Apoptotic mechanisms are involved in the death of Strongyloides venezuelensis after triggering of nitric oxide

Despite progress in understanding the role of nitric oxide (NO) in the pathogenesis of helminth infections, the role in strongyloidosis is unknown. Firstly, we studied the production of NO in mice infected with Strongyloides venezuelensis as well as in macrophage cultures stimulated with parasite antigens. Somatic larvae 3 (L3) and excretory-secretory female antigens stimulate specific NO production measured by Griess reaction and expression of inducible NO synthase by RT-PCR and quantitative PCR. Moreover, mice infected with S. venezuelensis produce NO in migration stages. Secondly, we analysed the effect of NO production on L3 and females of S. venezuelensis using NO donors such as diethylenetriamine and 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene. Parasites died after NO donor treatment in a dose-dependent manner. Finally, apoptotic mechanisms are involved in the death of S. venezuelensis larvae.

Involvement of lipid rafts in the localization and dysfunction effect of the antitumor ether phospholipid edelfosine in mitochondria

Lipid rafts and mitochondria are promising targets in cancer therapy. The synthetic antitumor alkyl-lysophospholipid analog edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine) has been reported to target lipid rafts. Here, we have found that edelfosine induced loss of mitochondrial membrane potential and apoptosis in human cervical carcinoma HeLa cells, both responses being abrogated by Bcl-x_L overexpression. We synthesized a number of new fluorescent edelfosine analogs, which preserved the proapoptotic activity of the parent drug, and colocalized with mitochondria in HeLa cells. Edelfosine induced swelling in isolated mitochondria, indicating an increase in mitochondrial membrane permeability. This mitochondrial swelling was independent of reactive oxygen species generation. A structurally related inactive analog was unable to promote mitochondrial swelling, highlighting the importance of edelfosine molecular structure in its effect on mitochondria. Raft disruption inhibited mitochondrial localization of the drug in cells and edelfosine-induced swelling in isolated mitochondria. Edelfosine promoted a redistribution of lipid rafts from the plasma membrane to mitochondria, suggesting a raft-mediated link between plasma membrane and mitochondria. Our data suggest that direct interaction of edelfosine with mitochondria eventually leads to mitochondrial dysfunction and apoptosis. These observations unveil a new framework in cancer chemotherapy that involves a link between lipid rafts and mitochondria in the mechanism of action of an antitumor drug, thus opening new avenues for cancer treatment.

Lipid raft-targeted therapy in multiple myeloma

Despite recent advances in treatment, multiple myeloma (MM) remains an incurable malignancy. By using in vitro, ex vivo and in vivo approaches, we have identified here that lipid rafts constitute a new target in MM. We have found that the phospholipid ether edelfosine targets and accumulates in MM cell membrane rafts, inducing apoptosis through co-clustering of rafts and death receptors. Raft disruption by cholesterol depletion inhibited drug uptake by tumor cells as well as cell killing. Cholesterol replenishment restored MM cell ability to take up edelfosine and to undergo drug-induced apoptosis. Ceramide addition displaced cholesterol from rafts, and inhibited edelfosine-induced apoptosis. In an MM animal model, edelfosine oral administration showed a potent in vivo antimyeloma activity, and the drug accumulated preferentially and dramatically in the tumor. A decrease in tumor cell cholesterol, a major raft component, inhibited the in vivo antimyeloma action of edelfosine and reduced drug uptake by the tumor. The results reported here provide the proof-of-principle and rationale for further clinical evaluation of edelfosine and for this raft-targeted therapy to improve patient outcome in MM. Our data reveal cholesterol-containing lipid rafts as a novel and efficient therapeutic target in MM, opening a new avenue in cancer treatment.

Proapoptotic role of Hsp90 by its interaction with c-Jun N-terminal kinase in lipid rafts in edelfosine-mediated antileukemic therapy

Heat shock protein 90 (Hsp90) is a survival signaling chaperone and a cancer chemotherapeutic target. However, we have found that inhibitors of Hsp90 diminished the apoptotic response induced in leukemic cells by the antitumor alkyl-lysophospholipid analog edelfosine, which acts through lipid raft reorganization. Edelfosine treatment recruited Hsp90, c-Jun N-terminal kinase (JNK) and apoptotic molecules in lipid rafts, but not the JNK regulators apoptosis signal-regulating kinase 1 (ASK1) and Daxx, or the survival signaling molecules extracellular signal-regulated kinase (ERK) and Akt. Following edelfosine treatment, Hsp90 bound to JNK in lipid rafts and Hsp90-JNK clusters were identified at the plasma membrane by immunoelectron microscopy. Hsp90 inhibition reduced JNK protein level in lipid rafts and turned proapoptotic persistent JNK activation into a transient response in edelfosine-treated cells. Decrease in edelfosine-induced JNK activation and apoptosis by Hsp90 inhibition was prevented through proteasome inhibition, suggesting that Hsp90 inhibition diminishes apoptosis by promoting JNK protein degradation. Expression of ASK1 dominant negative mutant did not affect JNK activation and apoptosis following edelfosine treatment. These data indicate that lipid raft-recruited JNK is ASK1-independent and becomes a novel Hsp90 client protein. Our results reveal a new chaperoning role of Hsp90 on JNK-mediated apoptosis following its recruitment in lipid rafts.

Microtubules, microtubule-interfering agents and apoptosis

Microtubules are dynamic polymers that play crucial roles in a large number of cellular functions. Their pivotal role in mitosis makes them a target for the development of anticancer drugs. Microtubule-damaging agents suppress microtubule dynamics, leading to disruption of the mitotic spindle in dividing cells, cell cycle arrest at M phase, and late apoptosis. A better understanding of the processes coupling microtubule damage to the onset of apoptosis will reveal sites of potential intervention in cancer chemotherapy. Inhibition of microtubule dynamics induces persistent modification of biological processes (M arrest) and signaling pathways (mitotic spindle assembly checkpoint activation, Bcl-2 phosphorylation, c-Jun NH(2)-terminal kinase activation), which ultimately lead to apoptosis through the accumulation of signals that finally reach the threshold for the onset of apoptosis or through diminishing the threshold for engagement of cell death. Microtubules serve also as scaffolds for signaling molecules that regulate apoptosis, such as Bim and survivin, and their release from microtubules affect the activities of these apoptosis regulators. Thus, sustained modification of signaling routes and changes in the scaffolding properties of microtubules seem to constitute two major processes in the apoptotic response induced by microtubule-interfering agents.

The antitumor ether lipid ET-18-OCH(3) induces apoptosis through translocation and capping of Fas/CD95 into membrane rafts in human leukemic cells

The antitumor ether lipid ET-18-OCH(3) promotes apoptosis in tumor cells through intracellular activation of Fas/CD95. Results of this study showed that ET-18-OCH(3) induces cocapping of Fas and membrane rafts, specialized plasma membrane regions involved in signaling, before the onset of apoptosis in human leukemic cells. Patches of membrane rafts accumulated Fas clusters in leukemic cells treated with ET-18-OCH(3). Sucrose gradient centrifugation of Triton X-100 cell lysates showed that Fas translocated into membrane rafts following ET-18-OCH(3) treatment of T-leukemic Jurkat cells. Disruption of membrane raft integrity by methyl-beta-cyclodextrin or filipin inhibited ET-18-OCH(3)-induced apoptosis in leukemic primary cells and cell lines. Fas clustering was also inhibited by methyl-beta-cyclodextrin. These data indicate that ET-18-OCH(3) reorganizes membrane rafts to trigger apoptosis in human leukemic cells, and that Fas coaggregation with membrane rafts is required for ET-18-OCH(3)-induced apoptosis. This translocation of Fas into membrane rafts may provide a mechanism for amplifying Fas signaling by reorganization of membrane microdomains.

Induction of apoptosis in leukemic cells by the reversible microtubule-disrupting agent 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1 -one: protection by Bcl-2 and Bcl-X(L) and cell cycle arrest

We have found that the bicyclic colchicine analogue 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-on e (MTC) induced a dose- and time-dependent apoptotic response in human leukemic cells. MTC and colchicine rapidly disrupted the microtubule integrity and arrested cells at the G2-M phase before the onset of apoptosis. These responses were mediated by microtubule inhibition because 2-methoxy-5-[[3-(3,4,5-trimethoxyphenyl)propionyl]amino]-2,4,6-cycloh eptatrien-1-one and lumicolchicine, inactive analogues of MTC and colchicine, respectively, were unable to promote microtubule disassembly, cell cycle arrest, and apoptosis. Although 1 microM MTC induced a complete microtubule disruption after 1 h of incubation in human leukemic HL-60 cells that led to an accumulation of cells at the G2-M phase, MTC-induced apoptosis occurred after 9 h of treatment. This indicates the existence of a rather long lag between microtubule disruption and the onset of apoptosis. Unlike colchicine, the removal of MTC during this lag resulted in rapid microtubule repolymerization, followed by restoration of normal cell cycle and cell growth. MTC, but not 2-methoxy-5-[[3-(3,4,5-trimethoxyphenyl)-propionyl]amino]-2,4,6-cyclo heptatrien-1-one, induced c-jun expression as well as c-Jun NH2-terminal kinase and caspase activation, indicating that these signaling pathways are triggered by the specific action of MTC on microtubules. Caspase inhibition prevented MTC-induced apoptosis. Overexpression of bcl-2 or bcl-xL by gene transfer in human erythroleukemic HEL cells abrogated MTC-induced apoptosis, but cells remained arrested in G2-M, suggesting that bcl-2 and bcl-xL block the signaling pathway between G2-M arrest and triggering of apoptosis. MTC-treated bcl-2 and bcl-xL-transfected HEL cells recovered their capacity to proliferate after MTC removal. These results indicate that microtubule inhibition induces G2-M arrest and apoptosis in leukemic cells, showing a lag phase between G2-M arrest and the onset of apoptosis, regulated by bcl-2 and bcl-xL, during which MTC displays a reversible action on microtubule depolymerization and G2-M cell cycle arrest. Thus, MTC is a potent apoptotic inducer on human leukemic cells and shows a remarkable reversible action on microtubule network and cell cycle before commitment for apoptosis is reached.

Involvement of mitochondria and caspase-3 in ET-18-OCH(3)-induced apoptosis of human leukemic cells

The induction of cell death in leukemic HL-60 cells by the ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH(3); edelfosine) followed the typical apoptotic changes in ultrastructural morphology, including blebbing, chromatin condensation, nuclear membrane breakdown and extensive vacuolation. Using a cytofluorimetric approach, we found that ET-18-OCH(3) induced disruption of the mitochondrial transmembrane potential (DeltaPsi(m)) followed by production of reactive oxygen species (ROS) and DNA fragmentation in leukemic cells. ET-18-OCH(3) also induced caspase-3 activation in human leukemic cells, as assessed by cleavage of caspase-3 into the p17 active form and cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase (PARP). ET-18-OCH(3) analogues unable to induce apoptosis failed to disrupt DeltaPsi(m) and to activate caspase-3. ET-18-OCH(3)-resistant Jurkat cells generated from sensitive Jurkat cells showed no caspase-3 activation and did not undergo DeltaPsi(m) disruption upon ET-18-OCH(3) incubation. Cyclosporin A partially inhibited DeltaPsi(m) dissipation, caspase activation and apoptosis in ET-18-OCH(3)-treated leukemic cells. Overexpression of bcl-2 by gene transfer prevented DeltaPsi(m) collapse, ROS generation, caspase activation and apoptosis in ET-18-OCH(3)-treated leukemic T cells. Pretreatment with the caspase inhibitor Z-Asp-2, 6-dichlorobenzoyloxymethylketone prevented ET-18-OCH(3)-induced PARP proteolysis and DNA fragmentation, but not DeltaPsi(m) dissipation. ET-18-OCH(3) did not affect the expression of caspases and bcl-2-related genes. ET-18-OCH(3)-induced apoptosis did not require protein synthesis. Our data indicate that DeltaPsi(m) dissipation and caspase-3 activation are critical events of the apoptotic cascade triggered by the antitumor ether lipid ET-18-OCH(3), and that the sequence of events in the apoptotic action of ET-18-OCH(3) on human leukemic cells is: DeltaPsi(m) disruption, caspase-3 activation and internucleosomal DNA degradation.

Intracellular triggering of Fas, independently of FasL, as a new mechanism of antitumor ether lipid-induced apoptosis

Antitumor ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH(3); edelfosine) induces apoptosis in cancer cells, sparing normal cells. We have found that the apoptotic action of ET-18-OCH(3) required drug uptake and Fas in the target cell. Failure to accomplish one of these requirements prevents cell killing by the ether lipid. In human lymphoid leukemic cells, ET-18-OCH(3) does not promote Fas or FasL expression and ET-18-OCH(3)-induced apoptosis is not inhibited by pre-incubation with an anti-Fas blocking antibody that abrogates cell killing mediated by Fas/FasL interactions. ET-18-OCH(3)-resistant normal human Fas-positive fibroblasts do not incorporate ET-18-OCH(3), but undergo apoptosis upon ET-18-OCH(3) microinjection. Murine fibroblasts L929 and L929-Fas, stably transfected with human Fas cDNA, do not incorporate ET-18-OCH(3) and are resistant to its action when added exogenously. Microinjection of ET-18-OCH(3) induces apoptosis in L929-Fas cells, but not in wild-type L929 cells. Confocal laser scanning microscopy shows that ET-18-OCH(3) induces Fas clustering and capping during triggering of ET-18-OCH(3)-induced apoptosis. Microinjection-induced apoptosis and Fas clustering are specific for the molecular structure of ET-18-OCH(3). Our data indicate that ET-18-OCH(3) induces apoptosis via Fas after the ether lipid is inside the cell, and this Fas activation is independent of the interaction of Fas with its natural ligand FasL. This explains the selective action of ET-18-OCH(3) on tumors since only cancer cells incorporate sufficient amounts of the drug.

Selective induction of apoptosis by capsaicin in transformed cells: the role of reactive oxygen species and calcium

Capsaicin is a vanilloid quinone analog that inhibits the plasma membrane electron transport (PMOR) system and induces apoptosis in transformed cells. Using a cytofluorimetric approach we have determined that capsaicin induces a rapid increase of reactive oxygen species (ROS) followed by a subsequent disruption of the transmembrane mitochondrial potential (DeltaPsim) and DNA nuclear loss in transformed cell lines and in mitogen activated human T cells. This apoptotic pathway is biochemically different from the typical one induced by either ceramide or edelfosine where, in our system, the DeltaPsim dissipation precedes the generation of reactive oxygen species. Neither production of ROS nor apoptosis was found in capsaicin-treated resting T cells where the activity of the PMOR system is minimal when compared with mitogen activated or transformed T cells. Capsaicin also induces Ca2+ mobilization in activated but not in resting T cells. However, preincubation of cells with BAPTA-AM, which chelate cytosolic free calcium, did not prevent ROS generation or apoptosis induced by capsaicin, suggesting that ROS generation in capsaicin treated cells is not a consequence of calcium signaling and that the apoptotic pathway may be separated from the one that mobilizes calcium. Moreover, we present data for the implication of a possible vanilloid receptor in calcium mobilization, but not in ROS generation. These results provide evidence that the PMOR system may be an interesting target to design antitumoral and anti-inflammatory drugs.

Physiological activation of human neutrophils down-regulates CD53 cell surface antigen

Tetraspanin transmembrane proteins have a metastasis suppressor effect by acting as cell motility brakes in tumor cells. CD53 is a panleukocyte antigen that belongs to the tetra-span superfamily. Human neutrophils express high levels of CD53. We tested the hypothesis that this antigen level changes when cells are activated. Treatment of human neutrophils with their physiological activators, tumor necrosis factor alpha or platelet-activating factor, resulted in down-regulation of this antigen from the cell surface, as assessed by immunofluorescence flow cytometry. Similar responses were observed when neutrophils were stimulated with chemotactic N-formyl-methionyl-leucyl-phenylalanine, phorbol ester, or the calcium ionophore ionomycin. The CD53 antigen down-regulation upon neutrophil stimulation was further confirmed by immunoblotting analysis and was not correlated with a change in the level of CD53 transcripts. This CD53 antigen down-regulation paralleled that of CD43 and CD44 antigens in these cells, despite their different protein structure. The down-regulation of the three antigens CD53, CD43, and CD44 could be inhibited by phenylmethylsulfonyl fluoride, suggesting that CD53 antigen down-regulation is the result of the activation of a proteolytic mechanism. Down-regulation of CD53 antigen level, as a result of cellular stimulation, might play a role in the different aspects of neutrophil biology, by modulating its interactions on the cell surface.

Involvement of c-Jun NH2-terminal kinase activation and c-Jun in the induction of apoptosis by the ether phospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine

The ether phospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3; edelfosine) is a potent inducer of apoptosis in human tumor cells. We show that ET-18-OCH3-induced apoptosis is associated with activation of the c-Jun NH2-terminal kinase (JNK) signaling. The addition of ET-18-OCH3 to distinct human leukemic cells (HL-60, U937, and Jurkat), which undergo rapid apoptosis on treatment with ET-18-OCH3, induced a dramatic and sustained increase in the of c-jun mRNA level that was associated with activation of activator protein-1 transcription factor. We found that ET-18-OCH3 induced a persistent activation of JNK in HL-60 cells that was detected before the onset of apoptosis, the latter being assessed by DNA fragmentation and by the appearance of phosphatidylserine on the external leaflet of the plasma membrane. The inductions of JNK after HL-60 monocyte/macrophage differentiation and ET-18-OCH3-mediated apoptosis were distinguished by the different activation patterns, transient versus persistent, respectively. ET-18-OCH3 analogues unable to induce apoptosis failed to activate JNK. ET-18-OCH3-dependent JNK activation was not detected in K562 cells, which did not undergo apoptosis on treatment with ET-18-OCH3. Phorbol myristate acetate inhibited both ET-18-OCH3-induced apoptosis and sustained JNK activation; thus, persistent JNK activation by ET-18-OCH3 is associated with the capacity of this ether phospholipid to induce apoptosis. Furthermore, antisense oligonucleotides directed against c-jun blocked ET-18-OCH3-induced apoptosis, indicating a role for c-Jun in this apoptotic response. These data indicate that JNK activation and c-Jun are involved in the induction of apoptosis by ET-18-OCH3.

Major co-localization of the extracellular-matrix degradative enzymes heparanase and gelatinase in tertiary granules of human neutrophils

The expression of cell-surface adhesion proteins and the release of extracellular-matrix degradative enzymes constitute crucial processes for the attachment of neutrophils to the endothelium and for the subsequent extravasation of these cells through the endothelial layer. We have analysed in resting human neutrophils the subcellular localization of heparanase, a heparan-sulphate-degrading endoglycosidase that can degrade basement-membrane components, thereby facilitating neutrophil passage into the tissue during an inflammatory reaction. By subcellular fractionation of postnuclear supernatants from resting human neutrophils on continuous sucrose gradients, we have found that heparanase activity was mainly located in gelatinase-containing tertiary granules. Using a specific antibody, the 96-kDa heparanase protein was further located in the gelatinase-rich subcellular fractions. Following immunoblotting and immunoprecipitation analysis in the distinct subcellular fractions, we also found co-localization of heparanase and Mo1 (CD11b/CD18), a leucocyte integrin involved in the attachment of neutrophils to the endothelium, in the fractions enriched in gelatinase-containing tertiary granules. Treatment of human neutrophils with tumour necrosis factor or granulocyte/macrophage colony-stimulating factor induced an increase in the CD11b/CD18 cell-surface expression, as well as the release of both gelatinase (matrix metalloproteinase-9) and heparanase, but not of other granule markers, indicating a major co-localization of gelatinase, heparanase and CD11b/CD18 in the same organelle. Furthermore, confocal laser scanning microscopy using specific antibodies against gelatinase and heparanase revealed a major co-localization of both enzymes in intracellular cytoplasmic granules. The major localization of heparanase and CD11b/CD18 in the gelatinase-containing tertiary granule supports the notion that mobilization of this organelle can regulate extravasation of human neutrophils.

Dissociation of the effects of the antitumour ether lipid ET-18-OCH3 on cytosolic calcium and on apoptosis

1. We have compared the effects of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH3) on the cytosolic free calcium concentration ([Ca2+]i) and on apoptosis in several normal and leukaemia cells, including human polymorphonuclear neutrophils (PMNs), U937 cells, and undifferentiated as well as dimethylsulphoxide-differentiated HL60 cells (uHL60 and dHL60, respectively). 2. ET-18-OCH3 produced apoptosis, as evidenced by DNA degradation into oligonucleosome-size fragments, in U937 and uHL60 cells, but not in dHL60 cells or PMNs. 3. ET-18-OCH3 induced an increase in [Ca2+]i mediated through the platelet-activating factor (PAF) receptor in U937, dHL60 cells and PMNs, as shown by cross-desensitization experiments and by prevention of the [Ca2+]i changes by the PAF antagonist WEB-2170. The EC50 values for the increase in [Ca2+]i induced by PAF and ET-18-OCH3 were 5 x 10(-11) and 2.5 x 10(-7) M, respectively. In uHL60 cells the effect of ET-18-OCH3 on [Ca2+]i was very small and was not affected by WEB-2170. 4. PAF did not produce apoptosis in any of the cell types tested. WEB-2170 did not prevent the apoptosis induced by ET-18-OCH3. 5. The uptake of [3H]-ET-18-OCH3 was much larger in U937 and uHL60 cells than in dHL60 cells and PMNs. 6. Our results indicate that the apoptotic effect of ET-18-OCH3 is not related to the changes in [Ca2+]i, effected by interaction with plasma membrane PAF receptors, but to other actions which are associated with the uptake of this drug into the cells.

Selective induction of apoptosis in cancer cells by the ether lipid ET-18-OCH3 (Edelfosine): molecular structure requirements, cellular uptake, and protection by Bcl-2 and Bcl-X(L)

The ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3; Edelfosine) has been shown to be a rapid inducer of apoptosis in human leukemic cells and has been considered as a promising drug in cancer treatment. Here we have found that ET-18-OCH3 induced apoptosis not only in human tumor cell lines but also in primary tumor cell cultures from cancer patients. Human leukemic cells were highly sensitive to ET-18-OCH3, whereas normal cells remained unaffected. Among the distinct modifications of the ET-18-OCH3 molecule assayed, we found that substitutions in positions sn-2 and sn-3 of the glycerol backbone resulted in a complete loss of its capacity to induce apoptosis, highlighting the importance of the molecular structure of ET-18-OCH3 in its apoptotic effect. Induction of apoptosis by ET-18-OCH3 was very well correlated with the uptake of this ether lipid. ET-18-OCH3-resistant 3T3 fibroblasts became sensitive and incorporated significant amounts of the ether lipid following transformation with the SV40 virus. ET-18-OCH3-induced apoptosis as well as ET-18-OCH3 uptake were not mediated through binding of the ether lipid to the platelet-activating factor receptor. Overexpression of bcl-2 or bcl-xL by gene transfer in the human erythroleukemic HEL cells abrogated apoptosis induced by ET-18-OCH3. ET-18-OCH3 did not affect the expression of bcl-2, bcl-xL, or bax in HEL and HL-60 human leukemic cells but induced expression of c-myc, an important effector of apoptosis in several systems. Thus, ET-18-OCH3 behaves as a potent and highly selective antitumor drug able to induce an apoptotic pathway of cell death in tumor cells but not in nonmalignant cells.

C-Fos is not essential for apoptosis

The transcription factor AP-1, made up of dimers of Fos and Jun proto-oncogene products, is involved in distinct cellular processes, including cell proliferation, differentiation and apoptosis. In this study, we have used mice in which both copies of the c-fos gene were disrupted by targeted mutagenesis in order to analyze how the apoptotic response was affected in these mice. We prepared primary cultures from the lymphoid organs, spleen and thymus, obtained from both wild-type and c-fos -/- mice and analyzed the induction of apoptosis in these cultures in the absence and presence of etoposide, an inducer of apoptosis in distinct cell types. Primary cultures from both organs, spleen and thymus, isolated from wild-type mice underwent apoptosis after 3 and 6 h of culture, respectively. Addition of etoposide enhanced the apoptotic response and c-fos mRNA levels in both spleen and thymic cells. Nevertheless, we found that induction of apoptosis in primary cultures of cells obtained from spleen and thymus of c-Fos-deficient mice was practically identical to that observed in wild-type mice. These results demonstrate that c-Fos is not essential for apoptosis and that cells lacking c-Fos may undergo normal apoptosis.

Involvement of phospholipase D in the activation of transcription factor AP-1 in human T lymphoid Jurkat cells

The induction of the AP-1 transcription factor has been ascribed to the early events leading to T lymphocyte activation. We have examined the possibility that stimulation of phospholipase D (PLD) may regulate activation of transcription factor AP-1 in human T cells by transfecting human T lymphocyte Jurkat cells with a plasmid containing an AP-1 enhancer element and a chloramphenicol acetyltransferase reporter gene. We have detected activatable PLD in Jurkat cells, and we have found that addition of phosphatidic acid (PA), the physiologic product of PLD action on phospholipids, is rapidly incorporated into Jurkat cells and leads to activation of transcription factor AP-1. Treatment of Jurkat cells with anti-CD3 mAb activated both PLD and transcription factor AP-1. Wortmannin, an inhibitor of receptor-coupled PLD activation, blocked the anti-CD3-induced increases in both PLD activity and AP-1 enhancer activity. We found a good correlation in the transfected cells between PLD activation and induction of AP-1 enhancer activity under different experimental conditions. Furthermore, ethanol, an inhibitor of the PLD pathway, blocked the anti-CD3-stimulated AP-1 enhancer activity. However, this anti-CD3-mediated response was not inhibited by neomycin, an inhibitor of phosphoinositide hydrolysis. The increases in AP-1 enhancer activity induced by PA or anti-CD3 mAb were efficiently abrogated by the presence of propranolol, an inhibitor of PA phosphohydrolase and protein kinase C (PKC). Furthermore, the PA- and the anti-CD3-induced increases in AP-1 enhancer activity were blocked by the presence of PKC inhibitors or by PKC down-regulation. These data indicate that PLD stimulation can activate the transcription factor AP-1 in T lymphocytes, and suggest that the induction of AP-1 enhancer factor activity by PA is mediated via PKC stimulation, either through a direct activating effect of PA or through PA-derived diacylglycerol formation. These data also provide evidence for a role of PLD-derived lipids in the induction of AP-1 enhancer activity resulting from stimulation of the TCR/CD3 complex, suggesting that increased PLD activity can play an important role in T lymphocyte activation.

Involvement of phospholipase D in the activation of transcription factor AP-1 in human T lymphoid Jurkat cells

The induction of the AP-1 transcription factor has been ascribed to the early events leading to T lymphocyte activation. We have examined the possibility that stimulation of phospholipase D (PLD) may regulate activation of transcription factor AP-1 in human T cells by transfecting human T lymphocyte Jurkat cells with a plasmid containing an AP-1 enhancer element and a chloramphenicol acetyltransferase reporter gene. We have detected activatable PLD in Jurkat cells, and we have found that addition of phosphatidic acid (PA), the physiologic product of PLD action on phospholipids, is rapidly incorporated into Jurkat cells and leads to activation of transcription factor AP-1. Treatment of Jurkat cells with anti-CD3 mAb activated both PLD and transcription factor AP-1. Wortmannin, an inhibitor of receptor-coupled PLD activation, blocked the anti-CD3-induced increases in both PLD activity and AP-1 enhancer activity. We found a good correlation in the transfected cells between PLD activation and induction of AP-1 enhancer activity under different experimental conditions. Furthermore, ethanol, an inhibitor of the PLD pathway, blocked the anti-CD3-stimulated AP-1 enhancer activity. However, this anti-CD3-mediated response was not inhibited by neomycin, an inhibitor of phosphoinositide hydrolysis. The increases in AP-1 enhancer activity induced by PA or anti-CD3 mAb were efficiently abrogated by the presence of propranolol, an inhibitor of PA phosphohydrolase and protein kinase C (PKC). Furthermore, the PA- and the anti-CD3-induced increases in AP-1 enhancer activity were blocked by the presence of PKC inhibitors or by PKC down-regulation. These data indicate that PLD stimulation can activate the transcription factor AP-1 in T lymphocytes, and suggest that the induction of AP-1 enhancer factor activity by PA is mediated via PKC stimulation, either through a direct activating effect of PA or through PA-derived diacylglycerol formation. These data also provide evidence for a role of PLD-derived lipids in the induction of AP-1 enhancer activity resulting from stimulation of the TCR/CD3 complex, suggesting that increased PLD activity can play an important role in T lymphocyte activation.

The ether lipid 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine induces expression of fos and jun proto-oncogenes and activates AP-1 transcription factor in human leukaemic cells

The ether lipid analogue 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) has been recently shown to induce apoptosis in the human leukaemic HL-60 and U937 myeloid cell lines [Mollinedo, Martinez-Dalmau and Modolell (1993) Biochem. Biophys. Res. Commun. 192, 603-609]. We have found that ET-18-OCH3 is also able to promote apoptosis in the human leukaemic Jurkat T lymphoid cell line. This lymphoid cell line as well as the two myeloid HL-60 and U937 cell lines incorporated significant amounts of exogenously added radiolabelled ET-18-OCH3. Addition of ET-18-OCH3 to these human leukaemic cells induced an increase in the steady-state mRNA levels of fos and jun proto-oncogenes, components of the transcription factor AP-1. These increases in fos and jun mRNA levels were associated with the activation of the AP-1 transcription factor after addition of ET-18-OCH3 to human leukaemic cells, as assessed by an enhanced binding activity of transcription factor AP-1 to its cognate DNA sequence as well as by stimulation of transcription from an AP-1 enhancer element. These data demonstrate that the ether lipid ET-18-OCH3 can affect gene expression by inducing expression of fos and jun proto-oncogenes and by modulating the activity of transcription factor AP-1.

Differences in expression of transcription factor AP-1 in human promyelocytic HL-60 cells during differentiation towards macrophages versus granulocytes

Commitment of HL-60 cells to macrophage or granulocytic differentiation was achieved by incubation with 4 beta-phorbol 12-myristate 13-acetate (PMA) for 30-60 min or with dimethyl sulphoxide (DMSO) for 24 h respectively. The commitment stage towards PMA-induced macrophage differentiation was associated with increases in jun B and c-fos mRNA levels, as well as with an increase in the binding activity of transcription factor AP-1. Nevertheless, gel retardation analysis indicated that the AP-1 activity detected in untreated cells was drastically reduced during the commitment stage of DMSO-induced HL-60 differentiation towards granulocytes. When HL-60 cells were treated with sodium butyrate, which induced monocytic differentiation, a remarkable increase in AP-1 binding activity was detected. Treatment of HL-60 cells with 1 alpha,25-dihydroxyvitamin D3, another monocytic differentiation agent, induced a weak, but appreciable, increase in AP-1 activity. Furthermore, addition of sodium butyrate or 1 alpha,25-dihydroxyvitamin D3 to HL-60 cells induced the expression of c-fos, c-jun, jun B and jun D proto-oncogenes. In contrast, when HL-60 cells were treated with retinoic acid, a granulocytic differentiation inducer, no enhanced AP-1 binding activity was observed, and only a weak increase in jun D mRNA level was detected. These data indicate that formation of AP-1 is not required for the induction of HL-60 differentiation towards granulocytes, whereas induction of monocytic differentiation is correlated with an increase in AP-1 activity. The differential expression of AP-1 activity may be critical in the differentiation of HL-60 cells towards monocytic or granulocytic lineages.

Localization of rap1 and rap2 proteins in the gelatinase-containing granules of human neutrophils

The subcellular localization of rap proteins in resting human neutrophils was investigated by immunoblot analysis with specific anti-rap2 and anti-rap1 antibodies of the membrane proteins obtained from distinct subcellular fractions. Rap2 protein was mainly located in gelatinase-containing granules, whereas rap1 protein was detected both in gelatinase-containing granules and in fractions enriched in plasma membrane. Neither rap1 nor rap2 proteins were found in the cytosol or in azurophilic granules. Rap2B, not rap2A, appeared to be the major rap2 protein in human neutrophils. The identification and subcellular localization of rap1 and rap2 proteins at the membranes of gelatinase-rich granules suggest that these proteins could play a role in the regulation of the rapid and selective mobilization of gelatinase-containing granules in human neutrophils.

Cytochrome b co-fractionates with gelatinase-containing granules in human neutrophils

Subcellular fractionation studies in resting human neutrophils indicated a bimodal distribution for cytochrome b. A major peak of cytochrome b co-sedimented with gelatinase under different experimental conditions. This localization was partially overlapped with specific granules (using lysozyme and lactoferrin as specific granule markers), but clearly resolved from azurophilic granules, plasma membrane, mitochondria, as well as from a novel alkaline phosphatase-rich intracellular organelle. A minor localization of cytochrome b was found in fractions enriched in both the plasma membrane marker 5'-nucleotidase and alkaline phosphatase. A significant portion of ubiquinone cell content co-fractionated with the gelatinase-containing granules. After phorbol myristate acetate (PMA)-cell stimulation, cytochrome b was mobilized to fractions showing respiratory burst activity and enriched in 5'-nucleotidase activity. This mobilization paralleled secretion of gelatinase and lysozyme to the extracellular medium. Furthermore, neutrophil stimulation with fluoride in the absence of cytochalasin B induced release of gelatinase and generation of superoxide anion with only minimal release of lysozyme. Preincubation of cells with the anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) prevented lysozyme release, but had only a minor effect on the release of gelatinase and did not inhibit the superoxide anion generation elicited by N-formyl-methionyl-leucyl-phenylalanine or PMA. These results suggest a main location of cytochrome b in mobilizable gelatinase-containing granules, which can constitute a subpopulation of specific granules. Furthermore, these findings show that the gelatinase-containing granule is functionally involved in the respiratory burst in neutrophils and that membrane fusion between plasma membrane and the gelatinase-containing granule occurs during activation of cells.