Activation of protein kinase C is required for protection of cells against apoptosis induced by singlet oxygen

Singlet Oxygen, Photodynamic Therapy, and Mechanisms of Cancer Cell Death

Photodynamic therapy (PDT) can be developed into an important arsenal against cancer; it is a minimally invasive therapy, which is used in the treatment or/and palliation of a variety of cancers and benign diseases. The removal of cancerous tissue is achieved with the use of photosensitizer and a light source, which excites the photosensitizer. This excitation causes the photosensitizer to generate singlet oxygen and other reactive oxygen species. PDT has been used in several types of cancers including nonmelanoma skin cancer, bladder cancer, esophageal cancer, head and neck cancer, and non-small cell lung cancer (NSCLC). Although it is routinely used in nonmelanoma skin cancer, it has not been widely adopted in other solid cancers due to a lack of clinical data showing the superiority of PDT over other forms of treatment. Singlet oxygen used in PDT can alter the activity of the catalase, which induces immunomodulation through HOCl signaling. The singlet oxygen can induce apoptosis through both the extrinsic and intrinsic pathways. The extrinsic pathway of apoptosis starts with the activation of the Fas receptor by singlet oxygen that leads to activation of the caspase-7 and caspase-3. In the case of the intrinsic pathway, disruption caused by singlet oxygen in the mitochondria membrane leads to the release of cytochrome c, which binds with APAF-1 and procaspase-9, forming a complex, which activates caspase-3. Mechanisms of PDT action can vary according to organelles affected. In the plasma membrane, membrane disruption is caused by the oxidative stress leading to the intake of calcium ions, which causes swelling and rupture of cells due to excess intake of water, whereas disruption of lysosome causes the release of the cathepsins B and D, which cleave Bid into tBid, which changes the mitochondrial outer membrane permeability (MOMP). Oxidative stress causes misfolding of protein in the endoplasmic reticulum. When misfolding exceeds the threshold, it triggers unfolding protein response (UPR), which leads to activation of caspase-9 and caspase-3. Finally, the activation of p38 MAPK works as an alternative pathway for the induction of MOMP.

Opsin3-A Link to Visible Light-Induced Skin Pigmentation

Skin pigmentation is primarily dependent on melanogenesis, a physiological process that occurs in melanosomes of melanocytes. Solar radiation modulates pigmentation through variety of signaling pathways, but the mechanism of visible light-induced hyperpigmentation remains uncharacterized. Passeron's group recently reported that visible light stimulates opsin3-regulated calcium-dependent microphthalmia-associated transcription factor activation that increases pigment gene expression and that it also causes the clustering of melanogenic enzymes. Together, these processes possibly contribute to long-lasting hyperpigmentation in the melanocompetent skins.

Rose Bengal suppresses gastric cancer cell proliferation via apoptosis and inhibits nitric oxide formation in macrophages

Rose Bengal (RB) has been used as a safe agent in clinical diagnosis. In addition, it is used as a photodynamic sensitizer for removing microorganisms and cancer cells. Recently, its preferential toxicity after direct exposure to cancer cells was proven. The present study focuses on anti-cancer and anti-inflammatory activities of RB. The toxicity of RB against AGS gastric cancer and NIH 3T3 fibroblast cell lines was studied using an MTT assay. Patterns of any cell death among the AGS cells were defined using Annexin-V and PI staining. In addition, the effect of RB on nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production induced by lipopolysaccha-ride in J774A.1 macrophages was determined. Modulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 expressions in the macrophages was also evaluated by Western blots. The results showed that AGS cells exhibited significant concentration-dependent decreases in growth in response to RB; these cells showed a greater growth inhibition than did non-malignant 3T3 cells, suggesting that anti-growth activity of RB could be cell-specific. Moreover, AGS cells exposed to RB exhibited a significant increase in apoptosis; only at high RB doses did the cells display significant levels of necrosis. While RB also caused a modest decrease in the growth of J774A.1 macrophages, the cells displayed remarkable decreases in NO production and iNOS expression without significant concurrent modulation in PGE(2) production or COX-2 expression. The data from this study appears to suggest that RB differentially impacts on transformed cell lines, preferentially suppresses growth of a gastric cancer cell line through induction of apoptosis, and induces changes in cells that could reflect potential anti-inflammatory effects that might be induced in situ.

Lipofection of Insulin-Producing RINm5F Cells: Methodological Improvements

Cationic lipid/DNA-complexes have been widely used as gene transfer vectors because they are less toxic and immunogenic than viral vectors. The aim of the present study was to improve and characterize lipofection of an insulin-producing cell line. We compared the transfection efficiency of seven commercially available lipid formulations (Lipotaxi, SuperFect, Fugene, TransFast, Dosper, GenePORTER and LipofectAMINE) by flow cytometry analysis of GFP-expression. In addition, we have determined the influences of centrifugation, serum and a nuclear localization signal peptide on the lipofection efficiency. We observed that two lipid formulations, GenePORTER and LipofectAMINE, were able to promote efficient gene transfer in RINm5F cells. However, GenePORTER exhibited the important advantage of being able to transfect cells in the presence of serum and with less cytotoxicity than LipofectAMINE. LipofectAMINE-induced RINm5F cell death could partially be counteracted by TPA, forskolin or fumonisin beta(1). Finally, both centrifugation and a nuclear localization signal peptide increased transfection efficiency.

Reactive oxygen species induce different cell death mechanisms in cultured neurons

Apoptosis is characterized by chromatin condensation, phosphatidylserine translocation, and caspase activation. Neuronal apoptotic death involves the participation of reactive oxygen species (ROS), which have also been implicated in necrotic cell death. In this study we evaluated the role of different ROS in neuronal death. Superoxide anion was produced by incubating cells with xanthine and xanthine oxidase plus catalase, singlet oxygen was generated with rose Bengal and luminic stimuli, and hydrogen peroxide was induced with the glucose and glucose oxidase. Cultured cerebellar granule neurons died with the characteristics of apoptotic death in the presence of superoxide anion or singlet oxygen. These two conditions induced caspase activation, nuclear condensation, phosphatidylserine translocation, and a decrease in intracellular calcium levels. On the other hand, hydrogen peroxide led to a necrosis-like cell death that did not induce caspase activation, phosphatidylserine translocation, or changes in calcium levels. Cell death produced by both singlet oxygen and superoxide anion, but not hydrogen peroxide, was partially reduced by an increase in intracellular calcium levels. These results suggest that formation of specific ROS can lead to different molecular cell death mechanisms (necrosis and apoptosis) and that ROS formed under different conditions could act as initiators or executioners on neuronal death.

A review of in vitro gamete maturation and embryo culture and potential impact on future animal biotechnology

This review considers the relationship of in vitro gamete maturation and embryo culture to the future development of animal biotechnology. The areas reviewed are oocyte maturation in vitro and embryo culture and their importance for successful in vitro embryo production. The rapidly developing area of spermatogonial cell transplantation and culture is also reviewed. The scientific milestones leading to the development of each area, the problems and prospects for future development and the possible significance of major advances in each area are discussed.

Ultraviolet A radiation induces rapid apoptosis of human leukemia cells by Fas ligand-independent activation of the Fas death pathways

Endogenous cellular chromophores absorb ultraviolet A radiation (UVA, 290-320 nm), the major UV component of terrestrial solar radiation, leading to the formation of reactive oxidizing species that initiate apoptosis, gene expression and mutagenesis. UVA-induced apoptosis of T helper cells is believed to underlie the UVA phototherapy for atopic dermatitis and other T cell-mediated inflammatory skin diseases. We have evaluated the involvement of the Fas-Fas ligand (FasL) pathway in rapid UVA-induced apoptosis in human leukemia HL-60 cells. UVA-induced apoptosis was not inhibited by pretreatment with a neutralizing anti-Fas antibody, although the same UVA treatment initiated cleavage of caspase-8 and subsequent processing of Bid and caspase-3-like proteases. Inhibition of caspase-8 by Lle-Glu (OMe)-Thr-Asp(OMe)-fluoromethyl ketone completely blocked caspase-3 cleavage and apoptosis in UVA-treated cells, suggesting that apoptosis was initiated by the Fas pathway. This inference was supported by demonstrating that immunoprecipitates obtained from UVA-treated cells using anti-Fas antibody contained caspase-8 and Fas-associating protein with death domain (FADD). In addition, Fas clustering in response to UVA treatment was observed by immunofluorescence microscopy. These data support a mechanism for rapid, UVA-induced apoptosis in HL-60 cells involving initial formation of the Fas-FADD-caspase-8 death complex in an FasL-independent manner.

Photodynamic inactivation of isolated crayfish neuron requires protein kinase C, PI 3-kinase and Ca2+

Involvement of some signalling pathways in response to photodynamic therapy (PDT) of sulfonated aluminium phthalocyanine Photosens has been studied in isolated nerve cell. Neurone photosensitisation with 10(-7) M Photosens gradually inhibited firing and irreversibly abolished neuronal activity. Activation of protein kinase C (PKC) by phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) precipitated PDT-induced abolition of neurone activity and caused nucleus swelling and impairment of the nucleus border. Elevation of cytosolic Ca(2+) concentration by ionomycin or thapsigargin also reduced neurone lifetime. In contrast, the PKC inhibitors staurosporine, hypericin or chelerythrine as well as the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitors wortmannin or LY294002 increased neurone lifetime. These results showed that PKC, PI 3-kinase and Ca(2+) are involved in PDT-induced neurone inactivation and following death.

Induction of tumor necrosis factor by bryostatin 1 is involved in synergistic interactions with paclitaxel in human myeloid leukemia cells

Interactions between the protein kinase C (PKC) activator/down-regulator bryostatin 1 and paclitaxel have been examined in human myeloid leukemia cells (U937) and in highly paclitaxel-resistant cells ectopically expressing a Bcl-2 phosphorylation loop-deleted protein (Delta Bcl-2). Treatment (24 hours) of wild-type cells with paclitaxel (eg, 5 to 20 nM) in combination with 10 nM bryostatin 1 induced a marked increase in mitochondrial damage (eg, cytochrome c and Smac/DIABLO [second mitochondria-derived activator of caspases/direct IAP binding protein with low pI] release), caspase activation, Bid cleavage, and apoptosis; moreover, bryostatin 1 circumvented the block to paclitaxel-induced mitochondrial injury and apoptosis conferred by ectopic expression of the loop-deleted protein. Coadministration of tumor necrosis factor (TNF) soluble receptors, or ectopic expression of CrmA or dominant-negative caspase-8, abrogated potentiation of paclitaxel-induced mitochondrial injury and apoptosis by bryostatin 1, implicating the extrinsic apoptotic pathway in this process. Similar events occurred in HL-60 leukemia cells. Potentiation of paclitaxel-induced apoptosis in wild-type and mutant cells by bryostatin 1 was associated with increases in TNF-alpha mRNA and protein and was mimicked by exogenous TNF-alpha. Coadministration of the selective PKC inhibitor GFX (1 microM) blocked the increase in TNF-alpha mRNA levels and apoptosis in bryostatin 1/paclitaxel-treated cells. Lastly, synchronization of cells in G(2)M increased their sensitivity to TNF-alpha-associated lethality. Collectively, these findings indicate that in U937 cells, bryostatin 1 promotes paclitaxel-mediated mitochondrial injury and apoptosis, and circumvents resistance to cell death conferred by loss of the Bcl-2 phosphorylation domain, through the PKC-dependent induction of TNF-alpha. They further suggest that this process is amplified by paclitaxel-mediated arrest of cells in G(2)M, where they are more susceptible to TNF-alpha-induced lethality.

PMA decreases the proliferation of retinal cells in vitro: the involvement of acetylcholine and BDNF

Protein kinase C (PKC) is involved in several cell events including proliferation, survival and differentiation. The aim of this work was to investigate the role of PKC activation on retinal cells proliferation. We demonstrated that PKC activation by phorbol 12-myristate 13-acetate (PMA), a tumor promoter phorbol ester, is able to decrease retinal cells proliferation. This effect was mediated by M1 receptors and dependent on intracellular Ca(2+) increase, tyrosine kinase activity, phosphatidylinositol 3-kinase activity, polypeptide secretion and activation of TrkB receptors. The effect of PMA was not via activation of mitogen-activated protein (MAP) kinase. Carbamylcholine and brain derived neurotrophic factor were both able to decrease retinal cells proliferation to the same level as PMA did. Our results suggest that PKC activation leads to a decrease in retinal cells proliferation through the release of acetylcholine and brain derived neurotrophic factor in the culture, and activation of M1 and TrkB receptors, respectively.

Acute endotoxemia prolongs the survival of rat lung neutrophils in response to 12-O-tetradecanoyl-phorbol 13-acetate

Acute endotoxemia is associated with prolonged survival of adherent neutrophils in the lung vasculature. In the present studies, the effects of inflammatory mediators on signaling pathways regulating neutrophil survival were examined. We found that the protein kinase C activator, 12-O-tetradecanoyl-phorbol 13-acetate (TPA), but not interferon-gamma (IFN-gamma), prolonged the survival of adherent vasculature lung neutrophils from endotoxemic rats, a response that was correlated with reduced apoptosis. Although endotoxin administration to rats induced the expression of the anti-apoptotic protein Mcl-1 in lung neutrophils, TPA had no effect on this response. Endotoxin administration also induced expression of total p38 and p44/42 mitogen activated protein kinases (MAPK) in neutrophils, as well as phosphatidyl inositol 3 kinase (PI3K) and its downstream target protein kinase B (PKB). Treatment of the cells with TPA increased p38 MAPK expression in cells from both control and endotoxin treated animals. Cells from endotoxin treated, but not control animals, were found to exhibit constitutive binding activity of nuclear factor kappa B (NF-kappaB) which was blocked by TPA. In contrast, constitutive CCAAT/enhancer binding protein (C/EBP) nuclear binding activity evident in neutrophils from control animals was reduced following endotoxin administration. Moreover, this response was independent of TPA. These data suggest that NF-kappaB plays a role in TPA-induced signaling leading to prolonged survival of adherent vascular neutrophils in the lung during acute endotoxemia.

Activation of protein kinase C for protection of cells against apoptosis induced by the immunosuppressor prodigiosin

Prodigiosin (PG) is a red pigment produced by Serratia marcescens with immunosuppressive activity. We had recently shown that PG-induced apoptosis in several cancer cell lines including Jurkat-T cells, while acting rapidly, potently and with no marked toxicity in non-malignant cells. Here we examine the role of protein kinase C (PKC) in the regulation of apoptosis triggered by PG. We evaluated the use of phorbol-myristate acetate (PMA) in the inhibition of apoptosis induced by PG in Jurkat-T cells by using FACS analysis of the phosphatidylserine externalisation, Hoechst 33342 staining and fragmentation pattern of DNA as well as proteolysis of poly-(ADP) ribose polymerase (PARP). The anti-apoptotic effect of PMA was accompanied by phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). Pretreatment of cells with MEK inhibitor PD98059 inhibited PMA-induced phosphorylation of ERK1/2 and the cytoprotective ability of PMA. These results suggest that activation of PKC in Jurkat-T cells confer protection against apoptosis induced by PG and that ERK1/2 mediate anti-apoptotic PKC signaling.

Activation of the MEK/MAPK pathway is involved in bryostatin1-induced monocytic differenciation and up-regulation of X-linked inhibitor of apoptosis protein

Induction of monocytic differentiation by bryostatin1 (bryo1) conferred on THP-1 leukemia cells the ability to resist Z-LLL-CHO-induced apoptosis. The mechanism of resistance developed during this process was investigated. Apoptosis resistance was associated with an enhanced expression of X-linked inhibitor of apoptosis protein (XIAP), an endogenous caspase inhibitor, in differentiated THP-1 cells. Bryo1 also increased the level of c-IAP-1, yet decreased the level of c-IAP-2 in THP-1 cells, indicating that distinct regulatory mechanisms are operative. In addition, treatment of THP-1 cells with bryo1 induced a rapid and sustained activation of MEK, prior to the upregulation of XIAP and monocytic differentiation. Pretreatment of THP-1 cells with MEK inhibitors (U0126 and PD98059) prior to bryo1 induction blocked the expression of both XIAP and the c-fms product (M-CSF receptor), a hallmark of monocytic differentiation, but not Bcl-2. In addition, the expression of XIAP in bryo1-treated cells was inhibited by CAPE, a NF-kappaB-specific inhibitor, indicating that its expression is under the transcriptional regulation of NF-kappaB downstream of the MEK/MAPK pathway. The importance of XIAP in mediating apoptosis resistance was illustrated in cells transiently transfected with XIAP, which conferred on THP-1 cells the ability to resist Z-LLL-CHO-induced apoptosis. These findings suggest that the expression of XIAP is linked to monocytic differentiation in bryo1-treated THP-1 cells and represents one of the potential antiapoptotic mechanisms acquired during this process.

Antisense oligonucleotides targeted against protein kinase c alpha inhibit proliferation of cultured avian myoblasts

Protein kinase C (PKC) has been implicated in the control of proliferation and differentiation of many cell types. There is evidence indicating that it plays a role in signal transduction mechanisms related to myogenesis, but little is known about the individual functions of PKC isoforms in muscle cell development. Data obtained in previous studies using cultured chick embryo skeletal muscle cells suggested that PKC alpha is linked to the regulation of myoblast proliferation. However, this causal relationship could not be definitively established as no experiments based on selective inhibition of this isoform were carried out. In the present work, specific inhibition of the expression of PKC alpha in cultured myoblasts by using antisense oligonucleotide technology resulted in a significant decrease of culture cell density and DNA synthesis, clearly showing that this isoenzyme is involved in signalling pathways which promote muscle cell proliferation.

Protein kinase C inhibits singlet oxygen-induced apoptosis by decreasing caspase-8 activation

Although activation of protein kinase C (PKC) inhibits apoptosis induced by a variety of stimuli including singlet oxygen, the step at which PKC activation interferes with apoptotic signaling is not well defined. We have shown previously that caspase-8 and p38 mediate singlet oxygen-induced apoptosis in HL-60 cells. In this study, we investigated the influence of PKC on regulation of the caspase and p38 pathways initiated by singlet oxygen. Singlet oxygen induced Fas clustering and subsequent recruitment of FADD and caspase-8. Treatment of cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a PKC activator, did not affect the binding of caspase-8 to the aggregated Fas. Surprisingly, under the same conditions PKC activation was still able to prevent singlet oxygen-induced activation of caspase-8 and block its downstream signaling events including cleavage of Bid and caspase-3, decrease in mitochondrial transmembrane potential and release of cytochrome c from mitochondria. Inhibition of PKC by GF109203 or H7 counteracted the TPA-mediated effects on the cleavage of caspases -3 and -8. However, neither activation nor inhibition of PKC affected p38 phosphorylation. These data indicate that PKC inhibits singlet oxygen-induced apoptosis by blocking activation of caspase-8.

Modulation of protein kinase C in antitumor treatment

PKC isoenzymes were found to be involved in proliferation, antitumor drug resistance and apoptosis. Therefore, it has been tried to exploit PKC as a target for antitumor treatment. PKC alpha activity was found to be elevated, for example, in breast cancers and malignant gliomas, whereas it seems to be underexpressed in many colon cancers. So it can be expected that inhibition of PKC activity will not show similar antitumor activity in all tumors. In some tumors it seems to be essential to inhibit PKC to reduce growth. However, for inhibition of tumor proliferation it may be an advantage to induce apoptosis. In this case an activation of PKC delta should be achieved. The situation is complicated by the facts that bryostatin leads to the activation of PKC and later to a downmodulation and that the PKC inhibitors available to date are not specific for one PKC isoenzyme. For these reasons, PKC modulation led to many contradicting results. Despite these problems, PKC modulators such as miltefosine, bryostatin, safingol, CGP41251 and UCN-01 are used in the clinic or are in clinical evaluation. The question is whether PKC is the major or the only target of these compounds, because they also interfere with other targets. PKC may also be involved in apoptosis. Oncogenes and growth factors can induce cell proliferation and cell survival, however, they can also induce apoptosis, depending on the cell type or conditions in which the cells or grown. PKC participates in these signalling pathways and cross-talks. Induction of apoptosis is also dependent on many additional factors, such as p53, bcl-2, mdm2, etc. Therefore, there are also many contradicting results on PKC modulation of apoptosis. Similar controversial data have been reported about MDR1-mediated multidrug resistance. At present it seems that PKC inhibition alone without direct interaction with PGP will not lead to successful reversal of PGP-mediated drug efflux. One possibility to improve chemotherapy would be to combine established antitumor drugs with modulators of PKC. However, here also very contrasting results were obtained. Many indicate that inhibition, others, that activation of PKC enhances the antiproliferative activity of anticancer drugs. The problem is that the exact functions of the different PKC isoenzymes are not clear at present. So further investigations into the role of PKC isoenzymes in the complex and interacting signalling pathways are essential. It is a major challenge in the future to reveal whether modulation of PKC can be used for the improvement of cancer therapy.

Singlet oxygen, but not oxidizing radicals, induces apoptosis in HL-60 cells

Oxidizing species (OS), produced by photosensitization or derived from cytotoxic agents, activate apoptotic pathways. We investigated whether two different OS, formed at the same subcellular sites, have equivalent ability to initiate apoptosis in HL-60 cells. Our previous work showed that absorption of visible light by rose bengal (RB) produces singlet oxygen exclusively, whereas absorption of ultraviolet A produces RB-derived radicals in addition to singlet oxygen. Singlet oxygen, but not the RB-derived radicals, induced nuclear condensation and DNA fragmentation into nucleosome-size fragments in a dose dependent manner. In contrast, the RB-derived radicals caused greater lipid oxidation than singlet oxygen. These results indicate that different OS, produced at the same subcellular sites, do not have the same ability to induce apoptosis and that the ability of an OS to initiate lipid oxidation does not necessarily correlate with its ability to induce apoptosis.

Reactive oxidizing species produced near the plasma membrane induce apoptosis in bovine aorta endothelial cells

Many cytotoxic agents initiate apoptosis by generating reactive oxidizing species (ROS). The goal of this study was to determine whether apoptosis could be induced by initial reactions of ROS near the plasma membrane. Bovine aorta endothelial cells (BAEC) were illuminated with evanescent wave visible radiation, which has limited penetration into the basal surface of cells, or by trans-radiation. Imaging of fluorescent dyes localizing in the plasma membrane, mitochondria, or nucleus confirmed that evanescent wave radiation excited only dyes in and near the plasma membrane. Singlet oxygen, an ROS generated by photosensitization, has a very short lifetime, ensuring that it oxidizes molecules residing in or very close to the plasma membrane when evanescent wave radiation is used. Cells with condensed nuclei were considered apoptotic and were quantified after treatment with varying doses of light. Annexin V staining without propidium iodide staining confirmed that these cells were apoptotic. The doses required to induce apoptosis using evanescent wave radiation were 10-fold greater than those needed for trans-irradiation. Quantitative analysis of the evanescent wave penetration into cells supports a mechanism in which the singlet oxygen created near the plasma membrane, rather than at intracellular sites, was responsible for initiation of apoptosis.

p38 mitogen-activated protein kinase mediates bid cleavage, mitochondrial dysfunction, and caspase-3 activation during apoptosis induced by singlet oxygen but not by hydrogen peroxide

p38 mitogen-activated protein kinase is activated and involved in cleavage of caspase-3 during apoptosis induced by a number of stimuli. However, the signaling events triggered by p38 that result in caspase-3 activation are still unknown. In human leukemia cells, two reactive oxygen species, singlet oxygen and hydrogen peroxide (H(2)O(2)), selectively stimulated the phosphorylation of p38. Preincubation of cells with SB203580, a specific inhibitor of p38, dose dependently inhibited DNA fragmentation induced by singlet oxygen but not by H(2)O(2). Protection from apoptosis by SB203580 correlated with inhibition of caspase-3, and several events that are associated with caspase-3 activation, including Bid cleavage, decrease in mitochondrial transmembrane potential and release of cytochrome c from mitochondria, whereas caspase-8 cleavage was not affected by this inhibitor. In contrast, blockade of caspase-8 with Ile-Glu-Thr-Asp-fluoromethyl ketone is sufficient to prevent formation of DNA fragments and to inhibit all the above signaling events, with exception of p38 phosphorylation, in both singlet oxygen- and H(2)O(2)-treated cells. These data suggest that caspase-3 activation is regulated through redundant signaling pathways that involve p38 and caspase-8 acting upstream of Bid during singlet oxygen-induced apoptosis, whereas the activation of caspase-3 by H(2)O(2) is only governed by a caspase-8-mediated apoptotic pathway.

Peroxynitrite-induced apoptosis involves activation of multiple caspases in HL-60 cells

In this study, we show that caspases 2, 3, 6, and 7 were activated during peroxynitrite-induced apoptosis in human leukemia HL-60 cells and that processing of these caspases was accompanied by cleavage of poly(ADP-ribose) polymerase and lamin B. Treatment of cells with DEVD-fluoromethyl ketone (FMK), a selective inhibitor for caspase 3-like proteases, resulted in a marked diminution of apoptotic cells. VAVAD-FMK, an inhibitor of caspase 2, partially inhibited the apoptotic response to peroxynitrite. However, selective inactivation of caspase 6 by VEID-FMK did not affect apoptosis rates. These data suggest that caspase 3-like proteases and caspase 2, but not caspase 6, are required for peroxynitrite-induced apoptosis in this cell type. Moreover, we demonstrate that peroxynitrite treatment stimulated activation of caspases 8 and 9, two initial caspases in the apoptotic signaling pathway, and preincubation of cells with their inhibitor, IETD-FMK, inhibited activation of caspase 3-like proteases and caspase 2 at the concentration that prevents the apoptosis. These observations, together, suggest that caspase 8 and/or caspase 9 mediates activation of caspase 3-like proteases and caspase 2 during the apoptosis induced by peroxynitrite in HL-60 cells.

Signaling pathways in cell death and survival after photodynamic therapy

Photodynamic therapy (PDT) is a cytotoxic treatment, which can induce cells to initiate a rescue response, or to undergo cell death, either apoptosis or necrosis. The many signaling pathways involved in these processes are the topic of this review. The subcellular localization of the photosensitizer has been shown to be a key factor in the outcome of PDT. Mitochondrial localized photosensitizers are able to induce apoptosis very rapidly. Lysosomal localized photosensitizers can elicit either a necrotic or an apoptotic response. In the plasma membrane, a target for various photosensitizers, rescue responses, apoptosis and necrosis is initiated. Several protein phosphorylation cascades are involved in the regulation of the response to PDT. Finally, a number of stress-induced proteins play a role in the rescue response after PDT. Notably, the induction of apoptosis by PDT might not be crucial for an optimal outcome. Recent studies indicate that abrogation of the apoptotic pathway does alter the clonogenic survival of the cells after PDT. Further studies, both in vitro and especially in vivo could lead to more efficient combination therapies in which signaling pathways, involved in cell death or rescue, are either up- or downregulated before PDT.

Glycochenodeoxycholic acid (GCDC) induced hepatocyte apoptosis is associated with early modulation of intracellular PKC activity

The effect of GCDC-induced apoptosis on PKC activity and PKC's role in GCDC-induced hepatocyte apoptosis is unclear. The specific aims of this study were to determine if GCDC-induced apoptosis changed intracellular PKC activity and if modulation of PKC activity affected GCDC-induced hepatocyte apoptosis. Apoptosis was induced in isolated hepatocytes using GCDC. PKC activity was measured and specific PKC and calpain inhibitors were used to study the effects of PKC and calpain modulation on GCDC-induced apoptosis. After 4 h exposure, 50 microM GCDC induced apoptosis in 42% of hepatocytes. Intracellular PKC activity decreased to 44% of controls 2 h after exposure of hepatocytes to GCDC (p < 0.001). Pre-incubation of hepatocytes with the calpain protease inhibitor restored PKC activity in GCDC exposed hepatocytes to 91 +/- 5% of control cells. Pre-incubation of hepatocytes with a calpain inhibitor decreased GCDC-induced apoptosis as did pre-incubation with the PKC activating phorbol ester, PMA. The combination of calpain inhibition and PMA further reduced GCDC-induced apoptosis but caused low level hepatic apoptosis. Inhibition of PKC with chelerythrine also substantially reduced GCDC-induced hepatocyte apoptosis. GCDC-induced apoptosis is associated with decreases in total cellular PKC activity, which appear to be dependent on intracellular calpain-like protease activity. The combination of protease inhibition and phorbol ester pretreatment preserved total cellular PKC activity and decreased GCDC-induced apoptosis but induced low level apoptosis in the absence of GCDC exposure. PKC inhibition also decreased GCDC-induced hepatocyte apoptosis highlighting the complex interactions of PKC and proteases during GCDC-induced apoptosis.

Opposing effects of protein kinase C delta and protein kinase B alpha on H(2)O(2)-induced apoptosis in CHO cells

H(2)O(2)-induced apoptosis was enhanced in the CHO cell line overproducing protein kinase C delta (PKCdelta) as judged by DNA fragmentation. In response to the H(2)O(2) treatment, PKCdelta was tyrosine phosphorylated and recovered as a constitutively active form, but its proteolytic fragment was not generated. In contrast, H(2)O(2)-induced apoptosis was suppressed in the CHO cell line overexpressing protein kinase B alpha (PKBalpha). Consistently, phosphorylation of BAD, a pro-apoptotic protein negatively regulated by PKBalpha, was sustained in the cells overproducing PKBalpha, but was not changed in the cells overexpressing PKCdelta. In the CHO cell line overproducing both PKCdelta and PKBalpha, H(2)O(2)-induced tyrosine phosphorylation of PKCdelta was suppressed, and DNA fragmentation was diminished concomitantly. These results suggest that PKCdelta contributes to H(2)O(2)-induced apoptosis by a mechanism independent of BAD and that PKCdelta is a target of PKB for the regulation of cell survival.

Caspase-8 mediates caspase-3 activation and cytochrome c release during singlet oxygen-induced apoptosis of HL-60 cells

We reported previously that singlet oxygen, generated by irradiation of rose bengal with visible light, induced apoptosis in human promyelocytic leukemia HL-60 cells. However, the mechanism of apoptosis caused by this reactive oxygen species is unclear. In this study, we demonstrate that singlet oxygen induced caspase-3 activation and Z-DEVD-FMK, a caspase-3 inhibitor, blocked apoptosis induction, while caspase-1 activity was not detectable and the caspase-1 inhibitor Z-YVAD-FMK had a very limited effect on apoptosis. This suggests that the activation of caspase-3 by singlet oxygen is essential for the commitment of cells to undergo apoptosis. Further studies showed that singlet oxygen induced an increase in caspase-8 activity and a reduction in mitochondrial cytochrome c. Time course analysis indicated that the cleavage of caspase-8 precedes that of caspase-3. In addition, blockade of caspase-8 by Z-IETD-FMK inhibited cleavage of pro-caspase-3 and prevented loss of mitochondrial cytochrome c. These results suggest that caspase-8 mediates caspase-3 activation and cytochrome c release during singlet oxygen-induced apoptosis in HL-60 cells.