of Z-VAD-FMK, application of CCCP concentrations that otherwise induced apoptosis, resulted in the appearance of two morphologically different groups of dead cells with intact DNA. The first group included cells with necrotic-like nuclear morphology, and therefore could be taken as being "truly" necrotic in nature, because they had intact DNA. The cells of the second group formed small single-spherical nuclei with condensed chromatin. In spite of having intact DNA, they could not be taken as "truly" necrotic cells. It is evident that in the experimental system, caspase proteases play an essential role in the formation of apoptotic bodies and in the cleavage of nucleosomal DNA, but not in the condensation of chromatin. Therefore, it is likely that the choice between cell death modalities is not solely a matter of the caspase proteases present.

A link between apoptosis and degree of phosphorylation of high mobility group A1a protein in leukemic cells

Nuclear phosphoprotein HMGA1a, high mobility group A1a, (previously HMGI) has been investigated during apoptosis. A change in the degree of phosphorylation of HMGA1a has been observed during apoptosis induced in four leukemic cell lines (HL60, K562, NB4, and U937) by drugs (etoposide, camptothecin) or herpes simplex virus type-1. Both hyper-phosphorylation and de-phosphorylation of HMGA1a have been ascertained by liquid chromatography-mass spectrometry. Hyper-phosphorylation (at least five phosphate groups/HMGA1a molecule) occurs at the early apoptotic stages and is probably related to HMGA1a displacement from DNA and chromatin release from the nuclear scaffold. De-phosphorylation (one phosphate or no phosphate groups/HMGA1a molecule) accompanies the later formation of highly condensed chromatin in the apoptotic bodies. We report for the first time a direct link between the degree of phosphorylation of HMGA1a protein and apoptosis according to a process that involves the entire amount of HMGA1a present in the cells and, consequently, whole chromatin. At the same time we report that variously phosphorylated forms of HMGA1a protein are also mono-methylated.

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.

Mast cell chymase induces apoptosis of vascular smooth muscle cells

In human coronary atheromas, the numbers of degranulated mast cells and of apoptotic smooth muscle cells (SMCs) are increased. Accordingly, the possibility exists that mast cells participate in the regulation of SMC apoptosis in the lesions. Mast cells isolated from the serosal cavities of rats were stimulated to release their secretory granules. The neutral protease chymase, present in the exocytosed granules, was found to induce apoptosis when added to rat aortic SMCs in culture. The chymase-induced apoptosis of SMCs was detected by flow cytometry, microscopic analysis of cellular morphology, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL), and electrophoretic demonstration of DNA laddering. Chymase induced SMC apoptosis in a dose- and time- dependent manner, and its proteolytic activity was essential for the proapoptotic effect. In addition to rat chymase, recombinant human chymase was also found to induce apoptosis of human coronary artery SMCs in culture. These results suggest that mast cells may participate in the apoptotic regulation of SMCs in atherosclerotic lesions.

Jasplakinolide induces apoptosis in various transformed cell lines by a caspase-3-like protease-dependent pathway

To clarify the mechanisms underlying the antiproliferative effects of jasplakinolide, a cyclic depsipeptide from marine sponges, we examined whether jasplakinolide induces apoptosis in a variety of transformed and nontransformed cells. Jasplakinolide inhibited proliferation of human Jurkat T cells, resulting in cell death. This was accompanied by chromatin condensation and DNA cleavage at the linker regions between the nucleosomes. When caspase-3-like activity in the cytosolic extracts of Jurkat T cells was examined with a fluorescent substrate, DEVD-MAC (N-acetyl-Asp-Glu-Val-Asp-4-methyl-coumaryl-7-amide), the activity in the cells treated with jasplakinolide was remarkably increased in a time-dependent manner. Pretreatment of Jurkat T cells with the caspase inhibitor zVAD [benzyloxycarbonyl(Cbz)-Val-Ala-beta-Asp(OMe)-fluoromethylketone] or DEVD-CHO (N-acetyl-Asp-Glu-Val-Asp-1-aldehyde) prevented the induction of apoptosis by jasplakinolide. Moreover, exposure of various murine transformed cell lines to jasplakinolide resulted in cell death, which was inhibited by zVAD. Although it has been well established that murine immature thymocytes are sensitive to apoptosis when exposed to various apoptotic stimuli, these cells as well as mature T lymphocytes were resistant to jasplakinolide-induced apoptosis. The results suggest that jasplakinolide induces apoptotic cell death through a caspase-3-like protease-dependent pathway. Another important outcome is that transformed cell lines were more susceptible to jasplakinolide-induced apoptosis than normal nontransformed cells.

Effector mechanisms of fenretinide-induced apoptosis in neuroblastoma

Fenretinide is an effective inducer of apoptosis in many malignancies but its precise mechanism(s) of action in the induction of apoptosis in neuroblastoma is unclear. To characterize fenretinide-induced apoptosis, neuroblastoma cell lines were treated with fenretinide and flow cytometry was used to measure apoptosis, free radical generation, and mitochondrial permeability changes. Fenretinide induced high levels of caspase-dependent apoptosis accompanied by an increase in free radicals and the release of cytochrome c in the absence of mitochondrial permeability transition. Apoptosis was blocked by two retinoic acid receptor (RAR)-beta/gamma-specific antagonists, but not by an RARalpha-specific antagonist. Free radical induction in response to fenretinide was not blocked by the caspase inhibitor ZVAD or by RAR antagonists and was only marginally reduced in cells selected for resistance to fenretinide. Therefore, free radical generation may be only one of a number of intracellular mechanisms of apoptotic signaling in response to fenretinide. These results suggest that the effector pathway of fenretinide-induced apoptosis of neuroblastoma is caspase dependent, involving mitochondrial release of cytochrome c independently of permeability changes, and mediated by specific RARs. As the mechanism of action of fenretinide may be different from other retinoids, this compound may be a valuable adjunct to neuroblastoma therapy with retinoic acid and conventional chemotherapeutic drugs.

Mechanism of dibucaine-induced apoptosis in promyelocytic leukemia cells (HL-60)

Dibucaine, a local anesthetic, inhibited the growth of promyelocytic leukemia cells (HL-60) without inducing arrest of the cell cycle and differentiation to granulocytes. Typical DNA fragmentation and DNA ladder formation were induced in a concentration- and time-dependent manner. The half-maximal concentration of dibucaine required to induce apoptosis was 100 microM. These effects were prevented completely by the pan-caspase inhibitor z-Val-Ala-Asp-(OMe)-fluoromethylketone (z-VAD-fmk), thereby implicating the cysteine aspartase (caspase) cascade in the process. Dibucaine activated various caspases, such as caspase-3, -6, -8, and -9 (-like) activities, but not caspase-1 (-like) activity, and induced mitochondrial membrane depolarization and the release of cytochrome c (Cyt.c) from mitochondria into the cytosol. Processing of pro-caspase-3, -8, and -9 by dibucaine was confirmed by western blot analysis. Bid, a death agonist member of the Bcl-2 family, was processed by caspases following exposure of cells to dibucaine. However, 100 microM dibucaine scarcely inhibited oxidative phosphorylation, but it induced membrane permeability transition in isolated rat liver mitochondria. Taken together, these data suggest that dibucaine induced apoptosis of HL-60 cells through activation of the caspase cascade in conjunction with Cyt.c release induced by a processed product of Bid and depolarization of the mitochondrial membrane potential.

Limitations to replication of hepatitis delta virus in avian cells

Human hepatitis delta virus (HDV) is a natural subviral agent that uses hepatitis B virus as a helper. Experimentally, HDV can be made to replicate in woodchucks, using woodchuck hepatitis B virus as a helper virus. Also, independent of such helper activity, replication of the HDV RNA genome can be achieved in many mammalian cells. In this study we examined whether such replication could also be achieved in avian cells. We used cotransfection strategies and initially found no detectable genome replication in chicken LMH cells relative to the mammalian cell line Huh7, used as a positive control. We also found that, in contrast to transfected Huh7 cells, the avian cell line was readily and efficiently killed by expression of the delta protein. Three strategies were used to reduce such killing: (i) the delta protein was expressed from a separate expression vector, the amount of which was then reduced as much as 33-fold; (ii) the protein was expressed transiently, using a promoter under tetracycline control; and (iii) the transfected cells were treated with Z-VAD-fmk, a broad-spectrum caspase inhibitor, which reduced cell killing. This last result indicated that cell killing occurred via an apoptotic pathway. After application of these three strategies to reduce cell killing, together with a novel procedure to improve the signal-to-noise ratio in Northern analyses, replication of the HDV genome was then detected in LMH cells. However, even after removal of obvious signs of toxicity, the amount was still >50 times lower than in the Huh7 cells. Our findings explain previous unsuccessful attempts to demonstrate replication of the HDV genome in avian cells and establish the precedent that in certain situations HDV replication can be cytotoxic.

The antiangiogenic factor 16K PRL induces programmed cell death in endothelial cells by caspase activation

We asked whether the antiangiogenic action of 16K human PRL (hPRL), in addition to blocking mitogen-induced vascular endothelial cell proliferation, involved activation of programmed cell death. Treatment with recombinant 16K hPRL increased DNA fragmentation in cultured bovine brain capillary endothelial (BBE) and human umbilical vein endothelial (HUVE) cells in a time- and dose-dependent fashion, independent of the serum concentration. The activation of apoptosis by 16K hPRL was specific for endothelial cells, and the activity of the peptide could be inhibited by heat denaturation, trypsin digestion, and immunoneutralization, but not by treatment with the endotoxin blocker, polymyxin-B. 16K hPRL-induced apoptosis was correlated with the rapid activation of caspases 1 and 3 and was blocked by pharmacological inhibition of caspase activity. Caspase activation was followed by inactivation of two caspase substrates, poly(ADP-ribose) polymerase (PARP) and the inhibitor of caspase-activated deoxyribonuclease (DNase) (ICAD). Furthermore, 16K hPRL increased the conversion of Bcl-X to its proapoptotic form, suggesting that the Bcl-2 protein family may also be involved in 16K hPRL-induced apoptosis. These findings support the hypothesis that the antiangiogenic action of 16K hPRL includes the activation of programmed cell death of vascular endothelial cells.